Simulation of thermo-mechanical effect in bulk-silicon FinFETs

OpenAIRE

Burenkov, Alex; Lorenz, Jürgen

2016-01-01

The thermo-mechanical effect in bulk-silicon FinFETs of the 14 nm CMOS technology node is studied by means of numerical simulation. The electrical performance of such devices is significantly enhanced by the intentional introduction of mechanical stress during the device processing. The thermo-mechanical effect modifies the mechanical stress distribution in active regions of the transistors when they are heated. This can lead to a modification of the electrical performance. Numerical simulati...

Finite element simulations of two rock mechanics tests

International Nuclear Information System (INIS)

Dahlke, H.J.; Lott, S.A.

1986-04-01

Rock mechanics tests are performed to determine in situ stress conditions and material properties of an underground rock mass. To design stable underground facilities for the permanent storage of high-level nuclear waste, determination of these properties and conditions is a necessary first step. However, before a test and its associated equipment can be designed, the engineer needs to know the range of expected values to be measured by the instruments. Sensitivity studies by means of finite element simulations are employed in this preliminary design phase to evaluate the pertinent parameters and their effects on the proposed measurements. The simulations, of two typical rock mechanics tests, the plate bearing test and the flat-jack test, by means of the finite element analysis, are described. The plate bearing test is used to determine the rock mass deformation modulus. The flat-jack test is used to determine the in situ stress conditions of the host rock. For the plate bearing test, two finite element models are used to simulate the classic problem of a load on an elastic half space and the actual problem of a plate bearing test in an underground tunnel of circular cross section. For the flat-jack simulation, a single finite element model is used to simulate both horizontal and vertical slots. Results will be compared to closed-form solutions available in the literature

Computer simulations of the mechanical properties of metals

DEFF Research Database (Denmark)

Schiøtz, Jakob; Vegge, Tejs

1999-01-01

Atomic-scale computer simulations can be used to gain a better understanding of the mechanical properties of materials. In this paper we demonstrate how this can be done in the case of nanocrystalline copper, and give a brief overview of how simulations may be extended to larger length scales....... Nanocrystline metals are metals with grain sizes in the nanometre range, they have a number of technologically interesting properties such as much increased hardness and yield strength. Our simulations show that the deformation mechanisms are different in these materials than in coarse-grained materials...

Pitfall in quantum mechanical/molecular mechanical molecular dynamics simulation of small solutes in solution.

Science.gov (United States)

Hu, Hao; Liu, Haiyan

2013-05-30

Developments in computing hardware and algorithms have made direct molecular dynamics simulation with the combined quantum mechanical/molecular mechanical methods affordable for small solute molecules in solution, in which much improved accuracy can be obtained via the quantum mechanical treatment of the solute molecule and even sometimes water molecules in the first solvation shell. However, unlike the conventional molecular mechanical simulations of large molecules, e.g., proteins, in solutions, special care must be taken in the technical details of the simulation, including the thermostat of the solute/solvent system, so that the conformational space of the solute molecules can be properly sampled. We show here that the common setup for classical molecular mechanical molecular dynamics simulations, such as the Berendsen or single Nose-Hoover thermostat, and/or rigid water models could lead to pathological sampling of the solutes' conformation. In the extreme example of a methanol molecule in aqueous solution, improper and sluggish setups could generate two peaks in the distribution of the O-H bond length. We discuss the factors responsible for this somewhat unexpected result and evoke a simple and ancient technical fix-up to resolve this problem.

Modelling and Simulation Based on Matlab/Simulink: A Press Mechanism

International Nuclear Information System (INIS)

Halicioglu, R; Dulger, L C; Bozdana, A T

2014-01-01

In this study, design and kinematic analysis of a crank-slider mechanism for a crank press is studied. The crank-slider mechanism is the commonly applied one as direct and indirect drive alternatives in practice. Since inexpensiveness, flexibility and controllability are getting more and more important in many industrial applications especially in automotive industry, a crank press with servo actuator (servo crank press) is taken as an application. Design and kinematic analysis of representative mechanism is presented with geometrical analysis for the inverse kinematic of the mechanism by using desired motion concept of slider. The mechanism is modelled in MATLAB/Simulink platform. The simulation results are presented herein

Modelling and Simulation Based on Matlab/Simulink: A Press Mechanism

Science.gov (United States)

Halicioglu, R.; Dulger, L. C.; Bozdana, A. T.

2014-03-01

In this study, design and kinematic analysis of a crank-slider mechanism for a crank press is studied. The crank-slider mechanism is the commonly applied one as direct and indirect drive alternatives in practice. Since inexpensiveness, flexibility and controllability are getting more and more important in many industrial applications especially in automotive industry, a crank press with servo actuator (servo crank press) is taken as an application. Design and kinematic analysis of representative mechanism is presented with geometrical analysis for the inverse kinematic of the mechanism by using desired motion concept of slider. The mechanism is modelled in MATLAB/Simulink platform. The simulation results are presented herein.

Numerical Simulation of Hydro-mechanical Deep Drawing — A Study on the Effect of Process Parameters on Drawability and Thickness Variation

Science.gov (United States)

Singh, Swadesh Kumar; Kumar, D. Ravi

2005-08-01

Hydro-mechanical deep drawing is a process for producing cup shaped parts with the assistance of a pressurized fluid. In the present work, numerical simulation of the conventional and counter pressure deep drawing processes has been done with the help of a finite element method based software. Simulation results were analyzed to study the improvement in drawability by using hydro-mechanical processes. The thickness variations in the drawn cups were analyzed and also the effect of counter pressure and oil gap on the thickness distribution was studied. Numerical simulations were also used for the die design, which combines both drawing and ironing processes in a single operation. This modification in the die provides high drawability, facilitates smooth material flow, gives more uniform thickness distribution and corrects the shape distortion.

A parametric study of surface roughness and bonding mechanisms of aluminum alloys with epoxies: a molecular dynamics simulation

Science.gov (United States)

Timilsina, Rajendra; Termaath, Stephanie

The marine environment is highly aggressive towards most materials. However, aluminium-magnesium alloys (Al-Mg, specifically, 5xxx series) have exceptionally long service life in such aggressive marine environments. For instance, an Al-Mg alloy, AA5083, is extensively used in naval structures because of its good mechanical strength, formability, seawater corrosion resistance and weldability. However, bonding mechanisms of these alloys with epoxies in a rough surface environment are not fully understood yet. It requires a rigorous investigation at molecular or atomic levels. We performed a molecular dynamics simulation to study an adherend surface preparation and surface bonding mechanisms of Al-Mg alloy (AA5083) with different epoxies by developing several computer models. Various distributions of surface roughness are introduced in the models and performed molecular dynamics simulations. Formation of a beta phase (Al3Mg2) , microstructures, bonding energies at the interface, bonding strengths and durability are investigated. Office of Naval Research.

Characterization of Bitumen Micro-Mechanical Behaviors Using AFM, Phase Dynamics Theory and MD Simulation

Directory of Open Access Journals (Sweden)

Yue Hou

2017-02-01

Full Text Available Fundamental understanding of micro-mechanical behaviors in bitumen, including phase separation, micro-friction, micro-abrasion, etc., can help the pavement engineers better understand the bitumen mechanical performances at macroscale. Recent researches show that the microstructure evolution in bitumen will directly affect its surface structure and micro-mechanical performance. In this study, the bitumen microstructure and micro-mechanical behaviors are studied using Atomic Force Microscopy (AFM experiments, Phase Dynamics Theory and Molecular Dynamics (MD Simulation. The AFM experiment results show that different phase-structure will occur at the surface of the bitumen samples under certain thermodynamic conditions at microscale. The phenomenon can be explained using the phase dynamics theory, where the effects of stability parameter and temperature on bitumen microstructure and micro-mechanical behavior are studied combined with MD Simulation. Simulation results show that the saturates phase, in contrast to the naphthene aromatics phase, plays a major role in bitumen micro-mechanical behavior. A high stress zone occurs at the interface between the saturates phase and the naphthene aromatics phase, which may form discontinuities that further affect the bitumen frictional performance.

Characterization of Bitumen Micro-Mechanical Behaviors Using AFM, Phase Dynamics Theory and MD Simulation.

Science.gov (United States)

Hou, Yue; Wang, Linbing; Wang, Dawei; Guo, Meng; Liu, Pengfei; Yu, Jianxin

2017-02-21

Fundamental understanding of micro-mechanical behaviors in bitumen, including phase separation, micro-friction, micro-abrasion, etc., can help the pavement engineers better understand the bitumen mechanical performances at macroscale. Recent researches show that the microstructure evolution in bitumen will directly affect its surface structure and micro-mechanical performance. In this study, the bitumen microstructure and micro-mechanical behaviors are studied using Atomic Force Microscopy (AFM) experiments, Phase Dynamics Theory and Molecular Dynamics (MD) Simulation. The AFM experiment results show that different phase-structure will occur at the surface of the bitumen samples under certain thermodynamic conditions at microscale. The phenomenon can be explained using the phase dynamics theory, where the effects of stability parameter and temperature on bitumen microstructure and micro-mechanical behavior are studied combined with MD Simulation. Simulation results show that the saturates phase, in contrast to the naphthene aromatics phase, plays a major role in bitumen micro-mechanical behavior. A high stress zone occurs at the interface between the saturates phase and the naphthene aromatics phase, which may form discontinuities that further affect the bitumen frictional performance.

QuVis interactive simulations: tools to support quantum mechanics instruction

Science.gov (United States)

Kohnle, Antje

2015-04-01

Quantum mechanics holds a fascination for many students, but its mathematical complexity and counterintuitive results can present major barriers. The QuVis Quantum Mechanics Visualization Project (www.st-andrews.ac.uk/physics/quvis) aims to overcome these issues through the development and evaluation of interactive simulations with accompanying activities for the learning and teaching of quantum mechanics. Over 90 simulations are now available on the QuVis website. One collection of simulations is embedded in the Institute of Physics Quantum Physics website (quantumphysics.iop.org), which consists of freely available resources for an introductory course in quantum mechanics starting from two-level systems. Simulations support model-building by reducing complexity, focusing on fundamental ideas and making the invisible visible. They promote engaged exploration, sense-making and linking of multiple representations, and include high levels of interactivity and direct feedback. Simulations are research-based and evaluation with students informs all stages of the development process. Simulations are iteratively refined using student feedback in individual observation sessions and in-class trials. Evaluation has shown that the simulations can help students learn quantum mechanics concepts at both the introductory and advanced undergraduate level and that students perceive simulations to be beneficial to their learning. Recent activity includes the launch of a new collection of HTML5 simulations that run on both desktop and tablet-based devices and the introduction of a goal and reward structure in simulations through the inclusion of challenges. This presentation will give an overview of the QuVis resources, highlight recent work and outline future plans. QuVis is supported by the UK Institute of Physics, the UK Higher Education Academy and the University of St Andrews.

A molecular dynamic simulation study of mechanical properties of graphene–polythiophene composite with Reax force field

International Nuclear Information System (INIS)

Nayebi, Payman; Zaminpayma, Esmaeil

2016-01-01

In this paper, we performed molecular dynamic simulations by Reax force field to study the mechanical properties of graphene–polythiophene nanocomposite. By computing elastic constant, breaking stress, breaking strain and Young's modulus from the stress–strain curve for the nanocomposites, we investigated effects of tension orientation, graphene loading to the polymer, temperature of nanocomposite and defect of graphene on these mechanical characters. It is found that mechanical characters of tension along the zigzag orientation are higher than other directions. Also, by increasing the weight concentration of graphene in composite, the Young's modulus and breaking strain increase. Our results showed that the Young's modulus decreased with increasing temperature. Finally by applying defect on graphene structure, we found that one atom missing defect has lower Young's modulus. Also, by increasing the defects concentration, elastic modulus decreases gradually. - Highlights: • We studied mechanical properties of graphene–polythiophene nanocomposite. • Mechanical characters of tension along the zigzag are higher than other directions. • By increasing the weight concentration of graphene in composite, the Young's modulus increases. • Young's modulus decreased with increasing temperature. • By increasing the defects concentration, elastic modulus decreases gradually.

Numerical simulation of damage evolution for ductile materials and mechanical properties study

Science.gov (United States)

El Amri, A.; Hanafi, I.; Haddou, M. E. Y.; Khamlichi, A.

2015-12-01

This paper presents results of a numerical modelling of ductile fracture and failure of elements made of 5182H111 aluminium alloys subjected to dynamic traction. The analysis was performed using Johnson-Cook model based on ABAQUS software. The modelling difficulty related to prediction of ductile fracture mainly arises because there is a tremendous span of length scales from the structural problem to the micro-mechanics problem governing the material separation process. This study has been used the experimental results to calibrate a simple crack propagation criteria for shell elements of which one has often been used in practical analyses. The performance of the proposed model is in general good and it is believed that the presented results and experimental-numerical calibration procedure can be of use in practical finite-element simulations.

Numerical simulation of damage evolution for ductile materials and mechanical properties study

International Nuclear Information System (INIS)

Amri, A El; Haddou, M E Y; Hanafi, I; Khamlichi, A

2015-01-01

This paper presents results of a numerical modelling of ductile fracture and failure of elements made of 5182H111 aluminium alloys subjected to dynamic traction. The analysis was performed using Johnson-Cook model based on ABAQUS software. The modelling difficulty related to prediction of ductile fracture mainly arises because there is a tremendous span of length scales from the structural problem to the micro-mechanics problem governing the material separation process. This study has been used the experimental results to calibrate a simple crack propagation criteria for shell elements of which one has often been used in practical analyses. The performance of the proposed model is in general good and it is believed that the presented results and experimental-numerical calibration procedure can be of use in practical finite-element simulations. (paper)

Using molecular dynamics simulations and finite element method to study the mechanical properties of nanotube reinforced polyethylene and polyketone

Science.gov (United States)

Rouhi, S.; Alizadeh, Y.; Ansari, R.; Aryayi, M.

2015-09-01

Molecular dynamics simulations are used to study the mechanical behavior of single-walled carbon nanotube reinforced composites. Polyethylene and polyketone are selected as the polymer matrices. The effects of nanotube atomic structure and diameter on the mechanical properties of polymer matrix nanocomposites are investigated. It is shown that although adding nanotube to the polymer matrix raises the longitudinal elastic modulus significantly, the transverse tensile and shear moduli do not experience important change. As the previous finite element models could not be used for polymer matrices with the atom types other than carbon, molecular dynamics simulations are used to propose a finite element model which can be used for any polymer matrices. It is shown that this model can predict Young’s modulus with an acceptable accuracy.

The atomic-scale nucleation mechanism of NiTi metallic glasses upon isothermal annealing studied via molecular dynamics simulations.

Science.gov (United States)

Li, Yang; Li, JiaHao; Liu, BaiXin

2015-10-28

Nucleation is one of the most essential transformation paths in phase transition and exerts a significant influence on the crystallization process. Molecular dynamics simulations were performed to investigate the atomic-scale nucleation mechanisms of NiTi metallic glasses upon devitrification at various temperatures (700 K, 750 K, 800 K, and 850 K). Our simulations reveal that at 700 K and 750 K, nucleation is polynuclear with high nucleation density, while at 800 K it is mononuclear. The underlying nucleation mechanisms have been clarified, manifesting that nucleation can be induced either by the initial ordered clusters (IOCs) or by the other precursors of nuclei evolved directly from the supercooled liquid. IOCs and other precursors stem from the thermal fluctuations of bond orientational order in supercooled liquids during the quenching process and during the annealing process, respectively. The simulation results not only elucidate the underlying nucleation mechanisms varied with temperature, but also unveil the origin of nucleation. These discoveries offer new insights into the devitrification mechanism of metallic glasses.

Application of simulation techniques in the probabilistic fracture mechanics

International Nuclear Information System (INIS)

De Ruyter van Steveninck, J.L.

1995-03-01

The Monte Carlo simulation is applied on a model of the fracture mechanics in order to assess the applicability of this simulation technique in the probabilistic fracture mechanics. By means of the fracture mechanics model the brittle fracture of a steel container or pipe with defects can be predicted. By means of the Monte Carlo simulation also the uncertainty regarding failures can be determined. Based on the variations in the toughness of the fracture and the defect dimensions the distribution of the chance of failure is determined. Also attention is paid to the impact of dependency between uncertain variables. Furthermore, the influence of the applied distributions of the uncertain variables and non-destructive survey on the chance of failure is analyzed. The Monte Carlo simulation results agree quite well with the results of other methods from the probabilistic fracture mechanics. If an analytic expression can be found for the chance of failure, it is possible to determine the variation of the chance of failure, next to an estimation of the chance of failure. It also appears that the dependency between the uncertain variables has a large impact on the chance of failure. It is also concluded from the simulation that the chance of failure strongly depends on the crack depth, and therefore of the distribution of the crack depth. 15 figs., 7 tabs., 12 refs

Application of Modern Simulation Technology in Mechanical Outstanding Engineer Training

Directory of Open Access Journals (Sweden)

Gongfa Li

2014-03-01

Full Text Available This text has described the relationship between outstanding engineer training and modern simulation technology, have recommended the characteristics of mechanical outstanding engineer in detail. Aiming at the importance of the teaching practice link to course of theory of mechanics, mechanical design and mechanical signal analysis, have expounded the function of modern simulation technology in the mechanical outstanding engineer training, especially on teaching practice in the theory of mechanics, mechanical design and mechanical signal analysis. It has the advantages of economizing the teaching cost, overcoming the hardware constrains, model prediction, promoting student's innovation and manipulative ability, so can popularize and develop in a more cost-effective manner in the university.

A Multiscale Simulation Method and Its Application to Determine the Mechanical Behavior of Heterogeneous Geomaterials

Directory of Open Access Journals (Sweden)

Shengwei Li

2017-01-01

Full Text Available To study the micro/mesomechanical behaviors of heterogeneous geomaterials, a multiscale simulation method that combines molecular simulation at the microscale, a mesoscale analysis of polished slices, and finite element numerical simulation is proposed. By processing the mesostructure images obtained from analyzing the polished slices of heterogeneous geomaterials and mapping them onto finite element meshes, a numerical model that more accurately reflects the mesostructures of heterogeneous geomaterials was established by combining the results with the microscale mechanical properties of geomaterials obtained from the molecular simulation. This model was then used to analyze the mechanical behaviors of heterogeneous materials. Because kernstone is a typical heterogeneous material that comprises many types of mineral crystals, it was used for the micro/mesoscale mechanical behavior analysis in this paper using the proposed method. The results suggest that the proposed method can be used to accurately and effectively study the mechanical behaviors of heterogeneous geomaterials at the micro/mesoscales.

A study of the free vibration of suspension rod based on four-stage arm mechanism by using computer simulation

Directory of Open Access Journals (Sweden)

Melnychuk S.V.

2016-08-01

Full Text Available We analyze the current state of the prospects and problems of using computer technology to determine the operating parameters of movement of the vehicle. Scientific works related to the study of the properties of the vehicle smooth ride are studied. The following example shows that the modern researches of smooth ride do not pay enough attention to issues associated with the processes that occur in the suspension rod of a vehicle. Scientific works related to the choice of the optimal and simple CAD system for conducting computer simulation tests are overviewed. We developed an animating model of experimental car in SOLIDWORKS environment with the staff suspension rod and the suspension rod based on four-stage arm mechanism, which allows a wide range of tests of components of the vehicle. Methodology and hardware-software complex for testing a car are developed. A test of a vehicle of category N1 is conducted. A computer simulation of the motion of the smooth ride of the car with suspension rod based on four-stage arm mechanism is conducted. The comparative analysis of suspension rod performance based on four-stage arm mechanism is conducted.

Simulated airplane headache: a proxy towards identification of underlying mechanisms.

Science.gov (United States)

Bui, Sebastian Bao Dinh; Petersen, Torben; Poulsen, Jeppe Nørgaard; Gazerani, Parisa

2017-12-01

Airplane Headache (AH) occurs during flights and often appears as an intense, short lasting headache during take-off or landing. Reports are limited on pathological mechanisms underlying the occurrence of this headache. Proper diagnosis and treatments would benefit from identification of potential pathways involved in AH pathogenesis. This study aimed at providing a simulated airplane headache condition as a proxy towards identification of its underlying mechanisms. Fourteen participants including 7 volunteers suffering from AH and 7 healthy matched controls were recruited after meeting the diagnostic and safety criteria based on an approved study protocol. Simulation of AH was achieved by entering a pressure chamber with similar characteristics of an airplane flight. Selected potential biomarkers including salivary prostaglandin E 2 (PGE 2 ), cortisol, facial thermo-images, blood pressure, pulse, and saturation pulse oxygen (SPO) were defined and values were collected before, during and after flight simulation in the pressure chamber. Salivary samples were analyzed with ELISA techniques, while data analysis and statistical tests were handled with SPSS version 22.0. All participants in the AH-group experienced a headache attack similar to AH experience during flight. The non-AH-group did not experience any headaches. Our data showed that the values for PGE 2 , cortisol and SPO were significantly different in the AH-group in comparison with the non-AH-group during the flight simulation in the pressure chamber. The pressure chamber proved useful not only to provoke AH-like attack but also to study potential biomarkers for AH in this study. PGE 2 , and cortisol levels together with SPO presented dysregulation during the simulated AH-attack in affected individuals compared with healthy controls. Based on these findings we propose to use pressure chamber as a model to induce AH, and thus assess new potential biomarkers for AH in future studies.

Evaluation of structural deformations of a mechanical connecting unit oxidizer supplies by thermo-mechanical simulation

International Nuclear Information System (INIS)

Kim, Sang Woo

2016-01-01

A Mechanical connecting unit (MCU) used in ground facilities for a Liquid propellant rocket (LPR) acts as a bridge between the onboard system and the ground oxidizer filling system. It should be resistant to structural deformations in order to guarantee successful supply of a cryogenic oxidizer and high pressure gases without reduction of sealing capability. The MCU consists of many components and linkages and operates under harsh conditions induced by a cryogenic oxidizer, high pressure gases and other mechanical forces. Thus, the evaluation of structural deformation of the MCU considering complex conditions is expensive and time consuming. The present study efficiently evaluates the structural deformations of the key components of the MCU by Thermo-mechanical simulation (TMS) based on the superposition principle. Deformations due to the mechanical loadings including weights, pressures, and spring forces are firstly evaluated by using a non-linear flexible body simulation module (FFlex) of Multi-body dynamics (MBD) software, RecurDyn. Then, thermal deformations for the deformed geometries obtained by RecurDyn were subsequently calculated. It was conducted by using a Finite element (FE) analysis software, ANSYS. The total deformations for the onboard plate and multi-channel plate in the connecting section due to the mechanical and thermal loadings were successfully evaluated. Moreover, the outer gaps at six points between two plates were calculated and verified by comparison to the measured data. Their values and tendencies showed a good agreement. The author concluded that the TMS using MBD software considering flexible bodies and an FE simulator can efficiently evaluate structural deformations of the MCU operating under the complex load and boundary conditions

Evaluation of structural deformations of a mechanical connecting unit oxidizer supplies by thermo-mechanical simulation

Energy Technology Data Exchange (ETDEWEB)

Kim, Sang Woo [Dept. of Mechanical Engineering, Institute of Machine Convergence Technology, Hankyong National University, Anseong (Korea, Republic of)

2016-10-15

A Mechanical connecting unit (MCU) used in ground facilities for a Liquid propellant rocket (LPR) acts as a bridge between the onboard system and the ground oxidizer filling system. It should be resistant to structural deformations in order to guarantee successful supply of a cryogenic oxidizer and high pressure gases without reduction of sealing capability. The MCU consists of many components and linkages and operates under harsh conditions induced by a cryogenic oxidizer, high pressure gases and other mechanical forces. Thus, the evaluation of structural deformation of the MCU considering complex conditions is expensive and time consuming. The present study efficiently evaluates the structural deformations of the key components of the MCU by Thermo-mechanical simulation (TMS) based on the superposition principle. Deformations due to the mechanical loadings including weights, pressures, and spring forces are firstly evaluated by using a non-linear flexible body simulation module (FFlex) of Multi-body dynamics (MBD) software, RecurDyn. Then, thermal deformations for the deformed geometries obtained by RecurDyn were subsequently calculated. It was conducted by using a Finite element (FE) analysis software, ANSYS. The total deformations for the onboard plate and multi-channel plate in the connecting section due to the mechanical and thermal loadings were successfully evaluated. Moreover, the outer gaps at six points between two plates were calculated and verified by comparison to the measured data. Their values and tendencies showed a good agreement. The author concluded that the TMS using MBD software considering flexible bodies and an FE simulator can efficiently evaluate structural deformations of the MCU operating under the complex load and boundary conditions.

Handsheet formation and mechanical testing via fiber-level simulations

Science.gov (United States)

Leonard H. Switzer; Daniel J. Klingenberg; C. Tim Scott

2004-01-01

A fiber model and simulation method are employed to investigate the mechanical response of planar fiber networks subjected to elongational deformation. The simulated responses agree qualitatively with numerous experimental observations. suggesting that such simulation methods may be useful for probing the relationships between fiber properties and interactions and the...

Interactive Simulations to Support Quantum Mechanics Instruction for Chemistry Students

Science.gov (United States)

Kohnle, Antje; Benfield, Cory; Hahner, Georg; Paetkau, Mark

2017-01-01

The QuVis Quantum Mechanics Visualization Project provides freely available research-based interactive simulations with accompanying activities for the teaching and learning of quantum mechanics across a wide range of topics and levels. This article gives an overview of some of the simulations and describes their use in an introductory physical…

Design of thermoelectric modules for both mechanical reliability and performance using FE simulation

DEFF Research Database (Denmark)

Sarhadi, Ali; Bjørk, Rasmus; Pryds, Nini

for these two objectives. The current study deals with FE simulation of the TE modules to optimize their geometrical dimension in terms of mechanical reliability and performance. First, FE simulation of a TE module consisting of bismuth telluride alloys is carried out and the induced thermal stresses, output......, the geometrical dimensions of the TE elements for both mechanical reliability and performance are optimized to obtain a compromise design. The present work provides a basis for optimizing the TE modules in terms of their life time and performance.......Thermo-mechanical modeling of the TE modules provides an efficient tool for assessing the mechanical strength of the modules against the induced thermal stresses and subsequently optimizing them in terms of the mechanical reliability. However, the design of TE modules in terms of mechanical...

Development of a mechanical maintenance training simulator in OpenSimulator for F-16 aircraft engines

OpenAIRE

Pinheiro, André; Fernandes, Paulo; Maia, Ana; Cruz, Gonçalo; Pedrosa, Daniela; Fonseca, Benjamim; Paredes, Hugo; Martins, Paulo; Morgado, Leonel; Rafael, Jorge

2014-01-01

Mechanical maintenance of F-16 engines is carried out as a team effort involving 3–4 skilled engine technicians, but the details of its procedures and requisites change constantly, to improve safety, optimize resources, and respond to knowledge learned from field outcomes. This provides a challenge for development of training simulators, since simulated actions risk becoming obsolete rapidly and require costly reimplementation. This paper presents the development of a 3D mechanical maintenanc...

A novel bioreactor to simulate urinary bladder mechanical properties and compliance for bladder functional tissue engineering.

Science.gov (United States)

Wei, Xin; Li, Dao-bing; Xu, Feng; Wang, Yan; Zhu, Yu-chun; Li, Hong; Wang, Kun-jie

2011-02-01

Bioreactors are pivotal tools for generating mechanical stimulation in functional tissue engineering study. This study aimed to create a bioreactor that can simulate urinary bladder mechanical properties, and to investigate the effects of a mechanically stimulated culture on urothelial cells and bladder smooth muscle cells. We designed a bioreactor to simulate the mechanical properties of bladder. A pressure-record system was used to evaluate the mechanical properties of the bioreactor by measuring the pressure in culture chambers. To test the biocompatibility of the bioreactor, viabilities of urothelial cells and smooth muscle cells cultured in the bioreactor under static and mechanically changed conditions were measured after 7-day culture. To evaluate the effect of mechanical stimulations on the vital cells, urethral cells and smooth muscle cells were cultured in the simulated mechanical conditions. After that, the viability and the distribution pattern of the cells were observed and compared with cells cultured in non-mechanical stimulated condition. The bioreactor system successfully generated waveforms similar to the intended programmed model while maintaining a cell-seeded elastic membrane between the chambers. There were no differences between viabilities of urothelial cells ((91.90 ± 1.22)% vs. (93.14 ± 1.78)%, P > 0.05) and bladder smooth muscle cells ((93.41 ± 1.49)% vs. (92.61 ± 1.34)%, P > 0.05). The viability of cells and tissue structure observation after cultured in simulated condition showed that mechanical stimulation was the only factor affected cells in the bioreactor and improved the arrangement of cells on silastic membrane. This bioreactor can effectively simulate the physiological and mechanical properties of the bladder. Mechanical stimulation is the only factor that affected the viability of cells cultured in the bioreactor. The bioreactor can change the growth behavior of urothelial cells and bladder smooth muscle cells, resulting in

Multiscale simulation of mechanical properties of TiNb alloy

Science.gov (United States)

Nikonov, A. Yu.

2017-12-01

The article presents a numerical simulation of the mechanical properties of a Ti-Nb β-alloy on three different scales. The ab-initio approach is used to estimate the concentrations of the Ti alloy with required elastic properties. On the basis of molecular dynamics simulation, we calculate the adhesive force between individual particles of the alloy. The calculated dependence is implemented within the movable cellular automata method to determine the mechanical properties of Ti-Nb depending on the interparticle free space.

Theoretical study of coupling mechanisms between oxygen diffusion, chemical reaction, mechanical stresses in a solid-gas reactive system

International Nuclear Information System (INIS)

Creton, N.; Optasanu, V.; Montesin, T.; Garruchet, S.

2008-01-01

This paper offers a study of oxygen dissolution into a solid, and its consequences on the mechanical behaviour of the material. In fact, mechanical strains strongly influence the oxidation processes and may be, in some materials, responsible for cracking. To realize this study, mechanical considerations are introduced into the classical diffusion laws. Simulations were made for the particular case of uranium dioxide, which undergoes the chemical fragmentation. According to our simulations, the hypothesis of a compression stress field into the oxidised UO 2 compound near the internal interface is consistent with some oxidation mechanisms of oxidation experimentally observed. More generally, this work will be extended to the simulation to an oxide layer growth on a metallic substrate. (authors)

Molecular Simulation and Biochemical Studies Support an Elevator-type Transport Mechanism in EIIC.

Science.gov (United States)

Lee, Jumin; Ren, Zhenning; Zhou, Ming; Im, Wonpil

2017-06-06

Enzyme IIC (EIIC) is a membrane-embedded sugar transport protein that is part of the phosphoenolpyruvate-dependent phosphotransferases. Crystal structures of two members of the glucose EIIC superfamily, bcChbC in the inward-facing conformation and bcMalT in the outward-facing conformation, were previously solved. Comparing the two structures led us to the hypothesis that sugar translocation could be achieved by an elevator-type transport mechanism in which a transport domain binds to the substrate and, through rigid body motions, transports it across the membrane. To test this hypothesis and to obtain more accurate descriptions of alternate conformations of the two proteins, we first performed collective variable-based steered molecular dynamics (CVSMD) simulations starting with the two crystal structures embedded in model lipid bilayers, and steered their transport domain toward their own alternative conformation. Our simulations show that large rigid-body motions of the transport domain (55° in rotation and 8 Å in translation) lead to access of the substrate binding site to the alternate side of the membrane. H-bonding interactions between the sugar and the protein are intact, although the side chains of the binding-site residues were not restrained in the simulation. Pairs of residues in bcMalT that are far apart in the crystal structure become close to each other in the simulated model. Some of these pairs can be cross-linked by a mercury ion when mutated to cysteines, providing further support for the CVSMD-generated model. In addition, bcMalT binds to maltose with similar affinities before and after the cross-linking, suggesting that the binding site is preserved after the conformational change. In combination, these results support an elevator-type transport mechanism in EIIC. Copyright © 2017 Biophysical Society. Published by Elsevier Inc. All rights reserved.

Dimensionless study on dynamics of pressure controlled mechanical ventilation system

International Nuclear Information System (INIS)

Shi, Yan; Niu, Jinglong; Cai, Maolin; Xu, Weiqing

2015-01-01

Dynamics of mechanical ventilation system can be referred in pulmonary diagnostics and treatments. In this paper, to conveniently grasp the essential characteristics of mechanical ventilation system, a dimensionless model of mechanical ventilation system is presented. For the validation of the mathematical model, a prototype mechanical ventilation system of a lung simulator is proposed. Through the simulation and experimental studies on the dimensionless dynamics of the mechanical ventilation system, firstly, the mathematical model is proved to be authentic and reliable. Secondly, the dimensionless dynamics of the mechanical ventilation system are obtained. Last, the influences of key parameters on the dimensionless dynamics of the mechanical ventilation system are illustrated. The study provides a novel method to study the dynamic of mechanical ventilation system, which can be referred in the respiratory diagnostics and treatment.

Dimensionless study on dynamics of pressure controlled mechanical ventilation system

Energy Technology Data Exchange (ETDEWEB)

Shi, Yan; Niu, Jinglong; Cai, Maolin; Xu, Weiqing [Beihang University, Beijing (Korea, Republic of)

2015-02-15

Dynamics of mechanical ventilation system can be referred in pulmonary diagnostics and treatments. In this paper, to conveniently grasp the essential characteristics of mechanical ventilation system, a dimensionless model of mechanical ventilation system is presented. For the validation of the mathematical model, a prototype mechanical ventilation system of a lung simulator is proposed. Through the simulation and experimental studies on the dimensionless dynamics of the mechanical ventilation system, firstly, the mathematical model is proved to be authentic and reliable. Secondly, the dimensionless dynamics of the mechanical ventilation system are obtained. Last, the influences of key parameters on the dimensionless dynamics of the mechanical ventilation system are illustrated. The study provides a novel method to study the dynamic of mechanical ventilation system, which can be referred in the respiratory diagnostics and treatment.

A mechanical breathing simulator for respirator test

International Nuclear Information System (INIS)

Murata, Mikio; Ikezawa, Yoshio; Yoshida, Yoshikazu

1976-01-01

A mechanical breathing simulator has been developed to produce the human respiration for use in respirator test. The respirations were produced through the strokes of piston controlled by a rockerarm with adjustable fulcrum. The respiration rate was governed by motor-speed control, independent of the tidal volume achieved by adjustment of the piston stroke. By the breather, the simulated respirations for work rate 0, 208, 415, 622 and 830 kg-m/min could be produced through the typical dummy head. (auth.)

Plasmonic resonances of nanoparticles from large-scale quantum mechanical simulations

Science.gov (United States)

Zhang, Xu; Xiang, Hongping; Zhang, Mingliang; Lu, Gang

2017-09-01

Plasmonic resonance of metallic nanoparticles results from coherent motion of its conduction electrons, driven by incident light. For the nanoparticles less than 10 nm in diameter, localized surface plasmonic resonances become sensitive to the quantum nature of the conduction electrons. Unfortunately, quantum mechanical simulations based on time-dependent Kohn-Sham density functional theory are computationally too expensive to tackle metal particles larger than 2 nm. Herein, we introduce the recently developed time-dependent orbital-free density functional theory (TD-OFDFT) approach which enables large-scale quantum mechanical simulations of plasmonic responses of metallic nanostructures. Using TD-OFDFT, we have performed quantum mechanical simulations to understand size-dependent plasmonic response of Na nanoparticles and plasmonic responses in Na nanoparticle dimers and trimers. An outlook of future development of the TD-OFDFT method is also presented.

Simulation and Analysis of Mechanical Properties of Silica Aerogels: From Rationalization to Prediction.

Science.gov (United States)

Ma, Hao; Zheng, Xiaoyang; Luo, Xuan; Yi, Yong; Yang, Fan

2018-01-30

Silica aerogels are highly porous 3D nanostructures and have exhibited excellent physio-chemical properties. Although silica aerogels have broad potential in many fields, the poor mechanical properties greatly limit further applications. In this study, we have applied the finite volume method (FVM) method to calculate the mechanical properties of silica aerogels with different geometric properties such as particle size, pore size, ligament diameter, etc. The FVM simulation results show that a power law correlation existing between relative density and mechanical properties (elastic modulus and yield stress) of silica aerogels, which are consistent with experimental and literature studies. In addition, depending on the relative densities, different strategies are proposed in order to synthesize silica aerogels with better mechanical performance by adjusting the distribution of pore size and ligament diameter of aerogels. Finally, the results suggest that it is possible to synthesize silica aerogels with ultra-low density as well as high strength and stiffness as long as the textural features are well controlled. It is believed that the FVM simulation methodology could be a valuable tool to study mechanical performance of silica aerogel based materials in the future.

Simulation and Analysis of Mechanical Properties of Silica Aerogels: From Rationalization to Prediction

Directory of Open Access Journals (Sweden)

Hao Ma

2018-01-01

Full Text Available Silica aerogels are highly porous 3D nanostructures and have exhibited excellent physio-chemical properties. Although silica aerogels have broad potential in many fields, the poor mechanical properties greatly limit further applications. In this study, we have applied the finite volume method (FVM method to calculate the mechanical properties of silica aerogels with different geometric properties such as particle size, pore size, ligament diameter, etc. The FVM simulation results show that a power law correlation existing between relative density and mechanical properties (elastic modulus and yield stress of silica aerogels, which are consistent with experimental and literature studies. In addition, depending on the relative densities, different strategies are proposed in order to synthesize silica aerogels with better mechanical performance by adjusting the distribution of pore size and ligament diameter of aerogels. Finally, the results suggest that it is possible to synthesize silica aerogels with ultra-low density as well as high strength and stiffness as long as the textural features are well controlled. It is believed that the FVM simulation methodology could be a valuable tool to study mechanical performance of silica aerogel based materials in the future.

Atomistic simulations of Mg-Cu metallic glasses: Mechanical properties

DEFF Research Database (Denmark)

Bailey, Nicholas; Schiøtz, Jakob; Jacobsen, Karsten Wedel

2004-01-01

The atomistic mechanisms of plastic deformation in amorphous metals are far from being understood. We have derived potential parameters for molecular dynamics simulations of Mg-Cu amorphous alloys using the Effective Medium Theory. We have simulated the formation of alloys by cooling from the melt...

Superlubricity mechanism of diamond-like carbon with glycerol. Coupling of experimental and simulation studies

International Nuclear Information System (INIS)

Bouchet, M I De Barros; Matta, C; Le-Mogne, Th; Martin, J Michel; Zhang, Q; III, W Goddard; Kano, M; Mabuchi, Y; Ye, J

2007-01-01

We report a unique tribological system that produces superlubricity under boundary lubrication conditions with extremely little wear. This system is a thin coating of hydrogen-free amorphous Diamond-Like-Carbon (denoted as ta-C) at 353 K in a ta-C/ta-C friction pair lubricated with pure glycerol. To understand the mechanism of friction vanishing we performed ToF-SIMS experiments using deuterated glycerol and 13 C glycerol. This was complemented by first-principles-based computer simulations using the ReaxFF reactive force field to create an atomistic model of ta-C. These simulations show that DLC with the experimental density of 3.24 g/cc leads to an atomistic structure consisting of a 3D percolating network of tetrahedral (sp 3 ) carbons accounting for 71.5% of the total, in excellent agreement with the 70% deduced from our Auger spectroscopy and XANES experiments. The simulations show that the remaining carbons (with sp 2 and sp 1 character) attach in short chains of length 1 to 7. In sliding simulations including glycerol molecules, the surface atoms react readily to form a very smooth carbon surface containing OH-terminated groups. This agrees with our SIMS experiments. The simulations find that the OH atoms are mostly bound to surface sp 1 atoms leading to very flexible elastic response to sliding. Both simulations and experiments suggest that the origin of the superlubricity arises from the formation of this OH-terminated surface

Mechanical property estimation with ABI and FEM simulation

International Nuclear Information System (INIS)

Sharma, Kamal; Singh, P.K.; Das, Gautam; Bhasin, Vivek; Vaze, K.K.; Ghosh, A.K.

2007-01-01

A combined mechanical property evaluation methodology with ABI (Automated Ball Indentation) simulation and Artificial Neural Network (ANN) analysis is evolved to evaluate the mechanical properties for material. The experimental load deflection data is converted into meaningful mechanical properties for this material. An ANN database is generated with the help of contact type finite element analysis by numerically simulating the ABI process for various magnitudes of yield strength (σ yp ) (200 MPa - 500 MPa) with a range of strain hardening exponent (n) (0.1 - 0.5) and strength coefficient (K) (500 MPa - 1500 MPa). For the present problem, a ball indenter of 1.57 mm diameter having Young's modulus approximately 100 times more than the test piece is used to minimize the error due to indenter deformation. Test piece dimension is kept large enough in comparison to the indenter configuration in the simulation to minimize the deflection at the outer edge of the test piece. Further this database after the neural network training; is used to analyze measured material properties of different test pieces. The ANN predictions are reconfirmed with contact type finite element analysis for an arbitrary selected test sample. The methodology evolved in this work can be extended to predict material properties for any irradiated nuclear material in the service. (author)

Theoretical studies on the selective mechanisms of GSK3β and CDK2 by molecular dynamics simulations and free energy calculations.

Science.gov (United States)

Zhao, Sufang; Zhu, Jingyu; Xu, Lei; Jin, Jian

2017-06-01

Glycogen synthase kinase 3 (GSK3) is a serine/threonine protein kinase which is widely involved in cell signaling and controls a broad number of cellular functions. GSK3 contains α and β isoforms, and GSK3β has received more attention and becomes an attractive drug target for the treatment of several diseases. The binding pocket of cyclin-dependent kinase 2 (CDK2) shares high sequence identity to that of GSK3β, and therefore, the design of highly selective inhibitors toward GSK3β remains a big challenge. In this study, a computational strategy, which combines molecular docking, molecular dynamics simulations, free energy calculations, and umbrella sampling simulations, was employed to explore the binding mechanisms of two selective inhibitors to GSK3β and CDK2. The simulation results highlighted the key residues critical for GSK3β selectivity. It was observed that although GSK3β and CDK2 share the conserved ATP-binding pockets, some different residues have significant contributions to protein selectivity. This study provides valuable information for understanding the GSK3β-selective binding mechanisms and the rational design of selective GSK3β inhibitors. © 2016 John Wiley & Sons A/S.

Experimental Study and Computational Simulations of Key Pebble Bed Thermo-mechanics Issues for Design and Safety

Energy Technology Data Exchange (ETDEWEB)

Tokuhiro, Akira; Potirniche, Gabriel; Cogliati, Joshua; Ougouag, Abderrafi

2014-07-08

An experimental and computational study, consisting of modeling and simulation (M&S), of key thermal-mechanical issues affecting the design and safety of pebble-bed (PB) reactors was conducted. The objective was to broaden understanding and experimentally validate thermal-mechanic phenomena of nuclear grade graphite, specifically, spheres in frictional contact as anticipated in the bed under reactor relevant pressures and temperatures. The contact generates graphite dust particulates that can subsequently be transported into the flowing gaseous coolent. Under postulated depressurization transients and with the potential for leaked fission products to be adsorbed onto graphite 'dust', there is the potential for fission products to escape from the primary volume. This is a design safety concern. Furthermore, earlier safety assessment identified the distinct possibility for the dispersed dust to combust in contact with air if sufficient conditions are met. Both of these phenomena were noted as important to design review and containing uncertainty to warrant study. The team designed and conducted two separate effects tests to study and benchmark the potential dust-generation rate, as well as study the conditions under which a dust explosion may occure in a standardized, instrumented explosion chamber.

Comprehensive Validation of Skeletal Mechanism for Turbulent Premixed Methane–Air Flame Simulations

KAUST Repository

Luca, Stefano

2017-08-01

A new skeletal mechanism, consisting of 16 species and 72 reactions, has been developed for lean methane–air premixed combustion from the GRI-Mech 3.0. The skeletal mechanism is validated for elevated unburnt temperatures (800 K) and pressures up to 4 atm, thereby addressing realistic gas turbine conditions. The skeletal mechanism is obtained by applying the directed relation graph method and performing sensitivity analysis on the detailed mechanism. The mechanism has been validated for flame speed and flame structure in a wide range of conditions and configurations. A good agreement between the skeletal mechanism and GRI-3.0 was obtained. The configurations considered include one-dimension laminar premixed flames, laminar non-premixed counterflow burners, and two- and three-dimensional unsteady configurations with variations of temperature, pressure, and composition. The skeletal mechanism allows for the inclusion of accurate finite rate chemistry in large-scale direct numerical simulations of lean turbulent premixed flames. In a large-scale direct numerical simulation, the use of the skeletal mechanism reduces the memory requirements by more than a factor of 3 and accelerates the simulation by a factor of 7 compared with the detailed mechanism. The skeletal mechanism is suitable for unsteady three-dimensional simulations of methane turbulent premixed, non-premixed, and globally lean partially premixed flames and is available as supplementary material.

A high-compression electron gun for C6+ production: concept, simulations and mechanical design

Science.gov (United States)

Mertzig, Robert; Breitenfeldt, M.; Mathot, S.; Pitters, J.; Shornikov, A.; Wenander, F.

2017-07-01

In this paper we report on simulations and the mechanical design of a high-compression electron gun for an Electron Beam Ion Source (EBIS) dedicated for production of high intensity and high repetition rate pulses of bare carbon ions for injection into linac-based hadron therapy facilities. The gun is presently under construction at CERN to be retrofitted into the TwinEBIS test bench for experimental studies. We describe the design constraints, show results of numeric simulations and report on the mechanical design featuring several novel ideas. The reported design makes use of combined-function units with reduced number of mechanical joints that were carefully controlled and tuned during the manufacturing phase. The simulations addressed a wide range of topics including the influence of thermal effects, focusing optics, symmetry-breaking misalignments and injection into a full 5 T field.

Seventeenth Workshop on Computer Simulation Studies in Condensed-Matter Physics

CERN Document Server

Landau, David P; Schütler, Heinz-Bernd; Computer Simulation Studies in Condensed-Matter Physics XVI

2006-01-01

This status report features the most recent developments in the field, spanning a wide range of topical areas in the computer simulation of condensed matter/materials physics. Both established and new topics are included, ranging from the statistical mechanics of classical magnetic spin models to electronic structure calculations, quantum simulations, and simulations of soft condensed matter. The book presents new physical results as well as novel methods of simulation and data analysis. Highlights of this volume include various aspects of non-equilibrium statistical mechanics, studies of properties of real materials using both classical model simulations and electronic structure calculations, and the use of computer simulations in teaching.

Interactive simulations as teaching tools for engineering mechanics courses

Science.gov (United States)

Carbonell, Victoria; Romero, Carlos; Martínez, Elvira; Flórez, Mercedes

2013-07-01

This study aimed to gauge the effect of interactive simulations in class as an active teaching strategy for a mechanics course. Engineering analysis and design often use the properties of planar sections in calculations. In the stress analysis of a beam under bending and torsional loads, cross-sectional properties are used to determine stress and displacement distributions in the beam cross section. The centroid, moments and products of inertia of an area made up of several common shapes (rectangles usually) may thus be obtained by adding the moments of inertia of the component areas (U-shape, L-shape, C-shape, etc). This procedure is used to calculate the second moments of structural shapes in engineering practice because the determination of their moments of inertia is necessary for the design of structural components. This paper presents examples of interactive simulations developed for teaching the ‘Mechanics and mechanisms’ course at the Universidad Politecnica de Madrid, Spain. The simulations focus on fundamental topics such as centroids, the properties of the moment of inertia, second moments of inertia with respect to two axes, principal moments of inertia and Mohr's Circle for plane stress, and were composed using Geogebra software. These learning tools feature animations, graphics and interactivity and were designed to encourage student participation and engagement in active learning activities, to effectively explain and illustrate course topics, and to build student problem-solving skills.

Molecular dynamics simulation study of thermodynamic and mechanical properties of the Cu-Pd random alloy

International Nuclear Information System (INIS)

Davoodi, J.; Ahmadi, M.; Rafii-Tabar, H.

2010-01-01

Molecular dynamics (MD) simulations have been performed to investigate the thermodynamic and mechanical properties of Cu-x% Pd (at%) random alloy, as well as those of the Cu 3 Pd and CuPd 3 ordered alloys, in the temperature range from 200 K up to the melting point. The quantum Sutton-Chen (Q-SC) many-body interatomic potentials have been used to describe the energetics of the Cu and Pd pure metals, and a standard mixing rule has been employed to obtain the potential parameters for the mixed (alloy) states. We have computed the variation of the melting temperature with the concentration of Pd. Furthermore, the variation of the cohesive energy, the order parameter, the thermal expansion coefficient, the density, the isobaric heat capacity, the bulk modulus, and the elastic stiffness constants were also calculated at different temperatures and concentrations for these materials. The computed variations of the thermodynamic and mechanical properties with temperature are fitted to a polynomial function. Our computed results show good agreement with other computational simulations, as well as with the experimental results where they have been available.

Mechanical tolerances study through simulations and experimental characterization for a 1000X micro-concentrator CPV module

Science.gov (United States)

Ritou, Arnaud; Voarino, Philippe; Goubault, Baptiste; David, Nadine; Bernardis, Sarah; Raccurt, Olivier; Baudrit, Mathieu

2017-09-01

Existing CPV technology markets are not compliant with a standard configuration. Concentrations vary from several suns to more than 1000 suns and the optical technology used could be very different. Nowadays, the market trends are moving toward more and more compact optical systems in order to exploit the Light Emitting Diode (LED) like approach. The aim is to increase the optical efficiency by using an ultra-short focal distance and to improve thermal management. Moreover the efficiency to weight ratio is increasing and the solar cell size becomes sub-millimetric. With these conditions, more stringent mechanical tolerances are essential to ensure an optimum optical alignment between cells and optics. A new process of micro-concentrator manufacturing is developed in this work. This process enables manufacturing and auto-alignment of Primary Optical Elements (POE) with Secondary Optical Elements (SOE) and solar cells with respect to certain mechanical tolerances. A 1000X micro-concentrator is manufactured with 0.6 x 0.6 mm² triple-junction cells and molded silicone optics. Mechanical alignment defects are studied by ray-tracing simulations and a prototype is characterized with respect to its mechanical behavior. An efficiency of 33.4% is measured with a Cell-to-Module ratio of 77.8%.

Effects of Geomechanical Mechanism on the Gas Production Behavior: A Simulation Study of Class-3 Type Four-Way-Closure Ridge Hydrate Deposit Offshore Southwestern Taiwan

Science.gov (United States)

Wu, Cheng-Yueh; Chiu, Yung-Cheng; Huang, Yi-Jyun; Hsieh, Bieng-Zih

2017-04-01

The future energy police of Taiwan will heavily rely on the clean energy, including renewable energy and low-carbon energy, to meet the target of mitigating CO2 emission. In addition to developing the renewable energies like solar and wind resources, Taiwan will increase the natural gas consumption to obtain enough electrical power with low-carbon emission. The vast resources of gas hydrates recognized in southwestern offshore Taiwan makes a great opportunity for Taiwan to have own energy resources in the future. Therefore, Taiwan put significant efforts on the evaluation of gas hydrate reserves recently. Production behavior of natural gas dissociated from gas hydrate deposits is an important issue to the hydrate reserves evaluation. The depressurization method is a useful engineering recovery method for gas production from a class-3 type hydrate deposit. The dissociation efficiency will be affected by the pressure drawdown disturbance. However, when the pore pressure of hydrate deposits is depressurized for gas production, the rock matrix will surfer more stresses and the formation deformation might be occurred. The purpose of this study was to investigate the effects of geomechanical mechanism on the gas production from a class-3 hydrate deposit using depressurization method. The case of a class-3 type hydrate deposit of Four-Way-Closure Ridge was studied. In this study a reservoir simulator, STARS, was used. STARS is a multiphase flow, heat transfer, geo-chemical and geo-mechanical mechanisms coupling simulator which is capable to simulate the dissociation/reformation of gas hydrate and the deformation of hydrate reservoirs and overburdens. The simulating ability of STARTS simulator was validated by duplicating the hydrate comparison projects of National Energy Technology Lab. The study target, Four-Way-Closure (FWC) Ridge hydrate deposit, was discovered by the bottom simulating reflectors (BSRs). The geological parameters were collected from the geological and

A pseudobond parametrization for improved electrostatics in quantum mechanical/molecular mechanical simulations of enzymes.

Science.gov (United States)

Parks, Jerry M; Hu, Hao; Cohen, Aron J; Yang, Weitao

2008-10-21

The pseudobond method is used in quantum mechanical/molecular mechanical (QM/MM) simulations in which a covalent bond connects the quantum mechanical and classical subsystems. In this method, the molecular mechanical boundary atom is replaced by a special quantum mechanical atom with one free valence that forms a bond with the rest of the quantum mechanical subsystem. This boundary atom is modified through the use of a parametrized effective core potential and basis set. The pseudobond is designed to reproduce the properties of the covalent bond that it has replaced, while invoking as small a perturbation as possible on the system. Following the work of Zhang [J. Chem. Phys. 122, 024114 (2005)], we have developed new pseudobond parameters for use in the simulation of enzymatic systems. Our parameters yield improved electrostatics and deprotonation energies, while at the same time maintaining accurate geometries. We provide parameters for C(ps)(sp(3))-C(sp(3)), C(ps)(sp(3))-C(sp(2),carbonyl), and C(ps)(sp(3))-N(sp(3)) pseudobonds, which allow the interface between the quantum mechanical and molecular mechanical subsystems to be constructed at either the C(alpha)-C(beta) bond of a given amino acid residue or along the peptide backbone. In addition, we demonstrate the efficiency of our parametrization method by generating residue-specific pseudobond parameters for a single amino acid. Such an approach may enable higher accuracy than general purpose parameters for specific QM/MM applications.

Synthesis, Analysis And Simulation Of a Four-Bar Mechanism Using ...

African Journals Online (AJOL)

Kinematic synthesis of the four-bar mechanism using the complex number method is presented. The results of the synthesis process are analyzed to determine motion characteristics of the mechanism. These motion characteristics are then used for simulation of the mechanism. Matlab programs are written for solving the ...

Effects of mechanical feedback on the stability of cardiac scroll waves: A bidomain electro-mechanical simulation study.

Science.gov (United States)

Colli Franzone, P; Pavarino, L F; Scacchi, S

2017-09-01

In this work, we investigate the influence of cardiac tissue deformation on re-entrant wave dynamics. We have developed a 3D strongly coupled electro-mechanical Bidomain model posed on an ideal monoventricular geometry, including fiber direction anisotropy and stretch-activated currents (SACs). The cardiac mechanical deformation influences the bioelectrical activity with two main mechanical feedback: (a) the geometric feedback (GEF) due to the presence of the deformation gradient in the diffusion coefficients and in a convective term depending on the deformation rate and (b) the mechano-electric feedback (MEF) due to SACs. Here, we investigate the relative contribution of these two factors with respect to scroll wave stability. We extend the previous works [Keldermann et al., Am. J. Physiol. Heart Circ. Physiol. 299, H134-H143 (2010) and Hu et al., PLoS One 8(4), e60287 (2013)] that were based on the Monodomain model and a simple non-selective linear SAC, while here we consider the full Bidomain model and both selective and non-selective components of SACs. Our simulation results show that the stability of cardiac scroll waves is influenced by MEF, which in case of low reversal potential of non-selective SACs might be responsible for the onset of ventricular fibrillation; GEF increases the scroll wave meandering but does not determine the scroll wave stability.

Mechanism study of pulsus paradoxus using mechanical models.

Directory of Open Access Journals (Sweden)

Chang-yang Xing

Full Text Available Pulsus paradoxus is an exaggeration of the normal inspiratory decrease in systolic blood pressure. Despite a century of attempts to explain this sign consensus is still lacking. To solve the controversy and reveal the exact mechanism, we reexamined the characteristic anatomic arrangement of the circulation system in the chest and designed these mechanical models based on related hydromechanic principles. Model 1 was designed to observe the primary influence of respiratory intrathoracic pressure change (RIPC on systemic and pulmonary venous return systems (SVR and PVR respectively. Model 2, as an equivalent mechanical model of septal swing, was to study the secondary influence of RIPC on the motion of the interventriclar septum (IVS, which might be the direct cause for pulsus paradoxus. Model 1 demonstrated that the simulated RIPC had different influence on the simulated SVR and PVR. It increased the volume of the simulated right ventricle (SRV when the internal pressure was kept constant (8.16 cmH2O, while it had the opposite effect on PVR. Model 2 revealed the three major factors determining the respiratory displacement of IVS in normal and different pathophysiological conditions: the magnitude of RIPC, the pressure difference between the two ventricles and the intrapericardial pressure. Our models demonstrate that the different anatomical arrangement of the two venous return systems leads to a different effect of RIPC on right and left ventricles, and thus a pressure gradient across IVS that tends to shift IVS left- and rightwards. When the leftward displacement of IVS reaches a considerable amplitude in some pathologic condition such as cardiac tamponade, the pulsus paradoxus occurs.

New Insight in Understanding the mechanical responses of polymer glasses using molecular dynamic simulation

Science.gov (United States)

Zheng, Yexin; Wang, Shi-Qing; Tsige, Mesfin

The Kremer-Grest bead-spring model has been the standard model in molecular dynamics simulation of polymer glasses. However, due to current computational limitations in accessing relevant time scales in polymer glasses in a reasonable amount of CPU time, simulation of mechanical response of polymer glasses in molecular dynamic simulations requires a much higher quenching rate and deformation rate than used in experiments. Despite several orders of magnitude difference in time scale between simulation and experiment, previous studies have shown that simulations can produce meaningful results that can be directly compared with experimental results. In this work we show that by tuning the quenching rate and deformation rate relative to the segmental relaxation times, a reasonable mechanical response shows up in the glassy state. Specifically, we show a younger glass prepared with a faster quenching rate shows glassy responses only when the imposed deformation rate is proportionally higher. the National Science Foundation (DMR-1444859 and DMR-1609977).

The Framework for Simulation of Bioinspired Security Mechanisms against Network Infrastructure Attacks

Directory of Open Access Journals (Sweden)

Andrey Shorov

2014-01-01

Full Text Available The paper outlines a bioinspired approach named “network nervous system" and methods of simulation of infrastructure attacks and protection mechanisms based on this approach. The protection mechanisms based on this approach consist of distributed prosedures of information collection and processing, which coordinate the activities of the main devices of a computer network, identify attacks, and determine nessesary countermeasures. Attacks and protection mechanisms are specified as structural models using a set-theoretic approach. An environment for simulation of protection mechanisms based on the biological metaphor is considered; the experiments demonstrating the effectiveness of the protection mechanisms are described.

The framework for simulation of bioinspired security mechanisms against network infrastructure attacks.

Science.gov (United States)

Shorov, Andrey; Kotenko, Igor

2014-01-01

The paper outlines a bioinspired approach named "network nervous system" and methods of simulation of infrastructure attacks and protection mechanisms based on this approach. The protection mechanisms based on this approach consist of distributed procedures of information collection and processing, which coordinate the activities of the main devices of a computer network, identify attacks, and determine necessary countermeasures. Attacks and protection mechanisms are specified as structural models using a set-theoretic approach. An environment for simulation of protection mechanisms based on the biological metaphor is considered; the experiments demonstrating the effectiveness of the protection mechanisms are described.

Provably unbounded memory advantage in stochastic simulation using quantum mechanics

Science.gov (United States)

Garner, Andrew J. P.; Liu, Qing; Thompson, Jayne; Vedral, Vlatko; Gu, mile

2017-10-01

Simulating the stochastic evolution of real quantities on a digital computer requires a trade-off between the precision to which these quantities are approximated, and the memory required to store them. The statistical accuracy of the simulation is thus generally limited by the internal memory available to the simulator. Here, using tools from computational mechanics, we show that quantum processors with a fixed finite memory can simulate stochastic processes of real variables to arbitrarily high precision. This demonstrates a provable, unbounded memory advantage that a quantum simulator can exhibit over its best possible classical counterpart.

Study on the mechanism and efficiency of simulated annealing using an LP optimization benchmark problem - 113

International Nuclear Information System (INIS)

Qianqian, Li; Xiaofeng, Jiang; Shaohong, Zhang

2010-01-01

Simulated Annealing Algorithm (SAA) for solving combinatorial optimization problems is a popular method for loading pattern optimization. The main purpose of this paper is to understand the underlying search mechanism of SAA and to study its efficiency. In this study, a general SAA that employs random pair exchange of fuel assemblies to search for the optimum fuel Loading Pattern (LP) is applied to an exhaustively searched LP optimization benchmark problem. All the possible LPs of the benchmark problem have been enumerated and evaluated via the use of the very fast and accurate Hybrid Harmonics and Linear Perturbation (HHLP) method, such that the mechanism of SA for LP optimization can be explicitly analyzed and its search efficiency evaluated. The generic core geometry itself dictates that only a small number LPs can be generated by performing random single pair exchanges and that the LPs are necessarily mostly similar to the initial LP. This phase space effect turns out to be the basic mechanism in SAA that can explain its efficiency and good local search ability. A measure of search efficiency is introduced which shows that the stochastic nature of SAA greatly influences the variability of its search efficiency. It is also found that using fuel assembly k-infinity distribution as a technique to filter the LPs can significantly enhance the SAA search efficiency. (authors)

Separating grain boundary migration mechanisms in molecular dynamics simulations

International Nuclear Information System (INIS)

Ulomek, Felix; Mohles, Volker

2016-01-01

In molecular dynamics (MD) simulations of grain boundary (GB) migration it is quite common to find a temperature dependence of GB mobility that deviates strongly from an Arrhenius-type dependence. This usually indicates that more than one mechanism is actually active. With the goal to separate different GB migration mechanisms we investigate a Σ7 <111> 38.2° GB by MD using an EAM potential for aluminium. To drive the GB with a well-known and adjustable force, the energy conserving orientational driving force (ECO DF) is used that had been introduced recently. The magnitude of the DF and the temperature are varied. This yielded a high and a low temperature range for the GB velocity, with a transition temperature that depends on the magnitude of the DF. A method is introduced which allows both a visual and a statistical characterization of GB motion on a per atom basis. These analyses reveal that two mechanisms are active in this GB, a shuffling mechanism and its initiation. These mechanisms operate in a sequential, coupled manner. Based on this, a simple model is introduced that describes all simulated GB velocities (and hence the mobility) very well, including the transition between the dominating mechanisms.

Rapid Convergence of Energy and Free Energy Profiles with Quantum Mechanical Size in Quantum Mechanical-Molecular Mechanical Simulations of Proton Transfer in DNA.

Science.gov (United States)

Das, Susanta; Nam, Kwangho; Major, Dan Thomas

2018-03-13

In recent years, a number of quantum mechanical-molecular mechanical (QM/MM) enzyme studies have investigated the dependence of reaction energetics on the size of the QM region using energy and free energy calculations. In this study, we revisit the question of QM region size dependence in QM/MM simulations within the context of energy and free energy calculations using a proton transfer in a DNA base pair as a test case. In the simulations, the QM region was treated with a dispersion-corrected AM1/d-PhoT Hamiltonian, which was developed to accurately describe phosphoryl and proton transfer reactions, in conjunction with an electrostatic embedding scheme using the particle-mesh Ewald summation method. With this rigorous QM/MM potential, we performed rather extensive QM/MM sampling, and found that the free energy reaction profiles converge rapidly with respect to the QM region size within ca. ±1 kcal/mol. This finding suggests that the strategy of QM/MM simulations with reasonably sized and selected QM regions, which has been employed for over four decades, is a valid approach for modeling complex biomolecular systems. We point to possible causes for the sensitivity of the energy and free energy calculations to the size of the QM region, and potential implications.

Collaborative Simulation Grid: Multiscale Quantum-Mechanical/Classical Atomistic Simulations on Distributed PC Clusters in the US and Japan

Science.gov (United States)

Kikuchi, Hideaki; Kalia, Rajiv; Nakano, Aiichiro; Vashishta, Priya; Iyetomi, Hiroshi; Ogata, Shuji; Kouno, Takahisa; Shimojo, Fuyuki; Tsuruta, Kanji; Saini, Subhash;

Numerical Simulation of a Mechanically Stacked GaAs/Ge Solar Cell

Directory of Open Access Journals (Sweden)

S. Enayat Taghavi Moghaddam

2017-06-01

Full Text Available In this paper, GaAs and Ge solar cells have been studied and simulated separately and the inner characteristics of each have been calculated including the energy band structure, the internal field, carrier density distribution in the equilibrium condition (dark condition and the voltage-current curve in the sun exposure with the output power of each one. Finally, the output power of these two mechanically stacked cells is achieved. Drift-diffusion model have been used for simulation that solved with numerically method and Gummel algorithm. In this simulation, the final cells exposed to sun light in a standard AM 1.5 G conditions and temperatures are 300° K. The efficiency of the proposed structure is 9.47%. The analytical results are compared with results of numerical simulations and the accuracy of the method used is shown.

Interactive simulations as teaching tools for engineering mechanics courses

International Nuclear Information System (INIS)

Carbonell, Victoria; Martínez, Elvira; Flórez, Mercedes; Romero, Carlos

2013-01-01

This study aimed to gauge the effect of interactive simulations in class as an active teaching strategy for a mechanics course. Engineering analysis and design often use the properties of planar sections in calculations. In the stress analysis of a beam under bending and torsional loads, cross-sectional properties are used to determine stress and displacement distributions in the beam cross section. The centroid, moments and products of inertia of an area made up of several common shapes (rectangles usually) may thus be obtained by adding the moments of inertia of the component areas (U-shape, L-shape, C-shape, etc). This procedure is used to calculate the second moments of structural shapes in engineering practice because the determination of their moments of inertia is necessary for the design of structural components. This paper presents examples of interactive simulations developed for teaching the ‘Mechanics and mechanisms’ course at the Universidad Politecnica de Madrid, Spain. The simulations focus on fundamental topics such as centroids, the properties of the moment of inertia, second moments of inertia with respect to two axes, principal moments of inertia and Mohr's Circle for plane stress, and were composed using Geogebra software. These learning tools feature animations, graphics and interactivity and were designed to encourage student participation and engagement in active learning activities, to effectively explain and illustrate course topics, and to build student problem-solving skills. (paper)

Molecular dynamics simulation of nanocrystalline nickel: structure and mechanical properties

Energy Technology Data Exchange (ETDEWEB)

Swygenhoven, H. van [Paul Scherrer Inst. (PSI), Villigen (Switzerland); Caro, A. [Comision Nacional de Energia Atomica, San Carlos de Bariloche (Argentina). Centro Atomico Bariloche

1997-09-01

Molecular dynamics computer simulations of low temperature elastic and plastic deformation of Ni nanophase samples (3-7 nm) are performed. The samples are polycrystals nucleated from different seeds, with random locations and orientations. Bulk and Young`s modulus, onset of plastic deformation and mechanism responsible for the plastic behaviour are studied and compared with the behaviour of coarse grained samples. (author) 1 fig., 3 refs.

Molecular dynamics simulation of nanocrystalline nickel: structure and mechanical properties

International Nuclear Information System (INIS)

Swygenhoven, H. van; Caro, A.

1997-01-01

Molecular dynamics computer simulations of low temperature elastic and plastic deformation of Ni nanophase samples (3-7 nm) are performed. The samples are polycrystals nucleated from different seeds, with random locations and orientations. Bulk and Young's modulus, onset of plastic deformation and mechanism responsible for the plastic behaviour are studied and compared with the behaviour of coarse grained samples. (author) 1 fig., 3 refs

Molecular dynamics simulation study of thermodynamic and mechanical properties of the Cu-Pd random alloy

Energy Technology Data Exchange (ETDEWEB)

Davoodi, J., E-mail: jdavoodi@znu.ac.ir [Departmant of Physics, University of Zanjan, P.O. Box 45371-38111, Zanjan (Iran, Islamic Republic of); Ahmadi, M. [Departmant of Physics, University of Zanjan, P.O. Box 45371-38111, Zanjan (Iran, Islamic Republic of); Rafii-Tabar, H. [Department of Medical Physics and Biomedical Engineering and Research Center for Medical Nanotechnology and Tissue Engineering, Shahid Beheshti University of Medical Sciences, Evin, Tehran (Iran, Islamic Republic of); Computational Physical Sciences Research Laboratory, Department of Nano-Science, Institute for Research in Fundamental Sciences (IPM), P.O. Box 19395-5531, Tehran (Iran, Islamic Republic of)

2010-06-25

Molecular dynamics (MD) simulations have been performed to investigate the thermodynamic and mechanical properties of Cu-x% Pd (at%) random alloy, as well as those of the Cu{sub 3}Pd and CuPd{sub 3} ordered alloys, in the temperature range from 200 K up to the melting point. The quantum Sutton-Chen (Q-SC) many-body interatomic potentials have been used to describe the energetics of the Cu and Pd pure metals, and a standard mixing rule has been employed to obtain the potential parameters for the mixed (alloy) states. We have computed the variation of the melting temperature with the concentration of Pd. Furthermore, the variation of the cohesive energy, the order parameter, the thermal expansion coefficient, the density, the isobaric heat capacity, the bulk modulus, and the elastic stiffness constants were also calculated at different temperatures and concentrations for these materials. The computed variations of the thermodynamic and mechanical properties with temperature are fitted to a polynomial function. Our computed results show good agreement with other computational simulations, as well as with the experimental results where they have been available.

Simulated effect on the compressive and shear mechanical properties of bionic integrated honeycomb plates.

Science.gov (United States)

He, Chenglin; Chen, Jinxiang; Wu, Zhishen; Xie, Juan; Zu, Qiao; Lu, Yun

2015-05-01

Honeycomb plates can be applied in many fields, including furniture manufacturing, mechanical engineering, civil engineering, transportation and aerospace. In the present study, we discuss the simulated effect on the mechanical properties of bionic integrated honeycomb plates by investigating the compressive and shear failure modes and the mechanical properties of trabeculae reinforced by long or short fibers. The results indicate that the simulated effect represents approximately 80% and 70% of the compressive and shear strengths, respectively. Compared with existing bionic samples, the mass-specific strength was significantly improved. Therefore, this integrated honeycomb technology remains the most effective method for the trial manufacturing of bionic integrated honeycomb plates. The simulated effect of the compressive rigidity is approximately 85%. The short-fiber trabeculae have an advantage over the long-fiber trabeculae in terms of shear rigidity, which provides new evidence for the application of integrated bionic honeycomb plates. Copyright © 2015 Elsevier B.V. All rights reserved.

Lung assist devices influence cardio-energetic parameters: Numerical simulation study.

Science.gov (United States)

De Lazzari, C; Quatember, B; Recheis, W; Mayr, M; Demertzis, S; Allasia, G; De Rossi, A; Cavoretto, R; Venturino, E; Genuini, I

2015-08-01

We aim at an analysis of the effects mechanical ventilators (MVs) and thoracic artificial lungs (TALs) will have on the cardiovascular system, especially on important quantities, such as left and right ventricular external work (EW), pressure-volume area (PVA) and cardiac mechanical efficiency (CME). Our analyses are based on simulation studies which were carried out by using our CARDIOSIM(©) software simulator. At first, we carried out simulation studies of patients undergoing mechanical ventilation (MV) without a thoracic artificial lung (TAL). Subsequently, we conducted simulation studies of patients who had been provided with a TAL, but did not undergo MV. We aimed at describing the patient's physiological characteristics and their variations with time, such as EW, PVA, CME, cardiac output (CO) and mean pulmonary arterial/venous pressure (PAP/PVP). We were starting with a simulation run under well-defined initial conditions which was followed by simulation runs for a wide range of mean intrathoracic pressure settings. Our simulations of MV without TAL showed that for mean intrathoracic pressure settings from negative (-4 mmHg) to positive (+5 mmHg) values, the left and right ventricular EW and PVA, right ventricular CME and CO decreased, whereas left ventricular CME and the PAP increased. The simulation studies of patients with a TAL, comprised all the usual TAL arrangements, viz. configurations "in series" and in parallel with the natural lung and, moreover, hybrid configurations. The main objective of the simulation studies was, as before, the assessment of the hemodynamic response to the application of a TAL. We could for instance show that, in case of an "in series" configuration, a reduction (an increase) in left (right) ventricular EW and PVA values occurred, whereas the best performance in terms of CO can be achieved in the case of an in parallel configuration.

Deformation mechanisms in nanotwinned copper by molecular dynamics simulation

Energy Technology Data Exchange (ETDEWEB)

Zhao, Xing [School of Mechanical, Materials and Mechatronic Engineering, University of Wollongong, Wollongong, NSW 2522 (Australia); State Key Laboratory of High Performance Complex Manufacturing, Central South University, Changsha 410083 (China); Lu, Cheng, E-mail: chenglu@uow.edu.au [School of Mechanical, Materials and Mechatronic Engineering, University of Wollongong, Wollongong, NSW 2522 (Australia); Tieu, Anh Kiet; Pei, Linqing; Zhang, Liang; Su, Lihong [School of Mechanical, Materials and Mechatronic Engineering, University of Wollongong, Wollongong, NSW 2522 (Australia); Zhan, Lihua [State Key Laboratory of High Performance Complex Manufacturing, Central South University, Changsha 410083 (China)

2017-02-27

Nanotwinned materials exhibit simultaneous ultrahigh strength and high ductility which is attributed to the interactions between dislocations and twin boundaries but the specific deformation mechanisms are rarely seen in experiments at the atomic level. Here we use large scale molecular dynamics simulations to explore this intricate interplay during the plastic deformation of nanotwinned Cu. We demonstrate that the dominant deformation mechanism transits dynamically from slip transfer to twin boundary migration to slip-twin interactions as the twin boundary orientation changes from horizontal to slant, and then to a vertical direction. Building on the fundamental physics of dislocation processes from computer simulations and combining the available experimental investigations, we unravel the underlying deformation mechanisms for nanotwinned Cu, incorporating all three distinct dislocation processes. Our results give insights into systematically engineering the nanoscale twins to fabricate nanotwinned metals or alloys that have high strength and considerable ductility.

Mechanical Properties of Boehmite Evaluated by Atomic Force Microscopy Experiments and Molecular Dynamic Finite Element Simulations

International Nuclear Information System (INIS)

Fankhanel, J.; Daum, B.; Kempe, A.; Rolfes, R.; Silbernagl, D.; Khorasani, M.Gh.Z.; Sturm, H.; Sturm, H.

2016-01-01

Boehmite nanoparticles show great potential in improving mechanical properties of fiber reinforced polymers. In order to predict the properties of nanocomposites, knowledge about the material parameters of the constituent phases, including the boehmite particles, is crucial. In this study, the mechanical behavior of boehmite is investigated using Atomic Force Microscopy (AFM) experiments and Molecular Dynamic Finite Element Method (MDFEM) simulations. Young’s modulus of the perfect crystalline boehmite nanoparticles is derived from numerical AFM simulations. Results of AFM experiments on boehmite nanoparticles deviate significantly. Possible causes are identified by experiments on complementary types of boehmite, that is, geological and hydrothermally synthesized samples, and further simulations of imperfect crystals and combined boehmite/epoxy models. Under certain circumstances, the mechanical behavior of boehmite was found to be dominated by inelastic effects that are discussed in detail in the present work. The studies are substantiated with accompanying X-ray diffraction and Raman experiments.

Carbon dioxide coronary angiography: A mechanical feasibility study with a cardiovascular simulator

Science.gov (United States)

Corazza, Ivan; Taglieri, Nevio; Pirazzini, Edoardo; Rossi, Pier Luca; Lombi, Alessandro; Scalise, Filippo; Caridi, James G.; Zannoli, Romano

2018-01-01

The aim of this study was to carry out a bench evaluation of the biomechanical feasibility of carbon dioxide (CO2) coronary arteriography. Many patients among the aging population of individuals requiring cardiac intervention have underlying renal insufficiency making them susceptible to contrast-induced nephropathy. To include those patients, it is imperative to find an alternative and safe technique to perform coronary imaging on cardiac ischemic patients. As CO2 angiography has no renal toxicity, it may be a possible solution offering good imaging with negligible collateral effects. Theoretically, by carefully controlling the gas injection process, new automatic injectors may avoid gas reflux into the aorta and possible cerebral damage. A feasibility study is mandatory. A mechanical mock of the coronary circulation was developed and employed. CO2 was injected into the coronary ostium with 2 catheters (2F and 6F) and optical images of bubbles flowing inside the vessels at different injection pressures were recorded. The gas behavior was then carefully studied for quantitative and qualitative analysis. Video recordings showed that CO2 injection at a precise pressure in the interval between the arterial dicrotic notch and the minimum diastolic value does not result in gas reflow into the aorta. Gas reflow was easier to control with the smaller catheter, but the gas bubbles were smaller with different vascular filling. Our simulation demonstrates that carefully selected injection parameters allow CO2 coronary imaging without any risk of gas reflux into the aorta.

Carbon dioxide coronary angiography: A mechanical feasibility study with a cardiovascular simulator

Directory of Open Access Journals (Sweden)

Ivan Corazza

2018-01-01

Full Text Available The aim of this study was to carry out a bench evaluation of the biomechanical feasibility of carbon dioxide (CO2 coronary arteriography. Many patients among the aging population of individuals requiring cardiac intervention have underlying renal insufficiency making them susceptible to contrast-induced nephropathy. To include those patients, it is imperative to find an alternative and safe technique to perform coronary imaging on cardiac ischemic patients. As CO2 angiography has no renal toxicity, it may be a possible solution offering good imaging with negligible collateral effects. Theoretically, by carefully controlling the gas injection process, new automatic injectors may avoid gas reflux into the aorta and possible cerebral damage. A feasibility study is mandatory. A mechanical mock of the coronary circulation was developed and employed. CO2 was injected into the coronary ostium with 2 catheters (2F and 6F and optical images of bubbles flowing inside the vessels at different injection pressures were recorded. The gas behavior was then carefully studied for quantitative and qualitative analysis. Video recordings showed that CO2 injection at a precise pressure in the interval between the arterial dicrotic notch and the minimum diastolic value does not result in gas reflow into the aorta. Gas reflow was easier to control with the smaller catheter, but the gas bubbles were smaller with different vascular filling. Our simulation demonstrates that carefully selected injection parameters allow CO2 coronary imaging without any risk of gas reflux into the aorta.

Predicting Silk Fiber Mechanical Properties through Multiscale Simulation and Protein Design.

Science.gov (United States)

Rim, Nae-Gyune; Roberts, Erin G; Ebrahimi, Davoud; Dinjaski, Nina; Jacobsen, Matthew M; Martín-Moldes, Zaira; Buehler, Markus J; Kaplan, David L; Wong, Joyce Y

2017-08-14

Silk is a promising material for biomedical applications, and much research is focused on how application-specific, mechanical properties of silk can be designed synthetically through proper amino acid sequences and processing parameters. This protocol describes an iterative process between research disciplines that combines simulation, genetic synthesis, and fiber analysis to better design silk fibers with specific mechanical properties. Computational methods are used to assess the protein polymer structure as it forms an interconnected fiber network through shearing and how this process affects fiber mechanical properties. Model outcomes are validated experimentally with the genetic design of protein polymers that match the simulation structures, fiber fabrication from these polymers, and mechanical testing of these fibers. Through iterative feedback between computation, genetic synthesis, and fiber mechanical testing, this protocol will enable a priori prediction capability of recombinant material mechanical properties via insights from the resulting molecular architecture of the fiber network based entirely on the initial protein monomer composition. This style of protocol may be applied to other fields where a research team seeks to design a biomaterial with biomedical application-specific properties. This protocol highlights when and how the three research groups (simulation, synthesis, and engineering) should be interacting to arrive at the most effective method for predictive design of their material.

Provably unbounded memory advantage in stochastic simulation using quantum mechanics

International Nuclear Information System (INIS)

Garner, Andrew J P; Thompson, Jayne; Vedral, Vlatko; Gu, Mile; Liu, Qing

2017-01-01

Simulating the stochastic evolution of real quantities on a digital computer requires a trade-off between the precision to which these quantities are approximated, and the memory required to store them. The statistical accuracy of the simulation is thus generally limited by the internal memory available to the simulator. Here, using tools from computational mechanics, we show that quantum processors with a fixed finite memory can simulate stochastic processes of real variables to arbitrarily high precision. This demonstrates a provable, unbounded memory advantage that a quantum simulator can exhibit over its best possible classical counterpart. (paper)

Quantum Mechanical Balance Equation Approach to Semiconductor Device Simulation

National Research Council Canada - National Science Library

Cui, Long

1997-01-01

This research project was focused on the development of a quantum mechanical balance equation based device simulator that can model advanced, compound, submicron devices, under all transport conditions...

Hardware-in-loop simulation of electric vehicles automated mechanical transmission system

Energy Technology Data Exchange (ETDEWEB)

Liao, C.; Wu, Y.; Wang, L. [Chinese Academy of Sciences, Beijing (China). Inst. of Electrical Engineering

2009-03-11

Automated mechanical transmission (AMT) can be used to enhance the performance of hybrid electric vehicles. In this study, hardware-in-loop (HIL) simulations were used to develop an AMT control system. HIL was used to simulate the running and fault status of the system as well as to optimize its performance. HIL was combined with a commercial simulation tool and an automatic code generation technology in a real time environment tool to develop the AMT control system. A hybrid vehicle system dynamics model was generated and then simulated in various real time operating vehicle environments. Virtual instrument technology was used to develop real time monitoring, parameter matching calibration, data acquisition and offline analyses for the optimization of the control system. Results of the analyses demonstrated that the AMT control system can be used to optimize the performance of hybrid electric vehicles. 5 refs., 9 figs.

Mechanical design of NASA Ames Research Center vertical motion simulator

Science.gov (United States)

Engelbert, D. F.; Bakke, A. P.; Chargin, M. K.; Vallotton, W. C.

1976-01-01

NASA has designed and is constructing a new flight simulator with large vertical travel. Several aspects of the mechanical design of this Vertical Motion Simulator (VMS) are discussed, including the multiple rack and pinion vertical drive, a pneumatic equilibration system, and the friction-damped rigid link catenaries used as cable supports.

Mechanism change in a simulation of peer review: from junk support to elitism.

Science.gov (United States)

Paolucci, Mario; Grimaldo, Francisco

2014-01-01

Peer review works as the hinge of the scientific process, mediating between research and the awareness/acceptance of its results. While it might seem obvious that science would regulate itself scientifically, the consensus on peer review is eroding; a deeper understanding of its workings and potential alternatives is sorely needed. Employing a theoretical approach supported by agent-based simulation, we examined computational models of peer review, performing what we propose to call redesign , that is, the replication of simulations using different mechanisms . Here, we show that we are able to obtain the high sensitivity to rational cheating that is present in literature. In addition, we also show how this result appears to be fragile against small variations in mechanisms. Therefore, we argue that exploration of the parameter space is not enough if we want to support theoretical statements with simulation, and that exploration at the level of mechanisms is needed. These findings also support prudence in the application of simulation results based on single mechanisms, and endorse the use of complex agent platforms that encourage experimentation of diverse mechanisms.

Tensile mechanical properties of Ni-based superalloy of nanophases using molecular dynamics simulation

Energy Technology Data Exchange (ETDEWEB)

Ma, Lei; Hu, Wangyu [College of Materials Science and Engineering, Hunan University, Changsha (China); Department of Applied Physics, Hunan University, Changsha (China); Xiao, Shifang; Deng, Huiqiu [Department of Applied Physics, Hunan University, Changsha (China)

2016-04-15

The mechanical properties of Ni/Ni{sub 3}Al monocrystal of nanophases with varying temperatures, strain rates, and phase sizes have been studied using molecular dynamics simulation. The simulation results show that the primary deformation mechanisms in Ni/Ni{sub 3}Al monocrystal of nanophases were slip bands and antiphase boundaries at room temperature. The studies on the effects of temperature showed that the yield strain, yield strength, and elastic module decreased as temperature increased. However, the influences of strain rate and phase size on the mechanical properties of Ni/Ni{sub 3}Al monocrystal of nanophases showed that the high strain rate led to the increase of yield stress, and the phase sizes had no significant influence on the maximum yield stress. In addition, the behavior of crack propagation in the model of Ni/Ni{sub 3}Al interface was investigated under cyclic loading, and it was found that the interface of Ni/Ni{sub 3}Al was resistance to the fatigue crack propagation. (copyright 2015 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Simulation study of self-sustainment mechanism in reversed-field pinch configuration

International Nuclear Information System (INIS)

Kusano, Kanya; Sato, Tetsuya.

1989-09-01

3D magnetohydrodynamic (MHD) simulations are carried out in order to reveal the fundamental mechanism of the self-sustainment process in the reversed-field pinch plasma. It is confirmed that the RFP configuration is sustained in a cyclic process, where the MHD relaxation phase and the resistive diffusion phase appear cyclically and alternatively. In the MHD relaxation process, the RFP plasma approaches a Taylor's minimum energy state, but it departs from there in the diffusion process. In other words, since MHD relaxation processes periodically release excess magnetic energy accumulated in the resistive diffusion phase, RFP plasma can stay in the neighborhood of the minimum energy state. The mechanism of this cyclic process is disclosed. Namely, when at least two ideal kink (m = 1) modes becomes unstable, MHD relaxation can take place. This is because the MHD relaxation progresses through nonlinear reconnection of the m = 0 mode, which is driven by nonlinear coupling between the unstable kink modes. Therefore, self-sustainment processes can be achieved by the nonlinear effects of essentially the m = 0 and 1 modes. The quantitative dependence of the relaxation-diffusion cycle on the aspect ratio of the device is considered along with its dependence on the magnetic Reynolds, number. These results are consistent with recent experiments and indicate that a coherent oscillation, which is often observed in experiments, is necessary for self-sustainment. The influence of self-sustainment processes on particle confinement is briefly discussed. (author)

Numerical simulation of volume-controlled mechanical ventilated respiratory system with 2 different lungs.

Science.gov (United States)

Shi, Yan; Zhang, Bolun; Cai, Maolin; Zhang, Xiaohua Douglas

2017-09-01

Mechanical ventilation is a key therapy for patients who cannot breathe adequately by themselves, and dynamics of mechanical ventilation system is of great significance for life support of patients. Recently, models of mechanical ventilated respiratory system with 1 lung are used to simulate the respiratory system of patients. However, humans have 2 lungs. When the respiratory characteristics of 2 lungs are different, a single-lung model cannot reflect real respiratory system. In this paper, to illustrate dynamic characteristics of mechanical ventilated respiratory system with 2 different lungs, we propose a mathematical model of mechanical ventilated respiratory system with 2 different lungs and conduct experiments to verify the model. Furthermore, we study the dynamics of mechanical ventilated respiratory system with 2 different lungs. This research study can be used for improving the efficiency and safety of volume-controlled mechanical ventilation system. Copyright © 2016 John Wiley & Sons, Ltd.

Study on modeling of operator's learning mechanism

International Nuclear Information System (INIS)

Yoshimura, Seichi; Hasegawa, Naoko

1998-01-01

One effective method to analyze the causes of human errors is to model the behavior of human and to simulate it. The Central Research Institute of Electric Power Industry (CRIEPI) has developed an operator team behavior simulation system called SYBORG (Simulation System for the Behavior of an Operating Group) to analyze the human errors and to establish the countermeasures for them. As an operator behavior model which composes SYBORG has no learning mechanism and the knowledge of a plant is fixed, it cannot take suitable actions when unknown situations occur nor learn anything from the experience. However, considering actual operators, learning is an essential human factor to enhance their abilities to diagnose plant anomalies. In this paper, Q learning with 1/f fluctuation was proposed as a learning mechanism of an operator and simulation using the mechanism was conducted. The results showed the effectiveness of the learning mechanism. (author)

Numerical simulation of mechanical behavior of composite materials

CERN Document Server

Oller, Sergio

2014-01-01

An original mechanical formulation to treat nonlinear orthotropic behavior of composite materials is presented in this book. It also examines different formulations that allow us to evaluate the behavior of composite materials through the composition of its components, obtaining a new composite material. Also two multiple scale homogenization methods are given, one based on the analytical study of the cells (Ad-hoc homogenization), and other one, more general based on the finite element procedure applied on the macro scale (upper-scale) and in the micro scale (sub-scale). A very general formulation to simulate the mechanical behavior for traditional composite structures (plywood, reinforced concrete, masonry, etc.), as well as the new composite materials reinforced with long and short fibers, nanotubes, etc., are also shown in this work. Typical phenomena occurring in composite materials are also described in this work, including fiber-matrix debounding, local buckling of fibers and its coupling with the over...

An efficient atomistic quantum mechanical simulation on InAs band-to-band tunneling field-effect transistors

Energy Technology Data Exchange (ETDEWEB)

Wang, Zhi [State Key Laboratory for Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, P.O. Box 912, Beijing 100083 (China); Jiang, Xiang-Wei; Li, Shu-Shen [State Key Laboratory for Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, P.O. Box 912, Beijing 100083 (China); Synergetic Innovation Center of Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei, Anhui 230026 (China); Wang, Lin-Wang, E-mail: lwwang@lbl.gov [Material Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States)

2014-03-24

We have presented a fully atomistic quantum mechanical simulation method on band-to-band tunneling (BTBT) field-effect transistors (FETs). Our simulation approach is based on the linear combination of bulk band method with empirical pseudopotentials, which is an atomist method beyond the effective-mass approximation or k.p perturbation method, and can be used to simulate real-size devices (∼10{sup 5} atoms) efficiently (∼5 h on a few computational cores). Using this approach, we studied the InAs dual-gate BTBT FETs. The I-V characteristics from our approach agree very well with the tight-binding non-equilibrium Green's function results, yet our method costs much less computationally. In addition, we have studied ways to increase the tunneling current and analyzed the effects of different mechanisms for that purpose.

An efficient atomistic quantum mechanical simulation on InAs band-to-band tunneling field-effect transistors

International Nuclear Information System (INIS)

Wang, Zhi; Jiang, Xiang-Wei; Li, Shu-Shen; Wang, Lin-Wang

2014-01-01

We have presented a fully atomistic quantum mechanical simulation method on band-to-band tunneling (BTBT) field-effect transistors (FETs). Our simulation approach is based on the linear combination of bulk band method with empirical pseudopotentials, which is an atomist method beyond the effective-mass approximation or k.p perturbation method, and can be used to simulate real-size devices (∼10 5 atoms) efficiently (∼5 h on a few computational cores). Using this approach, we studied the InAs dual-gate BTBT FETs. The I-V characteristics from our approach agree very well with the tight-binding non-equilibrium Green's function results, yet our method costs much less computationally. In addition, we have studied ways to increase the tunneling current and analyzed the effects of different mechanisms for that purpose

Simulative calculation of bromo-polystyrene mechanical properties

CERN Document Server

Wang Chao; Tang Yong Jian

2002-01-01

The non-crystal model of polystyrene and bromo-polystyrene was established with the help of simulative software in the computer. DREIDING was chosen as force field and its parameters is modified according to the published data. Based on the calculation results and other published data the mechanism properties of polystyrene and bromo-polystyrene, such as bulk module, Yong's module and Poisson's ratios, were discussed

Optimization of metabolite detection by quantum mechanics simulations in magnetic resonance spectroscopy.

Science.gov (United States)

Gambarota, Giulio

2017-07-15

Magnetic resonance spectroscopy (MRS) is a well established modality for investigating tissue metabolism in vivo. In recent years, many efforts by the scientific community have been directed towards the improvement of metabolite detection and quantitation. Quantum mechanics simulations allow for investigations of the MR signal behaviour of metabolites; thus, they provide an essential tool in the optimization of metabolite detection. In this review, we will examine quantum mechanics simulations based on the density matrix formalism. The density matrix was introduced by von Neumann in 1927 to take into account statistical effects within the theory of quantum mechanics. We will discuss the main steps of the density matrix simulation of an arbitrary spin system and show some examples for the strongly coupled two spin system. Copyright © 2016 Elsevier Inc. All rights reserved.

Molecular dynamics simulations indicate that deoxyhemoglobin, oxyhemoglobin, carboxyhemoglobin, and glycated hemoglobin under compression and shear exhibit an anisotropic mechanical behavior.

Science.gov (United States)

Yesudasan, Sumith; Wang, Xianqiao; Averett, Rodney D

2018-05-01

We developed a new mechanical model for determining the compression and shear mechanical behavior of four different hemoglobin structures. Previous studies on hemoglobin structures have focused primarily on overall mechanical behavior; however, this study investigates the mechanical behavior of hemoglobin, a major constituent of red blood cells, using steered molecular dynamics (SMD) simulations to obtain anisotropic mechanical behavior under compression and shear loading conditions. Four different configurations of hemoglobin molecules were considered: deoxyhemoglobin (deoxyHb), oxyhemoglobin (HbO 2 ), carboxyhemoglobin (HbCO), and glycated hemoglobin (HbA 1C ). The SMD simulations were performed on the hemoglobin variants to estimate their unidirectional stiffness and shear stiffness. Although hemoglobin is structurally denoted as a globular protein due to its spherical shape and secondary structure, our simulation results show a significant variation in the mechanical strength in different directions (anisotropy) and also a strength variation among the four different hemoglobin configurations studied. The glycated hemoglobin molecule possesses an overall higher compressive mechanical stiffness and shear stiffness when compared to deoxyhemoglobin, oxyhemoglobin, and carboxyhemoglobin molecules. Further results from the models indicate that the hemoglobin structures studied possess a soft outer shell and a stiff core based on stiffness.

Revealing Atomic-Level Mechanisms of Protein Allostery with Molecular Dynamics Simulations.

Directory of Open Access Journals (Sweden)

Samuel Hertig

2016-06-01

Full Text Available Molecular dynamics (MD simulations have become a powerful and popular method for the study of protein allostery, the widespread phenomenon in which a stimulus at one site on a protein influences the properties of another site on the protein. By capturing the motions of a protein's constituent atoms, simulations can enable the discovery of allosteric binding sites and the determination of the mechanistic basis for allostery. These results can provide a foundation for applications including rational drug design and protein engineering. Here, we provide an introduction to the investigation of protein allostery using molecular dynamics simulation. We emphasize the importance of designing simulations that include appropriate perturbations to the molecular system, such as the addition or removal of ligands or the application of mechanical force. We also demonstrate how the bidirectional nature of allostery-the fact that the two sites involved influence one another in a symmetrical manner-can facilitate such investigations. Through a series of case studies, we illustrate how these concepts have been used to reveal the structural basis for allostery in several proteins and protein complexes of biological and pharmaceutical interest.

Results From an International Simulation Study on Coupled Thermal, Hydrological, and Mechanical (THM) Processes Near Geological Nuclear Waste Repositories

International Nuclear Information System (INIS)

J. Rutqvist; D. Barr; J.T. Birkholzer; M. Chijimatsu; O. Kolditz; Q. Liu; Y. Oda; W. Wang; C. Zhang

2006-01-01

As part of the ongoing international DECOVALEX project, four research teams used five different models to simulate coupled thermal, hydrological, and mechanical (THM) processes near waste emplacement drifts of geological nuclear waste repositories. The simulations were conducted for two generic repository types, one with open and the other with back-filled repository drifts, under higher and lower postclosure temperatures, respectively. In the completed first model inception phase of the project, a good agreement was achieved between the research teams in calculating THM responses for both repository types, although some disagreement in hydrological responses is currently being resolved. In particular, good agreement in the basic thermal-mechanical responses was achieved for both repository types, even though some teams used relatively simplified thermal-elastic heat-conduction models that neglected complex near-field thermal-hydrological processes. The good agreement between the complex and simplified process models indicates that the basic thermal-mechanical responses can be predicted with a relatively high confidence level

Reduction of very large reaction mechanisms using methods based on simulation error minimization

Energy Technology Data Exchange (ETDEWEB)

Nagy, Tibor; Turanyi, Tamas [Institute of Chemistry, Eoetvoes University (ELTE), P.O. Box 32, H-1518 Budapest (Hungary)

2009-02-15

A new species reduction method called the Simulation Error Minimization Connectivity Method (SEM-CM) was developed. According to the SEM-CM algorithm, a mechanism building procedure is started from the important species. Strongly connected sets of species, identified on the basis of the normalized Jacobian, are added and several consistent mechanisms are produced. The combustion model is simulated with each of these mechanisms and the mechanism causing the smallest error (i.e. deviation from the model that uses the full mechanism), considering the important species only, is selected. Then, in several steps other strongly connected sets of species are added, the size of the mechanism is gradually increased and the procedure is terminated when the error becomes smaller than the required threshold. A new method for the elimination of redundant reactions is also presented, which is called the Principal Component Analysis of Matrix F with Simulation Error Minimization (SEM-PCAF). According to this method, several reduced mechanisms are produced by using various PCAF thresholds. The reduced mechanism having the least CPU time requirement among the ones having almost the smallest error is selected. Application of SEM-CM and SEM-PCAF together provides a very efficient way to eliminate redundant species and reactions from large mechanisms. The suggested approach was tested on a mechanism containing 6874 irreversible reactions of 345 species that describes methane partial oxidation to high conversion. The aim is to accurately reproduce the concentration-time profiles of 12 major species with less than 5% error at the conditions of an industrial application. The reduced mechanism consists of 246 reactions of 47 species and its simulation is 116 times faster than using the full mechanism. The SEM-CM was found to be more effective than the classic Connectivity Method, and also than the DRG, two-stage DRG, DRGASA, basic DRGEP and extended DRGEP methods. (author)

Simulation of fatigue damage in ferroelectric polycrystals under mechanical/electrical loading

Science.gov (United States)

Kozinov, S.; Kuna, M.

2018-07-01

The reliability of smart-structures made of ferroelectric ceramics is essentially reduced by the formation of cracks under the action of external electrical and/or mechanical loading. In the current research a numerical model for low-cycle fatigue in ferroelectric mesostructures is proposed. In the finite element simulations a combination of two user element routines is utilized. The first one is used to model a micromechanical ferroelectric domain switching behavior inside the grains. The second one is used to simulate fatigue damage of grain boundaries by a cohesive zone model (EMCCZM) based on an electromechanical cyclic traction-separation law (TSL). For numerical simulations a scanning electron microscope image of the ceramic's grain structure was digitalized and meshed. The response of this mesostructure to cyclic electrical or mechanical loading is systematically analyzed. As a result of the simulations, the distribution of electric potential, field, displacement and polarization as well as mechanical stresses and deformations inside the grains are obtained. At the grain boundaries, the formation and evolution of damage are analyzed until final failure and induced degradation of electric permittivity. It is found that the proposed model correctly mimics polycrystalline behavior during poling processes and progressive damage under cyclic electromechanical loading. To the authors' knowledge, it is the first model and numerical analysis of ferroelectric polycrystals taking into account both domain reorientation and cohesive modeling of intergranular fracture. It can help to understand failure mechanisms taking place in ferroelectrics during fatigue processes.

Nanometric mechanical cutting of metallic glass investigated using atomistic simulation

Energy Technology Data Exchange (ETDEWEB)

Wu, Cheng-Da, E-mail: nanowu@cycu.edu.tw [Department of Mechanical Engineering, Chung Yuan Christian University, 200, Chung Pei Rd., Chung Li District, Taoyuan City 32023, Taiwan (China); Fang, Te-Hua, E-mail: fang.tehua@msa.hinet.net [Department of Mechanical Engineering, National Kaohsiung University of Applied Sciences, Kaohsiung 807, Taiwan (China); Su, Jih-Kai, E-mail: yummy_2468@yahoo.com.tw [Department of Mechanical Engineering, National Kaohsiung University of Applied Sciences, Kaohsiung 807, Taiwan (China)

2017-02-28

Highlights: • A nanoscale chip with a shear plane of 135° is extruded by the tool. • Tangential force and normal force increase with increasing tool nose radius. • Resistance factor increases with increasing cutting depth and temperature. - Abstract: The effects of cutting depth, tool nose radius, and temperature on the cutting mechanism and mechanics of amorphous NiAl workpieces are studied using molecular dynamics simulations based on the second-moment approximation of the many-body tight-binding potential. These effects are investigated in terms of atomic trajectories and flow field, shear strain, cutting force, resistance factor, cutting ratio, and pile-up characteristics. The simulation results show that a nanoscale chip with a shear plane of 135° is extruded by the tool from a workpiece surface during the cutting process. The workpiece atoms underneath the tool flow upward due to the adhesion force and elastic recovery. The required tangential force and normal force increase with increasing cutting depth and tool nose radius; both forces also increase with decreasing temperature. The resistance factor increases with increasing cutting depth and temperature, and decreases with increasing tool nose radius.

Study on a mechanical snubber with an adjustment mechanism for resisting force

International Nuclear Information System (INIS)

Ohmata, Kenichiro; Miyanaga, Hiroyuki.

1991-01-01

The mechanical snubber is an earthquakeproof device for a piping system under particular circumstances such as high temperature and radioactivity. It restrains the piping system by a strong resisting force during an earthquake. This strong force can cause elastic failure of grooves on a brake disk, where steel balls are placed. In this report, an improved mechanical snubber having an adjustment mechanism for resisting force is proposed in order to obtain a mechanical snubber which has almost the same restraint effect and less resisting force in comparison with a conventional mechanical snubber. The resisting force characteristics and the restraint effect of the improved mechanical snubber applied to a simple beam are discussed both numerically and experimentally. The digital simulations are carried out using the Continuous System Simulation Language (CSSL). (author)

Restrained Proton Indicator in Combined Quantum-Mechanics/Molecular-Mechanics Dynamics Simulations of Proton Transfer through a Carbon Nanotube.

Science.gov (United States)

Duster, Adam W; Lin, Hai

2017-09-14

Recently, a collective variable "proton indicator" was purposed for tracking an excess proton solvated in bulk water in molecular dynamics simulations. In this work, we demonstrate the feasibility of utilizing the position of this proton indicator as a reaction coordinate to model an excess proton migrating through a hydrophobic carbon nanotube in combined quantum-mechanics/molecular-mechanics simulations. Our results indicate that applying a harmonic restraint to the proton indicator in the bulk solvent near the nanotube pore entrance leads to the recruitment of water molecules into the pore. This is consistent with an earlier study that employed a multistate empirical valence bond potential and a different representation (center of excess charge) of the proton. We attribute this water recruitment to the delocalized nature of the solvated proton, which prefers to be in high-dielectric bulk solvent. While water recruitment into the pore is considered an artifact in the present simulations (because of the artificially imposed restraint on the proton), if the proton were naturally restrained, it could assist in building water wires prior to proton transfer through the pore. The potential of mean force for a proton translocation through the water-filled pore was computed by umbrella sampling, where the bias potentials were applied to the proton indicator. The free energy curve and barrier heights agree reasonably with those in the literature. The results suggest that the proton indicator can be used as a reaction coordinate in simulations of proton transport in confined environments.

Dynamic simulation of road vehicle door window regulator mechanism of cross arm type

Science.gov (United States)

Miklos, I. Zs; Miklos, C.; Alic, C.

2017-01-01

The paper presents issues related to the dynamic simulation of a motor-drive operating mechanism of cross arm type, for the manipulation of road vehicle door windows, using Autodesk Inventor Professional software. The dynamic simulation of the mechanism involves a 3D modelling, kinematic coupling, drive motion parameters and external loads, as well as the graphically view of the kinematic and kinetostatic results for the various elements and kinematic couplings of the mechanism, under real operating conditions. Also, based on the results, the analysis of the mechanism components has been carried out using the finite element method.

Thermo-mechanical simulation of liquid-supported stretch blow molding

International Nuclear Information System (INIS)

Zimmer, J.; Stommel, M.

2015-01-01

Stretch blow molding is the well-established plastics forming method to produce Polyehtylene therephtalate (PET) bottles. An injection molded preform is heated up above the PET glass transition temperature (Tg∼85°C) and subsequently inflated by pressurized air into a closed cavity. In the follow-up filling process, the resulting bottle is filled with the final product. A recently developed modification of the process combines the blowing and filling stages by directly using the final liquid product to inflate the preform. In a previously published paper, a mechanical simulation and successful evaluation of this liquid-driven stretch blow molding process was presented. In this way, a realistic process parameter dependent simulation of the preform deformation throughout the forming process was enabled, whereas the preform temperature evolution during forming was neglected. However, the formability of the preform is highly reduced when the temperature sinks below Tg during forming. Experimental investigations show temperature-induced failure cases due to the fast heat transfer between hot preform and cold liquid. Therefore, in this paper, a process dependent simulation of the temperature evolution during processing to avoid preform failure is presented. For this purpose, the previously developed mechanical model is used to extract the time dependent thickness evolution. This information serves as input for the heat transfer simulation. The required material parameters are calibrated from preform cooling experiments recorded with an infrared-camera. Furthermore, the high deformation ratios during processing lead to strain induced crystallization. This exothermal reaction is included into the simulation by extracting data from preform measurements at different stages of deformation via Differential Scanning Calorimetry (DSC). Finally, the thermal simulation model is evaluated by free forming experiments, recorded by a high-speed infrared camera

Mechanism of ultra low friction of multilayer graphene studied by coarse-grained molecular simulation.

Science.gov (United States)

Washizu, Hitoshi; Kajita, Seiji; Tohyama, Mamoru; Ohmori, Toshihide; Nishino, Noriaki; Teranishi, Hiroshi; Suzuki, Atsushi

2012-01-01

Coarse-grained Metropolis Monte Carlo Brownian Dynamics simulations are used to clarify the ultralow friction mechanism of a transfer film of multilayered graphene sheets. Each circular graphene sheet consists of 400 to 1,000,000 atoms confined between the upper and lower sliders and are allowed to move in 3 translational and 1 rotational directions due to thermal motion at 300 K. The sheet-sheet interaction energy is calculated by the sum of the pair potential of the sp2 carbons. The sliding simulations are done by moving the upper slider at a constant velocity. In the monolayer case, the friction force shows a stick-slip like curve and the average of the force is high. In the multilayer case, the friction force does not show any oscillation and the average of the force is very low. This is because the entire transfer film has an internal degree of freedom in the multilayer case and the lowest sheet of the layer is able to follow the equipotential surface of the lower slider.

Systematic Quantum Mechanical Region Determination in QM/MM Simulation.

Science.gov (United States)

Karelina, Maria; Kulik, Heather J

2017-02-14

Hybrid quantum mechanical-molecular mechanical (QM/MM) simulations are widely used in enzyme simulation. Over ten convergence studies of QM/MM methods have revealed over the past several years that key energetic and structural properties approach asymptotic limits with only very large (ca. 500-1000 atom) QM regions. This slow convergence has been observed to be due in part to significant charge transfer between the core active site and the surrounding protein environment, which cannot be addressed by improvement of MM force fields or the embedding method employed within QM/MM. Given this slow convergence, it becomes essential to identify strategies for the most atom-economical determination of optimal QM regions and to gain insight into the crucial interactions captured only in large QM regions. Here, we extend and develop two methods for quantitative determination of QM regions. First, in the charge shift analysis (CSA) method, we probe the reorganization of electron density when core active site residues are removed completely, as determined by large-QM region QM/MM calculations. Second, we introduce the highly parallelizable Fukui shift analysis (FSA), which identifies how core/substrate frontier states are altered by the presence of an additional QM residue in smaller initial QM regions. We demonstrate that the FSA and CSA approaches are complementary and consistent on three test case enzymes: catechol O-methyltransferase, cytochrome P450cam, and hen eggwhite lysozyme. We also introduce validation strategies and test the sensitivities of the two methods to geometric structure, basis set size, and electronic structure methodology. Both methods represent promising approaches for the systematic, unbiased determination of quantum mechanical effects in enzymes and large systems that necessitate multiscale modeling.

Modelling and Simulation of Volume Controlled Mechanical Ventilation System

Directory of Open Access Journals (Sweden)

Yan Shi

2014-01-01

Full Text Available Volume controlled mechanical ventilation system is a typical time-delay system, which is applied to ventilate patients who cannot breathe adequately on their own. To illustrate the influences of key parameters of the ventilator on the dynamics of the ventilated respiratory system, this paper firstly derived a new mathematical model of the ventilation system; secondly, simulation and experimental results are compared to verify the mathematical model; lastly, the influences of key parameters of ventilator on the dynamics of the ventilated respiratory system are carried out. This study can be helpful in the VCV ventilation treatment and respiratory diagnostics.

Casting and stress-strain simulations of a cast ductile iron component using microstructure based mechanical behavior

International Nuclear Information System (INIS)

Olofsson, Jakob; Svensson, Ingvar L

2012-01-01

The industrial demand for increased component performance with concurrent reductions in component weight, development times and verifications using physical prototypes drives the need to use the full potential of casting and Finite Element Method (FEM) simulations to correctly predict the mechanical behavior of cast components in service. The mechanical behavior of the component is determined by the casting process, and factors as component geometry and casting process parameters are known to affect solidification and microstructure formation throughout the component and cause local variations in mechanical behavior as well as residual stresses. Though residual stresses are known to be an important factor in the mechanical behavior of the component, the importance of local mechanical behavior is not well established and the material is typically considered homogeneous throughout the component. This paper deals with the influence of solidification and solid state transformation on microstructure formation and the effect of local microstructure variations on the mechanical behavior of the cast component in service. The current work aims to investigate the coupling between simulation of solidification, microstructure and local variations in mechanical behavior and stress-strain simulation. This is done by performing several simulations of a ductile iron component using a recently developed simulation strategy, a closed chain of simulations for cast components, able to predict and describe the local variations in not only elastic but also plastic behavior throughout the component by using microstructural parameters determined by simulations of microstructural evolution in the component during the casting process. In addition the residual stresses are considered. The results show that the FEM simulation results are significantly affected by including microstructure based mechanical behavior. When the applied load is low and the component is subjected to stress levels

The non-separability of ''dielectric'' and ''mechanical'' friction in molecular systems: A simulation study

International Nuclear Information System (INIS)

Kumar, P. V.; Maroncelli, M.

2000-01-01

Simulations of the time-dependent friction controlling rotational, translational, and vibrational motions of dipolar diatomic solutes in acetonitrile and methanol have been used to examine the nature of ''dielectric'' friction. The way in which electrical interactions increase the friction beyond that present in nonpolar systems is found to be rather different than what is anticipated by most theories of dielectric friction. Long-range electrostatic forces do not simply add an independent contribution to the friction due to short-ranged or ''mechanical'' sources (modeled here in terms of Lennard-Jones forces). Rather, the electrical and Lennard-Jones contributions are found to be strongly anticorrelated and not separable in any useful way. For some purposes, the mechanism by which electrical interactions increase friction is better viewed as a static electrostriction effect: electrical forces cause a subtle increase in atomic density in the solute's first solvation shell, which increases the amplitude of the force fluctuations derived from the Lennard-Jones interactions, i.e., the mechanical friction. However, electrical interactions also modify the dynamics of the friction, typically adding a long-time tail, which significantly increases the integral friction. Both of these effects must be included in a correct description of friction in the presence of polar interactions. (c) 2000 American Institute of Physics

35. Conference of the DVM Working Group on Fracture Processes: Advances in fracture and damage mechanics - simulation methods of fracture mechanics

International Nuclear Information System (INIS)

2003-01-01

Subjects of the meeting were: Simulation of fatigue crack growth in real strucures using FEA (M. Fulland, Paderborn); Modelling of ductile crack growth (W. Brocks, Geesthacht); Advances in non-local modelling of ductile damage (F. Reusch et al., Berlin, Dortmund); Fracture mechanics of ceramics (D. Munz, Karlsruhe); From materials testing to vehicle crash testing (J.G. Blauel, Freiburg); Analytical simulation of crack growth in thin-walled structures (U. Zerbst, Geesthacht); The influence of intrinsic stresses on fatigue crack growth (C. Dalle Donne etc., Cologne, Dortmund, Pisa, and M. Sander, Paderborn); Fracture mechanical strength calculation in case of mixed mode loads on cracks (H.A. Richard, Paderborn); Numeric simulation of intrinsic stresses during welding (C. Veneziano, Freiburg); New research fields of the Fraunhofer-Institut fuer Werkstoffmechanik (P. Gumbsch, Head of the Institute, Freiburg); Modern developments and advances in fracture and damage mechanics; Numeric and experimental simulation of crack propagation and damage processes; Exemplary damage cases; Fracture mechanics in product development; Failure characteristics of lightweight constructional materials and joints [de

Computational simulation for creep fracture properties taking microscopic mechanism into account

International Nuclear Information System (INIS)

Tabuchi, Masaaki

2003-01-01

Relationship between creep crack growth rate and microscopic fracture mechanism i.e., wedge-type intergranular, transgranular and cavity-type intergranular crack growth, has been investigated. The growth rate of wedge-type and transgranular creep crack could be characterized by creep ductility. Creep damages formed ahead of the cavity-type crack tip accelerated the crack growth rate. Based on the experimental results, FEM code that simulates creep crack growth has been developed by taking the fracture mechanism into account. The effect of creep ductility and void formation ahead of the crack tip on creep crack growth behavior could be simulated. (author)

An agent-based simulation of power generation company behavior in electricity markets under different market-clearing mechanisms

International Nuclear Information System (INIS)

Aliabadi, Danial Esmaeili; Kaya, Murat; Şahin, Güvenç

2017-01-01

Deregulated electricity markets are expected to provide affordable electricity for consumers through promoting competition. Yet, the results do not always fulfill the expectations. The regulator's market-clearing mechanism is a strategic choice that may affect the level of competition in the market. We conceive of the market-clearing mechanism as composed of two components: pricing rules and rationing policies. We investigate the strategic behavior of power generation companies under different market-clearing mechanisms using an agent-based simulation model which integrates a game-theoretical understanding of the auction mechanism in the electricity market and generation companies' learning mechanism. Results of our simulation experiments are presented using various case studies representing different market settings. The market in simulations is observed to converge to a Nash equilibrium of the stage game or to a similar state under most parameter combinations. Compared to pay-as-bid pricing, bid prices are closer to marginal costs on average under uniform pricing while GenCos' total profit is also higher. The random rationing policy of the ISO turns out to be more successful in achieving lower bid prices and lower GenCo profits. In minimizing GenCos' total profit, a combination of pay-as-bid pricing rule and random rationing policy is observed to be the most promising. - Highlights: • An agent-based simulation of generation company behavior in electricity markets is developed. • Learning dynamics of companies is modeled with an extended Q-learning algorithm. • Different market clearing mechanisms of the regulator are compared. • Convergence to Nash equilibria is analyzed under different cases. • The level of competition in the market is studied.

Simulating Mechanics to Study Emergence in Games

NARCIS (Netherlands)

Dormans, Joris

2011-01-01

This paper presents the latest version of the Machinations framework. This framework uses diagrams to represent the flow of tangible and abstract resources through a game. This flow represents the mechanics that make up a game’s interbal economy and has a large impact on the emergent gameplay of

Structure and dynamics of hydrated Fe(II) and Fe(III) ions. Quantum mechanical and molecular mechanical simulations

International Nuclear Information System (INIS)

Remsungnen, T.

2002-11-01

Classical molecular dynamics (MD) and combined em ab initio quantum mechanical/molecular mechanical molecular dynamics (QM/MM-MD) simulations have been performed to investigate structural, dynamical and energetical properties of Fe(II), and Fe(III) transition metal ions in aqueous solution. In the QM/MM-MD simulations the ion and its first hydration sphere were treated at the Hartree-Fock ab initio quantum mechanical level, while ab initio generated pair plus three-body potentials were employed for the remaining system. For the classical MD simulation the pair plus three-body potential were employed for all ion-water interactions. The coordination number of the first hydration shell is 100 % of 6 in both cases. The number of waters in the second hydration shell obtained from classical simulations are 13.4 and 15.1 for Fe(II) and Fe(III), respectively, while QM/MM-MD gives the values of 12.4 and 13.4 for Fe(II) and Fe(III). The energies of hydration obtained from MD and QM/MM-MD for Fe(II) are 520 and 500 kcal/mol, and for Fe(III) 1160 and 1100 kcal/mol respectively. The mean residence times of water in the second shell obtained from QM/MM-MD are 24 and 48 ps for Fe(II) and Fe(III), respectively. In contrast to the data obtained from classical MD simulation, the QM/MM-MD values are all in good agreement with the experimental data available. These investigations and results clearly indicate that many-body effects are essential for the proper description of all properties of the aqueous solution of both Fe(II) and Fe(III) ions. (author)

Structural mechanics simulations

International Nuclear Information System (INIS)

Biffle, J.H.

1992-01-01

Sandia National Laboratory has a very broad structural capability. Work has been performed in support of reentry vehicles, nuclear reactor safety, weapons systems and components, nuclear waste transport, strategic petroleum reserve, nuclear waste storage, wind and solar energy, drilling technology, and submarine programs. The analysis environment contains both commercial and internally developed software. Included are mesh generation capabilities, structural simulation codes, and visual codes for examining simulation results. To effectively simulate a wide variety of physical phenomena, a large number of constitutive models have been developed

Realization of a Desktop Flight Simulation System for Motion-Cueing Studies

Directory of Open Access Journals (Sweden)

Berkay Volkaner

2016-05-01

Full Text Available Parallel robotic mechanisms are generally used in flight simulators with a motion-cueing algorithm to create an unlimited motion feeling of a simulated medium in a bounded workspace of the simulator. A major problem in flight simulators is that the simulation has an unbounded space and the manipulator has a limited one. Using a washout filter in the motion-cueing algorithm overcomes this. In this study, a low-cost six degrees of freedom (DoF desktop parallel manipulator is used to test a classical motion-cueing algorithm; the algorithm's functionality is confirmed with a Simulink real-time environment. Translational accelerations and angular velocities of the simulated medium obtained from FlightGear flight simulation software are processed through a generated washout filter algorithm and the simulated medium's motion information is transmitted to the desktop parallel robotic mechanism as a set point for each leg. The major issues of this paper are designing a desktop simulation system, controlling the parallel manipulator, communicating between the flight simulation and the platform, designing a motion-cueing algorithm and determining the parameters of the washout filters.

Numerical study by large-eddy simulation on effects and mechanism of air-cooling enhancing technologies

International Nuclear Information System (INIS)

Tamura, Akinori; Kawamura, Toshinori; Ishida, Naoyuki; Kitou, Kazuaki

2014-01-01

Learning from the lessons of the Fukushima Daiichi nuclear incident in which a long-term station black-out occurred, we have been developing an air-cooling system for boiling water reactors that can operate without electricity for a virtually indefinite time. Improvement in the heat transfer performance of air-cooling is key to the development of the air-cooling system. We developed air-cooling enhancing technologies for the air-cooling system by using heat transfer fins, turbulence-enhancing ribs and a micro-fabrication surface. In our previous study, the performance of these air-cooling enhancing technologies was evaluated by heat transfer tests using a single pipe of the air-cooling heat exchanger. To achieve further improvement of the heat transfer performance, it is important to understand the mechanism of the air-cooling enhancing technologies. In this study, we used the numerical analysis which is based on the filtered incompressible Navier-Stokes equation and the filtered energy equation with the large-eddy simulation in order to investigate the effects and the mechanism of the developed air-cooling enhancing technologies. We found that the analysis results agreed well with the experimental results and the empirical formula results. The heat transfer enhancement mechanism of the heat transfer fin is due to an increase in the heat transfer area. Due to a decrease in the flow velocity at the base of the fins, the increase in the Nusselt number was approximately 15% smaller than the estimated value from the area increase. In the heat transfer enhancement by the turbulence-enhancing ribs, the unsteady behavior of the large-scale vortex generated by the flow separation plays an important role. The enhancement ratio of the Nusselt number by the micro-fabrication surface can be explained by the apparent thermal conductivity. The Nusselt number was increased 4-8% by the micro-fabrication surface. The effect of the micro-fabrication surface is increased by applying

Numerical Simulation and Mechanical Design for TPS Electron Beam Position Monitors

Science.gov (United States)

Hsueh, H. P.; Kuan, C. K.; Ueng, T. S.; Hsiung, G. Y.; Chen, J. R.

2007-01-01

Comprehensive study on the mechanical design and numerical simulation for the high resolution electron beam position monitors are key steps to build the newly proposed 3rd generation synchrotron radiation research facility, Taiwan Photon Source (TPS). With more advanced electromagnetic simulation tool like MAFIA tailored specifically for particle accelerator, the design for the high resolution electron beam position monitors can be tested in such environment before they are experimentally tested. The design goal of our high resolution electron beam position monitors is to get the best resolution through sensitivity and signal optimization. The definitions and differences between resolution and sensitivity of electron beam position monitors will be explained. The design consideration is also explained. Prototype deign has been carried out and the related simulations were also carried out with MAFIA. The results are presented here. Sensitivity as high as 200 in x direction has been achieved in x direction at 500 MHz.

Numerical Simulation and Mechanical Design for TPS Electron Beam Position Monitors

International Nuclear Information System (INIS)

Hsueh, H. P.; Kuan, C. K.; Ueng, T. S.; Hsiung, G. Y.; Chen, J. R.

2007-01-01

Comprehensive study on the mechanical design and numerical simulation for the high resolution electron beam position monitors are key steps to build the newly proposed 3rd generation synchrotron radiation research facility, Taiwan Photon Source (TPS). With more advanced electromagnetic simulation tool like MAFIA tailored specifically for particle accelerator, the design for the high resolution electron beam position monitors can be tested in such environment before they are experimentally tested. The design goal of our high resolution electron beam position monitors is to get the best resolution through sensitivity and signal optimization. The definitions and differences between resolution and sensitivity of electron beam position monitors will be explained. The design consideration is also explained. Prototype deign has been carried out and the related simulations were also carried out with MAFIA. The results are presented here. Sensitivity as high as 200 in x direction has been achieved in x direction at 500 MHz

Molecular Dynamics Simulation for the Mechanical Properties of CNT/Polymer Nanocomposites

International Nuclear Information System (INIS)

Yang, Seung Hwa; Cho, Maeg Hyo

2007-01-01

In order to obtain mechanical properties of CNT/Polymer nano-composites, molecular dynamics simulation is performed. Overall system was modeled as a flexible unit cell in which carbon nanotubes are embedded into a polyethylene matrix for N σ T ensemble simulation. COMPASS force field was chosen to describe inter and intra molecular potential and bulk effect was achieved via periodic boundary conditions. In CNT-polymer interface, only Lennard-Jones non-bond potential was considered. Using Parrinello-Rahman fluctuation method, mechanical properties of orthotropic nano-composites under various temperatures were successfully obtained. Also, we investigated thermal behavior of the short CNT reinforced nanocomposites system with predicting glass transition temperature

Simulation and experimental analysis of nanoindentation and mechanical properties of amorphous NiAl alloys.

Science.gov (United States)

Wang, Chih-Hao; Fang, Te-Hua; Cheng, Po-Chien; Chiang, Chia-Chin; Chao, Kuan-Chi

2015-06-01

This paper used numerical and experimental methods to investigate the mechanical properties of amorphous NiAl alloys during the nanoindentation process. A simulation was performed using the many-body tight-binding potential method. Temperature, plastic deformation, elastic recovery, and hardness were evaluated. The experimental method was based on nanoindentation measurements, allowing a precise prediction of Young's modulus and hardness values for comparison with the simulation results. The indentation simulation results showed a significant increase of NiAl hardness and elastic recovery with increasing Ni content. Furthermore, the results showed that hardness and Young's modulus increase with increasing Ni content. The simulation results are in good agreement with the experimental results. Adhesion test of amorphous NiAl alloys at room temperature is also described in this study.

Reactive Molecular Dynamics Simulations to Understand Mechanical Response of Thaumasite under Temperature and Strain Rate Effects.

Science.gov (United States)

Hajilar, Shahin; Shafei, Behrouz; Cheng, Tao; Jaramillo-Botero, Andres

2017-06-22

Understanding the structural, thermal, and mechanical properties of thaumasite is of great interest to the cement industry, mainly because it is the phase responsible for the aging and deterioration of civil infrastructures made of cementitious materials attacked by external sources of sulfate. Despite the importance, effects of temperature and strain rate on the mechanical response of thaumasite had remained unexplored prior to the current study, in which the mechanical properties of thaumasite are fully characterized using the reactive molecular dynamics (RMD) method. With employing a first-principles based reactive force field, the RMD simulations enable the description of bond dissociation and formation under realistic conditions. From the stress-strain curves of thaumasite generated in the x, y, and z directions, the tensile strength, Young's modulus, and fracture strain are determined for the three orthogonal directions. During the course of each simulation, the chemical bonds undergoing tensile deformations are monitored to reveal the bonds responsible for the mechanical strength of thaumasite. The temperature increase is found to accelerate the bond breaking rate and consequently the degradation of mechanical properties of thaumasite, while the strain rate only leads to a slight enhancement of them for the ranges considered in this study.

Molecular-dynamics simulations of crosslinking and confinement effects on structure, segmental mobility and mechanics of filled elastomers

Science.gov (United States)

Davris, Theodoros; Lyulin, Alexey V.

2016-05-01

The significant drop of the storage modulus under uniaxial deformation (Payne effect) restrains the performance of the elastomer-based composites and the development of possible new applications. In this paper molecular-dynamics (MD) computer simulations using LAMMPS MD package have been performed to study the mechanical properties of a coarse-grained model of this family of nanocomposite materials. Our goal is to provide simulational insights into the viscoelastic properties of filled elastomers, and try to connect the macroscopic mechanics with composite microstructure, the strength of the polymer-filler interactions and the polymer mobility at different scales. To this end we simulate random copolymer films capped between two infinite solid (filler aggregate) walls. We systematically vary the strength of the polymer-substrate adhesion interactions, degree of polymer confinement (film thickness), polymer crosslinking density, and study their influence on the equilibrium and non-equilibrium structure, segmental dynamics, and the mechanical properties of the simulated systems. The glass-transition temperature increases once the mesh size became smaller than the chain radius of gyration; otherwise it remained invariant to mesh-size variations. This increase in the glass-transition temperature was accompanied by a monotonic slowing-down of segmental dynamics on all studied length scales. This observation is attributed to the correspondingly decreased width of the bulk density layer that was obtained in films whose thickness was larger than the end-to-end distance of the bulk polymer chains. To test this hypothesis additional simulations were performed in which the crystalline walls were replaced with amorphous or rough walls.

Effects of Zoledronate and Mechanical Loading during Simulated Weightlessness on Bone Structure and Mechanical Properties

Science.gov (United States)

Scott, R. T.; Nalavadi, M. O.; Shirazi-Fard, Y.; Castillo, A. B.; Alwood, J. S.

2016-01-01

Space flight modulates bone remodeling to favor bone resorption. Current countermeasures include an anti-resorptive drug class, bisphosphonates (BP), and high-force loading regimens. Does the combination of anti-resorptives and high-force exercise during weightlessness have negative effects on the mechanical and structural properties of bone? In this study, we implemented an integrated model to mimic mechanical strain of exercise via cyclical loading (CL) in mice treated with the BP Zoledronate (ZOL) combined with hindlimb unloading (HU). Our working hypothesis is that CL combined with ZOL in the HU model induces additive structural and mechanical changes. Thirty-two C57BL6 mice (male,16 weeks old, n8group) were exposed to 3 weeks of either HU or normal ambulation (NA). Cohorts of mice received one subcutaneous injection of ZOL (45gkg), or saline vehicle, prior to experiment. The right tibia was axially loaded in vivo, 60xday to 9N in compression, repeated 3xweek during HU. During the application of compression, secant stiffness (SEC), a linear estimate of slope of the force displacement curve from rest (0.5N) to max load (9.0N), was calculated for each cycle once per week. Ex vivo CT was conducted on all subjects. For ex vivo mechanical properties, non-CL left femurs underwent 3-point bending. In the proximal tibial metaphysis, HU decreased, CL increased, and ZOL increased the cancellous bone volume to total volume ratio by -26, +21, and +33, respectively. Similar trends held for trabecular thickness and number. Ex vivo left femur mechanical properties revealed HU decreased stiffness (-37),and ZOL mitigated the HU stiffness losses (+78). Data on the ex vivo Ultimate Force followed similar trends. After 3 weeks, HU decreased in vivo SEC (-16). The combination of CL+HU appeared additive in bone structure and mechanical properties. However, when HU + CL + ZOL were combined, ZOL had no additional effect (p0.05) on in vivo SEC. Structural data followed this trend with

Study the bonding mechanism of binders on hydroxyapatite surface and mechanical properties for 3DP fabrication bone scaffolds.

Science.gov (United States)

Wei, Qinghua; Wang, Yanen; Li, Xinpei; Yang, Mingming; Chai, Weihong; Wang, Kai; zhang, Yingfeng

2016-04-01

In 3DP fabricating artificial bone scaffolds process, the interaction mechanism between binder and bioceramics power determines the microstructure and macro mechanical properties of Hydroxyapatite (HA) bone scaffold. In this study, we applied Molecular Dynamics (MD) methods to investigating the bonding mechanism and essence of binders on the HA crystallographic planes for 3DP fabrication bone scaffolds. The cohesive energy densities of binders and the binding energies, PCFs g(r), mechanical properties of binder/HA interaction models were analyzed through the MD simulation. Additionally, we prepared the HA bone scaffold specimens with different glues by 3DP additive manufacturing, and tested their mechanical properties by the electronic universal testing machine. The simulation results revealed that the relationship of the binding energies between binders and HA surface is consistent with the cohesive energy densities of binders, which is PAM/HA>PVA/HA>PVP/HA. The PCFs g(r) indicated that their interfacial interactions mainly attribute to the ionic bonds and hydrogen bonds which formed between the polar atoms, functional groups in binder polymer and the Ca, -OH in HA. The results of mechanical experiments verified the relationship of Young׳s modulus for three interaction models in simulation, which is PVA/HA>PAM/HA>PVP/HA. But the trend of compressive strength is PAM/HA>PVA/HA>PVP/HA, this is consistent with the binding energies of simulation. Therefore, the Young׳s modulus of bone scaffolds are limited by the Young׳s modulus of binders, and the compressive strength is mainly decided by the viscosity of binder. Finally, the major reasons for differences in mechanical properties between simulation and experiment were found, the space among HA pellets and the incomplete infiltration of glue were the main reasons influencing the mechanical properties of 3DP fabrication HA bone scaffolds. These results provide useful information in choosing binder for 3DP fabrication

Thermo-mechanical simulations of early-age concrete cracking with durability predictions

Science.gov (United States)

Havlásek, Petr; Šmilauer, Vít; Hájková, Karolina; Baquerizo, Luis

2017-09-01

Concrete performance is strongly affected by mix design, thermal boundary conditions, its evolving mechanical properties, and internal/external restraints with consequences to possible cracking with impaired durability. Thermo-mechanical simulations are able to capture those relevant phenomena and boundary conditions for predicting temperature, strains, stresses or cracking in reinforced concrete structures. In this paper, we propose a weakly coupled thermo-mechanical model for early age concrete with an affinity-based hydration model for thermal part, taking into account concrete mix design, cement type and thermal boundary conditions. The mechanical part uses B3/B4 model for concrete creep and shrinkage with isotropic damage model for cracking, able to predict a crack width. All models have been implemented in an open-source OOFEM software package. Validations of thermo-mechanical simulations will be presented on several massive concrete structures, showing excellent temperature predictions. Likewise, strain validation demonstrates good predictions on a restrained reinforced concrete wall and concrete beam. Durability predictions stem from induction time of reinforcement corrosion, caused by carbonation and/or chloride ingress influenced by crack width. Reinforcement corrosion in concrete struts of a bridge will serve for validation.

Examining the mechanical equilibrium of microscopic stresses in molecular simulations

OpenAIRE

Torres Sánchez, Alejandro; Vanegas, Juan Manuel; Arroyo Balaguer, Marino

2015-01-01

The microscopic stress field provides a unique connection between atomistic simulations and mechanics at the nanoscale. However, its definition remains ambiguous. Rather than a mere theoretical preoccupation, we show that this fact acutely manifests itself in local stress calculations of defective graphene, lipid bilayers, and fibrous proteins. We find that popular definitions of the microscopic stress violate the continuum statements of mechanical equilibrium, and we propose an unambiguous a...

Towards mechanism-based simulation of impact damage using exascale computing

Science.gov (United States)

Shterenlikht, Anton; Margetts, Lee; McDonald, Samuel; Bourne, Neil K.

2017-01-01

Over the past 60 years, the finite element method has been very successful in modelling deformation in engineering structures. However the method requires the definition of constitutive models that represent the response of the material to applied loads. There are two issues. Firstly, the models are often difficult to define. Secondly, there is often no physical connection between the models and the mechanisms that accommodate deformation. In this paper, we present a potentially disruptive two-level strategy which couples the finite element method at the macroscale with cellular automata at the mesoscale. The cellular automata are used to simulate mechanisms, such as crack propagation. The stress-strain relationship emerges as a continuum mechanics scale interpretation of changes at the micro- and meso-scales. Iterative two-way updating between the cellular automata and finite elements drives the simulation forward as the material undergoes progressive damage at high strain rates. The strategy is particularly attractive on large-scale computing platforms as both methods scale well on tens of thousands of CPUs.

Results from an International Simulation Study on Couples Thermal, Hydrological, and Mechanical (THM) Processes Near Geological Nuclear Waste Repositories

International Nuclear Information System (INIS)

J. Rutqvist; J.T. Birkholzer; M. Chijimatsu; O. Kolditz; Q.S. Liu; Y. Oda; W. Wang; C.Y. Zhang

2006-01-01

As part of the ongoing international code comparison project DECOVALEX, four research teams used five different models to simulate coupled thermal, hydrological, and mechanical (THM) processes near underground waste emplacement drifts. The simulations were conducted for two generic repository types with open or back-filled repository drifts under higher and lower post-closure temperature, respectively. In the completed first model inception phase of the project, a good agreement was achieved between the research teams in calculating THM responses for both repository types, although some disagreement in hydrological responses are currently being resolved. Good agreement in the basic thermal-mechanical responses was achieved for both repository types, even with some teams using relatively simplified thermal-elastic heat-conduction models that neglect complex near-field thermal-hydrological processes. The good agreement between the complex and simplified (and well-known) process models indicates that the basic thermal-mechanical responses can be predicted with a relatively high confidence level. The research teams have now moved on to the second phase of the project, the analysis of THM-induced permanent (irreversible) changes and the impact of those changes on the fluid flow field near an emplacement drift

Computational modeling to predict mechanical function of joints: application to the lower leg with simulation of two cadaver studies.

Science.gov (United States)

Liacouras, Peter C; Wayne, Jennifer S

2007-12-01

Computational models of musculoskeletal joints and limbs can provide useful information about joint mechanics. Validated models can be used as predictive devices for understanding joint function and serve as clinical tools for predicting the outcome of surgical procedures. A new computational modeling approach was developed for simulating joint kinematics that are dictated by bone/joint anatomy, ligamentous constraints, and applied loading. Three-dimensional computational models of the lower leg were created to illustrate the application of this new approach. Model development began with generating three-dimensional surfaces of each bone from CT images and then importing into the three-dimensional solid modeling software SOLIDWORKS and motion simulation package COSMOSMOTION. Through SOLIDWORKS and COSMOSMOTION, each bone surface file was filled to create a solid object and positioned necessary components added, and simulations executed. Three-dimensional contacts were added to inhibit intersection of the bones during motion. Ligaments were represented as linear springs. Model predictions were then validated by comparison to two different cadaver studies, syndesmotic injury and repair and ankle inversion following ligament transection. The syndesmotic injury model was able to predict tibial rotation, fibular rotation, and anterior/posterior displacement. In the inversion simulation, calcaneofibular ligament extension and angles of inversion compared well. Some experimental data proved harder to simulate accurately, due to certain software limitations and lack of complete experimental data. Other parameters that could not be easily obtained experimentally can be predicted and analyzed by the computational simulations. In the syndesmotic injury study, the force generated in the tibionavicular and calcaneofibular ligaments reduced with the insertion of the staple, indicating how this repair technique changes joint function. After transection of the calcaneofibular

Math modeling and computer mechanization for real time simulation of rotary-wing aircraft

Science.gov (United States)

Howe, R. M.

1979-01-01

Mathematical modeling and computer mechanization for real time simulation of rotary wing aircraft is discussed. Error analysis in the digital simulation of dynamic systems, such as rotary wing aircraft is described. The method for digital simulation of nonlinearities with discontinuities, such as exist in typical flight control systems and rotor blade hinges, is discussed.

Wind Climate in Kongsfjorden, Svalbard, and Attribution of Leading Wind Driving Mechanisms through Turbulence-Resolving Simulations

Directory of Open Access Journals (Sweden)

Igor Esau

2012-01-01

Full Text Available This paper presents analysis of wind climate of the Kongsfjorden-Kongsvegen valley, Svalbard. The Kongsfjorden-Kongsvegen valley is relatively densely covered with meteorological observations, which facilitate joint statistical analysis of the turbulent surface layer structure and the structure of the higher atmospheric layers. Wind direction diagrams reveal strong wind channeled in the surface layer up to 300 m to 500 m. The probability analysis links strong wind channeling and cold temperature anomalies in the surface layer. To explain these links, previous studies suggested the katabatic wind flow mechanism as the leading driver responsible for the observed wind climatology. In this paper, idealized turbulence-resolving simulations are used to distinct between different wind driving mechanisms. The simulations were performed with the real surface topography at resolution of about 60 m. These simulations resolve the obstacle-induced turbulence and the turbulence in the non-stratified boundary layer core. The simulations suggest the leading roles of the thermal land-sea breeze circulation and the mechanical wind channeling in the modulation of the valley winds. The characteristic signatures of the developed down-slope gravity-accelerated flow, that is, the katabatic wind, were found to be of lesser significance under typical meteorological conditions in the valley.

Preliminary study of mechanical behavior for Cr coated Zr-4 Fuel Cladding

Energy Technology Data Exchange (ETDEWEB)

Kim, Do-Hyoung; Kim, Hak-Sung [Hanyang Univ., Seoul (Korea, Republic of); Kim, Hyo-Chan; Yang, Yong-Sik [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)

2015-05-15

To decrease the oxidation rate of Zr-based alloy components, many concepts of accident tolerant fuel (ATF) such as Mo-Zr cladding, SiC/SiCf cladding and iron-based alloy cladding are under development. One of the promised concept is the coated cladding which can remarkably increase the corrosion and wear resistance. Recently, KAERI is developing the Cr coated Zircaloy cladding as accident tolerance cladding. To coat the Cr powder on the Zircaloy, 3D laser coating technology has been employed because it is possible to make a coated layer on the tubular cladding surface by controlling the 3-diminational axis. Therefore, for this work, the mechanical integrity of Cr coated Zircaloy should be evaluated to predict the safety of fuel cladding during the operating or accident of nuclear reactor. In this work, the mechanical behavior of the Cr coated Zircaloy cladding has been studied by using finite element analysis (FEA). The ring compression test (RCT) of fuel cladding was simulated to evaluate the validity of mechanical properties of Zr-4 and Cr, which were referred from the literatures and experimental reports. In this work, the mechanical behavior of the Cr coated Zircaloy cladding has been studied by using finite element analysis (FEA). The ring compression test (RCT) of fuel cladding was simulated to evaluate the validity of mechanical properties of Zr-4 and Cr. The pellet-clad mechanical interaction (PCMI) properties of Cr coated Zr-4 cladding were investigated by thermo-mechanical finite element analysis (FEA) simulation. The mechanical properties of Zr-4 and Cr was validated by simulation of ring compression test (RCT) of fuel cladding.

Treating electrostatics with Wolf summation in combined quantum mechanical and molecular mechanical simulations.

Science.gov (United States)

Ojeda-May, Pedro; Pu, Jingzhi

2015-11-07

The Wolf summation approach [D. Wolf et al., J. Chem. Phys. 110, 8254 (1999)], in the damped shifted force (DSF) formalism [C. J. Fennell and J. D. Gezelter, J. Chem. Phys. 124, 234104 (2006)], is extended for treating electrostatics in combined quantum mechanical and molecular mechanical (QM/MM) molecular dynamics simulations. In this development, we split the QM/MM electrostatic potential energy function into the conventional Coulomb r(-1) term and a term that contains the DSF contribution. The former is handled by the standard machinery of cutoff-based QM/MM simulations whereas the latter is incorporated into the QM/MM interaction Hamiltonian as a Fock matrix correction. We tested the resulting QM/MM-DSF method for two solution-phase reactions, i.e., the association of ammonium and chloride ions and a symmetric SN2 reaction in which a methyl group is exchanged between two chloride ions. The performance of the QM/MM-DSF method was assessed by comparing the potential of mean force (PMF) profiles with those from the QM/MM-Ewald and QM/MM-isotropic periodic sum (IPS) methods, both of which include long-range electrostatics explicitly. For ion association, the QM/MM-DSF method successfully eliminates the artificial free energy drift observed in the QM/MM-Cutoff simulations, in a remarkable agreement with the two long-range-containing methods. For the SN2 reaction, the free energy of activation obtained by the QM/MM-DSF method agrees well with both the QM/MM-Ewald and QM/MM-IPS results. The latter, however, requires a greater cutoff distance than QM/MM-DSF for a proper convergence of the PMF. Avoiding time-consuming lattice summation, the QM/MM-DSF method yields a 55% reduction in computational cost compared with the QM/MM-Ewald method. These results suggest that, in addition to QM/MM-IPS, the QM/MM-DSF method may serve as another efficient and accurate alternative to QM/MM-Ewald for treating electrostatics in condensed-phase simulations of chemical reactions.

Dynamics of ligand exchange mechanism at Cu(II) in water: an ab initio quantum mechanical charge field molecular dynamics study with extended quantum mechanical region.

Science.gov (United States)

Moin, Syed Tarique; Hofer, Thomas S; Weiss, Alexander K H; Rode, Bernd M

2013-07-07

Ab initio quantum mechanical charge field molecular dynamics (QMCF-MD) were successfully applied to Cu(II) embedded in water to elucidate structure and to understand dynamics of ligand exchange mechanism. From the simulation studies, it was found that using an extended large quantum mechanical region including two shells of hydration is required for a better description of the dynamics of exchanging water molecules. The structural features characterized by radial distribution function, angular distribution function and other analytical parameters were consistent with experimental data. The major outcome of this study was the dynamics of exchange mechanism and reactions in the first hydration shell that could not be studied so far. The dynamical data such as mean residence time of the first shell water molecules and other relevant data from the simulations are close to the results determined experimentally. Another major characteristic of hydrated Cu(II) is the Jahn-Teller distortion which was also successfully reproduced, leading to the final conclusion that the dominating aqua complex is a 6-coordinated species. The ab initio QMCF-MD formalism proved again its capabilities of unraveling even ambiguous properties of hydrated species that are far difficult to explore by any conventional quantum mechanics/molecular mechanics (QM/MM) approach or experiment.

Dynamics of ligand exchange mechanism at Cu(II) in water: An ab initio quantum mechanical charge field molecular dynamics study with extended quantum mechanical region

International Nuclear Information System (INIS)

Moin, Syed Tarique; Hofer, Thomas S.; Weiss, Alexander K. H.; Rode, Bernd M.

2013-01-01

Ab initio quantum mechanical charge field molecular dynamics (QMCF-MD) were successfully applied to Cu(II) embedded in water to elucidate structure and to understand dynamics of ligand exchange mechanism. From the simulation studies, it was found that using an extended large quantum mechanical region including two shells of hydration is required for a better description of the dynamics of exchanging water molecules. The structural features characterized by radial distribution function, angular distribution function and other analytical parameters were consistent with experimental data. The major outcome of this study was the dynamics of exchange mechanism and reactions in the first hydration shell that could not be studied so far. The dynamical data such as mean residence time of the first shell water molecules and other relevant data from the simulations are close to the results determined experimentally. Another major characteristic of hydrated Cu(II) is the Jahn-Teller distortion which was also successfully reproduced, leading to the final conclusion that the dominating aqua complex is a 6-coordinated species. The ab initio QMCF-MD formalism proved again its capabilities of unraveling even ambiguous properties of hydrated species that are far difficult to explore by any conventional quantum mechanics/molecular mechanics (QM/MM) approach or experiment

Multiscale simulations in face-centered cubic metals: A method coupling quantum mechanics and molecular mechanics

International Nuclear Information System (INIS)

Yu Xiao-Xiang; Wang Chong-Yu

2013-01-01

An effective multiscale simulation which concurrently couples the quantum-mechanical and molecular-mechanical calculations based on the position continuity of atoms is presented. By an iterative procedure, the structure of the dislocation core in face-centered cubic metal is obtained by first-principles calculation and the long-range stress is released by molecular dynamics relaxation. Compared to earlier multiscale methods, the present work couples the long-range strain to the local displacements of the dislocation core in a simpler way with the same accuracy. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

Mechanism of mRNA-STAR domain interaction: Molecular dynamics simulations of Mammalian Quaking STAR protein.

Science.gov (United States)

Sharma, Monika; Anirudh, C R

2017-10-03

STAR proteins are evolutionary conserved mRNA-binding proteins that post-transcriptionally regulate gene expression at all stages of RNA metabolism. These proteins possess conserved STAR domain that recognizes identical RNA regulatory elements as YUAAY. Recently reported crystal structures show that STAR domain is composed of N-terminal QUA1, K-homology domain (KH) and C-terminal QUA2, and mRNA binding is mediated by KH-QUA2 domain. Here, we present simulation studies done to investigate binding of mRNA to STAR protein, mammalian Quaking protein (QKI). We carried out conventional MD simulations of STAR domain in presence and absence of mRNA, and studied the impact of mRNA on the stability, dynamics and underlying allosteric mechanism of STAR domain. Our unbiased simulations results show that presence of mRNA stabilizes the overall STAR domain by reducing the structural deviations, correlating the 'within-domain' motions, and maintaining the native contacts information. Absence of mRNA not only influenced the essential modes of motion of STAR domain, but also affected the connectivity of networks within STAR domain. We further explored the dissociation of mRNA from STAR domain using umbrella sampling simulations, and the results suggest that mRNA binding to STAR domain occurs in multi-step: first conformational selection of mRNA backbone conformations, followed by induced fit mechanism as nucleobases interact with STAR domain.

Thermo-Mechanical Properties of Semi-Degradable Poly(β-amino ester)-co-Methyl Methacrylate Networks under Simulated Physiological Conditions

Science.gov (United States)

Safranski, David L.; Crabtree, Jacob C.; Huq, Yameen R.; Gall, Ken

2011-01-01

Poly(β-amino ester) networks are being explored for biomedical applications, but they may lack the mechanical properties necessary for long term implantation. The objective of this study is to evaluate the effect of adding methyl methacrylate on networks' mechanical properties under simulated physiological conditions. The networks were synthesized in two parts: (1) a biodegradable crosslinker was formed from a diacrylate and amine, (2) and then varying concentrations of methyl methacrylate were added prior to photopolymerizing the network. Degradation rate, mechanical properties, and glass transition temperature were studied as a function of methyl methacrylate composition. The crosslinking density played a limited role on mechanical properties for these networks, but increasing methyl methacrylate concentration improved the toughness by several orders of magnitude. Under simulated physiological conditions, networks showed increasing toughness or sustained toughness as degradation occurred. This work establishes a method of creating degradable networks with tailorable toughness while undergoing partial degradation. PMID:21966028

Magnetization reversal mechanism and coercivity enhancement in three-dimensional granular Nd-Fe-B magnets studied by micromagnetic simulations

Science.gov (United States)

Lee, Jae-Hyeok; Choe, Jinhyeok; Hwang, Shinwon; Kim, Sang-Koog

2017-08-01

We studied the mechanism of magnetization reversals and coercivity enhancements in three-dimensional (3D) granular Nd-Fe-B permanent magnets using finite-element micromagnetic simulations. The magnetization reversals in the hard magnets consisting of hard-phase grains separated by relatively soft-phase grain boundaries were analyzed with reference to the simulation results for the magnetic field-dependent distributions of the local magnetizations. The saturation magnetization of the grain-boundary phase plays a crucial role in the transition between nucleation- and domain-wall-propagation-controlled reversal processes. The smaller the saturation magnetization of the grain-boundary phase is, the more preferable is the nucleation-controlled process, which results in a larger coercivity. The exchange stiffness of the grain-boundary phase determines the preferred paths of domain-wall propagations, whether inward into grains or along the grain boundaries for relatively small and large exchange stiffness, respectively. However, the exchange stiffness of the grain-boundary phase alone does not significantly contribute to coercivity enhancement in cases where the size of hard-phase grains is much greater than the exchange length. This work paves the way for the design of high-performance hard magnets of large coercivity and maximum-energy-product values.

Probing the Mechanism of pH-Induced Large-Scale Conformational Changes in Dengue Virus Envelope Protein Using Atomistic Simulations

Science.gov (United States)

Prakash, Meher K.; Barducci, Alessandro; Parrinello, Michele

2010-01-01

Abstract One of the key steps in the infection of the cell by dengue virus is a pH-induced conformational change of the viral envelope proteins. These envelope proteins undergo a rearrangement from a dimer to a trimer, with large conformational changes in the monomeric unit. In this article, metadynamics simulations were used to enable us to understand the mechanism of these large-scale changes in the monomer. By using all-atom, explicit solvent simulations of the monomers, the stability of the protein structure is studied under low and high pH conditions. Free energy profiles obtained along appropriate collective coordinates demonstrate that pH affects the domain interface in both the conformations of E monomer, stabilizing one and destabilizing the other. These simulations suggest a mechanism with an intermediate detached state between the two monomeric structures. Using further analysis, we comment on the key residue interactions responsible for the instability and the pH-sensing role of a histidine that could not otherwise be studied experimentally. The insights gained from this study and methodology can be extended for studying similar mechanisms in the E proteins of the other members of class II flavivirus family. PMID:20643078

Local mechanical properties of LFT injection molded parts: Numerical simulations versus experiments

Science.gov (United States)

Desplentere, F.; Soete, K.; Bonte, H.; Debrabandere, E.

2014-05-01

In predictive engineering for polymer processes, the proper prediction of material microstructure from known processing conditions and constituent material properties is a critical step forward properly predicting bulk properties in the finished composite. Operating within the context of long-fiber thermoplastics (LFT, length Autodesk Simulation Moldflow Insight 2014 software has been used. In this software, a fiber breakage algorithm for the polymer flow inside the mold is available. Using well known micro mechanic formulas allow to combine the local fiber length with the local orientation into local mechanical properties. Different experiments were performed using a commercially available glass fiber filled compound to compare the measured data with the numerical simulation results. In this investigation, tensile tests and 3 point bending tests are considered. To characterize the fiber length distribution of the polymer melt entering the mold (necessary for the numerical simulations), air shots were performed. For those air shots, similar homogenization conditions were used as during the injection molding tests. The fiber length distribution is characterized using automated optical method on samples for which the matrix material is burned away. Using the appropriate settings for the different experiments, good predictions of the local mechanical properties are obtained.

Numerical Simulation of Airfoil Aerodynamic Penalties and Mechanisms in Heavy Rain

Directory of Open Access Journals (Sweden)

Zhenlong Wu

2013-01-01

Full Text Available Numerical simulations that are conducted on a transport-type airfoil, NACA 64-210, at a Reynolds number of 2.6×106 and LWC of 25 g/m3 explore the aerodynamic penalties and mechanisms that affect airfoil performance in heavy rain conditions. Our simulation results agree well with the experimental data and show significant aerodynamic penalties for the airfoil in heavy rain. The maximum percentage decrease in CL is reached by 13.2% and the maximum percentage increase in CD by 47.6%. Performance degradation in heavy rain at low angles of attack is emulated by an originally creative boundary-layer-tripped technique near the leading edge. Numerical flow visualization technique is used to show premature boundary-layer separation at high angles of attack and the particulate trajectories at various angles of attack. A mathematic model is established to qualitatively study the water film effect on the airfoil geometric changes. All above efforts indicate that two primary mechanisms are accountable for the airfoil aerodynamic penalties. One is to cause premature boundary-layer transition at low AOA and separation at high AOA. The other occurs at times scales consistent with the water film layer, which is thought to alter the airfoil geometry and increase the mass effectively.

NEMD study for supercavitation mechanism with underwater object

Energy Technology Data Exchange (ETDEWEB)

Gong Bozhi [Department of Chemistry, Zhejiang University, Hangzhou, Zhejiang 310027 (China); Zhang Bingjian [Department of Chemistry, Zhejiang University, Hangzhou, Zhejiang 310027 (China)], E-mail: zbj@mail.ha.zj.cn; Zhang Hui [Department of Chemistry, Ohio State University, Columbus, OH 43210 (United States)

2008-11-24

An open system model was introduced for Non-Equilibrium Molecular Dynamics (NEMD) simulation for studying flow phenomenon surrounding different underwater object. Cavitation number {sigma} criterion was proved to be applicable in predicting local cavitation mechanism. An interesting phenomenon was found that low {sigma} areas and actual cavities were spatially separated in molecular scale, and stable supercavitation would require a large enough low {sigma} area to sustain. Effects of cavitator shape and flow velocity were compared with macro scale flow under similar {sigma}, providing a new computational method to study the molecular scale mechanism of this phenomenon.

NEMD study for supercavitation mechanism with underwater object

International Nuclear Information System (INIS)

Gong Bozhi; Zhang Bingjian; Zhang Hui

2008-01-01

An open system model was introduced for Non-Equilibrium Molecular Dynamics (NEMD) simulation for studying flow phenomenon surrounding different underwater object. Cavitation number σ criterion was proved to be applicable in predicting local cavitation mechanism. An interesting phenomenon was found that low σ areas and actual cavities were spatially separated in molecular scale, and stable supercavitation would require a large enough low σ area to sustain. Effects of cavitator shape and flow velocity were compared with macro scale flow under similar σ, providing a new computational method to study the molecular scale mechanism of this phenomenon

A quantum mechanics/molecular mechanics study on the hydrolysis mechanism of New Delhi metallo-β-lactamase-1.

Science.gov (United States)

Zhu, Kongkai; Lu, Junyan; Liang, Zhongjie; Kong, Xiangqian; Ye, Fei; Jin, Lu; Geng, Heji; Chen, Yong; Zheng, Mingyue; Jiang, Hualiang; Li, Jun-Qian; Luo, Cheng

2013-03-01

New Delhi metallo-β-lactamase-1 (NDM-1) has emerged as a major global threat to human health for its rapid rate of dissemination and ability to make pathogenic microbes resistant to almost all known β-lactam antibiotics. In addition, effective NDM-1 inhibitors have not been identified to date. In spite of the plethora of structural and kinetic data available, the accurate molecular characteristics of and details on the enzymatic reaction of NDM-1 hydrolyzing β-lactam antibiotics remain incompletely understood. In this study, a combined computational approach including molecular docking, molecular dynamics simulations and quantum mechanics/molecular mechanics calculations was performed to characterize the catalytic mechanism of meropenem catalyzed by NDM-1. The quantum mechanics/molecular mechanics results indicate that the ionized D124 is beneficial to the cleavage of the C-N bond within the β-lactam ring. Meanwhile, it is energetically favorable to form an intermediate if no water molecule coordinates to Zn2. Moreover, according to the molecular dynamics results, the conserved residue K211 plays a pivotal role in substrate binding and catalysis, which is quite consistent with previous mutagenesis data. Our study provides detailed insights into the catalytic mechanism of NDM-1 hydrolyzing meropenem β-lactam antibiotics and offers clues for the discovery of new antibiotics against NDM-1 positive strains in clinical studies.

Self-Radiolysis of Tritiated Water: Experimental Study and Simulation

International Nuclear Information System (INIS)

Heinze, Sylver; Stolz, Thibaut; Ducret, Didier; Colson, Jean-Claude

2005-01-01

Radioactive decay of tritium contained in tritiated water leads to the production of gaseous helium and, through self-radiolysis, to the formation of molecular hydrogen and oxygen. For safety management of tritiated water storage, it is essential to be able to predict pressure increase resulting from this phenomenon. The present study aims to identify the mechanisms that take place in self-radiolysis of chemically pure liquid tritiated water. The evolution of the concentration of hydrogen and oxygen in the gas phase of closed vessels containing tritiated water has been followed experimentally. Simulation of pure water radiolysis has been carried out using data from the literature. In order to fit experimental results, simulation should take into account gas phase recombination reaction between hydrogen and oxygen. A simplified system has been extracted from the complete chemical system used to simulate radiolysis. This system allows identifying the basic mechanisms that are responsible for tritiated water self-radiolysis

Tribology and total hip joint replacement: current concepts in mechanical simulation.

Science.gov (United States)

Affatato, S; Spinelli, M; Zavalloni, M; Mazzega-Fabbro, C; Viceconti, M

2008-12-01

Interest in the rheology and effects of interacting surfaces is as ancient as man. This subject can be represented by a recently coined word: tribology. This term is derived from the Greek word "tribos" and means the "science of rubbing". Friction, lubrication, and wear mechanism in the common English language means the precise field of interest of tribology. Wear of total hip prosthesis is a significant clinical problem that involves, nowadays, a too high a number of patients. In order to acquire further knowledge on the tribological phenomena that involve hip prosthesis wear tests are conducted on employed materials to extend lifetime of orthopaedic implants. The most basic type of test device is the material wear machine, however, a more advanced one may more accurately reproduce some of the in vivo conditions. Typically, these apparatus are called simulators, and, while there is no absolute definition of a joint simulator, its description as a mechanical rig used to test a joint replacement, under conditions approximating those occurring in the human body, is acceptable. Simulator tests, moreover, can be used to conduct accelerated protocols that replicate/simulate particularly extreme conditions, thus establishing the limits of performance for the material. Simulators vary in their level of sophistication and the international literature reveals many interpretations of the design of machines used for joint replacement testing. This paper aims to review the current state of the art of the hip joint simulators worldwide. This is specified through a schematic overview by describing, in particular, constructive solutions adopted to reproduce in vivo conditions. An exhaustive commentary on the evolution and actually existing simulation standards is proposed by the authors. The need of a shared protocol among research laboratories all over the world could lead to a consensus conference.

Probing the folded state and mechanical unfolding pathways of T4 lysozyme using all-atom and coarse-grained molecular simulation

Energy Technology Data Exchange (ETDEWEB)

Zheng, Wenjun, E-mail: wjzheng@buffalo.edu; Glenn, Paul [Department of Physics, University at Buffalo, Buffalo, New York 14260 (United States)

2015-01-21

The Bacteriophage T4 Lysozyme (T4L) is a prototype modular protein comprised of an N-terminal and a C-domain domain, which was extensively studied to understand the folding/unfolding mechanism of modular proteins. To offer detailed structural and dynamic insights to the folded-state stability and the mechanical unfolding behaviors of T4L, we have performed extensive equilibrium and steered molecular dynamics simulations of both the wild-type (WT) and a circular permutation (CP) variant of T4L using all-atom and coarse-grained force fields. Our all-atom and coarse-grained simulations of the folded state have consistently found greater stability of the C-domain than the N-domain in isolation, which is in agreement with past thermostatic studies of T4L. While the all-atom simulation cannot fully explain the mechanical unfolding behaviors of the WT and the CP variant observed in an optical tweezers study, the coarse-grained simulations based on the Go model or a modified elastic network model (mENM) are in qualitative agreement with the experimental finding of greater unfolding cooperativity in the WT than the CP variant. Interestingly, the two coarse-grained models predict different structural mechanisms for the observed change in cooperativity between the WT and the CP variant—while the Go model predicts minor modification of the unfolding pathways by circular permutation (i.e., preserving the general order that the N-domain unfolds before the C-domain), the mENM predicts a dramatic change in unfolding pathways (e.g., different order of N/C-domain unfolding in the WT and the CP variant). Based on our simulations, we have analyzed the limitations of and the key differences between these models and offered testable predictions for future experiments to resolve the structural mechanism for cooperative folding/unfolding of T4L.

Mechanical properties of pillared-graphene nanostructures using molecular dynamics simulations

International Nuclear Information System (INIS)

Wang, Chih-Hao; Fang, Te-Hua; Sun, Wei-Li

2014-01-01

The deformation behaviour and mechanical properties of three-dimensional (3D) pillared graphene are investigated using molecular dynamics simulations. The Tersoff–Brenner many-body potential model is employed to evaluate the interactions between 3D pillared-graphene carbon atoms and nanotube carbons. The Lennard-Jones potential model is used to compute the interactions between a conical indenter and 3D pillared-graphene carbon atoms. The effects of the size and geometric structure of 3D pillared-graphene are evaluated in terms of the indentation force and contact stiffness. The simulation results for an armchair nanotube of 3D pillared graphene show that the contact stiffness increases with increasing chiral vector of the 3D-pillared graphene. However, the adhesive force sharply decreases with increasing chiral vector of the 3D-pillared graphene. A zigzag nanotube of 3D-pillared graphene exhibits better mechanical properties compared with those of the armchair nanotube. (paper)

Understanding Creep Mechanisms in Graphite with Experiments, Multiscale Simulations, and Modeling

International Nuclear Information System (INIS)

2014-01-01

Disordering mechanisms in graphite have a long history with conflicting viewpoints. Using Raman and x-ray photon spectroscopy, electron microscopy, x-ray diffraction experiments and atomistic modeling and simulations, the current project has developed a fundamental understanding of early-to-late state radiation damage mechanisms in nuclear reactor grade graphite (NBG-18 and PCEA). We show that the topological defects in graphite play an important role under neutron and ion irradiation.

Understanding Creep Mechanisms in Graphite with Experiments, Multiscale Simulations, and Modeling

Energy Technology Data Exchange (ETDEWEB)

Eapen, Jacob [North Carolina State Univ., Raleigh, NC (United States); Murty, Korukonda [North Carolina State Univ., Raleigh, NC (United States); Burchell, Timothy [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)

2014-06-02

Disordering mechanisms in graphite have a long history with conflicting viewpoints. Using Raman and x-ray photon spectroscopy, electron microscopy, x-ray diffraction experiments and atomistic modeling and simulations, the current project has developed a fundamental understanding of early-to-late state radiation damage mechanisms in nuclear reactor grade graphite (NBG-18 and PCEA). We show that the topological defects in graphite play an important role under neutron and ion irradiation.

Deformation mechanisms and irradiation effects in zirconium alloys. A multi-scale study

International Nuclear Information System (INIS)

Onimus, Fabien

2015-01-01

Zirconium alloys have been used for more than 30 years in the nuclear industry as structural materials for the fuel assemblies of pressurized water reactors. In particular, the cladding tube, made of zirconium alloys, constitutes the first barrier against the dissemination of radioactive elements. It is therefore essential to have a good understanding and prediction of the mechanical behavior of these materials in various conditions. The work presented in this dissertation deals with an experimental study and numerical simulations, at several length scales, of the deformation mechanisms and the mechanical behavior of zirconium alloys before irradiation, but also after irradiation and under irradiation. The mechanical behavior of zirconium single crystal has been determined, during an original study, using tensile test specimens containing large grains. Based on this study, crystal plasticity constitutive laws have been proposed. A polycrystalline model has also been developed to simulate the behavior of unirradiated zirconium alloys. A thorough Transmission Electron Microscopy (TEM) study has been able to clarify the deformation mechanisms of zirconium alloys occurring after irradiation. The clearing of loops by gliding dislocations leading to the dislocation channeling mechanism has been studied in details. This phenomenon has also been simulated using a dislocation dynamics code. The macroscopic consequences of this process have also been analyzed. A polycrystalline model taking into account the specificity of this mechanism has eventually been proposed. This approach has then been extended to the post-irradiation creep behavior. The recovery of radiation defects during creep tests has been characterized by TEM and modeled using cluster dynamics method. Deformation modes during creep have also been studied and a simple model for the creep behavior has eventually been proposed. Finally, the mechanism responsible for the acceleration of irradiation growth that

Computational simulation of weld microstructure and distortion by considering process mechanics

Science.gov (United States)

Mochizuki, M.; Mikami, Y.; Okano, S.; Itoh, S.

2009-05-01

Highly precise fabrication of welded materials is in great demand, and so microstructure and distortion controls are essential. Furthermore, consideration of process mechanics is important for intelligent fabrication. In this study, the microstructure and hardness distribution in multi-pass weld metal are evaluated by computational simulations under the conditions of multiple heat cycles and phase transformation. Because conventional CCT diagrams of weld metal are not available even for single-pass weld metal, new diagrams for multi-pass weld metals are created. The weld microstructure and hardness distribution are precisely predicted when using the created CCT diagram for multi-pass weld metal and calculating the weld thermal cycle. Weld distortion is also investigated by using numerical simulation with a thermal elastic-plastic analysis. In conventional evaluations of weld distortion, the average heat input has been used as the dominant parameter; however, it is difficult to consider the effect of molten pool configurations on weld distortion based only on the heat input. Thus, the effect of welding process conditions on weld distortion is studied by considering molten pool configurations, determined by temperature distribution and history.

Measurements and Simulations on the Mechanisms of Efficiency Losses in HIT Solar Cells

Directory of Open Access Journals (Sweden)

Silvio Pierro

2015-01-01

Full Text Available We study the electrical and the optical behavior of HIT solar cell by means of measurements and optoelectrical simulations by TCAD simulations. We compare the HIT solar cell with a conventional crystalline silicon solar cell to identify the strengths and weaknesses of the HIT technology. Results highlight different mechanisms of electrical and optical efficiency losses caused by the presence of the amorphous silicon layer. The higher resistivity of the a-Si layers implies a smaller distance between the metal lines that causes a higher shadowing. The worst optical coupling between the amorphous silicon and the antireflective coating implies a slight increase of reflectivity around the 600 nm wavelength.

Simulation on Mechanical Properties of Tungsten Carbide Thin Films Using Monte Carlo Model

Directory of Open Access Journals (Sweden)

Liliam C. Agudelo-Morimitsu

2012-12-01

Full Text Available The aim of this paper is to study the mechanical behavior of a system composed by substrate-coating using simulation methods. The contact stresses and the elastic deformation were analyzed by applying a normal load to the surface of the system consisting of a tungsten carbide (WC thin film, which is used as a wear resistant material and a stainless steel substrate. The analysis is based on Monte Carlo simulations using the Metropolis algorithm. The phenomenon was simulated from a fcc facecentered crystalline structure, for both, the coating and the substrate, assuming that the uniaxial strain is taken in the z-axis. Results were obtained for different values of normal applied load to the surface of the coating, obtaining the Strain-stress curves. From this curve, the Young´s modulus was obtained with a value of 600 Gpa, similar to the reports.

Molecular Simulation Study of Montmorillonite in Contact with Variably Wet Supercritical Carbon Dioxide

KAUST Repository

Kadoura, Ahmad Salim; Nair, Arun Kumar Narayanan; Sun, Shuyu

2017-01-01

We perform grand canonical Monte Carlo simulations to study the detailed molecular mechanism of intercalation behavior of CO2 in Na-, Ca-, and Mg- montmorillonite exposed to variably hydrated supercritical CO2 at 323.15 K and 90 bar, The simulations

The Use of Model Matching Video Analysis and Computational Simulation to Study the Ankle Sprain Injury Mechanism

Directory of Open Access Journals (Sweden)

Daniel Tik-Pui Fong

2012-10-01

Full Text Available Lateral ankle sprains continue to be the most common injury sustained by athletes and create an annual healthcare burden of over $4 billion in the U.S. alone. Foot inversion is suspected in these cases, but the mechanism of injury remains unclear. While kinematics and kinetics data are crucial in understanding the injury mechanisms, ligament behaviour measures – such as ligament strains – are viewed as the potential causal factors of ankle sprains. This review article demonstrates a novel methodology that integrates model matching video analyses with computational simulations in order to investigate injury-producing events for a better understanding of such injury mechanisms. In particular, ankle joint kinematics from actual injury incidents were deduced by model matching video analyses and then input into a generic computational model based on rigid bone surfaces and deformable ligaments of the ankle so as to investigate the ligament strains that accompany these sprain injuries. These techniques may have the potential for guiding ankle sprain prevention strategies and targeted rehabilitation therapies.

Mechanical behaviour of synthetic surgical meshes: finite element simulation of the herniated abdominal wall.

Science.gov (United States)

Hernández-Gascón, B; Peña, E; Melero, H; Pascual, G; Doblaré, M; Ginebra, M P; Bellón, J M; Calvo, B

2011-11-01

The material properties of meshes used in hernia surgery contribute to the overall mechanical behaviour of the repaired abdominal wall. The mechanical response of a surgical mesh has to be defined since the haphazard orientation of an anisotropic mesh can lead to inconsistent surgical outcomes. This study was designed to characterize the mechanical behaviour of three surgical meshes (Surgipro®, Optilene® and Infinit®) and to describe a mechanical constitutive law that accurately reproduces the experimental results. Finally, through finite element simulation, the behaviour of the abdominal wall was modelled before and after surgical mesh implant. Uniaxial loading of mesh samples in two perpendicular directions revealed the isotropic response of Surgipro® and the anisotropic behaviour of Optilene® and Infinit®. A phenomenological constitutive law was used to reproduce the measured experimental curves. To analyze the mechanical effect of the meshes once implanted in the abdomen, finite element simulation of the healthy and partially herniated repaired rabbit abdominal wall served to reproduce wall behaviour before and after mesh implant. In all cases, maximal displacements were lower and maximal principal stresses higher in the implanted abdomen than the intact wall model. Despite the fact that no mesh showed a behaviour that perfectly matched that of abdominal muscle, the Infinit® mesh was able to best comply with the biomechanics of the abdominal wall. Copyright © 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Mechanisms of gas generation from simulated SY tank farm wastes: FY 1995 progress report

International Nuclear Information System (INIS)

Barefield, E.K.; Boatright, D.; Deshpande, A.; Doctorovich, F.; Liotta, C.L.; Neumann, H.M.; Seymore, S.

1996-07-01

The objective of this work is to develop a better understanding of the mechanism of formation of flammable gases in the thermal decomposition of metal complexants such as HEDTA and sodium glycolate in simulated SY tank farm waste mixtures. This report summarizes the results of work done at the Georgia Institute of Technology in fiscal year 1995. Topics discussed are (1) long-term studies of the decomposition of HEDTA in simulated waste mixtures under an argon atmosphere at 90 and 120 degrees C, including time profiles for disappearance of HEDTA and appearance of products and the quantitative analysis of the kinetic behavior; (2) considerations of hydroxylamine as an intermediate in the production of nitrogen containing gases by HEDTA decomposition; (3) some thoughts on the revision of the global mechanism for thermal decomposition of HEDTA under argon; (4) preliminary long-term studies of the decomposition of HEDTA in simulated waste under an oxygen atmosphere at 120 degrees C; (5) estimation of the amount of NH 3 in the gas phase above HEDTA reaction mixtures; and (6) further, examination of the interaction of aluminum with nitrite ion using 27 Al NMR spectroscopy. Section 2 of this report describes the work conducted over the last three years at GIT. Section 3 contains a discussion of the kinetic behavior of HEDTA under argon; Section 4 discusses the role of hydroxylamine. Thermal decomposition of HEDTA to ED3A is the subject of Section 5, and decomposition of HEDTA in simulated waste mixtures under oxygen is covered in Section 6. In Section 7 we estimate ammonia in the gas phase; the role of aluminum is discussed in Section 8

Defect-related internal dissipation in mechanical resonators and the study of coupled mechanical systems.

Energy Technology Data Exchange (ETDEWEB)

Friedmann, Thomas Aquinas; Czaplewski, David A.; Sullivan, John Patrick; Modine, Normand Arthur; Wendt, Joel Robert; Aslam, Dean (Michigan State University, Lansing, MI); Sepulveda-Alancastro, Nelson (University of Puerto Rico, Mayaguez, PR)

2007-01-01

Understanding internal dissipation in resonant mechanical systems at the micro- and nanoscale is of great technological and fundamental interest. Resonant mechanical systems are central to many sensor technologies, and microscale resonators form the basis of a variety of scanning probe microscopies. Furthermore, coupled resonant mechanical systems are of great utility for the study of complex dynamics in systems ranging from biology to electronics to photonics. In this work, we report the detailed experimental study of internal dissipation in micro- and nanomechanical oscillators fabricated from amorphous and crystalline diamond materials, atomistic modeling of dissipation in amorphous, defect-free, and defect-containing crystalline silicon, and experimental work on the properties of one-dimensional and two-dimensional coupled mechanical oscillator arrays. We have identified that internal dissipation in most micro- and nanoscale oscillators is limited by defect relaxation processes, with large differences in the nature of the defects as the local order of the material ranges from amorphous to crystalline. Atomistic simulations also showed a dominant role of defect relaxation processes in controlling internal dissipation. Our studies of one-dimensional and two-dimensional coupled oscillator arrays revealed that it is possible to create mechanical systems that should be ideal for the study of non-linear dynamics and localization.

Molecular Dynamics Simulation Study on the Binding and Stabilization Mechanism of Antiprion Compounds to the "Hot Spot" Region of PrPC.

Science.gov (United States)

Zhou, Shuangyan; Liu, Xuewei; An, Xiaoli; Yao, Xiaojun; Liu, Huanxiang

2017-11-15

Structural transitions in the prion protein from the cellular form, PrP C , into the pathological isoform, PrP Sc , are regarded as the main cause of the transmissible spongiform encephalopathies, also known as prion diseases. Hence, discovering and designing effective antiprion drugs that can inhibit PrP C to PrP Sc conversion is regarded as a promising way to cure prion disease. Among several strategies to inhibit PrP C to PrP Sc conversion, stabilizing the native PrP C via specific binding is believed to be one of the valuable approaches and many antiprion compounds have been reported based on this strategy. However, the detailed mechanism to stabilize the native PrP C is still unknown. As such, to unravel the stabilizing mechanism of these compounds to PrP C is valuable for the further design and discovery of antiprion compounds. In this study, by molecular dynamics simulation method, we investigated the stabilizing mechanism of several antiprion compounds on PrP C that were previously reported to have specific binding to the "hot spot" region of PrP C . Our simulation results reveal that the stabilization mechanism of specific binding compounds can be summarized as (I) to stabilize both the flexible C-terminal of α2 and the hydrophobic core, such as BMD42-29 and GN8; (II) to stabilize the hydrophobic core, such as J1 and GJP49; (III) to stabilize the overall structure of PrP C by high binding affinity, as NPR-056. In addition, as indicated by the H-bond analysis and decomposition analysis of binding free energy, the residues N159 and Q160 play an important role in the specific binding of the studied compounds and all these compounds interact with PrP C in a similar way with the key interacting residues L130 in the β1 strand, P158, N159, Q160, etc. in the α1-β2 loop, and H187, T190, T191, etc. in the α2 C-terminus although the compounds have large structural difference. As a whole, our obtained results can provide some insights into the specific binding

A MODELING AND SIMULATION LANGUAGE FOR BIOLOGICAL CELLS WITH COUPLED MECHANICAL AND CHEMICAL PROCESSES.

Science.gov (United States)

Somogyi, Endre; Glazier, James A

2017-04-01

Biological cells are the prototypical example of active matter. Cells sense and respond to mechanical, chemical and electrical environmental stimuli with a range of behaviors, including dynamic changes in morphology and mechanical properties, chemical uptake and secretion, cell differentiation, proliferation, death, and migration. Modeling and simulation of such dynamic phenomena poses a number of computational challenges. A modeling language describing cellular dynamics must naturally represent complex intra and extra-cellular spatial structures and coupled mechanical, chemical and electrical processes. Domain experts will find a modeling language most useful when it is based on concepts, terms and principles native to the problem domain. A compiler must then be able to generate an executable model from this physically motivated description. Finally, an executable model must efficiently calculate the time evolution of such dynamic and inhomogeneous phenomena. We present a spatial hybrid systems modeling language, compiler and mesh-free Lagrangian based simulation engine which will enable domain experts to define models using natural, biologically motivated constructs and to simulate time evolution of coupled cellular, mechanical and chemical processes acting on a time varying number of cells and their environment.

MHD simulation study of compact toroid injection into magnetized plasmas

International Nuclear Information System (INIS)

Suzuki, Yoshio; Kishimoto, Yasuaki

2000-01-01

To understand the fuelling process in a fusion device by a compact toroid (CT) plasmoid injection method, we have carried out MHD numerical simulations where a spheromak-like CT (SCT) is injected into a magnetized target plasma region. So far, we revealed that the penetration depth of the SCT plasma becomes shorter than that estimated from the conducting sphere (CS) model, because in the simulation the Lorentz force of the target magnetic field sequentially decelerates the injected SCT while in the CS model only the magnetic pressure force acts as the deceleration mechanism. In this study, we represent the new theoretical model where the injected SCT is decelerated by both the magnetic pressure force and the magnetic tension force (we call it the non-slipping sphere (NS) model) and investigate in detail the deceleration mechanism of the SCT by comparison with simulation results. As a result, it is found that the decrease of the SCT kinetic energy in the simulation coincides with that in the NS model more than in the CS model. It means that not only the magnetic pressure force but also the magnetic tension force acts as the deceleration mechanism of the SCT. Furthermore, it is revealed that magnetic reconnection between the SCT magnetic field and the target magnetic field plays a role to relax the SCT deceleration. (author)

Study of plasticity in metals by numerical simulations

International Nuclear Information System (INIS)

Clouet, E.

2013-01-01

We present a study of the plastic behaviour in metals based on the modelling of dislocation properties. Different simulation tools have been used and developed to study plasticity in structural materials, in particular metals used in the nuclear industry. In iron or zirconium alloys, plasticity is controlled at low temperature by the glide of screw dislocations. Atomistic simulations can be used to model dislocation core properties and thus to obtain a better knowledge of the mechanisms controlling dislocation glide. Such atomistic simulations need nevertheless some special care because of the long range elastic field induced by the dislocations. We have therefore developed a modelling approach relying both on atomistic simulations, using either empirical interatomic potentials or ab initio calculations, and on elasticity theory. Such an approach has been used to obtain dislocation intrinsic core properties. These simulations allowed us to describe, in iron, the variations of these core properties with the dislocation character. In zirconium, we could identity the origin of the high lattice friction and obtain a better understanding of the competition between the different glide systems. At high temperature, dislocations do not only glide but can also cross-slip or climb. This leads to a motion of the dislocations out of their glide plane which needs to be considered when modelling the plastic flow. We performed a study of dislocation climb at different scales, leading to the implementation of a dislocation climb model in dislocation dynamics simulations. (author) [fr

Thermal and thermo-mechanical simulation of laser assisted machining

International Nuclear Information System (INIS)

Germain, G.; Dal Santo, P.; Lebrun, J. L.; Bellett, D.; Robert, P.

2007-01-01

Laser Assisted Machining (LAM) improves the machinability of materials by locally heating the workpiece just prior to cutting. The heat input is provided by a high power laser focused several millimeters in front of the cutting tool. Experimental investigations have confirmed that the cutting force can be decreased, by as much as 40%, for various materials (tool steel, titanium alloys and nickel alloys). The laser heat input is essentially superficial and results in non-uniform temperature profiles within the depth of the workpiece. The temperature field in the cutting zone is therefore influenced by many parameters. In order to understand the effect of the laser on chip formation and on the temperature fields in the different deformation zones, thermo-mechanical simulation were undertaken. A thermo-mechanical model for chip formation with and without the laser was also undertaken for different cutting parameters. Experimental tests for the orthogonal cutting of 42CrMo4 steel were used to validate the simulation via the prediction of the cutting force with and without the laser. The thermo-mechanical model then allowed us to highlight the differences in the temperature fields in the cutting zone with and without the laser. In particular, it was shown that for LAM the auto-heating of the material in the primary shear zone is less important and that the friction between the tool and chip also generates less heat. The temperature fields allow us to explain the reduction in the cutting force and the resulting residual stress fields in the workpiece

Finite element simulation of the mechanism of laser ultrasound induced pain weapon

Science.gov (United States)

Zhou, Bo; Zhan, Ren Jun; Shan, Ning

2018-03-01

The Laser-Ultrasonic technique uses laser energy to generate ultrasound waves in various solids. In normal conditions, this technique is used to inspect large structures without destruction, but in military use, we hope get this destruction. Nociceptors in Human skin can feel cold, heat, mechanical and other stimuli, when the stimulus exceeds a certain threshold will produce pain. Based on this principle, a laser induced pain weapon may be made. The generated ultrasound wave form is affected by features of laser pulse. The results obtained from the finite element model of laser generated ultrasound are presented in terms of temperature and displacement. At first step, the transient temperature field can be precisely calculated by using the finite element method. Then, laser generated surface acoustic wave forms are calculated by coupling the temperature distribution. Displacement is used to represent the mechanical action of skin caused by laser ultrasound. Results from numerical simulation are compared with other references; the accuracy of the method is proved accordingly. The results of simulation in the given conditions demonstrate that the stresses generated by pulse laser in human skin model were about -8 and +4 MPa. According to the results of simulation, the max and min stress are both emerged in the range of 0 600 um, that is exactly the location of myelinated Aδ and unmyelinated C nociceptor. The value of stress is can be adjusted by chose suitable parameters of laser. The study provides a possibility for developing a new non-lethal weapon to control riots or crowd.

Co-simulation of Six DOF Wire Driven Parallel Mechanism Based on ADAMS and Matlab

Directory of Open Access Journals (Sweden)

Tang Aofei

2015-01-01

Full Text Available The dynamic model of the 6 DOF Wire Driven Parallel Mechanism (WDPM system is introduced. Based on MATLAB system, the simulation of the inverse dynamic model is achieved. According to the simulation result, the mechanical model for the WDPM system is reasonable. Using ADAMS system, the dynamic model of the virtual prototype is verified by the simulation analysis. The combined control model based on ADAMS/Simulink is derived. The WDPM control system is designed with MATLAB/Simulink. The torque control method is selected for the outer ring and the PD control method for the inner ring. Combined with the ADAMS control model and control law design, the interactive simulation analysis of the WDPM system is completed. According to the simulation results of the spatial circle tracking and line tracking at the end of the moving platform, the tracking error can be reduced by the designed control algorithm. The minimum tracking error is 0.2 mm to 0.3 mm. Therefore, the theoretical foundation for designing hardware systems of the WDPM control system is established.

Mechanical behavior of fast reactor fuel pin cladding subjected to simulated overpower transients

International Nuclear Information System (INIS)

Johnson, G.D.; Hunter, C.W.

1978-06-01

Cladding mechanical property data for analysis and prediction of fuel pin transient behavior were obtained under experimental conditions in which the temperature ramps of reactor transients were simulated. All cladding specimens were 20% CW Type 316 stainless steel and were cut from EBR-II irradiated fuel pins. It was determined that irradiation degraded the cladding ductility and failure strength. Specimens that had been adjacent to the fuel exhibited the poorest properties. Correlations were developed to describe the effect of neutron fluence on the mechanical behavior of the cladding. Metallographic examinations were conducted to characterize the failure mode and to establish the nature of internal and external surface corrosion. Various mechanisms for the fuel adjacency effect were examined and results for helium concentration profiles were presented. Results from the simulated transient tests were compared with TREAT test results

Quantum Mechanics/Molecular Mechanics Free Energy Maps and Nonadiabatic Simulations for a Photochemical Reaction in DNA: Cyclobutane Thymine Dimer.

Science.gov (United States)

Mendieta-Moreno, Jesús I; Trabada, Daniel G; Mendieta, Jesús; Lewis, James P; Gómez-Puertas, Paulino; Ortega, José

2016-11-03

The absorption of ultraviolet radiation by DNA may result in harmful genetic lesions that affect DNA replication and transcription, ultimately causing mutations, cancer, and/or cell death. We analyze the most abundant photochemical reaction in DNA, the cyclobutane thymine dimer, using hybrid quantum mechanics/molecular mechanics (QM/MM) techniques and QM/MM nonadiabatic molecular dynamics. We find that, due to its double helix structure, DNA presents a free energy barrier between nonreactive and reactive conformations leading to the photolesion. Moreover, our nonadiabatic simulations show that most of the photoexcited reactive conformations return to standard B-DNA conformations after an ultrafast nonradiative decay to the ground state. This work highlights the importance of dynamical effects (free energy, excited-state dynamics) for the study of photochemical reactions in biological systems.

Simulated weightlessness and synbiotic diet effects on rat bone mechanical strength

Science.gov (United States)

Sarper, Hüseyin; Blanton, Cynthia; DePalma, Jude; Melnykov, Igor V.; Gabaldón, Annette M.

2014-10-01

This paper reports results on exposure to simulated weightlessness that leads to a rapid decrease in bone mineral density known as spaceflight osteopenia by evaluating the effectiveness of dietary supplementation with synbiotics to counteract the effects of skeletal unloading. Forty adult male rats were studied under four different conditions in a 2 × 2 factorial design with main effects of diet (synbiotic and control) and weight condition (unloaded and control). Hindlimb unloading was performed at all times for 14 days followed by 14 days of recovery (reambulation). The synbiotic diet contained probiotic strains Lactobacillus acidophilus and Lactococcus lactis lactis and prebiotic fructooligosaccharide. This paper also reports on the development of a desktop three-point bending device to measure the mechanical strength of bones from rats subjected to simulated weightlessness. The importance of quantifying bone resistance to breakage is critical when examining the effectiveness of interventions against osteopenia resulting from skeletal unloading, such as astronauts experience, disuse or disease. Mechanical strength indices provide information beyond measures of bone density and microarchitecture that enhance the overall assessment of a treatment's potency. In this study we used a newly constructed three-point bending device to measure the mechanical strength of femur and tibia bones from hindlimb-unloaded rats fed an experimental synbiotic diet enriched with probiotics and fermentable fiber. Two calculated outputs for each sample were Young's modulus of elasticity and fracture stress. Bone major elements (calcium, magnesium, and phosphorous) were quantified using ICP-MS analysis. Hindlimb unloading was associated with a significant loss of strength in the femur, and with significant reductions in major bone elements. The synbiotic diet did not protect against these unloading effects. Tibia strength and major elements were not reduced by hindlimb unloading, as was

Combined quantum-mechanics/molecular-mechanics dynamics simulation of A-DNA double strands irradiated by ultra-low-energy carbon ions

Energy Technology Data Exchange (ETDEWEB)

Ngaojampa, C.; Nimmanpipug, P. [Computer Simulation and Modeling Laboratory (CSML), Department of Chemistry and Center for Innovation Chemistry, Faculty of Science, Chiang Mai University, Chiang Mai 50200 (Thailand); Yu, L.D., E-mail: yuld@fnrf.science.cmu.ac.t [Plasma and Beam Physics Research Facility, Department of Physics and Materials Science, Faculty of Science, Chiang Mai University, Chiang Mai 50200 (Thailand); Thailand Center of Excellence in Physics, Commission on Higher Education, 328 Si Ayutthaya Road, Bangkok 10400 (Thailand); Anuntalabhochai, S. [Molecular Biology Laboratory, Department of Biology, Faculty of Science, Chiang Mai University, Chiang Mai 50200 (Thailand); Lee, V.S., E-mail: vannajan@gmail.co [Computer Simulation and Modeling Laboratory (CSML), Department of Chemistry and Center for Innovation Chemistry, Faculty of Science, Chiang Mai University, Chiang Mai 50200 (Thailand); Thailand Center of Excellence in Physics, Commission on Higher Education, 328 Si Ayutthaya Road, Bangkok 10400 (Thailand)

2011-02-15

In order to promote understanding of the fundamentals of ultra-low-energy ion interaction with DNA, molecular dynamics simulations using combined quantum-mechanics/molecular-mechanics of poly-AT and poly-GC A-DNA double strands irradiated by <200 eV carbon ions were performed to investigate the molecular implications of mutation bias. The simulations were focused on the responses of the DNA backbones and nitrogenous bases to irradiation. Analyses of the root mean square displacements of the backbones and non-hydrogen atoms of base rings of the simulated DNA structure after irradiation revealed a potential preference of DNA double strand separation, dependent on the irradiating energy. The results show that for the backbones, the large difference in the displacement between poly-GC and poly-AT in the initial time period could be the reason for the backbone breakage; for the nitrogenous base pairs, A-T is 30% more sensitive or vulnerable to ion irradiation than G-C, demonstrating a preferential, instead of random, effect of irradiation-induced mutation.

Combined quantum-mechanics/molecular-mechanics dynamics simulation of A-DNA double strands irradiated by ultra-low-energy carbon ions

International Nuclear Information System (INIS)

Ngaojampa, C.; Nimmanpipug, P.; Yu, L.D.; Anuntalabhochai, S.; Lee, V.S.

2011-01-01

In order to promote understanding of the fundamentals of ultra-low-energy ion interaction with DNA, molecular dynamics simulations using combined quantum-mechanics/molecular-mechanics of poly-AT and poly-GC A-DNA double strands irradiated by <200 eV carbon ions were performed to investigate the molecular implications of mutation bias. The simulations were focused on the responses of the DNA backbones and nitrogenous bases to irradiation. Analyses of the root mean square displacements of the backbones and non-hydrogen atoms of base rings of the simulated DNA structure after irradiation revealed a potential preference of DNA double strand separation, dependent on the irradiating energy. The results show that for the backbones, the large difference in the displacement between poly-GC and poly-AT in the initial time period could be the reason for the backbone breakage; for the nitrogenous base pairs, A-T is 30% more sensitive or vulnerable to ion irradiation than G-C, demonstrating a preferential, instead of random, effect of irradiation-induced mutation.

Probabilistic Simulation of Combined Thermo-Mechanical Cyclic Fatigue in Composites

Science.gov (United States)

Chamis, Christos C.

2011-01-01

A methodology to compute probabilistically-combined thermo-mechanical fatigue life of polymer matrix laminated composites has been developed and is demonstrated. Matrix degradation effects caused by long-term environmental exposure and mechanical/thermal cyclic loads are accounted for in the simulation process. A unified time-temperature-stress-dependent multifactor-interaction relationship developed at NASA Glenn Research Center has been used to model the degradation/aging of material properties due to cyclic loads. The fast probability-integration method is used to compute probabilistic distribution of response. Sensitivities of fatigue life reliability to uncertainties in the primitive random variables (e.g., constituent properties, fiber volume ratio, void volume ratio, ply thickness, etc.) computed and their significance in the reliability-based design for maximum life is discussed. The effect of variation in the thermal cyclic loads on the fatigue reliability for a (0/+/-45/90)s graphite/epoxy laminate with a ply thickness of 0.127 mm, with respect to impending failure modes has been studied. The results show that, at low mechanical-cyclic loads and low thermal-cyclic amplitudes, fatigue life for 0.999 reliability is most sensitive to matrix compressive strength, matrix modulus, thermal expansion coefficient, and ply thickness. Whereas at high mechanical-cyclic loads and high thermal-cyclic amplitudes, fatigue life at 0.999 reliability is more sensitive to the shear strength of matrix, longitudinal fiber modulus, matrix modulus, and ply thickness.

Simulation studies of acceleration of heavy ions and their elemental compositions

International Nuclear Information System (INIS)

Toida, Mieko; Ohsawa, Yukiharu

1996-07-01

By using a one-dimensional, electromagnetic particle simulation code with full ion and electron dynamics, we have studied the acceleration of heavy ions by a nonlinear magnetosonic wave in a multi-ion-species plasma. First, we describe the mechanism of heavy ion acceleration by magnetosonic waves. We then investigate this by particle simulations. The simulation plasma contains four ion species: H, He, O, and Fe. The number density of He is taken to be 10% of that of H, and those of O and Fe are much lower. Simulations confirm that, as in a single-ion-species plasma, some of the hydrogens can be accelerated by the longitudinal electric field formed in the wave. Furthermore, they show that magnetosonic waves can accelerate all the particles of all the heavy species (He, O, and Fe) by a different mechanism, i.e., by the transverse electric field. The maximum speeds of the heavy species are about the same, of the order of the wave propagation speed. These are in good agreement with theoretical prediction. These results indicate that, if high-energy ions are produced in the solar corona through these mechanisms, the elemental compositions of these heavy ions can be similar to that of the background plasma, i.e., the corona

Molecular dynamics simulation of joining process of Ag-Au nanowires and mechanical properties of the hybrid nanojoint

Directory of Open Access Journals (Sweden)

Su Ding

2015-05-01

Full Text Available The nanojoining process of Ag-Au hybrid nanowires at 800K was comprehensively studied by virtue of molecular dynamics (MD simulation. Three kinds of configurations including end-to-end, T-like and X-like were built in the simulation aiming to understand the nanojoining mechanism. The detailed dynamic evolution of atoms, crystal structure transformation and defects development during the nanojoining processes were performed. The results indicate that there are two stages in the nanojoining process of Ag-Au nanowires which are atom diffusion and new bonds formation. Temperature is a key parameter affecting both stages ascribed to the energy supply and the optimum temperature for Ag-Au nanojoint with diameter of 4.08 nm has been discussed. The mechanical properties of the nanojoint were examined with simulation of tensile test on the end-to-end joint. It was revealed that the nanojoint was strong enough to resist fracture at the joining area.

Molecular simulation studies on thermophysical properties with application to working fluids

CERN Document Server

Raabe, Gabriele

2017-01-01

This book discusses the fundamentals of molecular simulation, starting with the basics of statistical mechanics and providing introductions to Monte Carlo and molecular dynamics simulation techniques. It also offers an overview of force-field models for molecular simulations and their parameterization, with a discussion of specific aspects. The book then summarizes the available know-how for analyzing molecular simulation outputs to derive information on thermophysical and structural properties. Both the force-field modeling and the analysis of simulation outputs are illustrated by various examples. Simulation studies on recently introduced HFO compounds as working fluids for different technical applications demonstrate the value of molecular simulations in providing predictions for poorly understood compounds and gaining a molecular-level understanding of their properties. This book will prove a valuable resource to researchers and students alike.

Force decay of elastomeric chains - a mechanical design and product comparison study.

Science.gov (United States)

Balhoff, David A; Shuldberg, Matthew; Hagan, Joseph L; Ballard, Richard W; Armbruster, Paul C

2011-03-01

To evaluate the percentage force decay of elastomeric chain products utilizing three different design mechanisms simulating canine retraction; and to evaluate the percentage force decay of elastomeric chain products from four different companies. In vitro, laboratory study. LSUHSC Dental School, New Orleans, LA, USA. Closed (non-spaced), grey elastomeric chains from four companies were selected for the study. Three acrylic resin jigs were constructed to provide a framework for three simulated space closure mechanisms. The 6-5-3, the chain loop, and the 6-3 were the configuration mechanisms used in the study. An electronic force gauge was used to measure the percentage force decay associated with each elastomeric chain over 28 days at preselected times. There was a significant difference in the mean percentage force decay for the three different mechanisms (P < 0·001). For all four companies, the 6-3 mechanical design had the smallest mean percentage force decay. There was a significant difference in the mean percentage force decay for the different companies (P < 0·001). For all three mechanisms, Ormco had the smallest percentage force decay while Unitek had the highest percentage force decay. The significant difference in the mean percentage force decay for the different mechanisms suggests that the 6-3 design is a more efficient means of closing extraction spaces utilizing elastomeric chains.

Magnetic force microscopy and simulation studies on Co 50 Fe 50 ...

Indian Academy of Sciences (India)

We studied the magnetization reversal mechanism of single-layered Co50Fe50 nanomagnets by measuring the magnetization reversal and using the micromagnetic simulations. The magnetization reversal strongly depends on the thickness of the nanomagnets. In the remanent state, the magnetic force microscopy studies ...

A Nanoscale Simulation Study of Elastic Properties of Gaspeite

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Benazzouz Brahim-Khalil

2015-02-01

Full Text Available The study of structural and mechanical properties of carbonate rock is an interesting subject in engineering and its different applications. In this paper, the crystal structure of gaspeite (NiCO3 is investigated by carrying out molecular dynamics simulations based on energy minimization technique using an interatomic interaction potential.

Neighbourhood generation mechanism applied in simulated annealing to job shop scheduling problems

Science.gov (United States)

Cruz-Chávez, Marco Antonio

2015-11-01

This paper presents a neighbourhood generation mechanism for the job shop scheduling problems (JSSPs). In order to obtain a feasible neighbour with the generation mechanism, it is only necessary to generate a permutation of an adjacent pair of operations in a scheduling of the JSSP. If there is no slack time between the adjacent pair of operations that is permuted, then it is proven, through theory and experimentation, that the new neighbour (schedule) generated is feasible. It is demonstrated that the neighbourhood generation mechanism is very efficient and effective in a simulated annealing.

A Mechanism Denial Study on the Madden-Julian Oscillation

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In-Sik Kang

2011-12-01

Full Text Available A series of Madden-Julian oscillation (MJO mechanism-denial experiments is performed using an atmospheric general circulation model (AGCM. Daily climatological seasonal cycles of i surface latent heat flux, ii net radiative heating rate, and iii surface wind stress are obtained from a control simulation and prescribed in place of the normal interactive computations of these fields in order to turn off the i wind-induced surface heat exchange (WISHE, ii cloud-radiation interaction (CRI, and iii frictional wave-CISK (FWC mechanisms, respectively. Dual and triple mechanism denial experiments are also conducted by switching off multiple mechanisms together. The influence of each mechanism is assessed by comparing experiments with that mechanism turned off to those in which it is not. CRI and WISHE are both found to be important to the simulated MJO amplitude and propagation speed, while FWC has weaker and less systematic effects. The MJO is weakened when CRI is turned off, but strengthened when WISHE is turned off, indicating that CRI amplifies the MJO in the control simulation while WISHE weakens it. The negative influence of WISHE is shown to result from simulated phase relationships between surface winds, surface fluxes and convection which differ significantly from those found in observations, and thus is not interpreted as evidence against a positive role for WISHE in the development and maintenance of the observed MJO. The positive influence of CRI in the model is consistent with a strong simulated relationship between daily grid-point column-integrated radiative and convective heating; the mean ratio of the latter to the former exceeds 0.2 for rain rates less than 14 mm d-1. CRI is also shown to suppress an excessive excitation of the convectively coupled Kelvin wave so that the amplitude and frequency of the MJO is maintained.

Effect of simulated mechanical recycling processes on the structure and properties of poly(lactic acid).

Science.gov (United States)

Beltrán, F R; Lorenzo, V; Acosta, J; de la Orden, M U; Martínez Urreaga, J

2018-06-15

The aim of this work is to study the effects of different simulated mechanical recycling processes on the structure and properties of PLA. A commercial grade of PLA was melt compounded and compression molded, then subjected to two different recycling processes. The first recycling process consisted of an accelerated ageing and a second melt processing step, while the other recycling process included an accelerated ageing, a demanding washing process and a second melt processing step. The intrinsic viscosity measurements indicate that both recycling processes produce a degradation in PLA, which is more pronounced in the sample subjected to the washing process. DSC results suggest an increase in the mobility of the polymer chains in the recycled materials; however the degree of crystallinity of PLA seems unchanged. The optical, mechanical and gas barrier properties of PLA do not seem to be largely affected by the degradation suffered during the different recycling processes. These results suggest that, despite the degradation of PLA, the impact of the different simulated mechanical recycling processes on the final properties is limited. Thus, the potential use of recycled PLA in packaging applications is not jeopardized. Copyright © 2017 Elsevier Ltd. All rights reserved.

Atomic scale numerical simulation study of elementary mechanisms of plasticity in aluminium and copper

International Nuclear Information System (INIS)

Aslanides, Antoine

1998-01-01

This study deals with elementary mechanisms of plasticity, such as the dissociation of a perfect edge dislocation into Shockley partials, the annihilation of dislocation dipoles and the interaction between a dislocation and an interface (free surface and grain boundary). Dislocation core effects are expected to influence crucially these interactions. A deeper understanding of these situations is thus achieved by resorting to an atomistic numerical approach, the application of the elastic theory of dislocations being no longer justified. Two FCC metals are considered: aluminium and copper, with respectively a small and a large dissociation width. An empirical potential for aluminium was designed to study the perfect as well as the dissociated states of the dislocation. The results are compared to the ones obtained with the interaction model for copper, for both the edge and the screw characters. The obtained core radius value ensures the continuity between the atomic and the elastic treatments. The calculations concerning edge dislocation dipole configurations show that there exists a critical distance between the glide planes of the two constitutive dislocations under which a spontaneous recombination occurs. We then compute the variation of the excess energy associated to the gradual approach of an edge dislocation toward the free surface of a crystal. An estimation of the energy required for the introduction of a dislocation in a thin film is obtained. The study of the interaction between a dislocation and a tilt grain boundary shows that the dislocation is absorbed in the interface, the stress required for its extraction being rather large. Finally, by proceeding to the simulation of a tensile test, we demonstrate that the surface steps constitute favoured sites for the nucleation of the dislocations. (author) [fr

Effect of flexural crack on plain concrete beam failure mechanism A numerical simulation

Directory of Open Access Journals (Sweden)

Abdoullah Namdar

2016-03-01

Full Text Available The flexural failure of plain concrete beam occurs along with development of flexural crack on beam. In this paper by using ABAQUS, mechanism failure of plain concrete beam under three steps have been simulated. The cracking moment has been analytically calculated and applied on the both sides of the fixed beam, and flexural crack has been simulated on beam. Displacement, von Mises, load reaction, displacementcrack length, von Mises-crack length and von Mises-displacement of beams have been graphical depicted. Results indicated that, the flexural crack governs beam mechanism failure and its effects on beam resistance failure. It has been found that the flexural crack in initial stage it developed slowly and changes to be fast at the final stage of collapsing beam due to reduction of the flexural resistance of beam. Increasing mechanical properties of concrete, collapse displacement is reduced.

Fundamental Insights into Proton-Coupled Electron Transfer in Soybean Lipoxygenase from Quantum Mechanical/Molecular Mechanical Free Energy Simulations.

Science.gov (United States)

Li, Pengfei; Soudackov, Alexander V; Hammes-Schiffer, Sharon

2018-02-28

The proton-coupled electron transfer (PCET) reaction catalyzed by soybean lipoxygenase has served as a prototype for understanding hydrogen tunneling in enzymes. Herein this PCET reaction is studied with mixed quantum mechanical/molecular mechanical (QM/MM) free energy simulations. The free energy surfaces are computed as functions of the proton donor-acceptor (C-O) distance and the proton coordinate, and the potential of mean force is computed as a function of the C-O distance, inherently including anharmonicity. The simulation results are used to calculate the kinetic isotope effects for the wild-type enzyme (WT) and the L546A/L754A double mutant (DM), which have been measured experimentally to be ∼80 and ∼700, respectively. The PCET reaction is found to be exoergic for WT and slightly endoergic for the DM, and the equilibrium C-O distance for the reactant is found to be ∼0.2 Å greater for the DM than for WT. The larger equilibrium distance for the DM, which is due mainly to less optimal substrate binding in the expanded binding cavity, is primarily responsible for its higher kinetic isotope effect. The calculated potentials of mean force are anharmonic and relatively soft at shorter C-O distances, allowing efficient thermal sampling of the shorter distances required for effective hydrogen tunneling. The primarily local electrostatic field at the transferring hydrogen is ∼100 MV/cm in the direction to facilitate proton transfer and increases dramatically as the C-O distance decreases. These simulations suggest that the overall protein environment is important for conformational sampling of active substrate configurations aligned for proton transfer, but the PCET reaction is influenced primarily by local electrostatic effects that facilitate conformational sampling of shorter proton donor-acceptor distances required for effective hydrogen tunneling.

Equivalence principle and quantum mechanics: quantum simulation with entangled photons.

Science.gov (United States)

Longhi, S

2018-01-15

Einstein's equivalence principle (EP) states the complete physical equivalence of a gravitational field and corresponding inertial field in an accelerated reference frame. However, to what extent the EP remains valid in non-relativistic quantum mechanics is a controversial issue. To avoid violation of the EP, Bargmann's superselection rule forbids a coherent superposition of states with different masses. Here we suggest a quantum simulation of non-relativistic Schrödinger particle dynamics in non-inertial reference frames, which is based on the propagation of polarization-entangled photon pairs in curved and birefringent optical waveguides and Hong-Ou-Mandel quantum interference measurement. The photonic simulator can emulate superposition of mass states, which would lead to violation of the EP.

Multi-agent simulation of the von Thunen model formation mechanism

Science.gov (United States)

Tao, Haiyan; Li, Xia; Chen, Xiaoxiang; Deng, Chengbin

2008-10-01

This research tries to explain the internal driving forces of circular structure formation in urban geography via the simulation of interaction between individual behavior and market. On the premise of single city center, unchanged scale merit and complete competition, enterprise migration theory as well, an R-D algorithm, that has agents searched the best behavior rules in some given locations, is introduced with agent-based modeling technique. The experiment conducts a simulation on Swarm platform, whose result reflects and replays the formation process of Von Thünen circular structure. Introducing and considering some heterogeneous factors, such as traffic roads, the research verifies several landuse models and discusses the self-adjustment function of price mechanism.

Temperature-dependent mechanical properties of single-layer molybdenum disulphide: Molecular dynamics nanoindentation simulations

Energy Technology Data Exchange (ETDEWEB)

Zhao, Junhua, E-mail: junhua.zhao@uni-weimar.de [Jiangsu Province Key Laboratory of Advanced Manufacturing Equipment and Technology of Food, Jiangnan University, 214122 Wuxi (China); Institute of Structural Mechanics, Bauhaus-University Weimar, 99423 Weimar (Germany); Jiang, Jin-Wu, E-mail: jwjiang5918@hotmail.com [Institute of Structural Mechanics, Bauhaus-University Weimar, 99423 Weimar (Germany); Rabczuk, Timon, E-mail: timon.rabczuk@uni-weimar.de [Institute of Structural Mechanics, Bauhaus-University Weimar, 99423 Weimar (Germany); School of Civil, Environmental and Architectural Engineering, Korea University, 136-701 Seoul (Korea, Republic of)

2013-12-02

The temperature-dependent mechanical properties of single-layer molybdenum disulphide (MoS{sub 2}) are obtained using molecular dynamics (MD) nanoindentation simulations. The Young's moduli, maximum load stress, and maximum loading strain decrease with increasing temperature from 4.2 K to 500 K. The obtained Young's moduli are in good agreement with those using our MD uniaxial tension simulations and the available experimental results. The tendency of maximum loading strain with different temperature is opposite with that of metal materials due to the short range Stillinger-Weber potentials in MoS{sub 2}. Furthermore, the indenter tip radius and fitting strain effect on the mechanical properties are also discussed.

The thermal and mechanical deformation study of up-stream pumping mechanical seal

International Nuclear Information System (INIS)

Chen, H L; Xu, C; Zuo, M Z; Wu, Q B

2015-01-01

Taking the viscosity-temperature relationship of the fluid film into consideration, a 3-D numerical model was established by ANSYS software which can simulate the heat transfer between the upstream pumping mechanical seal stationary and rotational rings and the fluid film between them as well as simulate the thermal deformation, structure deformation and the coupling deformation of them. According to the calculation result, thermal deformation causes the seal face expansion and the maximum thermal deformation appears at the inside of the seal ring. Pressure results in a mechanical deformation, the maximum deformation occurs at the top of the spiral groove and the overall trend is inward the mating face, opposite to the thermal deformation. The coupling deformation indicate that the thermal deformation can be partly counteracted by pressure deformation. Using this model, the relationship between deformation and shaft speed and the sealing liquid pressure was studied. It's found that the shaft speed will both enhance the thermal and structure deformation and the fluid pressure will enhance the structure deformation but has little to do with the thermal deformation. By changing the sealing material, it's found that material with low thermal expansion coefficient and low elastic modulus will suffer less thermal-pressure deformation

The thermal and mechanical deformation study of up-stream pumping mechanical seal

Science.gov (United States)

Chen, H. L.; Xu, C.; Zuo, M. Z.; Wu, Q. B.

2015-01-01

Taking the viscosity-temperature relationship of the fluid film into consideration, a 3-D numerical model was established by ANSYS software which can simulate the heat transfer between the upstream pumping mechanical seal stationary and rotational rings and the fluid film between them as well as simulate the thermal deformation, structure deformation and the coupling deformation of them. According to the calculation result, thermal deformation causes the seal face expansion and the maximum thermal deformation appears at the inside of the seal ring. Pressure results in a mechanical deformation, the maximum deformation occurs at the top of the spiral groove and the overall trend is inward the mating face, opposite to the thermal deformation. The coupling deformation indicate that the thermal deformation can be partly counteracted by pressure deformation. Using this model, the relationship between deformation and shaft speed and the sealing liquid pressure was studied. It's found that the shaft speed will both enhance the thermal and structure deformation and the fluid pressure will enhance the structure deformation but has little to do with the thermal deformation. By changing the sealing material, it's found that material with low thermal expansion coefficient and low elastic modulus will suffer less thermal-pressure deformation.

Study on Tensile Properties of Nanoreinforced Epoxy Polymer: Macroscopic Experiments and Nanoscale FEM Simulation Prediction

Directory of Open Access Journals (Sweden)

Zhenqing Wang

2013-01-01

Full Text Available The effect of nanosilica contents on mechanical properties of the epoxy matrix with some nanoparticle aggregations was studied in macroscopic experiments and nanoscale simulation, particularly with regard to the effective modulus and ultimate stress. Three analytical models were used to obtain the effective elastic modulus of nanoparticle-reinforced composites. Based on Monte-Carlo method, the special program for the automatic generation of 2D random distribution particles without overlapping was developed for nanocomposite modeling. Weight fractions of nanoparticles were converted to volume fractions, in order to coordinate the content unit in the simulation. In numerical analysis, the weak interface strengthening and toughening mechanism was adopted. Virtual crack closure technique (VCCT and extended finite element method (XFEM were used to simulate phenomena of nanoparticle debonding and matrix crack growth. Experimental and simulation results show a good agreement with each other. By way of simulation, the weak interface toughening and strengthening mechanism of nanocomposites is confirmed.

On the potential of computational methods and numerical simulation in ice mechanics

International Nuclear Information System (INIS)

Bergan, Paal G; Cammaert, Gus; Skeie, Geir; Tharigopula, Venkatapathi

2010-01-01

This paper deals with the challenge of developing better methods and tools for analysing interaction between sea ice and structures and, in particular, to be able to calculate ice loads on these structures. Ice loads have traditionally been estimated using empirical data and 'engineering judgment'. However, it is believed that computational mechanics and advanced computer simulations of ice-structure interaction can play an important role in developing safer and more efficient structures, especially for irregular structural configurations. The paper explains the complexity of ice as a material in computational mechanics terms. Some key words here are large displacements and deformations, multi-body contact mechanics, instabilities, multi-phase materials, inelasticity, time dependency and creep, thermal effects, fracture and crushing, and multi-scale effects. The paper points towards the use of advanced methods like ALE formulations, mesh-less methods, particle methods, XFEM, and multi-domain formulations in order to deal with these challenges. Some examples involving numerical simulation of interaction and loads between level sea ice and offshore structures are presented. It is concluded that computational mechanics may prove to become a very useful tool for analysing structures in ice; however, much research is still needed to achieve satisfactory reliability and versatility of these methods.

Simulation based engineering in solid mechanics

CERN Document Server

Rao, J S

2017-01-01

This book begins with a brief historical perspective of the advent of rotating machinery in 20th century Solid Mechanics and the development of the discipline of the Strength of Materials. High Performance Computing (HPC) and Simulation Based Engineering Science (SBES) have gradually replaced the conventional approach in Design bringing science directly into engineering without approximations. A recap of the required mathematical principles is given. The science of deformation, strain and stress at a point under the application of external traction loads is next presented. Only one-dimensional structures classified as Bars (axial loads), Rods (twisting loads) and Beams (bending loads) are considered in this book. The principal stresses and strains and von Mises stress and strain that used in design of structures are next presented. Lagrangian solution was used to derive the governing differential equations consistent with assumed deformation field and solution for deformations, strains and stresses were obtai...

The study, design and simulation of a free piston Stirling engine linear alternatorThe study, design and simulation of a free piston Stirling engine linear alternator

Directory of Open Access Journals (Sweden)

Teodora Susana Oros

2014-12-01

Full Text Available This paper presents a study, design and simulation of a Free Piston Stirling Engine Linear Alternator. There are presented the main steps of the magnetic and electric calculations for a permanent magnet linear alternator of fixed coil and moving magnets type. Finally, a detailed thermal, mechanical and electrical model for a Stirling engine linear alternator have been made in SIMULINK simulation program. The linear alternator simulation model uses a controllable DC voltage which simulates the linear alternator combined with a rectifier, a variable load and a DC-DC converter, which compensates for the variable nature of Stirling engine operation, and ensures a constant voltage output regardless of the load.

Numeric simulations of en-masse space closure with sliding mechanics.

Science.gov (United States)

Kojima, Yukio; Fukui, Hisao

2010-12-01

En-masse sliding mechanics have been typically used for space closure. Because of friction created at the bracket-wire interface, the force system during tooth movement has not been clarified. Long-term tooth movements in en-masse sliding mechanics were simulated with the finite element method. Tipping of the anterior teeth occurred immediately after application of retraction forces. The force system then changed so that the teeth moved almost bodily, and friction occurred at the bracket-wire interface. Net force transferred to the anterior teeth was approximately one fourth of the applied force. The amount of the mesial force acting on the posterior teeth was the same as that acting on the anterior teeth. Irrespective of the amount of friction, the ratio of movement distances between the posterior and anterior teeth was almost the same. By increasing the applied force or decreasing the frictional coefficient, the teeth moved rapidly, but the tipping angle of the anterior teeth increased because of the elastic deflection of the archwire. Finite element simulation clarified the tooth movement and the force system in en-masse sliding mechanics. Long-term tooth movement could not be predicted from the initial force system. The friction was not detrimental to the anchorage. Increasing the applied force or decreasing the friction for rapid tooth movement might result in tipping of the teeth. Copyright © 2010 American Association of Orthodontists. Published by Mosby, Inc. All rights reserved.

Mechanism of ENSO influence on the South Asian monsoon rainfall in global model simulations

Science.gov (United States)

Joshi, Sneh; Kar, Sarat C.

2018-02-01

Coupled ocean atmosphere global climate models are increasingly being used for seasonal scale simulation of the South Asian monsoon. In these models, sea surface temperatures (SSTs) evolve as coupled air-sea interaction process. However, sensitivity experiments with various SST forcing can only be done in an atmosphere-only model. In this study, the Global Forecast System (GFS) model at T126 horizontal resolution has been used to examine the mechanism of El Niño-Southern Oscillation (ENSO) forcing on the monsoon circulation and rainfall. The model has been integrated (ensemble) with observed, climatological and ENSO SST forcing to document the mechanism on how the South Asian monsoon responds to basin-wide SST variations in the Indian and Pacific Oceans. The model simulations indicate that the internal variability gets modulated by the SSTs with warming in the Pacific enhancing the ensemble spread over the monsoon region as compared to cooling conditions. Anomalous easterly wind anomalies cover the Indian region both at 850 and 200 hPa levels during El Niño years. The locations and intensity of Walker and Hadley circulations are altered due to ENSO SST forcing. These lead to reduction of monsoon rainfall over most parts of India during El Niño events compared to La Niña conditions. However, internally generated variability is a major source of uncertainty in the model-simulated climate.

COMPUTER SIMULATION THE MECHANICAL MOVEMENT BODY BY MEANS OF MATHCAD

Directory of Open Access Journals (Sweden)

Leonid Flehantov

2017-03-01

Full Text Available Here considered the technique of using computer mathematics system MathCAD for computer implementation of mathematical model of the mechanical motion of the physical body thrown at an angle to the horizon, and its use for educational computer simulation experiment in teaching the fundamentals of mathematical modeling. The advantages of MathCAD as environment of implementation mathematical models in the second stage of higher education are noted. It describes the creation the computer simulation model that allows you to comprehensively analyze the process of mechanical movement of the body, changing the input parameters of the model: the acceleration of gravity, the initial and final position of the body, the initial velocity and angle, the geometric dimensions of the body and goals. The technique aimed at the effective assimilation of basic knowledge and skills of students on the basics of mathematical modeling, it provides an opportunity to better master the basic theoretical principles of mathematical modeling and related disciplines, promotes logical thinking development of students, their motivation to learn discipline, improves cognitive interest, forms skills research activities than creating conditions for the effective formation of professional competence of future specialists.

Component simulation in problems of calculated model formation of automatic machine mechanisms

OpenAIRE

Telegin Igor; Kozlov Alexander; Zhirkov Alexander

2017-01-01

The paper deals with the problems of the component simulation method application in the problems of the automation of the mechanical system model formation with the further possibility of their CAD-realization. The purpose of the investigations mentioned consists in the automation of the CAD-model formation of high-speed mechanisms in automatic machines and in the analysis of dynamic processes occurred in their units taking into account their elasto-inertial properties, power dissipation, gap...

A mechanical mechanism for translocation of ring-shaped helicases on DNA and its demonstration in a macroscopic simulation system

Science.gov (United States)

Chou, Y. C.

2018-04-01

The asymmetry in the two-layered ring structure of helicases and the random thermal fluctuations of the helicase and DNA molecules are considered as the bases for the generation of the force required for translocation of the ring-shaped helicase on DNA. The helicase comprises a channel at its center with two unequal ends, through which strands of DNA can pass. The random collisions between the portion of the DNA strand in the central channel and the wall of the channel generate an impulsive force toward the small end. This impulsive force is the starting point for the helicase to translocate along the DNA with the small end in front. Such a physical mechanism may serve as a complementary for the chemomechanical mechanism of the translocation of helicase on DNA. When the helicase arrives at the junction of ssDNA and dsDNA (a fork), the collision between the helicase and the closest base pair may produce a sufficient impulsive force to break the weak hydrogen bond of the base pair. Thus, the helicase may advance and repeat the process of unwinding the dsDNA strand. This mechanism was tested in a macroscopic simulation system where the helicase was simulated using a truncated-cone structure and DNA was simulated with bead chains. Many features of translocation and unwinding such as translocation on ssDNA and dsDNA, unwinding of dsDNA, rewinding, strand switching, and Holliday junction resolution were reproduced.

Some experimental considerations regarding ion beam simulation of neutron irradiation for mechanical property measurements

International Nuclear Information System (INIS)

Styris, D.L.; Jones, R.H.; Harling, O.K.; Kulcinski, G.L.; Marshall, R.P.

1975-01-01

A preliminary assessment of the requirements for mechanical property data related to CTR materials is given. The status of ion simulation for mechanical property measurements is described. A damage analysis and calculations for light ions are presented along with sample size, heating and cooling, and surface considerations

Investigation of Mechanical Properties and Fracture Simulation of Solution-Treated AA 5754

Science.gov (United States)

Kumar, Pankaj; Singh, Akhilendra

2017-10-01

In this work, mechanical properties and fracture toughness of as-received and solution-treated aluminum alloy 5754 (AA 5754) are experimentally evaluated. Solution heat treatment of the alloy is performed at 530 °C for 2 h, and then, quenching is done in water. Yield strength, ultimate tensile strength, impact toughness, hardness, fatigue life, brittle fracture toughness (K_{Ic} ) and ductile fracture toughness (J_{Ic} ) are evaluated for as-received and solution-treated alloy. Extended finite element method has been used for the simulation of tensile and fracture behavior of material. Heaviside function and asymptotic crack tip enrichment functions are used for modelling of the crack in the geometry. Ramberg-Osgood material model coupled with fracture energy is used to simulate the crack propagation. Fracture surfaces obtained from various mechanical tests are characterized by scanning electron microscopy.

Study, simulation and design of a 3D clinostat

Science.gov (United States)

Pavone, Valentina; Guarnieri, Vincenzo; Lobascio, Cesare; Soma, Aurelio; Bosso, Nicola; Lamantea, Matteo Maria

High cost and limited number of physically executable experiments in space have introduced the need for ground simulation systems that enable preparing experiments to be carried out on board, identifying phenomena associated with the altered gravity conditions, and taking advantage of these conditions, as in Biotechnology. Among systems developed to simulate microgravity, especially for life sciences experiments, different types of clinostats were realized. This work deals with mechanical design of a three-dimensional clinostat and simulation of the dynamic behavior of the system by varying the operating parameters. The design and simulation phase was preceded by a careful analysis of the state of art and by the review of the most recent results, in particular from the major investigators of Life Sciences in Space. The mechanical design is quite innovative by adoption of a structure entirely in aluminum, which allows robustness while reducing the overall weight. The transmission system of motion has been optimized by means of brushless DC micro motors, light and compact, which helped to reduce weight, dimensions, power consumption and increase the reliability and durability of the system. The study of the dynamic behavior using SIMPACK, a multibody simulation software, led to results in line with those found in the most important and recent scientific publications. This model was also appropriately configured to represent any desired operating condition, and for eventual system scalability. It would be interesting to generate simulated hypogravity - e.g.: 0.38-g (Mars) or 0.17-g (Moon). This would allow to investigate how terrestrial life forms can grow in other planetary habitats, or to determine the gravity threshold response of different organisms. At the moment, such a system can only be achieved by centrifuges in real microgravity. We are confident that simulation and associated tests with our 3D clinostat can help adjusting the parameters allowing variable g

Hybrid simulation research on formation mechanism of tungsten nanostructure induced by helium plasma irradiation

Energy Technology Data Exchange (ETDEWEB)

Ito, Atsushi M., E-mail: ito.atsushi@nifs.ac.jp [National Institute for Fusion Science, 322-6 Oroshi-cho, Toki 509-5292 (Japan); Takayama, Arimichi; Oda, Yasuhiro [National Institute for Fusion Science, 322-6 Oroshi-cho, Toki 509-5292 (Japan); Tamura, Tomoyuki; Kobayashi, Ryo; Hattori, Tatsunori; Ogata, Shuji [Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya 466-8555 (Japan); Ohno, Noriyasu; Kajita, Shin [Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603 (Japan); Yajima, Miyuki [National Institute for Fusion Science, 322-6 Oroshi-cho, Toki 509-5292 (Japan); Noiri, Yasuyuki [Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603 (Japan); Yoshimoto, Yoshihide [University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656 (Japan); Saito, Seiki [Kushiro National College of Technology, Kushiro, Hokkaido 084-0916 (Japan); Takamura, Shuichi [Aichi Institute of Technology, 1247 Yachigusa, Yakusa-cho, Toyota 470-0392 (Japan); Murashima, Takahiro [Tohoku University, 6-3, Aramaki-Aza-Aoba, Aoba-Ward, Sendai 980-8578 (Japan); Miyamoto, Mitsutaka [Shimane University, Matsue, Shimane 690-8504 (Japan); Nakamura, Hiroaki [National Institute for Fusion Science, 322-6 Oroshi-cho, Toki 509-5292 (Japan); Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603 (Japan)

2015-08-15

The generation of tungsten fuzzy nanostructure by exposure to helium plasma is one of the important problems for the use of tungsten material as divertor plates in nuclear fusion reactors. In the present paper, the formation mechanisms of the helium bubble and the tungsten fuzzy nanostructure were investigated by using several simulation methods. We proposed the four-step process which is composed of penetration step, diffusion and agglomeration step, helium bubble growth step, and fuzzy nanostructure formation step. As the fourth step, the formation of the tungsten fuzzy nanostructure was successfully reproduced by newly developed hybrid simulation combining between molecular dynamics and Monte-Carlo method. The formation mechanism of tungsten fuzzy nanostructure observed by the hybrid simulation is that concavity and convexity of the surface are enhanced by the bursting of helium bubbles in the region around the concavity.

The mechanisms of substrates interaction with the active site of Mycobacterium tuberculosis tyrosyl-tRNA synthetase studied by molecular dynamics simulations

Directory of Open Access Journals (Sweden)

Mykuliak V. V.

2014-03-01

Full Text Available Aim. To study the mechanisms of substrates interaction with the active site of Mycobacterium tuberculosis tyrosyl-tRNA synthetase (MtTyrRS. Methods. Complexes of MtTyrRS with tyrosine, ATP and tyrosyl adenylate were constructed by superposition of the MtTyrRS structure and crystallographic structures of bacterial TyrRS. All complexes of MtTyrRS with substrates were investigated by molecular dynamics (MD simulations in solution. Results. It was shown the formation of network of hydrogen bonds between substrates and the MtTyrRS active center, which were stable in the course of MD simulations. ATP binds in the active site both by hydrogen bonds and via electrostatic interactions with Lys231 and Lys234 of catalytic KFGKS motif. Conclusions. The L-tyrosine binding site in the enzyme active site is negatively charged, whereas the ATP binding site contains positive Lys231 and Lys234 residues of catalytic KFGKS motif. The occupancy of H-bonds between substrates and the enzyme evidences a significant conformational mobility of the active site.

Control and Virtual Reality Simulation of Tendon Driven Mechanisms

International Nuclear Information System (INIS)

Londi, Fabio; Pennestri, Ettore; Valentini, Pier Paolo; Vita, Leonardo

2004-01-01

In this paper the authors present a control strategy for tendon driven mechanisms. The aim of the control system is to find the correct torques which the motors have to exert to make the end effector describe a specific trajectory. In robotic assemblies this problem is often solved with closed loop algorithm, but here a simpler method, based on a open loop strategy, is developed. The difficulties in the actuation are in keeping the belt tight during all working conditions. So an innovative solution of this problem is presented here. This methodology can be easily applied in real time monitoring or very fast operations. For this reason several virtual reality simulations, developed using codes written in Virtual Reality Markup Language, are also presented. This approach is very efficient because it requires a very low cpu computation time, small size files, and the manipulator can be easily put into different simulated scenarios

Development of mechanical analysis module for simulation of SFR fuel rod behavior using finite element method

International Nuclear Information System (INIS)

Shin, Andong; Jeong, Hyedong; Suh, Namduk; Kim, Hyochan; Yang, Yongsik

2014-01-01

Korean SFR developer decided to adapt metal fuel, current study focused on the metal fuel instead of oxide fuel. The SFR metal fuel has been developed by Korea Atomic Energy Research Institute (KAERI) and many efforts focused on designing and manufacturing the metal fuel. Since a nuclear fuel is the first barrier to protect radioactive isotope release, the fuel's integrity must be secured during steady-state operation and accident condition within an acceptable range. Whereas the design and evaluation methodologies, code systems and test procedures of a light water reactor fuel are sufficiently established, those of the SFR fuel needs more technical advances. In the view of regulatory point, there are still many challenging issues which are required to secure the safety of fuel and reactors. For this reason, the Korea Institute of Nuclear Safety (KINS) has launched the new project to develop the regulatory technology for SFR system including a fuel area. The ALFUS code was developed by CRIEPI and employs mechanistic model for fission gas release and swelling of fuel slug. In the code system, a finite element method was introduced to analyze the fuel and cladding's mechanical behaviors. The FEAST code is more advanced code system for SFR which adopted mechanistic FGR and swelling model but still use analytical model to simulate fuel and cladding mechanical behavior. Based on the survey of the previous studies, fuel and cladding mechanical model should be improved. Analysis of mechanical behavior for fuel rod is crucial to evaluate overall rod's integrity. In addition, it is because contact between fuel slug and cladding or an over-pressure of rod internal pressure can cause rod failure during steady-state and other operation condition. The most of reference codes have simplified mechanical analysis model, so called 'analytical mode', because the detailed mechanical analysis requires large amount of calculation time and computing power. Even

Development of mechanical analysis module for simulation of SFR fuel rod behavior using finite element method

Energy Technology Data Exchange (ETDEWEB)

Shin, Andong; Jeong, Hyedong; Suh, Namduk [Korea Institute of Nuclear Safety, Daejeon (Korea, Republic of); Kim, Hyochan; Yang, Yongsik [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)

2014-10-15

Korean SFR developer decided to adapt metal fuel, current study focused on the metal fuel instead of oxide fuel. The SFR metal fuel has been developed by Korea Atomic Energy Research Institute (KAERI) and many efforts focused on designing and manufacturing the metal fuel. Since a nuclear fuel is the first barrier to protect radioactive isotope release, the fuel's integrity must be secured during steady-state operation and accident condition within an acceptable range. Whereas the design and evaluation methodologies, code systems and test procedures of a light water reactor fuel are sufficiently established, those of the SFR fuel needs more technical advances. In the view of regulatory point, there are still many challenging issues which are required to secure the safety of fuel and reactors. For this reason, the Korea Institute of Nuclear Safety (KINS) has launched the new project to develop the regulatory technology for SFR system including a fuel area. The ALFUS code was developed by CRIEPI and employs mechanistic model for fission gas release and swelling of fuel slug. In the code system, a finite element method was introduced to analyze the fuel and cladding's mechanical behaviors. The FEAST code is more advanced code system for SFR which adopted mechanistic FGR and swelling model but still use analytical model to simulate fuel and cladding mechanical behavior. Based on the survey of the previous studies, fuel and cladding mechanical model should be improved. Analysis of mechanical behavior for fuel rod is crucial to evaluate overall rod's integrity. In addition, it is because contact between fuel slug and cladding or an over-pressure of rod internal pressure can cause rod failure during steady-state and other operation condition. The most of reference codes have simplified mechanical analysis model, so called 'analytical mode', because the detailed mechanical analysis requires large amount of calculation time and computing power. Even

COMPUTER SIMULATION IN MECHANICS TEACHING AND LEARNING: A CASE STUDY ON STUDENTS’ UNDERSTANDING OF FORCE AND MOTION

Directory of Open Access Journals (Sweden)

Dyah Permata Sari

2015-12-01

Full Text Available The objective of this research was to develop a force and motion simulation based on the open-source Easy Java Simulation. The process of computer simulation development was done following the ADDIE model. Based on the Analysis and Design phases, the Development phase used the open-source Easy Java Simulation (EJS to develop a computer simulation with physics content that was relevant to the subtopic. Computing and communication technology continue to make an increasing impact on all aspects of education. EJS is a powerful didactic resource that gives us the ability to focus our students’ attention on the principles of physics. Using EJS, a computer simulation was created through which the motion of a particle under the action of a specific force can be studied. The implementation phase is implemented the computer simulation in the teaching and learning process. To describe the improvements in the students’ understanding of the force and motion concepts, we used a t-test to evaluate each of the four phases. These results indicated that the use of the computer simulation could improve students’ force and motion conceptual competence regarding Newton's second law of motion.

Thermo-hydro-mechanical simulation of a 3D fractured porous rock: preliminary study of coupled matrix-fracture hydraulics

International Nuclear Information System (INIS)

Canamon, I.; Javier Elorza, F.; Ababou, R.

2007-01-01

We present a problem involving the modeling of coupled flow and elastic strain in a 3D fractured porous rock, which requires prior homogenization (up-scaling) of the fractured medium into an equivalent Darcian anisotropic continuum. The governing equations form a system of PDE's (Partial Differential Equations) and, depending on the case being considered, this system may involve two different types of 'couplings' (in a real system, both couplings (1) and (2) generally take place): 1) Hydraulic coupling in a single (no exchange) or in a dual matrix-fracture continuum (exchange); 2) Thermo-Hydro-Mechanical interactions between fluid flow, pressure, elastic stress, strain, and temperature. We present here a preliminary model and simulation results with FEMLAB R , for the hydraulic problem with anisotropic heterogeneous coefficients. The model is based on data collected at an instrumented granitic site (FEBEX project) for studying a hypothetical nuclear waste repository at the Grimsel Test Site in the Swiss Alps. (authors)

Thermo-hydro-mechanical simulation of a 3D fractured porous rock: preliminary study of coupled matrix-fracture hydraulics

Energy Technology Data Exchange (ETDEWEB)

Canamon, I.; Javier Elorza, F. [Universidad Politecnica de Madrid, Dept. de Matematica Aplicada y Metodos Informaticas, ETSI Minas (UPM) (Spain); Ababou, R. [Institut de Mecanique des Fluides de Toulouse (IMFT), 31 (France)

2007-07-01

We present a problem involving the modeling of coupled flow and elastic strain in a 3D fractured porous rock, which requires prior homogenization (up-scaling) of the fractured medium into an equivalent Darcian anisotropic continuum. The governing equations form a system of PDE's (Partial Differential Equations) and, depending on the case being considered, this system may involve two different types of 'couplings' (in a real system, both couplings (1) and (2) generally take place): 1) Hydraulic coupling in a single (no exchange) or in a dual matrix-fracture continuum (exchange); 2) Thermo-Hydro-Mechanical interactions between fluid flow, pressure, elastic stress, strain, and temperature. We present here a preliminary model and simulation results with FEMLAB{sup R}, for the hydraulic problem with anisotropic heterogeneous coefficients. The model is based on data collected at an instrumented granitic site (FEBEX project) for studying a hypothetical nuclear waste repository at the Grimsel Test Site in the Swiss Alps. (authors)

Phase transition and mechanical properties of tungsten nanomaterials from molecular dynamic simulation

Energy Technology Data Exchange (ETDEWEB)

Chen, L.; Fan, J. L.; Gong, H. R., E-mail: gonghr@csu.edu.cn [Central South University, State Key Laboratory of Powder Metallurgy (China)

2017-03-15

Molecular dynamic simulation is used to systematically find out the effects of the size and shape of nanoparticles on phase transition and mechanical properties of W nanomaterials. It is revealed that the body-centered cubic (BCC) to face-centered cubic (FCC) phase transition could only happen in cubic nanoparticles of W, instead of the shapes of sphere, octahedron, and rhombic dodecahedron, and that the critical number to trigger the phase transition is 5374 atoms. Simulation also shows that the FCC nanocrystalline W should be prevented due to its much lower tensile strength than its BCC counterpart and that the octahedral and rhombic dodecahedral nanoparticles of W, rather than the cubic nanoparticles, should be preferred in terms of phase transition and mechanical properties. The derived results are discussed extensively through comparing with available observations in the literature to provide a deep understanding of W nanomaterials.

Analysis of nanowire transistor based nitrogen dioxide gas sensor – A simulation study

Directory of Open Access Journals (Sweden)

Gaurav Saxena

2015-06-01

Full Text Available Sensors sensitivity, selectivity and stability has always been a prime design concern for gas sensors designers. Modeling and simulation of gas sensors aids the designers in improving their performance. In this paper, different routes for the modeling and simulation of a semiconducting gas sensor is presented. Subsequently, by employing one of the route, the response of Zinc Oxide nanowire transistor towards nitrogen dioxide ambient is simulated. In addition to the sensing mechanism, simulation study of gas species desorption by applying a recovery voltage is also presented.

Atomistic mechanism of microRNA translation upregulation via molecular dynamics simulations.

Directory of Open Access Journals (Sweden)

Wei Ye

Full Text Available MicroRNAs are endogenous 23-25 nt RNAs that play important gene-regulatory roles in animals and plants. Recently, miR369-3 was found to upregulate translation of TNFα mRNA in quiescent (G0 mammalian cell lines. Knock down and immunofluorescence experiments suggest that microRNA-protein complexes (with FXR1 and AGO2 are necessary for the translation upregulation. However the molecular mechanism of microRNA translation activation is poorly understood. In this study we constructed the microRNA-mRNA-AGO2-FXR1 quadruple complex by bioinformatics and molecular modeling, followed with all atom molecular dynamics simulations in explicit solvent to investigate the interaction mechanisms for the complex. A combined analysis of experimental and computational data suggests that AGO2-FXR1 complex relocalize microRNA:mRNA duplex to polysomes in G0. The two strands of dsRNA are then separated upon binding of AGO2 and FXR1. Finally, polysomes may improve the translation efficiency of mRNA. The mutation research confirms the stability of microRNA-mRNA-FXR1 and illustrates importance of key residue of Ile304. This possible mechanism can shed more light on the microRNA-dependent upregulation of translation.

Understanding Demographic and Behavioral Mechanisms that Guide Responses of Neotropical Migratory Birds to Urbanization: a Simulation Approach

Directory of Open Access Journals (Sweden)

Daniel P. Shustack

2008-12-01

Full Text Available Although studies often report that densities of many forest birds are negatively related to urbanization, the mechanisms guiding this pattern are poorly understood. Our objective was to use a population simulation to examine the relative influence of six demographic and behavioral processes on patterns of avian abundance in urbanizing landscapes. We constructed an individual-based population simulation model representing the annual cycle of a Neotropical migratory songbird. Each simulation was performed under two landscape scenarios. The first scenario had similar proportions of high- and low-quality habitat across the urban to rural gradient. Under the first scenario, avian density was negatively related to urbanization only when rural habitats were perceived to be of higher quality than they actually were. The second landscape scenario had declining proportions of high-quality habitat as urbanization increased. Under the second scenario, each mechanism generated a negative relationship between density and urbanization. The strongest effect on density resulted when birds preferentially selected habitats in landscapes from which they fledged or were constrained from dispersing. The next strongest patterns occurred when birds directly evaluated habitat quality and accurately selected the highest-quality available territories. When birds selected habitats based on the presence of conspecifics, the density-urbanization relationship was only one-third the strength of other habitat selection mechanisms and only occurred under certain levels of population survival. Although differences in adult or nest survival in the face of random habitat selection still elicited reduced densities in urban landscapes, the relationships between urbanization and density were weaker than those produced by the conspecific attraction mechanism. Results from our study identify key predictions and areas for future research, including assessing habitat quality in urban and

Simulating the mammalian blastocyst--molecular and mechanical interactions pattern the embryo.

Directory of Open Access Journals (Sweden)

Pawel Krupinski

2011-05-01

Full Text Available Mammalian embryogenesis is a dynamic process involving gene expression and mechanical forces between proliferating cells. The exact nature of these interactions, which determine the lineage patterning of the trophectoderm and endoderm tissues occurring in a highly regulated manner at precise periods during the embryonic development, is an area of debate. We have developed a computational modeling framework for studying this process, by which the combined effects of mechanical and genetic interactions are analyzed within the context of proliferating cells. At a purely mechanical level, we demonstrate that the perpendicular alignment of the animal-vegetal (a-v and embryonic-abembryonic (eb-ab axes is a result of minimizing the total elastic conformational energy of the entire collection of cells, which are constrained by the zona pellucida. The coupling of gene expression with the mechanics of cell movement is important for formation of both the trophectoderm and the endoderm. In studying the formation of the trophectoderm, we contrast and compare quantitatively two hypotheses: (1 The position determines gene expression, and (2 the gene expression determines the position. Our model, which couples gene expression with mechanics, suggests that differential adhesion between different cell types is a critical determinant in the robust endoderm formation. In addition to differential adhesion, two different testable hypotheses emerge when considering endoderm formation: (1 A directional force acts on certain cells and moves them into forming the endoderm layer, which separates the blastocoel and the cells of the inner cell mass (ICM. In this case the blastocoel simply acts as a static boundary. (2 The blastocoel dynamically applies pressure upon the cells in contact with it, such that cell segregation in the presence of differential adhesion leads to the endoderm formation. To our knowledge, this is the first attempt to combine cell-based spatial

Dynamic coarse-graining fills the gap between atomistic simulations and experimental investigations of mechanical unfolding

Science.gov (United States)

Knoch, Fabian; Schäfer, Ken; Diezemann, Gregor; Speck, Thomas

2018-01-01

We present a dynamic coarse-graining technique that allows one to simulate the mechanical unfolding of biomolecules or molecular complexes on experimentally relevant time scales. It is based on Markov state models (MSMs), which we construct from molecular dynamics simulations using the pulling coordinate as an order parameter. We obtain a sequence of MSMs as a function of the discretized pulling coordinate, and the pulling process is modeled by switching among the MSMs according to the protocol applied to unfold the complex. This way we cover seven orders of magnitude in pulling speed. In the region of rapid pulling, we additionally perform steered molecular dynamics simulations and find excellent agreement between the results of the fully atomistic and the dynamically coarse-grained simulations. Our technique allows the determination of the rates of mechanical unfolding in a dynamical range from approximately 10-8/ns to 1/ns thus reaching experimentally accessible time regimes without abandoning atomistic resolution.

Athermal mechanisms of size-dependent crystal flow gleaned from three-dimensional discrete dislocation simulations

International Nuclear Information System (INIS)

Rao, S.I.; Dimiduk, D.M.; Parthasarathy, T.A.; Uchic, M.D.; Tang, M.; Woodward, C.

2008-01-01

Recent experimental studies have revealed that micrometer-scale face-centered cubic (fcc) crystals show strong strengthening effects, even at high initial dislocation densities. We use large-scale three-dimensional discrete dislocation simulations (DDS) to explicitly model the deformation behavior of fcc Ni microcrystals in the size range of 0.5-20 μm. This study shows that two size-sensitive athermal hardening processes, beyond forest hardening, are sufficient to develop the dimensional scaling of the flow stress, stochastic stress variation, flow intermittency and high initial strain-hardening rates, similar to experimental observations for various materials. One mechanism, source-truncation hardening, is especially potent in micrometer-scale volumes. A second mechanism, termed exhaustion hardening, results from a breakdown of the mean-field conditions for forest hardening in small volumes, thus biasing the statistics of ordinary dislocation processes

Study on dynamic lifting characteristics of control rod drive mechanism

International Nuclear Information System (INIS)

Shen Xiaoyao

2012-01-01

Based on the equations of the electric circuit and the magnetic circuit and analysis of the dynamic lifting process for the control rod drive mechanism (CRDM), coupled magnetic-electric-mechanical equations both for the static status and the dynamic status are derived. The analytical method is utilized to obtain the current and the time when the lift starts. The numerical simulation method of dynamic analysis recommended by ASME Code is utilized to simulate the dynamic lifting process of CRDM, and the dynamic features of the system with different design gaps are studied. Conclusions are drawn as: (1) the lifting-start time increases with the design gap, and the time for the lifting process is longer with larger gaps; (2) the lifting velocity increases with time; (3) the lifting acceleration increases with time, and with smaller gaps, the impact acceleration is larger. (author)

Studies Regarding Design and Optimization of Mechanisms Using Modern Techniques of CAD and CAE

Directory of Open Access Journals (Sweden)

Marius Tufoi

2010-01-01

Full Text Available The paper presents applications of modern techniques of CAD (Computer Aided Design and CAE (Computer Aided Engineering to design and optimize the mechanisms used in mechanical engineering. The use exemplification of these techniques was achieved by designing and optimizing parts of a drawing installation for horizontal continuous casting of metals. By applying these design methods and using finite element method at simulations on designed mechanisms results a number of advantages over traditional methods of drawing and design: speed in drawing, design and optimization of parts and mechanisms, kinematic analysis option, kinetostatic and dynamic through simulation, without requiring physical realization of the part or mechanism, the determination by finite element method of tension, elongations, travel and safety factor and the possibility of optimization for these sizes to ensure the mechanical strength of each piece separately. Achieving these studies was possible using SolidWorks 2009 software suite.

Understanding the mechanisms of amorphous creep through molecular simulation.

Science.gov (United States)

Cao, Penghui; Short, Michael P; Yip, Sidney

2017-12-26

Molecular processes of creep in metallic glass thin films are simulated at experimental timescales using a metadynamics-based atomistic method. Space-time evolutions of the atomic strains and nonaffine atom displacements are analyzed to reveal details of the atomic-level deformation and flow processes of amorphous creep in response to stress and thermal activations. From the simulation results, resolved spatially on the nanoscale and temporally over time increments of fractions of a second, we derive a mechanistic explanation of the well-known variation of creep rate with stress. We also construct a deformation map delineating the predominant regimes of diffusional creep at low stress and high temperature and deformational creep at high stress. Our findings validate the relevance of two original models of the mechanisms of amorphous plasticity: one focusing on atomic diffusion via free volume and the other focusing on stress-induced shear deformation. These processes are found to be nonlinearly coupled through dynamically heterogeneous fluctuations that characterize the slow dynamics of systems out of equilibrium.

Development and mechanical properties of structural materials from lunar simulants

Science.gov (United States)

Desai, Chandra S.; Girdner, K.; Saadatmanesh, H.; Allen, T.

1991-01-01

Development of the technologies for manufacture of structural and construction materials on the Moon, utilizing local lunar soil (regolith), without the use of water, is an important element for habitats and explorations in space. Here, it is vital that the mechanical behavior such as strength and flexural properties, fracture toughness, ductility and deformation characteristics be defined toward establishment of the ranges of engineering applications of the materials developed. The objective is to describe the research results in two areas for the above goal: (1) liquefaction of lunar simulant (at about 100 C) with different additives (fibers, powders, etc.); and (2) development and use of a new triaxial test device in which lunar simulants are first compressed under cycles of loading, and then tested with different vacuums and initial confining or in situ stress.

3D numerical simulation and analysis of railgun gouging mechanism

Directory of Open Access Journals (Sweden)

Jin-guo Wu

2016-04-01

Full Text Available A gouging phenomenon with a hypervelocity sliding electrical contact in railgun not only shortens the rail lifetime but also affects the interior ballistic performance. In this paper, a 3-D numerical model was introduced to simulate and analyze the generation mechanism and evolution of the rail gouging phenomenon. The results show that a rail surface bulge is an important factor to induce gouging. High density and high pressure material flow on the contact surface, obliquely extruded into the rail when accelerating the armature to a high velocity, can produce gouging. Both controlling the bulge size to a certain range and selecting suitable materials for rail surface coating will suppress the formation of gouging. The numerical simulation had a good agreement with experiments, which validated the computing model and methodology are reliable.

Metal-ceramic materials. Study and prediction of effective mechanical properties

International Nuclear Information System (INIS)

Karakulov, Valerii V.; Smolin, Igor Yu.

2016-01-01

Mechanical behavior of stochastic metal-ceramic composite materials was numerically simulated on mesoscopic scale level. Deformation of mesoscopic volumes of composites, whose structure consists of a metal matrix and randomly distributed ceramic inclusions, was numerically simulated. The results of the numerical simulation were used for evaluation of the effective elastic and strength properties of metal-ceramic materials with different parameters of the structure. The values of the effective mechanical properties of investigated materials were obtained, and the character of the dependence of the effective elastic and strength properties on the structure parameters of composites was determined.

3D simulation studies of tokamak plasmas using MHD and extended-MHD models

International Nuclear Information System (INIS)

Park, W.; Chang, Z.; Fredrickson, E.; Fu, G.Y.

1996-01-01

The M3D (Multi-level 3D) tokamak simulation project aims at the simulation of tokamak plasmas using a multi-level tokamak code package. Several current applications using MHD and Extended-MHD models are presented; high-β disruption studies in reversed shear plasmas using the MHD level MH3D code, ω *i stabilization and nonlinear island saturation of TAE mode using the hybrid particle/MHD level MH3D-K code, and unstructured mesh MH3D ++ code studies. In particular, three internal mode disruption mechanisms are identified from simulation results which agree which agree well with experimental data

Study of anisotropic mechanical properties for aeronautical PMMA

Directory of Open Access Journals (Sweden)

Wei Shang

Full Text Available For the properties of polymer are relative to its structure, the main purpose of the present work is to investigate the mechanical properties of the aeronautical PMMA which has been treated by the directional tensile technology. Isodyne images reveal the stress state in directional PMMA. And then, an anisotropic mechanical model is established. Furthermore, all mechanical parameters are measured by the digital image correlation method. Finally, based on the anisotropic mechanical model and mechanical parameters, the FEM numerical simulation and experimental methods are applied to analyze the fracture mechanical properties along different directions.

Simulating and visualizing deflections of a remote handling mechanism

International Nuclear Information System (INIS)

Saarinen, Hannu; Hämäläinen, Vesa; Karjalainen, Jaakko; Määttä, Timo; Siuko, Mikko; Esqué, Salvador; Hamilton, David

2013-01-01

Highlights: ► An infinitesimal transformation represents elastic deflections. ► Equivalent spring factor is used to combine several deformations. ► Initial VR model accuracy improved from 80 to 5 mm. ► The deflection model is capable of adapting to changes in load at the end-effector. ► The algorithms and approach described are generic and can be adopted for other mechanisms. -- Abstract: Continuing ITER divertor second cassette (SC) remote handling (RH) test campaign has been carried out at divertor test platform (DTP2) in Finland. One of the goals has been to develop and implement efficient algorithms and software tools for simulating and visualizing for the operator the non-instrumented deflections of the RH mechanisms under loading conditions. Based on assumptions of the classical beam theory, the presented solution suggests utilization of an infinitesimal transformation to represent elastic deflections in a mechanical structure. Both structural analysis and measurements of the real structure are utilised during the process. The solution suggests one possible implementation strategy of a software component called structural simulator (SS), which is a software component of the remote handling control system (RHCS) architectural model specified by ITER organisation. Utilisation of the proposed SS necessitates modification of the initial virtual reality (VR) model of RH equipment to a format, which can visually represent the structural deflections. In practise this means adding virtual joints into the model. This will improve the accuracy of the VR visualization and will ensure that the virtual representation of the RH equipment closely aligns with the actual RH equipment. Cassette multifunctional mover (CMM) and second cassette end effector (SCEE) carrying SC were selected to be the initial target system for developing the approach. Demonstrations proved that the approach used can give high levels of accuracy even in complex structures such as the CMM

Simulating and visualizing deflections of a remote handling mechanism

Energy Technology Data Exchange (ETDEWEB)

Saarinen, Hannu, E-mail: hannu.saarinen@vtt.fi [VTT, Technical Research Centre of Finland, Tekniikankatu 1, 33720 Tampere (Finland); Hämäläinen, Vesa; Karjalainen, Jaakko; Määttä, Timo; Siuko, Mikko [VTT, Technical Research Centre of Finland, Tekniikankatu 1, 33720 Tampere (Finland); Esqué, Salvador [Fusion for Energy, Torres Diagonal Litoral B3, Josep Pla 2, 08019 Barcelona (Spain); Hamilton, David [ITER Organization, Route de Vinon sur Verdon, 13115 Saint Paul Lez Durance (France)

2013-10-15

Highlights: ► An infinitesimal transformation represents elastic deflections. ► Equivalent spring factor is used to combine several deformations. ► Initial VR model accuracy improved from 80 to 5 mm. ► The deflection model is capable of adapting to changes in load at the end-effector. ► The algorithms and approach described are generic and can be adopted for other mechanisms. -- Abstract: Continuing ITER divertor second cassette (SC) remote handling (RH) test campaign has been carried out at divertor test platform (DTP2) in Finland. One of the goals has been to develop and implement efficient algorithms and software tools for simulating and visualizing for the operator the non-instrumented deflections of the RH mechanisms under loading conditions. Based on assumptions of the classical beam theory, the presented solution suggests utilization of an infinitesimal transformation to represent elastic deflections in a mechanical structure. Both structural analysis and measurements of the real structure are utilised during the process. The solution suggests one possible implementation strategy of a software component called structural simulator (SS), which is a software component of the remote handling control system (RHCS) architectural model specified by ITER organisation. Utilisation of the proposed SS necessitates modification of the initial virtual reality (VR) model of RH equipment to a format, which can visually represent the structural deflections. In practise this means adding virtual joints into the model. This will improve the accuracy of the VR visualization and will ensure that the virtual representation of the RH equipment closely aligns with the actual RH equipment. Cassette multifunctional mover (CMM) and second cassette end effector (SCEE) carrying SC were selected to be the initial target system for developing the approach. Demonstrations proved that the approach used can give high levels of accuracy even in complex structures such as the CMM

Development of a Procedure to Apply Detailed Chemical Kinetic Mechanisms to CFD Simulations as Post Processing

DEFF Research Database (Denmark)

Skjøth-Rasmussen, Martin Skov; Glarborg, Peter; Jensen, Anker

2003-01-01

mechanism. It involves post-processing of data extracted from computational fluid dynamics simulations. Application of this approach successfully describes combustion chemistry in a standard swirl burner, the so-called Harwell furnace. Nevertheless, it needs validation against more complex combustion models......It is desired to make detailed chemical kinetic mechanisms applicable to the complex geometries of practical combustion devices simulated with computational fluid dynamics tools. This work presents a novel general approach to combining computational fluid dynamics and a detailed chemical kinetic...

3D simulation studies of tokamak plasmas using MHD and extended-MHD models

International Nuclear Information System (INIS)

Park, W.; Chang, Z.; Fredrickson, E.; Fu, G.Y.; Pomphrey, N.; Sugiyama, L.E.

1997-01-01

The M3D (Multi-level 3D) tokamak simulation project aims at the simulation of tokamak plasmas using a multi-level tokamak code package. Several current applications using MHD and Extended-MHD models are presented; high-β disruption studies in reversed shear plasmas using the MHD level MH3D code, ω *i stabilization and nonlinear island rotation studies using the two-fluid level MH3D-T code, studies of nonlinear saturation of TAE modes using the hybrid particle/MHD level MH3D-K code, and unstructured mesh MH3D ++ code studies. In particular, three internal mode disruption mechanisms are identified from simulation results which agree well with experimental data

Large eddy simulation of a mechanically ventilated compartment fire for nuclear applications

Energy Technology Data Exchange (ETDEWEB)

Xu, Bao P. [Dalian Univ. of Technology (China). Faculty of Energy and Power Engineering; Wen, Jennifer X. [Warwick Univ. (United Kingdom). Warwick FIRE, School of Engineering

2015-12-15

This paper deals with the modelling of a mechanically ventilated compartment fire which is a commonplace in nuclear fire scenarios. An advanced Computational Fluid Dynamics (CFD) field model with a wall conjugate heat transfer treatment is proposed. It simultaneously solves the compartment fire flow and the wall heat conduction. The flow solver is based on the Large Eddy Simulation (LES) based fire simulation solver FireFOAM within the frame of open source CFD code OpenFOAM {sup registered}. An extended eddy dissipation model is used to calculate the chemical reaction rate. A soot model based on the concept of smoke point height is employed to model the soot formation and oxidation. A finite volume method is adopted to model the radiative heat transfer. The ventilation flow is modelled by a simplified Bernoulli equation neglecting the detailed information on the ventilation system. The proposed model is validated against a single room fire test with forced mechanical ventilations. The predictions are in reasonably good agreement with experimental data.

[The virtual reality simulation research of China Mechanical Virtual Human based on the Creator/Vega].

Science.gov (United States)

Wei, Gaofeng; Tang, Gang; Fu, Zengliang; Sun, Qiuming; Tian, Feng

2010-10-01

The China Mechanical Virtual Human (CMVH) is a human musculoskeletal biomechanical simulation platform based on China Visible Human slice images; it has great realistic application significance. In this paper is introduced the construction method of CMVH 3D models. Then a simulation system solution based on Creator/Vega is put forward for the complex and gigantic data characteristics of the 3D models. At last, combined with MFC technology, the CMVH simulation system is developed and a running simulation scene is given. This paper provides a new way for the virtual reality application of CMVH.

Effect of thermal and mechanical parameter’s damage numerical simulation cycling effects on defects in hot metal forming processes

Science.gov (United States)

El Amri, Abdelouahid; el yakhloufi Haddou, Mounir; Khamlichi, Abdellatif

2017-10-01

Damage mechanisms in hot metal forming processes are accelerated by mechanical stresses arising during Thermal and mechanical properties variations, because it consists of the materials with different thermal and mechanical loadings and swelling coefficients. In this work, 3D finite element models (FEM) are developed to simulate the effect of Temperature and the stresses on the model development, using a general purpose FE software ABAQUS. Explicit dynamic analysis with coupled Temperature displacement procedure is used for a model. The purpose of this research was to study the thermomechanical damage mechanics in hot forming processes. The important process variables and the main characteristics of various hot forming processes will also be discussed.

Atomistic simulation study of the shear-band deformation mechanism in Mg-Cu metallic glasses

DEFF Research Database (Denmark)

Bailey, Nicholas; Schiøtz, Jakob; Jacobsen, Karsten Wedel

2006-01-01

We have simulated plastic deformation of a model Mg-Cu metallic glass in order to study shear banding. In uniaxial tension, we find a necking instability occurs rather than shear banding. We can force the latter to occur by deforming in plane strain, forbidding the change of length in one...... of the transverse directions. Furthermore, in most of the simulations a notch is used to initiate shear bands, which lie at a 45 degrees angle to the tensile loading direction. The shear bands are characterized by the Falk and Langer local measure of plastic deformation D-min(2), averaged here over volumes...... observe a slight decrease in density, up to 1%, within the shear band, which is consistent with notions of increased free volume or disorder within a plastically deforming amorphous material....

Theoretical Characterization of the Spectral Density of the Water-Soluble Chlorophyll-Binding Protein from Combined Quantum Mechanics/Molecular Mechanics Molecular Dynamics Simulations.

Science.gov (United States)

Rosnik, Andreana M; Curutchet, Carles

2015-12-08

Over the past decade, both experimentalists and theorists have worked to develop methods to describe pigment-protein coupling in photosynthetic light-harvesting complexes in order to understand the molecular basis of quantum coherence effects observed in photosynthesis. Here we present an improved strategy based on the combination of quantum mechanics/molecular mechanics (QM/MM) molecular dynamics (MD) simulations and excited-state calculations to predict the spectral density of electronic-vibrational coupling. We study the water-soluble chlorophyll-binding protein (WSCP) reconstituted with Chl a or Chl b pigments as the system of interest and compare our work with data obtained by Pieper and co-workers from differential fluorescence line-narrowing spectra (Pieper et al. J. Phys. Chem. B 2011, 115 (14), 4042-4052). Our results demonstrate that the use of QM/MM MD simulations where the nuclear positions are still propagated at the classical level leads to a striking improvement of the predicted spectral densities in the middle- and high-frequency regions, where they nearly reach quantitative accuracy. This demonstrates that the so-called "geometry mismatch" problem related to the use of low-quality structures in QM calculations, not the quantum features of pigments high-frequency motions, causes the failure of previous studies relying on similar protocols. Thus, this work paves the way toward quantitative predictions of pigment-protein coupling and the comprehension of quantum coherence effects in photosynthesis.

Multiaxial mechanical properties and constitutive modeling of human adipose tissue: a basis for preoperative simulations in plastic and reconstructive surgery.

Science.gov (United States)

Sommer, Gerhard; Eder, Maximilian; Kovacs, Laszlo; Pathak, Heramb; Bonitz, Lars; Mueller, Christoph; Regitnig, Peter; Holzapfel, Gerhard A

2013-11-01

A preoperative simulation of soft tissue deformations during plastic and reconstructive surgery is desirable to support the surgeon's planning and to improve surgical outcomes. The current development of constitutive adipose tissue models, for the implementation in multilayer computational frameworks for the simulation of human soft tissue deformations, has proved difficult because knowledge of the required mechanical parameters of fat tissue is limited. Therefore, for the first time, human abdominal adipose tissues were mechanically investigated by biaxial tensile and triaxial shear tests. The results of this study suggest that human abdominal adipose tissues under quasi-static and dynamic multiaxial loadings can be characterized as a nonlinear, anisotropic and viscoelastic soft biological material. The nonlinear and anisotropic features are consequences of the material's collagenous microstructure. The aligned collagenous septa observed in histological investigations causes the anisotropy of the tissue. A hyperelastic model used in this study was appropriate to represent the quasi-static multiaxial mechanical behavior of fat tissue. The constitutive parameters are intended to serve as a basis for soft tissue simulations using the finite element method, which is an apparent method for obtaining promising results in the field of plastic and reconstructive surgery. Copyright © 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Simulating direct shear tests with the Bullet physics library: A validation study.

Science.gov (United States)

Izadi, Ehsan; Bezuijen, Adam

2018-01-01

This study focuses on the possible uses of physics engines, and more specifically the Bullet physics library, to simulate granular systems. Physics engines are employed extensively in the video gaming, animation and movie industries to create physically plausible scenes. They are designed to deliver a fast, stable, and optimal simulation of certain systems such as rigid bodies, soft bodies and fluids. This study focuses exclusively on simulating granular media in the context of rigid body dynamics with the Bullet physics library. The first step was to validate the results of the simulations of direct shear testing on uniform-sized metal beads on the basis of laboratory experiments. The difference in the average angle of mobilized frictions was found to be only 1.0°. In addition, a very close match was found between dilatancy in the laboratory samples and in the simulations. A comprehensive study was then conducted to determine the failure and post-failure mechanism. We conclude with the presentation of a simulation of a direct shear test on real soil which demonstrated that Bullet has all the capabilities needed to be used as software for simulating granular systems.

The melting mechanism in binary Pd0.25Ni0.75 nanoparticles: molecular dynamics simulations

Science.gov (United States)

Domekeli, U.; Sengul, S.; Celtek, M.; Canan, C.

2018-02-01

The melting mechanism for Pd0.25Ni0.75 alloy nanoparticles (NPs) was investigated using molecular dynamics (MD) simulations with quantum Sutton-Chen many-body potentials. NPs of six different sizes ranging from 682 to 22,242 atoms were studied to observe the effect of size on the melting point. The melting temperatures of the NPs were estimated by following the changes in both the thermodynamic and structural quantities such as the total energy, heat capacity and Lindemann index. We also used a thermodynamics model to better estimate the melting point and to check the accuracy of MD simulations. We observed that the melting points of the NPs decreased as their sizes decreased. Although the MD simulations for the bulk system yielded higher melting temperatures because of the lack of a seed for the liquid phase, the melting temperatures determined for both the bulk material and the NPs are in good agreement with those predicted from the thermodynamics model. The melting mechanism proceeds in two steps: firstly, a liquid-like shell is formed in the outer regions of the NP with increasing temperature. The thickness of the liquid-like shell increases with increasing temperature until the shell reaches a critical thickness. Then, the entire Pd-Ni NP including core-related solid-like regions melts at once.

Quantum-mechanical simulations for in vivo MR spectroscopy: Principles and possibilities demonstrated with the program NMRScopeB.

Science.gov (United States)

Starčuk, Zenon; Starčuková, Jana

2017-07-15

Current possibilities and limitations of the simulation of in vivo magnetic resonance spectroscopic signals are demonstrated from the point of view of a simulation software user as well as its programmer. A brief review of the quantum-mechanical background addresses the specific needs of simulation implementation and in vivo MR spectroscopy in general. Practical application examples demonstrate how flexible simulation software, such as NMRScopeB, can be utilized not only for the preparation of metabolite basis signals for quantification of metabolite concentrations, but also in pulse sequence development, assessment of artifacts and analyzing mechanism leading to unexpected signal phenomena. Copyright © 2016 Elsevier Inc. All rights reserved.

Impact of Carbon Quota Allocation Mechanism on Emissions Trading: An Agent-Based Simulation

Directory of Open Access Journals (Sweden)

Wei Jiang

2016-08-01

Full Text Available This paper establishes an agent-based simulation system of the carbon emissions trading in accordance with the complex feature of the trading process. This system analyzes the impact of the carbon quota allocation mechanism on emissions trading for three different aspects including the amount of emissions reduction, the economic effect on the emitters, and the emissions reduction cost. Based on the data of the carbon emissions of different industries in China, several simulations were made. The results indicate that the emissions trading policy can effectively reduce carbon emissions in a perfectly competitive market. Moreover, by comparing separate quota allocation mechanisms, we obtain the result that the scheme with a small extent quota decrease in a comprehensive allocation mechanism can minimize the unit carbon emission cost. Implementing this scheme can also achieve minimal effects of carbon emissions limitation on the economy on the basis that the environment is not destroyed. However, excessive quota decrease cannot promote the emitters to reduce emission. Taking into account that several developing countries have the dual task of limiting carbon emissions and developing the economy, it is necessary to adopt a comprehensive allocation mechanism of the carbon quota and increase the initial proportion of free allocation.

Mechanical characterization of diesel soot nanoparticles: in situ compression in a transmission electron microscope and simulations

Science.gov (United States)

Jenei, Istvan Zoltan; Dassenoy, Fabrice; Epicier, Thierry; Khajeh, Arash; Martini, Ashlie; Uy, Dairene; Ghaednia, Hamed; Gangopadhyay, Arup

2018-02-01

Incomplete fuel burning inside an internal combustion engine results in the creation of soot in the form of nanoparticles. Some of these soot nanoparticles (SNP) become adsorbed into the lubricating oil film present on the cylinder walls, which adversely affects the tribological performance of the lubricant. In order to better understand the mechanisms underlying the wear caused by SNPs, it is important to understand the behavior of SNPs and to characterize potential changes in their mechanical properties (e.g. hardness) caused by (or during) mechanical stress. In this study, the behavior of individual SNPs originating from diesel engines was studied under compression. The experiments were performed in a transmission electron microscope using a nanoindentation device. The nanoparticles exhibited elasto-plastic behavior in response to consecutive compression cycles. From the experimental data, the Young’s modulus and hardness of the SNPs were calculated. The Young’s modulus and hardness of the nanoparticles increased with the number of compression cycles. Using an electron energy loss spectroscopy technique, it was shown that the sp2/sp3 ratio within the compressed nanoparticle decreases, which is suggested to be the cause of the increase in elasticity and hardness. In order to corroborate the experimental findings, molecular dynamics simulations of a model SNP were performed. The SNP model was constructed using carbon and hydrogen atoms with morphology and composition comparable to those observed in the experiment. The model SNP was subjected to repeated compressions between two virtual rigid walls. During the simulation, the nanoparticle exhibited elasto-plastic behavior like that in the experiments. The results of the simulations confirm that the increase in the elastic modulus and hardness is associated with a decrease in the sp2/sp3 ratio.

Molecular dynamics simulations for the examination of mechanical properties of hydroxyapatite/ poly α-n-butyl cyanoacrylate under additive manufacturing.

Science.gov (United States)

Wang, Yanen; Wei, Qinghua; Pan, Feilong; Yang, Mingming; Wei, Shengmin

2014-01-01

Molecular dynamics (MD) simulations emerged to be a helpful tool in the field of material science. In rapid prototyping artificial bone scaffolds process, the binder spraying volume and mechanism are very important for bone scaffolds mechanical properties. In this study, we applied MD simulations to investigating the binding energy of α-n-butyl cyanoacrylate (NBCA) on Hydroxyapatite (HA) crystallographic planes (001, 100 and 110), and to calculating and analyzing the mechanical properties and radial distribution function of the HA(110)/NBCA mixed system. The simulation results suggested that HA (110) has the highest binding energy with NBCA owing to the high planar atom density, and the mechanical properties of HA(110)/NBCA mixed system is stronger than pure HA system. Therefore, the multi-grade strength bone scaffold could be fabricated through spraying various volume NBCA binders during 3D printing process. By calculating the radial distribution function of HA(110)/NBCA, the essence of the interface interaction were successfully elucidated. The forming situation parameters can be referred to calculation results. There exists a strong interaction between HA crystallographic plane (110) and NBCA, it is mainly derived from the hydrogen bonds between O atoms which connect with C atoms of NBCA and H atoms in HA crystal. Furthermore, a strong adsorption effect can be demonstrated between HA and NBCA.

Atomistic simulations of diffusion mechanisms in off-stoichiometric Al-rich Ni3Al

International Nuclear Information System (INIS)

Duan, Jinsong

2007-01-01

This paper presents dynamics simulation results of diffusion in off-stoichiometric Al-rich Ni 3 Al (Ni 73 Al 27 ) at temperature ranging from 1300 to 1550 K. The interatomic forces are described by the Finnis-Sinclair type N-body potentials. Particular attention is devoted to the effect of the extra 2% of Al atoms sitting on the Ni sublattice as antisite point defects (Al Ni ) on diffusion. Simulation results show that Ni atoms mainly diffuse through the Ni sublattice at the temperatures investigated. Al atoms diffuse via both the intrasublattice and antistructure bridge (ASB) mechanisms. The contribution to Al diffusion from the ASB mechanism decreases at the lower temperature (T Ni ) enhances both Al and Ni diffusion in Ni 73 Al 27 . The Ni-Al coupled diffusion effect is observed and understood at the atomic level for the first time

[Application of fluid mechanics and simulation: urinary tract and ureteral catheters.

Science.gov (United States)

Gómez-Blanco, J C; Martínez-Reina, J; Cruz, D; Blas Pagador, J; Sánchez-Margallo, F M; Soria, F

2016-10-01

The mechanics of urine during its transport from the renal pelvis to the bladder is of great interest for urologists. The knowledge of the different physical variables and their interrelationship, both in physiologic movements and pathologies, will help a better diagnosis and treatment. The objective of this chapter is to show the physics principles and their most relevant basic relations in urine transport, and to bring them over the clinical world. For that, we explain the movement of urine during peristalsis, ureteral obstruction and in a ureter with a stent. This explanation is based in two tools used in bioengineering: the theoretical analysis through the Theory of concontinuous media and Ffluid mechanics and computational simulation that offers a practical solution for each scenario. Moreover, we review other contributions of bioengineering to the field of Urology, such as physical simulation or additive and subtractive manufacturing techniques. Finally, we list the current limitations for these tools and the technological development lines with more future projection. In this chapter we aim to help urologists to understand some important concepts of bioengineering, promoting multidisciplinary cooperation to offer complementary tools that help in diagnosis and treatment of diseases.

Modeling and Proposed Molecular Mechanism of Hydroxyurea Through Docking and Molecular Dynamic Simulation to Curtail the Action of Ribonucleotide Reductase.

Science.gov (United States)

Iman, Maryam; Khansefid, Zeynab; Davood, Asghar

2016-01-01

Ribonucleotide Reductase (RNR) is an important anticancer chemotherapy target. It has main key role in DNA synthesis and cell growth. Therefore several RNR inhibitors, such as hydroxyurea, have entered the clinical trials. Based on our proposed mechanism, radical site of RNR protein reacts with hydroxyurea in which hydroxyurea is converted into its oxidized form compound III, and whereby the tyrosyl radical is converted into a normal tyrosine residue. In this study, docking and molecular dynamics simulations were used for proposed molecular mechanism of hydroxyurea in RNR inhibition as anticancer agent. The binding affinity of hydroxyurea and compound III to RNR was studied by docking method. The docking study was performed for the crystal structure of human RNR with the radical scavenger Hydroxyurea and its oxidized form to inhibit the human RNR. hydroxyurea and compound III bind at the active site with Tyr-176, which are essential for free radical formation. This helps to understand the functional aspects and also aids in the development of novel inhibitors for the human RNR2. To confirm the binding mode of inhibitors, the molecular dynamics (MD) simulations were performed using GROMACS 4.5.5, based upon the docked conformation of inhibitors. Both of the studied compounds stayed in the active site. The results of MD simulations confirmed the binding mode of ligands, accuracy of docking and the reliability of active conformations which were obtained by AutoDock. MD studies confirm our proposed mechanism in which compound III reacts with the active site residues specially Tyr-176, and inhibits the radical generation and subsequently inhibits the RNR enzyme.

Skylab fluid mechanics simulations: Oscillation, rotation, collision and coalescence of water droplets under low-gravity environment

Science.gov (United States)

Vaughan, O. H., Jr.; Hung, R. J.

1975-01-01

Skylab 4 crew members performed a series of demonstrations showing the oscillations, rotations, as well as collision coalescence of water droplets which simulate various physical models of fluids under low gravity environment. The results from Skylab demonstrations provide information and illustrate the potential of an orbiting space-oriented research laboratory for the study of more sophisticated fluid mechanic experiments. Experiments and results are discussed.

Simulation of the Mechanical Response of the 11T Magnet by Means of COMSOL-MpCCI-ANSYS Coupling

CERN Document Server

Wilczek, Michal

2017-01-01

This report covers the work during my Summer Student internship at CERN as a part of the STEAM group (Simulation of Transient Effects in Accelerator Magnets) in the Technology Department, Machine Protection and Electrical Integrity group. I was responsible for the development of the ANSYS APDL model of the 11T superconducting magnet serving as a proof of concept for magneto-thermo-mechanical co-simulations of quench propagation in COMSOL and ANSYS software. The aforementioned co-simulation estimates the magnetic, thermal, and mechanical response of the magnet during the discharge process, while protected by a recently developed method, called Coupling-Loss Induced Quench (CLIQ). The already existing STEAM framework performs field/circuit coupling of a magneto-thermal field models previously developed by the STEAM. The next task of the group aimed at combining magneto-thermal field solution with the mechanical simulations. Such a coupling is of interest for the High-Luminosity upgrade of the Large Hadron Colli...

Superheating of Ag nanowires studied by molecular dynamics simulations

International Nuclear Information System (INIS)

Duan Wenshi; Ling Guangkong; Hong Lin; Li Hong; Liang Minghe

2008-01-01

The melting process of Ag nanowires was studied by molecular dynamics (MD) simulations at the atomic level. It is indicated that the Ag nanowires with Ni coating can be superheated depending on their radius and size. Also, in this paper the mechanism of superheating was analyzed and ascribed to the epitaxial Ag/Ni interface suppressing the nucleation and growth of melt. For the analysis, a thermodynamic model was constructed to describe the superheating mechanism of the Ni-coated Ag nanowires by considering the Ag/Ni interface free energy. We showed that the nucleation and growth of the Ag melt phase are both suppressed by the low energy Ag/Ni interfaces in Ni-coated Ag wires and the suppression of melt growth is crucial and plays a major role in the process of melting. The thermodynamic analysis gave a quantitative relation of superheating with the Ag wire radius and the contact angle of melting. The superheating decreased with Ag wire radius and also depended on the Ag/Ni interfacial condition. The results of the thermodynamic model were consistent with those of the MD simulations

Mechanical properties of lunar regolith and lunar soil simulant

Science.gov (United States)

Perkins, Steven W.

1989-01-01

Through the Surveyor 3 and 7, and Apollo 11-17 missions a knowledge of the mechanical properties of Lunar regolith were gained. These properties, including material cohesion, friction, in-situ density, grain-size distribution and shape, and porosity, were determined by indirect means of trenching, penetration, and vane shear testing. Several of these properties were shown to be significantly different from those of terrestrial soils, such as an interlocking cohesion and tensile strength formed in the absence of moisture and particle cementation. To characterize the strength and deformation properties of Lunar regolith experiments have been conducted on a lunar soil simulant at various initial densities, fabric arrangements, and composition. These experiments included conventional triaxial compression and extension, direct tension, and combined tension-shear. Experiments have been conducted at low levels of effective confining stress. External conditions such as membrane induced confining stresses, end platten friction and material self weight have been shown to have a dramatic effect on the strength properties at low levels of confining stress. The solution has been to treat these external conditions and the specimen as a full-fledged boundary value problem rather than the idealized elemental cube of mechanics. Centrifuge modeling allows for the study of Lunar soil-structure interaction problems. In recent years centrifuge modeling has become an important tool for modeling processes that are dominated by gravity and for verifying analysis procedures and studying deformation and failure modes. Centrifuge modeling is well established for terrestrial enginering and applies equally as well to Lunar engineering. A brief review of the experiments is presented in graphic and outline form.

Differential evolution and simulated annealing algorithms for mechanical systems design

Directory of Open Access Journals (Sweden)

H. Saruhan

2014-09-01

Full Text Available In this study, nature inspired algorithms – the Differential Evolution (DE and the Simulated Annealing (SA – are utilized to seek a global optimum solution for ball bearings link system assembly weight with constraints and mixed design variables. The Genetic Algorithm (GA and the Evolution Strategy (ES will be a reference for the examination and validation of the DE and the SA. The main purpose is to minimize the weight of an assembly system composed of a shaft and two ball bearings. Ball bearings link system is used extensively in many machinery applications. Among mechanical systems, designers pay great attention to the ball bearings link system because of its significant industrial importance. The problem is complex and a time consuming process due to mixed design variables and inequality constraints imposed on the objective function. The results showed that the DE and the SA performed and obtained convergence reliability on the global optimum solution. So the contribution of the DE and the SA application to the mechanical system design can be very useful in many real-world mechanical system design problems. Beside, the comparison confirms the effectiveness and the superiority of the DE over the others algorithms – the SA, the GA, and the ES – in terms of solution quality. The ball bearings link system assembly weight of 634,099 gr was obtained using the DE while 671,616 gr, 728213.8 gr, and 729445.5 gr were obtained using the SA, the ES, and the GA respectively.

The electro-thermal-mechanical performance of an OLED : a multi-physics model study

NARCIS (Netherlands)

Gielen, A.W.J.; Barink, M.; Brand, J. van de; Mol, A.M.B. van

2009-01-01

In order to study the electrical-thermo-mechanical interaction in OLEDs, finite element based simulation models were developed. Two dimensional models were used to study detailed design effects, such as the location of the bus bars, while a three dimensional model was used to study the effect of

Neurite, a finite difference large scale parallel program for the simulation of electrical signal propagation in neurites under mechanical loading.

Directory of Open Access Journals (Sweden)

Julián A García-Grajales

Full Text Available With the growing body of research on traumatic brain injury and spinal cord injury, computational neuroscience has recently focused its modeling efforts on neuronal functional deficits following mechanical loading. However, in most of these efforts, cell damage is generally only characterized by purely mechanistic criteria, functions of quantities such as stress, strain or their corresponding rates. The modeling of functional deficits in neurites as a consequence of macroscopic mechanical insults has been rarely explored. In particular, a quantitative mechanically based model of electrophysiological impairment in neuronal cells, Neurite, has only very recently been proposed. In this paper, we present the implementation details of this model: a finite difference parallel program for simulating electrical signal propagation along neurites under mechanical loading. Following the application of a macroscopic strain at a given strain rate produced by a mechanical insult, Neurite is able to simulate the resulting neuronal electrical signal propagation, and thus the corresponding functional deficits. The simulation of the coupled mechanical and electrophysiological behaviors requires computational expensive calculations that increase in complexity as the network of the simulated cells grows. The solvers implemented in Neurite--explicit and implicit--were therefore parallelized using graphics processing units in order to reduce the burden of the simulation costs of large scale scenarios. Cable Theory and Hodgkin-Huxley models were implemented to account for the electrophysiological passive and active regions of a neurite, respectively, whereas a coupled mechanical model accounting for the neurite mechanical behavior within its surrounding medium was adopted as a link between electrophysiology and mechanics. This paper provides the details of the parallel implementation of Neurite, along with three different application examples: a long myelinated axon

Numerical Simulation for Mechanism of Airway Narrowing in Asthma

Science.gov (United States)

Bando, Kiyoshi; Yamashita, Daisuke; Ohba, Kenkichi

A calculation model is proposed to examine the generation mechanism of the numerous lobes on the inner-wall of the airway in asthmatic patients and to clarify luminal occlusion of the airway inducing breathing difficulties. The basement membrane in the airway wall is modeled as a two-dimensional thin-walled shell having inertia force due to the mass, and the smooth muscle contraction effect is replaced by uniform transmural pressure applied to the basement membrane. A dynamic explicit finite element method is used as a numerical simulation method. To examine the validity of the present model, simulation of an asthma attack is performed. The number of lobes generated in the basement membrane increases when transmural pressure is applied in a shorter time period. When the remodeling of the basement membrane occurs characterized by thickening and hardening, it is demonstrated that the number of lobes decreases and the narrowing of the airway lumen becomes severe. Comparison of the results calculated by the present model with those measured for animal experiments of asthma will be possible.

Mechanisms of Diurnal Precipitation over the United States Great Plains: A Cloud-Resolving Model Simulation

Science.gov (United States)

Lee, M.-I.; Choi, I.; Tao, W.-K.; Schubert, S. D.; Kang, I.-K.

2010-01-01

The mechanisms of summertime diurnal precipitation in the US Great Plains were examined with the two-dimensional (2D) Goddard Cumulus Ensemble (GCE) cloud-resolving model (CRM). The model was constrained by the observed large-scale background state and surface flux derived from the Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) Program s Intensive Observing Period (IOP) data at the Southern Great Plains (SGP). The model, when continuously-forced by realistic surface flux and large-scale advection, simulates reasonably well the temporal evolution of the observed rainfall episodes, particularly for the strongly forced precipitation events. However, the model exhibits a deficiency for the weakly forced events driven by diurnal convection. Additional tests were run with the GCE model in order to discriminate between the mechanisms that determine daytime and nighttime convection. In these tests, the model was constrained with the same repeating diurnal variation in the large-scale advection and/or surface flux. The results indicate that it is primarily the surface heat and moisture flux that is responsible for the development of deep convection in the afternoon, whereas the large-scale upward motion and associated moisture advection play an important role in preconditioning nocturnal convection. In the nighttime, high clouds are continuously built up through their interaction and feedback with long-wave radiation, eventually initiating deep convection from the boundary layer. Without these upper-level destabilization processes, the model tends to produce only daytime convection in response to boundary layer heating. This study suggests that the correct simulation of the diurnal variation in precipitation requires that the free-atmospheric destabilization mechanisms resolved in the CRM simulation must be adequately parameterized in current general circulation models (GCMs) many of which are overly sensitive to the parameterized boundary layer heating.

Coarse-grained simulation of molecular mechanisms of recovery in thermally activated shape-memory polymers

Science.gov (United States)

Abberton, Brendan C.; Liu, Wing Kam; Keten, Sinan

2013-12-01

Thermally actuated shape-memory polymers (SMPs) are capable of being programmed into a temporary shape and then recovering their permanent reference shape upon exposure to heat, which facilitates a phase transition that allows dramatic increase in molecular mobility. Experimental, analytical, and computational studies have established empirical relations of the thermomechanical behavior of SMPs that have been instrumental in device design. However, the underlying mechanisms of the recovery behavior and dependence on polymer microstructure remain to be fully understood for copolymer systems. This presents an opportunity for bottom-up studies through molecular modeling; however, the limited time-scales of atomistic simulations prohibit the study of key performance metrics pertaining to recovery. In order to elucidate the effects of phase fraction, recovery temperature, and deformation temperature on shape recovery, here we investigate the shape-memory behavior in a copolymer model with coarse-grained potentials using a two-phase molecular model that reproduces physical crosslinking. Our simulation protocol allows observation of upwards of 90% strain recovery in some cases, at time-scales that are on the order of the timescale of the relevant relaxation mechanism (stress relaxation in the unentangled soft-phase). Partial disintegration of the glassy phase during mechanical deformation is found to contribute to irrecoverable strain. Temperature dependence of the recovery indicates nearly full elastic recovery above the trigger temperature, which is near the glass-transition temperature of the rubbery switching matrix. We find that the trigger temperature is also directly correlated with the deformation temperature, indicating that deformation temperature influences the recovery temperatures required to obtain a given amount of shape recovery, until the plateau regions overlap above the transition region. Increasing the fraction of glassy phase results in higher strain

Simulating Surface-Enhanced Hyper-Raman Scattering Using Atomistic Electrodynamics-Quantum Mechanical Models.

Science.gov (United States)

Hu, Zhongwei; Chulhai, Dhabih V; Jensen, Lasse

2016-12-13

Surface-enhanced hyper-Raman scattering (SEHRS) is the two-photon analogue of surface-enhanced Raman scattering (SERS), which has proven to be a powerful tool to study molecular structures and surface enhancements. However, few theoretical approaches to SEHRS exist and most neglect the atomistic descriptions of the metal surface and molecular resonance effects. In this work, we present two atomistic electrodynamics-quantum mechanical models to simulate SEHRS. The first is the discrete interaction model/quantum mechanical (DIM/QM) model, which combines an atomistic electrodynamics model of the nanoparticle with a time-dependent density functional theory description of the molecule. The second model is a dressed-tensors method that describes the molecule as a point-dipole and point-quadrupole object interacting with the enhanced local field and field-gradients (FG) from the nanoparticle. In both of these models, the resonance effects are treated efficiently by means of damped quadratic response theory. Using these methods, we simulate SEHRS spectra for benzene and pyridine. Our results show that the FG effects in SEHRS play an important role in determining both the surface selection rules and the enhancements. We find that FG effects are more important in SEHRS than in SERS. We also show that the spectral features of small molecules can be accurately described by accounting for the interactions between the molecule and the local field and FG of the nanoparticle. However, at short distances between the metal and molecule, we find significant differences in the SEHRS enhancements predicted using the DIM/QM and the dressed-tensors methods.

Hardware and software and machine-tool simulation with parallel structures mechanisms

Directory of Open Access Journals (Sweden)

Keba P.V.

2016-12-01

Full Text Available The usage spectrum of mechanisms with parallel structure is spreading all the time. The mechanisms of machine-tools and manipulators become more complicated and it is necessary to improve the program-controlled modules. Closed circuit mechanisms are mostly spread in robotic complexes, where manipulator performs complicated spatial movements by the given trajectory. The usage spectrum is very wide and the most popular are sorting, welding, assembling and others. However, the problem of designing the operating programs is still present even today. It is just because the developed post-processors are created for the equipment that we have for now. But new machine tool constructions appear every day and there is a necessity to control them. The problems associated with using of hardware and software of mechanisms with parallel structure in computer-aided simulation are considered. The program for inverse problem kinematics solving is designed. New method of designing the control programs is found. The kinematic analysis methods options and calculated data obtained by computer mathematics systems are shown with «Tools Glide» software taken as an example.

Blocking Mechanism Study of Self-Compacting Concrete Based on Discrete Element Method

Science.gov (United States)

Zhang, Xuan; Li, Zhida; Zhang, Zhihua

2017-11-01

In order to study the influence factors of blocking mechanism of Self-Compaction Concrete (SCC), Roussel’s granular blocking model was verified and extended by establishing the discrete element model of SCC. The influence of different parameters on the filling capacity and blocking mechanism of SCC were also investigated. The results showed that: it was feasible to simulate the blocking mechanism of SCC by using Discrete Element Method (DEM). The passing ability of pebble aggregate was superior to the gravel aggregate and the passing ability of hexahedron particles was bigger than tetrahedron particles, while the tetrahedron particle simulation results were closer to the actual situation. The flow of SCC as another significant factor affected the passing ability that with the flow increased, the passing ability increased. The correction coefficient λ of the steel arrangement (channel section shape) and flow rate γ in the block model were introduced that the value of λ was 0.90-0.95 and the maximum casting rate was 7.8 L/min.

Radial basis function (RBF) neural network control for mechanical systems design, analysis and Matlab simulation

CERN Document Server

Liu, Jinkun

2013-01-01

Radial Basis Function (RBF) Neural Network Control for Mechanical Systems is motivated by the need for systematic design approaches to stable adaptive control system design using neural network approximation-based techniques. The main objectives of the book are to introduce the concrete design methods and MATLAB simulation of stable adaptive RBF neural control strategies. In this book, a broad range of implementable neural network control design methods for mechanical systems are presented, such as robot manipulators, inverted pendulums, single link flexible joint robots, motors, etc. Advanced neural network controller design methods and their stability analysis are explored. The book provides readers with the fundamentals of neural network control system design.   This book is intended for the researchers in the fields of neural adaptive control, mechanical systems, Matlab simulation, engineering design, robotics and automation. Jinkun Liu is a professor at Beijing University of Aeronautics and Astronauti...

[Ex Vivo Testing of Mechanical Properties of Canine Metacarpal/Metatarsal Bones after Simulated Implant Removal].

Science.gov (United States)

Srnec, R; Fedorová, P; Pěnčík, J; Vojtová, L; Sedlinská, M; Nečas, A

2016-01-01

PURPOSE OF THE STUDY In a long-term perspective, it is better to remove implants after fracture healing. However, subsequent full or excessive loading of an extremity may result in refracture, and the bone with holes after screw removal may present a site with predilection for this. The aim of the study was to find ways of how to decrease risk factors for refracture in such a case. This involved support to the mechanical properties of a bone during its remodelling until defects following implant removal are repaired, using a material tolerated by bone tissue and easy to apply. It also included an assessment of the mechanical properties of a bone after filling the holes in it with a newly developed biodegradable polymer-composite gel ("bone paste"). The composite also has a prospect of being used to repair bony defects produced by pathological processes. MATERIAL AND METHODS Experiments were carried out on intact weight-bearing small bones in dogs. A total of 27 specimens of metacarpal/metatarsal bones were used for ex vivo testing. They were divided into three groups: K1 (n = 9) control undamaged bones; K2 (n = 9) control bones with iatrogenic damage simulating holes left after cortical screw removal; EXP (n = 9) experimental specimens in which simulated holes in bone were filled with the biodegradable self-hardening composite. The bone specimens were subjected to three-point bending in the caudocranial direction by a force acting parallel to the direction of drilling in their middiaphyses. The value of maximum load achieved (N) and the corresponding value of a vertical displacement (mm) were recorded in each specimen, then compared and statistically evaluated. RESULTS On application of a maximum load (N), all bone specimens broke in the mid-part of their diaphyses. In group K1 the average maximum force of 595.6 ± 79.5 N was needed to break the bone; in group K2 it was 347.6 ± 58.6 N; and in group EXP it was 458.3 ± 102.7 N. The groups with damaged bones, K2 and

Bio-mechanical Analysis of Human Joints and Extension of the Study to Robot

OpenAIRE

S. Parasuraman; Ler Shiaw Pei

2008-01-01

In this paper, the bio-mechanical analysis of human joints is carried out and the study is extended to the robot manipulator. This study will first focus on the kinematics of human arm which include the movement of each joint in shoulder, wrist, elbow and finger complexes. Those analyses are then extended to the design of a human robot manipulator. A simulator is built for Direct Kinematics and Inverse Kinematics of human arm. In the simulation of Direct Kinematics, the human joint angles can...

Implementation of Simulation Based-Concept Attainment Method to Increase Interest Learning of Engineering Mechanics Topic

Science.gov (United States)

Sultan, A. Z.; Hamzah, N.; Rusdi, M.

2018-01-01

The implementation of concept attainment method based on simulation was used to increase student’s interest in the subjects Engineering of Mechanics in second semester of academic year 2016/2017 in Manufacturing Engineering Program, Department of Mechanical PNUP. The result of the implementation of this learning method shows that there is an increase in the students’ learning interest towards the lecture material which is summarized in the form of interactive simulation CDs and teaching materials in the form of printed books and electronic books. From the implementation of achievement method of this simulation based concept, it is noted that the increase of student participation in the presentation and discussion as well as the deposit of individual assignment of significant student. With the implementation of this method of learning the average student participation reached 89%, which before the application of this learning method only reaches an average of 76%. And also with previous learning method, for exam achievement of A-grade under 5% and D-grade above 8%. After the implementation of the new learning method (simulation based-concept attainment method) the achievement of Agrade has reached more than 30% and D-grade below 1%.

A dissociative quantum mechanical/molecular mechanical molecular dynamics simulation and infrared experiments reveal characteristics of the strongly hydrolytic arsenic(III).

Science.gov (United States)

Canaval, Lorenz R; Lutz, Oliver M D; Weiss, Alexander K H; Huck, Christian W; Hofer, Thomas S

2014-11-17

This work presents a hybrid ab initio quantum mechanical/molecular mechanical simulation at the RI-MP2 level of theory investigating the hydrolysis process of arsenic(III), ultimately leading to arsenous acid (H3AsO3). A newly implemented dissociative water model has been applied to treat the interactions in the classical region, which is capable of describing non-neutral water species such as hydroxide and oxonium ions. Three stages of hydrolysis have been observed during the simulation and besides profound dynamical considerations, detailed insights into structural changes and atomic partial charge shifts are presented. In particular, the geometrical properties of H-bonds involved in each of the three proton transfer events and subsequent proton hopping reactions are discussed. A Laguerre tessellation analysis has been employed to estimate the molecular volume of H3AsO3. Estimations of pKa values of the arsenic(III)-aquo-complexes have been obtained at the G4 and CBS-Q//B3 levels of theory using a thermodynamic cycle, whereas rate constants for the final hydrolysis step have been determined via reaction path optimization and transition state theory. Newly recorded Fourier transform infrared (FT-IR) spectroscopy measurements have been compared to power spectra obtained from the simulation data, confirming its quality. The simulation findings, as well as results from computational spectroscopic calculations utilizing the PT2-VSCF methodology, proved valuable for the interpretation of the experimental FT-IR data, elucidating the particularities of the strongly observed IR Raman noncoincidence effect.

Crack growth and fracture toughness of amorphous Li-Si anodes: Mechanisms and role of charging/discharging studied by atomistic simulations

Science.gov (United States)

Khosrownejad, S. M.; Curtin, W. A.

2017-10-01

Fracture is the main cause of degradation and capacity fading in lithiated silicon during cycling. Experiments on the fracture of lithiated silicon show conflicting results, and so mechanistic models can help interpret experiments and guide component design. Here, large-scale K-controlled atomistic simulations of crack propagation (R-curve KI vs. Δa) are performed at LixSi compositions x = 0.5 , 1.0 , 1.5 for as-quenched/relaxed samples and at x = 0.5 , 1.0 for samples created by discharging from higher Li compositions. In all cases, the fracture mechanism is void nucleation, growth, and coalescence. In as-quenched materials, with increasing Li content the plastic flow stress and elastic moduli decrease but void nucleation and growth happen at smaller stress, so that the initial fracture toughness KIc ≈ 1.0 MPa√{ m} decreases slightly but the initial fracture energy JIc ≈ 10.5J/m2 is similar. After 10 nm of crack growth, the fracture toughnesses increase and become similar at KIc ≈ 1.9 MPa√{ m} across all compositions. Plane-strain equi-biaxial expansion simulations of uncracked samples provide complementary information on void nucleation and growth. The simulations are interpreted within the framework of Gurson model for ductile fracture, which predicts JIc = ασy D where α ≃ 1 and D is the void spacing, and good agreement is found. In spite of flowing plastically, the fracture toughness of LixSi is low because voids nucleate within nano-sized distances ahead of the crack (D ≈ 1nm). Scaling simulation results to experimental conditions, reasonable agreement with experimentally-estimated fracture toughnesses is obtained. The discharging process facilitates void nucleation but decreases the flow stress (as shown previously), leading to enhanced fracture toughness at all levels of crack growth. Therefore, the fracture behavior of lithiated silicon at a given composition is not a material property but instead depends on the history of charging

Thermo-dynamical contours of electronic-vibrational spectra simulated using the statistical quantum-mechanical methods

DEFF Research Database (Denmark)

Pomogaev, Vladimir; Pomogaeva, Anna; Avramov, Pavel

2011-01-01

Three polycyclic organic molecules in various solvents focused on thermo-dynamical aspects were theoretically investigated using the recently developed statistical quantum mechanical/classical molecular dynamics method for simulating electronic-vibrational spectra. The absorption bands of estradiol...

Component simulation in problems of calculated model formation of automatic machine mechanisms

Directory of Open Access Journals (Sweden)

Telegin Igor

2017-01-01

Full Text Available The paper deals with the problems of the component simulation method application in the problems of the automation of the mechanical system model formation with the further possibility of their CAD-realization. The purpose of the investigations mentioned consists in the automation of the CAD-model formation of high-speed mechanisms in automatic machines and in the analysis of dynamic processes occurred in their units taking into account their elasto-inertial properties, power dissipation, gaps in kinematic pairs, friction forces, design and technological loads. As an example in the paper there are considered a formalization of stages in the computer model formation of the cutting mechanism in cold stamping automatic machine AV1818 and methods of for the computation of their parameters on the basis of its solid-state model.

Characterization of the mechanical properties of polyphenylene polymer using molecular dynamics simulations

International Nuclear Information System (INIS)

Ansari, R.; Ajori, S.; Rouhi, S.

2016-01-01

Synthesizing polyphenylene polymer, a two-dimensional hydrocarbon known as porous graphene, has led to the initiation of a new age in nanoscience. In this investigation, molecular dynamics (MD) simulations are carried out to study the mechanical properties of porous graphene such as Young's modulus, Poisson's ratio, bulk modulus and ultimate strength and strain. The fracture initiation and propagation pattern of porous graphene are also considered in this study. The results show that Young's and bulk moduli of porous graphene are lower than those of graphene, graphene and graphyne. Unlikely, it is also observed that its Poisson's ratio is considerably more than that of graphene, graphene and graphyne. Furthermore, it is found out that Young's and bulk moduli as well as fracture strain and ultimate stress are extremely size-dependent and also the porous graphene can be considered as an isotropic material.

Nonlinear dynamic mechanism of vocal tremor from voice analysis and model simulations

Science.gov (United States)

Zhang, Yu; Jiang, Jack J.

2008-09-01

Nonlinear dynamic analysis and model simulations are used to study the nonlinear dynamic characteristics of vocal folds with vocal tremor, which can typically be characterized by low-frequency modulation and aperiodicity. Tremor voices from patients with disorders such as paresis, Parkinson's disease, hyperfunction, and adductor spasmodic dysphonia show low-dimensional characteristics, differing from random noise. Correlation dimension analysis statistically distinguishes tremor voices from normal voices. Furthermore, a nonlinear tremor model is proposed to study the vibrations of the vocal folds with vocal tremor. Fractal dimensions and positive Lyapunov exponents demonstrate the evidence of chaos in the tremor model, where amplitude and frequency play important roles in governing vocal fold dynamics. Nonlinear dynamic voice analysis and vocal fold modeling may provide a useful set of tools for understanding the dynamic mechanism of vocal tremor in patients with laryngeal diseases.

A hierarchical lattice spring model to simulate the mechanics of 2-D materials-based composites

Directory of Open Access Journals (Sweden)

Lucas eBrely

2015-07-01

Full Text Available In the field of engineering materials, strength and toughness are typically two mutually exclusive properties. Structural biological materials such as bone, tendon or dentin have resolved this conflict and show unprecedented damage tolerance, toughness and strength levels. The common feature of these materials is their hierarchical heterogeneous structure, which contributes to increased energy dissipation before failure occurring at different scale levels. These structural properties are the key to exceptional bioinspired material mechanical properties, in particular for nanocomposites. Here, we develop a numerical model in order to simulate the mechanisms involved in damage progression and energy dissipation at different size scales in nano- and macro-composites, which depend both on the heterogeneity of the material and on the type of hierarchical structure. Both these aspects have been incorporated into a 2-dimensional model based on a Lattice Spring Model, accounting for geometrical nonlinearities and including statistically-based fracture phenomena. The model has been validated by comparing numerical results to continuum and fracture mechanics results as well as finite elements simulations, and then employed to study how structural aspects impact on hierarchical composite material properties. Results obtained with the numerical code highlight the dependence of stress distributions on matrix properties and reinforcement dispersion, geometry and properties, and how failure of sacrificial elements is directly involved in the damage tolerance of the material. Thanks to the rapidly developing field of nanocomposite manufacture, it is already possible to artificially create materials with multi-scale hierarchical reinforcements. The developed code could be a valuable support in the design and optimization of these advanced materials, drawing inspiration and going beyond biological materials with exceptional mechanical properties.

Fast Simulation of Mechanical Heterogeneity in the Electrically Asynchronous Heart Using the MultiPatch Module.

Directory of Open Access Journals (Sweden)

John Walmsley

2015-07-01

Full Text Available Cardiac electrical asynchrony occurs as a result of cardiac pacing or conduction disorders such as left bundle-branch block (LBBB. Electrically asynchronous activation causes myocardial contraction heterogeneity that can be detrimental for cardiac function. Computational models provide a tool for understanding pathological consequences of dyssynchronous contraction. Simulations of mechanical dyssynchrony within the heart are typically performed using the finite element method, whose computational intensity may present an obstacle to clinical deployment of patient-specific models. We present an alternative based on the CircAdapt lumped-parameter model of the heart and circulatory system, called the MultiPatch module. Cardiac walls are subdivided into an arbitrary number of patches of homogeneous tissue. Tissue properties and activation time can differ between patches. All patches within a wall share a common wall tension and curvature. Consequently, spatial location within the wall is not required to calculate deformation in a patch. We test the hypothesis that activation time is more important than tissue location for determining mechanical deformation in asynchronous hearts. We perform simulations representing an experimental study of myocardial deformation induced by ventricular pacing, and a patient with LBBB and heart failure using endocardial recordings of electrical activation, wall volumes, and end-diastolic volumes. Direct comparison between simulated and experimental strain patterns shows both qualitative and quantitative agreement between model fibre strain and experimental circumferential strain in terms of shortening and rebound stretch during ejection. Local myofibre strain in the patient simulation shows qualitative agreement with circumferential strain patterns observed in the patient using tagged MRI. We conclude that the MultiPatch module produces realistic regional deformation patterns in the asynchronous heart and that

A Simulational approach to teaching statistical mechanics and kinetic theory

International Nuclear Information System (INIS)

Karabulut, H.

2005-01-01

A computer simulation demonstrating how Maxwell-Boltzmann distribution is reached in gases from a nonequilibrium distribution is presented. The algorithm can be generalized to the cases of gas particles (atoms or molecules) with internal degrees of freedom such as electronic excitations and vibrational-rotational energy levels. Another generalization of the algorithm is the case of mixture of two different gases. By choosing the collision cross sections properly one can create quasi equilibrium distributions. For example by choosing same atom cross sections large and different atom cross sections very small one can create mixture of two gases with different temperatures where two gases slowly interact and come to equilibrium in a long time. Similarly, for the case one kind of atom with internal degrees of freedom one can create situations that internal degrees of freedom come to the equilibrium much later than translational degrees of freedom. In all these cases the equilibrium distribution that the algorithm gives is the same as expected from the statistical mechanics. The algorithm can also be extended to cover the case of chemical equilibrium where species A and B react to form AB molecules. The laws of chemical equilibrium can be observed from this simulation. The chemical equilibrium simulation can also help to teach the elusive concept of chemical potential

Simulation of crack propagation in fiber-reinforced concrete by fracture mechanics

International Nuclear Information System (INIS)

Zhang Jun; Li, Victor C.

2004-01-01

Mode I crack propagation in fiber-reinforced concrete (FRC) is simulated by a fracture mechanics approach. A superposition method is applied to calculate the crack tip stress intensity factor. The model relies on the fracture toughness of hardened cement paste (K IC ) and the crack bridging law, so-called stress-crack width (σ-δ) relationship of the material, as the fundamental material parameters for model input. As two examples, experimental data from steel FRC beams under three-point bending load are analyzed with the present fracture mechanics model. A good agreement has been found between model predictions and experimental results in terms of flexural stress-crack mouth opening displacement (CMOD) diagrams. These analyses and comparisons confirm that the structural performance of concrete and FRC elements, such as beams in bending, can be predicted by the simple fracture mechanics model as long as the related material properties, K IC and (σ-δ) relationship, are known

Dual-energy mammography: simulation studies

International Nuclear Information System (INIS)

Bliznakova, K; Kolitsi, Z; Pallikarakis, N

2006-01-01

This paper presents a mammography simulator and demonstrates its applicability in feasibility studies in dual-energy (DE) subtraction mammography. This mammography simulator is an evolution of a previously presented x-ray imaging simulation system, which has been extended with new functionalities that are specific for DE simulations. The new features include incident exposure and dose calculations, the implementation of a DE subtraction algorithm as well as amendments to the detector and source modelling. The system was then verified by simulating experiments and comparing their results against published data. The simulator was used to carry out a feasibility study of the applicability of DE techniques in mammography, and more precisely to examine whether this modality could result in better visualization and detection of microcalcifications. Investigations were carried out using a 3D breast software phantom of average thickness, monoenergetic and polyenergetic beam spectra and various detector configurations. Dual-shot techniques were simulated. Results showed the advantage of using monoenergetic in comparison with polyenergetic beams. Optimization studies with monochromatic sources were carried out to obtain the optimal low and high incident energies, based on the assessment of the figure of merit of the simulated microcalcifications in the subtracted images. The results of the simulation study with the optimal energies demonstrated that the use of the DE technique can improve visualization and increase detectability, allowing identification of microcalcifications of sizes as small as 200 μm. The quantitative results are also verified by means of a visual inspection of the synthetic images

Improved simulation method of automotive spot weld failure with an account of the mechanical properties of spot welds

Science.gov (United States)

Wu, H.; Meng, X. M.; Fang, R.; Huang, Y. F.; Zhan, S.

2017-12-01

In this paper, the microstructure and mechanical properties of spot weld were studied, the hardness of nugget and heat affected zone (HAZ) were also tested by metallographic microscope and microhardness tester. The strength of the spot weld with the different parts' area has been characterized. According to the experiments result, CAE model of spot weld with HAZ structure was established, and simulation results of different lap-shear CAE models were analyzed. The results show that the spot weld model which contained the HAZ has good performance and more suitable for engineering application in spot weld simulation.

Study on the Depth, Rate, Shape, and Strength of Pulse with Cardiovascular Simulator

Directory of Open Access Journals (Sweden)

Ju-Yeon Lee

2017-01-01

Full Text Available Pulse diagnosis is important in oriental medicine. The purpose of this study is explaining the mechanisms of pulse with a cardiovascular simulator. The simulator is comprised of the pulse generating part, the vessel part, and the measurement part. The pulse generating part was composed of motor, slider-crank mechanism, and piston pump. The vessel part, which was composed with the aorta and a radial artery, was fabricated with silicon to implement pulse wave propagation. The pulse parameters, such as the depth, rate, shape, and strength, were simulated. With changing the mean pressure, the floating pulse and the sunken pulse were generated. The change of heart rate generated the slow pulse and the rapid pulse. The control of the superposition time of the reflected wave generated the string-like pulse and the slippery pulse. With changing the pulse pressure, the vacuous pulse and the replete pulse were generated. The generated pulses showed good agreements with the typical pulses.

Simulating mixed-phase Arctic stratus clouds: sensitivity to ice initiation mechanisms

Directory of Open Access Journals (Sweden)

G. McFarquhar

2009-07-01

Full Text Available The importance of Arctic mixed-phase clouds on radiation and the Arctic climate is well known. However, the development of mixed-phase cloud parameterization for use in large scale models is limited by lack of both related observations and numerical studies using multidimensional models with advanced microphysics that provide the basis for understanding the relative importance of different microphysical processes that take place in mixed-phase clouds. To improve the representation of mixed-phase cloud processes in the GISS GCM we use the GISS single-column model coupled to a bin resolved microphysics (BRM scheme that was specially designed to simulate mixed-phase clouds and aerosol-cloud interactions. Using this model with the microphysical measurements obtained from the DOE ARM Mixed-Phase Arctic Cloud Experiment (MPACE campaign in October 2004 at the North Slope of Alaska, we investigate the effect of ice initiation processes and Bergeron-Findeisen process (BFP on glaciation time and longevity of single-layer stratiform mixed-phase clouds. We focus on observations taken during 9–10 October, which indicated the presence of a single-layer mixed-phase clouds. We performed several sets of 12-h simulations to examine model sensitivity to different ice initiation mechanisms and evaluate model output (hydrometeors' concentrations, contents, effective radii, precipitation fluxes, and radar reflectivity against measurements from the MPACE Intensive Observing Period. Overall, the model qualitatively simulates ice crystal concentration and hydrometeors content, but it fails to predict quantitatively the effective radii of ice particles and their vertical profiles. In particular, the ice effective radii are overestimated by at least 50%. However, using the same definition as used for observations, the effective radii simulated and that observed were more comparable. We find that for the single-layer stratiform mixed-phase clouds simulated, process

Simulating mixed-phase Arctic stratus clouds: sensitivity to ice initiation mechanisms

Science.gov (United States)

Sednev, I.; Menon, S.; McFarquhar, G.

2009-07-01

The importance of Arctic mixed-phase clouds on radiation and the Arctic climate is well known. However, the development of mixed-phase cloud parameterization for use in large scale models is limited by lack of both related observations and numerical studies using multidimensional models with advanced microphysics that provide the basis for understanding the relative importance of different microphysical processes that take place in mixed-phase clouds. To improve the representation of mixed-phase cloud processes in the GISS GCM we use the GISS single-column model coupled to a bin resolved microphysics (BRM) scheme that was specially designed to simulate mixed-phase clouds and aerosol-cloud interactions. Using this model with the microphysical measurements obtained from the DOE ARM Mixed-Phase Arctic Cloud Experiment (MPACE) campaign in October 2004 at the North Slope of Alaska, we investigate the effect of ice initiation processes and Bergeron-Findeisen process (BFP) on glaciation time and longevity of single-layer stratiform mixed-phase clouds. We focus on observations taken during 9-10 October, which indicated the presence of a single-layer mixed-phase clouds. We performed several sets of 12-h simulations to examine model sensitivity to different ice initiation mechanisms and evaluate model output (hydrometeors' concentrations, contents, effective radii, precipitation fluxes, and radar reflectivity) against measurements from the MPACE Intensive Observing Period. Overall, the model qualitatively simulates ice crystal concentration and hydrometeors content, but it fails to predict quantitatively the effective radii of ice particles and their vertical profiles. In particular, the ice effective radii are overestimated by at least 50%. However, using the same definition as used for observations, the effective radii simulated and that observed were more comparable. We find that for the single-layer stratiform mixed-phase clouds simulated, process of ice phase initiation

QSAR, docking, dynamic simulation and quantum mechanics studies to explore the recognition properties of cholinesterase binding sites.

Science.gov (United States)

Correa-Basurto, J; Bello, M; Rosales-Hernández, M C; Hernández-Rodríguez, M; Nicolás-Vázquez, I; Rojo-Domínguez, A; Trujillo-Ferrara, J G; Miranda, René; Flores-Sandoval, C A

2014-02-25

A set of 84 known N-aryl-monosubstituted derivatives (42 amides: series 1 and 2, and 42 imides: series 3 an 4, from maleic and succinic anhydrides, respectively) that display inhibitory activity toward both acetylcholinesterase and butyrylcholinesterase (ChEs) was considered for Quantitative structure-activity relationship (QSAR) studies. These QSAR studies employed docking data from both ChEs that were previously submitted to molecular dynamics (MD) simulations. Donepezil and galanthamine stereoisomers were included to analyze their quantum mechanics properties and for validating the docking procedure. Quantum parameters such as frontier orbital energies, dipole moment, molecular volume, atomic charges, bond length and reactivity parameters were measured, as well as partition coefficients, molar refractivity and polarizability were also analyzed. In order to evaluate the obtained equations, four compounds: 1a (4-oxo-4-(phenylamino)butanoic acid), 2a ((2Z)-4-oxo-4-(phenylamino)but-2-enoic acid), 3a (2-phenylcyclopentane-1,3-dione) and 4a (2-phenylcyclopent-4-ene-1,3-dione) were employed as independent data set, using only equations with r(m(test))²>0.5. It was observed that residual values gave low value in almost all series, excepting in series 1 for compounds 3a and 4a, and in series 4 for compounds 1a, 2a and 3a, giving a low value for 4a. Consequently, equations seems to be specific according to the structure of the evaluated compound, that means, series 1 fits better for compound 1a, series 3 or 4 fits better for compounds 3a or 4a. Same behavior was observed in the butyrylcholinesterase (BChE). Therefore, obtained equations in this QSAR study could be employed to calculate the inhibition constant (Ki) value for compounds having a similar structure as N-aryl derivatives described here. The QSAR study showed that bond lengths, molecular electrostatic potential and frontier orbital energies are important in both ChE targets. Docking studies revealed that

From Solidification Processing to Microstructure to Mechanical Properties: A Multi-scale X-ray Study of an Al-Cu Alloy Sample

Science.gov (United States)

Tourret, D.; Mertens, J. C. E.; Lieberman, E.; Imhoff, S. D.; Gibbs, J. W.; Henderson, K.; Fezzaa, K.; Deriy, A. L.; Sun, T.; Lebensohn, R. A.; Patterson, B. M.; Clarke, A. J.

2017-11-01

We follow an Al-12 at. pct Cu alloy sample from the liquid state to mechanical failure, using in situ X-ray radiography during directional solidification and tensile testing, as well as three-dimensional computed tomography of the microstructure before and after mechanical testing. The solidification processing stage is simulated with a multi-scale dendritic needle network model, and the micromechanical behavior of the solidified microstructure is simulated using voxelized tomography data and an elasto-viscoplastic fast Fourier transform model. This study demonstrates the feasibility of direct in situ monitoring of a metal alloy microstructure from the liquid processing stage up to its mechanical failure, supported by quantitative simulations of microstructure formation and its mechanical behavior.

A Study on Bipedal and Mobile Robot Behavior Through Modeling and Simulation

Directory of Open Access Journals (Sweden)

Nirmala Nirmala

2015-05-01

Full Text Available The purpose of this work is to study and analyze mobile robot behavior. In performing this, a framework is adopted and developed for mobile and bipedal robot. The robots are design, build, and run as proceed from the development of mechanical structure, electronics and control integration, and control software application. The behavior of those robots are difficult to be observed and analyzed qualitatively. To evaluate the design and behavior quality, modeling and simulation of robot structure and its task capability is performed. The stepwise procedure to robot behavior study is explained. Behavior cases study are experimented to bipedal robots, transporter robot and Autonomous Guided Vehicle (AGV developed at our institution. The experimentation are conducted on those robots by adjusting their dynamic properties and/or surrounding environment. Validation is performed by comparing the simulation result and the real robot execution. The simulation gives a more idealistic behavior execution rather than realistic one. Adjustments are performed to fine tuning simulation's parameters to provide a more realistic performance.

Temperature Effects on Tensile and Compressive Mechanical Behaviors of C-S-H Structure via Atomic Simulation

Directory of Open Access Journals (Sweden)

Hao Xin

2017-01-01

Full Text Available An atomic scale model of amorphous calcium silicate hydrate (C-S-H with Ca/Si ratio of 1.67 is constructed. Effects of temperature on mechanical properties of C-S-H structure under tensile and compressive loading in the layered direction are investigated via molecular dynamics simulations. Results from present simulations show that (1 the tensile strength and Young’s modulus of C-S-H structure significantly decrease with the increase of the temperature; (2 the water layer plays an important role in the mechanical properties of C-S-H structure; (3 the compressive strength is stronger than tensile strength, which corresponds with the characteristic of cement paste.

Application of discrete element method to study mechanical behaviors of ceramic breeder pebble beds

International Nuclear Information System (INIS)

An Zhiyong; Ying, Alice; Abdou, Mohamed

2007-01-01

In this paper, the discrete element method (DEM) approach has been applied to study mechanical behaviors of ceramic breeder pebble beds. Directly simulating the contact state of each individual particle by the physically based interaction laws, the DEM numerical program is capable of predicting the mechanical behaviors of non-standard packing structures. The program can also provide the data to trace the evolution of contact characteristics and forces as deformation proceeds, as well as the particle movement when the pebble bed is subjected to external loadings. Our numerical simulations focus on predicting the mechanical behaviors of ceramic breeder pebble beds, which include typical fusion breeder materials in solid breeder blankets. Current numerical results clearly show that the packing density and the bed geometry can have an impact on the mechanical stiffness of the pebble beds. Statistical data show that the contact forces are highly related to the contact status of the pebbles

Microstructure distribution and mechanical properties prediction of boron alloy during hot forming using FE simulation

International Nuclear Information System (INIS)

Cui Junjia; Lei Chengxi; Xing Zhongwen; Li Chunfeng

2012-01-01

Highlights: ► We model microstructural evolution during hot forming using a metallo-thermo-mechanical model. ► The effect of water-cooled on temperature distribution of blank and tools was investigated. ► The effect of process parameters on microstructure and mechanical properties were investigated. ► FE results were compared to experimental results and the errors of mechanical properties were in a reasonable scope. - Abstract: As a theoretical tool predicting microstructural evolution of boron alloy, the finite element (FE) method has received considerable attention in recent years. In this work, we focus on the boron alloy under non-isothermal hot forming conditions and establish a fully coupled metallo-thermo-mechanical model taking account of cooling and oxide. Based on the proposed model, we investigate the phase transformation and predict the hardness during the hot forming process via FE simulation. In addition, according to the hardness, the tensile strength during non-isothermal forming is predicted. Supporting the feasibility of the proposed model is the experiments where BR1500HS alloy is hot-worked at various conditions that derive a promising agreement of microstructures, hardness, and tensile strength to the simulation data.

Numerical Simulation on a Possible Formation Mechanism of Interplanetary Magnetic Cloud Boundaries

Science.gov (United States)

Fan, Quan-Lin; Wei, Feng-Si; Feng, Xue-Shang

2003-08-01

The formation mechanism of the interplanetary magnetic cloud (MC) boundaries is numerically investigated by simulating the interactions between an MC of some initial momentum and a local interplanetary current sheet. The compressible 2.5D MHD equations are solved. Results show that the magnetic reconnection process is a possible formation mechanism when an MC interacts with a surrounding current sheet. A number of interesting features are found. For instance, the front boundary of the MCs is a magnetic reconnection boundary that could be caused by a driven reconnection ahead of the cloud, and the tail boundary might be caused by the driving of the entrained flow as a result of the Bernoulli principle. Analysis of the magnetic field and plasma data demonstrates that at these two boundaries appear large value of the plasma parameter β, clear increase of plasma temperature and density, distinct decrease of magnetic magnitude, and a transition of magnetic field direction of about 180 degrees. The outcome of the present simulation agrees qualitatively with the observational results on MC boundary inferred from IMP-8, etc. The project supported by National Natural Science Foundation of China under Grant Nos. 40104006, 49925412, and 49990450

Shock Mechanism Analysis and Simulation of High-Power Hydraulic Shock Wave Simulator

Directory of Open Access Journals (Sweden)

Xiaoqiu Xu

2017-01-01

Full Text Available The simulation of regular shock wave (e.g., half-sine can be achieved by the traditional rubber shock simulator, but the practical high-power shock wave characterized by steep prepeak and gentle postpeak is hard to be realized by the same. To tackle this disadvantage, a novel high-power hydraulic shock wave simulator based on the live firing muzzle shock principle was proposed in the current work. The influence of the typical shock characteristic parameters on the shock force wave was investigated via both theoretical deduction and software simulation. According to the obtained data compared with the results, in fact, it can be concluded that the developed hydraulic shock wave simulator can be applied to simulate the real condition of the shocking system. Further, the similarity evaluation of shock wave simulation was achieved based on the curvature distance, and the results stated that the simulation method was reasonable and the structural optimization based on software simulation is also beneficial to the increase of efficiency. Finally, the combination of theoretical analysis and simulation for the development of artillery recoil tester is a comprehensive approach in the design and structure optimization of the recoil system.

Experimental and numerical study of the mechanical behaviour modelling of a metal-ceramic composite: MoTiC30%

International Nuclear Information System (INIS)

Cedat, D.

2008-11-01

In the scope of refractory materials development for structural applications in the core of the future nuclear reactors, several studies have been developed. The aim of this work is to increase the knowledge of the mechanical behaviour and the damage of the ceramic-metal composite Mo(TiC)x% under the temperature range [25-700 C]. The identification of the third phase, formed by diffusion during the sintering step was identified by microstructural characterization. Experimental study also revealed the percolation of the ceramic particles through the structure. Mechanical tests highlight the main characteristics of the material: the macroscopic behaviour depends on the strain rate on the first hand and the temperature on the other hand. These mechanisms are attributed to the thermally activated behaviour of molybdenum. Simulations have been made on several microstructures considering elastic-brittle inclusion in a viscoelastic matrix. A polycrystalline model was used to simulate the evolution of the mechanical behaviour of the composite. The numerical aggregate, used for the simulation, was built from a 3D reconstruction technique thanks to acquisition of FIB/EBSD/SEM data. (author)

The Simulation of Precipitation Evolutions and Mechanical Properties in Friction Stir Welding with Post-Weld Heat Treatments

Science.gov (United States)

Zhang, Z.; Wan, Z. Y.; Lindgren, L.-E.; Tan, Z. J.; Zhou, X.

2017-12-01

A finite element model of friction stir welding capable of re-meshing is used to simulate the temperature variations. Re-meshing of the finite element model is used to maintain a fine mesh resolving the gradients of the solution. The Kampmann-Wagner numerical model for precipitation is then used to study the relation between friction stir welds with post-weld heat treatment (PWHT) and the changes in mechanical properties. Results indicate that the PWHT holding time and PWHT holding temperature need to be optimally designed to obtain FSW with better mechanical properties. Higher precipitate number with lower precipitate sizes gives higher strength in the stirring zone after PWHT. The coarsening of precipitates in HAZ are the main reason to hinder the improvement of mechanical property when PWHT is used.

Computer Simulation Studies of Trishomocubane Heptapeptide of ...

African Journals Online (AJOL)

As part of an extension on the cage peptide chemistry, the present work involves an assessment of the conformational profile of trishomocubane heptapeptide of the type Ac-Ala3-Tris-Ala3-NHMe using molecular dynamics (MD) simulations. All MD protocols were explored within the framework of a molecular mechanics ...

Computational simulation of static/cyclic cell stimulations to investigate mechanical modulation of an individual mesenchymal stem cell using confocal microscopy

International Nuclear Information System (INIS)

Alihemmati, Zakieh; Vahidi, Bahman; Haghighipour, Nooshin; Salehi, Mohammad

2017-01-01

It has been found that cells react to mechanical stimuli, while the type and magnitude of these cells are different in various physiological and pathological conditions. These stimuli may affect cell behaviors via mechanotransduction mechanisms. The aim of this study is to evaluate mechanical responses of a mesenchymal stem cell (MSC) to a pressure loading using finite elements method (FEM) to clarify procedures of MSC mechanotransduction. The model is constructed based on an experimental set up in which statics and cyclic compressive loads are implemented on a model constructed from a confocal microscopy 3D image of a stem cell. Both of the applied compressive loads are considered in the physiological loading regimes. Moreover, a viscohyperelastic material model was assumed for the cell through which the finite elements simulation anticipates cell behavior based on strain and stress distributions in its components. As a result, high strain and stress values were captured from the viscohyperelastic model because of fluidic behavior of cytosol when compared with the obtained results through the hyperelastic models. It can be concluded that the generated strain produced by cyclic pressure is almost 8% higher than that caused by the static load and the von Mises stress distribution is significantly increased to about 150 kPa through the cyclic loading. In total, the results does not only trace the efficacy of an individual 3D model of MSC using biomechanical experiments of cell modulation, but these results provide knowledge in interpretations from cell geometry. The current study was performed to determine a realistic aspect of cell behavior. - Graphical abstract: Based on confocal microscopy images and through finite elements analysis, we simulate mechanical behavior of the stem cell components (the cell membrane, cytoplasm and nucleus) under a compressive load. A major novelty of this investigation is the usage of viscohyperelastic behavior for the realistic stem

Three-dimensional numerical study on the mechanism of anisotropic MCCI by improved MPS method

Energy Technology Data Exchange (ETDEWEB)

Li, Xin, E-mail: lixin@fuji.waseda.jp; Yamaji, Akifumi

2017-04-01

Highlights: • 3-D simulation of a MCCI test was presented with improved moving particle method. • The influence of thermally stable silica aggregates on MCCI has been investigated. • The mechanisms for isotropic/anisotropic ablation have been clarified mechanistically. - Abstract: In two-dimensional (2-D) molten corium-concrete interaction (MCCI) experiments with prototypic corium and siliceous concrete, the more pronounced lateral concrete erosion behavior than that in the axial direction, namely anisotropic ablation, has been a research interest. However, the knowledge of the mechanism on this anisotropic ablation behavior, which is important for severe accident analysis and management, is still limited. In this paper, 3-D simulation of 2-D MCCI experiment VULCANO VB-U7 has been carried out with improved Moving Particle Semi-implicit (MPS) method. Heat conduction, phase change, and corium viscosity models have been developed and incorporated into MPS code MPS-SW-MAIN-Ver.2.0 for current study. The influence of thermally stable silica aggregates has been investigated by setting up different simulation cases for analysis. The simulation results suggested reasonable models and assumptions to be considered in order to achieve best estimation of MCCI with prototypic oxidic corium and siliceous concrete. The simulation results also indicated that silica aggregates can contribute to anisotropic ablation. The mechanisms for anisotropic ablation pattern in siliceous concrete as well as isotropic ablation pattern in limestone-rich concrete have been clarified from a mechanistic perspective.

Characterization of the mechanical properties of polyphenylene polymer using molecular dynamics simulations

Energy Technology Data Exchange (ETDEWEB)

Ansari, R.; Ajori, S. [Department of Mechanical Engineering, University of Guilan, P.O. Box 3756, Rasht (Iran, Islamic Republic of); Rouhi, S., E-mail: s_rouhi@iaul.ac.ir [Young Researchers and Elite Club, Langroud Branch, Islamic Azad University, Langroud, Guilan (Iran, Islamic Republic of)

2016-01-15

Synthesizing polyphenylene polymer, a two-dimensional hydrocarbon known as porous graphene, has led to the initiation of a new age in nanoscience. In this investigation, molecular dynamics (MD) simulations are carried out to study the mechanical properties of porous graphene such as Young's modulus, Poisson's ratio, bulk modulus and ultimate strength and strain. The fracture initiation and propagation pattern of porous graphene are also considered in this study. The results show that Young's and bulk moduli of porous graphene are lower than those of graphene, graphene and graphyne. Unlikely, it is also observed that its Poisson's ratio is considerably more than that of graphene, graphene and graphyne. Furthermore, it is found out that Young's and bulk moduli as well as fracture strain and ultimate stress are extremely size-dependent and also the porous graphene can be considered as an isotropic material.

Effect of Welding Thermal Cycles on Microstructure and Mechanical Properties of Simulated Heat Affected Zone for a Weldox 1300 Ultra-High Strength Alloy Steel

Directory of Open Access Journals (Sweden)

Węglowski M. St.

2016-03-01

Full Text Available In the present study, the investigation of weldability of ultra-high strength steel has been presented. The thermal simulated samples were used to investigate the effect of welding cooling time t8/5 on microstructure and mechanical properties of heat affected zone (HAZ for a Weldox 1300 ultra-high strength steel. In the frame of these investigation the microstructure was studied by light and transmission electron microscopies. Mechanical properties of parent material were analysed by tensile, impact and hardness tests. In details the influence of cooling time in the range of 2,5 ÷ 300 sec. on hardness, impact toughness and microstructure of simulated HAZ was studied by using welding thermal simulation test. The microstructure of ultra-high strength steel is mainly composed of tempered martensite. The results show that the impact toughness and hardness decrease with increase of t8/5 under condition of a single thermal cycle in simulated HAZ. The increase of cooling time to 300 s causes that the microstructure consists of ferrite and bainite mixture. Lower hardness, for t8/5 ≥ 60 s indicated that low risk of cold cracking in HAZ for longer cooling time, exists.

Comparative study on deformation and mechanical behavior of corroded pipe: Part I–Numerical simulation and experimental investigation under impact load

Directory of Open Access Journals (Sweden)

Dong-Man Ryu

2017-09-01

Full Text Available Experiments and a numerical simulation were conducted to investigate the deformation and impact behavior of a corroded pipe, as corrosion, fatigue, and collision phenomena frequently occur in subsea pipelines. This study focuses on the deformation of the corrosion region and the variation of the geometry of the pipe under impact loading. The experiments for the impact behavior of the corroded pipe were performed using an impact test apparatus to validate the results of the simulation. In addition, during the simulation, material tests were performed, and the results were applied to the simulation. The ABAQUS explicit finite element analysis program was used to perform numerical simulations for the parametric study, as well as experiment scenarios, to investigate the effects of defects under impact loading. In addition, the modified ASME B31.8 code formula was proposed to define the damage range for the dented pipe.

Photochemical reactions in biological systems: probing the effect of the environment by means of hybrid quantum chemistry/molecular mechanics simulations.

Science.gov (United States)

Boggio-Pasqua, Martial; Burmeister, Carl F; Robb, Michael A; Groenhof, Gerrit

2012-06-14

Organisms have evolved a wide variety of mechanisms to utilize and respond to light. In many cases, the biological response is mediated by structural changes that follow photon absorption in a protein complex. The initial step in such cases is normally the photoisomerization of a highly conjugated prosthetic group. To understand better the factors controlling the isomerization, we perform atomistic molecular dynamics simulations. In this perspective article we briefly review the key theoretical concepts of photochemical reactions and present a practical simulation scheme for simulating photochemical reactions in biomolecular systems. In our scheme, a multi-configurational quantum mechanical description is used to model the electronic rearrangement for those parts of the system that are involved in the photon absorption. For the remainder, typically consisting of the apo-protein and the solvent, a simple force field model is used. The interactions in the systems are thus computed within a hybrid quantum/classical framework. Forces are calculated on-the-fly, and a diabatic surface hopping procedure is used to model the excited-state decay. To demonstrate how this method is used we review our studies on photoactivation of the photoactive yellow protein, a bacterial photoreceptor. We will show what information can be obtained from the simulations, and, by comparing to recent experimental findings, what the limitations of our simulations are.

ISRU Soil Mechanics Vacuum Facility: Soil Bin Preparation and Simulant Strength Characterization

Science.gov (United States)

Kleinhenz, Julie; Wilkinson, Allen

2012-01-01

Testing in relevant environments is key to exploration mission hardware development. This is true on both the component level (in early development) and system level (in late development stages). During ISRU missions the hardware will interface with the soil (digging, roving, etc) in a vacuum environment. A relevant test environment will therefore involve a vacuum chamber with a controlled, conditioned simulant bed. However, in earth-based granular media, such as lunar soil simulant, gases trapped within the material pore structures and water adsorbed to all particle surfaces will release when exposed to vacuum. Early vacuum testing has shown that this gas release can occur violently, which loosens and weakens the simulant, altering the consolidation state. The Vacuum Facility #13, a mid-size chamber (3.66m tall, 1.5m inner diameter) at the NASA Glenn Research Center has been modified to create a soil mechanics test facility. A 0.64m deep by 0.914m square metric ton bed of lunar simulant was placed under vacuum using a variety of pumping techniques. Both GRC-3 and LHT-3M simulant types have been used. An electric cone penetrometer was used to measure simulant strength properties at vacuum including: cohesion, friction angle, bulk density and shear modulus. Simulant disruptions, caused by off gassing, affected the strength properties, but could be mitigated by reducing pump rate. No disruptions were observed at pressures below 2.5Torr, regardless of the pump rate. However, slow off gassing of the soil lead to long test times, a full week, to reach 10-5Torr. This work highlights the need for robotic machine-simulant hardware and operations in vacuum to expeditiously perform (sub-)systems tests.

Temperature dependence of creep compliance of highly cross-linked epoxy: A molecular simulation study

International Nuclear Information System (INIS)

Khabaz, Fardin; Khare, Ketan S.; Khare, Rajesh

2014-01-01

We have used molecular dynamics (MD) simulations to study the effect of temperature on the creep compliance of neat cross-linked epoxy. Experimental studies of mechanical behavior of cross-linked epoxy in literature commonly report creep compliance values, whereas molecular simulations of these systems have primarily focused on the Young’s modulus. In this work, in order to obtain a more direct comparison between experiments and simulations, atomistically detailed models of the cross-linked epoxy are used to study their creep compliance as a function of temperature using MD simulations. The creep tests are performed by applying a constant tensile stress and monitoring the resulting strain in the system. Our results show that simulated values of creep compliance increase with an increase in both time and temperature. We believe that such calculations of the creep compliance, along with the use of time temperature superposition, hold great promise in connecting the molecular insight obtained from molecular simulation at small length- and time-scales with the experimental behavior of such materials. To the best of our knowledge, this work is the first reported effort that investigates the creep compliance behavior of cross-linked epoxy using MD simulations

Development and mechanical properties of construction materials from lunar simulant

Science.gov (United States)

Desai, Chandra S.

1992-01-01

Development of versatile engineering materials from locally available materials in space is an important step toward the establishment of outposts on the Moon and Mars. Development of the technologies for manufacture of structural and construction materials on the Moon, utilizing local lunar soil (regolith), without the use of water, is an important element for habitats and explorations in space. It is also vital that the mechanical behavior such as strength and tensile, flexural properties, fracture toughness, ductility, and deformation characteristics are defined toward establishment of the ranges of engineering applications of the materials developed. The objectives include two areas: (1) thermal 'liquefaction' of lunar simulant (at about 1100 C) with different additives (fibers, powders, etc.), and (2) development and use of a new triaxial test device in which lunar simulants are first compacted under cycles of loading, and then tested with different vacuums and initial confining or in situ stress. Details of the development of intermediate ceramic composites (ICC) and testing for their flexural and compression characteristics were described in various reports and papers. The subject of behavior of compacted simulant under vacuum was described in previous progress reports and publications; since the presently available device allows vacuum levels up to only 10(exp -4) torr, it is recommended that a vacuum pump that can allow higher levels of vacuum be utilized for further investigation.

Adaptive coupling between damage mechanics and peridynamics: a route for objective simulation of material degradation up to complete failure

KAUST Repository

Han, Fei

2016-05-17

The objective (mesh-independent) simulation of evolving discontinuities, such as cracks, remains a challenge. Current techniques are highly complex or involve intractable computational costs, making simulations up to complete failure difficult. We propose a framework as a new route toward solving this problem that adaptively couples local-continuum damage mechanics with peridynamics to objectively simulate all the steps that lead to material failure: damage nucleation, crack formation and propagation. Local-continuum damage mechanics successfully describes the degradation related to dispersed microdefects before the formation of a macrocrack. However, when damage localizes, it suffers spurious mesh dependency, making the simulation of macrocracks challenging. On the other hand, the peridynamic theory is promising for the simulation of fractures, as it naturally allows discontinuities in the displacement field. Here, we present a hybrid local-continuum damage/peridynamic model. Local-continuum damage mechanics is used to describe “volume” damage before localization. Once localization is detected at a point, the remaining part of the energy is dissipated through an adaptive peridynamic model capable of the transition to a “surface” degradation, typically a crack. We believe that this framework, which actually mimics the real physical process of crack formation, is the first bridge between continuum damage theories and peridynamics. Two-dimensional numerical examples are used to illustrate that an objective simulation of material failure can be achieved by this method.

Adaptive coupling between damage mechanics and peridynamics: a route for objective simulation of material degradation up to complete failure

KAUST Repository

Han, Fei; Lubineau, Gilles; Azdoud, Yan

2016-01-01

The objective (mesh-independent) simulation of evolving discontinuities, such as cracks, remains a challenge. Current techniques are highly complex or involve intractable computational costs, making simulations up to complete failure difficult. We propose a framework as a new route toward solving this problem that adaptively couples local-continuum damage mechanics with peridynamics to objectively simulate all the steps that lead to material failure: damage nucleation, crack formation and propagation. Local-continuum damage mechanics successfully describes the degradation related to dispersed microdefects before the formation of a macrocrack. However, when damage localizes, it suffers spurious mesh dependency, making the simulation of macrocracks challenging. On the other hand, the peridynamic theory is promising for the simulation of fractures, as it naturally allows discontinuities in the displacement field. Here, we present a hybrid local-continuum damage/peridynamic model. Local-continuum damage mechanics is used to describe “volume” damage before localization. Once localization is detected at a point, the remaining part of the energy is dissipated through an adaptive peridynamic model capable of the transition to a “surface” degradation, typically a crack. We believe that this framework, which actually mimics the real physical process of crack formation, is the first bridge between continuum damage theories and peridynamics. Two-dimensional numerical examples are used to illustrate that an objective simulation of material failure can be achieved by this method.

Electrochemical Study of Esculetin Nitration by Digital Simulation of Cyclic Voltammograms

Directory of Open Access Journals (Sweden)

Lida Khalafi

2013-01-01

Full Text Available The reaction of electrochemically generated o-quinones from oxidation of esculetin as Michael acceptor with nitrite ion as nucleophile has been studied using cyclic voltammetry. The reaction mechanism is believed to be EC, including oxidation of catechol moiety of esculetin followed by Michael addition of nitrite ion. The observed homogeneous rate constants (obs for reactions were estimated by comparing the experimental voltammetric responses with the digitally simulated results based on the proposed mechanism. Also the effects of pH and nucleophile concentration on voltammetric behavior and the rate constants of chemical reactions were described.

Simulation of the mechanical behavior of a spent fuel shipping cask in a rail accident environment

International Nuclear Information System (INIS)

Fields, S.R.

1977-02-01

A preliminary mathematical model has been developed to simulate the dynamic mechanical response of a large spent fuel shipping cask to the impact experienced in a hypothetical rail accident. The report was written to record the status of the development of the mechanical response model and to supplement an earlier report on spent fuel shipping cask accident evaluation

A Numerical Study of Scalable Cardiac Electro-Mechanical Solvers on HPC Architectures

Directory of Open Access Journals (Sweden)

Piero Colli Franzone

2018-04-01

Full Text Available We introduce and study some scalable domain decomposition preconditioners for cardiac electro-mechanical 3D simulations on parallel HPC (High Performance Computing architectures. The electro-mechanical model of the cardiac tissue is composed of four coupled sub-models: (1 the static finite elasticity equations for the transversely isotropic deformation of the cardiac tissue; (2 the active tension model describing the dynamics of the intracellular calcium, cross-bridge binding and myofilament tension; (3 the anisotropic Bidomain model describing the evolution of the intra- and extra-cellular potentials in the deforming cardiac tissue; and (4 the ionic membrane model describing the dynamics of ionic currents, gating variables, ionic concentrations and stretch-activated channels. This strongly coupled electro-mechanical model is discretized in time with a splitting semi-implicit technique and in space with isoparametric finite elements. The resulting scalable parallel solver is based on Multilevel Additive Schwarz preconditioners for the solution of the Bidomain system and on BDDC preconditioned Newton-Krylov solvers for the non-linear finite elasticity system. The results of several 3D parallel simulations show the scalability of both linear and non-linear solvers and their application to the study of both physiological excitation-contraction cardiac dynamics and re-entrant waves in the presence of different mechano-electrical feedbacks.

Numerical simulation of the heat extraction in EGS with thermal-hydraulic-mechanical coupling method based on discrete fractures model

International Nuclear Information System (INIS)

Sun, Zhi-xue; Zhang, Xu; Xu, Yi; Yao, Jun; Wang, Hao-xuan; Lv, Shuhuan; Sun, Zhi-lei; Huang, Yong; Cai, Ming-yu; Huang, Xiaoxue

2017-01-01

The Enhanced Geothermal System (EGS) creates an artificial geothermal reservoir by hydraulic fracturing which allows heat transmission through the fractures by the circulating fluids as they extract heat from Hot Dry Rock (HDR). The technique involves complex thermal–hydraulic–mechanical (THM) coupling process. A numerical approach is presented in this paper to simulate and analyze the heat extraction process in EGS. The reservoir is regarded as fractured porous media consisting of rock matrix blocks and discrete fracture networks. Based on thermal non-equilibrium theory, the mathematical model of THM coupling process in fractured rock mass is used. The proposed model is validated by comparing it with several analytical solutions. An EGS case from Cooper Basin, Australia is simulated with 2D stochastically generated fracture model to study the characteristics of fluid flow, heat transfer and mechanical response in geothermal reservoir. The main parameters controlling the outlet temperature of EGS are also studied by sensitivity analysis. The results shows the significance of taking into account the THM coupling effects when investigating the efficiency and performance of EGS. - Highlights: • EGS reservoir comprising discrete fracture networks and matrix rock is modeled. • A THM coupling model is proposed for simulating the heat extraction in EGS. • The numerical model is validated by comparing with several analytical solutions. • A case study is presented for understanding the main characteristics of EGS. • The THM coupling effects are shown to be significant factors to EGS's running performance.

Sub-discretized surface model with application to contact mechanics in multi-body simulation

Energy Technology Data Exchange (ETDEWEB)

Johnson, S; Williams, J

2008-02-28

The mechanics of contact between rough and imperfectly spherical adhesive powder grains are often complicated by a variety of factors, including several which vary over sub-grain length scales. These include several traction factors that vary spatially over the surface of the individual grains, including high energy electron and acceptor sites (electrostatic), hydrophobic and hydrophilic sites (electrostatic and capillary), surface energy (general adhesion), geometry (van der Waals and mechanical), and elasto-plastic deformation (mechanical). For mechanical deformation and reaction, coupled motions, such as twisting with bending and sliding, as well as surface roughness add an asymmetry to the contact force which invalidates assumptions for popular models of contact, such as the Hertzian and its derivatives, for the non-adhesive case, and the JKR and DMT models for adhesive contacts. Though several contact laws have been offered to ameliorate these drawbacks, they are often constrained to particular loading paths (most often normal loading) and are relatively complicated for computational implementation. This paper offers a simple and general computational method for augmenting contact law predictions in multi-body simulations through characterization of the contact surfaces using a hierarchically-defined surface sub-discretization. For the case of adhesive contact between powder grains in low stress regimes, this technique can allow a variety of existing contact laws to be resolved across scales, allowing for moments and torques about the contact area as well as normal and tangential tractions to be resolved. This is especially useful for multi-body simulation applications where the modeler desires statistical distributions and calibration for parameters in contact laws commonly used for resolving near-surface contact mechanics. The approach is verified against analytical results for the case of rough, elastic spheres.

Mechanics of Sister Chromatids studied with a Polymer Model

Directory of Open Access Journals (Sweden)

Yang eZhang

2013-10-01

Full Text Available Sister chromatid cohesion denotes the phenomenon that sister chromatids are initially attached to each other in mitosis to guarantee the error-free distribution into the daughter cells. Cohesion is mediated by binding proteins and only resolved after mitotic chromosome condensation is completed. However, the amount of attachement points required to maintain sister chromatid cohesion while still allowing proper chromosome condensation is not known yet. Additionally the impact of cohesion on the mechanical properties of chromosomes also poses an interesting problem. In this work we study the conformational and mechanical properties of sister chromatids by means of computer simulations. We model both protein-mediated cohesion between sister chromatids and chromosome condensation with a dynamic binding mechanisms. We show in a phase diagram that only specific link concentrations lead to connected and fully condensed chromatids that do not intermingle with each other nor separate due to entropic forces. Furthermore we show that dynamic bonding between chromatids decrease the Young's modulus compared to non-bonded chromatids.

Influence of circumferential notch and fatigue crack on the mechanical integrity of biodegradable magnesium-based alloy in simulated body fluid.

Science.gov (United States)

Bobby Kannan, M; Singh Raman, R K; Witte, F; Blawert, C; Dietzel, W

2011-02-01

Applications of magnesium alloys as biodegradable orthopaedic implants are critically dependent on the mechanical integrity of the implant during service. In this study, the mechanical integrity of an AZ91 magnesium alloy was studied using a constant extension rate tensile (CERT) method. The samples in two different geometries that is, circumferentially notched (CN), and circumferentially notched and fatigue cracked (CNFC), were tested in air and in simulated body fluid (SBF). The test results show that the mechanical integrity of the AZ91 magnesium alloy decreased substantially (∼50%) in both the CN and CNFC samples exposed to SBF. Fracture surface analysis revealed secondary cracks suggesting stress corrosion cracking susceptibility of the alloy in SBF. Copyright © 2010 Wiley Periodicals, Inc.

The Passive Film Growth Mechanism of New Corrosion-Resistant Steel Rebar in Simulated Concrete Pore Solution: Nanometer Structure and Electrochemical Study.

Science.gov (United States)

Jiang, Jin-Yang; Wang, Danqian; Chu, Hong-Yan; Ma, Han; Liu, Yao; Gao, Yun; Shi, Jinjie; Sun, Wei

2017-04-14

An elaborative study was carried out on the growth mechanism and properties of the passive film for a new kind of alloyed corrosion-resistant steel (CR steel). The passive film naturally formed in simulated concrete pore solutions (pH = 13.3). The corrosion resistance was evaluated by various methods including open circuit potential (OCP), linear polarization resistance (LPR) measurements, and electrochemical impedance spectroscopy (EIS). Meanwhile, the 2205 duplex stainless steel (SS steel) was evaluated for comparison. Moreover, the passive film with CR steel was studied by means of X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), Atomic Force Microscope (AFM), and the Mott‑Schottky approach. The results showed that the excellent passivity of CR steel could be detected in a high alkaline environment. The grain boundaries between the fine passive film particles lead to increasing Cr oxide content in the later passivation stage. The filling of cation vacancies in the later passivation stage as well as the orderly crystalized inner layer contributed to the excellent corrosion resistance of CR steel. A passive film growth model for CR steel was proposed.

BSim models for 2 case-studies of naturally and mechanically ventilated daycare institutions

Energy Technology Data Exchange (ETDEWEB)

Kalyanova, O.; Heiselberg, P.

2009-06-15

The report intends to provide complete information necessary for evaluation of assumptions made in the models and conclusions derived from the results of simulation of two different institutions in various operational modes. Thermal models are prepared for two day-care buildings, one which is mechanically ventilated and one which is naturally ventilated. All simulations were preformed in BSim, and all the models are simulated in the current version og BSim which is version 6,8,9,8. The results of the simulations showed that it is possible to reduce energy use for ventilation, both in mechanically and naturally ventilated child care center without compromising indoor air quality. (ln)

Thermal and Mechanical Non-Equilibrium Effects on Turbulent Flows: Fundamental Studies of Energy Exchanges Through Direct Numerical Simulations, Molecular Simulations and Experiments

Science.gov (United States)

2016-02-26

photochemical TNE generation, and chemistry of non- equilibrium phenomena. We have investigated a new concept to generate turbulence using photo-initiated...AFRL-AFOSR-VA-TR-2016-0104 Thermal and mechanical non- equilibrium effects on turbulent flows:fundamental studies of energy exchanges through direct...Performance 3. DATES COVERED (From - To) 15-09-2012 to 14-11-2015 4. TITLE AND SUBTITLE Thermal and mechanical non- equilibrium effects on turbulent

Quantum mechanical force fields for condensed phase molecular simulations

Science.gov (United States)

Giese, Timothy J.; York, Darrin M.

2017-09-01

Molecular simulations are powerful tools for providing atomic-level details into complex chemical and physical processes that occur in the condensed phase. For strongly interacting systems where quantum many-body effects are known to play an important role, density-functional methods are often used to provide the model with the potential energy used to drive dynamics. These methods, however, suffer from two major drawbacks. First, they are often too computationally intensive to practically apply to large systems over long time scales, limiting their scope of application. Second, there remain challenges for these models to obtain the necessary level of accuracy for weak non-bonded interactions to obtain quantitative accuracy for a wide range of condensed phase properties. Quantum mechanical force fields (QMFFs) provide a potential solution to both of these limitations. In this review, we address recent advances in the development of QMFFs for condensed phase simulations. In particular, we examine the development of QMFF models using both approximate and ab initio density-functional models, the treatment of short-ranged non-bonded and long-ranged electrostatic interactions, and stability issues in molecular dynamics calculations. Example calculations are provided for crystalline systems, liquid water, and ionic liquids. We conclude with a perspective for emerging challenges and future research directions.

Gating mechanisms of mechanosensitive channels of large conductance, I: a continuum mechanics-based hierarchical framework.

Science.gov (United States)

Chen, Xi; Cui, Qiang; Tang, Yuye; Yoo, Jejoong; Yethiraj, Arun

2008-07-01

A hierarchical simulation framework that integrates information from molecular dynamics (MD) simulations into a continuum model is established to study the mechanical response of mechanosensitive channel of large-conductance (MscL) using the finite element method (FEM). The proposed MD-decorated FEM (MDeFEM) approach is used to explore the detailed gating mechanisms of the MscL in Escherichia coli embedded in a palmitoyloleoylphosphatidylethanolamine lipid bilayer. In Part I of this study, the framework of MDeFEM is established. The transmembrane and cytoplasmic helices are taken to be elastic rods, the loops are modeled as springs, and the lipid bilayer is approximated by a three-layer sheet. The mechanical properties of the continuum components, as well as their interactions, are derived from molecular simulations based on atomic force fields. In addition, analytical closed-form continuum model and elastic network model are established to complement the MDeFEM approach and to capture the most essential features of gating. In Part II of this study, the detailed gating mechanisms of E. coli-MscL under various types of loading are presented and compared with experiments, structural model, and all-atom simulations, as well as the analytical models established in Part I. It is envisioned that such a hierarchical multiscale framework will find great value in the study of a variety of biological processes involving complex mechanical deformations such as muscle contraction and mechanotransduction.

Study of photo-oxidative reactivity of sunscreening agents based on photo-oxidation of uric acid by kinetic Monte Carlo simulation

International Nuclear Information System (INIS)

Moradmand Jalali, Hamed; Bashiri, Hadis; Rasa, Hossein

2015-01-01

In the present study, the mechanism of free radical production by light-reflective agents in sunscreens (TiO 2 , ZnO and ZrO 2 ) was obtained by applying kinetic Monte Carlo simulation. The values of the rate constants for each step of the suggested mechanism have been obtained by simulation. The effect of the initial concentration of mineral oxides and uric acid on the rate of uric acid photo-oxidation by irradiation of some sun care agents has been studied. The kinetic Monte Carlo simulation results agree qualitatively with the existing experimental data for the production of free radicals by sun care agents. - Highlights: • The mechanism and kinetics of uric acid photo-oxidation by irradiation of sun care agents has been obtained by simulation. • The mechanism has been used for free radical production of TiO 2 (rutile and anatase), ZnO and ZrO 2 . • The ratios of photo-activity of ZnO to anastase, rutile and ZrO have been obtained. • By doubling the initial concentrations of mineral oxide, the rate of reaction was doubled. • The optimum ratio of initial concentration of mineral oxides to uric acid has been obtained

Influence of grain size on the mechanical properties of nano-crystalline copper; insights from molecular dynamics simulation

Science.gov (United States)

Rida, A.; Makke, A.; Rouhaud, E.; Micoulaut, M.

2017-10-01

We use molecular dynamics simulations to study the mechanical properties of a columnar nanocrystalline copper with a mean grain size between 8.91 nm and 24 nm. The used samples were generated by using a melting cooling method. These samples were submitted to uniaxial tensile test. The results reveal the presence of a critical mean grain size between 16 and 20 nm, where there is an inversion in the conventional Hall-Petch tendency. This inversion is illustrated by the increase of flow stress with the increase of the mean grain size. This transition is caused by shifting of the deformation mechanism from dislocations to a combination of grain boundaries sliding and dislocations. Moreover, the effect of temperature on the mechanical properties of nanocrystalline copper has been investigated. The results show a decrease of the flow stress and Young's modulus when the temperature increases.

Numerical simulation of mechanisms of deformation,failure and energy dissipation in porous rock media subjected to wave stresses

Institute of Scientific and Technical Information of China (English)

无

2010-01-01

The pore characteristics,mineral compositions,physical and mechanical properties of the subarkose sandstones were acquired by means of CT scan,X-ray diffraction and physical tests.A few physical models possessing the same pore characteristics and matrix properties but different porosities compared to the natural sandstones were developed.The 3D finite element models of the rock media with varied porosities were established based on the CT image processing of the physical models and the MIMICS software platform.The failure processes of the porous rock media loaded by the split Hopkinson pressure bar(SHPB) were simulated by satisfying the elastic wave propagation theory.The dynamic responses,stress transition,deformation and failure mechanisms of the porous rock media subjected to the wave stresses were analyzed.It is shown that an explicit and quantitative analysis of the stress,strain and deformation and failure mechanisms of porous rocks under the wave stresses can be achieved by using the developed 3D finite element models.With applied wave stresses of certain amplitude and velocity,no evident pore deformation was observed for the rock media with a porosity less than 15%.The deformation is dominantly the combination of microplasticity(shear strain),cracking(tensile strain) of matrix and coalescence of the cracked regions around pores.Shear stresses lead to microplasticity,while tensile stresses result in cracking of the matrix.Cracking and coalescence of the matrix elements in the neighborhood of pores resulted from the high transverse tensile stress or tensile strain which exceeded the threshold values.The simulation results of stress wave propagation,deformation and failure mechanisms and energy dissipation in porous rock media were in good agreement with the physical tests.The present study provides a reference for analyzing the intrinsic mechanisms of the complex dynamic response,stress transit mode,deformation and failure mechanisms and the disaster

Development and Validation of Chemical Kinetic Mechanism Reduction Scheme for Large-Scale Mechanisms

DEFF Research Database (Denmark)

Poon, Hiew Mun; Ng, Hoon Kiat; Gan, Suyin

2014-01-01

This work is an extension to a previously reported work on chemical kinetic mechanism reduction scheme for large-scale mechanisms. Here, Perfectly Stirred Reactor (PSR) was added as a criterion of data source for mechanism reduction instead of using only auto-ignition condition. As a result......) simulations were performed to study the spray combustion phenomena within a constant volume bomb. Both non-reacting and reacting conditions were applied in this study. Liquid and vapor penetration lengths were replicated for non-reacting diesel spray. For reacting diesel spray, both ignition delay and lift......-off length were simulated. The simulation results were then compared to the experimental data of Sandia National Laboratories and No. 2 Diesel Fuel (D2) was designated as the reference fuel. Both liquid and vapor penetrations for non-reacting condition were well-matched, while ignition delay was advanced...

Development of a finite element code to solve thermo-hydro-mechanical coupling and simulate induced seismicity.

Science.gov (United States)

María Gómez Castro, Berta; De Simone, Silvia; Rossi, Riccardo; Larese De Tetto, Antonia; Carrera Ramírez, Jesús

2015-04-01

Coupled thermo-hydro-mechanical modeling is essential for CO2 storage because of (1) large amounts of CO2 will be injected, which will cause large pressure buildups and might compromise the mechanical stability of the caprock seal, (2) the most efficient technique to inject CO2 is the cold injection, which induces thermal stress changes in the reservoir and seal. These stress variations can cause mechanical failure in the caprock and can also trigger induced earthquakes. To properly assess these effects, numerical models that take into account the short and long-term thermo-hydro-mechanical coupling are an important tool. For this purpose, there is a growing need of codes that couple these processes efficiently and accurately. This work involves the development of an open-source, finite element code written in C ++ for correctly modeling the effects of thermo-hydro-mechanical coupling in the field of CO2 storage and in others fields related to these processes (geothermal energy systems, fracking, nuclear waste disposal, etc.), and capable to simulate induced seismicity. In order to be able to simulate earthquakes, a new lower dimensional interface element will be implemented in the code to represent preexisting fractures, where pressure continuity will be imposed across the fractures.

Fluctuating Finite Element Analysis (FFEA: A continuum mechanics software tool for mesoscale simulation of biomolecules.

Directory of Open Access Journals (Sweden)

Albert Solernou

2018-03-01

Full Text Available Fluctuating Finite Element Analysis (FFEA is a software package designed to perform continuum mechanics simulations of proteins and other globular macromolecules. It combines conventional finite element methods with stochastic thermal noise, and is appropriate for simulations of large proteins and protein complexes at the mesoscale (length-scales in the range of 5 nm to 1 μm, where there is currently a paucity of modelling tools. It requires 3D volumetric information as input, which can be low resolution structural information such as cryo-electron tomography (cryo-ET maps or much higher resolution atomistic co-ordinates from which volumetric information can be extracted. In this article we introduce our open source software package for performing FFEA simulations which we have released under a GPLv3 license. The software package includes a C ++ implementation of FFEA, together with tools to assist the user to set up the system from Electron Microscopy Data Bank (EMDB or Protein Data Bank (PDB data files. We also provide a PyMOL plugin to perform basic visualisation and additional Python tools for the analysis of FFEA simulation trajectories. This manuscript provides a basic background to the FFEA method, describing the implementation of the core mechanical model and how intermolecular interactions and the solvent environment are included within this framework. We provide prospective FFEA users with a practical overview of how to set up an FFEA simulation with reference to our publicly available online tutorials and manuals that accompany this first release of the package.

Fluctuating Finite Element Analysis (FFEA): A continuum mechanics software tool for mesoscale simulation of biomolecules.

Science.gov (United States)

Solernou, Albert; Hanson, Benjamin S; Richardson, Robin A; Welch, Robert; Read, Daniel J; Harlen, Oliver G; Harris, Sarah A

2018-03-01

Fluctuating Finite Element Analysis (FFEA) is a software package designed to perform continuum mechanics simulations of proteins and other globular macromolecules. It combines conventional finite element methods with stochastic thermal noise, and is appropriate for simulations of large proteins and protein complexes at the mesoscale (length-scales in the range of 5 nm to 1 μm), where there is currently a paucity of modelling tools. It requires 3D volumetric information as input, which can be low resolution structural information such as cryo-electron tomography (cryo-ET) maps or much higher resolution atomistic co-ordinates from which volumetric information can be extracted. In this article we introduce our open source software package for performing FFEA simulations which we have released under a GPLv3 license. The software package includes a C ++ implementation of FFEA, together with tools to assist the user to set up the system from Electron Microscopy Data Bank (EMDB) or Protein Data Bank (PDB) data files. We also provide a PyMOL plugin to perform basic visualisation and additional Python tools for the analysis of FFEA simulation trajectories. This manuscript provides a basic background to the FFEA method, describing the implementation of the core mechanical model and how intermolecular interactions and the solvent environment are included within this framework. We provide prospective FFEA users with a practical overview of how to set up an FFEA simulation with reference to our publicly available online tutorials and manuals that accompany this first release of the package.

3D Finite Element Simulation of Pellet-Cladding Mechanical Interaction

International Nuclear Information System (INIS)

Seo, Sang Kyu; Lee, Sung Uk; Lee, Eun Ho; Yang, Dong Yol; Kim, Hyo Chan; Yang, Dong Yol

2016-01-01

In a nuclear power plant, the fuel assembly, which is composed of fuel rods, burns, and the high temperature can generate power. The fuel rod consists of pellets and a cladding that covers the pellets. It is important to understand the pellet-cladding mechanical interaction with regard to nuclear safety. This paper proposes simulation of the PCMI. The gap between the pellets and the cladding, and the contact pressure are very important for conducting thermal analysis. Since the gap conductance is not known, it has to be determined by a suitable method. This paper suggests a solution. In this study, finite element (FE) contact analysis is conducted considering thermal expansion of the pellets. As the contact causes plastic deformation, this aspect is considered in the analysis. A 3D FE module is developed to analyze the PCMI using FORTRAN 90. The plastic deformation due to the contact between the pellets and the cladding is the major physical phenomenon. The simple analytical solution of a cylinder is proposed and compared with the fuel rod performance code results

Mechanical Properties of a Unidirectional Basalt-Fiber-Reinforced Plastic Under a Loading Simulating Operation Conditions

Science.gov (United States)

Lobanov, D. S.; Slovikov, S. V.

2017-01-01

The results of experimental investigations of unidirectional composites based on basalt fibers and different marks of epoxy resins are presented. Uniaxial tensile tests were carried out using a specimen fixation technique simulating the operation conditions of structures. The mechanical properties of the basalt-fiber-reinforced plastics (BFRPs) were determined. The diagrams of loading and deformation of BFRP specimens were obtain. The formulations of the composites with the highest mechanical properties were revealed.

Atomic Scale Simulation on the Anti-Pressure and Friction Reduction Mechanisms of MoS2 Monolayer

Directory of Open Access Journals (Sweden)

Yang Liu

2018-04-01

Full Text Available MoS2 nanosheets can be used as solid lubricants or additives of lubricating oils to reduce friction and resist wear. However, the atomic scale mechanism still needs to be illustrated. Herein, molecular simulations on the indentation and scratching process of MoS2 monolayer supported by Pt(111 surface were conducted to study the anti-pressure and friction reduction mechanisms of the MoS2 monolayer. Three deformation stages of Pt-supported MoS2 monolayer were found during the indentation process: elastic deformation, plastic deformation and finally, complete rupture. The MoS2 monolayer showed an excellent friction reduction effect at the first two stages, as a result of enhanced load bearing capacity and reduced deformation degree of the substrate. Unlike graphene, rupture of the Pt-supported MoS2 monolayer was related primarily to out-of-plane compression of the monolayer. These results provide a new insight into the relationship between the mechanical properties and lubrication properties of 2D materials.

Computer simulations of neural mechanisms explaining upper and lower limb excitatory neural coupling

Directory of Open Access Journals (Sweden)

Ferris Daniel P

2010-12-01

Full Text Available Abstract Background When humans perform rhythmic upper and lower limb locomotor-like movements, there is an excitatory effect of upper limb exertion on lower limb muscle recruitment. To investigate potential neural mechanisms for this behavioral observation, we developed computer simulations modeling interlimb neural pathways among central pattern generators. We hypothesized that enhancement of muscle recruitment from interlimb spinal mechanisms was not sufficient to explain muscle enhancement levels observed in experimental data. Methods We used Matsuoka oscillators for the central pattern generators (CPG and determined parameters that enhanced amplitudes of rhythmic steady state bursts. Potential mechanisms for output enhancement were excitatory and inhibitory sensory feedback gains, excitatory and inhibitory interlimb coupling gains, and coupling geometry. We first simulated the simplest case, a single CPG, and then expanded the model to have two CPGs and lastly four CPGs. In the two and four CPG models, the lower limb CPGs did not receive supraspinal input such that the only mechanisms available for enhancing output were interlimb coupling gains and sensory feedback gains. Results In a two-CPG model with inhibitory sensory feedback gains, only excitatory gains of ipsilateral flexor-extensor/extensor-flexor coupling produced reciprocal upper-lower limb bursts and enhanced output up to 26%. In a two-CPG model with excitatory sensory feedback gains, excitatory gains of contralateral flexor-flexor/extensor-extensor coupling produced reciprocal upper-lower limb bursts and enhanced output up to 100%. However, within a given excitatory sensory feedback gain, enhancement due to excitatory interlimb gains could only reach levels up to 20%. Interconnecting four CPGs to have ipsilateral flexor-extensor/extensor-flexor coupling, contralateral flexor-flexor/extensor-extensor coupling, and bilateral flexor-extensor/extensor-flexor coupling could enhance

Mechanical characterization of atherosclerotic arteries using finite-element modeling: feasibility study on mock arteries.

Science.gov (United States)

Pazos, Valérie; Mongrain, Rosaire; Tardif, Jean-Claude

2010-06-01

Clinical studies on lipid-lowering therapy have shown that changing the composition of lipid pools reduced significantly the risk of cardiac events associated with plaque rupture. It has been shown also that changing the composition of the lipid pool affects its mechanical properties. However, knowledge about the mechanical properties of human atherosclerotic lesions remains limited due to the difficulty of the experiments. This paper aims to assess the feasibility of characterizing a lipid pool embedded in the wall of a pressurized vessel using finite-element simulations and an optimization algorithm. Finite-element simulations of inflation experiments were used together with nonlinear least squares algorithm to estimate the material model parameters of the wall and of the inclusion. An optimal fit of the simulated experiment and the real experiment was sought with the parameter estimation algorithm. The method was first tested on a single-layer polyvinyl alcohol (PVA) cryogel stenotic vessel, and then, applied on a double-layered PVA cryogel stenotic vessel with a lipid inclusion.

Macromolecule simulation and CH4 adsorption mechanism of coal vitrinite

Science.gov (United States)

Yu, Song; Yan-ming, Zhu; Wu, Li

2017-02-01

The microscopic mechanism of interactions between CH4 and coal macromolecules is of significant practical and theoretical importance in CBM development and methane storage. Under periodic boundary conditions, the optimal energy configuration of coal vitrinite, which has a higher torsion degree and tighter arrangement, can be determined by the calculation of molecular mechanics (MM) and molecular dynamics (MD), and annealing kinetics simulation based on ultimate analysis, 13C NMR, FT IR and HRTEM. Macromolecular stabilization is primarily due to the van der Waals energy and covalent bond energy, mainly consisting of bond torsion energy and bond angle energy. Using the optimal configuration as the adsorbent, GCMC simulation of vitrinite adsorption of CH4 is conducted. A saturated state is reached after absorbing 17 CH4s per coal vitrinite molecule. CH4 is preferentially adsorbed on the edge, and inclined to gathering around the branched chains of the inner vitrinite sites. Finally, the adsorption parameters are calculated through first principle DFT. The adsorbability order is as follows: aromatic structure> heteroatom rings > oxygen functional groups. The adsorption energy order is as follows: Top graphene. However, the energy of the most preferential location is much lower than that of graphite/graphene. CH4 is more easily absorbed on the surface of vitrinite. Adsorbability varies considerably at different adsorption locations and sites on the surface of vitrinite. Crystal parameter of vitrinite is a = b = c = 15.8 Å and majority of its micropores are blow 15.8 Å, indicating that the vitrinite have the optimum adsorption aperture. It can explain its higher observed adsorption capacities for CH4 compared with graphite/graphene.

Numerical Simulation and Experimental Investigation of the Viscoelastic Heating Mechanism in Ultrasonic Plasticizing of Amorphous Polymers for Micro Injection Molding

Directory of Open Access Journals (Sweden)

Bingyan Jiang

2016-05-01

Full Text Available Ultrasonic plasticizing of polymers for micro-injection molding has been proposed and studied for its unique potential in materials and energy-saving. In our previous work, we have demonstrated the characteristics of the interfacial friction heating mechanism in ultrasonic plasticizing of polymer granulates. In this paper, the other important heating mechanism in ultrasonic plasticizing, i.e., viscoelastic heating for amorphous polymer, was studied by both theoretical modeling and experimentation. The influence mechanism of several parameters, such as the initial temperature of the polymer, the ultrasonic frequency, and the ultrasonic amplitude, was investigated. The results from both numerical simulation and experimentation indicate that the heat generation rate of viscoelastic heating can be significantly influenced by the initial temperature of polymer. The glass transition temperature was found to be a significant shifting point in viscoelastic heating. The heat generation rate is relatively low at the beginning and can have a steep increase after reaching glass transition temperature. In comparison with the ultrasonic frequency, the ultrasonic amplitude has much greater influence on the heat generation rate. In light of the quantitative difference in the viscoelastic heating rate, the limitation of the numerical simulation was discussed in the aspect of the assumptions and the applied mathematical models.

Mechanical properties of stanene under uniaxial and biaxial loading: A molecular dynamics study

Energy Technology Data Exchange (ETDEWEB)

Mojumder, Satyajit [Department of Mechanical Engineering, Bangladesh University of Engineering and Technology, Dhaka 1000 (Bangladesh); Amin, Abdullah Al [Department of Mechanical and Aerospace Engineering, Case western Reverse University, Cleveland, Ohio 44106 (United States); Islam, Md Mahbubul, E-mail: mmi122@psu.edu [Department of Mechanical and Nuclear Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802 (United States)

2015-09-28

Stanene, a graphene like two dimensional honeycomb structure of tin has attractive features in electronics application. In this study, we performed molecular dynamics simulations using modified embedded atom method potential to investigate mechanical properties of stanene. We studied the effect of temperature and strain rate on mechanical properties of α-stanene for both uniaxial and biaxial loading conditions. Our study suggests that with the increasing temperature, both the fracture strength and strain of the stanene decrease. Uniaxial loading in zigzag direction shows higher fracture strength and strain compared to the armchair direction, while no noticeable variation in the mechanical properties is observed for biaxial loading. We also found at a higher loading rate, material exhibits higher fracture strength and strain. These results will aid further investigation of stanene as a potential nano-electronics substitute.

Computer-controlled mechanical lung model for application in pulmonary function studies

NARCIS (Netherlands)

A.F.M. Verbraak (Anton); J.E.W. Beneken; J.M. Bogaard (Jan); A. Versprille (Adrian)

1995-01-01

textabstractA computer controlled mechanical lung model has been developed for testing lung function equipment, validation of computer programs and simulation of impaired pulmonary mechanics. The construction, function and some applications are described. The physical model is constructed from two

Study of physical properties, gas generation and gas retention in simulated Hanford waste

International Nuclear Information System (INIS)

Bryan, S.A.; Pederson, L.R.; Scheele, R.D.

1993-04-01

The purpose of this study was to establish the chemical and physical processes responsible for the generation and retention of gases within high-level waste from Tank 101-SY on the Hanford Site. This research, conducted using simulated waste on a laboratory scale, supports the development of mitigation/remediation strategies for Tank 101-SY. Simulated waste formulations are based on actual waste compositions. Selected physical properties of the simulated waste are compared to properties of actual Tank 101-SY waste samples. Laboratory studies using aged simulated waste show that significant gas generation occurs thermally at current tank temperatures (∼60 degrees C). Gas compositions include the same gases produced in actual tank waste, primarily N 2 , N 2 O, and H 2 . Gas stoichiometries have been shown to be greatly influenced by several organic and inorganic constituents within the simulated waste. Retention of gases in the simulated waste is in the form of bubble attachment to solid particles. This attachment phenomenon is related to the presence of organic constituents (HEDTA, EDTA, and citrate) of the simulated waste. A mechanism is discussed that relates the gas bubble/particle interactions to the partially hydrophobic surface produced on the solids by the organic constituents

A unified mobility model for quantum mechanical simulation of MOSFETs

International Nuclear Information System (INIS)

Park, Ji Sun; Lee, Ji Young; Lee, Sang Kyung; Shin, Hyung Soon; Jin, Seong Hoon; Park, Young June; Min, Hong Shik

2004-01-01

A unified electron and hole mobility model for inversion and accumulation layers with quantum effect is presented for the first time. By accounting for the screened Coulomb scattering based on the well-known bulk mobility model and allowing the surface roughness scattering term to be a function of net charge, the new model is applicable to the bulk, inversion, and accumulation layers with only one set of fitting parameters. The new model is implemented in the 2-D quantum mechanical device simulator and gives excellent agreement with the experimentally measured effective mobility data over a wide range of effective transverse field, substrate doping, substrate bias, and temperature.

Fatigue mechanisms in an austenitic steel under cyclic loading: Experiments and atomistic simulations

Energy Technology Data Exchange (ETDEWEB)

Soppa, E.A., E-mail: ewa.soppa@mpa.uni-stuttgart.de; Kohler, C., E-mail: christopher.kohler@mpa.uni-stuttgart.de; Roos, E., E-mail: eberhard.roos@mpa.uni-stuttgart.de

2014-03-01

Experimental investigations on the austenitic stainless steel X6CrNiNb18-10 (AISI – 347) and concomitant atomistic simulations of a FeNi nanocrystalline model system have been performed in order to understand the basic mechanisms of fatigue damage under cyclic loading. Using electron backscatter diffraction (EBSD) the influence of deformation induced martensitic transformation and NbC size distribution on the fatigue crack formation has been demonstrated. The martensite nucleates prevalently at grain boundaries, triple points and at the specimen free surface and forms small (∼1 µm sized) differently oriented grains. The atomistic simulations show the role of regions of a high density of stacking faults for the martensitic transformation.

Computer Simulation Study of the Stability Mechanism of Thermophile, MJ0305

Science.gov (United States)

Song, Hyundeok; Beck, Thomas

2011-04-01

Methanococcus jannaschii (MJ) is a methane-producing thermophile, which was discovered in a 2600m-deep Pacific Ocean vent in 1983. It has the ability to thrive at high temperatures and high pressures, which are unfavorable for most life forms. There have been some experiments to study its stability under extreme conditions, but still the origin of the stability of MJ is not exactly known. MJ0305 is MJ's chloride channel protein. The structure of MJ0305 was built by homology modeling. We compared the stability of MJ0305 with mesophilic Ecoli at 300K, 330K, and 360K by computer simulation to test the effects of temperature. Our results show that high temperatures significantly affect the number of salt bridges and hydrogen bonds. High temperatures decreased the average number of hydrogen bonds for Ecoli and MJ0305. Increased salt bridges at 330K make MJ0305 more stable. Network analysis of MJ0305 showed an increase in the number of hubs at high temperatures. In contrast, the number of hubs of Ecoli was decreased at high temperatures. Calculated network entropy is proportional to the number of hubs. Increased network entropy of MJ0305 at 330K implies increased robustness.

A numerical study on the mechanical properties and the processing behaviour of composite high strength steels

Energy Technology Data Exchange (ETDEWEB)

Muenstermann, Sebastian [RWTH Aachen (Germany). Dept. of Ferrous Metallurgy; Vajragupta, Napat [RWTH Aachen (Germany). Materials Mechanics Group; Weisgerber, Bernadette [ThyssenKrupp Steel Europe AG (Germany). Patent Dept.; Kern, Andreas [ThyssenKrupp Steel Europe AG (Germany). Dept. of Quality Affairs

2013-06-01

The demand for lightweight construction in mechanical and civil engineering has strongly promoted the development of high strength steels with excellent damage tolerance. Nowadays, the requirements from mechanical and civil engineering are even more challenging, as gradients in mechanical properties are demanded increasingly often for components that are utilized close to the limit state of load bearing capacity. A metallurgical solution to this demand is given by composite rolling processes. In this process components with different chemical compositions were jointed, which develop after heat treatment special properties. These are actually evaluated in order to verify that structural steels with the desired gradients in mechanical properties can be processed. A numerical study was performed aiming to numerically predict strenght and toughness properties, as well as the procesing behaviour using Finite Element (FE) simulations with damage mechanics approaches. For determination of mechanical properties, simulations of tensile specimen, SENB sample, and a mobile crane have been carried out for different configurations of composite rolled materias out of high strebght structural steels. As a parameter study, both the geometrical and the metallurgical configurations of the composite rolled steels were modified. Thickness of each steel layer and materials configuration have been varied. Like this, a numerical procedure to define optimum tailored configurations of high strenght steels could be established.

Study on a New Steering Mechanism for Point-the-Bit Rotary Steerable System

Directory of Open Access Journals (Sweden)

Yuanzhi Li

2014-02-01

Full Text Available This paper presents a novel steering mechanism embedded in a point-the-bit rotary steerable system (RSS for oilfield exploitation. The new steering mechanism adopts a set of universal joints to alleviate the high alternative strain on drilling mandrel and employs a specially designed planetary gear small tooth number difference (PGSTD to achieve directional steering. Its principle and characteristics are explained and examined through a series of analyses. First, the eccentric displacement vector of the offset point on the drilling mandrel is formulated and kinematic solutions are established. Next, structural design for the new steering mechanism is addressed. Then, procedures and program architectures for simulating offset state of the drilling mandrel and motion trajectory of the whole steering mechanism are presented. After that, steering motion simulations of the new steering mechanism for both 2D and 3D well trajectories are then performed by combining LabVIEW and SolidWorks. Finally, experiments on the steering motion control of the new steering mechanism prototype are carried out. The simulations and experiments reveal that the steering performance of the new steering mechanism is satisfied. The research can provide good guidance for further research and engineering application of the point-the-bit RSS.

New jump mechanisms for dumbbell and induced migration of point defects by molecular dynamics simulation

International Nuclear Information System (INIS)

Doan, N.V.; Pontikis, V.; Tenenbaum, A.

1978-01-01

The induced migration of the (100) - dumbbell is studied using the molecular dynamics simulation. Two new types of jumps are discovered for the dumbbell: first the jump takes place through an intermediate crowdion configuration (110), then the crowdion is converted into the dumbbell configuration with some other orientation. The threshold energy is found for different knocked-on directions. The dependence of the interstitial jump frequency on the incident electron energy is determined for copper. The induced interstitial migration shows a maximum value, but for an electron energy around 15 Kev. The effect of new jump mechanisms on the effective recombination volume is discussed

Study into the mechanisms of hydrogen contamination of niobium as a material for superconducting radiofrequency cavities. Molecular dynamics studies for simulation of the hydrogen diffusion processes

International Nuclear Information System (INIS)

Roux, B.

1993-01-01

Superconducting radiofrequency cavities were chosen for most of the future particle accelerators. In the case of pure niobium cavities, several laboratories have observed degradation of superconducting properties related to the conditions of the cooling down process. This effect seems to stem from hydrogen contamination which occurs during surface treatments. With the aim to study the influence of different surface treatments on the hydrogen contamination depth concentration profiling of the near surface region (the first 200 nm) was first carried out by the classical ERDA technique with 30 nm depth resolution. In order to better localize hydrogen, the initial particle selecting device (Teflon foil) was replaced by an electromagnetic (ExB) filter improving then the depth resolution by a factor three. This study reveals an hydrogen segregation at the niobium surface. Such a result is in contradiction with the relative high experimental value of the hydrogen diffusion coefficient given by the literature. To understand the trapping mechanism of hydrogen, a simulation by molecular dynamics of this impurity diffusion process was performed. This approach requires the knowledge of the interatomic potential. The potential parameters were fitted with static and dynamic tests. Nb-Nb interaction is based on many body potential. Nb-H is represented by two body potential. The Arrhenius diagram of the diffusion coefficient achieved by dynamic for a single crystal provides too small activation energy in comparison with experimental results. However, in presence of defects, a simulation proves a large increase of these values. It is only around 1000 K that the diffusion of hydrogen is not altered by defects. This conclusion confirms the experimental results concerning a good characteristic of superconducting cavities after thermal treatments. (orig.)

3D FE simulation of PCMI (Pellet-Cladding Mechanical Interaction) considering frictionless contact

International Nuclear Information System (INIS)

Seo, Sang-Kyu; Lee, Sung-Uk; Lee, Eun-Ho; Yang, Dong-Yol; Kim, Hyo-Chan; Yang, Yong-Sik

2014-01-01

The goal of this code is coupling every aspect of physical phenomenon. Monodimensional FE model has been made for METEOR. It is good to evaluate the global behavior in high burn up levels. However, the multi-dimensional PCI analysis code is necessary to precisely analyze the stress distribution especially in case of the crack analysis. CAST3M 3D finite element code has been developed considering thermo-mechanical interaction in detail for TOUTATIS code. The advanced multidimensional code called ALCYONE has been developed considering chemical-physics and thermomechanical aspects. Although there are many codes that analyze pellet and cladding interaction, it is difficult to consider every physical aspect. In this paper, pellet to cladding mechanical interaction in 3D has been simulated with frictionless contact using the developed module, which is written in FORTRANN90. In this paper, 3D PCMI FE model is simulated with frictionless contact and elastic deformation. From the frictionless contact analysis, the interfacial pressure has been calculated and then this is used to obtain the solid heat coefficient which is a main factor to analyze the thermal distribution

Study of photo-oxidative reactivity of sunscreening agents based on photo-oxidation of uric acid by kinetic Monte Carlo simulation.

Science.gov (United States)

Moradmand Jalali, Hamed; Bashiri, Hadis; Rasa, Hossein

2015-05-01

In the present study, the mechanism of free radical production by light-reflective agents in sunscreens (TiO2, ZnO and ZrO2) was obtained by applying kinetic Monte Carlo simulation. The values of the rate constants for each step of the suggested mechanism have been obtained by simulation. The effect of the initial concentration of mineral oxides and uric acid on the rate of uric acid photo-oxidation by irradiation of some sun care agents has been studied. The kinetic Monte Carlo simulation results agree qualitatively with the existing experimental data for the production of free radicals by sun care agents. Copyright © 2015 Elsevier B.V. All rights reserved.

A study on the creep characteristics of simulated DUPIC fuel

International Nuclear Information System (INIS)

Kang, Kweon Ho; Ryu, H. J.; Kim, H. S.; Song, K. C.; Yang, M. S.; Na, S.

2001-09-01

Compression creep test was performed using simulated DUPIC fuel in the temperature range from 1773 to 1973 K under the stress range of 21 - 60 MPa. Creep rate and the activation energy were obtained. The activation energy for creep was 649.35 - 675.94 kJ/mol at the low stress region, where creep mechanism was controlled by diffusion. On the other hand, the activation energy at high stress region was 750.68 - 792.18 kJ/mol, where creep mechanism was controlled by dislocation motion. The activation energy for dislocation creep was higher than that for diffusion creep. The activation energy of reference simulated DUPIC fuel was higher than that of UO2

Mechanical properties of granular materials: A variational approach to grain-scale simulations

Energy Technology Data Exchange (ETDEWEB)

Holtzman, R.; Silin, D.B.; Patzek, T.W.

2009-01-15

The mechanical properties of cohesionless granular materials are evaluated from grain-scale simulations. A three-dimensional pack of spherical grains is loaded by incremental displacements of its boundaries. The deformation is described as a sequence of equilibrium configurations. Each configuration is characterized by a minimum of the total potential energy. This minimum is computed using a modification of the conjugate gradient algorithm. Our simulations capture the nonlinear, path-dependent behavior of granular materials observed in experiments. Micromechanical analysis provides valuable insight into phenomena such as hysteresis, strain hardening and stress-induced anisotropy. Estimates of the effective bulk modulus, obtained with no adjustment of material parameters, are in agreement with published experimental data. The model is applied to evaluate the effects of hydrate dissociation in marine sediments. Weakening of the sediment is quantified as a reduction in the effective elastic moduli.

Development and mechanical properties of structural materials from lunar simulant

Science.gov (United States)

Desai, Chandra S.

1991-01-01

Development of versatile engineering materials from locally available materials in space is an important step toward establishment of outposts such as on the moon and Mars. Here development of the technologies for manufacture of structural and construction materials on the moon, utilizing local lunar soil (regolith), without the use of water, is an important element for habitats and explorations in space. It is also vital that the mechanical behavior such as strength and flexural properties, fracture toughness, ductility, and deformation characteristics are defined toward establishment of the ranges of engineering applications of the materials developed. The objectives include two areas: (1) thermal liquefaction of lunar simulant (at about 1100 C) with different additives (fibers, powders, etc.); and (2) development and use of a traxial test device in which lunar simulants are first compacted under cycles of loading, and then tested with different vacuums and initial confining or insitu stress. The second area was described in previous progress reports and publications; since the presently available device allows vacuum levels up to only 10(exp -4) torr, it is recommended that a vacuum pump that can allow higher levels of vacuum is acquired.

External chest compressions using a mechanical feedback device : cross-over simulation study.

Science.gov (United States)

Skorning, M; Derwall, M; Brokmann, J C; Rörtgen, D; Bergrath, S; Pflipsen, J; Beuerlein, S; Rossaint, R; Beckers, S K

2011-08-01

External chest compressions (ECC) are essential components of resuscitation and are usually performed without any adjuncts in professional healthcare. Even for healthcare professionals during in-hospital and out-of-hospital resuscitation poor performance in ECC has been reported in recent years. Although several stand-alone devices have been developed none has been implemented as a standard in patient care. The aim of this study was to examine if the use of a mechanical device providing visual feedback and audible assistance during ECC improves performance of healthcare professionals following minimal and simplified instructions. In a prospective, randomized cross-over study 81 healthcare professionals performed ECC for 3 min (in the assumed setting of a secured airway) twice on a manikin (Skillreporter ResusciAnne®, with PC-Skillreporting System Version 1.3.0, Laerdal, Stavanger, Norway) in a mock cardiac arrest scenario. Group 1 (n=40) performed ECC with the device first followed by classic ECC and group 2 (n=41) in the opposite order. Minimal instructions were standardized and provided by video instruction (1 min 38 s). Endpoints were achievement of a mean compression rate between 90 and 110/min and a mean compression depth of 40-50 mm. In addition participants had to answer questionnaires about demographic data, professional experience and recent recommendations for ECC as well as their impression of the device concerning the ease of use and their personal level of confidence. Data were analyzed for group-related and inter-group differences using SAS (Version 9.1.3, SAS Institute, Cary, NC). A total of 81 healthcare professionals regularly involved in resuscitation attempts in pre-hospital or in-hospital settings took part in the study with no differences between the groups: females 35.8% (n=52), emergency medical technicians 32.1% (n=26), anesthesia nurses 32.1% (n=26), physicians (anesthesiology) 45% (n=29). In group 1 33 out of 40 (82.5%; 99.7±4

An Experimental Study to Measure the Mechanical Properties of the Human Liver.

Science.gov (United States)

Karimi, Alireza; Shojaei, Ahmad

2018-01-01

Since the liver is one of the most important organs of the body that can be injured during trauma, that is, during accidents like car crashes, understanding its mechanical properties is of great interest. Experimental data is needed to address the mechanical properties of the liver to be used for a variety of applications, such as the numerical simulations for medical purposes, including the virtual reality simulators, trauma research, diagnosis objectives, as well as injury biomechanics. However, the data on the mechanical properties of the liver capsule is limited to the animal models or confined to the tensile/compressive loading under single direction. Therefore, this study was aimed at experimentally measuring the axial and transversal mechanical properties of the human liver capsule under both the tensile and compressive loadings. To do that, 20 human cadavers were autopsied and their liver capsules were excised and histologically analyzed to extract the mean angle of a large fibers population (bundle of the fine collagen fibers). Thereafter, the samples were cut and subjected to a series of axial and transversal tensile/compressive loadings. The results revealed the tensile elastic modulus of 12.16 ± 1.20 (mean ± SD) and 7.17 ± 0.85 kPa under the axial and transversal loadings respectively. Correspondingly, the compressive elastic modulus of 196.54 ± 13.15 and 112.41 ± 8.98 kPa were observed under the axial and transversal loadings respectively. The compressive axial and transversal maximum/failure stress of the capsule were 32.54 and 37.30 times higher than that of the tensile ones respectively. The capsule showed a stiffer behavior under the compressive load compared to the tensile one. In addition, the axial elastic modulus of the capsule was found to be higher than that of the transversal one. The findings of the current study have implications not only for understanding the mechanical properties of the human capsule tissue under tensile

Inspiration, simulation and design for smart robot manipulators from the sucker actuation mechanism of cephalopods.

Science.gov (United States)

Grasso, Frank W; Setlur, Pradeep

2007-12-01

Octopus arms house 200-300 independently controlled suckers that can alternately afford an octopus fine manipulation of small objects and produce high adhesion forces on virtually any non-porous surface. Octopuses use their suckers to grasp, rotate and reposition soft objects (e.g., octopus eggs) without damaging them and to provide strong, reversible adhesion forces to anchor the octopus to hard substrates (e.g., rock) during wave surge. The biological 'design' of the sucker system is understood to be divided anatomically into three functional groups: the infundibulum that produces a surface seal that conforms to arbitrary surface geometry; the acetabulum that generates negative pressures for adhesion; and the extrinsic muscles that allow adhered surfaces to be rotated relative to the arm. The effector underlying these abilities is the muscular hydrostat. Guided by sensory input, the thousands of muscle fibers within the muscular hydrostats of the sucker act in coordination to provide stiffness or force when and where needed. The mechanical malleability of octopus suckers, the interdigitated arrangement of their muscle fibers and the flexible interconnections of its parts make direct studies of their control challenging. We developed a dynamic simulator (ABSAMS) that models the general functioning of muscular hydrostat systems built from assemblies of biologically constrained muscular hydrostat models. We report here on simulation studies of octopus-inspired and artificial suckers implemented in this system. These simulations reproduce aspects of octopus sucker performance and squid tentacle extension. Simulations run with these models using parameters from man-made actuators and materials can serve as tools for designing soft robotic implementations of man-made artificial suckers and soft manipulators.

Molecular dynamics simulations of graphoepitaxy of organic semiconductors, sexithiophene, and pentacene: Molecular-scale mechanisms of organic graphoepitaxy

Science.gov (United States)

Ikeda, Susumu

2018-03-01

Molecular dynamics (MD) simulations of the organic semiconductors α-sexithiophene (6T) and pentacene were carried out to clarify the mechanism of organic graphoepitaxy at the molecular level. First, the models of the grooved substrates were made and the surfaces of the inside of the grooves were modified with -OH or -OSi(CH3)3, making the surfaces hydrophilic or hydrophobic. By the MD simulations of 6T, it was found that three stable azimuthal directions exist (0, ˜45, and 90° the angle that the c-axis makes with the groove), being consistent with experimental results. MD simulations of deposition processes of 6T and pentacene were also carried out, and pentacene molecules showed the spontaneous formation of herringbone packing during deposition. Some pentacene molecules stood on the surface and formed a cluster whose a-axis was parallel to the groove. It is expected that a deep understanding of the molecular-scale mechanisms will lead graphoepitaxy to practical applications, improving the performance of organic devices.

Conducting Simulation Studies in the R Programming Environment.

Science.gov (United States)

Hallgren, Kevin A

2013-10-12

Simulation studies allow researchers to answer specific questions about data analysis, statistical power, and best-practices for obtaining accurate results in empirical research. Despite the benefits that simulation research can provide, many researchers are unfamiliar with available tools for conducting their own simulation studies. The use of simulation studies need not be restricted to researchers with advanced skills in statistics and computer programming, and such methods can be implemented by researchers with a variety of abilities and interests. The present paper provides an introduction to methods used for running simulation studies using the R statistical programming environment and is written for individuals with minimal experience running simulation studies or using R. The paper describes the rationale and benefits of using simulations and introduces R functions relevant for many simulation studies. Three examples illustrate different applications for simulation studies, including (a) the use of simulations to answer a novel question about statistical analysis, (b) the use of simulations to estimate statistical power, and (c) the use of simulations to obtain confidence intervals of parameter estimates through bootstrapping. Results and fully annotated syntax from these examples are provided.

Design and simulative experiment of an innovative trailing edge morphing mechanism driven by artificial muscles embedded in skin

Science.gov (United States)

Li, Hongda; Liu, Long; Xiao, Tianhang; Ang, Haisong

2016-09-01

In this paper, conceptual design of a tailing edge morphing mechanism developed based on a new kind of artificial muscle embedded in skin, named Driving Skin, is proposed. To demonstrate the feasibility of this conceptual design, an experiment using ordinary fishing lines to simulate the function of artificial muscles was designed and carried out. Some measures were designed to ensure measurement accuracy. The experiment result shows that the contraction ratio and force required by the morphing mechanism can be satisfied by the new artificial muscles, and a relationship between contraction ratios and morphing angles can be found. To demonstrate the practical application feasibility of this conceptual design, a wing section using ordinary ropes to simulate the function of the Driving Skin mechanism was designed and fabricated. The demonstration wing section, extremely light in weight and capable of changing thickness, performs well, with a -30^\\circ /+30^\\circ morphing angle achieved. The trailing edge morphing mechanism is efficient in re-contouring the wing profile.

Study of photo-oxidative reactivity of sunscreening agents based on photo-oxidation of uric acid by kinetic Monte Carlo simulation

Energy Technology Data Exchange (ETDEWEB)

Moradmand Jalali, Hamed; Bashiri, Hadis, E-mail: hbashiri@kashanu.ac.ir; Rasa, Hossein

2015-05-01

In the present study, the mechanism of free radical production by light-reflective agents in sunscreens (TiO{sub 2}, ZnO and ZrO{sub 2}) was obtained by applying kinetic Monte Carlo simulation. The values of the rate constants for each step of the suggested mechanism have been obtained by simulation. The effect of the initial concentration of mineral oxides and uric acid on the rate of uric acid photo-oxidation by irradiation of some sun care agents has been studied. The kinetic Monte Carlo simulation results agree qualitatively with the existing experimental data for the production of free radicals by sun care agents. - Highlights: • The mechanism and kinetics of uric acid photo-oxidation by irradiation of sun care agents has been obtained by simulation. • The mechanism has been used for free radical production of TiO{sub 2} (rutile and anatase), ZnO and ZrO{sub 2}. • The ratios of photo-activity of ZnO to anastase, rutile and ZrO have been obtained. • By doubling the initial concentrations of mineral oxide, the rate of reaction was doubled. • The optimum ratio of initial concentration of mineral oxides to uric acid has been obtained.

SIMULATION STUDY OF LONGITUDINAL FORCES IN THE COUPLING DEVICE OF HEAVY FREIGHT TRAINS

Directory of Open Access Journals (Sweden)

Józef Stokłosa

2014-03-01

Full Text Available On the LHS line (Broad-gauge Metallurgical Line, far out West of the railway line with a gauge of 1520 mm, heavy goods trains for a gross weight 5500 tons and a length of 850 m are operated. The article presents the results of a simulation study of the forces that occur in the automatic coupling device of SA-3 type of Russian production train consisting of 60 coal wagons of Russian construction of gross mass 91 tons each. The train moves on the 1520 mm gauge tracks curve S type (the radius of curvature of curves 300 m. Simulation studies were conducted using the Train Module of program to dynamic study multi-elements systems of Universal Mechanism UM 6.0.

Numerical simulations of enhanced gas recovery at the Zalezcze gas field in Poland confirm high CO2 storage capacity and mechanical integrity

International Nuclear Information System (INIS)

Klimkowski, Lukasz; Nagy, Stanislaw; Papiernik, Bartosz; Orlic, Bogdan; Kempka, Thomas

2015-01-01

Natural gas from the Zalecze gas field located in the Fore-Sudetic Monocline of the Southern Permian Basin has been produced since November 1973, and continuous gas production led to a decrease in the initial reservoir pressure from 151 bar to about 22 bar until 2010. We investigated a prospective enhanced gas recovery operation at the Zalecze gas field by coupled numerical hydro-mechanical simulations to account for the CO 2 storage capacity, trapping efficiency and mechanical integrity of the reservoir, cap-rock and regional faults. Dynamic flow simulations carried out indicate a CO 2 storage capacity of 106.6 Mt with a trapping efficiency of about 43% (45.8 Mt CO 2 ) established after 500 years of simulation. Two independent strategies on the assessment of mechanical integrity were followed by two different modeling groups resulting in the implementation of field- to regional-scale hydro-mechanical simulation models. The simulation results based on application of different constitutive laws for the lithological units show deviations of 31% to 93% for the calculated maximum vertical displacements at the reservoir top. Nevertheless, results of both simulation strategies indicate that fault reactivation generating potential leakage pathways from the reservoir to shallower units is very unlikely due to the low fault slip tendency (close to zero) in the Zechstein cap-rocks. Consequently, our simulation results also emphasise that the supra- and sub-saliferous fault systems at the Zalecze gas field are independent and very likely not hydraulically connected. Based on our simulation results derived from two independent modeling strategies with similar simulation results on fault and cap-rock integrity, we conclude that the investigated enhanced gas recovery scheme is feasible, with a negligibly low risk of relevant fault reactivation or formation fluid leakage through the Zechstein cap-rocks. (authors)

Mechanical Study of Standard Six Beat Front Crawl Swimming by Using Swimming Human Simulation Model

Science.gov (United States)

Nakashima, Motomu

There are many dynamical problems in front crawl swimming which have not been fully investigated by analytical approaches. Therefore, in this paper, standard six beat front crawl swimming is analyzed by the swimming human simulation model SWUM, which has been developed by the authors. First, the outline of the simulation model, the joint motion for one stroke cycle, and the specifications of calculation are described respectively. Next, contribution of each fluid force component and of each body part to the thrust, effect of the flutter kick, estimation of the active drag, roll motion, and the propulsive efficiency are discussed respectively. The following results were theoretically obtained: The thrust is produced at the upper limb by the normal drag force component. The flutter kick plays a role in raising the lower half of the body. The active drag coefficient in the simulation becomes 0.082. Buoyancy determines the primal wave of the roll motion fluctuation. The propulsive efficiency in the simulation becomes 0.2.

Mechanical properties of nano and bulk Fe pillars using molecular dynamics and dislocation dynamics simulation

Directory of Open Access Journals (Sweden)

S. K. Deb Nath

2017-10-01

Full Text Available Using molecular dynamics simulation, tension and bending tests of a Fe nanopillar are carried out to obtain its Young’s modulus and yield strength. Then the comparative study of Young’s modulus and yield strength of a Fe nanopillar under bending and tension are carried out varying its diameter in the range of diameter 1-15nm. We find out the reasons why bending Young’s modulus and yield strength of a Fe nanopillar are higher than those of tension Young’s modulus and yield strength of a Fe nanopillar. Using the mobility parameters of bulk Fe from the experimental study [N. Urabe and J. Weertman, Materials Science and Engineering 18, 41 (1975], its temperature dependent stress-strain relationship, yield strength and strain hardening modulus are obtained from the dislocation dynamics simulations. Strain rate dependent yield strength and strain hardening modulus of bulk Fe pillars under tension are studied. Temperature dependent creep behaviors of bulk Fe pillars under tension are also studied. To verify the soundness of the present dislocation dynamics studies of the mechanical properties of bulk Fe pillars under tension, the stress vs. strain relationship and dislocation density vs. strain of bulk Fe pillars obtained by us are compared with the published results obtained by S. Queyreau, G. Monnet, and B. Devincre, International Journal of Plasticity 25, 361 (2009.

Simulation Study on Identifiability of UHE Gamma-ray Air Showers

International Nuclear Information System (INIS)

Wada, Y.; Inoue, N.; Miyazawa, K.; Vankov, H.P.

2008-01-01

The chemical composition of Ultra-High-Energy (UHE) comic rays is one of unsolved mysteries, and its study will give us fruitful information on the origin and acceleration mechanism of UHE cosmic rays. Especially, a detection of UHE gamma-rays by hybrid experiments, such as AUGER and TA, will be a key to solve these questions. The characteristics of UHE gamma-ray showers have been studied by comparing the lateral and longitudinal structures of shower particles calculated with AIRES and our own simulation code, so far. There are apparent differences in a slope of lateral distribution (η) and a depth of shower maximum (Xmax) between gamma-ray and proton induced showers because UHE gamma-ray showers are affected by the LPM effect and the geomagnetic cascading process in an energy region of >10 19.5 eV. Different features between gamma-ray and proton showers are pointed out from the simulation study and an identifiability of gamma-ray showers from proton ones is also discussed by the method of Neural-Network-Analysis

Simulation Study on Identifiability of UHE Gamma-ray Air Showers

Energy Technology Data Exchange (ETDEWEB)

Wada, Y.; Inoue, N.; Miyazawa, K. [Graduate School of Science and Engineering, Saitama University, Saitama 338-8570 (Japan); Vankov, H.P. [Institute for Nuclear Research and Nuclear Energy, Bulgaria Academy, Sofia (Bulgaria)

2008-01-15

The chemical composition of Ultra-High-Energy (UHE) comic rays is one of unsolved mysteries, and its study will give us fruitful information on the origin and acceleration mechanism of UHE cosmic rays. Especially, a detection of UHE gamma-rays by hybrid experiments, such as AUGER and TA, will be a key to solve these questions. The characteristics of UHE gamma-ray showers have been studied by comparing the lateral and longitudinal structures of shower particles calculated with AIRES and our own simulation code, so far. There are apparent differences in a slope of lateral distribution ({eta}) and a depth of shower maximum (Xmax) between gamma-ray and proton induced showers because UHE gamma-ray showers are affected by the LPM effect and the geomagnetic cascading process in an energy region of >10{sup 19.5}eV. Different features between gamma-ray and proton showers are pointed out from the simulation study and an identifiability of gamma-ray showers from proton ones is also discussed by the method of Neural-Network-Analysis.

The Influence of Drift Gas Composition on the Separation Mechanism in Traveling Wave Ion Mobility Spectrometry: Insight from Electrodynamic Simulations.

Science.gov (United States)

May, Jody C; McLean, John A

2003-06-01

The influence of three different drift gases (helium, nitrogen, and argon) on the separation mechanism in traveling wave ion mobility spectrometry is explored through ion trajectory simulations which include considerations for ion diffusion based on kinetic theory and the electrodynamic traveling wave potential. The model developed for this work is an accurate depiction of a second-generation commercial traveling wave instrument. Three ion systems (cocaine, MDMA, and amphetamine) whose reduced mobility values have previously been measured in different drift gases are represented in the simulation model. The simulation results presented here provide a fundamental understanding of the separation mechanism in traveling wave, which is characterized by three regions of ion motion: (1) ions surfing on a single wave, (2) ions exhibiting intermittent roll-over onto subsequent waves, and (3) ions experiencing a steady state roll-over which repeats every few wave cycles. These regions of ion motion are accessed through changes in the gas pressure, wave amplitude, and wave velocity. Resolving power values extracted from simulated arrival times suggest that momentum transfer in helium gas is generally insufficient to access regions (2) and (3) where ion mobility separations occur. Ion mobility separations by traveling wave are predicted to be effectual for both nitrogen and argon, with slightly lower resolving power values observed for argon as a result of band-broadening due to collisional scattering. For the simulation conditions studied here, the resolving power in traveling wave plateaus between regions (2) and (3), with further increases in wave velocity contributing only minor improvements in separations.

Mechanism of crack healing at room temperature revealed by atomistic simulations

International Nuclear Information System (INIS)

Li, J.; Fang, Q.H.; Liu, B.; Liu, Y.; Liu, Y.W.; Wen, P.H.

2015-01-01

Three dimensional molecular dynamics (MD) simulations are systematically carried out to reveal the mechanism of the crack healing at room temperature, in terms of the dislocation shielding and the atomic diffusion to control the crack closure, in a copper (Cu) plate suffering from a shear loading. The results show that the process of the crack healing is actualized through the dislocation emission at a crack tip accompanied with intrinsic stacking faults ribbon forming in the crack tip wake, the dislocation slipping in the matrix and the dislocation annihilation in the free surface. Dislocation included stress compressing the crack tip is examined from the MD simulations and the analytical models, and then the crack closes rapidly due to the assistance of the atomic diffusion induced by the thermal activation when the crack opening displacement is less than a threshold value. This phenomenon is very different from the previous results for the crack propagation under the external load applied because of the crack healing (advancing) largely dependent on the crystallographic orientations of crack and the directions of external loading. Furthermore, based on the energy characteristic and considering the crack size effect, a theoretical model is established to predict the relationships between the crack size and the shear stress which qualitatively agree well with that obtained in the MD simulations

Tight binding simulation study on zigzag single-walled carbon nanotubes

Science.gov (United States)

Sharma, Deepa; Jaggi, Neena; Gupta, Vishu

2018-01-01

Tight binding simulation studies using the density functional tight binding (DFTB) model have been performed on various zigzag single-walled carbon-nanotubes (SWCNTs) to investigate their electronic properties using DFTB module of the Material Studio Software version 7.0. Various combinations of different eigen-solvers and charge mixing schemes available in the DFTB Module have been tried to chalk out the electronic structure. The analytically deduced values of the bandgap of (9, 0) SWCNT were compared with the experimentally determined value reported in the literature. On comparison, it was found that the tight binding approximations tend to drastically underestimate the bandgap values. However, the combination of Anderson charge mixing method with standard eigensolver when implemented using the smart algorithm was found to produce fairly close results. These optimized model parameters were then used to determine the band structures of various zigzag SWCNTs. (9, 0) Single-walled Nanotube which is extensively being used for sensing NH3, CH4 and NO2 has been picked up as a reference material since its experimental bandgap value has been reported in the literature. It has been found to exhibit a finite energy bandgap in contrast to its expected metallic nature. The study is of utmost significance as it not only probes and validates the simulation route for predicting suitable properties of nanomaterials but also throws light on the comparative efficacy of the different approximation and rationalization quantum mechanical techniques used in simulation studies. Such simulation studies if used intelligently prove to be immensely useful to the material scientists as they not only save time and effort but also pave the way to new experiments by making valuable predictions.

Poor chest compression quality with mechanical compressions in simulated cardiopulmonary resuscitation: a randomized, cross-over manikin study.

Science.gov (United States)

Blomberg, Hans; Gedeborg, Rolf; Berglund, Lars; Karlsten, Rolf; Johansson, Jakob

2011-10-01

Mechanical chest compression devices are being implemented as an aid in cardiopulmonary resuscitation (CPR), despite lack of evidence of improved outcome. This manikin study evaluates the CPR-performance of ambulance crews, who had a mechanical chest compression device implemented in their routine clinical practice 8 months previously. The objectives were to evaluate time to first defibrillation, no-flow time, and estimate the quality of compressions. The performance of 21 ambulance crews (ambulance nurse and emergency medical technician) with the authorization to perform advanced life support was studied in an experimental, randomized cross-over study in a manikin setup. Each crew performed two identical CPR scenarios, with and without the aid of the mechanical compression device LUCAS. A computerized manikin was used for data sampling. There were no substantial differences in time to first defibrillation or no-flow time until first defibrillation. However, the fraction of adequate compressions in relation to total compressions was remarkably low in LUCAS-CPR (58%) compared to manual CPR (88%) (95% confidence interval for the difference: 13-50%). Only 12 out of the 21 ambulance crews (57%) applied the mandatory stabilization strap on the LUCAS device. The use of a mechanical compression aid was not associated with substantial differences in time to first defibrillation or no-flow time in the early phase of CPR. However, constant but poor chest compressions due to failure in recognizing and correcting a malposition of the device may counteract a potential benefit of mechanical chest compressions. Copyright © 2011 Elsevier Ireland Ltd. All rights reserved.

Phototactic orientation mechanism in the ciliate Fabrea salina, as inferred from numerical simulations.

Science.gov (United States)

Marangoni, R; Preosti, G; Colombetti, G

2000-02-01

The marine ciliate Fabrea salina shows a clear positive phototaxis, but the mechanism by which a single cell is able to detect the direction of light and orient its swimming accordingly is still unknown. A simple model of phototaxis is that of a biased random walk, where the bias due to light can affect one or more of the parameters that characterize a random walk, i.e., the mean speed, the frequency distribution of the angles of directional changes and the frequency of directional changes. Since experimental evidence has shown no effect of light on the mean speed of Fabrea salina, we have excluded models depending on this parameter. We have, therefore, investigated the phototactic orientation of Fabrea salina by computer simulation of two simple models, the first where light affects the frequency distribution of the angles of directional changes (model M1) and the second where the light bias modifies the frequency of directional changes (model M2). Simulated M1 cells directly orient their swimming towards the direction of light, regardless of their current swimming orientation; simulated M2 cells, on the contrary, are unable to actively orient their motion, but remain locked along the light direction once they find it by chance. The simulations show that these two orientation models lead to different macroscopic behaviours of the simulated cell populations. By comparing the results of the simulations with the experimental ones, we have found that the phototactic behaviour of real cells is more similar to that of the M2 model.

Conducting Simulation Studies in the R Programming Environment

Directory of Open Access Journals (Sweden)

Kevin A. Hallgren

2013-10-01

Full Text Available Simulation studies allow researchers to answer specific questions about data analysis, statistical power, and best-practices for obtainingaccurate results in empirical research. Despite the benefits that simulation research can provide, many researchers are unfamiliar with available tools for conducting their own simulation studies. The use of simulation studies need not be restricted toresearchers with advanced skills in statistics and computer programming, and such methods can be implemented by researchers with a variety of abilities and interests. The present paper provides an introduction to methods used for running simulationstudies using the R statistical programming environment and is written for individuals with minimal experience running simulation studies or using R. The paper describes the rationale and benefits of using simulations and introduces R functions relevant for many simulation studies. Three examples illustrate different applications for simulation studies, including (a the use of simulations to answer a novel question about statistical analysis, (b the use of simulations to estimate statistical power, and (c the use of simulations to obtain confidence intervals of parameter estimates throughbootstrapping. Results and fully annotated syntax from these examples are provided.

Correlation between self-diffusion in Si and the migration mechanisms of vacancies and self-interstitials: An atomistic study

International Nuclear Information System (INIS)

Posselt, M.; Gao, F.; Bracht, H.

2008-01-01

The migration of point defects in silicon and the corresponding atomic mobility are investigated by comprehensive classical molecular-dynamics simulations using the Stillinger-Weber potential and the Tersoff potential. In contrast to most of the previous studies both the point defect diffusivity and the self-diffusion coefficient per defect are calculated separately so that the diffusion-correlation factor can be determined. Simulations with both the Stillinger-Weber and the Tersoff potential show that vacancy migration is characterized by the transformation of the tetrahedral vacancy to the split vacancy and vice versa and the diffusion-correlation factor f V is about 0.5. This value was also derived by the statistical diffusion theory under the assumption of the same migration mechanism. The mechanisms of self-interstitial migration are more complex. The detailed study, including a visual analysis and investigations with the nudged elastic band method, reveals a variety of transformations between different self-interstitial configurations. Molecular-dynamics simulations using the Stillinger-Weber potential show that the self-interstitial migration is dominated by a dumbbell mechanism, whereas in the case of the Tersoff potential the interstitialcy mechanism prevails. The corresponding values of the correlation factor f I are different, namely, 0.59 and 0.69 for the dumbbell and the interstitialcy mechanisms, respectively. The latter value is nearly equal to that obtained by the statistical theory which assumes the interstitialcy mechanism. Recent analysis of experimental results demonstrated that in the framework of state-of-the-art diffusion and reaction models the best interpretation of point defect data can be given by assuming f I ≅0.6. The comparison with the present atomistic study leads to the conclusion that the self-interstitial migration in Si should be governed by a dumbbell mechanism

Dislocation mechanism of void growth at twin boundary of nanotwinned nickel based on molecular dynamics simulation

International Nuclear Information System (INIS)

Zhang, Yanqiu; Jiang, Shuyong; Zhu, Xiaoming; Zhao, Yanan

2016-01-01

Molecular dynamics simulation was performed to investigate dislocation mechanism of void growth at twin boundary (TB) of nanotwinned nickel. Simulation results show that the deformation of nanotwinned nickel containing a void at TB is dominated by the slip involving both leading and trailing partials, where the trailing partials are the dissociation products of stair-rod dislocations formed by the leading partials. The growth of a void at TB is attributed to the successive emission of the leading partials followed by trailing partials as well as the escape of these partial dislocations from the void surface. - Highlights: • Dislocation mechanism of void growth at TB of nanotwinned nickel is investigated. • Deformation of the nanotwinned nickel is dominated by leading and trailing partials. • Growth of void at TB is caused by successive emission and escape of these partials.

Insights into carbon nanotube and graphene formation mechanisms from molecular simulations: a review

International Nuclear Information System (INIS)

Page, A J; Ding, F; Irle, S; Morokuma, K

2015-01-01

The discovery of carbon nanotubes (CNTs) and graphene over the last two decades has heralded a new era in physics, chemistry and nanotechnology. During this time, intense efforts have been made towards understanding the atomic-scale mechanisms by which these remarkable nanostructures grow. Molecular simulations have made significant contributions in this regard; indeed, they are responsible for many of the key discoveries and advancements towards this goal. Here we review molecular simulations of CNT and graphene growth, and in doing so we highlight the many invaluable insights gained from molecular simulations into these complex nanoscale self-assembly processes. This review highlights an often-overlooked aspect of CNT and graphene formation—that the two processes, although seldom discussed in the same terms, are in fact remarkably similar. Both can be viewed as a 0D → 1D → 2D transformation, which converts carbon atoms (0D) to polyyne chains (1D) to a complete sp 2 -carbon network (2D). The difference in the final structure (CNT or graphene) is determined only by the curvature of the catalyst and the strength of the carbon–metal interaction. We conclude our review by summarizing the present shortcomings of CNT/graphene growth simulations, and future challenges to this important area. (review article)

Re-entry simulation chamber for thermo-mechanical characterisation of space materials

Science.gov (United States)

Liedtke, Volker

2003-09-01

During re-entry, materials and components are subject to very high thermal and mechanical loads. Any failure may cause loss of mission. Therefore, materials and components have to be tested under most rigid conditions to verify the suitability of the material and to verify the design of the components. The Re-Entry Simulation Chamber (RESiC) at ARC Seibersdorf research (ARCS) allows simulating the high thermal loads as well as complex mechanical load profiles that may occur during a re-entry; additionally, the influence of chemical reactions of materials with gaseous components of the atmosphere can be studied. The high vacuum chamber (better than 1×10-6 mbar) has a diameter of 650 mm and allows a sample height of 500 mm, or 1000 mm with extension flange. The gas dosing system is designed to emulate the increasing atmospheric pressure during the re-entry trajectory of a vehicle. Heating is performed by a 30 kW induction generator that allows a sufficiently rapid heating of larger components; electrically conductive materials such as metals or carbon fibre reinforced ceramics are directly heated, while for electrical insulators, susceptor plates or tubes will be employed. The uniaxial servo-hydraulic testing machine has a maximum load of 70 kN, either static or with a frequency of up to 70 Hz, with any given load profile (sinus, rectangular, triangular, ...). Strain measurements will be done by non-contacting laser speckle system for maximum flexibility and minimum instrumentation time effort (currently under application testing), or by strain gauges. All relevant process parameters are controlled and recorded by microcomputer. The highly sophisticated control software allows a convenient and reliable multi-channel data acquisition, e.g. temperatures at various positions of the test piece, pressure, loads, strains, and any other test data according to customer specifications; the data format is suitable for any further data processing. During the set-up and

Mechanical Degradation of Graphite/PVDF Composite Electrodes: A Model-Experimental Study

Energy Technology Data Exchange (ETDEWEB)

Takahashi, K; Higa, K; Mair, S; Chintapalli, M; Balsara, N; Srinivasan, V

2015-12-11

Mechanical failure modes of a graphite/polyvinylidene difluoride (PVDF) composite electrode for lithium-ion batteries were investigated by combining realistic stress-stain tests and mathematical model predictions. Samples of PVDF mixed with conductive additive were prepared in a similar way to graphite electrodes and tested while submerged in electrolyte solution. Young's modulus and tensile strength values of wet samples were found to be approximately one-fifth and one-half of those measured for dry samples. Simulations of graphite particles surrounded by binder layers given the measured material property values suggest that the particles are unlikely to experience mechanical damage during cycling, but that the fate of the surrounding composite of PVDF and conductive additive depends completely upon the conditions under which its mechanical properties were obtained. Simulations using realistic property values produced results that were consistent with earlier experimental observations.

Numerical simulation of the generation mechanism of axisymmetric supersonic jet screech tones

Science.gov (United States)

Li, X. D.; Gao, J. H.

2005-08-01

In this paper an axisymmetric computational aeroacoustic procedure is developed to investigate the generation mechanism of axisymmetric supersonic jet screech tones. The axisymmetric Navier-Stokes equations and the two equations standard k-ɛ turbulence model modified by Turpin and Troyes ["Validation of a two-equation turbulence model for axisymmetric reacting and non-reaction flows," AIAA Paper No. 2000-3463 (2000)] are solved in the generalized curvilinear coordinate system. A generalized wall function is applied in the nozzle exit wall region. The dispersion-relation-preserving scheme is applied for space discretization. The 2N storage low-dissipation and low-dispersion Runge-Kutta scheme is employed for time integration. Much attention is paid to far-field boundary conditions and turbulence model. The underexpanded axisymmetric supersonic jet screech tones are simulated over the Mach number from 1.05 to 1.2. Numerical results are presented and compared with the experimental data by other researchers. The simulated wavelengths of A0, A1, A2, and B modes and part of simulated amplitudes agree very well with the measurement data by Ponton and Seiner ["The effects of nozzle exit lip thickness on plume resonance," J. Sound Vib. 154, 531 (1992)]. In particular, the phenomena of modes jumping have been captured correctly although the numerical procedure has to be improved to predict the amplitudes of supersonic jet screech tones more accurately. Furthermore, the phenomena of shock motions are analyzed. The predicted splitting and combination of shock cells are similar with the experimental observations of Panda ["Shock oscillation in underexpanded screeching jets," J. Fluid. Mech. 363, 173 (1998)]. Finally, the receptivity process is numerically studied and analyzed. It is shown that the receptivity zone is associated with the initial thin shear layer, and the incoming and reflected sound waves.

Thermal hydraulic-Mechanic Integrated Simulation for Advanced Cladding Thermal Shock Fracture Analysis during Reflood Phase in LBLOCA

Energy Technology Data Exchange (ETDEWEB)

Son, Seong Min; Lee, You Ho; Cho, Jae Wan; Lee, Jeong Ik [KAERI, Daejeon (Korea, Republic of)

2016-05-15

This study suggested thermal hydraulic-mechanical integrated stress based methodology for analyzing the behavior of ATF type claddings by SiC-Duplex cladding LBLOCA simulation. Also, this paper showed that this methodology could predict real experimental result well. That concept for enhanced safety of LWR called Advanced Accident-Tolerance Fuel Cladding (ATF cladding, ATF) is researched actively. However, current nuclear fuel cladding design criteria for zircaloy cannot be apply to ATF directly because those criteria are mainly based on limiting their oxidation. So, the new methodology for ATF design criteria is necessary. In this study, stress based analysis methodology for ATF cladding design criteria is suggested. By simulating LBLOCA scenario of SiC cladding which is the one of the most promising candidate of ATF. Also we'll confirm our result briefly through comparing some facts from other experiments. This result is validating now. Some of results show good performance with 1-D failure analysis code for SiC fuel cladding that already developed and validated by Lee et al,. It will present in meeting. Furthermore, this simulation presented the possibility of understanding the behavior of cladding deeper. If designer can predict the dangerous region and the time precisely, it may be helpful for designing nuclear fuel cladding geometry and set safety criteria.

Success and failure of the defibrillation shock: insights from a simulation study.

Science.gov (United States)

Skouibine, K; Trayanova, N; Moore, P

2000-07-01

This simulation study presents a further inquiry into the mechanisms by which a strong electric shock fails to halt life-threatening cardiac arrhythmias. The research uses a model of the defibrillation process that represents a sheet of myocardium as a bidomain. The tissue consists of nonuniformly curved fibers in which spiral wave reentry is initiated. Monophasic defibrillation shocks are delivered via two line electrodes that occupy opposite tissue boundaries. In some simulation experiments, the polarity of the shock is reversed. Electrical activity in the sheet is compared for failed and successful shocks under controlled conditions. The maps of transmembrane potential and activation times calculated during and after the shock demonstrate that weak shocks fail to terminate the reentrant activity via two major mechanisms. As compared with strong shocks, weak shocks result in (1) smaller extension of refractoriness in the areas depolarized by the shock, and (2) slower or incomplete activation of the excitable gap created by deexcitation of the negatively polarized areas. In its turn, mechanism 2 is associated with one or more of the following events: (a) lack of some break excitations, (b) latency in the occurrence of the break excitations, and (c) slower propagation through deexcited areas. Reversal of shock polarity results in a change of the extent of the regions of deexcitation, and thus, in a change in defibrillation threshold. The results of this study indicate the paramount importance of shock-induced deexcitation in both defibrillation and postshock arrhythmogenesis.

Mechanical properties of jennite: A theoretical and experimental study

Energy Technology Data Exchange (ETDEWEB)

Moon, Juhyuk, E-mail: juhyuk.moon@stonybrook.edu [Civil Engineering Program, Department of Mechanical Engineering, Stony Brook University, NY 11794 (United States); Yoon, Seyoon [School of Engineering, Kings College, University of Aberdeen, Aberdeen AB24 3UE (United Kingdom); Monteiro, Paulo J.M. [Department of Civil and Environmental Engineering, University of California, Berkeley, CA 94720 (United States)

2015-05-15

The objective of this study is to determine the mechanical properties of jennite. To date, several hypotheses have been proposed to predict the structural properties of jennite. For the first time as reported herein, the isothermal bulk modulus of jennite was measured experimentally. Synchrotron-based high-pressure x-ray diffraction experiments were performed to observe the variation of lattice parameters under pressure. First-principles calculations were applied to compare with the experimental results and predict additional structural properties. Accurately measured isothermal bulk modulus herein (K{sub 0} = 64(2) GPa) and the statistical assessment on experimental and theoretical results suggest reliable mechanical properties of shear and Young's modulus, Poisson's ratio, and elastic tensor coefficients. Determination of these fundamental structural properties is the first step toward greater understanding of calcium–silicate–hydrate, as well as provides a sound foundation for forthcoming atomic level simulations.

More than just a game: the role of simulation in the teaching of product design and entrepreneurship to mechanical engineering students

Science.gov (United States)

Costello, Gabriel J.

2017-11-01

The purpose of this work is to contribute to the debate on the best pedagogical approach to developing undergraduate mechanical engineering skills to meet the requirements of contemporary complex working environments. The paper provides an example of using student-entrepreneur collaboration in the teaching of modules to Mechanical Engineering final-year students. Problem-based learning (PBL) is one of the most significant recent innovations in the area of education for the professions. This work proposes to make an original contribution by simulating a real-life entrepreneur interaction for the students. The current literature largely confines simulation-based learning to computer applications such as games. However, this paper argues that role playing by students interfacing with technology start-ups can also be regarded as 'simulation' in a wider sense. Consequently, the paper proposes the concept of simulation-action learning as an enhancement of PBL and to distinguish it from computer simulation.

Electrophysiological potentials reveal cortical mechanisms for mental imagery, mental simulation, and grounded (embodied cognition

Directory of Open Access Journals (Sweden)

Haline E. Schendan

2012-09-01

Full Text Available Grounded cognition theory proposes that cognition, including meaning, is grounded in sensorimotor processing. The mechanism for grounding cognition is mental simulation, which is a type of mental imagery that re-enacts modal processing. To reveal top-down, cortical mechanisms for mental simulation of shape, event-related potentials were recorded to face and object pictures preceded by mental imagery of a picture. Mental imagery of the identical face or object (congruous condition facilitated not only categorical perception (VPP/N170 but also later visual knowledge (N3[00] complex and linguistic knowledge (N400 for faces more than objects, and strategic semantic analysis (late positive complex between 200 and 700 ms. The later effects resembled semantic congruity effects with pictures. Mental imagery also facilitated category decisions, as a P3(00 peaked earlier for congruous than incongruous (other category pictures, resembling the case when identical pictures repeat immediately. Thus mental imagery mimics semantic congruity and immediate repetition priming processes with pictures. Perception control results showed the opposite for faces and were in the same direction for objects: Perceptual repetition adapts (and so impairs processing of perceived faces from categorical perception onwards, but primes processing of objects during categorical perception, visual knowledge processes, and strategic semantic analysis. For both imagery and perception, differences between faces and objects support domain-specificity and indicate that cognition is grounded in modal processing. Altogether, this direct neural evidence reveals that top-down processes of mental imagery sustain an imagistic representation that mimics perception well enough to prime subsequent perception and cognition. This also suggests that automatic mental simulation of the visual shape of faces and objects operates between 200 and 400 ms, and strategic mental simulation operates between

Micro-Vibration Performance Prediction of SEPTA24 Using SMeSim (RUAG Space Mechanism Simulator Tool)

Science.gov (United States)

Omiciuolo, Manolo; Lang, Andreas; Wismer, Stefan; Barth, Stephan; Szekely, Gerhard

2013-09-01

Scientific space missions are currently challenging the performances of their payloads. The performances can be dramatically restricted by micro-vibration loads generated by any moving parts of the satellites, thus by Solar Array Drive Assemblies too. Micro-vibration prediction of SADAs is therefore very important to support their design and optimization in the early stages of a programme. The Space Mechanism Simulator (SMeSim) tool, developed by RUAG, enhances the capability of analysing the micro-vibration emissivity of a Solar Array Drive Assembly (SADA) under a specified set of boundary conditions. The tool is developed in the Matlab/Simulink® environment throughout a library of blocks simulating the different components a SADA is made of. The modular architecture of the blocks, assembled by the user, and the set up of the boundary conditions allow time-domain and frequency-domain analyses of a rigid multi-body model with concentrated flexibilities and coupled- electronic control of the mechanism. SMeSim is used to model the SEPTA24 Solar Array Drive Mechanism and predict its micro-vibration emissivity. SMeSim and the return of experience earned throughout its development and use can now support activities like verification by analysis of micro-vibration emissivity requirements and/or design optimization to minimize the micro- vibration emissivity of a SADA.

Towards a quantification of stress corrosion mechanisms: numerical simulations of hydrogen-dislocations at the very crack tip

International Nuclear Information System (INIS)

Chateau, J.P.

1999-01-01

We discuss the respective roles played by anodic dissolution and hydrogen in SCC mechanisms of f.c.c. materials, by studying the fracture of copper in nitrite for which we compare the results with that previously obtained in 316L steel in hot chloride. It is surprising to note that even the crystallographies at the scale of the micron are different, the macroscopic inclination of the fracture surfaces are the same. In the case of 316L steel, the formation of strong pile-ups in the presence of hydrogen leads to a zigzag fracture along alternated slip planes in the most general case. In the absence of hydrogen, as in copper, this mechanism effectively disappears. Furthermore, numerical simulations of crack shielding by dislocations emitted on one plane predict the macroscopic inclination. It shows that it is due to the mere dissolution which confines slip activity at the very crack tip in f.c.c. materials. In order to quantify the mechanism involved in 316L steel, we developed simulations which numerically solve the coupled diffusion and elasticity equations for hydrogen in the presence of a crack and shielding dislocations. They reproduce the mechanisms of hydrogen segregation on edge dislocations and of a localised softening effect by decreasing pair interactions. These mechanisms lead to i) a localisation of hydrogen embrittlement along the activated slip planes, ii) an increase of the dislocation density in pile-ups, and iii) a decrease of the cross slip probability. These three factors enhance micro-fracture at the head of a pile-up, which is responsible of the zigzag fracture. Introducing the free surface effects for hydrogen, we point out a new mechanism: the inhibition of dislocation sources at the crack tip, which is relevant with the brittle fracture surfaces observed in some cases in 316L steel. The quantification of these different mechanisms allows to give a relation between the local fracture possibility and the macroscopic parameters. A general law for

Conducting Simulation Studies in Psychometrics

Science.gov (United States)

Feinberg, Richard A.; Rubright, Jonathan D.

2016-01-01

Simulation studies are fundamental to psychometric discourse and play a crucial role in operational and academic research. Yet, resources for psychometricians interested in conducting simulations are scarce. This Instructional Topics in Educational Measurement Series (ITEMS) module is meant to address this deficiency by providing a comprehensive…

STRESS LOADING SIMULATION OF HYDRO-MECHANICAL TRANSMISSION OF DUMP TRUCK

Directory of Open Access Journals (Sweden)

S. A. Sidorov

2006-01-01

Full Text Available The Transmission model and software package to investigate stress loading of a hydromechanical transmission of a dump truck have been developed. The given software package allows to model stress loading of transmission gears in taking-off and acceleration modes at various road resistance, positions of an engine control pedal and initial revolutions of an engine crankshaft, various laws of friction clutch switching and some other parameters that permit to reveal a rate of various operational mode influence on stress loading of a dump truck transmission. An equivalence of the developed software is proved by the comparison of the experimentally obtained stress loading process of the hydro-mechanical transmission of a BelAZ- 7555 dump truck with the results of the simulation 

Multiscale Simulation of Thermo-mechanical Processes in Irradiated Fission-reactor Materials

International Nuclear Information System (INIS)

Phillpot, Simon R.

2012-01-01

The work funded from this project has been published in six papers, with two more in draft form, with submission planned for the near future. The papers are: (1) Kinetically-Evolving Irradiation-Induced Point-Defect Clusters in UO 2 by Molecular-Dynamics Simulation; (2) Kinetically driven point-defect clustering in irradiated MgO by molecular-dynamics simulation; (3) Grain-Boundary Source/Sink Behavior for Point Defect: An Atomistic Simulation Study; (4) Energetics of intrinsic point defects in uranium dioxide from electronic structure calculations; (5) Thermodynamics of fission products in UO 2±x ; and (6) Atomistic study of grain boundary sink strength under prolonged electron irradiation. The other two pieces of work that are currently being written-up for publication are: (1) Effect of Pores and He Bubbles on the Thermal Transport Properties of UO2 by Molecular Dynamics Simulation; and (2) Segregation of Ruthenium to Edge Dislocations in Uranium Dioxide.

NUMERICAL SIMULATION AND EXPERIMENTAL STUDY OF DRAGREDUCING SURFACE OF A REAL SHARK SKIN*

Institute of Scientific and Technical Information of China (English)

ZHANG De-yuan; LUO Yue-hao; LI Xiang; CHEN Hua-wei

2011-01-01

It is well known that shark skin surface can effectively inhabit the occurrence of turbulence and reduce the wall friction,but in order to understand the mechanism of drag reduction, one has to solve the problem of the turbulent flow on grooved-scale surface, and in that respect, the direct numerical simulation is an important tool.In this article, based on the real biological shark skin,the model of real shark skin is built through high-accurate scanning and data processing.The turbulent flow on a real shark skin is comprehensively simulated, and based on the simulation, the drag reduction mechanism is discussed.In addition, in order to validate the drag-reducing effect of shark skin surface, actual experiments were carried out in water tunnel, and the experimental results are approximately consistent with the numerical simulation.

Atomistic simulation study of deformation twinning of nanocrystalline body-centered cubic Mo

Energy Technology Data Exchange (ETDEWEB)

Tian, Xiaofeng [The College of Nuclear Technology and Automation Engineering, Chengdu University of Technology, Chengdu (China); Li, Dan, E-mail: txf8378@163.com [The College of Nuclear Technology and Automation Engineering, Chengdu University of Technology, Chengdu (China); Yu, You [College of Optoelectronic Technology, Chengdu University of Information Technology, Chengdu (China); You, Zhen Jiang [Australian School of Petroleum, University of Adelaide, SA 5005 (Australia); Li, Tongye [The National Key Laboratory of Nuclear Fuel and Materials, Nuclear Power Institute of China, Chengdu (China); Ge, Liangquan [The College of Nuclear Technology and Automation Engineering, Chengdu University of Technology, Chengdu (China)

2017-04-06

Deformation twinning of nanocrystalline body-centered cubic Mo was studied using molecular dynamics simulations, and the effects of grain sizes and temperatures on the deformation were evaluated. With small grain size, grain rotation accompanying grain growth was found to play important role in nanocrystalline Mo during tensile deformation. Additionally, grain rotation and the deformation controlled by GB-mediated processes induce to the difficulty of creating crack. Twin was formed by successive emission of twinning partials from grain boundaries in small grain size systems. However, the twin mechanisms of GB splitting and overlapping of two extended dislocations were also found in larger size grain. Twin induced crack tips were observed in our simulation, and this confirmed the results of previous molecular dynamics simulations. At higher temperatures, GB activities can be thermally activated, resulting in suppression of twinning tendency and improvement of ductility of nanocrystalline Mo.

Quantum mechanical study of solvent effects in a prototype SN2 reaction in solution: Cl- attack on CH3Cl.

Science.gov (United States)

Kuechler, Erich R; York, Darrin M

2014-02-07

The nucleophilic attack of a chloride ion on methyl chloride is an important prototype SN2 reaction in organic chemistry that is known to be sensitive to the effects of the surrounding solvent. Herein, we develop a highly accurate Specific Reaction Parameter (SRP) model based on the Austin Model 1 Hamiltonian for chlorine to study the effects of solvation into an aqueous environment on the reaction mechanism. To accomplish this task, we apply high-level quantum mechanical calculations to study the reaction in the gas phase and combined quantum mechanical/molecular mechanical simulations with TIP3P and TIP4P-ew water models and the resulting free energy profiles are compared with those determined from simulations using other fast semi-empirical quantum models. Both gas phase and solution results with the SRP model agree very well with experiment and provide insight into the specific role of solvent on the reaction coordinate. Overall, the newly parameterized SRP Hamiltonian is able to reproduce both the gas phase and solution phase barriers, suggesting it is an accurate and robust model for simulations in the aqueous phase at greatly reduced computational cost relative to comparably accurate ab initio and density functional models.

A study of sodium oxide crystallization mechanisms and kinetics in cold traps

International Nuclear Information System (INIS)

Latge, C.

1984-04-01

After showing up the present lack of data on crystallization mechanisms and kinetics, a number of tests were conducted on a sodium test loop equipped with two experimental cold traps. The effects of several geometric and thermohydraulic parameters on purification efficiency were also studied. The test results were used to develop a simulation model. An optimization code based on the model can be used to determine the nucleation and growth kinetics

QM/MM MD and Free Energy Simulation Study of Methyl Transfer Processes Catalyzed by PKMTs and PRMTs.

Science.gov (United States)

Chu, Yuzhuo; Guo, Hong

2015-09-01

Methyl transfer processes catalyzed by protein lysine methyltransferases (PKMTs) and protein arginine methyltransferases (PRMTs) control important biological events including transcriptional regulation and cell signaling. One important property of these enzymes is that different PKMTs and PRMTs catalyze the formation of different methylated product (product specificity). These different methylation states lead to different biological outcomes. Here, we review the results of quantum mechanics/molecular mechanics molecular dynamics and free energy simulations that have been performed to study the reaction mechanism of PKMTs and PRMTs and the mechanism underlying the product specificity of the methyl transfer processes.

Modeling and Dynamic Simulation of the Adjust and Control System Mechanism for Reactor CAREM-25

International Nuclear Information System (INIS)

Larreteguy, A.E; Mazufri, C.M

2000-01-01

The adjust and control system mechanism, MSAC, is an advanced, and in some senses unique, hydromechanical device.The efforts in modeling this mechanism are aimed to: Get a deep understanding of the physical phenomena involved,Identify the set of parameters relevant to the dynamics of the system,Allow the numerical simulation of the system,Predict the behavior of the mechanism in conditions other than that obtainable within the range of operation of the experimental setup (CEM), and Help in defining the design of the CAPEM (loop for testing the mechanism under high pressure/high temperature conditions).Thanks to the close interaction between the mechanics, the experimenters, and the modelists that compose the MSAC task force, it has been possible to suggest improvements, not only in the design of the mechanism, but also in the design and the operation of the pulse generator (GDP) and the rest of the CEM.This effort has led to a design mature enough so as to be tested in a high-pressure loop

Substrate binding and catalytic mechanism in phospholipase C from Bacillus cereus. a molecular mechanics and molecular dynamics study

DEFF Research Database (Denmark)

da Graça Thrige, D; Buur, J R; Jørgensen, Flemming Steen

1997-01-01

cereus including a docked substrate molecule was subjected to a stepwise molecular mechanics energy minimization. Second, the location of the nucleophilic water molecule in the active site of the fully relaxed enzyme-substrate complex was determined by evaluation of nonbonded interaction energies between...... water molecule was verified during a 100 ps molecular dynamics simulation. During the simulation the substrate undergoes a conformational change, but retains its localization in the active site. The contacts between the enzyme, the substrate, and the nucleophilic water molecule display some fluctuations...... the strong electrostatic interactions in the active site realistically during energy minimization, delocalization of the charges from the three zinc ions was considered. Therefore, quantum mechanics calculations on the zinc ions and the zinc-coordinating residues were carried out prior to the molecular...

Study on Mechanical Characteristics of Fully Grouted Rock Bolts for Underground Caverns under Seismic Loads

Directory of Open Access Journals (Sweden)

Guoqing Liu

2017-01-01

Full Text Available This study establishes an analytical model for the interaction between the bolt and surrounding rock based on the bearing mechanism of fully grouted rock bolts. The corresponding controlled differential equation for load transfer is deduced. The stress distributions of the anchorage body are obtained by solving the equations. A dynamic algorithm for the bolt considering shear damage on the anchoring interface is proposed based on the dynamic finite element method. The rationality of the algorithm is verified by a pull-out test and excavation simulation of a rounded tunnel. Then, a case study on the mechanical characteristics of the bolts in underground caverns under seismic loads is conducted. The results indicate that the seismic load may lead to stress originating from the bolts and damage on the anchoring interface. The key positions of the antiseismic support can be determined using the numerical simulation. The calculated results can serve as a reference for the antiseismic optimal design of bolts in underground caverns.

Statistical methods to correct for verification bias in diagnostic studies are inadequate when there are few false negatives: a simulation study

Directory of Open Access Journals (Sweden)

Vickers Andrew J

2008-11-01

Full Text Available Abstract Background A common feature of diagnostic research is that results for a diagnostic gold standard are available primarily for patients who are positive for the test under investigation. Data from such studies are subject to what has been termed "verification bias". We evaluated statistical methods for verification bias correction when there are few false negatives. Methods A simulation study was conducted of a screening study subject to verification bias. We compared estimates of the area-under-the-curve (AUC corrected for verification bias varying both the rate and mechanism of verification. Results In a single simulated data set, varying false negatives from 0 to 4 led to verification bias corrected AUCs ranging from 0.550 to 0.852. Excess variation associated with low numbers of false negatives was confirmed in simulation studies and by analyses of published studies that incorporated verification bias correction. The 2.5th – 97.5th centile range constituted as much as 60% of the possible range of AUCs for some simulations. Conclusion Screening programs are designed such that there are few false negatives. Standard statistical methods for verification bias correction are inadequate in this circumstance.

Molecular simulation of the role of interlayer water on the mechanical properties of montmorillonite

International Nuclear Information System (INIS)

Carrier, Benoit; Vandamme, Matthieu; Ebrahimi, Davoud; Whittle, Andrew J.; Pellenq, Roland J.M.; Van Damme, Henri

2012-01-01

Document available in extended abstract form only. Full text of publication follows: Montmorillonite - a swelling clay - is the main component of the clay fraction of the Callovo-Oxfordian argillite, which is considered as a possible host rock for radioactive waste disposal, and of the sealing bentonite plugs of storage tunnels. Montmorillonite layers have a great ability to adsorb water, resulting in the swelling of the clay. Montmorillonite consists of water molecules and sodium or calcium cations between negatively charged layers. Both the water content of the interlayer space and the nature of the charge-balancing cations are expected to have an effect on the mechanical properties of the clay layer. Computer simulations allow to reproduce the experimental swelling isotherms of the layers and to gain a deeper understanding of the physical mechanisms of the swelling process. They show how water is organized in discrete layers and how this process depends on the type of inter-layer cation. However, the effect of the swelling on the mechanical properties of the nano-scale have not been fully investigated. The objective of this work is to compute the elastic properties of a Na + - Montmorillonite and a Ca 2+ -Montmorillonite versus relative humidity at 300 K. The results of this work is the first step to build a macroscopic state equation of unsaturated clay-based materials. We use a simulation cell containing two Montmorillonite layers and sodium or calcium counterions. The partial charges of the atoms and the interatomic interaction parameters are given by the CLAYFF force field. Grand Canonical Monte-Carlo simulations are used to compute the adsorption/desorption isotherm. Each equilibrium configuration is then strained in all directions of space. Then, we perform Molecular Dynamics and compute the stress tensor and all the components of the elasticity tensor. We present the evolution of the elastic properties of the clay layers with the relative humidity. In

Bio-inspired passive actuator simulating an abalone shell mechanism for structural control

International Nuclear Information System (INIS)

Yang, Henry T Y; Lin, Chun-Hung; Bridges, Daniel; Randall, Connor J; Hansma, Paul K

2010-01-01

An energy dispersion mechanism called 'sacrificial bonds and hidden length', which is found in some biological systems, such as abalone shells and bones, is the inspiration for new strategies for structural control. Sacrificial bonds and hidden length can substantially increase the stiffness and enhance energy dissipation in the constituent molecules of abalone shells and bone. Having been inspired by the usefulness and effectiveness of such a mechanism, which has evolved over millions of years and countless cycles of evolutions, the authors employ the conceptual underpinnings of this mechanism to develop a bio-inspired passive actuator. This paper presents a fundamental method for optimally designing such bio-inspired passive actuators for structural control. To optimize the bio-inspired passive actuator, a simple method utilizing the force–displacement–velocity (FDV) plots based on LQR control is proposed. A linear regression approach is adopted in this research to find the initial values of the desired parameters for the bio-inspired passive actuator. The illustrative examples, conducted by numerical simulation with experimental validation, suggest that the bio-inspired passive actuator based on sacrificial bonds and hidden length may be comparable in performance to state-of-the-art semi-active actuators

Bio-inspired passive actuator simulating an abalone shell mechanism for structural control

Science.gov (United States)

Yang, Henry T. Y.; Lin, Chun-Hung; Bridges, Daniel; Randall, Connor J.; Hansma, Paul K.

2010-10-01

An energy dispersion mechanism called 'sacrificial bonds and hidden length', which is found in some biological systems, such as abalone shells and bones, is the inspiration for new strategies for structural control. Sacrificial bonds and hidden length can substantially increase the stiffness and enhance energy dissipation in the constituent molecules of abalone shells and bone. Having been inspired by the usefulness and effectiveness of such a mechanism, which has evolved over millions of years and countless cycles of evolutions, the authors employ the conceptual underpinnings of this mechanism to develop a bio-inspired passive actuator. This paper presents a fundamental method for optimally designing such bio-inspired passive actuators for structural control. To optimize the bio-inspired passive actuator, a simple method utilizing the force-displacement-velocity (FDV) plots based on LQR control is proposed. A linear regression approach is adopted in this research to find the initial values of the desired parameters for the bio-inspired passive actuator. The illustrative examples, conducted by numerical simulation with experimental validation, suggest that the bio-inspired passive actuator based on sacrificial bonds and hidden length may be comparable in performance to state-of-the-art semi-active actuators.

A novel regenerative shock absorber with a speed doubling mechanism and its Monte Carlo simulation

Science.gov (United States)

Zhang, Ran; Wang, Xu; Liu, Zhenwei

2018-03-01

A novel regenerative shock absorber has been designed and fabricated. The novelty of the presented work is the application of the double speed regenerative shock absorber that utilizes the rack and pinion mechanism to increase the magnet speed with respect to the coils for higher power output. The simulation models with parameters identified from finite element analysis and the experiments are developed. The proposed regenerative shock absorber is compared with the regenerative shock absorber without the rack and pinion mechanism, when they are integrated into the same quarter vehicle suspension system. The sinusoidal wave road profile displacement excitation and the random road profile displacement excitation with peak amplitude of 0.035 m are applied as the inputs in the frequency range of 0-25 Hz. It is found that with the sinusoidal and random road profile displacement input, the proposed innovative design can increase the output power by 4 times comparing to the baseline design. The proposed double speed regenerative shock absorber also presents to be more sensitive to the road profile irregularity than the single speed regenerative shock absorber as suggested by Monte Carlo simulation. Lastly the coil mass and amplification factor are studied for sensitivity analysis and performance optimization, which provides a general design method of the regenerative shock absorbers. It shows that for the system power output, the proposed design becomes more sensitive to either the coil mass or amplification factor depending on the amount of the coil mass. With the specifically selected combination of the coil mass and amplification factor, the optimized energy harvesting performance can be achieved.

Softening mechanisms of the AISI 410 martensitic stainless steel under hot torsion simulation

Energy Technology Data Exchange (ETDEWEB)

Oliveira, Thiago Santana de; Silva, Eden Santos; Rodrigues, Samuel Filgueiras; Nascimento, Carmem Celia Francisco; Leal, Valdemar Silva; Reis, Gedeon Silva, E-mail: samuel.filgueiras@ifma.edu.br [Instituto Federal do Maranhao (PPGEM/IFMA), Sao Luis, MA (Brazil)

2017-03-15

This study investigated the softening mechanisms of the AISI 410 martensitic stainless steel during torsion simulation under isothermal continuous in the temperature range of 900 to 1150 °C and strain rates of 0.1 to 5.0s{sup -1}. In the first part of the curves, before the peak, the results show that the critical (ε-c) and peak (ε-p) strains are elevated for higher strain rate and lower temperatures contributing for higher strain hardening rate (h). Moreover, this indicated that dynamic recrystallization (DRX) and dynamic recovery (DRV) are not effective in this region. After the peak, the reductions in stresses are associated to the different DRX/DRV competitions. For lower temperatures and higher strain rates there is a delay in the DRX while the DRV is acting predominantly (with low Avrami exponent (n) and high t{sub 0.5}). The steady state was reached after large strains showing DRX grains, formation of retained austenite and the presence of chromium carbide (Cr{sub 23}C{sub 6}) and ferrite δ at the martensitic grain boundaries. These contribute for impairing the toughness and ductility on the material. The constitutive equations at the peak strain indicated changes in the deformation mechanism, with variable strain rate sensitivity (m), which affected the final microstructure. (author)

A simulation study of active feedback supression of dynamic response in helicopter rotor blades

Science.gov (United States)

Kana, D. D.; Bessey, R. L.; Dodge, F. T.

1975-01-01

A parameter study is presented for active feedback control applied to a helicopter rotor blade during forward flight. The study was performed on an electromechanical apparatus which included a mechanical model rotor blade and electronic analog simulation of interaction between blade deflections and aerodynamic loading. Blade response parameters were obtained for simulated vortex impinging at the blade tip at one pulse per revolution, and for a pulse which traveled from the blade tip toward its root. Results show that the response in a 1 - 10-per-rev frequency band is diminished by the feedback action, but at the same time responses at frequencies above 10-per-rev become increasingly more prominent with increased feedback amplitude, and can even lead to instability at certain levels. It appears that the latter behavior results from limitations of the laboratory simulation apparatus, rather than genuine potential behavior for a prototype helicopter.