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August 15,2011
Volume 4,Issue 15
Pages -
Subject Area:Explosion Mechanics,Fatigue,Fluid Mechanics,Fracture Mechanics,Elastic Mechanics,Condensed Matter Physics

Title: Simulation analysis of underwater explosion based on AUTODYN

Authors: SUN Xuewu
PP: 1430-1435
Abstract: The underwater explosion models of the TNT charges were simulated by AUTODYN software, the peak pressures of the explosions were obtained and analyzed. The influences of the state equation and the grid density towards the simulation results were analyzed, and the numerical simulation method with faster computation speed and numerical simulation modified precision was deduced accordingly. Taking the small amount of powder s far field underwater explosion as the study, the result showed several referable conditions: the smaller state residual if the SHOCK polynomial equation is adopted; proper grid density affects the computation precision much, yet if the grid density is too high, this effect would be weakened. Through the comparison with experimental data, the reliability of the method was verified.
Keywords: marine technology; underwater explosion; state equation; mesh; peak pressure; far field analysis

Title: High accuracy time marching scheme to solve motion equations

Authors: LIU Zhongbo
PP: 1425-1429
Abstract: To effectively solve motion equations in mechanical problem, the equation was split to two equations. Based on these equations, a composite third order Adams Bashforth predict and fourth order Adams Moulton correct was applied and a finite difference method numerical model was established, and iterative method was used in the solution process. To prove the presented algorithm, numerical simulations were carried out upon a one degree freedom spring vibration without damping problem, and the Crank Nicolson scheme was also applied to solve the equations to make a comparison. The computed results of the presented method and those of Crank Nicolson method were compared against analytical solution with different time steps. The presented could give better results and the agreement is quite good, which shows the presented high accuracy time marching method can be effectively applied to solve the motion equations and Crank Nicolson scheme is not applicable for this problem.
Keywords: physical mechanics; motion equation; numerical model; predict correct; Adams Bashforth Moulton scheme

Title: Simulation for temperature and stress field about composite coating

Authors: MU Ruimin, ZHOU Xia
PP: 1418-1424
Abstract: In this paper, temperature and stress field of 25 steel is simulated by finite element analysis using ANSYS codes. Based on ANSYS (ANSYS parametric design language, APDL) developing platform, the indirect method is used to make the grid of welds fine and make the grid away from the welds rough. The program is to simulate the GAUSS function heat load and obtain the three dimensional dynamical temperature filed for build up welding. At last, the result of welding temperature field, stress and strain field is obtained, and it is found that a suitable temperature between layers can reduce residual stress and improve the welding quality. It provides foundation for the further study of the method for eliminating welding residual stress.
Keywords: damage mechanics; stress field; finite element method; temperature field; layer temperature

Title: Stwdy on nonlinear characteristics of turbulent spot flow fields

Authors: YANG Yingzhao, TANG Dengbin
PP: 1409-1417
Abstract: The formation and development of turbulent spot flow fields are researched by the direct numerical simulation of Navier Stokes equations. The turbulent spots are the isolated local regions surrounded by laminar flows in the transitional late stage of the boundary layer, and possess some turbulent properties including the random pulse and complex vortices, etc. The high order compact difference schemes with the high resolution are constructed by the high order three dimensional coupling centric difference schemes combined with the time splitting method and high order upwind scheme. This method can be used in the all computational area including in the vicinity of the boundary. The distribution of the disturbances sources and the change of the disturbances values are designed in the paper. The computed results show clearly nonlinear properties of turbulent spot flow fields, such as the increase of the pulse amplitude, the distribution of the disturbance energy, and the generation of Reynolds stress and vortices, and interaction, etc. The computed results show that, when turbulent spots intersect with each other, the nonlinear effect strengthening becomes a main characteristic of multiple turbulent spot flow fields.
Keywords: fluid mechanics; turbulent spots; random pulse; Reynolds stress; nonlinear characteristics; direct numerical simulation

Title: Experimental study on fatigue behavior of the metal honeycomb sandwich panel at elevated temperature

Authors: ZOU Guangping, LU Jie, CAO Yang, LIU Baojun
PP: 1403-1408
Abstract: In this paper, fatigue behavior of the steel honeycomb sandwich panel at elevated temperature was investigated by three point bending fatigue test and fatigue failure modes of the specimens were analyzed and discussed. Three point bending fatigue tests were conducted in two directions of the orthotropic steel honeycomb sandwich panel respectively and fatigue lives of the specimens in several stress levels at high temperature reach to 400℃ were obtained. S N curves and the three point bending fatigue limits of two directions of the specimen were obtained with least square method. The experimental results indicated that fatigue properties of the specimen in W direction were better than that in L direction, and the major fatigue damage pattern at the high stress level was core collapsing while failure mode at lower stress level was face sheet of bottom side cracked and propagated to the honeycomb core which resulted in suddenly failure.
Keywords: solid mechanics; high temperature fatigue behavior; three point bending fatigue test; honeycomb sandwich panels; S N curve; failure mode

Title: Study of rock crack extension under dynamic and static stress

Authors: SHI Fang, GAO Feng
PP: 1398-1402
Abstract: In this paper, fracture growth rules under strong stress wave action are researched by the derivation of the crack initiation angle function and fracture growth angle function under dynamic and static stress. The result is obviously different from the situation that has only static stress. Instantaneous changes in crack propagation speed will increase the complexity of the extended orientation. At last, the function s accuracy is confirmed with the aid of the RFPA2D software, which can simulate the failure process of jointed rock under dynamic stress.
Keywords: fracture mechanics; stress wave; RFPA2D; jointed rock

Title: General form of variational principles in elasticity & Lagrange multiplier procedure

Authors: JIANG Zhongxiang
PP: 1390-1397
Abstract: This paper deduces the general form of the variational principle in elasticity by Lagrange multiplier procedure. It is approved that the formula (2) is the variational principle s functional with the three kinds of variables under certain conditions. But it seems that the universality of formula (2) can t be approved by Lagrange multiplier procedure. It is a difficulty for Lagrange multiplier procedure.
Keywords: elasticity; three kinds of variables; general form of variational principle; Lagrange multiplier procedure

Title: Fine structure of detonation wave for propulsion

Authors: ZHANG Xudong, FAN Baochun, GUI Mingyue, PAN Zhenhua
PP: 1382-1389
Abstract: In this paper, the calculated cellular structures and flow fields of oblique detonation wave (ODW) and rotating detonation wave (RDW) are obtained numerically, and the fundamental characteristics and self sustaining mechanisms of those detonations are analyzed and discussed. ODW front consists of three parts: the ZND like front, the single headed triple point front and the dual headed triple point front. Cellular structures of RDW front are heterogeneous, and the cell size along the outer wall is smaller than that along the inner wall.
Keywords: explosion mechanics; propulsion system; fundamental characteristics; self sustaining mechanisms; classic CJ theory

Title: State model of physical stability

Authors: ZHAO Feng
PP: 1376-1381
Abstract: Based on the physical state equations of the system, analytical methods of mathematical physics were used to obtain the condition that meets physical state stability is the state variable is zero. Further analyzed the conditions to achieve physical stability under the continuous input state of the system, input stop state of the system, superposition state of the system. This method which uses mathematical model to express and studies physical stability through the control of the boundary conditions provides a new idea for the study of dynamic stability, nonlinear physics, and other aspects of system control.
Keywords:

Title: Chaotic communication with DPSK modulation

Authors: WANG Yang, FENG Ye
PP: 1371-1375
Abstract: This paper presents a simulation research on subcarrier modulation in chaotic communication based on distributed feedback (DFB) producing chaos, and proposes apply differential phase shift keying (DPSK) modulation in subcarrier chaotic communication. The result shows that the performance of subcarrier chaotic communication can be improved effectively by using DPSK modulation, and it is beneficial to improve the message-hide effect. With subcarrier multiplexing frequency gets close to the relaxation oscillation frequency of the laser diode, the decoding performance would decrease.
Keywords: optics; secure communication; simulation; differential phase shift keying modulation

Title: Controllable synthesis and multicolor fluorescence of lanthanide doped sodium gadolinium fluoride nanocrystals

Authors: QI Fei, HE Dingfei, LIANG Liangbo, YU Xuefeng
PP: 1366-1370
Abstract: This paper presents a way to synthesize the water soluble sodium gadolinium fluoride nanocrystals doped with lanthanide ions. Transmission electron microscopy (TEM), X ray diffraction (XRD), Fourier transform infrared spectroscopy (FT IR) and fluorescence spectrophotometer are used to characterize the nanocrystals. The results indicate that the obtained nanocrystals are in cubic phase, water soluble, and have an elongated spherical shape with diameters of 20 35 nm. Compared with the samples synthesized in water, the sodium gadolinium fluoride nanocrystals synthesized in this way exhibit much stronger fluorescence. Furthermore, multicolor fluorescence can be obtained through doping with different lanthanide ions in the nanocrystals.
Keywords: optics; fluorescent labels; liquid phase method; sodium gadolinium fluoride

Title: Research on modification of Kirchhoff approximation at low frequency

Authors: WANG Bin, FAN Jun
PP: 1359-1365
Abstract: In this paper, modification of Kirchhoff approximation at low frequency has been discussed. By analyzing the frequency characteristics of typical structures surface acoustic impedance, approximate relationship between surface pressure and surface velocity is proposed to be adapted for both low and high frequencies. Kirchhoff approximation is modified and extended over low frequency. Numerical analysis proves that the modified Kirchhoff approximation has a reasonable precision in the whole frequency band.
Keywords: underwater acoustics; Kirchhoff approximation; surface acoustic impedance; Predicfion of sound radiation

Title: Data processing system software development for moment of inertia measuring instrument

Authors: YUAN Shuqing, FAN Xuedong, LIU Jiao
PP: 1352-1358
Abstract: This paper introduces a data processing system for moment of inertia measuring instrument based on virtual instrument, using LabVIEW software. This system can automatically store, display and process experimental data, and it can also present the experimental results. This paper describes the composition of this system, shows the system s front panel and rear panel system program, and gives a detailed description of the serial port selection, data collection and recording, data processing and validation routines parallel axis theorem. Experimental results show that this system is reliable and easy to use.
Keywords: theoretical physics; software development; moment of inertia measuring instrument; virtual instrument

Title: Study on energy attenuation coefficient in granular chain

Authors: CHEN Qiong, YANG Xianqing, WANG Zhenhui, GUO Haiping, YE Jianlan, ZHAO Xinyin, WU Fangfang
PP: 1346-1351
Abstract: In this paper, the dynamics behavior of a solitary wave delivered in the granular chain which is made of different materials is studied by computer simulating. The equation of motion of each ball is solved by using a five order Rung Kutta formula. From the result about velocity changing of each ball and the energy transmitting, it is obtained that there is a universal power low behavior in time for the leakage of the impulse energy confined inside various granular containers. The attenuation coefficient is got by choosing a horizontal free boundary chain as a standard chain which consists of 420 balls with the same radius and mass ratio 100∶1 (120 hard balls 180 soft balls 120 hard balls). Then the energy leaking within different chains is studied by changing radius ratio, mass ratio, arrangement way of the two kinds of particles, the number of soft balls and so on. The calculations suggest that the value of the exponent γ is smallest when the radius ratio is 1∶1, and increases with the increase of soft balls number, interface and friction coefficient.
Keywords: theoretical physics; attenuation coefficient; five order Rung Kutta; granular chain; energy decay

Title: Investigation on mechanism of brittle ductile transition of Si nanowires at room temperature

Authors: ZHENG Kun, HAN Xiaodong, ZHANG Yuefei, ZHANG Ze
PP: 1340-1345
Abstract: Using new developed method for deformation of nanomaterials, Si nanowires were performed plastic deformation under axial tension and bent in transmission electron microscope (TEM). Dislocation nucleation was the dominated factor to achieve brittle ductile transition which was disclosed by high resolution TEM images. The density of dislocations of the surface was about 1017/m2, while that of interior was 1016/m2. Dislocations nucleation can be taken place on two equivalent {111} planes. They were easily pinned to form Lomer lock once they met, which induced the increase of dislocation density.
Keywords: condensed matter physics; room temperature brittle ductile transition; transmission electron microscope; Si nanowire

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