Holman, B W B; Alvarenga, T I R C; van de Ven, R J; Hopkins, D L
2015-07-01
The Warner-Bratzler shear force (WBSF) of 335 lamb m. longissimus lumborum (LL) caudal and cranial ends was measured to examine and simulate the effect of replicate number (r: 1-8) on the precision of mean WBSF estimates and to compare LL caudal and cranial end WBSF means. All LL were sourced from two experimental flocks as part of the Information Nucleus slaughter programme (CRC for Sheep Industry Innovation) and analysed using a Lloyd Texture analyser with a Warner-Bratzler blade attachment. WBSF data were natural logarithm (ln) transformed before statistical analysis. Mean ln(WBSF) precision improved as r increased; however the practical implications support an r equal to 6, as precision improves only marginally with additional replicates. Increasing LL sample replication results in better ln(WBSF) precision compared with increasing r, provided that sample replicates are removed from the same LL end. Cranial end mean WBSF was 11.2±1.3% higher than the caudal end. PMID:25828163
Silva, Douglas R G; Torres Filho, Robledo A; Cazedey, Henrique P; Fontes, Paulo R; Ramos, Alcinéia L S; Ramos, Eduardo M
2015-05-01
This study was conducted to investigate the effect of core sampling on Warner-Bratzler shear force evaluations of beef and pork loins (Longissimus thoracis et lumborum muscles) and to determine the relationship between them. Steaks of 2.54 cm from beef and pork loins were cooked and five round cross-section cores and five square cross-section cores of each steak were taken for shear force evaluation. Core sampling influenced both beef and pork shear force values with higher (P<0.05) average values and standard deviations for square cross-section cores. There was a strong and linear relationship (P<0.01) between round and square cross-section cores for beef (R(2)=0.78), pork (R(2)=0.70) and for beef+pork (R(2)=0.82) samples. These results indicate that it is feasible to use square cross-section cores in Warner-Bratzler shear force protocol as an alternative and potential method to standardize sampling for shear force measurements. PMID:25569815
Guelker, M R; Haneklaus, A N; Brooks, J C; Carr, C C; Delmore, R J; Griffin, D B; Hale, D S; Harris, K B; Mafi, G G; Johnson, D D; Lorenzen, C L; Maddock, R J; Martin, J N; Miller, R K; Raines, C R; VanOverbeke, D L; Vedral, L L; Wasser, B E; Savell, J W
2013-02-01
The tenderness and palatability of retail and food service beef steaks from across the United States (12 cities for retail, 5 cities for food service) were evaluated using Warner-Bratzler shear (WBS) and consumer sensory panels. Subprimal postfabrication storage or aging times at retail establishments averaged 20.5 d with a range of 1 to 358 d, whereas postfabrication times at the food service level revealed an average time of 28.1 d with a range of 9 to 67 d. Approximately 64% of retail steaks were labeled with a packer/processor or store brand. For retail, top blade had among the lowest (P 0.05) in WBS values between moist-heat and dry-heat cookery methods for the top round and bottom round steaks or between enhanced (contained salt or phosphate solution) or nonenhanced steaks. Food service top loin and rib eye steaks had the lowest (P < 0.05) WBS values compared with top sirloin steaks. Retail top blade steaks and food service top loin steaks received among the greatest (P < 0.05) consumer sensory panel ratings compared with the other steaks evaluated. Prime food service rib eye steaks received the greatest ratings (P < 0.05) for overall like, like tenderness, tenderness level, like juiciness, and juiciness level, whereas ungraded rib eye steaks received the lowest ratings (P < 0.05) for like tenderness and tenderness level. The WBS values for food service steaks were greater (P < 0.05) for the Select and ungraded groups compared with the Prime, Top Choice, and Low Choice groups. The WBS values and sensory ratings were comparable to the last survey, signifying that no recent or substantive changes in tenderness have occurred. PMID:23230117
Zhuang, H.; E.M. Savage; Smith, D.P.; M.E. Berrang
2008-01-01
Advantages of air chilling (AC) methods over immersion chilling (IC) methods in quality retention and improvement of deboned chicken breast meat depend on experimental conditions, such as deboning time. The objective of this study was to evaluate the effect of a dry-AC method on shear force and water-holding capacity (WHC) of broiler breast meat deboned 4h postmortem compared to hot-boned (no chill) or immersion-chilled meat. Ready-to-cook broiler carcasses were hot-boned, chilled by ice wate...
Comparison between Allo-Kramer and Warner-Bratzler devices to assess rabbit meat tenderness
Directory of Open Access Journals (Sweden)
C. Cavani
2010-04-01
Full Text Available A study was conducted to compare Allo-Kramer (AK and Warner-Bratzler (WB devices to evaluate rabbit meat texture and to assess their correlations with sensory tenderness. Meat samples characterized by a wide range of tenderness were prepared by boning longissimus lumborum muscles from 90 carcasses at different post mortem times (1, 3, 24h. The right loin of each carcass was used for WB and AK tests, whereas the left loin to assess sensory tenderness and juiciness. The sensory test indicated a higher tenderness and juiciness of rabbit meat obtained from carcasses boned at 24h post mortem in comparison with 1 and 3h post mortem. Both AK and WB methods were able to detect these differences. The AK shear force as well as the WB shear force and area were significantly correlated to meat sensory tenderness (r=-0.58, -0.43 and -0.56, respectively; P<0.001 and juiciness, whereas no correlation was found between sensory tenderness and WB firmness. These results indicate that both WB and AK methods can be used to evaluate the rabbit meat tenderness and give similar levels of correlation with sensory scores. However, AK method is characterized by a sample preparation procedure easier to standardize and less time consuming than WB method.
Measurements of texture properties related to tenderness at different locations within deboned broiler breast fillets have been used to validate techniques for texture analysis and establish correlations between different texture evaluation methods. However, it has been demonstrated that meat text...
Exudate protein composition and Warner-Bratzler shear force in broiler breast fillets
Muscle exudate is often associated with pale color and poor water-holding capacity in broiler breast meat. The relationship between exudate protein composition and breast meat tenderness is unknown. The objective of this study was to determine the relationship between exudate protein composition a...
Scientific Electronic Library Online (English)
Marcos Franke, Pinto; Elisa Helena Giglio, Ponsano; Ana Paula da Silva, Almeida.
1405-14-01
Full Text Available A padronização da textura é um dos principais problemas relacionados à qualidade da carne bovina. Por isso, a avaliação objetiva da maciez, por métodos mecânicos, vem sendo estudada há muitos anos. Para que a avaliação instrumental da textura seja uma ferramenta efetiva nos estudos envolvendo a maci [...] ez da carne, é necessário minimizar as causas de variação envolvidas na análise. Atualmente, a força de cisalhamento Warner-Bratzler é o método mais amplamente empregado para essa finalidade. O protocolo padrão dessa técnica analítica preconiza a utilização de uma lâmina de cisalhamento de 1,016mm de espessura. Neste trabalho, foram comparados dados de textura de carne bovina obtidos com a lâmina de cisalhamento padrão Warner-Bratzler, de 1,016mm de espessura, e uma lâmina mais grossa, de 3,05mm de espessura. Após o abate, amostras de músculo Longissimus dorsi, semelhantes em relação aos teores de umidade, lipídeos e proteínas, foram submetidas a duas diferentes temperaturas de resfriamento, atingindo diferentes velocidades de queda de temperatura e, consequentemente, diferentes graus de contração do tecido muscular, o que foi confirmado pela determinação do comprimento dos sarcômeros. Os resultados demonstraram uma maior sensibilidade da lâmina padrão Warner-Bratzler na detecção de variações da textura da carne, em função da velocidade de resfriamento. Abstract in english Standardization of texture is one of the main problems related to beef quality. Because of that, objective evaluation of tenderness performed by mechanic methodologies has been studied for years. In order to count on instrumental texture evaluation as a valuable tool in meat tenderness studies, it i [...] s necessary to minimize the causes of variation that might be involved in the trial. Nowadays, Warner-Bratzler shear force is widely used for meat tenderness determination. The standard protocol of this methodology establishes the utilization of shear blade 1.016mm tick. The aim of this study was to compare beef texture data provided by Warner-Bratzler standard shear blade, 1.016mm thick, with those provided by a thicker one, 3.05mm thick. After slaughtering, Longissimus dorsi muscle samples with similar contents of moisture, lipids and proteins were subjected to two different cooling temperatures,reaching different rates of temperature drop and hence different muscle contraction extents, which were confirmed by the determination of sarcomere length. Results indicated the superior sensibility of the Warner-Bratzler standard shear blade to detect variations in meat texture due to cooling velocity.
Directory of Open Access Journals (Sweden)
C. Gomes
2013-04-01
Full Text Available Avaliaram-se as características sensoriais e determinou-se a força de cisalhamento de cortes de carne de paca (Agouti paca. As análises foram realizadas nos cortes desossados de paleta, lombo e pernil de nove pacas, preparados por cocção até a temperatura interna de 70ºC. A avaliação de aspecto, cor, sabor, odor e maciez foi realizada pela aplicação de teste afetivo a 146 provadores, utilizando-se escala hedônica, e a força de cisalhamento foi determinada pela técnica Warner Bratzler. Na avaliação sensorial, os cortes de paleta, lombo e pernil de paca mostraram diferença significativa (p0,05 entre os cortes, que se mostraram igualmente macios. A carne de paca apresentou-se sensorialmente semelhante à carne suína e com boa aceitação pelos consumidores. O estudo evidenciou o potencial da paca como uma espécie silvestre para a produção comercial de carne para o mercado de carnes vermelhas ou exóticas.Sensory characteristics and shear force of paca meat (Agouti paca were assessed in this study. Analyses were performed in the bonelessshoulder,loin andhamobtained from nine paca carcassesprepared by cookinguntil reaching the internal temperatureof 70°C. The evaluation of flavor, aroma, color, appearance and tenderness was carried out by the application of an affective test using the hedonic scaleand a 146 consumer panel. Shear force was determined by the Warner-Bratzler technique. Shoulder, loin and ham had significant differences (p 0.05 among the cuts, which were similarly tender. Paca meat was found to resemble pork meat in sensory evaluation and had good acceptance by consumers. This study showed the potential of paca (Agouti paca asa wild species for meat production in the red or exotic meat market.
Scientific Electronic Library Online (English)
C., Gomes; L.B., Karam; R.E.F., Macedo.
2013-04-01
Full Text Available Avaliaram-se as características sensoriais e determinou-se a força de cisalhamento de cortes de carne de paca (Agouti paca). As análises foram realizadas nos cortes desossados de paleta, lombo e pernil de nove pacas, preparados por cocção até a temperatura interna de 70ºC. A avaliação de aspecto, co [...] r, sabor, odor e maciez foi realizada pela aplicação de teste afetivo a 146 provadores, utilizando-se escala hedônica, e a força de cisalhamento foi determinada pela técnica Warner Bratzler. Na avaliação sensorial, os cortes de paleta, lombo e pernil de paca mostraram diferença significativa (p0,05) entre os cortes, que se mostraram igualmente macios. A carne de paca apresentou-se sensorialmente semelhante à carne suína e com boa aceitação pelos consumidores. O estudo evidenciou o potencial da paca como uma espécie silvestre para a produção comercial de carne para o mercado de carnes vermelhas ou exóticas. Abstract in english Sensory characteristics and shear force of paca meat (Agouti paca) were assessed in this study. Analyses were performed in the bonelessshoulder,loin andhamobtained from nine paca carcassesprepared by cookinguntil reaching the internal temperatureof 70°C. The evaluation of flavor, aroma, color, appea [...] rance and tenderness was carried out by the application of an affective test using the hedonic scaleand a 146 consumer panel. Shear force was determined by the Warner-Bratzler technique. Shoulder, loin and ham had significant differences (p 0.05) among the cuts, which were similarly tender. Paca meat was found to resemble pork meat in sensory evaluation and had good acceptance by consumers. This study showed the potential of paca (Agouti paca) asa wild species for meat production in the red or exotic meat market.
2004-01-01
It is with great sadness that we learned that our friend and former colleague, David Warner, passed away on Christmas Eve. The funeral was held the following Monday. David was a "linac man". His career centred around linacs, but with a multitude of different subjects. He began at CERN by building the 3 MeV linac in the extension of the South Hall. He did pioneering work on this machine, which paved the way towards the design of the Alvarez cavities for the CERN Linac 2, for which he was responsible. After this challenge was successfully finished, David was the first member of the small but growing team, that was in charge of building the LEP Injector Linacs (LIL). After having been recognised as a proton linac expert, he quickly converted to electron linacs where he soon became the respected key expert for the design, parameters and ultimate performance of LIL. His predilection for precise and detailed documentation, and his vision that the know-how acquired with LIL should be preserved a...
DEFF Research Database (Denmark)
Christensen, L.; Andersen, L.
2011-01-01
Long term heat treatment at low temperature (LTLT) is known to decrease toughness of meat. However, the contribution from the connective tissue to the toughness of LTLT treated meat is not clear. The aim of the present study was to investigate the effect of LTLT treatments on shear force and cooking loss in semitendinosus from cows (4-6 years) and young bulls (12-14 months), representing 2 categories of beef with varying thermal strength of connective tissue. Vacuum packed muscle samples were heat treated at 53°C, 55°C, 58°C and 63°C in water baths for 2½, 7½ and 19½ h. Cooking loss and Warner-Bratzler shear force were measured after heat treatment and subsequent cooling. Shear force of semitendinosus from young bulls heated at 53°C for 2½ h was significantly higher compared with all other heat treatments. A decrease of app. 40 N was observed when increasing the heating temperature from 53°C to 55°C, or when increasing heating time from 2½ to 7½ h at 53°C. In semitendinosus from cows shear force decreased significantly with increasing temperature, and with increasing heating time from 2½ to 19½ h at 55°C and 63°C. Cooking loss increased with increasing heating temperature in both beef categories. The results show that prolonged heating at low temperatures reduce toughness in beef semitendinosus, and that a reduction in toughness require higher temperatures and longer heating times in semitendinosus from cows compared with young bulls.
This morning, Time Warner and EMI announced that they have decided to abandon plans to merge. The merger plan, which was estimated at $20 billion, was ditched after the two companies were unable to meet the concerns of anti-trust watchdog groups. Explaining that they wanted more time to deal with the objections of the merger, the two companies withdrew their application from the European Commission (EC). The main concern of the European Commission officials was that the merger would place 80 percent of the European recording music business in just four major global companies. At the last minute, EMI and Time Warner proposed selling off several music catalogs, distribution networks, and recording labels including Virgin Records and Chappell Music in order to sooth the worries of the EC. The EC commended the companies on a "substantial" improvement, but officials still had strong doubts about the tie-up. While the two companies will continue to consider ways to successfully merge, Paul Richards, a media analyst at WestLB Panmure in London, suggested that the EMI merger may have been abandoned to ensure Time Warner's merger with AOL. Richards stated, "The AOL-Time deal must go through, it's $200 billion (in terms of the combined company's market value), whereas the EMI deal is a $20 billion joint venture."
Corbin, C H; O'Quinn, T G; Garmyn, A J; Legako, J F; Hunt, M R; Dinh, T T N; Rathmann, R J; Brooks, J C; Miller, M F
2015-02-01
The palatability of tender [Warner-Bratzler shear force values umami (r=0.59) flavors. Fat level was the primary driver of beef flavor acceptability in all samples when no undesirable off-flavors were present. PMID:25299587
Scientific Electronic Library Online (English)
Oscar, Martínez-Morales; Edith G., Estrada-Venegas; Armando, Equihua-Martínez; Jorge, Valdez-Carrasco.
Full Text Available En este trabajo se describen e ilustran características morfológicas de Neochetina eichhorniae (Warner, 1970). Esta especie se ha utilizado para el control biológico del lirio acuático (Eichhornia crassipes (Mart.) Solms-Laubach, 1883). En el huevo, el aspecto cambiante del corion es dado por el des [...] arrollo embrionario. En la larva se realizó una descripción de la quetotaxia de la cápsula cefálica y se identificaron tres ínstares larvales con la medición de su anchura; también se revisó la microescultura del cuerpo de la larva, sobresaliendo unas microespinas, cuyo arreglo es diferente en tórax y abdomen, también se observaron dos tipos de espiráculos; el más característico es el espiráculo abdominal por su posición dorsal, que además de ser esclerosado, posee órganos sensoriales en su ápice. La morfología externa de los adultos de N. eichorniae es muy parecida en ambos sexos; su principal diferencia se encuentra en el rostrum. Además se proporciona una descripción de las alas, proventrículo y genitalia, estructuras importantes en la taxonomía. Las características morfológicas de N. eichhorniae encontradas en éste trabajo pueden ser útiles para diferenciar a esta especie de Neochetina bruchi (Hustache, 1926), la cual ha sido liberada en muchos países. Es el primer trabajo de morfología N. eichhorniae en México. Abstract in english In this study morphological characteristics of Neochetina eichhorniae (Warner, 1970) are described and illustrated. This species has been used for the Biological Control of waterhyacinth (Eichhornia crassipes (Mart.) Solms-Laubach, 1883). In the egg, the changing appearance of the chorion is given b [...] y the embryonic development. Description of larval head capsule chaetotaxy was done. Three larval instars were identified by measuring the head capsule width; microsculpture of the body larva was studied, microspines were evident with different arrangements in thorax and abdomen, two types of spiracles were found; the more distinctive was the dorsal spiracle in the abdomen, which is sclerotized, with sensory organs at its apex. The external morphology of N. eichorniae adult is very similar in both sexes, the main difference among them is the rostrum. Description of the wings, proventriculus and genitalia, important structures in the taxonomy, is provided. The morphological characteristics of N. eichhorniae found in this study can be use to separate from N. bruchi (Hustache) which has been released in many countries. This is the first morphological study of N. eichhorniae in Mexico.
ESTIMATED GENETIC PARAMETERS FOR PALATABILITY TRAITS OF STEAKS FROM BRAHMAN CATTLE
Heritabilities and genetic and phenotypic correlations were estimated from carcass and beef palatability data collected from Brahman calves (n = 504) born in central Florida from 1996 to 2000. Traits evaluated included Warner-Bratzler shear force (after 7, 14, and 21 d of aging), panel tenderness sc...
SARCOMERE LENGTH INFLUENCES IN VITRO CALPAIN-INDUCED PROTEOLYSIS OF BEEF MYOFIBRILS
The objective of this study was to determine the influence of sarcomere length on the extent of postmortem proteolysis and beef tenderness. First a model was developed to evaluate the effect of sarcomere length on tenderness, utilizing Warner-Bratzler shear force. Bovine semitendinosus and psoas maj...
The Warner Map Collection at the W.S. Hoole Special Collections Library
Based at the University of Alabama Libraries, the Warner Map Collection was a gift from the estate of Mildred Westervelt Warner, who passed away in 1974. Warner was an inveterate collector of antiquarian maps, and her collection ranges from 16th-century maps of the "New World" to an 1831 map of Alabama and Georgia. On the website, users can learn more about the Warner collection, and then peruse the fifteen different sections here. The sections include geographic regions ("The Caribbean") and cartographers, such as "Maps by Blaeu". There are only two maps in the collection by Blaeu, but they are both worth a look, as they are both interesting renderings of America in the 17th century. It's worth nothing that all of the maps also have high-resolution versions available, which makes it quite easy to examine each item in scrupulous detail.
Andrés, S.; SILVA, A; Soares-Pereira, A.L.; Martins, C; Bruno-Soares, A.M.; MURRAY, I
2008-01-01
Visible and near infrared reflectance spectroscopy was used to predict pH at 24 h (pH24) post-mortem, sarcomere length (SL), cooking loss (CL), Warner–Bratzler Shear Force (WBSF) and colour parameters (L*, a*, b*) in beef cattle samples. Samples from M. longissimus thoracis et lumborum from 30 bulls were aged at 4 C for 1, 3, 7 and 14 days and analysed for pH, SL, CL, WBSF and colour. NIRS calibrations for pH24, luminosity at 0 (L*t0) and 60 min (L*t60) showed good predictability ...
Andrés, S.; Silva, António; Soares-Pereira, Arminda L.; Martins, Conceição; Murrey, I.
2008-01-01
Visible and near infrared reflectance spectroscopy was used to predict pH at 24 hours(pH 24 ) post-mortem, sarcomere length (SL), cooking loss (CL), Warner-Bratzler shear force (WBSF) and colour parameters (L*, a*, b*) in beef cattle samples. Samples from M. longissimus thoracis et lumborum from 30 bulls were aged at 4º C for 1, 3, 7 and 14 days and analysed for pH, SL, CL, WBSF and colour. NIRS calibrations for pH 24,luminosity at 0 (L*t 0 ) and 60 minutes (L*t 60 ) showed go...
Use of near infrared spectroscopy for assessment of beef quality traits
Directory of Open Access Journals (Sweden)
L. Gallo
2010-04-01
Full Text Available Chemical and physical traits and fatty acid composition of meat samples from 148 Piemontese beef samples were predicted by near infrared spectroscopy. Coefficients of determination in calibration (R2 ranged between 0.44 and 0.99 for chemical composition and between 0.02 and 0.98 for fatty acid (FA profile, being in general more accurate for the major FA. The calibration results gave inaccurate prediction for cholesterol and collagen content and for most physical traits, such as Warner-Bratzler shear force, cooking loss, drip loss, colour (L, a, b and pH.
Energy Technology Data Exchange (ETDEWEB)
Hussain, Md.S.; Jamil, K. (Indian Institute of Chemical Technology, Hyderabad (India))
1990-08-01
Water hyacinth growth is kept under control by the week eating weevils, Neochetina eichhornae (Warner) and N. bruchi (Hustache). Water hyacinth is generally considered an aquatic weed because it clogs waterways, although it has recently been evaluated as a potential biological filter for sewage effluents. Water hyacinth plants are continuously subjected to contamination by mercury and other heavy metals from industrial effluents and fertilizer impurities. Little is known about the interaction of heavy metals/plants/insects. Aminotransferases are generally considered as indices for metabolic disturbances during Hg exposure. These enzymes are key enzymes for transamination, i.e., transfer of amino group from amino acid to keto acids which are ubiquitous in insects. The objective of the present study was to examine the bioaccumulation of mercury through the food chain in Neochetina eichhornae and its impact on protein metabolism.
Semiconductor laser shearing interferometer
International Nuclear Information System (INIS)
The application of semiconductor laser on grating shearing interferometry is studied experimentally in the present paper. The method measuring the coherence of semiconductor laser beam by ion etching double frequency grating is proposed. The experimental result of lens aberration with semiconductor laser shearing interferometer is given. Talbot shearing interferometry of semiconductor laser is also described. (author). 2 refs, 9 figs
Directory of Open Access Journals (Sweden)
Ebrahim Alfaig
2014-05-01
Full Text Available A study was conducted to determine the effect of probiotics and thyme essential oil (TEO as feed additives on the sensory attributes, cooking loss and the texture of broiler chicken meat. Day-old broilers Ross 308 (n = 400 were randomly divided into four groups based on the feed supplement as follows: control, probiotics 0.05%, TEO 0.05% and combination of probiotics and TEO, while the fattening period was 42 days. Warner Bratzler shear force, cooking loss and the following sensory attributes (colour, odour, taste, texture, meat decomposing and overall acceptability were tested. The obtained results of the Warner Bratzler shear force show that there was significant different (P < 0.05 between control and TEO group and for the cooking loss there was no significant difference between groups. The descriptive sensory analysis results show that the probiotics group results were somewhat similar to that obtained by control while the TEO group and the combination group results were similar. Regarding the sensory analysis we can state that the combination of the probiotics and TEO have a positive effect on the chicken meat sensory characteristics.
Scientific Electronic Library Online (English)
Lindon W, Mamani-Linares; Carmen, Gallo.
2011-12-01
Full Text Available Se comparó la composición química y calidad instrumental de carne de bovino, llama, y caballo finalizados bajo pastoreo. Los bovinos (n=31), llamas (n=21) y caballos (n=27) fueron faenados bajo procedimientos estándares de Chile. Las canales fueron refrigeradas durante 24 horas a 4 ºC. En el músculo [...] Longissimus lumborum (LL) se determinó la composición proximal, contenido de colesterol y colágeno, pH, color (L*, a*, b*, H*, C*), capacidad de retención de agua (WHC), pérdida de cocción, pérdida del descongelado y fuerza de corte Warner-Bratzler (WBSF). La carne de llama presentó mayores niveles de proteína y colágenos totales (p Abstract in english This study compared the chemical composition and instrumental meat quality of bovine, llama and horse from animals finished under grazing systems. The bovines (n=31), llamas (n=21) and horses (n=27) were slaughtered using Chilean standard procedures. Carcasses were stored for 24 h in a cold room (4 [...] ºC). The Longissimus lumborum muscle (LL) was collected for determining the chemical composition, cholesterol, collagen content, pH, colour (L*, a*, b*, H*, C*), water holding capacity (WHC) and Warner-Bratzler shear-force (WBSF). Llama meat had higher levels of protein and total collagen (p
A “coherent and sustained program” of improved radar detection of weather, pilot training, and better communication between pilots and air controllers can greatly reduce the risk of wind shear to airplanes landing or taking off, according to a National Research Council (NRC) committee.Wind shear, characterized by winds rapidly changing direction and speed, has caused several serious accidents in recent years; among the most notable is the July 8, 1982, crash of a Pan American World Airlines jetliner at the New Orleans International Airport, which killed 153 persons. Following the accident, Congress directed the Federal Aviation Administration (FAA) to contract with the NRC to study wind shear.
Mixing through shear instabilities
Bru?ggen, M.; Hillebrandt, W.
2000-01-01
In this paper we present the results of numerical simulations of the Kelvin-Helmholtz instability in a stratified shear layer. This shear instability is believed to be responsible for extra mixing in differentially rotating stellar interiors and is the prime candidate to explain the abundance anomalies observed in many rotating stars. All mixing prescriptions currently in use are based on phenomenological and heuristic estimates whose validity is often unclear. Using three-d...
Rusconi, Roberto; Guasto, Jeffrey S.; Stocker, Roman
2012-11-01
Bacteria are ubiquitously exposed to flow, both in natural environments and artificial devices (e.g., catheters), where confining surfaces create non-uniform shear. While the effects of shear on passive particles are well understood, little is known about the consequences of shear on motile bacteria. We exposed bacteria having different motility strategies (e.g., run-and-tumble, run-and-reverse) to microfluidic Poiseuille flows and quantified the swimming kinematics and cell distribution in the channel using video-microscopy. We discovered that the coupling of motility and a spatially varying shear results in a dramatic trapping of motile cells in high-shear regions, and conversely a strong depletion in the low-shear portion of the channel. We demonstrate experimentally that this trapping process is robust across species such as Bacillus subtilis and Pseudomonas aeruginosa, and can have far-reaching consequences on bacterial transport, by (i) counteracting bacterial chemotactic responses; and (ii) enhancing surface attachment and thus biofilm formation by trapping cells near walls. More generally, this work shows that-despite the low Reynolds number-the coupling of flow and self-propulsion can be nonlinear and not simply a superposition of the two effects.
Scientific Electronic Library Online (English)
María C., Miquel; Edgardo, Villarreal; Carlos, Mezzadra; Lilia, Melucci; Liliana, Soria; Pablo, Corva; Alejandro, Schor.
Full Text Available The objective of this paper was to determine the association of a SNP in the µ-calpain gene at position 316 with growth and quality of meat traits of steers grown on pasture. Fifty-nine Brangus and 20 Angus steers were genotyped for CAPN1 316. Warner Bratzler shear force was measured in l. lumborum [...] samples after a 7-day aging period. A multivariate analysis of variance was performed, including shear force (WBSF), final weight (FW), average daily gain (ADG), backfat thickness (BFT), average monthly fat thickness gain (AMFTG), rib-eye area (REA), and beef rib-eye depth (RED) as dependent variables. The CAPN1 316 genotype was statistically significant. Univariate analyses were done with these variables. The marker genotype was statistically significant (p
Baek, Hyung M.; Mix, Adam W.; Giacomin, A. Jeffrey
2014-05-01
For highly viscous fluids that slip in parallel sliding plate rheometers, we want to use a slightly converging flow to suppress this wall slip. In this work, we first attack the steady shear flow of a highly viscous Newtonian fluid between two gently converging plates with no slip boundaries using the equation of motion in cylindrical coordinates, which yields no analytical solution. Then we treat the same problem using the lubrication approximation in Cartesian coordinates to yield exact, explicit solutions for dimensionless velocity, pressure and shear stress. This work deepens our understanding of a drag flow through a gently converging slit of arbitrary convergence angle. We also employ the corotational Maxwell model to explore the role of viscoelasticity in this converging shear flow. We then compare these analytical solutions to finite element calculations for both Newtonian and corotational Maxwell cases. A worked example for determining the Newtonian viscosity using a converging shear rheometer is also included. With this work, we provide the framework for exploring other constitutive equations or other boundary conditions in future work. Our results can also be used to design the linear bearings used for the parallel sliding plate rheometer (SPR). This work can also be used to evaluate the error in the shear stress that is caused by bearing misalignment and specify the parallelism tolerance for the linear bearings incorporated into a SPR.
Development of conjugate shear bands during bulk simple shearing
Harris, L. B.; Cobbold, P. R.
In rocks possessing a strong planar fabric, shear bands of constant shear sense and oriented at an oblique angle to the foliation are considered by many authors to be characteristic of a non-coaxial bulk deformation history, whereas conjugate shear bands are considered to indicate coaxial shortening. However, in two areas where bulk deformation history appears to be non-coaxial (Cap Corse, Corsica and Ile de Groix, Brittany), conjugate shear bands are observed. In order to investigate this problem, experiments were performed by bulk simple shearing using Plasticine as a rock analogue. When slip between layers of the model is permitted, shear bands of normal-fault geometry form with both the same and opposite shear sense as the bulk simple shearing at approximately the same angle with the layering (40°) irrespective of layer orientation in the undeformed state (for initial orientations of 50, 30 and 15°). Shear bands are initially formed within individual layers and may propagate across layer interfaces when further movement along these is inhibited. The existence of conjugate shear bands in Corsica and Ile de Groix is therefore not incompatible with a model of bulk simple shearing for these two regions. In field studies, one should perhaps exercise care in using shear bands to determine the kind of motion or the sense of bulk shearing.
Britt, Charles L.
1988-01-01
Viewgraphs used in a presentation on wind shear radar simulation are given. Information on a microburst model of radar reflectivity and wind velocity, radar pulse output, the calculation of radar return, microburst power spectrum, and simulation plans are given. A question and answer session is transcribed.
van Deen, Merlijn; Janssen, Vera; Siemens, Alexander; van Hecke, Martin
2015-03-01
We experimentally apply a cyclic pure shear deformation to a two-dimensional foam at different densities. We probe the onset of irreversibility and relate this to local rearrangements in the system and show the behavior close to jamming is different from that in dense systems.
International Nuclear Information System (INIS)
Neglecting the second order corrections in weak lensing measurements can lead to a few percent uncertainties on cosmic shears, and becomes more important for cluster lensing mass reconstructions. Existing methods which claim to measure the reduced shears are not necessarily accurate to the second order when a point spread function (PSF) is present. We show that the method of Zhang (2008) exactly measures the reduced shears at the second order level in the presence of PSF. A simple theorem is provided for further confirming our calculation, and for judging the accuracy of any shear measurement method at the second order based on its properties at the first order. The method of Zhang (2008) is well defined mathematically. It does not require assumptions on the morphologies of galaxies and the PSF. To reach a sub-percent level accuracy, the CCD pixel size is required to be not larger than 1/3 of the Full Width at Half Maximum (FWHM) of the PSF, regardless of whether the PSF has a power-law or exponential profile at large distances. Using a large ensemble (?>107) of mock galaxies of unrestricted morphologies, we study the shear recovery accuracy under different noise conditions. We find that contaminations to the shear signals from the noise of background photons can be removed in a well defined way because they are not correlated with the source shapes. The residual shear measurement errors due to background noise are consistent with zero at the sub-percent level even when the amplitude of such noise reaches about 1/10 of the source flux within the half-light radius of the source. This limit can in principle be extended further with a larger galaxy ensemble in our simulations. On the other hand, the source Poisson noise remains to be a cause of systematic errors. For a sub-percent level accuracy, our method requires the amplitude of the source Poisson noise to be less than 1/80 ? 1/100 of the source flux within the half-light radius of the source, corresponding to collecting roughly 104 source photons
Hillary Clinton / Judith Warner
Warner, Judith
1994-01-01
Kõige mõjuvõimsam naine maailmas - algus EA 22. veebruar 1994. May/4,11,18,25 lk. 22;22;22;21; Jun/1,8,15,22,29 lk. 21; Jul/6,13,20,27 21; Aug/3,10,17,24,31 lk. 21; Sep/7,14,21,28 lk. 21; Oct/5,12,19 lk. 21
Shearing behavior of polydisperse media
Wackenhut, M; Herrmann, H; Wackenhut, Martin; Namara, Sean Mc; Herrmann, Hans
2004-01-01
We study the shearing of polydisperse and bidisperse media with a size ratio of 10. Simulations are performed with a the two dimensional shear cell using contact dynamics. With a truncated power law for the polydisperse media we find that they show a stronger dilatancy and greater resistance to shearing than bidisperse mixtures. Motivated by the practical problem of reducing the energy needed to shear granular media, we introduce "point-like particles" representing charged particles in the distribution. Even though changing the kinematic behavior very little, they reduce the force necessary to maintain a fixed shearing velocity.
Plasticity Approach to Shear Design
DEFF Research Database (Denmark)
Hoang, Cao Linh; Nielsen, Mogens Peter
1998-01-01
The paper presents some plastic models for shear design of reinforced concrete beams. Distinction is made between two shear failure modes, namely web crushing and crack sliding. The first mentioned mode is met in beams with large shear reinforcement degrees. The mode of crack sliding is met in non-shear reinforced beams as well as in lightly shear reinforced beams. For such beams the shear strength is determined by the recently developed crack sliding model. This model is based upon the hypothesis that cracks can be transformed into yield lines, which have lower sliding resistance than yield lines formed in uncracked concrete. Good agree between theory and tests has been found.Keywords: dsign, plasticity, reinforced concrete, reinforcement, shear, web crushing.
Energy Technology Data Exchange (ETDEWEB)
Butler, B.D.; Hanley, H.J.M.; Straty, G.C. [National Institute of Standards and Technology, Boulder, CO (United States); Muzny, C.D. [Univ. of Colorado, Boulder, CO (United States)
1995-12-31
An experimental small angle neutron scattering (SANS) study of dense silica gels, prepared from suspensions of 24 nm colloidal silica particles at several volume fractions {theta} is discussed. Provided that {theta}{approx_lt}0.18, the scattered intensity at small wave vectors q increases as the gelation proceeds, and the structure factor S(q, t {yields} {infinity}) of the gel exhibits apparent power law behavior. Power law behavior is also observed, even for samples with {theta}>0.18, when the gel is formed under an applied shear. Shear also enhances the diffraction maximum corresponding to the inter-particle contact distance of the gel. Difficulties encountered when trying to interpret SANS data from these dense systems are outlined. Results of computer simulations intended to mimic gel formation, including computations of S(q, t), are discussed. Comments on a method to extract a fractal dimension characterizing the gel are included.
Saunders, W
2008-01-01
Cosmic shear offers a remarkbly clean way to measure the equation of state of the Universe and its evolution. Resolution over a wide field is paramount, and Antarctica offers unique possibilities in this respect. There is an order of magnitude gain in speed over temperate sites, or a factor three in surface density. This means that PILOT outperforms much larger telescopes elsewhere, and can compete with the proposed DUNE space mission. Keywords: Antarctic astronomy, Surveys, Adaptive optics, Weak lensing
Onuki, A; Minam, A; Onuki, Akira; Furukawa, Akira; Minam, Akihiko
2004-01-01
We present a time-dependent Ginzburg-Landau model of nonlinear elasticity in solid materials. We assume that the elastic energy density is a periodic function of the shear and tetragonal strains owing to the underlying lattice structure. With this new ingredient, solving the equations yields formation of dislocation dipoles or slips. In plastic flow high-density dislocations emerge at large strains to accumulate and grow into shear bands where the strains are localized. In addition to the elastic displacement, we also introduce the local free volume {\\it m}. For very small $m$ the defect structures are metastable and long-lived where the dislocations are pinned by the Peierls potential barrier. However, if the shear modulus decreases with increasing {\\it m}, accumulation of {\\it m} around dislocation cores eventually breaks the Peierls potential leading to slow relaxations in the stress and the free energy (aging). As another application of our scheme, we also study dislocation formation in two-phase alloys (...
Schmidt, J R; Miller, M C; Andrae, J G; Ellis, S E; Duckett, S K
2013-09-01
Angus-cross steers (n = 60) were used to assess the effect of forage species [alfalfa (AL; Medicago sativa L.), bermudagrass (BG; Cynodon dactylon), chicory (CH; Cichorium intybus L.), cowpea (CO; Vigna unguiculata L.), and pearl millet (PM; Pennisetum glaucum (L. R Br.)] in replicated 2-ha paddocks for finishing on cattle performance, carcass quality, and meat quality in a 2-yr study. Steers were blocked by BW and assigned randomly to finishing-forage treatments before the start of the experiment. Steers grazing AL and CH had greater (P grasses (BG and PM). Marbling scores tended to be greater (P = 0.06) for CO, but carcasses from steers grazing CO received greater (P 1 kg/d). Finishing on legumes (AL and CO) increased dressing percentage, reduced Warner-Bratzler shear force values, and increased consumers preference, whereas finishing on grasses (BG and PM) enhanced anticarcinogenic fatty acid concentrations. PMID:23825343
Duan, Q; Tait, R G; Schneider, M J; Beitz, D C; Wheeler, T L; Shackelford, S D; Cundiff, L V; Reecy, J M
2015-08-01
The objective of this study was to evaluate sire breed effect on mineral concentration in beef longissimus thoracis (LT) and investigate the correlations between beef mineral concentrations and carcass and palatability traits. Steer progeny (N=246) from the Germplasm Evaluation project-Cycle VIII were used in this study. In addition to carcass traits, LT was evaluated for mineral concentrations, Warner-Bratzler shear force, and palatability traits. A mixed linear model estimated breed effects on mineral concentrations. No significant sire breed (P?0.43) or dam breed (P?0.20) effects were identified for mineral concentrations. Pearson correlation coefficients were calculated among mineral concentrations, carcass, and sensory traits. Zinc concentration was positively correlated (P?0.05) with total iron (r=0.14), heme iron (r=0.13), and magnesium (r=0.19). Significant (Ppalatability traits. PMID:25866932
Directory of Open Access Journals (Sweden)
A. Girolami
2010-04-01
Full Text Available The experiment was performed with thirty-two Altamurana and Trimeticcio lambs slaughtered at 42 and at 70 days of age. Meat organoleptic characteristics were determined on samples of M. Longissimus lumborum and Longissimus thoracis. Colour parameters were not affected by genotype, while L* value and index of yellow decreased (P<0.01 and P<0.05, respectively as age of slaughtering increased. Meat from Altamurana lambs showed lower juiciness (P<0.01 and fatness (P<0.05 than Trimeticcio lambs. No genotype and age of slaughtering effects were found for Warner-Bratzler shear force (WBSF values. Meat from younger lambs was more tender and chewable (P<0.01 but less juicy (P<0.001 and fatty (P<0.05 than meat from lambs slaughterd at 70 days.
Effect of Breed of Sire on Carcass Traits and Meat Quality of Katahdin Lambs
Directory of Open Access Journals (Sweden)
José A. Partida
2012-09-01
Full Text Available Crossbred lambs (n = 40 of 137 ± 3 days of age from Katahdin ewes with either Charollais (KCh, Dorper (KD, Suffolk (KS and Texel (KT sires were used in this study. The effect of sire breeds on carcass traits, chemical composition of muscle, meat quality and consumer acceptability was determined. Regarding carcass traits, KCh animals had the highest fat thickness. KT lambs had the smallest M. Longissimusdorsi (MLD area compared tothat of KCh, KD and KS (17.0, 15.9, 15.5 and 13.9 cm2; respectively. Breed of sire had no effect (P>0.05 on the chemical composition, pH or Warner-Bratzler shear force (WBSF of lamb; however, it did affect meat color. KS lambs had lower L*, a*, b* and Ch* values compared to the other crossbreeds (P<0.05. Consumer acceptability of lamb was similar (P>0.05 across genotypes.
Comparison of textural atributes of selected meat sausages using instrumental analysis
Directory of Open Access Journals (Sweden)
Vladimír Vietoris
2013-03-01
Full Text Available Normal 0 21 false false false SK X-NONE X-NONE The aim of the study was to compare textural atributes of selected meat sausages using instrumental analysis. For this purpose, seven different meat sausage samples were treated by instrumental analysis, by the use of Warner-Bratzler probe, to find differences for two selected textural parameter firmness and work of shear. As expected, various values of mentioned atributes were obtained for different samples tested in fresh stage and after storage under controlled conditions (48 hrs., 30 °C temp., and 60 % R.H. before and after cooking. For statistical evaluation of results, paired T test was used, statistically significant differences were taken at pdoi:10.5219/273
The Hypertrophic Marchigiana: physical and biochemical parameters for meat quality evaluation
Directory of Open Access Journals (Sweden)
F. M. Sarti
2010-04-01
Full Text Available The aim of this study was to evaluate the meat quality of double muscled Marchigiana young bulls characterized by different genotypes for the hypertrophy: normal and mutated (heterozygous. Calpain and calpastatin activities were determined to verify the state of aging meat on a sample of Longissimus thoracis muscle (XIII thoracic rib taken at slaughtering (0h and after 24 hours (24h. After 14 days of aging, another sample of muscle was taken to evaluate physical and chemical parameters of meat quality. The results showed a better meat quality of mutated animals respect normal animals. Another interesting result was the correlation between the biochemical parameters and some physical parameters, such as WBS (Warner Bratzler Shear Force, CL (Cooking loss. These results showed the relationship between the proteolytic activity of calpain system and meat tenderness.
Orange peel flour effect on physicochemical, textural and sensory properties of cooked sausages
Directory of Open Access Journals (Sweden)
Sonia Hernandez Garcia
2010-06-01
Full Text Available Orange peel flours as a source of fiber, protein, and flavonoids as antioxidants was added to meat batters in order to improve nutritional quality and physicochemical, textural and sensory properties. Orange peel flour in meat batters improved yield and reduced expressible moisture. Hardness in orange peel flour samples was higher, but less resilient and cohesive. Warner-Bratzler shear force was not different between control (no orange peel flour and samples with this functional ingredient. A no trained panel determinate that there was no difference between control and orange peel flour added sausages at a 5% (w/w level. In this view, orange peel flour can be employed to improve yield and texture of cooked meat products.
Oltra, O R; Farmer, L J; Gordon, A W; Moss, B W; Birnie, J; Devlin, D J; Tolland, E L C; Tollerton, I J; Beattie, A M; Kennedy, J T; Farrell, D
2015-02-01
In this study, important eating quality attributes that influence consumer liking for grilled lamb loin have been identified using preference mapping techniques. The eating quality attributes identified as driving the consumer liking of lamb loin steaks were “tenderness”, “sweet flavour”, “meaty aftertaste”, “roast lamb flavour” and “roast lamb aftertaste”. In contrast, the texture attribute “rubbery” and the flavour attributes “bitter flavour” and "bitter aftertaste" had a negative influence on consumer perceptions. Associations were observed between eating quality and a number of instrumental and chemical measurements. Warner Bratzler Shear Force showed an association with “rubbery” texture and a negative association with “tenderness” and consumer liking scores. The compounds, glucose, glucose-6-phosphate, inosine, inosine monophosphate and adenosine monophosphate were associated with the attributes, “sweet flavour”,“meaty aftertaste”, “roast lamb flavour”, “roast lamb aftertaste” and with consumer scores for liking of lamb which is probably caused by the role some of these compounds play as precursors of flavour and as taste compounds. PMID:25460112
ADIABATIC SHEAR IN POROUS MEDIA
Kotoul, M.; Bi?lek, Z.
1988-01-01
An advanced model of shear deformation occuring in high strain rate deformation of ductile porous solids is proposed under simple planar shear loading superposed by hydrostatic pressure. To describe porous - rigid thermoplastic material the Gurson theory of dilatant plasticity is applied and appearance of an adiabatic shear is interpreted in terms of mathematical instabilities in the underlying differential equations. The substantial influence of porosity on strain hardening and thermal softe...
Direct Measurement of Turbulent Shear
Stefanus, Stefanus; Steers, Stanley; Goldburg, Walter
2010-01-01
A photon correlation method is introduced for measuring components of the shear rate tensor in a turbulent soap film. This new scheme, which is also applicable to three-dimensional flows, is shown to give the same results as Laser Doppler velocimetry, but with less statistical noise. The technique yields the mean shear rate s, its standard deviation, and a simple mathematical transform of the probability density function P(s) of the shear rate itself.
Shear viscosity of nuclear matter
Xu, Jun
2013-01-01
In this talk I report my recent study on the shear viscosity of neutron-rich nuclear matter from a relaxation time approach. An isospin- and momentum-dependent interaction is used in the study. Effects of density, temperature, and isospin asymmetry of nuclear matter on its shear viscosity have been discussed. Similar to the symmetry energy, the symmetry shear viscosity is defined and its density and temperature dependence are studied.
Dislocation kinetics behind shear shocks
International Nuclear Information System (INIS)
High velocity oblique impact experiments result in both compression and shear shock waves. Behind the shear shock wave the particle velocity is transverse to the shock front. At large transverse particle velocities, dislocation kinetics can contribute a portion of the velocity. Based on a kinematic and thermodynamic model of dislocation kinetics, an analysis is made of the transverse strain and velocity behind a shear shock. Kinematics of dislocations in transverse motion behind the shock is formulated. A solution is given for an ideal case where the dislocation density function propagates as a pulse behind the shear shock. 9 refs
Dislocation kinetics behind shear shocks
Energy Technology Data Exchange (ETDEWEB)
Stout, R.B.; Anderson, G.D.
1985-06-01
High velocity oblique impact experiments result in both compression and shear shock waves. Behind the shear shock wave the particle velocity is transverse to the shock front. At large transverse particle velocities, dislocation kinetics can contribute a portion of the velocity. Based on a kinematic and thermodynamic model of dislocation kinetics, an analysis is made of the transverse strain and velocity behind a shear shock. Kinematics of dislocations in transverse motion behind the shock is formulated. A solution is given for an ideal case where the dislocation density function propagates as a pulse behind the shear shock. 9 refs.
Tempo de cozimento e textura de raízes de mandioca / Cooking time and texture of cassava roots
Scientific Electronic Library Online (English)
Simone Vilela, Talma; Selma Bergara, Almeida; Rozana Moreira Pereira, Lima; Henrique Duarte, Vieira; Pedro Amorim, Bebert.
2013-06-01
Full Text Available O objetivo deste trabalho foi avaliar a adequação de medidas instrumentais de textura como índice de qualidade de raízes da mandioca de mesa e sua correlação com o tempo de cozimento. Quinze raízes de mandioca foram colhidas no 11.º mês de cultivo na região noroeste fluminense. Pedaços de raízes for [...] am cozidos em água, sendo o tempo de cozimento determinado, em triplicata, quando se observou pouca resistência à penetração do garfo. A resistência ao corte foi realizada nas polpas cruas e cozidas, em cinco a nove repetições, operando o texturômetro TA. XT Plus Texture Analyser com probe Warner-Bratzler Blade HDP/BSW, velocidades de pré-teste de 0,2 cm/s, de pós-teste e de teste de 0,5 cm/s, e distância de 5 cm. Os dados foram analisados por ANOVA e teste de média Tukey (tempo de cozimento); GLM, LSMEANS e PDIFF (resistência ao corte) e análise de correlação de Pearson (p Abstract in english The objective of this work was to evaluate the adequacy of instrumental texture analyses as a quality index for cassava roots for direct consumption, and the correlation with cooking time. Fifteen cassava roots were harvested in the eleventh month of growth in the northwest of the State of Rio de Ja [...] neiro. Pieces of roots were boiled in water and the cooking time determined in triplicate, to the point where there was little resistance to penetration by a fork. The shear strength was determined in the raw and cooked pulps with five to nine replicates, using the texturometer TA-XT Plus Texture Analyser with the Warner-Bratzler Blade HDP / BSW probe, a pre-test speed of 0.2 cm/s, post-test and test speed of 0.5 cm/s and distance of 5 cm. The data were analyzed by ANOVA and Tukey (cooking time), GLM, LSMEANS and PDIFF (shear resistance) and Pearson's correlation analysis (p
Effect of probiotics and thyme essential oil on the texture of cooked chicken breast meat
Directory of Open Access Journals (Sweden)
Ebrahim Alfaig
2013-12-01
Full Text Available Background. Texture is probably the single most critical quality factor associated with the consumers’ ultimate satisfaction with a poultry meat product and can be affected by several factors including the type of feed used for chickens fattening. The use of probiotics for meat and carcass quality improvement has been questioned, while the possibility of deposition of essential oils in various muscle tissues can alter the sensory attributes of the chicken’s meat. Material and methods. Probiotics and thyme essential oil in the percentage of 0.05% were used as feed supplements for Ross 308 broiler chickens, as the broilers were reared in four separated groups based on the feed supplement as follows: control, probiotics, thyme essential oil and combination of probiotics and thyme essential oil group, while the fattening period was 42 days. TA.XT Plus-Texture analyser apparatus was used for determination of the texture profile and Warner Bratzler shear force for the cooked breast meat. Results. Warner Bratzler shear test results showed that the tested feed additives were not affecting the texture of the chicken breast meat, while probiotic appears to have moderately effect on the hardness, cohesiveness, springiness and chewiness attributes of the cooked breast meat compared with the other groups, this effect of probiotics considered as negligible, as the results showed that all the tested groups meat were very tender according to the tenderness scale. Conclusions. According to the obtained results it can be concluded the combination of probiotics and thyme group resulted in the lowest score for the hardness, cohesiveness, springiness and chewiness attributes, while probiotics group scored the highest compared with the control.
Jiang, Weifeng; Xuan, Shouhu; Gong, Xinglong
2015-04-01
Dense non-Brownian suspension has rich rheology and is hard to understand, especially for distinguishing continuous shear thickening (CST) from discontinuous shear thickening (DST). By studying the shear stress dependent rheology of a well-known DST suspension of cornstarch in water, we find that the transition from CST to DST could occur not only by increasing the volume fraction ? but also by increasing the shear stress ?. For the recovery process of jammed suspension, we observe that the shear activates the time-dependent nature of particle rearrangement. DST can then be interpreted as the consequence of shear-induced jamming. Based on the test data, we plot the schematic phase diagram in the ?-? plane and find out that ? and ? perform almost the same effect on flow-state transition.
Scaling of Entropic Shear Rigidity
Xing, Xiangjun; Mukhopadhyay, Swagatam; Goldbart, Paul M.
2004-01-01
The scaling of the shear modulus near the gelation/vulcanization transition is explored heuristically and analytically. It is found that in a dense melt the effective chains of the infinite cluster have sizes that scale sub-linearly with their contour length. Consequently, each contributes k_B T to the rigidity, which leads to a shear modulus exponent d\
Bayesian Lensing Shear Measurement
Bernstein, Gary M
2013-01-01
We derive an estimator of weak gravitational lensing shear from background galaxy images that avoids noise-induced biases through a rigorous Bayesian treatment of the measurement. The Bayesian formalism requires a prior describing the (noiseless) distribution of the target galaxy population over some parameter space; this prior can be constructed from low-noise images of a subsample of the target population, attainable from long integrations of a fraction of the survey field. We find two ways to combine this exact treatment of noise with rigorous treatment of the effects of the instrumental point-spread function and sampling. The Bayesian model fitting (BMF) method assigns a likelihood of the pixel data to galaxy models (e.g. Sersic ellipses), and requires the unlensed distribution of galaxies over the model parameters as a prior. The Bayesian Fourier domain (BFD) method compresses galaxies to a small set of weighted moments calculated after PSF correction in Fourier space. It requires the unlensed distributi...
Shear angle of magnetic fields.
Yanping, Lü; Wang, Jingxiu; Wang, Huaning
1993-11-01
The authors introduce a new parameter, the shear angle of vector magnetic fields, ??, to describe the non-potentiality of magnetic fields in active regions, which is defined as the angle between the observed vector magnetic field and its corresponding current-free field. In the case of highly inclined field configurations, this angle is approximately equal to the "angular shear", ??, defined by Hagyard et al. (1984). ?? can be considered as the projection of the shear angle, ??, on the photosphere. For the active region studied, the shear angle, ??, seems to have a better and neater correspondence with flare activity than does ??. It gives a clearer explanation of the non-potentiality of magnetic fields. It is a better measure of the deviation of the observed magnetic field from a potential field, and is directly related to the magnetic free energy stored in non-potential fields.
Localized states in sheared electroconvection
Tsai, Peichun; Daya, Zahir A
2008-01-01
Electroconvection in a thin, sheared fluid film displays a rich sequence of bifurcations between different flow states as the driving voltage is increased. We present a numerical study of an annular film in which a radial potential difference acts on induced surface charges to drive convection. The film is also sheared by independently rotating the inner edge of the annulus. This simulation models laboratory experiments on electroconvection in sheared smectic liquid crystal films. The applied shear competes with the electrical forces, resulting in oscillatory and strongly subcritical bifurcations between localized vortex states close to onset. At higher forcing, the flow becomes chaotic via a Ruelle-Takens-Newhouse scenario. The simulation allows flow visualization not available in the physical experiments, and sheds light on previously observed transitions in the current-voltage characteristics of electroconvecting smectic films.
Shear behaviour of reinforced phyllite concrete beams
International Nuclear Information System (INIS)
Highlights: ? Phyllite concrete beams often exhibited shear with anchorage bond failure. ? Different shear design provisions for reinforced phyllite beams are compared. ? Predicted shear capacity of phyllite beams must be modified by a reduction factor. -- Abstract: The shear behaviour of concrete beams made from phyllite aggregates subjected to monotonic and cyclic loading is reported. First diagonal shear crack load of beams with and without shear reinforcement was between 42–58% and 42–92% of the failure loads respectively. The phyllite concrete beams without shear links had lower post-diagonal cracking shear resistance compared to corresponding phyllite beams with shear links. As a result of hysteretic energy dissipation, limited cyclic loading affected the stiffness, strength and deformation of the phyllite beams with shear reinforcement. Generally, beams with and without shear reinforcement showed anchorage bond failure in addition to the shear failure due to high stress concentration near the supports. The ACI, BS and EC codes are conservative for the prediction of phyllite concrete beams without shear reinforcement but they all overestimate the shear strength of phyllite concrete beams with shear reinforcement. It is recommended that the predicted shear capacity of phyllite beams reinforced with steel stirrups be modified by a reduction factor of 0.7 in order to specify a high enough safety factor on their ultimate strength. It is also recommended that susceptibility of phyllite concrete beams to undergo anchorage bond failure is averted in design by the provision of greater anchorage lengths than usually permitted.
Shear shocks in fragile networks.
Ulrich, Stephan; Upadhyaya, Nitin; van Opheusden, Bas; Vitelli, Vincenzo
2013-12-24
A minimal model for studying the mechanical properties of amorphous solids is a disordered network of point masses connected by unbreakable springs. At a critical value of its mean connectivity, such a network becomes fragile: it undergoes a rigidity transition signaled by a vanishing shear modulus and transverse sound speed. We investigate analytically and numerically the linear and nonlinear visco-elastic response of these fragile solids by probing how shear fronts propagate through them. Our approach, which we tentatively label shear front rheology, provides an alternative route to standard oscillatory rheology. In the linear regime, we observe at late times a diffusive broadening of the fronts controlled by an effective shear viscosity that diverges at the critical point. No matter how small the microscopic coefficient of dissipation, strongly disordered networks behave as if they were overdamped because energy is irreversibly leaked into diverging nonaffine fluctuations. Close to the transition, the regime of linear response becomes vanishingly small: the tiniest shear strains generate strongly nonlinear shear shock waves qualitatively different from their compressional counterparts in granular media. The inherent nonlinearities trigger an energy cascade from low to high frequency components that keep the network away from attaining the quasi-static limit. This mechanism, reminiscent of acoustic turbulence, causes a superdiffusive broadening of the shock width. PMID:24309379
Scientific Electronic Library Online (English)
Lindon W., Mamani-Linares; Faustina, Cayo; Carmen, Gallo.
2013-04-01
Full Text Available Se compararon las características tecnológicas de doce músculos de llamas que fueron criadas al pastoreo. Las llamas (n=10) fueron faenadas bajo procedimientos estándares de Bolivia. Las canales fueron refrigeradas durante 24 horas a 4 ºC. Los músculos fueron removidos de cada canal después del desp [...] oste. Cinco bifes de 2.54 cm de espesor fueron cortados de cada músculo. En cada músculo se determinó el pH24, color (L*, a*, b*), capacidad de retención de agua y fuerza de corte Warner-Bratzler (WBSF). No se observaron diferencias estadísticas en el pH entre los músculos. Los valores de L* (luminosidad) y b* (tenor de amarrillo) de los músculos L. thoracis, L. lumborum y Semimembranosus fueron mayores que en Triceps brachii y Psoas major (p Abstract in english This study compared the technological quality of twelve muscles of llama that were raised in a grazing system. The llamas (n=10) were slaughtered using Bolivian standard procedures. Carcasses were stored for 24 h in a cold room (4 ºC). Muscles were removed from the left side of each carcass in the s [...] laughter house. Five steaks (2.54 cm thick) were cut from each muscle. In each muscle was determined pH, colour (L*, a*, b*), water holding capacity (WHC) and Warner-Bratzler shear-force (WBSF). No statistical difference was found in pH between muscles. Values of L* (lightness) and b* (tenor of yellow) in L. thoracis, L. lumborum and Semimembranosus were higher than those in Triceps brachii and Psoas major (p
Palotti, Matthew Lee
The outflows from young, massive protostars are observed to contain, in many instances, more mass than the protostar producing them. Entrainment, spurred on by hydrodynamical or magnetohydrodynamical instabilities, is one possible mechanism of gathering the extra mass. The instability found at a shear flow boundary layer is known as the Kelvin-Helmholtz instability (KHI). This thesis lays the groundwork to start answering the outflow question by examining the KHI in more detail through the use of 2D simulations. I investigate the role of resistivity on the saturation and non-linear evolution of the KHI under the influence of a weak magnetic field. The models run cover magnetic Reynolds numbers ranging from Rm = 1000 toRm = 50000 which, admittedly, is much lower than the Reynolds numbers found in the ISM (Rm ˜ 10 15). Wherever possible, I have tried to postulate the effects of going to even higher Reynolds numbers. Additionally, I have also examined the mixing properties of the KHI by utilizing passive Lagrangian particles initially distributed evenly within the boundary layer. The particles are then tracked as they are advected through the velocity field. Finally, I examine the KHI in a weakly ionized medium. In reality, the molecular interstellar medium is partially ionized, with an ionization fraction Xe ˜ 10-8--10-7. In the absence of collisions, the ions will evolve as the MHD instability does and the neutrals will evolve as the HD instability. However, collisions between the ions and neutrals will affect that evolution. I found that the role of resistivity has a large effect on the non-linear evolution, causing the kinetic and magnetic energy to decay on a much longer timescale. The transport of momentum is greater in the MHD model, with an increasing effect with magnetic Reynolds number, than in the HD model. However, the particle transport remains the same for both the HD and MHD models. The effect is attributed to a large effect on the momentum transport from the Maxwell Stress. Collisions tend to damp out the energy in the instability for a strong magnetic field case.
Scientific Electronic Library Online (English)
Wesley Oliveira de, Sousa; Germano Henrique, Rosado-Neto; Marinêz Isaac, Marques.
2012-09-01
Full Text Available A teoria plastrão foi testada em adultos de Neochetina eichhorniae Warner, 1970, por meio da análise da estrutura que reveste o tegumento destes insetos e em experimentos laboratoriais de submersão. Os processos tegumentares foram reconhecidos em três tipos: escamas aglutinadas e com perfurações lar [...] gas; escamas plumosas de tamanhos e formas variadas; e pêlos. Os experimentos realizados com 264 indivíduos adultos os quais permaneciam submersos por diferentes intervalos de tempo (n = 11) e em dois tratamentos, água natural não aerada e água previamente fervida, com quatro repetições para cada tratamento, revelaram uma mortalidade máxima após 24 horas de mergulho no tratamento água previamente fervida. A sobrevivência dos adultos foi negativa e significativamente correlacionada com os tratamentos empregados e entre os diferentes intervalos de tempo. Os valores de oxigênio dissolvido (mg/l) na água diferiram significativamente entre os tratamentos aplicados, sendo positivamente correlacionado com a sobrevivência dos adultos nos dois tratamentos, embora mais acentuadamente no tratamento com água previamente fervida. A mortalidade dos adultos após 24 horas de mergulho no tratamento com água previamente fervida pode estar associada às condições físico-químicas da água não testadas neste estudo, como, por exemplo, baixa tensão superficial e concentração de solutos. Estes resultados sugerem uma funcionalidade do plastrão nos adultos desta espécie. Abstract in english The plastron theory was tested in adults of Neochetina eichhorniae Warner, 1970, through the analysis of the structure that coats these insects' integument and also through submersion laboratorial experiments. The tegument processes were recognized in three types: agglutinated scales with large perf [...] orations, plumose scales of varied sizes and shapes, and hairs. The experiments were carried out on 264 adult individuals which were kept submerged at different time intervals (n = 11) and in two types of treatment, natural non-aerated water and previously boiled water, with four repetitions for each treatment. The tests showed a maximum mortality after 24 hours of immersion in the previously boiled water treatment. The survival of the adults was negative and significantly correlated with the types of treatment employed and within the different time intervals. The values of oxygen dissolved in water (mg/l) differed significantly within the types of treatment employed. They were positively correlated with the survival of the adults in the two types of treatment, although more markedly in the treatment with previously boiled water. The mortality of adults after 24 hours of submersion in the treatment with previously boiled water may be associated with the physical-chemical conditions of the non-tested water in this study, such as low surface tension and concentration of solutes. These results suggest plastron functionality in the adults of this species.
Unexpected shear strength change in magnetorheological fluids
Directory of Open Access Journals (Sweden)
Yu Tian
2014-09-01
Full Text Available Smart materials of magnetorheological (MR fluids could be turned from a liquid state into a solid state, which solidification extent or shear strength often increases monotonically with the applied magnetic field. In this study, the shear stress of a dilute MR fluid decreased with increasing applied magnetic field at a constant shear rate. The dynamic shear stress was significantly higher than the stable counterpart at medium magnetic fields. They are ascribed to the slow particle structure transformation. A higher shear rate and particle volume fraction could reduce the transient time and the shear strength difference.
Experimental observation of shear thickening oscillation
Nagahiro, Shin-ichiro; Mitarai, Namiko
2012-01-01
We report experimental observation of the shear thickening oscillation, i.e. the spontaneous macroscopic oscillation in the shear flow of severe shear thickening fluid. The shear thickening oscillation is caused by the interplay between the fluid dynamics and the shear thickening, and has been predicted theoretically by the present authors using a phenomenological fluid dynamics model for the dilatant fluid, but never been reported experimentally. Using a density-matched starch-water mixture, in the cylindrical shear flow of a few centimeters flow width, we observed strong vibrations of the frequency around 20 Hz, which is consistent with our theoretical prediction.
Shear loading of costal cartilage
Subit, Damien
2014-01-01
A series of tests were performed on a single post-mortem human subject at various length scales. First, tabletop tests were performed. Next, the ribs and intercostal muscles were tested with the view to characterize the load transfer between the ribs. Finally, the costal cartilage was tested under shear loading, as it plays an important in the transfer of the load between the ribs and the sternum. This paper reports the results of dynamic shear loading tests performed on three samples of costal cartilage harvested from a single post-mortem human subject, as well as the quantification of the effective Young's modulus estimated from the amount of cartilage calcification.
International Nuclear Information System (INIS)
Experiments at RHIC suggest that the quark-gluon plasma created in heavy-ion collisions is an almost-perfect fluid. Furthermore, the ?/s ratio (shear viscosity per entropy density) turns out to be minimal at the phase transition. We discuss the formalism which connects quantum field theory at finite temperature and the macroscopic transport coefficients for dissipative hydrodynamical systems. Within the framework of ChPT we compute the shear viscosity of an interacting pion gas in the confined phase. The results are compared to the AdS/CFT bound of 1/4?.
The Influence of Shearing Velocity on Shear Behavior of Artificial Joints
Atapour, Hadi; Moosavi, Mahdi
2014-09-01
In this paper, the effects of shear velocity on the shearing behavior of artificial joints have been studied at different normal stress levels. Here, artificial joints with planar and rough surfaces were prepared with the plaster (simulating soft rock joints) and concrete (medium-hard rock joints) materials. The rough joints had triangular shaped asperities with 10° and 20° inclination angles. Direct shear tests were performed on these joints under various shear velocities in the range of 0.3-30 mm/min. The planar plaster-plaster and planer concrete-concrete joints were sheared at three levels of normal stress under constant normal load boundary condition. Also, the rough plaster-plaster and concrete-concrete joints were sheared at one level of normal stress under constant normal stiffness boundary condition. The results of the shear tests show that the shearing parameters of joints, such as shear strength, shear stiffness and friction angle, are related to the shear velocity. Shear strength of planar and rough plaster-plaster joints were decreased when the shear velocity was increased. Shear strength of concrete joints, except for rough joints with 10° inclination, increased with increasing shear velocity. Regardless of the normal stress level, shear stiffness of both planar plaster-plaster and concrete-concrete joints were decreased when the shear velocity was increased.
Granular Couette Flow at High Shear Rates
Voth, Greg; Sundquist, Jamie; Gollub, Jerry
2002-11-01
We present an experimental study of couette flow of granular material at very high shear rates. Wall velocities up to 9.4 m/s and shear rates up to 2400 s-1 (based on a shear band that is 4 particle diameters thick) are achieved. We find a surprising non-monotonic dependence of the torque on the shear rate. This effect shows large variability even when the obvious variables such as temperature, humidity and preparation history are controlled. We interpret the variability as arising from particle wear that changes the frictional interactions that dominate the torque at lower shear rates. At very high shear rates, the torque increases monotonically with shear rate and is quite reproducible. We interpret this behavior as reflecting collisional dynamics at high shear rates. Non-dimensional parameters that control the change from friction dominated to collision dominated interactions will be discussed. (Work supported by NSF Division of Materials Research)
Shear Dynamics in Higher Dimensional FLRW Cosmology
Pahwa, Isha; Nandan, Hemwati; Goswami, Umananda Dev
2014-01-01
We study the shear dynamics of higher dimensional Friedmann-Lema\\^{i}tre-Robertson-Walker (FLRW) cosmology by considering a non-perfect fluid which exerts different pressure in the normal and extra dimensions. We generalise the definition of shear tensor for higher dimensional space-time and prove it to be consistent with the evolution equation for shear tensor obtained from the Ricci identities. The evolution of shear tensor is investigated numerically. The role of extra di...
Boundary Shear Stress in Rectangular Compound Channels
AL-KHATIB, Issam A.
1999-01-01
Experimental results are presented concerning the boundary shear stress distribution in a rectangular compound section channel comprising rectangular main channel and two symmetrically disposed floodplains. Different dimensionless ratios of shear stress distributions are obtained and related to relevant parameters. The floodplains due to the momentum transfer between the deep section and floodplains has been investigated. Some important results concerning the uniformity of shear str...
Collisional shear Alfven waves in sheared magnetic fields
International Nuclear Information System (INIS)
The structure of the shear Alfven waves is investigated in a collisional plasma with shear. The fourth-order equation obtained by combining Ampere's law and the quasi-neutrality condition is solved by the method of matched asymptotic expansions for k/sub perpendicular/ rho/sub s/>><<1 to obtain the dispersion relation. A hierarchy of damped, localized modes are found which can have either even or odd parity. The solutions basically have the structure of kinetic Alfven modes trapped between the two Alfven cutoffs on either side of the rational surface. The mode damping arises from Ohmic dissipation by electrons near the rational surface. The relation between these modes, microtearing modes, and the Alfven continuum is discussed
Ideal stability limits of reverse shear equilibria
International Nuclear Information System (INIS)
The dependence on various plasma parameters of the ideal stability limit of reverse shear current profiles in TFTR and other tokamaks has been thoroughly explored. Profiles with reverse shear allow core access to the second ballooning stability region. In addition, for sufficient shear reversal, modes with n = 2 and greater are also stabilized. The n = 1 stability threshold is only slightly affected by reverse shear and becomes the limiting instability. The mode is predominately an infernal mode with a significant external contribution. Particular emphasis will be on analysis of recent experimental results of enhanced reverse shear (ERS) profiles in TFTR and a study of those profile characteristics which optimize TFTR performance
Pure shear axes and elastic strain energy
Norris, Andrew N.
2006-01-01
It is well known that a state of pure shear has distinct sets of basis vectors or coordinate systems: the principal axes, in which the stress is diagonal, and pure shear bases, in which diag(stress)=0. The latter is commonly taken as the definition of pure shear, although a state of pure shear is more generally defined by tr(stress)=0. New results are presented that characterize all possible pure shear bases. A pair of vector functions are derived which generate a set of pur...
Shear Dynamics in Higher Dimensional FLRW Cosmology
Pahwa, Isha; Goswami, Umananda Dev
2014-01-01
We study the shear dynamics of higher dimensional Friedmann-Lema\\^{i}tre-Robertson-Walker (FLRW) cosmology by considering a non-perfect fluid which exerts different pressure in the normal and extra dimensions. We generalise the definition of shear tensor for higher dimensional space-time and prove it to be consistent with the evolution equation for shear tensor obtained from the Ricci identities. The evolution of shear tensor is investigated numerically. The role of extra dimensions and other parameters involved in shear dynamics is discussed in detail. We find that with increase in anisotropy parameter, time of decay of shear increases while with increase in number of extra dimensions, shear tends to decay early.
Shear shocks in fragile matter
Ulrich, Stephan; Vitelli, Vincenzo; Upadhyaya, Nitin
2013-03-01
Random media, like polymer networks, covalent network glasses, or grains under pressure can be viewed as elastic networks composed of springs and balls. The shear moduli of these types of materials typically vanish as the network connectivity z approaches a critical value. In this talk, I show that shear strains propagate as diffusive fronts, whose width diverges and whose transverse speed of sound vanishes, as the transition is approached. Consequently, in this regime, linear theory breaks down, giving rise to nonlinear transverse waves. Comparison of the analytical front profile to molecular dynamics simulations allows the extraction of the material constants of the network. Interestingly, even an undamped network yields a diverging effective viscosity caused by leaking of energy into non-affine degrees of freedom.
Controlled shear/tension fixture
Hsueh, Chun-Hway (Knoxville, TN); Liu, Chain-tsuan (Knoxville, TN); George, Easo P. (Knoxville, TN)
2012-07-24
A test fixture for simultaneously testing two material test samples is provided. The fixture provides substantially equal shear and tensile stresses in each test specimens. By gradually applying a load force to the fixture only one of the two specimens fractures. Upon fracture of the one specimen, the fixture and the load train lose contact and the second specimen is preserved in a state of upset just prior to fracture. Particular advantages of the fixture are (1) to control the tensile to shear load on the specimen for understanding the effect of these stresses on the deformation behavior of advanced materials, (2) to control the location of fracture for accessing localized material properties including the variation of the mechanical properties and residual stresses across the thickness of advanced materials, (3) to yield a fractured specimen for strength measurement and an unfractured specimen for examining the microstructure just prior to fracture.
Shear Stabilization in the Levitron
International Nuclear Information System (INIS)
The levitron is a toroidal hard-core tube of 30-cm minor diameter, with a ring core left unsupported for 20 msec. A 5-kG toroidal field, and a comparable poloidal field based on a ring-core current, are pulsed on with 60-to 16,000-?sec rise times. The magnetic shear is always large, insuring infinite-conductivity hydromagnetic stability. Finite-resistivity and non-hydromagnetic instabilities are expected, however; and their study is the object of the experiment. Levitron experiments in the high-current regime (for example, ?50-kA induced current, lasting 1 to 2 msec, at ?3 x 1013 -cm-3 plasma density and electron temperatures in the 100-eV range) show a small-scale ''magnetic flutter'' (?5 G, ?100 kc/sec) of flutelike structure. The stability analysis for the hard-core geometry, however, proves categorically that the observed mode cannot be of the finite-resistivity ''tearing'' type. To what extent shear stabilization is valid even in the absence of directed current, is theoretically still disputed. In this context we are studying electron-cyclotron heating at 10 Gc/sec. Hot-electron plasmas with the usual dilute high-energy (10 to 1000 keV) and dense (?1012 cm-3) low-energy components have been contained for 1 to 10 msec times after ?-wave cut off. When the initially generated high-energy component is left by itself, it proves highly unstable to cross-field transport, with or without shear, due partly to the mirror localization associated with the hard-core field in toroidal geometry. In the absence of shear (pure poloidal field), the flute instability limits the electron temperature of the dense-plasma component to ? 5 eV. With an additional toroidal field ?150 G, electron temperatures of 50 eV are attained, but they are still limited by a (presumably resistive) flute instability that is insensitive to a further 10-fold increase in shear. (author)
Shear strength properties of wet granular materials
Richefeu, V; Radja"i, F; Richefeu, Vincent; Youssoufi, Moulay Sa\\"{i}d El; Radja\\"{i}, Farhang
2006-01-01
We investigate shear strength properties of wet granular materials in the pendular state (i.e. the state where the liquid phase is discontinuous) as a function of water content. Sand and glass beads were wetted and tested in a direct shear cell and under various confining pressures. In parallel, we carried out three-dimensional molecular dynamics simulations by using an explicit equation expressing capillary force as a function of interparticle distance, water bridge volume and surface tension. We show that, due to the peculiar features of capillary interactions, the major influence of water content over the shear strength stems from the distribution of liquid bonds. This property results in shear strength saturation as a function of water content. We arrive at the same conclusion by a microscopic analysis of the shear strength. We propose a model that accounts for the capillary force, the granular texture and particle size polydispersity. We find fairly good agreement of the theoretical estimate of the shear...
Hierarchical Cosmic Shear Power Spectrum Inference
Alsing, Justin; Jaffe, Andrew H; Kiessling, Alina; Wandelt, Benjamin; Hoffmann, Till
2015-01-01
We develop a Bayesian hierarchical modelling approach for cosmic shear power spectrum inference, jointly sampling from the posterior distribution of the cosmic shear field and its (tomographic) power spectra. Inference of the shear power spectrum is a powerful intermediate product for a cosmic shear analysis, since it requires very few model assumptions and can be used to perform inference on a wide range of cosmological models \\emph{a posteriori} without loss of information. We show that joint posterior for the shear map and power spectrum can be sampled effectively by Gibbs sampling, iteratively drawing samples from the map and power spectrum, each conditional on the other. This approach neatly circumvents difficulties associated with complicated survey geometry and masks that plague frequentist power spectrum estimators, since the power spectrum inference provides prior information about the field in masked regions at every sampling step. We demonstrate this approach for inference of tomographic shear $E$-...
Convectively driven shear and decreased heat flux
Goluskin, David; Johnston, Hans; Flierl, Glenn R.; Spiegel, Edward A.
2014-01-01
We report on direct numerical simulations of two-dimensional, horizontally periodic Rayleigh-B\\'enard convection, focusing on its ability to drive large-scale horizontal flow that is vertically sheared. For the Prandtl numbers ($Pr$) between 1 and 10 simulated here, this large-scale shear can be induced by raising the Rayleigh number ($Ra$) sufficiently, and we explore the resulting convection for $Ra$ up to $10^{10}$. When present in our simulations, the sheared mean flow a...
Shear wall experiments and design in Japan
International Nuclear Information System (INIS)
This paper summarizes the results of recent survey studies on the available experimental data bases and design codes/standards for reinforced concrete (RC) shear wall structures in Japan. Information related to the seismic design of RC reactor buildings and containment structures was emphasized in the survey. The seismic requirements for concrete structures, particularly those related to shear strength design, are outlined. Detailed descriptions are presented on the development of Japanese shear wall equations, design requirements for containment structures, and ductility requirements
Developments in Plasticity Approach to Shear
DEFF Research Database (Denmark)
Hoang, Cao Linh; Nielsen, Mogens Peter
1999-01-01
The paper deals with plastic methods applied to shear design of reinforced concrete beams. Emphasis is put on the recently developed crack sliding model applicable to non-shear reinforced and lightly shear reinforced beams and slabs. The model, which is an upper bound plasticity approach, takes into account the mechanism of crack formation followed by crack sliding. Comparisons between the model and test results are carried out. Good agreement has been found over a wide range of cases.
Glass transitions and shear thickening suspension rheology
Holmes, Colin B.; Cates, Michael E.; Fuchs, Matthias; Sollich, Peter
2004-01-01
We introduce a class of simple models for shear thickening and/ or `jamming' in colloidal suspensions. These are based on schematic mode coupling theory (MCT) of the glass transition, having a memory term that depends on a density variable, and on both the shear stress and the shear rate. (Tensorial aspects of the rheology, such as normal stresses, are ignored for simplicity.) We calculate steady-state flow curves and correlation functions. Depending on model parameters, we ...
Periodic Exponential Shear of Complex Fluids
Kalelkar, Chirag; Mckinley, Gareth
2012-01-01
We define a class of flows with exponential kinematics termed Periodic Exponential Shear (PES) flow which involve periodic exponential stretching of fluid elements along with their rotation. We exhibit analytical and numerical results for PES flow by using the Oldroyd-B model for viscoelastic fluids. We calculate the growth in the shear and the normal stresses analytically as well as demonstrate that repeated application of the flow leads to stable oscillatory shear and norm...
Collision statistics in sheared inelastic hard spheres
Bannerman, Marcus N.; Green, Thomas E.; Grassia, Paul; Lue, Leo
2009-01-01
The dynamics of sheared inelastic-hard-sphere systems are studied using non-equilibrium molecular dynamics simulations and direct simulation Monte Carlo. In the molecular dynamics simulations Lees-Edwards boundary conditions are used to impose the shear. The dimensions of the simulation box are chosen to ensure that the systems are homogeneous and that the shear is applied uniformly. Various system properties are monitored, including the one-particle velocity distribution, g...
Mixing in shear thinning fluids
Scientific Electronic Library Online (English)
H., Ameur; M., Bouzit.
2012-06-01
Full Text Available In the present study, a CFD characterization of the flow generated by curved-blade impellers in a cylindrical unbaffled vessel was carried out. The tank diameter was 300 mm, with a flat bottom. The liquid height was equal to the vessel diameter. The fluids simulated have a shear thinning behavior. A [...] nalyses concern the effect of the impeller speed, the fluid rheology and the number of impeller blades on the induced flow patterns and the power consumption. The predictions were compared with literature data and a satisfactory agreement was found.
Shear bands in aluminium-lithium alloys
International Nuclear Information System (INIS)
The formation of shear bands in Al-Li alloys in cold rolling and their influence on mechanical properties of rolled and heat treated sheets are under consideration. It is shown that shear bands as well as the network of recrystallized grains along previous bands are undesirable structural constituents in aluminum alloy sheets as they decrease processing and operational properties of alloys. In further metal forming the localization of strain is observed along shear bands or zones of recrystallized grains. To avoid failure due to shear band formation it is recommended to roll alloys in as-annealed state and properly regulate reduction degree
Study on magnetorheological shear thickening fluid
International Nuclear Information System (INIS)
In this paper, a magnetic-field-controlled and speed-activated magnetorheological shear thickening fluid (MRSTF) is presented. We fabricated a kind of shear thickening fluid (STF) which was composed of nanosize silica particles suspended in a solvent, ethylene glycol, at high concentrations. Then the micron-size carbonyl iron particles with different volume fractions were added to the STF to fabricate the MRSTF. Their dynamic properties in different shear strain rates and magnetic fields were tested by using a rheometer. The suspension shows an abrupt increase in complex viscosity beyond a critical dynamic shear rate and a magnetic-field-controllable characteristic, as well as being reversible
Inertial shear bands in granular materials
Berzi, Diego; Jenkins, James T.
2015-03-01
We provide numerical solutions to the momentum and energy balance of a kinetic theory for the steady, collisional shearing of identical, inelastic, frictional spheres between two different types of boundaries—rigid-bumpy and erodible, in the absence of gravity. A rigid-bumpy boundary is a source of fluctuation energy for the flow, an erodible boundary is a sink. As a consequence, the characteristics of shearing between two rigid-bumpy boundaries, two erodible boundaries, and a rigid-bumpy and an erodible boundary are all different. Here, we display these differences and relate them to measurements of inhomogeneous shearing and the development of shear bands in laboratory experiments.
Effect of Friction on Shear Jamming
Wang, Dong; Ren, Jie; Dijksman, Joshua; Bares, Jonathan; Behringer, Robert
2015-03-01
Shear jamming of granular materials was first found for systems of frictional disks, with a static friction coefficient ? ~ 0 . 6 (Bi et al. Nature (2011)). Jamming by shear is obtained by starting from a zero-stress state with a packing fraction ? between ?J (isotropic jamming) and a lowest ?S for shear jamming. This phenomenon is associated with strong anisotropy in stress and the contact network in the form of force chains, which are stabilized and/or enhanced by the presence of friction. Whether shear jamming occurs for frictionless particles is under debate. The issue we address experimentally is how reducing friction affects shear jamming. We put the Teflon-wrapped photoelastic disks, lowering the friction substantially from previous experiments, in a well-studied 2D shear apparatus (Ren et al. PRL (2013)), which provides a uniform simple shear. Shear jamming is still observed; however, the difference ?J -?S is smaller with lower friction. We also observe larger anisotropies in fragile states compared to experiments with higher friction particles at the same density. In ongoing work we are studying systems using photoelastic disks with fine gears on the edge to generate very large effective friction. Shear jamming of granular materials was first found for systems of frictional disks, with a static friction coefficient ? ~ 0 . 6 (Bi et al. Nature (2011)). Jamming by shear is obtained by starting from a zero-stress state with a packing fraction ? between ?J (isotropic jamming) and a lowest ?S for shear jamming. This phenomenon is associated with strong anisotropy in stress and the contact network in the form of force chains, which are stabilized and/or enhanced by the presence of friction. Whether shear jamming occurs for frictionless particles is under debate. The issue we address experimentally is how reducing friction affects shear jamming. We put the Teflon-wrapped photoelastic disks, lowering the friction substantially from previous experiments, in a well-studied 2D shear apparatus (Ren et al. PRL (2013)), which provides a uniform simple shear. Shear jamming is still observed; however, the difference ?J -?S is smaller with lower friction. We also observe larger anisotropies in fragile states compared to experiments with higher friction particles at the same density. In ongoing work we are studying systems using photoelastic disks with fine gears on the edge to generate very large effective friction. We acknowledge support from NSF Grant DMR1206351, NSF Grant DMS-1248071, NASA Grant NNX10AU01G and William M. Keck Foundation.
Novel shear mechanism in nanolayered composites
Energy Technology Data Exchange (ETDEWEB)
Mara, Nathan [Los Alamos National Laboratory; Bhattacharyya, Dhriti [Los Alamos National Laboratory; Hirth, John P [Los Alamos National Laboratory; Dickerson, Patricia O [Los Alamos National Laboratory; Misra, Amit [Los Alamos National Laboratory
2009-01-01
Recent studies have shown that two-phase nanocomposite materials with semicoherent interfaces exhibit enhanced strength, deformability, and radiation damage resistance. The remarkable behavior exhibited by these materials has been attributed to the atomistic structure of the bi-metal interface that results in interfaces with low shear strength and hence, strong barriers for slip transmission due to dislocation core spreading along the weak interfaces. In this work, the low interfacial shear strength of Cu/Nb nanoscale multilayers dictates a new mechanism for shear banding and strain softening during micropillar compression. Previous work investigating shear band formation in nanocrystalline materials has shown a connection between insufficient strain hardening and the onset of shear banding in Fe and Fe-10% Cu, but has also shown that hardening does not necessarily offset shear banding in Pd nanomaterials. Therefore, the mechanisms behind shear localization in nanocrystalline materials are not completely understood. Our findings, supported by molecular dynamics simulations, provide insight on the design of nanocomposites with tailored interface structures and geometry to obtain a combination of high strength and deformability. High strength is derived from the ability of the interfaces to trap dislocations through relative ease of interfacial shear, while deformability can be maximized by controlling the effects of loading geometry on shear band formation.
Shear alters motility of Escherichia coli
Molaei, Mehdi; Jalali, Maryam; Sheng, Jian
2013-11-01
Understanding of locomotion of microorganisms in shear flows drew a wide range of interests in microbial related topics such as biological process including pathogenic infection and biophysical interactions like biofilm formation on engineering surfaces. We employed microfluidics and digital holography microscopy to study motility of E. coli in shear flows. We controlled the shear flow in three different shear rates: 0.28 s-1, 2.8 s-1, and 28 s-1 in a straight channel with the depth of 200 ?m. Magnified holograms, recorded at 15 fps with a CCD camera over more than 20 minutes, are analyzed to obtain 3D swimming trajectories and subsequently used to extract shear responses of E.coli. Thousands of 3-D bacterial trajectories are tracked. The change of bacteria swimming characteristics including swimming velocity, reorientation, and dispersion coefficient are computed directly for individual trajectory and ensemble averaged over thousands of realizations. The results show that shear suppresses the bacterial dispersions in bulk but promote dispersions near the surface contrary to those in quiescent flow condition. Ongoing analyses are focusing to quantify effect of shear rates on tumbling frequency and reorientation of cell body, and its implication in locating the hydrodynamic mechanisms for shear enhanced angular scattering. Understanding of locomotion of microorganisms in shear flows drew a wide range of interests in microbial related topics such as biological process including pathogenic infection and biophysical interactions like biofilm formation on engineering surfaces. We employed microfluidics and digital holography microscopy to study motility of E. coli in shear flows. We controlled the shear flow in three different shear rates: 0.28 s-1, 2.8 s-1, and 28 s-1 in a straight channel with the depth of 200 ?m. Magnified holograms, recorded at 15 fps with a CCD camera over more than 20 minutes, are analyzed to obtain 3D swimming trajectories and subsequently used to extract shear responses of E.coli. Thousands of 3-D bacterial trajectories are tracked. The change of bacteria swimming characteristics including swimming velocity, reorientation, and dispersion coefficient are computed directly for individual trajectory and ensemble averaged over thousands of realizations. The results show that shear suppresses the bacterial dispersions in bulk but promote dispersions near the surface contrary to those in quiescent flow condition. Ongoing analyses are focusing to quantify effect of shear rates on tumbling frequency and reorientation of cell body, and its implication in locating the hydrodynamic mechanisms for shear enhanced angular scattering. NIH, NSF, GoMRI.
Shear banding phenomena in a Laponite suspension
Ianni, F; Gentilini, S; Ruocco, G
2007-01-01
Shear localization in an aqueous clay suspension of Laponite is investigated through dynamic light scattering, which provides access both to the dynamics of the system (homodyne mode) and to the local velocity profile (heterodyne mode). When the shear bands form, a relaxation of the dynamics typical of a gel phase is observed in the unsheared band soon after flow stop, suggesting that an arrested dynamics is present during the shear localization regime. Periodic oscillations of the flow behavior, typical of a stick-slip phenomenon, are also observed when shear localization occurs. Both results are discussed in the light of various theoretical models for soft glassy materials.
Shear strength in one- and two-way slabs according to the critical shear crack theory
Muttoni, Aurelio; Ferna?ndez Ruiz, Miguel
2008-01-01
Currently, there is no generally-accepted theory giving a physical explanation of the shear strength in one- and two-way slabs. Furthermore, for members without transverse reinforcement, shear strength is estimated in most codes of practice following empirical or semi-empirical approaches. In this paper, the fundamentals of the Critical Shear Crack Theory (CSCT) are introduced. This theory, based on a mechanical model, is shown to provide a unified approach for one- and two-way shear in...
Shear Behavior Of Reinforced High-Strength Concrete Beams Without Shear Reinforcement
Wafa, Faisal F.
1994-01-01
Eighteen rectangular singly reinforced high-strength concrete beams without web reinforcement were tested in combined shear and flexure. The main variables were the longitudinal steel reinforcement ratio and the shear-span to effective depth ratio. The uniaxial compressive strength of concrete was about 93 MPa (13,500 psi). The experimental shear capacities were compared with the shear capacities predicted by different empirical equations presented in literatures. Two empirical equations have...
DEFF Research Database (Denmark)
Christensen, M.; Torngren, M. A.
2009-01-01
BACKGROUND: Marination of beef muscles with brine solutions containing proteolytic enzymes from fruit extracts has been shown to tenderize meat. However, the effect of marination with actinidin on tenderness of pork muscles has not been investigated. Tenderness and eating quality of porcine M. biceps femoris was investigated by Warner-Bratzler (WB) shear test and sensory evaluation after injection of brine containing up to 11 g L-1 actinidin-containing kiwi fruit powder and 2, 5 or 9 days of storage. RESULTS: actinidin decreased WB shear force, increased tenderness and did not affect flavour and juiciness. Injection of 2.8g L-1 actinidin powder and storage for 2 days resulted in WB shear force values similar to control samples stored for 5 or 9 days. In samples injected with 10 g L-1 actinidin powder, degradation of desmin and percentage of heat-soluble collagen (P <0.05) increased compared to control samples. Myofibrillar particle size tended to decrease (P <0.1) with increasing actinidin concentration. No major changes were observed by proteome analysis. Atomic force microscopy showed actinidin-induced damage of endomysium surrounding isolated single muscle fibres. CONCLUSION: Our results indicate that actinidin tenderizes pork M. biceps femoris by affecting both the myofibrils and connective tissue.
Statistical Model of Extreme Shear
DEFF Research Database (Denmark)
Hansen, Kurt Schaldemose; Larsen, Gunner Chr.
2005-01-01
In order to continue cost-optimisation of modern large wind turbines, it is important to continuously increase the knowledge of wind field parameters relevant to design loads. This paper presents a general statistical model that offers site-specific prediction of the probability density function (PDF) of turbulence driven short-term extreme wind shear events, conditioned on the mean wind speed, for an arbitrary recurrence period. The model is based on an asymptotic expansion, and only a few and easily accessible parameters are needed as input. The model of the extreme PDF is supplemented by a model that, on a statistically consistent basis, describes the most likely spatial shape of an extreme wind shear event. Predictions from the model have been compared with results from an extreme value data analysis, based on a large number of full-scale measurements recorded with a high sampling rate. The measurements have been extracted from "Database on Wind Characteristics" (http://www.winddata.com/), and they refer to a site characterised by a flat homogeneous terrain. The comparison has been conducted for three different mean wind speeds in the range 15m/s – 19m/s, and model predictions and experimental results are consistent, given the inevitable uncertainties associated with the model as well as with the extreme value data analysis.
Martin, Stefan; Szwaykowski, Piotr
2007-01-01
A technique for measuring optical beam shear is based on collecting light from the four quadrants of the beam and comparing the optical power collected from each quadrant with that from the other three quadrants. As used here, "shear" signifies lateral displacement of a beam of light from a nominal optical axis. A sensor for implementing this technique consists of a modified focusing lens and a quad-cell photodetector, both centered on the nominal optical axis. The modification of the lens consists in cutting the lens into four sectors (corresponding to the four quadrants) by sawing along two orthogonal diameters, then reassembling the lens following either of two approaches described next. In one approach, the lens is reassembled by gluing the sectors back together. In the simplest variant of this approach, the kerf of the saw matches the spacing of the photodetector cells, so that the focus of each sector crosses the axis of symmetry to fall on the opposite photodetector cell (see figure). In another variant of this approach, the lens sectors are spaced apart to make their individual foci to fall on separate photodetector cells, without crossing the optical axis. In the case of a sufficiently wide beam, the modified lens could be replaced with four independent lenses placed in a square array, each focusing onto an independent photodetector
Shear wall ultimate drift limits
International Nuclear Information System (INIS)
Drift limits for reinforced-concrete shear walls are investigated by reviewing the open literature for appropriate experimental data. Drift values at ultimate are determined for walls with aspect ratios ranging up to a maximum of 3.53 and undergoing different types of lateral loading (cyclic static, monotonic static, and dynamic). Based on the geometry of actual nuclear power plant structures exclusive of containments and concerns regarding their response during seismic (i.e.,cyclic) loading, data are obtained from pertinent references for which the wall aspect ratio is less than or equal to approximately 1, and for which testing is cyclic in nature (typically displacement controlled). In particular, lateral deflections at ultimate load, and at points in the softening region beyond ultimate for which the load has dropped to 90, 80, 70, 60, and 50 percent of its ultimate value, are obtained and converted to drift information. The statistical nature of the data is also investigated. These data are shown to be lognormally distributed, and an analysis of variance is performed. The use of statistics to estimate Probability of Failure for a shear wall structure is illustrated
Shear Flows and Shear Viscosity in a Two-Dimensional Yukawa System (Dusty Plasma)
Nosenko, V
2004-01-01
The shear viscosity of a two-dimensional liquid-state dusty plasma was measured experimentally. A monolayer of highly charged polymer microspheres, with a Yukawa interaction, was suspended in a plasma sheath. Two counter-propagating Ar laser beams pushed the particles, causing shear-induced melting of the monolayer and a shear flow in a planar Couette configuration. By fitting the particle velocity profiles in the shear flow to a Navier-Stokes model, the kinematic viscosity was calculated; it was of order 1 mm^2/s, depending on the monolayer's parameters and shear stress applied.
Two fluid shear-free composites
Krisch, J. P.; Glass, E. N.
2013-08-01
Shear-free composite fluids are constructed from two Letelier rotated unaligned perfect fluids. The component fluid parameters necessary to construct a shear-free composite are investigated. A metric in the Stephani-Barnes solution family and a simple stationary metric are discussed.
Two Fluid Shear-Free Composites
Krisch, J P
2013-01-01
Shear-free composite fluids are constructed from two Letelier rotated unaligned perfect fluids. The component fluid parameters necessary to construct a shear-free composite are investigated. A metric in the Stephani-Barnes solution family and a simple stationary metric are discussed.
Finite element modelling of fabric shear
Lin, Hua; Clifford, Mike J.; Long, Andrew C.; Sherburn, Martin
2009-01-01
In this study, a finite element model to predict shear force versus shear angle for woven fabrics is developed. The model is based on the TexGen geometric modelling schema, developed at the University of Nottingham and orthotropic constitutive models for yarn behaviour, coupled with a unified displacement-difference periodic boundary condition. A major distinction from prior modelling of fabric shear is that the details of picture frame kinematics are included in the model, which allows the mechanisms of fabric shear to be represented more accurately. Meso- and micro-mechanisms of deformation are modelled to determine their contributions to energy dissipation during shear. The model is evaluated using results obtained for a glass fibre plain woven fabric, and the importance of boundary conditions in the analysis of deformation mechanisms is highlighted. The simulation results show that the simple rotation boundary condition is adequate for predicting shear force at large deformations, with most of the energy being dissipated at higher shear angles due to yarn compaction. For small deformations, a detailed kinematic analysis is needed, enabling the yarn shear and rotation deformation mechanisms to be modelled accurately.
Finite element modelling of fabric shear
International Nuclear Information System (INIS)
In this study, a finite element model to predict shear force versus shear angle for woven fabrics is developed. The model is based on the TexGen geometric modelling schema, developed at University of Nottingham and orthotropic constitutive models for yarn behaviour, coupled with a unified displacement-difference periodic boundary condition. A major distinction from prior modelling of fabric shear is that the details of picture frame kinematics are included in the model, which allows the mechanisms of fabric shear to be represented more accurately. Meso- and micro-mechanisms of deformation are modelled to determine their contributions to energy dissipation during shear. The model is evaluated using results obtained for a glass fibre plain woven fabric, and the importance of boundary conditions in the analysis of deformation mechanisms is highlighted. The simulation results show that the simple rotation boundary condition is adequate for predicting shear force at large deformations, with most of the energy being dissipated at higher shear angles due to yarn compaction. For small deformations, a detailed kinematic analysis is needed, enabling the yarn shear and rotation deformation mechanisms to be modelled accurately
Shear free solutions of Maxwell's equations
International Nuclear Information System (INIS)
A twisting shear free solution of Maxwell's equations is obtained by transforming to a complex coordinate system in which the corresponding solution is complex but twist free. The equations in this system are easily solved, and, by transforming back to the original coordinates, a twisting shear free solution of Maxwell's equations is obtained. (author)
Rearrangements and Dilatancy for Sheared Dense Materials
Lemai?tre, Anae?l
2001-01-01
Constitutive equations are proposed for dense materials, based on the identification of two types of free-volume activated rearrangements associated to shear and compaction. Two situations are studied: the case of an amorphous solid in a stress-strain test, and the case of a lubricant in tribology test. Varying parameters, strain softening, shear thinning, and stick-slip motion can be observed.
Solvable groups and a shear construction
DEFF Research Database (Denmark)
Freibert, Marco; Swann, Andrew Francis
2015-01-01
The twist construction is a geometric model of T-duality that includes constructions of nilmanifolds from tori. This paper shows how one-dimensional foliations on manifolds may be used in a shear construction, which in algebraic form builds certain solvable Lie groups from Abelian ones. We discuss other examples of geometric structures that may be obtained from the shear construction.
Compressibility effects in turbulent shear layers
Bogdanoff, D. W.
1983-06-01
For a number of reasons, it would be desirable to have a better understanding of the behavior of compressible turbulent shear layers. Such shear layers are important in the production of jet and rocket engine noise. They are present in supersonic combustion jet engine designs. Compressible shear layers are also important in many high power laser systems. In the present investigation, it is proposed to employ a Mach number M+ which may be of value in correlating compressibility effects. Experimental results showing the decrease of shear layer width with increasing Mach number are compared with the corresponding variations of theoretical instability growth rates calculated by Blumen et al. (1975). The agreement between theoretical and experimental results suggests that an important factor contributing to the decrease in the shear layer growth rate with increasing M+ is the decrease in the maximum growth rates of the large-scale Kelvin-Helmholtz instabilities.
Numerical analysis of cross shear plate rolling
DEFF Research Database (Denmark)
Zhang, Wenqi; Bay, Niels
1997-01-01
The rolling process is widely applied for industrial production of metal plates. In conventional plate rolling the two work rolls are rotating at the same peripheral speed. By introducing a specific difference in the speed of the two work rolls, cross shear rolling is introduced forming a central shear zone between the forward and backward slip zones in the deformation zone thus lowering the rolling load. A numerical analysis of the cross shear rolling process is carried out based on the slab method adopting Wanheim and Bay's general friction model. The pressure distribution along the contact are in the roll gap, the position and the size of the shear zone and the rolling load are calculated. Experimental results are presented verifying the calculations. The numerical analysis facilitates a better understanding of the mechanics in cross shear plate rolling.
Experimental study on the adiabatic shear bands
International Nuclear Information System (INIS)
Four martensitic steels (Z50CDV5 steel, 28CND8 steel, 35NCDV16 steel and 4340 steel) with different hardness between 190 and 600 Hsub(B) (Brinell hardness), have been studied by means of dynamic compressive tests on split Hopkinson pressure bar. Microscopic observations show that the fracture are associated to the development of adiabatic shear bands (except 4340 steel with 190 Hsub(B) hardness). By means of tests for which the deformation is stopped at predetermined levels, the measurement of shear and hardness inside the band and the matrix indicates the chronology of this phenomenon: first the localization of shear, followed by the formation of adiabatic shear band and ultimatly crack initiation and propagation. These results correlated with few simulations by finite elements have permitted to suggest two mecanisms of deformation leading to the formation of adiabatic shear bands in this specific test
Miyamoto, Naokazu; Hirata, Kosuke; Kanehisa, Hiroaki; Yoshitake, Yasuhide
2015-01-01
Ultrasound shear wave elastography is becoming a valuable tool for measuring mechanical properties of individual muscles. Since ultrasound shear wave elastography measures shear modulus along the principal axis of the probe (i.e., along the transverse axis of the imaging plane), the measured shear modulus most accurately represents the mechanical property of the muscle along the fascicle direction when the probe’s principal axis is parallel to the fascicle direction in the plane of the ultrasound image. However, it is unclear how the measured shear modulus is affected by the probe angle relative to the fascicle direction in the same plane. The purpose of the present study was therefore to examine whether the angle between the principal axis of the probe and the fascicle direction in the same plane affects the measured shear modulus. Shear modulus in seven specially-designed tissue-mimicking phantoms, and in eleven human in-vivo biceps brachii and medial gastrocnemius were determined by using ultrasound shear wave elastography. The probe was positioned parallel or 20° obliquely to the fascicle across the B-mode images. The reproducibility of shear modulus measurements was high for both parallel and oblique conditions. Although there was a significant effect of the probe angle relative to the fascicle on the shear modulus in human experiment, the magnitude was negligibly small. These findings indicate that the ultrasound shear wave elastography is a valid tool for evaluating the mechanical property of pennate muscles along the fascicle direction. PMID:25853777
Transient dynamics in dense colloidal suspensions under shear: shear rate dependence
International Nuclear Information System (INIS)
A combination of confocal microscopy and rheology experiments, Brownian dynamics (BD) and molecular dynamics (MD) simulations and mode coupling theory (MCT) have been applied in order to investigate the effect of shear rate on the transient dynamics and stress-strain relations in supercooled and glassy systems under shear. Immediately after shear is switched on, the microscopic dynamics display super-diffusion and the macroscopic rheology a stress overshoot, which become more pronounced with increasing shear rate. MCT relates both to negative sections of the generalized shear modulus, which grow with increasing shear rate. When the inverse shear rate becomes much smaller than the structural relaxation time of the quiescent system, relaxation through Brownian motion becomes less important. In this regime, larger stresses are accumulated before the system yields and the transition from localization to flow occurs earlier and more abruptly.
Keyser, Daniel; Anthes, Richard A.
1982-08-01
A series of numerical experiments with the Hoskins-Bretherton horizontal shear model of frontogenesis in an, amplifying, two-dimensional baroclinic wave is performed. The analytic solutions from the Boussinesq, semi-geostrophic model provide initial conditions for numerical integrations with a two-dimensional, dry version of the fully compressible, hydrostatic primitive equation (PE) model of Anthes and Warner with 40 km horizontal resolution. The PE model is integrated 1) without planetary boundary layer (PBL) physics; 2) with a one-layer bulk-drag scheme; and 3) with a high-vertical-resolution PBL model. The lower boundary is thermally insulated in order to isolate the effect of the internal mixing of heat in the PBL.The simulation with the high-resolution PBL physics resolves several realistic features including 1) a narrow updraft at the top of the PBL above the sea-level pressure trough at the warm edge of the frontal zone; 2) a stable layer capping the PBL to the rear of the frontal zone; and 3) slightly unstable or neutral lapse rates in the PBL behind the front and stable lapse rates in the PBL ahead of the front. A diagnostic analysis of the frontogenesis indicates that the fine structure resulting from adding PBL physics can be attributed to the frictionally driven, ageostrophic inflow in the PBL toward the surface pressure trough in which the frontal zone is located. A finding of particular interest is that the stability patterns in the PBL on either side of the front evolve independently of sensible heating at the surface.
IMAGE ANALYSIS FOR MODELLING SHEAR BEHAVIOUR
Directory of Open Access Journals (Sweden)
Philippe Lopez
2011-05-01
Full Text Available Through laboratory research performed over the past ten years, many of the critical links between fracture characteristics and hydromechanical and mechanical behaviour have been made for individual fractures. One of the remaining challenges at the laboratory scale is to directly link fracture morphology of shear behaviour with changes in stress and shear direction. A series of laboratory experiments were performed on cement mortar replicas of a granite sample with a natural fracture perpendicular to the axis of the core. Results show that there is a strong relationship between the fracture's geometry and its mechanical behaviour under shear stress and the resulting damage. Image analysis, geostatistical, stereological and directional data techniques are applied in combination to experimental data. The results highlight the role of geometric characteristics of the fracture surfaces (surface roughness, size, shape, locations and orientations of asperities to be damaged in shear behaviour. A notable improvement in shear understanding is that shear behaviour is controlled by the apparent dip in the shear direction of elementary facets forming the fracture.
Shear rheology of molten crumb chocolate.
Taylor, J E; Van Damme, I; Johns, M L; Routh, A F; Wilson, D I
2009-03-01
The shear rheology of fresh molten chocolate produced from crumb was studied over 5 decades of shear rate using controlled stress devices. The Carreau model was found to be a more accurate description than the traditional Casson model, especially at shear rates between 0.1 and 1 s(-1). At shear rates around 0.1 s(-1) (shear stress approximately 7 Pa) the material exhibited a transition to a solid regime, similar to the behavior reported by Coussot (2005) for other granular suspensions. The nature of the suspension was explored by investigating the effect of solids concentration (0.20 cocoa butter, and (2) a suspension of sugar of a similar size distribution (volume mean 15 mum) in cocoa butter and emulsifier. The chocolate and synthetic chocolate showed very similar rheological profiles under both steady shear and oscillatory shear. The chocolate and the sugar suspension showed similar Krieger-Dougherty dependency on volume fraction, and a noticeable transition to a stiff state at solids volume fractions above approximately 0.5. Similar behavior has been reported by Citerne and others (2001) for a smooth peanut butter, which had a similar particle size distribution and solids loading to chocolate. The results indicate that the melt rheology of the chocolate is dominated by hydrodynamic interactions, although at high solids volume fractions the emulsifier may contribute to the departure of the apparent viscosity from the predicted trend. PMID:19323742
Generalized shear of a soft rectangular block
Wang, Dong; Wu, M. S.
2014-10-01
The problem of the simple shear of a block has been treated in terms of a shear displacement, applied uniformly in a lateral direction and assumed to be a linear function of the height above the base. In this paper, simple shear is generalized: the shear displacement is neither uniform in the lateral direction nor necessarily a linear function of the height. Using second-order isotropic elasticity, the analytical solutions show that the shear displacements are characterized by the product of sine and hyperbolic sine functions of the height and depth variables, respectively. The height dependence of the shear displacement is predicted to be a combination of linear and sinusoidal functions, and is verified against the test data of agar-gelatin cuboidal blocks. If the gravity effect is incorporated, a quadratic dependence on height is additionally predicted. The calculation of stresses reveals the presence of not only negative normal stresses but also sinusoidally varying shear stresses on the lateral planes tending to distort the block about the height direction. These results can be of great importance in tissue/cell mechanics.
Convectively driven shear and decreased heat flux
Goluskin, David; Flierl, Glenn R; Spiegel, Edward A
2014-01-01
We report on direct numerical simulations of two-dimensional, horizontally periodic Rayleigh-B\\'enard convection, focusing on its ability to drive large-scale horizontal flow that is vertically sheared. For the Prandtl numbers ($Pr$) between 1 and 10 simulated here, this large-scale shear can be induced by raising the Rayleigh number ($Ra$) sufficiently, and we explore the resulting convection for $Ra$ up to $10^{10}$. When present in our simulations, the sheared mean flow accounts for a large fraction of the total kinetic energy, and this fraction tends towards unity as $Ra\\to\\infty$. The shear helps disperse convective structures, and it reduces vertical heat flux; in parameter regimes where one state with large-scale shear and one without are both stable, the Nusselt number of the state with shear is smaller and grows more slowly with $Ra$. When the large-scale shear is present with $Pr\\lesssim2$, the convection undergoes strong global oscillations on long timescales, and heat transport occurs in bursts. N...
Shear effects on crystalline structures of poly(L-lactide)
DEFF Research Database (Denmark)
Xiao, Peitao; Li, Hongfei
2013-01-01
The shearing effects of sheared polymer melts on their finally formed crystalline structures of poly(L-lactide) (PLLA) were investigated by means of small angle X-ray scattering (SAXS) and wide angle X-ray diffraction (WAXD). The results of WAXD prove that shear has no effects on the crystal structure of PLLA. The SAXS results demonstrate that both of the long period and the thickness of crystalline lamellae increase with rising shear rates when vertical to the shear direction, but remains constant when being parallel to the shear direction. The structural changes for samples prepared with different shear temperature or under the same shear strain but different shear rate were investigated. The mesophase of polymer melts and shearing effects on their pre-ordered phase turned out to be the key factor affecting the crystal structure of PLLA under different shearing conditions.
Development of Short Stroke Shearing Technology For FBR Fuel Pin
Higuchi, Hidetoshi; Koizumi, Kenji; Hirano, Hiroyasu; Tasaka, Masayuki; Washiya, Tadahiro; Kobayashi, Tsuguyuki
The short stroke shearing tests with simulated fuel pin bundle were carried out in engineering scale. The shearing device was designed to handle the simulated Monju (FBR prototype reactor) type fuel pin bundle. Monju type and Commercial reactor type simulated fuel pins were used for the test. The sheared pin length and the opening ratio of sheared section were measured under several shearing conditions such as the pressure to hold pin bundle, the shearing speed and the filling-ratio of pins in the pin magazine. Both types of fuel pin were able to be sheared accurately at the length of about 10mm, and the opening ratio of sheared section was not significantly reduced. As the results, fundamental data of the short stroke shearing characteristics were obtained and that shearing method was confirmed to be promising with the reliable shearing device.
Shear viscosity from effective couplings of gravitons
International Nuclear Information System (INIS)
We calculate the shear viscosity of field theories with gravity duals using Kubo formula by calculating the Green function of dual transverse gravitons and confirm that the value of the shear viscosity is fully determined by the effective coupling of transverse gravitons on the horizon. We calculate the effective coupling of transverse gravitons for Einstein and Gauss-Bonnet gravities coupled with matter fields, respectively. Then we apply the resulting formula to the case of AdS Gauss-Bonnet gravity with F4 term corrections of Maxwell field and discuss the effect of F4 terms on the ratio of the shear viscosity to entropy density.
Shear instability in magnetized, collisional dusty plasmas
Energy Technology Data Exchange (ETDEWEB)
Pandey, B. P. [Department of Physics and Astronomy, Macquarie University, Sydney, New South Wales 2109 (Australia); Vladimirov, S. V.; Samarian, A. A. [School of Physics, University of Sydney, New South Wales 2006 (Australia)
2012-06-15
The shear instability of magnetized, collisional dusty plasma is investigated in the present work. It is demonstrated that the relative drift between the charged dust and magnetised electrons and ions which give rise to the Hall effect is crucial to this instability. Although the nature of present shear instability is similar to the Kelvin-Helmholtz instability, the role of magnetic field in the present case is important in destabilising waves. The maximum growth rate of the instability is proportional only to the shear gradient and is independent of the ambient magnetic field strength. Most unstable wavenumber is a function of ambient dust parameters.
Shear viscosity of liquid mixtures: Mass dependence
International Nuclear Information System (INIS)
Expressions for zeroth, second, and fourth sum rules of transverse stress autocorrelation function of two component fluid have been derived. These sum rules and Mori's memory function formalism have been used to study shear viscosity of Ar-Kr and isotopic mixtures. It has been found that theoretical result is in good agreement with the computer simulation result for the Ar-Kr mixture. The mass dependence of shear viscosity for different mole fraction shows that deviation from ideal linear model comes even from mass difference in two species of fluid mixture. At higher mass ratio shear viscosity of mixture is not explained by any of the emperical model. (author)
Stelzleni, A M; Froetschel, M A; Pringle, T D
2013-09-01
The objective of this study was to examine the effects of supplemental feeding of full-fat extruded cottonseed pellets (FFECS) compared with tallow on carcass characteristics, sensory traits, retail display color, and fatty acid profiles, especially CLA isomers in finishing heifers. Twenty-one Angus heifers (450 ± 5 kg) were assigned randomly to 1 of 3 experimental diets: 1) 100% supplemental fat from tallow at 4.1% of ration DM (TAL), 2) a 50:50 ratio of supplemental fat from a combination of tallow at 2.1% and FFECS at 12.8% of ration DM (TAL/ECS), and 3) 100% supplemental fat from FFECS at 25.6% ration DM (ECS). All rations were formulated to contain 7.5% fat on a DM basis. Heifers were individually fed, ad libitum, for 82 d, and BW, G:F, DMI, ADG, and body composition via ultrasound were collected at 3 to 4 wk intervals. After 82 d on feed heifers were slaughtered under federal inspection, and carcass characteristics were measured (at 24 h). The LM was removed for retail display color (1, 3, 6, 10 d), Warner-Bratzler shear force (1, 3, 7, 14, 21 d postmortem aging), sensory analysis (1, 7, 14, 21 d postmortem aging), and fatty acid profile analysis. Subcutaneous fat, including all layers, was removed from the LM for fatty acid profile analysis, and ground beef patties (80:20) were produced with lean from the brisket and fat from the plate for retail color analysis (1, 2, 4, 7 d). Supplemental fat source did not influence feedlot performance for any of the traits measured (P > 0.12) or any carcass traits related to yield, quality, or LM color at the 12th- to 13th-rib interface (P > 0.15). Supplemental fat source did not affect Warner-Bratzler shear force or any sensory traits (P > 0.20), but LM steaks became more tender as postmortem aging time increased up to 14 d (P beef patties, the only difference was LM steaks from ECS were darker (lower L* value) than TAL or TAL/ECS steaks (P beef patty objective and subjective color deteriorated (P 0.90). Full-fat extruded cottonseed pellets are interchangeable with tallow in heifer finishing diets without impacting feeding performance, meat quality, shelf life color, or CLA content of adipose sites. PMID:23893987
Amorphous silicon under mechanical shear deformations: shear velocity and temperature effects
Kerrache, Ali; Mousseau, Normand; Lewis, Laurent J.
2010-01-01
Mechanical shear deformations lead, in some cases, to effects similar to those resulting from ion irradiation. Here we characterize the effects of shear velocity and temperature on amorphous silicon (\\aSi) modelled using classical molecular dynamics simulations based on the empirical Environment Dependent Inter-atomic Potential (EDIP). With increasing shear velocity at low temperature, we find a systematic increase in the internal strain leading to the rapid appearance of st...
Phenomenology and physical origin of shear-localization and shear-banding in complex fluids
Ovarlez, Guillaume; Rodts, Ste?phane; Chateau, Xavier; Coussot, Philippe
2010-01-01
We review and compare the phenomenological aspects and physical origin of shear-localization and shear-banding in various material types, namely emulsions, suspensions, colloids, granular materials and micellar systems. It appears that shear-banding, which must be distinguished from the simple effect of coexisting static-flowing regions in yield stress fluids, occurs in the form of a progressive evolution of the local viscosity towards two significantly different values in t...
Dynamic Modes of Microcapsules in Steady Shear Flow: Effects of Bending and Shear Elasticities
Noguchi, Hiroshi
2010-01-01
The dynamics of microcapsules in steady shear flow was studied using a theoretical approach based on three variables: The Taylor deformation parameter $\\alpha_{\\rm D}$, the inclination angle $\\theta$, and the phase angle $\\phi$ of the membrane rotation. It is found that the dynamic phase diagram shows a remarkable change with an increase in the ratio of the membrane shear and bending elasticities. A fluid vesicle (no shear elasticity) exhibits three dynamic modes: (i) Tank-t...
Acoustic waves in unbounded shear flows
International Nuclear Information System (INIS)
The linear evolution of acoustic waves in fluid flow with constant density and uniform shear of velocity is investigated. The process of the mean flow energy extraction by the three-dimensional acoustic waves which is due to the non-normality of linear dynamics in shear flows is analyzed. The thorough examination of the dynamics of different physical quantities, specifying the wave evolution, is outlined. The revealing of the behaviour becomes possible owing to the nonmodal approach that has been extensively used in the study of the perturbations evolution in shear flows since the beginning of the nineties. In addition, a detailed analyses of the physics of shear energy gain by vortex and acoustic perturbations is presented. (author). 28 refs, 7 figs
Shear thickening, frictionless and frictional rheologies
Mari, Romain; Morris, Jeffrey F; Denn, Morton M
2014-01-01
Particles suspended in a Newtonian fluid raise the viscosity and also generally give rise to a shear-rate dependent rheology. In particular, pronounced shear thickening is observed at large solid volume fractions. In a recent article (R. Seto, R. Mari, J. F. Morris, and M. M. Denn., Phys. Rev. Lett., 111:218301, 2013) we have considered the minimum set of components to reproduce the experimentally observed shear thickening behavior, including Discontinuous Shear Thickening (DST). We have found frictional contact forces to be essential, and were able to reproduce the experimental behavior by a simulation including this physical ingredient. In the present article, we thoroughly investigate the effect of friction and express it in the framework of the jamming transition. The viscosity divergence at the jamming transition has been a well known phenomenon in suspension rheology, as reflected in many empirical laws for the viscosity. Friction can affect this divergence, and in particular the jamming packing fractio...
Torsion and shear stresses in ships
Shama, Mohamed
2010-01-01
This book covers an area of ship structure analysis and design that has not been exhaustively examined by other references. It presents the basic concepts of the methods and procedures required to calculate torsion and shear stresses in ship structures.
Turbulence evolution in plasma shear flows
International Nuclear Information System (INIS)
The renormalized nonlinear analysis of the temporal evolution of drift-type modes in plasma shear flows is developed. The theory accounts for the effect of the turbulent motions of plasma on the saturation of the resistive drift instability. The nonlinear balance equation, which determines the saturation level of the resistive drift instability in shear flow is obtained. It was prowed that the “nonlinear effect of the enhanced decorrelation by shear flow” has nothing in common with process of the saturation. The same conclusion is applicable to all fluid models of plasma, obtained in drift approximation, in which all nonlinearities, other than E×B are ignored. The linear non-modal kinetic theory to the Vlasov-Poisson system is developed. This theory reveals the velocity shear in a non-modal time-dependent effect of the finite Larmor radius. (author)
Heterogeneous shear in hard sphere glasses
Mandal, Suvendu; Raabe, Dierk; Varnik, Fathollah
2012-01-01
There is growing evidence that the flow of driven amorphous solids is not homogeneous, even if the macroscopic stress is constant across the system. Via event driven molecular dynamics simulations of a hard sphere glass, we provide the first direct evidence for a correlation between the fluctuations of the local volume-fraction and the fluctuations of the local shear rate. Higher shear rates do preferentially occur at regions of lower density and vice versa. The temporal behavior of fluctuations is governed by a characteristic time scale, which, when measured in units of strain, is independent of shear rate in the investigated range. Interestingly, the correlation volume is also roughly constant for the same range of shear rates. A possible connection between these two observations is discussed.
Directory of Open Access Journals (Sweden)
R.E. Dyer
2005-01-01
Full Text Available The effects of Zeranol and castration on organoleptic and mechanically assessed tenderness were studied using the 193 young beef cattle described in the companion paper (Impact of castration and zeranol implants on bullocks: I. Behavior, growth and carcass traits. Sensory panel evaluations showed that steaks from control and implanted steer carcasses had higher mean scores for tenderness, juiciness, flavor and overall palatability than those from control and implanted bulls. Implanting did not influence juiciness or flavor within the bull or steer groups, but control bulls and steers were significantly (P<.005 more tender and more palatable overall than were implanted bulls and steers. When comparing the mechanical measurements there was considerable variation among the instruments. The Armour tenderometer ranked meat from the implanted steers significantly tougher than either the control or implanted bulls. The Warner-Bratzler shear, Krammer shear and Instron Press ranked steaks from steers significantly more tender than those from bulls. Implanted and control groups of animals were similar in tenderness when judged by the mechanical measurements. Behavior and palatability characteristics of implanted and control bulls and steers were also studied. Implantation made bulls and steers more docile. The libido measurements were also lower for the implanted bulls and steers. Within group of implanted bulls and steers those that were least aggressive tended to be more tender than their more aggressive counterparts.
Special Ronchi grating as the shearing element of shearing ESPI for nondestructive testing
Wu, Xiaoping; Fu, Shaojun; Pang, Lin-yong
1997-03-01
A new electronic shearing speckle pattern interferometry using a special Ronchi grating as the shearing element has been developed and applied to deformation measurement and non destructive testing (NDT) in the practical environment. This special designed Ronchi grating is a kind of phase grating. It can make zero order and all even order beams disappear and among all odd order beams the +/- 1 order beams are much stronger than others. This new shearing element has many advantages, such as small volume, light weight, lower price, lower energy lost and good quality of shearing image. The experimental results show that it is good at electronic shearography.
The shear-stress intensity factor for a centrally cracked stiff-flanged shear web
Fichter, W. B.
1976-01-01
By use of the principle of superposition the stiff-flanged shear web is modeled mathematically by an infinite elastic strip with fixed longitudinal edges. The shear-stress intensity factor for a central longitudinal crack is calculated for various values of the ratio of strip width to crack length, h/a, in the range 0.1-10. The interaction of the crack with the boundaries is illustrated by boundary shear-stress distributions for three values of h/a. Some implications of the results for the design of damage-tolerant shear webs are discussed briefly.
Punching shear capacity of reinforced concrete slabs with headed shear studs
DEFF Research Database (Denmark)
Hoang, Linh Cao; Pop, Anamaria
2015-01-01
Punching shear in slabs is analogous to shear in beams. Despite this similarity, current design codes provide distinctly different methods for the design of shear reinforcement in the two situations. For example, the Eurocode method for beam shear design is founded on the theory of rigid plasticity. To design shear reinforcement in slabs, on the other hand, the engineer must settle for an empirical equation. The aim of the study reported is to demonstrate that it is possible in a simple manner to design shear reinforcement in slabs based on the same rigid-plasticity foundation as for beam shear design. For this purpose, an extension of the upper-bound crack sliding model is proposed. This involves analysis of sliding mechanisms in yield lines developed both within and outside the zone with shear reinforcement. Various types of headed shear studs were considered. The results obtained using the model were compared with a large number of published test results, and satisfactory agreements were found.
Fan-structure shear rupture mechanism as a source of shear rupture rockbursts
Scientific Electronic Library Online (English)
B.G., Tarasov.
2014-10-01
Full Text Available This paper proposes the further development of a recently identified shear rupture mechanism (fan mechanism) that elucidates a paradoxical feature of hard rocks - the possibility of shear rupture propagation through a highly confined intact rock mass at shear stresses that can be significantly less [...] than frictional strength. In the fan mechanism, failure is associated with consecutive creation of small slabs (known as 'domino blocks') from the intact rock in the rupture tip, driven by a fan-shaped domino structure representing the rupture head. The fan head combines such unique features as extremely low shear resistance, self-sustaining stress intensification, and self-unbalancing conditions. Consequently, the failure process caused by the mechanism is inevitably spontaneous and violent. Physical and mathematical models explain unique and paradoxical features of the mechanism, which can be generated in primary ruptures and segmented faults. The fan mechanism provides a novel point of view for understanding the nature of spontaneous failure processes, including shear rupture rockbursts. The process explains, in particular, features of shear rupture rockbursts such as activation at great depths, generation of new shear ruptures in intact rock mass, nucleation of hypocentres at significant distances from the excavation, shear rupture development at low shear stresses, and abnormal rupture violence.
Influence of Shear on Rotation Capacity of Reinforced Concrete Members Without Shear Reinforcement
Vaz Rodrigues, Rui; Muttoni, Aurelio; Ferna?ndez Ruiz, Miguel
2010-01-01
The influence of shear on the rotation capacity of one-way slabs without shear reinforcement is investigated in this paper by means of an experimental study. The experimental program consisted of 11 slab strips 8400 mm (331 in.) long and 450 mm (17.7 in.) thick with a flexural reinforcement ratio of 0.79%. The rotation capacity was investigated for various values of the shear span and for two types of flexural reinforcement (hot-rolled and cold-worked bars). The specimens developed shear fail...
Samuel, R E; Guzman, A E; Briehl, R W
1993-12-01
The kinetics of hemoglobin S gelation are critical in sickle disease because microvascular obstruction can be avoided if red blood cells pass these vessels during the delay time, before polymerization and gelation occur in sufficient degree to rigidify the cells. Kinetics, including the delay time and the closely related exponential progress rate, are highly sensitive to hemoglobin concentration and degree of deoxygenation. Kinetics are also greatly accelerated by shear, an effect that may contribute to pathogenesis, since red blood cells deform and can undergo shear in vivo. Here we examine the joint dependence of kinetics on shear and hemoglobin concentration. As shear rate increases, the concentration dependence of the exponential progress rate decreases. The large decrease in concentration dependence supports the conclusion that acceleration of gelation by shear is due to breakage and not to enhancement of heterogeneous nucleation. Under shear, new fibers are created by breakage of existing ones, as well as by heterogeneous nucleation. At high shear, the rate of new fiber creation by breakage is very great and dominates that by heterogeneous nucleation. Therefore, if breakage depended only on shear rate and were independent of the concentration of hemoglobin in solution, the concentration dependence of kinetics should vanish. Although it decreases, it does not disappear. The concentration dependence that remains at high shear arises from (1) the direct contribution of fiber growth rate to the exponential progress rate, (2) the dependence of breakage rate on fiber growth rate, and (3) the dependence of solution viscosity on hemoglobin concentration. PMID:8241514
Fine Scale Features of Turbulent Shear Flows
Buxton, Oliver R. H.
2011-01-01
This thesis presents an investigation into kinematic features of fine scale turbulence in free shear flows. In particular it seeks to examine the interaction between the different length scales present in shear flow turbulence as well as the interaction between the strain-rate tensor and the rotation tensor, which are the symmetric and skew-symmetric components of the velocity gradient tensor respectively. A new multi-scale particle image velocimetry (PIV) technique is develope...
Shear stress and the endothelial transport barrier
Tarbell, John M.
2010-01-01
The shear stress of flowing blood on the surfaces of endothelial cells that provide the barrier to transport of solutes and water between blood and the underlying tissue modulates the permeability to solutes and the hydraulic conductivity. This review begins with a discussion of transport pathways across the endothelium and then considers the experimental evidence from both in vivo and in vitro studies that shows an influence of shear stress on endothelial transport properties after both acut...
Hydrodynamical fluctuations in smooth shear flows
International Nuclear Information System (INIS)
Background of hydrodynamical fluctuations in a intrinsically/stochastically forced, laminar, uniform shear flow is studied. The employment of so-called nonmodal mathematical analysis makes it possible to represent the background of fluctuations in a new light and to get more insight into the physics of its formation. The basic physical processes responsible for the formation of vortex and acoustic wave fluctuation backgrounds are analyzed. Interplay of the processes at low and moderate shear rates is described. Three-dimensional vortex fluctuations around a given macroscopic state are numerically calculated. The correlation functions of the fluctuations of physical quantities are analyzed. It is shown that there exists subspace Dk in the wave-number space (k-space) that is limited externally by spherical surface with radius k? ? A/? (where A is the velocity shear parameter, ? - the kinematic viscosity) in the nonequilibrium open system under study. The spatial Fourier harmonics of vortex as well as acoustic wave fluctuations are strongly subjected by flow shear (by the open character of the system) at wave-numbers satisfying the condition k ?. Specifically it is shown that in Dk: The fluctuations are non-Markovian; the spatial spectral density of energy of the vortex fluctuations by far exceeds the white-noise; the term of a new type associated to the hydrodynamical fluctuation of velocity appears in the correlation function of pressure; the fluctuation background of the acoustic waves is completely different at low and moderate shear rates (at low shear rates it is reduced in Dk in comparison to the uniform (non-shear) flow; at moderate shear rates it it comparable to the background of the vortex fluctuations). The fluctuation background of both the vortex and the acoustic wave modes is anisotropic. The possible significance of the fluctuation background of vortices for the subcritical transition to turbulence and Brownian motion of small macroscopic particles is also discussed. (author)
Buckling of sheared and compressed microfibrils
Nadermann, Nichole; Kumar, Ajeet; Goyal, Sachin; Hui, Chung-yuen
2010-01-01
In this paper, we study the stability of an initially straight elastic fibril clamped at one end, while the other end is subjected to a constant normal compressive force and a prescribed shear displacement. We found the buckling load of a sheared fibril to be always less than the Euler buckling load. Furthermore, if the end of the fibril loses adhesion, then the buckling load can be considerably less. Our result suggests that the static friction of microfibre arrays can decrease with increasi...
IMAGE ANALYSIS FOR MODELLING SHEAR BEHAVIOUR
Philippe Lopez; Joëlle Riss; Sylvie Gentier; Rock Flamand; Guy Archambault; Soizic Bouvet
2011-01-01
Through laboratory research performed over the past ten years, many of the critical links between fracture characteristics and hydromechanical and mechanical behaviour have been made for individual fractures. One of the remaining challenges at the laboratory scale is to directly link fracture morphology of shear behaviour with changes in stress and shear direction. A series of laboratory experiments were performed on cement mortar replicas of a granite sample with a natural fracture perpendic...
Equilibrium states of homogeneous sheared compressible turbulence
Riahi, M.; Lili, T.
2011-01-01
Equilibrium states of homogeneous compressible turbulence subjected to rapid shear is studied using rapid distortion theory (RDT). The purpose of this study is to determine the numerical solutions of unsteady linearized equations governing double correlations spectra evolution. In this work, RDT code developed by authors solves these equations for compressible homogeneous shear flows. Numerical integration of these equations is carried out using a second-order simple and accurate scheme. The ...
Shear strength properties of wet granular materials
Richefeu, Vincent; El Youssoufi, Moulay Saïd; Radjai, Farhang
2006-01-01
We investigate shear strength properties of wet granular materials in the pendular state (i.e. the state where the liquid phase is discontinuous) as a function of water content. Sand and glass beads were wetted and tested in a direct shear cell and under various confining pressures. In parallel, we carried out three-dimensional molecular dynamics simulations by using an explicit equation expressing capillary force as a function of interparticle distance, water bridge volume ...
4-D ultrafast shear-wave imaging.
Gennisson, Jean-Luc; Provost, Jean; Deffieux, Thomas; Papadacci, Clément; Imbault, Marion; Pernot, Mathieu; Tanter, Mickael
2015-06-01
Over the last ten years, shear wave elastography (SWE) has seen considerable development and is now routinely used in clinics to provide mechanical characterization of tissues to improve diagnosis. The most advanced technique relies on the use of an ultrafast scanner to generate and image shear waves in real time in a 2-D plane at several thousands of frames per second. We have recently introduced 3-D ultrafast ultrasound imaging to acquire with matrix probes the 3-D propagation of shear waves generated by a dedicated radiation pressure transducer in a single acquisition. In this study, we demonstrate 3-D SWE based on ultrafast volumetric imaging in a clinically applicable configuration. A 32 × 32 matrix phased array driven by a customized, programmable, 1024-channel ultrasound system was designed to perform 4-D shear-wave imaging. A matrix phased array was used to generate and control in 3-D the shear waves inside the medium using the acoustic radiation force. The same matrix array was used with 3-D coherent plane wave compounding to perform high-quality ultrafast imaging of the shear wave propagation. Volumetric ultrafast acquisitions were then beamformed in 3-D using a delay-and-sum algorithm. 3-D volumetric maps of the shear modulus were reconstructed using a time-of-flight algorithm based on local multiscale cross-correlation of shear wave profiles in the three main directions using directional filters. Results are first presented in an isotropic homogeneous and elastic breast phantom. Then, a full 3-D stiffness reconstruction of the breast was performed in vivo on healthy volunteers. This new full 3-D ultrafast ultrasound system paves the way toward real-time 3-D SWE. PMID:26067040
Poloidal Rotation in TFTR Reversed Shear Plasmas
Bell, R. E.; Levinton, F. M.; Batha, S. H.; Synakowski, E. J.; Zarnstorff, M. C.
1998-08-01
A bifurcation in the core poloidal rotation of carbon impurity ions in the Tokamak Fusion Test Reactor (TFTR) has been observed prior to the transport bifurcation associated with enhanced reverse shear plasmas. In a narrow radial region of the plasma, the impurity ion poloidal rotation reverses direction. This poloidal flow is associated with the establishment of a large negative radial electric field with strong shear. The measured poloidal velocities before, during, and after this precursor differ from neoclassical predictions.
Mean magnetic field generation in sheared rotators
Blackman, Eric G
1999-01-01
A generalized mean magnetic field induction equation for differential rotators is derived, including a compressibility, and the anisotropy induced on the turbulent quantities from the mean magnetic field itself and a mean velocity shear. Derivations of the mean field equations often do not emphasize that there must be anisotropy and inhomogeneity in the turbulence for mean field growth. The anisotropy from shear is the source of a term involving the product of the mean veloc...
Vlasov simulation of kinetic shear Alfven waves
Dannert, Tilman; Jenko, Frank
2004-01-01
The treatment of kinetic shear Alfven waves in homogeneous magnetized plasmas by means of Vlasov simulation is examined. To this end, the driftkinetic version of the Vlasov-Maxwell equations is solved via various numerical schemes, all employing a grid in (1 + 1)D phase space. Since kinetic shear Alfven waves are Landau damped, the use of an equidistant grid in velocity space leads to a recurrence problem. The latter can be circumvented, however, by damping the finest velocity space scales th...
Shear thinning in dilute polymer solutions.
Ryder, Jf; Yeomans, Jm
2006-01-01
We use bead-spring models for a polymer coupled to a solvent described by multiparticle collision dynamics to investigate shear thinning effects in dilute polymer solutions. First, we consider the polymer motion and configuration in a shear flow. For flexible polymer models we find a sharp increase in the polymer radius of gyration and the fluctuations in the radius of gyration at a Weissenberg number approximately 1. We then consider the polymer viscosity and the effect of solvent quality, e...
Resolution of axial shear strain elastography
International Nuclear Information System (INIS)
The technique of mapping the local axial component of the shear strain due to quasi-static axial compression is defined as axial shear strain elastography. In this paper, the spatial resolution of axial shear strain elastography is investigated through simulations, using an elastically stiff cylindrical lesion embedded in a homogeneously softer background. Resolution was defined as the smallest size of the inclusion for which the strain value at the inclusion/background interface was greater than the average of the axial shear strain values at the interface and inside the inclusion. The resolution was measured from the axial shear strain profile oriented at 450 to the axis of beam propagation, due to the absence of axial shear strain along the normal directions. The effects of the ultrasound system parameters such as bandwidth, beamwidth and transducer element pitch along with signal processing parameters such as correlation window length (W) and axial shift (?W) on the estimated resolution were investigated. The results show that the resolution (at 450 orientation) is determined by the bandwidth and the beamwidth. However, the upper bound on the resolution is limited by the larger of the beamwidth and the window length, which is scaled inversely to the bandwidth. The results also show that the resolution is proportional to the pitch and not significantly affected by the axial window shift
Resolution of axial shear strain elastography
Energy Technology Data Exchange (ETDEWEB)
Thitaikumar, Arun [Ultrasonics Laboratory, Department of Diagnostic and Interventional Imaging, University of Texas Medical School, Houston, TX (United States); Righetti, Raffaella [Ultrasonics Laboratory, Department of Diagnostic and Interventional Imaging, University of Texas Medical School, Houston, TX (United States); Krouskop, Thomas A [Ultrasonics Laboratory, Department of Diagnostic and Interventional Imaging, University of Texas Medical School, Houston, TX (United States); Ophir, Jonathan [Ultrasonics Laboratory, Department of Diagnostic and Interventional Imaging, University of Texas Medical School, Houston, TX (United States)
2006-10-21
The technique of mapping the local axial component of the shear strain due to quasi-static axial compression is defined as axial shear strain elastography. In this paper, the spatial resolution of axial shear strain elastography is investigated through simulations, using an elastically stiff cylindrical lesion embedded in a homogeneously softer background. Resolution was defined as the smallest size of the inclusion for which the strain value at the inclusion/background interface was greater than the average of the axial shear strain values at the interface and inside the inclusion. The resolution was measured from the axial shear strain profile oriented at 45{sup 0} to the axis of beam propagation, due to the absence of axial shear strain along the normal directions. The effects of the ultrasound system parameters such as bandwidth, beamwidth and transducer element pitch along with signal processing parameters such as correlation window length (W) and axial shift ({delta}W) on the estimated resolution were investigated. The results show that the resolution (at 45{sup 0} orientation) is determined by the bandwidth and the beamwidth. However, the upper bound on the resolution is limited by the larger of the beamwidth and the window length, which is scaled inversely to the bandwidth. The results also show that the resolution is proportional to the pitch and not significantly affected by the axial window shift.
Accurate shear measurement with faint sources
Zhang, Jun; Luo, Wentao; Foucaud, Sebastien
2015-01-01
For cosmic shear to become an accurate cosmological probe, systematic errors in the shear measurement method must be unambiguously identified and corrected for. Previous work of this series has demonstrated that cosmic shears can be measured accurately in Fourier space in the presence of background noise and finite pixel size, without assumptions on the morphologies of galaxy and PSF. The remaining major source of error is source Poisson noise, due to the finiteness of source photon number. This problem is particularly important for faint galaxies in space-based weak lensing measurements, and for ground-based images of short exposure times. In this work, we propose a simple and rigorous way of removing the shear bias from the source Poisson noise. Our noise treatment can be generalized for images made of multiple exposures through MultiDrizzle. This is demonstrated with the SDSS and COSMOS/ACS data. With a large ensemble of mock galaxy images of unrestricted morphologies, we show that our shear measurement method can achieve sub-percent level accuracy even for images of signal-to-noise ratio less than 5 in general, making it the most promising technique for cosmic shear measurement in the ongoing and upcoming large scale galaxy surveys.
Shear induced structures in crystallizing cocoa butter
Mazzanti, Gianfranco; Guthrie, Sarah E.; Sirota, Eric B.; Marangoni, Alejandro G.; Idziak, Stefan H. J.
2004-03-01
Cocoa butter is the main structural component of chocolate and many cosmetics. It crystallizes in several polymorphs, called phases I to VI. We used Synchrotron X-ray diffraction to study the effect of shear on its crystallization. A previously unreported phase (phase X) was found and a crystallization path through phase IV under shear was observed. Samples were crystallized under shear from the melt in temperature controlled Couette cells, at final crystallization temperatures of 17.5^oC, 20^oC and 22.5^oC in Beamline X10A of NSLS. The formation of phase X was observed at low shear rates (90 s-1) and low crystallization temperature (17.5^oC), but was absent at high shear (720 s-1) and high temperature (20^oC). The d-spacing and melting point suggest that this new phase is a mixture rich on two of the three major components of cocoa butter. We also found that, contrary to previous reports, the transition from phase II to phase V can happen through the intermediate phase IV, at high shear rates and temperature.
Magnetic shear damping of dissipative drift wave turbulence
International Nuclear Information System (INIS)
The influence of local and global magnetic field line shear on structure formation and transport in dissipative drift-Alfven turbulence is explored. It is found that the generation of zonal flow shear is connected to magnetic shear in ways not accounted previously. The concept of a locally sheared slab flux tube model (including toroidicity) is introduced in order to extend previous analyses to general local variations of magnetic field line shear. It is shown that local shear damping is efficient even when flux surface averaged shear is low
Study of shear thickening behavior in colloidal suspensions
Directory of Open Access Journals (Sweden)
N Maleki Jirsaraee
2015-01-01
Full Text Available We studied the shear thickening behavior of the nano silica suspension (silica nanoparticles 12 nm in size suspended in ethylene glycol under steady shear. The critical shear rate for transition into shear thickening phase was determined at different concentrations and temperatures. The effect of temperature and concentration was studied on the shear thickening behavior. In silica suspension, it was observed that all the samples had a transition into shear thickening phase and also by increasing the temperature, critical shear rate increased and viscosity decreased. Our observations showed that movement in silica suspension was Brownian and temperature could cause a delay in transition into shear thickening phase. Yet, we observed that increasing the concentration would decrease critical shear rate and increase viscosity. Increasing temperature increased Brownian forces and increasing concentration increased hydrodynamic forces, confirming the contrast between these two forces for transition into shear thickening phase for the suspensions containing nano particles
Magnetized stratified rotating shear waves
Salhi, A.; Lehner, T.; Godeferd, F.; Cambon, C.
2012-02-01
We present a spectral linear analysis in terms of advected Fourier modes to describe the behavior of a fluid submitted to four constraints: shear (with rate S), rotation (with angular velocity ?), stratification, and magnetic field within the linear spectral theory or the shearing box model in astrophysics. As a consequence of the fact that the base flow must be a solution of the Euler-Boussinesq equations, only radial and/or vertical density gradients can be taken into account. Ertel's theorem no longer is valid to show the conservation of potential vorticity, in the presence of the Lorentz force, but a similar theorem can be applied to a potential magnetic induction: The scalar product of the density gradient by the magnetic field is a Lagrangian invariant for an inviscid and nondiffusive fluid. The linear system with a minimal number of solenoidal components, two for both velocity and magnetic disturbance fields, is eventually expressed as a four-component inhomogeneous linear differential system in which the buoyancy scalar is a combination of solenoidal components (variables) and the (constant) potential magnetic induction. We study the stability of such a system for both an infinite streamwise wavelength (k1=0, axisymmetric disturbances) and a finite one (k1?0, nonaxisymmetric disturbances). In the former case (k1=0), we recover and extend previous results characterizing the magnetorotational instability (MRI) for combined effects of radial and vertical magnetic fields and combined effects of radial and vertical density gradients. We derive an expression for the MRI growth rate in terms of the stratification strength, which indicates that purely radial stratification can inhibit the MRI instability, while purely vertical stratification cannot completely suppress the MRI instability. In the case of nonaxisymmetric disturbances (k1?0), we only consider the effect of vertical stratification, and we use Levinson's theorem to demonstrate the stability of the solution at infinite vertical wavelength (k3=0): There is an oscillatory behavior for ?>1+|K2/k1|, where ?=St is a dimensionless time and K2 is the radial component of the wave vector at ?=0. The model is suitable to describe instabilities leading to turbulence by the bypass mechanism that can be relevant for the analysis of magnetized stratified Keplerian disks with a purely azimuthal field. For initial isotropic conditions, the time evolution of the spectral density of total energy (kinetic + magnetic + potential) is considered. At k3=0, the vertical motion is purely oscillatory, and the sum of the vertical (kinetic + magnetic) energy plus the potential energy does not evolve with time and remains equal to its initial value. The horizontal motion can induce a rapid transient growth provided K2/k1?1. This rapid growth is due to the aperiodic velocity vortex mode that behaves like Kh/kh where kh(?)=[k12+(K2-k1?)2]1/2 and Kh=kh(0). After the leading phase (?>K2/k1?1), the horizontal magnetic energy and the horizontal kinetic energy exhibit a similar (oscillatory) behavior yielding a high level of total energy. The contribution to energies coming from the modes k1=0 and k3=0 is addressed by investigating the one-dimensional spectra for an initial Gaussian dense spectrum. For a magnetized Keplerian disk with a purely vertical field, it is found that an important contribution to magnetic and kinetic energies comes from the region near k1=0. The limit at k1=0 of the streamwise one-dimensional spectra of energies, or equivalently, the streamwise two-dimensional (2D) energy, is then computed. The comparison of the ratios of these 2D quantities with their three-dimensional counterparts provided by previous direct numerical simulations shows a quantitative agreement.
Microscopic Mechanism of Shear Bands in Amorphous Solids
Ratul Dasgupta; Hentschel, H. George E.; Itamar Procaccia
2012-01-01
The fundamental instability responsible for the shear localization which results in shear bands in amorphous solids remains unknown despite enormous amount of research, both experimental and theoretical. As this is the main mechanism for the failure of metallic glasses, understanding the instability is invaluable in finding how to stabilize such materials against the tendency to shear localize. In this Letter we explain the mechanism for shear localization under shear, which...
Logarithmic Wind Profile: A Stability Wind Shear Term
Sakagami, Yoshiaki; Santos, Pedro A. A.; Haas, Reinaldo; Passos, Julio C.; Taves, Frederico F.
2014-01-01
A stability wind shear term of logarithmic wind profile based on the terms of turbulent kinetic energy equation is proposed. The fraction influenced by thermal stratification is considered in the shear production term. This thermally affected shear is compared with buoyant term resulting in a stability wind shear term. It is also considered Reynolds stress as a sum of two components associated with wind shear from mechanical and thermal stratification process. The stability ...
Shear strength properties of wet granular materials.
Richefeu, Vincent; El Youssoufi, Moulay Saïd; Radjaï, Farhang
2006-05-01
We investigate shear strength properties of wet granular materials in the pendular state (i.e., the state where the liquid phase is discontinuous) as a function of water content. Sand and glass beads were wetted and tested in a direct shear cell and under various confining pressures. In parallel, we carried out three-dimensional molecular dynamics simulations by using an explicit equation expressing capillary force as a function of interparticle distance, water bridge volume, and surface tension. We show that, due to the peculiar features of capillary interactions, the major influence of water content over the shear strength stems from the distribution of liquid bonds. This property results in shear strength saturation as a function of water content. We arrive at the same conclusion by a microscopic analysis of the shear strength. We propose a model that accounts for the capillary force, the granular texture, and particle size polydispersity. We find fairly good agreement of the theoretical estimate of the shear strength with both experimental data and simulations. From numerical data, we analyze the connectivity and anisotropy of different classes of liquid bonds according to the sign and level of the normal force as well as the bond direction. We find that weak compressive bonds are almost isotropically distributed whereas strong compressive and tensile bonds have a pronounced anisotropy. The probability distribution function of normal forces is exponentially decreasing for strong compressive bonds, a decreasing power-law function over nearly one decade for weak compressive bonds, and an increasing linear function in the range of tensile bonds. These features suggest that different bond classes do not play the same role with respect to the shear strength. PMID:16802930
Studies of instability and transport in sheared-slab plasmas with very weak magnetic shear
Dong, J. Q.; Zhang, Y. Z.; Mahajan, S. M.
1997-09-01
Ion temperature gradient (ITG or ?i) driven microinstabilities are studied, using kinetic theory, for tokamak plasmas with very weak (positive or negative) magnetic shear (VWS). The gradient of magnetic shear as well as the effects of parallel and perpendicular velocity shear (v?' and vE') are included in the defining equations. Two eigenmodes: the double (D) and the global (G) are found to coexist. Parametric dependence of these instabilities, and of the corresponding quasilinear transport is systematically analyzed. It is shown that, in VWS plasmas, a parallel velocity shear (PVS) may stabilize or destabilize the modes, depending on the individual as well as the relative signs of PVS and of the gradient of magnetic shear. The quasilinear transport induced by the instabilities may be significantly reduced with PVS in VWS plasmas. The vE' values required to completely suppress the instabilities are much lower in VWS plasmas than they are in normal plasmas. Possible correlations with tokamak experiments are discussed.
Microstructural Evolution in Adiabatic Shear Localization
Meyers, M. A.; Perez-Prado, M. T.; McNelley, T. R.; Xue, Q.; Xu, Y.
2001-06-01
Shear bands were generated under prescribed and controlled conditions in stainless steel( Fe-18Hat-shaped specimens, deformed in a Hopkinson bar were used, yielding strain rates of approximately 104s-1 and shear strains that could be varied between 1 and 100.Specimens recovered from the collapse of thick-walled cylinders were also investigated. Microstructural characterization was performed by electron backscattered diffraction (EBSD) with orientation imaging microscopy(OIM), and transmission electron microscopy (TEM). The shear-band thickness was approximately 8 µm. This low-stacking fault energy alloy deforms, at the imposed strain rates (outside of the shear band), by planar dislocations and stacking fault packets, twinning, and occasional martensitic phase transformations at twin-twin intersections. EBSD reveals gradual lattice rotations of the grains approaching the core of the band. A [110] fiber texture (with the [110] direction perpendicular to both shear direction and shear plane normal) develops both within the shear band and in the adjacent grains. The formation of this texture, under an imposed global simple shear, suggests that rotations take place concurrently with the shearing deformation. This can be explained by compatibility requirements between neighboring deforming regions.EBSD could not reveal the deformation features at large strains because their scale was beklow thwe resolution of this technique.Transmission electron microscopy reveals a number of features that are interpreted in terms of the mechanisms of deformation and recovery/recrystallization postulated. They include the observation of grains with sizes in the nanocrystalline domain. The microstructural changes are described by an evolutionary model, leading from the initial grain size of 15 µm to the final submicronic (sub)grain size. Calculations are performed on the rotations of grain boundaries by grain-boundary diffusion, which is 3 orders of magnitude higher than bulk diffusion at the deformation temperatures. They indicate that the microstructural reorganization can take place within the deformation times of a few milliseconds. Research supported by US Army Research Office MURI Program under Contract DAAH04-96-1-0376 and the Department of Energy Grant DEFG0300SF2202.
Extreme model reduction of shear layers
Qawasmeh, Bashar Rafee
The aim of this research is to develop nonlinear low-dimensional models (LDMs) to describe vortex dynamics in shear layers. A modified Proper Orthogonal Decomposition (POD)/Galerkin projection method is developed to obtain models at extremely low dimension for shear layers. The idea is to dynamically scale the shear layer along y direction to factor out the shear layer growth and capture the dynamics by only a couple of modes. The models are developed for two flows, incompressible spatially developing and weakly compressible temporally developing shear layers, respectively. To capture basic dynamics, the low-dimensional models require only two POD modes for each wavenumber/frequency. Thus, a two-mode model is capable of representing single-wavenumber/frequency dynamics such as vortex roll-up, and a four-mode model is capable of representing the nonlinear dynamics involving a fundamental wavenumber/frequency and its subharmonic, such as vortex pairing/merging. Most of the energy is captured by the first mode of each wavenumber/frequency, the second POD mode, however, plays a critical role and needs to be included. In the thesis, we first apply the approach on temporally developing weakly compressible shear layers. In compressible flows, the thermodynamic variables are dynamically important, and must be considered. We choose isentropic Navier-Stokes equations for simplicity, and choose a proper inner product to present both kinetic energy and thermal energy. Two cases of convective Mach numbers are studied for low compressibility and moderate compressibility. Moreover, we study the sensitivity of the compressible four-mode model to several flow parameters: Mach number, the strength of initial perturbations of the fundamental and its subharmonic, and Reynolds number. Secondly we apply the approach on spatially developing incompressible shear layers with periodicity in time. We consider a streamwise parabolic form of the Navier-Stokes equations. When we add arbitrary excitation at different harmonics to the model, we observe the promoting or delaying/eliminating of vortex merging events as a result of mode competition. To study coherent structures in shear layers, we solve the Direct Lyapunov Exponents (DLEs) to identify the Lagrangian coherent structures (LCS). The negative-time LCS provide structures similar to the ones shown by flow visualization in experiments. The positive-time LCS are also important in describing the dynamics. Both negative and positive LCS are plotted together to give a complete picture of dynamics in shear layers.
Dynamics of Discontinuous Shear Thickening suspensions
Brown, Eric
2015-03-01
Concentrated suspensions of hard particles such as cornstarch in water exhibit Discontinuous Shear Thickening, in which an increasing shear rate drives a transition from liquid- to solid-like mechanical behavior. In steady-state shear this phenomena is a result of a dynamic version of jamming in which forces are transmitted along particle contact networks that span to system boundaries and repeatedly form and break up. Several dynamic phenomena observed in such suspensions have long been assumed to be a consequence of this shear thickening, but cannot be explained as a direct result of shear thickening; for example a uniquely strong impact response which allows a person to run on the fluid surface. We perform experiments in which a concentrated suspension is subjected to transient impact. We find that the strong impact response is due a short-lived jammed contact network spanning to the boundaries and a delay time required for this dynamically jammed region to propagate to the boundary. The resulting ability of this system-spanning solid-like region to support loads can explain the ability of a person to run on the surface of these fluids. This delay before a solid-like response may also explain several other dynamic phenomena observed in these fluids.
Accurate Shear Measurement with Faint Sources
Zhang, Jun; Foucaud, Sebastien
2013-01-01
For cosmic shear to become an accurate cosmological probe, systematic errors in the shear measurement method must be unambiguously identified and corrected for. Previous work of this series has demonstrated that cosmic shears can be measured accurately in Fourier space in the presence of background noise and finite pixel size, without assumptions on the morphologies of galaxy and PSF. The remaining major source of error is source Poisson noise, due to the finiteness of source photon number. This problem is particularly important for faint galaxies in space-based weak lensing measurements. In this work, we propose a simple and rigorous way of removing the shear bias from the source Poisson noise. Our noise treatment can be generalized for images made of multiple exposures through MultiDrizzle. This is demonstrated with the COSMOS/ACS data. With a large ensemble of mock galaxy images of unrestricted morphologies, we show that our shear measurement method can achieve sub-percent accuracy even for images of signa...
Colloidal Aggregate Structure under Shear by USANS
Chatterjee, Tirtha; van Dyk, Antony K.; Ginzburg, Valeriy V.; Nakatani, Alan I.
2015-03-01
Paints are complex formulations of polymeric binders, inorganic pigments, dispersants, surfactants, colorants, rheology modifiers, and other additives. A commercially successful paint exhibits a desired viscosity profile over a wide shear rate range from 10-5 s-1 for settling to >104 s-1 for rolling, and spray applications. Understanding paint formulation structure is critical as it governs the paint viscosity profile. However, probing paint formulation structure under shear is a challenging task due to the formulation complexity containing structures with different hierarchical length scales and their alterations under the influence of an external flow field. In this work mesoscale structures of paint formulations under shear are investigated using Ultra Small-Angle Neutron Scattering (rheo-USANS). Contrast match conditions were utilized to independently probe the structure of latex binder particle aggregates and the TiO2 pigment particle aggregates. Rheo-USANS data revealed that the aggregates are fractal in nature and their self-similarity dimensions and correlations lengths depend on the chemistry of the binder particles, the type of rheology modifier present and the shear stress imposed upon the formulation. These results can be explained in the framework of diffusion and reaction limited transient aggregates structure evolution under simple shear.
Pressure-shear experiments on granular materials.
Energy Technology Data Exchange (ETDEWEB)
Reinhart, William Dodd (Sandia National Laboratories, Albuquerque, NM); Thornhill, Tom Finley, III (, Sandia National Laboratories, Albuquerque, NM); Vogler, Tracy John; Alexander, C. Scott (Sandia National Laboratories, Albuquerque, NM)
2011-10-01
Pressure-shear experiments were performed on granular tungsten carbide and sand using a newly-refurbished slotted barrel gun. The sample is a thin layer of the granular material sandwiched between driver and anvil plates that remain elastic. Because of the obliquity, impact generates both a longitudinal wave, which compresses the sample, and a shear wave that probes the strength of the sample. Laser velocity interferometry is employed to measure the velocity history of the free surface of the anvil. Since the driver and anvil remain elastic, analysis of the results is, in principal, straightforward. Experiments were performed at pressures up to nearly 2 GPa using titanium plates and at higher pressure using zirconium plates. Those done with the titanium plates produced values of shear stress of 0.1-0.2 GPa, with the value increasing with pressure. On the other hand, those experiments conducted with zirconia anvils display results that may be related to slipping at an interface and shear stresses mostly at 0.1 GPa or less. Recovered samples display much greater particle fracture than is observed in planar loading, suggesting that shearing is a very effective mechanism for comminution of the grains.
Piezoelectric energy harvesting through shear mode operation
Malakooti, Mohammad H.; Sodano, Henry A.
2015-05-01
Piezoelectric materials are excellent candidates for use in energy harvesting applications due to their high electromechanical coupling properties that enable them to convert input mechanical energy into useful electric power. The electromechanical coupling coefficient of the piezoelectric material is one of the most significant parameters affecting energy conversion and is dependent on the piezoelectric mode of operation. In most piezoceramics, the d15 piezoelectric shear coefficient is the highest coefficient compared to the commonly used axial and transverse modes that utilize the d33 and the d31 piezoelectric strain coefficients. However, complicated electroding methods and challenges in evaluating the performance of energy harvesting devices operating in the shear mode have slowed research in this area. The shear deformation of a piezoelectric layer can be induced in a vibrating sandwich beam with a piezoelectric core. Here, a model based on Timoshenko beam theory is developed to predict the electric power output from a cantilever piezoelectric sandwich beam under base excitations. It is shown that the energy harvester operating in the shear mode is able to generate ?50% more power compared to the transverse mode for a numerical case study. Reduced models of both shear and transverse energy harvesters are obtained to determine the optimal load resistance in the system and perform an efficiency comparison between two models with fixed and adaptive resistances.
Shear alignment of a disordered lamellar mesophase
Kumaran, V.; Raman, D. S. S.
2011-03-01
The shear alignment of an initially disordered lamellar phase is examined using lattice Boltzmann simulations of a mesoscopic model based on a free-energy functional for the concentration modulation. For a small shear cell of width 8?, the qualitative features of the alignment process are strongly dependent on the Schmidt number Sc=?/D (ratio of kinematic viscosity and mass diffusion coefficient). Here, ? is the wavelength of the concentration modulation. At low Schmidt number, it is found that there is a significant initial increase in the viscosity, coinciding with the alignment of layers along the extensional axis, followed by a decrease at long times due to the alignment along the flow direction. At high Schmidt number, alignment takes place due to the breakage and reformation of layers because diffusion is slow compared to shear deformation; this results in faster alignment. The system size has a strong effect on the alignment process; perfect alignment takes place for a small systems of width 8? and 16?, while a larger system of width 32? does not align completely even at long times. In the larger system, there appears to be a dynamical steady state in which the layers are not perfectly aligned—where there is a balance between the annealing of defects due to shear and the creation due to an instability of the aligned lamellar phase under shear. We observe two types of defect creation mechanisms: the buckling instability under dilation, which was reported earlier, as well as a second mechanism due to layer compression.
Nonmonotonic flow curves of shear thickening suspensions
Mari, Romain; Seto, Ryohei; Morris, Jeffrey F.; Denn, Morton M.
2015-05-01
The discontinuous shear thickening (DST) of dense suspensions is a remarkable phenomenon in which the viscosity can increase by several orders of magnitude at a critical shear rate. It has the appearance of a first-order phase transition between two hypothetical "states" that we have recently identified as Stokes flows with lubricated or frictional contacts, respectively. Here we extend the analogy further by means of stress-controlled simulations and show the existence of a nonmonotonic steady-state flow curve analogous to a nonmonotonic equation of state. While we associate DST with an S -shaped flow curve, at volume fractions above the shear jamming transition the frictional state loses flowability and the flow curve reduces to an arch, permitting the system to flow only at small stresses. Whereas a thermodynamic transition leads to phase separation in the coexistence region, we observe a uniform shear flow all along the thickening transition. A stability analysis suggests that uniform shear may be mechanically stable for the small Reynolds numbers and system sizes in a rheometer.
Stochastic parametric resonance in shear flows
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F. J. Poulin
2005-01-01
Full Text Available Time-periodic shear flows can give rise to Parametric Instability (PI, as in the case of the Mathieu equation (Stoker, 1950; Nayfeh and Mook, 1995. This mechanism results from a resonance between the oscillatory basic state and waves that are superimposed on it. Farrell and Ioannou (1996a, b explain that PI occurs because the snap-shots of the velocity profile are subject to transient growth. If the flows were purely steady the transient growth would subside and not have any long lasting effect. However, the coupling between transient growth and the time variation of the basic state create PI. Mathematically, transient growth, and therefore PI, are due to the nonorthogonal eigenspace in the linearized system. Poulin et al. (2003 studied a time-periodic barotropic shear flow that exhibited PI, and thereby produced mixing at the interface between Potential Vorticity (PV fronts. The instability led to the formation of vortices that were stretched. A later study of an oscillatory current in the Cape Cod Bay illustrated that PI can occur in realistic shear flows (Poulin and Flierl, 2005. These studies assumed that the basic state was periodic with a constant frequency and amplitude. In this work we study a shear flow similar to that found in Poulin et al. (2003, but now where the magnitude of vorticity is a stochastic variable. We determine that in the case of stochastic shear flows the transient growth of perturbations of the snapshots of the basic state still generate PI.
Shear modulation experiments with ECCD on TCV
International Nuclear Information System (INIS)
Anomalous electron transport is determined by turbulence, which in turn is affected by magnetic shear. A novel application of Electron Cyclotron Current Drive (ECCD), aiming at localized shear modulation, has been applied on TCV tokamak for experiments on shear-dependent electron transport. Pairs of EC beams, absorbed at the same radius but oriented for co and counter injection, are modulated out of phase in order to force a local modulation of current density at constant input power. Off-axis deposition (?dep=0.24) is performed for sawteeth control. A significant impact on local shear is achieved with IECCD?0.1IOH even if the modulation period is much shorter than current diffusion time. Although source (heat and particle) terms are constant, both electron density and temperature are modulated during alternated ECCD. Thomson Scattering is the diagnostic for local Te and ne measurement, in order to overcome suprathermal problems on ECE from high field side. Once equilibrium effects are taken into account for appropriate mapping of TS measurements onto flux coordinates, Te and electron pressure modulation, peaked on-axis, is confirmed at all radii internal to EC deposition. Best confinement (?ne,0Te,0=+12%) is for co-injection, when shear drops from ?0.5 to less than 0.2. (author)
Dynamic Modes of Red Blood Cells in Oscillatory Shear Flow
Noguchi, Hiroshi
2010-01-01
The dynamics of red blood cells (RBCs) in oscillatory shear flow was studied using differential equations of three variables: a shape parameter, the inclination angle $\\theta$, and phase angle $\\phi$ of the membrane rotation. In steady shear flow, three types of dynamics occur depending on the shear rate and viscosity ratio. i) tank-treading (TT): $\\phi$ rotates while the shape and $\\theta$ oscillate. ii) tumbling (TB): $\\theta$ rotates while the shape and $\\phi$ oscillate. iii) intermediate motion: both $\\phi$ and $\\theta$ rotate synchronously or intermittently. In oscillatory shear flow, RBCs show various dynamics based on these three motions. For a low shear frequency with zero mean shear rate, a limit-cycle oscillation occurs, based on the TT or TB rotation at a high or low shear amplitude, respectively. This TT-based oscillation well explains recent experiments. In the middle shear amplitude, RBCs show an intermittent or synchronized oscillation. As shear frequency increases, the vesicle oscillation beco...
Experimental and 3D Numerical Simulation of Reinforced Shear Joints
Jalalifar, Hossein; Aziz, N.
2010-02-01
The load transfer capacity and failure mechanism of a fully grouted bolt installed across a joint in shear is investigated, both experimentally and numerically, in five types of bolt. The double-shearing testing of bolts were studied in concrete blocks of 20, 40 and 100 MPa strengths, subjected to different pretension loads of 0, 5, 10, 20, 50 and 80 KN, respectively. The parameters examined include: shear resistance, shear displacement, induced strains and stresses during the bolt-bending process, and its ultimate failure across the sheared joint planes. The conclusions drawn from the study were that the strength of the concrete, bolt profile configuration and bolt pretension load played a significant influence on the shear resistance, shear displacement and failure mechanism of the reinforced medium. Experimental and numerical simulations showed that the failure occurs as a result of the induced axial and shear stresses acting between the hinge point distances in the vicinity of the shear joint plane.
A dynamic jamming point for shear thickening suspensions
Brown, Eric; Jaeger, Heinrich
2008-11-01
Densely packed suspensions can shear thicken, in which the viscosity increases with shear rate. We performed rheometry measurements on two model systems: corn starch in water and glass spheres in oils. In both systems we observed shear thickening up to a critical packing fraction ?c (=0.55 for spherical grains) above which the flow abruptly transitions to shear thinning. The viscosity and yield stress diverge as power laws at ?c. Extrapolating the dynamic ranges of shear rate and stress in the shear thickening regime up to ?c suggests a finite change in shear stress with zero change in shear rate. This is a dynamic analog to the jamming point with a yield stress at zero shear rate.
Transversely Compressed- and Restrained Shear Joints
DEFF Research Database (Denmark)
Schmidt, Jacob Wittrup; Hansen, Christian Skodborg
2013-01-01
Anchorage of FRP strengthening systems where the deformation perpendicular to the FRP material is restrained or a compressive force is applied on the strengthening, seems to provide ductility, increased utilization of the FRP and failure modes which can be controlled through the anchorage method. This paper presents theoretical model which can predict the response of transversely compressed and restrained single- and double lap shear joints. The interface material model is based on a cohesive law in the shear-slip plane with a descending branch and a uniform frictional stress added due to the friction in the crack, emanating from the transverse pressure or restraint. The theoretical model is compared with experimental results from transversely compressed single- and double shear joints. Also theoretical predictions of a mechanical integrated sleeve-wedge anchorage load capacity are carried out and compared with tests. It is seen that the theory correlates well with the experimental results.
Shear-Induced Diffusion of Cubic Colloids
Hudson, Steven; Royer, John; Blair, Daniel
2013-11-01
Particles in many industrially relevant fluid suspensions have directional or anisotropic interactions, yet it is not understood how these interactions influence particle self-association or the rheology of a suspension. We therefore use confocal rheometry to study simultaneously the micro-scale particle motion and macro-scale rheology of a model colloidal suspension. Specifically, we study mono-disperse, hollow, silica cubes exhibiting well-characterized, well-controlled and tunable directional interactions. Tracking the 3-D position and orientation of the cubes as they move under steady shear, we characterize the packing structure and shear-induced diffusion of the cubes varying the shear rate, packing density, and depletion-induced attraction.
Role of high shear rate in thrombosis.
Casa, Lauren D C; Deaton, David H; Ku, David N
2015-04-01
Acute arterial occlusions occur in high shear rate hemodynamic conditions. Arterial thrombi are platelet-rich when examined histologically compared with red blood cells in venous thrombi. Prior studies of platelet biology were not capable of accounting for the rapid kinetics and bond strengths necessary to produce occlusive thrombus under these conditions where the stasis condition of the Virchow triad is so noticeably absent. Recent experiments elucidate the unique pathway and kinetics of platelet aggregation that produce arterial occlusion. Large thrombi form from local release and conformational changes in von Willebrand factor under very high shear rates. The effect of high shear hemodynamics on thrombus growth has profound implications for the understanding of all acute thrombotic cardiovascular events as well as for vascular reconstructive techniques and vascular device design, testing, and clinical performance. PMID:25704412
Miocene dextral shearing between Himalaya and Tibet
Pécher, Arnaud; Bouchez, Jean-Luc; Le Fort, Patrick
1991-07-01
The Main Central thrust zone is the major structural feature of the Himalayas. It was active during Miocene time and accommodated at least 100 km, and possibly as much as 300 km, of convergence between India and Tibet. We present evidence that late in the tectonic history, another large shear zone, located north of the High Himalayas (the North Himalayan shear zone), underwent a phase of dextral strike-slip motion. The most plausible explanation for this phase of motion is that it reflects the onset of extension in Tibet. It is usually thought that extension began about 2.5 Ma. The phase of dextral shear we report occurred between 25 and 15 Ma. If our explanation for this movement is correct, it places the onset of extension at least 12 m.y. earlier than previously thought.
Integration of the TDWR and LLWAS wind shear detection system
Cornman, Larry
1991-01-01
Operational demonstrations of a prototype TDWR/LLWAS (Terminal Doppler Weather Radar/Low Level Wind shear Alarm System) integrated wind shear detection system were conducted. The integration of wind shear detection systems is needed to provide end-users with a single, consensus source of information. A properly implemented integrated system provides wind shear warnings of a higher quality than stand-alone LLWAS or TDWR systems. The algorithmic concept used to generate the TDWR/LLWAS integrated products and several case studies are discussed, indicating the viability and potential of integrated wind shear detection systems. Implications for integrating ground and airborne wind shear detection systems are briefly examined.
Compressibility and shock wave interaction effects on free shear layers
Samimy, M.; Erwin, D. E.; Elliott, G. S.
1989-01-01
Two compressible free shear layers with convective Mach numbers of .51 and .86 were studied as baseline configurations to investigate the effects of compressibility on the turbulence characteristics. These shear layers were then disturbed by the placement of an obstruction in the shear layer in an attempt to enhance the shear layer growth rate. These models produced a curved shock in the supersonic side of the shear layer. The results indicate a significant reduction in turbulence levels with increased compressibility. However, there are not any significant changes due to the bow shock interaction with the shear layer.
Yamakoshi, Yoshiki; Yamamoto, Atsushi; Kasahara, Toshihiro; Iijima, Tomohiro; Yuminaka, Yasushi
2015-07-01
We have proposed a quantitative shear wave imaging technique for continuous shear wave excitation. Shear wave wavefront is observed directly by color flow imaging using a general-purpose ultrasonic imaging system. In this study, the proposed method is applied to experiments in vivo, and shear wave maps, namely, the shear wave phase map, which shows the shear wave propagation inside the medium, and the shear wave velocity map, are observed for the skeletal muscle in the shoulder. To excite the shear wave inside the skeletal muscle of the shoulder, a hybrid ultrasonic wave transducer, which combines a small vibrator with an ultrasonic wave probe, is adopted. The shear wave velocity of supraspinatus muscle, which is measured by the proposed method, is 4.11 ± 0.06 m/s (N = 4). This value is consistent with those obtained by the acoustic radiation force impulse method.
International Nuclear Information System (INIS)
A simple physical model for the toroidal sheared flow stabilization of ion temperature gradient-driven instability in a tokamak plasma with negative magnetic shear is presented. Reduced fluid equations and modified magnetic shear slab geometry including variation of magnetic shear with magnetic surface are adopted. Analytical and numerical calculations show that the toroidal rotation sheared flow can modify the sheared slab ?i instability. That is, it has a stabilizing role in the plasma core near minimum-q magnetic surface, but as magnetic shear increases, it can give rise to stronger slab ?i instability. In addition, the slow variation of the magnetic shear with the magnetic surface has almost no important influence on the sheared slab ?i instability
Shear banding in soft glassy materials
Fielding, S. M.
2014-10-01
Many soft materials, including microgels, dense colloidal emulsions, star polymers, dense packings of multilamellar vesicles, and textured morphologies of liquid crystals, share the basic ‘glassy’ features of structural disorder and metastability. These in turn give rise to several notable features in the low frequency shear rheology (deformation and flow properties) of these materials: in particular, the existence of a yield stress below which the material behaves like a solid, and above which it flows like a liquid. In the last decade, intense experimental activity has also revealed that these materials often display a phenomenon known as shear banding, in which the flow profile across the shear cell exhibits macroscopic bands of different viscosity. Two distinct classes of yield stress fluid have been identified: those in which the shear bands apparently persist permanently (for as long as the flow remains applied), and those in which banding arises only transiently during a process in which a steady flowing state is established out of an initial rest state (for example, in a shear startup or step stress experiment). Despite being technically transient, such bands may in practice persist for a very long time and so be mistaken for the true steady state response of the material in experimental practice. After surveying the motivating experimental data, we describe recent progress in addressing it theoretically, using the soft glassy rheology model and a simple fluidity model. We also briefly place these theoretical approaches in the context of others in the literature, including elasto-plastic models, shear transformation zone theories, and molecular dynamics simulations. We discuss finally some challenges that remain open to theory and experiment alike.
Herle, V.; Manneville, S.; Fischer, P.
2008-05-01
We carried out pointwise local velocity measurements on 40mM cetylpyridinium chloride-sodium salicylate (CPyCl-NaSal) wormlike micellar solution using high-frequency ultrasound velocimetry in a Couette shear cell. The studied wormlike solution exhibits Newtonian, shear-thinning and shear-thickening rheological behavior in a stress-controlled environment. Previous rheology, flow visualization and small-angle light/neutron scattering experiments in the shear-thickening regime of this system showed the presence of stress-driven alternating transparent and turbid rings or vorticity bands along the axis of the Couette geometry. Through local velocity measurements we observe a homogeneous flow inside the 1mm gap of the Couette cell in the shear-thinning (stress-plateau) region. Only when the solution is sheared beyond the critical shear stress (shear-thickening regime) in a stress-controlled experiment, we observe inhomogeneous flow characterized by radial or velocity gradient shear bands with a highly sheared band near the rotor and a weakly sheared band near the stator of the Couette geometry. Furthermore, fast measurements performed in the shear-thickening regime to capture the temporal evolution of local velocities indicate coexistence of both radial and vorticity shear bands. However the same measurements carried out in shear rate controlled mode of the rheometer do not show such rheological complexity.
Fuhrmann, Alexander; Engler, Adam J
2015-02-01
Several methods have been developed to quantify population level changes in cell attachment strength given its large heterogeneity. One such method is the rotating disk chamber or 'spinning disk' in which a range of shear forces are applied to attached cells to quantify detachment force, i.e. attachment strength, which can be heterogeneous within cell populations. However, computing the exact force vectors that act upon cells is complicated by complex flow fields and variable cell morphologies. Recent observations suggest that cells may remodel their morphology and align during acute shear exposure, but contrary to intuition, shear is not orthogonal to the radial direction. Here we theoretically derive the magnitude and direction of applied shear and demonstrate that cells, under certain physiological conditions, align in this direction within minutes. Shear force magnitude is also experimentally verified which validates that for spread cells shear forces and not torque or drag dominate in this assay, and demonstrates that the applied force per cell area is largely independent of initial morphology. These findings suggest that direct quantified comparison of the effects of shear on a wide array of cell types and conditions can be made with confidence using this assay without the need for computational or numerical modeling. PMID:25619322
Mesoscale hydrodynamic modeling of a colloid in shear-thinning viscoelastic fluids under shear flow.
Ji, Shichen; Jiang, Run; Winkler, Roland G; Gompper, Gerhard
2011-10-01
In order to study the dynamics of colloidal suspensions with viscoelastic solvents, a simple mesoscopic model of the solvent is required. We propose to extend the multiparticle collision dynamics (MPC) technique--a particle-based simulation method, which has been successfully applied to study the hydrodynamic behavior of many complex fluids with Newtonian solvent--to shear-thinning viscoelastic solvents. Here, the normal MPC particles are replaced by dumbbells with finite-extensible nonlinear elastic (FENE) springs. We have studied the properties of FENE-dumbbell fluids under simple shear flow with shear rate ??. The stress tensor is calculated, and the viscosity ? and the first normal-stress coefficient ?(1) are obtained. Shear-thinning behavior is found for reduced shear rates ?= ???>1, where ? is a characteristic dumbbell relaxation time. Here, both ? and ?(1) display power-law behavior in the shear-thinning regime. Thus, the FENE-dumbbell fluid with MPC collisions provides a good description of viscoelastic fluids. As a first application, we study the flow behavior of a colloid in a shear-thinning viscoelastic fluid in two dimensions. A slowing down of the colloid rotation in a viscoelastic fluid compared to a Newtonian fluid is obtained, in agreement with recent numerical calculations and experimental results. PMID:21992291
Fuhrmann, Alexander; Engler, Adam J.
2015-02-01
Several methods have been developed to quantify population level changes in cell attachment strength given its large heterogeneity. One such method is the rotating disk chamber or ‘spinning disk’ in which a range of shear forces are applied to attached cells to quantify detachment force, i.e. attachment strength, which can be heterogeneous within cell populations. However, computing the exact force vectors that act upon cells is complicated by complex flow fields and variable cell morphologies. Recent observations suggest that cells may remodel their morphology and align during acute shear exposure, but contrary to intuition, shear is not orthogonal to the radial direction. Here we theoretically derive the magnitude and direction of applied shear and demonstrate that cells, under certain physiological conditions, align in this direction within minutes. Shear force magnitude is also experimentally verified which validates that for spread cells shear forces and not torque or drag dominate in this assay, and demonstrates that the applied force per cell area is largely independent of initial morphology. These findings suggest that direct quantified comparison of the effects of shear on a wide array of cell types and conditions can be made with confidence using this assay without the need for computational or numerical modeling.
Buckling of sheared and compressed microfibrils
Nadermann, Nichole; Kumar, Ajeet; Goyal, Sachin; Hui, Chung-Yuen
2010-01-01
In this paper, we study the stability of an initially straight elastic fibril clamped at one end, while the other end is subjected to a constant normal compressive force and a prescribed shear displacement. We found the buckling load of a sheared fibril to be always less than the Euler buckling load. Furthermore, if the end of the fibril loses adhesion, then the buckling load can be considerably less. Our result suggests that the static friction of microfibre arrays can decrease with increasing normal compressive load and, in some cases, friction force can actually become negative. PMID:20444710
A Numerical Study of Cosmic Shear Statistics
Thion, A.; Mellier, Y.; Bernardeau, F.; Bertin, E.; Erben, T.; Waerbeke, L.
2000-01-01
We explore the stability of the variance and skewness of the cosmic gravitational convergence field, using two different approaches: first we simulate a whole MEGACAM survey (100 sq. degrees). The reconstructed mass map, obtained from a shear map, shows that the state-of-the-art data analysis methods can measure weak-lensing statistics at angular scales ranging from 2.5' to 25'. We looked also at the influence of a varying signal-to-noise ratio over the shear map (due to loc...
Velocity Profiles in Slowly Sheared Bubble Rafts
Lauridsen, J; Dennin, M; Lauridsen, John; Chanan, Greg; Dennin, Michael
2004-01-01
Measurements of average velocity profiles in a bubble raft subjected to slow, steady-shear demonstrate the coexistence between a flowing state and a jammed state similar to that observed for three-dimensional foams and emulsions [Coussot {\\it et al,}, Phys. Rev. Lett. {\\bf 88}, 218301 (2002)]. For sufficiently slow shear, the flow is generated by nonlinear topological rearrangements. We report on the connection between this short-time motion of the bubbles and the long-time averages. We find that a smooth, average velocity is reached after averaging over only a relatively few number of rearrangement events.
Size Segregation in Sheared Jammed Colloids
Mbi, Armstrong; Blair, Daniel
2013-03-01
It is well known that granular materials can spontaneously size segregate when continuously driven. However, in jammed colloidal suspensions, this phenomenon is not well understood. Colloidal dispersions provide a unique system to study the structure and dynamics of jammed matter. In this talk, we present results of size segregation of a continuously sheared binary colloidal suspension well above point J. Our colloidal system is comprised of indexed-matched bi-disperse silica particles with diameters a = { 2 . 3 ?m and 3 . 2 ?m } and at ? 61 % , well above the colloidal glass transition. We apply a highly controlled shear at a constant shear rate through the use of a rheometer. By coupling our rheometer with a high-speed laser scanning confocal microscope, we directly image the structure and flow profiles of the suspension as it un-jams. We observe migration of the small and large species; large particles move to the top while the small particles move toward the bottom conserving the total volume fraction in all regions. Moreover, we find that an associating feature of segregation is a sustained shear band. Our results are consistent with a recently proposed void filling and squeeze expulsion mechanism. It is well known that granular materials can spontaneously size segregate when continuously driven. However, in jammed colloidal suspensions, this phenomenon is not well understood. Colloidal dispersions provide a unique system to study the structure and dynamics of jammed matter. In this talk, we present results of size segregation of a continuously sheared binary colloidal suspension well above point J. Our colloidal system is comprised of indexed-matched bi-disperse silica particles with diameters a = { 2 . 3 ?m and 3 . 2 ?m } and at ? 61 % , well above the colloidal glass transition. We apply a highly controlled shear at a constant shear rate through the use of a rheometer. By coupling our rheometer with a high-speed laser scanning confocal microscope, we directly image the structure and flow profiles of the suspension as it un-jams. We observe migration of the small and large species; large particles move to the top while the small particles move toward the bottom conserving the total volume fraction in all regions. Moreover, we find that an associating feature of segregation is a sustained shear band. Our results are consistent with a recently proposed void filling and squeeze expulsion mechanism. Funding is provided by NSF DMR #0847490.
Shear viscosity in a gluon gas
Xu, Zhe
2007-01-01
The relation of the shear viscosity coefficient to the recently introduced transport rate is derived within relativistic kinetic theory. We calculate the shear viscosity over entropy ratio \\eta/s for a gluon gas, which involves elastic gg-> gg pQCD scatterings as well as inelastic ggggg pQCD bremsstrahlung. For \\alpha_s=0.3 we find \\eta/s=0.13 and for \\alpha_s=0.6 \\eta/s=0.076. The small \\eta/s values, which suggest strongly coupled systems, are due to the gluon bremsstrahlung incorporated.
Shear Viscosity in a Gluon Gas
Xu, Zhe; Greiner, Carsten
2007-01-01
The relation of the shear viscosity coefficient to the recently introduced transport rate is derived within relativistic kinetic theory. We calculate the shear viscosity over entropy ratio \\eta/s for a gluon gas, which involves elastic gg-> gg perturbative QCD (PQCD) scatterings as well as inelastic ggggg PQCD bremsstrahlung. For \\alpha_s=0.3 we find \\eta/s=0.13 and for \\alpha_s=0.6, \\eta/s=0.076. The small \\eta/s values, which suggest strongly coupled systems, are due to th...
Halo abundances and shear in void models
DEFF Research Database (Denmark)
Alonso, David; García-Bellido, Juan
2012-01-01
We study the non-linear gravitational collapse of dark matter into halos through numerical N-body simulations of Lemaitre-Tolman-Bondi void models. We extend the halo mass function formalism to these models in a consistent way. This extension not only compares well with the simulated data at all times and radii, but it also gives interesting clues about the impact of the background shear on the growth of perturbations. Our results give hints about the possibility of constraining the background shear via cluster number counts, which could then give rise to strong constraints on general inhomogeneous models, of any scale.
Compressibility effects in free shear layers
Samimy, M.; Elliott, G. S.
1990-01-01
High-Reynolds-number compressible free shear layers were studied experimentally to explore the effects of compressibility on the turbulence field. A reduction in both the level and the lateral extent of turbulence fluctuations with increasing convective Mach number (Mc) (reported earlier for Mc of 0.51 and 0.64) is much higher at Mc of 0.86. The higher-order moments of turbulence fluctuations such as skewness and flatness show that the intermittency due to the excursion of large-scale structures into the free streams at the edge of shear layers was significantly reduced (both in the level and the extent) due to increased Mc.
Seismic behaviour of concrete shear walls
International Nuclear Information System (INIS)
Concrete shear walls have an important contribution to building stiffness. So, it is necessary to know their behaviour under seismic loads. The ultimate behaviour of shear walls under dynamic loadings has been studied. The study includes: - A description of the non linear global model based on cyclic static tests. - Non linear time history calculations for various forcing functions. The comparison of linear and non linear results have shown important margins related to the ductility when the bandwidth of the forcing function is narrow and centred on the wall natural frequency
Shear alfven resonances in Tokapole II
International Nuclear Information System (INIS)
It has been suggested that efficient heating can occur by coupling energy through the shear Alfven resonance that is predicted to occur at particular locations within inhomogeneous plasmas. This heating mechanism should be applicable to tokamaks; however, the existence of the resonances in tokamaks has not yet been established experimentally. We present here direct observations of localized enhancement in the driven wave magnetic field which are compatible with theoretical predictions for the shear Alfven resonance in tokamak geometry. These resonance studies at low absorbed power will be followed by higher power heating (approx. 1 MW) presently being developed
Evolution of anomalous transport in shear flow of toroidal devices
International Nuclear Information System (INIS)
The experimentally determined velocity shear in Uragan-3M (U-3M) torsatron in (L-H) - like transition is up to ten times greater than the drift wave frequency. The temporal evolution of the drift and Alfven turbulence and the resulted anomalous transport are considered under the conditions of modest (flow shear parameter v0' is of the order of the instabilities growth rate) and strong flow shear (flow shear parameter v0' is greater than the drift frequency) on the grounds of the non-modal approach. The studies of the dynamics of packets of nonmodal drift waves, eta-i modes, Alfven waves have shown that the wave packets are stagnated or reflected by the shear flow. The components of the group velocity along the flow shear rapidly vanish with time. The calculated anomalous ion transport displays rapid decreasing with time. The comparative analysis of the linear non-modal effects and nonlinear turbulent effects, such as the effect of the enhanced by flow shear nonlinear decorrelation, on the instabilities evolution and saturation is performed. The renormalized kinetic theory of drift and drift-cyclotron instabilities of a plasma with a transverse inhomogeneous shear flow, which accounts for the turbulent scattering of ions across the shear flow and the enhanced scattering of ions along the shear flow, is developed. The saturation level of the shear-flow-modified drift turbulence and the reduced by the shear flow anomalous fluxe reduced by the shear flow anomalous fluxes of ions and electrons are determined. (author)
Shear heating in continental strike-slip shear zones:model and field examples
Leloup, Philippe Hervé; Ricard, Yannick; Battaglia, Jean; Lacassin, Robin
1999-01-01
A two-layer (crust and upper mantle), finite difference steady-state thermomechanical model of a long-lived (several million years) lithospheric strike-slip fault is presented, and its predictions compared with field observations from various major fault zones. In order to estimate the maximum amount of shear heating, all mechanical energy is assumed to be dissipated in heat, in ductile as well as in brittle layers. Deformation follows a friction law in the brittle layer(s), and a power-flow law in the ductile one(s). Variations of several independent parameters and their influence on the thermo-mechanical state of the fault zone and on shear heating are systematically explored. Shear heating is found to be more important in fault zones affecting an initially cold lithosphere, and increases with slip rate, friction coefficient and stiffness of materials. In extreme cases (slip rate of 10 cm yr^-1, stiff lithosphere), shear heating could lead to temperature increases close to 590 degC at the Moho, and 475 degC at 20 km depth. For more common cases, shear heating leads to smaller temperature increases, but can still explain high-grade metamorphic conditions encountered in strike-slip shear zones. However, modelled temperature conditions often fall short of those observed. This could be due to heat transport by mechanisms more efficient than conduction. Common syntectonic emplacement of granitic melts in ductile strike-slip shear zones can be explained by lower crust partial melting induced by shear heating in the upper mantle. Besides slip rate, the possibility of such melting depends mostly on the upper mantle rheology and on the fertility of the lower crust: for hard upper mantle and highly fertile lower crust, partial melting could occur at rates of 1 cm yr^-1, while in most cases it would result from the breakdown of micas for slip rates over 3 cm yr^-1. As a result of shear heating, partial melting of the upper mantle could occur in the presence of small amounts of fluids. Rise of magmas and/or hot fluids in the shear zone will further enhance the temperature increase in shallower parts of the fault zone. In nature, shear heating would inevitably cause strain localization in the deeper parts of strike-slip faults, as is often observed in the field for crustal shear zones.
Instabilities in Pulsating Pipe Flow of Shear-Thinning and Shear-Thickening Fluids
Sadrizadeh, Sasan
2012-01-01
In this study, we have considered the modal and non-modal stability of fluids with shear-dependent viscosity flowing in a rigid straight pipe. A second order finite-difference code is used for the simulation of pipe flow in the cylindrical coordinate system. The Carreau-Yasuda model where the rheological parameters vary in the range of 0.3 < n < 1.5 and 0.1 < ? < 100 is represents the viscosity of shear- thinning and shear thickening fluids. Variation of the periodic pulsatile f...
Scientific Electronic Library Online (English)
Gaspar Manuel, Parra-Bracamonte; Ana María, Sifuentes-Rincón; Williams, Arellano-Vera; Juan Gabriel, Magaña-Monforte; José Alberto, Ramírez-De León; Gonzalo, Velázquez.
2014-04-01
Full Text Available La suavidad de la carne bovina es un rasgo importante para la satisfacción del consumidor y es la principal característica asociada a su palatabilidad, por lo que es importante evaluar su variabilidad en diferentes razas bovinas. Un experimento fue diseñado para evaluar la Fuerza de Corte de Warner- [...] Bratzler (FCWB) de carne del ojo de la costilla de bovinos Brangus rojos y su aceptabilidad. La suavidad de la carne fue evaluada mediante la FCWB; además, se realizó una evaluación de preferencia de consumo para estimar cuantitativamente la suavidad, jugosidad, sabor, término y aceptación general de los cortes evaluados. La media de la FCWB fue 5.03 kg ± 0.93 kg, lo que teóricamente representa una carne dura. En la distribución de las muestras se registraron 21 % y 11 % de cortes, respectivamente, de carne moderadamente suave y suave. La condición de los animales (toros o novillos) no fue significativa para la FCWB (p > 0.5). Todas las características evaluadas en la evaluación hedónica tuvieron alrededor de 6 puntos de un total de 8 (8 era mejor). La suavidad, jugosidad y sabor mostraron una correlación alta y significativa (p Abstract in english Beef tenderness is an important trait in consumer satisfaction and has been considered as the main trait for palatability, for which reason it is important to evaluate its variability in different cattle breeds. An experiment was designed to evaluate the Warner Bratzler Shear Force (WBSF) of Red Bra [...] ngus cattle rib eye steaks and consumer acceptance. The tenderness of beef rib eye steaks was evaluated by the WBSF. A consumer preference evaluation test was carried out to quantitatively estimate tenderness, juiciness, flavor, doneness and general acceptance of the evaluated steaks. Mean WBSF was 5.03 kg ± 0.93 kg, theoretically indicating a tough beef. The distribution of the samples showed 21 % and 11 % of moderately tender and tender beef cuts, respectively. Cattle condition (bulls and steers) was not significant for the WBSF (p > 0.5). All the traits evaluated in the hedonic evaluation had approximately 6 points of a total of 8 (8 was best). Tenderness, juiciness and flavor presented a high and significant correlation (p
Shear crack formation and propagation in reinforced Engineered Cementitious Composites
DEFF Research Database (Denmark)
Paegle, Ieva; Fischer, Gregor
2011-01-01
This paper describes an experimental investigation of the shear behaviour of beams consisting of steel reinforced Engineered Cementitious Composites (R/ECC). Based on the strain hardening and multiple cracking behaviour of ECC, this study investigates the extent to which ECC influences the shear capacity of beams loaded primarily in shear. The experimental program consists of ECC with short randomly distributed polyvinyl alcohol (PVA) fiber beams with different stirrup arrangements and conventional reinforced concrete (R/C) counterparts for comparison. The shear crack formation mechanism of ECC is investigated in detail and can be characterized by an opening and sliding of the crack. Photogrammetry was utilized to monitor the shear deformations of the specimens. Multiple shear cracking and strain hardening of ECC was observed under shear loading and based upon photogrammetric results fundamental descriptions of shear crack opening, sliding and subsequent failure are presented.
Chaotic dynamics in shear-thickening surfactant solutions
Bandyopadhyay, R M
2000-01-01
We report the observation of dynamical behaviour in dilute, aqueous solutions of a surfactant CTAT (cetyl trimethylammonium p-toluenesulphonate), below the overlap concentration c$^{\\star}$. At these concentrations, CTAT forms cylindrical micelles and shows a pronounced shear thickening transition above a concentration-dependent critical shear rate $\\dot\\gamma_{c}$. An analysis of the time-series of the stress relaxations at controlled shear rates in the shear-thickening regime shows the existence of correlation dimensions greater than two and positive Lyapunov exponents. This indicates the existence of deterministic chaos in the dynamics of stress relaxation at these concentrations and shear rates. The observed chaotic behaviour may be attributed to the stick-slip between the shear - induced structure (SIS) formed in the sheared surfactant solution and the coexisting dilute phase. At still higher shear rates, when the SIS spans the Couette, there is a transition to higher-dimensional dynamics arising out of ...
Transient and steady state behaviors of rapid granular shear flows
Jalali, P.; Ritvanen, J.; Sarkomaa, P.
2005-09-01
Rapid granular shear flow is a classical example in granular materials which exhibits fluid-like behavior solely or fluid-like and solid-like behaviors simultaneously. We have performed experiments on annular granular shear flows using monodisperse steel spheres with 2-mm and 3-mm diameters. We discuss some transient (static failure of material due to shear) and steady-state (completely sheared and partially sheared flows) features of rapid granular flows. Our results map out the boundary between overall compaction and dilation that characterizes multiphase behavior of the system. Dimensionless stresses rise as more material is loaded into the system. On the other hand, increasing the compressive force or shear rate is equal to easing the process of shearing by decreasing the ratio of shear to normal stress.
Turbulent transport in tokamak plasmas with rotational shear.
Barnes, M; Parra, F I; Highcock, E G; Schekochihin, A A; Cowley, S C; Roach, C M
2011-04-29
Nonlinear gyrokinetic simulations are conducted to investigate turbulent transport in tokamak plasmas with rotational shear. At sufficiently large flow shears, linear instabilities are suppressed, but transiently growing modes drive subcritical turbulence whose amplitude increases with flow shear. This leads to a local minimum in the heat flux, indicating an optimal E×B shear value for plasma confinement. Local maxima in the momentum fluxes are observed, implying the possibility of bifurcations in the E×B shear. The critical temperature gradient for the onset of turbulence increases with flow shear at low flow shears; at higher flow shears, the dependence of heat flux on temperature gradient becomes less stiff. The turbulent Prandtl number is found to be largely independent of temperature and flow gradients, with a value close to unity. PMID:21635042
Wall Shear Stress Measurements in Microfluidic Systems.
Czech Academy of Sciences Publication Activity Database
Tihon, Jaroslav; P?nkavová, V?ra; Stanovský, Petr; Vejražka, Ji?í
- : -, 2014, s. 607. ISBN N. [European Fluid Mechanics Conference EFMC10 /10./. Copenhagen (DK), 15.09.2014-18.09.2014] R&D Projects: GA ?R(CZ) GAP101/12/0585 Institutional support: RVO:67985858 Keywords : microfluidics * electrodiffusion method * wall shear stress Subject RIV: CI - Industrial Chemistry, Chemical Engineering http://www.efmc10.org/
Crossing of shears bands in 196Pb
International Nuclear Information System (INIS)
High-spin states in 196Pb have been populated using the reaction 170Er(30Si, 4n). The previously observed shear bands in this nucleus have been extended and some of their transitions have been reordered. They now form regular bands with band crossings. One of the bands splits into two pathways at high spin. (orig.)
Shear jamming for highly strained granular materials
Bares, Jonathan; Berhinger, Robert
2015-03-01
Bi et al. (Nature 2011) have shown that, if sheared, a granular material can jam even if its packing fraction (?) is lower than the critical isotropic jamming point ?J. They have introduced a new critical packing fraction value ?S such that for ?S photoelasticity. This talk will present this novel apparatus and discuss inital results.
International Nuclear Information System (INIS)
The experimental data from RHIC, especially the measured elliptic flow indicate that the matter produced in Au+Au collisions exhibit properties which are more like a strongly interacting liquid than a weakly interacting gas. The shear viscosity ? or the internal friction of the fluid symbolizes the ability to transfer momentum over a distance of ? mean free path. Therefore, in a system where the constituents interact strongly the transfer of momentum is performed easily - resulting in lower values of ?. Consequently such a system may be characterized by a small value of ?/s. The importance of viscosity also lies in the fact that it damps out the variation in the velocity and make the fluid flow laminar. A very small viscosity (large Reynold number) may make the flow turbulent. Although a large amount of work has been done on shear viscosity in QGP phase, the shear viscosity in hadronic matter has received much less attention so far. In the present work shear viscosity has been evaluated in a kinetic theory approach by solving Boltzmann transport equation using the relaxation time approximation
Equilibrium states of homogeneous sheared compressible turbulence
Riahi, M.; Lili, T.
2011-06-01
Equilibrium states of homogeneous compressible turbulence subjected to rapid shear is studied using rapid distortion theory (RDT). The purpose of this study is to determine the numerical solutions of unsteady linearized equations governing double correlations spectra evolution. In this work, RDT code developed by authors solves these equations for compressible homogeneous shear flows. Numerical integration of these equations is carried out using a second-order simple and accurate scheme. The two Mach numbers relevant to homogeneous shear flow are the turbulent Mach number Mt, given by the root mean square turbulent velocity fluctuations divided by the speed of sound, and the gradient Mach number Mg which is the mean shear rate times the transverse integral scale of the turbulence divided by the speed of sound. Validation of this code is performed by comparing RDT results with direct numerical simulation (DNS) of [A. Simone, G.N. Coleman, and C. Cambon, Fluid Mech. 330, 307 (1997)] and [S. Sarkar, J. Fluid Mech. 282, 163 (1995)] for various values of initial gradient Mach number Mg0. It was found that RDT is valid for small values of the non-dimensional times St (St RDT is also valid for large values of St (St > 10) in particular for large values of Mg0. This essential feature justifies the resort to RDT in order to determine equilibrium states in the compressible regime.
Shear deformation in thick auxetic plates
International Nuclear Information System (INIS)
This paper aims to understand the effect of auxeticity on shear deformation in thick plates. Three models for the shear correction factor of plates as a function of Poisson’s ratio were proposed: an analytical model, a cubic fit model and a modified model. Of these three, the cubic fit model exhibits the best accuracy over the entire range of Poisson’s ratio from ?1 to 0.5. The extent of shear deformation is herein investigated using the example of uniformly loaded circular plates. It was found that the maximum deformation of such plates based on Mindlin theory approximates to those according to Kirchhoff theory when the Poisson’s ratio of the plate material is highly negative. When the Poisson’s ratio of the plate material is ?1 and the edge of the plate is simply supported, the calculation of the maximum deflection by Mindlin theory simplifies into that by Kirchhoff theory. These results suggest that auxeticity reduces shear deformation in thick plates, permitting the use of classical plate theory for thick plates only if the plate material is highly auxetic. (paper)
Towards shear tactile displays with DEAs
Knoop, Lars E.; Rossiter, Jonathan
2014-03-01
Much research has been done on the development of tactile displays using Dielectric Elastomer Actuators (DEAs). It has been argued that they offer the potential to create low-cost full-page tactile displays — not achievable with conventional actuator technologies. All research to date has considered tactile elements moving perpendicular to the skin and thus applying a normal force distribution. In contrast to previous work, we have investigated the use of laterally moving tactile elements that apply shear forces to the skin. This allows for the areal expansion of the DEA to be exploited directly, and a tactile display could be made with no elements moving out of the plane. There is evidence that humans are very sensitive to shear force distributions, and that in some cases a shear stimulus is indistinguishable from a normal stimulus. We present a prototype shear tactile display actuated by a DEA, and demonstrate that the DEA can generate the necessary forces and displacements. We also present and discuss different display topologies.
Modeling of Turbulent Free Shear Flows
Yoder, Dennis A.; DeBonis, James R.; Georgiadis, Nicolas J.
2013-01-01
The modeling of turbulent free shear flows is crucial to the simulation of many aerospace applications, yet often receives less attention than the modeling of wall boundary layers. Thus, while turbulence model development in general has proceeded very slowly in the past twenty years, progress for free shear flows has been even more so. This paper highlights some of the fundamental issues in modeling free shear flows for propulsion applications, presents a review of past modeling efforts, and identifies areas where further research is needed. Among the topics discussed are differences between planar and axisymmetric flows, development versus self-similar regions, the effect of compressibility and the evolution of compressibility corrections, the effect of temperature on jets, and the significance of turbulent Prandtl and Schmidt numbers for reacting shear flows. Large eddy simulation greatly reduces the amount of empiricism in the physical modeling, but is sensitive to a number of numerical issues. This paper includes an overview of the importance of numerical scheme, mesh resolution, boundary treatment, sub-grid modeling, and filtering in conducting a successful simulation.
Shear of ordinary and elongated granular mixtures
Hensley, Alexander; Kern, Matthew; Marschall, Theodore; Teitel, Stephen; Franklin, Scott
2015-03-01
We present an experimental and computational study of a mixture of discs and moderate aspect-ratio ellipses under two-dimensional annular planar Couette shear. Experimental particles are cut from acrylic sheet, are essentially incompressible, and constrained in the thin gap between two concentric cylinders. The annular radius of curvature is much larger than the particles, and so the experiment is quasi-2d and allows for arbitrarily large pure-shear strains. Synchronized video cameras and software identify all particles and track them as they move from the field of view of one camera to another. We are particularly interested in the global and local properties as the mixture ratio of discs to ellipses varies. Global quantities include average shear rate and distribution of particle species as functions of height, while locally we investigate the orientation of the ellipses and non-affine events that can be characterized as shear transformational zones or possess a quadrupole signature observed previously in systems of purely circular particles. Discrete Element Method simulations on mixtures of circles and spherocylinders extend the study to the dynamics of the force network and energy dissipated as the system evolves. Supported by NSF CBET #1243571 and PRF #51438-UR10.
Stability of a compressible shear flow
Bakas, N.
2012-04-01
A comprehensive understanding of the stability of compressible shear flows has been the subject of both theoretical and practical interest in astrophysics. Applications include the maintenance of turbulence in accretion disks around massive bodies and stability of supersonic shear layers in astrophysical jets. In this work, we study non-modal mechanisms underlying transient growth of propagating acoustic waves and non-propagating vorticity perturbations in an unbounded compressible shear flow, and investigate their potential of instigating a transition to turbulence. Propagating acoustic waves amplify mainly due to two mechanisms: growth due to advection of streamwise velocity and growth due to the downgradient irrotational component of the Reynolds stress. Synergy between these mechanisms along with the downgradient solenoidal component of the Reynolds stress produces large and robust energy amplification. On the other hand, non-propagating vorticity perturbations amplify due to kinematic deformation of vorticity by the shear flow. For moderate Mach numbers, a strong coupling between vorticity perturbations and acoustic waves is found with the energy gained by vorticity perturbations being transferred to acoustic waves that are abruptly excited by the vortex. Calculation of the optimal perturbations for a viscous flow showed that for low Mach numbers, acoustic wave excitation by vorticity perturbations and the subsequent growth of acoustic waves leads to robust energy growth of the order of Reynolds number, while for large Mach numbers, synergy between the lift-up mechanism and the downgradient solenoidal component of the Reynolds stress dominates the growth and leads to a comparable large amplification of streamwise velocity.
Excitation of vortex meandering in shear flow
Schröttle, Josef; Dörnbrack, Andreas; Schumann, Ulrich
2015-06-01
This paper investigates the evolution of a streamwise aligned columnar vortex with vorticity {\\boldsymbol{ ? }} in an axial background shear of magnitude ? by means of linear stability analysis and numerical simulations. A long wave mode of vorticity normal to the plane spanned by the background shear vector {\\boldsymbol{ ? }} and the vorticity of the vortex are excited by an instability. The stationary wave modes of the vertical and lateral vorticity are amplified. In order to form a helical vortex, the lateral and vertical vorticity can be phase shifted by half a wavelength. The linear and nonlinear evolutions of the vortex in the shear flow are studied numerically. Linearized simulations confirm the results of the stability analysis. The nonlinear simulations reveal further evolution of the helix in the shear flow. The linearly excited mode persists in co-existence with evolving smaller scale instabilities until the flow becomes fully turbulent at the time of O(100 {{? }-1}). Turbulent mixing dampens the amplifying mode. The described phenomenon of vortex meandering may serve as an alternative explanation for the excitation of wind turbine wake meandering in the atmospheric boundary layer.
Predicting km-scale shear zone formation
Gerbi, Christopher; Culshaw, Nicholas; Shulman, Deborah; Foley, Maura; Marsh, Jeffrey
2015-04-01
Because km-scale shear zones play a first-order role in lithospheric kinematics, accurate conceptual and numerical models of orogenic development require predicting when and where they form. Although a strain-based algorithm in the upper crust for weakening due to faulting appears to succeed (e.g., Koons et al., 2010, doi:10.1029/2009TC002463), a comparable general rule for the viscous crust remains unestablished. Here we consider two aspects of the geological argument for a similar algorithm in the viscous regime, namely (1) whether predicting km-scale shear zone development based on a single parameter (such as strain or shear heating) is reasonable; and (2) whether lithologic variability inherent in most orogenic systems precludes a simple predictive rule. A review of tectonically significant shear zones worldwide and more detailed investigations in the Central Gneiss belt of the Ontario segment of the Grenville Province reveals that most km-scale shear zones occur at lithological boundaries and involve mass transfer, but have fairly little else in common. As examples, the relatively flat-lying Twelve Mile Bay shear zone in the western Central Gneiss belt bounds the Parry Sound domain and is likely the product of both localized anatexis and later retrograde hydration with attendant metamorphism. Moderately dipping shear zones in granitoids of the Grenville Front Tectonic Zone apparently resulted from cooperation among several complementary microstructural processes, such as grain size reduction, enhanced diffusion, and a small degree of metamorphic reaction. Localization into shear zones requires the operation of some spatially restricted processes such as stress concentration, metamorphism/fluid access, textural evolution, and thermal perturbation. All of these could be due in part to strain, but not necessarily linearly related to strain. Stress concentrations, such as those that form at rheological boundaries, may be sufficient to nucleate high strain gradients but are insufficient to maintain them because the stress perturbations will dissipate with deformation. Metamorphism can unquestionably cause sufficient rheological change, but only in certain rock types: for example, granitoids have much less capacity for metamorphically induced rheologic change than do mafic rocks. The magnitude of phase geometry variation observed in natural systems suggests that morphological change (e.g., interconnection of weak phases) likely has little direct affect on strength changes, although other textural factors related to diffusion paths and crystallographic orientation could play a significant role. Thermal perturbation, mainly in the form of shear heating, remains potentially powerful but inconclusive. Taken together, these observations indicate that a simple algorithm predicting shear zone formation will not succeed in many geologically relevant instances. One significant reason may be that the inherent lithologic variation at the km scale, such as observed in the Central Gneiss belt, prevents the development of self-organized strain patterns that would form in more rheologically uniform systems.
High strength semi-active energy absorbers using shear- and mixedmode operation at high shear rates
Becnel, Andrew C.
This body of research expands the design space of semi-active energy absorbers for shock isolation and crash safety by investigating and characterizing magnetorheological fluids (MRFs) at high shear rates ( > 25,000 1/s) under shear and mixed-mode operation. Magnetorheological energy absorbers (MREAs) work well as adaptive isolators due to their ability to quickly and controllably adjust to changes in system mass or impact speed while providing fail-safe operation. However, typical linear stroking MREAs using pressure-driven flows have been shown to exhibit reduced controllability as impact speed (shear rate) increases. The objective of this work is to develop MREAs that improve controllability at high shear rates by using pure shear and mixed shear-squeeze modes of operation, and to present the fundamental theory and models of MR fluids under these conditions. A proof of concept instrument verified that the MR effect persists in shear mode devices at shear rates corresponding to low speed impacts. This instrument, a concentric cylinder Searle cell magnetorheometer, was then used to characterize three commercially available MRFs across a wide range of shear rates, applied magnetic fields, and temperatures. Characterization results are presented both as flow curves according to established practice, and as an alternate nondimensionalized analysis based on Mason number. The Mason number plots show that, with appropriate correction coefficients for operating temperature, the varied flow curve data can be collapsed to a single master curve. This work represents the first shear mode characterization of MRFs at shear rates over 10 times greater than available with commercial rheometers, as well as the first validation of Mason number analysis to high shear rate flows in MRFs. Using the results from the magnetorheometer, a full scale rotary vane MREA was developed as part of the Lightweight Magnetorheological Energy Absorber System (LMEAS) for an SH-60 Seahawk helicopter crew seat. Characterization tests were carried out on the LMEAS using a 40 vol% MRF used in the previous magnetorheometer tests. These were analyzed using both flow curves and apparent viscosity vs. Mason number diagrams. The nondimensionalized Mason number analysis resulted in data for all conditions of temperature, fluid composition, and shear rate, to collapse onto a single characteristic or master curve. Significantly, the temperature corrected Mason number results from both the bench top magnetorheometer and full scale rotary vane MREA collapse to the same master curve. This enhances the ability of designers of MRFs and MREAs to safely and effectively apply characterization data collected in low shear rate, controlled temperature environments to operational environments that may be completely different. Finally, the Searle cell magnetorheometer was modified with an enforced eccentricity to work in both squeeze and shear modes simultaneously to achieve so called squeeze strengthening of the working MRF, thereby increasing the apparent yield stress and the specific energy absorption. By squeezing the active MR fluid, particles undergo compression-assisted aggregation into stronger, more robust columns which resist shear better than single chains. A hybrid model describing the squeeze strengthening behavior is developed, and recommendations are made for using squeeze strengthening to improve practical MREA devices.
Turbulent transport across shear layers in magnetically confined plasmas
Energy Technology Data Exchange (ETDEWEB)
Nold, B.; Ramisch, M. [Institut für Grenzflächenverfahrenstechnik und Plasmatechnologie, Universität Stuttgart, D-70569 Stuttgart (Germany); Manz, P.; Birkenmeier, G. [Physik-Department E28, Technische Universität München, James-Franck-Str.1, D-85748 Garching (Germany); Max-Planck-Institut für Plasmaphysik, Boltzmannstr. 2, D-85748 Garching (Germany); Ribeiro, T. T.; Müller, H. W.; Scott, B. D. [Max-Planck-Institut für Plasmaphysik, Boltzmannstr. 2, D-85748 Garching (Germany); Fuchert, G. [IJL, Université de Lorraine, CNRS (UMR 7198), BP 40239 Vandoeuvre-lès-Nancy (France); Stroth, U. [Max-Planck-Institut für Plasmaphysik, Boltzmannstr. 2, D-85748 Garching (Germany); Physik-Department E28, Technische Universität München, James-Franck-Str.1, D-85748 Garching (Germany)
2014-10-15
Shear layers modify the turbulence in diverse ways and do not only suppress it. A spatial-temporal investigation of gyrofluid simulations in comparison with experiments allows to identify further details of the transport process across shear layers. Blobs in and outside a shear layer merge, thereby exchange particles and heat and subsequently break up. Via this mechanism particles and heat are transported radially across shear layers. Turbulence spreading is the immanent mechanism behind this process.
Vorticity Alignment and Negative Normal Stresses in Sheared Attractive Emulsions
Montesi, Alberto; Pena, Alejandro A.; Pasquali, Matteo
2003-01-01
Attractive emulsions near the colloidal glass transition are investigated by rheometry and optical microscopy under shear. We find that (a) the apparent viscosity \\eta drops with increasing shear rate, then remains approximately constant in a range of shear rates, then continues to decay; (b) the first normal stress difference N1 transitions sharply from nearly zero to negative in the region of constant shear viscosity; (c) correspondingly, cylindrical flocs form, align alon...
Chaotic Dynamics in Shear-thickening Surfactant Solutions
Bandyopadhyay, Ranjini; Sood, A. K.
2000-01-01
We report the observation of dynamical behaviour in dilute, aqueous solutions of a surfactant CTAT (cetyl trimethylammonium p-toluenesulphonate), below the overlap concentration c$^{\\star}$. At these concentrations, CTAT forms cylindrical micelles and shows a pronounced shear thickening transition above a concentration-dependent critical shear rate $\\dot\\gamma_{c}$. An analysis of the time-series of the stress relaxations at controlled shear rates in the shear-thickening reg...
Band formation in HPC subjected to steady and oscillatory shear
Fischer, C. L. Bower; H.
The formation of a regular banded structure perpendicular to the direction of applied shear, in the lyotropic liquid crystal hydroxypropylcellulose (HPC) as observed by optical microscopy is presented. This is a phenomenon that has been the subject of much attention in the literature. Use of a specialised optical shear cell allowed in-situ observation of the HPC whilst subjected to steady or oscillatory shear stress in a parallel plate geometry. Using the shear cell, textural observations of the formation of band structure during and after cessation of shear stress were obtained. Band formation was found to be dependent on the magnitude of reduction in steady shear rate. A reduction of the shear rate by more than 10 1/s was required for effective band formation. A larger reduction in shear rate led to more rapid and extensive band formation. When subjected to oscillatory shear, larger transverse bands were observed during oscillation at sufficiently high frequency and amplitude;formation of the smaller bands was also apparent on cessation. Higher oscillation frequencies yielded more extensive band formation. Application of steady shear rate greater than 10 reciprocal seconds to HPC showed the gradual build up of wavy herring-bone texture. On relaxation of the shear stress the sample was seen to decelerate slowly with residual flow in the shear direction. The bands formed as a result of this crumpling motion inducing a sinusoidal ripple in the sample. The bands were also visible without crossed-polars indicating a periodic density distribution in addition to the orientational distribution. The texture observed was found to be dependent on shear rate; at applied shear rates of less than 10 1/s, the stable texture was vertically-striated whilst at shear rates greater than 10 1/s a herring-bone texture was observed. No transverse bands were seen on cessation of a shear rate of less than 10 1/s in the absence of the herring-bone texture.
Shear thickening in electrically stabilized non-aqueous colloidal suspensions
Kaldasch, J (Joachim); B. Senge; Lavèn, J (Jozua=Jos)
2012-01-01
The authors previously introduced an activation model for the onset of shear thickening in electrically stabilized colloidal suspensions. It predicts that shear thickening occurs, when particles arranged along the compression axis in a sheared suspension do overcome the electrostatic repulsion at a critical shear stress, and are captured in the primary minimum of the DLVO interaction potential. A comparison with an experimental investigation on non-aqueous silica suspensions...
Turbulent transport across shear layers in magnetically confined plasmas
International Nuclear Information System (INIS)
Shear layers modify the turbulence in diverse ways and do not only suppress it. A spatial-temporal investigation of gyrofluid simulations in comparison with experiments allows to identify further details of the transport process across shear layers. Blobs in and outside a shear layer merge, thereby exchange particles and heat and subsequently break up. Via this mechanism particles and heat are transported radially across shear layers. Turbulence spreading is the immanent mechanism behind this process
Management of distal humeral coronal shear fractures
Yari, Shahram S; Bowers, Nathan L; Craig, Miguel A; Reichel, Lee M
2015-01-01
Coronal shear fractures of the distal humerus are rare, complex fractures that can be technically challenging to manage. They usually result from a low-energy fall and direct compression of the distal humerus by the radial head in a hyper-extended or semi-flexed elbow or from spontaneous reduction of a posterolateral subluxation or dislocation. Due to the small number of soft tissue attachments at this site, almost all of these fractures are displaced. The incidence of distal humeral coronal shear fractures is higher among women because of the higher rate of osteoporosis in women and the difference in carrying angle between men and women. Distal humeral coronal shear fractures may occur in isolation, may be part of a complex elbow injury, or may be associated with injuries proximal or distal to the elbow. An associated lateral collateral ligament injury is seen in up to 40% and an associated radial head fracture is seen in up to 30% of these fractures. Given the complex nature of distal humeral coronal shear fractures, there is preference for operative management. Operative fixation leads to stable anatomic reduction, restores articular congruity, and allows initiation of early range-of-motion movements in the majority of cases. Several surgical exposure and fixation techniques are available to reconstruct the articular surface following distal humeral coronal shear fractures. The lateral extensile approach and fixation with countersunk headless compression screws placed in an anterior-to-posterior fashion are commonly used. We have found a two-incision approach (direct anterior and lateral) that results in less soft tissue dissection and better outcomes than the lateral extensile approach in our experience. Stiffness, pain, articular incongruity, arthritis, and ulnohumeral instability may result if reduction is non-anatomic or if fixation fails. PMID:25984515
Collision statistics in sheared inelastic hard spheres.
Bannerman, Marcus N; Green, Thomas E; Grassia, Paul; Lue, Leo
2009-04-01
The dynamics of sheared inelastic-hard-sphere systems is studied using nonequilibrium molecular-dynamics simulations and direct simulation Monte Carlo. In the molecular-dynamics simulations Lees-Edwards boundary conditions are used to impose the shear. The dimensions of the simulation box are chosen to ensure that the systems are homogeneous and that the shear is applied uniformly. Various system properties are monitored, including the one-particle velocity distribution, granular temperature, stress tensor, collision rates, and time between collisions. The one-particle velocity distribution is found to agree reasonably well with an anisotropic Gaussian distribution, with only a slight overpopulation of the high-velocity tails. The velocity distribution is strongly anisotropic, especially at lower densities and lower values of the coefficient of restitution, with the largest variance in the direction of shear. The density dependence of the compressibility factor of the sheared inelastic-hard-sphere system is quite similar to that of elastic-hard-sphere fluids. As the systems become more inelastic, the glancing collisions begin to dominate over more direct, head-on collisions. Examination of the distribution of the times between collisions indicates that the collisions experienced by the particles are strongly correlated in the highly inelastic systems. A comparison of the simulation data is made with direct Monte Carlo simulation of the Enskog equation. Results of the kinetic model of Montanero [J. Fluid Mech. 389, 391 (1999)] based on the Enskog equation are also included. In general, good agreement is found for high-density, weakly inelastic systems. PMID:19518225
Spurious Shear in Weak Lensing with LSST
Energy Technology Data Exchange (ETDEWEB)
Chang, C.; Kahn, S.M.; Jernigan, J.G.; Peterson, J.R.; AlSayyad, Y.; Ahmad, Z.; Bankert, J.; Bard, D.; Connolly, A.; Gibson, R.R.; Gilmore, K.; Grace, E.; Hannel, M.; Hodge, M.A.; Jee, M.J.; Jones, L.; Krughoff, S.; Lorenz, S.; Marshall, P.J.; Marshall, S.; Meert, A.
2012-09-19
The complete 10-year survey from the Large Synoptic Survey Telescope (LSST) will image {approx} 20,000 square degrees of sky in six filter bands every few nights, bringing the final survey depth to r {approx} 27.5, with over 4 billion well measured galaxies. To take full advantage of this unprecedented statistical power, the systematic errors associated with weak lensing measurements need to be controlled to a level similar to the statistical errors. This work is the first attempt to quantitatively estimate the absolute level and statistical properties of the systematic errors on weak lensing shear measurements due to the most important physical effects in the LSST system via high fidelity ray-tracing simulations. We identify and isolate the different sources of algorithm-independent, additive systematic errors on shear measurements for LSST and predict their impact on the final cosmic shear measurements using conventional weak lensing analysis techniques. We find that the main source of the errors comes from an inability to adequately characterise the atmospheric point spread function (PSF) due to its high frequency spatial variation on angular scales smaller than {approx} 10{prime} in the single short exposures, which propagates into a spurious shear correlation function at the 10{sup -4}-10{sup -3} level on these scales. With the large multi-epoch dataset that will be acquired by LSST, the stochastic errors average out, bringing the final spurious shear correlation function to a level very close to the statistical errors. Our results imply that the cosmological constraints from LSST will not be severely limited by these algorithm-independent, additive systematic effects.
Edge Sheared Flows and Blob Dynamics
Myra, J. R.
2012-10-01
The dynamics of blob-filaments [S. I. Krasheninnikov, et al. J. Plasma Phys. 74, 679 (2008); D. A. D'Ippolito, et al., Phys. Plasmas 18, 060501 (2011)] in the strongly radially inhomogeneous edge and scrape-off-layer (SOL) region of a tokamak plasma is considered, with emphasis on sheared flow generation and interaction. The work is motivated by the potential importance of edge sheared flows for turbulence regulation, (e.g. the L-H transition), and the influence of flows on the character of emitted blob-filament structures which ultimately contact plasma-facing components. To study the dynamics of blobs and sheared flows, we employ both numerical simulations and experimental data analysis. The simulations use the fluid-based 2D curvature-interchange model embedded in the SOLT (SOL turbulence) code [D. A. Russell, et al, Phys. Plasmas 16, 122304 (2009)]. A blob-tracking algorithm has also been developed and applied to NSTX and Alcator C-Mod data. The algorithm is based on 2D time-resolved images from the gas puff imaging (GPI) diagnostic [S. J. Zweben, et al. Phys. Plasmas 9, 1981 (2002)]. The algorithm is able to track the blob motion and changes in blob structure, such as elliptical deformations, that can be affected by sheared flows. Results of seeded blob simulations are compared with the experimental data to determine the role of plasma parameters on the blob tracks and to evaluate the exchange of momentum between the blobs and flows. Seeded blob simulations are shown to reproduce many qualitative and quantitative features of the data including size, scale and direction of perpendicular (approximately poloidal) flows and the inferred Reynolds forces, poloidal reversal of blob tracks, and blob trapping and/or ejection. Simulation and experimental data comparisons permit the inference of dynamical mechanisms associated with blob motion and sheared flow generation in these shots, and their relation to previous theoretical work.
Buckley, Mark R.; Bonassar, Lawrence J; Cohen, Itai
2013-01-01
Though remarkably robust, articular cartilage becomes susceptible to damage at high loading rates, particularly under shear. While several studies have measured the local static and steady-state shear properties of cartilage, it is the local viscoelastic properties that determine the tissue's ability to withstand physiological loading regimens. However, measuring local viscoelastic properties requires overcoming technical challenges that include resolving strain fields in both space and time ...
Fluid Effects on Shear Waves in Finely Layered Porous Media
International Nuclear Information System (INIS)
Although there are five effective shear moduli for any layered VTI medium, one and only one effective shear modulus for the layered system contains all the dependence of pore fluids on the elastic or poroelastic constants that can be observed in vertically polarized shear waves. Pore fluids can increase the magnitude the shear energy stored by this modulus by a term that ranges from the smallest to the largest shear moduli of the VTI system. But, since there are five shear moduli in play, the increase in shear energy overall is reduced by a factor of about 5 in general. We can therefore give definite bounds on the maximum increase of shear modulus, being about 20% of the permitted range, when gas is fully replaced by liquid. An attendant increase of density (depending on porosity and fluid density) by approximately 5 to 10% partially offsets the effect of this shear modulus increase. Thus, an increase of shear wave speed on the order of 5 to 10% is shown to be possible when circumstances are favorable - i.e., when the shear modulus fluctuations are large (resulting in strong anisotropy), and the medium behaves in an undrained fashion due to fluid trapping. At frequencies higher than seismic (such as sonic and ultrasonic waves for well-logging or laboratory experiments), short response times also produce the requisite undrained behavior and, therefore, fluids also affect shear waves at high frequencies by increasing rigidity
Spatially-resolved microstructure in shear banding wormlike micellar solutions
International Nuclear Information System (INIS)
Recently proposed theories for shear banding in wormlike micellar solutions (WLMs) rely on a shear-induced isotropic-nematic (I-N) phase separation as the mechanism for banding. Critical tests of such theories require spatially-resolved measurements of flow-kinematics and local mesoscale microstructure within the shear bands. We have recently developed such capabilities using a short gap Couette cell for flow-small angle neutron scattering (flow-SANS) measurements in the 1-2 plane of shear with collaborators at the NIST Center for Neutron Research. This work combines flow-SANS measurements with rheology, rheo-optics and velocimetry measurements to present the first complete spatially-resolved study of WLMs through the shear banding transition for a model shear banding WLM solution near the I-N phase boundary. The shear rheology is well-modeled by the Giesekus constitutive equation, with incorporated stress diffusion to predict shear banding. By fitting the stress diffusivity at the onset of banding, the model enables prediction of velocity profiles in the shear banded state which are in quantitative agreement with measured flow-kinematics. Quantitative analysis of the flow-SANS measurements shows a critical segmental alignment for banding and validates the Giesekus model predictions, linking segmental orientation to shear banding and providing the first rigorous evidence for the shear-induced I-N transition mechanism for shear banding banding
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Hiroshi Yoshihara
2012-03-01
Full Text Available Square-plate twist (SPT tests were conducted to measure the shear modulus and shear strength using the method, which was a modification of the International Organization for Standardization (ISO 15310 standardized method. In the SPT test, the length/thickness ratio varied. In addition, asymmetric four-point bending (AFPB tests were conducted, and the shear modulus and shear strength obtained were compared with those obtained by the SPT tests. The shear modulus was obtained effectively by the SPT test when the specimen was thin enough. Although the shear strength was evaluated as higher than that obtained by the AFPB tests, it might be regarded as an apparent value of shear strength when the range of length/thickness is limited. To obtain the actual shear strength by the SPT test, some modification of the equation is required.
International Nuclear Information System (INIS)
The shear strength of NSC (Normal Strength Concrete) has been extensively researched. However, very little data is available on the shear strength of HSC beams for fc > 6000 psi (40MPa). In this research, 35 beams with five values of longitudinal steel and seven values of shear span to depth (aid) ratio have been tested to study the effect of longitudinal steel and shear span to depth ratio. The results have been compared with the provisions of ACI 318-06 as well. The results have shown that shear failure is anticipated when the longitudinal steel ratio for p > 1 %. The shear strength of HSC normally increases with the increase of longitudinal steel and decreases with the increase in shear span to depth ratio, as exhibited in normal strength, but the failure is more sudden and brittle. The ACI 318 provisions for shear strength of beams are normally good predictors but for a/d >5. (author)
Estimation of seabed shear-wave velocity profiles using shear-wave source data.
Dong, Hefeng; Nguyen, Thanh-Duong; Duffaut, Kenneth
2013-07-01
This paper estimates seabed shear-wave velocity profiles and their uncertainties using interface-wave dispersion curves extracted from data generated by a shear-wave source. The shear-wave source generated a seismic signature over a frequency range between 2 and 60 Hz and was polarized in both in-line and cross-line orientations. Low-frequency Scholte- and Love-waves were recorded. Dispersion curves of the Scholte- and Love-waves for the fundamental mode and higher-order modes are extracted by three time-frequency analysis methods. Both the vertically and horizontally polarized shear-wave velocity profiles in the sediment are estimated by the Scholte- and Love-wave dispersion curves, respectively. A Bayesian approach is utilized for the inversion. Differential evolution, a global search algorithm is applied to estimate the most-probable shear-velocity models. Marginal posterior probability profiles are computed by Metropolis-Hastings sampling. The estimated vertically and horizontally polarized shear-wave velocity profiles fit well with the core and in situ measurements. PMID:23862796
Dynamic modes of microcapsules in steady shear flow: effects of bending and shear elasticities.
Noguchi, Hiroshi
2010-05-01
The dynamics of microcapsules in steady shear flow were studied using a theoretical approach based on three variables: the Taylor deformation parameter ?D , the inclination angle ? , and the phase angle ? of the membrane rotation. It is found that the dynamic phase diagram shows a remarkable change with an increase in the ratio of the membrane shear and bending elasticities. A fluid vesicle (no shear elasticity) exhibits three dynamic modes: (i) tank treading at low viscosity ?in of internal fluid (?D and ? relaxes to constant values), (ii) tumbling (TB) at high ?in (? rotates), and (iii) swinging (SW) at middle ?in and high shear rates ? (? oscillates). All of three modes are accompanied by a membrane (?) rotation. For microcapsules with low shear elasticity, the TB phase with no ? rotation and the coexistence phase of SW and TB motions are induced by the energy barrier of ? rotation. Synchronization of ? rotation with TB rotation or SW oscillation occurs with integer ratios of rotational frequencies. At high shear elasticity, where a saddle point in the energy potential disappears, intermediate phases vanish and either ? or ? rotation occurs. This phase behavior agrees with recent simulation results of microcapsules with low bending elasticity. PMID:20866334
Herle, Vishweshwara; Manneville, Se?bastien; Fischer, Peter
2008-01-01
We carried out pointwise local velocity measurements on 40mM cetylpyridinium chloride-sodium salicylate (CPyCl-NaSal) wormlike micellar solution using high-frequency ultrasound velocimetry in a Couette shear cell. The studied wormlike solution exhibits Newtonian, shear-thinning and shear-thickening rheological behavior in a stress-controlled environment. Previous rheology, flow visualization and small-angle light/neutron scattering experiments in the shear-thickening regime of this system sho...
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Markus S. Friedrich
2014-12-01
Full Text Available Beef quality parameters can be negatively affected by pre-slaughter stress. Slaughter via gunshot directly on the pasture appears to be suitable for the reduction of pre-slaughter stress by avoiding stressors such as transportation, lairage and human contact. The effect of slaughtering via gunshot on sensory and objective measures of beef quality parameters for the Musculus longissimus dorsi of Galloway steers was analyzed and compared to conventional slaughter at the abattoir using captive-bolt stunning. The Warner-Bratzler shear force (WBSF was significantly (P < 0.01 lower for the meat of the animals slaughtered via gunshot (arithmetic mean (AM gunshot: 4.34 kg; AM captive-bolt pistol: 4.77 kg. However, trained assessors were not able to recognize this difference (P > 0.05. No significant differences (P > 0.05 were observed for cooking loss and the sensory quality evaluation of juiciness. As measured by the WBSF, the meat of the animals slaughtered via gunshot was slightly more tender than was the meat of the animals stunned with a captive-bolt pistol. However, for the cooking loss and sensory evaluations, no effect of the slaughter methods was observed. Nevertheless, this study reveals the potential that slaughter via gunshot provides for the improvement of beef quality.
Duckett, S K; Fernandez Rosso, C; Volpi Lagreca, G; Miller, M C; Neel, J P S; Lewis, R M; Swecker, W S; Fontenot, J P
2014-10-01
Angus-cross steers (n = 96; BW = 309 ± 34 kg; 13.5 mo of age) were used to determine the effects of frame size (medium or small) and time-on-pasture (TOP) on meat composition and palatability in a 2-yr study. Finishing steers grazed mixed pastures (bluegrass/white clover; April start) and were slaughtered after 89-, 146-, and 201-d TOP. At 24 h postmortem, carcass traits were collected and a rib from each carcass was obtained for proximate and fatty acid composition, Warner-Bratzler shear force (WBSF), and postmortem proteolysis. In yr 1, postmortem aging treatments included 14 and 28 d, whereas in yr 2, postmortem aging treatments included 2, 4, 7, 14, and 28 d. Increasing frame size of the finishing steers produced greater (P 0.05) due to frame size or 2-way interaction with TOP. Increasing TOP resulted in quadratic increases (P 0.05) compared to the 14-d postmortem aging WBSF values. However, in steaks from 201-d TOP, additional postmortem aging to 28 d reduced (P < 0.001) WBSF. In pasture-based beef finishing systems, increasing TOP increases animal age, HCW, fat thickness, and marbling score; however, tenderness of ribeye steaks decreased with advanced TOP such that longer postmortem aging times were required to achieve similar tenderness levels. PMID:25267999
Scientific Electronic Library Online (English)
J.J.E., Cloete; L.C., Hoffman; S.W.P., Cloete.
2008-04-01
Full Text Available This study details the slaughter traits of lambs born from a terminal crossbreeding experiment that involved five Merino type dam lines crossed with Dormer and Suffolk sires. Dam lines included dual purpose types; South African Mutton Merino (SAMM), Dohne Merino, SAMM rams crossed to commercial Meri [...] no ewes (SAMM cross) and specialist Merino lines selected either for clean fleece weight (FW+) or for an increased fertility (Rep+). Data include between 228 and 483 individual records, depending on the trait. The unadjusted fat depth 25 mm from the midline at the 13th rib of lambs from dual-purpose ewes was between 22 and 32% greater than that of lambs from FW+ Merino ewes. Progeny from Rep+ Merino ewes showed a closer resemblance to the progeny of dual-purpose breeds than to those of FW+ Merino ewes in this instance. Adjustment for slaughter weight eliminated these differences. The initial pH of meat from progeny of FW+ Merino ewes was lower than that from progeny of dual-purpose ewes, and Rep+ Merino ewes. No differences in Warner-Bratzler shear values of the meat were found between the different crosses. Crossbred progeny of the Merino lines performed satisfactorily for all the traits considered, and will not be discriminated against in the market. No conclusive differences in favour of either sire breed were found.
Picard, Brigitte; Gagaoua, Mohammed; Micol, Didier; Cassar-Malek, Isabelle; Hocquette, Jean-François; Terlouw, Claudia E M
2014-10-01
Previous proteomic analyses established a list of proteins biomarkers of beef tenderness. The present study quantified the relative abundance of 21 of these proteins by dot-blot technique in the Longissimus thoracis and Semitendinosus muscles of 71 young bulls from three breeds: Aberdeen Angus (AA), Limousin (LI), and Blond d'Aquitaine (BA). For both muscles overall tenderness was estimated by sensory analysis; shear force was measured with a Warner-Bratzler instrument, and an index combining sensory and mechanical measurements was calculated. Multiple regressions based on relative abundances of these proteins were used to propose equations of prediction of the three evaluations of tenderness. Hsp70-1B appeared to be a good biomarker of low tenderness in the three breeds and in the two muscles. Proteins such as lactate dehydrogenase-B, myosin heavy chain IIx, and small heat shock proteins (Hsp27, Hsp20, and ?B-crystallin) were related to tenderness but inversely according to the muscle and breed. The results demonstrate that prediction of tenderness must take into account muscle characteristics and animal type. PMID:25175407
International Nuclear Information System (INIS)
The effect of five mixtures of sodium chloride, sodium tripolyphosphate and tetrasodiumpyrophosphate on the texture and sensory properties of irradiated beef M. biceps femoris and M. semitendinosus muscles sterilised at 45 kGy were evaluated using pH after injection, drip loss measurement, Instron texture measurement and descriptive sensory analysis. The effect of cattle race was also investigated. Three breeds of cattle namely Afrikaner (Bos indicus), Hereford (Bos taurus) and Simmentaler (Bos taurus) were used. Steers were fed and raised in a controlled environment until 18 months of age, followed by slaughtering using the same procedure for each carcass. It was found that cattle breed had a significant influence on irradiated meat tenderness and juiciness. Afrikaner breed meat was the most tender and the most juicy. The Energy to break point measured using a Warner Bratzler Shear cell correlated with the ease of fragmentation (using fingers) as well as Initial Juiciness and Sustained Juiciness. Using polyphosphate levels of 13.2 mmol/kg produced undesirable flavours in the meat. The same tenderness was obtained using levels of 8.2 mmol/kg in the meat without undesirable taste. No differences were found between sodium tripolyphosphate and tetrasodium pyrophosphate treatments. Warmed Over Flavour was a significant factor influencing the quality of the products. (author)
Effect of bleeding method and low voltage electrical stimulation on meat quality of ostriches
Scientific Electronic Library Online (English)
L.C., Hoffman; S.W.P., Cloete; S.J., van Schalkwyk; S.St.C., Botha.
Full Text Available The effect on ostrich muscle quality of an additional thoracic stick (TS) to the normal ventral throat slit to bleed ostriches after electrical stunning was evaluated. The additional TS had no negative or positive effect on the drip loss, cooking loss, colour or pH and temperature readings of the fi [...] llet (Muscularis iliofibularis), big drum (M. gastrocnemius, pars interna) and inside loin (M. iliotibialis cranialis). None the less, personal observations would recommend the use of TS due to ethical considerations. An early post mortem low voltage electrical stimulation (ES) of the carcasses also had no influence on the cooking loss, drip loss and colour of these muscles. Electrical stimulation did result in a lower pH45 in both the fillet and big drum muscles. However, after 24 h the pH of the muscles did not differ. Electrical stimulation also caused elevated initial muscle temperatures, although this effect was only temporary due to the efficient cooling mechanism used in the abattoir. Electrical stimulation also had no effect on the Warner Bratzler shear force values in the fillet. It can be concluded that low voltage ES has no advantage pertaining to physical quality characteristics of importance in an ostrich abattoir.
Scientific Electronic Library Online (English)
Isabella Dias Barbosa, Silveira; Vivian, Fischer; Luis Henrique Ebling, Farinatti; João, Restle; Dari Celestino, Alves Filho; Luís Fernando Glasenapp de, Menezes.
1468-14-01
Full Text Available The relation between temperament with performance and meat quality was determined in 79 Charolais × Nellore steers kept in feedlot. Temperament was evaluated according to exit velocity, scale composite score and flight distance four times in the finishing phase, along with body weight, intake and fe [...] ed conversion measures. Cattle were classified as calm, intermediate and excited according to exit velocity measures at the beginning of the trial. Excited cattle presented larger values for composite score and flight distance. Irrespective of genotype, excited cattle presented lower average daily gain, dry matter intake and worse feed conversion. Temperament categories did not affect most of beef quality traits, except for calm Bos indicus steers, which presented greater pH measured 1 hour post mortem compared with more reactive steers. However, moderate but negative correlations were detected between exit velocity, flight distance and composite score and beef quality as well as Warner-Bratzler shear value, luminosity, pH measured 24 hours post mortem, although they were not consistent between genotypes raised under the same conditions.
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ALINA NARCISA POSTOLACHE
2014-11-01
Full Text Available This research is subscribed of an extensive project that has as main objective the production of crossbred specialized beef hybrids from reformed Romanian Black Spotted cattle's with bulls from breeds specialized for meat production (Blue Blanch Belgique, Aberdeen-Angus and Limousin. Averaged biochemical indicators analyzed showed a normal state of animal's health. The obtained half-breeds products (bulls were raised under semi-intensively conditions and slaughtered at 12 months of age. Live weight, back-fat thickness and carcass traits were significantly influenced by breed, all fat parameters being lower at this age than at standard minimum age of slaughter for meat production (18 months. Drip loss and chemical composition were similar for the breeds. The meat was lighter and pH24 values of longissimus muscle were between 5.57 and 5.64. Sensory panel tenderness and Warner-Bratzler shear force values indicated tougher meat at RBSxAA than at RBSxL1 or RBSxBBB. Differences in meat quality were probably due to the combined effects of brute chemical composition and pH dynamic during ripening. It is concluded that slaughtering steers at younger ages may require supplementary feeding, being recommended a slaughter age between 18 and 25 months old.
Scientific Electronic Library Online (English)
S., Y& #252; ksel; M., Yanar; L., Turgut; A., & #214; zl& #252; t& #252; rk; S., Kopuzlu; E., Sezgin.
Full Text Available Fifteen young Holstein Friesian bulls (18 mo of age) were divided into three groups of five. All groups were fed a diet consisting of 60% concentrate and 40% roughage. The control (C) group received a mixture of dry meadow hay, dry lucerne and wheat straw as roughage. The second and third treatment [...] groups were fed a similar mixture of roughage partially substituting wheat straw with wet sugar beet pulp (SBP) at levels of 4% and 8% on a dry matter (DM) basis, respectively. Dry matter intake and feed efficiency ratio (kg DM intake/kg weight gain) of the C group were significantly higher than those of the 4% SBP and 8% SBP groups. Slaughter and carcass traits indicated that there were no significant differences between dietary treatments. The inclusion of 8% SBP significantly improved panel ratings for tenderness, juiciness, beef flavour intensity and general acceptance, as well as number of chews before swallowing and the Warner Bratzler Shear value. Proximate analysis of the meat did not demonstrate differences between meat from the bulls fed C and the SBP diets. It was concluded that wheat straw could be replaced by 8% SBP in the finishing diet for young Holstein Friesian bulls in order to improve feed efficiency and sensory quality characteristics of their meat.
Comparison of breeding value prediction for two traits in a Nellore-Angus crossbred population using different Bayesian modeling methodologies
Scientific Electronic Library Online (English)
Lauren L. Hulsman, Hanna; Dorian J., Garrick; Clare A., Gill; Andy D., Herring; James O., Sanders; David G., Riley.
2014-12-01
Full Text Available The objectives of this study were to 1) compare four models for breeding value prediction using genomic or pedigree information and 2) evaluate the impact of fixed effects that account for family structure. Comparisons were made in a Nellore-Angus population comprising F2, F3 and half-siblings to em [...] bryo transfer F2 calves with records for overall temperament at weaning (TEMP; n = 769) and Warner-Bratzler shear force (WBSF; n = 387). After quality control, there were 34,913 whole genome SNP markers remaining. Bayesian methods employed were BayesB ( ? = 0.995 or 0.997 for WBSF or TEMP, respectively) and BayesC (? = 0 and ?), where ? is the ideal proportion of markers not included. Direct genomic values (DGV) from single trait Bayesian analyses were compared to conventional pedigree-based animal model breeding values. Numerically, BayesC procedures (using ?) had the highest accuracy of all models for WBSF and TEMP ( ?gg = 0.843 and 0.923, respectively), but BayesB had the least bias (regression of performance on prediction closest to 1, ?y,x = 2.886 and 1.755, respectively). Accounting for family structure decreased accuracy and increased bias in prediction of DGV indicating a detrimental impact when used in these prediction methods that simultaneously fit many markers.
The inclusion of Duroc breed in maternal line affects pork quality and fatty acid profile.
Alonso, Verónica; Muela, Erica; Gutiérrez, Beatriz; Calanche, Juan Benito; Roncalés, Pedro; Beltrán, José A
2015-09-01
The aim of this study was to evaluate the effect of including different percentages of Duroc (D) breed in maternal line [Landrace (LR)×Large White (LW); LR×(LW×D); LR×D] and gender on meat quality and intramuscular (IMF) and subcutaneous (SCF) fatty acid composition. No significant differences were found among dam lines in ultimate pH, L* values and drip and cooking losses. There were higher percentages of saturated fatty acids in LR×D and LR×(LW×D) lines and higher percentages of polyunsaturated fatty acids in LR×LW line in IMF and SCF. Also, LR×D line produced pork with a lower Warner-Bratzler shear force values and higher IMF content and potential of lipid oxidation. Furthermore, the L*, a* and b* values and drip loss were greater in pork from entire males than females. The IMF and SCF of females were more monounsaturated and less polyunsaturated than those from entire males. PMID:25938812
Peña, F; Avilés, C; Domenech, V; González, A; Martínez, A; Molina, A
2014-12-01
One-hundred-and-twenty-four young bulls of three Continental beef cattle breeds were used to study the effect of pre-slaughter stress by unfamiliar sounds on carcass traits and quality characteristics of beef aged for three different periods. Stress due to unfamiliar noises had a moderately negative effect on carcass and meat quality. Carcasses from group Stressed had higher (P<0.05) values of pH0, pH24, a*, and Warner-Bratzler shear force, and lower (P<0.05) values of L*, b* and pressure losses than from Unstressed animals. There were significant differences (P<0.05) among breeds in L*, a* and pressure losses. The ageing time had a significant effect on chromatic variables, WBSF and pressure losses. The cooking losses were not significantly affected by any of the three factors discussed. These results emphasize the importance of implementing appropriate management practices during pre-slaughter handling of cattle in order to reduce any possible risk factor for stress, as well as the different sensitivity of the breeds to similar stimuli. PMID:25105491
Reda, Daniel C.; Wilder, Michael C.; Nixon, David (Technical Monitor)
1998-01-01
The shear-sensitive liquid crystal coating (SSLCC) method is an image-based technique for both visualizing dynamic surface-flow phenomena, such as transition and separation, and for measuring the continuous shear-stress vector distribution acting on an aerodynamic surface. Under proper lighting and viewing conditions (discussed below), the coating changes color in response to an applied aerodynamic shear. This color-change response is continuous and reversible, with a response time of milliseconds, and is a function of both the shear magnitude and the shear vector orientation relative to the observer. The liquid crystal phase of matter is a weakly-ordered, viscous, non-Newtonian fluid state that exists between the nonuniform liquid phase and the ordered solid phase of certain organic compounds. Cholesteric liquid crystal compounds possess a helical molecular arrangement that selectively scatters white light, incident along the helical axis, as a three-dimensional spectrum. This property is linked to the helical pitch length, which is within the range of wavelengths in the visible spectrum. The pitch length, and hence the wavelength of the scattered light, is influenced by shear stress normal to the helical axis. This unique optical property produces a measurable color change in response to an applied shearing force. The full-surface shear stress vector measurement method, developed at NASA-Ames, is schematically illustrated. As with the visualization method, the coated test surface is illuminated from the normal direction with white light and the camera is positioned at an above-plane view angle of approximately 30 deg. Experiments have been initiated at NASA Ames to begin the process of quantifying surface-inclination (surface-curvature) effects on shear vector measurement accuracy. In preliminary experiments, surface-inclination angles theta(sub x), theta(sub y) of 0, +/-5, +/-10, and +/-15 deg were employed. In this arrangement, white-light illumination was positioned normal to the untilted test surface, and the camera above-plane view angle was set at 30 deg relative to the untilted test surface. As can be seen, vector-aligned lambda(sub d) values showed no dependence on theta(sub x) or theta(sub y) for absolute values of these tilt angles is less than or equal to 15 deg. Acquisition and analyses of full-surface color images are presently underway to definitively document the insensitivity limits of the shear vector measurement methodology to surface-slope variations.
Shear induced orientation of edible fat and chocolate crystals
Mazzanti, Gianfranco; Welch, Sarah E.; Marangoni, Alejandro G.; Sirota, Eric B.; Idziak, Stefan H. J.
2003-03-01
Shear-induced orientation of fat crystallites was observed during crystallization of cocoa butter, milk fat, stripped milk fat and palm oil. This universal effect was observed in systems crystallized under high shear. The minor polar components naturally present in milk fat were found to decrease the shear-induced orientation effect in this system. The competition between Brownian and shear forces, described by the Peclet number, determines the crystallite orientation. The critical radius size, from the Gibbs-Thomson equation, provides a tool to understand the effect of shear at the onset stages of crystallization.
Chemical reactions in controlled high-strain-rate shear bands
International Nuclear Information System (INIS)
Controlled high-strain-rate shear bands were generated in porous mixtures (Nb+Si, Ti+Si) using axially symmetric experimental configurations (open-quotes Thick-Walled Cylinderclose quotes) method. Shear strains up to 100 and strain rates of approximately 107sec-1 were generated inside shear bands. Particle fracture, melting, and regions of partial reaction were observed inside shear bands for the Nb+Si system. Under the same conditions of deformation, for the Ti-Si system the reaction initiated inside shear bands and propagated through the entire sample. copyright 1996 American Institute of Physics
Shear-accelerated crystallization in a supercooled atomic liquid.
Shao, Zhen; Singer, Jonathan P; Liu, Yanhui; Liu, Ze; Li, Huiping; Gopinadhan, Manesh; O'Hern, Corey S; Schroers, Jan; Osuji, Chinedum O
2015-02-01
A bulk metallic glass forming alloy is subjected to shear flow in its supercooled state by compression of a short rod to produce a flat disk. The resulting material exhibits enhanced crystallization kinetics during isothermal annealing as reflected in the decrease of the crystallization time relative to the nondeformed case. The transition from quiescent to shear-accelerated crystallization is linked to strain accumulated during shear flow above a critical shear rate ??(c)?0.3 s(-1) which corresponds to Péclet number, Pe?O(1). The observation of shear-accelerated crystallization in an atomic system at modest shear rates is uncommon. It is made possible here by the substantial viscosity of the supercooled liquid which increases strongly with temperature in the approach to the glass transition. We may therefore anticipate the encounter of nontrivial shear-related effects during thermoplastic deformation of similar systems. PMID:25768445
Shear sensing based on a microstrip patch antenna
International Nuclear Information System (INIS)
A microstrip patch antenna sensor was studied for shear sensing with a targeted application of measuring plantar shear distribution on a diabetic foot. The antenna shear sensor consists of three components, namely an antenna patch, a soft foam substrate and a slotted ground plane. The resonant frequency of the antenna sensor is sensitive to the overlapping length between the slot in the ground plane and the antenna patch. A shear force applied along the direction of the slot deforms the foam substrate and causes a change in the overlapping length, which can be detected from the antenna frequency shift. The antenna shear sensor was designed based on simulated antenna frequency response and validated by experiments. Experimental results indicated that the antenna sensor exhibits high sensitivity to shear deformation and responds to the applied shear loads with excellent linearity and repeatability. (paper)
Quasi phase transition model of shear bands in metallic glasses
International Nuclear Information System (INIS)
A quasi phase transition model of shear bands in metallic glasses (MGs) is presented from the thermodynamic viewpoint. Energy changes during shear banding in a sample-machine system are analyzed following fundamental energy theorems. Three characteristic parameters, i.e. the critical initiation energy ?Gc, the shear band stability index k0, and the critical shear band length lc, are derived to elucidate the initiation and propagation of shear bands. The criteria for good plasticity in MGs with predominant thermodynamic arrest of shear bands are proposed as low ?Gc, large k0, and small lc. The model, combined with experimental results, is used to analyze some controversial phenomena of deformation behavior in MGs, such as the size effect, the effect of testing machine stiffness and the relationship between elastic modulus and plasticity. This study has important implications for a fundamental understanding of shear banding as well as deformation mechanisms in MGs and provides a theoretical basis for improving the ductility of MGs.
Turbulent transport in tokamak plasmas with rotational shear
Barnes, M; Highcock, E G; Schekochihin, A A; Cowley, S C; Roach, C M
2010-01-01
Nonlinear gyrokinetic simulations have been conducted to investigate turbulent transport in tokamak plasmas with rotational shear. At sufficiently large flow shears, linear instabilities are suppressed, but transiently growing modes drive subcritical turbulence whose amplitude increases with flow shear. This leads to a local minimum in the heat flux, indicating an optimal E x B shear value for plasma confinement. Local maxima in the momentum fluxes are also observed, allowing for the possibility of bifurcations in the E x B shear. The sensitive dependence of heat flux on temperature gradient is relaxed for large flow shear values, with the critical temperature gradient increasing at lower flow shear values. The turbulent Prandtl number is found to be largely independent of temperature and flow gradients, with a value close to unity.
Dynamics of a trapped Brownian particle in shear flows
Holzer, Lukas; Rzehak, Roland; Zimmermann, Walter
2009-01-01
The Brownian motion of a particle in a harmonic potential, which is simultaneously exposed either to a linear shear flow or to a plane Poiseuille flow is investigated. In the shear plane of both flows the probability distribution of the particle becomes anisotropic and the dynamics is changed in a characteristic manner compared to a trapped particle in a quiescent fluid. The particle distribution takes either an elliptical or a parachute shape or a superposition of both depending on the mean particle position in the shear plane. Simultaneously, shear-induced cross-correlations between particle fluctuations along orthogonal directions in the shear plane are found. They are asymmetric in time. In Poiseuille flow thermal particle fluctuations perpendicular to the flow direction in the shear plane induce a shift of the particle's mean position away from the potential minimum. Two complementary methods are suggested to measure shear-induced cross-correlations between particle fluctuations along orthogonal directio...
Shear strength of oil palm shell foamed concrete beams
International Nuclear Information System (INIS)
Four reinforced oil palm shell foamed concrete (OPSFC) beams were fabricated, and their shear behaviour was tested. The OPSFC has a target density of approximately 1600 kg/m3 and a 28-day compressive strength of about 20 MPa. Two beams were cast with shear reinforcements while the other two were cast without such reinforcements. For comparison, four reinforced normal weight concrete (NWC) beams were also cast. The beams that contained shear links failed in flexure mode, while those without links failed in shear mode. The experimental results indicated that the shear capacities of OPSFC beams without shear links are higher than those of the NWC beams and exhibit more flexural and shear cracks.
Pulsatile Fluid Shear in Bone Remodeling
Frangos, John A.
1997-01-01
The objective of this investigation was to elucidate the sensitivity to transients in fluid shear stress in bone remodeling. Bone remodeling is clearly a function of the local mechanical environment which includes interstitial fluid flow. Traditionally, load-induced remodeling has been associated with low frequency (1-2 Hz) signals attributed to normal locomotion. McLeod and Rubin, however, demonstrated in vivo remodeling events associated with high frequency (15-30 Hz) loading. Likewise, other in vivo studies demonstrated that slowly applied strains did not trigger remodeling events. We therefore hypothesized that the mechanosensitive pathways which control bone maintenance and remodeling are differentially sensitive to varying rates of applied fluid shear stress.
Super-diffusion in sheared suspensions
Souzy, Mathieu; Yin, Xiaolong; Villermaux, Emmanuel; Abid, Chérifa; Metzger, Bloen
2015-04-01
We investigate the dispersion of a layer of dye initially applied at the outer wall of a cylindrical Couette-cell into a sheared suspension of non-Brownian spherical particles. The process is directly visualized and quantified at the particle scale. A "rolling-coating" mechanism is found to convectively transport the dye at a constant rate directly from the wall towards the bulk. The fluid velocity fluctuations, u', measured with particle image velocimetry, and the imposed shear-rate, ? ? , are used to define a diffusion coefficient, D ? / ? ? , which is found to increase linearly with the distance from the wall. A solution of the transport equation accounting for this inhomogeneous stirring field describes quantitatively the concentration profiles measured experimentally. It exhibits a super-diffusive character, a consequence of the increase of the stirring strength with distance from the wall. Movies are available with the online version of the paper.
The shear viscosity of rigid water models
González, Miguel Angel; Abascal, José L. F.
2010-03-01
In this work, the shear viscosity at ambient conditions of several water models (SPC/E, TIP4P, TIP5P, and TIP4P/2005) is evaluated using the Green-Kubo formalism. The performance of TIP4P/2005 is excellent, that of SPC/E and TIP5P is more or less acceptable, whereas TIP4P and especially TIP3P give a poor agreement with experiment. Further calculations have been carried out for TIP4P/2005 to provide a wider assessment of its performance. In accordance with experimental data, TIP4P/2005 predicts a minimum in the shear viscosity for the 273 K isotherm, a shift in the minimum toward lower pressures at 298 K, and its disappearance at 373 K.
A Numerical Study of Cosmic Shear Statistics
Thion, A; Bernardeau, F; Bertin, E; Erben, T; Van Waerbeke, L
2000-01-01
We explore the stability of the variance and skewness of the cosmic gravitational convergence field, using two different approaches: first we simulate a whole MEGACAM survey (100 sq. degrees). The reconstructed mass map, obtained from a shear map, shows that the state-of-the-art data analysis methods can measure weak-lensing statistics at angular scales ranging from 2.5' to 25'. We looked also at the influence of a varying signal-to-noise ratio over the shear map (due to local variations of source density) on the mass reconstruction, by means of Monte-Carlo simulation. The effect at small scales can easily be corrected-for in most of the relevant cases. These results enhance the confidence in the capability of future large surveys to measure accurately cosmologically interesting quantities.
Direct measurement of shear properties of microfibers
Behlow, H.; Saini, D.; Oliveira, L.; Durham, L.; Simpson, J.; Serkiz, S. M.; Skove, M. J.; Rao, A. M.
2014-09-01
As novel fibers with enhanced mechanical properties continue to be synthesized and developed, the ability to easily and accurately characterize these materials becomes increasingly important. Here we present a design for an inexpensive tabletop instrument to measure shear modulus (G) and other longitudinal shear properties of a micrometer-sized monofilament fiber sample, such as nonlinearities and hysteresis. This automated system applies twist to the sample and measures the resulting torque using a sensitive optical detector that tracks a torsion reference. The accuracy of the instrument was verified by measuring G for high purity copper and tungsten fibers, for which G is well known. Two industrially important fibers, IM7 carbon fiber and Kevlar® 119, were also characterized with this system and were found to have G = 16.5 ± 2.1 and 2.42 ± 0.32 GPa, respectively.
Direct measurement of shear properties of microfibers
Energy Technology Data Exchange (ETDEWEB)
Behlow, H.; Saini, D.; Durham, L.; Simpson, J.; Skove, M. J.; Rao, A. M. [Department of Physics and Astronomy, and Clemson Nanomaterials Center, Clemson University, Clemson, South Carolina 29634 (United States); Oliveira, L. [School of Materials Science and Engineering, Clemson University, Clemson, South Carolina 29634 (United States); Serkiz, S. M. [Department of Physics and Astronomy, and Clemson Nanomaterials Center, Clemson University, Clemson, South Carolina 29634 (United States); Savannah River National Laboratory, Aiken, South Carolina 29808 (United States)
2014-09-15
As novel fibers with enhanced mechanical properties continue to be synthesized and developed, the ability to easily and accurately characterize these materials becomes increasingly important. Here we present a design for an inexpensive tabletop instrument to measure shear modulus (G) and other longitudinal shear properties of a micrometer-sized monofilament fiber sample, such as nonlinearities and hysteresis. This automated system applies twist to the sample and measures the resulting torque using a sensitive optical detector that tracks a torsion reference. The accuracy of the instrument was verified by measuring G for high purity copper and tungsten fibers, for which G is well known. Two industrially important fibers, IM7 carbon fiber and Kevlar{sup ®} 119, were also characterized with this system and were found to have G = 16.5 ± 2.1 and 2.42 ± 0.32 GPa, respectively.
Shear viscosity, cavitation and hydrodynamics at LHC
International Nuclear Information System (INIS)
We study evolution of quark-gluon matter in the ultrarelativistic heavy-ion collisions within the frame work of relativistic second-order viscous hydrodynamics. In particular, by using the various prescriptions of a temperature-dependent shear viscosity to the entropy ratio, we show that the hydrodynamic description of the relativistic fluid becomes invalid due to the phenomenon of cavitation. For most of the initial conditions relevant for LHC, the cavitation sets in very early stage. The cavitation in this case is entirely driven by the large values of shear viscosity. Moreover we also demonstrate that the conformal terms used in equations of the relativistic dissipative hydrodynamic can influence the cavitation time.
Flocculation of model algae under shear.
Energy Technology Data Exchange (ETDEWEB)
Pierce, Flint; Lechman, Jeremy B.
2010-11-01
We present results of molecular dynamics simulations of the flocculation of model algae particles under shear. We study the evolution of the cluster size distribution as well as the steady-state distribution as a function of shear rates and algae interaction parameters. Algal interactions are modeled through a DLVO-type potential, a combination of a HS colloid potential (Everaers) and a yukawa/colloid electrostatic potential. The effect of hydrodynamic interactions on aggregation is explored. Cluster strucuture is determined from the algae-algae radial distribution function as well as the structure factor. DLVO parameters including size, salt concentration, surface potential, initial volume fraction, etc. are varied to model different species of algae under a variety of environmental conditions.
Stochastically driven instability in rotating shear flows
Mukhopadhyay, Banibrata
2012-01-01
Origin of hydrodynamic turbulence in rotating shear flows is investigated. The particular emphasis is the flows whose angular velocity decreases but specific angular momentum increases with increasing radial coordinate. Such flows are Rayleigh stable, but must be turbulent in order to explain observed data. Such a mismatch between the linear theory and observations/experiments is more severe when any hydromagnetic/magnetohydrodynamic instability and then the corresponding turbulence therein is ruled out. The present work explores the effect of stochastic noise on such hydrodynamic flows. We essentially concentrate on a small section of such a flow which is nothing but a plane shear flow supplemented by the Coriolis effect. This also mimics a small section of an astrophysical accretion disk. It is found that such stochastically driven flows exhibit large temporal and spatial correlations of perturbation velocities, and hence large energy dissipations of perturbation, which presumably generate instability. A ra...
Turbulent Shear Layers in Supersonic Flow
Smits, Alexander J
2006-01-01
A good understanding of turbulent compressible flows is essential to the design and operation of high-speed vehicles. Such flows occur, for example, in the external flow over the surfaces of supersonic aircraft, and in the internal flow through the engines. Our ability to predict the aerodynamic lift, drag, propulsion and maneuverability of high-speed vehicles is crucially dependent on our knowledge of turbulent shear layers, and our understanding of their behavior in the presence of shock waves and regions of changing pressure. Turbulent Shear Layers in Supersonic Flow provides a comprehensive introduction to the field, and helps provide a basis for future work in this area. Wherever possible we use the available experimental work, and the results from numerical simulations to illustrate and develop a physical understanding of turbulent compressible flows.
Undulatory swimming in shear-thinning fluids
Gagnon, David A; Arratia, Paulo E
2014-01-01
The swimming behaviour of microorganisms can be strongly influenced by the rheology of their fluid environment. In this manuscript, we experimentally investigate the effects of shear-thinning viscosity on the swimming behaviour of an undulatory swimmer, the nematode Caenorhabditis elegans. Tracking methods are used to measure the swimmer's kinematic data (including propulsion speed) and velocity fields. We find that shear-thinning viscosity modifies the velocity fields produced by the swimming nematode but does not modify the nematode's speed and beating kinematics. Velocimetry data show significant enhancement in local vorticity and circulation, and an increase in fluid velocity near the nematode's tail, compared to Newtonian fluids of similar effective viscosity. These findings are in good agreement with recent theoretical and numerical results.
Drop impact of shear thickening liquids
Boyer, Francois; Dijksman, J Frits; Lohse, Detlef
2013-01-01
The impact of drops of concentrated non-Brownian suspensions (cornstarch and polystyrene spheres) onto a solid surface is investigated experimentally. The spreading dynamics and maxi- mal deformation of the droplet of such shear thickening liquids are found to be markedly different from the impact of Newtonian drops. A particularly striking observation is that the maximal de- formation is independent of the drop velocity and that the deformation suddenly stops during the impact phase. Both observations are due to the shear-thickening rheology of the suspensions, as is theoretically explained from a balance between the kinetic energy and the viscously-dissipated en- ergy, from which we establish a scaling relation between drop maximal deformation and rheological parameters of concentrated suspensions.
Shear instabilities in shallow-water magnetohydrodynamics
Mak, Julian; Hughes, D W
2015-01-01
Within the framework of shallow-water magnetohydrodynamics, we investigate the linear instability of horizontal shear flows, influenced by an aligned magnetic field and stratification. Various classical instability results, such as H{\\o}iland's growth rate bound and Howard's semi-circle theorem, are extended to this shallow-water system for quite general profiles. Two specific piecewise-constant velocity profiles, the vortex sheet and the rectangular jet, are studied analytically and asymptotically; it is found that the magnetic field and stratification (as measured by the Froude number) are generally both stabilising, but weak instabilities can be found at arbitrarily large Froude number. Numerical solutions are computed for corresponding smooth velocity profiles, the hyperbolic-tangent shear layer and the Bickley jet, for a uniform background field. A generalisation of the long-wave asymptotic analysis of Drazin & Howard (1962) is employed in order to understand the instability characteristics for both ...
Study of shear-stiffened elastomers
International Nuclear Information System (INIS)
This paper presents a novel shear-stiffened elastomer (SSE) fabricated with a mixture of silicone rubber and silicone oil. A total of four SSE samples were fabricated in this study. Their mechanical and rheological properties under both steady-state and dynamic loading conditions were tested with a parallel plate rheometer. The effects of silicone oil composition, strain amplitude and angular frequency were summarized. When raising the angular frequency in the dynamic shear test, the storage modulus of conventional silicone rubber shows a small increasing trend with the frequency. However, if silicone oil is selected to be mixed with silicone rubber, the storage modulus increases dramatically when the frequency and strain are both beyond the critical values. (paper)
The cosmic shear three-point functions
Benabed, K
2005-01-01
We investigate the three-point functions of the weak lensing cosmic shear, using both analytic methods and numerical results from N-body simulations. The analytic model, an isolated dark matter halo with a powerlaw profile chosen to fit the effective index at the scale probed, can be used to understand the basic properties of the eight three-point functions observed in simulations. We use this model to construct a single three-point function estimator that "optimally" combines the eight three-point functions. This new estimator is an alternative to Map statistics and provides up to a factor of two improvement in signal to noise compared to previously used combinations of cosmic shear three-point functions.
Implications of Orientation in Sheared Cocoa Butter
Guthrie, Sarah E.; Mazzanti, Gianfranco; Marangoni, Alejandro; Idziak, Stefan H. J.
2004-03-01
We will present x-ray and mechanical studies of oriented phases of cocoa butter. The structural elements of foods play an important role in determining such things as quality and shelf stability. The specific structure and properties of cocoa butter, however, are complicated due to the ability of the cocoa butter to form crystals in six polymorphic forms. Recent work has shown that the application of shear not only accelerates the transitions to more stable polymorphs, but also causes orientation of the crystallites[1]. The implications of orientation on the structures formed under conditions of shear and cooling will be described using x-ray diffraction and mechanical measurements. 1 G. Mazzanti, S. E. Guthrie, E. B. Sirota et al., Crystal Growth & Design 3 (5), 721 (2003).
ALFVEN WAVES IN SHEAR FLOWS REVISITED
Energy Technology Data Exchange (ETDEWEB)
Hollweg, Joseph V. [Space Science Center, Morse Hall, University of New Hampshire, Durham, NH 03824 (United States); Kaghashvili, Edisher Kh., E-mail: joe.hollweg@unh.edu [Atmospheric and Environmental Research, Inc., 131 Hartwell Avenue, Lexington, MA 02421 (United States)
2012-01-10
We revisit our earlier study of the evolution of an initial propagating Alfven wave in a magnetic-field-aligned flow with a cross-field velocity shear. Our goal is to show how the Alfven wave drives up plasma density fluctuations which might be observed and serve as a signature of the presence of Alfven waves in regions such as the solar corona which are inaccessible to direct observations. Here, we introduce a new initial condition which takes into account the initial distortion of the streamlines by the Alfven wave, and we present new analytical results for the driven waves. We find that the density fluctuations of a properly placed linearly polarized Alfven wave in a shear flow are much smaller than we originally estimated.
Microstructure and velocity fluctuations in sheared suspensions
Drazer, G; Khusid, B; Acrivos, A
2003-01-01
The velocity fluctuations present in macroscopically homogeneous suspensions of neutrally buoyant, non-Brownian spheres undergoing simple shear flow, and their dependence on the microstructure developed by the suspensions, are investigated in the limit of vanishingly small Reynolds numbers using Stokesian dynamics simulations. We show that, in the dilute limit, the standard deviation of the velocity fluctuations is proportional to the volume fraction, in both the transverse and the flow directions, and that a theoretical prediction, which considers only for the hydrodynamic interactions between isolated pairs of spheres, is in good agreement with the numerical results at low concentrations. We also simulate the velocity fluctuations that would result from a random hard-sphere distribution of spheres in simple shear flow, and thereby investigate the effects of the microstructure on the velocity fluctuations. Analogous results are discussed for the fluctuations in the angular velocity of the suspended spheres. ...
Structures and shear response of lipid monolayers
International Nuclear Information System (INIS)
This report discusses our work during the last 3 years using x-ray diffraction and shear measurements to study lipid monolayers (membranes). The report is divided into: (1) structure: phase diagram of saturated fatty acid Langmuir monolayers, effect of head group interactions, studies of transferred monolayers (LB films); (2) mechanical properties: fiber=optic capillary wave probe and centrosymmetric trough, mechanical behavior of heneicosanoic acid monolayer phases
Shear Viscosity Coefficient from Microscopic Models
Muronga, Azwinndini
2003-01-01
The transport coefficient of shear viscosity is studied for a hadron matter through microscopic transport model, the Ultra--relativistic Quantum Molecular Dynamics (UrQMD), using the Green--Kubo formulas. Molecular--dynamical simulations are performed for a system of light mesons in a box with periodic boundary conditions. Starting from an initial state composed of $\\pi, \\eta ,\\omega ,\\rho ,\\phi$ with a uniform phase--space distribution, the evolution takes place through ela...
Supersonic Shear Instabilities in Astrophysical Boundary Layers
Belyaev, Mikhail; Rafikov, Roman
2011-01-01
Disk accretion onto weakly magnetized astrophysical objects often proceeds via a boundary layer that forms near the object's surface, in which the rotation speed of the accreted gas changes rapidly. Here we study the initial stages of formation for such a boundary layer around a white dwarf or a young star by examining the hydrodynamical shear instabilities that may initiate mixing and momentum transport between the two fluids of different densities moving supersonically wit...
Chaotic transport in reversed shear tokamaks
Marcus, F. A.; Kroetz, T.; Roberto, M.; Caldas, I. L.; da Silva, E. C.; Viana, R. L.; Guimarães-Filho, Z. O.
2008-02-01
For tokamak models using simplified geometries and reversed shear plasma profiles, we have numerically investigated how the onset of Lagrangian chaos at the plasma edge may affect the plasma confinement in two distinct but closely related problems. Firstly, we have considered the motion of particles in drift waves in the presence of an equilibrium radial electric field with shear. We have shown that the radial particle transport caused by this motion is selective in phase space, being determined by the resonant drift waves and depending on the parameters of both the resonant waves and the electric field profile. Moreover, we have shown that an additional transport barrier may be created at the plasma edge by increasing the electric field. In the second place, we have studied escape patterns and magnetic footprints of chaotic magnetic field lines in the region near a tokamak wall, when there are resonant modes due to the action of an ergodic magnetic limiter. A non-monotonic safety factor profile has been used in the analysis of field line topology in a region of negative magnetic shear. We have observed that, if internal modes are perturbed, the distributions of field line connection lengths and magnetic footprints exhibit spatially localized escape channels. For typical physical parameters of a fusion plasma, the two Lagrangian chaotic processes considered in this work can be effective in usual conditions so as to influence plasma confinement. The reversed shear effects discussed in this work may also contribute to evaluate the transport barrier relevance in advanced confinement scenarios in future tokamak experiments.
Symmetry related dynamics in parallel shear flows
Kreilos, Tobias; Zammert, Stefan; Eckhardt, Bruno
2013-01-01
Parallel shear flows come with continuous symmetries of translation in the downstream and spanwise direction. As a consequence, flow states that differ in their spanwise or downstream location but are otherwise identical are dynamically equivalent. In the case of travelling waves, this trivial degree of freedom can be removed by going to a frame of reference that moves with the state, thereby turning the travelling wave in the laboratory frame to a fixed point in the comovin...
Shear viscosity of a crosslinked polymer melt
Broderix, Kurt; Loewe, Henning; Mueller, Peter; Zippelius, Annette
1998-01-01
We investigate the static shear viscosity on the sol side of the vulcanization transition within a minimal mesoscopic model for the Rouse-dynamics of a randomly crosslinked melt of phantom polymers. We derive an exact relation between the viscosity and the resistances measured in a corresponding random resistor network. This enables us to calculate the viscosity exactly for an ensemble of crosslinks without correlations. The viscosity diverges logarithmically as the critical...
Motional Effect on Wall Shear Stresses
DEFF Research Database (Denmark)
Kock, Samuel Alberg; Torben Fründ, Ernst
Atherosclerosis is the leading cause of death and severe disability. Wall Shear Stress (WSS), the stress exerted on vessel walls by the flowing blood is a key factor in the development of atherosclerosis. Computational Fluid Dynamics (CFD) is widely used for WSS estimations. Most CFD simulations are based on static models to ease computational burden leading to inaccurate estimations. The aim of this work was to estimate the effect of vessel wall deformations (expansion and bending) on WSS levels.
Energy nonequipartition in a sheared granular mixture
Garzo, Vicente; Montanero, Jose Maria
2002-01-01
The kinetic granular temperatures of a binary granular mixture in simple shear flow are determined from the Boltzmann kinetic theory by using a Sonine polynomial expansion. The results show that the temperature ratio is clearly different from unity (as may be expected since the system is out of equilibrium) and strongly depends on the restitution coefficients as well as on the parameters of the mixture. The approximate analytical calculations are compared with those obtained...
Transition to turbulence in a shear flow
Eckhardt, Bruno; Mersmann, Alois
1999-01-01
We analyze the properties of a 19 dimensional Galerkin approximation to a parallel shear flow. The laminar flow with a sinusoidal shape is stable for all Reynolds numbers Re. For sufficiently large Re additional stationary flows occur; they are all unstable. The lifetimes of finite amplitude perturbations show a fractal dependence on amplitude and Reynolds number. These findings are in accord with observations on plane Couette flow and suggest a universality of this transiti...
Shear viscosity, cavitation and hydrodynamics at LHC
Bhatt, Jitesh R.; Mishra, Hiranmaya; Sreekanth, V.
2011-01-01
We study evolution of quark-gluon matter in the ultrarelativistic heavy-ion collisions within the frame work of relativistic second-order viscous hydrodynamics. In particular, by using the various prescriptions of a temperature-dependent shear viscosity to the entropy ratio, we show that the hydrodynamic description of the relativistic fluid become invalid due to the phenomenon of cavitation. For most of the initial conditions relevant for LHC, the cavitation sets in very ea...
Quenching of combustion by shear flows
Kiselev, Alexander; Zlatos, Andrej
2004-01-01
We consider a simple model describing premixed combustion in the presence of fluid flow: reaction diffusion equation with passive advection and ignition type nonlinearity. Strong advection can suppress flames - a process we call quenching. A flow is called quenching if any compactly supported initial data will become extinct provided that the amplitude of the flow is chosen sufficiently large. In this paper, we provide a sharp characterization of quenching shear flows.The ef...
Microstructure and velocity fluctuations in sheared suspensions
Drazer, G.; Koplik, J.; Khusid, B.; Acrivos, A.
2003-01-01
The velocity fluctuations present in macroscopically homogeneous suspensions of neutrally buoyant, non-Brownian spheres undergoing simple shear flow, and their dependence on the microstructure developed by the suspensions, are investigated in the limit of vanishingly small Reynolds numbers using Stokesian dynamics simulations. We show that, in the dilute limit, the standard deviation of the velocity fluctuations is proportional to the volume fraction, in both the transverse ...
Textures in pure shear deformed rock salt
Skrotzki, W.; Helming, K.; Brokmeier, H. -g; Dornbusch, H. -j; Welch, P.
1995-01-01
Texture formation in pure shear deformed rock salt has been studied by neutron diffraction. The textures developed are comparable to those of rolled face-centered cubic metals with high stacking fault energy. At room temperature the texture consists of a strong S and copper and a weaker brass component. It is replaced by static and/or dynamic recrystallization by a strong cube and a subordinate Goss component. Comparison of the experimental textures with simulations based on different models ...
On the persistence of adiabatic shear bands
Bassim M.N.; Boakye-Yiadom S.; Al-Ameeri S.
2012-01-01
It is generally agreed that the initiation and development of adiabatic shear bands (ASBs) are manifestations of damage in metallic materials subjected to high strain rates and large strains as those due to impact in a Hopkinson Bar system. Models for evolution of these bands have been described in the literature. One question that has not received attention is how persistent these bands are and whether their presence and effect can be reversed or eliminated by using a process of thermal (hea...
Behaviour of voids in a shear field
DEFF Research Database (Denmark)
Tvergaard, Viggo
2009-01-01
When voids are present in a ductile material subject to a shear dominated stress state under low stress triaxiality the voids collapse to micro-cracks, which subsequently rotate and elongate in the shear field. In the present plane strain analyses for cylindrical voids a surface load normal to a plane connecting the ends of the micro-crack is used as an approximate representation of contact stresses during frictionless sliding. In a previous study of the same problem the author applied hydrostatic pressure inside the nearly closed micro-crack to approximate contact conditions. The transverse surface loads used in the present analyses avoid the tendency to unrealistically elongate the voids. It is found that even though the model applied here gives significantly later occurrence of a maximum overall shear stress than that found by using hydrostatic pressure, the present model does predict a maximum in all the cases analyzed and thus illustrates the micro-mechanism leading to failure of the material by localization of plastic flow.
Supersonic Shear Instabilities in Astrophysical Boundary Layers
Belyaev, Mikhail
2011-01-01
Disk accretion onto weakly magnetized astrophysical objects often proceeds via a boundary layer that forms near the object's surface, in which the rotation speed of the accreted gas changes rapidly. Here we study the initial stages of formation for such a boundary layer around a white dwarf or a young star by examining the hydrodynamical shear instabilities that may initiate mixing and momentum transport between the two fluids of different densities moving supersonically with respect to each other. We find that an initially laminar boundary layer is unstable to two different kinds of instabilities. One is an instability of a supersonic vortex sheet (implying a discontinuous initial profile of the angular speed of the gas) in the presence of gravity, which we find to have a growth rate of order (but less than) the orbital frequency. The other is a sonic instability of a finite width, supersonic shear layer, which is similar to the Papaloizou-Pringle instability. It has a growth rate proportional to the shear i...
Spurious Shear in Weak Lensing with LSST
Chang, C; Jernigan, J G; Peterson, J R; AlSayyad, Y; Ahmad, Z; Bankert, J; Bard, D; Connolly, A; Gibson, R R; Gilmore, K; Grace, E; Hannel, M; Hodge, M A; Jee, M J; Jones, L; Krughoff, S; Lorenz, S; Marshall, P J; Marshall, S; Meert, A; Nagarajan, S; Peng, E; Rasmussen, A P; Shmakova, M; Sylvestre, N; Todd, N; Young, M
2012-01-01
The Large Synoptic Survey Telescope (LSST) is one of the most powerful ground-based weak lensing survey telescopes in the upcoming decade. The complete 10-year survey will image $\\sim$ 20,000 square degrees of sky in six filter bands every few nights, bringing the final survey depth to $r\\sim27.5$, with over 4 billion well measured galaxies. To take full advantage of this unprecedented statistical power, the systematic errors associated with weak lensing measurements need to be controlled to a level similar to the statistical errors. This work is the first attempt to quantitatively estimate the absolute level and statistical properties of the systematic errors on weak lensing shear measurements due to the most important physical effects in the LSST system via high fidelity ray-tracing simulations. We identify and isolate the different sources of \\textit{additive} systematic errors on shear measurements for LSST and predict their impact on the final cosmic shear measurements using conventional weak lensing ana...
Shear viscosity and out of equilibrium dynamics
El, Andrej; Xu, Zhe; Greiner, Carsten
2009-01-01
Using Grad’s method, we calculate the entropy production and derive a formula for the second-order shear viscosity coefficient in a one-dimensionally expanding particle system, which can also be considered out of chemical equilibrium. For a one-dimensional expansion of gluon matter with Bjorken boost invariance, the shear tensor and the shear viscosity to entropy density ratio ?/s are numerically calculated by an iterative and self-consistent prescription within the second-order Israel-Stewart hydrodynamics and by a microscopic parton cascade transport theory. Compared with ?/s obtained using the Navier-Stokes approximation, the present result is about 20% larger at a QCD coupling ?s ? 0.3 (with ?/s ? 0.18) and is a factor of 2–3 larger at a small coupling ?s ? 0.01. We demonstrate an agreement between the viscous hydrodynamic calculations and the microscopic transport results on ?/s, except when employing a small ?s . On the other hand, we demonstrate that for such small ?s , the gluon syst...
Singular eigenfunctions for shearing fluids I
International Nuclear Information System (INIS)
The authors construct singular eigenfunctions corresponding to the continuous spectrum of eigenvalues for shear flow in a channel. These modes are irregular as a result of a singularity in the eigenvalue problem at the critical layer of each mode. They consider flows with monotonic shear, so there is only a single critical layer for each mode. They then solve the initial-value problem to establish that these continuum modes, together with any discrete, growing/decaying pairs of modes, comprise a complete basis. They also view the problem within the framework of Hamiltonian theory. In that context, the singular solutions can be viewed as the kernel of an integral, canonical transformation that allows us to write the fluid system, an infinite-dimensional Hamiltonian system, in action-angle form. This yields an expression for the energy in terms of the continuum modes and provides a means for attaching a characteristic signature (sign) to the energy associate with each eigenfunction. They follow on to consider shear-flow stability within the Hamiltonian framework. Next, the authors show the equivalence of integral superpositions of the singular eigenfunctions with the solution derived with Laplace transform techniques. In the long-time limit, such superpositions have decaying integral averages across the channel, revealing phase mixing or continuum damping. Under some conditions, this decay is exponential and is then the fluid analogue of Landau damping. Finally, the authors discuss the energetics of continuum damping
Alfven eigenmodes in shear reversed plasmas
International Nuclear Information System (INIS)
Experiments on JT-60U and JET have shown that plasma configurations with shear reversal are prone to the excitation of unusual Alfven Eigenmodes by energetic particles. These modes emerge outside the TAE frequency gap, where one might expect them to be strongly damped. The modes often appear in bunches and they exhibit a quasi-periodic pattern of predominantly upward frequency sweeping (Alfven Cascades) as the safety factor q changes in time. This work presents a theory that explains the key features of the observed unusual modes including their connection to TAE's as well as the modifications of TAE's themselves near the shear reversal point. The developed theory has been incorporated into a reduced numerical model and verified with full geometry codes. JET experimental data on Alfven spectroscopy have been simulated to infer the mode numbers and the evolution of qmin in the discharge. This analysis confirms the values of q that characterize the internal transport barrier triggering in reversed shear plasmas. (author)
Dynamic Modes of Microcapsules in Steady Shear Flow: Effects of Bending and Shear Elasticities
Noguchi, Hiroshi
2010-01-01
The dynamics of microcapsules in steady shear flow was studied using a theoretical approach based on three variables: The Taylor deformation parameter $\\alpha_{\\rm D}$, the inclination angle $\\theta$, and the phase angle $\\phi$ of the membrane rotation. It is found that the dynamic phase diagram shows a remarkable change with an increase in the ratio of the membrane shear and bending elasticities. A fluid vesicle (no shear elasticity) exhibits three dynamic modes: (i) Tank-treading (TT) at low viscosity $\\eta_{\\rm {in}}$ of internal fluid ($\\alpha_{\\rm D}$ and $\\theta$ relaxes to constant values), (ii) Tumbling (TB) at high $\\eta_{\\rm {in}}$ ($\\theta$ rotates), and (iii) Swinging (SW) at middle $\\eta_{\\rm {in}}$ and high shear rate $\\dot\\gamma$ ($\\theta$ oscillates). All of three modes are accompanied by a membrane ($\\phi$) rotation. For microcapsules with low shear elasticity, the TB phase with no $\\phi$ rotation and the coexistence phase of SW and TB motions are induced by the energy barrier of $\\phi$ rotat...
Property of Alfven eigenmode in JT-60U reversed shear and weak shear discharges
International Nuclear Information System (INIS)
This paper reports activity of Alfven eigenmode (AE) in the JT-60U reversed shear (RS) and weak shear (WS) plasmas. The AEs with a rapid frequency sweeping and then saturation of frequency as qmin decreases has been observed in low-?h RS discharges with Negative-ion-based NBI (NNBI) or ICRH. We introduce the new type of AE which we call reversed-shear-induced Alfven Eigenmode (RSAE) near qmin. This puzzling frequency change can be explained by considering the properties of RSAE and their transition to toroidal Alfven Eigenmodes (TAEs). We verify the existence of RSAEs and their transition to TAEs from magnetic fluctuations and measured q-profile in JT-60U plasmas. The AE amplitude is maximum during this transition, e.g., ?2.4 min min transition range of n = 1 AE to avoid substantial fast ion loss by large amplitude AEs in RS plasmas. (author)
Property of Alfven eigenmode in JT-60U reversed shear and weak shear discharges
International Nuclear Information System (INIS)
This paper reports activity of Alfven Eigenmode (AE) in the JT-60U reversed shear (RS) and weak shear (WS) plasmas. The AEs with a rapid frequency sweeping and then saturation of frequency as qmin decreases has been observed in low- ?h RS discharges with Negative-ion-based NBI (NNBI) or ICRH. We introduce the new type of AE which we call reversed-shear-induced Alfven Eigenmode (RSAE) near qmin. This puzzling frequency change can be explained by considering the properties of RSAE and their transition to toroidal Alfven Eigenmodes (TAEs). We verify the existence of RSAEs and their transition to TAEs from magnetic fluctuations and measured q-profile in JT-60U plasmas. The AE amplitude is maximum during this transition, e.g., ?2.4 min min transition range of n = 1 AE to avoid substantial fast ion loss by large amplitude AEs in RS plasmas. (author)
Shear strength of non-shear reinforced concrete elements : Part 3. Prestressed hollow-core slabs
DEFF Research Database (Denmark)
Hoang, Cao linh
1997-01-01
The paper deals with the shear strength of prestressed hollow-core slabs determined by the theory of plasticity. Two failure mechanisms are considered in order to derive the solutions.In the case of sliding failure in a diagonal crack, the shear strength is determined by means of the crack sliding model developed by Jin-Ping Zhang. The model takes into account the resistance against formation of cracks due to prestressing as well as the variation of the prestressing force in the transfer zone.Due to the fact that the anchorage of the reinforcement takes place by bond, a rotation failure, which is induced by a crack formed at the support with subsequent slip of the reinforcement, is also considered. This failure mode is likely to occur in cases with a high prestressing force combined with a short shear span.The theoretical calculations are compared with test results from the literature. A good agreement has been found.
Jaishankar, Aditya; Wee, May; Matia-Merino, Lara; Goh, Kelvin K T; McKinley, Gareth H
2015-06-01
Mamaku gum is a polysaccharide extracted from the fronds of the black tree fern found in New Zealand. The cooked pith has traditionally been used for various medicinal purposes and as a food source by the Ma¯ori people of New Zealand. It has potential applications as a thickener in the food industry and as a palliative for patients with dysphagia. Studies on the shear rheology of Mamaku gum have revealed that the gum exhibits shear thickening at a critical shear rate due to a transition from intra- to inter-molecular chain interactions upon shear-induced chain elongation. In this paper, we demonstrate that these interactions are primarily due to hydrogen bonding. We perform extensional rheology on mixtures of Mamaku gum and urea (a known disruptor of hydrogen bonds) to quantify the nature of these interactions. Capillary Breakup Extensional Rheometry (CaBER) performed on the pure Mamaku gum solutions yield plateau values of the Trouton ratio as high as ?10(4), showing that the viscoelasticity of the gum in uniaxial elongation is much higher than in shear. For all Mamaku concentrations tested, the extensional viscosity decreases upon increasing urea concentration. Furthermore, the relaxation time decreases exponentially with increasing urea concentration. This exponential relationship is independent of the Mamaku concentration, and is identical to the relationships between urea concentration and characteristic timescales measured in nonlinear shear rheology. We show using the sticky reptation model for polymers with multiple sticker groups along the backbone how such a relationship is consistent with a linear decrease in the free energy for hydrogen bond dissociation. We then demonstrate that a time-concentration superposition principle can be used to collapse the viscoelastic properties of the Mamaku-gum/urea mixtures. PMID:25843844
Evolution of thermal ion transport barriers in reversed shear/optimised shear plasmas
International Nuclear Information System (INIS)
The effects of the magnetic and ExB rotation shears on the thermal ion transport in advanced tokamak scenarios are analyzed through the predictive modelling of the evolution of internal transport barriers. Such a modelling is performed with an experimentally validated L-mode thermal diffusivity completed with a semi-empirical shear correction which is based on simple theoretical arguments from turbulence studies. A multi-machine test of the model on relevant discharges from the ITER Data Base (TFTR, DIII-D and JET) is presented. (author)
Evolution of thermal ion transport barriers in reversed shear/ optimised shear plasmas
International Nuclear Information System (INIS)
The effects of the magnetic and ExB rotation shears on the thermal ion transport in advanced tokamak scenarios are analyzed through the predictive modelling of the evolution of internal transport barriers. Such a modelling is performed with an experimentally validated L-mode thermal diffusivity completed with a semi-empirical shear correction which is based on simple theoretical arguments from turbulence studies. A multi-machine test of the model on relevant discharges from the ITER Data Base (TFTR, DIII-D and JET) is presented. (author)
Hysteresis and Lubrication in Shear Thickening of Cornstarch Suspensions
Chu, Clarence E; Sieber, Hannah L; Miller, James G; Okamoto, Ruth J; Katz, Jonathan I
2014-01-01
Aqueous and brine suspensions of corn starch show striking discontinuous shear thickening. We have found that a suspension shear-thickened throughout may remain in the jammed thickened state as the strain rate is reduced, but an unjamming front may propagate from any unjammed regions. Transient shear thickening is observed at strain rates below the thickening threshold, and above it the stress fluctuates. The jammed shear-thickened state may persist to low strain rates, with stresses resembling sliding friction and effective viscosity inversely proportional to the strain rate. At the thickening threshold fluid pressure depins the suspension's contact lines on solid boundaries so that it slides, shears, dilates and jams. In oil suspensions lubrication and complete wetting of confining surfaces eliminate contact line forces and prevent jamming and shear thickening, as does addition of immiscible liquid surfactant to brine suspensions. Starch suspensions in glycerin-water solutions, viscous but incompletely wett...
Flexure of thick orthotropic plates by exponential shear deformation theory
Scientific Electronic Library Online (English)
A. S., Sayyad.
2013-05-01
Full Text Available In the present paper, a variationally consistent exponential shear deformation theory taking into account transverse shear deformation effect is presented for the flexural analysis of thick orthotropic plates. The inplane displacement field uses exponential function in terms of thickness coordinate [...] to include the shear deformation effect. The transverse shear stress can be obtained directly from the constitutive relations satisfying the shear stress free surface conditions on the top and bottom surfaces of the plate, hence the theory does not require shear correction factor. Governing equations and boundary conditions of the theory are obtained using the principle of virtual work. Results obtained for static flexure of simply supported orthotropic plates are compared with those of other refined theories and elasticity solution wherever applicable. The results obtained by present theory are in excellent agreement with those of exact results and other higher order theories. Thus the efficacy of the present refined theory is established.
Shear banding deformation in Cu/Ta nano-multilayers
Energy Technology Data Exchange (ETDEWEB)
Wang, F. [MOE Key Laboratory for Strength and Vibration, School of Aerospace, Xi' an Jiaotong University, Xi' an, 710049 (China); Huang, P., E-mail: huangping@mail.xjtu.edu.cn [State Key Laboratory for Mechanical Behavior of Material, Xi' an Jiaotong University, Xi' an, 710049 (China); Xu, M. [State Key Laboratory for Mechanical Behavior of Material, Xi' an Jiaotong University, Xi' an, 710049 (China); Lu, T.J. [MOE Key Laboratory for Strength and Vibration, School of Aerospace, Xi' an Jiaotong University, Xi' an, 710049 (China); Xu, K.W. [State Key Laboratory for Mechanical Behavior of Material, Xi' an Jiaotong University, Xi' an, 710049 (China)
2011-09-15
Highlights: {yields} Formation of shear bands in Cu/Ta multilayers is layer thickness dependent. {yields} Unique layer-morphology with prevalent mismatched laminate structure was observed. {yields} A new physical mechanism that dominates shear band formation is suggested. - Abstract: Nanoscale Cu/Ta multilayers with individual layer thickness ranging from 3 to 70 nm were deformed under nanoindentation at room temperature. Shear bands can be observed only when individual layer thickness is reduced to 9 nm or below, indicating formation of shear bands in the Cu/Ta multilayers is layer thickness dependent. By observing the cross sectional transmission electron microscope images of the indentation fabricated through focused ion beam technique, shear banding deformation causing a unique layer-morphology with prevalent mismatched laminate structure has been reported for the first time. By capturing and analyzing a series of typical indentation-induced deformed microstructures, a new physical mechanism of shear banding behavior in metallic nano-multilayers is suggested.
Transport Bifurcation Induced by Sheared Toroidal Flow in Tokamak Plasmas
Highcock, E G; Parra, F I; Schekochihin, A A; Roach, C M; Cowley, S C
2011-01-01
First-principles numerical simulations are used to describe a transport bifurcation in a differentially rotating tokamak plasma. Such a bifurcation is more probable in a region of zero magnetic shear, where the component of the sheared toroidal flow that is perpendicular to the magnetic field has the strongest suppressing effect on the turbulence, than one of finite magnetic shear. Where the magnetic shear is zero, there are no growing linear eigenmodes at any finite value of flow shear. However, subcritical turbulence can be sustained, owing to the transient growth of modes driven by the ion temperature gradient (ITG) and the parallel velocity gradient (PVG). Nonetheless, in a parameter space containing a wide range of temperature gradients and velocity shears, there is a sizeable window where all turbulence is suppressed. Combined with the relatively low transport of momentum by collisional (neoclassical) mechanisms, this produces the conditions for a bifurcation from low to high temperature and velocity gr...
Assessment of susceptibility of rape stems to shearing
Directory of Open Access Journals (Sweden)
Vielikanov L.
2000-12-01
Full Text Available In the present study, the authors used a dynamic shearing and densitometric method for the asses- sment of susceptibility of stems of winter rape, vars Mar, Bolko, Leo, Ceres and Libravo to shearing. They determi- ned dynamic shearing energy per a unit of the stem cross section area, in the natural state as well as after the removed of parenchyma, density and DOD parameter, indicating the amount of X-ray energy absorbed by the stems. It was found that susceptibility of rape stems to shearing depends on their structure. A strict correlation was shown to exist between the dynamic shearing energy and the amount of X-ray radiation energy absorbed by the stem. Moreover, in study showed that the application of the X-ray method greatly enhanced the possibility to determine of the suscep- tibility of rape stems to shearing.
Self-organization in periodically sheared granular materials
Wilken, Sam; Hunter, Gary L.; Chaikin, Paul M.
2015-03-01
Self-organization as a result of periodic shear is becoming a feature observed in an increasing number of systems. In our experiments, we enforce cyclic shear on a three dimensional system of non-Brownian particles to investigate the global packing behavior of the granular assembly. By starting with a dilated, loosely packed system and measuring the packing fraction after each shear cycle, we find the system compacts to reach a steady state with a well defined packing fraction. The shear amplitude determines the steady state packing fraction, where large amplitude shear produces a lower packing density and small amplitude shear produces a higher packing density. We also study the phase diagram of this system which exhibits caged motion and a transition to vorticity.
Predictions of turbulent mixing in axisymmetric compressible shear layers
Viswanathan, K.; Morris, P. J.
1992-06-01
Models are described for the turbulent mixing of compressible, axisymmetric shear layers. The models assume that the mixing process is dominated by large-scale coherent structures. These large-scale structures are described locally as linear instability waves. Calculations are made for the development of the axisymmetric shear layer as a function of free stream Mach numbers and velocity and density ratios. The predictions for the axisymmetric shear layer are compared with both experimental measurements and predictions for a plane shear layer. The effects of the initial thickness of the shear layer and the initial amplitudes of the large-scale structures on the growth of the shear layer are examined. The effect of the description of the mean velocity profile is considered.
Strain localization in experimentally sheared gouge layers
Di Toro, G.; Rempe, M.; Smith, S. A.; Mitchell, T. M.
2013-12-01
Laboratory studies designed to understand fault and earthquake processes often use rotary-shear apparatus to investigate the frictional properties of rocks. Rotary-shear apparatus can apply a wide range of slip velocities and impose high displacements on cohesive and non-cohesive rocks and are thus ideal to study deformation processes taking place throughout the seismic cycle. However, in experiments performed on gouges, the mechanical results and the developing microstructures are often hard to interpret, because little is known about the distribution of strain (i.e., the ratio of displacement to the thickness of the deforming zones) within the gouge layer. A better understanding of the strain distribution may help to interpret microstructures associated with varying degrees of strain localization and infer the underlying physical-chemical processes. We report preliminary results from a series of experiments carried out with strain markers using the rotary-shear apparatus SHIVA at INGV in Rome. Within an annular steel sample holder (with outer and inner radii of 55 and 35 mm, respectively), a 3 mm thick calcite gouge layer (starting grain size <250 ?m) was prepared with a 2 mm wide dolomite gouge strain marker cutting vertically through the calcite layer. The marker was orientated perpendicular to the imposed shear direction. Dolomite was selected for the strain marker because it has similar mechanical properties to calcite. The strain marker experiments were conducted at varying slip rates (10-3 m/s and 1 m/s), displacements (8 cm to 1.5 m), normal stresses (3 to 20 MPa) and ambient conditions (room-humid and wet) to test the dependence of the strain distribution. Mechanical data (shear stress, shortening and dilation, etc.) were recorded during the experiments. Afterwards, the preserved samples were cut vertically through the dolomite strain markers (approximately parallel to the slip direction) and microstructural analysis was conducted with the scanning electron microscope. Preliminary results show that at a slip velocity of 0.1 m/s and normal stress of 3 MPa, localization to a relatively high-strain slipping zone occurs rapidly. Progressive strain localization at the onset of shearing is associated with gouge layer dilation and strain hardening. The onset of dynamic weakening (i.e. at the end of the strain hardening phase) broadly correlates with the establishment of a discrete slip surface that develops within the high strain slipping zone. Interestingly, the value of strain (? ~2) in the low-strain zone does not change significantly with increasing displacement, suggesting that, once formed, the high strain slipping zone and slip surface accommodate most of the ongoing displacement. More quantitative information on the dependence of strain distribution on displacement, slip rate, and normal stress will be gained from further microstructural analysis.
Punching shear strength of steel fibre reinforced concrete slabs
Maya Duque, L. Felipe; Ferna?ndez Ruiz, Miguel; Muttoni, Aurelio; Foster, S. J.
2012-01-01
The ultimate strength of reinforced concrete slabs is frequently governed by the punching shear capacity, which may be increased with addition of traditional fitments such as reinforcing steel, headed studs or shear heads. In addition to these traditional methods of strengthening against punching, steel fibre reinforcement has proved to be an effective and viable alternative. The addition of fibres into the concrete improves not only the shear behaviour but also the deformation capacity of re...
Low-n shear Alfven spectra in axisymmetric toroidal plasmas
International Nuclear Information System (INIS)
In toroidal plasmas, the toroidal magnetic field is nonuniform over a magnetic surface and causes coupling of different poloidal harmonics. It is shown both analytically and numerically that the toroidicity not only breaks up the shear Alfven continuous spectrum, but also creates new, discrete, toroidicity-induced shear Alfven eigenmodes with frequencies inside the continuum gaps. Potential applications of the low-n toroidicity-induced shear Alfven eigenmodes on plasma heating and instabilities are addressed. 17 refs., 4 figs
Shear stress regulates aquaporin-5 and airway epithelial barrier function
Sidhaye, Venkataramana K.; Schweitzer, Kelly S.; Caterina, Michael J.; Shimoda, Larissa; King, Landon S.
2008-01-01
As the interface with the outside world, the airway epithelial barrier is critical to lung defense. Because of respiratory efforts, the airways are exposed to shear stress; however, little is known regarding the effects of shear on epithelial function. We report that low-level shear stress enhances epithelial barrier function, an effect that requires serial activation of the transient receptor potential vanilloid (TRPV) 4 and L-type voltage-gated calcium channel (VGCC) and an increase in intr...
Shear-free gravitational collapse is strongly censored
Goncalves, Sergio M. C. V.
2003-01-01
We consider spherically symmetric spacetimes with matter whose timelike flow is assumed to be shear-free. A number of results on the formation and visibility of spacetime singularities is proven, with the main one being that shear-free collapse cannot admit locally naked singularities (which implies absence of globally naked singularities). We conjecture that shear is a necessary condition for the occurrence of locally naked singularities in generic gravitational collapse.
Shear-Induced Collapse in a Lyotropic Lamellar Phase
International Nuclear Information System (INIS)
An entropically stabilized cetylpyridinium chloride, hexanol, and heavy brine lyotropic lamellar phase subjected to shear flow has been observed here by small angle neutron scattering to undergo collapse of smectic order above a threshold shear rate. The results are compared with theories predicting that such a lamellar phase sheared above a critical rate should lose its stability by a loss of resistance to compression due to the suppression of membrane fluctuations
Shear-Induced Collapse in a Lyotropic Lamellar Phase
Porcar, L.; Warr, G. G.; Hamilton, W. A.; Butler, P. D.
2005-08-01
An entropically stabilized cetylpyridinium chloride, hexanol, and heavy brine lyotropic lamellar phase subjected to shear flow has been observed here by small angle neutron scattering to undergo collapse of smectic order above a threshold shear rate. The results are compared with theories predicting that such a lamellar phase sheared above a critical rate should lose its stability by a loss of resistance to compression due to the suppression of membrane fluctuations.
Polarized Shear Waves for Crack Detection and Characterization
Turner, S. J.; Maxfield, B. W.
2010-02-01
This paper describes a new approach to the detection and sizing of cracks in metals. It uses a newly developed technique based on interrogating materials with shear waves having varying polarization direction generated by a specially designed EMAT where the polarization direction is established by a combination of coil design and system software and hardware parameters. The reflected/scattered shear wave resulting from each incident shear wave is received and detected with respect to the excitation pulse parameters.
A shear localization mechanism for lubricity of amorphous carbon materials
Tian-Bao Ma; Lin-Feng Wang; Yuan-Zhong Hu; Xin Li; Hui (Wendy) Wang
2014-01-01
Amorphous carbon is one of the most lubricious materials known, but the mechanism is not well understood. It is counterintuitive that such a strong covalent solid could exhibit exceptional lubricity. A prevailing view is that lubricity of amorphous carbon results from chemical passivation of dangling bonds on surfaces. Here we show instead that lubricity arises from shear induced strain localization, which, instead of homogeneous deformation, dominates the shearing process. Shear localization...
Transverse shear warping functions for anisotropic multilayered plates
Loredo, Alexandre
2012-01-01
In this work, transverse shear warping functions for an equivalent single layer plate model are formulated from a variational approach. The part of the strain energy which involves the shear phenomenon is expressed in function of the warping functions and their derivatives. The variational calculus leads to a differential system of equations which warping functions must verify. Solving this system requires the choice of values for the (global) shear strains and their derivat...
Shear Jamming in Granular Experiments without Basal Friction
Zheng, Hu; Dijksman, Joshua A.; Behringer, Robert P.
2014-01-01
Jammed states of frictional granular systems can be induced by shear strain at densities below the isostatic jamming density ($\\phi_c$). It remains unclear, however, how much friction affects this so-called shear-jamming. Friction appears in two ways in this type of experiment: friction between particles, and friction between particles and the base on which they rest. Here, we study how particle-bottom friction, or basal friction, affects shear jamming in quasi-two dimension...
Generalization of Shear Stress Distribution in Rectangular Compound Channels
ABAZA, Khaled A.
2003-01-01
Experimental testing of 5 different types of boundary shear stress distribution in a symmetrical rectangular compound section channel was conducted. Shear stress distributions in the main channel and floodplains of 6 different rectangular compound cross-sections are presented. Numerical values of regression coefficients for the resulting 36 single-variable models representing 5 types of shear stress for each of the 6 cross-sections have been derived. All obtained statistics indicate...
Tension, compression and shear fatigue of a closed cell foam
Zenkert, Dan; Burman, Magnus
2007-01-01
A closed cell foam of Polymetacrylimide (Rohacell) with three different densities is studied. The foam is tested quasistatically in tension, compression and shear. The tensile properties scale very well with the relative density of the foam, but the compression and shear properties do not. It is believed to be due to cell edge and cell wall buckling being the dominated deformation mechanism in compression and shear for lower densities that does not occur for higher densities. Fatigue testing ...
HYBRID SHEARWALL SYSTEM — SHEAR STRENGTH AT THE INTERFACE CONNECTION
Ulrich Wirth; Nuri Shirali; Vladimír K?ístek; Helmut Kurth
2013-01-01
Based on a series of alternating, displacement-controlled load tests on ten one-third scale models, to study the behaviour of the interface of a hybrid shear wall system, it was proved that the concept of hybrid construction in earthquake prone regions is feasible. The hybrid shear-wall system consists of typical reinforced concrete shear walls with composite edge members or flanges. Ten different anchorage bar arrangements were developed and tested to evaluate the column-shearwall interface ...
Shear viscosity for a moderately dense granular binary mixture
Garzo, Vicente; Montanero, Jose Maria
2003-01-01
The shear viscosity for a moderately dense granular binary mixture of smooth hard spheres undergoing uniform shear flow is determined. The basis for the analysis is the Enskog kinetic equation, solved first analytically by the Chapman-Enskog method up to first order in the shear rate for unforced systems as well as for systems driven by a Gaussian thermostat. As in the elastic case, practical evaluation requires a Sonine polynomial approximation. In the leading order, we det...
A transport bifurcation model for enhanced confinement with negative shear
International Nuclear Information System (INIS)
A magnetic shear driven transport bifurcation model for transition to enhanced confinement regime with negative shear and neutral beams is proposed. Strong fueling by high power beams leads to peaking of pressure profile and generation of large bootstrap current. The resulting negative shear reduces the growth of fluctuations. The transition to enhanced confinement regime occurs when fluctuations are completely quenched. Relevance of this to recent results from TFTR is briefly discussed. (author)
Shear-free gravitational collapse is strongly censored
Gonçalves, S M C V
2004-01-01
We consider spherically symmetric spacetimes with matter whose timelike flow is assumed to be shear-free. A number of results on the formation and visibility of spacetime singularities is proven, with the main one being that shear-free collapse cannot admit locally naked singularities (which implies absence of globally naked singularities). We conjecture that shear is a necessary condition for the occurrence of locally naked singularities in generic gravitational collapse.
Shear-free gravitational collapse is strongly censored
International Nuclear Information System (INIS)
We consider spherically symmetric spacetimes with matter whose timelike flow is assumed to be shear-free. A number of results on the formation and visibility of spacetime singularities is proven, with the main one being that shear-free collapse cannot admit locally naked singularities (which implies the absence of globally naked singularities). We conjecture that shear is a necessary condition for the occurrence of locally naked singularities in generic gravitational collapse
Shear Viscosity of a Superfluid Dipolar Gas at Low Temperatures
Directory of Open Access Journals (Sweden)
M. Khademi Dehkordi
2014-02-01
Full Text Available We compute the shear viscosity of superfluid Bose and Fermi gases on the base of Boltzmann equation and relaxation times. We show that, in the low temperature limit, the shear viscosities of Bose and Fermi gases are proportional to T-1evp0/T and T-4, respectively. For the superfluid Bose gas at low temperature limit, only splitting processes contribute to the shear viscosity.
Shear zones between rock units with no relative movement
DEFF Research Database (Denmark)
Koyi, Hemin; Schmeling, Harro
2013-01-01
Shear zones are normally viewed as relatively narrow deformation zones that accommodate relative displacement between two “blocks” that have moved past each other in opposite directions. This study reports localized zones of shear between adjacent blocks that have not moved past each other. Such deformation zones, which we call wakes, form due to the movement of exotic blocks within a viscous medium (denser blocks sinking within a salt structure, (the paths) between separated boudins), melt in partially molten surroundings (melt movement during migmatisation), or solid blocks sinking through a partially molten magma body (stoping). From the fluid dynamics perspective these shear zones can be regarded as low Reynolds number deformation zones within the wake of a body moving through a viscous medium. While compact moving bodies (aspect ratio 1:1:1) generate axial symmetric (cone like) shear zones or wakes, elongated bodies (vertical plates or horizontal rod-like bodies) produce tabular shear zones or wakes. Unlike conventional shear zones across which shear indicators usually display consistent symmetries, shear indicators on either side of the shear zone or wake reported here show reverse kinematics. Thus profiles exhibit shear zones with opposed senses of movement across their center-lines or -planes. We have used field observations and results from analytical and numerical models to suggest that examples of wakes are the transit paths that develop where denser blocks sink within salt structures, bodies of melt rise through migmatites, between boudins separated by progressive extension and (perhaps) where slabs of subducted oceanic lithosphere delaminate from the continental crust and sink into the asthenosphere. We also argue that such shear zones may be more common than they have been given credit for and may be responsible for some reverse kinematics reported in shear zones.
Bulk and shear viscosities of hot and dense hadron gas
Kadam, Guru Prakash; Mishra, Hiranmaya
2014-01-01
We estimate bulk and shear viscosity at finite temperature and baryon densities of hadronic matter within hadron resonance gas model. For bulk viscosity we use low energy theorems of QCD for the energy momentum tensor correlators. For shear viscosity coefficient, we estimate the same using molecular kinetic theory to relate the shear viscosity coefficient to average momentum of the hadrons in the hot and dense hadron gas. The bulk viscosity to entropy ratio increases with ch...
SHEARING STRENGTH TESTING ON »ROBERTSON RESEARCH« AND »AMP-1«
Directory of Open Access Journals (Sweden)
Miroslav Petzel
1994-12-01
Full Text Available Paper describes shearing machines »Robertson Research« and shearing machine »AMP-1« for »softer« rocks. Maximal horizontal and vertical power for »AMP-1« is 400 kN for sample surface between 100 and 200 cm2, and can be used for shear tests along the plane of discontinuity of very hard rocks. Average content of CaCO3 in tested samples is 71,39%.
Propagation of waves in shear flows
Fabrikant, A L
1998-01-01
The state of the art in a theory of oscillatory and wave phenomena in hydrodynamical flows is presented in this book. A unified approach is used for waves of different physical origins. A characteristic feature of this approach is that hydrodynamical phenomena are considered in terms of physics; that is, the complement of the conventionally employed formal mathematical approach. Some physical concepts such as wave energy and momentum in a moving fluid are analysed, taking into account induced mean flow. The physical mechanisms responsible for hydrodynamic instability of shear flows are conside
THE SUBSURFACE-SHEAR-SHAPED SOLAR ?? DYNAMO
International Nuclear Information System (INIS)
We propose a solar dynamo model distributed in the bulk of the convection zone with toroidal magnetic-field flux concentrated in a near-surface layer. We show that if the boundary conditions at the top of the dynamo region allow the large-scale toroidal magnetic fields to penetrate close to the surface, then the modeled butterfly diagram for the toroidal magnetic field in the upper convection zone is formed by the subsurface rotational shear layer. The model is in agreement with observed properties of the magnetic solar cycle.
Explosion Shear Wave Generation and Scattering
Baker, G. E.; Stevens, J. L.; Xu, H.
2004-12-01
We use observations of explosion-generated Lg together with three separate types of numerical models to determine how underground nuclear explosions generate shear wave phases. This question is fundamental to how Lg phases are interpreted for use in explosion yield estimation and earthquake/explosion discrimination. A simple point explosion in a uniform medium generates no shear waves, so the Lg phase is generated entirely by non-spherical components of the source and conversions through reflections and scattering. Our results indicate that the most important sources of high frequency explosion shear waves are P to S conversions at the free surface and S waves generated directly by a realistic distributed explosion source including nonlinear effects due to the free surface and gravity. In addition, Rg scattering may contribute to lower frequency Lg. Near source S is observed on both radial and tangential component records from a diverse set of explosion data. The data sets include 1) Degelen Mountain explosions recorded at distances less than 100 km and corresponding recordings at Borovoye (BOR) at 650 km; 2) recordings from Russian deep seismic sounding experiments; 3) Nevada Test Site (NTS) explosion sources including the Nonproliferation Experiment (NPE) and nuclear tests covering a range of source depths and media properties. We model the overburied NPE, and underburied and overburied Degelen explosions, using point sources and two-dimensional nonlinear finite difference calculations to quantify the source effects. We use energy conservation to determine an upper bound on Rg to Lg scattering. Results indicate that Rg to Lg scattering may be important at frequencies less than 1 Hz, and in Lg coda, but is less than Lg generated directly by the explosion at higher frequencies. We use 2D and 3D finite difference calculations, using the known topography and velocity structure at Degelen Mt. and lateral heterogeneities within the crust, to estimate the effect of surface and crustal scattering on Lg. Results indicate that topographic scattering can significantly disrupt the surface pS scattered phase, so more shear wave energy is trapped in the crust. The topography also appears to be the most significant scatterer of Rg, and has a profound effect on its dispersion.
Discontinuous shear thickening for frictional granular particles
Grob, Matthias; Heussinger, Claus; Zippelius, Annette
2015-03-01
We study the rheology of frictional granular particles with analytical modelling and numerical simulations in two dimensions. We derive a phase diagram with a topology different from the well known Liu-Nagel phase diagram for frictionless particles with a zero stress critical point. In contrast to the frictionless scenario, jamming first occurs at finite stress at a critical packing fraction ?C while a finite yield stress emerges only at ?? >?C . Remarkably, the flow is reentrant and we observe discontinuous shear thickening in the flow curves for ? ? (?C ,??) with ?? >?? . All these features can be rationalized with a simple constitutive equation which contains the frictionless scenario as a limiting case.
Energy nonequipartition in a sheared granular mixture
Garzó, V; Garzo, Vicente; Montanero, Jose Maria
2002-01-01
The kinetic granular temperatures of a binary granular mixture in simple shear flow are determined from the Boltzmann kinetic theory by using a Sonine polynomial expansion. The results show that the temperature ratio is clearly different from unity (as may be expected since the system is out of equilibrium) and strongly depends on the restitution coefficients as well as on the parameters of the mixture. The approximate analytical calculations are compared with those obtained from Monte Carlo simulations of the Boltzmann equation showing an excellent agreement over the range of parameters investigated. Finally, the influence of the temperature differences on the rheological properties is also discussed.
Shear Horizontal Acoustic Plate Mode Viscosity Sensor
Sato, Toshio; Okajima, Hiroshi; Kashiwase, Yutaka; Motegi, Ryohei; Nakajima, Haruhiko
1993-05-01
Mode analysis of a LiTaO3 (LTO) plate has been carried out numerically, and an interference-free shear horizontal acoustic plate mode (SH-APM) suitable for measuring the liquid viscosity was found. A viscosity sensor having a liquid container on the side opposite to interdigital transducers (IDTs) was fabricated on X-cut 148° Y-prop LTO. Satisfactory agreement was obtained between the calculated frequency spectrum and the experimental one. A loading test was carried out for a series of Newtonian liquids, which showed good agreement with the perturbation theory.
On nonlinear physics of shear Alfvén waves
International Nuclear Information System (INIS)
Shear Alfvén waves (SAW) are electromagnetic oscillations prevalent in laboratory and nature magnetized plasmas. Due to their anisotropic nature, it is well known that the linear wave propagation and dispersiveness of SAW are fundamentally affected by plasma nonuniformities and magnetic field geometries, such as the existence of continuous spectrum, spectral gaps, and discrete eigenmodes in toroidal plasmas. This work discusses the pure Alfvénic state and demonstrates the crucial roles that finite ion compressibility, non-ideal kinetic effects, and geometry play in breaking it and, thereby, the nonlinear physics of SAW wave-wave interactions
Shear-Alfven waves in gyrokinetic plasmas
Energy Technology Data Exchange (ETDEWEB)
Lee, W. W.; Lewandowski, J. L. V.; Hahm, T. S.; Lin, Z.
2001-10-01
It is found that the thermal fluctuation level of the shear-Alfven waves in a gyrokinetic plasma is dependent on plasma {beta}((equivalent to)c{sub s}{sup 2}/v{sub A}{sup 2}), where c{sub s} is the ion acoustic speed and v{sub A} is the Alfven velocity. This unique thermodynamic property based on the fluctuation--dissipation theorem is verified in this paper using a new gyrokinetic particle simulation scheme, which splits the particle distribution function into the equilibrium part as well as the adiabatic and nonadiabatic parts. The numerical implication of this property is discussed.
Shear-Alfven Waves in Gyrokinetic Plasmas
International Nuclear Information System (INIS)
It is found that the thermal fluctuation level of the shear-Alfven waves in a gyrokinetic plasma decreases with plasma b(* cs2/uA2), where cs is the ion acoustic speed and uA is the Alfven velocity. This unique thermodynamic property based on the fluctuation-dissipation theorem is verified in this paper using a new gyrokinetic particle simulation scheme, which splits the particle distribution function into the equilibrium part as well as the adiabatic and nonadiabatic parts
Scientific Electronic Library Online (English)
Rodrigo, Cruz; Elizabeth, Barthel; Jaime, Espinoza.
2013-06-01
Full Text Available Curvularia inaequalis (Shear) Boedijn es un hongo dematiáceo, saprófito y fitopatógeno, presente principalmente en áreas tropicales y subtropicales, asociado a distintos sustratos orgánicos. Se ha identificado escasamente en infecciones sistémicas, cutáneas y sólo existe una comunicación de un caso [...] de rinosinusitis alérgica descrito anteriormente. Presentamos el caso clínico de un paciente con una rinosinusitis alérgica fúngica por Curvularia inaequalis (Shear) Boedijn en cuyo diagnóstico se consideró los síntomas y signos clínicos, la TAC de senos paranasales y el cultivo de la mucina. El paciente fue tratado con un aseo quirúrgico por vía endoscópica, además del uso de corticoesteroides inhalatorios e itra-conazol sistémico. Presentó una buena respuesta clínica, encontrándose asintomático a un año del tratamiento. Abstract in english Curvularia inaequalis (Shear) Boedijn is a fungus dematiaceo, saprophyte and plant pathogen found mainly in tropical and subtropical areas, associated with various organic substrates. Rarely been identified in systemic infections, skin and there is only one report of allergic rhinosinusitis describe [...] d above. A case of allergic fungal rhinosinusitis by Curvularia inaequalis (Shear) Boedijn in which diagnosis was considered the signs and symptoms, sinus CT and cultivation of mucin.The patient was treated with endoscopic surgical toilet, plus use of inhaled steroids and itraconazole systemic. With good clinical response, is asymptomatic at one year.
From supersonic shear wave imaging to full-field optical coherence shear wave elastography.
Nahas, Amir; Tanter, Mickaël; Nguyen, Thu-Mai; Chassot, Jean-Marie; Fink, Mathias; Claude Boccara, A
2013-12-01
Elasticity maps of tissue have proved to be particularly useful in providing complementary contrast to ultrasonic imaging, e.g., for cancer diagnosis at the millimeter scale. Optical coherence tomography (OCT) offers an endogenous contrast based on singly backscattered optical waves. Adding complementary contrast to OCT images by recording elasticity maps could also be valuable in improving OCT-based diagnosis at the microscopic scale. Static elastography has been successfully coupled with full-field OCT (FF-OCT) in order to realize both micrometer-scale sectioning and elasticity maps. Nevertheless, static elastography presents a number of drawbacks, mainly when stiffness quantification is required. Here, we describe the combination of two methods: transient elastography, based on speed measurements of shear waves induced by ultrasonic radiation forces, and FF-OCT, an en face OCT approach using an incoherent light source. The use of an ultrafast ultrasonic scanner and an ultrafast camera working at 10,000 to 30,000 images/s made it possible to follow shear wave propagation with both modalities. As expected, FF-OCT is found to be much more sensitive than ultrafast ultrasound to tiny shear vibrations (a few nanometers and micrometers, respectively). Stiffness assessed in gel phantoms and an ex vivo rat brain by FF-OCT is found to be in good agreement with ultrasound shear wave elastography. PMID:24357549
The role of shear in dissipative gravitational collapse
Govender, M; Maharaj, S D
2013-01-01
In this paper we investigate the physics of a radiating star undergoing dissipative collapse in the form of a radial heat flux. Our treatment clearly demonstrates how the presence of shear affects the collapse process; we are in a position to contrast the physical features of the collapsing sphere in the presence of shear with the shear-free case. By employing a causal heat transport equation of the Maxwell-Cattaneo form we show that the shear leads to an enhancement of the core temperature thus emphasizing that relaxational effects cannot be ignored when the star leaves hydrostatic equilibrium.
The Role of Shear in Dissipative Gravitational Collapse
Govender, M.; Reddy, K. P.; Maharaj, S. D.
2014-11-01
In this paper, we investigate the physics of a radiating star undergoing dissipative collapse in the form of a radial heat flux. Our treatment clearly demonstrates how the presence of shear affects the collapse process; we are in a position to contrast the physical features of the collapsing sphere in the presence of shear with the shear-free case. By employing a causal heat transport equation of the Maxwell-Cattaneo form we show that the shear leads to an enhancement of the core temperature thus emphasizing that relaxational effects cannot be ignored when the star leaves hydrostatic equilibrium.
Vesicle to micelle transitions in surfactant mixtures induced by shear
Mendes, E.; Menon, S. V. G.
1997-09-01
Small angle neutron scattering data from aqueous solutions of mixtures of a catanionic surfactant and a detergent at rest and under shear flow are presented. These data show a shear-induced vesicle to worm-like micelle transition. A thermodynamic model of the vesicle to micelle transition in lipid-detergent mixtures is extended to include shear effects. Predictions of the extended model are compared with the shear dependence of the micelle volume fraction estimated from scattering experiments. The experimental results agree qualitatively with the predictions.
Shear jamming in granular experiments without basal friction
Zheng, Hu; Dijksman, Joshua A.; Behringer, R. P.
2014-08-01
Jammed states of frictional granular systems can be induced by shear strain at densities below the isostatic jamming density (\\phi_c) . It remains unclear, however, how much friction affects this so-called shear jamming. Friction appears in two ways in this type of experiment: friction between particles, and friction between particles and the base on which they rest. Here, we study how particle-bottom friction, or basal friction, affects shear jamming in quasi-two-dimensional experiments. In order to study this issue experimentally, we apply simple shear to a disordered packing of photoelastic disks. We can tune the basal friction of the particles by immersing the particles in a density matched liquid, thus removing the normal force, hence the friction, between the particles and base. We record the overall shear stress, and particle motion, and the photoelastic response of the particles. We compare the shear response of dry and immersed samples, which enables us to determine how basal friction affects shear jamming. Our findings indicate that changing the basal friction shifts the point of shear jamming, but it does not change the basic phenomenon of shear jamming.
Compressive and shear properties of commercially available polyurethane foams.
Thompson, MS; McCarthy, ID; Lidgren, L.; Ryd, L.
2003-01-01
BACKGROUND: The shear properties of rigid polyurethane (PU-R) foams, routinely used to simulate cancellous bone, are not well characterized. METHOD OF APPROACH: The present assessment of the shear and compressive properties of four grades of Sawbones "Rigid cellular" PU-R foam tested 20 mm gauge diameter dumb-bell specimens in torsion and under axial loading. RESULTS: Shear moduli ranged from 13.3 to 99.7 MPa, shear strengths from 0.7 MPa to 4.2 MPa. Compressive yield strains varied little wi...
Development of shear capacity equations for rectangular reinforced concrete beams
International Nuclear Information System (INIS)
The problem of shear is not yet fully understood due to involvement of number of parameters. Designers are extra careful about shear, especially in beams and consequently higher safety factors are used in shear design. Several equations are available in literature to determine the shear capacity of beams, i.e. ACI equation, Zsutty equation and KIM and White equation. To verify the application of these equations, extensive experimental study was carried out on rectangular reinforced concrete beams without web reinforcement. Three parameters i.e. compressive strength, percentage of tension steel and shear span to depth ratio were considered and equations were developed for the shear strength prediction. Results of the study show that the concrete shear capacity ranges from 1.7' 1fc' to 1.B 'If c' before any cracking is observed. After cracking, concrete shear capacity is almost exhausted and most of the applied shear is taken by steel till failure. It is also revealed that ACI equation is most conservative for all values of aid, ft and p. (author)
Turbulent bands in a planar shear flow without walls
Chantry, Matthew; Barkley, Dwight
2015-01-01
Turbulent bands are a ubiquitous feature of transition in wall-bounded shear flows. We show that these are also a robust feature of Waleffe flow -- a shear flow driven by a sinusoidal body force between stress-free boundaries -- thus demonstrating that rigid walls are not a prerequisite for band formation. Exploiting the Fourier dependence of Waleffe forcing, we construct a model flow that uses only four wavenumbers in the shear direction and yet captures uniform turbulence, turbulent bands, and spot expansion. The model is simultaneously a reduction of the full Navier-Stokes equations and an extension of minimal models of the self-sustaining process of shear turbulence.
Nonlinear Brownian dynamics of interfacial fluctuations in a shear flow
Thiébaud, Marine; Amarouchene, Yacine; Bickel, Thomas
2014-12-01
Using Brownian dynamics simulations, we investigate the effect of an external flow on the fluctuations of a liquid–liquid interface for a wide range of shear rates. Although the statistics is Gaussian at low shear, we observe a transition to a nonlinear phenomenology above a critical shear rate. In particular, we show that statistical properties at high forcing share striking similarities with Burgers turbulence. An energy criterion allows us to predict the onset of non-Gaussian statistics. It also provides a simple explanation for the development of shock singularities through the exchange of kinetic energy from regions with positive to negative gradients in the shear direction.
Interface shear and pressure characteristics of wheelchair seat cushions
Directory of Open Access Journals (Sweden)
Jonathan S. Akins
2011-03-01
Full Text Available Pressure ulcer incidence rates have remained constant despite advances in support surface technology. Interface shear stress is recognized as a risk factor for pressure ulcer development and is the focus of many shear reduction technologies incorporated into wheelchair cushions; however, shear reduction has not been quantified in the literature. We evaluated 21 commercial wheelchair seat cushions using a new methodology developed to quantify interface shear stress, interface pressure, and horizontal stiffness. Interface shear stress increased significantly with applied horizontal indenter displacement, while no significant difference was found for interface pressure. Material of construction resulted in significant differences in interface shear stress, interface pressure, and horizontal stiffness. This study shows that the existing International Organization for Standardization (ISO 16840-2 horizontal stiffness measure provides similar information to the new horizontal stiffness measure. The lack of a relationship between interface shear stress and the overall horizontal stiffness measure, however, suggests that a pressure and shear force sensor should be used with the ISO 16840-2 horizontal stiffness measure to fully quantify a cushion's ability to reduce interface shear stress at the patient's bony prominences.
Shear and friction between carbon nanotubes in bundles and yarns.
Paci, Jeffrey T; Furmanchuk, Al'ona; Espinosa, Horacio D; Schatz, George C
2014-11-12
We perform a detailed density functional theory assessment of the factors that determine shear interactions between carbon nanotubes (CNTs) within bundles and in related CNT and graphene structures including yarns, providing an explanation for the shear force measured in recent experiments (Filleter, T. etal. Nano Lett. 2012, 12, 73). The potential energy barriers separating AB stacked structures are found to be irrelevant to the shear analysis for bundles and yarns due to turbostratic stacking, and as a result, the tube-tube shear strength for pristine CNTs is estimated to be yarns is discussed, providing general guidelines for the manufacture of strong yarns composed of CNTs. PMID:25279773
Diagonal Cracking and Shear Strength of Reinforced Concrete Beams
DEFF Research Database (Denmark)
Zhang, Jin-Ping
1997-01-01
The shear failure of non-shear-reinforced concrete beams with normal shear span ratios is observed to be governed in general by the formation of a critical diagonal crack. Under the hypothesis that the cracking of concrete introduces potential yield lines which may be more dangerous than the ones found by the usual plastic theory, a physical explanation is given for this phenomenon and a way to estimate the shear capacity of reinforced concrete beams, based on the theory of plasticity, is described. The theoretical calculations are shown to be in fairly good agreement with test results from a large number of experiments carried out by previous investigators.
Shear-induced structures in concentrated surfactant micellar phases
International Nuclear Information System (INIS)
Constant and oscillatory Couette shear flow have been used in combination with small-angle neutron scattering to observe the shear-induced ordering in concentrated surfactant micellar phases. For the lamellar phase of hexaethylene glycol monohexadecyl ether, C16E6, two distinct lamellae orientations have been identified. At low shear gradients the lamellae are ordered parallel to the flow-vorticity plane, whereas at higher shear gradients the lamellae order parallel to the flow-shear gradient plane, corresponding to a rotation through 90 of the axis of orientation. At intermediate values of constant shear and for oscillatory shear, both lamellae orientations are simultaneously observed for the first time in a surfactant lamellar phase. For the lamellar phase, a dispersion of the binary surfactant mixtures of dioleyl cationic and 2-ethyl hexaglycerol monoether surfactants, a high degree of alignment, in the direction parallel to the flow-vorticity plane, is observed at zero and low shear. With time, during the application of a shear gradient of 25 s-1, the lamellar phase transforms to a highly ordered solution of monodisperse multi-lamellar vesicles. (orig.)
Strain localization across main continental strike-slip shear zones
Boutonnet, E.; Leloup, P.; Rozel, A.
2011-12-01
Whether deformation within the deep continental crust is fundamentally concentrated in narrow shear zones or distributed in wide zones stays a major controversy of the earth sciences. This is in part because direct measurements of ductile shear or strain rate are difficult, especially when deformation is intense as it is the case in ductile shear zones. The QPSRM (quartz paleo strain rates metry) method allows indirect measurements of strain rates in natural rocks, using shear stress, an estimation of the temperature of deformation, and assuming a flow law. This method has been recently calibrated for ductile continental shear zones conditions, giving the users the best power flow law/ piezometer combination to calculate accurate local strain rates. By comparing the local strain rates with the equivalent global strain rates, measured by dividing the shear rates (mm/yr) by the shear zone width, we estimated the amount of strain localization across ductile shear zones. We applied this method to two major shear zones located in the India-Asia collision zone: the Ailao Shan Red River shear zone (ASRR, SE Asia) and the Karakorum shear zone (Ksz, SW Tibet). We used the Hirth et al. (2001) flow law and the Twiss (1977) piezometer. Within the ASRR, a gradient of strain rates is observed between the shear zone border (5.4 x10-15 s-1) and the shear zone center (3.6 x10-12 s-1). The equivalent global strain rates range between 8.0 x10-15 and 1.7 x10-13 s-1, assuming a shear rate of ~1 cm/yr and a homogenous deformation across the ~15 km-large shear zone. We interpret the local strain rates, which are higher than the global strain rates, as strain localization. The strain localization in the core of the ASRR shear zone had been observed by field studies, and also predicted by numerical models. This study brings a measurement of this strain localization. Within the Ksz, the equivalent shear rate is 4.4 x10-14 s-1, assuming a shear rate of ~11 mm/yr and a homogenous deformation across the 8 km-large shear zone. The local strain rates measured inside the two mylonitic strands of the fault zone are higher than the reference value (6.7 x10-14 s-1 to 11.3 x10-14 s-1). Contrary to that, the local strain rates measured in the exhumed core of the shear zone where deformation is weak are lower than de reference value (6.5 x10-15 s-1). We made 1-D numerical models of the Ksz with the Tangtse (India) region geometry, in order to understand the causes of the strain localization. We calculated the temperature and the strain rates profiles across the 8-km width shear zone during shearing. Two main parameters were tested: (1) the heat created by shear heating and advected by granites emplacement, and (2) the rheology contrast in a heterogeneous crust. The first conclusions are that deformation localized in zones where the rocks are less viscous, and that granites emplacement does not modify the local strain rates for a long-standing.
Directory of Open Access Journals (Sweden)
María C. Miquel
2009-01-01
Full Text Available The objective of this paper was to determine the association of a SNP in the µ-calpain gene at position 316 with growth and quality of meat traits of steers grown on pasture. Fifty-nine Brangus and 20 Angus steers were genotyped for CAPN1 316. Warner Bratzler shear force was measured in l. lumborum samples after a 7-day aging period. A multivariate analysis of variance was performed, including shear force (WBSF, final weight (FW, average daily gain (ADG, backfat thickness (BFT, average monthly fat thickness gain (AMFTG, rib-eye area (REA, and beef rib-eye depth (RED as dependent variables. The CAPN1 316 genotype was statistically significant. Univariate analyses were done with these variables. The marker genotype was statistically significant (p < 0.05 for WBSF (kg: CC: 4.41 ± 0.57; CG: 5.58 ± 0.20; GG: 6.29 ± 0.18, FW (kg: CC: 360.23 ± 14.71; CG: 381.34 ± 5.26; GG: 399.23 ± 4.68, and ADG (kg/d: CC: 0.675 ± 0.046; CG: 0.705 ± 0.016; GG: 0.765 ± 0.014 Shear force, final weight and average daily gain were significantly different according to the CAPN1 316 marker genotypes. The marker genotype was statistically significant in the multivariate analysis (p = 0.001. The first characteristic root explained 89% of the differences among genotypes. WBSF, FW and ADG were the most important traits in the first vector, indicating that animals with the marker genotype for lowest WBSF also have the lowest FW and ADG.
Buckley, Mark R; Bonassar, Lawrence J; Cohen, Itai
2013-03-01
Though remarkably robust, articular cartilage becomes susceptible to damage at high loading rates, particularly under shear. While several studies have measured the local static and steady-state shear properties of cartilage, it is the local viscoelastic properties that determine the tissue's ability to withstand physiological loading regimens. However, measuring local viscoelastic properties requires overcoming technical challenges that include resolving strain fields in both space and time and accurately calculating their phase offsets. This study combined recently developed high-speed confocal imaging techniques with three approaches for analyzing time- and location-dependent mechanical data to measure the depth-dependent dynamic modulus and phase angles of articular cartilage. For sinusoidal shear at frequencies f = 0.01 to 1 Hz with no strain offset, the dynamic shear modulus |G*| and phase angle ? reached their minimum and maximum values (respectively) approximately 100 ?m below the articular surface, resulting in a profound focusing of energy dissipation in this narrow band of tissue that increased with frequency. This region, known as the transitional zone, was previously thought to simply connect surface and deeper tissue regions. Within 250 ?m of the articular surface, |G*| increased from 0.32 ± 0.08 to 0.42 ± 0.08 MPa across the five frequencies tested, while ? decreased from 12 deg ± 1 deg to 9.1 deg ± 0.5 deg. Deeper into the tissue, |G*| increased from 1.5 ± 0.4 MPa to 2.1 ± 0.6 MPa and ? decreased from 13 deg ± 1 deg to 5.5 deg ± 0.2 deg. Viscoelastic properties were also strain-dependent, with localized energy dissipation suppressed at higher shear strain offsets. These results suggest a critical role for the transitional zone in dissipating energy, representing a possible shift in our understanding of cartilage mechanical function. Further, they give insight into how focal degeneration and mechanical trauma could lead to sustained damage in this tissue. PMID:24231813
Xu, Dingping; Cui, Yu-jun; Feng, Xiating; Jiang, Yali; Huang, Ke
2012-01-01
In order to evaluate the overall stability of the underground powerhouse at the future Baihetan hydropower station in China, the shear strength of a weak intercalation soil in the host rock has been investigated by carrying out in-situ direct shear and laboratory shear tests. A comparative study was performed based on the two testing results. It has been observed that both tests show elastic perfect-plastic behaviour. A significant heterogeneity of the samples has been identified under both l...
Bierwage, Andreas; Yu, Qingquan; Günter, Sibylle
2007-01-01
The effect of a narrow sub-Alfvenic shear flow layer near the minimum q_min of the tokamak safety factor profile in a configuration with reversed central shear is analyzed. Sufficiently strong velocity shear gives rise to a broad spectrum of fast growing Kelvin-Helmholtz (KH)-like ideal magnetohydrodynamic (MHD) modes with dominant mode numbers m,n ~ 10. Nonlinear simulations with finite resistivity show magnetic reconnection near ripples caused by KH-like vortices, the form...
Shear viscosity coefficient from microscopic models
International Nuclear Information System (INIS)
The transport coefficient of shear viscosity is studied for a hadron matter through microscopic transport model, the ultrarelativistic quantum molecular dynamics (UrQMD), using the Green-Kubo formulas. Molecular-dynamical simulations are performed for a system of light mesons in a box with periodic boundary conditions. Starting from an initial state composed of ?,?,?,?,? with a uniform phase-space distribution, the evolution takes place through elastic collisions, production, and annihilation. The system approaches a stationary state of mesons and their resonances, which is characterized by common temperature. After equilibration, thermodynamic quantities such as the energy density, particle density, and pressure are calculated. From such an equilibrated state the shear viscosity coefficient is calculated from the fluctuations of stress tensor around equilibrium using Green-Kubo relations. We do our simulations here at zero net baryon density so that the equilibration times depend on the energy density. We do not include hadron strings as degrees of freedom so as to maintain detailed balance. Hence we do not get the saturation of temperature but this leads to longer equilibration times
DSMC Simulations of Transiently Decaying Shear Flow
Torczynski, J. R.; Gallis, M. A.; Rader, D. J.
2006-11-01
The accuracy of the Direct Simulation Monte Carlo (DSMC) method is investigated for simulating the transient decay of a shear flow between two parallel specular walls. In the continuum limit, the exact solution is determined numerically from the Navier-Stokes equations, and an approximate closed-form solution is determined for linear isothermal flow (i.e., small shear stress). DSMC simulations are performed using hard-sphere argon from free-molecular to continuum conditions. Initially, the tangential velocity component varies spatially according to one half-cycle of a cosine wave. The velocity amplitude is low enough to ensure that the flow remains linear and isothermal. Simulations are performed with various cell sizes and time steps while using an extremely large number of molecules (10 million). For each continuum case, the effective viscosity is determined by matching the closed-form solution for the velocity profile to the simulation results. The Chapman-Enskog value of the viscosity is obtained to within 0.3% in the resolved limit, and the departures at finite spatial and temporal resolution are in reasonable agreement with Green-Kubo theory. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.
Amorphous Systems in Athermal, Quasistatic Shear
Maloney, C E; Maloney, Craig E.; Lema\\^{\\i}tre, Ana\\"el
2005-01-01
We present results on a series of 2D atomistic computer simulations of amorphous systems subjected to simple shear in the athermal, quasistatic limit. The athermal quasistatic trajectories are shown to separate into smooth, reversible elastic branches which are intermittently broken by discrete catastrophic plastic events. The onset of a typical plastic event is studied with precision, and it is shown that the mode of the system which is responsible for the loss of stability has structure in real space which is consistent with a quadrupolar source acting on an elastic matrix. The plastic events themselves are shown to be composed of localized shear transformations which organize into lines of slip which span the length of the simulation cell, and a mechanism for the organization is discussed. Although within a single event there are strong spatial correlations in the deformation, we find little correlation from one event to the next, and these transient lines of slip are not to be confounded with the persiste...
Testing Modified Gravity with Cosmic Shear
Harnois-Déraps, Joachim; Valageas, Patrick; van Waerbeke, Ludovic; Brax, Philippe; Coles, Peter; Rizzo, Luca
2015-01-01
We use the cosmic shear data from the Canada-France-Hawaii Telescope Lensing Survey to place constraints on $f(R)$ and {\\it Generalized Dilaton} models of modified gravity. This is highly complimentary to other probes since the constraints mainly come from the non-linear scales: maximal deviations with respects to the General-Relativity + $\\Lambda$CDM scenario occurs at $k\\sim1 h \\mbox{Mpc}^{-1}$. At these scales, it becomes necessary to account for known degeneracies with baryon feedback and massive neutrinos, hence we place constraints jointly on these three physical effects. To achieve this, we formulate these modified gravity theories within a common tomographic parameterization, we compute their impact on the clustering properties relative to a GR universe, and propagate the observed modifications into the weak lensing $\\xi_{\\pm}$ quantity. Confronted against the cosmic shear data, we reject the $f(R)$ $\\{ |f_{R_0}|=10^{-4}, n=1\\}$ model with more than 99.9% confidence interval (CI) when assuming a $\\Lam...
Coupling effects in multiphase free shear flows
International Nuclear Information System (INIS)
The primary goal of this research program is to examine the effects of two-way multiphase coupling on the development of organized vortex structures in free shear flows and the resultant multiphase dispersion. Previous research studies have determined that one-way coupled particle dispersion in free shear flows is strongly dependent on the vortex structures present in these flows and their interactions as well as the ratio of the particle aerodynamic response time to the time scale of the dominant vortex structures. Current research efforts are directed towards exploring the effects that two-way momentum, mass and energy coupling have on the multiphase dispersion processes previously uncovered. These efforts involve analytical, numerical and experimental investigations. Recent analytical and numerical results indicate that momentum coupling effects can significantly alter the global stability and potentially the large scale features of the multiphase flow field. These multiphase coupling effects may have significant importance with regard to predicting the performance of many energy conversion systems
Developing accurate quantified speckle shearing data
Wan Abdullah, W. S.; Petzing, Jon N.; Tyrer, John R.
1999-08-01
Electronic Speckle Pattern Shearing Interferometry (ESPSI) is becoming a common tool for the qualitative analysis of material defects in the aerospace and marine industries. Current trends in the development of this optical metrology nondestructive testing (NDT) technique is the introduction of quantitative analysis, which attempts to detail the defects examined and identified by the ESPSI systems. Commercial systems use divergent laser illumination, this being a design feature imposed by the typically large sizes of objects being examined, which negates the use of collimated optics. Furthermore, commercial systems are being applied to complex surfaces which distort the understanding of the instrumentation results. The growing commercial demand for quantitative out-of-lane and in-plane ESPSI for NDT is determining the quality of optical and analysis instrument. However very little attention is currently being paid to understanding, quantifying and compensating for the numerous error sources which are a function of ESPSI interferometers. This paper presents work which has been carried out on the measurement accuracy due to the divergence of the illumination wavefront and associated with the magnitude of lateral shearing function. The error is measured by comparing measurements using divergent (curvature) illumination with respect to collimated illumination. Results show that the error is increased by approximately a power factor as the distance from the illumination source to the object surface decreases.
Toroidal Flow Shear Driven turbulence and Transport
Wang, Weixing; Ethier, S.; Hinton, F. L.; Hahm, T. S.; Tang, W. M.
2012-10-01
New results from global nonlinear gyrokinetic simulations with the GTS code show that strong flow shear can drive a negative compressibility mode [1-3] unstable in tokamak geometry in some experimentally relevant parameter regimes. The modes reside in a low-k range, similar to that of ITG mode, with smaller but almost constant growth rate over a wider k? range, while the mode frequency increases strongly with k?. More interestingly, the flow shear modes show significantly finite k//, unlike ITG and TEM. The nonlinear energy transfer to longer wavelength via toroidal mode coupling and corresponding strong zonal flow and geodestic acoustic mode (GAM) generation are shown to play a critical role in the nonlinear saturation of the instability. The associated turbulence fluctuations can produce significant momentum and energy transport, including an intrinsic torque in the co-current direction. Remarkably, strong ``resonance'' in the fluctuations and associated transport peaks at the lowest order rational surfaces with integer q-number (rather than fractional), consistent with theoretical calculation. As a consequence, local ``corrugations'' are generated in all plasma profiles (temperatures, density and toroidal rotation), potentially impacting transport barrier formation near the rational surface. Discussions on flow optimization for minimizing plasma transport will be reported.[4pt] [1] N. Mattor and P. H. Diamond, Phys. Fluids 31, 1180 (1988).[0pt] [2] P. J. Catto et al., Phys. Fluids 16, 1719 (1973).[0pt] [3] M. Artun and W. M. Tang, Phys. Fluids B4, 1102 (1992).
Plasticity Approach to HSC Shear Wall Design
DEFF Research Database (Denmark)
Liu, Lunying; Nielsen, Mogens Peter
1998-01-01
The paper describes a simple theory for determining the ultimate strength of shear walls. It is based on application of the theory of perfectly plastic materials. When applied to concrete the theoretical solutions must be modified by inserting into the solutions a reduced compressive strength of concrete. The reduced strength is named the effective strength. The paper describes simple lower bound solutions. They consist of pure strut action or strut action combined with diagonal compression fields outside the struts. Near moment maximum and near supports the stress fields are modified to save longitudinal reinforcement. Upper bound solutions are summarized briefly. The lower bound method has been compared with around 200 tests taken from the literature. With very simple formulas for the effectiveness factor, excellent agreement has been obtained. The testscover concrete compressive strengths up to 140 MPa and reinforcement yield strengths up to 1420 MPa. The work was carried out as a Ph.D. study by the first author, the second author supervising the study.Keywords: shear wall, plasticity, strut and tie, load-carrying capacity, concrete, reinforcement.
An Implementation of Bayesian Lensing Shear Measurement
Sheldon, Erin S
2014-01-01
The Bayesian gravitational shear estimation algorithm developed by Bernstein and Armstrong (2014) can potentially be used to overcome noise bias and recover shear using very low signal-to-noise ratio (S/N) galaxy images. In that work the authors confirmed the method is sufficiently unbiased for planned surveys (fractional error less than 2 x 10^{-3}) in a simplified demonstration, but no test was performed on images. Here I present a full implementation for fitting models to galaxy images, including the effects of a point spread function (PSF) and pixelization. I tested the implementation using simulated galaxy images modeled as Sersic profiles with n=1 (exponential) and n=4 (De Vaucouleurs'), convolved with a PSF and a flat pixel response function. I used a round Gaussian model for the PSF to avoid potential PSF-fitting errors. I simulated galaxies with mean observed, post-PSF full-width at half maximum equal to approximately 1.2 times that of the PSF, with log-normal scatter. I also drew fluxes from a log-n...
Zhu, Jiang; Qu, Yueqiao; Ma, Teng; Li, Rui; Du, Yongzhao; Huang, Shenghai; Shung, K Kirk; Zhou, Qifa; Chen, Zhongping
2015-05-01
We report on a novel acoustic radiation force orthogonal excitation optical coherence elastography (ARFOE-OCE) technique for imaging shear wave and quantifying shear modulus under orthogonal acoustic radiation force (ARF) excitation using the optical coherence tomography (OCT) Doppler variance method. The ARF perpendicular to the OCT beam is produced by a remote ultrasonic transducer. A shear wave induced by ARF excitation propagates parallel to the OCT beam. The OCT Doppler variance method, which is sensitive to the transverse vibration, is used to measure the ARF-induced vibration. For analysis of the shear modulus, the Doppler variance method is utilized to visualize shear wave propagation instead of Doppler OCT method, and the propagation velocity of the shear wave is measured at different depths of one location with the M scan. In order to quantify shear modulus beyond the OCT imaging depth, we move ARF to a deeper layer at a known step and measure the time delay of the shear wave propagating to the same OCT imaging depth. We also quantitatively map the shear modulus of a cross-section in a tissue-equivalent phantom after employing the B scan. PMID:25927794
Evolution of twist-shear and dip-shear during X-class flare of 13 December 2006: Hinode observations
Gosain, Sanjay; Venkatakrishnan, P.
2010-01-01
The non-potentiality (NP) of the solar magnetic fields is measured traditionally in terms of magnetic shear angle i.e., the angle between observed and potential field azimuth. Here, we introduce another measure of shear that has not been studied earlier in solar active regions, i.e. the one that is associated with the inclination angle of the magnetic field. This form of shear, which we call as the "dip-shear", can be calculated by taking the difference between the observed ...
Shear degradation in fiber reinforced laminates due to matrix damage
Salavatian, Mohammedmahdi
The objective of this study was to develop and implement a shear modulus degradation model to improve the failure analysis of the fiber reinforced composite structures. Matrix damage, involving transverse and shear cracks, is a common failure mode for composite structures, yet little is known concerning their interaction. To understand the material behavior after matrix failure, the nonlinear response of the composite laminate was studied using pressure vessels made from a [+/-o] bias orientation, which tend to exhibit a matrix dominated failure. The result of this work showed laminate matrix hardening in shear and softening in the transverse direction. A modified Iosipescu coupon was proposed to study the evolution of shear and transverse damage and their mutual effects. The proposed method showed good agreement with tubular results and has advantages of simplified specimen fabrication using standard test fixtures. The proposed method was extended by introducing a novel experimental technique to study the shear degradation model under biaxial loading. Experimental results of the transverse modulus reduction were in good agreement with material degradation models, while the predicted shear modulus reduction was higher than experiment. The discrepancy between available models and observations was due to the presence of a traction between the crack surfaces. Accordingly, a closed form solution was proposed for the shear stress-strain field of a cracked laminate by replacing the cracks with cohesive zones. The constitutive equations of the crack laminate were derived including the effects of internal tractions and transverse stress on the shear modulus. The proposed analytical model was shown to be the most comprehensive model for shear modulus degradation reduction of the fiber reinforced laminates. A numerical implementation of the shear degradation model was done using continuum damage mechanics. Through this work it was shown the common assumption of a linear relation between matrix damage variables do not sufficiently describe shear response. Therefore, a modified damage model for matrix failure was developed and implemented in ABAQUS using a UMAT subroutine.
Speed and Direction Shear in the Stable Nocturnal Boundary Layer
Energy Technology Data Exchange (ETDEWEB)
Walter, K.; Weiss, C. C.; Swift, A. H. P.; Chapman, J.; Kelley, N. D.
2009-02-01
Numerous previous works have shown that vertical shear in wind speed and wind direction exist in the atmospheric boundary layer. In this work, meteorological forcing mechanisms, such as the Ekman spiral, thermal wind, and inertial oscillation, are discussed as likely drivers of such shears in the statically stable environment. Since the inertial oscillation, the Ekman spiral, and statically stable conditions are independent of geography, potentially significant magnitudes of speed and direction shear are hypothesized to occur to some extent at any inland site in the world. The frequency of occurrence of non-trivial magnitudes of speed and direction shear are analyzed from observation platforms in Lubbock, Texas and Goodland, Indiana. On average, the correlation between speed and direction shear magnitudes and static atmospheric stability are found to be very high. Moreover, large magnitude speed and direction shears are observed in conditions with relatively high hub-height wind speeds. The effects of speed and direction shear on wind turbine power performance are tested by incorporating a simple steady direction shear profile into the fatigue analysis structures and turbulence simulation code from the National Renewable Energy Laboratory. In general, the effect on turbine power production varies with the magnitude of speed and direction shear across the turbine rotor, with the majority of simulated conditions exhibiting power loss relative to a zero shear baseline. When coupled with observational data, the observed power gain is calculated to be as great as 0.5% and depletion as great as 3% relative to a no shear baseline. The average annual power change at Lubbock is estimated to be -0.5%
Distribution of Magnetic Shear Angle in an Emerging Flux Region
Gosain, Sanjay
2010-01-01
We study the distribution of magnetic shear in an emerging flux region using the high-resolution Hinode/SOT SP observations. The distribution of mean magnetic shear angle across the active region shows large values near region of flux emergence i.e., in the middle of existing bipolar region and decreases while approaching the periphery of the active region.
[Influence of fluid shear stress on cultured vascular endothelial cells].
Takakuwa, O
1990-03-01
Vascular endothelial cells modulate their functions in response to hemodynamic forces such as fluid shear stress. In the present study, we applied shear to cultured bovine aortic endothelial cells (EC) by using a saecially designed apparatus and examined the effects of their homogenate and conditioned medium on such EC and smooth muscle cell (SMC) functions as adhesion, growth, migration or collagen synthesis. Cultured bovine aortic SMC were stimulated to adhere to wells and grow in the presence of EC conditioned medium. This conditioned medium had no effect on EC adhesion and growth. The activities of stimulating SMC adhesion and growth were almost the same in both EC conditioned medium obtained from static cultures and shear-loaded cultures. Studies with filters in a modified Boyden chamber showed that shear-loaded EC homogenate yielded stimulated SMC migration. Also shear-loaded EC cell layer contained increased amount of collagen compared with static EC cell layer. These observations indicate that:(a) EC secrets the substances which stimulate SMC adhesion and growth, but these functions are not affected by shear stress application, (b) EC produces SMC migration stimulators in response to shear stress, and (c) shear stress can enhance EC collagen synthesis. These results are relevant to EC response to hemodynamic forces and its role in the localization of atherosclerotic lesions in vivo. PMID:2365276
Effect of linear shear flow on interchange modes
International Nuclear Information System (INIS)
Effect of the linear shear flow on linear interchange modes in incompressible neutral fluid, and linear two-dimensional electromagnetic interchange instabilities in incompressible plasmas are investigated. Although the transient growth may occur in a short period, background shear flow overcomes the interchange instability and makes it damped away in a long term due to phase mixing. (author)
Conductivity measurements in a shear-banding wormlike micellar system
Photinos, Panos J.; López-González, M. R.; Hoven, Corey V.; Callaghan, Paul T.
2010-07-01
Shear banding in the cetylpyridinium chloride/sodium salicylate micellar system is investigated using electrical conductivity measurements parallel to the velocity and parallel to the vorticity in a cylindrical Couette cell. The measurements show that the conductivity parallel to the velocity (vorticity) increases (decreases) monotonically with applied shear rate. The shear-induced anisotropy is over one order of magnitude lower than the anisotropy of the Nc nematic phase. The steady-state conductivity measurements indicate that the anisotropy of the shear induced low-viscosity (high shear rate) phase is not significantly larger than the anisotropy of the high viscosity (low shear rate) phase. We estimate that the micelles in the shear induced low viscosity band are relatively short, with a characteristic length to diameter ratio of 5-15. The relaxation behavior following the onset of shear is markedly different above and below the first critical value ??1 , in agreement with results obtained by other methods. The transient measurements show that the overall anisotropy of the sample decreases as the steady state is approached, i.e., the micellar length/the degree of order decrease.
A refined shear deformation theory for flexure of thick beams
Scientific Electronic Library Online (English)
Yuwaraj M., Ghugal; Rajneesh, Sharma.
2011-06-01
Full Text Available A Hyperbolic Shear Deformation Theory (HPSDT) taking into account transverse shear deformation effects, is used for the static flexure analysis of thick isotropic beams. The displacement field of the theory contains two variables. The hyperbolic sine function is used in the displacement field in ter [...] ms of thickness coordinate to represent shear deformation. The transverse shear stress can be obtained directly from the use of constitutive relations, satisfying the shear stress-free boundary conditions at top and bottom of the beam. Hence, the theory obviates the need of shear correction factor. Governing differential equations and boundary conditions of the theory are obtained using the principle of virtual work. General solutions of thick isotropic simply supported, cantilever and fixed beams subjected to uniformly distributed and concentrated loads are obtained. Expressions for transverse displacement of beams are obtained and contribution due to shear deformation to the maximum transverse displacement is investigated. The results of the present theory are compared with those of other refined shear deformation theories of beam to verify the accuracy of the theory.
Shear strain anomalies in composite beam specimens by moire interferometry
Post, D.; Czarnek, R.; Joh, D.; Wood, J. D.
1985-01-01
Experimental analyses were performed for determination of in-plane deformations and shear strains in unidirectional and quasi-isotropic graphite-epoxy beams. Forty-eight-ply beams were subjected to five-point and three-point flexure. Whole-field measurements were recorded at load levels from about 20 percent to more than 90 percent of failure loads. Contour maps of U and W displacement fields were obtained by moire interferometry, using reference gratings of 2400 lines/mm. Clearly defined fringes with fringe orders exceeding 1000 were obtained. Whole-field contour maps of shear strains were obtained. Various anomalous effects were detected in the displacement fields. Their analysis indicated excess shear strains in resin-rich zones in regions of shear tractions; free-edge shear strains in quasi-isotropic specimens in regions of normal stresses, and shear stresses associated with cyclic shear compliances of quasi-isotropic laminates in regions of shear tractions. Their contributions could occur independently or in superposition. Qualitative analyses addressed questions of the effect of specimen overhang, nonlinearity, and characteristics of five-point and three-point flexure tests.
Shear band formation in sub-microcrystalline Ni
Energy Technology Data Exchange (ETDEWEB)
Beausir, Benoit; Hollang, Lutz; Skrotzki, Werner [Institut fuer Strukturphysik, Technische Universitaet Dresden, 01062 Dresden (Germany); Dey, Suhash Ranjan [Department of Materials Science and Engineering, Indian Institute of Technology Hyderabad, Ordnance Factory Estate, Yeddumailaram-502205, Andhra Pradesh (India); Hieckmann, Ellen [Institut fuer Angewandte Physik, Technische Universitaet Dresden, 01062 Dresden (Germany)
2011-07-01
The stability of sub-microcrystalline nickel produced by pulsed electrodeposition without any additives was investigated during cyclic deformation at very high plastic strain amplitude of 1% at room temperature. The initial microstructure having an average grain size of 160 nm in the growth plane and a weak <110> fibre texture along the growth direction undergoes considerable grain growth during cyclic loading without significant changes in texture. After a certain number of loading cycles the specimen suddenly developed a single macro shear band. The shear band appeared in the tensile half cycle under 45 to the loading axis and acts as crack starter. Investigations in the scanning electron microscope using electron backscatter diffraction revealed that the main macro shear band consists of relaxed grains elongated along the shear plane displaying a texture induced by shear. The texture in the shear band was reproduced with the viscoplastic self-consistent polycrystal model using {l_brace}111{r_brace}<110> slip systems. Detailed investigations of the surrounding of the macro shear band reveal the existence of a large number of regularly spaced micro shear bands.
Micromechanics of sea ice gouge in shear zones
Sammonds, Peter; Scourfield, Sally; Lishman, Ben
2015-04-01
The deformation of sea ice is a key control on the Arctic Ocean dynamics. Shear displacement on all scales is an important deformation process in the sea cover. Shear deformation is a dominant mechanism from the scale of basin-scale shear lineaments, through floe-floe interaction and block sliding in ice ridges through to the micro-scale mechanics. Shear deformation will not only depend on the speed of movement of ice surfaces but also the degree that the surfaces have bonded during thermal consolidation and compaction. Recent observations made during fieldwork in the Barents Sea show that shear produces a gouge similar to a fault gouge in a shear zone in the crust. A range of sizes of gouge are exhibited. The consolidation of these fragments has a profound influence on the shear strength and the rate of the processes involved. We review experimental results in sea ice mechanics from mid-scale experiments, conducted in the Hamburg model ship ice tank, simulating sea ice floe motion and interaction and compare these with laboratory experiments on ice friction done in direct shear, and upscale to field measurement of sea ice friction and gouge deformation made during experiments off Svalbard. We find that consolidation, fragmentation and bridging play important roles in the overall dynamics and fit the model of Sammis and Ben-Zion, developed for understanding the micro-mechanics of rock fault gouge, to the sea ice problem.
E x B shearing rate in quasi-symmetric plasmas
International Nuclear Information System (INIS)
The suppression of turbulence by the E x B shear is studied in systems with quasi-symmetry using the nonlinear analysis of eddy decorrelation previously utilized in finite aspect ratio tokamak plasmas. The analytically derived E x B shearing rate which contains the relevant geometric dependence can be used for quantitative assessment of the fluctuation suppression in stellarators with quasi-symmetry
Development of shear bands in amorphous-crystalline metallic alloys
International Nuclear Information System (INIS)
A theoretical study is made into conditions of shear band evolution in amorphous-crystalline alloys with various morphological types of structural constituents. The condition of shear band evolution in thin amorphous alloys in the interior of the crystalline matrix is obtained. It is shown that a scale effect exists which manifests itself in suppression of the process of localized plastic flow with amorphous alloy thickness decreasing down to the limit. The analysis of the condition for shear band evolution in an amorphous alloy with nanocrystalline inclusions is accomplished. The relationship of a critical stress of shear band evolution to a volume fraction of disperse crystal inclusions is obtained. A consideration is also given to the evolution of shear bands in the material containing amorphous and crystalline areas of micro meter size. For the alloy with the structure of this type conditions for propagation of localized flows by a relay race type mechanism are determined
The DES Science Verification Weak Lensing Shear Catalogs
Jarvis, M; Zuntz, J; Kacprzak, T; Bridle, S L; Amara, A; Armstrong, R; Becker, M R; Bernstein, G M; Bonnett, C; Chang, C; Das, R; Dietrich, J P; Drlica-Wagner, A; Eifler, T F; Gangkofner, C; Gruen, D; Hirsch, M; Huff, E M; Jain, B; Kent, S; MacCrann, N; Melchior, P; Plazas, A A; Refregier, A; Rowe, B; Rykoff, E S; Samuroff, S; Sánchez, C; Suchyta, E; Troxel, M A; Vikram, V; Abbott, T; Abdalla, F B; Allam, S; Annis, J; Benoit-Lévy, A; Bertin, E; Brooks, D; Buckley-Geer, E; Burke, D L; Capozzi, D; Rosell, A Carnero; Kind, M Carrasco; Carretero, J; Castander, F J; Crocce, M; Cunha, C E; D'Andrea, C B; da Costa, L N; DePoy, D L; Desai, S; Diehl, H T; Doel, P; Neto, A Fausti; Flaugher, B; Fosalba, P; Frieman, J; Gaztanaga, E; Gerdes, D W; Gruendl, R A; Gutierrez, G; Honscheid, K; James, D J; Kuehn, K; Kuropatkin, N; Lahav, O; Li, T S; Lima, M; March, M; Martini, P; Miquel, R; Mohr, J J; Neilsen, E; Nord, B; Ogando, R; Reil, K; Romer, A K; Roodman, A; Sako, M; Sanchez, E; Scarpine, V; Schubnell, M; Sevilla-Noarbe, I; Smith, R C; Soares-Santos, M; Sobreira, F; Swanson, M E C; Tarle, G; Thaler, J; Thomas, D; Walker, A R; Wechsler, R H
2015-01-01
We present weak lensing shear catalogs for 139 square degrees of data taken during the Science Verification (SV) time for the new Dark Energy Camera (DECam) being used for the Dark Energy Survey (DES). We describe our object selection, point spread function estimation and shear measurement procedures using two independent shear pipelines, IM3SHAPE and NGMIX, which produce catalogs of 2.12 million and 3.44 million galaxies respectively. We detail a set of null tests for the shear measurements and find that they pass the requirements for systematic errors at the level necessary for weak lensing science applications using the SV data. We also discuss some of the planned algorithmic improvements that will be necessary to produce sufficiently accurate shear catalogs for the full 5-year DES, which is expected to cover 5000 square degrees.
Dynamic pressure-shear loading of materials using anisotropic crystals
International Nuclear Information System (INIS)
An experimental technique is described which uses anisotropic crystals to generate dynamic pressure-shear loading in materials. The coupled longitudinal and shear motion generated upon planar impact of the anisotropic crystal can be transmitted into a specimen bonded to the rear surface of the crystal, and monitored using velocity interferometer techniques. Test results using y-cut quartz generators and x-cut quartz and y-cut quartz samples indicate that shear stresses up to 0.35 GPa can be transmitted across epoxy-bonded interfaces. The technique has been successfully used to detect a 0.2 GPa shear wave in 6061-T6 aluminum at 0.7 GPa longitudinal stress. The shear wave velocity profiles have an accuracy of +- 12%. The use of longer delay legs in the interferometer is suggested to improve the accuracy. Results obtained in this investigation are compared with numerical solutions obtained using the finite-difference wave propagation code TOODY
Velocity shear and low-frequency plasma instabilities
International Nuclear Information System (INIS)
The effects of transverse velocity shear on the low-frequency stability of a plasma are examined theoretically for a low-? resistive plasma in a uniform magnetic field. Cylindrical geometry is used and the velocity shear is introduced by a nonuniform E X B rotation. Both numerical and analytic methods are used. The principal analytic result is a dispersion relation for instabilities caused by a thin velocity shear layer. This dispersion relation describes the Q machine edge oscillation, which is identified either as a Kelvin-Helmholtz instability or as a velocity-shear analogue of the resistive drift wave, depending on the parallel wave-length. The numerical results show that properties of instabilities observed in several experiments agree reasonably well with theory. The effect of velocity shear on the drift instability is to make it into either a local or nonlocal type of normal mode. 24 refs., 9 figs
Shear viscosity for a moderately dense granular binary mixture
Garzó, V; Garzo, Vicente; Montanero, Jose Maria
2003-01-01
The shear viscosity for a moderately dense granular binary mixture of smooth hard spheres undergoing uniform shear flow is determined. The basis for the analysis is the Enskog kinetic equation, solved first analytically by the Chapman-Enskog method up to first order in the shear rate for unforced systems as well as for systems driven by a Gaussian thermostat. As in the elastic case, practical evaluation requires a Sonine polynomial approximation. In the leading order, we determine the shear viscosity in terms of the control parameters of the problem: solid fraction, composition, mass ratio, size ratio and restitution coefficients. Both kinetic and collisional transfer contributions to the shear viscosity are considered. To probe the accuracy of the Chapman-Enskog results, the Enskog equation is then numerically solved for systems driven by a Gaussian thermostat by means of an extension to dense gases of the well-known Direct Simulation Monte Carlo (DSMC) method for dilute gases. The comparison between theory ...
Impact of Vertical Wind Shear on Tropical Cyclone Rainfall
Cecil, Dan; Marchok, Tim
2014-01-01
While tropical cyclone rainfall has a large axisymmetric component, previous observational and theoretical studies have shown that environmental vertical wind shear leads to an asymmetric component of the vertical motion and precipitation fields. Composites consistently depict a precipitation enhancement downshear and also cyclonically downwind from the downshear direction. For consistence with much of the literature and with Northern Hemisphere observations, this is subsequently referred to as "Downshear-Left". Stronger shear magnitudes are associated with greater amplitude precipitation asymmetries. Recent work has reinforced the prior findings, and explored details of the response of the precipitation and kinematic fields to environmental vertical wind shear. Much of this research has focused on tropical cyclones away from land, to limit the influence of other processes that might distort the signal related to vertical wind shear. Recent evidence does suggest vertical wind shear can also play a major role in precipitation asymmetries during and after landfall.
Smoothing and roughening of slip surfaces in direct shear experiments
Sagy, Amir; Badt, Nir; Hatzor, Yossef H.
2015-04-01
Faults in the upper crust contain discrete slip surfaces which have absorbed a significant part of the shear displacement along them. Field measurements demonstrate that these surfaces are rough at all measurable scales and indicate that surfaces of relatively large-slip faults are statistically smoother than those of small-slip faults. However, post faulting and surface erosion process that might affect the geometry of outcrops cannot be discounted in such measurements. Here we present experimental results for the evolution of shear surface topography as function of slip distance and normal stress in direct shear experiments. A single prismatic fine grain limestone block is first fractured in tension mode using the four-point bending test methodology and then the fracture surface topography is scanned using a laser profilometer. We then shear the obtained tensile fracture surfaces in direct shear, ensuring the original fracture surfaces are in a perfectly matching configuration at the beginning of the shear test. First, shearing is conducted to distances varying from 5 to 15 mm under constant normal stress of 2MPa and a constant displacement rate of 0.05 mm/s using two closed-loop servo controlled hydraulic pistons, supplying normal and shear forces (Davidesko et al., 2014). In the tested configuration peak shear stress is typically attained after a shear displacement of about 2-3 mm, beyond which lower shear stress is required to continue shearing at the preset displacement rate of 0.05 mm/s as is typical for initially rough joints. Following some initial compression the interface begins to dilate and continues to do so until the end of the test. The sheared tensile fracture surface is then scanned again and the geometrical evolution, in term of RMS roughness and power spectral density (PSD) is analyzed. We show that shearing smooth the surface along all our measurements scales. The roughness ratio, measured by initial PSD / final PSD for each wavelength, increases as a function of slip amount. The roughness measured after slip can be fitted by a power-law similar to that of the initial tensile surface. In the next series of experiments a similar procedure is applied when the roughness evolution is measured as a function of increasing normal stress for a fixed displacement amount of 10 mm. While samples sheared under a constant normal stress of 5 MPa generated surface smoothing, shearing under normal stress of 7.5 MPa to 15 MPa exhibited surface roughening at the measured range of scales. We find that roughening is correlated with the attained peak shear stress values, stress drop (peak shear stress minus residual shear stress) and with wear accumulation, a novel measurement procedure of which is developed here. Analysis of the sheared samples shows that roughening is generated by sets of dense fractures that significantly damaged the sample in the immediate proximity to large asperities. This roughening is related to penetrative damage during transient wear in rough surfaces.
Shear induced phase transitions induced in edible fats
Mazzanti, Gianfranco; Welch, Sarah E.; Marangoni, Alejandro G.; Sirota, Eric B.; Idziak, Stefan H. J.
2003-03-01
The food industry crystallizes fats under different conditions of temperature and shear to obtain products with desired crystalline phases. Milk fat, palm oil, cocoa butter and chocolate were crystallized from the melt in a temperature controlled Couette cell. Synchrotron x-ray diffraction studies were conducted to examine the role of shear on the phase transitions seen in edible fats. The shear forces on the crystals induced acceleration of the alpha to beta-prime phase transition with increasing shear rate in milk fat and palm oil. The increase was slow at low shear rates and became very strong above 360 s-1. In cocoa butter the acceleration between beta-prime-III and beta-V phase transition increased until a maximum of at 360 s-1, and then decreased, showing competition between enhanced heat transfer and viscous heat generation.
Surface Shear Transformation Zones in Amorphous Solids
Cao, Penghui; Park, Harold S
2014-01-01
We perform a systematic study of the characteristics of shear transformation zones (STZs) that nucleate at free surfaces of two-dimensional amorphous solids subject to tensile loading using two different atomistic simulation methods, the standard athermal, quasistatic (AQ) approach and our recently developed self-learning metabasin escape (SLME) method to account for the finite temperature and strain-rate effects. In the AQ, or strain-driven limit, the nonaffine displacement fields of surface STZs decay exponentially away from their centers at similar decay rates as their bulk counterparts, though the direction of maximum nonaffine displacement is tilted away from the tensile axis due to surface effects. Using the SLME method at room temperature and at the high strain rates that are seen in classical molecular dynamics simulations, the characteristics for both bulk and surface STZs are found to be identical to those seen in the AQ simulations. However, using the SLME method at room temperature and experimenta...
Spatially localized solutions of shear flows
Gibson, J F
2013-01-01
We present several new spatially localized equilibrium and traveling-wave solutions of plane Couette and channel flows. The solutions exhibit strikingly concentrated regions of vorticity that are flanked on either side by high-speed streaks. For several traveling-wave solutions of channel flow, the concentrated vortex structures are confined to the near-wall region and form particularly isolated and elemental coherent structures in the near-wall region of shear flows. The solutions are constructed by a variety of methods: application of windowing functions to previously known spatially periodic solutions, continuation from plane Couette to channel flow conditions, and from initial guesses obtained from turbulent simulation data. We show how the symmetries of localized solutions derive from the symmetries of their periodic counterparts, analyze the exponential decay of their tails, examine the scale separation and scaling of their streamwise Fourier modes, and show that they develop critical layers for large R...
Cockpit display of hazardous wind shear information
Wanke, Craig; Hansman, R. John, Jr.
1990-01-01
Information on cockpit display of wind shear information is given in viewgraph form. Based on the current status of windshear sensors and candidate data dissemination systems, the near-term capabilities for windshear avoidance will most likely include: (1) Ground-based detection: TDWR (Terminal Doppler Weather Radar), LLWAS (Low-Level Windshear Alert System), Automated PIREPS; (2) Ground-Air datalinks: Air traffic control voice channels, Mode-S digital datalink, ACARS alphanumeric datalink. The possible datapaths for integration of these systems are illustrated in a diagram. In the future, airborne windshear detection systems such as lidars, passive IR detectors, or airborne Doppler radars may also become available. Possible future datalinks include satellite downlink and specialized en route weather channels.
Shearing box simulations of accretion disk winds
Moll, R
2012-01-01
The launching process of a magnetically driven outflow from an accretion disk is investigated in a local, shearing box model which allows a study of the feedback between accretion and angular momentum loss. The mass-flux instability found in previous linear analyses of this problem is recovered in a series of 2D (axisymmetric) simulations in the MRI-stable (high magnetic field strength) regime. At low field strengths that are still sufficient to suppress MRI, the instability develops on a short radial length scale and saturates at a modest amplitude. At high field strengths, a long-wavelength "clump" instability of large amplitude is observed, with growth times of a few orbits. As speculated before, the unstable connection between disk and outflow may be relevant for the time dependence observed in jet-producing disks. The success of the simulations is due in a large part to the implementation of an effective wave-transmitting upper boundary condition.
The phase mixing of shear Alfven waves
International Nuclear Information System (INIS)
The phase mixing of shear Alfven waves is discussed as a current sheets crossover phenomena by using the well-behaved time dependent solution of the Alfven wave equation. This method is a more direct approach than the initial value problem technique to find the collisionless damping time of the surface waves, which as it represents the coherency loss is argued to be the phase mixing time. The phase mixing time obtained by both the methods compares well. The direct method however, has an advantage that no particular profile for the magnetic field variation need to be chosen and secondly the phase mixing time and the time scale for which the resistivity effects become important can be expressed conveniently in terms of Alfven transit times before crossover. (author). 11 refs
Fluidization of Wet Granulates under Hydrodynamic Shear
Battiato, I
2012-01-01
We investigate the fluidization threshold of three-dimensional cohesive granulates under hydrodynamic shear forces exerted by a creeping ow. A continuum model of flow through porous media provides an analytical expression for the average drag force on a single grain. The balance equation for the forces and a force propagation model are then used to investigate the effects of porosity and packing structure on the stability of the pile. We obtain a closed-form expression for the fluidization threshold of a regular packing of mono-disperse frictionless cohesive spherical grains in a planar fracture. The compound effect of structural (packing orientation and porosity) and dynamical properties of the system on its stability is quantified.
A Mechanism for Propagative Shear Flow
Franklin, Scott
1997-03-01
In the Portevin-Le Chatelier effect a metal deforms through the initiation and propagation of shear fronts. While plausible reasons for front initiation exist, a satisfactory mechanism for front propagation --- which must predict important front characteristics such as width and velocity --- has not yet been found. Most theories have focused on diffusion of some sort but have been found to be either catastrophically unstable or incapable of selecting realistic front velocities. Here we propose a new phenomenological viewpoint which appears to capture all essential features of the Portevin-Le Chatelier effect and obtain a quantitative comparison with recent experiments. The mechanism for flow can be thought of as the creation of active dislocations which are ejected out into neighboring material. One prediction of our model is that deformation proceeds at constant stress rather than only with increasing stress. This prediction is confirmed by our experiments, together with predictions about the dependance of stress and front velocity on imposed strain-rate.
Relativistic r-modes and shear viscosity
Gualtieri, L; Miralles, J A; Ferrari, V
2006-01-01
We derive the relativistic equations for stellar perturbations, including in a consistent way shear viscosity in the stress-energy tensor, and we numerically integrate our equations in the case of large viscosity. We consider the slow rotation approximation, and we neglect the coupling between polar and axial perturbations. In our approach, the frequency and damping time of the emitted gravitational radiation are directly obtained. We find that, approaching the inviscid limit from the finite viscosity case, the continuous spectrum is regularized. Constant density stars, polytropic stars, and stars with realistic equations of state are considered. In the case of constant density stars and polytropic stars, our results for the viscous damping times agree, within a factor two, with the usual estimates obtained by using the eigenfunctions of the inviscid limit. For realistic neutron stars, our numerical results give viscous damping times with the same dependence on mass and radius as previously estimated, but sys...
Shear flow generation due to electromagnetic instabilities
International Nuclear Information System (INIS)
Saturation mechanism for electromagnetic instabilities such as resistive drift-Alfven modes (RDAMs) and resistive wall modes (RWMs) has been studied by solving nonlinear fluid model equations in cylindrical plasmas. For suppressing nonlinear growth of these modes poloidal shear flows are essential. However, the Maxwell stress due to magnetic fluctuations has a tendency to reduce the generation of poloidal flow and may change nonlinear behavior of these instabilities expected from linear properties. For weakly unstable RDAMs a stationary poloidal flow is achieved, although an oscillatory behavior is obtained for fairly unstable cases. For RWMs the Maxwell stress becomes dominant and an initial poloidal flow almost disappears near a rational surface particularly when a resistive wall is close to a main plasma. In case that the resistive wall is not close, stabilization of RWMs due to a poloidal flow remains. (author)
Elasto-plastic impact response analysis of shear-failure-type RC beams with shear rebars
International Nuclear Information System (INIS)
In this paper, to establish a simple elasto-plastic impact analysis method for shear-failure-type reinforced concrete (RC) beams, falling-weight impact tests and three-dimensional finite element (FE) analyses were conducted. Here, twelve simply supported rectangular RC beams were used, each with dimensions of (width x depth x length) 200 x 400 x 2,400 mm. Shear rebar ratio and impact velocity were taken as variables. Impact load was applied at the mid-span of RC beam by dropping a 400 kg steel weight from pre-determined position. LS-DYNA nonlinear transient finite element analysis code was used for this research. From this study, it is seen that the time histories of impact force, reaction force and mid-span displacement, and crack patterns on the side-surface of RC beam can be predicted accurately by using the proposed FE analysis method
Single-fluid stability of stationary plasma equilibria with velocity shear and magnetic shear
International Nuclear Information System (INIS)
By using incompressible single-fluid equations with a generalized Ohm's law neglecting the electron inertia, a linear eigenmode equation for a magnetic field perturbation is derived for stationary equilibria in a slab geometry with velocity and magnetic shears. The general eigenmode equation contains a fourth-order derivative of the perturbation in the highest order and contains Alfven and whistler mode components for a homogeneous plasma. The ratio of the characteristic ion inertia length to the characteristic inhomogeneity scale length is chosen as a small parameter for expansion. Neglecting whistler mode in the lowest order, the eigenmode equation becomes a second-order differential equation similar to the ideal magnetohydrodynamic eigenmode equation except for the fact that the unperturbed perpendicular velocity contains both electric and ion diamagnetic drifts. A sufficient condition for stability against the Kelvin-Helmholtz instability driven by shear in the ion diamagnetic drift velocity is derived and then applied to tokamaks.
Shear behavior of reinforced Engineered Cementitious Composites (ECC) beams
DEFF Research Database (Denmark)
Paegle, Ieva; Fischer, Gregor
2010-01-01
This paper describes an experimental investigation of the shear behavior of beams consisting of steel reinforced Engineered Cementitious Composites (ECC). Based on the strain hardening and multiple cracking behavior of ECC, this study investigates the extent to which ECC can improve the shear capacity of beams loaded primarily in shear and if ECC can partially or fully replace the conventional transverse steel reinforcement in beams. However, there is a lack of understanding of how the fibers affect the shear carrying capacity and deformation behavior of structural members if used either in combination with conventional transverse reinforcement or exclusively to provide shear resistance. The experimental investigation focuses on the influence of fibers on the shear caring capacity and the crack development in ECC beams subjected to shear. The experimental program consists of ECC with short randomly distributed PVA (polyvinyl alcohol) fiber beams with different stirrup spacing and reinforced concrete (RC) beams for comparison. Displacement and strain measurements taken using the ARAMIS photogrammetric data acquisition system by means of processing at high frame rate captured images of applied a high contrast speckle pattern to the beams surface. The multiple micro cracking resulting from the strain-hardening response of ECC in tension develop in a di-agonal between the load and support point. The formation of multiple micro cracks is highly dependent on the tensile stress-strain behavior of the ECC. The shear crack formation mechanism of ECC is investigated and found to be characterized by an opening of the cracks prior to sliding. Several analytical models on shear de-sign of ECC and concrete beams are evaluated and compared to the experimentally obtained results. The pro-visions of the Eurocode and ACI Code are found to be over-conservative but can be modified by utilizing the tensile strength of ECC. An expression for the load carrying capacity is proposed by expressing the ECC shear strength in terms of the crack angle.
Wave-equation shear wave splitting tomography
Long, Maureen D.; de Hoop, Maarten V.; van der Hilst, Robert D.
2008-01-01
The main focus of this paper is the development of a theoretical framework for the tomographic inversion of (broad-band) shear wave splitting measurements in terms of anisotropic structure in the upper mantle. We show that the partial differential equations (PDEs) that govern wave equation shear wave splitting tomography are, upon linearization with the Born approximation, similar in structure to the equations that describe wave equation transmission and reflection tomography. For full broad-band analysis these PDEs can be evaluated numerically, but we show here the leading order asymptotic (i.e. `ray born') behaviour of the associated finite-frequency sensitivity kernels. For simplicity we assume that the anisotropic model is invariant in one horizontal direction. This 2.5-D geometry is well suited for studying upper-mantle anisotropy associated with subduction of lithospheric plates if the trench-slab system is approximately 2-D. With the so-called splitting intensity as the metric for data fit, and under the assumption of weak anisotropy, we derive expressions for the sensitivity kernels. We focus on two anisotropic parameters that describe tilted transverse isotropy: the dip ?0 of the symmetry axis with respect to the horizontal plane and the anellipticity parameter ?A, which represents the strength of the anisotropy. We illustrate the finite-frequency effects both for homogeneous and heterogeneous (anisotropic) background models. The sensitivity kernels in heterogeneous media are calculated for initial models obtained from numerical modelling of flow and finite strain beneath the Ryukyu arc. Kernels calculated in heterogeneous media differ substantially from those in a homogeneous background. This demonstrates the importance of iterative model (and kernel) assessment for reaching the full (resolution) potential of finite frequency tomography.
Passive wireless wall shear stress sensors
Sells, Jeremy
The design and realization of the first ever passive wireless wall shear stress sensors are presented. The sensors are capable of directly measuring shear forces, 4 mPa to 4 Pa, created at the solid-fluid boundary of a flow. To capture the spatially small structures of a turbulent flow, a micromachined, variable-capacitor floating element sensor is designed. Passive wireless capability is achieved with the addition of an inductive coil and interrogating antenna. These sensors will enable characterization of complex flow phenomena. The primary benefit of the system is that the sensors operate without the need of a direct electrical connection. This simplifies installation of the sensors and enables their placement in locations where the rest of the system either will not fit or cannot survive. By using a passive wireless technique, a power source is not required, extending the life of the sensor and simplifying fabrication. The system makes use of frequency separation, allowing one interrogating antenna to query multiple sensors configured as an array simultaneously. Two generations of the wireless sensor are presented. The design, fabrication, packaging, and characterization of two first-generation sensors have dynamic ranges of 37 and 52 dB. Following this work, specific design improvements were identified and integrated into a second-generation sensor design, resulting in an improvement to 62 dB dynamic range and an order of magnitude reduction in parasitic capacitance and humidity sensitivity. Ideas for a third generation are presented, but realization of this design is left for future work.
Improved Shear Performance of Bent-Up Bars in Reinforced Concrete Beams .
Najmi, Abdul Qader S.; Al-nasra, Moayyad M.; Asha, Naiem M.
2013-01-01
Shear failure of reinforced concrete beams is often sudden and catastrophic. This sudden failure, due to shear, made it necessary to explore more effective ways to design reinforced concrete beam for shear. The reinforced concrete beams show different behavior at the failure stage in shear compare to the bending, which is considered to be unsafe mode of failure. The shear cracks progressive rapidly without sufficient advanced warning, and the diagonal cracks that develop due to excess shear f...
Failure Dependence Analysis of Shear Walls with Different Openings under Fortification Earthquakes
Junfeng Zhu; Donghui Zheng; Yifan Li
2013-01-01
It is necessary to study failure dependence problem in order to solve system reliability in the field of Civil Engineering. In this paper, failure dependence of reinforced concrete shear walls with different openings (including the whole shear wall, the shear wall with small opening, the coupled shear wall, the shear wall frame) are studied under fortification earthquakes using Monte Carlo method. The results demonstrate that failure of reinforced concrete shear walls with different openings ...
Strengthening of flat slabs against punching shear using post-installed shear reinforcement
Ferna?ndez Ruiz, Miguel; Muttoni, Aurelio; Kunz
2010-01-01
A significant number of existing flat slabs currently require strengthening against punching shear for safety reasons (the increase of applied loads and deficiencies during design or construction) or to comply with more stringent code requirements. Available strengthening methods are, however, not completely satisfactory, or they cannot be applied in many cases (depending on the possibilities to enlarge column sizes or to intervene on the upper face of slabs). In this paper, an innovative sys...
Directory of Open Access Journals (Sweden)
Ammar N. HANOON
2014-12-01
Full Text Available Self-compacting concrete (SCC is a new generation of high-performance concrete, known for its excellent deformability and high resistance to segregation and bleeding. Nonetheless, SCC may be incapable of resisting shear because the shear resistance mechanisms of this concrete are uncertain, especially the aggregate interlock mechanism. This uncertainty is attributed to the fact that SCC contains a smaller amount of coarse aggregates than normal concrete (NC does. This study focuses on the shear strength of self-compacting reinforced concrete (RC beams with and without shear reinforcement. A total of 16 RC beam specimens was manufactured and tested in terms of shear span-to-depth ratio and flexural and shear reinforcement ratio. The test results were compared with those of the shear design equations developed by ACI, BS, CAN and NZ codes. Results show that an increase in web reinforcement enhanced cracking strength and ultimate load. Shear-tension failure was the control failure in all tested beams.
Supersonic shear imaging provides a reliable measurement of resting muscle shear elastic modulus.
Lacourpaille, Lilian; Hug, François; Bouillard, Killian; Hogrel, Jean-Yves; Nordez, Antoine
2012-03-01
The aim of the present study was to assess the reliability of shear elastic modulus measurements performed using supersonic shear imaging (SSI) in nine resting muscles (i.e. gastrocnemius medialis, tibialis anterior, vastus lateralis, rectus femoris, triceps brachii, biceps brachii, brachioradialis, adductor pollicis obliquus and abductor digiti minimi) of different architectures and typologies. Thirty healthy subjects were randomly assigned to the intra-session reliability (n = 20), inter-day reliability (n = 21) and the inter-observer reliability (n = 16) experiments. Muscle shear elastic modulus ranged from 2.99 (gastrocnemius medialis) to 4.50 kPa (adductor digiti minimi and tibialis anterior). On the whole, very good reliability was observed, with a coefficient of variation (CV) ranging from 4.6% to 8%, except for the inter-operator reliability of adductor pollicis obliquus (CV = 11.5%). The intraclass correlation coefficients were good (0.871 ± 0.045 for the intra-session reliability, 0.815 ± 0.065 for the inter-day reliability and 0.709 ± 0.141 for the inter-observer reliability). Both the reliability and the ease of use of SSI make it a potentially interesting technique that would be of benefit to fundamental, applied and clinical research projects that need an accurate assessment of muscle mechanical properties. PMID:22370174
Composite Interlaminar Shear Fracture Toughness, G(sub 2c): Shear Measurement of Sheer Myth?
OBrien, T. Kevin
1997-01-01
The concept of G2c as a measure of the interlaminar shear fracture toughness of a composite material is critically examined. In particular, it is argued that the apparent G2c as typically measured is inconsistent with the original definition of shear fracture. It is shown that interlaminar shear failure actually consists of tension failures in the resin rich layers between plies followed by the coalescence of ligaments created by these failures and not the sliding of two planes relative to one another that is assumed in fracture mechanics theory. Several strain energy release rate solutions are reviewed for delamination in composite laminates and structural components where failures have been experimentally documented. Failures typically occur at a location where the mode 1 component accounts for at least one half of the total G at failure. Hence, it is the mode I and mixed-mode interlaminar fracture toughness data that will be most useful in predicting delamination failure in composite components in service. Although apparent G2c measurements may prove useful for completeness of generating mixed-mode criteria, the accuracy of these measurements may have very little influence on the prediction of mixed-mode failures in most structural components.
Use of Axisymmetric Shearing as Technological Test Method to gather Flow Stress Data for Metals
Kandis, Janis; Valberg, Henry; Wenbin, Wu
2011-01-01
Cutting by shearing creates heavy shear deformation in a layer extending between the two applied shearing edges. Prediction of FEM-simulation is that effective strain and strain rates in the shear zone would reach very high levels even at mode rate shearing velocity. In this article experiments coupled with FEM-analysis are used to evaluate the potential of using a xisymmetric shearing for collecting flow stress data for metal forming purposes. It is shown that if accurate flow stress data are to be collected this way it is important to know how shearing occurs inside the shear zone.
Friction and degradation of rock joint surfaces under shear loads
Homand, F.; Belem, T.; Souley, M.
2001-08-01
The morpho-mechanical behaviour of one artificial granite joint with hammered surfaces, one artificial regularly undulated joint and one natural schist joint was studied. The hammered granite joints underwent 5 cycles of direct shear under 3 normal stress levels ranging between 0.3 and 4 MPa. The regularly undulated joint underwent 10 cycles of shear under 6 normal stress levels ranging between 0.5 and 5 MPa and the natural schist replicas underwent a monotonics shear under 5 normal stress levels ranging between 0.4 and 2.4 MPa. These direct shear tests were performed using a new computer-controlled 3D-shear apparatus. To characterize the morphology evolution of the sheared joints, a laser sensor profilometer was used to perform surface data measurements prior to and after each shear test. Based on a new characterization of joint surface roughness viewed as a combination of primary and secondary roughness and termed by the joint surface roughness, SRs, one parameter termed joint surface degradation, Dw, has been defined to quantify the degradation of the sheared joints. Examinations of SRs and Dw prior to and after shearing indicate that the hammered surfaces are more damaged than the two other surfaces. The peak strength of hammered joint with zero-dilatancy, therefore, significantly differs from the classical formulation of dilatant joint strength. An attempt has been made to model the peak strength of hammered joint surfaces and dilatant joints with regard to their surface degradation in the course of shearing and two peak strength criteria are proposed. Input parameters are initial morphology and initial surface roughness. For the hammered surfaces, the degradation mechanism is dominant over the phenomenon of dilatancy, whereas for a dilatant joint both mechanisms are present. A comparison between the proposed models and the experimental results indicates a relatively good agreement. In particular, compared to the well-known shear strength criteria of Ladanyi and Archambault or Saeb, these classical criteria significantly underestimate and overestimate the observed peak strength, respectively, under low and high normal stress levels. In addition and based on our experimental investigations, we put forward a model to predict the evolution of joint morphology and the degree of degradation during the course of shearing.Degradations of the artificial undulated joint and the natural schist joint enable us to verify the proposed model with a relatively good agreement. Finally, the model of Ladanyi and Archambault dealing with the proportion of total joint area sheared through asperities, as, once again, tends to underestimate the observed degradation.
Shear band propagation from a crack tip subjected to shear wave loading
Zhang, Zhizhou
Pressure-shear plate impact experiments have been used to study the response of semi-infinite cracks in 4340 VAR steel subjected to either pure Mode II or pure Mode III loading. The material is heat-treated to achieve a fully-martensitic microstructure, which is confirmed through hardness tests and optical microscope observations of etched samples. Half-through, mid-plane cracks are grown in the target plates by means of fatigue loading. In order to obtain pure shear wave loading, flyer and target plate geometries are designed to ensure that the compressive wave passes through the crack plane before the shear wave arrives. The rear surface motion of the target is monitored by a combined normal displacement interferometer (NDI) and transverse displacement interferometer (TDI). For the case of Mode II loading, an improved TDI using a combined lens-beamsplitter unit is introduced to obtain high quality records in the presence of substantial rotation of the rear surface of the target. Both normal velocity-time profiles and transverse velocity-time profiles are obtained through post-processing from interferometric data. Numerical simulations based on both elastic and elastic viscoplastic response indicate that the deformation is essentially elastic except near the crack tip. Simulated velocity-time profiles for the case of a stationary crack agree quite well with those obtained in the experiments. Numerical simulations based on elastic response are also used to probe the effects of various parameters, e.g. friction coefficients, surface roughness, surface flatness, tilt, and etc., on the velocity-time profiles. Microscopic examinations of the recovered samples show long shear bands emanating from the tip of the fatigue crack. Numerical simulations using a power law viscoplasticity model are performed on a supercomputer to gain insight into the shear band formation process. Mesh size effects of the FEM calculations are noted and extrapolation is used to obtain temperature distributions for a mesh with zero size. The length of the band and the level of the temperature rise fall far short of what are suggested by microscopical observations. Further simulations following adjustments of power law model parameters to enhance localization fail to produce the shear band features observed in the experiments. Several closely related investigations are reported in appendices. An analytic approach employing a Green's function is used to estimate a shear band speed and a displacement jump across the band for the case of a mode III crack problem. Further improvement of this approach by including a band of failed material is also considered. Weiner-Hopf methodology is used for the Mode II case to obtain an analytical solution for assessing the accuracy of the FEM simulations. Finally, an attempt to remove the reflected tensile wave by introducing a transparent window is also described.
Yielding of colloidal gels under steady and oscillatory shear
Petekidis, George; Moghimi, Esmaeel; Koumakis, Nick; Forth Team
2015-03-01
The structural and rheological properties of intermediate volume fraction colloid polymer gels are examined during and after steady and oscillatory shear flow using rheometry, confocal microscopy, light scattering and Brownian Dynamics simulations. Our main objective is to rationalize the microscopic mechanisms through which one can tune the mechanical properties of such metastable colloidal gels by imposing different types of external shear and flow. Experimentally, the gels consist of model hard sphere particle dispersions of ? = 0.44 with the addition of non-adsorbing linear chains, while BD simulations are conducted for hard spheres with the superposition of an AO potential for depletion attractions. Structural analysis shows that variation of the applied shear rate produces strong changes in the structure of the gels both when under shear and during gel reformation at cessation. Larger rates are characterized by disperse particles and the total breakage of structures at rest, which after cessation evolve with time into strong solids with relatively homogeneous structures. However, smaller rates show large inhomogeneous structures under flow, which do not evolve after cessation and additionally exhibit reduced elasticity and as such are weaker solids. Furthermore oscillatory shear is far more efficient than steady shear creating gels with stronger differences in their elastic modulus. Thus by tuning the way a gel is sheared, one may vary the final strength and structure of the resulting gel. Work in collaboration with R. Besseling, W. C. K. Poon and J. F. Brady
Shear band dynamics from a mesoscopic modeling of plasticity
International Nuclear Information System (INIS)
The ubiquitous appearance of regions of localized deformation (shear bands) in different kinds of disordered materials under shear is studied in the context of a mesoscopic model of plasticity. The model allows us to include relaxational (ageing) effects. In the absence of relaxational effects the model displays a monotonically increasing dependence of stress on strain rate, and stationary shear bands do not occur. However in start-up experiments transient (although long lived) shear bands occur, that widen without bound in time. I investigate this transient effect in detail, reproducing and explaining a t1/2 law for the thickness increase of the shear band that has been obtained in atomistic numerical simulations. Relaxation produces a negatively sloped region in the stress versus strain-rate curve that stabilizes the formation of shear bands of a well-defined width, which is a function of strain rate. Simulations at very low strain rates reveal a non-trivial stick–slip dynamics of very thin shear bands that has relevance in the study of seismic phenomena. In addition, other non-stationary processes, such as stop-and-go, or strain-rate inversion situations display a phenomenology that matches very well the results of recent experimental studies
Depth Dependence of Shear Properties in Articular Cartilage
Buckley, Mark; Gleghorn, Jason; Bonassar, Lawrence; Cohen, Itai
2007-03-01
Articular cartilage is a highly complex and heterogeneous material in its structure, composition and mechanical behavior. Understanding these spatial variations is a critical step in designing replacement tissue and developing methods to diagnose and treat tissue affected by damage or disease. Existing techniques in particle image velocimetry (PIV) have been used to map the shear properties of complex materials; however, these methods have yet to be applied to understanding shear behavior in cartilage. In this talk, we will show that confocal microscopy in conjunction with PIV techniques can be used to determine the depth dependence of the shear properties of articular cartilage. We will show that the shear modulus of this tissue varies by over an order of magnitude over its depth, with the least stiff region located about 200 microns from the surface. Furthermore, our data indicate that the shear strain profile of articular cartilage is sensitive to both the degree of compression and the total applied shear strain. In particular, we find that cartilage strain stiffens most dramatically in a region 200-500 microns below the surface. Finally, we will describe a physical model that accounts for this behavior by taking into account the local buckling of collagen fibers just below the cartilage surface and present second harmonic generation (SHG) imaging data addressing the collagen orientation before and after shear.
Estimated strength of shear keys in concrete dams
Energy Technology Data Exchange (ETDEWEB)
Curtis, D.D. [Hatch Energy, Niagara Falls, ON (Canada); Lum, K.K.Y. [BC Hydro, Burnaby, BC (Canada)
2008-07-01
BC Hydro requested that Hatch Energy review the seismic stability of Ruskin Dam which was constructed in 1930 at Hayward Lake in British Columbia. The concrete gravity dam is founded nearly entirely on rock in a narrow valley. The vertical joints between blocks are keyed and grouted. The strength of the shear keys was assessed when a non-linear finite element model found that significant forces were being transferred laterally to the abutments during an earthquake. The lateral transfer of loads to the abutment relies on the strength of the shear keys. The dynamic finite element analysis was used to determine the stability of the dam. A review of the shear strength measurements reported in literature showed that the measurements compared well to those obtained by BC Hydro from cores taken from Ruskin Dam. The cohesive strength obtained using the Griffith failure criteria was also in good agreement with both sets of measurements. A simple ultimate shear strength equation was developed using the Mohr-Coulomb failure criteria to determine combined cohesive and frictional strength of shear keys. Safety factors of 2.0 for static loads and 1.5 for seismic loads were proposed to reduce the ultimate strength to allowable values. It was concluded that given the relatively high shear strength established for the shear keys, the abutment rock or dam/abutment contact will control the amount of load which can arch to the abutments. 8 refs., 4 tabs., 5 figs.
Velocity shear generated Alfven waves in electron-positron plasmas
International Nuclear Information System (INIS)
Linear MHD modes in cold, nonrelativistic electron-positron plasma shear flow are considered. The general set of differential equations, describing the evolution of perturbations in the framework of the nonmodal approach is derived. It is found, that under certain circumstances, the compressional and shear Alfven perturbations may exhibit large transient growth fuelled by the mean kinetic energy of the shear flow. The velocity shear also induces mode coupling allowing the exchange of energy as well as the possibility of a strong mutual transformation of these modes into each other. The compressional Alfven mode may extract the energy of the mean flow and transfer it to the shear Alfven mode via this coupling. The relevance of these new physical effects to provide a better understanding of the laboratory e+ e- plasma is emphasized. It is speculated that the shear-induced effects in the electron-positron plasmas could also help solve some astrophysical puzzles (e.g., the generation of pulsar radio emission). Since most astrophysical plasma are relativistic, it is shown that the major results of the study remain valid for weakly sheared relativistic plasmas. (author). 21 refs, 4 figs
Shear strength of palm oil clinker concrete beams
International Nuclear Information System (INIS)
Highlights: ? Palm oil clinker can be used as lightweight aggregate for the production of structural concrete. ? The palm oil clinker concrete can be classified as lightweight concrete. ? Full scale reinforced palm oil clinker concrete beams without shear reinforcement were tested. ? The CSA based design equation can be used for the prediction of shear capacity with a limit. - Abstract: This paper presents experimental results on the shear behavior of reinforced concrete beams made of palm oil clinker concrete (POCC). Palm oil clinker (POC) is a by-product of palm oil industry and its utilization in concrete production not only solves the problem of disposing this solid waste but also helps to conserve natural resources. Seven reinforced POCC beams without shear reinforcement were fabricated and their shear behavior was tested. POCC has been classified as a lightweight structural concrete with air dry density less than 1850 kg/m3 and a 28-day compressive strength more than 20 MPa. The experimental variables which have been considered in this study were the POCC compressive strength, shear span–depth ratio (a/d) and the ratio of tensile reinforcement (?). The results show that the failure mode of the reinforced POCC beam is similar to that of conventional reinforced concrete beam. In addition, the shear equation of the Canadian Standard Association (CSA) can be used in designing reinforced POCC beam with ? ? 1. However, a 0.5 safety factor should be included in the formula for ? < 1
Structure parameter of electrorheological fluids in shear flow.
Jiang, Jile; Tian, Yu; Meng, Yonggang
2011-05-17
A structure parameter, Sn = ?(c)?/?(E), is proposed to represent the increase of effective viscosity due to the introduction of particles into a viscous liquid and to analyze the shear behavior of electrorheological (ER) fluids. Sn can divide the shear curves of ER fluids, ?/E(2) versus Sn, into three regimes, with two critical values Sn(c) of about 10(-4) and 10(-2), respectively. The two critical Sn(c) are applicable to ER fluids with different particle volume fractions ? in a wide range of shear rate ? and electric field E. When Sn 10(-2). The electric current of ER fluids under E varied with shear stress in the same or the opposite trend in different shear rate ranges. Sn(c) also separates the conductivity variation of ER fluids into three regimes, corresponding to different structure evolutions. The change of Sn with particle volume fraction and E has also been discussed. The shear thickening in ER fluids can be characterized by Sn(c)(L) and Sn(c)(H) with a critical value about 10(-6). As an analogy to friction, the correspondence between ?/E(2) and friction coefficient, Sn and bearing numbers, as well as the similarity between the shear curve of ER fluids and the Stribeck curve of friction, indicate a possible friction origin in ER effect. PMID:21488694
Rheology of semisolid alloys under rapid change in shear rate
Energy Technology Data Exchange (ETDEWEB)
Liu, Tze Yong
2002-07-01
Industrial thixoforming processes are carried out within a second. Characterisation of the rheological behaviour of the semisolid metal slurry during this short space of time is therefore important. Rheological experiments were carried out on Sn15%Pb alloy (fraction solid 0.2-0.5) in a HAAKE cylindrical rotational viscometer using {approx}1kHz data collection rate to obtain the shear stress response to a rapid change in shear rate (range: 1 s{sup -1}-200 s{sup -1}). The slurry undergoes an initial rapid structural breakdown during a jump upwards in shear rate, followed by a more gradual breakdown. The former occurs within a second of the start of the jump. The metal slurry breaks down more rapidly with a higher final shear rate, but is independent of the initial shear rate. The reverse is found with downward jumps in shear rate: recovery times increase with increasing final shear rate. Again, the breakdown time is independent of the starting shear rate. The rheological behaviour of aluminium alloys with solid fraction >0.5 was studied by compressing cylindrical slugs at high speed against a load cell. The slurry exhibits a near-Newtonian behaviour at the thixoforming temperature, after an appropriate soaking time is employed and a near-spheroidal microstructure develops. Use of image analysis to quantify the spheroidicity indicates that particle shape affects the flow of the slurry, a higher spheroidicity corresponding to a lower load. Using solid-state mechanical deformation to break up the dendrites, produces thixoforming feedstock with lower resistance to flow than magnetohydrodynamic stirring. Power law index values were more negative than -1, for both rapid compression and viscometry experiments were obtained, indicating shear thinning behaviour in the semisolid metal slurry. Results from this work have shown the importance of understanding the rheological behaviour of a semisolid slurry in the transient state. (author)
Rheology of semisolid alloys under rapid change in shear rate
International Nuclear Information System (INIS)
Industrial thixoforming processes are carried out within a second. Characterisation of the rheological behaviour of the semisolid metal slurry during this short space of time is therefore important. Rheological experiments were carried out on Sn15%Pb alloy (fraction solid 0.2-0.5) in a HAAKE cylindrical rotational viscometer using ?1kHz data collection rate to obtain the shear stress response to a rapid change in shear rate (range: 1 s-1-200 s-1. The slurry undergoes an initial rapid structural breakdown during a jump upwards in shear rate, followed by a more gradual breakdown. The former occurs within a second of the start of the jump. The metal slurry breaks down more rapidly with a higher final shear rate, but is independent of the initial shear rate. The reverse is found with downward jumps in shear rate: recovery times increase with increasing final shear rate. Again, the breakdown time is independent of the starting shear rate. The rheological behaviour of aluminium alloys with solid fraction >0.5 was studied by compressing cylindrical slugs at high speed against a load cell. The slurry exhibits a near-Newtonian behaviour at the thixoforming temperature, after an appropriate soaking time is employed and a near-spheroidal microstructure develops. Use of image analysis to quantify the spheroidicity indicates that particle shape affects the flow of the slurry, a higher spheroidicity corresponding to a lower load. Using solid-state mechanicallower load. Using solid-state mechanical deformation to break up the dendrites, produces thixoforming feedstock with lower resistance to flow than magnetohydrodynamic stirring. Power law index values were more negative than -1, for both rapid compression and viscometry experiments were obtained, indicating shear thinning behaviour in the semisolid metal slurry. Results from this work have shown the importance of understanding the rheological behaviour of a semisolid slurry in the transient state. (author)
High-Frequency Shear Viscosity of Low-Viscosity Liquids
Kaatze, U.; Behrends, R.
2014-11-01
A thickness shear quartz resonator technique is described to measure the shear viscosity of low-viscosity liquids in the frequency range from 6 MHz to 130 MHz. Examples of shear-viscosity spectra in that frequency range are presented to show that various molecular processes are accompanied by shear-viscosity relaxation. Among these processes are conformational variations of alkyl chains, with relaxation times of about 0.3 ns for -pentadecane and -hexadecane at 25 C. These variations can be well represented in terms of a torsional oscillator model. Also featured briefly are shear-viscosity relaxations associated with fluctuations of hydrogen-bonded clusters in alcohols, for which values between 0.3 ns (-hexanol) and 1.5 ns (-dodecanol) have been found at 25 C. In addition, the special suitability of high-frequency shear-viscosity spectroscopy to the study of critically demixing mixtures is demonstrated by some illustrative examples. Due to slowing, critical fluctuations do not contribute to the shear viscosity at sufficiently high frequencies of measurements so that the non-critical background viscosity of critical systems can be directly determined from high-frequency shear-viscosity spectroscopy. Relaxations in appear also in the shear-viscosity spectra with, for example, 2 ns for the critical triethylamine-water binary mixture at temperatures between 10 C and 18 C. Such relaxations noticeably influence the relaxation rate of order parameter fluctuations. They may be also the reason for the need of a special mesoscopic viscosity when mutual diffusion coefficients of critical polymer solutions are discussed in terms of mode-coupling theory.
Microstructural evolution in adiabatic shear localization in stainless steel
International Nuclear Information System (INIS)
Shear bands were generated under prescribed and controlled conditions in stainless steel (Fe-18%Cr-8%Ni). Hat-shaped specimens, deformed in a Hopkinson bar were used, yielding strain rates of approximately 104s-1 and shear strains that could be varied between 1 and 100. Specimens recovered from the collapse of thick-walled cylinders were also investigated. Microstructural characterization was performed by electron backscattered diffraction (EBSD) with orientation imaging microscopy(OIM), and transmission electron microscopy (TEM). The shear-band thickness was approximately 8 ?m. This low-stacking fault energy alloy deforms, at the imposed strain rates (outside of the shear band), by planar dislocations and stacking fault packets, twinning, and occasional martensitic phase transformations at twin-twin intersections. EBSD reveals gradual lattice rotations of the grains approaching the core of the band. A [110] fiber texture (with the [110] direction perpendicular to both shear direction and shear plane normal) develops both within the shear band and in the adjacent grains. The formation of this texture, under an imposed global simple shear, suggests that rotations take place concurrently with the shearing deformation. This can be explained by compatibility requirements between neighboring deforming regions. EBSD could not reveal the deformation features at large strains because their scale was below the resolution of this technique. Transmission electron microscopy revque. Transmission electron microscopy reveals a number of features that are interpreted in terms of the mechanisms of deformation and recovery/recrystallization postulated. They include the observation of grains with sizes in the nanocrystalline domain. The microstructural changes are described by an evolutionary model, leading from the initial grain size of 15 ?m to the final submicronic (sub)grain size. Calculations are performed on the rotations of grain boundaries by grain-boundary diffusion, which is 3 orders of magnitude higher than bulk diffusion at the deformation temperatures. They indicate that the microstructural reorganization can take place within the deformation times of a few milliseconds
Microstructural Evolution in Adiabatic Shear Localization in Stainless Steel
Meyers, M. A.; Perez-Prado, M. T.; Xue, Q.; Xu, Y.; McNelley, T. R.
2002-07-01
Shear bands were generated under prescribed and controlled conditions in stainless steel (Fe-18%Cr-8%Ni). Hat-shaped specimens, deformed in a Hopkinson bar were used, yielding strain rates of approximately 104s-1 and shear strains that could be varied between 1 and 100. Specimens recovered from the collapse of thick-walled cylinders were also investigated. Microstructural characterization was performed by electron backscattered diffraction (EBSD) with orientation imaging microscopy(OIM), and transmission electron microscopy (TEM). The shear-band thickness was approximately 8 ?m. This low-stacking fault energy alloy deforms, at the imposed strain rates (outside of the shear band), by planar dislocations and stacking fault packets, twinning, and occasional martensitic phase transformations at twin-twin intersections. EBSD reveals gradual lattice rotations of the grains approaching the core of the band. A [110] fiber texture (with the [110] direction perpendicular to both shear direction and shear plane normal) develops both within the shear band and in the adjacent grains. The formation of this texture, under an imposed global simple shear, suggests that rotations take place concurrently with the shearing deformation. This can be explained by compatibility requirements between neighboring deforming regions. EBSD could not reveal the deformation features at large strains because their scale was below the resolution of this technique. Transmission electron microscopy reveals a number of features that are interpreted in terms of the mechanisms of deformation and recovery/recrystallization postulated. They include the observation of grains with sizes in the nanocrystalline domain. The microstructural changes are described by an evolutionary model, leading from the initial grain size of 15 ?m to the final submicronic (sub)grain size. Calculations are performed on the rotations of grain boundaries by grain-boundary diffusion, which is 3 orders of magnitude higher than bulk diffusion at the deformation temperatures. They indicate that the microstructural reorganization can take place within the deformation times of a few milliseconds.
Shear behaviors of single crystal nickel at different temperatures: molecular dynamics simulations
Li, Lili; Han, Ming
2015-06-01
Shear behaviors of a single crystal nickel along the [], [], [] and [] directions in the (111) crystallographic plane have been investigated at different temperatures by performing molecular dynamics simulations with an embedded atom method potential. Results show that shear stress-shear strain curves and atomic trajectory during shear process exhibit periodic behaviors, while the periods are varied for different shear directions. It sheds light on the inherent relationship between shear displacement for a period of the curve and the atomic configuration in corresponding crystallographic direction. Furthermore, shear modulus is extracted from the curves over a temperature range from 0 to 1700 K. It is demonstrated that the modulus is independent from the size of shear models and the shear directions, and that the modulus decreases with increasing temperature. In addition, this work also demonstrates that the classical description of shear modulus is still valid at the nanoscale, which might suggest a simple and direct way to obtain shear modulus at the atomic scale.
Shear-layer structures in near-wall turbulence
Johansson, A. V.; Alfredsson, P. H.; Kim, J.
1987-01-01
The structure of internal shear layer observed in the near-wall region of turbulent flows is investigated by analyzing flow fields obtained from numerical simulations of channel and boundary-layer flows. It is found that the shear layer is an important contributor to the turbulence production. The conditionally averaged production at the center of the structure was almost twice as large as the long-time mean value. The shear-layer structure is also found to retain its coherence over streamwise distances on the order of a thousand viscous length units, and propagates with a constant velocity of about 10.6 u sub rho throughout the near wall region.
Digital speckle pattern shearing interferometry: Limitations and prospects
DEFF Research Database (Denmark)
Owner-Petersen, Mette
1996-01-01
Since shearing interferometry, also called shearography, does not depict fringes caused by object tilt, it is a tool well suited for either nondestructive testing of objects under load or for quantitative evaluation of flexural strains. In traditional shearing interferometry, observation of fringes requires optical processing of double exposed interferograms. Hence the technique is not in real time. This paper explores the possibilities and limitations for real time shearing fringe observation using the electronic speckle pattern interferometry technique. Prospects for quantitative determination of local tilt and flexural strain using the the phase shifting technique are commented on, and some preliminary results are shown.
Role of shear in the isotropic-to-lamellar transition
Cates, M. E.; Milner, S. T.
1989-04-01
In the isotropic-to-lamellar transition, nonlinear fluctuation terms lower the transition temperature ?c and drive the transition first order. Here we show that steady shear, by suppressing the fluctuations, raises ?c in a certain temperature range the lamellar phase can be induced by applying shear. A study ofo the effective potential indicates that the transition remains first order, though becoming very weak at high shear rate. We argue heuristically that the lamellar ordering first occurs with wave vector normal to both the velocity and the velocity gradient.
Adapting a commercial shear rheometer for applications in cartilage research
Boettcher, K.; Grumbein, S.; Winkler, U.; Nachtsheim, J.; Lieleg, O.
2014-09-01
Cartilage research typically requires a broad range of experimental characterization techniques and thus various testing setups. Here, we describe how several of those tests can be performed with a single experimental platform, i.e. a commercial shear rheometer. Although primarily designed for shear experiments, such a rheometer can be equipped with different adapters to perform indentation and creep measurements, quantify alterations in the sample thickness, and conduct friction measurements in addition to shear rheology. Beyond combining four distinct experimental methods into one setup, the modified rheometer allows for performing material characterizations over a broad range of time scales, frequencies, and normal loads.
The Palomares brittle—ductile Shear Zone of southern Spain
Weijermars, Ruud
The Palomares Shear Zone is a major Neogene-Quaternary strike—slip zone which transects the crust of the Betic Cordillera in SE Spain. The shear zone and the mechanisms that led to its formation are discussed and illustrated on the basis of detailed compilations of both the local and regional geology. It is emphasized that the formation of the Palomares Shear Zone was not an isolated tectonic event, but part of a complex Neogene tectonic history. The Neogene evolution of the Betic-Rif orogen and its central Alboran Basin is characterised by the following events: (1) emplacement of the Alboran Diapir with resulting nappe-shedding from the overlying crust between 25 and 20 Ma ago; (2) onset of the subsidence of the Alboran Basin between 20 and 15 Ma ago due to cooling of the Alboran Diapir and the overlying crust; (3) formation of the Cabo de Gata Volcanic Chain between 15 and 8 Ma ago; and (4) refolding of the nappe sheets in the Betic-Rif orogen into a basin and range structure about 7 Ma ago. Continuous activity of the Crevillente Fault of southern Spain may have occured over a period from 20 Ma ago up to the present. The interrelated Palomare Fault in SE Spain was probably formed between 15 and 8 Ma ago and seem to be active still. The Palomares Shear Zone affects a rock volume 44 km wide, at least 80 km long and 30 km deep. A shear strain—distance diagram constructed across the Palomares Shear Zone and its axial Palomares Fault involves a new method to estimate or constrain the shear strain magnitude along brittle-ductile shears. The typical tensor shear strain rates in the approximately 20 km thick ductilely deformed walls of the Palomares Fault are of the order 10 -13-10 -14 s -1. The tensor shear strain rate along the Palomares Fault itself is of the order 10 -12s -1 and the time averaged relative displacement rate of its walls is about 2 mm a -1. The range of strain rates within the Palomares Shear Zone are interpreted to be due to a combination of various flow-softening mechanisms: geometric, structural, thermal and strain-rate softening. These softening mechanisms might explain the difference in vertically averaged viscosities of 10 20 Pa s and 10 25 Pa s or lower suggested for the crustal rocks in the Palomares Fault proper and that of the relatively rigid boundaries of the Palomares Shear Zone, respectively.
Wall shear stress hot film sensor for use in gases
International Nuclear Information System (INIS)
The purpose of this work is to present the construction and characterization of a wall shear stress hot film sensor for use in gases made with MEMS technology. For this purpose, several associated devices were used, including a constant temperature feedback bridge and a shear stress calibration device that allows the sensor performance evaluation. The sensor design adopted here is simple, economical and is manufactured on a flexible substrate allowing its application to curved surfaces. Stationary and transient wall shear stress tests were carried on by means of the calibration device, determining its performance for different conditions.
Self-Diffusion of Drops in a Dilute Sheared Emulsion
Loewenberg, Michael; Hinch, E. J.
1996-01-01
Self-diffusion coefficients that describe cross-flow migration of non-Brownian drops in a dilute sheared emulsion were obtained by trajectory calculations. A boundary integral formulation was used to describe pairwise interactions between deformable drops; interactions between undeformed drops were described with mobility functions for spherical drops. The results indicate that drops have large anisotropic self-diffusivities which depend strongly on the drop viscosity and modestly on the shear-rate. Pairwise interactions between drops in shear-flow do not appreciably promote drop breakup.
Structure and shear deformation of metallic crystalline–amorphous interfaces
International Nuclear Information System (INIS)
The structure and shear properties of crystalline–amorphous laminar nanocomposites are studied in an atomistic model of face-centered cubic copper with amorphous Cu46Zr54 bulk metallic glass in the quasi-static limit. The plastic shear deformation response is determined by the production and motion of interface dislocations at the crystalline–amorphous interface, which is closely linked to the structural and chemical transition from crystalline Cu to the amorphous Cu/Zr phase. The implication of interfacial shear are discussed in context of dislocation–interface interactions and co-deformation of a crystalline–amorphous nanocomposite
Microscopic Mechanism for Shear Thickening of Non-Brownian Suspensions
Fernandez, Nicolas; Mani, Roman; Rinaldi, David; Kadau, Dirk; Mosquet, Martin; Lombois-Burger, Hélène; Cayer-Barrioz, Juliette; Herrmann, Hans J.; Spencer, Nicholas D.; Isa, Lucio
2013-09-01
We propose a simple model, supported by contact-dynamics simulations as well as rheology and friction measurements, that links the transition from continuous to discontinuous shear thickening in dense granular pastes to distinct lubrication regimes in the particle contacts. We identify a local Sommerfeld number that determines the transition from Newtonian to shear-thickening flows, and then show that the suspension’s volume fraction and the boundary lubrication friction coefficient control the nature of the shear-thickening transition, both in simulations and experiments.
Influence of viscoelasticity on drop dynamics in shear flow
Renardy, Yuriko; Verhulst, K.; Moldenaers, P.; Cardinaels, R.; Afkhami, S.
2008-11-01
A computational and experimental study of drop dynamics under shear is conducted for fluid pairs in which one of the liquids is a Boger fluid. The drop to matrix viscosity ratio is either 0.75 or 1.5, Deborah numbers range to 2 and capillary numbers range to above breakup conditions. The results focus on three aspects: relaxation after cessation of shear, a novel viscoelastic drop breakup scenario, and the effect of shear flow history on drop breakup. Numerical simulations are performed with our in-house 3D volume-of-fluid PROST (Paraboloid Representation of the interface in the Surface Tension force) method.
DYNAMIC BEHAVIOR OF ELASTOHYDRODYNAMIC LUBRICANTS IN SHEARING AND COMPRESSION
Feng, R.; Ramesh, K.
1991-01-01
An experimental investigation has been conducted into the response of elastohydrodynamic (EHD) lubricants subjected to the high shear rates and pressures encountered in EHD lubrication and over comparable time scales. New techniques have been developed to measure the dynamic compressibility of EHD lubricants at pressures as high as 1 GPa, and the response to dynamic shearing at shear rates as high as 4.0 x 104 sec-1, over timescales of about 10-4 sec, and for a range of initial temperatures.
Instrumented Bolts Would Measure Shear Forces In Joints
Sawyer, James Wayne; Mcwithey, Robert R.
1994-01-01
Bolts instrumented with strain gauges used to measure shear forces. Bolts installed in multiple-bolt lap joints to obtain data on distribution of stresses and deformations in and around joints. Strain gauges indicate share of applied load borne by each individual bolt. In original application, bolted panels made of advanced refractory composite materials designed to withstand use at temperatures up to 4,000 degrees F. Also applicable to other joint materials and measurement of shear loads in other connections such as, shear loads on shafts in pulleys or gears.
Impact of a shear flow on double tearing nonlinear dynamics
International Nuclear Information System (INIS)
The dynamics of global reconnection in the presence of a poloidal shear flow located in between magnetic islands is investigated. Different linear and nonlinear regimes are identified depending on the resistivity, the equilibrium velocity amplitude, and the distance between the low-order resonant surfaces. It is found that nonlinearly, the shear flow can significantly delay DTM generation and global reconnection. It is shown that this delay is linked to a symmetry breaking imposed by the shear flow and the generation of mean poloidal flows in the resistive layers. It is also found that turbulence can be generated by Kelvin-Helmholtz instability in between the resonance layers and enhance magnetic reconnection processes.
Impact of a shear flow on double tearing nonlinear dynamics
Voslion, T.; Agullo, O.; Beyer, P.; Yagi, M.; Benkadda, S.; Garbet, X.; Itoh, K.; Itoh, S.-I.
2011-06-01
The dynamics of global reconnection in the presence of a poloidal shear flow located in between magnetic islands is investigated. Different linear and nonlinear regimes are identified depending on the resistivity, the equilibrium velocity amplitude, and the distance between the low-order resonant surfaces. It is found that nonlinearly, the shear flow can significantly delay DTM generation and global reconnection. It is shown that this delay is linked to a symmetry breaking imposed by the shear flow and the generation of mean poloidal flows in the resistive layers. It is also found that turbulence can be generated by Kelvin-Helmholtz instability in between the resonance layers and enhance magnetic reconnection processes.
Shear waves in vegetal tissues at ultrasonic frequencies
Fariñas, M. D.; Sancho-Knapik, D.; Peguero-Pina, J. J.; Gil-Pelegrín, E.; Gómez Álvarez-Arenas, T. E.
2013-03-01
Shear waves are investigated in leaves of two plant species using air-coupled ultrasound. Magnitude and phase spectra of the transmission coefficient around the first two orders of the thickness resonances (normal and oblique incidence) have been measured. A bilayer acoustic model for plant leaves (comprising the palisade parenchyma and the spongy mesophyll) is proposed to extract, from measured spectra, properties of these tissues like: velocity and attenuation of longitudinal and shear waves and hence Young modulus, rigidity modulus, and Poisson's ratio. Elastic moduli values are typical of cellular solids and both, shear and longitudinal waves exhibit classical viscoelastic losses. Influence of leaf water content is also analyzed.
Shear flows induced by nonlinear evolution of double tearing modes
International Nuclear Information System (INIS)
Shear flows induced by nonlinear evolution of double tearing modes are investigated in a resistive magnetohydrodynamic model with slab geometry. It is found that intensive and thin poloidal shear flow layers are generated in the magnetic island region driven by coupled reconnection process at both rational surfaces. The structure of the flow layers keeps evolving after the merging of magnetic separatrices and forms a few narrow vortices along the open field lines in the final stage of magnetic reconnection. The effects of the distance between both rational surfaces and the initial magnetic shear on the nonlinear evolution of the plasma flows are also taken into consideration and the relevant mechanism is discussed
Stimulated bioluminescence by fluid shear stress associated with pipe flow
International Nuclear Information System (INIS)
Dinoflagellate can be stimulated bioluminescence by hydrodynamic agitation. Two typical dinoflagellate (Lingulodinium polyedrum and Pyrocystis noctiluca) was choosed to research stimulated bioluminescence. The bioluminescence intensity and shear stress intensity were measured using fully developed pipe flow. There is shear stress threshold to agitate organism bioluminescence. From these experiment, the response thresholds of the stimulated bioluminscence always occurred in laminar flows at a shear stress level of 0.6-3 dyn/cm2. At the same time, the spectral characteristc of dinoflagellate was recorded, the wavelength of them is about 470nm, and the full width at half maximum is approximate 30nm.
Shear flow effects on double tearing mode global magnetic reconnection
International Nuclear Information System (INIS)
The dynamics of a global reconnection in the presence of a poloidal shear flow which is located in between magnetic islands is investigated. Different linear regimes are identified according to the value of the resistivity and the distance between the low-order resonant surfaces. It is found that the presence of a small shear flow affects and significantly delays the global reconnection processes. It is shown that this delay is linked to a breaking of symmetry imposed by the existence of the shear flow and the generation of a mean poloidal flow in the resistive layers. (author)
Performance testing of a Savonius windmill rotor in shear flows
Mojola, O. O.; Onasanya, O. E.
The effects of flow shear and/or unsteady behavior on the power generation capability of a Savonius wind turbine rotor are assessed in view of measurements conducted, both in two statistically steady shear flows and in the wind, of rotor tip speed and torque at a number of streamwise stations for each of four values of the rotor bucket overlap ratio. It is found that, even in the absence of shear, the power coefficient of a Savonius wind turbine rotor is most strongly dependent on tip speed ratio.
Stimulated bioluminescence by fluid shear stress associated with pipe flow
Energy Technology Data Exchange (ETDEWEB)
Cao Jing; Wang Jiangan; Wu Ronghua, E-mail: caojing981@126.com [Col. of Electronic Eng., Naval University of Engineering, Wuhan 430033 (China)
2011-01-01
Dinoflagellate can be stimulated bioluminescence by hydrodynamic agitation. Two typical dinoflagellate (Lingulodinium polyedrum and Pyrocystis noctiluca) was choosed to research stimulated bioluminescence. The bioluminescence intensity and shear stress intensity were measured using fully developed pipe flow. There is shear stress threshold to agitate organism bioluminescence. From these experiment, the response thresholds of the stimulated bioluminscence always occurred in laminar flows at a shear stress level of 0.6-3 dyn/cm{sup 2}. At the same time, the spectral characteristc of dinoflagellate was recorded, the wavelength of them is about 470nm, and the full width at half maximum is approximate 30nm.
Estimation of shear viscosity based on transverse momentum correlations
Sharma, Monika
2009-01-01
Event anisotropy measurements at RHIC suggest the strongly interacting matter created in heavy ion collisions flows with very little shear viscosity. Precise determination of "shear viscosity-to-entropy" ratio is currently a subject of extensive study. We present preliminary results of measurements of the evolution of transverse momentum correlation function with collision centrality of $Au +Au$ interactions at $\\sqrt{s_{NN}}$ = 200 GeV. We compare two differential correlation functions, namely {\\it inclusive} and a differential version of the correlation measure $\\tilde C$ introduced by Gavin ${\\it et. al.}$. These observables can be used for the experimental study of the shear viscosity per unit entropy.
Shear flow effects on double tearing mode global magnetic reconnection
Voslion, Thibaut; Beyer, Peter; Yagi, Masatoshi; Benkadda, Sadruddin; Garbet, Xavier; Itoh, Kimitaka; Itoh, Sanae-I
2009-01-01
The dynamics of a global reconnection in the presence of a poloidal shear flow which is located in between magnetic islands is investigated. Different linear regimes are identified according to the value of the resistivity and the distance between the low-order resonant surfaces. It is found that the presence of a small shear flow affects and significantly delays the global reconnection processes. It is shown that this delay is linked to a breaking of symmetry imposed by the existence of the shear flow and the generation of a mean poloidal flow in the resistive layers.
Profile control studies for JET optimised shear regime
International Nuclear Information System (INIS)
This report summarises the profile control studies, i.e. preparation and analysis of JET Optimised Shear plasmas, carried out during the year 1999 within the framework of the Task-Agreement (RF/CEA/02) between JET and the Association Euratom-CEA/Cadarache. We report on our participation in the preparation of the JET Optimised Shear experiments together with their comprehensive analyses and the modelling. Emphasis is put on the various aspects of pressure profile control (core and edge pressure) together with detailed studies of current profile control by non-inductive means, in the prospects of achieving steady, high performance, Optimised Shear plasmas. (authors)
Coherent structures in compressible free-shear-layer flows
Energy Technology Data Exchange (ETDEWEB)
Aeschliman, D.P.; Baty, R.S. [Sandia National Labs., Albuquerque, NM (United States). Engineering Sciences Center; Kennedy, C.A.; Chen, J.H. [Sandia National Labs., Livermore, CA (United States). Combustion and Physical Sciences Center
1997-08-01
Large scale coherent structures are intrinsic fluid mechanical characteristics of all free-shear flows, from incompressible to compressible, and laminar to fully turbulent. These quasi-periodic fluid structures, eddies of size comparable to the thickness of the shear layer, dominate the mixing process at the free-shear interface. As a result, large scale coherent structures greatly influence the operation and efficiency of many important commercial and defense technologies. Large scale coherent structures have been studied here in a research program that combines a synergistic blend of experiment, direct numerical simulation, and analysis. This report summarizes the work completed for this Sandia Laboratory-Directed Research and Development (LDRD) project.
Viscous dissipations in simple shear zones- analytical models and a Himalayan example
Nasipuri, P.; Mukherjee, S.
2012-04-01
An analytical model is presented for shear heating (viscous dissipation) due to simple shear in inclined ductile Newtonian viscous simple shear zones. Considering the presence of an extrusive pressure gradient and a downdip flow due to a component of gravity, the models show that the viscous dissipation is (i) inversely proportional to the thermal conductivity. (ii) When both the boundaries are sheared and a resultant pressure gradient acts, a cubic profile of shear heating across the shear zone is produced. (iii) For a horizontal shear zone with no pressure gradient, and also in inclined shear zones where there is no effective pressure gradient, shear heating is inversely proportional to the viscosity, and is proportional to the square of the total slip rates at the boundaries. (iv) For a purely Poiseuille type flow, no shear heating is produced. (v) Where the boundaries are sheared and the effective pressure gradient is zero, the shear heating profile is parabolic. (vi) In all the cases the shear heating is maximum at the center of the shear zone, and is zero at the boundaries. This remains the same for any type of velocity profiles as described by Mukherjee (Geol Mag, in press). Taking known parameters from the Higher Himalayan Shear Zone along the entire Himalayan chain, it is estimated that the shear heating at the middle of the shear zone could have reached as high as 1200 0C during ~ mid-Miocene Period when crustal channel flow mechanism of extrusion was active in the terrain.
Directory of Open Access Journals (Sweden)
Ivona ?urkin
2009-12-01
Full Text Available The present study was performed in order to investigate a relationship between polymorphisms on the calpastatin gene (CAST and pig meat quality traits. The investigation was carried out on 29 gilts and barrows, crosses of Large White x German Landrace randomly selected at slaughter line. Pigs were slaughtered at 130-150 kg of live weight and blood samples were taken for genomic DNA analysis. The following indicators of meat quality and meat chemical composition were evaluated: pH and electric conductivity measured 45 minutes post mortem in m. Longissimus dorsi (LD muscle and in M. Semimembranosus (SM muscle; electric conductivity measured at the same locations after 24h of cooling; drip loss (determined by “bag method”; colour (measured with Minolta chromameter and expressed as Hunter L, a, b values; instrumental tenderness assessed as Warner-Bratzler (WB shear force and moisture, fat, protein and collagen content (% determined on cooked LD muscle after 24h of thawing. The amplification products of the CAST gene were digested with HinfI restriction endonuclease and three genotypes (AA, BB and AB were revealed. Statistical analysis showed that meat originated from pigs of AB genotype had the lowest WB shear force and the highest protein content of cooked LD muscle. As for the indicators of technological meat quality, statistically significant differences (p<0.05 were found between genotype AA and both BB and AB genotype for electric conductivity measured in LD muscle after 24h of cooling, as well as between BB and both AA and AB genotypes for drip loss.
Morales, Pilar; Calzada, Javier; Avila, Marta; Nuñez, Manuel
2008-04-01
The effect of single- and multiple-cycle high-pressure treatments on the survival of Escherichia coli CECT 4972, a strain belonging to the O157:H7 serotype, in ground beef was investigated. Beef patties were inoculated with 10(7) CFU/g E. coli O157:H7, and held at 4 degrees C for 20 h before high-pressure treatments. Reduction of the E. coli O157:H7 population by single-cycle treatments at 400 MPa and 12 degrees C ranged from 0.82 log CFU/g for a 1-min cycle to 4.39 log CFU/g for a 20-min cycle. Multiple-cycle treatments were very effective, with four 1-min cycles at 400 MPa and 12 degrees C reducing the E. coli O157:H7 population by 4.38 log CFU/g, and three 5-min cycles by 4.96 log CFU/g. The color parameter L* increased significantly with high-pressure treatments in the interior and the exterior of beef patties, whereas a* decreased in the interior, and b* increased in the exterior-changes that might diminish consumer acceptance of the product. Kramer shear force and energy were generally higher in pressurized than in control ground beef. Maximum values for these texture parameters, which corresponded to tougher patties, were reached after one 10-min cycle in the case of single-cycle treatments or two 5-min cycles in the case of multiple-cycle treatments. High-pressure treatments had no significant effect on Warner-Bratzler shear force. PMID:18468038
The extent of proteolysis is independent of sarcomere length in lamb longissimus and psoas major.
Wheeler, T L; Koohmaraie, M
1999-09-01
The objective of this experiment was to determine the effect of sarcomere length on postmortem proteolysis and meat tenderness. Eighteen Dorset market-weight sheep were slaughtered conventionally. The longissimus thoracis et lumborum and psoas major from each carcass were either left intact on the carcass (control), which was chilled at 0 degrees C, or excised from the carcass and chilled in an ice slurry (0 degrees C). At 24 h, control muscles were excised, and all muscles were cut into sections and assigned to 1 or 10 d of postmortem storage at 2 degrees C. Sarcomere length was shorter (P .05) by aging time. Western blot analysis of troponin-T and desmin indicated no effect (P > .05) of the shortened treatment compared to the control on the extent of proteolysis. Regardless of aging time or treatment, troponin-T was more degraded (P < .01) in longissimus than in psoas major (38.1 vs 23.5%) and desmin tended to be more degraded (P = .08) in longissimus than in psoas major (50.4 vs 35.1%). Regardless of muscle or treatment, aging 10 d compared to 1 d increased degradation of troponin-T (46.3 vs 15.3%) and desmin (69.3 vs 16.1%). Warner-Bratzler shear force was greater (P < .01) in the shortened treatment than in control (6.9 vs 3.8 kg), greater (P < .01) in longissimus than in the psoas major (6.5 vs 4.2 kg), and greater (P < .01) with 1 d than with 10 d of aging time (6.1 vs 4.6 kg). A muscle x aging time interaction (P < .05) indicated shear force declined more in longissimus than in psoas major during aging. We conclude that sarcomere length did not affect the extent of proteolysis. However, sarcomere length may have an indirect effect on tenderization during aging due to its effect on initial tenderness. PMID:10492451
Scientific Electronic Library Online (English)
Marielen de Lima, Silva; Carmen Josefina, Contreras-Castillo; Edwin Moisés Marcos, Ortega.
2007-09-01
Full Text Available O presente experimento foi realizado para determinar a efetividade do tratamento térmico em água e vapor a 80 °C tendo como objetivo a inativação do Clostridium botulinum tipo E, utilizando-se amostras de Semintendinosus. Foram realizadas ainda a avaliação da maciez objetiva, utilizando-se a análise [...] de força de cisalhamento, e a avaliação sensorial dos atributos de suculência, maciez subjetiva, "flavor" e presença de colágeno. O tratamento a 80 °C foi efetivo na eliminação do microrganismo, contudo não houve diferença significativa no atributo maciez objetiva (força de cisalhamento) avaliado nos dois tratamentos utilizados. A avaliação sensorial apresentou correlação positiva entre os atributos maciez e suculência, enquanto o colágeno apresentou correlação negativa com a maciez. O "flavor" não apresentou correlação com os atributos maciez, suculência e presença de colágeno. Abstract in english The purpose of the experiment reported here was to determine the effectiveness of heat treatments in water and in steam at 80 °C to inactivate the bacterium Clostridium botulinum type E in samples of beef Semitendinosus muscle. The product’s tenderness was evaluated based on a Warner-Bratzler Shear [...] Force (WBSF) analysis and its attributes of juiciness, subjective tenderness, flavor and connective tissue were evaluated sensorially. The treatment at 80 °C effectively killed the bacterium, but no significant difference was found in the attribute of objective tenderness (shear force) evaluated after the two treatments. The sensorial analysis indicated a positive correlation between the attributes of juiciness and tenderness, while the connective tissue showed a negative correlation to tenderness. Flavor proved uncorrelated with tenderness, juiciness and connective tissue.
MEAT SCIENCE AND MUSCLE BIOLOGY SYMPOSIUM--implant and beta agonist impacts on beef palatability.
Garmyn, A J; Miller, M F
2014-01-01
The use of anabolic implants has a long-standing place in the cattle feeding industry, due to their positive impact on growth performance and subsequent profitability. However, implants can have adverse effects on carcass quality, shear force, and eating quality depending on the dose and frequency, or what some refer to as the aggressiveness of the implant regimen administered. Within the past decade, a new class of growth promotants, known as ?-adrenergic agonists (?AA), has emerged in the beef feeding industry in the United States. Currently, 2 have gained U.S. Food and Drug Administration approval for use in beef finishing diets to improve performance and carcass yields. Much like anabolic implants, these repartitioning agents can have negative effects on Warner-Bratzler shear force (WBSF), but the differences do not necessarily translate directly to consumer responses for palatability and acceptance in some instances, especially when tenderness is managed through proper postmortem aging. As researchers continued to investigate the mechanisms responsible for the impact of ?AA, inevitably this led to consideration of the interaction between ?AA and anabolic implants. Early work combining zilpaterol hydrochloride (ZH) with anabolic implants improved performance, carcass yield, and meat yield with additive negative effects on WBSF. Similar results were produced when pairing ZH with anabolic steroids equipped with various release patterns. As with any tool, the key to success is proper management. Certain cattle populations may be better suited to receive growth promotants such as implants and ?AA, and postmortem management of subprimal cuts becomes vital when producers take more aggressive approaches to improve performance and yield. The objective of this review is to overview research findings related to the impact of growth promotant technologies on beef palatability, focusing specifically on the role of implants and ?AA on carcass quality, beef tenderness, and consumer responses for meat palatability. PMID:24158364
International Nuclear Information System (INIS)
One of the scientific success stories of fusion research over the past decade is the development of the ExB shear stabilization model to explain the formation of transport barriers in magnetic confinement devices. This model was originally developed to explain the transport barrier formed at the plasma edge in tokamaks after the L (low) to H (high) transition. This concept has the universality needed to explain the edge transport barriers seen in limiter and divertor tokamaks, stellarators, and mirror machines. More recently, this model has been applied to explain the further confinement improvement from H (high)-mode to VH (very high)-mode seen in some tokamaks, where the edge transport barrier becomes wider. Most recently, this paradigm has been applied to the core transport barriers formed in plasmas with negative or low magnetic shear in the plasma core. These examples of confinement improvement are of considerable physical interest; it is not often that a system self-organizes to a higher energy state with reduced turbulence and transport when an additional source of free energy is applied to it. The transport decrease that is associated with ExB velocity shear effects also has significant practical consequences for fusion research. The fundamental physics involved in transport reduction is the effect of ExB shear on the growth, radial extent and phase correlation of turbulent eddies in the plasma. The same fundamental transport reduction process can be operational in various portions of the plasma because there are a number ways to change the radial electric field Er. An important theme in this area is the synergistic effect of ExB velocity shear and magnetic shear. Although the ExB velocity shear appears to have an effect on broader classes of microturbulence, magnetic shear can mitigate some potentially harmful effects of ExB velocity shear and facilitate turbulence stabilization
A New Annular Shear Piezoelectric Accelerometer
DEFF Research Database (Denmark)
Liu, Bin; Kriegbaum, B.
2000-01-01
This paper describes the construction and performance of a recently introduced Annular Shear piezoelectric accelerometer, Type 4511. The design has insulated and double-shielded case. The accelerometer housing is made of stainless steel, AISI 316L. Piezoceramic PZ23 is used. The seismic mass is made of tungsten. All processes and materials comply with MIL-STD-11268. The mounted resonance frequency exceeds 40kHz. The sensitivity is 10mV/g ±5%. During the design process, the new design is evaluated and sufficiently optimized by using the Finite Element (FE) simulation before making actual prototype. Reasonable agreement between the experimental results of the physical prototype and the simulation results is achieved. The design becomes more efficient. In addition, Type 4511 has a built in DeltaTronâ charge amplifier with ID and complies with IEEE-P1451.4 standard, which is a smart transducer interface for sensors including mixed-mode communication protocols and transducer electronic data sheet (TEDS).
Breaking up: Fault zone evolution during shear
Mair, K.; Abe, S.; Bjork, T.
2007-12-01
To better understand fault zone dynamics we need an improved understanding of the underlying micro- mechanics of the fault evolution process. Our basic data is gleaned from quantitative observations of structural fabrics associated with natural fault systems. However, such datasets generally record the final state of evolution, from which it is often difficult to discern the dynamic micro-scale processes involved, such as preferential fragmentation and strain partitioning, or the macro-mechanical behaviour of a fault. Laboratory experiments give valuable insights into links between microscale processes and macro-mechanical behaviour. Similarly, numerical simulations are very useful tools for visualising dynamic grain-scale interactions not readily visible from nature. Together these tools can help us identify and isolate first order parameters that are relevant for the faulting process. We present recent results from 3D simulations that implement realistic gouge evolution during shear. Our particle based simulation includes breakable elastic bonds between individual particles allowing fracture of aggregate grains that are composed of many bonded particles. With accumulated strain, aggregate grains fragment in different ways, gradually evolve in size and shape to produce a textural signature reminiscent of natural faults. We use a new image analysis tool to characterise grain shape and size distributions from thin sections obtained from natural and experimental fault rocks and are now applying this tool to 3D model results. This approach allows us to build on existing observations and permits closer investigation of dynamic bumping, grinding and fragmentation processes that may be operating in evolving fault zones.
Symmetry related dynamics in parallel shear flows
Kreilos, Tobias
2013-01-01
Parallel shear flows come with continuous symmetries of translation in the downstream and spanwise direction. Flow states that differ in their spanwise or downstream location but are otherwise identical are dynamically equivalent. In the case of travelling waves, this trivial degree of freedom can be removed by going to a frame of reference that moves with the state, thereby turning the travelling wave in the laboratory frame to a fixed point in the co-moving frame of reference. Further exploration of the symmetry suggests a general method by which the translational displacements can be removed also for more complicated and dynamically active states. We will describe the method and discuss its relation to general symmetry reductions and to the Taylor frozen flow hypothesis. We will demonstrate the method for the case of the asymptotic suction boundary layer. When applied to the oscillatory edge state with its long period, the method allows to find local phase speeds which remove the fast oscillations so that ...
Shear Flow Generation in Stellarators - Configurational Variations
International Nuclear Information System (INIS)
Plasma momentum transport within magnetic surfaces plays a fundamental role in a number of toroidal plasma physics issues, such as turbulence suppression, impurity transport, bootstrap current generation and the shielding of resonant magnetic error field perturbations. Stellarators provide opportunities for improved understanding of plasma flow effects because (a) new forms of quasi-symmetry (e.g. helical, poloidal) can be produced that differ significantly from the tokamak and (b) symmetry-breaking effects (always present to some degree) reduce the close coupling between parallel and cross-field transport characteristics of symmetric systems. External control coils can also be used to further enhance or suppress such effects. A method has been developed to evaluate the variation of neoclassical self-generated plasma flows in stellarators both within and across magnetic surfaces. This introduces a new dimension into both the optimization of stellarators and to the improved understanding of the existing confinement database. Application of this model to a range of configurations indicates that flow directionality and shearing rates are significantly influenced by the magnetic structure. In addition, it is demonstrated that flows in stellarators are sensitive to profile effects and the presence of external momentum sources, such as neutral beams
Shear flow generation in stellarators - Configurational variations
International Nuclear Information System (INIS)
Plasma momentum transport within magnetic surfaces plays a fundamental role in a number of toroidal plasma physics issues, such as: turbulence suppression, impurity transport, bootstrap current generation, and the shielding of resonant magnetic error field perturbations. Stellarators provide opportunities for improved understanding of plasma flow effects because (a) new forms of quasi-symmetry (e.g., helical, poloidal) can be produced that differ significantly from the tokamak; and (b) symmetry-breaking effects (always present to some degree) remove the degeneracy between parallel and cross-field transport characteristic of symmetric systems. External control coils can also be used to further enhance or suppress such effects. A method has been developed to evaluate the variation of neoclassical self-generated plasma flows in stellarators both within and across magnetic surfaces. This introduces a new dimension into both the optimization of stellarators and to the improved understanding of the existing confinement database. Application of this model to a range of configurations indicates that flow directionality and shearing rates are significantly influenced by the magnetic structure. In addition, it is demonstrated that flows in stellarators are sensitive to profile effects and the presence of external momentum sources, such as neutral beams. (author)
Shear rheology of a cell monolayer
International Nuclear Information System (INIS)
We report a systematic investigation of the mechanical properties of fibroblast cells using a novel cell monolayer rheology (CMR) technique. The new technique provides quantitative rheological parameters averaged over ?106 cells making the experiments highly reproducible. Using this method, we are able to explore a broad range of cell responses not accessible using other present day techniques. We perform harmonic oscillation experiments and step shear or step stress experiments to reveal different viscoelastic regimes. The evolution of the live cells under externally imposed cyclic loading and unloading is also studied. Remarkably, the initially nonlinear response becomes linear at long timescales as well as at large amplitudes. Within the explored rates, nonlinear behaviour is only revealed by the effect of a nonzero average stress on the response to small, fast deformations. When the cell cytoskeletal crosslinks are made permanent using a fixing agent, the large amplitude linear response disappears and the cells exhibit a stress stiffening response instead. This result shows that the dynamic nature of the cross-links and/or filaments is responsible for the linear stress-strain response seen under large deformations. We rule out the involvement of myosin motors in this using the inhibitor drug blebbistatin. These experiments provide a broad framework for understanding the mechanical responses of the cortical actin cytoskeleton of fibroblasts to differen cytoskeleton of fibroblasts to different imposed mechanical stimuli
The Lamella High Shear Rate REFLUX™ Classifier
Scientific Electronic Library Online (English)
T, Orupold; D, Starr; T, Kenefick.
2014-07-01
Full Text Available This paper covers the commercial development of gravity separation of fine particles using a Lamella High Shear Rate REFLUX™ Classifier (REFLUX™ Classifier), focusing primarily on coal applications. The REFLUX™ Classifier is a fluidized bed device that incorporates a system of closely spaced paralle [...] l inclined channels located above the fluidized bed. These channels make it possible to achieve a significant suppression of the effects of particle size, resulting in a highly effective separation on the basis of density. The improved gravity separation performance is shown to be remarkably high, with a significant reduction in the variation of separation density with particle size, and a significant reduction in the change in Ecart probable error (Ep) with size. The first full commercial-sized units of the REFLUX™ Classifier were field-tested in late 2009 in coal applications. More recently, the technology has been applied in fine particle separation in minerals applications and there are a number of full-sized units operating in chrome applications in South Africa. Initially, pilot-scaled units (typically the RC™300) were trialled in iron ore, mineral sands, and manganese plants amongst other minerals, typically after other technologies failed to achieve the desired results. Currently a number of laboratories globally are carrying out more testing in minerals applications. More than 50 RC™ units are now operating in coal and minerals applications. This paper introduces the REFLUX™ Classifier technology, identifies commercial applications, and gives some commercial results.
On the persistence of adiabatic shear bands
Directory of Open Access Journals (Sweden)
Bassim M.N.
2012-08-01
Full Text Available It is generally agreed that the initiation and development of adiabatic shear bands (ASBs are manifestations of damage in metallic materials subjected to high strain rates and large strains as those due to impact in a Hopkinson Bar system. Models for evolution of these bands have been described in the literature. One question that has not received attention is how persistent these bands are and whether their presence and effect can be reversed or eliminated by using a process of thermal (heat treatment or thermo-mechanical treatment that would relieve the material from the high strain associated with ASBs and their role as precursors to crack initiation and subsequent failure. Since ASBs are more prevalent and more defined in BCC metals including steels, a study was conducted to investigate the best conditions of generating ASBs in a heat treatable steel, followed by determining the best conditions for heat treatment of specimens already damaged by the presence of ASBs in order to relieve the strains due to ASBs and restore the material to an apparent microstructure without the “scars” due to the previous presence of ASBs. It was found that heat treatment achieves the curing from ASBs. This presentation documents the process undertaken to achieve this objective.
International Nuclear Information System (INIS)
This paper describes the ultimate load capacities of typical post-installed anchor bolts under static tension, shear and combined tension and shear (combination) loads. The static loading test applying tension, shear, and combination loads was carried out on post-installed anchor bolts, such as resin-anchor bolt, and two types of mechanical anchor bolt: undercut type and sleeve-expansion type. Based on the test results, the equations currently used to calculate the ultimate allowable loading capacity of post-installed anchor bolts were investigated to establish the confidence level. Particular attention was paid to the ultimate load carrying capacities for combination loads
Shear wave splitting and shear wave splitting tomography of the southern Puna plateau
Calixto, Frank J.; Robinson, Danielle; Sandvol, Eric; Kay, Suzanne; Abt, David; Fischer, Karen; Heit, Ben; Yuan, Xiaohui; Comte, Diana; Alvarado, Patricia
2014-11-01
We have investigated the seismic anisotropy beneath the Central Andean southern Puna plateau by applying shear wave splitting analysis and shear wave splitting tomography to local S waves and teleseismic SKS, SKKS and PKS phases. Overall, a very complex pattern of fast directions throughout the southern Puna plateau region and a circular pattern of fast directions around the region of the giant Cerro Galan ignimbrite complex are observed. In general, teleseismic lag times are much greater than those for local events which are interpreted to reflect a significant amount of sub and inner slab anisotropy. The complex pattern observed from shear wave splitting analysis alone is the result of a complex 3-D anisotropic structure under the southern Puna plateau. Our application of shear wave splitting tomography provides a 3-D model of anisotropy in the southern Puna plateau that shows different patterns depending on the driving mechanism of upper-mantle flow and seismic anisotropy. The trench parallel a-axes in the continental lithosphere above the slab east of 68W may be related to deformation of the overriding continental lithosphere since it is under compressive stresses which are orthogonal to the trench. The more complex pattern below the Cerro Galan ignimbrite complex and above the slab is interpreted to reflect delamination of continental lithosphere and upwelling of hot asthenosphere. The a-axes beneath the Cerro Galan, Cerro Blanco and Carachi Pampa volcanic centres at 100 km depth show some weak evidence for vertically orientated fast directions, which could be due to vertical asthenospheric flow around a delaminated block. Additionally, our splitting tomographic model shows that there is a significant amount of seismic anisotropy beneath the slab. The subslab mantle west of 68W shows roughly trench parallel horizontal a-axes that are probably driven by slab roll back and the relatively small coupling between the Nazca slab and the underlying mantle. In contrast, the subslab region (i.e. depths greater than 200 km) east of 68W shows a circular pattern of a-axes centred on a region with small strength of anisotropy (Cerro Galan and its eastern edge) which suggest the dominant mechanism is a combination of slab roll back and flow driven by an overlying abnormally heated slab or possibly a slab gap. There seems to be some evidence for vertical flow below the slab at depths of 200-400 km driven by the abnormally heated slab or slab gap. This cannot be resolved by the tomographic inversion due to the lack of ray crossings in the subslab mantle.
Stress Analysis of Shear Thinning Synovial Fluid Flow
Ashrafi, Nariman
2008-07-01
Stress analysis is carried out for normal (shear thinning) and pathological (Newtonian) synovial fluid in joint articulation in general. The fluid is assumed to follow the Carreau-Bird model in the concentric-cylinder flow. The effect of shear thinning phenomena on velocities and consequently stresses is then explored. Obtained from the conservation of mass and momentum equations, the dynamical system includes additional nonlinear terms in the velocity and stress components through the shear-dependent viscosity otherwise non existent in Newtonian systems. The analysis shows that change of stability picture of base flow due to the nonlinearity actually causes stress regularization. Clinical data show rapid increase of both shear and normal stresses for pathological synovial fluid (inflammatory or degenerative) during certain angles of articulation which corresponds to the evaluated stresses in this study as the fluid approaches Newtonian range.
On the behaviour of gelled fibre suspensions in steady shear
Energy Technology Data Exchange (ETDEWEB)
Wolf, Bettina [Unilever Corporate Research, Bedford (United Kingdom); University of Nottingham, Division of Food Sciences, Loughborough (United Kingdom); White, Duncan; Melrose, John R.; Frith, William J. [Unilever Corporate Research, Bedford (United Kingdom)
2007-03-15
The shear rheological properties of suspensions of gelled agar fibres in a low viscosity Newtonian matrix fluid were investigated. Two classes of fibres, low aspect ratio fibres and high aspect ratio fibres with an aspect ratio of the order of 10 and 100 respectively were included in the investigations. For all fibre phase volumes investigated, from as low as 0.01 upwards, the flow curves are characterised by an apparent yield stress followed by shear-thinning which was independent of the fibre aspect ratio. Based on our analysis of the flow curves, we conclude that the high aspect ratio fibres behave like flexible threads in contrast to the low aspect ratio fibres whose high shear relative viscosity is successfully described by a relation for long rigid rods. These findings are supported by flow visualisation using an optical shearing stage coupled to a light microscope. (orig.)
Electromagnetic effects in the stabilization of turbulence by sheared flow
Cole, M D J; Cowley, S C; Loureiro, N F; Dickinson, D; Roach, C; Connor, J W
2013-01-01
We have extended our study of the competition between the drive and stabilization of plasma microinstabilities by sheared flow to include electromagnetic effects at low plasma $\\beta$ (the ratio of plasma to magnetic pressure). The extended system of characteristic equations is formulated, for a dissipative fluid model developed from the gyrokinetic equation, using a twisting mode representation in sheared slab geometry and focusing on the ion temperature gradient mode. Perpendicular flow shear convects perturbations along the field at the speed we denote as $Mc_s$ (where $c_s$ is the sound speed). $M > 1/ \\sqrt{\\beta}$ is required to make the system characteristics unidirectional and inhibit eigenmode formation, leaving only transitory perturbations in the system. This typically represents a much larger flow shear than in the electrostatic case, which only needs $M>1$. Numerical investigation of the region $M < 1/\\sqrt{\\beta}$ shows the driving terms can conflict, as in the electrostatic case, giving low ...
Stability of two-layer shear-thinning film flows
Millet, S.; Botton, V.; Ben Hadid, H.; Henry, D.; Rousset, F.
2013-10-01
The stability of a two-layer film flow of non-Newtonian fluids is studied with a linear temporal approach. Shear-thinning fluids are considered, which follow the four-parameter inelastic Carreau model. A modified Orr-Sommerfeld equation system is obtained, which is solved by using a spectral Tau collocation method based on Chebyshev polynomials. The effects of density and viscosity stratification are considered, as well as the influence of the shear-thinning properties of the fluid. It is found that, when the viscosity is stronger in the upper layer, the base flow and the stability properties are almost not influenced by the change of the shear-thinning properties in this upper layer. In the other situations, the shear-thinning properties have an influence on the different instabilities, the long-wave surface instability and the short- and long-wave interface instabilities.
Critical transition model of edge shear flow formation
International Nuclear Information System (INIS)
Recently, the experimental results for the emergence of the plasma shear flow layer in TJ-II have been explained as a second-order phase transition like process by using a simple model of envelope equations for the fluctuation level, the averaged poloidal velocity shear, and the pressure gradient. Here, we extend this model by incorporating radial coupling. The model is applied to the study of the turbulence-shear flow interaction when the energy flux is low. Transition dynamics and their concomitant thresholds are examined within the context of this model. The effect of an external torque has also been considered. In particular, we analyze the damping rate of the shear flow once the external torque has been removed. (author)
Interaction of equal-size bubbles in shear flow.
Prakash, Jai; Lavrenteva, Olga M; Byk, Leonid; Nir, Avinoam
2013-04-01
The inertia-induced forces on two identical spherical bubbles in a simple shear flow at small but finite Reynolds number, for the case when the bubbles are within each other's inner viscous region, are calculated making use of the reciprocal theorem. This interaction force is further employed to model the dynamics of air bubbles injected to a viscous fluid sheared in a Couette device at the first shear flow instability where the bubbles are trapped inside the stable Taylor vortex. It was shown that, during a long time scale, the inertial interaction between the bubbles in the primary shear flow drives them away from each other and, as a result, equal-size bubbles eventually assume an ordered string with equal separation distances between all neighbors. We report on experiments showing the dynamic evolution of various numbers of bubbles. The results of the theory are in good agreement with the experimental observations. PMID:23679508
Order-disorder transitions in a sheared many body system
Pfeifer, Jens C; Ehlers, Georg; Eckhardt, Bruno
2015-01-01
Motivated by experiments on sheared suspensions that show a transition between ordered and disordered phases, we here study the long-time behavior of a sheared and overdamped 2-d system of particles interacting by repulsive forces. As a function of interaction strength and shear rate we find transitions between phases with vanishing and large single-particle diffusion. In the phases with vanishing single-particle diffusion, the system evolves towards regular lattices, usually on very slow time scales. Different lattices can be approached, depending on interaction strength and forcing amplitude. The disordered state appears in parameter regions where the regular lattices are unstable. Correlation functions between the particles reveal the formation of shear bands. In contrast to single particle densities, the spatially resolved two-particle correlation functions vary with time and allow to determine the phase within a period. As in the case of the suspensions, motion in the state with low diffusivity is essent...
Shear Transfer Mechanism of RC Plates After Cracking
International Nuclear Information System (INIS)
The Nuclear Power Engineering Corporation (NUPEC) has been conducting a project of 'Model Tests of Multi-axis Loading on RC Shear Walls', and as a part of the project, loading tests of RC (reinforced concrete) plates have been carried out. The plates were designed to represent part of a RC seismic shear wall of a reactor building, and test conditions were determined from actual reactor building conditions. The purpose of the test is to clarify the shear transfer mechanisms (constitutive equation) of RC plates which have small cracks due to tensile force, and to apply the formula deduced from test results to non-linear FEM analysis code. Other activities of NUPEC related to the non-linear behavior of RC walls are also briefly introduced. Results from the test will be used for the evaluation and formulation of shear transfer mechanisms, and will be utilized for the simulation of other tests performed in this project
Magnetic diffusion driven shear instability of solar flux tubes
Pandey, B P
2012-01-01
Macroscopic motion of the gas is widespread throughout the solar atmosphere and shearing motions couple to the non-ideal MHD effects, altogether destabilising low frequency fluctuations in the medium. The origin of such non-ideal magnetohydrodynamic instability lies in the collisional coupling of the neutral particles to the magnetized plasma in the presence of sheared background flows. Expectedly the maximum growth rate and most unstable wavenumber depend on the flow gradient and ambient diffusivities. The orientation of the magnetic field, velocity shear and perturbation wavevector play crucial role in assisting the instability. In the presence of only vertical field and vertical wavevector, ambipolar and Ohm diffusion can be combined together as Pedersen diffusion and causes only damping; in this case only Hall drift in tandem with shear flow drives the instability. However, for non-vertical field and oblique wavevector, both ambipolar diffusion and Hall drift assist the instability. We investigate the sta...
Clouds of particles in a periodic shear flow
Metzger, Bloen; Butler, Jason E.
2012-02-01
We have investigated the time evolution of a cloud of non-Brownian particles subjected to a periodic shear flow in an otherwise pure liquid at low Reynolds number. This experiment illustrates the irreversible nature of particulate systems submitted to a shear. When repeating the cycles of shear, we have found that clouds of particles progressively disperse in the flow direction until reaching a threshold critical volume fraction that depends upon the strain amplitude; this critical volume fraction coincides with measurements of the threshold for reversibility found from experiments on homogeneous suspensions in periodic shear. Two distinct patterns, including a "galaxy-like" shape, are observed for the evolution of the clouds and the transition between the patterns is identified using a simple scaling analysis. Movies are available with the online version of the paper.
Stress fluctuations in monodisperse and bidisperse rapid granular shear flows
Jalali, Payman; Ritvanen, Jouni; Sarkomaa, Pertti
2006-09-01
Local stress fluctuations are measured in annular rapid shear flows of granular medium made of steel spheres with 2 and 3 mm in diameter. Both monodisperse packing and bidisperse packing are investigated to reveal the influence of size diversity on intermittent features of granular materials. Experiments are conducted in an annulus that can contain up to 15 kg of the spherical steel balls. Shearing of granular medium takes place via the rotation of the upper plate which compresses the material loaded inside the annulus. Fluctuations of compressive force are locally measured at the bottom of the annulus based on piezoelectric phenomenon. Rapid shear flow experiments are pursued at different compressive forces and shear rates and the sensitivity of fluctuations is then investigated by different means through monodisperse and bidisperse packings.
Shear dilatancy in unconsolidated laboratory samples improves relative permeability performance
Energy Technology Data Exchange (ETDEWEB)
Khan, Hasnain A.; Olson, Jon E. [Society of Petroleum Engineers (Canada); Holder, Jon [University of Texas at Austin (United States)
2011-07-01
Dilatant shear failure can occur in unconsolidated heavy oil reservoirs as a result of steam assisted gravity drainage (SAGD). This paper discusses the changes induced by dilatant shear failure in absolute permeability, relative permeability to oil and water and residual saturations. Synthetic specimens 2 inches in diameter made from lower fine to medium grain size Ottawa sand were tested. Triaxial compression and radial extension loading paths were used. During deformation, volumetric and axial strains were measured directly. The relative permeability was determined using the unsteady state method. Shearing strongly affects relative permeabilities. The effect is slightly greater for finer grain than for medium grain. During triaxial testing, it was seen that absolute permeability increased with shearing at 50 psi stress. But at 200 psi, absolute permeability decreased, even though the volumetric strain was still dilatant. From both triaxial and radial extension tests, it was evident that oil and water relative permeability is affected by stresses acting on the sand pack.
Production of functional proteins: balance of shear stress and gravity
Goodwin, Thomas John (Inventor); Hammond, Timothy Grant (Inventor); Kaysen, James Howard (Inventor)
2011-01-01
A method for the production of functional proteins including hormones by renal cells in a three dimensional culturing process responsive to shear stress uses a rotating wall vessel. Natural mixture of renal cells expresses the enzyme 1-.alpha.-hydroxylase which can be used to generate the active form of vitamin D: 1,25-diOH vitamin D.sub.3. The fibroblast cultures and co-culture of renal cortical cells express the gene for erythropoietin and secrete erythropoietin into the culture supernatant. Other shear stress response genes are also modulated by shear stress, such as toxin receptors megalin and cubulin (gp280). Also provided is a method of treating an in-need individual with the functional proteins produced in a three dimensional co-culture process responsive to shear stress using a rotating wall vessel.
Sheared coronal arcades - An evaluation of recent studies
International Nuclear Information System (INIS)
The family of magnetic force-free equilibria obtained by Low (1977) using the generating function method is really a sequence of Gold-Hoyle flux tubes. This sequence is stable under a wide range of solar conditions since each member, specified by the shear parameter mu, is anchored to the photosphere along an axial slice. Recent magnetic relaxation simulations by Klimchuk and Sturrock (1989) are fundamentally incapable of representing the unconnected helical field lines inherent in the high-shear (mu greater than 1) Low solutions. Nonetheless, the numerical simulations are more likely to describe the equilibria of highly sheared arcades, since they involve no change in topology with increasing shear. This view is reinforced by magnetic energy calculations which confirm that the Gold-Hoyle solutions are more energetic for mu greater than 1 than the numerical equilibria of Klimchuk and Sturrock. 14 refs
Hydrodynamic instabilities in a periodically sheared nematic liquid crystal
Guazzelli, E.; Koch, A.-J.
1985-01-01
We report the observation of roll and square instabilities induced by various periodical shears in a nematic liquid cell. The experimental threshold curves are compared with the theoretical model of Koch, Rothen, Sadik and Schöri.
Stratified shear flow instabilities in the non-Boussinesq regime
Heifetz, Eyal
2015-01-01
Effects of the baroclinic torque on wave propagation normally neglected under the Boussinesq approximation is investigated here, with a special focus on the associated consequences for the mechanistic interpretation of shear instability arising from the interaction between a pair of vorticity-propagating waves. To illustrate and elucidate the physical effects that modify wave propagation, we consider three examples of increasing complexity: wave propagation supported by a uniform background flow; wave propagation supported on a piecewise-linear basic state possessing one jump; and an instability problem of a piecewise-linear basic state possessing two jumps, which supports the possibility of shear instability. We find that the non-Boussinesq effects introduces a preference for the direction of wave propagation that depends on the sign of the shear in the region where waves are supported. This in turn affects phase-locking of waves that is crucial for the mechanistic interpretation for shear instability, and i...
Finite element analyses for Seismic Shear Wall International Standard Problem
International Nuclear Information System (INIS)
In the seismic design of shear wall structures, e.g., nuclear reactor buildings, a linear FEM analysis is frequently used to quantify the stresses under the design loading condition. The final design decisions, however, are still based on empirical design rules established over decades from accumulated laboratory test data. This paper presents an overview of the state-of-the-art on the application of nonlinear FEM analysis to reinforced concrete (RC) shear wall structures under severe earthquake loadings based on the findings obtained during the Seismic Shear Wall International Standard Problem (SSWISP) Workshop in 1996. Also, BNL's analysis results of the International Standard Problem (ISP) shear walls under monotonic static, cyclic static and dynamic loading conditions are described
Density gradient effects on transverse shear driven lower hybrid waves
DuBois, Ami M.; Thomas, Edward; Amatucci, William E.; Ganguli, Gurudas
2014-06-01
Shear driven instabilities are commonly observed in the near-Earth space, particularly in boundary layer plasmas. When the shear scale length (LE) is much less than the ion gyro-radius (?i) but greater than the electron gyro-radius (?e), the electrons are magnetized in the shear layer, but the ions are effectively un-magnetized. The resulting shear driven instability, the electron-ion hybrid (EIH) instability, is investigated in a new interpenetrating plasma configuration in the Auburn Linear EXperiment for Instability Studies. In order to understand the dynamics of magnetospheric boundary layers, the EIH instability is studied in the presence of a density gradient located at the boundary layer between two plasmas. This paper reports on a recent experiment in which electrostatic lower hybrid waves are identified as the EIH instability, and the effect of a density gradient on the instability properties are investigated.
Bulk and shear viscosities of hot and dense hadron gas
Kadam, Guru Prakash
2014-01-01
We estimate bulk and shear viscosity at finite temperature and baryon densities of hadronic matter within hadron resonance gas model. For bulk viscosity we use low energy theorems of QCD for the energy momentum tensor correlators. For shear viscosity coefficient, we estimate the same using molecular kinetic theory to relate the shear viscosity coefficient to average momentum of the hadrons in the hot and dense hadron gas. The bulk viscosity to entropy ratio increases with chemical potential and is related to the reduction of velocity of sound at nonzero chemical potential. The shear viscosity to entropy ratio on the other hand, shows a nontrivial behavior with the ratio decreasing with chemical potential for small temperatures but increasing with chemical potential at high temperatures and is related to decrease of entropy density with chemical potential at high temperature due to finite volume of the hadrons.
Large In Situ Shear Test Box for Mine Waste Dump
Rai, R.; Shrivastva, B. K.
2012-04-01
Shear strength of the dump material is very important in the stability analysis of slope. Determination of shear strength of dump or vegetated dump is very complicated and also requires large size of specimen so that it represents the true behaviour of dump mass with and without vegetation. Large size shear box (1.5 × 1.5 × 0.75 m) and small shear boxes (0.3 × 0.3 × 0.15 m) have been fabricated and used for the present study. Various types of plants have been grown in the mine waste dump in the laboratory. The grasses increased cohesion of the dump mass up to 27 kPa whereas the shrubs increased the cohesion up to 32 kPa in given conditions. The increased cohesion depends on the depth of root and age of tree. It generally varies from 10 to 80 kPa or more depending on the age of the tree.
Simple shear behaviour of palm biodiesel contaminated soil
Directory of Open Access Journals (Sweden)
Chew S. J.
2010-12-01
Full Text Available Palm biodiesel contaminations may bring adverse effect on basic geotechnical properties of foundation soils. This paper presents the results of an experimental study on shear behaviour of palm biodiesel contaminated sandy soil. A comprehensive set of laboratory experiments have been undertaken in a direct simple shear device on samples of palm biodiesel contaminated sandy soil. In the experiments the soil samples were prepared by mixing the sandy soil with B20 palm biodiesel ranging from 0% to 20% by weight. Stress-strain and shear strength response for the samples were monitored continuously during the experiments. The effect of the palm biodiesel content, relative density and normal stress on the shear behaviour of the sandy soil is investigated and discussed.
Shear Capacity of Steel and Polymer Fibre Reinforced Concrete Beams
Kragh-poulsen, Jens C.; Hoang, Cao Linh; Goltermann, Per
2010-01-01
This paper deals with the application of a plasticity model for shear strength estimation of fibre reinforced concrete beams without stirrups. When using plastic theory to shear problems in structural concrete, the so-called effective strengths are introduced, usually determined by calibrating the plastic solutions with tests. This approach is, however, problematic when dealing with fibre reinforced concrete (FRC), as the effective strengths depend also on the type and the amount of fibres. I...
Shear Induced Structural Ordering of a Model Metallic Glass
Mokshin, Anatolii; Barrat, Jean-louis
2008-01-01
We report results of non-equilibrium molecular dynamics simulations of a one-component glassy system under the influence of a shear flow, with the aim of investigating shear induced ordering of this system. In spite of the very low temperature, the system transforms into a strained crystalline state through well defined nucleation events. Various characteristics of the observed ordering at different strain rates and temperatures are discussed. We also define and discuss the ...
Postbuckling behaviour of rectangular plates under pure shear
Kumar, Ashwini; Sindhi, Paras R.
1992-11-01
The postbuckling behavior of isotropic and orthotropic rectangular plates under pure shear is investigated by considering a plate which is simply supported on all edges and by assuming inplane conditions corresponding to the NASTRAN model reported by Agarwal (1981). Results are presented on the analyses of plates of different aspect ratios, including the load-deflection curves, deflection contours, load-shear displacement curves, and stress distributions.
Thermonuclear Fusion with the Sheared Flow Stabilized Z-Pinch
Winterberg, F.; Wanex, L. F.
2008-01-01
Two basic approaches to producing thermonuclear fusion with a sheared flow stabilized z-pinch are considered. One consists of heating the entire length of the z-pinch column to the required temperatures. The other basic approach considered here involves the concept of fast ignition. A localized "hot-spot" is produced under the proper conditions to ignite a thermonuclear burn wave in the z-pinch plasma. Here we demonstrate that sheared flow stabilization is more efficient in ...
On shear flow stabilization concepts for the dense z pinch
Winterberg, F.
2009-01-01
Different ways to achieve the stabilization of a linear z-pinch by a superimposed shear flow are analyzed. They are: 1) Axial shear flow proposed by Arber and Howell with the pinch discharge in its center, and experimentally tested by Shumlak et al. 2) Spiral flow of a dense low temperature plasma surrounding a dense pinch discharge. 3) A thin metallic projectile shot at a high velocity through the center of the pinch discharge. 4) The replacement of the high velocity projec...
Shear-Wave Elastography of Segmental Infarction of the Testis
Energy Technology Data Exchange (ETDEWEB)
Kantarci, Faith; Olgun, Deniz Cebi; Mihmanli, Ismail [Dept. of Radiology, Istanbul University, Cerrahpasa Medical Faculty, Istanbul (Turkey)
2012-11-15
Segmental testicular infarction (STI) is a rare cause of acute scrotum. The spectrum of findings on gray-scale and color Doppler ultrasonography differ depending on the time between the onset of testicular pain and the ultrasonography examination. We are not aware of the usefulness of shear-wave elastography for the diagnosis of STI. We report the shear-wave elastography features in a case of STI and discuss the role of this diagnostic modality in the differential diagnosis.
Boundary shear stress distribution and flow structures in trapezoidal channels
Ansari, Kamran
2011-01-01
The commercially available Computational Fluid Dynamics (CFD) software ANSYS-CFX version 11 (2008) is employed to predict the distribution of the bed and sidewall shear stresses in trapezoidal open channels. The investigation includes computation of wall shear stress (1) directly, using CFD for a range of channels layouts (straight, turning, with ridges), and (2), building on the division line concept initially formulated by Leighly in 1932 and later by Einstein in 1942, through the evaluatio...
Microstructure of a liquid complex (dusty) plasma under shear
Nosenko, V.; Ivlev, A. V.; Morfill, G. E.
2012-01-01
The microstructure of a strongly coupled liquid undergoing a shear flow was studied experimentally. The liquid was a shear melted two-dimensional plasma crystal, i.e., a single-layer suspension of micrometer-size particles in a rf discharge plasma. Trajectories of particles were measured using video microscopy. The resulting microstructure was anisotropic, with compressional and extensional axes at around $\\pm 45^{\\circ}$ to the flow direction. Corresponding ellipticity of t...
Dynamical regimes and hydrodynamic lift of viscous vesicles under shear
Linger, Sebastian Meß; Schmidt, Benjamin; Noguchi, Hiroshi; Gompper, Gerhard
2009-01-01
The dynamics of two-dimensional viscous vesicles in shear flow, with different fluid viscosities $\\eta_{\\rm in}$ and $\\eta_{\\rm out}$ inside and outside, respectively, is studied using mesoscale simulation techniques. Besides the well-known tank-treading and tumbling motions, an oscillatory swinging motion is observed in the simulations for large shear rate. The existence of this swinging motion requires the excitation of higher-order undulation modes (beyond elliptical defo...