EXACT ANALYSIS OF WAVE PROPAGATION IN AN INFINITE RECTANGULAR BEAM
孙卫明; 杨光松; 李东旭
2004-01-01
The Fourier series method was extended for the exact analysis of wave propagation in an infinite rectangular beam. Initially, by solving the three-dimensional elastodynamic equations a general analytic solution was derived for wave motion within the beam. And then for the beam with stress-free boundaries, the propagation characteristics of elastic waves were presented. This accurate wave propagation model lays a solid foundation of simultaneous control of coupled waves in the beam.
Numerical prediction of wave impact loads on multiple rectangular beams
Mayer, Stefan; Nielsen, Kristian Bendix; Hansen, E.A.
2005-01-01
corresponding to a wave impact scenario in the experimental database of Sterndorff [2002]. For the case of wave impact on a single structural element the numerical results show good agreement with measured force time histories. In the computations featuring two beams, the prediction of the shadowing effect......Wave impact on one and two structural beams with rectangular cross section is simulated with a two-dimensional finite volume method, solving the unsteady Euler equations and employing a VOF-type method for the description of the free surface. Four different test series are carried out, each...
Small-signal analysis of a rectangular helix structure traveling-wave-tube
Fu Cheng-Fang; Wei Yan-Yu; Duan Zhao-Yun; Wang Wen-Xiang; Gong Yu-Bin
2009-01-01
This paper investigates the properties of traveling wave-beam interaction in a rectangular helix traveling-wave-tube (TWT) for a solid sheet electron beam. The 'hot' dispersion equation is obtained by means of the self-consistent field theory. The small signal analysis, which includes the effects of the beam parameters and slow-wave structure (SWS)parameters, is carried out by theoretical computation. The numerical results show that the bandwidth and the smallsignal gain of the rectangular helix TWT increase as the beam current increases; and the beam voltage not obviously influences the small signal gain. Among different rectangular helix structures, the small-signal gain increases as the width of the rectangular helix SWS increases, however, the bandwidth decreases whether structure parameters a and Lor ψ and L are fixed or not. In addition, a comparison of the small-signal gain of this structure with a conventional round helix is made. The presented analysis will be useful for the design of the TWT with a rectangular helix circuit.
Critical current studies of a HTS rectangular coil
Zhong, Z. [Department of Engineering, University of Cambridge (United Kingdom); Chudy, M., E-mail: Michal.chudy@stuba.sk [Graduate School of Technology Management, University of Pretoria (South Africa); Institute of Power and Applied Electrical Engineering, Slovak University of Technology in Bratislava (Slovakia); Ruiz, H.S. [Department of Engineering, University of Leicester, Leicester LE1 7RH (United Kingdom); Zhang, X.; Coombs, T. [Department of Engineering, University of Cambridge (United Kingdom)
2017-05-15
Highlights: • Unique square pancake coil was manufactured. • Measurements in relatively high magnetic field were performed. • Different sections of the coil were characterized. • Parts of the coil which are limiting critical current were identified. - Abstract: Nowadays, superconducting high field magnets are used in numerous applications due to their superior properties. High temperature superconductors (HTS) are usually used for production of circular pancake or racetrack coils. However different geometries of HTS coils might be required for some specific applications. In this study, the HTS coil wound on a rectangular frame was fully characterized in homogeneous DC background field. The study contains measurements of critical current angular dependencies. The critical current of the entire coil and two selected strands under different magnitudes and orientations of external magnetic fields are measured. The critical regions of the coil in different angular regimes are determined. This study brings better understanding of the in- field performance of HTS coils wound on frames with right-angles.
A Research of 140-GHz Folded Rectangular Gro ove Waveguide Traveling-Wave Tub e
ZHANG Minghao; WEI Yanyu; YUE Lingna; GUO Guo; WANG Yuanyuan; SHI Xianbao; WANG Wenxiang
2015-01-01
A two-section Folded rectangular groove waveguide (FRGWG) Slow wave structure (SWS) Travel-ing wave tube (TWT) with large dimension of beam tunnel is studied. Compared with the Folded waveguide (FWG) under the same size parameters conditions, the interac-tion impedance and center frequency of the FRGWG are higher. The advantage is that a beam tunnel with large dimension can be applied to the FRGWG without the influence caused by signal decrease, reflection and oscil-lation. The microwave amplification capability based on beam-wave interaction is obtained through the particle-in-cell method. This circuit structure can produce an output power of over 100W ranging from 136 to 142GHz when the operation voltage and beam current are set as 18.4kV and 150mA, respectively, for a 95mm long circuit.
Radio-Frequency Characteristics of a Printed Rectangular Helix Slow-Wave Structure
FU Cheng-Fang; WEI Yan-Yu; WANG Wen-Xiang; GONG Yu-Bin
2008-01-01
A new type of printed rectangular he/ix slow-wave structure (SWS) is investigated using the field-matching method and the electromagnetic integral equations at the boundaries. The radio-frequency characteristics including the dispersion equation and the coupling impedance for transverse antisymmetric (odd) modes of this structure are analysed. The numerical results agree well with the results obtained by the EM simulation software HFSS. It is shown that the dispersion of the rectangular helix circuit is weakened, the phase velocity is reduced after filling the dielectric materials in the rectangular helix SWS. As a planar slow-wave structure, this structure has potential applications in compact TWTs.
Different localized states of travelling-wave convection in a rectangular container
Li Guo-Dong; Huang Yong-Nian
2006-01-01
We have performed numerical simulations of localized travelling-wave convection in a binary fluid mixture heated from below in a long rectangular container. Calculations are carried out in a vertical cross section of the rolls perpendicular to their axes. For a negative enough separation ratio, two types of quite different confined states were documented by applying different control processes. One branch of localized travelling waves survives only in a very narrow band within subcritical regime, while another branch straddles the onset of convection existing both in subcritical and supercritical regions. We elucidated that concentration field and its current are key to understand how confined convection is sustained when conductive state is absolutely unstable. The weak structures in the conducting region are demonstrated too.
On the existence of guided acoustic waves at rectangular anisotropic edges.
Pupyrev, Pavel D; Lomonosov, Alexey M; Nikodijevic, Aleksandar; Mayer, Andreas P
2016-09-01
The existence of acoustic waves with displacements localized at the tip of an isotropic elastic wedge was rigorously proven by Kamotskii, Zavorokhin and Nazarov. This proof, which is based on a variational approach, is extended to rectangular anisotropic wedges. For two high-symmetry configurations of rectangular edges in elastic media with tetragonal symmetry, a criterion is derived that allows identifying the boundary between the regions of existence for wedge modes of even and odd symmetry in regions of parameter space, where even- and odd-symmetry modes do not exist simultaneously. Furthermore, rectangular edges with non-equivalent surfaces are analyzed, and it is shown that at rectangular edges of cubic elastic media with one (110) surface and one (001) surface, a tip-localized guided wave always exists, apart from special cases that are characterized.
Yu, J G; Zhang, Ch; Lefebvre, J E
2014-08-01
Wave propagation in multilayered piezoelectric structures has received much attention in past forty years. But the research objects of previous research works are only for semi-infinite structures and one-dimensional structures, i.e., structures with a finite dimension in only one direction, such as horizontally infinite flat plates and axially infinite hollow cylinders. This paper proposes an extension of the orthogonal polynomial series approach to solve the wave propagation problem in a two-dimensional (2-D) piezoelectric structure, namely, a multilayered piezoelectric bar with a rectangular cross-section. Through numerical comparison with the available reference results for a purely elastic multilayered rectangular bar, the validity of the extended polynomial series approach is illustrated. The dispersion curves and electric potential distributions of various multilayered piezoelectric rectangular bars are calculated to reveal their wave propagation characteristics.
Chih-Chung WEN; Li-Hung TSAI
2008-01-01
A numerical model, Evolution Equation of Mild-Slope Equation (EEMSE) developed by Hsu et al. (2003), was applied to study the Bragg reflection of water waves over a series of rectangular seabed. Three key parameters of the Bragg reflection including the peak coefficient of primary Bragg reflection, its corresponding relative wavelength, and the bandwidth, have shown to be effective in describing the characteristics of the primary Bragg reflection. The characteristics of the Bragg reflection were investigated under the various conditions comprising number, height, and spacing interval of a series of rectangular seabed. The results reveal that the peak of Bragg reflection increases with the increase of rectangular seabed height and number, the bandwidth and the shift value of the Bragg reflection depend on the increase of the rectangular seabed height as well as the decrease of rectangular seabed number, and the relative rectangular seabed spacing in the rang of 3 and 4 could produce higher Bragg reflection. Finally, a correlative and regressive analysis is performed by use of the calculated data. Based on the results of the analysis, empirical equations were established. Our study results can provide an appropriate choice of a series of rectangular seabed field for a practical design.
Oblique detonation waves stabilized in rectangular-cross-section bent tubes
2011-01-01
Oblique detonation waves, which are generated by a fundamental detonation phenomenon occurring in bent tubes, may be applied to fuel combustion in high-efficiency engines such as a pulse detonation engine (PDE) and a rotating detonation engine (RDE). The present study has experimentally demonstrated that steady-state oblique detonation waves propagated stably through rectangular-cross-section bent tubes by visualizing these waves using a high-speed camera and the shadowgraph method. The obliq...
Numerical Study of Shock Waves Propagating in an Elbow : 1st Report, A Rectangular Elbow
1993-01-01
In this paper, the shock waves propagating in a rectangular elbow were investigated numerically in order to clarify how the transmitted shock wave past the elbow is stabilized to the uniform shock and the flow field induced by the shock. The computations were carried out by solving the two-dimensional compressible Navier-Stokes equations by means of the TVD finite difference method. The calculations were performed for three incident shock strengths and three Reynolds numbers of the flow, and ...
One-dimensional nonlinear theory for rectangular helix traveling-wave tube
Fu, Chengfang, E-mail: fchffchf@126.com; Zhao, Bo; Yang, Yudong; Ju, Yongfeng [Faculty of Electronic Information Engineering, Huaiyin Institute of Technology, Huai' an 223003 (China); Wei, Yanyu [School of Physical Electronics, University of Electronic and Technology of China, Chengdu 610054 (China)
2016-08-15
A 1-D nonlinear theory of a rectangular helix traveling-wave tube (TWT) interacting with a ribbon beam is presented in this paper. The RF field is modeled by a transmission line equivalent circuit, the ribbon beam is divided into a sequence of thin rectangular electron discs with the same cross section as the beam, and the charges are assumed to be uniformly distributed over these discs. Then a method of computing the space-charge field by solving Green's Function in the Cartesian Coordinate-system is fully described. Nonlinear partial differential equations for field amplitudes and Lorentz force equations for particles are solved numerically using the fourth-order Runge-Kutta technique. The tube's gain, output power, and efficiency of the above TWT are computed. The results show that increasing the cross section of the ribbon beam will improve a rectangular helix TWT's efficiency and reduce the saturated length.
One-dimensional nonlinear theory for rectangular helix traveling-wave tube
Fu, Chengfang; Wei, Yanyu; Zhao, Bo; Yang, Yudong; Ju, Yongfeng
2016-08-01
A 1-D nonlinear theory of a rectangular helix traveling-wave tube (TWT) interacting with a ribbon beam is presented in this paper. The RF field is modeled by a transmission line equivalent circuit, the ribbon beam is divided into a sequence of thin rectangular electron discs with the same cross section as the beam, and the charges are assumed to be uniformly distributed over these discs. Then a method of computing the space-charge field by solving Green's Function in the Cartesian Coordinate-system is fully described. Nonlinear partial differential equations for field amplitudes and Lorentz force equations for particles are solved numerically using the fourth-order Runge-Kutta technique. The tube's gain, output power, and efficiency of the above TWT are computed. The results show that increasing the cross section of the ribbon beam will improve a rectangular helix TWT's efficiency and reduce the saturated length.
Study of the double rectangular waveguide grating slow-wave structure
Lu Zhi-Gang; Gong Yu-Bin; Wei Yan-Yu; Wang Wen-Xiang
2006-01-01
A slow-wave structure (SWS) with two opposite gratings inside a rectangular waveguide is presented and analysed. As an all-metal slow-wave circuit, this structure is especially suited for use in millimetre-wave travelling wave tubes (TWTs) due to its advantages of large size, high manufacturing precision and good heat dissipation. The first part of this paper concerns the wave properties of this structure in vacuum. The influence of the geometrical dimensions on dispersion characteristics and coupling impedance is investigated. The theoretical results show that this structure has a very strong dispersion and the coupling impedance for the fundamental wave is several tens of ohms, but the coupling impedance for -1 space harmonic wave is much lower than that for the fundamental wave, so the risk of backward wave oscillation is reduced. Besides these, the CST microwave studio is also used to simulate the dispersion property of the SWS. The simulation results from CST and the theoretical results agree well with each other, which supports the theory. In the second part, a small-signal analysis of a double rectangular waveguide grating TWT is presented. The typical small-signal gain per period is about 0.45 dB, and the 3-dB small-signal gain bandwidth is only 4%.
Cavity mode waves during terahertz radiation from rectangular Bi(2)Sr(2)CaCu(2)O(8 + δ) mesas.
Klemm, Richard A; Laberge, Erica R; Morley, Dustin R; Kashiwagi, Takanari; Tsujimoto, Manabu; Kadowaki, Kazuo
2011-01-19
We re-examined the angular dependence of the radiation from the intrinsic Josephson junctions in rectangular mesas of Bi(2)Sr(2)CaCu(2)O(8 + δ), in order to determine if the cavity mode part of the radiation arises from waves across the width w or along the length l of the mesas, associated with 'hot spots' (Wang et al 2010 Phys. Rev. Lett. 105 057002). We derived analytical forms for the angular dependence expected in both cases for a general cavity mode in which the width of the mesa corresponds to an integer multiple of one-half the wavelength of the radiation. Assuming the coherent radiation from the ac Josephson current source and the cavity magnetic surface current density source combine incoherently, fits to the data of Kadowaki et al (2010 J. Phys. Soc. Japan 79 023703) on a mesa with mean l/ω = 5.17 for both wave directions using two models for the incoherent combination were made, which correspond to standing and traveling waves, respectively. The results suggest that the combined output from the uniform ac Josephson current source plus a cavity wave forming along the rectangle length is equally probable as that of the combined output from the uniform ac Josephson current plus a cavity wave across the width. However, for mesas in which nl/2ω is integral, where n is the index of the rectangular TM(z)(n, 0) mode, it is shown that standing cavity mode waves along the length of the mesa do not radiate in the xz plane perpendicular to the length of the mesa, suggesting experiments on such mesas could help to resolve the question.
Cavity mode waves during terahertz radiation from rectangular Bi2Sr2CaCu2O8 + δ mesas
Klemm, Richard A.; LaBerge, Erica R.; Morley, Dustin R.; Kashiwagi, Takanari; Tsujimoto, Manabu; Kadowaki, Kazuo
2011-01-01
We re-examined the angular dependence of the radiation from the intrinsic Josephson junctions in rectangular mesas of Bi2Sr2CaCu2O8 + δ, in order to determine if the cavity mode part of the radiation arises from waves across the width w or along the length \\ell of the mesas, associated with 'hot spots' (Wang et al 2010 Phys. Rev. Lett. 105 057002). We derived analytical forms for the angular dependence expected in both cases for a general cavity mode in which the width of the mesa corresponds to an integer multiple of one-half the wavelength of the radiation. Assuming the coherent radiation from the ac Josephson current source and the cavity magnetic surface current density source combine incoherently, fits to the data of Kadowaki et al (2010 J. Phys. Soc. Japan 79 023703) on a mesa with mean \\ell /w=5.17 for both wave directions using two models for the incoherent combination were made, which correspond to standing and traveling waves, respectively. The results suggest that the combined output from the uniform ac Josephson current source plus a cavity wave forming along the rectangle length is equally probable as that of the combined output from the uniform ac Josephson current plus a cavity wave across the width. However, for mesas in which n\\ell /2w is integral, where n is the index of the rectangular TMzn, 0 mode, it is shown that standing cavity mode waves along the length of the mesa do not radiate in the xz plane perpendicular to the length of the mesa, suggesting experiments on such mesas could help to resolve the question.
Parametric study of rectangular coil for Eddy Current Testing of lamination
Wang, Peng Fei; Zeng, Zhi Wei [School of Aerospace Engineering, Xiamen University, Xiamen (China)
2016-04-15
Eddy current testing (ECT) is an important nondestructive testing technology for the inspection of flaws in conductive materials. However, this widely used technology is not suitable for inspecting lamination when a conventional pancake coil is used because the eddy current (EC) generated by the pancake coil is parallel to the lamination and will not be perturbed. A new method using a rectangular coil placed vertical to the work piece is proposed for lamination detection. The vertical sections of the rectangular coil induce ECs that are vertical to the lamination and can be perturbed by the lamination. A parametric study of a rectangular coil by finite element analysis was performed in order to examine the capability of generating vertical EC sent data 1221-1237.
STUDY ON RECTANGULAR WAVEGUIDE GRATING SLOW-WAVE STRUCTURE WITH COSINE-SHAPED GROOVES
Lu Zhigang; Wei Yanyu; Gong Yubin; Wu Zhoumiao; Wang Wenxiang
2007-01-01
This paper focuses on a new rectangular waveguide grating Slow-Wave Structure(SWS)with cosine-shaped grooves and studies the propagation characteristics of the wave in the SWS.By using the approximate field-matching conditions,the dispersion equation and the coupling impedance of this circuit are obtained.The dispersion curves and coupling impedances of the fundamental wave are calculated and the influences of the various geometrical dimensions are discussed.The results show that the bandwidth of the cosine-shaped groove SWS is much wider than that of rectangular-shaped groove one.And reducing the groove width can broaden the frequency-band and decrease the phase-velocity,while increment of the groove-depth can also decrease phase-velocity.For above cases,the coupling impedance is more than 16Ω.The present analysis will be helpful on further study and design of the RF systems used in millimeter wave Traveling Wave Tube(TWT).
A numerical simulation of surface wave excitation in a rectangular planar-type plasma source
Chen Zhao-Quan; Liu Ming-Hai; Lan Chao-Hui; Chen Wei; Tang Liang; Luo Zhi-Qing; Yan Bao-Rong; Lu Jian-Hong; Hu Xi-Wei
2009-01-01
The principle of surface wave plasma discharge in a rectangular cavity is introduced simply based on surface plasmon polariton theory.The distribution of surface-wave electric field at the interface of the plasma-dielectric slab is investigated by using the three-dimensional finite-difference time-domain method (3D-FDTD) with different slotantenna structures.And the experimental image of discharge with a novel slot antenna array and the simulation of the electric field with this slot antenna array are both displayed.Combined with the distribution of surface wave excitation and experimental results,the numerical simulation performed by using 3D-FDTD is shown to be a useful tool in the computer-aided antenna design for large area planar-type surface-wave plasma sources.
The current distribution on the feeding probe in an air filled rectangular microstrip antenna
Brown, K
1989-01-01
The current distribution on the probe and the input impedance of the rectangular air-filled microstrip antenna are calculated using the electrical-field integral equation (EFIE) formulation. A rigorous model for the coaxial line excitation is adopted which makes the formulation valid...... for electrically thick microstrip antennas. The EFIE is solved numerically using the moment method with a piecewise linear approximation of the patch current and a polynomial approximation of the probe current. It was found by numerous calculations that operating the microstrip antenna at the resonant frequency...... of the microstrip patch gives the best results with respect to the sidelobe level and cross-polar level. To validate the calculations, the impedance of the rectangular air-filled microstrip antenna was measured for the case h=6 mm and was found to agree with the calculated impedance...
Yue Wang
2016-04-01
Full Text Available Transmission spectra of terahertz waves through a two-dimensional array of asymmetric rectangular apertures on super-aligned multi-walled carbon nanotube films were obtained experimentally. In this way, the anisotropic transmission phenomena of carbon nanotube films were observed. For a terahertz wave polarization parallel to the orientation of the carbon nanotubes and along the aperture short axis, sharp resonances were observed and the resonance frequencies coincided well with the surface plasmon polariton theory. In addition, the minima of the transmission spectra were in agreement with the location predicted by the theory of Wood’s anomalies. Furthermore, it was found that the resonance profiles through the carbon nanotube films could be well described by the Fano model.
Smith, Robert; Fuss, Franz Konstantin
2013-09-06
This paper is a theoretical analysis of mirror tilt in a Michelson interferometer and its effect on the radiant flux over the active area of a rectangular photodetector or image sensor pixel. It is relevant to sensor applications using homodyne interferometry where these opto-electronic devices are employed for partial fringe counting. Formulas are derived for radiant flux across the detector for variable location within the fringe pattern and with varying wave front angle. The results indicate that the flux is a damped sine function of the wave front angle, with a decay constant of the ratio of wavelength to detector width. The modulation amplitude of the dynamic fringe pattern reduces to zero at wave front angles that are an integer multiple of this ratio and the results show that the polarity of the radiant flux changes exclusively at these multiples. Varying tilt angle causes radiant flux oscillations under an envelope curve, the frequency of which is dependent on the location of the detector with the fringe pattern. It is also shown that a fringe count of zero can be obtained for specific photodetector locations and wave front angles where the combined effect of fringe contraction and fringe tilt can have equal and opposite effects. Fringe tilt as a result of a wave front angle of 0.05° can introduce a phase measurement difference of 16° between a photodetector/pixel located 20 mm and one located 100 mm from the optical origin.
Franz Konstantin Fuss
2013-09-01
Full Text Available This paper is a theoretical analysis of mirror tilt in a Michelson interferometer and its effect on the radiant flux over the active area of a rectangular photodetector or image sensor pixel. It is relevant to sensor applications using homodyne interferometry where these opto-electronic devices are employed for partial fringe counting. Formulas are derived for radiant flux across the detector for variable location within the fringe pattern and with varying wave front angle. The results indicate that the flux is a damped sine function of the wave front angle, with a decay constant of the ratio of wavelength to detector width. The modulation amplitude of the dynamic fringe pattern reduces to zero at wave front angles that are an integer multiple of this ratio and the results show that the polarity of the radiant flux changes exclusively at these multiples. Varying tilt angle causes radiant flux oscillations under an envelope curve, the frequency of which is dependent on the location of the detector with the fringe pattern. It is also shown that a fringe count of zero can be obtained for specific photodetector locations and wave front angles where the combined effect of fringe contraction and fringe tilt can have equal and opposite effects. Fringe tilt as a result of a wave front angle of 0.05° can introduce a phase measurement difference of 16° between a photodetector/pixel located 20 mm and one located 100 mm from the optical origin.
Simulation analysis of rectangular dielectric-loaded traveling wave amplifiers for THz sources
Changbiao Wang
2007-12-01
Full Text Available Nonlinear simulation results for a 220-GHz rectangular dielectric-loaded traveling-wave amplifier are presented. Simulations are used to check a linear theory that is developed by phenomenological introduction of an effective dielectric parameter for electron beam channel, and it is found that the rf power gains from Pierce three-wave theory and particle simulations are in reasonable agreement. It is shown that the rf power gain during initial beam-wave interaction is positive; the falling on the initial rf power profile, which has been thought to be the rf power transferred to the beam for bunching buildup (negative gain effect, is probably resulting from numerical errors. Beam-wave interaction mechanism is analyzed by examining the evolution of beam bunching centers. Influences of various parameters on amplifier performance are examined, and transverse space-charge effect is analyzed. A symmetric excitation scheme for rf couplers is proposed, and rf field jumps on the common intersection line of vacuum, dielectric, and metal wall, which were found in rf simulations, are explained theoretically.
1994-01-01
In this paper, the shock wave propagating in a rectangular elbow and the transient flow induced by the shock were investigated numerically in order to clarify how the transmitted shock wave past the elbow is stabilized to uniformity by the effects of area reduction and the rounded corner. Computations were carried out by solving the two-dimensional compressible Navier-Stokes equations by using the total variation diminishing (TVD) scheme. Calculations were performed for three kinds of area re...
Sloshing waves in a heated viscoelastic fluid layer in an excited rectangular tank
Sirwah, Magdy A.
2014-10-03
In this paper, we have investigated the motion of a heated viscoelastic fluid layer in a rectangular tank that is subjected to a horizontal periodic oscillation. The mathematical model of the current problem is communicated with the linearized Navier–Stokes equation of the viscoelastic fluid and heat equation together with the boundary conditions that are solved by means of Laplace transform. Time domain solutions are consequently computed by using Durbin's numerical inverse Laplace transform scheme. Various numerical results are provided and thereby illustrated graphically to show the effects of the physical parameters on the free-surface elevation time histories and heat distribution. The numerical applications revealed that increasing the Reynolds number as well as the relaxation time parameter leads to a wider range of variation of the free-surface elevation, especially for the short time history. - Highlights: • A heated viscoelastic fluid layer in a rectangular tank. • The tank is subjected to a horizontal periodic oscillation. • The system of equations is solved by means of Laplace transform. • The inversion of the Laplace transform is carried out using a numerical approach. • Numerical results are provided to illustrate the effects of the parameters.
Plasma-ﬁlled rippled wall rectangular backward wave oscillator driven by sheet electron beam
A Hadap; J Mondal; K C Mittal; K P Maheshwari
2011-03-01
Performance of the backward wave oscillator (BWO) is greatly enhanced with the introduction of plasma. Linear theory of the dispersion relation and the growth rate have been derived and analysed numerically for plasma-ﬁlled rippled wall rectangular waveguide driven by sheet electron beam. To see the effect of plasma on the TM01 cold wave structure mode and on the generated frequency, the parameters used are: relativistic factor = 1.5 (i.e. / = 0.741), average waveguide height 0 = 1.445 cm, axial corrugation period 0 = 1.67 cm, and corrugation amplitude = 0.225 cm. The plasma density is varied from zero to 2 × 1012 cm-3. The presence of plasma tends to raise the TM01 mode cut-off frequency (14 GH at 2 × 1012 cm-3 plasma density) relative to the vacuum cut-off frequency (5 GH) which also causes a decrease in the group velocity everywhere, resulting in a ﬂattening of the dispersion relation. With the introduction of plasma, an enhancement in absolute instability was observed.
Longo, S.; Ungarish, M.; Di Federico, V.; Chiapponi, L.; Addona, F.
2016-09-01
We present an experimental investigation, supported by a theoretical model, of the motion of lock-release, constant inflow, and time varying inflow gravity currents (GCs) into a linearly stratified ambient fluid at large Reynolds number. The aim is the experimental validation of a simple model able to predict the slumping phase front speed and the asymptotic self-similar front speed for rectangular and circular cross section channels. The first investigated system is of Boussinesq type with the dense current (salt water dyed with aniline) released in a circular channel of 19 cm diameter and 400 cm long (605 cm in the inflow experiments), half-filled of linearly stratified ambient fluid (salt water with varying salt concentration). The second system has the same components but with a channel of rectangular cross section of 14 cm width, 11 cm ambient fluid depth, and 504 cm length. The density stratification of the ambient fluid was obtained with a computer controlled set of pumps and of mixing tanks. For the experiments with inflow, a multi-pipes drainage system was set at the opposite end with respect to the inflow section, computer controlled to avoid the selective withdrawal. The numerous experiments (28 for circular cross section, lock release; 26 for circular and 14 for rectangular cross section, constant inflow (fluid volume ∝tα, with α = 1); 6 for circular cross section, linearly increasing inflow (α = 2)), with several combination of the stratification parameter (0 view of the various underlying simplifications and approximations. The results on the front speed of the GCs are discussed in the presence of the internal waves, which have a celerity given by a theoretical and experimentally tested model for the rectangular but not for the circular cross section. The theoretical analysis of internal waves in circular cross sections has been extended and experimentally validated.
Pramod Kumar Vaishnav; Santimoy Kundu; Shishir Gupta; Anup Saha
2016-01-01
Propagation of Love-type wave in an initially stressed porous medium over a semi-infinite orthotropic medium with the irregular interface has been studied. The method of separation of variables has been adopted to get the dispersion relation of Love-type wave. The irregularity is assumed to be rectangular at the interface of the layer and half-space. Finally, the dispersion relation of Love wave has been obtained in classical form. The presence of porosity, irregularity, and initial stress in...
Spin wave eigenmodes in single and coupled sub-150 nm rectangular permalloy dots
Carlotti, G., E-mail: giovanni.carlotti@fisica.unipg.it; Madami, M. [Dipartimento di Fisica e Geologia, Università di Perugia, Perugia (Italy); Tacchi, S. [Istituto Officina dei Materiali del CNR (CNR-IOM), Dipartimento di Fisica e Geologia, Perugia (Italy); Gubbiotti, G.; Dey, H.; Csaba, G.; Porod, W. [Center for Nano Science and Technology, Department of Electrical Engineering, University of Notre Dame, Notre Dame, Indiana 46556 (United States)
2015-05-07
We present the results of a Brillouin light scattering investigation of thermally excited spin wave eigenmodes in square arrays of either isolated rectangular dots of permalloy or twins of dipolarly coupled elements, placed side-by-side or head-to-tail. The nanodots, fabricated by e-beam lithography and lift-off, are 20 nm thick and have the major size D in the range between 90 nm and 150 nm. The experimental spectra show the presence of two main peaks, corresponding to modes localized either at the edges or in the center of the dots. Their frequency dependence on the dot size and on the interaction with adjacent elements has been measured and successfully interpreted on the basis of dynamical micromagnetic simulations. The latter enabled us also to describe the spatial profile of the eigenmodes, putting in evidence the effects induced by the dipolar interaction between coupled dots. In particular, in twinned dots the demagnetizing field is appreciably modified in proximity of the “internal edges” if compared to the “external” ones, leading to a splitting of the edge mode. These results can be relevant for the exploitation of sub-150 nm magnetic dots in new applications, such as magnonic metamaterials, bit-patterned storage media, and nano-magnetic logic devices.
Microwave pre-heating of natural rubber using a rectangular wave guide (MODE: TE10
Doo-ngam, N.
2007-11-01
Full Text Available This paper presents an application of microwave radiation for pre-heating of natural rubbercompounding with various sulphur contents. The natural rubber-compounding was pre-heated by microwave radiation using a rectangular wave guide system (MODE: TE10 operating at frequency of 2.45 GHz in which the power can vary from 0 to 1500 W. In the present work, the influence of power input, sample thickness, and sulphur content were examined after applying microwave radiation to the rubber samples. Results are discussed regarding the thermal properties, 3-D network, dielectric properties and chemical structures. From the result, firstly, it was found that microwave radiation can be applied to pre-heating natural rubber-compounding before the vulcanization process. Secondly, microwave radiation was very useful for pre-heating natural rubber-compounding that has a thickness greater than 5mm. Thirdly, crosslinking in natural rubber-compounding may occurs after pre-heating by microwave radiation though Fourier Transform Infrared Spectroscopy(FTIR. Finally, there a little effect of sulphur content on temperature profiles after applying microwave radiation to the natural rubber-compounding. Moreover, natural rubber-compounding without carbon black showed a lower heat absorption compared with natural rubbercompounding filled carbon black. This is due to the difference in dielectric loss factor. This preliminary result will be useful information in terms of microwave radiation for pre-heating natural rubber-compounding and rubber processing in industry.
Pramod Kumar Vaishnav
2016-01-01
Full Text Available Propagation of Love-type wave in an initially stressed porous medium over a semi-infinite orthotropic medium with the irregular interface has been studied. The method of separation of variables has been adopted to get the dispersion relation of Love-type wave. The irregularity is assumed to be rectangular at the interface of the layer and half-space. Finally, the dispersion relation of Love wave has been obtained in classical form. The presence of porosity, irregularity, and initial stress in the dispersion equation approves the significant effect of these parameters in the propagation of Love-type waves in porous medium bounded below by an orthotropic half-space. The scientific effect of porosity, irregularity, and initial stress in the phase velocity of the Love-type wave propagation has been studied and shown graphically.
Curvilinear parabolic approximation for surface wave transformation with wave current interaction
Shi, Fengyan; Kirby, James T.
2005-04-01
The direct coordinate transformation method, which only transforms independent variables and retains Cartesian dependent variables, may not be an appropriate method for the purpose of simplifying the curvilinear parabolic approximation of the vector form of the wave-current equation given by Kirby [Higher-order approximations in the parabolic equation method for water waves, J. Geophys. Res. 91 (1986) 933-952]. In this paper, the covariant-contravariant tensor method is used for the curvilinear parabolic approximation. We use the covariant components of the wave number vector and contravariant components of the current velocity vector so that the derivation of the curvilinear equation closely follows the higher-order approximation in rectangular Cartesian coordinates in Kirby [Higher-order approximations in the parabolic equation method for water waves, J. Geophys. Res. 91 (1986) 933-952]. The resulting curvilinear equation can be easily implemented using the existing model structure and numerical schemes adopted in the Cartesian parabolic wave model [J.T. Kirby, R.A. Dalrymple, F. Shi, Combined Refraction/Diffraction Model REF/DIF 1, Version 2.6. Documentation and User's Manual, Research Report, Center for Applied Coastal Research, Department of Civil and Environmental Engineering, University of Delaware, Newark, 2004]. Several examples of wave simulations in curvilinear coordinate systems, including a case with wave-current interaction, are shown with comparisons to theoretical solutions or measurement data.
Particle-driven gravity currents in non-rectangular cross section channels
Zemach, T., E-mail: tamar.zemach@yahoo.com [Department of Computer Science, Tel-Hai College, Tel-Hai (Israel)
2015-10-15
We consider a high-Reynolds-number gravity current generated by suspension of heavier particles in fluid of density ρ{sub i}, propagating along a channel into an ambient fluid of the density ρ{sub a}. The bottom and top of the channel are at z = 0, H, and the cross section is given by the quite general −f{sub 1}(z) ≤ y ≤ f{sub 2}(z) for 0 ≤ z ≤ H. The flow is modeled by the one-layer shallow-water equations obtained for the time-dependent motion which is produced by release from rest of a fixed volume of mixture from a lock. We solve the problem by the finite-difference numerical code to present typical height h(x, t), velocity u(x, t), and volume fraction of particles (concentration) ϕ(x, t) profiles. The methodology is illustrated for flow in typical geometries: power-law (f(z) = z{sup α} and f(z) = (H − z){sup α}, where α is positive constant), trapezoidal, and circle. In general, the speed of propagation of the flows driven by suspensions decreases compared with those driven by a reduced gravity in homogeneous currents. However, the details depend on the geometry of the cross section. The runout length of suspensions in channels of power-law cross sections is analytically predicted using a simplified depth-averaged “box” model. The present approach is a significant generalization of the classical gravity current problem. The classical formulation for a rectangular channel is now just a particular case, f(z) = const., in the wide domain of cross sections covered by this new model.
无
1998-01-01
An Experimental investigation on the behavior and characteristics of interfacial waves in downward inclined rectangular channel was conducted.The interfacial waves were traced and measured by using conductance technique.The wave patterns were distingushed and defined.The characteristics of the interfacial waves.such as time-averaged film thickness,wave height,wave propagation speed,wavelength and wave frequency,were systematically examined in terms of gas and liquid superficial volumetric fluxes.The effect of the inclination and flow channel geometry of the test section on the interfacial wave was also investigated.
Chen Ye; Zhao Ding; Wang Yong; Shu Wen
2012-01-01
The hybrid-mode dispersion equation of the metal-grating periodic slow-wave structure for a rectangular Cerenkov maser is derived by using the Borgnis function and field-matching methods.An equivalent-circuit model for the taper of the groove depth that matches the smooth waveguide to the metal-grating structure is proposed.By using the equivalentcircuit method,as well as the Ansoft high frequency structure simulator(HFSS)code,an appropriate electromagnetic mode for beam-wave interaction is selected and the equivalent-circuit analysis on the taper is given.The calculated results show that a cumulative reflection coefficient of 0.025 for the beam-wave interaction structure at a working frequency of 78.1 GHz can be reached by designing the exponential taper with a TEz10 rectangular waveguide mode as the input and the desired TEχ10 mode as the output.It is worth pointing out that by using the equivalent-circuit method,the complex field-matching problems from the traditional field-theory method for taper design can be avoided,so the taper analysis process is markedly simplified.
Jialong Wu
2014-01-01
Full Text Available Aiming at the surface defect inspection of carbon fiber reinforced composite, the differential and the direct measurement finite element simulation models of pulsed eddy current flaw detection were built. The principle of differential pulsed eddy current detection was analyzed and the sensitivity of defect detection was compared through two kinds of measurements. The validity of simulation results was demonstrated by experiments. The simulation and experimental results show that the pulsed eddy current detection method based on rectangular differential probe can effectively improve the sensitivity of surface defect detection of carbon fiber reinforced composite material.
Annotated Bibliography on Wave-Current Interaction
1983-03-01
Rotational Fluid," Journal of Computational Physics, Bruges , Belgium, Vol. 24, No. 1, May 1977, pp. 29-42. Keywords. Currents, Vertical Shear; Numerical...realistic representa- tion of the current field and wave history . 14. GADD, G.E., "An Interaction Between Surface Water Waves and a Turbulent
Regional Wave Climates along Eastern Boundary Currents
Semedo, Alvaro; Soares, Pedro
2016-04-01
Two types of wind-generated gravity waves coexist at the ocean surface: wind sea and swell. Wind sea waves are waves under growing process. These young growing waves receive energy from the overlaying wind and are strongly coupled to the local wind field. Waves that propagate away from their generation area and no longer receive energy input from the local wind are called swell. Swell waves can travel long distances across entire ocean basins. A qualitative study of the ocean waves from a locally vs. remotely generation perspective is important, since the air sea interaction processes is strongly modulated by waves and vary accordingly to the prevalence of wind sea or swell waves in the area. A detailed climatology of wind sea and swell waves along eastern boundary currents (EBC; California Current, Canary Current, in the Northern Hemisphere, and Humboldt Current, Benguela Current, and Western Australia Current, in the Southern Hemisphere), based on the ECMWF (European Centre for Medium-Range Weather Forecasts) ERA-Interim reanalysis will be presented. The wind regime along EBC varies significantly from winter to summer. The high summer wind speeds along EBC generate higher locally generated wind sea waves, whereas lower winter wind speeds in these areas, along with stronger winter extratropical storms far away, lead to a predominance of swell waves there. In summer, the coast parallel winds also interact with coastal headlands, increasing the wind speed through a process called "expansion fan", which leads to an increase in the height of locally generated waves downwind of capes and points. Hence the spatial patterns of the wind sea or swell regional wave fields are shown to be different from the open ocean along EBC, due to coastal geometry and fetch dimensions. Swell waves will be shown to be considerably more prevalent and to carry more energy in winter along EBC, while in summer locally generated wind sea waves are either more comparable to swell waves or
Tian Shan; Liu Yuli; Yang He
2013-01-01
Inner flange and side wrinkling often occur in rotary-draw bending process of rectangular aluminum alloy wave-guide tubes,and the distribution and magnitude of wrinkling is related to geometrical parameters of the tubes.In order to study the effects of geometrical parameters on wrinkling of rectangular wave-guide tubes,a 3D-FE model for rotary-draw bending processes of thin-walled rectangular aluminum alloy wave-guide tubes was built based on the platform of ABAQUS/Explicit,and its reliability was validated by experiments.Simulation and analysis of the influence laws of geometrical parameters on the wave heights of inner flange and side wrinkling were then carried out.The results show that inner flange wrinkling is the main wrinkling way to rectangular wave-guide tubes in rotary-draw bending processes,but side wrinkling cannot be neglected because side wrinkling is 2/3 of inner flange wrinkling when b and h are smaller.Inner flange and side wrinkling increase with increasing b and h; the influence of b on side wrinkling is larger than that of h,while both b and h affect inner flange wrinkling greatly.Inner flange and side wrinkling decrease with increasing R/h; the influence of h on inner flange and side wrinkling is larger than that of R.
Xu, Fuxing; Wang, Liang; Dai, Xinhua; Fang, Xiang; Ding, Chuan-Fan
2014-04-01
Collision-induced dissociation (CID) of ions by resonance activation in a quadrupole ion trap is usually accomplished by resonance exciting the ions to higher kinetic energy, whereby the high kinetic energy ions collide with a bath gas, such as helium or argon, inside the trap and dissociate to fragments. A new ion activation method using a well-defined rectangular wave dipolar potential formed by dividing down the trapping rectangular waveform is developed and examined herein. The mass-selected parent ions are resonance excited to high kinetic energies by simply changing the frequency of the rectangular wave dipolar potential and dissociation proceeds. A relationship between the ion mass and the activation waveform frequency is also identified and described. This highly efficient (CID) procedure can be realized by simply changing the waveform frequency of the dipolar potential, which could certainly simplify tandem mass spectrometry analysis methods.
Lan Chao-Hui; Lan Chao-Zhen; Hu Xi-Wei; Chen Zhao-Quan; Liu Ming-Hai
2009-01-01
A self-consistent and three-dimensional (3D) model of argon discharge in a large-scale rectangular surface-wave plasma (SWP) source is presented in this paper, which is based on the finite-difference time-domain (FDTD) approximation to Maxwell's equations self-consistently coupled with a fluid model for plasma evolution. The discharge characteristics at an input microwave power of 1200 W and a filling gas pressure of 50 Pa in the SWP source are analyzed. The simulation shows the time evolution of deposited power density at different stages, and the 3D distributions of electron density and temperature in the chamber at steady state. In addition, the results show that there is a peak of plasma density approximately at a vertical distance of 3 cm from the quartz window.
Mathematical analysis of inertial waves in rectangular basins with one sloping boundary
Troitskaya, S D
2016-01-01
Here we consider the problem of small oscillations of a rotating inviscid incompressible fluid. From a mathematical point of view, new exact solutions to the two-dimensional Poincar\\'e-Sobolev equation in a class of domains including trapezoid are found in an explicit form and their main properties are described. These solutions correspond to the absolutely continuous spectrum of a linear operator that is associated with this system of equations. For specialists in Astrophysics and Geophysics the existence of these solutions signifies the existence of some previously unknown type of inertial waves corresponding to the continuous spectrum of inertial oscillations. A fundamental distinction between monochromatic inertial waves and waves of the new type is shown: usual characteristics (frequency, amplitude, wave vector, dispersion relation, direction of energy propagation, and so on) are not applicable to the last. Main properties of these waves are described. In particular it is proved that they are progressive...
Shear Flow Dispersion Under Wave and Current
无
2007-01-01
The longitudinal dispersion of solute in open channel flow with short period progressive waves is investigated. The waves induce second order drift velocity in the direction of propagation and enhance the mixing process in concurrent direction. The 1-D wave-period-averaged dispersion equation is derived and an expression for the wave-current induced longitudinal dispersion coefficient (WCLDC) is proposed based on Fischer's expression (1979) for dispersion in unidirectional flow. The result shows that the effect of waves on dispersion is mainly due to the cross-sectional variation of the drift velocity. Furthermore, to obtain a more practical expression of the WCLDC, the longitudinal dispersion coefficient due to Seo and Cheong (1998) is modified to incluee the effect of drift velocity. Laboratory experiments have been conducted to verify the proposed expression. The experimental results, together with dimensional analysis, show that the wave effect can be reflected by the ratio between the wave amplitude and wave period. A comparative study between the cases with and without waves demonstrates that the magnitude of the longitudinal dispersion coefficient is increased under the presence of waves.
Gravitational wave astronomy: the current status
Blair, David; Ju, Li; Zhao, ChunNong; Wen, LinQing; Chu, Qi; Fang, Qi; Cai, RongGen; Gao, JiangRui; Lin, XueChun; Liu, Dong; Wu, Ling-An; Zhu, ZongHong; Reitze, David H.; Arai, Koji; Zhang, Fan; Flaminio, Raffaele; Zhu, XingJiang; Hobbs, George; Manchester, Richard N.; Shannon, Ryan M.; Baccigalupi, Carlo; Gao, Wei; Xu, Peng; Bian, Xing; Cao, ZhouJian; Chang, ZiJing; Dong, Peng; Gong, XueFei; Huang, ShuangLin; Ju, Peng; Luo, ZiRen; Qiang, Li'E.; Tang, WenLin; Wan, XiaoYun; Wang, Yue; Xu, ShengNian; Zang, YunLong; Zhang, HaiPeng; Lau, Yun-Kau; Ni, Wei-Tou
2015-12-01
In the centenary year of Einstein's General Theory of Relativity, this paper reviews the current status of gravitational wave astronomy across a spectrum which stretches from attohertz to kilohertz frequencies. Sect. 1 of this paper reviews the historical development of gravitational wave astronomy from Einstein's first prediction to our current understanding the spectrum. It is shown that detection of signals in the audio frequency spectrum can be expected very soon, and that a north-south pair of next generation detectors would provide large scientific benefits. Sect. 2 reviews the theory of gravitational waves and the principles of detection using laser interferometry. The state of the art Advanced LIGO detectors are then described. These detectors have a high chance of detecting the first events in the near future. Sect. 3 reviews the KAGRA detector currently under development in Japan, which will be the first laser interferometer detector to use cryogenic test masses. Sect. 4 of this paper reviews gravitational wave detection in the nanohertz frequency band using the technique of pulsar timing. Sect. 5 reviews the status of gravitational wave detection in the attohertz frequency band, detectable in the polarisation of the cosmic microwave background, and discusses the prospects for detection of primordial waves from the big bang. The techniques described in sects. 1-5 have already placed significant limits on the strength of gravitational wave sources. Sects. 6 and 7 review ambitious plans for future space based gravitational wave detectors in the millihertz frequency band. Sect. 6 presents a roadmap for development of space based gravitational wave detectors by China while sect. 7 discusses a key enabling technology for space interferometry known as time delay interferometry.
Gravitational wave astronomy: the current status
Blair, David; Ju, Li; Zhao, ChunNong; Wen, LinQing; Chu, Qi; Fang, Qi; Cai, RongGen; Gao, JiangRui; Lin, XueChun; Liu, Dong; Wu, Ling-An; Zhu, ZongHong; Reitze, David H.; Arai, Koji; Zhang, Fan; Flaminio, Raffaele; Zhu, XingJiang; Hobbs, George; Manchester, Richard N.; Shannon, Ryan M.; Baccigalupi, Carlo; Gao, Wei; Xu, Peng; Bian, Xing; Cao, ZhouJian; Chang, ZiJing; Dong, Peng; Gong, XueFei; Huang, ShuangLin; Ju, Peng; Luo, ZiRen; Qiang, Li'E.; Tang, WenLin; Wan, XiaoYun; Wang, Yue; Xu, ShengNian; Zang, YunLong; Zhang, HaiPeng; Lau, Yun-Kau; Ni, Wei-Tou
2015-12-01
In the centenary year of Einstein's General Theory of Relativity, this paper reviews the current status of gravitational wave astronomy across a spectrum which stretches from attohertz to kilohertz frequencies. Sect. 1 of this paper reviews the historical development of gravitational wave astronomy from Einstein's first prediction to our current understanding the spectrum. It is shown that detection of signals in the audio frequency spectrum can be expected very soon, and that a north-south pair of next generation detectors would provide large scientific benefits. Sect. 2 reviews the theory of gravitational waves and the principles of detection using laser interferometry. The state of the art Advanced LIGO detectors are then described. These detectors have a high chance of detecting the first events in the near future. Sect. 3 reviews the KAGRA detector currently under development in Japan, which will be the first laser interferometer detector to use cryogenic test masses. Sect. 4 of this paper reviews gravitational wave detection in the nanohertz frequency band using the technique of pulsar timing. Sect. 5 reviews the status of gravitational wave detection in the attohertz frequency band, detectable in the polarisation of the cosmic microwave background, and discusses the prospects for detection of primordial waves from the big bang. The techniques described in sects. 1-5 have already placed significant limits on the strength of gravitational wave sources. Sects. 6 and 7 review ambitious plans for future space based gravitational wave detectors in the millihertz frequency band. Sect. 6 presents a roadmap for development of space based gravitational wave detectors by China while sect. 7 discusses a key enabling technology for space interferometry known as time delay interferometry.
Gravitational wave astronomy: the current status
Blair, David; Zhao, Chunnong; Wen, Linqing; Chu, Qi; Fang, Qi; Cai, RongGen; Gao, JiangRui; Lin, XueChun; Liu, Dong; Wu, Ling-An; Zhu, ZongHong; Reitze, David H; Arai, Koji; Zhang, Fan; Flaminio, Raffaele; Zhu, Xingjiang; Hobbs, George; Manchester, Richard N; Shannon, Ryan M; Baccigalupi, Carlo; Xu, Peng; Bian, Xing; Cao, Zhoujian; Chang, ZiJing; Dong, Peng; Gong, XueFei; Huang, ShuangLin; Ju, Peng; Luo, ZiRen; Qiang, Li'E; Tang, WenLin; Wan, XiaoYun; Wang, Yue; Xu, ShengNian; Zhang, YunLong; Zhang, HaiPeng; Lau, Yun-Kau; Ni, Wei-Tou
2016-01-01
In the centenary year of Einstein's General Theory of Relativity, this paper reviews the current status of gravitational wave astronomy across a spectrum which stretches from attohertz to kilohertz frequencies. Sect. 1 of this paper reviews the historical development of gravitational wave astronomy from Einstein's first prediction to our current understanding the spectrum. It is shown that detection of signals in the audio frequency spectrum can be expected very soon, and that a north-south pair of next generation detectors would provide large scientific benefits. Sect. 2 reviews the theory of gravitational waves and the principles of detection using laser interferometry. The state of the art Advanced LIGO detectors are then described. These detectors have a high chance of detecting the first events in the near future. Sect. 3 reviews the KAGRA detector currently under development in Japan, which will be the first laser interferometer detector to use cryogenic test masses. Sect. 4 of this paper reviews gravit...
Pakdaman, S. A.; Garcia, M.; Teh, E.; Lincoln, D.; Trivedi, M.; Alves, M.; Johansen, C.
2016-11-01
Shock wave formation and acceleration in a high-aspect ratio cross section shock tube were studied experimentally and numerically. The relative importance of geometric effects and diaphragm opening time on shock formation are assessed. The diaphragm opening time was controlled through the use of slit-type (fast opening time) and petal-type (slow opening time) diaphragms. A novel method of fabricating the petal-type diaphragms, which results in a consistent burst pressure and symmetric opening without fragmentation, is presented. High-speed schlieren photography was used to visualize the unsteady propagation of the lead shock wave and trailing gas dynamic structures. Surface-mounted pressure sensors were used to capture the spatial and temporal development of the pressure field. Unsteady Reynolds-Averaged Navier-Stokes simulation predictions using the shear-stress-transport turbulence model are compared to the experimental data. Simulation results are used to explain the presence of high-frequency pressure oscillations observed experimentally in the driver section as well as the cause of the initial acceleration and subsequent rapid decay of shock velocity measured along the top and bottom channel surfaces. A one-dimensional theoretical model predicting the effect of the finite opening time of the diaphragm on the rate of driver depressurization and shock acceleration is proposed. The model removes the large amount of empiricism that accompanies existing models published in the literature. Model accuracy is assessed through comparisons with experiments and simulations. Limitations of and potential improvements in the model are discussed.
Unz, H.; Roskam, J.
1979-01-01
The theory of acoustic plane wave normally incident on a clamped panel in a rectangular duct is developed. The coupling theory between the elastic vibrations of the panel (plate) and the acoustic wave propagation in infinite space and in the rectangular duct is considered. The partial differential equation which governs the vibration of the panel (plate) is modified by adding to its stiffness (spring) forces and damping forces, and the fundamental resonance frequency and the attenuation factor are discussed. The noise reduction expression based on the theory is found to agree well with the corresponding experimental data of a sample aluminum panel in the mass controlled region, the damping controlled region, and the stiffness controlled region. All the frequency positions of the upward and downward resonance spikes in the sample experimental data are identified theoretically as resulting from four cross interacting major resonance phenomena: the cavity resonance, the acoustic resonance, the plate resonance, and the wooden back panel resonance.
无
2010-01-01
A parallel algorithm and code MVFT(multi-viscous-fluid and turbulence) of large-eddy simulation(LES) is developed from our MVPPM(multi-viscous-fluid piecewise parabolic method),and performed to solve the multi compressible Navier-Stokes(N-S) equations.The effect of the unresolved subgrid-scale(SGS) motions on the large scales is represented by different SGS stress models in LES.A Richtmyer-Meshkov instability experiment of the evolution of a rectangular block of SF6,which occupies half of the height of the shock tube test section,following the interaction with a planar shock wave,is numerically and exhaustively simulated by this code.The comparison between experimental and simulated images of the evolving SF6 block shows that they are consistent.The numerical simulations reproduce the complex developing process of SF6 block,which grows overturningly.The geometric quantities that characterize the extents of SF6 block are also compared in detail between numerical simulations and experiment with good agreements between them,a quantitative demonstration of the developing law of SF6 block.There is an evident discrepancy between the three numerical simulations for the maximum position of the right edge of block at the late stage,because the right interface grows complicated and the dissipation is different for different SGS models.The SGS turbulent dissipation,molecular viscosity dissipation and SGS turbulent kinetic energy have been studied and analyzed.They have a similar distribution to the large eddy structures.The SGS turbulent dissipation is much greater than the molecular viscosity dissipation;the SGS turbulent dissipation of Vreman model is smaller than the Smagorinsky model.In general,the simulated results of Vreman SGS model are better compared with the dynamic viscosity and Smagorinsky SGS model.The vorticity and circulation deposition on the block interface have also been investigated.
Study on Directivity of Rectangular Piezoelectric Sensors Sensing Lamb Waves%矩形压电片对Lamb波传感的方向性研究
陈西府; 刘建; 周海; 葛友华
2012-01-01
矩形压电片被广泛用作超声Lamb波的传感器与驱动器.理论推导了矩形压电片对Lamb波(A0模式)的传感灵敏度系数的函数表达式,同时对推导结果进行了实验验证.研究结果表明矩形压电片对Lamb波的传感具有很强的方向性.当Lamb波传播方向沿着矩形压电片长度方向时,矩形压电片传感响应电压最大.随着Lamb波入射角度的增大,响应电压幅值越来越小,当入射方向与矩形压电片长度方向垂直时,响应幅值达到最小.%Rectangular piezoelectric sensors are widely used as Lamb waves sensors and actuators. The function of sensitivity of rectangular piezoelectric sensors sensing Lamb waves (A0 mode) is deduced, and the results are testified by experiments. Results show that rectangular piezoelectric sensors have high directivity to sense Lamb waves. The amplitude of response gets its maximum when Lamb waves are in line with sensor lengthwise direction, the amplitude will turn smaller as the propagating angle increasing and the amplitude of response gets its minimum when Lamb waves are perpendicular to sensor lengthwise direction.
Experimental study of blockage of monochromatic waves by counter currents
Suastika, I.K.
1999-01-01
Blockage of waves by a current can occur if waves are propagating on a spatially varying opposing current in which the velocity is increasing in the wave propagation direction. The ongoing waves become shorter and steeper while they are propagating against the current. Blocking occurs at the
Planetary wave variability of Sq currents
Elhawary, R.; Forbes, J. M.
2016-11-01
The E region wind dynamo is a key linkage in atmosphere-ionosphere coupling, but relatively little is known about variability of the corresponding E region currents in terms of connections with atmosphere dynamics. In this paper we analyze ground magnetic variations ΔB during 2009 at two midlatitude stations to reveal planetary wave (PW) periodicities near those of well-known atmospheric normal modes, i.e., 5, 10, and 16 days. In the neutral atmosphere these waves are westward propagating with zonal wave number s = 1. The two stations are at the same magnetic latitude and are nearly conjugate in longitude, which leads to following new insights: First, the amplitude and phase variations between the two stations do not conform to simple westward propagating waves with zonal wave number s = 1, implying that the underlying physics is more complex, in part due to modulation by the predominantly s = 1 longitude-dependent magnetic field. There is also compelling evidence that much ΔB variability near PW periods arises through the product of solar-controlled conductivity and PW-related electric field in the expression for electric current, mainly arising from solar radiation periodicities longer than the solar rotation period. For instance, interactions between solar periodicities in conductivity near 53d and 83d and PW periodicities in total electric field yield secondary peaks in the ΔB spectrum that contribute to its variability at periods less than 20d. In fact, most of the observed ΔB variability arises from these two latter sources, rather than directly from the original driving PW oscillations.
Longshore Currents of Random Waves on Different Plane Beaches
邹志利; 王淑平; 邱大洪; 王艳; 王风龙; 董国海
2003-01-01
Model tests and numerical calculation of longshore currents and wave heights produced by irregular waves on two beaches with slopes of 1:100 and 1:40 are studied. The cross-shore distributions of longshore current velocities and wave heights are given and the influences of wave heights, wave periods, and beach slopes on longshore currents are discussed. The discussion is also made on the influences of different eddy viscosity coefficients on the numerical results of longshore current velocities.
Turbulent wind waves on a water current
M. V. Zavolgensky
2008-05-01
Full Text Available An analytical model of water waves generated by the wind over the water surface is presented. A simple modeling method of wind waves is described based on waves lengths diagram, azimuthal hodograph of waves velocities and others. Properties of the generated waves are described. The wave length and wave velocity are obtained as functions on azimuth of wave propagation and growth rate. Motionless waves dynamically trapped into the general picture of three dimensional waves are described. The gravitation force does not enter the three dimensional of turbulent wind waves. That is why these waves have turbulent and not gravitational nature. The Langmuir stripes are naturally modeled and existence of the rogue waves is theoretically proved.
Current status of gravitational-wave observations
Fairhurst, Stephen; Guidi, Gianluca M.; Hello, Patrice; Whelan, John T; Woan, Graham
2009-01-01
The first generation of gravitational wave interferometric detectors has taken data at, or close to, their design sensitivity. This data has been searched for a broad range of gravitational wave signatures. An overview of gravitational wave search methods and results are presented. Searches for gravitational waves from unmodelled burst sources, compact binary coalescences, continuous wave sources and stochastic backgrounds are discussed.
Longshore currents of regular waves on different beaches
邹志利; 王淑平; 邱大洪; 王艳; 王风龙; 董国海
2003-01-01
The experiment and numerical computations of longshore currents produced by regularwaves on the two beaches with the slopes of 1:100 and 1: 40 are made. The cross-shore distributions oflongshore current velocities and wave heights are given and the influences of wave heights, wave periodsand beach slopes on the longshore currents are discussed. The discussion is also made for the influencesof different eddy viscosity coefficients on the numerical results of longshore current velocities.
Modeling of random wave transformation with strong wave-induced coastal currents
Zheng Jinhai; H. Mase; Li Tongfei
2008-01-01
The propagation and transformation of multi-directional and uni-directional random waves over a coast with complicated bathymetric and geometric features are studied experimentally and numerically. Laboratory investigation indicates that wave energy convergence and divergence cause strong coastal currents to develop and inversely modify the wave fields. A coastal spectral wave model, based on the wave action balance equation with diffraction effect (WABED), is used to simulate the transformation of random waves over the complicated bathymetry. The diffraction effect in the wave model is derived from a parabolic approximation of wave theory, and the mean energy dissipation rate per unit horizontal area due to wave breaking is parameterized by the bore-based formulation with a breaker index of 0.73. The numerically simulated wave field without considering coastal currents is different from that of experiments, whereas model results considering currents clearly reproduce the intensification of wave height in front of concave shorelines.
矩形方箱浮式防波堤消浪性能研究%Experimental study on wave attenuation of rectangular-pontoon floating breakwater
何超勇; 王登婷; 冯卫兵
2014-01-01
Adopting the method of physical model, this paper studies the laws for the development of wave attenuation of the rectangular-pontoon floating breakwater in different plate widths, underwater penetrations and initial tensions of the chain. The result shows that the increase of the plate width and underwater penetration may reduce the transmission coefficient;While the increase of the initial tension of the chain can confine the motion of rectangular pontoon, and the transmission coefficient decreases.%通过物理模型试验，探讨矩形方箱锚链锚泊浮式防波堤在规则波作用时，透射系数随浮箱宽度、吃水深度、锚链初始张力等因素的变化规律。研究结果表明：增大浮箱的宽度和吃水深度，可以减小透射系数；增加锚链的初始张力，可以限制浮箱运动，减小透射系数。
Lieske, Mike; Schlurmann, Torsten
2016-04-01
INTRODUCTION & MOTIVATION The design of structures in coastal and offshore areas and their maintenance are key components of coastal protection. Usually, assessments of processes and loads on coastal structures are derived from experiments with flow and wave parameters in separate physical models. However, Peregrin (1976) already points out that processes in natural shallow coastal waters flow and sea state processes do not occur separately, but influence each other nonlinearly. Kemp & Simons (1982) perform 2D laboratory tests and study the interactions between a turbulent flow and following waves. They highlight the significance of wave-induced changes in the current properties, especially in the mean flow profiles, and draw attention to turbulent fluctuations and bottom shear stresses. Kemp & Simons (1983) also study these processes and features with opposing waves. Studies on the wave-current interaction in three-dimensional space for a certain wave height, wave period and water depth were conducted by MacIver et al. (2006). The research focus is set on the investigation of long-crested waves on obliquely opposing and following currents in the new 3D wave-current basin. METHODOLOGY In a first step the flow analysis without waves is carried out and includes measurements of flow profiles in the sweet spot of the basin at predefined measurement positions. Five measuring points in the water column have been delineated in different water depths in order to obtain vertical flow profiles. For the characterization of the undisturbed flow properties in the basin, an uniformly distributed flow was generated in the wave basin. In the second step wave analysis without current, the unidirectional wave propagation and wave height were investigated for long-crested waves in intermediate wave conditions. In the sweet spot of the wave basin waves with three different wave directions, three wave periods and uniform wave steepness were examined. For evaluation, we applied a common
The proper longshore current in a wave basin
Visser, P.J.
1982-01-01
This report describes the investigation into a method how to obtain the proper longshore current in a wave basin. In this method the basin geometry is optimized and the proper recirculation flow through openings in the wave guides is determined by minimizing the circulation flow between the wave gui
Analysis of Mixing of Pollutants in Water Waves and Currents
YUAN Li-rong; SHEN Yong-ming; TANG Jun
2007-01-01
A vertical two-dimensional turbulence numerical model for the interaction of waves and currents is developed in the paper based on the nonlinear two-equation k-ε model with the VOF method.The one-dimensional equivalent advection velocity and equivalent mixing coefficient are defined and the solving process is introduced: The pollutant concentration field,generated by an instant source in waves and currents,is calculated with the model,and then the equivalent advection velocity and equivalent mixing coefficient are obtained by calculating the time derivative of the mean and variance of pollutant concentration probability distribution.The effects of wave period and wave height on the equivalent mixing coefficient for waves and wave-currents are also investigated.
Wave-current interaction near the Gulf Stream during the surface wave dynamics experiment
Wang, David W.; Liu, Antony K.; Peng, Chih Y.; Meindl, Eric A.
1994-01-01
This paper presents a case study on the wave-current interaction near the local curvature of a Gulf Stream meander. The wave data were obtained from in situ measurements by a pitch-roll discus buoy during the Surface Wave Dynamics Experiment (SWADE) conducted off Wallops Island, Virginia, from October 1990 to March 1991. Owing to the advection of the Gulf Stream by the semidiurnal tide, the discus buoy was alternately located outside and inside the Gulf Stream. The directional wave measurements from the buoy show the changes in wave direction, wave energy, and directional spreading when waves encountered the current in the Gulf Stream meanders. A wave refraction model, using the ray-tracing method with an estimated Gulf Stream velocity field and meandering condition, was used to simulate wave refraction patterns and to estimate wave parameters at relative locations corresponding to buoy measurements. The numerical simulation shows that a focusing zone of wave rays was formed near the boundary and behind the crest of a simulated Gulf Stream meander. The focusing of wave rays causes changes in wave direction, increases in wave energy, and decreases in wave directional spreading, which are in good agreement with the results from the buoy measurements.
A possible mechanism of current in medium under electromagnetic wave
Zhang Tao
2006-01-01
In this paper a possible mechanism of current in medium is presented. Comparison between this current and the magnetization current was made. Expression for this current was derived. This work is helpful to understanding the interaction between medium and electromagnetic wave.
Wave plus current over a ripple-covered bed
Fredsøe, Jørgen; Andersen, Ken Haste; Sumer, B. Mutlu
1999-01-01
-visualization study in the laboratory with ripples, 22 cm in length, and 3.5 cm in height. One wave-alone, three current-alone, and three combined waves and current tests were conducted. The wave-velocity-to-current-velocity ratio ranges from 1 to 2.4. The orbiral-amplitude-ro-ripple-length ratio (at the bed) is 0...... of the now around fixed ripples by use of a k - w model to calculate the roughness, and friction of a rippled bed. (C) 1999 Elsevier Science B.V. All rights reserved....
Experimental study on rectangular tidal current turbines%矩形潮流能水轮机性能的实验研究
陈展; 马勇; 张亮; 苏国卿
2013-01-01
To study the performance of rectangular tidal current turbines,a rectangular tidal current turbine and its experimental model were designed.An experiment platform was established and the experiment instrument and devices were selected.Then,some experiments were conducted,including the model of reciprocating flow experiment,the changing installation angle experiments,the impact of compactness experiment and the output power in different flow velocity experiment.The experimental results show that the rectangular tidal current turbine has good two-way flow of unidirectional rotation characteristic and the forward and reverse flows with the same energy capture capacity in the case of a constant flow velocity; when installation angle Ψ=±15°,the tidal turbine's ability of energy-capture is superior to the one when the installation angle Ψ=± 5°; the tidal turbine's ability of energycapture increases as the compactness increases within different speed ratio intervals; the peak value of output power increases with the increase of the flow velocity and the peak point moves right.%为了研究矩形潮流能水轮机的性能,设计了矩形潮流能水轮机及其实验模型装置,构建了实验平台,选配了实验仪器和设备,进行矩形潮流能水轮机模型的往复流及变安装摆角实验、密实度影响实验和不同流速下的功率输出实验.实验结果表明:矩形水轮机具有良好的双向来流单向旋转特性,在来流速度大小恒定的情况下,正向来流和反向来流具有相同的能量捕获能力;当安装摆角Ψ=±15°时,水轮机的能量捕获能力优于Ψ=±5°时的;不同速比区间内,随密实度增加,水轮机的获能能力也相应增加;流速增加,输出功率峰值增大,峰值点右移.
Current drive with combined electron cyclotron wave and high harmonic fast wave in tokamak plasmas
Li, J. C.; Gong, X. Y.; Dong, J. Q.; Wang, J.; Zhang, N.; Zheng, P. W.; Yin, C. Y.
2016-12-01
The current driven by combined electron cyclotron wave (ECW) and high harmonic fast wave is investigated using the GENRAY/CQL3D package. It is shown that no significant synergetic current is found in a range of cases with a combined ECW and fast wave (FW). This result is consistent with a previous study [Harvey et al., in Proceedings of IAEA TCM on Fast Wave Current Drive in Reactor Scale Tokamaks (Synergy and Complimentarily with LHCD and ECRH), Arles, France, IAEA, Vienna, 1991]. However, a positive synergy effect does appear with the FW in the lower hybrid range of frequencies. This positive synergy effect can be explained using a picture of the electron distribution function induced by the ECW and a very high harmonic fast wave (helicon). The dependence of the synergy effect on the radial position of the power deposition, the wave power, the wave frequency, and the parallel refractive index is also analyzed, both numerically and physically.
Numerical simulation of sediment transport in coastal waves and wave-induced currents
TANG Jun; LYU Yigang; SHEN Yongming
2016-01-01
Prediction of coastal sediment transport is of particularly importance for analyzing coast erosion accurately and solving the corresponding coast protection engineering problems. The present study provided a numerical scheme for sediment transport in coastal waves and wave-induced currents. In the scheme, the sand transport model was implemented with wave refraction-diffraction model and near-shore current model. Coastal water wave was simulated by using the parabolic mild-slope equation in which wave refraction, diffraction and breaking effects are considered. Wave-induced current was simulated by using the nonlinear shallow water equations in which wave provides radiation stresses for driving current. Then, sediment transport in waves and wave-induced currents was simulated by using the two-dimensional suspended sediment transport equations for suspended sediment and the bed-load transport equation for bed load. The numerical scheme was validated by experiment results from the Large-scale Sediment Transport Facility at the US Army Corps of Engineer Research and Development Center in Vicksburg. The numerical results showed that the present scheme is an effective tool for modeling coastal sediment transport in waves and near-shore currents.
Wave Current Interactions and Wave-blocking Predictions Using NHWAVE Model
2013-03-01
release; distribution is unlimited 12b. DISTRIBUTION CODE 13. ABSTRACT (maximum 200 words) Wave blocking in river inlets is examined using the...14. SUBJECT TERMS wave blocking, wave-current interactions, SWASH, NHWAVE 15. NUMBER OF PAGES 61 16. PRICE CODE 17. SECURITY CLASSIFICATION...Renold’s Averaged Navier-Stokes Equations VOF Volume of Fluid MAC Marker and Cell SPH Smoothed Partical Hydrodynamics SWASH Simulating Waves
Littoral drift computations on mutual wave and current influence
Bijker, E.W.
1971-01-01
11th Conference on Coastal Engineering in London 1968, the author presented a method for computing the littoral drift starting from the longshore current velocity as this is generated by the waves and with the assumption that the material is stirred up by the waves. In this paper measurements in a m
Spin current-induced by a sound wave.
Lyapilin, Igor I
2013-04-01
The interaction of conduction electrons with a longitudinal sound wave propagating in a crystal in a constant magnetic field is investigated. It is shown that the transverse spin current arises when the longitudinal sound wave propagation through the system. The average power absorbed by the spin subsystem of the conduction electrons and the spin-Hall conductivity have a resonant character.
EFFECTS OF WAVE-CURRENT INTERACTIONS ON BOTTOM STRESS AND CURRENTS
Yin Bao-shu; Yang De-zhou; Lin Xiang; Hou Yi-jun; Cheng Ming-hua; Will Perrie
2003-01-01
This paper presents a high-resolution (2′×2′) numerical model of coastal coupled wave-current interaction with explicit consideration of the effects of wave-current interaction on bottom stress. For two selected storms with measured data in the Yellow River coastal area of the Bohai Sea, it is shown that the bottom stress calculated by using a coupled wave-current model is increased, as one would expect, compared with the bottom stress computed with an uncoupled current model. Moreover, the current velocity field is also changed, but the corresponding current directions show less influence in the two simulations. The extents of changes in bottom stress and current velocity vary with storm intensities. The results further imply that the coupled wave-current model should be used as the basis for simulating the current velocity and sea level in the near shore region.
Full-wave current conveyor precision rectifier
Đukić Slobodan R.
2008-01-01
Full Text Available A circuit that provides precision rectification of small signal with low temperature sensitivity for frequencies up to 100 kHz without waveform distortion is presented. It utilizes an improved second type current conveyor based on current-steering output stage and biased silicon diodes. The use of a DC current source to bias the rectifying diodes provides higher temperature stability and lower DC offset level at the output. Proposed design of the precision rectifier ensures good current transfer linearity in the range that satisfy class A of the amplifier and good voltage transfer characteristic for low level signals. Distortion during the zero crossing of the input signal is practically eliminated. Design of the proposed rectifier is realized with standard components.
Surface waves on currents with arbitrary vertical shear
Smeltzer, Benjamin K.; Ellingsen, Simen Å.
2017-04-01
We study dispersion properties of linear surface gravity waves propagating in an arbitrary direction atop a current profile of depth-varying magnitude using a piecewise linear approximation and develop a robust numerical framework for practical calculation. The method has been much used in the past for the case of waves propagating along the same axis as the background current, and we herein extend and apply it to problems with an arbitrary angle between the wave propagation and current directions. Being valid for all wavelengths without loss of accuracy, the scheme is particularly well suited to solve problems involving a broad range of wave vectors, such as ship waves and Cauchy-Poisson initial value problems. We examine the group and phase velocities over different wavelength regimes and current profiles, highlighting characteristics due to the depth-variable vorticity. We show an example application to ship waves on an arbitrary current profile and demonstrate qualitative differences in the wake patterns between concave down and concave up profiles when compared to a constant shear profile with equal depth-averaged vorticity. We also discuss the nature of additional solutions to the dispersion relation when using the piecewise-linear model. These are vorticity waves, drifting vortical structures which are artifacts of the piecewise model. They are absent for a smooth profile and are spurious in the present context.
Yuan, Jing
2016-04-01
A full-scale experimental study of turbulent boundary layer flows under irregular waves and currents is conducted with the primary objective to investigate the equivalent-wave concept by Madsen (1994). Irregular oscillatory flows following the bottom-velocity spectrum under realistic surface irregular waves are produced over two fixed rough bottoms in an oscillatory water tunnel, and flow velocities are measured using a Particle Image Velocimetry. The root-mean-square (RMS) value and representative phase lead of wave velocities have vertical variations very similar to those of the first-harmonic velocity of periodic wave boundary layers, e.g., the RMS wave velocity follows a logarithmic distribution controlled by the physical bottom roughness in the very near-bottom region. The RMS wave bottom shear stress and the associated representative phase lead can be accurately predicted using the equivalent-wave approach. The spectra of wave bottom shear stress and boundary layer velocity are found to be proportional to the spectrum of free-stream velocity. Currents in the presence of irregular waves exhibit the classic two-log-profile structure with the lower log-profile controlled by the physical bottom roughness and the upper log-profile controlled by a much larger apparent roughness. Replacing the irregular waves by their equivalent sinusoidal waves virtually makes no difference for the coexisting currents. These observations, together with the excellent agreement between measurements and model predictions, suggest that the equivalent-wave representation adequately characterizes the basic wave-current interaction under irregular waves.
Wave-current interaction, experiments with controlled uniform shear
Simon, Bruno; Touboul, Julien; Rey, Vincent
2016-04-01
Vertically varying currents have a non negligible impact on the propagation of waves. Even though the analytical aspect of the interaction between wave and sheared current is being an active subject of research, experimental data remain rare. Here, the effects of a uniformly shear were investigated in the 10 m long by 0.3 m wide wave flume of the Université de Toulon, France. The main difficulty of the study was to produce several conditions of current with constant shear (du/dz = cst) that would persist along the channel. This was achieved by using curved wire screens upstream the channel (Dunn and Tavoularis, 2007). The geometry and properties of the screens were adjusted to deflect the streamline towards the channel bed or the free surface in order to change the velocity profile. The study focused on regular wave propagating against the current for several wave frequencies and amplitudes. Properties of the free surface and flow velocity are discussed for current with positive and negative shear in order to quantify the influence of the current on the waves. ACKNOWLEDGEMENTS The DGA (Direction Générale de l'Armement, France) is acknowledged for its financial support through the ANR grant N° ANR-13-ASTR-0007.
The Dynamics of Flat Surface Internal Geophysical Waves with Currents
Compelli, Alan; Ivanov, Rossen I.
2016-08-01
A two-dimensional water wave system is examined consisting of two discrete incompressible fluid domains separated by a free common interface. In a geophysical context this is a model of an internal wave, formed at a pycnocline or thermocline in the ocean. The system is considered as being bounded at the bottom and top by a flatbed and wave-free surface respectively. A current profile with depth-dependent currents in each domain is considered. The Hamiltonian of the system is determined and expressed in terms of canonical wave-related variables. Limiting behaviour is examined and compared to that of other known models. The linearised equations as well as long-wave approximations are presented.
The Dynamics of Flat Surface Internal Geophysical Waves with Currents
Compelli, Alan
2016-01-01
A two-dimensional water wave system is examined consisting of two discrete incompressible fluid domains separated by a free common interface. In a geophysical context this is a model of an internal wave, formed at a pycnocline or thermocline in the ocean. The system is considered as being bounded at the bottom and top by a flatbed and wave-free surface respectively. A current profile with depth-dependent currents in each domain is considered. The Hamiltonian of the system is determined and expressed in terms of canonical wave-related variables. Limiting behaviour is examined and compared to that of other known models. The linearised equations as well as long-wave approximations are presented.
Toroidal equilibrium with low frequency wave driven currents
Ehst, D.A.
1984-12-01
In the absence of an emf the parallel current, j/sub parallel/, in a steady state tokamak will consist of a neoclassical portion plus a wave-driven contribution. Using the drift kinetic equation, the quasilinear (wave-driven) current is computed for high phase speed waves in a torus, and this is combined with the neoclassical term to obtain the general expression for the flux surface average
Wave measurement in severe ocean currents
Diwan, S.G.; Suryavanshi, A.K.; Nayak, B.U.
from 2 to 5 knots are observed. As a consequence of prevailing high currents, significant drag forces have been experiencEd. by the buoys and their mooring system causing occasional submergence. Some of the mooring systems and the components adopted...
Xiao-Pin Tang; Zi-Qiang Yang; Zong-Jun Shi; Feng Lan
2016-01-01
A method of designing an E-plane power combiner composed of two quarter-arc bent rectangular waveguides is proposed for sub-THz and THz waves.The quarter-arc bent-waveguide power combiner has a simple geometry which is easy to design and fabricate.By HFSS codes,the physical mechanism and performance of the power combiner are analyzed,and the relationship between the output characteristics and the structure/operating parameters is given.Simulation results show that our power combiner is suitable for the combining of two equalpower and reversed-phase signals,the bandwidth of the combiner is wide and can be adjusted by the radius of the quarter-arc,and the isolation performance of the combiner can be improved by adding thin film resistive septa at the junction of two quarter-arc bent waveguides.Meanwhile,an approximate method based on the analytic geometrical analysis is given to design this power combiner for different frequency bands.
Simplified nonlinear theory of the dielectric loaded rectangular Cerenkov maser
Zhao Ding; Ding Yao-Gen
2012-01-01
To rapidly and accurately investigate the performance of the dielectric loaded rectangular Cerenkov maser,a simplified nonlinear theory is proposed,in which the variations of wave amplitude and wave phase are determined by two coupled first-order differential equations.Through combining with the relativistic equation of motion and adopting the forward wave assumption,the evolutions of the forward wave power,the power growth rate,the axial wave number,the accumulated phase offset,and the information of the particle movement can be obtained in a single-pass calculation.For an illustrative example,this method is used to study the influences of the beam current,the gap distance between the beam and the dielectric surface,and the momentum spread on the forward wave.The variations of the saturated power and the saturation length with the working frequency for the beams with different momentum spreads have also been studied.The result shows that the beam-wave interaction is very sensitive to the electron beam state.To further verify this simplified theory,a comparison with the result produced from a rigorous method is also provided,we find that the evolution curves of the forward wave power predicted by the two methods exhibit excellent agreement.In practical applications,the developed theory can be used for the design and analysis of the rectangular Cerenkov maser.
Wave-current interactions at the FloWave Ocean Energy Research Facility
Noble, Donald; Davey, Thomas; Steynor, Jeffrey; Bruce, Tom; Smith, Helen; Kaklis, Panagiotis
2015-04-01
Physical scale model testing is an important part of the marine renewable energy development process, allowing the study of forces and device behaviour in a controlled environment prior to deployment at sea. FloWave is a new state-of-the-art ocean energy research facility, designed to provide large scale physical modelling services to the tidal and wave sector. It has the unique ability to provide complex multi-directional waves that can be combined with currents from any direction in the 25m diameter circular tank. The facility is optimised for waves around 2s period and 0.4m height, and is capable of generating currents upwards of 1.6m/s. This offers the ability to model metocean conditions suitable for most renewable energy devices at a typical scale of between 1:10 and 1:40. The test section is 2m deep, which can be classed as intermediate-depth for most waves of interest, thus the full dispersion equation must be solved as the asymptotic simplifications do not apply. The interaction between waves and currents has been studied in the tank. This has involved producing in the tank sets of regular waves, focussed wave groups, and random sea spectra including multi-directional sea states. These waves have been both inline-with and opposing the current, as well as investigating waves at arbitrary angles to the current. Changes in wave height and wavelength have been measured, and compared with theoretical results. Using theoretical wave-current interaction models, methods have been explored to "correct" the wave height in the central test area of the tank when combined with a steady current. This allows the wave height with current to be set equal to that without a current. Thus permitting, for example, direct comparison of device motion response between tests with and without current. Alternatively, this would also permit a specific wave height and current combination to be produced in the tank, reproducing recorded conditions at a particular site of interest. The
The Wave and Current Characteristic at Eretan, Indramayu
Hadikusumah
2009-11-01
Full Text Available Erosion process occurs in many places, but each of these processes have their respective characteristics. The purpose of research for understanding the dynamics of the process that caused the coastline of the interaction between air, sea and land. Research has been conducted in Eretan, Indramayu in 2006. The results show the average wave height (H1/3 in February obtained higher (60.4 cm compared with August (23.6 cm and in May obtained a much lower (5.7 cm. Current velocity in February and in August obtained dominant raised due to by field of wave and the influence of tidal currents do not exist. Instead current velocity obtained in May was raised by the dominant tidal currents and very small currents generated by the wave field. The influence of the wave field to the velocity and direction of flow will distribute sediment transport in the area of wave breack (breack water to the coastline. Characteristic wave has a period of 3, 5, and 7 second is the trigger shoreline retreat 1.5 m/year.
Zeeman effects on Josephson current in d-wave superconductor/d-wave superconductor junctions
Liao Yan-Hua; Dong Zheng-Chao; Yin Zai-Feng; Fu Hao
2008-01-01
This paper solves a self-consistent equation for the d-wave superconducting gap and the effective exchange field in the mean-field approximation,and studies the Zeeman effects on the d-wave superconducting gap and thermodynamic potential.The Josephson currents in the d-wave superconductor(S)/insulating layer(I)/d-wave S junctions are calculated as a function of the temperature,exchange field,and insulating barrier strength under a Zeeman magnetic field on the two d-wave Ss.It is found that the Josephson critical currents in d-wave S/d-wave S junction to a great extent depend on the relative orientation of the effective exchange field of the two S electrodes,and the crystal orientation of the d-wave S.The exchange field under certain conditions can enhance the Josephson critical current in a d-wave S/I/d-wave S junction.
Ring Current-Electromagnetic Ion Cyclotron Waves Coupling
Khazanov, G. V.
2005-01-01
The effect of Electromagnetic Ion Cyclotron (EMIC) waves, generated by ion temperature anisotropy in Earth s ring current (RC), is the best known example of wave- particle interaction in the magnetosphere. Also, there is much controversy over the importance of EMIC waves on RC depletion. Under certain conditions, relativistic electrons, with energies 21 MeV, can be removed from the outer radiation belt (RB) by EMIC wave scattering during a magnetic storm. That is why the calculation of EMIC waves must be a very critical part of the space weather studies. The new RC model that we have developed and present for the first time has several new features that we have combine together in a one single model: (a) several lower frequency cold plasma wave modes are taken into account; (b) wave tracing of these wave has been incorporated in the energy EMIC wave equation; (c) no assumptions regarding wave shape spectra have been made; (d) no assumptions regarding the shape of particle distribution have been made to calculate the growth rate; (e) pitch-angle, energy, and mix diffusions are taken into account together for the first time; (f) the exact loss-cone RC analytical solution has been found and coupled with bounce-averaged numerical solution of kinetic equation; (g) the EMIC waves saturation due to their modulation instability and LHW generation are included as an additional factor that contributes to this process; and (h) the hot ions were included in the real part of dielectric permittivity tensor. We compare our theoretical results with the different EMIC waves models as well as RC experimental data.
Jialong Wu; Deqiang Zhou; Jun Wang
2014-01-01
Aiming at the surface defect inspection of carbon fiber reinforced composite, the differential and the direct measurement finite element simulation models of pulsed eddy current flaw detection were built. The principle of differential pulsed eddy current detection was analyzed and the sensitivity of defect detection was compared through two kinds of measurements. The validity of simulation results was demonstrated by experiments. The simulation and experimental results show that the pulsed ed...
Oblique waves on a vertically sheared current are rotational
Ellingsen, Simen Å
2015-01-01
In the study of surface waves in the presence of a shear current, a useful and much studied model is that in which the shear flow has constant vorticity. Recently it was shown by Constantin [Eur. J. Mech. B/Fluids 30 (2011) 12-16] that a flow of constant vorticity can only permit waves travelling exactly upstream or downstream, but not at oblique angles to the current, and several proofs to the same effect have appeared thereafter. Physical waves cannot possibly adhere to such a restriction, however. We resolve the paradox by showing that an oblique plane wave propagating atop a current of constant vorticity according to the linearized Euler equation carries with it an undulating perturbation of the vorticity field, hence is not prohibited by the Constantin theorem since vorticity is not constant. The perturbation of the vorticity field is readily interpreted in a Lagrangian perspective as the wave motion gently shifting and twisting the vortex lines as the wave passes. In the special case of upstream or down...
Eduardo Martinez
2012-01-01
Full Text Available The current-induced domain wall motion along thin ferromagnetic strips with high perpendicular magnetocrystalline anisotropy is studied by means of full micromagnetic simulations and the extended one-dimensional model, taking into account thermal effects and edge roughness. A slow creep regime, where the motion is controlled by wall pinning and thermal activation, and a flow regime with linear variation of the DW velocity, are observed. In asymmetric stacks, where the Rashba spin-orbit field stabilizes the domain wall against turbulent transformations, the steady linear regime is extended to higher currents, leading to higher velocities than in single-layer or symmetric stacks. The pinning and depinning at and from a local constriction were also studied. The results indicate that engineering pinning sites in these strips provide an efficient pathway to achieve both high stability against thermal fluctuations and low-current depinning avoiding Joule heating. Finally, the current-driven dynamics of a pinned domain wall is examined, and both the direct and the alternating contributions to the induced voltage signal induced are characterized. It was confirmed that the direct contribution to the voltage signal can be linearly enhanced with the number of pinned walls, an observation which could be useful to develop domain-wall-based nano-oscillators.
Secondary Flows and Sediment Transport due to Wave - Current Interaction
Ismail, Nabil; Wiegel, Robert
2015-04-01
Objectives: The main purpose of this study is to determine the modifications of coastal processes driven by wave-current interaction and thus to confirm hydrodynamic mechanisms associated with the interaction at river mouths and tidal inlets where anthropogenic impacts were introduced. Further, the aim of the work has been to characterize the effect of the relative strength of momentum action of waves to the opposing current on the nearshore circulation where river flow was previously effective to entrain sediments along the shoreline. Such analytical information are useful to provide guidelines for sustainable design of coastal defense structures. Methodology and Analysis: Use is made of an earlier study reported by the authors (1983) on the interaction of horizontal momentum jets and opposing shallow water waves at shorelines, and of an unpublished laboratory study (1980). The turbulent horizontal discharge was shore-normal, directed offshore, and the incident wave direction was shore-normal, travelling toward shore. Flow visualization at the smooth bottom and the water surface, velocity and water surface elevation measurements were made. Results were obtained for wave , current modifications as well as the flow pattern in the jet and the induced circulation on both sides of the jet, for a range of wave and jet characteristics. The experimental data, obtained from measurement in the 3-D laboratory basin, showed several distinct flow pattern regimes on the bottom and the water surface. The observed flow circulation regimes were found to depend on the ratio of the wave momentum action on the jet to the jet initial momentum. Based on the time and length scales of wave and current parameters and using the time average of the depth integrated conservation equations, it is found that the relative strength of the wave action on the jet could be represented by a dimensionless expression; Rsm ( ) 12ρSa20g-L0h-Cg- 2 Rsm ≈ (C0 - U) /ρ0U w (1) In the above dimensionless
Calculation of wave and current loads on launching offshore jacket
ZHANG Guang-fa; JI Zhuo-shang; LI Tie-li; LIN Yan
2006-01-01
It's very complicated to calculate and analyze the wave and current loads on naval architectures since the sea condition is uncertain and complicated and the determinants vary from different form types and dimensions. For calculating the wave and current loads on upright small-long-size pipe, the Morrison equation is practical and applied. Jacket platform is a kind of offshore space frame structure comprised of lots of poles that are circular cylinders with small diameter and in the oblique status relative to seabed. In this paper, based on Morrison equation, the specific method and procedure calculating the wave and current loads on launching jacket are given and applied on a typical launching jacket. The instance shows that the method and procedure are convenient and make the calculation and analysis in good agreement with actual launching.
Ring Current Ion Coupling with Electromagnetic Ion Cyclotron Waves
Khazanov, George V.
2002-01-01
A new ring current global model has been developed for the first time that couples the system of two kinetic equations: one equation describes the ring current (RC) ion dynamic, and another equation describes wave evolution of electromagnetic ion cyclotron waves (EMIC). The coupled model is able to simulate, for the first time self-consistently calculated RC ion kinetic and evolution of EMIC waves that propagate along geomagnetic field lines and reflect from the ionosphere. Ionospheric properties affect the reflection index through the integral Pedersen and Hall coductivities. The structure and dynamics of the ring current proton precipitating flux regions, intensities of EMIC, global RC energy balance, and some other parameters will be studied in detail for the selected geomagnetic storms. The space whether aspects of RC modelling and comparison with the data will also be discussed.
吴波; 常山; 王伟杨
2014-01-01
利用瑞利-索末菲矢量衍射公式导出偏振光波矩孔矢量夫琅禾费衍射的解析计算式，通过模拟实验研究了椭圆偏振光的一般孔和亚波长孔的矢量夫琅禾费衍射情形，可应用于偏振光波偏振度检测和偏振成像等方面，表明所得计算式的有效性和可靠性，可在微光学、近场光学、衍射成像、光束传输变换以及光信息处理等方面发挥作用。%The analytic calculation formula of the vector Fraunhofer diffraction of polarized light wave through-out rectangular aperture is derived with Rayleigh-Sommerfeld vector diffraction formula. Then Fraunhofer vector dif-fraction of elliptically polarized light throughout general aperture or sub-wavelength aperture cases are studied with simulation experiments, these can be used for the detection of the polarization degree of polarized light and polariza-tion imaging, etc. the vector diffraction and the diffraction situation of general aperture and sub-wavelength aperture is discussed. The simulations show that the calculation formula is valid and reliable, it can play a role in micro-op-tics, near-field optics, diffraction imaging, light beam transmission and transformation, and light information process-ing and so on.
Energetics of internal solitary waves in a background sheared current
K. G. Lamb
2010-10-01
Full Text Available The energetics of internal waves in the presence of a background sheared current is explored via numerical simulations for four different situations based on oceanographic conditions: the nonlinear interaction of two internal solitary waves; an internal solitary wave shoaling through a turning point; internal solitary wave reflection from a sloping boundary and a deep-water internal seiche trapped in a deep basin. In the simulations with variable water depth using the Boussinesq approximation the combination of a background sheared current, bathymetry and a rigid lid results in a change in the total energy of the system due to the work done by a pressure change that is established across the domain. A final simulation of the deep-water internal seiche in which the Boussinesq approximation is not invoked and a diffuse air-water interface is added to the system results in the energy remaining constant because the generation of surface waves prevents the establishment of a net pressure increase across the domain. The difference in the perturbation energy in the Boussinesq and non-Boussinesq simulations is accounted for by the surface waves.
A hydrodynamic model of nearshore waves and wave-induced currents
Ahmed Khaled Seif
2011-09-01
Full Text Available In This study develops a quasi-three dimensional numerical model of wave driven coastal currents with accounting the effects of the wave-current interaction and the surface rollers. In the wave model, the current effects on wave breaking and energy dissipation are taken into account as well as the wave diffraction effect. The surface roller associated with wave breaking was modeled based on a modification of the equations by Dally and Brown (1995 and Larson and Kraus (2002. Furthermore, the quasi-three dimensional model, which based on Navier-Stokes equations, was modified in association with the surface roller effect, and solved using frictional step method. The model was validated by data sets obtained during experiments on the Large Scale Sediment Transport Facility (LSTF basin and the Hazaki Oceanographical Research Station (HORS. Then, a model test against detached breakwater was carried out to investigate the performance of the model around coastal structures. Finally, the model was applied to Akasaki port to verify the hydrodynamics around coastal structures. Good agreements between computations and measurements were obtained with regard to the cross-shore variation in waves and currents in nearshore and surf zone.
Simulation of Wave-Plus-Current Scour beneath Submarine Pipelines
Eltard-Larsen, Bjarke; Fuhrman, David R.; Sumer, B. Mutlu
2016-01-01
A fully coupled hydrodynamic and morphologic numerical model was utilized for the simulation of wave-plus-current scour beneath submarine pipelines. The model was based on incompressible Reynolds-averaged Navier–Stokes equations, coupled with k-ω turbulence closure, with additional bed and suspen......A fully coupled hydrodynamic and morphologic numerical model was utilized for the simulation of wave-plus-current scour beneath submarine pipelines. The model was based on incompressible Reynolds-averaged Navier–Stokes equations, coupled with k-ω turbulence closure, with additional bed...... and suspended load descriptions forming the basis for seabed morphology. The model was successfully validated against experimental measurements involving scour development and eventual equilibrium in pure-current flows over a range of Shields parameters characteristic of both clear-water and live-bed regimes....... This validation complements previously demonstrated accuracy for the same model in simulating pipeline scour processes in pure-wave environments. The model was subsequently utilized to simulate combined wave-plus-current scour over a wide range of combined Keulegan–Carpenter numbers and relative current strengths...
Run-up on a structure due to second-order waves and current in a numerical wave tank
Buchmann, Bjarne; Skourup, Jesper; Cheung, Kwok Fai
1998-01-01
A numerical wave tank is considered in which the interaction between waves, current and a structure is simulated by a 3D boundary element model in the time domain. Through a Taylor series expansion and a perturbation procedure the model is formulated to second order in wave steepness and to first...... order in current speed. The boundary-value problem is separated into a known incident wave field and an unknown scattered wave field, the latter being absorbed at the radiation boundaries using active wave absorption. The present paper focuses on the wave run-up on a structure in waves and current....... For the simulations a bottom mounted vertical circular cylinder is chosen. The numerical results show good agreement with previous analytical and numerical solutions for second-order wave diffraction without a current and first-order wave diffraction with a collinear current. The inclusion of a current...
Numerical study on water waves and wave-induced longshore currents in Obaköy coastal water
TANG Jun; LYU Yigang; SHEN Yongming
2014-01-01
In this paper, the water waves and wave-induced longshore currents in Obaköy coastal water which is lo-cated at the Mediterranean coast of Turkey were numerically studied. The numerical model is based on the parabolic mild-slope equation for coastal water waves and the nonlinear shallow water equation for the wave-induced currents. The wave transformation under the effects of shoaling, refraction, diffraction and breaking is considered, and the wave provides radiation stresses for driving currents in the model. The numerical results for the water wave-induced longshore currents were validated by the measured data to demonstrate the efficiency of the numerical model. Then the water waves and longshore currents induced by the waves from main directions were numerically simulated and analyzed based on the numerical re-sults. The numerical results show that the movement of the longshore currents was different while the wave propagated to a coastal zone from different directions.
Generation of sheet currents by high frequency fast MHD waves
Núñez, Manuel, E-mail: mnjmhd@am.uva.es
2016-07-01
The evolution of fast magnetosonic waves of high frequency propagating into an axisymmetric equilibrium plasma is studied. By using the methods of weakly nonlinear geometrical optics, it is shown that the perturbation travels in the equatorial plane while satisfying a transport equation which enables us to predict the time and location of formation of shock waves. For plasmas of large magnetic Prandtl number, this would result into the creation of sheet currents which may give rise to magnetic reconnection and destruction of the original equilibrium. - Highlights: • Regular solutions of quasilinear hyperbolic systems may evolve into shocks. • The shock location is found for high frequency fast MHD waves. • The result is applied to static axisymmetric equilibria. • The previous process may lead to the formation of sheet currents and destruction of the equilibrium.
Stochastic generation of currents by lower-hybrid waves
Gell, Y.; Nakach, R.
1984-03-01
A scheme for current generation based on a stochastic driving mechanism is proposed. The current in this approach is generated by launching into the plasma two lower-hybrid waves having appropriate different frequencies, wave numbers, and amplitudes. The phase-space analysis of the electron motion in such a configuration reveals the existence of a relatively broad stochastic layer far away from the separatrix, allowing for diffusion in velocity space of high-velocity electrons. The diffusion coefficient of this process is evaluated and the solution of the Fokker-Planck equation for the electron velocity distribution function is used to calculate the current J and the power dissipated P/sub d/ in generating it. A favorable J-to-P/sub d/ ratio for steady-current drive is found.
Analyses of Current And Wave Forces on Velocity Caps
Christensen, Erik Damgaard; Buhrkall, Jeppe; Eskesen, Mark C. D.
2015-01-01
) this paper investigates the current and wave forces on the velocity cap and the vertical cylinder. The Morison’s force model was used in the analyses of the extracted force time series in from the CFD model. Further the distribution of the inlet velocities around the velocity cap was also analyzed in detail...
Nonlinear Wave-Currents interactions in shallow water
Lannes, David
2015-01-01
We study here the propagation of long waves in the presence of vorticity. In the irrotational framework, the Green-Naghdi equations (also called Serre or fully nonlinear Boussinesq equations) are the standard model for the propagation of such waves. These equations couple the surface elevation to the vertically averaged horizontal velocity and are therefore independent of the vertical variable. In the presence of vorticity, the dependence on the vertical variable cannot be removed from the vorticity equation but it was however shown in [?] that the motion of the waves could be described using an extended Green-Naghdi system. In this paper we propose an analysis of these equations, and show that they can be used to get some new insight into wave-current interactions. We show in particular that solitary waves may have a drastically different behavior in the presence of vorticity and show the existence of solitary waves of maximal amplitude with a peak at their crest, whose angle depends on the vorticity. We als...
A 20-Year High-Resolution Wave Resource Assessment of Japan with Wave-Current Interactions
Webb, A.; Waseda, T.; Kiyomatsu, K.
2016-02-01
Energy harvested from surface ocean waves and tidal currents has the potential to be a significant source of green energy, particularly for countries with extensive coastlines such as Japan. As part of a larger marine renewable energy project*, The University of Tokyo (in cooperation with JAMSTEC) has conducted a state-of-the-art wave resource assessment (with uncertainty estimates) to assist with wave generator site identification and construction in Japan. This assessment will be publicly available and is based on a large-scale NOAA WAVEWATCH III (version 4.18) simulation using NCEP and JAMSTEC forcings. It includes several key components to improve model skill: a 20-year simulation to reduce aleatory uncertainty, a four-nested-layer approach to resolve a 1 km shoreline, and finite-depth and current effects included in all wave power density calculations. This latter component is particularly important for regions near strong currents such as the Kuroshio. Here, we will analyze the different wave power density equations, discuss the model setup, and present results from the 20-year assessment (with a focus on the role of wave-current interactions). Time permitting, a comparison will also be made with simulations using JMA MSM 5 km winds. *New Energy and Industrial Technology Development Organization (NEDO): "Research on the Framework and Infrastructure of Marine Renewable Energy; an Energy Potential Assessment"
[Musculoskeletal shock wave therapy--current database of clinical research].
Rompe, J D; Buch, M; Gerdesmeyer, L; Haake, M; Loew, M; Maier, M; Heine, J
2002-01-01
During the past decade application of extracorporal shock waves became an established procedure for the treatment of various musculoskeletal diseases in Germany. Up to now the positive results of prospective randomised controlled trials have been published for the treatment of plantar fasciitis, lateral elbow epicondylitis (tennis elbow), and of calcifying tendinitis of the rotator cuff. Most recently, contradicting results of prospective randomised placebo-controlled trials with adequate sample size calculation have been reported. The goal of this review is to present information about the current clinical database on extracorporeal shock wave treatment (ESWT).
Time scale of scour around a pile in combined waves and current
Petersen, Thor Ugelvig; Sumer, B. Mutlu; Fredsøe, Jørgen
The time scale of the scour process around a circular vertical pile is studied in combined waves and current. A series of tests were carried out in a flume with pile diameters 40 mm and 75 mm, in both steady current, waves and combined waves and current. In the combined wave and current flow regime...
Direct Calculations of Current Drive with a Full Wave Code
Wright, John C.; Phillips, Cynthia K.
1997-11-01
We have developed a current drive package that evaluates the current driven by fast magnetosonic waves in arbitrary flux geometry. An expression for the quasilinear flux has been derived which accounts for coupling between modes in the spectrum of waves launched from the antenna. The field amplitudes are calculated in the full wave code, FISIC, and the current response function, \\chi, also known as the Spitzer function, is determined with Charles Karney's Fokker-Planck code, adj.f. Both codes have been modified to incorporate the same numerical equilibria. To model the effects of a trapped particle population, the bounce averaged equations for current and power are used, and the bounce averaged flux is calculated. The computer model is benchmarked against the homogenous equations for a high aspect ratio case in which the expected agreement is confirmed. Results from cases for TFTR, NSTX and CDX-U are contrasted with the predictions of the Ehst-Karney parameterization of current drive for circular equilibria. For theoretical background, please see the authors' archive of papers. (http://w3.pppl.gov/ ~jwright/Publications)
Surface waves on arbitrary vertically-sheared currents
Smeltzer, Benjamin K
2016-01-01
We study dispersion properties of linear surface gravity waves propagating in an arbitrary direction atop a current profile of arbitrary depth-varying magnitude using a piecewise linear approximation, and develop a robust numerical framework for practical calculation. The method has been much used in the past in 2D, and we herein extend and apply it to 3D problems. Being valid for all wavelengths without loss of accuracy, the scheme is particularly well suited to solve problems involving Fourier transformations in the horizontal plane. We examine the group and phase velocities over different wavelength regimes and current profiles, highlighting characteristics due to the depth-variable vorticity. We show an example application to ship waves on an arbitrary current profile, and demonstrate qualitative differences in the wake patterns between a concave down profile when compared to a constant shear profile with equal depth-averaged vorticity. New insight is given concerning the nature of extra spurious solution...
Fast wave current drive antenna performance on D3-D
Mayberry, M. J.; Pinsker, R. I.; Petty, C. C.; Chiu, S. C.; Jackson, G. L.; Lippmann, S. I.; Prater, R.; Porkolab, M.
1991-10-01
Fast wave current drive (FWCD) experiments at 60 MHz are being performed on the D3-D tokamak for the first time in high electron temperature, high (beta) target plasmas. A four-element phased-array antenna is used to launch a directional wave spectrum with the peak n(sub parallel) value (approximately = 7) optimized for strong single-pass electron absorption due to electron Landau damping. For this experiment, high power FW injection (2 MW) must be accomplished without voltage breakdown in the transmission lines or antenna, and without significant impurity influx. In addition, there is the technological challenge of impedance matching a four-element antenna while maintaining equal currents and the correct phasing (90 degrees) in each of the straps for a directional spectrum. We describe the performance of the D3-D FWCD antenna during initial FW electron heating and current drive experiments in terms of these requirements.
Fast Wave Current Drive Antenna Performance on DIII-D
Mayberry, M. J.; Pinsker, R. I.; Petty, C. C.; Chiu, S. C.; Jackson, G. L.; Lippmann, S. I.; Porkolab, M.; Prater, R.; Baity, F. W.; Goulding, R. H.; Hoffman, D. J.
1992-01-01
Fast wave current drive (FWCD) experiments at 60 MHz are being performed on the DIII-D tokamak for the first time in high electron temperature, high β target plasmas. A four-element phased-array antenna is used to launch a directional wave spectrum with the peak n∥ value (≂7) optimized for strong single-pass electron absorption due to electron Landau damping. For this experiment, high power FW injection (2 MW) must be accomplished without voltage breakdown in the transmission lines or antenna, and without significant impurity influx. In addition, there is the technological challenge of impedance matching a four-element antenna while maintaining equal currents and the correct phasing (90°) in each of the straps for a directional spectrum. In this paper we describe the performance of the DIII-D FWCD antenna during initial FW electron heating and current drive experiments in terms of these requirements.
付成芳; 魏彦玉; 宫玉彬; 王文祥
2009-01-01
The high-frequency characteristics,including its dispersion characteristics and its coupling impedance,of rectangular helical slow-wave circuits,were simulated with the software package HFSS10.0 provided by ANSOFT.The simulated results show that the rectangular helical slow-wave structure has higher coupling impedance,smaller size in a traveling wave tube(TWT)than that of a circular one.Moreover,at the given height and helix pitch,when the height/width ratio of the rectangular helical slow-wave structure is greater than 4 i.e.b/a＞4,the phase velocity remains unchanged.However,the coupling impedance decreases with an increase of its width.In addition,the phase velocity and the operating voltage can be favorably decreased by reducing the pitch angle.The rectangular helical slow-wave structure has wide applications in printed compact TWT because of its strengths,such as its compatibility to micro electro-mechanical system(MEMS)technology,its capability of coupling with a sheet beam to improve the efficiency.%介绍了用ANSOFT公司提供的HFSS 10.0软件模拟计算色散特性和耦合阻抗的理论方法,并对矩形螺旋线慢波结构的高频特性进行了数值模拟.结果表明:和传统的圆螺旋线结构相比,矩形结构具有更高的耦合阻抗,能有效减小器件体积;在横截面厚度和螺旋角一定的情况下,当矩形螺旋线的宽高比大于4时,相速几乎不变,但是耦合阻抗随着宽度的增加而下降;同时螺旋角的减小可以降低系统的相速,减小工作电压.由于可利用微电子机械系统(MEMS)印制技术制作,具有可与带状电子束作用,提高效率等优点,矩形螺旋线在紧凑型行波管(TWT)领域有广阔的应用前景.
Observability of surface currents in p-wave superconductors
Bakurskiy, S. V.; Klenov, N. V.; Soloviev, I. I.; Kupriyanov, M. Yu; Golubov, A. A.
2017-04-01
A general approach is formulated to describe spontaneous surface current distribution in a chiral p-wave superconductor. We use the quasiclassical Eilenberger formalism in the Ricatti parametrization to describe various types of the superconductor surface, including arbitrary roughness and metallic behavior of the surface layer. We calculate angle resolved distributions of the spontaneous surface currents and formulate the conditions of their observability. We argue that local measurements of these currents by muon spin rotation technique may provide an information on the underlying pairing symmetry in the bulk superconductor.
ICRF fast wave current drive and mode conversion current drive in EAST tokamak
Yin, L.; Yang, C.; Gong, X. Y.; Lu, X. Q.; Du, D.; Chen, Y.
2017-10-01
Fast wave in the ion-cyclotron resonance frequency (ICRF) range is a promising candidate for non-inductive current drive (CD), which is essential for long pulse and high performance operation of tokamaks. A numerical study on the ICRF fast wave current drive (FWCD) and mode-conversion current drive (MCCD) in the Experimental Advanced Superconducting Tokamak (EAST) is carried out by means of the coupled full wave and Ehst-Karney parameterization methods. The results show that FWCD efficiency is notable in two frequency regimes, i.e., f ≥ 85 MHz and f = 50-65 MHz, where ion cyclotron absorption is effectively avoided, and the maximum on-axis driven current per unit power can reach 120 kA/MW. The sensitivity of the CD efficiency to the minority ion concentration is confirmed, owing to fast wave mode conversion, and the peak MCCD efficiency is reached for 22% minority-ion concentration. The effects of the wave-launch position and the toroidal wavenumber on the efficiency of current drive are also investigated.
Internal solitary waves propagating through variable background hydrology and currents
Liu, Z.; Grimshaw, R.; Johnson, E.
2017-08-01
Large-amplitude, horizontally-propagating internal wave trains are commonly observed in the coastal ocean, fjords and straits. They are long nonlinear waves and hence can be modelled by equations of the Korteweg-de Vries type. However, typically they propagate through regions of variable background hydrology and currents, and over variable bottom topography. Hence a variable-coefficient Korteweg-de Vries equation is needed to model these waves. Although this equation is now well-known and heavily used, a term representing non-conservative effects, arising from dissipative or forcing terms in the underlying basic state, has usually been omitted. In particular this term arises when the hydrology varies in the horizontal direction. Our purpose in this paper is to examine the possible significance of this term. This is achieved through analysis and numerical simulations, using both a two-layer fluid model and a re-examination of previous studies of some specific ocean cases.
陈淑文; 胡萍; 于天宝; 廖清华; 黄永箴
2009-01-01
利用转移矩阵方法对基于杂质带的光子晶体矩形波形滤波器的实现进行了研究.除了可选择不同折射率的材料外,该滤波器还可通过调整光子晶体本身的结构参量来实现.对较平杂质带的形成机制做了具体的理论分析和解释,通过数值计算光子晶体原子耦合成光子晶体分子的过程,发现光子晶体原子的线宽与光子晶体分子线宽之间的相对大小是决定能否形成较平杂质带的重要参量.%The realization of rectangular wave filter based on the photonic crystals impurity band has been investigated by means of transfer matrix method. The formation of the quasi-flat bands can be achieved not only by choosing different materials with different refractive indexes but also by adjusting the structure parameters of photonic crystal itself. The theory analysis about the rectangular wave formation mechanism was given. The processing when two PC atoms (signal defect) were coupled to form a PC molecule (two coupled defects) was analyzed. It is found that the ratio of the PC atom linewidth to the PC molecule linewidth plays an important role in the forming of quasi-flat bands. The physical picture about the rectangular wave was also clearly illustrated in this paper.
High Harmonic Fast Wave heating and current drive for NSTX
Robinson, J. A.; Majeski, R.; Hosea, J.; Menard, J.; Ono, M.; Phillips, C. K.; Wilson, J. R.; Wright, J.; Batchelor, D. B.; Carter, M. D.; Jaeger, E. F.; Ryan, P.; Swain, D.; Mau, T. K.; Chiu, S. C.; Smithe, D.
1997-11-01
Heating and noninductive current drive in NSTX will initially use 6 MW of rf power in the high harmonic fast wave (HHFW) regime. We present numerical modelling of HHFW heating and current drive in NSTX using the PICES, CURRAY, FISIC, and METS95 codes. High electron β during the discharge flattop in NSTX is predicted to result in off-axis power deposition and current drive. However, reductions in the trapped electron fraction (due also to high β effects) are predicted to result in adequate current drive efficiency, with ~ 400 - 500 kA of noninductive current driven. Sufficient per-pass absorption (>10%) to ensure effective electron heating is also expected for the startup plasma. Present plans call for a single twelve strap antenna driven by six FMIT transmitters operating at 30 MHz. The design for the antenna and matching system will also be discussed.
Numerical study of pollutant movement in waves and wave-induced long-shore currents in surf zone
TANG Jun; SHEN Yongming; QIU Dahong
2008-01-01
Water waves,wave-induced long-shore currents and movement of pollutants in waves and currents have been numerically studied based on the hyperbolic mild-slope equation,the shallow water equation,as well as the pollutant movement equation,and the nu- merical results have also been validated by experimental data.It is shown that the long-shore current velocity and wave set-up in- crease with the increasing incident wave amplitude and slope steepness of the shore plane;the wave set-up increases with the in- creasing incident wave period;and the pollutant morement proceeds more quiekly with the increasing incident wave amplitude and slope steepness of the shore palane.In surf zones,the long-shore currents induced by the inclined incident waves have effectively affected the pollutant movement.
Mediterranea Forecasting System: a focus on wave-current coupling
Clementi, Emanuela; Delrosso, Damiano; Pistoia, Jenny; Drudi, Massimiliano; Fratianni, Claudia; Grandi, Alessandro; Pinardi, Nadia; Oddo, Paolo; Tonani, Marina
2016-04-01
The Mediterranean Forecasting System (MFS) is a numerical ocean prediction system that produces analyses, reanalyses and short term forecasts for the entire Mediterranean Sea and its Atlantic Ocean adjacent areas. MFS became operational in the late 90's and has been developed and continuously improved in the framework of a series of EU and National funded programs and is now part of the Copernicus Marine Service. The MFS is composed by the hydrodynamic model NEMO (Nucleus for European Modelling of the Ocean) 2-way coupled with the third generation wave model WW3 (WaveWatchIII) implemented in the Mediterranean Sea with 1/16 horizontal resolution and forced by ECMWF atmospheric fields. The model solutions are corrected by the data assimilation system (3D variational scheme adapted to the oceanic assimilation problem) with a daily assimilation cycle, using a background error correlation matrix varying seasonally and in different sub-regions of the Mediterranean Sea. The focus of this work is to present the latest modelling system upgrades and the related achieved improvements. In order to evaluate the performance of the coupled system a set of experiments has been built by coupling the wave and circulation models that hourly exchange the following fields: the sea surface currents and air-sea temperature difference are transferred from NEMO model to WW3 model modifying respectively the mean momentum transfer of waves and the wind speed stability parameter; while the neutral drag coefficient computed by WW3 model is passed to NEMO that computes the turbulent component. In order to validate the modelling system, numerical results have been compared with in-situ and remote sensing data. This work suggests that a coupled model might be capable of a better description of wave-current interactions, in particular feedback from the ocean to the waves might assess an improvement on the prediction capability of wave characteristics, while suggests to proceed toward a fully
Lossy-Transmission-Line Analysis of Frequency Reconfigurable Rectangular-Ring Microstrip Antenna
Bambang Setia Nugroho
2014-01-01
Full Text Available An analytical model for a frequency reconfigurable rectangular-ring microstrip antenna is proposed. The resonant frequencies and input impedance of the reconfigurable antenna are analyzed using a lossy-transmission-line (LTL model. By making use of Y-admittance matrices, a formulation for the input impedance is analytically derived. The structure of the frequency reconfigurable antenna consists of a rectangular-ring shaped microstrip antenna which is loaded with a rectangular patch in the middle of the rectangular-ring antenna and fed by a microstrip line. RF switches are applied to connect the load to the antenna in order to reconfigure the operating frequencies. By modeling the antenna into a multiport equivalent circuit, the total input impedance is analytically derived to predict the resonant frequencies. To verify the analysis, the model input impedance and reflection coefficient calculation have been compared with the full-wave simulation and measurement results. The proposed model shows good agreement with full-wave simulated and measured results in the range of 1–3 GHz.
Backfilling of a Scour Hole around a Pile in Waves and Current
Sumer, B. Mutlu; Petersen, Thor Ugelvig; Locatelli, Luca;
2013-01-01
This paper presents the results of an experimental investigation of the backfilling of scour holes around circular piles. Scour holes around a pile are generated either by a current or a wave. Subsequently, the flow climate is changed from current to wave, combined waves and current, or wave...... around the pile for the same wave (or combined waves and current) climate. The time scale of backfilling has been determined as a function of three parameters, namely, (1) the Keulegan-Carpenter number of the initial wave or current (which generates the initial scour hole); (2) that of the subsequent...
Kranenburg, Wouter; Ribberink, Jan S.; Uittenbogaard, R.E.; Hulscher, Suzanne J.M.H.
2012-01-01
The net current (streaming) in a turbulent bottom boundary layer under waves above a flat bed, identified as potentially relevant for sediment transport, is mainly determined by two competing mechanisms: an onshore streaming resulting from the horizontal non-uniformity of the velocity field under pr
Kranenburg, Wouter; Ribberink, Jan S.; Uittenbogaard, R.E.; Hulscher, Suzanne J.M.H.
2012-01-01
The net current (streaming) in a turbulent bottom boundary layer under waves above a flat bed, identified as potentially relevant for sediment transport, is mainly determined by two competing mechanisms: an onshore streaming resulting from the horizontal non-uniformity of the velocity field under
Ship waves on uniform shear current at finite depth: wave resistance and critical velocity
Li, Yan
2016-01-01
We present a comprehensive theory for linear gravity-driven ship waves in the presence of a shear current with uniform vorticity, including the effects of finite water depth. The wave resistance in the presence of shear current is calculated for the first time, containing in general a non-zero lateral component. While formally apparently a straightforward extension of existing deep water theory, the introduction of finite water depth is physically non-trivial, since the surface waves are now affected by a subtle interplay of the effects of the current and the sea bed. This becomes particularly pronounced when considering the phenomenon of critical velocity, the velocity at which transversely propagating waves become unable to keep up with the moving source. The phenomenon is well known for shallow water, and was recently shown to exist also in deep water in the presence of a shear current [Ellingsen, J.~Fluid Mech.\\ {\\bf 742} R2 (2014)]. We derive the exact criterion for criticality as a function of an intrin...
Kranenburg, W.M.; Ribberink, J.S.; Uittenbogaard, R.E.; Hulscher, S.J.M.H.
2012-01-01
The net current (streaming) in a turbulent bottom boundary layer under waves above a flat bed, identified as potentially relevant for sediment transport, is mainly determined by two competing mechanisms: an onshore streaming resulting from the horizontal non-uniformity of the velocity field under pr
Magnetization oscillations and waves driven by pure spin currents
Demidov, V. E.; Urazhdin, S.; de Loubens, G.; Klein, O.; Cros, V.; Anane, A.; Demokritov, S. O.
2017-02-01
Recent advances in the studies of pure spin currents-flows of angular momentum (spin) not accompanied by the electric currents-have opened new horizons for the emerging technologies based on the electron's spin degree of freedom, such as spintronics and magnonics. The main advantage of pure spin current, as compared to the spin-polarized electric current, is the possibility to exert spin transfer torque on the magnetization in thin magnetic films without the electrical current flow through the material. In addition to minimizing Joule heating and electromigration effects, this enables the implementation of spin torque devices based on the low-loss insulating magnetic materials, and offers an unprecedented geometric flexibility. Here we review the recent experimental achievements in investigations of magnetization oscillations excited by pure spin currents in different nanomagnetic systems based on metallic and insulating magnetic materials. We discuss the spectral properties of spin-current nano-oscillators, and relate them to the spatial characteristics of the excited dynamic magnetic modes determined by the spatially-resolved measurements. We also show that these systems support locking of the oscillations to external microwave signals, as well as their mutual synchronization, and can be used as efficient nanoscale sources of propagating spin waves.
Emergent loop current order from pair density wave superconductivity
Kashyap, Manoj; Melchert, Drew; Agterberg, Daniel
2015-03-01
In addition to charge density wave (CDW) order, there is evidence that the pseudogap phase in the cuprates breaks time reversal symmetry. Here we show that pair density wave (PDW) states give rise to a translational invariant non-superconducting order parameter that breaks time reversal and parity symmetries, but preserves their product. This secondary order parameter has a different origin, but shares the same symmetry properties as a magnetoelectric loop current order that has been proposed earlier in the context of the cuprates to explain the appearance of intra-cell magnetic order. We further show that, due to fluctuations, this secondary loop current order, which represents the breaking of discrete symmetries, can preempt PDW order, which breaks both continuous and discrete symmetries. In such a phase, the emergent loop current order coexists with spatial short range CDW and short range superconducting order. Finally, we propose a PDW phase that accounts for intra-cell magnetic order and the Kerr effect, has CDW order consistent with x-ray scattering and nuclear magnetic resonance observations, and quasi-particle properties consistent with angle resolved photoemission scattering. We acknowledge support from NSF Grant No. DMR-1335215
Wave Energy Converter (WEC) Array Effects on Wave Current and Sediment Circulation: Monterey Bay CA.
Roberts, Jesse D.; Jones, Craig; Magalen, Jason
2014-09-01
The goal s of this study were to develop tools to quantitatively characterize environments where wave energy converter ( WEC ) devices may be installed and to assess e ffects on hydrodynamics and lo cal sediment transport. A large hypothetical WEC array was investigated using wave, hydrodynamic, and sediment transport models and site - specific average and storm conditions as input. The results indicated that there were significant changes in sediment s izes adjacent to and in the lee of the WEC array due to reduced wave energy. The circulation in the lee of the array was also altered; more intense onshore currents were generated in the lee of the WECs . In general, the storm case and the average case show ed the same qualitative patterns suggesting that these trends would be maintained throughout the year. The framework developed here can be used to design more efficient arrays while minimizing impacts on nearshore environmen ts.
Analyses of Current And Wave Forces on Velocity Caps
Christensen, Erik Damgaard; Buhrkall, Jeppe; Eskesen, Mark C. D.;
2015-01-01
Velocity caps are often used in connection with for instance offshore intake sea water for the use of for cooling water for power plants or as a source for desalinization plants. The intakes can also be used for river intakes. The velocity cap is placed on top of a vertical pipe. The vertical pipe......) this paper investigates the current and wave forces on the velocity cap and the vertical cylinder. The Morison’s force model was used in the analyses of the extracted force time series in from the CFD model. Further the distribution of the inlet velocities around the velocity cap was also analyzed in detail...
Linear-circular proton accelerator with energy 0.8 GeV based on a rectangular cavity with E110 wave
Dolya, S N
2011-01-01
We consider acceleration of protons in a cavity with such dimensions as length l = 10 m, width b = 20 m, height a = 1.01 m, located between two bending (180)degree magnets with isochronous magnetic field. The cavity is loaded with rows of drift plates (tubes), being excited by a wave of E110 type at the frequency fo = 148.5 MHz, excitation power P1 = 5.65 MW. Additionally, the cavity is fed with the power P2 = 8 MW, transmitted into a beam of protons with such parameters as the final energy 0.8 GeV, pulse beam current I = 10 mA, pulse width 25 microseconds, repetition rate 10 Hz. We discuss the possibility of creating a pulsed neutron source with the intensity In = 3e14 neutrons /s on the basis of such an accelerator.
Wave-Current Conditions and Navigation Safety at an Inlet Entrance
2015-06-26
Wind wave generation and growth, diffraction, reflection, dissipation due to bottom friction , white-capping and breaking, wave-current interaction...the Coriolis force, wind stress, wave stress, bottom stress, vegetation flow drag, bottom friction , wave roller, and turbulent diffusion. Governing...H s , m), spectral peak period ( pT , sec ) and mean wave direction ( , deg), wave steepness ( /H Ls p , where L p is the spectral peak wavelength
ZHENG Jin-hai; TANG Yu
2009-01-01
A quasi three-dimensional numerical model of wave-driven coastal currents with the effects of surface rollers is developed for the study of the spatial lag between the location of the maximum wave-induced current and the wave breaking point.The governing equations are derived from Navier-Stokes equations and solved by the hybrid method combining the fractional step finite different method in the horizontal plane with a Galerkin finite element method in the vertical direction.The surface rollers effects are considered through incorporating the creation and evolution of the roller area into the free surface shear stress.An energy equation facilitates the computation process which transfers the wave breaking energy dissipation to the surface roller energy.The wave driver model is a phase-averaged wave model based on the wave action balance equation.Two sets of laboratory experiments producing breaking waves that generated longshore currents on a planar beach are used to evaluate the model's performance.The present wave-driven coastal current model with the roller effect in the surface shear stress term can produce satisfactory results by increasing the wave-induced nearshore current velocity inside the surf zone and shifting the location of the maximum longshore current velocity landward.
Tao, Xie; Shang-Zhuo, Zhao; William, Perrie; He, Fang; Wen-Jin, Yu; Yi-Jun, He
2016-06-01
To study the electromagnetic backscattering from a one-dimensional drifting fractal sea surface, a fractal sea surface wave-current model is derived, based on the mechanism of wave-current interactions. The numerical results show the effect of the ocean current on the wave. Wave amplitude decreases, wavelength and kurtosis of wave height increase, spectrum intensity decreases and shifts towards lower frequencies when the current occurs parallel to the direction of the ocean wave. By comparison, wave amplitude increases, wavelength and kurtosis of wave height decrease, spectrum intensity increases and shifts towards higher frequencies if the current is in the opposite direction to the direction of ocean wave. The wave-current interaction effect of the ocean current is much stronger than that of the nonlinear wave-wave interaction. The kurtosis of the nonlinear fractal ocean surface is larger than that of linear fractal ocean surface. The effect of the current on skewness of the probability distribution function is negligible. Therefore, the ocean wave spectrum is notably changed by the surface current and the change should be detectable in the electromagnetic backscattering signal. Project supported by the National Natural Science Foundation of China (Grant No. 41276187), the Global Change Research Program of China (Grant No. 2015CB953901), the Priority Academic Development Program of Jiangsu Higher Education Institutions (PAPD), Program for the Innovation Research and Entrepreneurship Team in Jiangsu Province, China, the Canadian Program on Energy Research and Development, and the Canadian World Class Tanker Safety Service.
Wave shoaling and diffraction in current over a mild-slope
LI Yucheng; LIU Deliang; CHEN Bing; LI Linpu
2004-01-01
The wave relative frequency in the coordinate system moving with current and the angle between the direction of wave propagation and that of current are computed based on the wave dispersion relation. The current field is computed by solving the depth averaged shallow water equations. The wave field is computed by solving the mildslope equation which has taken the current's effect into account. A numerical model is established using a finite element method for simulating the wave shoaling and diffraction in current over a mild-slope, and the numerical results are reasonable to compare with the experimental data.
Conditional Short-crested second order waves in shallow water and with superimposed current
Jensen, Jørgen Juncher
2004-01-01
For bottom-supported offshore structures like oil drilling rigs and oil production platforms, a deterministic design wave approach is often applied using a regular non-linear Stokes' wave. Thereby, the procedure accounts for non-linear effects in the wave loading but the randomness of the ocean...... wave, given the value of the wave crest at a specific point in time or space. In the present paper a derivation of the expected second order short-crested wave riding on a uniform current is given. The analysis is based on the second order Sharma and Dean shallow water wave theory and the direction...... of the main wind direction can make any direction with the current. Numerical results showing the importance of the water depth, the directional spreading and the current on the conditional mean wave profile and the associated wave kinematics are presented. A discussion of the use of the conditional wave...
Linear surface capillary-gravity short-crested waves on a current
HUANG Hu
2008-01-01
One of the forward situations in the study of water waves is the basic three-dimensional surface wave motion of short-crested waves. Capillary waves result in rich effects concerned closely with remote sensing in the open ocean. Ocean currents experience a complete process in surface wave motion. Based on the above ideas, a linear dynamical system of surface capillary-gravity short-crested waves is developed by considering the current effects, thus leading to the following analytical expressions of the kinematic and dynamic variables: the wave height, the wave steepness, the phase velocity, the wave-particle velocities, accelerations and trajectories and the wave pressure. A number of the classi-cal, typical and latest special wave cases can arise from these expressions.
Current drive by electron cyclotron waves in stellarators
Castejon, F.; Alejaldre, C.; Coarasa, J. A.
1992-07-01
In this paper we propose a method to estimate the induced current by Electron Cyclotron waves fast enough, from the numerical point of view, to be included in a ray-tracing code, and yet accounting for the complicated geometry of stellarators. Since trapped particle effects are particularly important in this Current Drive method and in stellarator magnetic configuration, they are considered by the modification they introduce in the current drive efficiency. Basically, the method consists of integrating the Fisch and Boozer relativistic efficiency, corrected with the effect of trapped particles, times the absorbed power per momentum interval. This one is calculated for a Maxwellian distribution function, assuming a nearly linear regime. The influence of impurities and of species which are not protons is studied, calculating the efficiency for plasmas with Zeff) - Finally, a numerical analysis particularized to TJ-II stellarator is presented. The absorbed power density is calculated by the ray tracing code RAYS, taking into account the actual microwave beam structure. (Author) 23 refs.
Heating and Current Drive by Electron Cyclotron Waves
Prater, R.
2003-10-01
The physics model of electron cyclotron heating (ECH) and current drive (ECCD) is becoming well validated through systematic comparisons of theory and experiment. Work has shown that ECCD can be highly localized and robustly controlled, leading to applications including stabilization of MHD instabilities like neoclassical tearing modes, control and sustainment of desired profiles of current density and plasma pressure, and studies of localized transport. These physics applications and the study of the basic physics of ECH and ECCD were enabled by the advent of the gyrotron in the 1980s and of the diamond window for megawatt gyrotrons in the 1990s. The experimental work stimulated a broad base of theory based on first principles which is encapsulated in linear ray tracing codes and fully relativistic quasilinear Fokker-Planck codes. Recent experiments use measurements of the local poloidal magnetic field through the motional Stark effect to determine the magnitude and profile of the locally driven current. The subtle balance between wave-induced diffusion and Coulomb relaxation in velocity space provides an understanding of the effects of trapping of current-carrying electrons in the magnetic well, an effect which can be used to advantage. Strong quasilinear effects and radial transport of electrons which may broaden the driven current profile have also been observed under some conditions and appear to be consistent with theory, but in large devices these are usually insignificant. Additional advantages of ECH compared with other rf heating methods are that the antenna can be far removed from the plasma and the power density can be very high. The agreement of theory and experiment, the broad base of established applications, and the technical advantages of ECH support the application of ECH in next-step tokamaks and stellarators.
Conditional short-crested waves in shallow water and with superimposed current
Jensen, Jørgen Juncher
2002-01-01
For bottom-supported offshore structures like oil drilling rigs and oil production platforms, a deterministic design wave approach is often applied using a regular non-linear Stokes´ wave. Thereby, the procedure accounts for non-linear effects in the wave loading but the randomness of the ocean...... wave, given the value of the wave crest at a specific point in time or space. In the present paper a derivation of the expected linear short-crested wave riding on a uniform current is given. The analysis is based on the conventional shallow water Airy wave theory and the direction of the main wind...... direction can make any direction with the current. A consistent derivation of the wave spectrum taking into account current and finite water depth is used. The numerical results show a significant effect of the water depth, the directional spreading and the current on the conditional mean wave profile...
Effect of nonlinear wave-current interaction on flow fields and hydrodynamic forces
王涛; 李家春
1997-01-01
A fifth-order theory for solving the problem of interaction between Stokes waves and exponential profile currents is proposed. The calculated flow fields are compared with measurements. Then the errors caused by the linear superposition method and approximate theory are discussed. It is found that the total wave-current field consists of pure wave, pure current and interaction components. The shear current not only directly changes the flow field, but also indirectly does so by changing the wave parameters due to wave-current interaction. The present theory can predict the wave kinematics on shear currents satisfactorily. The linear superposition method may give rise to more than 40% loading error in extreme conditions. When the apparent wave period is used and the Wheeler stretching method is adopted to extrapolate the current, application of the approximate theory is the best.
Kelly, A. J.; Jahn, R. G.; Choueiri, E. Y.
1990-01-01
The dominant unstable electrostatic wave modes of an electromagnetically accelerated plasma are investigated. The study is the first part of a three-phase program aimed at characterizing the current-driven turbulent dissipation degrading the efficiency of Lorentz force plasma accelerators such as the MPD thruster. The analysis uses a kinetic theory that includes magnetic and thermal effects as well as those of an electron current transverse to the magnetic field and collisions, thus combining all the features of previous models. Analytical and numerical solutions allow a detailed description of threshold criteria, finite growth behavior, destabilization mechanisms and maximized-growth characteristics of the dominant unstable modes. The lower hybrid current-driven instability is implicated as dominant and was found to preserve its character in the collisional plasma regime.
Wave refraction and littoral currents off Colva Beach, Goa
Veerayya, M.; Murty, C.S.; Varadachari, V.V.R.
Wave refraction studies have been carried out for waves of different periods approaching the coast at Colva, with directions of approach lying between180 degrees and 340 degrees, to obtain a qualitative picture of littoral flows along the beach...
Background current affects the internal wave structure of the northern South China Sea
Shuqun Cai; Xiaomin Long; Danpeng Dong; Shengan Wang
2008-01-01
The internal wave modal equations are solved with the consideration of background currents.Analytical and numerical solutions of some specific examples,including observations in the northern South China Sea(SCS),are obtained to investigate the effect of background current on internal wave vertical structure.The effects of current shear and curvature on intemal wave vertical structure are evaluated separately.It is found that the phase speed and wave structure are modified by background currents,the current shear has little effect on wave structure.whilst the current curvature Could have a strong impact on the wave structure.The extent of the effect by the current curvature on the wave structure depends on the magnitudes of current curvature,relative wave speed,and buoyancy frequency,sometimes the effect by the current curvature may even cause the wave to attenuate severely with depth.A new method to obtain the real eigenfunction with depth in the case that the waves become evanescent is also put forward.It is shown that the residual tidal current in the northern SCS is strong enough to cause the wave to attenuate severely at the upper layer.
Best connected rectangular arrangements
Krishnendra Shekhawat
2016-03-01
Full Text Available It can be found quite often in the literature that many well-known architects have employed either the golden rectangle or the Fibonacci rectangle in their works. On contrary, it is rare to find any specific reason for using them so often. Recently, Shekhawat (2015 proved that the golden rectangle and the Fibonacci rectangle are one of the best connected rectangular arrangements and this may be one of the reasons for their high presence in architectural designs. In this work we present an algorithm that generates n-4 best connected rectangular arrangements so that the proposed solutions can be further used by architects for their designs.
A wave guide model of lightning currents and their electromagnetic field
Volland, H.
1980-01-01
Lightning channels are considered as resonant wave guides in which only standing resonant wave modes can be excited. Two types of discharging currents develop. Type 1 is an aperiodic wave; type 2 is a damped oscillation. The electromagnetic radiation field of both types of currents is calculated and compared with the observation.
Assessment of existing sediment transport models for sand barrier dynamics under wave and currents
Thuy, T.T.V.; Nghiem, L.T.; Jayakumar, S.; Nielsen, P.
The paper summarizes morphology changes over rippled sand barriers under wave and wave combined current of 27 laboratorial experiments. Data of 4 wave conditions (H=10cm, T=1s; H=12cm, T=1s; H=12cm, T=1.5s; H=14cm, T=1.5s) and 6 currents (Q= 10, -10...
沙莎; 陈志华; 韩珺礼
2013-01-01
Based on the 2D Euler equations, the shock wave propagation through the tube with rectangular grooves was numerically simulated by combining the fifth-order weighted essentially nonoscil-latory (WENO) scheme and the adaptive mesh refinement (AMR) technique. The numerical results display the interaction of the incident shock wave with the grooves during its propagation inside the tube as well as its evolution within every single groove, and agree with the existent experimental results by N. Gongora-Orozco, et al. In addition, the numerical results reveal that the phenomena of expansion wave induced by shock wave diffraction and reflected shock wave due to collision appear during the interaction of the incident wave with a single groove. The expansion wave attenuates the incident shock wave, the reflected wave amplifies its intensity, but the attenuation effect dominates the process, resulting in the front intensity decrease of the incident wave in a vibrating way.%基于二维Euler方程,结合五阶加权基本无振荡(weighted essentially nonoscillatory,WENO)格式以及自适应网格加密(adaptive mesh refinement,AMR)技术对入射激波在矩形凹槽管道内传播过程进行了数值模拟.数值结果清晰地显示了入射激波传播过程中与多个矩形凹槽作用以及在凹槽内变化的整个过程,且与已有的实验结果吻合较好.另外,结果还揭示了入射激波与单个凹槽作用时,会发生绕射产生膨胀波,还会发生碰撞从而诱导反射激波.膨胀波会导致入射激波压力降低,而反射激波则导致其升高,但膨胀波的影响占主导作用,因而入射激波波阵面强度出现振荡下降.
WAVE CURRENT FORCES ON THE PILE GROUP OF BASE FOUNDATION FOR THE EAST SEA BRIDGE, CHINA
无
2007-01-01
On the basis of the two structures of the bridge foundation designed for the East Sea Bridge, the wave current forces on four types of oblique piles, the pile group and the single piles at different positions in the pile group considering the effect of the super structures were experimentally investigated. The relationship between the wave current forces and the associated wave parameters, and the comparison of the wave current forces on the pile groups and the single piles were systematically analyzed. The group effectiveness and the reduction coefficient for the wave current forces on the group were examined for engineering design.
Current and Voltage Conveyors in Current- and Voltage-Mode Precision Full-Wave Rectifiers
J. Koton
2011-04-01
Full Text Available In this paper new versatile precision full-wave rectifiers using current and/or voltage conveyors as active elements and two diodes are presented. The performance of these circuit solutions is analysed and compared to the opamp based precision rectifier. To analyze the behavior of the functional blocks, the frequency dependent RMS error and DC transient value are evaluated for different values of input voltage amplitudes. Furthermore, experimental results are given that show the feasibilities of the conveyor based rectifiers superior to the corresponding operational amplifier based topology.
Conditional Short-crested second order waves in shallow water and with superimposed current
Jensen, Jørgen Juncher
2004-01-01
wave, given the value of the wave crest at a specific point in time or space. In the present paper a derivation of the expected second order short-crested wave riding on a uniform current is given. The analysis is based on the second order Sharma and Dean shallow water wave theory and the direction......For bottom-supported offshore structures like oil drilling rigs and oil production platforms, a deterministic design wave approach is often applied using a regular non-linear Stokes' wave. Thereby, the procedure accounts for non-linear effects in the wave loading but the randomness of the ocean...... waves is poorly represented, as the shape of the wave spectrum does not enter the wave kinematics. To overcome this problem and still keep the simplicity of a deterministic approach, Tromans, Anaturk and Hagemeijer (1991) suggested the use of a deterministic wave, defined as the expected linear Airy...
Conditional short-crested waves in shallow water and with superimposed current
Jensen, Jørgen Juncher
2002-01-01
For bottom-supported offshore structures like oil drilling rigs and oil production platforms, a deterministic design wave approach is often applied using a regular non-linear Stokes´ wave. Thereby, the procedure accounts for non-linear effects in the wave loading but the randomness of the ocean...... wave, given the value of the wave crest at a specific point in time or space. In the present paper a derivation of the expected linear short-crested wave riding on a uniform current is given. The analysis is based on the conventional shallow water Airy wave theory and the direction of the main wind...
Pecher, Arthur; Kofoed, Jens Peter
This report presents the results of an experimental study that was performed on small scale model that was a replication of the full-scale Weptos WEC intended for DanWEC. The tests were performed in the circular basin at FloWave at Edinburgh University in October 2014. The laboratory facilities h...... the capabilities to have simultaneously currents and waves from any possible direction and also to produce advanced wave specifications....
Effect of Rectangle Wave Pulse Current on Solidification Structure of ZA27 Alloy
无
2006-01-01
The effect of rectangle wave pulse current on solidification structure of ZA27 alloy was studied.The results show that the wave pattern relies on the frequency range of harmonic wave and the energy of pulse current within the frequency range of pulse current.Imposed pulse current could induce the solidification system to oscillate.The frequency range and the relevant energy distribution of pulse current exert an influence on the amount of atoms involved for forming critical nucleus, the surface states of clusters in melt, the oscillating state of melt on the surface of clusters, the active energy of atom diffusion , the frequnce response of the resonance of bulk melt and the absorbability of the solidification system to the external work.Rectangle wave pulse current involves rich harmonic waves; the amplitudes of high order of harmonic waves are higher and reduce slowly, so it has a better effect on inoculation and modification.
CHANGES OF MEAN VELOCITY PROFILES IN THE WAVE-CURRENT COMBINED FLOW
无
2001-01-01
In this paper, a mathematical model is developed to simulate thechange in mean velocity for the coexistent case of waves and current. The experimental results of mean velocity profile in a wave-current flume have shown following features: Eulerian mean current profile for following current is more uniformly distributed than the corresponding pure current case, whereas, the case of an opposing current leads to the more straight profile. This model is based on Eulerian mean framework, and motions of wave and current are solved simultaneously. The comparisons of numerical results and experimental data show that the mathematical model presented in this paper is reasonable and feasible.
Modeling of Propagation and Transformation of Transient Nonlinear Waves on A Current
Wojciech Sulisz; Maciej Paprota
2013-01-01
A novel theoretical approach is applied to predict the propagation and transformation of transient nonlinear waves on a current. The problem was solved by applying an eigenfunction expansion method and the derived semi-analytical solution was employed to study the transformation of wave profile and the evolution of wave spectrum arising from the nonlinear interactions of wave components in a wave train which may lead to the formation of very large waves. The results show that the propagation of wave trains is significantly affected by a current. A relatively small current may substantially affect wave train components and the wave train shape. This is observed for both opposing and following current. The results demonstrate that the application of the nonlinear model has a substantial effect on the shape of a wave spectrum. A train of originally linear and very narrow-banded waves changes its one-peak spectrum to a multi-peak one in a fairly short distance from an initial position. The discrepancies between the wave trains predicted by applying the linear and nonlinear models increase with the increasing wavelength and become significant in shallow water even for waves with low steepness. Laboratory experiments were conducted in a wave flume to verify theoretical results. The free-surface elevations recorded by a system of wave gauges are compared with the results provided by the nonlinear model. Additional verification was achieved by applying a Fourier analysis and comparing wave amplitude spectra obtained from theoretical results with experimental data. A reasonable agreement between theoretical results and experimental data is observed for both amplitudes and phases. The model predicts fairly well multi-peak spectra, including wave spectra with significant nonlinear wave components.
A note on the horizontal momentum exchange in combined waves and current
Deigaard, Rolf; Okayasu, Akio; Frederiksen, Jørgen Hansgaard
1998-01-01
The horizontal exchange of momentum due to the organized motion in combined waves and current has been analyzed. The combination of the vertical orbital wave motion and the mean current gives a periodic variation in the horizontal velocity in addition to the wave orbital motion. This periodic var....... It is demonstrated that the new contribution changes the resulting momentum exchange considerably. (C) 1998 Elsevier Science B.V. All rights reserved....... variation, combined with the wave orbital motion, gives a significant contribution to the momentum exchange. Two examples are considered, the interaction of a pure wave motion and a current normal to the direction of wave propagation, and a wave driven longshore current with an undertow velocity profile...
Wave-Current Interaction in Coastal Inlets and River Mouths
2014-09-30
model to investigate the effects of a submarine canyon on wave statistics using measurements from the Nearshore Canyon Experiment (NCEX) conducted in 2003...at Scripps Canyon on the Southern California coast (Figure 2). In this experiment, 7 Datawell Directional Waverider buoys, 17 bottom pressure...recorders and 12 pressure-velocity sensors were deployed to capture the transformation of ocean swell over the steep canyon topography. Observed wave
Bayindir, Cihan
2016-01-01
In this paper we propose an extended Kundu-Eckhaus equation (KEE) for modeling the dynamics of skewed rogue waves emerging in the vicinity of a wave blocking point due to opposing current. The equation we propose is a KEE with an additional potential term therefore the results presented in this paper can easily be generalized to study the quantum tunneling properties of the rogue waves and ultrashort (femtosecond) pulses of the KEE. In the frame of the extended KEE, we numerically show that the chaotic perturbations of the ocean current trigger the occurrence of the rogue waves on the ocean surface. We propose and implement a split-step scheme and show that the extended KEE that we propose is unstable against random chaotic perturbations in the current profile. These perturbations transform the monochromatic wave field into a chaotic sea state with many peaks. We numerically show that the shapes of rogue waves due to perturbations in the current profile closely follow the form of rational rogue wave solutions...
Charland, Jenna; Touboul, Julien; Rey, Vincent
2013-04-01
Wave propagation against current : a study of the effects of vertical shears of the mean current on the geometrical focusing of water waves J. Charland * **, J. Touboul **, V. Rey ** jenna.charland@univ-tln.fr * Direction Générale de l'Armement, CNRS Délégation Normandie ** Université de Toulon, 83957 La Garde, France Mediterranean Institute of Oceanography (MIO) Aix Marseille Université, 13288 Marseille, France CNRS/INSU, IRD, MIO, UM 110 In the nearshore area, both wave propagation and currents are influenced by the bathymetry. For a better understanding of wave - current interactions in the presence of a 3D bathymetry, a large scale experiment was carried out in the Ocean Basin FIRST, Toulon, France. The 3D bathymetry consisted of two symmetric underwater mounds on both sides in the mean wave direction. The water depth at the top the mounds was hm=1,5m, the slopes of the mounds were of about 1:3, the water depth was h=3 m elsewhere. For opposite current conditions (U of order 0.30m/s), a huge focusing of the wave up to twice its incident amplitude was observed in the central part of the basin for T=1.4s. Since deep water conditions are verified, the wave amplification is ascribed to the current field. The mean velocity fields at a water depth hC=0.25m was measured by the use of an electromagnetic current meter. The results have been published in Rey et al [4]. The elliptic form of the "mild slope" equation including a uniform current on the water column (Chen et al [1]) was then used for the calculations. The calculated wave amplification of factor 1.2 is significantly smaller than observed experimentally (factor 2). So, the purpose of this study is to understand the physical processes which explain this gap. As demonstrated by Kharif & Pelinovsky [2], geometrical focusing of waves is able to modify significantly the local wave amplitude. We consider this process here. Since vertical velocity profiles measured at some locations have shown significant
Boundary Conditions for 2D Boussinesq-type Wave-Current Interaction Equations
Mera M.
2011-01-01
Full Text Available This research focuses on the development of a set of two-dimensional boundary conditions for specific governing equations. The governing equations are existing Boussinesqtype equations which is capable of simulating wave-current interaction. The present boundary conditions consist of for waves only case and for currents only case. To simulate wave-current interaction, the two kinds of the present boundary conditions are then combined. A numerical model based on both the existing governing equations and the present boundary conditions is applied to simulation of currents only and of wave-current interaction propagating over a basin with a submerged shoal. The results of the numerical model show that the present boundary conditions go well with the existing Boussinesq-type wave-current interaction equations.
Calculations of circular waveguide with a rectangular metal insert.
Yu. K. Sydoruk
2010-05-01
Full Text Available Calculated and analyzed the basic parameters of electromagnetic wave in a circular waveguide with a rectangular metal plate in the following cases: when the circular waveguide without metal plate for a H11 wave of subcritical, critical and supercritical. For calculations was used a finite element method and Ansoft HFSS program.
Excitation of plasma waves by nonlinear currents induced by a high-frequency electromagnetic pulse
Grishkov, V. E.; Uryupin, S. A., E-mail: uryupin@sci.lebedev.ru [Russian Academy of Sciences, Lebedev Physical Institute (Russian Federation)
2017-03-15
Excitation of plasma waves by nonlinear currents induced by a high-frequency electromagnetic pulse is analyzed within the kinetic approach. It is shown that the most efficient source of plasma waves is the nonlinear current arising due to the gradient of the energy density of the high-frequency field. Generation of plasma waves by the drag current is usually less efficient but not negligibly small at relatively high frequencies of electron–ion collisions. The influence of electron collisions on the excitation of plasma waves by pulses of different duration is described quantitatively.
Nonlinear acoustic propagation in rectangular ducts
Nayfeh, A. H.; Tsai, M.-S.
1974-01-01
The method of multiple scales is used to obtain a second-order uniformly valid expansion for nonlinear acoustic wave propagation in a rectangular duct whose walls are treated with a nonlinear acoustic material. The wave propagation in the duct is characterized by the unsteady nonlinear Euler equations. The results show that nonlinear materials attenuate sound more than linear materials except at high acoustic frequencies. The nonlinear materials produce higher and combination tones which have higher attenuation rates than the fundamentals. Moreover, the attenuation rates of the fundamentals increase with increasing amplitude.
SAR detected river mixing and coastal wave/current difusion
Diez, Margarita; Martinez-Benjamin, Juan Jose; Sekula, Emil
2014-05-01
The Synthetic Aperture Radar SAR is an active radar which emits its energy in the centimetre frequencies. Due to the large orbital velocity of the satellite (7.5km s-1) approximately, the path of the antenna itself may be converted as a virtual antenna of a much larger size. The SAR instrument may also be installed on a plane, or on a helicopter. The SAR backscattering depends on the roughness of the small scale surface of the ocean. When the surface is rougher (mostly due to capillary waves in the surface) the intensity of the receiving signal is stronger due to Bragg resonant dispersion [1,2] and a white zone is observed in the image when the surface is very rough. Rivers and tensioactive slicks and spills are well detected as dark areas in the ocean surface. An image selection of SAR images in order to identify coastal river plumes or oil spills of more than 1000 ERS-1/2 and RADARSAT Synthetic Aperture Radar SAR images for the test site in the NW Mediterranean seawere clasified and stored by [2,3,7] during the "Clean Seas" International project and the "Marine pollution and surface dynamics in the NW Mediterranean Sea" European Spatial Agency ESA project AO-ID C1P.2240. A geometry of gray scale ranges and boundaries of spatial dynamic surface features may contain new helpful information about the turbulent structure at different distances from the coast. Already we used multi-fractal analysis techniques to investigate man-made oil spills [3-5] We apply these techniques to the analysis of ocean surface multi-fractal features (eddies, mushroom-like currents, etc.) to understand the scale to scale transport and coastal effects. (Redondo et al. 1998)(Diez et al. 2008) [4,7]. The effect of bathymetry and local currents are important in describing the ocean surface behavior. In the NW Mediterranean the maximum eddy size agrees remarkably well with the limit imposed by the local Rossby deformation radius using the usual thermocline induced stratification, the
Drifter Observations Of Wave-Current Evolution Through The San Francisco Bight
Pearman, D. W.; Herbers, T. H.; Janssen, T. T.; McIntyre, S.; Jessen, P.
2012-12-01
Ocean waves approaching the Golden Gate, the narrow strait connecting the San Francisco Bay to the Pacific Ocean, are affected by refraction over the San Francisco Bar and the strong tidal currents in the area. During ebb tides, when currents through the Golden Gate can exceed 2.5 m/s, the approach to San Francisco Bay is characterized by focusing and steepening of the incident wave field on the opposing current jet. These dynamics are not uncommon in coastal inlets and are known to present hazardous navigation conditions. The strong inhomogeneity and enhanced nonlinearity of the waves can result in deviations from non-Gaussian statistics and changes in the likelihood of extreme waves. However, since observations of wave-current dynamics are so difficult to make with conventional instruments, these dynamics remain still poorly understood. In this work we present the development and testing of a compact, low-cost, Wave-Resolving Drifter (WRD), designed to resolve the wave orbital surface motions and surface drifts in high-energy areas. The WRDs consist of a 30cm buoy equipped with an off-the-shelf GPS receiver and a three-axis accelerometer. The combined GPS-accelerometer package is functionally equivalent to a conventional pitch-roll (or PUV) wave height and direction instrument, but at a fraction of the price. In our presentation we will discuss results from several WRD array deployments in the San Francisco Bight during high-energy conditions with strong ebb currents. The buoys are shown to resolve the surface waves and surface drift with remarkable accuracy and allow the analysis of the evolution of the wave group structure over the opposing current. To obtain statistical results for currents and waves, WRDs were released in clusters (ensemble) from which shoaling effects over the bar and wave-current interaction can be identified.
Effect of oceanic current on typhoon-wave modeling in the East China Sea
Cui Hong; He Hai-Lun; Liu Xiao-Hui; Li Yi
2012-01-01
We use the WAVEWATCH-Ⅲ model to quantify the effect of oceanic current on typhoon-wave modeling in the East-China-Sea (ECS).Typhoons Jelawat and Saomai in the autumn of 2000 are hindcasted.The oceanic currents in the ECS are mainly constituted of Kuroshio and typhoon-generated currents.The results show distinguishable differences in wave height and wave period under the typhoon conditions.The oceanic current causes the maximum differences,of up to a 0.5 m significant wave height and a 1 s mean wave period.Comparisons between typhoons Jelawat and Saomai show the dependence of the current effect on the typhoon characteristics.
Second-Order Solutions for Random Interfacial Waves Under Steady Uniform Currents
SONG Jin-bao
2005-01-01
In the present research, the study of Song (2004) for random interfacial waves in two-layer fluid is extended to the case of fluids moving at different steady uniform speeds. The equations describing the random displacements of the density interface and the associated velocity potentials in two-layer fluid are solved to the second order, and the wave-wave interactions of the wave components and the interactions between the waves and currents are described. As expected, the extended solutions include those obtained by Song (2004) as one special case where the steady uniform currents of the two fluids are taken as zero, and the solutions reduce to those derived by Sharma and Dean (1979) for random surface waves if the density of the upper fluid and the current of the lower fluid are both taken as zero.
Evolution of Wave Energy Deposition Profile in HT-7 Lower Hybrid Current Drive Experiment
方瑜德; 石跃江; 匡光力; 刘岳修; 沈慰慈; 丁伯江
2001-01-01
Lower hybrid waves (LHWs) with a selected n‖ spectrum have been used to control the energy deposition profiles, and then the wave driven current profiles effectively in tokamak discharges. In our lower hybrid current drive experiment in the HT-7 tokamak, it was found that the set-up of the wave energy deposition profile is a graduation process. In the beginning phase of the wave injection duration, the waves (with different n‖ spectra)deposit almost all their energy in the central region of the plasma column, even if their n‖ are very different. Up to around one hundred milliseconds, the wave energy deposition profiles can only take their corresponding shapes according to the n‖ spectra of LHWs. It also shown that this evolution process is affected obviously by the LHW driven current profile, which has been formed early.
Current-induced modulation of backward spin-waves in metallic microstructures
Sato, Nana; Lee, Seo-Won; Lee, Kyung-Jin; Sekiguchi, Koji
2017-03-01
We performed a propagating spin-wave spectroscopy for backward spin-waves in ferromagnetic metallic microstructures in the presence of electric-current. Even with the smaller current injection of 5× {{10}10} A m-2 into ferromagnetic microwires, the backward spin-waves exhibit a gigantic 200 MHz frequency shift and a 15% amplitude change, showing 60 times larger modulation compared to previous reports. Systematic experiments by measuring dependences on a film thickness of mirowire, on the wave-vector of spin-wave, and on the magnitude of bias field, we revealed that for the backward spin-waves a distribution of internal magnetic field generated by electric-current efficiently modulates the frequency and amplitude of spin-waves. The gigantic frequency and amplitude changes were reproduced by a micromagnetics simulation, predicting that the current-injection of 5× {{10}11} A m-2 allows 3 GHz frequency shift. The effective coupling between electric-current and backward spin-waves has a potential to build up a logic control method which encodes signals into the phase and amplitude of spin-waves. The metallic magnonics cooperating with electronics could suggest highly integrated magnonic circuits both in Boolean and non-Boolean principles.
Wave-current interactions: model development and preliminary results
Mayet, Clement; Lyard, Florent; Ardhuin, Fabrice
2013-04-01
The coastal area concentrates many uses that require integrated management based on diagnostic and predictive tools to understand and anticipate the future of pollution from land or sea, and learn more about natural hazards at sea or activity on the coast. The realistic modelling of coastal hydrodynamics needs to take into account various processes which interact, including tides, surges, and sea state (Wolf [2008]). These processes act at different spatial scales. Unstructured-grid models have shown the ability to satisfy these needs, given that a good mesh resolution criterion is used. We worked on adding a sea state forcing in a hydrodynamic circulation model. The sea state model is the unstructured version of WAVEWATCH III c (Tolman [2008]) (which version is developed at IFREMER, Brest (Ardhuin et al. [2010]) ), and the hydrodynamic model is the 2D barotropic module of the unstructured-grid finite element model T-UGOm (Le Bars et al. [2010]). We chose to use the radiation stress approach (Longuet-Higgins and Stewart [1964]) to represent the effect of surface waves (wind waves and swell) in the barotropic model, as previously done by Mastenbroek et al. [1993]and others. We present here some validation of the model against academic cases : a 2D plane beach (Haas and Warner [2009]) and a simple bathymetric step with analytic solution for waves (Ardhuin et al. [2008]). In a second part we present realistic application in the Ushant Sea during extreme event. References Ardhuin, F., N. Rascle, and K. Belibassakis, Explicit wave-averaged primitive equations using a generalized Lagrangian mean, Ocean Modelling, 20 (1), 35-60, doi:10.1016/j.ocemod.2007.07.001, 2008. Ardhuin, F., et al., Semiempirical Dissipation Source Functions for Ocean Waves. Part I: Definition, Calibration, and Validation, J. Phys. Oceanogr., 40 (9), 1917-1941, doi:10.1175/2010JPO4324.1, 2010. Haas, K. A., and J. C. Warner, Comparing a quasi-3D to a full 3D nearshore circulation model: SHORECIRC and
张顺鑫; 李朝东
2012-01-01
With the aim of realizing quasi-traveling wave drive in ultrasonic linear micromotor, a novel quasi-traveling wave ultrasonic linear motor using a ring type rectangular vibrator with the size of 39 mmx6 mmxl2. 7 mm was proposed. Combined with the finite element modal analysis, the motor operating principle was described, that the traveling wave was excited and propagated along the ring type rectangular vibrator depending on the superposition of two orthogonal flexural-vi-bration modes with a spatial phase shift of 90 degrees. 7 piezoelectric ceramic elements were used to excite two working modes of the vibrator. In order to amplify the amplitude, the comb-tooth structure was designed in the bottom of the vibrator. The vibrator structure was designed and eigenfrequency degeneration was realized by Finite Element Analysis ( FEA) method. The modal test showed that the design scheme was tenable. The excitation and propagation of quasi-traveling wave was proved by tip rotation direction test. The trial motor gave a maximum driving velocity of 162. 5 mm/s and a maximum load of 8. 5 N,while the excitation frequency was 66 kHz and voltage peak-peak was 160 V. The motor can satisfy the preliminary design objective.%探索了在微型直线超声波电动机中实现近似行波驱动的途径,研制了一种外形尺寸为39 mm×6 mm×12.7 mm的环状矩形振子近似行波型直线超声波电动机.结合电机振子的有限元模态分析,阐述了依靠激发空间相位差为90°的两个正交弯曲振动模态,实现行波在环状矩形振子上被激发和传播的电机运动原理.使用7块压电陶瓷片来分别激发振子的两个工作模态.在振子底部设计了梳齿状结构,以放大振幅.利用有限元法进行结构设计,使两个工作模态的频率简并.通过激光测振,证实了电机振子设计方案的有效性.通过对实际样机的驱动齿旋向测试,初步证实近似行波的形成及传播的存在.初步的样机特
Small-scale open ocean currents have large effects on wind wave heights
Ardhuin, Fabrice; Gille, Sarah T.; Menemenlis, Dimitris; Rocha, Cesar B.; Rascle, Nicolas; Chapron, Bertrand; Gula, Jonathan; Molemaker, Jeroen
2017-06-01
Tidal currents and large-scale oceanic currents are known to modify ocean wave properties, causing extreme sea states that are a hazard to navigation. Recent advances in the understanding and modeling capability of open ocean currents have revealed the ubiquitous presence of eddies, fronts, and filaments at scales 10-100 km. Based on realistic numerical models, we show that these structures can be the main source of variability in significant wave heights at scales less than 200 km, including important variations down to 10 km. Model results are consistent with wave height variations along satellite altimeter tracks, resolved at scales larger than 50 km. The spectrum of significant wave heights is found to be of the order of 70>>2/>(g2>>2>) times the current spectrum, where >> is the spatially averaged significant wave height, >> is the energy-averaged period, and g is the gravity acceleration. This variability induced by currents has been largely overlooked in spite of its relevance for extreme wave heights and remote sensing.Plain Language SummaryWe show that the variations in currents at scales 10 to 100 km are the main source of variations in wave heights at the same scales. Our work uses a combination of realistic numerical models for currents and waves and data from the Jason-3 and SARAL/AltiKa satellites. This finding will be of interest for the investigation of extreme wave heights, remote sensing, and air-sea interactions. As an immediate application, the present results will help constrain the error budget of the up-coming satellite missions, in particular the Surface Water and Ocean Topography (SWOT) mission, and decide how the data will have to be processed to arrive at accurate sea level and wave measurements. It will also help in the analysis of wave measurements by the CFOSAT satellite.
The influence of an electromagnetic field on the wave-current interaction
Rousseaux, Germain
2010-01-01
We study the propagation of surface waves on a current in the presence of an electromagnetic field. A horizontal (vertical) field strengthens (weakens) the counter-current which blocks the waves. We compute the phase space diagrams (blocking velocities versus period of the waves) with and without surface tension. Three new dimensionless numbers are introduced to compare the relative strengths of gravity, surface tension and field effects. This work shows the importance of an electromagnetic field in order to design wave-breakers or in microfluidics applications.
Yeo, Taehan; Hwang, Hayoung; Cho, Yonghwan; Shin, Dongjoon; Choi, Wonjoon
2015-07-01
Combustion wave propagation in micro/nanostructured materials generates a chemical-thermal-electrical energy conversion, which enables the creation of an unusual source of electrical energy, called a thermopower wave. In this paper, we report that high electrical resistance regimes would significantly amplify the output voltage of thermopower waves, because the current crowding creates a narrow path for charge carrier transport. We show that the structurally defective regions in the hybrid composites of chemical fuels and carbon nanotube (CNT) arrays determine both the resistance levels of the hybrid composites and the corresponding output voltage of thermopower waves. A sudden acceleration of the crowded charges would be induced by the moving reaction front of the combustion wave when the supplied driving force overcomes the potential barrier to cause charge carrier transport over the defective region. This property is investigated experimentally for the locally manipulated defective areas using diverse methods. In this study, thermopower waves in CNT-based hybrid composites are able to control the peak voltages in the range of 10-1000 mV by manipulating the resistance from 10 Ω to 100 kΩ. This controllable voltage generation from thermopower waves may enable applications using the combustion waves in micro/nanostructured materials and better understanding of the underlying physics.
Simulation of Wave-Plus-Current Induced Scour Beneath Submarine Pipelines
Eltard-Larsen, Bjarke; Fuhrman, David R.; Sumer, B. Mutlu
of combined wave-plus-current scour processes beneath pipelines. The results of 77 simulated wave-plus-current scour cases will be presented and analysed. The cases considered will consist of waves characterized by 10 different Keulegan-Carpenter numbers, KC=UmTw/D and up to eight different values of m......-plus-current environments. The present study, which is published in Larsen et al. (2016) focuses on the numerical simulation of wave-plus-current induced scour beneath submarine pipelines, based on a model solving Reynolds-averaged Navier-Stokes (RANS) equations, fully coupled with turbulence closure, bed and suspended...... load sediment transport descriptions, and a seabed morphological model. The model was utilized in simulating breaker bar development by Jacobsen et al. (2014) and has been used in simulating wave induced scour beneath pipelines by Fuhrman et al. (2014) . The model is utilized for the numerical study...
A two-component NZRI metamaterial based rectangular cloak
Islam, Sikder Sunbeam; Faruque, Mohammd Rashed Iqbal; Islam, Mohammad Tariqul
2015-10-01
A new two-component, near zero refractive index (NZRI) metamaterial is presented for electromagnetic rectangular cloaking operation in the microwave range. In the basic design a pi-shaped, metamaterial was developed and its characteristics were investigated for the two major axes (x and z-axis) wave propagation through the material. For the z-axis wave propagation, it shows more than 2 GHz bandwidth and for the x-axis wave propagation; it exhibits more than 1 GHz bandwidth of NZRI property. The metamaterial was then utilized in designing a rectangular cloak where a metal cylinder was cloaked perfectly in the C-band area of microwave regime. The experimental result was provided for the metamaterial and the cloak and these results were compared with the simulated results. This is a novel and promising design for its two-component NZRI characteristics and rectangular cloaking operation in the electromagnetic paradigm.
Transport of time-varying plasma currents by whistler wave packets
Stenzel, R. L.; Urrutia, J. M.; Rousculp, C.
1992-01-01
The relationship between pulsed currents and electromagnetic waves is examined in a regime characterized by electron MHD. Pulsed currents are generated by (1) collection/emission of charged particles by/from biased electrodes and (2) induction of currents by time-varying and moving magnetic fields. Pulsed currents are observed to propagate at the speed of whistler wave packets. Their field structure forms ropelike configurations which are electromagnetically force-free. Moving sources induce 'eddy' currents which excite waves and form Cerenkov-like whistler 'wings'. The radiation patterns of moving magnetic antennas and electrodynamic tethers are investigated. Nonlinear effects of large-amplitude, antenna-launched whistler pulses are observed. These involve a new modulational instability in which a channel of high conductivity which permits the wave/currents to penetrate deeply into a collisional plasma is formed.
Wave-Current Interaction in Coastal Inlets and River Mouths
2012-09-30
R/V Salty Dog, both operated from the Romberg Tiburon Center for Environmental Studies. Instrument validation One of the new developments...Waverider buoy. These observations were made in energetic swell (3.3 m significant wave height) in deep water off the coast of Monterey. Spectral...test where the new drifter was deployed alongside a Datawell Waverider in deep water off the central California coast are shown in Figure 3. Data
Combined Wave and Current Bottom Boundary Layers: A Review
2016-03-01
viscoelastic surface (Dalrymple and Liu 1978; Foda et al. 1993; Jain and Mehta 2009; Mallard and Dalrymple 1977; Mei et al. 2010; Ng and Zhang 2007...parameters. They noted good agreement between the damping coefficient and wave number as a function of layer thickness with available measurements. Foda et...attenuation tended to increase as a function of the layer thickness and bed stiffness. Foda et al. (1993) further surmised that the mud behaved like
Generalized Mean-Flow Theory of Wave-Current-Bottom Interactions
无
2006-01-01
The interaction between waves, currents and bottoms in estuarine and coastal regions is ubiquitious, in particular the dynamic mechanism of waves on large-scale slowly varying currents. The wave action concept may be extended and applicated to the study of the mechanism. Considering the effects of moving bottoms and starting from the Navier-Stokes equation of motion of a viscous fluid including the Coriolis force, a generalized mean-flow model theory for the nearshore region, that is, a set of mean-flow equations and their generalized wave action equation involving the three new kinds of actions termed respectively as the current wave action, the bottom wave action and the dissipative wave action which can be applied to arbitrary depth over moving bottoms and ambient currents with a typical vertical structure, is developed by vertical integration and time-averaging over a wave period, thus extending the classical concept, wave action, from the ideal averaged flow conservative system to the real averaged flow dissipative dynamical system, and having a large range of application.
The wave plus current flow over vortex ripples at an arbitrary angle
Andersen, Ken Haste; Faraci, C
2003-01-01
to a regular ripple pattern formation. Numerical simulations were conducted changing the direction between the waves and the current from 0degrees to 90degrees and the ratio between the current strength and the wave orbital velocity from 0.2 to 1.5. Close to the bed, the current aligns parallel to the ripple....... (C) 2002 Elsevier Science B.V. All rights reserved....
Self-Consistent Ring Current/Electromagnetic Ion Cyclotron Waves Modeling
Khazanov, G. V.; Gamayunov, K. V.; Gallagher, D. L.
2006-01-01
The self-consistent treatment of the RC ion dynamics and EMIC waves, which are thought to exert important influences on the ion dynamical evolution, is an important missing element in our understanding of the storm-and recovery-time ring current evolution. For example, the EMlC waves cause the RC decay on a time scale of about one hour or less during the main phase of storms. The oblique EMIC waves damp due to Landau resonance with the thermal plasmaspheric electrons, and subsequent transport of the dissipating wave energy into the ionosphere below causes an ionosphere temperature enhancement. Under certain conditions, relativistic electrons, with energies 21 MeV, can be removed from the outer radiation belt by EMIC wave scattering during a magnetic storm. That is why the modeling of EMIC waves is critical and timely issue in magnetospheric physics. This study will generalize the self-consistent theoretical description of RC ions and EMIC waves that has been developed by Khazanov et al. [2002, 2003] and include the heavy ions and propagation effects of EMIC waves in the global dynamic of self-consistent RC - EMIC waves coupling. The results of our newly developed model that will be presented at the meeting, focusing mainly on the dynamic of EMIC waves and comparison of these results with the previous global RC modeling studies devoted to EMIC waves formation. We also discuss RC ion precipitations and wave induced thermal electron fluxes into the ionosphere.
Assessment of the importance of the current-wave coupling in the shelf ocean forecasts
G. Jordà
2006-10-01
Full Text Available The effects of wave-current interactions on shelf ocean forecasts is investigated in the framework of the MFSTEP (Mediterranean Forecasting System Project Towards Enviromental Predictions project. A one way sequential coupling approach is adopted to link the wave model (WAM to the circulation model (SYMPHONIE. The coupling of waves and currents has been done considering four main processes: wave refraction due to currents, surface wind drag and bo€ttom drag modifications due to waves, and the wave induced mass flux. The coupled modelling system is implemented in the southern Catalan shelf (NW Mediterranean, a region with characteristics similar to most of the Mediterranean shelves. The sensitivity experiments are run in a typical operational configuration. The wave refraction by currents seems to be not very relevant in a microtidal context such as the western Mediterranean. The main effect of waves on current forecasts is through the modification of the wind drag. The Stokes drift also plays a significant role due to its spatial and temporal characteristics. Finally, the enhanced bottom friction is just noticeable in the inner shelf.
Assessment of the importance of the current-wave coupling in the shelf ocean forecasts
G. Jordà
2007-07-01
Full Text Available The effects of wave-current interactions on shelf ocean forecasts is investigated in the framework of the MFSTEP (Mediterranean Forecasting System Project Towards Enviromental Predictions project. A one way sequential coupling approach is adopted to link the wave model (WAM to the circulation model (SYMPHONIE. The coupling of waves and currents has been done considering four main processes: wave refraction due to currents, surface wind drag and bottom drag modifications due to waves, and the wave induced mass flux. The coupled modelling system is implemented in the southern Catalan shelf (NW Mediterranean, a region with characteristics similar to most of the Mediterranean shelves. The sensitivity experiments are run in a typical operational configuration. The wave refraction by currents seems to be not very relevant in a microtidal context such as the western Mediterranean. The main effect of waves on current forecasts is through the modification of the wind drag. The Stokes drift also plays a significant role due to its spatial and temporal characteristics. Finally, the enhanced bottom friction is just noticeable in the inner shelf.
Fichte, Lars Ole
2007-07-01
The author of the contribution under consideration investigates the distribution of the current density in the interior of a plurality of straight parallel conductors with a rectangular cross section after the decay of the transient switch-on processes. The cross-sectional dimensions of the electrical conductors substantially are smaller than the longitudinal extension of the arrangement. Only those conductors are investigated in which the edges of the conductor cross-sections are parallel to each other. The resulting spatially varying distributions of the current density are computed numerically. The results of the numerical computations are compared with solutions from commercial field calculation programs.
Potential of ion cyclotron resonance frequency current drive via fast waves in DEMO
Kazakov, Ye O.; Van Eester, D.; Wauters, T.; Lerche, E.; Ongena, J.
2015-02-01
For the continuous operation of future tokamak-reactors like DEMO, non-inductively driven toroidal plasma current is needed. Bootstrap current, due to the pressure gradient, and current driven by auxiliary heating systems are currently considered as the two main options. This paper addresses the current drive (CD) potential of the ion cyclotron resonance frequency (ICRF) heating system in DEMO-like plasmas. Fast wave CD scenarios are evaluated for both the standard midplane launch and an alternative case of exciting the waves from the top of the machine. Optimal ICRF frequencies and parallel wave numbers are identified to maximize the CD efficiency. Limitations of the high frequency ICRF CD operation are discussed. A simplified analytical method to estimate the fast wave CD efficiency is presented, complemented with the discussion of its dependencies on plasma parameters. The calculated CD efficiency for the ICRF system is shown to be similar to those for the negative neutral beam injection and electron cyclotron resonance heating.
Loads on a 3D body due to second order waves and a current
Skourup, Jesper; Cheung, K. F.; Bingham, Harry B.;
2000-01-01
Non-linear loads on a fixed body due to waves and a current are investigated. Potential theory is used to describe the flow, and a three-dimensional (3D) boundary element method (BEM), combined with a time-stepping procedure, is used to solve the problem. The exact free-surface boundary conditions......-order oscillatory forces and for the second-order mean force on a fixed vertical circular cylinder in waves and a current. The second-order oscillatory forces on the body in waves and current are new results, while the remaining force components are verified by comparison with established numerical and analytical...
Wave Scattering by Double Slotted Barriers in A Steady Current: Experiments
无
2008-01-01
The adoption of slotted breakwaters can be an ideal option in the protection of very large near-shore floating structures that may extend offshore to a considerable water depth. In this paper, we experimently investigated the behaviour of wave transmission and reflection coefficients of double slotted barriers in the presence of a steady opposing current. The experimental results show that opposing currents have only minor effects on wave reflection, but can significantly reduce the wave transmission through double slotted barriers. The experimental results suggest that coastal currents should be taken into consideration for an economical design of slotted breakwaters.
Transfer of Energy, Potential, and Current by Alfv\\'en Waves in Solar Flares
Melrose, D B
2013-01-01
Alfv\\'en waves play three related roles in the impulsive phase of a solar flare: they transport energy from a generator region to an acceleration region; they map the cross-field potential (associated with the driven energy release) from the generator region onto the acceleration region; and within the acceleration region they damp by setting up a parallel electric field that accelerates electrons and transfers the wave energy to them. The Alfv\\'en waves may also be regarded as setting up new closed current loops, with field-aligned currents that close across field lines at boundaries. A model is developed for large-amplitude Alfv\\'en waves that shows how Alfv\\'en waves play these roles in solar flares. A picket-fence structure for the current flow is incorporated into the model to account for the "number problem" and the energy of the accelerated electrons.
Rectangular spectral collocation
Driscoll, Tobin A.
2015-02-06
Boundary conditions in spectral collocation methods are typically imposed by removing some rows of the discretized differential operator and replacing them with others that enforce the required conditions at the boundary. A new approach based upon resampling differentiated polynomials into a lower-degree subspace makes differentiation matrices, and operators built from them, rectangular without any row deletions. Then, boundary and interface conditions can be adjoined to yield a square system. The resulting method is both flexible and robust, and avoids ambiguities that arise when applying the classical row deletion method outside of two-point scalar boundary-value problems. The new method is the basis for ordinary differential equation solutions in Chebfun software, and is demonstrated for a variety of boundary-value, eigenvalue and time-dependent problems.
Application of High Harmonic Fast Waves to Off-Axis Current Drive in DIII-D
Prater, R.; Pinsker, R. I.; Moeller, C. P.; Porkolab, M.; Vdovin, V. L.
2013-10-01
High harmonic fast waves, also called ``whistlers'' or ``helicons,'' may be an effective means of driving current off-axis in high performance discharges in DIII-D. Modeling using the GENRAY ray tracing code APP shows that fast waves launched with frequency 500 MHz tend to spiral around the magnetic axis. If the electron beta is above 1.7%, the waves are damped around ρ = 0 . 5 for a broad range of conditions. The fast wave current drive in the test discharge is 2 to 4 times larger per MW than that from the electron cyclotron heating or neutral beam injection systems on DIII-D. Interestingly, the current drive location and magnitude are nearly independent of the launched n| | over the range 2 to 4. Use of a moderately large value, n| | = 3 , reduces the possibility of mode conversion to the slow wave. A traveling wave antenna is expected to be effective at launching the wave with a narrow spectrum of n| |, which also helps avoid mode conversion. A test of the physics of high harmonic fast wave current drive is planned for DIII-D. Work supported in part by the US Department of Energy under DE-FC02-04ER54698.
Firing wave instability of the current filaments in a semiconductor. An analogy with neurodynamics
Aoki, K.; Yamamoto, K.
1983-10-01
Periodic oscillations and chaos have been observed in the firing density wave of the current filaments in n-GaAs at 4.2 K. The mechanism of the firing-wave instability has been discussed by an analogy with neurodynamics.
Gravity waves on water with non-uniform depth and current
Booij, N.
1981-01-01
A mathematical model for the combined refraction-diffraction of linear periodic gravity waves on water is developed, in which the influence of inhomogeneities of depth and current is taken into account. The model is used to compute partial reflection of waves a gully or an undersea slope, with influ
Gravity waves on water with non-uniform depth and current
Booij, N.
1981-01-01
A mathematical model for the combined refraction-diffraction of linear periodic gravity waves on water is developed, in which the influence of inhomogeneities of depth and current is taken into account. The model is used to compute partial reflection of waves a gully or an undersea slope, with influ
Modeling waves, currents and sandbars on natural beaches: The effect of surface rollers
Ribas, F.; de Swart, H.E.; Calvete, D.; Falqués, A.
2011-01-01
A morphodynamic model has been extended to gain more fundamental knowledge about the formation of nearshore sand bars. The model describes feedbacks between waves, rollers, depth-averaged currents and bed evolution, so that self-organized processes can develop. Offshore wave, wind and tide condition
Assessment of current effect on waves in a semi-enclosed basin
Benetazzo, A.; Carniel, S.; Sclavo, M.; Bergamasco, A.
2012-04-01
The wave-current interaction process in the semi-enclosed Adriatic Sea is studied using the Coupled Ocean-Atmosphere-Wave-Sediment Transport (COAWST) modeling system, which is used to exchange data fields between the ocean model ROMS (Regional Ocean Modeling System) and the wave model SWAN (Simulating WAves Nearshore). The 2-way data transfer between circulation and wave models is synchronous with ROMS providing current fields, free surface elevation, and bathymetry to SWAN. In particular, the 3-D current profiles are averaged using a formulation that integrates the near-surface velocity over a depth controlled by the spectral mean wave number. This coupling procedure is carried out up to coastal areas by means of an offline grid nesting. The parent grid covers the whole Adriatic Sea and has a horizontal resolution of 2.0 km, whereas the child grid resolution increases to 0.5 km but it is limited to the northern Adriatic Sea (Gulf of Venice), where the current effect on waves is investigated. The most frequent winds blowing on the Adriatic Sea are the so-called Bora and Sirocco which cause high waves in the Adriatic Sea, although Bora waves are generally fetch-limited. In fact, Bora winds blow orthogonal to the main basin axis (approximately aligned with the NW-SE direction), while Sirocco has large spatial scale being a southeasterly wind. For the numerical simulations, the meteorological forcings are provided by the operational meteorological model COSMO-I7, which is the Italian version of the COSMO Model, a mesoscale model developed in the framework of the COSMO Consortium. During the analysis period, the simulated wind, current and wave are compared with observations at the ISMAR oceanographic tower located off the Venice littoral. Wave heights and sea surface winds are also compared with satellite-derived data. To account for the variability of sea states during a storm, the expected maximum individual wave height in a sea storm with a given history is also
Wave-current interactions in deep water conditions: field measurements and analyses
Rougier, Gilles; Rey, Vincent; Molcard, Anne
2015-04-01
The study of wave - current interaction has drawn interest in oceanography, ocean engineering, maritime navigation and for tides or waves power device design. In the context of the hydrodynamics study along the French Mediterranean coast, a current profiler was deployed near Toulon at the south of the "Port Cros" island. This coastal zone is characterized by a steep slope, the water depth varying from tens meters to several thousand meters over few kilometers from the coast. An ambient current, the "Northern Current", coming from the Ligurian sea (area of Genoa, Italy) and following the coast up to Toulon, is present all over the year. Its mean surface velocity is of about 0.30 m/s, its flow rate of about 1.5 Sv. The region is exposed to two dominating winds: the Mistral, coming from North-West, and Eastern winds. Both generate swell and/or wind waves in either following or opposing current conditions with respect to the Northern Current. A current profiler equipped with a wave tracking system (ACPD workhorse from RDI) was deployed from July to October 2014 in deep water conditions (depth of about 500m). The mooring system allowed the ADCP to measure the current profile from the sea surface down to 25m depth, which corresponds more or less to the depth of influence of waves of periods up to 10s. The collected data include energetic wave conditions in either following or opposing current conditions. The current intensity and its vertical profiles have shown a significant temporal variability according to the meteorological conditions. Effects of the wave conditions on the current properties are discussed. ACKNOWLEDGEMENTS This work was supported by the program BOMBYX and the ANR grant No ANR-13-ASTR-0007.
Loads on a 3D body due to second order waves and a current
Skourup, Jesper; Cheung, K. F.; Bingham, Harry B.
2000-01-01
Non-linear loads on a fixed body due to waves and a current are investigated. Potential theory is used to describe the flow, and a three-dimensional (3D) boundary element method (BEM), combined with a time-stepping procedure, is used to solve the problem. The exact free-surface boundary conditions...... are expanded about the still-water level by Taylor series so that the solution is evaluated on a time-invariant geometry. A formulation correct to second order in the wave steepness and to first order in the current speed is used. Numerical results are obtained for the first-order and the second......-order oscillatory forces and for the second-order mean force on a fixed vertical circular cylinder in waves and a current. The second-order oscillatory forces on the body in waves and current are new results, while the remaining force components are verified by comparison with established numerical and analytical...
Computation of Wave, Tide and Wind Current for the South China Sea Under Tropical Cyclones
朱良生; 宋运法; 邱章; 陈秀华; 麦波强; 丘耀文; 宋丽莉
2003-01-01
Based on the third-generation oceanic wave prediction model (WAVEWATCH Ⅲ),the third-generation nearshore wave calculation model (SWAN) and the mathematical tide, tidal current and cyclone current model, which have been improved, interconnected and expanded, a coupled model of offshore wave, tide and sea current under tropical cyclone surges in the South China Sea has been established. The coupled model is driven by the tropical cyclone field containing the background wind field. In order to test the hindcasting effect of the mathematical model, a comparison has been made between the calculated results and the observational results of waves of 15 cyclone cases, water levels and current velocities of the of 7 cyclones. The results of verification indicate that the calculated and observed results are basically identical.
Fast wave current drive modeling using the combined RANT3D and PICES codes
Jaeger, E.F.; Murakami, M.; Stallings, D.C. [and others
1995-07-01
Two numerical codes are combined to give a theoretical estimate of the current drive and direct electron heating by fast waves launched from phased antenna arrays on the DIII-D tokamak. Results are compared with experiment.
Fast wave current drive modeling using the combined RANT3D and PICES Codes
Jaeger, E. F.; Murakami, M.; Stallings, D. C.; Carter, M. D.; Wang, C. Y.; Galambos, J. D.; Batchelor, D. B.; Baity, F. W.; Bell, G. L.; Wilgen, J. B.; Chiu, S. C.; DeGrassie, J. S.; Forest, C. B.; Kupfer, K.; Petty, C. C.; Pinsker, R. T.; Prater, R.; Lohr, J.; Lee, K. M.
1996-02-01
Two numerical codes are combined to give a theoretical estimate of the current drive and direct electron heating by fast waves launched from phased antenna arrays on the DIII-D tokamak. Results are compared with experiment.
Fokker-Planck Simulation of Fast Wave Current Drive and Heating in the Reversed Field Pinch
Uchimoto, E.; Shiina, S.; Harvey, R. W.; Smirnov, A. P.; Forest, C. B.; Prager, S. C.; Wright, J. C.
1999-11-01
Fast wave current drive (FWCD) has been shown theoretically to be a good candidate for improving plasma confinement characteristics of a high-beta, reactor-grade RFP via current profile control.footnote S. Shiina, Y. Kondoh, H. Ishii, Nuclear Fusion 34, 1473 (1994); T. Nagai et al., Proc. ICPP (Nagoya, 1996), p. 1042; K. Kusano et al., 17th IAEA Fusion Energy Conf. (Yokohama, 1998), paper THP1/12. To assess the effects of toroidicity and quasilinear modifications to the electron distribution function on FWCD, we are using the RFP version of ray-tracing and Fokker-Planck codes (GENRAY and CQL3D). Although lower hybrid slow waves are ideally suited for poloidal current drive in large RFPs presently in operation, possible use of fast waves is being considered for core current drive and heating in these devices. For MST parameters, our calculations focus on intermediate to high harmonic fast waves for which geometric optics is valid.
Effect of Alfvén resonance on low-frequency fast wave current drive
Wang, C. Y.; Batchelor, D. B.; Carter, M. D.; Jaeger, E. F.; Stallings, D. C.
1995-08-01
The Alfvén resonances may occur on the low- and high-field sides for a low-frequency fast wave current drive scenario proposed for the International Thermonuclear Experimental Reactor (ITER) [Nucl. Fusion 31, 1135 (1991)]. At the resonance on the low-field side, the fast wave may be mode converted into a short-wavelength slow wave, which can be absorbed by electrons at the plasma edge, before the fast wave propagates into the core area of the plasma. Such absorption may cause a significant parasitic power loss.
Effect of Alfven resonance on low-frequency fast wave current drive
Wang, C.Y.; Batchelor, D.B.; Carter, M.D.; Jaeger, E.F.; Stallings, D.C. [Fusion Energy Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (United States)
1995-07-01
The Alfven resonances may occur on the low- and high-field sides for a low-frequency fast wave current drive scenario proposed for the International Thermonuclear Experimental Reactor (ITER) [Nucl. Fusion {bold 31}, 1135 (1991)]. At the resonance on the low-field side, the fast wave may be mode converted into a short-wavelength slow wave, which can be absorbed by electrons at the plasma edge, before the fast wave propagates into the core area of the plasma. Such absorption may cause a significant parasitic power loss. {copyright} {ital 1995} {ital American} {ital Institute} {ital of} {ital Physics}.
Reduced sodium current in the lateral ventricular wall induces inferolateral J-waves
Veronique Marlinde Frederica Meijborg
2016-08-01
Full Text Available Background: J-waves in inferolateral leads are associated with a higher risk for idiopathic ventricular fibrillation. We aimed to test potential mechanisms (depolarization or repolarization dependent responsible for inferolateral J-waves. We hypothesized that inferolateral J-waves can be caused by regional delayed activation of myocardium that is activated late during normal conditions. Methods: Computer simulations were performed to evaluate how J-point elevation is influenced by reducing sodium current conductivity (GNa, increasing transient outward current conductivity (Gto or cellular uncoupling in three predefined ventricular regions (lateral, anterior or septal. Two pig hearts were Langendorff-perfused with selective perfusion with a sodium channel blocker of lateral or anterior/septal regions. Volume-conducted pseudo-electrocardiograms (ECG were recorded to detect the presence of J-waves. Epicardial unipolar electrograms were simultaneously recorded to obtain activation times (AT.Results: Simulation data showed that conduction slowing, caused by reduced sodium current, in lateral, but not in other regions induced inferolateral J-waves. An increase in transient outward potassium current or cellular uncoupling in the lateral zone elicited slight J-point elevations which did not meet J-wave criteria. Additional conduction slowing in the entire heart attenuated J-waves and J-point elevations on the ECG, because of masking by the QRS. Experimental data confirmed that conduction slowing attributed to sodium channel blockade in the left lateral but not in the anterior/septal ventricular region induced inferolateral J-waves. J-waves coincided with the delayed activation.Conclusion: Reduced sodium current in the left lateral ventricular myocardium can cause inferolateral J-waves on the ECG.
Josephson Current in Superconductor-Ferromagnet/Insulator/d-Wave Superconductor Junctions
LI Xiao-Wei; DONG Zheng-Chao
2005-01-01
Solving the Bogoliubov-de Gennes equation, the energy levels of bound states are obtained in the ferromagnetic superconductor. The Josephson currents in a ferromagnetic superconductor/Insulator/d-wave superconductor junction are calculated as a function of the exchange field, temperature, and insulating barrier strength. It is found that the Josephson critical current is always suppressed by the presence of exchange field h and depends on crystalline axis orientation of d-wave superconductor.
MODELING OF THE HIGH CONCENTRATION LAYER OF COHESIVE SEDIMENT UNDER THE ACTION OF WAVES AND CURRENTS
Qinghe ZHANG; Yongsheng WU; Jijian LIAN; Pingxing DING
2001-01-01
High concentration layer of cohesive sediment frequently occurs in muddy estuaries and coastal zones, and causes rapid siltation of the waterways. A one dimensional vertical coupled model describing the interactions between waves, currents and suspended cohesive sediment is developed in the present paper. The numerical results and analyses with field measurements reveal the mechanism of the formation and transport behaviors of the layer under the action of waves and currents.
Wave-Current Interactions in the Vicinity of the Sea Bed
Holmedal, Lars Erik
2002-01-01
The intention of the work carried out in the present thesis is to span a part of the range of sea bed boundary layer research by three separate parts. The two first parts deal with the sea bed boundary layer beneath random waves and current, while the third part represents a more fundamental approach towards the smooth turbulent boundary layer under a horizontally uniform sinusoidal plus steady forcing. The first part focuses on the bottom shear stress amplitudes under random waves plus current. Shear stresses on a rough seabed under irregular waves plus current are calculated. Parameterized models valid for regular waves plus current have been used in Monte Carlo simulations, assuming the wave amplitudes to be Rayleigh distributed. Numerical estimates of the probability distribution functions are presented. For waves only, the shear stress maxima follow a two-parameter Weibull distribution, while for waves plus current, both the maximum and time-averaged shear stresses are well represented by a three-parameter Weibull distribution. The behaviour of the maximum shear stresses under a wide range of wave-current conditions has been investigated, and it appears that under certain conditions the current has a significant influence on the maximum shear stresses. Results of comparison between predictions and measurements of the maximum bottom shear stresses from laboratory and field experiments are presented. The second part extends the first approach by applying a dynamic eddy viscosity model; the boundary layer under random waves alone as well as under random waves plus current have been examined by a dynamic turbulent boundary layer model based on the linearized boundary layer equations with horizontally uniform forcing. The turbulence closure is provided by a high Reynolds number k - {epsilon} model. The model appears to be verified as far as data exists, i.e., for sinusoidal waves alone as well as for sinusoidal waves plus a mean current. The time and space
Modelling wave-current interactions off the east coast of Scotland
Sabatino, Alessandro D.; McCaig, Chris; O'Hara Murray, Rory B.; Heath, Michael R.
2016-07-01
Densely populated coastal areas of the North Sea are particularly vulnerable to severe wave conditions, which overtop or damage sea defences leading to dangerous flooding. Around the shallow southern North Sea, where the coastal margin is lying low and population density is high, oceanographic modelling has helped to develop forecasting systems to predict flood risk. However, coastal areas of the deeper northern North Sea are also subject to regular storm damage, but there has been little or no effort to develop coastal wave models for these waters. Here, we present a high spatial resolution model of northeast Scottish coastal waters, simulating waves and the effect of tidal currents on wave propagation, driven by global ocean tides, far-field wave conditions, and local air pressure and wind stress. We show that the wave-current interactions and wave-wave interactions are particularly important for simulating the wave conditions close to the coast at various locations. The model can simulate the extreme conditions experienced when high (spring) tides are combined with sea-level surges and large Atlantic swell. Such a combination of extremes represents a high risk for damaging conditions along the Scottish coast.
How linear surface waves are affected by a current with constant vorticity
Ellingsen, Simen Å
2013-01-01
The interaction of surface waves with Couette-type current with uniform vorticity is a well suited problem for students approaching the theory of surface waves. The problem, although mathematically simple, contains rich physics, and is moreover important in several situations from oceanography and marine technology to microfluidics. We here lay out a simple two-dimensional theory of waves propagating upon a basic flow of uniform vorticity of constant depth. The dispersion relation is found, showing how the shearing current introduces different phase velocities for upstream and downstream propagating waves. The role of surface tension is discussed and applied to the case of a wave pattern created by a moving source, stationary as seen by the source. We conclude by discussing how the average potential and kinetic energies are no longer equal in the presence of shear.
Spatially extended sound equalization in rectangular rooms
Santillan, Arturo Orozco
2001-01-01
of broadband signals can be achieved by the simulation of a traveling plane wave using FIR filters. The optimal solution has been calculated following the traditional least-squares approximation, where a modeling delay has been applied to minimize reverberation. An advantage of the method is that the sound......The results of a theoretical study on global sound equalization in rectangular rooms at low frequencies are presented. The zone where sound equalization can be obtained is a continuous three-dimensional region that occupies almost the complete volume of the room. It is proved that the equalization...
Spatially extended sound equalization in rectangular rooms
Santillan, Arturo Orozco
2001-01-01
The results of a theoretical study on global sound equalization in rectangular rooms at low frequencies are presented. The zone where sound equalization can be obtained is a continuous three-dimensional region that occupies almost the complete volume of the room. It is proved that the equalization...... of broadband signals can be achieved by the simulation of a traveling plane wave using FIR filters. The optimal solution has been calculated following the traditional least-squares approximation, where a modeling delay has been applied to minimize reverberation. An advantage of the method is that the sound...
An Optimized Combined Wave and Current Bottom Boundary Layer Model for Arbitrary Bed Roughness
2017-06-30
studies of shelf circulation patterns that incorporate wave-current effects in the bottom boundary layer have been conducted in the past (e.g...presence of surface waves reemphasizes the fact that wave-current effects are important on storm- dominated continental shelves. In addition to these...can be defined for / rz z1 (i.e., */ rrzz ακR1 ), where * * / )(r cw rR u z ω . The two expressions are related by * */ /r r zR zR 0 , where
Efficient Algorithm for Rectangular Spiral Search
Brugarolas, Paul; Breckenridge, William
2008-01-01
An algorithm generates grid coordinates for a computationally efficient spiral search pattern covering an uncertain rectangular area spanned by a coordinate grid. The algorithm does not require that the grid be fixed; the algorithm can search indefinitely, expanding the grid and spiral, as needed, until the target of the search is found. The algorithm also does not require memory of coordinates of previous points on the spiral to generate the current point on the spiral.
The impact of sea surface currents in wave power potential modeling
Zodiatis, George; Galanis, George; Kallos, George; Nikolaidis, Andreas; Kalogeri, Christina; Liakatas, Aristotelis; Stylianou, Stavros
2015-11-01
The impact of sea surface currents to the estimation and modeling of wave energy potential over an area of increased economic interest, the Eastern Mediterranean Sea, is investigated in this work. High-resolution atmospheric, wave, and circulation models, the latter downscaled from the regional Mediterranean Forecasting System (MFS) of the Copernicus marine service (former MyOcean regional MFS system), are utilized towards this goal. The modeled data are analyzed by means of a variety of statistical tools measuring the potential changes not only in the main wave characteristics, but also in the general distribution of the wave energy and the wave parameters that mainly affect it, when using sea surface currents as a forcing to the wave models. The obtained results prove that the impact of the sea surface currents is quite significant in wave energy-related modeling, as well as temporally and spatially dependent. These facts are revealing the necessity of the utilization of the sea surface currents characteristics in renewable energy studies in conjunction with their meteo-ocean forecasting counterparts.
Development of an unstructured-grid wave-current coupled model and its application
Feng, Xingru; Yin, Baoshu; Yang, Dezhou
2016-08-01
An unstructured grid wave-current coupled model was developed by coupling the SWAN (Simulating Waves Nearshore) wave model and ADCIRC (Advanced Circulation model) ocean model through the Model Coupling Toolkit (MCT). The developed coupled model has high spatial resolution in the coastal area and is efficient for computation. The efficiency of the newly developed SWAN + ADCIRC model was compared with that of the widely-used SWAN + ADCIRC coupled model, in which SWAN and ADCIRC are coupled directly rather than through the MCT. Results show that the directly-coupled model is more efficient when the total number of computational cores is small, but the MCT-coupled model begin to run faster than the directly-coupled model when more computational cores are used. The MCT-coupled model maintains the scalability longer and can increase the simulation efficiency more than 35% by comparing the minimum wall clock time of one day simulation in the test runs. The MCT-coupled SWAN + ADCIRC model was used to simulate the storm surge and waves during the typhoon Usagi which formed in the western Pacific on September 17, 2013 and landed at Shanwei, China. Three numerical experiments were performed to investigate the effect of wave-current interaction on the storm surge and waves. The results show that the coupled model can better simulate the storm surge and waves when considering the wave-induced radiation stress, the wave effect on the wind stress drag coefficient and the modulation of current and water level on waves. During the typhoon Usagi, the effect of wave radiation stress could result in a maximum of 0.75 m increase in the extreme storm surge, and the wave induced wind stress could cause a -0.82∼0.48 m change of the extreme storm surge near the coastal area. Besides, the radiation stress forced currents cannot be ignored either in the study of mass transport at coastal zones. Results of this study are useful for understanding the wave-current interaction processes and
Bed forms created by simulated waves and currents in a large flume
Lacy, Jessica R.; Rubin, David M.; Ikeda, Hiroshi; Mokudai, Kuniyasu; Hanes, Daniel M.
2007-01-01
The morphology and evolution of bed forms created by combinations of waves and currents were investigated using an oscillating plate in a 4-m-wide flume. Current speed ranged from 0 to 30 cm/s, maximum oscillatory velocity ranged from 20 to 48 cm/s, oscillation period was 8 s (except for one run with 12 s period), and the median grain size was 0.27 mm. The angle between oscillations and current was 90°, 60°, or 45°. At the end of each run the sand bed was photographed and ripple dimensions were measured. Ripple wavelength was also determined from sonar images collected throughout the runs. Increasing the ratio of current to wave (i.e., oscillatory) velocity decreased ripple height and wavelength, in part because of the increased fluid excursion during the wave period. Increasing the ratio of current to waves, or decreasing the angle between current and waves, increased the three-dimensionality of bed forms. During the runs, ripple wavelength increased by a factor of about 2. The average number of wave periods for evolution of ripple wavelength to 90% of its final value was 184 for two-dimensional ripples starting from a flat bed. Bed form orientations at the end of each run were compared to four potential controlling factors: the directions of waves, current, maximum instantaneous bed shear stress, and maximum gross bed form normal transport (MGBNT). The directions of waves and of MGBNT were equally good predictors of bed form orientations, and were significantly better than the other two factors.
CUI Lei; TONG Fei-fei; SHI Feng
2011-01-01
Researches on breaking-induced currents by waves are summarized firstly in this paper.Then,a combined numerical model in orthogonal curvilinear coordinates is presented to simulate wave-induced current in areas with curved boundary or irregular coastline.The proposed wave-induced current model includes a nearshore current module established through orthogonal curvilinear transformation form of shallow water equations and a wave module based on the curvilinear parabolic approximation wave equation.The wave module actually serves as the driving force to provide the current module with required radiation stresses.The Crank-Nicolson finite difference scheme and the alternating directions implicit method are used to solve the wave and current module,respectively.The established surf zone currents model is validated by two numerical experiments about longshore currents and rip currents in basins with rip channel and breakwater.The numerical results are compared with the measured data and published numerical results.
Non-inductive current driven by Alfvén waves in solar coronal loops
Elfimov, A. G.; de Azevedo, C. A.; de Assis, A. S.
1996-08-01
It has been shown that Alfvén waves can drive non-inductive current in solar coronal loops via collisional or collisionless damping. Assuming that all the coronal-loop density of dissipated wave power (W= 10-3 erg cm-3 s-1), which is necessary to keep the plasma hot, is due to Alfvén wave electron heating, we have estimated the axial current density driven by Alfvén waves to be ≈ 103 105 statA cm-2. This current can indeed support the quasi-stationary equilibrium and stability of coronal loops and create the poloidal magnetic field up to B θ≈1-5 G.
无
2007-01-01
Surface waves comprise an important aspect of the interaction between the atmosphere and the ocean, so a dynamically consistent framework for modelling atmosphere-ocean interaction must take account of surface waves, either implicitly or explicitly. In order to calculate the effect of wind forcing on waves and currents, and vice versa, it is necessary to employ a consistent formulation of the energy and momentum balance within the airflow, wave field, and water column. It is very advantageous to apply surface-following coordinate systems, whereby the steep gradients in mean flow properties near the air-water interface in the cross-interface direction may be resolved over distances which are much smaller than the height of the waves themselves. We may account for the waves explicitly by employing a numerical spectral wave model, and applying a suitable theory of wave-mean flow interaction. If the mean flow is small compared with the wave phase speed, perturbation expansions of the hydrodynamic equations in a Lagrangian or generalized Lagrangian mean framework are useful: for stronger flows, such as for wind blowing over waves, the presence of critical levels where the mean flow velocity is equal to the wave phase speed necessitates the application of more general types of surface-following coordinate system. The interaction of the flow of air and water and associated differences in temperature and the concentration of various substances (such as gas species) gives rise to a complex boundary-layer structure at a wide range of vertical scales, from the sub-millimetre scales of gaseous diffusion, to several tens of metres for the turbulent Ekman layer. The balance of momentum, heat, and mass is also affected significantly by breaking waves, which act to increase the effective area of the surface for mass transfer, and increase turbulent diffusive fluxes via the conversion of wave energy to turbulent kinetic energy.
Long, S. R.; Huang, N. E.
1976-01-01
Laboratory measurements utilizing a laser probe are made for the slopes of wind waves generated on both positive and negative currents at different values of fetch. The data are then processed electronically to yield an average wave-slope spectrum in frequency space with 128 degrees of freedom. These spectra are used to obtain the growth of the spectral components at various frequency bands for increasing wind and different values of fetch and current. The results indicate that the growth of these components is not monotonic with the frictional wind speed, but rather exhibits an 'overshoot' phenomena at lower values of frictional wind speed, and in addition, displays a significant effect due to current. The peak location and spectral intensity of the spectra also show strong influence by the current condition. This results in the rms surface slope value increasing with negative current and decreasing with positive current. The results agree qualitatively with some theoretical predictions. The potential use of the current-induced effects as a means for remote sensing of ocean current is also briefly discussed.
Shapes and Statistics of the Rogue Waves Generated by Chaotic Ocean Current
Bayindir, Cihan
2015-01-01
In this study we discuss the shapes and statistics of the rogue (freak) waves emerging due to wave-current interactions. With this purpose, we use a simple governing equation which is a nonlinear Schrodinger equation (NLSE) extended by R. Smith (1976). This extended NLSE accounts for the effects of current gradient on the nonlinear dynamics of the ocean surface near blocking point. Using a split-step scheme we show that the extended NLSE of Smith is unstable against random chaotic perturbation in the current profile. Therefore the monochromatic wave field with unit amplitude turns into a chaotic sea state with many peaks. By comparing the numerical and analytical results, we show that rogue waves due to perturbations in the current profile are in the form of rational rogue wave solutions of the NLSE. We also discuss the effects of magnitude of the chaotic current profile perturbations on the statistics of the rogue wave generation at the ocean surface. The extension term in Smith's extended NLSE causes phase ...
NONLINEAR DYNAMICS RESPONSE OF CASING PIPE UNDER COMBINED WAVE-CURRENT
TANG You-gang; GU Jia-yang; ZUO Jian-li; MIN Jian-qin
2005-01-01
The vortex-induced nonlinear vibration of casing pipes in the deep water was studied considering the loads of current and combined wave-current. The vortex-induced vibration equation of a casing pipe was set up considering the beam mode and Morison's nonlinear fluid loads as well as the vortex-excited loads. The approach of calculating vortex-excited nonlinear vibration by Galerkin's method was proposed. The natural vibration frequencies and modes were obtained, and the response including primary resonance induced by current and the composite resonance under combined wave-current for the 170 m long casing pipe in the 160 m depth of water were investigated. The results show that the dynamics response of casing pipe obviously increases, and the complicated response behaviors of casing pipe are described under combined wave-current.
Model analysis of the currents and wind waves in the Vistula Lagoon of the Baltic Sea
Chubarenko, B. V.; Leitsina, L. V.; Esiukova, E. E.; Kurennoy, D. N.
2012-11-01
This paper considers the results of the numerical simulation of the steady currents and waves field structures in the Vistula Lagoon under constant wind forcing. The currents' structure is essentially 3-dimensional. The direction of the near-shore drift is determined by the wind and shore orientation, but the currents involve two layers in the deeper part of the basin: the upper layer downwind current and the upwind compensative current in the underlying layer. The wind waves depend upon the wind speed, fetch, and depth until the wind speed is less than 6-8 m/s. As the wind increases, the fetch's dependence disappears. The wind height depends only on the wind's magnitude, and, under stormy conditions (when the wind's speed exceeds 15 m/s), the waves are limited by the water depth alone.
Characterizing Wave- and Current-Induced Bottom Shear Stress: U.S. Middle Atlantic Bight
Dalyander, S.; Butman, B.
2011-12-01
The combined action of waves and currents at the seabed creates bottom shear stress, impacting local geology, habitat, and anthropogenic use. In this study, a methodology is developed to characterize the magnitude of benthic disturbance based on spatially and seasonally-resolved statistics (mean, standard deviation, 95th percentile) of wave-current bottom shear stress. The frequency of stress forcing is used to distinguish regions dominated by storms (return interval longer than 33 hours) from those dominated by the tides (periods shorter than 33 hours). In addition, the relative magnitude of the contribution to stress from waves, tides, and storm-driven currents is investigated by comparing wave stress, tidal current stress, and stress from the residual current (currents with tides removed), as well as through cross-correlation of wave and current stress. The methodology is applied to numerical model time-series data for the Middle Atlantic Bight (MAB) off the U.S. East Coast for April 2010 to April 2011; currents are provided from the Integrated Ocean Observing System (IOOS) operational hydrodynamic forecast Experimental System for Predicting Shelf and Slope Optics (ESPreSSO) and waves are provided from a Simulating WAves Nearshore (SWAN) hindcast developed for this project. Spatial resolution of the model is about 5 km and time-series wave and current data are at 1 and 2-hours respectively. Regions of the MAB delineated by stress characteristics include a tidally-dominated shallow region with relative high stress southeast of Massachusetts over Nantucket Shoals; a coastal band extending offshore to about 30 m water depth dominated by waves; a region dominated by waves and wind-driven currents offshore of the Outer Banks of North Carolina; and a low stress region southeast of Long Island, approximately coincident with an area of fine-grained sediments called the "Mud Patch". Comparison of the stress distribution with surface sediment texture data shows that
Estrada, Ernesto
2015-01-01
A generalization of the random geometric graph (RGG) model is proposed by considering a set of points uniformly and independently distributed on a rectangle of unit area instead of on a unit square \\left[0,1\\right]^{2}. The topological properties, such as connectivity, average degree, average path length and clustering, of the random rectangular graphs (RRGs) generated by this model are then studied as a function of the rectangle sides lengths a and b=1/a, and the radius r used to connect the nodes. When a=1 we recover the RGG, and when a\\rightarrow\\infty the very elongated rectangle generated resembles a one-dimensional RGG. We provided computational and analytical evidence that the topological properties of the RRG differ significantly from those of the RGG. The connectivity of the RRG depends not only on the number of nodes as in the case of the RGG, but also on the side length of the rectangle. As the rectangle is more elongated the critical radius for connectivity increases following first a power-law an...
Shocks, Rarefaction Waves, and Current Fluctuations for Anharmonic Chains
Mendl, Christian B.; Spohn, Herbert
2016-10-01
The nonequilibrium dynamics of anharmonic chains is studied by imposing an initial domain-wall state, in which the two half lattices are prepared in equilibrium with distinct parameters. We analyse the Riemann problem for the corresponding Euler equations and, in specific cases, compare with molecular dynamics. Additionally, the fluctuations of time-integrated currents are investigated. In analogy with the KPZ equation, their typical fluctuations should be of size t^{1/3} and have a Tracy-Widom GUE distributed amplitude. The proper extension to anharmonic chains is explained and tested through molecular dynamics. Our results are calibrated against the stochastic LeRoux lattice gas.
High-current Standing Wave Linac With Gyrocon Power Source
Karliner, M M; Makarov, I G; Nezhevenko, O A; Ostreiko, G N; Persov, B Z; Serdobintsev, G V
2004-01-01
A gyrocon together with high-voltage 1.5 MeV accelerator ELIT-3A represents a power generator at 430 MHz serving for linear electron accelerator pulse driving. The facility description and results of calorimetric measurements of ELIT-3A electron beam power and accelerated beam at the end of accelerator are presented in the paper. 2.2 amps of pulsed current have been obtained at electron energy of 20 MeV. The achieved energy conversion efficiency is about 55%.
宁德志; 林红星; 滕斌; 邹青萍
2014-01-01
To investigate higher harmonics induced by a submerged obstacle in the presence of uniform current, a 2D fully nonlinear numerical wave flume (NWF) is developed by use of a time-domain higher-order boundary element method (HOBEM) based on potential flow theory. A four-point method is developed to decompose higher bound and free harmonic waves propagating upstream and downstream around the obstacle. The model predictions are in good agreement with the experimental data for free harmonics induced by a submerged horizontal cylinder in the absence of currents. This serves as a benchmark to reveal the current effects on higher harmonic waves. The peak value of non-dimensional second free harmonic amplitude is shifted upstream for the opposing current relative to that for zero current with the variation of current-free incident wave amplitude, and it is vice versa for the following current. The second-order analysis shows a resonant behavior which is related to the ratio of the cylinder diameter to the second bound mode wavelength over the cylinder. The second-order resonant position slightly downshifted for the opposing current and upshifted for the following current.
Influence of various physics phenomena on fast-wave current drive in advanced tokamaks
Batchelor, D.B.; Jaeger, E.F.; Carter, M.D.; Goldfinger, R.C.; Stallings, D.C. [Oak Ridge National Lab., TN (United States)
1992-12-31
The need for some type of noninductive current drive in advanced tokamaks has been recognized for some time. In reactor-grade plasmas, as envisioned in the International Thermonuclear Experimental Reactor (ITER), high density and temperature may limit the penetration of lower hybrid (LH) waves to only the outer layers of the plasma. Fast waves in the ion cyclotron range of frequencies (ICRF), however, can easily penetrate to the center of such high-density plasmas. With sufficient directivity in the launched wave spectrum, currents can be driven by combined damping of the fast waves on resonant electrons through electron Landau damping (ELD) and transit-time magnetic pumping (TTMP). Experiments to study the feasibility of fast-wave current drive (FWCD) have only recently begun, but theoretical predictions look promising. In this paper we analyze the influence of the relevant physics phenomena, which are not necessarily independent, on current drive performance. Such phenomena include diffraction and other nongeometrical optics processes, k{sub ||} modification, single-pass absorption, and antenna characteristics, such as poloidal extent and poloidal location. To do this, we apply a two-and-one-half dimensional (2 1/2-D), full-wave code (PICES) for modeling ion cyclotron resonance heating (ICRH) and current drive based on the poloidal mode expansion method and the reduced-order expansion. By 2 1/2-D, we mean that 3-D wave fields are calculated in axisymmetric geometry (2-D solution domain - r, {theta}), while the correct toroidal dependence of the antenna source currents is obtained from a 2-D (r, {phi}) recessed antenna code. The model includes the poloidal and toroidal structure of the antennas, the modification of the k{sub ||} spectrum due to the poloidal magnetic field, and a nonperturbative solution for E{sub ||}. A semianalytical model for current drive, including trapped electron effects, is employed. (author) 10 refs., 4 figs.
Energy from Ocean Waves, River Currents, and Wind
Guha, Shyamal
2006-05-01
The earth we live in is surrounded by fluids, which are in perpetual motion. There is air in the atmosphere, water in lakes, oceans and rivers. The air and water around us form our natural environment. Much of the fluid medium is in constant motion. The kinetic energy of this moving fluid is astronomical in magnitude. Over the years, I considered methods of converting a fraction of the vast reserve of this kinetic energy into electro-mechanical energy. I conceived a few schemes of such conversion. The fluids whose kinetic energy can be converted into electro-mechanical energy are: ocean waters, river current and atmospheric air. In a book to be published in 2006, I have described different techniques of energy conversion. In the APS meeting, I plan to discuss some of these techniques.
An efficient rectangular plate element
无
2001-01-01
A new 12-parameter rectangular plate element is presented by useof the double set parameter method. The error in the energy norm is of order O(h2), one order higher than the commonly used Adini nonconforming element.
Water-waves on linear shear currents. A comparison of experimental and numerical results.
Simon, Bruno; Seez, William; Touboul, Julien; Rey, Vincent; Abid, Malek; Kharif, Christian
2016-04-01
Propagation of water waves can be described for uniformly sheared current conditions. Indeed, some mathematical simplifications remain applicable in the study of waves whether there is no current or a linearly sheared current. However, the widespread use of mathematical wave theories including shear has rarely been backed by experimental studies of such flows. New experimental and numerical methods were both recently developed to study wave current interactions for constant vorticity. On one hand, the numerical code can simulate, in two dimensions, arbitrary non-linear waves. On the other hand, the experimental methods can be used to generate waves with various shear conditions. Taking advantage of the simplicity of the experimental protocol and versatility of the numerical code, comparisons between experimental and numerical data are discussed and compared with linear theory for validation of the methods. ACKNOWLEDGEMENTS The DGA (Direction Générale de l'Armement, France) is acknowledged for its financial support through the ANR grant N° ANR-13-ASTR-0007.
Current Mode Full-Wave Rectifier Based on a Single MZC-CDTA
Neeta Pandey
2013-01-01
Full Text Available This paper presents a current mode full-wave rectifier based on single modified Z copy current difference transconductance amplifier (MZC-CDTA and two switches. The circuit is simple and is suitable for IC implementation. The functionality of the circuit is verified with SPICE simulation using 0.35 μm TSMC CMOS technology parameters.
Near-surface current meter array measurements of internal gravity waves
Jones, H.B.E. [Lawrence Livermore National Lab., CA (United States)
1994-11-15
We have developed various processing algorithms used to estimate the wave forms produced by hydrodynamic Internal Waves. Furthermore, the estimated Internal Waves are used to calculate the Modulation Transfer Function (MTF) which relates the current and strain rate subsurface fields to surface scattering phenomenon imaged by radar. Following a brief discussion of LLNL`s measurement platform (a 10 sensor current meter array) we described the generation of representative current and strain rate space-time images from measured or simulated data. Then, we present how our simulation capability highlighted limitations in estimating strain rate. These limitations spurred the application of beamforming techniques to enhance our estimates, albeit at the expense of collapsing our space-time images to 1-D estimates. Finally, we discuss progress with regard to processing the current meter array data captured during the recent Loch Linnhe field trials.
A Bingham-Plastic Model for Fluid Mud Transport Under Waves and Currents
刘春嵘; 吴博; 呼和敖德
2014-01-01
Simplified equations of fluid mud motion, which is described as Bingham-Plastic model under waves and currents, are presented by order analysis. The simplified equations are non-linear ordinary differential equations which are solved by hybrid numerical-analytical technique. As the computational cost is very low, the effects of wave current parameters and fluid mud properties on the transportation velocity of the fluid mud are studied systematically. It is found that the fluid mud can move toward one direction even if the shear stress acting on the fluid mud bed is much smaller than the fluid mud yield stress under the condition of wave and current coexistence. Experiments of the fluid mud motion under current with fluctuation water surface are carried out. The fluid mud transportation velocity predicted by the presented mathematical model can roughly match that measured in experiments.
Wave-induced stress and estimation of its driven effect on currents
SUN Fu; GAO Shan; WANG Wei; QIAN Chengchun
2004-01-01
A genuine geostrophic small amplitude wave solution is deduced for the first time from the general form of linear fluid dynamic equations with the f-plane approximation, where the horizontal component of angular velocity of the earth rotation is taken into account. The Coriolisinduced stress obtained from this solution consists of lateral and reverse component, while its first order approximation is reduced to the result of Hasselmann or Xu Zhigang. Accordingly,combining the Coriolis-induced wave stress with the virtual wave stress proposed by Longuet-Higgins, the ratio of total wave-induced stress to wind stress on the sea surface is estimated, through which the importance of the wave-induced stress is emphasized in the study of the currents in the seas around China, especially in the Bohai Sea and the Yellow Sea.
Second-Order Resonant Interaction of Ring Current Protons with Whistler-Mode Waves
XIAO Fu-Liang; CHEN Liang-Xu; HE Hui-Yong; ZHOU Qing-Hua
2008-01-01
We present a study on the second-order resonant interaction between the ring current protons with Whistler-mode waves propagating near the quasi electrostatic limit following the previous second-order resonant theory.The diffusion coefficients are proportional to the electric field amplitude E,much greater than those for the regular first-order resonance.which are proportional to the electric field amplitudes square E2.Numerical calculations for the pitch angle scattering are performed for typical energies of protons Ek=50ke V and 100ke V at locations L=2 and L=3.5.The timescale for the loss process of protons by the Whistler waves is found to approach one hour,comparable to that by the EMIC waves,suggesting that Whistler waves may also contribute significantly to the ring current decay under appropriate conditions.
Theory of travelling wave antenna for ICRH and fast wave current drive in tokamaks
Vdovin, V.L. [NFI RNC Kurchatov Institute, Moscow (Russian Federation)
1993-12-31
Tokamaks` FWCD antennae require many loops with significant difficulties of location of large coaxes in a region of first wall and their matching with a generator due to mutual coupling between loops (LMC) (mainly through the plasma). It is natural to convert LMC from a defect into advantage by feeding a periodical structure at the edge loop creating the travelling wave. In this work we will give the self consistent theory of poloidal loop antennae with a Faraday screen (FS) loaded at the edges by lumped capacitances. (author) 2 refs.
Wave-current interactions in the southern North Sea: The impact on salinity
Schloen, Julia; Stanev, Emil V.; Grashorn, Sebastian
2017-03-01
The interplay between wind waves and currents in the coastal zone of the southern North Sea along with the resulting changes in the salinity distribution are quantified using simulations with the unstructured-grid ocean model SCHISM coupled with the wind wave model WWM III. Several sensitivity runs, which are carried out to estimate the individual contributions of different physical mechanisms and forcing, demonstrated that the density gradients in the coastal zone reduce tidal current by 18%, whereas the wind waves enhance the circulation in some cases. The latter happens when along-shore wind speed approaches ∼10 m s-1 resulting in long-shore currents following the western Dutch coast and the German Wadden Sea islands. The wave-induced transport of salt leads to changes in the horizontal salinity distribution. These are most pronounced in front of barrier islands where coherent patterns caused by the coupling between tides, surface drift, and wind waves reveal salinity changes up to 0.5. The weak stratification of salinity in the coastal zone is mostly destroyed by wind waves. Thus, effects created by wind waves tend to substantially modify the estuarine circulation. An explanation of these important processes in the coastal zone has been given based on an analysis of the ratio between significant wave height and tidal range. This control-parameter, which is relatively small under mild weather conditions, can exceed unity under strong wind conditions in the coastal zone, thus mixing due to waves becomes dominant. The effect of fresh water fluxes from subterranean estuaries is relatively small and confined only in the vicinity of corresponding sources.
Efficient non-hydrostatic modelling of 3D wave-induced currents using a subgrid approach
Rijnsdorp, Dirk P.; Smit, Pieter B.; Zijlema, Marcel; Reniers, Ad J. H. M.
2017-08-01
Wave-induced currents are an ubiquitous feature in coastal waters that can spread material over the surf zone and the inner shelf. These currents are typically under resolved in non-hydrostatic wave-flow models due to computational constraints. Specifically, the low vertical resolutions adequate to describe the wave dynamics - and required to feasibly compute at the scales of a field site - are too coarse to account for the relevant details of the three-dimensional (3D) flow field. To describe the relevant dynamics of both wave and currents, while retaining a model framework that can be applied at field scales, we propose a two grid approach to solve the governing equations. With this approach, the vertical accelerations and non-hydrostatic pressures are resolved on a relatively coarse vertical grid (which is sufficient to accurately resolve the wave dynamics), whereas the horizontal velocities and turbulent stresses are resolved on a much finer subgrid (of which the resolution is dictated by the vertical scale of the mean flows). This approach ensures that the discrete pressure Poisson equation - the solution of which dominates the computational effort - is evaluated on the coarse grid scale, thereby greatly improving efficiency, while providing a fine vertical resolution to resolve the vertical variation of the mean flow. This work presents the general methodology, and discusses the numerical implementation in the SWASH wave-flow model. Model predictions are compared with observations of three flume experiments to demonstrate that the subgrid approach captures both the nearshore evolution of the waves, and the wave-induced flows like the undertow profile and longshore current. The accuracy of the subgrid predictions is comparable to fully resolved 3D simulations - but at much reduced computational costs. The findings of this work thereby demonstrate that the subgrid approach has the potential to make 3D non-hydrostatic simulations feasible at the scale of a
Stability of steady rotational water-waves of finite amplitude on arbitrary shear currents
Seez, William; Abid, Malek; Kharif, Christian
2016-04-01
A versatile solver for the two-dimensional Euler equations with an unknown free-surface has been developed. This code offers the possibility to calculate two-dimensional, steady rotational water-waves of finite amplitude on an arbitrary shear current. Written in PYTHON the code incorporates both pseudo-spectral and finite-difference methods in the discretisation of the equations and thus allows the user to capture waves with large steepnesses. As such it has been possible to establish that, in a counter-flowing situation, the existence of wave solutions is not guaranteed and depends on a pair of parameters representing mass flux and vorticity. This result was predicted, for linear solutions, by Constantin. Furthermore, experimental comparisons, both with and without vorticity, have proven the precision of this code. Finally, waves propagating on top of highly realistic shear currents (exponential profiles under the surface) have been calculated following current profiles such as those used by Nwogu. In addition, a stability analysis routine has been developed to study the stability regimes of base waves calculated with the two-dimensional code. This linear stability analysis is based on three dimensional perturbations of the steady situation which lead to a generalised eigenvalue problem. Common instabilities of the first and second class have been detected, while a third class of wave-instability appears due to the presence of strong vorticity. {1} Adrian Constantin and Walter Strauss. {Exact steady periodic water waves with vorticity}. Communications on Pure and Applied Mathematics, 57(4):481-527, April 2004. Okey G. Nwogu. {Interaction of finite-amplitude waves with vertically sheared current fields}. Journal of Fluid Mechanics, 627:179, May 2009.
Offshore Measurement System for Wave Power—Using Current Loop Feedback
Liselotte Ulvgård; Tobias Kamf; Mats Leijon
2016-01-01
This paper presents the design and testing of a measurement system for wave power generators. The work is part of a project to build a robust and cheap measurement system for offshore monitoring of wave power farms. Due to the harsh offshore environment, low accessibility and high cost for installation and maintenance, it is of key importance to minimize power consumption, complexity and cost of each measurement unit. For the first prototype, the objective was to measure voltage, current and ...
Nonlinear Resonant Excitation of Fast Sausage Waves in Current-Carrying Coronal Loops
Mikhalyaev, B. B.; Bembitov, D. B.
2014-11-01
We consider a model of a coronal loop that is a cylindrical magnetic tube with two surface electric currents. Its principal sausage mode has no cut-off in the long-wavelength limit. For typical coronal conditions, the period of the mode is between one and a few minutes. The sausage mode of flaring loops could cause long-period pulsations observed in microwave and hard X-ray ranges. There are other examples of coronal oscillations: long-period pulsations of active-region quiet loops in the soft X-ray emission are observed. We assume that these can also be caused by sausage waves. The question arises of how the sausage waves are generated in quiet loops. We assume that they can be generated by torsional oscillations. This process can be described in the framework of the nonlinear three-wave interaction formalism. The periods of interacting torsional waves are similar to the periods of torsional oscillations observed in the solar atmosphere. The timescale of the sausage-wave excitation is not much longer than the periods of interacting waves, so that the sausage wave is excited before torsional waves are damped.
Analysis of a cylindrical-rectangular microstrip structure with an airgap
Wong, Kin-Lu; Cheng, Yuan-Tung; Row, Jeen-Sheen
1994-06-01
The resonance problem of the cylindrical-rectangular microstrip structure with an airgap between the substrate layer and the ground conducting cylinder is studied by using a rigorous full-wave approach and a moment method calculation.
Yamaguchi, T; Nakamura, K; Yamaguchi, S; Hasegawa, Y
2002-01-01
Experiments of Peltier current lead (PCL) were performed by the way of half-wave-rectified current (HWRC) for an evaluation of the PCL system in the drive with the large-rippled current. The current ripple of the HWRC is large, and we discussed the cooling capability of the current ripple. The experimental results revealed that the temperature difference of the thermoelectric-element (TE) increased with the magnitude of the current in the PCL system, despite the large current ripple. Calorimetric measurements revealed that the PCL reduced the heat leak of 60% for the peak current 90A. We compared the PCL systems of the direct current (dc) mode and the HWRC mode. The results showed that the current dependence of the temperature difference in the HWRC mode did not match that of the dc mode, but those of the heat leak matched well. The performance of the Peltier cooling in the HWRC mode is reduced to be 2/pi time of the Seebeck coefficient for the dc mode by using the time-average method. (author)
Yamaguchi, Takayuki; Ohtaki, Naohiro; Nakamura, Keiji; Yamaguchi, Satarou [Chubu Univ., Kasugai, Aichi (Japan); Hasegawa, Yasuhiro [Saitama Univ., Saitama (Japan)
2002-09-01
Experiments of Peltier current lead (PCL) were performed by the way of half-wave-rectified current (HWRC) for an evaluation of the PCL system in the drive with the large-rippled current. The current ripple of the HWRC is large, and we discussed the cooling capability of the current ripple. The experimental results revealed that the temperature difference of the thermoelectric-element (TE) increased with the magnitude of the current in the PCL system, despite the large current ripple. Calorimetric measurements revealed that the PCL reduced the heat leak of 60% for the peak current 90A. We compared the PCL systems of the direct current (dc) mode and the HWRC mode. The results showed that the current dependence of the temperature difference in the HWRC mode did not match that of the dc mode, but those of the heat leak matched well. The performance of the Peltier cooling in the HWRC mode is reduced to be 2/{pi} time of the Seebeck coefficient for the dc mode by using the time-average method. (author)
High efficiency off-axis current drive by high frequency fast waves
Prater, R.; Pinsker, R. I.; Moeller, C. P.; Porkolab, M.; Vdovin, V.
2014-02-01
Modeling work shows that current drive can be done off-axis with high efficiency, as required for FNSF and DEMO, by using very high harmonic fast waves ("helicons" or "whistlers"). The modeling indicates that plasmas with high electron beta are needed in order for the current drive to take place off-axis, making DIII-D a highly suitable test vehicle for this process. The calculations show that the driven current is not very sensitive to the launched value of n∥, a result that can be understood from examination of the evolution of n∥ as the waves propagate in the plasma. Because of this insensitivity, relatively large values (˜3) of n∥ can be launched, thereby avoiding some of the problems with mode conversion in the boundary found in some previous experiments. Use of a traveling wave antenna provides a very narrow n∥ spectrum, which also helps avoid mode conversion.
Analysis of errors induced by λ/4 wave plate in fiber-optic current sensor system
杨瑞峰
2008-01-01
1/4λ wave plate is a key element in the fiber-optic current sensor system. When a retardation error or an orientation error of birefringence axes of 1/4λ wave plate with respect to the hi-bi fiber axes occurs in the 1/4λ wave plate, the sensor system will output a wrong result of the measured current. The contributions of these two errors to the final result of the whole system were studied and the errors functions were deduced by establishing the measurement function of the current sensor system with Jones matrixes of the optical elements. The results show that that the greater the orientation error or the retardation error, the larger the final error, and that these two errors cannot be compensated each other.
Damping of an ion acoustic surface wave due to surface currents
Lee, H J
1999-01-01
The well-known linear dispersion relation for an ion acoustic surface wave has been obtained by including the linear surface current density J sub z parallel to the interface and by neglecting the linear surface current density J sub x perpendicular to the interface. The neglect of J sub x is questionable although it leads to the popular boundary condition that the tangential electric field is continuous. In this work, linear dispersion relation for an ion acoustic surface wave is worked out by including both components of the linear current density J . When that is done, the ion acoustic wave turns out to be heavily damped. If the electron mass is taken to be zero (electrons are Bolzmann-distributed), the perpendicular component of the surface current density vanishes, and we have the well-known ion acoustic surface wave eigenmode. We conclude that an ion acoustic surface wave propagates as an eigenmode only when its phase velocity is much smaller than the electron thermal velocity.
THREE-DIMENSIONAL NUMERICAL MODELLING OF THE WAVE-INDUCED RIP CURRENTS UNDER IRREGULAR BATHYMETRY
XIE Ming-xiao
2012-01-01
A process-based 3-D hydrodynamic model is established to simulate the rip current structures under irregular bathymetty.The depth-varying wave-induced residual momentum,the surface rollers,the turbulent mixing and the wave-current interactions are considered.Experimental datasets are used to validate the model,and it is shown that the model can effectively describe the 3-D structures of the rip currents in both normal and oblique wave incident cases.The flow patterns of the rip currents see various characteristics for different incident wave directions.In the normal incident case,pairs of counter-rotating primary circulation cells are formed,and an offshore rip flow occurs in the embayment troughs.The peak seaward velocities occur at the top of the bed boundary layer,and the undertow is incorporated in addition to the rip currents.In the oblique incident case,the longshore currents are dominant,which result in a meandering flow along the depth contour,and the undertow is weaker compared to that in the normal incident condition.
A High-Resolution, Wave and Current Resource Assessment of Japan: The Web GIS Dataset
Webb, Adrean; Fujimoto, Wataru; Horiuchi, Kazutoshi; Kiyomatsu, Keiji; Matsuda, Kazuhiro; Miyazawa, Yasumasa; Varlamov, Sergey; Yoshikawa, Jun
2016-01-01
The University of Tokyo and JAMSTEC have conducted state-of-the-art wave and current resource assessments to assist with generator site identification and construction in Japan. These assessments are publicly-available and accessible via a web GIS service designed by WebBrain that utilizes TDS and GeoServer software with Leaflet libraries. The web GIS dataset contains statistical analyses of wave power, ocean and tidal current power, ocean temperature power, and other basic physical variables. The data (2D maps, time charts, depth profiles, etc.) is accessed through interactive browser sessions and downloadable files.
Experimental study on bed-load sediment transport under irregular wave and current combined flow
无
2001-01-01
Using an irregularly oscillating tray and flume, a series of experiments are completed to evaluate bed-load sediment transport rate under irregular wave- current coexistent fild. Testing conditions include three interaction angles 0°, 45°, 90° and two kinds of median sizes (0.38 and 1.10 mm).The results of transport rate show that the net sediment transport rate can be expressed approximately as the function of the maximum bottom shear stress of waves, mean shear stress of current and the grain size.
New Squarer Circuits and a Current-Mode Full-Wave Rectifier Topology Suitable for Integration
S. Minaei
2010-12-01
Full Text Available In this paper, three squarer configurations and a current-mode (CM full-wave rectifier circuit are suggested. The first and second squarer configurations respectively use two PMOS and two NMOS transistors while the third one employs three PMOS and one NMOS transistors. A CM full-wave rectifier with high output impedance current is developed. All of the proposed circuits provide several advantages such as low number of components and less power consumption. The proposed circuits are simulated using SPICE program to demonstrate their performance and workability.
Are Ring Current Ions Lost in Electromagnetic Ion Cyclotron Wave Dispersion Relation?
Khazanov, G. V.; Gamayunov, K. V.
2006-01-01
Electromagnetic ion cyclotron (EMIC) waves are widely observed in the inner and outer magnetosphere, at geostationary orbit, at high latitudes along the plasmapause, and at the ionospheric altitudes. Interaction of the Ring Current (RC) ions and EMIC waves causes ion scattering into the loss cone and leads to decay of the RC, especially during the main phase of storms when the RC decay times of about one hour or less are observed. The oblique EMIC waves damp due to Landau resonance with the thermal plasmaspheric electrons, and subsequent transport of the dissipating wave energy into the ionosphere below causes an ionosphere temperature enhancement. Induced scattering of these waves by the plasmaspheric thermal ions leads to ion temperature enhancement, and forms a so-called hot zone near the plasmapause where the temperature of core plasma ions can reach tens of thousands of degrees. Relativistic electrons in the outer radiation belt also interact well with the EMIC waves, and during the main and/or recovery phases of the storms these electrons can easily be scattered into the loss cone over a time scale from several hours to a day. The plasma density distribution in the magnetosphere and the ion content play a critical role in EMIC wave generation and propagation, but the wave dispersion relation in the known RC-EMIC wave interaction models is assumed to be determined by the thermal plasma distribution only. In these models, the modification of the EMIC wave dispersion relation caused by the RC ions is not taken into account, and the RC ions are only treated as a source of free energy in order to generate EMIC waves. At the same time, the RC ions can dominate the thermal magnetospheric content in the night MLT sector at great L shells during the main and/or recovery storm phase. In this study, using our self-consistent RC-EMIC wave model [Khazanov et al., 2006], we simulate the May 1998 storm in order to quantify the global EMIC wave redistribution caused by
Effect of Ring Current Ions on Electromagnetic Ion Cyclotron Wave Dispersion Relation
Gamayunov, K. V.; Khazanov, G. V.
2006-01-01
Electromagnetic ion cyclotron (EMIC) waves are widely observed in the inner and outer magnetosphere, at geostationary orbit, at high latitudes along the plasmapause, and at the ionospheric altitudes. Interaction of the Ring Current (RC) ions and EMIC waves causes ion scattering into the loss cone and leads to decay of the RC, especially during the main phase of storms when the RC decay times of about one hour or less are observed. The oblique EMIC waves damp due to Landau resonance with the thermal plasmaspheric electrons, and subsequent transport of the dissipating wave energy into the ionosphere below causes an ionosphere temperature enhancement. Induced scattering of these waves by the plasmaspheric thermal ions leads to ion temperature enhancement, and forms a so-called hot zone near the plasmapause where the temperature of core plasma ions can reach tens of thousands of degrees. Relativistic electrons in the outer radiation belt also interact well with the EMIC waves, and during the main and/or recovery phases of the storms these electrons can easily be scattered into the loss cone over a time scale from several hours to a day. The plasma density distribution in the magnetosphere and the ion content play a critical role in EMIC wave generation and propagation, but the wave dispersion relation in the known RC-EMIC wave interaction models is assumed to be determined by the thermal plasma distribution only. In these models, the modification of the EMIC wave dispersion relation caused by the RC ions is not taken into account, and the RC ions are only treated as a source of free energy in order to generate EMIC waves. At the same time, the RC ions can dominate the thermal magnetospheric content in the night MLT sector at great L shells during the main and/or recovery storm phase. In this study, using our self-consistent RC-EMIC wave model [Khazanov et al., 2006], we simulate the May 1998 storm in order to quantify the global EMIC wave redistribution caused by
Hu Huang; Jia Fu
2006-01-01
A fully three-dimensional surface gravitycapillary short-crested wave system is studied as two progressive wave-trains of equal amplitude and frequency, which are collinear with uniform currents and doubly-periodic in the horizontal plane, are propagating at an angle to each other. The first-and second-order asymptotic analytical solutions of the short-crested wave system are obtained via a perturbation expansion in a small parameter associated with the wave steepness, therefore depicting a series of typical three-dimensional wave patterns involving currents, shallow and deep water, and surface capillary waves, and comparing them with each other.
Secondary current properties generated by wind-induced water waves in experimental conditions
Michio Sanjou
2014-06-01
Full Text Available Secondary currents such as the Langmuir circulation are of high interest in natural rivers and the ocean because they have striking impacts on scour, sedimentation, and mass transport. Basic characteristics have been well-studied in straight open-channel flows. However, little is known regarding secondary circulation induced by wind waves. The presented study describes the generation properties of wind waves observed in the laboratory tank. Wind-induced water waves are known to produce large scale circulations. The phenomenon is observed together with high-speed and low-speed streaks, convergence and divergence zones, respectively. Therefore, it is important to determine the hydrodynamic properties of secondary currents for wind-induced water waves within rivers and lakes. In this study, using two high-speed CMOS cameras, stereoscopic particle image velocimetry (PIV measurements were conducted in order to reveal the distribution of all three components of velocity vectors. The experiments allowed us to investigate the three-dimensional turbulent structure under water waves and the generation mechanism of large-scale circulations. Additionally, a third CMOS camera was used to measure the spanwise profile of thefree-surface elevation. The time-series of velocity components and the free-surface were obtained simultaneously. From our experiments, free-surface variations were found to influence the instantaneous velocity distributions of the cross-sectional plane. We also considered thegeneration process by the phase analysis related to gravity waves and compared the contribution of the apparent stress.
Laser-driven Beat-Wave Current Drive in Dense Plasmas with Demo on CTIX
Liu, Fei; Horton, Robert; Hwang, David; Zhu, Ben; Evans, Russell; Hong, Sean; Hsu, Scott
2010-11-01
The ability to remotely generate plasma current in dense plasmas hanging freely in vacuum in voluminous amount without obstruction to diagnostics will greatly enhance our ability to study the physics of high energy density plasmas in strong magnetic fields. Plasma current can be generated through nonlinear beat-wave process by launching two intense electromagnetic waves into unmagnetized plasma. Beat-wave acceleration of electrons has been demonstrated in a low-density plasma using microwaves [1]. The proposed PLX experimental facility presently under construction at Los Alamos offers the opportunity to test the method at a density level scalable to the study of HED plasmas. For PLX beat-wave experiments, CO2 lasers will be used as pump waves due to their high power and tunability. For a typical PLX density ne=10^17cm-3, two CO2 lasers can be separately tuned to 9P(28) and 10P(20) to match the 2.84THz plasma frequency. The beat-wave demo experiment will be conducted on CTIX. The laser arrangement is being converted to two independent single lasers. Frequency-tuning methods, optics focusing system and diagnostics system will be discussed. The laser measurements and results of synchronization of two lasers will be presented, and scaling to PLX experiments will be given. [1] Rogers, J. H. and Hwang, D. Q., PRL. v68 p3877 (1992).
Energy transfer between energetic ring current H(+) and O(+) by electromagnetic ion cyclotron waves
Thorne, Richard M.; Horne, Richard B.
1994-01-01
Electromagnetic ion cyclotron (EMIC) waves in the frequency range below the helium gyrofrequency can be excited in the equatorial region of the outer magnetosphere by cyclotron resonant instability with anisotropic ring current H(+) ions. As the unducted waves propagate to higher latitudes, the wave normal should become highly inclined to the ambient magnetic field. Under such conditions, wave energy can be absorbed by cyclotron resonant interactions with ambient O(+), leading to ion heating perpendicular to the ambient magnetic field. Resonant wave absorption peaks in the vicinity of the bi-ion frequency and the second harmonic of the O(+) gyrofrequrency. This absorption should mainly occur at latitudes between 10 deg and 30 deg along auroral field lines (L is greater than or equal to 7) in the postnoon sector. The concomitant ion heating perpendicular to the ambient magnetic field can contribute to the isotropization and geomagnetic trapping of collapsed O(+) ion conics (or beams) that originate from a low-altitude ionospheric source region. During geomagnetic storms when the O(+) content of the magnetosphere is significantly enhanced, the absorption of EMIC waves should become more efficient, and it may contribute to the observed acceleration of O(+) ions of ionospheric origin up to ring current energies.
Chang, C. L.; Lipatov, A. S.; Drobot, A. T.; Papadopoulos, K.; Satya-Narayana, P.
1994-01-01
The dynamic response of a magnetized collisionless plasma to an externally driven, finite size, sudden switch-on current source across the magnetic field has been studied using a two dimensional hybrid code. It was found that the predominant plasma response was the excitation of whistler waves and the formation of current closure by induced currents in the plasma. The results show that the current closure path consists of: (a) two antiparallel field-aligned current channels at the end of the imposed current sheet; and (b) a cross-field current region connecting these channels. The formation of the current closure path occured in the whistler timescale much shorter than that of MHD and the closure region expanded continuously in time. The current closure process was accompanied by significant energy loss due to whistler radiation.
On the Dynamics of Two-Dimensional Capillary-Gravity Solitary Waves with a Linear Shear Current
Dali Guo
2014-01-01
Full Text Available The numerical study of the dynamics of two-dimensional capillary-gravity solitary waves on a linear shear current is presented in this paper. The numerical method is based on the time-dependent conformal mapping. The stability of different kinds of solitary waves is considered. Both depression wave and large amplitude elevation wave are found to be stable, while small amplitude elevation wave is unstable to the small perturbation, and it finally evolves to be a depression wave with tails, which is similar to the irrotational capillary-gravity waves.
Effects of Topography and Current on Horizontal Irrotational Waves in Shallow Water
孙明光; 高虎山
2000-01-01
Based on the Boussinesq assumption, derived are couple equations of free surface elevation and horizontal velocities for horizontal irrotational flow, and analytical expressions of the corresponding pressure and vertical velocity. After the free surface elevation and horizontal velocity at a certain depth are obtained by numerical method, the pressure and vertical velocity distributions can be obtained by simple calculation. The dispersion at different depths is the same at the O (ε) approximation. The wave amplitude will decrease with increasing time due to viscosity, but it will increase due to the matching of viscosity and the bed slope, thus. flow is unstable. Numerical or analytical results show that the wave amplitude, velocity and length will increase as the current increases along the wave direction, but the amplitude will increase, and the wave velocity and length will decrease as the water depth decreases.
Energy extraction from ocean currents and waves: Mapping the most promising locations
Ordonez, A.; Hamlington, P.; Fox-Kemper, B.
2012-12-01
Concerns about fossil fuel supplies and an ever-increasing demand for energy have prompted the search for alternative power sources. One option is the ocean, a power-dense and renewable source of energy, but its capacity to meet human energy demands is poorly understood. Although raw wave energy resources have been investigated at many scales, there is still substantial uncertainty regarding how much useful power can be extracted. Even less is known about the energy available in ocean currents, especially on a global scale. Moreover, no studies have attempted to examine wave and current energy simultaneously while at the same time taking into account geographical, environmental, and technical factors that can substantially limit the amount of extractable energy. In this study, we use high fidelity oceanographic model data to assess the availability, recoverability, and value of energy in ocean wind waves and currents. Global wave energy transport, coastal wave energy flux, and current energy are calculated and mapped using the model data. These maps are then incorporated into a geographic information system (GIS) in order to assess the U.S. recoverable ocean energy resource. In the GIS, the amount of recoverable energy is estimated by combining the power output from realistic wave and current energy farms with physical and ecological data such as bathymetry and environmentally protected areas. This holistic approach is then used to examine the distribution and value of extractable wave and current energy along the U.S. coast. The results support previous studies that show that the U.S. West Coast has large potential for wave energy extraction and that the Florida Strait has high potential for current energy extraction. We also show that, at any particular location, the amount of available ocean energy is only one factor of many that determines the ultimate feasibility and value of the energy. We outline ways in which the GIS framework used in this assessment can be
Dynamics of wave-current-surge interactions in Lake Michigan: A model comparison
Mao, Miaohua; Xia, Meng
2017-02-01
Wave, storm surge dynamics, and wave-current-surge interactions (WCSI) were investigated by applying a pair of unstructured-grid-based models to Lake Michigan under two strong wind events. The effects of wind field sources, wind drag coefficient bulk formula, and parameterizations of the bottom friction term were explored to understand lake dynamics. Two wave models were calibrated by using alternative wave physics settings under the 2011 northeasterly wind event. Forced by the southwesterly wind event in 2013, the calibrated models using the atmosphere-ocean fully coupled Climate Forecast System Version 2 wind field were further validated. It is found that the northwesterly winds induced 0.57 m setup near the southwestern coast, whereas the southwesterly winds produced 0.28 m setup and -0.43 m setdown near the northern and southwestern coasts, respectively. The WCSI mostly influence waves and storm surge in shallow-water areas near coasts and islands through depth-induced breaking, current-induced frequency shift and refraction, and wave-induced setup/setdown through wave radiation stress. Owing to the adoption of different discretization algorithms and bottom friction formulations, the modeled storm surge and waves exhibit some variation between the paired models. Even though the storm surge difference with and without WCSI is smaller than that between the two WCSI-coupled models, both circulation models adopt WCSI considering their consistent improvement on model accuracy under both wind events. The analysis of water transport indicates that wind speed, direction, and coastal geometry and bathymetry are also important factors in storm surge.
ANALYTIC EXPRESSION OF MAGNETIC FIELD DISTRIBUTION OF RECTANGULAR PERMANENT MAGNETS
苟晓凡; 杨勇; 郑晓静
2004-01-01
From the molecular current viewpoint,an analytic expression exactly describing magnetic field distribution of rectangular permanent magnets magnetized sufficiently in one direction was derived from the Biot-Savart's law. This expression is useful not only for the case of one rectangular permanent magnet bulk, but also for that of several rectangular permanent magnet bulks. By using this expression,the relations between magnetic field distribution and the size of rectangular permanent magnets as well as the magnitude of magnetic field and the distance from the point in the space to the top (or bottom) surface of rectangular permanent magnets were discussed in detail. All the calculating results are consistent with experimental ones. For transverse magnetic field which is a main magnetic field of rectangular permanent magnets,in order to describe its distribution,two quantities,one is the uniformity in magnitude and the other is the uniformity in distribution of magnetic field,were defined. Furthermore, the relations between them and the geometric size of the magnet as well as the distance from the surface of permanent magnets were investigated by these formulas. The numerical results show that the geometric size and the distance have a visible influence on the uniformity in magnitude and the uniformity in distribution of the magnetic field.
Evolution of Ring Current Protons Induced by Electromagnetic Ion Cyclotron Waves
XIAO Fu-Liang; TIAN Tian; CHEN Liang-Xu; SU Zhen-Peng; ZHENG Hui-Nan
2009-01-01
We investigate the evolution of the phase space density (PSD) of ring current protons induced by electromagnetic ion cyclotron (EMIC) waves at the location L=3.5, calculate the diffusion coefficients in pitch angle and momentum, and solve the standard two-dimensional Fokker-Planck diffusion equation. The pitch angle diffusion coefficient is found to be larger than the momentum diffusion coefficient by a factor of about 10~3 or above at lower pitch angles. We show that EMIC waves can produce efficient pitch angle scattering of energetic (～100 keV) protons, yielding a rapid decrement in PSD, typically by a factor of ～10 within a few hours, consistent with observational data. This result further supports previous findings that wave-particle interaction is responsible for the rapid ring current decay.
Abderraouf Messai
2013-01-01
Full Text Available A rigorous full-wave analysis of high Tc superconducting rectangular microstrip patch over ground plane with rectangular aperture in the case where the patch is printed on a uniaxially anisotropic substrate material is presented. The dyadic Green’s functions of the considered structure are efficiently determined in the vector Fourier transform domain. The effect of the superconductivity of the patch is taken into account using the concept of the complex resistive boundary condition. The accuracy of the analysis is tested by comparing the computed results with measurements and previously published data for several anisotropic substrate materials. Numerical results showing variation of the resonant frequency and the quality factor of the superconducting antenna with regard to operating temperature are given. Finally, the effects of uniaxial anisotropy in the substrate on the resonant frequencies of different TM modes of the superconducting microstrip antenna with rectangular aperture in the ground plane are presented.
Offshore Measurement System for Wave Power—Using Current Loop Feedback
Liselotte Ulvgård
2016-12-01
Full Text Available This paper presents the design and testing of a measurement system for wave power generators. The work is part of a project to build a robust and cheap measurement system for offshore monitoring of wave power farms. Due to the harsh offshore environment, low accessibility and high cost for installation and maintenance, it is of key importance to minimize power consumption, complexity and cost of each measurement unit. For the first prototype, the objective was to measure voltage, current and translator position inside the linear wave power generator. For this, two printed circuit boards (PCBs were developed, using a two wire current loop transmitter setup. They were tested separately and in a three phase setup inside a wave power generator during onshore tests. To ensure stability, speed and accuracy in the signal transfer, the PCBs were tested for linearity, frequency response and step response. In addition, power consumption was measured, for operational time evaluation. Results show good agreement between expected and measured performance, with an input range of ±1560 V and ±420 A for alternating current measurements and a bandwidth of 10 kHz and 7 kHz, for voltage and current measurements, respectively. The power consumption was measured to 0.5 W for each measurement unit, at 24 V feed.
Varga, Edina T; Terney, Daniella; Atkins, Mary D
2011-01-01
Cathodal transcranial direct current stimulation (tDCS) decreases cortical excitability. The purpose of the study was to investigate whether cathodal tDCS could interrupt the continuous epileptiform activity. Five patients with focal, refractory continuous spikes and waves during slow sleep were ...
Lower Hybrid Wave Current Drive Efficiency on the HT-7 Tokamak
CHEN Zhong-Yong; WAN Bao-Nian; SHI Yue-Jiang; HU Li-Qun; XU Han-Dong; LI Guo-Chao
2005-01-01
@@ Lower hybrid (LH) wave current drive efficiency on our HT-7 tokamak has been investigated based on the hot electrical conductivity theory.The interaction of the residual toroidal electric field with fast electrons has been included in the determination of current drive efficiency.The LH wave power scan was performed in the plasma parameter ranges of Ip = 50-156kA, (n)e = 0.5 × 1019-1.6 × 1019 m-3, PLH = 50-350kW.The current drive efficiency is derived to be about 0.1 × 1019-0.4 × 1019 Am-2W-1 on the HT-7 tokamak, which depends on the electron density and the LH wave phase velocity.At the electron density of about 1.5 × 1019 m-3, with the LH wave parallel refraction index peaked at 1.8, the highest current drive efficiency was obtained.A more generally normalized method is introduced to analyse the experimental data, which combines all the data in one curve.The normalized parameters are independent of the plasma parameters.
Diffuser Design For Marine Outfalls in Areas With Strong Currents, High Waves and Sediment Transport
Larsen, Torben
1995-01-01
of this uncompromising accept of environmental demands. Two examples of unconventional design are given in the paper. Both cases involved risk of blockage of the diffuser section because of wave and current induced sediment transport. The paper also discusses how acceptable far field dilution conditions can be achieved...
Fast wave current drive modeling using the combined RANT3D and PICES Codes
Jaeger, E.F.; Murakami, M.; Stallings, D.C.; Carter, M.D.; Wang, C.Y.; Galambos, J.D.; Batchelor, D.B.; Baity, F.W.; Bell, G.L.; Wilgen, J.B. [Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-8071 (United States); Chiu, S.C.; DeGrassie, J.S.; Forest, C.B. [General Atomics, San Diego, California 92186-9784 (United States); Kupfer, K. [ORISE Postdoctoral Fellow at General Atomics, San Diego, California 92186-9784 (United States); Petty, C.C.; Pinsker, R.T.; Prater, R.; Lohr, J. [General Atomics, San Diego, California 92186-9784 (United States); Lee, K.M. [University of California, Los Angeles, California 90024-1597 (United States)
1996-02-01
Two numerical codes are combined to give a theoretical estimate of the current drive and direct electron heating by fast waves launched from phased antenna arrays on the DIII-D tokamak. Results are compared with experiment. {copyright} {ital 1996 American Institute of Physics.}
A New International Standard for "Actions from Waves and Currents on Coastal Structures"
Tørum, Alf; Burcharth, Hans F.; Goda, Yoshimi
2007-01-01
The International Organization for Standardization (ISO) is going to issue a new standard concerning "Actions from Waves and Currents on Coastal Structures," which becomes the first international standard in coastal engineering. It is composed of a normative part (29 pages), an informative part (80...... standard on coastal engineering practice....
Filamentation instability of current-driven dust ion-acoustic waves in a collisional dusty plasma
Niknam, A. R. [Laser and Plasma Research Institute, Shahid Beheshti University, G.C., Tehran 19839-63113 (Iran, Islamic Republic of); Haghtalab, T.; Khorashadizadeh, S. M. [Physics Department, Birjand University, Birjand 97179-63384 (Iran, Islamic Republic of)
2011-11-15
A theoretical investigation has been made of the dust ion-acoustic filamentation instability in an unmagnetized current-driven dusty plasma by using the Lorentz transformation formulas. The effect of collision between the charged particles with neutrals and their thermal motion on this instability is considered. Developing the filamentation instability of the current-driven dust ion-acoustic wave allows us to determine the period and the establishment time of the filamentation structure and threshold for instability development.
Charge and spin currents in normal metal sandwiched by tow p-wave
Y Rahnavard
2010-09-01
Full Text Available Charge and spin transport properties of a clean $SNS$ Josephson junction (triplet superconductor-normal metal-triplet superconductor are studied using the quasiclassical Eilenberger equation of Green’s function. Our system consists of two p-wave superconducting crystals separated by a Copper nano layer. Effects of thickness of normal layer between superconductors on the spin and charge currents are investigated. Also misorientation between triplet superconductors which creates the spin current is another subject of this paper.
An Analytical Model of Wave-Induced Longshore Current Based on Power Law Wave Height Decay.
1988-01-01
the notation (0, v) is used to denote the x and y-components of tne steady current. The arrows indicate vector quantlties. me absolute value c - the...8217n - ’ ,F4.2,2X, ’P =’ ,FLS.2,2X, ’Brea~ing wiav e’,*. A-N2-1 .0 -HETAP-3A14159*THETA/180.0 3>NT32-(S:N(THETAR))**2 BETA1) -1 .0 DELTA(1) =1.0 SUMA ...LT1.1.0)FACN2.0 A(II)-A(II)*SINT32 *#7 SINT32*A(I::-l BETA(II).SINTB2*BETA I: -I SUMA -SU;MA+A(I SUXB=S’UMB+BETA ) SUC=SUMC+DELTA(rI SNMA=-sNMA<’N+Z) A (I
Modelling of a non-buoyant vertical jet in waves and currents
徐振山; 陈永平; 陶建峰; 潘毅; 张长宽; 李志伟
2016-01-01
A generic numerical model using the large eddy simulation (LES) technique is developed to simulate a non-buoyant vertical jet in wave and/or current environments. The experimental data obtained in five different cases, i.e., one case of the jet in a wave only environment, two cases of the jet in a cross-flow only environment and two cases of the jet in a wave and cross-flow coexisting environment, are used to validate the model. The grid sensitivity tests are conducted based on four different grid systems and the results illustrate that the non-uniform grid system C (205×99×126 nodes with the minimum size of 1/10 jet diameter) is sufficiently fine for the modelling. The comparative study shows that the wave-current non-linear interaction should be taken into account at the inflow boundary while modelling the jet in wave and cross-flow coexisting environments. All numerical results agree well with the experimental data, showing that: (1) the jet under the influence of the wave action has a faster centerline velocity decay and a higher turbulence level than that in the stagnant ambience, meanwhile the “twin peaks” phenomenon exists on the cross-sectional velocity profiles, (2) the jet under a cross-flow scenario is deflected along the cross-flow with the node in the downstream, (3) the jet in wave and cross-flow coexisting environments has a flow structure of “effluent clouds”, which enhances the mixing of the jet with surrounding waters.
L Haibin; XIE Jieshuo; YAO Yuan; XU Jiexin; CHEN Zhiwu; HE Yinghui; CAI Shuqun
2016-01-01
Based on modifications of the observed background parabolic current in upper layer of the northeastern South China Sea (SCS), the effects of eight kinds of background currents on the characteristics and energy conversion of internal solitary waves (ISWs) are investigated by an Internal Gravity Wave (IGW) model. It is found that, although the background current has little effect on the number of the generated ISWs, it reduces the resulted phase speed of ISW. When the background parabolic current appears with its lower boundary near or above the main thermocline, the ISW amplitude and the depth of the isopycnal undergoing maximum displacement increase;when the background parabolic current curvature is reduced, the ISW amplitude and the ratio of baroclinic to barotropic energy reduce, whilst the phase speed of ISW, the baroclinic energy, and the ratio of baroclinic kinetic energy (KE) to available potential energy (APE) increase; when the lower boundary of background parabolic current extends down to the seabed and the background current curvature is reduced, the ISW amplitude and phase speed decrease, whilst the barotropic kinetic energy, the baroclinic energy and the ratio of KE to APE increase. At a whole depth, when the lower background current curvature is reduced and the upper current curvature is increased, the ISW amplitude, and phase speed, the ratio of baroclinic to barotropic energy, the baroclinic energy, and the ratio of KE to APE all increase.
Linear analysis of a three-dimensional rectangular Cerenkov maser with a sheet electron beam
Chen Ye; Zhao Ding; Wang Yong
2011-01-01
A linear theory of a rectangular Cerenkov maser (RCM) with a sheet electron beam is developed by using the fieldmatch method.Based on the three-dimensional beam-wave interaction model proposed in this paper,a hybrid-mode dispersion equation and its analytical solution are derived for the RCM.Through numerical calculations,the effects of the beam-grating gap,beam thickness,current density,beam voltage and waveguide width on the linear growth rate are analysed.Moreover,the performance difference between the RCM with the closed transverse boundary and that with the upper open boundary is compared.The results show that the closed RCM model can avoid the effect of RF radiation on beam-wave interaction,which is more rational for practical applications.
Laboratory modelling of resonant wave-current interaction in the vicinity wind farm masts
Gunnoo, Hans; Abcha, Nizar; Garcia-Hermosa, Maria-Isabel; Ezersky, Alexander
2015-04-01
In the nearest future, by 2020, about 4% of electricity in Europe will be supplied by sea stations operating from renewable sources: ocean thermal energy, wave and tidal energy, wind farms. By now the wind stations located in the coastal zone, provide the most part of electricity in different European countries. Meanwhile, effects of wind farms on the environment are not sufficiently studied. We report results of laboratory simulations aimed at investigation of hydrodynamic fields arising in the vicinity of wind farm masts under the action of currents and surface waves. The main attention is paid to modeling the resonance effects when the amplitude of velocity pulsations in the vicinity of the masts under the joint action of currents and harmonic waves demonstrate significant growth. This resonance can lead to an increase in Reynolds stress on the bottom, intensification of sediment transport and sound generation. The experiments are performed in the 17 meters hydrodynamical channel of laboratory Morphodynamique Continentale et Côtière UMR CNRS 6143. Mast are modeled by vertical cylinder placed in a steady flow. Behind the cylinder turbulent Karman vortex street occurs. Results are obtained in interval of Reynolds numbers Re=103 - 104(Re=Ud/v, where U is the velocity of the flow, d is diameter of the cylinder, ν is cinematic viscosity). Harmonic surface waves of small amplitude propagating upstream are excited by computer controlled wave maker. In the absence of surface waves, turbulent Karman street with averaged frequency f is observed. It is revealed experimentally that harmonic surface waves with a frequencies closed to 2f can synchronize vortex shedding and increase the amplitude of velocity fluctuations in the wake of the cylinder. Map of regimes is found on the parameter plane amplitude of the surface wave - wave frequency. In order to distinguish the synchronization regimes, we defined phase of oscillations using the Hilbert transform technique. We
Ren Min; Zhang Lei; Hu Jiu-Ning; Dong Hao; Deng Ning; Chen Pei-Yi
2009-01-01
This paper proposes a symmetry ensemble model for the magnetic dynamics caused by spin transfer torque in nanoscale pseudo-spin-valves, in which individual spin moments in the free layer are considered as subsystems to form a spinor ensemble. The magnetization dynamics equation of the ensemble was developed. By analytically investigating the equation, many magnetization dynamics properties excited by polarized current reported in experiments, such as double spin wave modes and the abrupt frequency jump, can be successfully explained. It is pointed out that an external field is not necessary for spin wave emitting (SWE) and a novel perpendicular configuration structure can provide much higher SWE efficiency in zero magnetic field.
Nosaeva, T. A.; Syrodoev, G. A.
2016-12-01
We study the effect of electron drag in a semiconductor superlattice during intraband absorption of a biharmonic electromagnetic wave in a process accompanied by the emission (absorption) of a phonon. The problem has been solved in the second order of perturbation theory. The effective interaction Hamiltonian method makes it possible to take into account the multiphoton nature of the electromagnetic wave absorption. With increasing field, the current increases and attains a peak value, after which it decreases in an oscillatory manner due to the ionization stabilization effect.
Bottom currents and sediment waves on a shallow carbonate shelf, Northern Carnarvon Basin, Australia
Belde, Johannes; Reuning, Lars; Back, Stefan
2017-04-01
The modern seafloor of the Australian Northwest Shelf between Exmouth and Dampier was analyzed for large scale sedimentary bedforms on 3D seismic reflection data. The Carnarvon MegaSurvey of Petroleum Geo-Services (PGS), a merged dataset of multiple industrial 3D seismic reflection surveys with a total size of 49,717 km2, offers an extensive view of the continental shelf, slope and rise of the Northern Carnarvon Basin. Over the shelf two fields of large scale sediment waves were observed in water depths between 55-130 m, where the seafloor may be influenced by different processes including internal waves, tides and storms. Based on the dimensions and orientations of the sediment waves the dominant direction and approximate strength of local bottom currents could be estimated. Information on local sediment grain-size distribution was provided by the auSEABED database allowing a classification of the observed sediment waves into sand- or mudwaves. The first sediment wave field is positioned northwest of the Montebello Islands where the shelf is comparatively narrow and local sediment is mainly sand-sized. It most likely formed by increased bottom currents induced by the diversion of tidal flows around the islands. The second sediment wave field is located north of the Serrurier and Bessieres Islands within a local seafloor depression. Local sediments are poorly sorted, containing significant amounts of mud and gravel in addition to the mainly sand-sized grains. The coarser sediment fraction could have been reworked to sandwaves by cyclone-induced bottom currents. Alternatively, the finer sediment fraction could form mudwaves shaped by less energetic along-slope oriented currents in the topographic depression. The sediment waves consist partially of carbonate grains such as ooids and peloids that formed in shallow water during initial stages of the post glacial sea-level rise. These stranded carbonate grains thus formed in a different environment than the sediment
Assessment of Current State of Mooring Design in the Danish Wave Energy Sector
Thomsen, Jonas Bjerg; Ferri, Francesco; Kofoed, Jens Peter
2015-01-01
The mooring system is a vital part of any floating wave energy converter, both in terms of ensuring station keeping but also as it constitutes a significant share of the total cost. Motivatedby the considerable amount of failures due to insufficient mooring and the cost of mooring today......, the present study outlines the design procedure recommended by design standards and provides considerations on choice of tools for analysis. This is compared to the procedure used by four wave energy converter developers, to illustrate the state of their current mooring design. The study shows a clear...
Advances in sediment transport under combined action of waves and currents
Yongjun Lu; Shouqian Li; Liqin Zuo; Huaixiang Liu; J.A. Roelvink
2015-01-01
The coastal zone continuously changes due to natural processes and human activities. In order to understand and predict these morphological changes, an accurate description of sediment transport, caused by waves and currents (tidal or wave-induced), is important. This paper presents a review of the state-of-the-art knowledge in this field, including sediment incipient motion, bed forms, bed roughness, bed-load transport, suspended-load transport, equilibrium sediment concentration, and sheet flow. Some possible research fields and topics for future study also are proposed.
EXPERIMENTAL STUDY ON BED-LOAD SEDIMENT TRANSPORT IN IRREGULAR WAVE-CURRENT COEXISTENT FIELD
无
2000-01-01
In order to evaluate bed-load sediment transport in an irregular wave-current coexistent field, a series of experiments were completed in laboratory with an irregularly oscillating tray, which was specially designed to simulate the irregular wave-current coexistent field. Experimental results are presented on the initial motion of sediment and the rates of transport over flat horizontal bed. Testing conditions included three interaction angles, 0°, 45°, 90° and six kinds of grain sizes. Four kinds (0.2mm, 0.46mm, 0.85mm and 1.3mm) were used for the tests of initial motion, while the other two kinds (0.38mm and 1.1mm) for the tests of transport rate. Comparisons between experimental results of initial motion and modified Shields curve indicate that the Shields curve is still valid for the case of irregular wave-current coexistent field. Analysis of flow regime shows that initial conditions fall within smooth-turbulent transitional region. The results of transport rate show us that net sediment transport rate can be expressed approximately as the function of the maximum bottom shear stress and mean shear stress. A dimensionless formula is proposed on the basis of mechanism "Waves erode sediments, tides transport sediments".
An upper ocean current jet and internal waves in a Gulf Stream warm core ring
Joyce, T. M.; Stalcup, M. C.
1984-01-01
On June 22, 1982, the R/V Endeavor, while participating in a multi-ship study of a warm core ring 82B, encountered a strong front in the core of the ring. The vessel was headed on a radial section outward from ring center while a CTD was repeatedly raised and lowered between 10 and 300 m. Current profiles in the upper 100 m were obtained continuously with a Doppler acoustic profiling system. Above the shallow 45 m seasonal thermocline, a current jet of 4 km width was encountered having a central core of relatively light water and a maximum current of 1.1 m/s. This jet was both highly nonlinear and totally unexpected. A high frequency packet of directional internal waves was acoustically observed in the seasonal thermocline at the outer edge of the jet. Vertical velocities were large enough (6 cm/s) as to be directly observable in the Doppler returns. The waves were propagating from the northeast, parallel to the ship track, and orthogonal to the jet toward the center of the warm core ring. While a nonlinear, centrifugal term was required for the force balance of the jet, the high-frequency internal wave packet could be explained with linear, gravest-mode wave dynamics.
Computational Modeling of Submarine Oil Spill with Current and Wave by FLUENT
Wei Li
2013-05-01
Full Text Available As the oil spill models are usually based on the sea surface and few researches are for submarine oil spill nowadays, the simulation for submarine pipeline oil spill is discussed by FLUENT to forecast the trajectory of oil. The coupling of pressure and velocity under unsteady-state condition is solved by pressure implicit with splitting of operator’s algorithm and the boundary condition of nonlinear free surface is solved by volume of fluid. The simulation of oil particles motion is carried out. Furthermore, the quantity and trajectory of spilled oil under different operating pressure, current velocities and wave lengths are compared and analyzed. The results show that wave and current have important effects on the location and oil film area on sea surface. The submarine diffusion scope of spilled oil is smaller with larger operating pressure or lower current velocity. With wave length increasing, the water depth influenced by wave, the scope of oil dispersion underwater and the oil film area on surface increase.
The structure of fast sausage waves in current-carrying coronal loops
Bembitov, D. B.; Mikhalyaev, B. B.; Ruderman, M. S.
2014-09-01
We study fast sausage waves in a model coronal loop that consists of a cylindrical core with axial magnetic field and coaxial annulus with purely azimuthal magnetic field. The magnetic field is discontinuous at the tube and core boundaries, and there are surface currents with the opposite directions on these boundaries. The principal mode of fast sausage waves in which the magnetic pressure perturbation has no nodes in the radial direction can exist for arbitrary wavelength. The results for the fundamental radial mode of sausage waves are applied to the interpretation of observed periodic pulsations of microwave emission in flaring loops with periods of a few tens of seconds. Radial plasma motion has opposite directions at the tube and core boundaries. This leads to the periodic contraction and expansion of the annulus. We assume that the principal mode of fast sausage waves in the current-carrying coronal loops is able to produce a current sheet. However, the nonlinear analysis is needed to confirm this conjecture.
Kodaira, Tsubasa; Waseda, Takuji
2013-04-01
We have conducted ADCP and CTD measurements from 31/8/2010 to 2/9/2010 at the Miyake Island, located approximately 180 km south of Tokyo. The Kuroshio Current approached the island in this period, and the PALSAR image showed parabolic bright line upstream of the island. This bright line may be a surface signature of large amplitude internal solitary wave. Although our measurements did not explicitly show evidence of the internal solitary wave, critical condition might have been satisfied because of the Kuroshio Current and strong seasonal thermocline. To discover the generation mechanism of the large amplitude internal solitary wave at the Miyake Island, we have conducted non-hydrostatic numerical simulation with the MITgcm. A simple box domain, with open boundaries at all sides, is used. The island is simplified to circular cylinder or Gaussian Bell whose radius is 3km at ocean surface level. The size of the domain is 40kmx40kmx500m for circular cylinder cases and 80kmx80kmx500m for Gaussian bell cases. By looking at our CTD data, we have chosen for initial and boundary conditions a tanh function for vertical temperature profile. Salinity was kept constant for simplicity. Vertical density profile is also described by tanh function because we adopt linear type of equation of state. Vertical velocity profile is constant or linearly changed with depth; the vertical mean speed corresponds to the linear phase speed of the first baroclinic mode obtained by solving the eigen-value problem. With these configurations, we have conducted two series of simulations: shear flow through cylinder and uniform flow going through Gaussian Bell topography. Internal solitary waves were generated in front of the cylinder for the first series of simulations with shear flow. The generated internal waves almost purely consisted of 1st baroclinic component. Their intensities were linearly related with upstream vertical shear strength. As the internal solitary wave became larger, its width
Plasma current start-up using the lower hybrid wave on the TST-2 spherical tokamak
Takase, Y.; Ejiri, A.; Inada, T.; Moeller, C. P.; Shinya, T.; Tsujii, N.; Yajima, S.; Furui, H.; Homma, H.; Imamura, K.; Nakamura, K.; Nakamura, K.; Sonehara, M.; Takeuchi, T.; Togashi, H.; Tsuda, S.; Yoshida, Y.
2015-12-01
Non-inductive plasma current start-up, ramp-up and sustainment by waves in the lower hybrid wave (LHW) frequency range at 200 MHz were investigated on the TST-2 spherical tokamak (R0 ≤ 0.38 m, a ≤ 0.25 m, Bt0 ≤ 0.3T, Ip ≤ 0.14 MA). Experimental results obtained using three types of antenna were compared. Both the highest plasma current (Ip = 18 kA) and the highest current drive figure of merit ηCD≡n¯eIpR0/PRF=1.4 ×1017 A/W/m2 were achieved using the capacitively-coupled combline (CCC) antenna, designed to excite the LHW with a sharp and highly directional wavenumber spectrum. For Ip greater than about 5 kA, high energy electrons accelerated by the LHW become the dominant carrier of plasma current. The low value of ηCD observed so far are believed to be caused by a rapid loss of energetic electrons and parasitic losses of the LHW energy in the plasma periphery. ηCD is expected to improve by an order of magnitude by increasing the plasma current to improve energetic electron confinement. In addition, edge power losses are expected to be reduced by increasing the toroidal magnetic field to improve wave accessibility to the plasma core, and by launching the LHW from the inboard upper region of the torus to achieve better single-pass absorption.
Effects of Tidal Currents on Nonlinear Internal Solitary Waves in the South China Sea
FAN Zhisong; SHI Xingang; Antony K. Liu; LIU Hailong; LI Peiliang
2013-01-01
The propagation and fission process of intemal solitary waves (ISWs) with amplitudes of about 170m are simulated in the northeast of the South China Sea (NSCS) by using the generalized Korteweg-de Vries (KdV) equation under continuous stratification.More attention is paid to the effects of the ebb and flood background currents on the fission process of ISWs.This kind of background current is provided by the composed results simulated in terms of monthly mean baroclinic circulation and barotropic tidal current.It is found that the obtained relation of the number of fission solitons to the water depth and stratification is roughly in accordance with the fission law derived by Djordjevic and Redekopp in 1978; however,there exists obvious difference between the effects of the ebb and flood background currents on the wave-lengths of fission solitons (defined as the distance between two neighboring peaks of ISWs).The difference in nonlinearity coefficient α between the ebb and flood background currents is a main cause for the different wave-lengths of fission solitons.
Drag reduction through wave-current interactions with a marine hydrofoil
Tully, Susan; Viola, Ignazio Maria; Ingram, David
2015-11-01
A hydrofoil exposed to oscillating flow experiences a reduction in drag due to the Knoller-Betz effect. This is experimentally identifiable by an increasingly inverted von Kármán wake and a corresponding thrust force on the foil. The rate of drag reduction, dependent on plunge amplitude and frequency, reduces with unsteady flow phenomena at higher reduced frequencies. For experimental ease, investigations of this effect have relied on actively plunging/pitching a foil within a steady current. However, one potential application is to drag reduction in high-speed ships adopting submerged foils. In this case the foil is travelling through wave-current induced oscillatory flow, resulting in an additional dynamic variation of hydrostatic pressure across the chord; a phenomena not fully addressed in previous experiments. Here we investigate the effects of this pressure gradient on drag reduction for a stationary foil in combined waves and current, through a combination of force measurements and particle image velocimetry.
James eDowsett
2016-03-01
Full Text Available Transcranial alternating current stimulation (tACS has until now mostly been administered as an alternating sinusoidal wave. Despite modern tACS stimulators being able to deliver alternating current with any arbitrary shape there has been no systematic exploration into the relative benefits of different waveforms. As tACS is a relatively new technique there is a huge parameter space of unexplored possibilities which may prove superior or complimentary to the traditional sinusoidal waveform. Here we begin to address this with an investigation into the effects of sawtooth wave tACS on individual alpha power. Evidence from animal models suggests that the gradient and direction of an electric current should be important factors for the subsequent neural firing rate; we compared positive and negative ramp sawtooth waves to test this. An additional advantage of sawtooth waves is that the resulting artefact in the electroencephalogram (EEG recording is significantly simpler to remove than a sine wave; accordingly we were able to observe alpha oscillations both during and after stimulation.We found that positive ramp sawtooth, but not negative ramp sawtooth, significantly enhanced alpha power during stimulation relative to sham (p<0.01. In addition we tested for an after-effect of both sawtooth and sinusoidal stimulation on alpha power but in this case did not find any significant effect. This preliminary study paves the way for further investigations into the effect of the gradient and direction of the current in tACS which could significantly improve the usefulness of this technique.
Chen Xiao-Gang; Guo Zhi-Ping; Song Jin-Bao
2008-01-01
In the present paper,the random interfacial waves in N-layer density-stratified fluids moving at different steady uniform speeds are researched by using an expansion technique,and the second-order asymptotic solutions of the random displacements of the density interfaces and the associated velocity potentials in N-layer fluid are presented based on the small amplitude wave theory.The obtained results indicate that the wave-wave second-order nonlinear interactions of the wave components and the second-order nonlinear interactions between the waves and currents are described.As expected,the solutions include those derived by Chen(2006)as a special case where the steady uniform currents of the N-layer fluids are taken as zero,and the solutions also reduce to those obtained by Song(2005)for second-order solutions for random interracial waves with steady uniform currents if N=2.
Waves, Currents, and Sediment Transport in the Surf Zone Along Long, Straight Beaches
2005-08-01
bmx + F bwx + F srx + F swmx + F srmx (4.49) τ cby = F bmy + F bwy...F sry + F swmy + F srmy +F bvy (4.50) with F bhpx = −ρgh ∂¯η ∂x (4.51) 119 F bmx = −ρ ∂ ∂x ( aU 2 s + q bx U 0 ) (4.52) F bwx = − ∂ ∂x S xx (4.53) F...shows “mean-current- associated” forcing terms due to the mean current advection, F bmx (thin full line), the interaction of waves and mean currents,
Modelling Infragravity Waves and Currents across a Fringing Reef: Ningaloo Reef, Western Australia
van Dongeren, A. R.; Duong Minh, T.; Lowe, R.; Roelvink, J.; Ranasinghe, R.; Symonds, G.
2010-12-01
The majority of the world’s coastlines contain submerged reef structures of various types, i.e. tropical coral reefs, relic temperate limestone platforms, and other submerged rock formations. Relatively little research has been conducted to study nearshore hydrodynamic processes that occur in reef environments. A good understanding of these processes is important because waves and wave-induced currents drive sediment transport, nutrient dynamics, and dispersal of larval coral and fish. Through the development of improved hydrodynamic models, the impact of environmental changes and human impacts on reefs may be accurately assessed. However, predictive models have historically been developed and tested using sandy coast environments. There are some important differences with reefs: wave breaking over the reef results in onshore flows with a higher bed friction coefficient, as well as set-up. Recent field studies (e.g., Lowe et al. JPO, 2009a) have shown the transformation of swell energy on reefs, and numerical model studies (Symonds and Black, JCR 2001, Ranasinghe et al., Coastal Eng. 2006, Lowe et al. J. Geoph. Res. 2009b) have shown that the spatial pattern of mean wave heights and mean currents can be qualitatively reproduced. However, the bulk of the measured variability is often in the infragravity frequency band (Pequignet et al. Geoph. Res. Lett., 2009 and Lowe et al., in prep.). The recently developed open-source model XBeach (Roelvink et al, Coastal Eng. 2009) is specifically designed to model these wave motions and associated sediment transport and has been successfully applied to sandy coasts (McCall et al., Coastal Eng. 2010). The objective of this paper is to apply XBeach to simulate infragravity forcing at Ningaloo Reef, a large fringing coral reef located along the northwest coastline of Western Australia. A field experiment at Ningaloo Reef (Western Australia) conducted in June 2009 by Lowe et al (in prep.) specifically aimed at measuring
Early stages of wind wave and drift current generation under non-stationary wind conditions.
Robles-Diaz, Lucia; Ocampo-Torres, Francisco J.; Branger, Hubert
2016-04-01
Generation and amplification mechanisms of ocean waves are well understood under constant wind speed or limited fetch conditions. Under these situations, the momentum and energy transfers from air to water are also quite well known. However during the wind field evolution over the ocean, we may observe sometime high wind acceleration/deceleration situations (e.g. Mexican Tehuano or Mediterranean Mistral wind systems). The evolution of wave systems under these conditions is not well understood. The purpose of these laboratory experiments is to better understand the early stages of water-waves and surface-drift currents under non-stationary wind conditions and to determine the balance between transfers creating waves and surface currents during non-equilibrium situations. The experiments were conducted in the Institut Pythéas wind-wave facility in Marseille-France. The wave tank is 40 m long, 2.7 m wide and 1 m deep. The air section is 50 m long, 3 m wide and 1.8 m height. We used 11 different resistive wave-gauges located along the tank. The momentum fluxes in the air column were estimated from single and X hot-film anemometer measurements. The sampling frequency for wind velocity and surface displacement measurements was 256 Hz. Water-current measurements were performed with a profiling velocimeter. This device measures the first 3.5 cm of the water column with a frequency rate of 100Hz. During the experiments, the wind intensity was abruptly modified with a constant acceleration and deceleration over time. We observed that wind drag coefficient values for accelerated wind periods are lower than the ones reported in previous studies for constant wind speed (Large and Pond 1981; Ocampo-Torres et al. 2010; Smith 1980; Yelland and Taylor 1996). This is probably because the turbulent boundary layer is not completely developed during the increasing-wind sequence. As it was reported in some theoretical studies (Miles 1957; Phillips 1957; Kahma and Donelan 1988), we
A Mechanism of the Effect of Non-uniform Current on the Spectrum of Short Wind Waves
ZHENG Guizhen; SHENG Lifang; CONG Peixiu
2004-01-01
A mechanism is suggested in this paper concerning the effect of non-uniform current on the spectrum of short wind waves. According to this mechanism, a non-uniform current brings changes to the breaking criteria of short wind waves through modulating the surface drift, and hence enhances or weakens wave breaking. Some modification is proposed to the source term, which represents the spectral rate of wave energy dissipation due to wave breaking so that the source term can incorporate this mechanism. In order to illustrate whether this mechanism is significant, a real case is studied, in which the wind waves propagate on a tidal current flowing over the sea bottom covered with sand waves. Finally, the effect of the new mechanism on the equilibrium spectrum of small scale gravity waves is discussed. Numerical estimates suggest that, for water depths less than 50 m and wavelengths less than 1 m, this current field may result in distinct spatial variations of the wave breaking criteria, the spectral rate of wave energy dissipation and the equilibrium spectrum of short gravity waves.
Turbidity current flow over an obstacle and phases of sediment wave generation
Strauss, Moshe
2011-01-01
We study the flow of particle-laden turbidity currents down a slope and over an obstacle. A high-resolution 2D computer simulation model is used, based on the Navier-Stokes equations. It includes poly-disperse particle grain sizes in the current and substrate. Particular attention is paid to the erosion and deposition of the substrate particles, including application of an active layer model. Multiple flows are modeled from a lock release that can show the development of sediment waves (SW). These are stream-wise waves that are triggered by the increasing slope on the downstream side of the obstacle. The initial obstacle is completely erased by the resuspension after a few flows leading to self consistent and self generated SW that are weakly dependant on the initial obstacle. The growth of these waves is directly related to the turbidity current being self sustaining, that is, the net erosion is more than the net deposition. Four system parameters are found to influence the SW growth: (1) slope, (2) current ...
Khazanov, G. V.
2004-01-01
The excitation of lower hybrid waves (LHWs) is a widely discussed mechanism of interaction between plasma species in space, and is one of the unresolved questions of magnetospheric multi-ion plasmas. In this paper we present the morphology, dynamics, and level of LHW activity generated by electromagnetic ion cyclotron (EMIC) waves during the May 2-7, 1998 storm period on the global scale. The LHWs were calculated based on a newly developed self-consistent model (Khazanov et. al., 2002, 2003) that couples the system of two kinetic equations: one equation describes the ring current (RC) ion dynamic, and another equation describes the evolution of EMIC waves. It is found that the LHWs are excited by helium ions due to their mass dependent drift in the electric field of EMIC waves. The level of LHW activity is calculated assuming that the induced scattering process is the main saturation mechanism for these waves. The calculated LHWs electric fields are consistent with the observational data.
Wave- and Current-Supported Gravity Flows: Insights from Direct Numerical Simulations (DNS)
Ozdemir, C. E.
2016-12-01
Discoveries over the last three decades have shown that current- and wave-enhanced gravity flows (CWEGFs) are among the significant agents that carry substantial amounts of sediments across low-gradient shelves and thereby they are important elements of sediment source-to-sink. Computational fluid dynamics (CFD) complement the existing field and laboratory experiments in that it offers unprecedented details of participating physical processes. Also, since the state-of-the-art optical and acoustic sensors are limited to measure 50 kg/m3 of suspended sediment concentration, CFD becomes the only means to evaluate the physical processes when the turbid layer is highly concentrated. In this presentation, the roles of wave- and alongshore current-induced turbulent boundary layers are investigated separately on across-shelf fine sediment transport. Turbulence-resolving simulations (Direct Numerical Simulations) that utilize a simplified Eulerian-Eulerian two-phase flow model are conducted. The results show that the sediment carrying capacity of wave boundary layers far exceeds the ones carried by along-shelf currents. The results also show that across-shelf velocity in wall units obeys a logarithmic profile, u+=α ln(z+)+β . However, this logarithmic velocity profile is far apart from the log-law and parameters α and β are dependent on sediment loading and the representative settling velocity of sediments. The key parameters that characterize CWEGFs, such as drag coefficient, Cd, and their variation are also calculated and are found to be close to the ones that are observed in the field experiments. It is also found that for wave boundary layers, drag coefficient increases as the wave orbital velocity increases. Further discussion on the details of the sediment-turbulence interaction is also warranted.
Run-up on a body in waves and current. Fully nonlinear and finite-order calculations
Büchmann, Bjarne; Ferrant, P.; Skourup, J.
2001-01-01
Run-up on a large fixed body in waves and current have been calculated using both a fully nonlinear time-domain boundary element model and a finite-order time-domain boundary element model, the latter being correct to second order in the wave steepness and to first-order in the current strength...
Low-current traveling wave tube for use in the microwave power module
Palmer, Raymond W.; Ramins, Peter; Force, Dale A.; Dayton, James A.; Ebihara, Ben T.; Gruber, Robert P.
1993-01-01
The results of a traveling-wave-tube/multistage depressed-collector (TWT-MDC) design study in support of the Advanced Research Projects Agency/Department of Defense (ARPA/DOD) Microwave Power Module (MPM) Program are described. The study stressed the possible application of dynamic and other tapers to the RF output circuit of the MPM traveling wave tube as a means of increasing the RF and overall efficiencies and reducing the required beam current (perveance). The results indicate that a highly efficient, modified dynamic velocity taper (DVT) circuit can be designed for the broadband MPM application. The combination of reduced cathode current (lower perveance) and increased RF efficiency leads to (1) a substantially higher overall efficiency and reduction in the prime power to the MPM, and (2) substantially reduced levels of MDC and MPM heat dissipation, which simplify the cooling problems. However, the selected TWT circuit parameters need to be validated by cold test measurements on actual circuits.
Spontaneous reconnection at a separator current layer. II. Nature of the waves and flows
Stevenson, Julie E H
2015-01-01
Sudden destabilisations of the magnetic field, such as those caused by spontaneous reconnection, will produce waves and/or flows. Here, we investigate the nature of the plasma motions resulting from spontaneous reconnection at a 3D separator. In order to clearly see the perturbations generated by the reconnection, we start from a magnetohydrostatic equilibrium containing two oppositely-signed null points joined by a generic separator along which lies a twisted current layer. The nature of the magnetic reconnection initiated in this equilibrium as a result of an anomalous resistivity is discussed in detail in \\cite{Stevenson15_jgra}. The resulting sudden loss of force balance inevitably generates waves that propagate away from the diffusion region carrying the dissipated current. In their wake a twisting stagnation-flow, in planes perpendicular to the separator, feeds flux back into the original diffusion site (the separator) in order to try to regain equilibrium. This flow drives a phase of slow weak impulsiv...
Dynamic response of jetting and cementing bucket platform to wave and current loading
Wang Hu; Wang Deyu
2006-01-01
The jetting and cementing bucket platform (JCBP) is a new type offshore oil-drilling platform. This paper aims to establish an analysis method for calculating the dynamic response of this platform. Based on the theory of elastic half space, the dynamic stiffness and damping of the platform's foundation were obtained and attached to the end of the platform's main jackets as a boundary condition. Then using finite element method (FEM), the dynamic response of the platform due to wave and current loading was calculated. Furthermore, the whole platform's finite element model was established and the dynamic response of the platform was calculated. The numerical results demonstrate that the present method by the usage of elastic half space theory and FEM is simple and it is reliable and efficient to calculate dynamic behavior of the platform in response to wave and current loading.
An operational coupled wave-current forecasting system for the northern Adriatic Sea
Russo, A.; Coluccelli, A.; Deserti, M.; Valentini, A.; Benetazzo, A.; Carniel, S.
2012-04-01
Since 2005 an Adriatic implementation of the Regional Ocean Modeling System (AdriaROMS) is being producing operational short-term forecasts (72 hours) of some hydrodynamic properties (currents, sea level, temperature, salinity) of the Adriatic Sea at 2 km horizontal resolution and 20 vertical s-levels, on a daily basis. The main objective of AdriaROMS, which is managed by the Hydro-Meteo-Clima Service (SIMC) of ARPA Emilia Romagna, is to provide useful products for civil protection purposes (sea level forecasts, outputs to run other forecasting models as for saline wedge, oil spills and coastal erosion). In order to improve the forecasts in the coastal area, where most of the attention is focused, a higher resolution model (0.5 km, again with 20 vertical s-levels) has been implemented for the northern Adriatic domain. The new implementation is based on the Coupled-Ocean-Atmosphere-Wave-Sediment Transport Modeling System (COAWST)and adopts ROMS for the hydrodynamic and Simulating WAve Nearshore (SWAN) for the wave module, respectively. Air-sea fluxes are computed using forecasts produced by the COSMO-I7 operational atmospheric model. At the open boundary of the high resolution model, temperature, salinity and velocity fields are provided by AdriaROMS while the wave characteristics are provided by an operational SWAN implementation (also managed by SIMC). Main tidal components are imposed as well, derived from a tidal model. Work in progress is oriented now on the validation of model results by means of extensive comparisons with acquired hydrographic measurements (such as CTDs or XBTs from sea-truth campaigns), currents and waves acquired at observational sites (including those of SIMC, CNR-ISMAR network and its oceanographic tower, located off the Venice littoral) and satellite-derived wave-heights data. Preliminary results on the forecast waves denote how, especially during intense storms, the effect of coupling can lead to significant variations in the wave
Input impedance and mutual coupling of rectangular microstrip antennas
Pozar, D. M.
1982-01-01
A moment method solution to the problem of input impedance and mutual coupling of rectangular microstrip antenna elements is presented. The formulation uses the grounded dielectric slab Green's function to account rigorously for the presence of the substrate and surface waves. Both entire basis (EB) and piecewise sinusoidal (PWS) expansion modes are used, and their relative advantages are noted. Calculations of input impedance and mutual coupling are compared with measured data and other calculations.
Sand-Mud Sediment Transport induced by tidal currents and wind waves in shallow microtidal basins
Carniello, L.; Defina, A.; D'Alpaos, L.
2011-12-01
Field data and mathematical modeling have demonstrated that the morphological evolution of shallow tidal basins is the result of the combined effect of tidal currents and wind waves. Tidal currents, in particular, drive the morphological evolution of shallow tidal systems in proximity of the inlets and within the channel network, whereas in shallow areas tidal current mainly acts enhancing the bottom shear stress due to wind waves and redistributing sediments within the basin. In this study we present a mathematical model for sediment entrainment, transport and deposition due to the combined effect of tidal currents and wind waves. The model is coupled with a hydrodynamic module based on the shallow water equations and with a module for the generation and propagation of wind waves. The sediment transport model describes the sediments by the way of a bi-granular mixtures composed by both cohesive and non-cohesive sediments thus considering the contemporary presence of clay, silt and sand which usually characterizes estuaries and tidal basins. Moreover, the model describes the bed evolution and evaluates the variation of bed sediment composition considering also the transition between cohesive and non-cohesive behavior. Attention is focused on some issues concerning the definition of a reliable initial bed composition and the incipient sediment motion which is treated following a stochastic approach for the bottom shear stress and for the critical shear stress distribution. The model is applied to the Lagoon of Venice (Italy) and the results of different simulations are compared, with good agreement, to a series of turbidity measurements collected inside the lagoon. The application of the model to the present bathymetry of the Venice lagoon allows for a first estimation of the actual net amount of sand and mud flowing through the three inlets and also gives some information on bottom evolution in terms of elevation and composition.
Varga, Edina T; Terney, Daniella; Atkins, Mary D;
2011-01-01
Cathodal transcranial direct current stimulation (tDCS) decreases cortical excitability. The purpose of the study was to investigate whether cathodal tDCS could interrupt the continuous epileptiform activity. Five patients with focal, refractory continuous spikes and waves during slow sleep were...... recruited. Cathodal tDCS and sham stimulation were applied to the epileptic focus, before sleep (1 mA; 20 min). Cathodal tDCS did not reduce the spike-index in any of the patients....
High efficiency off-axis current drive by high frequency fast waves
Prater, R.; Pinsker, R. I.; Moeller, C. P. [General Atomics, PO Box 85608, San Diego, California 92186-5608 (United States); Porkolab, M.; Vdovin, V. [Massachusetts Institute of Technology, 77 Massachusetts Ave., Cambridge, Massachusetts 02139 (United States)
2014-02-12
Modeling work shows that current drive can be done off-axis with high efficiency, as required for FNSF and DEMO, by using very high harmonic fast waves (“helicons” or “whistlers”). The modeling indicates that plasmas with high electron beta are needed in order for the current drive to take place off-axis, making DIII-D a highly suitable test vehicle for this process. The calculations show that the driven current is not very sensitive to the launched value of n{sub ∥}, a result that can be understood from examination of the evolution of n{sub ∥} as the waves propagate in the plasma. Because of this insensitivity, relatively large values (∼3) of n{sub ∥} can be launched, thereby avoiding some of the problems with mode conversion in the boundary found in some previous experiments. Use of a traveling wave antenna provides a very narrow n{sub ∥} spectrum, which also helps avoid mode conversion.
焦重庆; 李月月
2015-01-01
According to the reciprocity principle, we propose an efficient model to compute the shielding effectiveness of a rectangular cavity with apertures covered by conductive sheet against an external incident electromagnetic wave. This problem is converted into another problem of solving the electromagnetic field leakage from the cavity when the cavity is excited by an electric dipole placed within it. By the combination of the unperturbed cavity field and the transfer impedance of the sheet, the tangential electric field distribution on the outer surface of the sheet is obtained. Then, the field distribution is regarded as an equivalent surface magnetic current source responsible for the leakage field. The validation of this model is verified by a comparison with the circuital model and the full-wave simulations. This time-saving model can deal with arbitrary aperture shape, various wave propagation and polarization directions, and the near-field effect.
Design study of a beta=0.09 high current superconducting half wave resonator
Zhong, Hu-Tan-Xiang; Fan, Pei-Liang; Quan, Sheng-Wen; Liu, Ke-Xin
2016-01-01
There's presently a growing demand for high current proton and deuteron linear accelerators based on superconducting technology to better support various fields of science. A \\b{eta}=0.09 162.5 MHz high current superconducting half wave resonator (HWR) has been designed at Peking University to accelerate 100 mA proton beam or 50 mA deuteron beam after the RFQ accelerating structure. The detailed electromagnetic design, multipacting simulation, mechanical analysis of the cavity will be given in this paper.
Design of long-pulse fast wave current drive antennas for DIII-D
Baity, F. W.; Batchelor, D. B.; Bills, K. C.; Fogelman, C. H.; Jaeger, E. F.; Ping, J. L.; Riemer, B. W.; Ryan, P. M.; Stallings, D. C.; Taylor, D. J.; Yugo, J. J.
1994-10-01
Two new long-pulse fast wave current drive (FWCD) antennas will be installed on DIII-D in early 1994. These antennas will increase the available FWCD power from 2 MW to 6 MW for pulse lengths of up to 2 s, and to 4 MW for up to 10 s. Power for the new antennas is from two ASDEX-type 30- to 120-MHz transmitters. When operated at 90° phasing into a low-density plasma (˜4×1019m-3) with hot electrons (˜10 keV), these two new antennas are predicted to drive approximately 1 MA of plasma current.
National Oceanic and Atmospheric Administration, Department of Commerce — High-resolution measurements of waves, currents, water levels, temperature, salinity and turbidity were made in Hanalei Bay, Kauai,Hawaii during the summer of 2006....
Wave glider observations of surface winds and currents in the core of Typhoon Danas
Mitarai, S.; McWilliams, J. C.
2016-11-01
Simultaneous monitoring of surface winds and currents is essential to understand oceanic responses to tropical cyclones. We used a new platform, a Wave Glider (Liquid Robotics) to observe air-sea processes during a typhoon, equivalent to a category 4-hurricane, at peak strength, near Okinawa, Japan. Surface winds showed strong asymmetry in both speed and direction, faster fore than aft. Rotations of surface winds and currents were not coupled; currents rotated clockwise in the wake of the typhoon eye after passage of rapid wind rotations. Wind work was mostly done ahead of the eye, amplifying prior inertial motions with a phase shift. Wind-induced energy was nearly balanced with an increase in estimated kinetic energy of the upper ocean current, relative to prior inertial oscillations. This study provides a newer, more complete view of actual atmosphere-ocean interactions in a typhoon.
A FINITE ELEMENT METHOD WITH RECTANGULAR PERFECTLY MATCHED LAYERS FOR THE SCATTERING FROM CAVITIES
Deyue Zhang; Fuming Ma; Heping Dong
2009-01-01
We develop a finite element method with rectangular perfectly matched layers (PMLs) for the wave scattering from two-dimensional cavities. The unbounded computational domain is truncated to a bounded one by using of a rectangular perfectly matched layer at the open aperture. The PML parameters such as the thickness of the layer and the fictitious medium property are determined through sharp a posteriori error estimates. Numerical experiments are carried out to illustrate the competitive behavior of the proposed method.
Jing-Xin ZHANG; Hua LIU
2009-01-01
This paper extends the conventional concept of radiation stress (Longuet-Higgins and Stewart, 1964)in progressive water waves to standing waves, so that its vertical profile could be defined and calculated in a new technical way. The hydrodynamic numerical model being coupled with the vertically varying radiation stress in standing waves is used to simulate the currents being induced by standing waves in the vertical section. Numerical modeling of suspended sediment transport is then carried out to simulate the evolution of the bed composed of fine sediments by the currents. The scour and deposition patterns simulated are in qualitative agreement with prior laboratory and field observations.
Experimental and Numerical Study of Wave-Induced Long-Shore Currents on A Mild Slope Beach
SUN Tao; TAO Jian-hua
2005-01-01
The long-shore current distribution on a mild slope beach is studied by combining the numerical model and the physical experiment. The experiments of long-shore currents under the action of regular and irregular waves are conducted on mild beaches with different slopes in a wave basin. A numerical model is established, which includes a wave propagation model, a wave breaking model and a long-shore current model. The validity of the numerical model is proved by the comparison of its results with the results of the experimental model. It is concluded that the wave-induced long-shore current is influenced significantly by the incident wave height, the wave angle and the beach slope. Its application to the Bohai Bay indicates that the wave-induced currents have the same order of magnitude as the tide currents in the near-shore zone of mill slope beach. In the design of wastewater outfall locations on a mild-slope beach with shallow water of the Bohai Bay, the position of the outfall should be 10 km away from the shoreline, which is outside of the surf-zone.
Research on Fatigue Invalidation of A Submarine Pipeline Span Subjected to Waves and Currents
YU Jian-xing; XI Zhao-scheng; LI Hong-tao
2006-01-01
Considering both the axial force on the spanning pipeline and influence of sea waves and currents, a perpendicular nonlinear vibration equation which satisfies given boundary conditions is set up according to the factual soil supports for the pipeline. Based on the inherent modes of vibration determined from the equation of motion describing free vibrations, the differential equations for the time domain of the equation solution are deduced and established. By the application of time and frequency domain analysis, the sea wave and current force spectrum is derived from wave spectrum and is used as the input spectrum of the vibration equation to deduce the output spectrum, and further determine the probability distribution of displacement and strain. On this basis, the fatigue invalidation probability of the spanning pipeline is found out according to the theory of reliability. Finally, by means of calculation and analysis of a practical sample, the degree of effect of some important parameters on fatigue invalidation of the spanning pipeline span is determined.
Rectangular and Circular Antenna Design on Thick Substrate
kumar, Harsh
2010-01-01
Millimeter wave technology being an emerging area is still very undeveloped. A substantial research needs to be done in this area as its applications are numerous. In the present endeavor, a rectangular patch antenna is designed on thick substrate and simulated using SONNET software, also a novel analysis technique is developed for circular patch antenna for millimeter wave frequency. The antenna is designed at 39 GHz on thick substrate and has been analyzed and simulated.The results of the theoretical analysis are in good agreement with the simulated results.
Diffusion in coastal and harbour zones, effects of Waves,Wind and Currents
Diez, M.; Redondo, J. M.
2009-04-01
As there are multiple processes at different scales that produce turbulent mixing in the ocean, thus giving a large variation of horizontal eddy diffusivities, we use a direct method to evaluate the influence of different ambient parameters such as wave height and wind on coastal dispersion. Measurements of the diffusivity are made by digital processing of images taken from from video recordings of the sea surface near the coast. The use of image analysis allows to estimate both spatial and temporal characteristics of wave fields, surface circulation and mixing in the surf zone, near Wave breakers and inside Harbours. The study of near-shore dispersion [1], with the added complexity of the interaction between wave fields, longshore currents, turbulence and beach morphology, needs detailed measurements of simple mixing processes to compare the respective influences of forcings at different scales. The measurements include simultaneous time series of waves, currents, wind velocities from the studied area. Cuantitative information from the video images is accomplished using the DigImage video processing system [3], and a frame grabber. The video may be controlled by the computer, allowing, remote control of the processing. Spectral analysis on the images has also used n order to estimate dominant wave periods as well as the dispersion relations of dominant instabilities. The measurements presented here consist mostly on the comarison of difussion coeficients measured by evaluating the spread of blobs of dye (milk) as well as by measuring the separation between different buoys released at the same time. We have used a techniques, developed by Bahia(1997), Diez(1998) and Bezerra(2000)[1-3] to study turbulent diffusion by means of digital processing of images taken from remote sensing and video recordings of the sea surface. The use of image analysis allows to measure variations of several decades in horizontal diffusivity values, the comparison of the diffusivities
Sinking of armour layer around a vertical cylinder exposed to waves and current
Nielsen, Anders Wedel; Probst, Thomas; Petersen, Thor Ugelvig
2015-01-01
The mechanisms of the sinking of a scour protection adjacent to a monopile are described in this paper, together with the determination of the equilibrium sinking depth in various wave and combined wave and current conditions based on physical model tests.Sinking of the rocks may ultimately lead...... the mechanisms that could lead to unacceptable sinking of the scour protection.The study showed that the sinking is controlled by two mechanisms: removal of sediment adjacent to the pile (destabilizing) and infilling of sediment into the scour protection from the surrounding seabed (stabilizing). The latter...... mechanism is found to be the strongest, but it might take some time to fill the pores of the scour protection with sediment and during the time delay considerable sinking might take place. This means that the larger the scour protection, the larger the sinking will be (for a given KC-number smaller than...
Relation between Wind and Wind Currents on the Synoptic Scale with Account of Wave Conditions
Polnikov, Vladislav
2011-01-01
A version of model is proposed, which is aimed for getting parameters of the atmospheric layer and upper water layer with account of the wind-wave state. The dynamics of the atmospheric boundary layer is realized in version of papers [1, 2], and the dynamics of the upper layer is realized in the framework of Ekman layers in the atmosphere and the sea [3]. In the latter case, the Kitaigorodskii [4, 5] approach was used for describing the dynamics of the air-water interface. The key parameters of the atmospheric layer and upper water layer (the friction velocity and the speed of drift currents) are calculated for typical wind-wave situations. Satisfactory quantitative agreement between calculated and traditionally observed values is shown.
Zhang, X.; Stone, G. W.; Gibson, W. J.; Braud, D.
2005-05-01
WAVCIS is a regional ocean observing and forecasting system. It was designed to measure, process, forecast, and distribute oceanographic and meteorological information. WAVCIS was developed and is maintained by the Coastal Studies Institute at Louisiana State University. The in-situ observing stations are distributed along the central Louisiana and Mississippi coast. The forecast region covers the entire Gulf of Mexico with emphasis on offshore Louisiana. By using state-of-the-art instrumentation, WAVCIS measures directional waves, currents, temperature, water level, conductivity, turbidity, salinity, dissolved oxygen, chlorophyll, Meteorological parameters include wind speed and direction, air pressure and temperature visibility and humidity. Through satellite communication links, the measured data are transmitted to the WAVCIS laboratory. After processing, they are available to the public via the internet on a near real-time basis. WAVCIS also includes a forecasting capability. Waves, tides, currents, and winds are forecast daily for up to 80 hours in advance. There are a number of numerical wave and surge models that can be used for forecasts. WAM and SWAN are used for operational purposes to forecast sea state. Tides at each station are predicted based on the harmonic constants calculated from past in-situ observations at respective sites. Interpolated winds from the ETA model are used as input forcing for waves. Both in-situ and forecast information are available online to the users through WWW. Interactive GIS web mapping is implemented on the WAVCIS webpage to visualize the model output and in-situ observational data. WAVCIS data can be queried, retrieved, downloaded, and analyzed through the web page. Near real-time numerical model skill assessment can also be performed by using the data from in-situ observing stations.
Aldridge, J. N.; Parker, E. R.; Bricheno, L. M.; Green, S. L.; van der Molen, J.
2015-10-01
Natural seabed disturbance was quantified by estimating the number of days in a year that movement of the seabed occurred due to waves and currents. Disturbance over gravel substrates was based on the concept of a critical threshold for bed movement. For mud substrates disturbance was assessed on the basis of bed failure under extreme hydrodynamic stress. For sand beds the disturbance frequency was calculated by reference to the predicted occurrence of small scale bedforms using established relationships for estimating ripple and megaripple height. The method was applied to the northern European Continental Shelf (48°N to 58.5°N and 10°W to 10°E) using modelled annual wave and current forcing with a temporal resolution of one hour and spatial resolution of approximately 11 km. Highest levels of disturbance occurred in areas of high tidal stress where dune/megaripple type bedforms were predicted and in shallow regions exposed to waves with large fetch. However, the detailed distribution of disturbance showed a complex relationship between water depth, tidal stress, wave fetch and grain size. An assessment of the uncertainty in the results was made by use of a simple Monte Carlo approach. In most locations this indicated a large uncertainty in disturbance frequency values suggesting that present predictive relationships need improvement if assessments of natural disturbance are to be made with confidence. Nevertheless the results give a broad understanding of the location and intensity of natural physical bed disturbance and the ability to compare the relative intensity between different regions. This has applications to management of the seabed where human impacts have to be assessed in the context of the underlying natural disturbance. Recommendations are given for further research that might help decrease the uncertainty in natural disturbance prediction.
Application of ESPRIT in Broad Beam HF Ground Wave Radar Sea Surface Current Mapping
Liu Dan-hong; Wu Xiong-bin; Wen Bi-yang; Cheng Feng
2004-01-01
HF surface wave radar system OSMAR2000 is a broad-beam sea-state detecting radar. ESPRIT (Estimation of Signal Parameters via Rotational Invariance Technique) algorithm is proposed to apply in DOA (direction of arrival) determination of sea echoes. The algorithm of ESPRIT is briefly introduced first. Then discussions are made on the technique for application in the OSMAR2000 framework. Numerical simulation results are presented to demonstrate the feasibility of radial current mapping based on this method. The algorithm manifests significant performance and computational advantages compared with that of MUSIC. Data acquired by OSMAR2000 are processed to give radial current map and the synthesized vector currents are compared with the in-situ measurement with traditional means. The results show the validity of ESPRIT application in DOA determination for broad-beam radar.
An analysis of JET fast-wave heating and current drive experiments directly related to ITER
Bhatnagar, V.P.; Eriksson, L.; Gormezano, C.; Jacquinot, J.; Kaye, A.; Start, D.F.H. [Commission of the European Communities, Abingdon (United Kingdom). JET Joint Undertaking
1994-07-01
The ITER fast-wave system is required to serve a variety of purposes, in particular, plasma heating to ignition, current profile and burn control and eventually, in conjunction with other schemes, a central non-inductive current drive (CD) for the steady-state operation of ITER. The ICRF heating and current drive data that has been obtained in JET are analyzed in terms of dimensionless parameters, with a view to ascertaining its direct relevance to key ITER requirements. The analysis is then used to identify areas both in physics and technological aspects of ion-cyclotron resonance heating (ICRH) and CD that require further experimentation in ITER-relevant devices such as JET to establish the required data base. (authors). 12 refs., 8 figs.
A three-dimensional, wave-current coupled, sediment transport model for POM
WANG Xiao-hua
2010-01-01
In the high-energy environment of coastal seas and estuaries,strong sediment resuspension/ deposition events are driven by surface waves,tides,winds and buoyancy driven currents.In recent years,A POM based three-dimensional ,wave-current coupled ,sediment transport model has been developed by the University of New South Wales.This paper presents several examples of the model applications to study sediment dynamics in the environments where forcings such as waves,tides, and winds are equally important to affect sediment fluxes and distributions.Firstly,the sediment transport model coupled to the Yellow Sea general circulation model and a third generation wave model SWAN was implemented in the Yellow Sea to study the dynamics of the sediment transport and resuspension in the northern Jiangsu shoal-water(NJSW).The sediment distributions and fluxes and their inter-annual variability were studied by realistic numerical simulations.The study found that the surface waves played a dominant role over the tides to form the turbidity maxima along the muddy coast of NJSW. Secondly,the sediment transport model was used to explore the effect of suspended sediment-induced stratificationin the bottom boundary layer(BBL).The model uses a re-parameterized bottom drag coefficient Cd that incorporates a linear stability function of flux Richardson number RsThe study has shown that the sediment induced stratification in the BBL reduces the vertical eddy viscosity and bottom shear stress in comparison with the model prediction in a neutrally stratified BBL.In response to these apparent reductions,the tidal current shear is increased and sediments are abnormally concentrated within a thin wall layer that is overlain by a thicker layer with much smaller concentration.The formation of this fluid-mud layer near the seabed has led to a significant reduction in the total sediment transport.This study contributes to the understanding of formations of tidal flats along the coasts of turbid seas
Morphodynamic modeling of low energy beaches under waves, tides and currents
Ruiz, G.; Marino-Tapia, I.
2013-05-01
Natural processes such as coastal erosion or sediment accretion on beaches are produced by the interaction of physical forces in the littoral zone; these coastal processes can attain equilibrium states in the mid- and long term at beaches. Elements that contribute to such behaviour are the cumulative effects of waves, tides and shelf currents, which generate flow, sediment and wave patterns that shape the beach. However, over recent decades, coastal erosion has been intensified by the accelerated growth of the human population, urbanization and land development on coastal boundaries, which modify natural processes. This study shows the results of hydro-morphological numerical modeling of the northern beaches of Yucatán, Mexico, in which erosion problems are identified. The 2D-numerical simulations were carried out using the WAVE, FLOW and MOR models of DELFT 3D. The forcing elements which were used in the simulations, such as wave, tide and wind data were determined from oceanographical equipment and meteorological instruments that were located at the Yucatan coast. A nested model was used in the simulations in order to incorporate a detailed grid with a spatial resolution of 3 m within an overall larger grid. The detailed grid had 27,000 cells and covered a littoral cell of 800 x 200 m. Subsequently, an analysis of kinetic energy was performed to evaluate the grid and WAVE+ FLOW model stability. On the other hand, the calibration and validation tests were carried out through the comparison of computed and measured volumetric changes; the measured data were obtained from two field surveys where the change in the volume sediments was calculated from the evolution of a beach profile, over a span of 55 days. As a result of the validation test, the error between data and model was of ±3%. In order to identify which forcing is the most relevant for the coastal processes of these beaches, various scenarios were tested. Furthermore, an arrangement of six control volume
Depth averaged wave-current interaction in the multi bank morphology of the southern North Sea
Komijani, Homayoon; Osuna, Pedro; Ocampo Torres, Francisco; Monbaliu, Jaak
2017-04-01
The effects of wind induced waves on the barotropic mean flow during a storm event in the southern North Sea are investigated. The well known radiation stress gradient theory of Longuet-Higgins and Stewart (1962, 1964) together with the influence of waves through the Stokes drift (Hasselmann, 1971 and Garret, 1976) are incorporated in the RANS equation system of the COHERENS circulation model (Luyten et al., 2005) following the methodology worked out by Bennis et al. (2011) . The SWAN spectral wave model (version 40.91, http://www.swan.tudelft.nl/) is used to provide the wave information. This allows us to take into account the dissipative terms of wave momentum flux to the mean flow such as depth induced wave breaking and bottom friction as well as the conservative terms of wave effects such as the vortex-force and wave induced pressure gradient. The resulting coupled COHERENS-SWAN model has been validated using the well known planar beach test case proposed by Haas and Warner (2009) in depth averaged mode. For the application in the southern North Sea, a series of nested grids using COHERENS (circulation model) and WAM cycle 4.5.3 (spectral wave model applied to the North Sea shelf area, Monbaliu et al. 2000; Günther, H. and A. Behrens, personal communications, May 2012) is set up to provide the hydrodynamic and wave boundary conditions for the COHERENS-SWAN two way coupled wave-current model for the Belgian coastal zone model. The improvements obtained in hindcasting the circulation processes in the Belgian coastal area during a storm event will be highlighted. But also difficulties faced in the coupling of the models and in the simulation of a real case storm will be discussed. In particular, some of the approaches for dealing with the numerical instabilities due to multi bank morphology of the southern North Sea will be addressed. References : Bennis, A.-C., F. Ardhuin, and F. Dumas (2011). "On the coupling of wave and three-dimensional circulation models
Manning, Robert M.
1993-01-01
The formation of the Vision-21 conference held three years ago allowed the present author to reflect and speculate on the problem of converting electromagnetic energy to a direct current by essentially reversing the process used in traveling wave tubes that converts energy in the form of a direct current to electromagnetic energy. The idea was to use the electric field of the electromagnetic wave to produce electrons through the field emission process and accelerate these electrons by the same field to produce an electric current across a large potential difference. The acceleration process was that of cyclotron auto-resonance. Since that time, this rather speculative ideas has been developed into a method that shows great promise and for which a patent is pending and a prototype design will be demonstrated in a potential laser power beaming application. From the point of view of the author, a forum such as Vision-21 is becoming an essential component in the rather conservative climate in which our initiatives for space exploration are presently formed. Exchanges such as Vision-21 not only allows us to deviate from the 'by-the-book' approach and rediscover the ability and power in imagination, but provides for the discussion of ideas hitherto considered 'crazy' so that they may be given the change to transcend from the level of eccentricity to applicability.
Deep currents in the Gulf of Guinea: along slope propagation of intraseasonal waves
C. Guiavarc'h
2009-05-01
Full Text Available In the Gulf of Guinea, intraseasonal variability is large at the equator and along the coast. Current data on the continental slope near 7.5° S show very energetic biweekly oscillations at 1300 m depth. A high resolution primitive equation numerical model demonstrates that this deep variability is forced by equatorial winds, through the generation of equatorial Yanai waves that propagate eastward and at depth, and then poleward as coastally-trapped waves upon reaching the coast of Africa. Intraseasonal variability is intensified along the coast of the Gulf of Guinea, especially in the 10–20 day period range and at depths between 500 and 1500 m. The kinetic energy distribution is well explained at first order by linear theory. Along the equator, eastward intensification of energy and bottom intensification are in qualitative agreement with vertically propagating Yanai waves, although the signal is influenced by the details of the bathymetry. Along the coast, baroclinic modes 3 to 5 are important close to the equator, and the signal is dominated by lower vertical modes farther south. Additional current meter data on the continental slope near 3° N display an energy profile in the 10–20 day period band that is strikingly different from the one at 7.5° S, with surface intensification rather than bottom intensification and a secondary maximum near 800 m. The model reproduces these features and explains them: the surface intensification in the north is due to the regional wind forcing, and the north-south asymmetry of the deep signal is due to the presence of the zonal African coast near 5° N. A 4 years time series of current measurements at 7.5° S shows that the biweekly oscillations are intermittent and vary from year to year. This intermittency is not well correlated with fluctuations of the equatorial winds and does not seem to be a simple linear response to the wind forcing.
G. Franz
2017-09-01
Full Text Available Coastal defence structures are often constructed to prevent beach erosion. However, poorly designed structures may cause serious erosion problems in the downdrift direction. Morphological models are useful tools to predict such impacts and assess the efficiency of defence structures for different scenarios. Nevertheless, morphological modelling is still a topic under intense research effort. The processes simulated by a morphological model depend on model complexity. For instance, undertow currents are neglected in coastal area models (2DH, which is a limitation for simulating the evolution of beach profiles for long periods. Model limitations are generally overcome by predefining invariant equilibrium profiles that are allowed to shift offshore or onshore. A more flexible approach is described in this paper, which can be generalised to 3-D models. The present work is based on the coupling of the MOHID modelling system and the SWAN wave model. The impacts of different designs of detached breakwaters and groynes were simulated in a schematic beach configuration following a 2DH approach. The results of bathymetry evolution are in agreement with the patterns found in the literature for several existing structures. The model was also tested in a 3-D test case to simulate the formation of sandbars by undertow currents. The findings of this work confirmed the applicability of the MOHID modelling system to study sediment transport and morphological changes in coastal zones under the combined action of waves and currents. The same modelling methodology was applied to a coastal zone (Costa da Caparica located at the mouth of a mesotidal estuary (Tagus Estuary, Portugal to evaluate the hydrodynamics and sediment transport both in calm water conditions and during events of highly energetic waves. The MOHID code is available in the GitHub repository.
Franz, Guilherme; Delpey, Matthias T.; Brito, David; Pinto, Lígia; Leitão, Paulo; Neves, Ramiro
2017-09-01
Coastal defence structures are often constructed to prevent beach erosion. However, poorly designed structures may cause serious erosion problems in the downdrift direction. Morphological models are useful tools to predict such impacts and assess the efficiency of defence structures for different scenarios. Nevertheless, morphological modelling is still a topic under intense research effort. The processes simulated by a morphological model depend on model complexity. For instance, undertow currents are neglected in coastal area models (2DH), which is a limitation for simulating the evolution of beach profiles for long periods. Model limitations are generally overcome by predefining invariant equilibrium profiles that are allowed to shift offshore or onshore. A more flexible approach is described in this paper, which can be generalised to 3-D models. The present work is based on the coupling of the MOHID modelling system and the SWAN wave model. The impacts of different designs of detached breakwaters and groynes were simulated in a schematic beach configuration following a 2DH approach. The results of bathymetry evolution are in agreement with the patterns found in the literature for several existing structures. The model was also tested in a 3-D test case to simulate the formation of sandbars by undertow currents. The findings of this work confirmed the applicability of the MOHID modelling system to study sediment transport and morphological changes in coastal zones under the combined action of waves and currents. The same modelling methodology was applied to a coastal zone (Costa da Caparica) located at the mouth of a mesotidal estuary (Tagus Estuary, Portugal) to evaluate the hydrodynamics and sediment transport both in calm water conditions and during events of highly energetic waves. The MOHID code is available in the GitHub repository.
Universal Voltage Conveyor and Current Conveyor in Fast Full-Wave Rectifier
Josef Burian
2012-12-01
Full Text Available This paper deals about the design of a fast voltage-mode full-wave rectifier, where universal voltage conveyor and second-generation current conveyor are used as active elements. Thanks to the active elements, the input and output impedance of the non-linear circuit is infinitely high respectively zero in theory. For the rectification only two diodes and three resistors are required as passive elements. The performance of the circuit is shown on experimental measurement results showing the dynamic range, time response, frequency dependent DC transient value and RMS error for different values of input voltage amplitudes.
Adrian, M. L.; Wendel, D. E.
2011-01-01
We investigate observations of intense bursts of electromagnetic wave energy in association with the thin current layers of turbulent magnetosheath reconnection. These observed emissions form two distinct types: (i) broadband emissions that extend continuously to lOs of Hertz; and (ii) structured bursts of emitted energy that occur above 80-Hz, often displaying features reminiscent of absorption bands and are observed at local minima in the magnetic field. We present detailed analyses of these intense bursts of electromagnetic energy and quantify their proximity to X- and O-nulls, as well as their correlation to the amount of magnetic energy converted by the process of magnetic reconnection.
Malaspina, David M.; Newman, David L.; Wilson, Lynn Bruce; Goetz, Keith; Kellogg, Paul J.; Kerstin, Kris
2013-01-01
A strong spatial association between bipolar electrostatic solitary waves (ESWs) and magnetic current sheets (CSs) in the solar wind is reported here for the first time. This association requires that the plasma instabilities (e.g., Buneman, electron two stream) which generate ESWs are preferentially localized to solar wind CSs. Distributions of CS properties (including shear angle, thickness, solar wind speed, and vector magnetic field change) are examined for differences between CSs associated with ESWs and randomly chosen CSs. Possible mechanisms for producing ESW-generating instabilities at solar wind CSs are considered, including magnetic reconnection.
Effect of Distortion Ratio on Local Scour Under Tidal Currents and Waves
窦希萍; 董凤舞
2004-01-01
Five generalized physical models of different distortion ratios were built according to DOU Guo-ren' s similarity theory of total sediment transport modeling for estuarine and coastal regions. Experiments on local scour in front of groins were made under the actions of tidal currents and waves with clear and sediment entraining water. The scour depths under different dynamic actions are compared. The effect of the distortion ratio on the depth of scour hole is discussed. A relationship between scour depths for distorted and undistorted models is given.
Stability of current-driven electrostatic waves in a magnetized and collisional negative ion plasma
Venugopal, Chandu; Varghese, Anu; S, Jyothi [School of Pure and Applied Physics, Mahatma Gandhi University, Priyadarshini Hills, Kottayam 686 560, Kerala (India); Issac, Molly [Department of Physics, All Saints' College, Thiruvananthapuram 695 007, Kerala (India); Renuka, G [Department of Physics, University of Kerala, Kariavattom, Thiruvananthapuram 695 581, Kerala (India)], E-mail: cvgmgphys@yahoo.co.in
2008-10-15
The stability of electrostatic waves, propagating nearly parallel to a uniform external magnetic field, is studied in a fully ionized, collisional plasma of positive and negative ions and a field-aligned current of drifting electrons. Expressions have been derived for the dispersion relation and growth rate using fluid theory and retaining the collisional and conductivity terms for the electrons. The plasma can, in general, support two modes, which have frequencies that are a composite of the ion acoustic and ion gyro frequencies. The growth rate of the modes increases with increasing drift velocities of the electrons and decreases with increasing negative ion densities.
Wang, Shilong; Yin, Changchun; Lin, Jun; Yang, Yu; Hu, Xueyan
2016-03-01
Cooperative work of multiple magnetic transmitting sources is a new trend in the development of transient electromagnetic system. The key is the bipolar current waves shutdown, concurrently in the inductive load. In the past, it was difficult to use the constant clamping voltage technique to realize the synchronized shutdown of currents with different peak values. Based on clamping voltage technique, we introduce a new controlling method with constant shutdown time. We use the rising time to control shutdown time and use low voltage power source to control peak current. From the viewpoint of the circuit energy loss, by taking the high-voltage capacitor bypass resistance and the capacitor of the passive snubber circuit into account, we establish the relationship between the rising time and the shutdown time. Since the switch is not ideal, we propose a new method to test the shutdown time by the low voltage, the high voltage and the peak current. Experimental results show that adjustment of the current rising time can precisely control the value of the clamp voltage. When the rising time is fixed, the shutdown time is unchanged. The error for shutdown time deduced from the energy consumption is less than 6%. The new controlling method on current shutdown proposed in this paper can be used in the cooperative work of borehole and ground transmitting system.
Wang, Shilong; Yin, Changchun; Lin, Jun; Yang, Yu; Hu, Xueyan
2016-03-01
Cooperative work of multiple magnetic transmitting sources is a new trend in the development of transient electromagnetic system. The key is the bipolar current waves shutdown, concurrently in the inductive load. In the past, it was difficult to use the constant clamping voltage technique to realize the synchronized shutdown of currents with different peak values. Based on clamping voltage technique, we introduce a new controlling method with constant shutdown time. We use the rising time to control shutdown time and use low voltage power source to control peak current. From the viewpoint of the circuit energy loss, by taking the high-voltage capacitor bypass resistance and the capacitor of the passive snubber circuit into account, we establish the relationship between the rising time and the shutdown time. Since the switch is not ideal, we propose a new method to test the shutdown time by the low voltage, the high voltage and the peak current. Experimental results show that adjustment of the current rising time can precisely control the value of the clamp voltage. When the rising time is fixed, the shutdown time is unchanged. The error for shutdown time deduced from the energy consumption is less than 6%. The new controlling method on current shutdown proposed in this paper can be used in the cooperative work of borehole and ground transmitting system.
Interaction of Streamwise and Wall-Normal Velocities in Combined Wave-Current Motion
Shu-Qing YANG; In-Soo KIM; Daniel S. KOH; Young-Chae SONG
2005-01-01
The aim of this paper is to present an analytical expression for the streamwise velocity distribution in a non-uniform flow in the presence of waves; the correlation between the horizontal and vertical velocity components has been comprehensively examined. Different from previous researches which attributed the deviation of velocity from the classical log-law to the wave Reynolds stress, i.e. -ρ(uv)only, this study demonstrates that the momentum flux caused by mean velocities, i.e.,(u)and(v) , is also responsible for the velocity deviation, and it is found that the streamwise velocity for a flow in the presence of non-zero wall-normal velocity does not follow the classical log-law, but the modified log-law proposed in this study based on simplified mixing-length theorem. The validity of the modified log-law has been verified by use of available experimental data from published sources for combined wave-current flows, and good agreement between the predicted and observed velocity profiles has been achieved.
Quality assurance and control issues for HF radar wave and current measurements
Wyatt, Lucy
2015-04-01
HF radars are now widely used to provide surface current measurements over wide areas of the coastal ocean for scientific and operational applications. In general data quality is acceptable for these applications but there remain issues that impact on the quantity and quality of the data. These include problems with calibration and interference which impact on both phased array (e.g. WERA, Pisces) and direction-finding (e.g. SeaSonde) radars. These same issues and others (e.g. signal-to-noise, in-cell current variability, antenna sidelobes) also impact on the quality and quantity of wave data that can be obtained. These issues will be discussed in this paper, illustrated with examples from deployments of WERA, Pisces and SeaSonde radars in the UK, Europe, USA and Australia. These issues involve both quality assurance (making sure the radars perform to spec and the software is fully operational) and in quality control (identifying problems with the data due to radar hardware or software performance issues and flagging these in the provided data streams). Recommendations for the former, and current practice (of the author and within the Australian Coastal Ocean Radar Network, ACORN*) for the latter, will be discussed. The quality control processes for wave measurement are not yet as well developed as those for currents and data from some deployments can be rather noisy. Some new methods, currently under development by SeaView Sensing Ltd and being tested with ACORN data, will be described and results presented. *ACORN is a facility of the Australian Integrated Marine Observing System, IMOS. IMOS is a national collaborative research infrastructure, supported by Australian Government. It is led by University of Tasmania in partnership with the Australian marine and climate science community.
Stenzel, R. L.
1978-01-01
Pulsed electron beam injection into a weakly collisional magnetized background plasma is investigated experimentally; properties of the electron beam and background plasma, as well as the low-frequency instabilities and wave dynamics, are discussed. The current of the injected beam closes via a field-aligned return current of background electrons. Through study of the frequency and wavenumber distribution, together with the electron distribution function, the low-frequency instabilities associated with the pulsed injection are identified as ion acoustic waves driven unstable by the return current. The frequency cut-off of the instabilities predicted from renormalized plasma turbulence theory, has been verified experimentally.
Xu, Ting; You, Xue-yi
2017-04-01
A 3D sediment transport model based on the modified environmental fluid dynamics code (EFDC) and the nearshore waves simulation model (SWAN) is developed to study the change of suspended sediment concentration and bottom shear stress under the actions of pure current and wave-current. After being validated by the field measured data, the proposed sediment transport model is applied in the Oujiang River Estuary, China. The results show that the ratios of both bottom shear stress and suspended sediment concentration of pure current to those of wave-current show a gradually increase from shallow nearshore water to deep open sea. The results also show that the proportion of wave contributions on bottom shear stress and sediment concentration are above 60%, approximately 20-30% and less than 10% for the water depth of less than 5 m, 5-10 m and more than 20 m, respectively. For the waters among islands, the proportion of wave contribution to bottom shear stress and sediment concentration is reduced to 10-20% for -5 m water depth and this is more obvious for the waves of large amplitude. The bottom stress and suspended sediment concentration between islands are mainly controlled by tidal current, and the effect of wave is not significant.
Development of a three-dimensional, regional, coupled wave, current, and sediment-transport model
Warner, J.C.; Sherwood, C.R.; Signell, R.P.; Harris, C.K.; Arango, H.G.
2008-01-01
We are developing a three-dimensional numerical model that implements algorithms for sediment transport and evolution of bottom morphology in the coastal-circulation model Regional Ocean Modeling System (ROMS v3.0), and provides a two-way link between ROMS and the wave model Simulating Waves in the Nearshore (SWAN) via the Model-Coupling Toolkit. The coupled model is applicable for fluvial, estuarine, shelf, and nearshore (surfzone) environments. Three-dimensional radiation-stress terms have been included in the momentum equations, along with effects of a surface wave roller model. The sediment-transport algorithms are implemented for an unlimited number of user-defined non-cohesive sediment classes. Each class has attributes of grain diameter, density, settling velocity, critical stress threshold for erosion, and erodibility constant. Suspended-sediment transport in the water column is computed with the same advection-diffusion algorithm used for all passive tracers and an additional algorithm for vertical settling that is not limited by the CFL criterion. Erosion and deposition are based on flux formulations. A multi-level bed framework tracks the distribution of every size class in each layer and stores bulk properties including layer thickness, porosity, and mass, allowing computation of bed morphology and stratigraphy. Also tracked are bed-surface properties including active-layer thickness, ripple geometry, and bed roughness. Bedload transport is calculated for mobile sediment classes in the top layer. Bottom-boundary layer submodels parameterize wave-current interactions that enhance bottom stresses and thereby facilitate sediment transport and increase bottom drag, creating a feedback to the circulation. The model is demonstrated in a series of simple test cases and a realistic application in Massachusetts Bay. ?? 2008 Elsevier Ltd. All rights reserved.
Symbolic Algorithmic Analysis of Rectangular Hybrid Systems
Hai-Bin Zhang; Zhen-Hua Duan
2009-01-01
This paper investigates symbolic algorithmic analysis of rectangular hybrid systems. To deal with the symbolic reachability problem, a restricted constraint system called hybrid zone is formalized for the representation and manipulation of rectangular automata state-spaces. Hybrid zones are proved to be closed over symbolic reachability operations of rectangular hybrid systems. They are also applied to model-checking procedures for verifying some important classes of timed computation tree logic formulas. To represent hybrid zones, a data structure called difference constraint matrix is defined.These enable us to deal with the symbolic algorithmic analysis of rectangular hybrid systems in an efficient way.
DENG Zengan; ZHAO Dongliang; WU Kejian; YU Ting; SHI Jian
2008-01-01
By taking into consideration the effects of ocean surface wave-induced Stokes drift velocity U,w and current velocityU,c on the drag coefficient,the spatial distributions of drag coefficient and wind stress in 2004 are computed over the tropical andnorthern Pacific using an empirical drag coefficient parameterization formula based on wave steepness and wind speed.The globalocean current field is generated from the Hybrid Coordinate Ocean Model (HYCOM) and the wave data are generated from Wave-watch Ⅲ (WW3).The spatial variability of the drag coefficient and wind stress is analyzed.Preliminary results indicate that theocean surface Stokes drift velocity and current velocity exert an important influence on the wind stress.The results also show thatconsideration of the effects of the ocean surface Stokes drift velocity and current velocity on the wind stress can significantly im-prove the modeling of ocean circulation and air-sea interaction processes.
Design of long-pulse fast wave current drive antennas for DIII-D
Baity, F.W.; Batchelor, D.B.; Bills, K.C.; Fogelman, C.H.; Jaeger, E.F.; Ping, J.L.; Riemer, B.W.; Ryan, P.M.; Stallings, D.C.; Taylor, D.J.; Yugo, J.J. (Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-8071 (United States))
1994-10-15
Two new long-pulse fast wave current drive (FWCD) antennas will be installed on DIII-D in early 1994. These antennas will increase the available FWCD power from 2 MW to 6 MW for pulse lengths of up to 2 s, and to 4 MW for up to 10 s. Power for the new antennas is from two ASDEX-type 30- to 120-MHz transmitters. When operated at 90[degree] phasing into a low-density plasma ([similar to]4[times]10[sup 19]m[sup [minus]3]) with hot electrons ([similar to]10 keV), these two new antennas are predicted to drive approximately 1 MA of plasma current.
Takahashi, K; Kajiwara, K; Oda, Y; Kasugai, A; Kobayashi, N; Sakamoto, K; Doane, J; Olstad, R; Henderson, M
2011-06-01
High power, long pulse millimeter (mm) wave experiments of the RF test stand (RFTS) of Japan Atomic Energy Agency (JAEA) were performed. The system consists of a 1 MW/170 GHz gyrotron, a long and short distance transmission line (TL), and an equatorial launcher (EL) mock-up. The RFTS has an ITER-relevant configuration, i.e., consisted by a 1 MW-170 GHz gyrotron, a mm wave TL, and an EL mock-up. The TL is composed of a matching optics unit, evacuated circular corrugated waveguides, 6-miter bends, an in-line waveguide switch, and an isolation valve. The EL-mock-up is fabricated according to the current design of the ITER launcher. The Gaussian-like beam radiation with the steering capability of 20°-40° from the EL mock-up was also successfully proved. The high power, long pulse power transmission test was conducted with the metallic load replaced by the EL mock-up, and the transmission of 1 MW/800 s and 0.5 MW/1000 s was successfully demonstrated with no arcing and no damages. The transmission efficiency of the TL was 96%. The results prove the feasibility of the ITER electron cyclotron heating and current drive system.
Spontaneous reconnection at a separator current layer: 2. Nature of the waves and flows
Stevenson, J. E. H.; Parnell, C. E.
2015-12-01
Sudden destabilizations of the magnetic field, such as those caused by spontaneous reconnection, will produce waves and/or flows. Here we investigate the nature of the plasma motions resulting from spontaneous reconnection at a 3-D separator. In order to clearly see these perturbations, we start from a magnetohydrostatic equilibrium containing two oppositely signed null points joined by a generic separator along which lies a twisted current layer. The nature of the magnetic reconnection initiated in this equilibrium as a result of an anomalous diffusivity is discussed in detail in Stevenson and Parnell (2015). The resulting sudden loss of force balance inevitably generates waves that propagate away from the diffusion region carrying the dissipated current. In their wake a twisting stagnation flow, in planes perpendicular to the separator, feeds flux back into the original diffusion site (the separator) in order to try to regain equilibrium. This flow drives a phase of slow weak impulsive bursty reconnection that follows on after the initial fast-reconnection phase.
Study of Bridging of the Spectral Gap in the Lower Hybrid Wave Current Drive in the HT-7 Tokamak
WANG Mao; DING Bojiang; XU Handong; ZHAO Lianmin; LIU Liang; LIN Shiyao; XU Ping; SUN Youwen; HU Huaichuan; YANG Yong; JIA Hua; WANG Xiaojie; WANG Dongxia; QIN Yongliang; FENG Jianqiang; LIU Fukun; SHAN Jiafang; ZHAO Yanping; HT-7 team
2009-01-01
An additional lower hybrid wave (LHW) with a higher refractive index(N//)was investigated in the HT-7 tokamak to bridge the spectral gap.It was found that the spectral gap between the wave and the electrons in the outer region was bridged by the additional wave with a higher N// spectrum.The results showed that the sawteeth oscillation was suppressed by launching the additional wave,and that the power deposition profile was moved outwards and the current profile was broadened due to the application of the additional wave.Our study indicates that the spectral gap may be bridged by an additional wave with a higher N// spectrum in the outer region.
Li, Yan
2015-01-01
We obtain a general solution for the water waves resulting from a general, time-dependent surface pressure distribution, in the presence of a shear current of uniform vorticity beneath the surface, in three dimensions. Linearized governing equations and boundary conditions including the effects of gravity, a distributed external pressure disturbance, and constant finite depth, are solved analytically, and particular attention is paid to classic initial value problems: an initial pressure impulse and a steady pressure distribution which appears suddenly. In the present paper, good agreement with previous results is demonstrated. We subsequently show both analytically and numerically how transient waves from a suddenly appearing steady pressure distribution vanis for large times, and steady ship waves remain. The transient contribution to wave resistance was derived. The results show that a shear current has significant impact on the transient wave motions, resulting in asymmetry between upstream and downstream...
Hysteresis-controlled instability waves in a scale-free driven current sheet model
V. M. Uritsky
2005-01-01
Full Text Available Magnetospheric dynamics is a complex multiscale process whose statistical features can be successfully reproduced using high-dimensional numerical transport models exhibiting the phenomenon of self-organized criticality (SOC. Along this line of research, a 2-dimensional driven current sheet (DCS model has recently been developed that incorporates an idealized current-driven instability with a resistive MHD plasma system (Klimas et al., 2004a, b. The dynamics of the DCS model is dominated by the scale-free diffusive energy transport characterized by a set of broadband power-law distribution functions similar to those governing the evolution of multiscale precipitation regions of energetic particles in the nighttime sector of aurora (Uritsky et al., 2002b. The scale-free DCS behavior is supported by localized current-driven instabilities that can communicate in an avalanche fashion over arbitrarily long distances thus producing current sheet waves (CSW. In this paper, we derive the analytical expression for CSW speed as a function of plasma parameters controlling local anomalous resistivity dynamics. The obtained relation indicates that the CSW propagation requires sufficiently high initial current densities, and predicts a deceleration of CSWs moving from inner plasma sheet regions toward its northern and southern boundaries. We also show that the shape of time-averaged current density profile in the DCS model is in agreement with steady-state spatial configuration of critical avalanching models as described by the singular diffusion theory of the SOC. Over shorter time scales, SOC dynamics is associated with rather complex spatial patterns and, in particular, can produce bifurcated current sheets often seen in multi-satellite observations.
Urpin, Vadim
2016-01-01
We consider diffusion caused by a combined influence of the Hall effect and electric currents, and argue that such diffusion forms chemical inhomogeneities in plasma. The considered mechanism can be responsible for the formation of element spots in laboratory and astrophysical plasmas. Such current-driven diffusion can be accompanied by the propagation of a particular type of waves which have not been considered earlier. In these waves, the impurity number density oscillare alone and their frequency is determined by the electric currents and sort of impurity ions. These compositional waves exist if the magnetic pressure in plasma is much greater than the gas pressure. Such waves lead to local variations of chemical composition and, hence, can manifest themselves by variations of the emission in spectral lines.
Sound Radiation Characteristics of a Rectangular Duct with Flexible Walls
Praveena Raviprolu
2016-01-01
Full Text Available Acoustic breakout noise is predominant in flexible rectangular ducts. The study of the sound radiated from the thin flexible rectangular duct walls helps in understanding breakout noise. The current paper describes an analytical model, to predict the sound radiation characteristics like total radiated sound power level, modal radiation efficiency, and directivity of the radiated sound from the duct walls. The analytical model is developed based on an equivalent plate model of the rectangular duct. This model has considered the coupled and uncoupled behaviour of both acoustic and structural subsystems. The proposed analytical model results are validated using finite element method (FEM and boundary element method (BEM. Duct acoustic and structural modes are analysed to understand the sound radiation behaviour of a duct and its equivalence with monopole and dipole sources. The most efficient radiating modes are identified by vibration displacement of the duct walls and for these the radiation efficiencies have been calculated. The calculated modal radiation efficiencies of a duct compared to a simple rectangular plate indicate similar radiation characteristics.
Flow Characteristics of Rectangular Underexpanded Impinging Jets
Minoru YAGA; Yoshio KINJO; Masumi TAMASHIRO; Kenyu OYAKAWA
2006-01-01
In this paper, the flow fields of underexpanded impinging jet issued from rectangular nozzles of aspect ratio 1,3 and 5 are numerically and experimentally studied. Two dimensional temperature and pressure distributions are measured by using infrared camera and the combination of a pressure scanning device and a stepping motor, respectively. The variation of the stagnation pressure on the impinging plate reveals that a hystcretic phenomenon exists during the increasing and decreasing of the pressure ratio for the aspect ratio of 3.0 and 5.0. It is also found that the nozzle of aspect ratio 1.0 caused the largest total pressure loss pc/p0 = 0.27 at the pressure ratio of p0/pb, = 6.5, where pc is the stagnation center pressure on the wall, p0 the upstream stagnation pressure, pb the ambient pressure. The other two nozzles showed that the pressure loss pc / p0=0.52 and 0.55 were achieved by the nozzles of the aspect ratio 3,0 and 5.0, respectively. The comparison between the calculations and experiments is fairly good, showing the three dimensional streamlines and structures of the shock waves in the jets. However, the hysteresis of the pressure variations observed in the experiments between the pressure ratio of 3.5 and 4.5 cannot be confirmed in the calculations.
The efficiency of fast wave current drive for a weakly relativistic plasma
Chiu, S. C.; Lin-Liu, Y. R.; Karney, C. F. F.
1994-10-01
Current drive by fast waves (FWCD) is an important candidate for steady-state operation of tokamaks. Major experiments using this scheme are being carried out on DIII-D. There has been considerable study of the theoretical efficiency of FWCD. In Refs. 4 and 5, the nonrelativistic efficiency of FWCD at arbitrary frequencies was studied. For DIII-D parameters, the results can be considerably different from the Landau and Alfvén limits. At the high temperatures of reactors and DIII-D upgrade, relativistic effects become important. In this paper, the relativistic FWCD efficiency for arbitrary frequencies is studied. Assuming that the plasma is weakly relativistic, i.e., Te/mc2 is small, an analytic expression for FWCD is obtained for high resonant energies (uph/uTe≫1). Comparisons with the results from a numerical code ADJ and the nonrelativistic results shall be made and analytical fits in the whole range of velocities shall be presented.
Development of a Magnetostrictive FeNi Coated Surface Acoustic Wave Current Sensor
Jie Tong
2017-07-01
Full Text Available A magnetostrictive FeNi-coated surface acoustic wave (SAW-based current sensor was proposed in this work. The weak remanence and hysteresis effect of the FeNi itself contributes to suppress the asymmetry in sensor response at increasing and decreasing current. The sensor response was simulated by solving the coupled electromechanical field equation in layered structure considering the magnetostrictive effect and an approach of effective dielectric constant. The effects from the aspect ratio and thickness of the FeNi film on sensor response were analyzed to determine the optimal design parameters. Differential oscillation structure was used to form the sensor, in which, the FeNi thin film was deposited along the SAW propagation of the sensor chip by using RF magnetron sputtering. The magnetostrictive effect of the FeNi coating induced by the magnetic loading generates the perturbation in SAW velocity, and corresponding oscillation frequency. High sensitivity of 10.7 KHz/A, good linearity and repeatability, lower hysteresis error of 0.97% were obtained from the developed prototype 150 MHz SAW FeNi coated current sensor.
Brannon, Sean R.; Longcope, Dana; Qiu, Jiong
2015-04-01
A flare ribbon is the chromospheric image of reconnection at a coronal current sheet. The dynamics and structure of the ribbon can thus reveal properties of the current sheet, including motion of the reconnecting flare loops. We present imaging and spectroscopic observations from the Interface Region Imaging Spectrograph (IRIS) of the evolution of a flare ribbon at high spatial resolution and time cadence. These reveal small-scale substructure in the ribbon, which manifest as oscillations in both position and Doppler velocities. We consider various alternative explanations for these oscillations, including modulation of chromospheric evaporation flows. Among these we find the best support for some form of elliptical wave localized to the coronal current sheet, such as a tearing mode or Kelvin-Helmholtz instability.IRIS is a NASA Small Explorer mission developed and operated by Lockheed Martin Solar and Astrophysics Laboratory. This work is supported by contract 8100002702 from Lockheed Martin to Montana State University, a Montana Space Grant Consortium fellowship, and by NASA through HSR.
Sediment Dynamics in Shallow Tidal Landscapes: The Role of Wind Waves and Tidal Currents
Carniello, L.; D'Alpaos, A.
2014-12-01
A precise description of sediment dynamics (resuspension and re-distribution of sediments) is crucial when investigating the long term evolution of the different morphological entities characterizing tidal landscapes. It has been demonstrated that wind waves are the main responsible for sediment resuspension in shallow micro-tidal lagoons where tidal currents, which produce shear stresses large enough to carry sediments into suspension only within the main channels, are mainly responsible for sediment redistribution. A mathematical model has been developed to describe sediment entrainment, transport and deposition due to the combined effect of tidal currents and wind waves in shallow lagoons considering both cohesive and non-cohesive sediments. The model was calibrated and tested using both in situ point observations and turbidity maps obtained analyzing satellite images. Once calibrated the model can integrate the high temporal resolution of point observations with the high spatial resolution of remote sensing, overcoming the intrinsic limitation of these two types of observations. The model was applied to the specific test case of the Venice lagoon simulating an entire year (2005) which was shown to be a "representative" year for wind and tide characteristics. The time evolution of the computed total bottom shear stresses (BSS) and suspended sediment concentration (SSC) was analyzed on the basis of a "Peaks Over Threshold" method once a critical value for shear stress and turbidity were chosen. The analyses of the numerical results enabled us to demonstrate that resuspension events can be modeled as marked Poisson processes: interarrival time, intensity of peak excesses and duration being exponentially distributed random variable. The probability distributions of the interarrival time of overthreshold exceedances in both BSS and SSC as well as their intensity and duration can be used in long-term morphodynamic studies to generate synthetic series statistically
A Novel Dual-Band Circularly Polarized Rectangular Slot Antenna
Biao Li
2016-01-01
Full Text Available A coplanar waveguide fed dual-band circularly polarized rectangular slot antenna is presented. The proposed antenna consists of a rectangular metal frame acting as a ground and an S-shaped monopole as a radiator. The spatial distribution of the surface current density is employed to demonstrate that the circular polarization is generated by the S-shaped monopole which controls the path of the surface currents. An antenna prototype, having overall dimension 37 × 37 × 1 mm3, has been fabricated on FR4 substrate with dielectric constant 4.4. The proposed antenna achieves 10 dB return loss bandwidths and 3 dB axial ratio (AR in the frequency bands 2.39–2.81 GHz and 5.42–5.92 GHz, respectively. Both these characteristics are suitable for WLAN and WiMAX applications.
Liu Yongjun
2015-01-01
Full Text Available In this thesis, the influence of complete Coriolis force (the model includes both the vertical and horizontal components of Coriolis force on the dispersion relation of ocean internal-wave under background currents field are studied, it is important to the study of ocean internal waves in density-stratified ocean. We start from the control equation of sea water movement in the background of the non-traditional approximation, and the vertical velocity solution is derived where buoyancy frequency N(z gradually varies with the ocean depth z. The results show that the influence of complete Coriolis force on the dispersion relation of ocean internal-wave under background currents field is obvious, and these results provide strong evidence for the understanding of dynamic process of density stratified ocean internal waves.
Seki, K.; Amano, T.; Saito, S.; Kamiya, K.; Miyoshi, Y.; Keika, K.; Matsumoto, Y.
2016-12-01
Terrestrial inner magnetosphere is the region where different plasma regimes over a wide range of energy such as the plasmasphere, ring current, and radiation belt coexist. Among them, the ring current carries most of plasma pressure and is thus responsible for deformation of the magnetic field. Since the deformation changes drift paths of charged particles including the ring current ions, it is important to describe this coupling between the ring current and electric/magnetic fields self-consistently. It is known that short-timescale phenomena such as ULF waves and substorm related ion injections from the plasma sheet play important roles in the inner magnetospheric dynamics during magnetic storms. While ULF waves contribute to the radial transport of relativistic electrons to form the radiation belt, the ion injections contribute to excitation of storm-time Pc5 ULF waves as well as to plasma supply to the ring current from the magnetotail. Aiming at a self-consistent description of the coupling between ring current ions and electric/magnetic fields, we have developed a global ring current model (GEMSIS-RC model). The model is a self-consistent and kinetic numerical simulation code solving the five-dimensional collisionless drift-kinetic equation for the ring-current ions coupled with Maxwell equations. Without assuming a force-balanced equilibrium, the GEMSIS-RC model allows the force-imbalance to exist, which generates induced electric field through the polarization current. In this study, we applied the GEMSIS-RC model for simulation of ULF waves in the inner magnetosphere with a focus on the short-timescale phenomena described above. Comparison between runs with/without ring current ions show that the existence of hot ring current ions can deform and amplify the original sinusoidal waveforms. The deformation causes the energy cascade to higher frequency range (Pc4 and Pc3 ranges). The cascade is more pronounced in high plasma beta cases. It is also shown that
an asymmetrically heated rectangular minichannel
Strąk Kinga
2017-01-01
Full Text Available This paper discusses test results concerning flow boiling heat transfer in a minichannel 1.7 mm in depth, 16 mm in width and 180 mm in length. The essential part of the experimental stand was a vertically oriented rectangular minichannel, which was heated asymmetrically with a plate made of Haynes-230 alloy. Distilled water was used as the cooling fluid. Changes in the temperature on the outer side of the heated plate in the central, axially symmetric part of the channel were measured using infrared thermography. Simultaneously, the other side of the heated plate in contact with the fluid was observed through a glass pane to identify the two-phase flow patterns. The one-dimensional model used for the heat transfer analysis took into account the heat flow direction, which was perpendicular to the direction of the fluid flow in the minichannel. The study involved determining local values of the heat transfer coefficient and generating boiling curves. The data for water were compared with the findings reported for the FC-72 fluid.
Xia, Hong; Chen, Jie; Zeng, Xiaoyan; Yan, Ming
2016-04-01
The Doppler effect is a fundamental physical phenomenon observed for waves propagating in vacuum or various media, commonly gaseous or liquid. Here, we report on the occurrence of a Doppler effect in a solid medium. Instead of a real object, a topological soliton, i.e., a magnetic domain wall (DW) traveling in a current-carrying ferromagnetic nanowire, plays the role of the moving wave source. The Larmor precession of the DW in an external field stimulates emission of monochromatic spin waves (SWs) during its motion, which show a significant Doppler effect, comparable to the acoustic one of a train whistle. This process involves two prominent spin-transfer-torque effects simultaneously, the current-driven DW motion and the current-induced SW Doppler shift. The latter gives rise to an interesting feature, i.e., the observed SW Doppler effect appears resulting from a stationary source and a moving observer, contrary to the laboratory frame.
Hamiltonian Approach to Internal Wave-Current Interactions in a Two-Media Fluid with a Rigid Lid
Compelli, Alan
2016-01-01
We examine a two-media 2-dimensional fluid system consisting of a lower medium bounded underneath by a flatbed and an upper medium with a free surface with wind generated surface waves but considered bounded above by a lid by an assumption that surface waves have negligible amplitude. An internal wave driven by gravity which propagates in the positive $x$-direction acts as a free common interface between the media. The current is such that it is zero at the flatbed but a negative constant, due to an assumption that surface winds blow in the negative $x$-direction, at the lid. We are concerned with the layers adjacent to the internal wave in which there exists a depth dependent current for which there is a greater underlying than overlying current. Both media are considered incompressible and having non-zero constant vorticities. The governing equations are written in canonical Hamiltonian form in terms of the variables, associated to the wave (in a presence of a constant current). The resultant equations of m...
Scotti, A.; Butman, B.; Beardsley, R.C.; Alexander, P.S.; Anderson, S.
2005-01-01
The algorithm used to transform velocity signals from beam coordinates to earth coordinates in an acoustic Doppler current profiler (ADCP) relies on the assumption that the currents are uniform over the horizontal distance separating the beams. This condition may be violated by (nonlinear) internal waves, which can have wavelengths as small as 100-200 m. In this case, the standard algorithm combines velocities measured at different phases of a wave and produces horizontal velocities that increasingly differ from true velocities with distance from the ADCP. Observations made in Massachusetts Bay show that currents measured with a bottom-mounted upward-looking ADCP during periods when short-wavelength internal waves are present differ significantly from currents measured by point current meters, except very close to the instrument. These periods are flagged with high error velocities by the standard ADCP algorithm. In this paper measurements from the four spatially diverging beams and the backscatter intensity signal are used to calculate the propagation direction and celerity of the internal waves. Once this information is known, a modified beam-to-earth transformation that combines appropriately lagged beam measurements can be used to obtain current estimates in earth coordinates that compare well with pointwise measurements. ?? 2005 American Meteorological Society.
Vdovin, V. L., E-mail: vdov@nfi.kiae.ru [National Research Centre ' Kurchatov Institute,' (Russian Federation)
2013-02-15
The innovative concept and 3D full-wave code modeling the off-axis current drive by radio-frequency (RF) waves in large-scale tokamaks, ITER and DEMO, for steady-state operation with high efficiency is proposed. The scheme uses the helicon radiation (fast magnetosonic waves at high (20-40) ion cyclotron frequency harmonics) at frequencies of 500-700 MHz propagating in the outer regions of the plasmas with a rotational transform. It is expected that the current generated by helicons, in conjunction with the bootstrap current, ensure the maintenance of a given value of the total current in the stability margin q(0) {>=} 2 and q(a) {>=} 4, and will help to have regimes with a negative magnetic shear and internal transport barrier to ensure stability at high normalized plasma pressure {beta}{sub N} > 3 (the so-called advanced scenarios) of interest for the commercial reactor. Modeling with full-wave three-dimensional codes PSTELION and STELEC showed flexible control of the current profile in the reactor plasmas of ITER and DEMO, using multiple frequencies, the positions of the antennae and toroidal wave slow down. Also presented are the results of simulations of current generation by helicons in the DIII-D, T-15MD, and JT-60AS tokamaks. Commercially available continuous-wave klystrons of the MW/tube range are promising for commercial stationary fusion reactors. The compact antennae of the waveguide type are proposed, and an example of a possible RF system for today's tokamaks is given. The advantages of the scheme (partially tested at lower frequencies in tokamaks) are a significant decline in the role of parametric instabilities in the plasma periphery, the use of electrically strong resonator-waveguide type antennae, and substantially greater antenna-plasma coupling.
Vdovin, V. L.
2013-02-01
The innovative concept and 3D full-wave code modeling the off-axis current drive by radio-frequency (RF) waves in large-scale tokamaks, ITER and DEMO, for steady-state operation with high efficiency is proposed. The scheme uses the helicon radiation (fast magnetosonic waves at high (20-40) ion cyclotron frequency harmonics) at frequencies of 500-700 MHz propagating in the outer regions of the plasmas with a rotational transform. It is expected that the current generated by helicons, in conjunction with the bootstrap current, ensure the maintenance of a given value of the total current in the stability margin q(0) ≥ 2 and q( a) ≥ 4, and will help to have regimes with a negative magnetic shear and internal transport barrier to ensure stability at high normalized plasma pressure β N > 3 (the so-called advanced scenarios) of interest for the commercial reactor. Modeling with full-wave three-dimensional codes PSTELION and STELEC showed flexible control of the current profile in the reactor plasmas of ITER and DEMO, using multiple frequencies, the positions of the antennae and toroidal wave slow down. Also presented are the results of simulations of current generation by helicons in the DIII-D, T-15MD, and JT-60AS tokamaks. Commercially available continuous-wave klystrons of the MW/tube range are promising for commercial stationary fusion reactors. The compact antennae of the waveguide type are proposed, and an example of a possible RF system for today's tokamaks is given. The advantages of the scheme (partially tested at lower frequencies in tokamaks) are a significant decline in the role of parametric instabilities in the plasma periphery, the use of electrically strong resonator-waveguide type antennae, and substantially greater antenna-plasma coupling.
Three-dimensional modelling of wave-induced current from the surf zone to the inner shelf
H. Michaud
2011-12-01
Full Text Available We develop and implement a new method to take into account the impact of waves into the 3-D circulation model SYMPHONIE (Marsaleix et al., 2008, 2009a, following the simplified equations of Bennis et al. (2011 which use glm2z-RANS theory (Ardhuin et al., 2008b. These adiabatic equations are completed by additional parameterizations of wave breaking, bottom friction and wave-enhanced vertical mixing, making the forcing valid from the surf zone through to the open ocean. The wave forcing is performed by wave generation and propagation models WAVEWATCH III® (Tolman, 2008, 2009; Ardhuin et al., 2010 and SWAN (Booij et al., 1999. The model is tested and compared with other models for a plane beach test case, previously tested by Haas and Warner (2009 and Uchiyama et al. (2010. A comparison is also made with the laboratory measurements of Haller et al. (2002 of a barred beach with channels. Results fit with previous simulations performed by other models and with available observational data.
Finally, a realistic case of energetic waves travelling over a coast of the Gulf of Lion (in the northwest of the Mediterranean Sea for which currents are available at different depths as well as an accurate bathymetric database of the 0–10 m depth range, is then simulated. A grid nesting approach is used to account for the different forcings acting at different spatial scales. The simulation coupling the effects of waves and currents is successful to reproduce the powerful northward littoral drift in the 0–15 m depth zone. More precisely, two distinct cases are identified: when waves have a normal angle of incidence with the coast, they are responsible for complex circulation cells and rip currents in the surf zone, and when they travel obliquely, they generate a northward littoral drift. These features are more complicated than in the test cases, due to the complex bathymetry and the consideration of wind and non-stationary processes. Wave impacts
Three-dimensional modelling of wave-induced current from the surf zone to the inner shelf
H. Michaud
2012-08-01
Full Text Available We develop and implement a new method to take into account the impact of waves into the 3-D circulation model SYMPHONIE (Marsaleix et al., 2008, 2009a following the simplified equations of Bennis et al. (2011 which use glm2z-RANS theory (Ardhuin et al., 2008c. These adiabatic equations are completed by additional parameterizations of wave breaking, bottom friction and wave-enhanced vertical mixing, making the forcing valid from the surf zone through to the open ocean. The wave forcing is performed by wave generation and propagation models WAVEWATCH III® (Tolman, 2008, 2009; Ardhuin et al., 2010 and SWAN (Booij et al., 1999. The model is tested and compared with other models for a plane beach test case, previously tested by Haas and Warner (2009and Uchiyama et al. (2010. A comparison is also made with the laboratory measurements of Haller et al. (2002 of a barred beach with channels. Results fit with previous simulations performed by other models and with available observational data.
Finally, a realistic case is simulated with energetic waves travelling over a coast of the Gulf of Lion (in the northwest of the Mediterranean Sea for which currents are available at different depths as well as an accurate bathymetric database of the 0–10 m depth range. A grid nesting approach is used to account for the different forcings acting at different spatial scales. The simulation coupling the effects of waves and currents is successful to reproduce the powerful northward littoral drift in the 0–15 m depth zone. More precisely, two distinct cases are identified: When waves have a normal angle of incidence with the coast, they are responsible for complex circulation cells and rip currents in the surf zone, and when they travel obliquely, they generate a northward littoral drift. These features are more complicated than in the test cases, due to the complex bathymetry and the consideration of wind and non-stationary processes. Wave impacts in the
Ashirbayev, Nurgali; Ashirbayeva, Zhansaya; Sultanbek, Turlybek; Bekmoldayeva, Raina
2016-08-01
In this work we consider the problem of the propagation of non stationary stress waves in an elastic body with a rectangular hole in the linear formulation. The wave process is caused by applying an external dynamic load on the front boundary of the rectangular region and the lateral boundaries are free of the stress. The lower boundary of the rectangular region is rigidly fixed, and the contour of the rectangular hole is free from the stress. The problem is solved by using the difference method of the spatial characteristics. On the basis of the developed numerical methods it is obtained the computational finite - difference relations of the dynamic problems at the corner points of the rectangular hole, where the first and second derivatives of the unknown functions have a discontinuity of the first kind. We analyze the dynamic stress fields in an elastic body with a rectangular hole and we studied the concentration of dynamic stresses in the vicinity of the corner points of the rectangular opening.
Comparison of CAD Formulas, Method of Moments and Experiments for Rectangular Microstrip Antennas
Z. Novacek
2003-04-01
Full Text Available Calculations of several cases for rectangular microstrip patchantennas using more accurate cavity model have been compared with theconventional cavity calculations, expressions generated by curvefitting to full wave solutions and method of moments. Calculated aswell as experimental values have been studied for different thickness,patch sizes and substrate materials with different permittivities andlosses.
Analysis of the relationship of the radial cavity with a rectangular waveguide
A. Yu. Bovsunovskii
1987-12-01
Full Text Available The analytically obtained a simple expression for the radial connection vnutrivolnovodnogo hollow waveguide resonator with a rectangular cross section for the main types of waves. The results may be useful in the design of solid-state generators range microwave waveguide.
Superconvergence for rectangular serendipity finite elements
CHEN; Chuanmiao(陈传淼)
2003-01-01
Based on an orthogonal expansion and orthogonality correction in an element, superconvergenceat symmetric points for any degree rectangular serendipity finite element approximation to second order ellipticproblem is proved, and its behaviour up to the boundary is also discussed.
Thermal Impedance of Rectangular Microwave Oven Linings
SHIShang－zhao; XUFu－qiu; 等
1996-01-01
Amodel was preseted for calcultaing the thermal impedance of the insulation and refractory linings of rectangular microwave ovens,of which the oven cavity's dimensions are relatively small,while the linings re relatively thick.
Demagnetizing effects in stacked rectangular prisms
Christensen, Dennis; Nielsen, Kaspar Kirstein; Bahl, Christian Robert Haffenden;
2011-01-01
A numerical, magnetostatic model of the internal magnetic field of a rectangular prism is extended to the case of a stack of rectangular prisms. The model enables the calculation of the spatially resolved, three-dimensional internal field in such a stack given any magnetic state function, stack...... configuration, temperature distribution and applied magnetic field. In this paper the model is applied to the case of a stack of parallel, ferromagnetic rectangular prisms and the resulting internal field is found as a function of the orientation of the applied field, the number of prisms in the stack...... a direct impact on the design of, e.g., active magnetic regenerators made of stacked rectangular prisms in terms of optimizing the internal field....
Interface-Optical-Phonon Modes in Quasi-one-dimensional Wurtzite Rectangular Quantum Wires
ZHANG Li
2006-01-01
By employing the dielectric continuum model and Loudon's uniaxial crystal model, the interface optical(IO) phonon modes in a freestanding quasi-one-dimensional (Q1D) wurtzite rectangular quantum wire are derived and analyzed. Numerical calculation on a freestanding wurtzite GaN quantum wire is performed. The results reveal that the dispersion frequencies of IO modes sensitively depend on the geometric structures of the Q1D wurtzite rectangular quantum wires, the free wave-number kz in z-direction and the dielectric constant of the nonpolar matrix. The degenerating behavior of the IO modes in Q1D wurtzite rectangular quantum wire has been clearly observed in the case of small wave-number kz and large ratio of length to width of the rectangular crossing profile. The limited frequency behaviors of IO modes have been analyzed deeply, and detailed comparisons with those in wurtzite planar quantum wells and cylindrical quantum wires are also done. The present theories can be looked on as a generalization of that in isotropic rectangular quantum wires, and it can naturally reduce to the case of Q1D isotropic quantum wires once the anisotropy of the wurtzite material is ignored.
Sajiv Philip CHEMPALAYIL; V Sanil KUMAR; G Udhaba DORA; Glejin JOHNSON
2014-01-01
Coastlines are undergoing constant geomorphologic changes with respect to the incident wave climate. Based on waves measured at 9 m water depth, simulation of near shore wave transformation is done using REFDIF-1 numerical model and the near shore breaker parameters are estimated at two micro-tidal beaches along central west coast of India. Model results are validated with measured values. From the breaker parameters, long-shore current and long-shore sediment transport rates (LSTR) are computed by using semi-empirical equations. Estimated long-shore current and LSTR are showing dramatic variations with respect to seasons. Predominant direction of LSTR is observed towards north since the approach waves are from south-west direction during pre-monsoon and post monsoon. During monsoon season, waves are from west south-west and resulted in southerly transport. The estimated annual net and gross LSTR by Cambridge Environmental Research Consultants (CERC) at two locations are in the same order whereas LSTR estimated by Walton & Bruno and Kamphuis equations are showing different estimations because of difference in surf-zone width and foreshore slope between the two locations. For micro-tidal beaches with length less than 6 km, Kamphuis equation is giving agreeable estimation of LSTR. Sensitivity analysis of LSTR estimate shows that coastal inclination is the prominent factor in determining LSTR than incident wave angle.
Finite-difference calculation of traveltimes based on rectangular grid
李振春; 刘玉莲; 张建磊; 马在田; 王华忠
2004-01-01
To the most of velocity fields, the traveltimes of the first break that seismic waves propagate along rays can be computed on a 2-D or 3-D numerical grid by finite-difference extrapolation. Under ensuring accuracy, to improve calculating efficiency and adaptability, the calculation method of first-arrival traveltime of finite-difference is derived based on any rectangular grid and a local plane wavefront approximation. In addition, head waves and scattering waves are properly treated and shadow and caustic zones cannot be encountered, which appear in traditional ray-tracing. The testes of two simple models and the complex Marmousi model show that the method has higher accuracy and adaptability to complex structure with strong vertical and lateral velocity variation, and Kirchhoff prestack depth migration based on this method can basically achieve the position imaging effects of wave equation prestack depth migration in major structures and targets. Because of not taking account of the later arrivals energy, the effect of its amplitude preservation is worse than that by wave equation method, but its computing efficiency is higher than that by total Green's function method and wave equation method.
Fluid in Rectangular Tank – Frequency Analysis
Kotrasová Kamila
2014-06-01
Full Text Available Ground-supported tanks are used to store a variety of liquids. During earthquake activity the liquid exerts impulsive and convective pressures (sloshing on the walls and bottom of the rectangular tank. This paper provides theoretical background for analytical calculating of circular frequencies and hydrodynamic pressures developed during an earthquake in rectangular container. Analytical results of first natural frequency are compared with experiment.
Random Young diagrams in a Rectangular Box
Beltoft, Dan; Boutillier, Cédric; Enriquez, Nathanaël
We exhibit the limit shape of random Young diagrams having a distribution proportional to the exponential of their area, and confined in a rectangular box. The Ornstein-Uhlenbeck bridge arises from the fluctuations around the limit shape.......We exhibit the limit shape of random Young diagrams having a distribution proportional to the exponential of their area, and confined in a rectangular box. The Ornstein-Uhlenbeck bridge arises from the fluctuations around the limit shape....
Evaluation of TEP Deaeration Tower Rectangular Flange
WANG; Zhi-hao
2013-01-01
The rectangular flange is adapted in the heater of TEP deaeration tower(Fig.1).The rectangular flange is no-round type flange,the evaluation of which is worked on equivalent round flange method.Thecalculation is based on no-round type flange evaluation chapter in HGT 20582—2011 Steel chemical vessel strength calculation code.The loads on the flange are inner pressure,nozzle loads and seismic loads.The nozzle loads is
Random Young diagrams in a Rectangular Box
Beltoft, Dan; Boutillier, Cédric; Enriquez, Nathanaël
We exhibit the limit shape of random Young diagrams having a distribution proportional to the exponential of their area, and confined in a rectangular box. The Ornstein-Uhlenbeck bridge arises from the fluctuations around the limit shape.......We exhibit the limit shape of random Young diagrams having a distribution proportional to the exponential of their area, and confined in a rectangular box. The Ornstein-Uhlenbeck bridge arises from the fluctuations around the limit shape....
Gamayunov, K. V.; Khazanov, G. V.; Liemohn, M. W.; Fok, M.-C.; Ridley, A. J.
2009-01-01
Further development of our self-consistent model of interacting ring current (RC) ions and electromagnetic ion cyclotron (EMIC) waves is presented. This model incorporates large scale magnetosphere-ionosphere coupling and treats self-consistently not only EMIC waves and RC ions, but also the magnetospheric electric field, RC, and plasmasphere. Initial simulations indicate that the region beyond geostationary orbit should be included in the simulation of the magnetosphere-ionosphere coupling. Additionally, a self-consistent description, based on first principles, of the ionospheric conductance is required. These initial simulations further show that in order to model the EMIC wave distribution and wave spectral properties accurately, the plasmasphere should also be simulated self-consistently, since its fine structure requires as much care as that of the RC. Finally, an effect of the finite time needed to reestablish a new potential pattern throughout the ionosphere and to communicate between the ionosphere and the equatorial magnetosphere cannot be ignored.
A Rectangular Planar Spiral Antenna for GIS Partial Discharge Detection
Xiaoxing Zhang
2014-01-01
Full Text Available A rectangular planar spiral antenna sensor was designed for detecting the partial discharge in gas insulation substations (GIS. It can expediently receive electromagnetic waves leaked from basin-type insulators and can effectively suppress low frequency electromagnetic interference from the surrounding environment. Certain effective techniques such as rectangular spiral structure, bow-tie loading, and back cavity structure optimization during the antenna design process can miniaturize antenna size and optimize voltage standing wave ratio (VSWR characteristics. Model calculation and experimental data measured in the laboratory show that the antenna possesses a good radiating performance and a multiband property when working in the ultrahigh frequency (UHF band. A comparative study between characteristics of the designed antenna and the existing quasi-TEM horn antenna was made. Based on the GIS defect simulation equipment in the laboratory, partial discharge signals were detected by the designed antenna, the available quasi-TEM horn antenna, and the microstrip patch antenna, and the measurement results were compared.
Zodiatis, George; Galanis, George; Nikolaidis, Andreas; Stylianoy, Stavros; Liakatas, Aristotelis
2015-04-01
The use of wave energy as an alternative renewable is receiving attention the last years under the shadow of the economic crisis in Europe and in the light of the promising corresponding potential especially for countries with extended coastline. Monitoring and studying the corresponding resources is further supported by a number of critical advantages of wave energy compared to other renewable forms, like the reduced variability and the easier adaptation to the general grid, especially when is jointly approached with wind power. Within the framework, a number of countries worldwide have launched research and development projects and a significant number of corresponding studies have been presented the last decades. However, in most of them the impact of wave-sea surface currents interaction on the wave energy potential has not been taken into account neglecting in this way a factor of potential importance. The present work aims at filling this gap for a sea area with increased scientific and economic interest, the Eastern Mediterranean Sea. Based on a combination of high resolution numerical modeling approach with advanced statistical tools, a detailed analysis is proposed for the quantification of the impact of sea surface currents, which produced from downscaling the MyOcean-FO regional data, to wave energy potential. The results although spatially sensitive, as expected, prove beyond any doubt that the wave- sea surface currents interaction should be taken into account for similar resource analysis and site selection approaches since the percentage of impact to the available wave power may reach or even exceed 20% at selected areas.
Total reflection and cloaking by zero index metamaterials loaded with rectangular dielectric defects
Wu, Ying
2013-05-06
In this work, we investigate wave transmission property through a zero index metamaterial (ZIM) waveguide embedded with rectangular dielectric defects. We show that total reflection and total transmission (cloaking) can be achieved by adjusting the geometric sizes and/or permittivities of the defects. Our work provides another possibility of manipulating wave propagation through ZIM in addition to the widely studied dielectric defects with cylindrical geometries.
A Comment on Interaction of Lower Hybrid Waves with the Current-Driven Ion-Acoustic Instability
Schrittwieser, R.; Juul Rasmussen, Jens
1985-01-01
Majeski et al. (1984) have investigated the interaction between the current-driven 'ion-acoustic' instability and high frequency lower hybrid waves. The 'ion-acoustic' instability was excited by drawing an electron current through the plasma column of a single-ended Q-machine by means of a positi......Majeski et al. (1984) have investigated the interaction between the current-driven 'ion-acoustic' instability and high frequency lower hybrid waves. The 'ion-acoustic' instability was excited by drawing an electron current through the plasma column of a single-ended Q-machine by means...... of a positively biased cold plate. Schmittwieser et al. do not believe that the observed instability is of the ion-acoustic type but that it is rather the so-called potential relaxation instability....
Kim, Sun-Ho, E-mail: shkim95@kaeri.re.kr [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of); Jeong, Seung-Ho [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of); Lee, Hyunwoo; Lee, Byungje [KwangWoon University, Seoul (Korea, Republic of); Jo, Jong-Gab; Lee, Hyun-Young; Hwang, Yong-Seok [Seoul National University, Seoul (Korea, Republic of)
2016-11-01
An efficient heating and current drive scheme in central or off-axis region is required to realize steady state operation of tokamak fusion reactor. And the fast wave in lower hybrid resonance range of frequency could be a candidate for such an efficient scheme in high density and high temperature plasmas. Its propagation and absorption characteristics including current drive and coupling efficiency are analyzed for Versatile Experiment Spherical Torus and it is shown that it is possible to drive current with considerable current drive efficiency in central region. The RF system for the fast wave experiment including klystron, transmission systems, inter-digital antenna, and RF diagnostics are given as well in this paper.
Han, Shuzong; Yang, Hua; Xue, Wenhu; Wang, Xingchi
2017-06-01
This paper introduces the assimilation technology in an ocean dynamics model and discusses the feasibility of inverting the sea surface current in the detection zone by assimilating the sea current radial velocity detected by single station HF ground wave radar in ocean dynamics model. Based on the adjoint assimilation and POM model, the paper successfully inverts the sea surface current through single station HF ground wave radar in the Zhoushan sea area. The single station HF radar inversion results are also compared with the bistatic HF radar composite results and the fixed point measured results by Annderaa current meter. The error analysis shows that acquisition of flow velocity and flow direction data from the single station HF radar based on adjoint assimilation and POM model is viable and the data obtained have a high correlation and consistency with the flow field observed by HF radar.
Heat waves and morbidity: current knowledge and further direction-a comprehensive literature review.
Li, Mengmeng; Gu, Shaohua; Bi, Peng; Yang, Jun; Liu, Qiyong
2015-05-18
In the past few decades, several devastating heat wave events have significantly challenged public health. As these events are projected to increase in both severity and frequency in the future, it is important to assess the relationship between heat waves and the health indicators that can be used in the early warning systems to guide the public health response. Yet there is a knowledge gap in the impact of heat waves on morbidity. In this study, a comprehensive review was conducted to assess the relationship between heat waves and different morbidity indicators, and to identify the vulnerable populations. The PubMed and ScienceDirect database were used to retrieve published literature in English from 1985 to 2014 on the relationship between heat waves and morbidity, and the following MeSH terms and keywords were used: heat wave, heat wave, morbidity, hospital admission, hospitalization, emergency call, emergency medical services, and outpatient visit. Thirty-three studies were included in the final analysis. Most studies found a short-term negative health impact of heat waves on morbidity. The elderly, children, and males were more vulnerable during heat waves, and the medical care demand increased for those with existing chronic diseases. Some social factors, such as lower socioeconomic status, can contribute to heat-susceptibility. In terms of study methods and heat wave definitions, there remain inconsistencies and uncertainties. Relevant policies and guidelines need to be developed to protect vulnerable populations. Morbidity indicators should be adopted in heat wave early warning systems in order to guide the effective implementation of public health actions.
Pol, F. van der; Sluyters-Rehbach, M.; Sluyters, J.H.
1975-01-01
A theoretical study is presented concerning the application of a high-frequency alternating current, amplitude modulated by a low-frequency sine wave, to a galvanic cell. Based on the correlation with the faradaic rectification technique, expressions are given for the low-frequency demodulation
Three-wave interaction during electron cyclotron resonance heating and current drive
Nielsen, Stefan Kragh; Jacobsen, Asger Schou; Hansen, Søren Kjer
2016-01-01
Non-linear wave-wave interactions in fusion plasmas, such as the parametric decay instability (PDI) of gyrotron radiation, can potentially hamper the use of microwave diagnostics. Here we report on anomalous scattering in the ASDEX Upgrade tokamak during electron cyclotron resonance heating...
Linear and nonlinear dynamics of current-driven waves in dusty plasmas
Ahmad, Ali [National Centre for Physics (NCP), Shahdara Valley Road, 44000 Islamabad (Pakistan); Department of Physics, COMSATS Institute of Information Technology (CIIT), Islamabad (Pakistan); Theoretical Plasma Physics Division, PINSTECH, P. O. Nilore, Islamabad (Pakistan); Ali Shan, S.; Haque, Q. [National Centre for Physics (NCP), Shahdara Valley Road, 44000 Islamabad (Pakistan); Theoretical Plasma Physics Division, PINSTECH, P. O. Nilore, Islamabad (Pakistan); Saleem, H. [National Centre for Physics (NCP), Shahdara Valley Road, 44000 Islamabad (Pakistan); Department of Physics, COMSATS Institute of Information Technology (CIIT), Islamabad (Pakistan)
2012-09-15
The linear and nonlinear dynamics of a recently proposed plasma mode of dusty plasma is studied using kappa distribution for electrons. This electrostatic wave can propagate in the plasma due to the sheared flow of electrons and ions parallel to the external magnetic field in the presence of stationary dust. The coupling of this wave with the usual drift wave and ion acoustic wave is investigated. D'Angelo's mode is also modified in the presence of superthermal electrons. In the nonlinear regime, the wave can give rise to dipolar vortex structures if the shear in flow is weaker and tripolar vortices if the flow has steeper gradient. The results have been applied to Saturn's magnetosphere corresponding to negatively charged dust grains. But the theoretical model is applicable for positively charged dust as well. This work will be useful for future observations and studies of dusty environments of planets and comets.
SUN Weitao; YANG Huizhu
2004-01-01
This paper presents a finite-difference (FD) method with spatially non-rectangular irregular grids to simulate the elastic wave propagation. Staggered irregular grid finite difference operators with a second-order time and spatial accuracy are used to approximate the velocity-stress elastic wave equations. This method is very simple and the cost of computing time is not much. Complicated geometries like curved thin layers, cased borehole and nonplanar interfaces may be treated with nonrectangular irregular grids in a more flexible way. Unlike the multi-grid scheme, this method requires no interpolation between the fine and coarse grids and all grids are computed at the same spatial iteration. Compared with the rectangular irregular grid FD, the spurious diffractions from "staircase"interfaces can easily be eliminated without using finer grids. Dispersion and stability conditions of the proposed method can be established in a similar form as for the rectangular irregular grid scheme. The Higdon's absorbing boundary condition is adopted to eliminate boundary reflections. Numerical simulations show that this method has satisfactory stability and accuracy in simulating wave propagation near rough solid-fluid interfaces. The computation costs are less than those using a regular grid and rectangular grid FD method.
Wu, Ping; Sun, Jun; Song, Zhimin; Teng, Yan
2017-01-01
Explosive emission cathodes (EECs) are widely used in high power microwave generators. This paper researches the influence of the emission threshold and the current increase rate of annular EECs on the microwave starting time of a relativistic backward wave oscillator (RBWO) when the current amplitude is not affected. The results show that a moderate delay in explosive emission, as long as it's not too long and the current increase rate keeps fast enough, won't bring about a corresponding delay in the starting time of microwave, but inversely, may suppress the mode competition and thus expedite the starting process slightly. The current increase rate, however, has more prominent influence on the starting time of the RBWO. A slower current increase rate will delay the time when the beam current reaches the starting current and lead to a longer starting time.
Guerreiro, Gabriela V; Zaitouna, Anita J; Lai, Rebecca Y
2014-01-31
Here we report the characterization of an electrochemical mercury (Hg(2+)) sensor constructed with a methylene blue (MB)-modified and thymine-containing linear DNA probe. Similar to the linear probe electrochemical DNA sensor, the resultant sensor behaved as a "signal-off" sensor in alternating current voltammetry and cyclic voltammetry. However, depending on the applied frequency or pulse width, the sensor can behave as either a "signal-off" or "signal-on" sensor in square wave voltammetry (SWV) and differential pulse voltammetry (DPV). In SWV, the sensor showed "signal-on" behavior at low frequencies and "signal-off" behavior at high frequencies. In DPV, the sensor showed "signal-off" behavior at short pulse widths and "signal-on" behavior at long pulse widths. Independent of the sensor interrogation technique, the limit of detection was found to be 10nM, with a linear dynamic range between 10nM and 500nM. In addition, the sensor responded to Hg(2+) rather rapidly; majority of the signal change occurred in <20min. Overall, the sensor retains all the characteristics of this class of sensors; it is reagentless, reusable, sensitive, specific and selective. This study also highlights the feasibility of using a MB-modified probe for real-time sensing of Hg(2+), which has not been previously reported. More importantly, the observed "switching" behavior in SWV and DPV is potentially generalizable and should be applicable to most sensors in this class of dynamics-based electrochemical biosensors. Copyright © 2013 Elsevier B.V. All rights reserved.
Gulyaev, Yuri V.
1974-01-01
It is shown that the principal characteristic feature of the surface acoustic waves in piezoelectrics—the presence of an alternating electric field transverse to the surface, which can be of the same order of magnitude as the longitudinal field—may not only give rise to the known transverse...... acoustoelectric effect but also lead to amplification of surface acoustic waves by electron drift perpendicular to the surface. For Love waves in a piezoelectric semiconductor film on a highly conducting substrate, the amplification coefficient is found and the conditions necessary for amplification...
Design of Three-Dimensional Hypersonic Inlets with Rectangular to Elliptical Shape Transition
Smart, M. K.
1998-01-01
A methodology has been devised for the design of three-dimensional hypersonic inlets which include a rectangular to elliptical shape transition. This methodology makes extensive use of inviscid streamtracing techniques to generate a smooth shape transition from a rectangular-like capture to an elliptical throat. Highly swept leading edges and a significantly notched cowl enable use of these inlets in fixed geometry configurations. The design procedure includes a three dimensional displacement thickness calculation and uses established correlations to check for boundary layer separation due to shock wave interactions. Complete details of the design procedure are presented and the characteristics of a modular inlet with rectangular to elliptical shape transition and a design point of Mach 7.1 are examined. Comparison with a classical two-dimensional inlet optimized for maximum total pressure recovery indicates that this three-dimensional inlet demonstrates good performance even well below its design point.
Kourtzanidis, K.; Raja, L. L.
2017-04-01
We report on a computational modeling study of small scale plasma discharge formation with rectangular dielectric resonators (DR). An array of rectangular dielectric slabs, separated by a gap of millimeter dimensions is used to provide resonant response when illuminated by an incident wave of 1.26 GHz. A coupled electromagnetic (EM) wave–plasma model is used to describe the breakdown, early response and steady state of the argon discharge. We characterize the plasma generation with respect to the input power, background gas pressure and gap size. It is found that the plasma discharge is generated mainly inside the gaps between the DR at positions that correspond to the antinodes of the resonant enhanced electric field pattern. The enhancement of the electric field inside the gaps is due to a combination of leaking and displacement current radiation from the DR. The plasma is sustained in over-critical densities due to the large skin depth with respect to the gap and plasma size. Electron densities are calculated in the order of {10}18{--}{10}19 {{{m}}}-3 for a gas pressure of 10 Torr, while they exceed 1020 {{{m}}}-3 in atmospheric conditions. Increase of input power leads to more intense ionization and thus faster plasma formation and results to a more symmetric plasma pattern. For low background gas pressure the discharge is diffusive and extends away from the gap region while in high pressure it is constricted inside the gap. An optimal gap size can be found to provide maximum EM energy transfer to the plasma. This fact demonstrates that the gap size dictates to a certain extent the resonant frequency and the Q-factor of the dielectric array and the breakdown fields can not be determined in a straight-forward way but they are functions of the resonators geometry and incident field frequency.
Khazanov, G. V.; Gamayunov, K. V.; Gallagher, D. L.; Kozyra, J. W.
2007-01-01
It is well-known that the effects of electromagnetic ion cyclotron (EMIC) waves on ring current (RC) ion and radiation belt (RB) electron dynamics strongly depend on such particle/wave characteristics as the phase-space distribution function, frequency, wavenormal angle, wave energy, and the form of wave spectral energy density. The consequence is that accurate modeling of EMIC waves and RC particles requires robust inclusion of the interdependent dynamics of wave growth/damping, wave propagation, and[ particles. Such a self-consistent model is being progressively developed by Khazanov et al. [2002, 2006, 2007]. This model is based on a system of coupled kinetic equations for the RC and EMIC wave power spectral density along with the ray tracing equations. Thome and Home [2007] (hereafter referred to as TH2007) call the Khazanov et al. [2002, 2006] results into question in their Comment. The points in contention can be summarized as follows. TH2007 claim that: (1) "the important damping of waves by thermal heavy ions is completely ignored", and Landau damping during resonant interaction with thermal electrons is not included in our model; (2) EMIC wave damping due to RC O + is not included in our simulation; (3) non-linear processes limiting EMIC wave amplitude are not included in our model; (4) growth of the background fluctuations to a physically significantamplitude"must occur during a single transit of the unstable region" with subsequent damping below bi-ion latitudes,and consequently"the bounce averaged wave kinetic equation employed in the code contains a physically erroneous 'assumption". Our reply will address each of these points as well as other criticisms mentioned in the Comment. TH2007 are focused on two of our papers that are separated by four years. Significant progress in the self-consistent treatment of the RC-EMIC wave system has been achieved during those years. The paper by Khazanov et al. [2006] presents the latest version of our model, and in
Influence of deposited energy on shock wave induced by underwater pulsed current discharge
Li, Xian-Dong; Liu, Yi; Liu, Si-Wei; Li, Zhi-Yuan; Zhou, Gu-Yue; Li, Hua; Lin, Fu-Chang; Pan, Yuan
2016-10-01
In this paper, an integrated experimental system is established to study the influence of deposited energy on the intensity of the shock wave induced by underwater pulse discharge. Considering the time varying behavior of the arc, the calculation methods of the deposited energy into the plasma channel and the average arc resistance are proposed and presented. The effect of the breakdown process on the deposited energy and the shock wave is analyzed. It can be concluded that the shock wave intensity can be improved by depositing more energy in the first half oscillation period and increasing the arc resistance. It is also found that the energy deposition and the shock wave intensity are significantly influenced by the breakdown time delay and the shape of the initial plasma channel.
Current Status of Blast Wave Theory and Computations. Volume 2. The Quasi-Similar Solution
1984-03-01
0.02 0.04 y Fig. IV.4.17 - 260 - SIV.5. ANALYSIS OF REACTIVE BLAST WAVES PROPAGATING THROUGH GASEOUS MIXTURES WITH A SPATIALLY VARYING HEAT OF DETONATION * i...a Spatially Varying Heat of Detonation " Paper Presented at the 8th International Colloquium on Gasdynamics of Ex- plosions and Reactive Systems... of Detonation 260 6. Blast Waves in a Detonating Medium with Transport Properties Taken into Account 287 REFERENCES 326 iii CHAPTER I NON-SELF-SIMILAR
Measurements of current speed using an Aanderaa RCM4 current meter in the presence of surface waves
Sherwin, T. J.
1988-02-01
It is shown that the Aanderaa RCM4 with Savonius rotor integrates motions that have a period significantly smaller than the recording interval, thus causing a quantifiable amplification of the observed mean speed. The minimum speed that can be recorded is 2ν/;π, where ν is the amplitude of the speed of the oscillating motion. In general, the amplification factor decreases as the ratio of mean speed over ν increases. The theory appears to explain the difference in observations made by an Aanderaa RCM4 and a neighbouring EG&G VMCM when particle velocities due to swell are included. It is recommended that vector averaging current meters should be used for current measurement in the upper 50-100 m of shelf sea regions that experience small tidal currents and a large oceanic swell.
Jackson, H. W.; Barmatz, M.; Shipley, C.
1988-01-01
The effect of a standing wave field in a rectangular chamber on the shape and location of an acoustically positioned drop or bubble is calculated. The sample deformation and equilibrium position are obtained from an analysis of the spherical harmonic projections of the total surface stress tensor. The method of calculation relies on the assumed condition that the sample is only slightly distorted from a spherical form. The equilibrium location of a levitated drop is combined with a formula introduced by Hasegawa (1979) to calcualte the ka dependence of the radiation force function. The present theory is valid for large as well as small ka values. Calculations in the small ka limit agree with previous theories and experimental results. Examples are presented for nonplane-wave modes as well as plane-wave rectangular modes.
Ekino, T.; Gabovich, A. M.; Li, Mai Suan; Szymczak, H.; Voitenko, A. I.
2016-11-01
The quasiparticle tunnel current J(V) between the superconducting ab-planes along the c-axis and the corresponding conductance G(V)=\\text{d}J/\\text{d}V were calculated for symmetric junctions composed of disordered d-wave layered superconductors partially gapped by charge density waves (CDWs). Here, V is the voltage. Both the checkerboard and unidirectional CDWs were considered. It was shown that the spatial spread of the CDW-pairing strength substantially smears the peculiarities of G(V) appropriate to uniform superconductors. The resulting curves G(V) become very similar to those observed for a number of cuprates in intrinsic junctions, e.g. mesas. In particular, the influence of CDWs may explain the peak-dip-hump structures frequently found for high-T c oxides.
High-Precision Multi-Wave Rectifier Circuit Operating in Low Voltage + 1.5 Volt Current Mode
Bancha Burapattanasiri
2009-12-01
Full Text Available This article is present high-precision multi-wave rectifier circuit operating in low voltage +/- 1.5 Volt current modes by CMOS technology 0.5 μm, receive input and give output in current mode, respond at high frequency period. The structure compound with high-speed current comparator circuit, current mirror circuit, and CMOS inverter circuit. PSpice program used for confirmation the performance of testing. The PSpice program shows operating of circuit is able to working at maximum input current 400 μAp-p, maximum frequency responding 200 MHz, high precision and low power losses, and non-precision zero crossing output signal.Keywords-component; rectifier circuit; high-precision; low voltage; current mode;
Experimental Investigation of a Rectangular Airlift Pump
I. I. Esen
2010-01-01
Full Text Available Hydraulic performance of an airlift pump having a rectangular cross-section 20 mm × 80 mm was investigated through an experimental program. The pump was operated at six different submergence ratios and the liquid flow rate was measured at various flowrates of air injected. The effectiveness of the pump, defined as the ratio of the mass of liquid pumped to the mass of air injected, was determined as a function of the mass of air injected for different submergence ratios. Results obtained were compared with those for circular airlift pumps using an analytical model for circular pumps. Effectiveness of the rectangular airlift pump was observed to be comparable to that of the circular pumps. Hydraulic performance of the rectangular airlift pump investigated was then described by a set of semilogarithmic empirical equations.
Zhao, Shuang-ren; Yang, Kang; Yang, Xingang; Yang, Xintie
2016-01-01
Quantum physics has the probability interpretation. From the knowledge of light, we know that wave is always spread out, and hence the electron wave should also spread out. That means the electron wave beam should like the light wave beam become diverged from the source. When the electron is received by an atom we thought the wave collapse. The place to collapse is depends on the probability calculated from the square of absolute value of the wave function. The recent new discovery tell us that the light is not just wave, it is a combination of waves, retarded potential and advanced potential. These two potentials together produce the mutual energy current or referred as M-current. Another light energy current is P-current related to Poynting vector. We found P-current doesn't carry any energy for light. The contribution of P-current to energy transfer can be omitted. The light energy is transferred only by M-current. The beam of M-current doesn't like the beam of P-current which is diverged from the source, ...
National Oceanic and Atmospheric Administration, Department of Commerce — Current direction, chemical, phytoplankton, zooplankton, wind wave spectra, and other data were collected using moored current meter casts and other instruments in...
National Oceanic and Atmospheric Administration, Department of Commerce — Current direction, zooplankton, benthic organisms, wind wave spectra, and other data were collected using moored current meter casts and other instruments in the...
National Oceanic and Atmospheric Administration, Department of Commerce — Current direction, benthic organisms, wind wave spectra, and other data were collected using moored current meter casts in the Gulf of Mexico from March 25, 1977 to...
National Oceanic and Atmospheric Administration, Department of Commerce — Current direction, marine toxic substances, and wind wave spectra data were collected using moored current meter casts and other instruments in the Gulf of Mexico...
National Oceanic and Atmospheric Administration, Department of Commerce — Current direction, salinity, and wind wave spectra data were collected using moored current meter casts in the Gulf of Mexico from June 28, 1978 to February 28,...
National Oceanic and Atmospheric Administration, Department of Commerce — Current direction, wind wave spectra, and other data were collected using moored current meter casts and other instruments from the CAPT JACK and EXCELLENCE in the...
National Oceanic and Atmospheric Administration, Department of Commerce — Current direction, wind wave spectra, and CTD data were collected using moored current meter and CTD casts in the Gulf of Mexico from September 3, 1982 to September...
National Oceanic and Atmospheric Administration, Department of Commerce — Current direction, salinity, and wind wave spectra data were collected using moored current meter casts in the Gulf of Mexico from February 2, 1978 to January 31,...
National Oceanic and Atmospheric Administration, Department of Commerce — Current direction, benthic organisms, wind wave spectra, and other data were collected using moored current meter casts and other instruments from the CAPT JACK and...
National Oceanic and Atmospheric Administration, Department of Commerce — Current direction, marine toxic substances, and wind wave spectra data were collected using moored current meter casts and other instruments in the Gulf of Mexico...
National Oceanic and Atmospheric Administration, Department of Commerce — Current direction, temperature, and wind wave spectra data were collected using moored current meter casts in the Gulf of Mexico from December 22, 1977 to October...
National Oceanic and Atmospheric Administration, Department of Commerce — Current direction, temperature, and wind wave spectra data were collected using moored current meter casts in the Gulf of Mexico from June 28, 1978 to December 31,...
National Oceanic and Atmospheric Administration, Department of Commerce — Current direction and wind wave spectra data were collected using moored current meter casts in the Gulf of Mexico from November 1, 1980 to November 1, 1980. Data...
National Oceanic and Atmospheric Administration, Department of Commerce — Current direction, wind wave spectra, phytoplankton, temperature, salinity, and other data were collected using moored current meter casts in the Gulf of Mexico from...
National Oceanic and Atmospheric Administration, Department of Commerce — Current direction, phytoplankton, zooplankton, wind wave spectra, and other data were collected using moored current meter casts and other instruments in the Gulf of...
孟艳秋; 陈国平; 严士常; 童朝锋
2014-01-01
The impact pressure from waves is an important issue to be considered in the design of coastal structures. In this paper, the waves acting on the deck of a shore-connecting jetty on a slope exposed to oblique waves and in the presence of current are examined based on laboratory experiments. The impact pressures are measured on a 1:50 scale model of a jetty head with down-standing beams and berthing members. The relations of the impact pressure with the incident wave angle and the current velocity are examined. It is shown that the impact pressure is sensitive to the wave angle and the current velocity. A computational model for the impact load on the deck of shore-connecting jetties exposed to oblique waves and current is developed.
Topology optimization design of space rectangular mirror
Qu, Yanjun; Wang, Wei; Liu, Bei; Li, Xupeng
2016-10-01
A conceptual lightweight rectangular mirror is designed based on the theory of topology optimization and the specific structure size is determined through sensitivity analysis and size optimization in this paper. Under the load condition of gravity along the optical axis, compared with the mirrors designed by traditional method using finite element analysis method, the performance of the topology optimization reflectors supported by peripheral six points are superior in lightweight ratio, structure stiffness and the reflective surface accuracy. This suggests that the lightweight method in this paper is effective and has potential value for the design of rectangular reflector.
Rectangular-to-circular groove waveguide junction
CUI; Licheng; (崔立成); YANG; Hongsheng; (杨鸿生)
2003-01-01
Mode matching method is used to analyze the scattering characteristics of the rectangular-to-circular groove waveguide junction. Firstly, the scattering matrix equation is obtained by matching the electromagnetic fields at the boundary of the junction. The scattering coefficients can be obtained from the equation. Secondly the scattering characteristics of the iris with rectangular window positioned in circular groove waveguide are briefly analyzed. Thirdly, the convergent problem is discussed and the numerical results are given. At last experiment is made and good agreement is found between the calculated results and the measured results.
Electrochemical apparatus comprising modified disposable rectangular cuvette
Dattelbaum, Andrew M; Gupta, Gautam; Morris, David E
2013-09-10
Electrochemical apparatus includes a disposable rectangular cuvette modified with at least one hole through a side and/or the bottom. Apparatus may include more than one cuvette, which in practice is a disposable rectangular glass or plastic cuvette modified by drilling the hole(s) through. The apparatus include two plates and some means of fastening one plate to the other. The apparatus may be interfaced with a fiber optic or microscope objective, and a spectrometer for spectroscopic studies. The apparatus are suitable for a variety of electrochemical experiments, including surface electrochemistry, bulk electrolysis, and flow cell experiments.
Zheng, Jun; Li, Ruijie; Yu, Yonghai; Suo, Anning
2014-01-01
In nearshore waters, spatial and temporal scales of waves, tidal currents, and circulation patterns vary greatly. It is, therefore, difficult to combine these factors' effects when trying to predict sediment transport processes. This paper proposes the concept of significant wave velocity, which combines the effects of waves, tides, and ocean currents using the horizontal kinetic energy superposition principle. Through a comparison of the relationship between shear stress at the water-sediment interface and sediment-carrying capacity, assuming equilibrium sediment flux, a new formula for sediment-carrying capacity, which incorporates the concept of significant wave velocities, is derived. Sediment-carrying capacity is a function of the critical velocity, which increases with water depth and decreases with increasing relative roughness of the sea bed. Finally, data from field observation stations and simulations are used to test the proposed formula. The results show that the new formula is in good agreement with both field and simulation data. This new formula for sediment-carrying capacity can be used to simulate nearshore sediment transport.
Ibsen, Lars Bo
2008-01-01
Estimates for the amount of potential wave energy in the world range from 1-10 TW. The World Energy Council estimates that a potential 2TW of energy is available from the world’s oceans, which is the equivalent of twice the world’s electricity production. Whilst the recoverable resource is many t...
Guerreiro, Gabriela V.; Zaitouna, Anita J.; Lai, Rebecca Y., E-mail: rlai2@unl.edu
2014-01-31
Graphical abstract: -- Highlights: •An electrochemical Hg(II) sensor based on T–Hg(II)–T sensing motif was fabricated. •A methylene blue-modified DNA probe was used to fabricate the sensor. •Sensor performance was evaluated using ACV, CV, SWV, and DPV. •The sensor behaves as a “signal-off” sensor in ACV and CV. •The sensor behaves as either a “signal-on” or “signal-off” sensor in SWV and DPV. -- Abstract: Here we report the characterization of an electrochemical mercury (Hg{sup 2+}) sensor constructed with a methylene blue (MB)-modified and thymine-containing linear DNA probe. Similar to the linear probe electrochemical DNA sensor, the resultant sensor behaved as a “signal-off” sensor in alternating current voltammetry and cyclic voltammetry. However, depending on the applied frequency or pulse width, the sensor can behave as either a “signal-off” or “signal-on” sensor in square wave voltammetry (SWV) and differential pulse voltammetry (DPV). In SWV, the sensor showed “signal-on” behavior at low frequencies and “signal-off” behavior at high frequencies. In DPV, the sensor showed “signal-off” behavior at short pulse widths and “signal-on” behavior at long pulse widths. Independent of the sensor interrogation technique, the limit of detection was found to be 10 nM, with a linear dynamic range between 10 nM and 500 nM. In addition, the sensor responded to Hg{sup 2+} rather rapidly; majority of the signal change occurred in <20 min. Overall, the sensor retains all the characteristics of this class of sensors; it is reagentless, reusable, sensitive, specific and selective. This study also highlights the feasibility of using a MB-modified probe for real-time sensing of Hg{sup 2+}, which has not been previously reported. More importantly, the observed “switching” behavior in SWV and DPV is potentially generalizable and should be applicable to most sensors in this class of dynamics-based electrochemical biosensors.
Sakai, J. I.; Zhao, J.; Nishikawa, K.-I.
1994-01-01
We have shown that a current-carrying plasma loop can be heated by magnetic pinch driven by the pressure imbalance between inside and outside the loop, using a 3-dimensional electromagnetic (EM) particle code. Both electrons and ions in the loop can be heated in the direction perpendicular to the ambient magnetic field, therefore the perpendicular temperature can be increased about 10 times compared with the parallel temperature. This temperature anisotropy produced by the magnetic pinch heating can induce a plasma instability, by which high-frequency electromagnetic waves can be excited. The plasma current which is enhanced by the magnetic pinch can also excite a kinetic kink instability, which can heat ions perpendicular to the magnetic field. The heating mechanism of ions as well as the electromagnetic emission could be important for an understanding of the coronal loop heating and the electromagnetic wave emissions from active coronal regions.
Current evidence of extracorporeal shock wave therapy in chronic Achilles tendinopathy.
Gerdesmeyer, Ludger; Mittermayr, Rainer; Fuerst, Martin; Al Muderis, Munjed; Thiele, Richard; Saxena, Amol; Gollwitzer, Hans
2015-12-01
Chronic Achilles tendinopathy has been described as the most common overuse injury in sports medicine. Several treatment modalities such as activity modification, heel lifts, arch supports, stretching exercises, nonsteroidal anti-inflammatories, and eccentric loading are known as standard treatment mostly without proven evidence. After failed conservative therapy, invasive treatment may be considered. Extracorporeal shock wave therapy (ESWT) has been successfully used in soft-tissue pathologies like lateral epicondylitis, plantar fasciitis, tendinopathy of the shoulder and also in bone and skin disorders. Conclusive evidence recommending ESWT as a treatment for Achilles tendinopathy is still lacking. In plantar fasciitis as well as in calcific shoulder tendinopathy shock wave therapy is recently the best evaluated treatment option. This article analysis the evidence based literature of ESWT in chronic Achilles tendinopathy. Recently published data have shown the efficacy of focused and radial extracorporeal shock wave therapy. Copyright © 2015 IJS Publishing Group Limited. All rights reserved.
3-D LDA study of a rectangular jet
Morrison, Gerald L.; Tatterson, Gary B.; Swan, David H.
1988-01-01
The flow field of a rectangular jet with a 2:1 aspect ratio was studied at an axial Reynolds number of 100,000 (Mach number 0.09) using three-dimensional laser Doppler velocimetry. The flow field survey resulted in mean velocity vector field plots and contour plots of the Reynolds stress tensor components. This paper presents contour plots in the planes of the jet minor and major axes at different axial locations. These data contribute substantially to currently available data of jet flow fields and will provide a valuable database for three-dimensional modeling.
Using Wave-Current Observation to Predict Bottom Sediment Processes on Muddy Beaches
2011-09-30
hypothesized stages of bed evolution: (A) solid bed; (B) breaking of the bed matrix and water absorption (liquefaction/ fluidization /expansion); (C) bed erosion...Geophys. Res. Lett. 35/7, L07611. Foda, A.M., J.R. Hunt, and H.-T. Chou (1993). A nonlinear model for the fluidization of marine mud by waves, J...Geophys. Res. 98, 7039-7047. Foda M.A. and S.Y., Tzang (1994). Resonant fluidization of silty soil by water waves, J. Geophys. Res. 99(C10), 20463
García-Hermosa, Isabel; Abcha, Nizar; Brossard, Jérôme; Bennis, Anne-Claire; Ezersky, Alexander; Gross, Marcus; Iglesias, Gregorio; Magar, Vanesa; Miles, Jon; Mouazé, Dominique; Perret, Gaële; Pinon, Grégory; Rivier, Aurélie; Rogan, Charlie; Simmonds, David
2015-04-01
Offshore wind technology is currently the most widespread and advanced source of marine renewable energy. Offshore wind farms populate waters through the North Sea and the English Channel. The UK and French governments devised deadlines to achieve percentages of electricity from renewable sources by 2020, these deadlines and the direct translation of land based wind farm technology to the offshore environment resulted in the rapid expansion of the offshore wind energy. New wind farms have been designed with a larger number of masts and are moving from shallow offshore banks to deeper waters and in order to produce more power the diameters of monopoles masts are becoming larger to support larger turbines. The three-partner EU INTERREG funded project OFELIA (http://www.interreg-ofelia.eu/) aims to establish a cross-channel (between the UK and France) research collaboration to improve understanding of the environmental impacts of offshore wind farm foundations. The objective of the present study is to characterise changes in the hydrodynamics and sea bed in the vicinity of an offshore wind farm mast and in the wake area under wave and wave-current conditions corresponding to events in the French wind farm site of Courseulles-sur-mer (offshore of Lower Normandy, in the English Channel). Experiments were carried out in two laboratory facilities: a wave flume of 35 m long, 0.9 m wide and 1.2 m in depth with regular and irregular waves (García-Hermosa et al., 2014); and a wave and current flume of 17 m long, 0.5 m wide and 0.4 m depth with regular waves, currents from 180° to the waves and a mobile bed (Gunnoo et al., 2014). Flow velocity measurements were taken with an Acoustic Dopple Velocimeter (ADV) at various points around the cylinder and Particle Image Velocitmetry (PIV) techniques were applied to larger areas upstream and downstream of the cylinder. During the assessment of waves and currents' effects on the bed evolution were assessed using a laser and camera
Tae Ho Kim; David W. Fredriksson; Judson DeCew
2012-01-01
A numerical model was used to analyze the motion response and mooring tension of a submerged fish reef system.The system included a net attached to a rigid structure suspended up from the bottom with a single,high tension mooring by fixed flotation.The analysis was performed by using a Morison equation type finite element model configured with truss elements.Input forcing parameters into the model consisted of both regular and irregular waves,with and without a steady current.Heave,surge and pitch dynamic calculations of the reef structure were made.Tension response results of the attached mooring line were also computed.Results were analyzed in both the time and frequency domain in which appropriate,linear transfer functions were calculated.The influence of the current was more evident in the tension and heave motion response data.This is most likely the result of the large buoyancy characteristics of the reef structure and the length of the mooring cable.Maximum mooring component tension was found to be 13.9 kN and occurred when the reef was subjected to irregular waves with a co-linear current of 1.0 m/s velocity.The results also showed that the system had little damping (in heave) with damped natural periods of 2.8 s.This combination of system characteristics promotes a possible resonating situation in typical open sea conditions with similar wave periods.
Wanjun Lei
2015-01-01
Full Text Available Electric arc furnace (EAF causes the harmonics to impact on the supply network greatly and harmonic elimination is a very important research work for the power quality associated with EAF. In the paper, a fundamental wave amplitude prediction algorithm based on fuzzy neural network for harmonic elimination of EAF current is proposed. The proposed algorithm uses the learning ability of the neural network to refine Takagi-Sugeno type fuzzy rules and the inputs are the average of the current measured value in different time intervals. To verify the effectiveness of the proposed algorithm, some experiments are performed to compare the proposed algorithm with the back-propagation neural networks, and the field data collected at an EAF are used in the experiments. Moreover, the measured amplitudes of fundamental waves of field data are obtained by the sliding-window-based discrete Fourier transform on the field data. The experiments results show that the proposed algorithm has higher precision. The real curves also verify that the amplitude of fundamental wave current could be predicted accurately and the harmonic elimination of EAF would be realized based on the proposed algorithm.
Residual stresses of thin, short rectangular plates
Andonian, A. T.; Danyluk, S.
1985-01-01
The analysis of the residual stresses in thin, short rectangular plates is presented. The analysis is used in conjunction with a shadow moire interferometry technique by which residual stresses are obtained over a large spatial area from a strain measurement. The technique and analysis are applied to a residual stress measurement of polycrystalline silicon sheet grown by the edge-defined film growth technique.
BIVARIATE FRACTAL INTERPOLATION FUNCTIONS ON RECTANGULAR DOMAINS
Xiao-yuan Qian
2002-01-01
Non-tensor product bivariate fractal interpolation functions defined on gridded rectangular domains are constructed. Linear spaces consisting of these functions are introduced.The relevant Lagrange interpolation problem is discussed. A negative result about the existence of affine fractal interpolation functions defined on such domains is obtained.
Spin-Up in a Rectangular Cylinder
1993-12-01
cylinder by scaling as follows: I I IElt , and p = E’,X, 3.22 where we have scaled the radial and vertical flow to be higher order in Ekman number than the...two flow visualization systems, and the rectangular tank with prepared water. Fig- ure 4.1 is a schematic of this system, which we describe below.I I
Wave and Current Observations in a Tidal Inlet Using GPS Drifter Buoys
2013-03-01
Micro-Electro-Mechanical System MRU Motion Reference Unit NDBC National Data Buoy Center NOAA National Oceanic and Atmospheric Administration...made by accelerometers integrated into a motion reference unit ( MRU ). The vertical accelerations (heave measurements) were used to calculate the wave
The Interaction of Short-Wavelength Internal Waves with a Background Current,
1982-12-01
challenging feature of the internal wave field is its maintenance of high and uniform energy levels. A central difficulty arises from our poor...coefficient of the Taylor-Goldstein equation. The asymptotic predicitions (dashed lines), obtained by neglecting the curvature term U/(c- U) in the Taylor
Using Wave-Current Observations to Predict Bottom Sediment Processes on Muddy Beaches
2012-09-30
Arrows mark the hypothesized stages of bed evolution: (A) solid bed; (B) breaking of the bed matrix and water absorption (liquefaction/ fluidization ...for the fluidization of marine mud by waves, J. Geophys. Res. 98, 7039-7047. Foda M.A. and S.Y., Tzang (1994). Resonant fluidization of silty soil
A Laboratory Study of Wind-Wave-Current Interactions. Part I
1975-01-01
showed that non- linear modification of surface drift occurs near long wave crests and troughs to modulate the drift experienced by caper - imposed...Polytechnic Inst. of Brooklyn Route 110, Room 205 Farmingdale NY 11735 Dr. Harold W. Lewis Inst. for Defense Analysis P. 0. Box 62 3,l- Santa Barbara
A Novel Current-Mode Full-Wave Rectifier Based on One CDTA and Two Diodes
F. Khateb
2010-09-01
Full Text Available Precision rectifiers are important building blocks for analog signal processing. The traditional approach based on diodes and operational amplifiers (OpAmps exhibits undesirable effects caused by limited OpAmp slew rate and diode commutations. In the paper, a full-wave rectifier based on one CDTA and two Schottky diodes is presented. The PSpice simulation results are included.
Wave refraction and longshore current patterns along Calangute beach (Goa), west coast of India
Krishnakumar, V.; Murty, C.S.; Shenoi, S.S.C.; Heblekar, A.K.
are qualitatively assessed. The degree of refraction is less and no abnormal energy concentrations occur along this stretch. The waves after breaking give rise to many opposing flows forming circulation cells along the entire stretch. Zones of quasi-permanent rip...
Let it flow: how does an underlying current affect wave propagation over a natural seagrass meadow?
Paul, M.; Gillis, L.G.
2015-01-01
Temperate seagrass beds can be found within intertidal and tidal areas of variable hydrodynamic forcing. To investigate the interaction between hydrodynamics and seagrass plants, Zostera noltii meadows were exposed to a range of combinations of waves and flow in a flume. Velocity profiles were obtai
黄虎; 周锡礽
2001-01-01
The effect of nonlinearity on the free surface wave resonated by an incident flow over rippled beds, which consist of fast varying topography superimposed on an otherwise slowly varying mean depth, is studied using a WKBJ-type perturbation approach. Synchronous, superharmonic and in particular subharmonic resonance were selectively excited over the fast varying topography with corresponding wavelengths. For a steady current the dynamical system is autonomous and the possible nonlinear steady states and their stability were investigated. When the current has a small oscillatory component the dynamical system becomes non-autonomous, chaos is now possible.
J. S. Pickett
2009-06-01
Full Text Available Electrostatic Solitary Waves (ESWs have been observed by several spacecraft in the current layers of Earth's magnetosphere since 1982. ESWs are manifested as isolated pulses (one wave period in the high time resolution waveform data obtained on these spacecraft. They are thus nonlinear structures generated out of nonlinear instabilities and processes. We report the first observations of ESWs associated with the onset of a super-substorm that occurred on 24 August 2005 while the Cluster spacecraft were located in the magnetotail at around 18–19 R_{E} and moving northward from the plasma sheet to the lobes. These ESWs were detected in the waveform data of the WBD plasma wave receiver on three of the Cluster spacecraft. The majority of the ESWs were detected about 5 min after the super-substorm onset during which time 1 the PEACE electron instrument detected significant field-aligned electron fluxes from a few 100 eV to 3.5 keV, 2 the EDI instrument detected bursts of field-aligned electron currents, 3 the FGM instrument detected substantial magnetic fluctuations and the presence of Alfvén waves, 4 the STAFF experiment detected broadband electric and magnetic waves, ion cyclotron waves and whistler mode waves, and 5 CIS detected nearly comparable densities of H+ and O+ ions and a large tailward H+ velocity. We compare the characteristics of the ESWs observed during this event to those created in the laboratory at the University of California-Los Angeles Plasma Device (LAPD with an electron beam. We find that the time durations of both space and LAPD ESWs are only slightly larger than the respective local electron plasma periods, indicating that electron, and not ion, dynamics are responsible for generation of the ESWs. We have discussed possible mechanisms for generating the ESWs in space, including the beam and kinetic Buneman type instabilities and the acoustic instabilities. Future studies will examine these mechanisms in
An Analysis of Elasto-Plastic Bending of Rectangular Plate
Matsuda, Hiroshi; Sakiyama, Takeshi
1988-01-01
In this paper, a discrete method for analyzing the problem of elasto-plastic bending of a rectangular plate is proposed. The solutions for partial differential equation of rectangular plate are obtained in discrete forms by applying numerical integnltion. An incremental variable elasticity procedure has been used for the clasta-plastic analysis of the rectangular plate. As the applications of the proposed method, clasta-plastic bending of rectangular plate with four types of boundary conditio...
Optimal design for rectangular isolated footings using the real soil pressure
Arnulfo Luévanos Rojas
2017-05-01
Full Text Available The standard design method (classical method for reinforced concrete rectangular footings is: First, a dimension is proposed and should comply with the allowable stresses; subsequently, the effective depth is obtained from the maximum moment and is checked against the bending shear and the punching shear until, it complies with these conditions and, then, steel reinforcement is obtained, but it is not guarantee that the minimum cost will be obtained. This paper shows an optimal design for reinforced concrete rectangular footings using the new model. A numerical experimentation is presented to show the model capability to estimate the minimum cost design of the materials used for a rectangular footing that supports an axial load and moments in two directions in accordance to the building code requirements for structural concrete and commentary (ACI 318-13. Also, a comparison is made between the optimal design and current design for rectangular footings. The solutions show that the optimal design is more economical and more precise with respect to the current design, because standard design is done by trial and error. Then, the optimal design should be used to obtain the minimum cost design for reinforced concrete rectangular footings.
2009-09-01
Sonar to Determine Regional Bedload Sediment Transport Patterns in the San Francisco Bay Coastal System. Sedimentology , In: Li, M., Sherwood, C., and...Hill, P. (Eds.), International Association of Sedimentologist’s Special Publication Book on Shelf Sedimentology , 33 pp. Blondeaux, P. (2001...its Relationship to bedforms and Deposition of Mud. Journal of Sedimentology and Petrolium, 41, 89-96. McCave, I. N. (1971b). Sand waves of the
A Numerical Modeling Framework for Cohesive Sediment Transport Driven by Waves and Tidal Currents
2013-09-30
friction due to seabed processes, hydrodynamics and seabed dynamics become highly coupled and large-scale numerical models must incorporate appropriate...wave cycles. Therefore we conclude that flow in the range of Re=600 to 700 to be classified as self -sustaining transitional flow. For higher Reynolds...directly relevant to RIVET I & II where the seabed is mainly sandy or mixed sand-mud environments. 4
g-Weak Contraction in Ordered Cone Rectangular Metric Spaces
S. K. Malhotra
2013-01-01
Full Text Available We prove some common fixed-point theorems for the ordered g-weak contractions in cone rectangular metric spaces without assuming the normality of cone. Our results generalize some recent results from cone metric and cone rectangular metric spaces into ordered cone rectangular metric spaces. Examples are provided which illustrate the results.
Tuning of band gaps for a two-dimensional piezoelectric phononic crystal with a rectangular lattice
Yize Wang; Fengming Li; Yuesheng Wang; Kikuo Kishimoto; Wenhu Huang
2009-01-01
In this paper, the elastic wave propagation in a two-dimensional piezoelectric phononic crystal is studied by considering the mechanic-electric coupling. The gener-alized eigenvalue equation is obtained by the relation of the mechanic and electric fields as well as the Bloch-Floquet the-orem. The band structures of both the in-plane and anti-plane modes are calculated for a rectangular lattice by the plane-wave expansion method. The effects of the lattice constant ratio and the piezoelectricity with different filling fractions are analyzed. The results show that the largest gap width is not always obtained for a square lattice. In some situations, a rectangular lattice may generate larger gaps. The band gap characteristics are influenced obviously by the piezoelectric-ity with the larger lattice constant ratios and the filling frac-tions.
Performance improvement of rectangular-plate linear ultrasonic motors using dual-frequency drive.
Ming, Yang; Richardson, Robert C; Levesley, Martin C; Walker, Peter G; Watterson, Kevin
2004-12-01
To improve the performances of a rectangular-plate linear ultrasonic motor for specific applications, a dual-frequency drive has been proposed and investigated. Through careful design of the rectangular piezoelectric ceramic plate, its first longitudinal resonant frequency coincides with its second lateral bending resonant frequency and is one-third of its higher lateral bending resonant frequency. When a square-wave voltage is used to drive the motor, its first longitudinal and second bending and the higher bending vibration modes are excited. Experimental results show that the maximum thrust force and maximum velocity of the motor are over 170% of those obtained from the single-frequency sine-wave drive when the voltage performance of the motor becomes saturated.
舒雯; 赵鼎; 王勇
2011-01-01
分析了矩形截面切伦柯夫脉塞周期金属慢波结构的色散特性,以及结构参数的变化对色散曲线的影响.为避免慢波结构两端突变引起的反射振荡,采用等效电路法分析了用于连接光滑波导和慢波结构的渐变段.将线性形、两段形和指数形的渐变段进行了比较.指数形渐变段末端的功率反射系数最小,并且整体的变化最平缓,因此可将其作为实现慢波与快波间转换的较优选择.分析了频率和实际加工误差对指数形渐变段功率反射系数的影响:在频率较小时,功率反射系数也较小；固定频率下,较小的加工误差能使交界处功率反射系数的变化较平缓.在此基础上设计了一个功率反射系数小于0.01的指数渐变段,实现了工作模式和快波模式之间的良好匹配.与耦合模理论分析方法相比,等效电路方法更为简洁,二者结果相符合.%The dispersion characteristics of metal periodic slow-wave structure in rectangular cross-section Cerenkov maser have been analyzed. The effects of the geometrical parameters on the dispersion curves were investigated. In order to avoid the reflect oscillation induced by the changes at two ends of the slow-wave structure, the taper for matching the smooth waveguide and the slow-wave structure was analyzed by use of equivalent circuit method. Through comparing the linear, the two-piece linear and the exponential tapers, we know that the exponential taper gives the lowest total power reflection coefficient at the end, and the total change is mild. So the exponential taper can be used as an optimal solution for transition between slow and fast modes. The effects of frequency and fabrication error to the exponential taper were analyzed. The lower the frequency is, the lower the total power reflection coefficient is. Under the same frequency, the lower fabrication errors smooth the abrupt jumps of the total power reflection coefficient. With this analysis
Development of rolling mill for rectangular orthodontic wires production
G.E. Totten
2007-09-01
Full Text Available Purpose: In orthodontic treatments, wires of different metallic alloys are used for alignment, leveling, correction of the molar position, space closing, finish and retention. The purpose of the paper is the characteristics of austenitic stainless steel wires, with a square traverse section, which were produced using a rolling mill built for this purpose, are presented hereDesign/methodology/approach: With respect to finish and retention, these wires are responsible for adequate positioning of the upper teeth on the lower teeth. Wires that are subjected to incisor torque require high resistance and stiffness. For this, wires of rectangular austenitic stainless steel are used due to high modulus of elasticity and good corrosion resistance in the oral environment. Because of the rectangular geometry, wire production requires process development suitable for industrial scale manufacture with geometric characteristics and mechanical properties better adapted to the use conditions.Findings: To obtain wires with such characteristics, a rolling mill was developed for the production of rectangular wires by a rolling process with the objective of reducing cost of the cold drawing process that is currently used which utilize complex and expensive wire-drawing dies. In addition to the rolling process itself, wire deformation, microhardness, tension and bend tests were also performed.Research limitations/implications: A rolling-mill was built that successfully produced dental wires within acceptable tolerances and physical/mechanical properties.These wires exhibited excellent hardness and tensile strength, although slightly less than analogous commercial wires. It is expected that this problem are corrected by using initial wires with a higher hardness, since this property is directly related with the tensile strength.Originality/value: In these tests, wire geometry, surface finish and mechanical properties were successfully adapted for use in orthodontic
Sauter, O.; Henderson, M. A.; Hofmann, F.; Goodman, T.; Alberti, S.; Angioni, C.; Appert, K.; Behn, R.; Blanchard, P.; Bosshard, P.; Chavan, R.; Coda, S.; Duval, B. P.; Fasel, D.; Favre, A.; Furno, I.; Gorgerat, P.; Hogge, J.-P.; Isoz, P.-F.; Joye, B.; Lavanchy, P.; Lister, J. B.; Llobet, X.; Magnin, J.-C.; Mandrin, P.; Manini, A.; Marlétaz, B.; Marmillod, P.; Martin, Y.; Mayor, J.-M.; Martynov, A. A.; Mlynar, J.; Moret, J.-M.; Nieswand, C.; Nikkola, P.; Paris, P.; Perez, A.; Pietrzyk, Z. A.; Pitts, R. A.; Pochelon, A.; Pochon, G.; Refke, A.; Reimerdes, H.; Rommers, J.; Scavino, E.; Tonetti, G.; Tran, M. Q.; Troyon, F.; Weisen, H.
2000-04-01
A steady-state, fully noninductive plasma current has been sustained for the first time in a tokamak using electron cyclotron current drive only. In this discharge, 123 kA of current have been sustained for the entire gyrotron pulse duration of 2 s. Careful distribution across the plasma minor radius of the power deposited from three 0.5-MW gyrotrons was essential for reaching steady-state conditions. With central current drive, up to 153 kA of current have been fully replaced transiently for 100 ms. The noninductive scenario is confirmed by the ability to recharge the Ohmic transformer. The dependence of the current drive efficiency on the minor radius is also demonstrated.
The forced vibrational response of a rectangular parallelepiped with rigid-lubricated boundaries
Hill, E. v. K.; Egle, D. M.
1982-01-01
The Green function for a rectangular parallelepiped with rigid-lubricated boundaries is developed by a normal mode approach, the free vibration solutions being used. Explicit solutions are presented for a concentrated impulse, which serves as a model for an acoustic emission stress wave, and for a concentrated step force. Numerical results for short times show good agreement with the infinite space solution. Analogous solutions are developed for the inverse boundary conditions.
De Dominicis, M.; Bruciaferri, D.; Gerin, R.; Pinardi, N.; Poulain, P. M.; Garreau, P.; Zodiatis, G.; Perivoliotis, L.; Fazioli, L.; Sorgente, R.; Manganiello, C.
2016-11-01
Validation of oil spill forecasting systems suffers from a lack of data due to the scarcity of oil slick in situ and satellite observations. Drifters (surface drifting buoys) are often considered as proxy for oil spill to overcome this problem. However, they can have different designs and consequently behave in a different way at sea, making it not straightforward to use them for oil spill model validation purposes and to account for surface currents, waves and wind when modelling them. Stemming from the need to validate the MEDESS4MS (Mediterranean Decision Support System for Marine Safety) multi-model oil spill prediction system, which allows access to several ocean, wave and meteorological operational model forecasts, an exercise at sea was carried out to collect a consistent dataset of oil slick satellite observations, in situ data and trajectories of different type of drifters. The exercise, called MEDESS4MS Serious Game 1 (SG1), took place in the Elba Island region (Western Mediterranean Sea) during May 2014. Satellite images covering the MEDESS4MS SG1 exercise area were acquired every day and, in the case an oil spill was observed from satellite, vessels of the Italian Coast Guard (ITCG) were sent in situ to confirm the presence of the pollution. During the exercise one oil slick was found in situ and drifters, with different water-following characteristics, were effectively deployed into the oil slick and then monitored in the following days. Although it was not possible to compare the oil slick and drifter trajectories due to a lack of satellite observations of the same oil slick in the following days, the oil slick observations in situ and drifters trajectories were used to evaluate the quality of MEDESS4MS multi-model currents, waves and winds by using the MEDSLIK-II oil spill model. The response of the drifters to surface ocean currents, different Stokes drift parameterizations and wind drag has been examined. We found that the surface ocean currents
Effect of coastal-trapped waves and wind on currents and transport in the Gulf of California
Gutiérrez, Manuel O.; López, Manuel; Candela, Julio; Castro, Rubén.; Mascarenhas, Affonso; Collins, Curtis A.
2014-08-01
Subsurface pressure (SsP) observations from stations inside and outside of the Gulf of California (GC) are used to analyze the relationship between low-frequency currents, temperature, and transport inside the GC and intraseasonal coastal-trapped waves (CTWs), which propagate poleward along the coast toward the GC. Correlation functions and coherences of SsP stations were consistent with intraseasonal CTWs splitting in two at the mouth of the gulf: one part enters the gulf, propagates around the gulf, and eventually, toward the mouth, and another part that appears to "jump" the mouth of the gulf and travels poleward along the west coast of the peninsula. The correlation and coherence estimates of SsP at Manzanillo with currents showed that downwelling CTWs generated along-gulf current anomalies toward the head of the gulf at the mainland shelf of the mouth, whereas at Ballenas Channel sill (San Lorenzo sill) these waves generated current anomalies toward the mouth near the surface (bottom). At the San Lorenzo (SL) sill, downwelling CTWs increased the near-bottom (˜400 m) temperature and reduced the bottom transport of deep, fresher, and colder water that flows toward the head of the gulf. Cross-Calibrated Multiplatform winds were used to investigate their relationship with currents. The first empirical orthogonal function of the along-gulf wind stress showed that wind blowing toward the head of the gulf generated a reduction of bottom transport toward the head of the gulf through the SL sill, and intensified surface geostrophic current fluctuations toward the head of the gulf. There was also significant correlation between inflow bottom transport and outflow surface geostrophic velocities averaged across the gulf, consistent with the exchange pattern for the Northern Gulf.
Metamaterial Embedded Wearable Rectangular Microstrip Patch Antenna
J. G. Joshi
2012-01-01
Full Text Available This paper presents an indigenous low-cost metamaterial embedded wearable rectangular microstrip patch antenna using polyester substrate for IEEE 802.11a WLAN applications. The proposed antenna resonates at 5.10 GHz with a bandwidth and gain of 97 MHz and 4.92 dBi, respectively. The electrical size of this antenna is 0.254λ×0.5λ. The slots are cut in rectangular patch to reduce the bending effect. This leads to mismatch the impedance at WLAN frequency band; hence, a metamaterial square SRR is embedded inside the slot. A prototype antenna has been fabricated and tested, and the measured results are presented in this paper. The simulated and measured results of the proposed antenna are found to be in good agreement. The bending effect on the performance of this antenna is experimentally verified.
Kim, Sun Ho; Jeong, Seung Ho [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of); Lee, Hyun Woo; Lee, Byung Je [Kwang Woon University, Chuncheon (Korea, Republic of); Jo, Jong Gab; Lee, Hyun Young; Hwang, Yong Seok [Seoul National University, Seoul (Korea, Republic of)
2015-10-15
Continuous current drive is one of the key issues for tokamak to be a commercial fusion reactor. As a part of new and efficient current drive concept research by using a Lower Hybrid Fast Wave (LHFW), the experimental study is planned on Versatile Experiment Spherical Torus (VEST) and a RF system is being developed in collaboration with Kwang Woon University (KWU), Korea Accelerator Plasma Research Association (KAPRA) and Seoul National University (SNU). The LHFW RF system includes UHF band klystron, inter-digital antenna, RF diagnostics and power transmission sub components such as circulator, DC breaker, vacuum feed-thru. The design and preparation status of the RF system will be presented in the meeting in detail. A RF system has been designed and prepared for the experimental study of efficient current drive by using Lower Hybrid Fast Wave. Overall LHFW RF system including diagnostics is designed to deliver about 10 kW in UHF band. And the key hardware components including klystron and antenna are being prepared and designed through the collaboration with KWU, KAPRA and SNU.
Rectangular Wilson Loops at Large N
Lohmayer, Robert
2012-01-01
This work is about pure Yang Mills theory in four Euclidean dimensions with gauge group SU(N). We study rectangular smeared Wilson loops on the lattice at large N and relatively close to the large-N transition point in their eigenvalue density. We show that the string tension can be extracted from these loops but obtain a shape dependence different from the prediction of effective string theory.
On rectangular HOMFLY for twist knots
Kononov, Ya
2016-01-01
As a new step in the study of rectangularly-colored knot polynomials, we reformulate the prescription of arXiv:1606.06015 for twist knots in the double-column representations $R=[rr]$ in terms of skew Schur polynomials. These, however, are mysteriously shifted from the standard topological locus, what makes further generalization to arbitrary $R=[r^s]$ not quite straightforward.
Rectangular Blocks vs Polygonal Walls in Archaeoseismology
Klaus-G. Hinzen
2017-07-01
Full Text Available Collapsed or deformed walls in ancient structures constitute important evidence in archaeoseismology, where damage is interpreted in terms of earthquake ground motion. A large variety of wall types have been developed during the millennia in different cultural backgrounds. Often walls with polygonal-shaped building blocks are regarded as more earthquake-resistant than a wall consisting of rectangular elements and, as is sometimes speculated, that the irregular wall types were intentionally developed for that purpose. We use simply structured discrete element models of four walls with different block geometries, perfect rectangular, an Inka-type structure and two polygonal designs, to test their dynamic behavior. In addition to an analytic calculation of ground motion, we use measured strong motion signals as boundary conditions for the 3D wall models with varying height to width ratios. At peak ground accelerations between 1.0 and 9.0 m/s2 and major frequencies of 0.5 to 3 Hz, numeric experiments with the horizontally applied analytic ground motions result in clear differences in the resistance of the four wall types with the rectangular block wall being most vulnerable. For more complex measured 3D motions the Inka-type wall proves more stable than the rectangular block wall; however, height to width ratio still has equally strong influence on the stability. Internal deformation of non-collapsed walls shows some correlation with the parameters of the driving motion. For simple impulsive ground motions, a peak ground displacement threshold exists between toppling and remaining upright for all four models but peak acceleration cannot be reliably back calculated.
Anisotropic rectangular metric for polygonal surface remeshing
Pellenard, Bertrand
2013-06-18
We propose a new method for anisotropic polygonal surface remeshing. Our algorithm takes as input a surface triangle mesh. An anisotropic rectangular metric, defined at each triangle facet of the input mesh, is derived from both a user-specified normal-based tolerance error and the requirement to favor rectangle-shaped polygons. Our algorithm uses a greedy optimization procedure that adds, deletes and relocates generators so as to match two criteria related to partitioning and conformity.
The Effects of a Rectangular Rapid-Flashing Beacon on Vehicle Speed
VanWagner, Michelle; Van Houten, Ron; Betts, Brian
2011-01-01
In 2008, nearly 31% of vehicle fatalities were related to failure to adhere to safe vehicle speeds (National Highway Traffic Safety Administration [NHTSA], 2009). The current study evaluated the effect of a rectangular rapid-flashing beacon (RRFB) triggered by excessive speed on vehicle speed using a combined alternating treatments and reversal…
The Effects of a Rectangular Rapid-Flashing Beacon on Vehicle Speed
VanWagner, Michelle; Van Houten, Ron; Betts, Brian
2011-01-01
In 2008, nearly 31% of vehicle fatalities were related to failure to adhere to safe vehicle speeds (National Highway Traffic Safety Administration [NHTSA], 2009). The current study evaluated the effect of a rectangular rapid-flashing beacon (RRFB) triggered by excessive speed on vehicle speed using a combined alternating treatments and reversal…
Turbulent jets issuing from rectangular nozzle with a rectangular notch at the midspan
Fujita, Shigetaka; Harima, Takashi; Osaka, Hideo
2012-04-01
The turbulent flowfield of turbulent jet issuing from rectangular nozzle (Aspect Ratio=12.5) with a rectangular notch at the midspan, has been investigated experimentally. Four aspect ratios of rectangular notch (NAR: Notch Aspect Ratio) used in this experiment were 2.5, 7.5, 12.5 and 165. The Reynolds number based on the nozzle width d and the exit mean velocity Ue, was kept constant 30000 (NAR=2.5 and 7.5), 15000 (NAR=12.5) and 13000 (NAR=165), respectively. Longitudinal mean velocity and turbulent intensities were measured using an X-array Hot-Wire Probe (5 µm in diameter, 1 mm effective length) operated by the linearized constant temperature anemometers (DANTEC), and the spanwise and the lateral mean velocities were measured using a yaw meter. The signals from the anemometers were passed through the low-pass filters and sampled using A.D. converter. The processing of the signals was made by a personal computer. Acquisition time of the signals was usually 80 seconds. From this experiment, it was revealed that the attachment of a rectangular notch to the rectangular jet suppressed the development of the turbulent velocity scales near the jet centre in the upstream region for the cases of NAR≥7.5.
Turbulent jets issuing from rectangular nozzle with a rectangular notch at the midspan
Osaka Hideo
2012-04-01
Full Text Available The turbulent flowfield of turbulent jet issuing from rectangular nozzle (Aspect Ratio=12.5 with a rectangular notch at the midspan, has been investigated experimentally. Four aspect ratios of rectangular notch (NAR: Notch Aspect Ratio used in this experiment were 2.5, 7.5, 12.5 and 165. The Reynolds number based on the nozzle width d and the exit mean velocity Ue, was kept constant 30000 (NAR=2.5 and 7.5, 15000 (NAR=12.5 and 13000 (NAR=165, respectively. Longitudinal mean velocity and turbulent intensities were measured using an X-array Hot-Wire Probe (5 µm in diameter, 1 mm effective length operated by the linearized constant temperature anemometers (DANTEC, and the spanwise and the lateral mean velocities were measured using a yaw meter. The signals from the anemometers were passed through the low-pass filters and sampled using A.D. converter. The processing of the signals was made by a personal computer. Acquisition time of the signals was usually 80 seconds. From this experiment, it was revealed that the attachment of a rectangular notch to the rectangular jet suppressed the development of the turbulent velocity scales near the jet centre in the upstream region for the cases of NAR≥7.5.
RF current drive by electron cyclotron waves in the presence of magnetic islands
Da Silva Rosa, P.; Giruzzi, G
1999-11-01
The influence of the presence of magnetic islands, and the consequent modification of the tokamak magnetic surface topology, on electron current drive is analyzed. To this end, a new 3D Fokker-Planck code has been developed, taking into account the modifications of the magnetic equilibrium topology owing to the presence of the islands. Significant differences between electron cyclotron current drive efficiency with and without island inside the plasma are found, particularly in the case of interaction with locked modes. (authors)
Power allocation and mode selection methods for cooperative communication in the rectangular tunnel
Zhai Wenyan; Sun Yanjing; Xu Zhao; Li Song
2015-01-01
For the multipath fading on electromagnetic waves of wireless communication in the confined areas, the rectangular tunnel cooperative communication system was established based on the multimode channel model and the channel capacity formula derivation was obtained. On the optimal criterion of the channel capacity, the power allocation methods of both amplifying and forwarding (AF) and decoding and forwarding (DF) cooperative communication systems were proposed in the limitation of the total power to maximize the channel capacity. The mode selection methods of single input single output (SISO) and single input multiple output (SIMO) models in the rectangular tunnel, through which the higher channel capacity can be obtained, were put forward as well. The theoretical analysis and simulation comparison show that, channel capacity of the wireless communication system in the rectangular tunnel can be effectively enhanced through the cooperative technology; channel capacity of the rectangular tunnel under complicated conditions is maximized through the proposed power allocation methods, and the optimal cooperative mode of the channel capacity can be chosen according to the cooperative mode selection methods given in the paper.
Effects of rectangular microchannel aspect ratio on laminar friction constant
Papautsky, Ian; Gale, Bruce K.; Mohanty, Swomitra K.; Ameel, Timothy A.; Frazier, A. Bruno
1999-08-01
In this paper, the effects of rectangular microchannel aspect ratio on laminar friction constant are described. The behavior of fluids was studied using surface micromachined rectangular metallic pipette arrays. Each array consisted of 5 or 7 pipettes with widths varying from 150 micrometers to 600 micrometers and heights ranging from 22.71 micrometers to 26.35 micrometers . A downstream port for static pressure measurement was used to eliminate entrance effects. A controllable syringe pump was used to provide flow while a differential pressure transducer was used to record the pressure drop. The experimental data obtained for water for flows at Reynolds numbers below 10 showed an approximate 20% increase in the friction constant for a specified driving potential when compared to macroscale predictions from the classical Navier-Stokes theory. When the experimental data are studied as a function of aspect ratio, a 20% increase in the friction constant is evident at low aspect ratios. A similar increase is shown by the currently available experimental data for low Reynolds number (flows of water.
National Oceanic and Atmospheric Administration, Department of Commerce — This data set contains time series coastal ocean wave and current data collected during the Atlantic Remote Sensing Land/Ocean Experiment (ARSLOE). ARSLOE was...
Philip, C.S.; SanilKumar, V.; Dora, G.U.; Johnson, G.
Coastlines are undergoing constant geomorphologic changes with respect to the incident wave climate. Based on waves measured at 9 m water depth, simulation of near shore wave transformation is done using REFDIF-1 numerical model and the near shore...
Veerayya, M.; Pankajakshan, T.
For predominant waves approaching from directions varying between SW and WNW and periods varying from 6 to 11 sec, the refraction function (Kd) shows amplification of wave heights resulting in concentration of wave energy on headlands and reduction...
A Lakshmi Narayana; Krishnamohana Rao; R Vijaya Kumar
2014-06-01
A numerical study is carried out using finite element method, to examine the effects of square and rectangular cutout on the buckling behavior of a sixteen ply quasi-isotropic graphite/epoxy symmetrically laminated rectangular composite plate $[0^\\circ /+45^\\circ /-45^\\circ /90^\\circ ]_{2s}$, subjected to various linearly varying in-plane compressive loads. Further, this paper addresses the effects of size of square/rectangular cutout, orientation of square/rectangular cutout, plate aspect ratio(a/b), plate length/thickness ratio(a/t), boundary conditions on the buckling bahaviour of symmetrically laminated rectangular composite plates subjected to various linearly varying in-plane compressive loading. It is observed that the various linearly varying in-plane loads and boundary conditions have a substantial influence on buckling strength of rectangular composite plate with square/rectangular cutout.
Langone, Leonardo; Miserocchi, Stefano; Boldrin, Alfredo; Turchetto, Margherita; Foglini, Federica; Trincardi, Fabio
2010-05-01
The dense water forming in the North Adriatic (NAdDW) spreading southward along the Italian continental shelf, sinks in the Southern Adriatic basin through particular cascading events. Such events are seasonal, occurring specially in April, with variable intensity. These phenomena control the water mass mixing, the deep ocean ventilation, the behaviour of deep ecosystems, the formation of complex erosive and depositional bedforms and the abyssal export and burial of nutrients and carbon. Because of the NadDW formation is linked to climate factors (frequency, duration and size of Bura winds), the temporal variations of the NadDW dispersion into the Southern Adriatic allow to make inferences of the impact of recent climate changes on the ecosystems of the deep Mediterranean Sea. Previous research projects (EuroStrataform, HERMES) acquired a large data set of bathymetric, side-scan sonar (TOBI) and Chirp sonar profiles, which were used to build detailed morpho-bathymetric maps of the Southern Adriatic margin. There, the seabed is extremely complex, characterized by a large variety of bedforms (sediment waves, erosive scours, longitudinal furrows and giant comet marks). A branch of the cascading NAdDW is confined and accelerated through the Bari canyon where it produces a strong current capable of reaching down-slope velocities greater than 60 cm s-1 near the bottom at ~600 m of water depth, eroding the canyon thalweg and entraining large amounts of fine-grained sediment. At the exit of the canyon, in water depth greater than 800 m, the current becomes less confined, spreads laterally and generates an 80-km2-wide field of mud waves; these bedforms migrate up current and show amplitudes up to 50 m and wavelengths of about 1 km. Cruise IMPACT-09 of RV Urania was carried out in the Southern Adriatic Sea from 17-30 March 2009 with main scope of studying the impact of NadDW cascading events on the deep ecosystems of the Southern Adriatic. Experiments planned in the cruise
Markus, D.; Ferri, Francesco; Wüchner, R.
2015-01-01
that focuses on differences in load curves resulting from 2D and 3D flows. It is shown that the major trends predicted by the numerical simulations are also captured in the experiment, highlighting the potential of CFD as a powerful tool for shape optimization studies. The overall aim of the paper...... variations of the structure on the resulting horizontal forces. Steady current conditions, dynamic loading due to waves, and combined wave–current scenarios are considered. A clear focus is put on simplicity and reproducibility, allowing for efficient testing of related methods and codes. This is achieved...... by defining a simple test geometry, altered in one design variable only, and by designing the test case such that a two dimensional analysis of the flow fields is possible. The force sensitivities to changes in the geometry are determined both numerically and experimentally for a great bandwidth of different...
Voltage-Controlled Square/Triangular Wave Generator with Current Conveyors and Switching Diodes
Martin Janecek
2012-12-01
Full Text Available A novel relaxation oscillator based on integrating the diode-switched currents and Schmitt trigger is presented. It is derived from a known circuit with operational amplifiers where these active elements were replaced by current conveyors. The circuit employs only grounded resistances and capacitance and is suitable for high frequency square and triangular signal generation. Its frequency can be linearly and accurately controlled by voltage that is applied to a high-impedance input. Computer simulation with a model of a manufactured conveyor prototype verifies theoretic assumptions.
Field Study on the Effects of Waves and Currents on a Distributed Explosive Array
1993-12-01
taken during each deployment. Table 1 Summary of Video Camera Resources Used During Study Camra ID [LoGato Formal Availabilty BWTEL Top of tower Black... usage . First, the offshore-flowing current would help extend the array seaward from the rocket anchors while reducing the longshore deformation
Waves and currents in tide-dominated location off Dahej, Gulf of Khambhat, India
SanilKumar, V.; AshokKumar, K.
was found to be around 4.5 times stronger than that of the major diurnal constituent K1. Currents were predominantly tide induced with speeds up to 3.3 m/s and were north-northwest during flood tide and south-southeast during ebb tide. Residual cross...
Breinbjerg, Olav
1992-01-01
An approach for including higher order edge diffraction in the equivalent edge current (EEC) method is proposed. This approach, which applies to monostatic as well as bistatic radar configurations with perfectly conducting polygonal plates, involves three distinct sets of EECs. All of these sets ...
Nakai, Kenji; Takahashi, Shin; Suzuki, Atsushi; Hagiwara, Nobuhisa; Futagawa, Keisuke; Shoda, Morio; Shiga, Tsuyoshi; Takahashi, Ken; Okabayashi, Hitoshi; Itoh, Manabu; Kasanuki, Hiroshi
2011-03-01
The noninvasive evaluation of ventricular T-wave alternans (TWA) in patients with lethal ventricular arrhythmias is an important issue. In this study, we propose a novel algorithm to identify T-wave current density alternans (TWCA) using synthesized 187-channel vector-projected body surface mapping (187-ch SAVP-ECG). We recorded 10 min of 187-ch SAVP-ECG using a Mason-Likar lead system in the supine position. A recovery time (RT) dispersion map was obtained by averaging the 187-ch SAVP-ECG. The TWCA value was determined from the relative changes in the averaged current density in the T-wave zone (Tpeak ± 50 ms) for two T-wave types. We registered 20 ECG recordings from normal controls and 11 ECG recordings from nine subjects with long QT syndrome (LQT). We divided LQT syndrome subjects into two groups: group 1 provided 9 ECG recordings without visually apparent TWAs, and group 2 provided 2 ECG recordings with visually apparent TWAs. The QTc interval values in the LQT groups were higher than those in the control (515 ± 60 ms in LQT G-1, 600 ± 27 ms in LQT G-2 vs. 415 ± 19 ms in control, P < 0.001). The RTendc dispersion values among the LQT subjects were higher than those of the control subjects (48 ± 19 ms in LQT G-1, 65 ± 30 ms in LQT G-2 vs. 24 ± 10 ms in control, P < 0.01). The mean TWCA value was significantly higher in the LQT G-2 group with visually apparent TWCAs (0.5 ± 0.2% in control, 2.1 ± 1.2% in LQT G-1, and 32.3 ± 6.9% in LQT G-2). Interestingly, the two-dimensional distribution of TWCA in LQT was inhomogeneous and correlated with the distribution of increased RT dispersion. We conclude that a novel algorithm using 187-ch SAVP-ECG might provide new insights into body surface TWCA.
姜桂宾; 裴云庆; 王兆安
2003-01-01
Objective For the inverters used in UPS, it is important to maintain the pure sinusoidal AC output voltage waveform over all loading conditions and transients. Methods A novel sinusoidal output voltage control strategy is pregented in this paper. The output voltage is controlled by introducing filtering eapacitor current feedback. Two simple PI regulators are used for the current and voltage control loops. Results With the new control strategy, the inverter achieves very low output voltage distortion, good output voltage regulation and strong perturbation rejection, fast dynamic response, and good performance under nonlinear loads. The THD under capacitance rectifying load is better than 0.2%, the output voltage regulation within 0 to full load is less than 0.1%. The resting time under load transient is within 200μs. Conclusion The merits of the new control strategy include rapid response and good steady state stiffness.
Milanesio, D.; Maggiora, R.
2015-12-01
Ion Cyclotron (IC) antennas are routinely adopted in most of the existing nuclear fusion experiments, even though their main goal, i.e. to couple high power to the plasma (MW), is often limited by rather severe drawbacks due to high fields on the antenna itself and on the unmatched part of the feeding lines. In addition to the well exploited auxiliary ion heating during the start-up phase, some non-ohmic current drive (CD) at the IC range of frequencies may be explored in view of the DEMO reactor. In this work, we suggest and describe a compact high frequency DEMO relevant antenna, based on the high impedance surfaces concept. High-impedance surfaces are periodic metallic structures (patches) usually displaced on top of a dielectric substrate and grounded by means of vertical posts embedded inside the dielectric, in a mushroom-like shape. These structures present a high impedance, within a given frequency band, such that the image currents are in-phase with the currents of the antenna itself, thus determining a significant efficiency increase. After a general introduction on the properties of high impedance surfaces, we analyze, by means of numerical codes, a dielectric based and a full metal solution optimized to be tested and benchmarked on the FTU experiment fed with generators at 433MHz.
Milanesio, D., E-mail: daniele.milanesio@polito.it; Maggiora, R. [Politecnico di Torino, Dipartimento di Elettronica e Telecomunicazioni (DET), Torino (Italy)
2015-12-10
Ion Cyclotron (IC) antennas are routinely adopted in most of the existing nuclear fusion experiments, even though their main goal, i.e. to couple high power to the plasma (MW), is often limited by rather severe drawbacks due to high fields on the antenna itself and on the unmatched part of the feeding lines. In addition to the well exploited auxiliary ion heating during the start-up phase, some non-ohmic current drive (CD) at the IC range of frequencies may be explored in view of the DEMO reactor. In this work, we suggest and describe a compact high frequency DEMO relevant antenna, based on the high impedance surfaces concept. High-impedance surfaces are periodic metallic structures (patches) usually displaced on top of a dielectric substrate and grounded by means of vertical posts embedded inside the dielectric, in a mushroom-like shape. These structures present a high impedance, within a given frequency band, such that the image currents are in-phase with the currents of the antenna itself, thus determining a significant efficiency increase. After a general introduction on the properties of high impedance surfaces, we analyze, by means of numerical codes, a dielectric based and a full metal solution optimized to be tested and benchmarked on the FTU experiment fed with generators at 433MHz.
Extracorporeal shock wave therapy (ESWT) for the treatment of cellulite--A current metaanalysis.
Knobloch, Karsten; Kraemer, Robert
2015-12-01
The aim of this metaanalysis was to investigate the effectiveness of extracorporeal shock wave therapy (ESWT) in cellulite. Electronic databases (such as Ovid MEDLINE, Scopus and Ovid) as well as reference lists of the available studies were evaluated in June 2015 by two expert examiners. Assessment of each study's methodological quality was performed with the help of the published quality index tool by Downs and Black. This metanalysis included a total of eleven clinical trials on the effects of ESWT on cellulite with a total of 297 included females. Among the eleven clinical trials five randomized controlled trials on ESWT in cellulite with a total number of 123 females have been published so far. Both, focused as well as radial ESWT devices have been found effective in treating cellulite so far. Typically, one or two sessions per week and six to eight sessions overall were studied in the published clinical trials. Overall, outcome parameters mainly focused on digital standardized photographs, circumference measurements and specific ultrasound examinations. Reporting quality showed substantial heterogenity from 22 to 82 points with a mean of 57 points. This metanalysis identified eleven published clinical studies on ESWT in cellulite with five randomized-controlled trials among them. There is growing evidence that both, radial as well as focused ESWT and the combination of both are able to improve the degree of cellulite. Typically, six to eight treatments once or twice a week have been studied. Long-term follow-up data beyond one year are lacking as well as details on potential combination therapies in cellulite such as with low level laser therapy (LLLT), cryolipolysis and others. Copyright © 2015 IJS Publishing Group Limited. Published by Elsevier Ltd. All rights reserved.
Chang, Pengxiang; Wu, Bin; Wang, Jinfang; Li, Yingying; Wang, Xiaoguang; Xu, Handong; Wang, Xiaojie; Liu, Yong; Zhao, Hailin; Hao, Baolong; Yang, Zhen; Zheng, Ting; Hu, Chundong
2016-11-01
Both neutral beam injection (NBI) and electron cyclotron resonance heating (ECRH) have been applied on the Experimental Advanced Superconducting Tokamak (EAST) in the 2015 campaign. In order to achieve more effective heating and current drive, the effects of NBI on the heating and current drive with electron cyclotron wave (ECW) are analyzed utilizing the code TORAY and experimental data in the shot #54411 and #54417. According to the experimental and simulated results, for the heating with ECW, NBI can improve the heating efficiency and move the power deposition place towards the inside of the plasma. On the other hand, for the electron cyclotron current drive (ECCD), NBI can also improve the efficiency of ECCD and move the place of ECCD inward. These results will be valuable for the center heating, the achievement of fully non-inductive current drive operation and the suppression of magnetohydrodynamic (MHD) instabilities with ECW on EAST or ITER with many auxiliary heating methods. supported by the National Magnetic Confinement Fusion Science Program of China (Nos. 2013GB101001 and 2014DFG61950) and National Natural Science Foundation of China (Nos. 11405212 and 11175211)
Wijnands, T.J. [Association Euratom-CEA, Centre d`Etudes Nucleaires de Cadarache, 13 - Saint-Paul-lez-Durance (France). Dept. de Recherches sur la Fusion Controlee]|[CEA Centre d`Etudes de Cadarache, 13 - Saint-Paul-lez-Durance (France). Direction des Sciences de la Matiere
1997-03-01
This work is focussed on an important and recent development in present day Controlled Nuclear Fusion Research and Tokamaks. The aim is to optimise the energy confinement for a certain magnetic configuration by adapting the radial distribution of the current. Of particular interest are feedback control scenarios with stationary modifications of the current profile using current, driven by Lower Hybrid waves. A new feedback control system has been developed for Tore Supra and has made a large number of new operation scenarios possible. In one of the experiments described here, there is no energy exchange between the poloidal field system and the plasma, the current is controlled by the power of the Lower Hybrid waves while the launched wave spectrum is used to optimise the current profile shape and the energy confinement. (author) 151 refs.
High-current quasi-square-wave millisecond light source for high-speed photography
Lin, Wenzheng; Jiang, Aibao; Zhuo, Meizhen
1993-01-01
A novel powerful strobe for high-speed photography is described which can replace the high power cw light source, to save energy and synchroflash with the camera. In this strobe, three- phase transformerless direct rectifier, high current SCR switch and pre-ionization technique are used so that the energy consumption goes down greatly, and its total weight is less than 25 Kg. Its principal parameters are as follows: average power, 50 KW; light emitting pulse width, 1 - 100 ms; pulse rise time, less than 0.05 ms; pulse fall time, less than 0.1 ms.
Huang, Lei; Fang, Hongwei; He, Guojian; Jiang, Helong; Wang, Changhui
2016-12-01
Wind-driven sediment resuspension exerts significant effects on the P behavior in shallow lake ecosystems. In this study, a comprehensive dynamic phosphorus (P) model that integrates hydrodynamic, wind wave and sediment transport is proposed to assess the importance of internal P cycling due to sediment resuspension on water column P levels. The primary contribution of the model is detailed modeling and rigorous coupling of sediment and P dynamics. The proposed model is applied to predict the P behavior in the shallow Taihu Lake, which is the third largest lake in China, and quantitatively estimate the effects of wind waves and lake currents on P release and distribution. Both the prevailing southeast winds in summer and northwest winds in winter are applied for the simulation, and different wind speeds of 5 m/s and 10 m/s are also considered. Results show that sediment resuspension and the resulting P release have a dominant effect on P levels in Taihu Lake, and likely similar shallow lakes. Wind-driven waves at higher wind speeds significantly enhance sediment resuspension and suspended sediment concentration (SSC). Total P concentration in the water column is also increased but not in proportion to the SSC. The different lake circulations resulting from the different prevailing wind directions also affect the distribution of suspended sediment and P around the lake ultimately influencing where eutrophication is likely to occur. The proposed model demonstrates that internal cycling in the lake is a dominant factor in the lake P and must be considered when trying to manage water quality in this and similar lakes. The model is used to demonstrate the potential effectiveness of remediation of an area where historical releases have led to P accumulation on overall lake quality. Copyright © 2016 Elsevier Ltd. All rights reserved.
Slovinsky, William Stanley
A "millimeter wave" (MMW) is an electromagnetic oscillation with a wavelength between 1 and 10 mm, and a corresponding frequency of 30 to 300 GHz. In the spectrum of electromagnetic radiation, this band falls above the frequencies of radio waves and microwaves, and below that of infrared radiation. Since the 1950s, frequencies in this regime have been used for short range communications and beginning in the 1970s, a form of therapy known as "millimeter wave therapy" (MWT) , or microwave resonance therapy, in some publications. This form of therapy has been widely used in the republics of the former Soviet Union (FSU). As of 1995, it is estimated that more than one thousand medical centers in the FSU have performed MWT and more than three million patients have received this method of treatment. Despite the abundant use of this form of medicine, very little is known about the mechanisms by which it works. Early accounts of use are limited to Soviet government documents, largely unavailable to the scientific public, and limited translations and oral accounts from FSU scientists and literature reviews . This anecdotal body of evidence lacks the scrutiny of peer-reviewed journal publications. In order to gain more widespread acceptance in Western medicine, the pathway through which this regime of the electromagnetic radiation spectrum affects the human body must be rigorously mapped and quantified. Despite the anecdotal nature of a large portion of the existing research on biological MMW effects, a common link is the idea of an interaction occurring at the skin level, which is transduced into a signal used at a remote location in the body. This study explores a possible mechanism for the generation of this signal. The effects of therapeutic frequency MMW on the ionic currents through two different types of ion transport channels were studied, and the results are discussed with emphasis on how they relate to possible changes in nerve signals used by the body for
Dumont, R
2001-08-01
The subject of this thesis is the study of the cyclotronic electron wave as a monitoring tool of the current profile. The first chapter is dedicated to basic notions concerning tokamak plasmas and current generation. The second chapter is centered on the use of fast electrons to generate current and on its modelling. The propagation and absorption of the cyclotronic electron wave require a specific polarization state whose characteristics must be carefully chosen according to some parameters of the discharge, the chapter 3 deals with this topic. The absorption of a wave in a plasma depends greatly on the velocity distribution of the particles that make up the plasma and this distribution is constantly modified by the energy of the wave, so this phenomenon is non-linear and its physical description is difficult. In a case of a fusion plasma, a sophisticated approximation called quasi-linear theory can be applied with some restrictions that are presented in chapter 4. Chapters 5 and 6 are dedicated to kinetics scenarios involving the low hybrid wave and the cyclotronic electron wave inside the plasma. Some experiments dedicated to the study of the cyclotronic electron wave have been performed in Tore-supra (France) and FTU (Italy) tokamaks, they are presented in the last chapter. (A.C.)