Papers by Keyword: Numerical Method

Abstract: Ordinary differential equation with periodical boundary value and small parameter multiplied in the highest derivative was considered. The solution of the problem has boundary layers, which is thin region in the neighborhood of the boundary of the domain. Firstly, the properties of boundary layer were discussed. The solution was decomposed into the smooth component and the singular component. The derivatives of the smooth component and the singular component were estimated. Secondly, mesh partition techniques were presented according to one transition point method and multi-transition points method. Thirdly numerical methods based on non-equidistant mesh partition were presented to solve the problem. Finally error estimations were given for both computational methods.

Abstract: The work presents a summary of previous studies on fatigue crack propagation within various Aluminum alloys. The effective characteristics on crack growth are first highlighted and the influence of surface engineering such as polishing, shot peening and skimming to enhance the failure resistance are discussed. Several different existing developed models for predicting the rate of crack propagation are compared in terms of incorporated effective parameters. Finally numerical and computational analyses as the accurate, fast and cheap methods which have attracted the Engineers’ interest are reviewed and compared with other methods.

Abstract: The procedure of beam subjected to transverse impact by bar is simulated using numerical method. The method considers the propagation of the expansion wave and shear wave in beam. The effect of beam height on elastic impact loads with different bar lengths and beam heights are investigated. With condition that the length of beam is longer than or equal to that of bar, the numerical solution shows that: when the bar length is constant, if the length of bar is shorter than the height of beam, the longer the bar, the bigger the peak value of impact force; the impact load curve consists of ascending and descending part basically; When the bar length is longer than or equal to beam height, the peak value of impact force is not related to the bar length and equal to that of bar with the same length as the beam height; the impact load curve is trapezium. The contact time is proportional to bar length and equal to the duration time of stress wave propagation in the bar for once return. If the bar length is constant, when bar length is shorter than beam height, the impact load is not related to beam height; when bar length longer than or equal to beam height, the peak value of impact force increases along with the beam height and approach to that of bar with the same length as the beam height.

Abstract: For numerical simulation, the shear strength reduction technique (SSRT) is often used to evaluate slope or landslide stability. According to numerical computation results of slopes or landslides analyzed by SSRT, it can be found that with increase of the shear strength reduction factor, some of the soil elements will yield gradually to form a connected plastic zone, which is the potential slip surface of the slope or landslide. In view of the plastic resistance of soils, formation of the connected plastic zone does not always indicate that the landslide is about to failure. Other auxiliary criterion is necessary to predict whether a slope or landslide is in a critical state or not. Here, difference of the incremental percent of horizontal displacement of the outcropping slip surface node is regarded as the auxiliary indicator to distinguish the critical state of slopes or landslides after formation of the potential slip surface. With the ideas mentioned above, stability of a fossil landslide, Xietan landslide has been analyzed for the natural and the long-term reservoir water level conditions. Factors of safety of Xietan landslide by the numerical method have been compared with that by the limit equilibrium method, which indicates that the method used here for evaluating stability of Xietan landslide is feasible. Because numerical method has more advantages over the limit equilibrium method, the approach for evaluating stability of landslide here can be applied to more complicated or three-dimensional landslides or slopes further.

Abstract: In this study, a two-dimensional numerical method based on the volume of fluid method is used to solve for water sloshing. The 2D equations of fluid motion are derived in a moving coordinate system. For modeling impact pressure induced by large amplitude sloshing, an emphasis is given to the numerical treatment of the free surface, which is sensitive to the simulation. Liquid sloshing inside a rectangular tank is simulated. The time histories of the free surface shape and the dynamic pressure inside the tank are obtained. The results are compared with an experimental data. These comparisons show that this method can be used to simulate the sloshing induced impact loads. Then series of violent sloshing phenomenon is given and compared.

Abstract: The heat transfer and the fluid dynamics characteristics of subsonic gas flows through micro-channels are examined using numerical method. Detailed analysis on the Stirling MEMS device has been examined for the feasibility of the performance. The 1-D Stirling engine design code was utilized to provide basic information to meet the design parameters and criteria. Furthermore a 2-D CFD code has been used to perform a detailed analysis. The simulation results show that the numerical method used here could be used for the prediction of MEMS performance before experimental test and manufacture process start.

Abstract: The evaluation of the correct stability factor of tunnel is a critical element in the various design and construction phases of a tunnel excavated in difficult geotechnical conditions. An innovative, and well-applied, procedure for optimize the construction phase management is described in this article. The starting point of this procedure involves the verification of the results of numerical methods obtained from referenced analytical methods. In the first step of the procedure the results obtained through the analytical method are verified by means of a numerical method in order to evaluate the practical consequences in terms of development of deformations and plastic zone. In this manner, the assumed design risk is evaluated for the different methods and the solution that gives the best correspondence with numerical simulation is selected. Finally, residual uncertainties and parametric variations are incorporated in the analysis and Monte Carlo simulation is used to calculate the statistical distribution of the face-stabilizing pressure and the design value is selected on the basis of an acceptable probability of failure.

Abstract: This work presents a workspace solving approach for a tomato harvesting manipulator with seven degrees of freedom (7 DOF) based on a special envelope method. In this method, the joints of the manipulator was categoried into two groups, and the workspace boundary of each group was formulated according to the envelope equation by MATLAB and AutoCAD by considering the joint limits. To analyze the reachable and dexterous workspace, the position and orientation of the last link was plotted. The results show that the width and height of the wrist workspace of the tomato harvesting manipulator are 1.5 and 1.2m respectively, which can satisfy the tomato picking requirements. The reachable workspace and the dexterous workspace are affected by the length of the last link and the end-effector. In order to minimize the hollow in the workspace, it is necessary to choose the rational length of the 5th link and the 3rd link and the angle range of the 5th joint. The algorithm can make the workspace visualized and be applicable to all practical manipulator configurations.

Abstract: 2-D computational analyses were conducted for unsteady viscous flow and heat transfer across cylinders of different geometries and different incident angle. Circular, square (both at 0° and 90° angles of incidence) and elliptic cylinders were examined. The calculations were performed by solving the unsteady 2-D Navier-Stokes equations at Re = 100. The calculated results produce drag and lift coefficients, as well as Strouhal number in excellent agreement with published data. Calculations for unsteady, incompressible 2-D flow around a square cylinder at incidence angle of 0° and 45° and for Reynolds number = 100 were carried out. Cycle independence and grid independence results were obtained for the Strouhal number. The results were in excellent agreement with the available experimental and numerical results. Numerical results show that the Strouhal number increases with fluid angle of incidence on the cylinder. The wake behind the cylinder is wider and more violent for a square cylinder at 45° incidence compared to a square at 0° this is due to the increase in the characteristic length in the flow direction. The present studywas carried out for a 2-D single cylinder at fixed location inside a channel for unidirectional velocity. To get more accurate results computation on 3-D geometry should be carried out.

Abstract: Obtaining a uniform thickness of the final product using thermoforming is difficult, and the thickness distribution depends strongly on the distribution of the sheet temperature. In this paper, the time-dependent temperature distribution of the total sheets in the stage of storing was studied using the analysis code which has been verified based on the experimental data. It was found out that the time for storing should be managed for decreasing the temperature difference between the sheets. The time-dependent temperature distribution of the total sheets and the method for analysis in this study will be used to improve the quality of the final products.