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AbstractThis research studies the robustness of permanence and the continuous dependence of the stationary distribution on the parameters for a stochastic predator–prey model with Beddington–DeAngelis functional response. We show that if the model is extinct (resp. permanent) for a parameter, it is still extinct (resp. permanent) in a neighbourhood of this parameter. In the case of extinction, the Lyapunov exponent of predator quantity is negative and the prey quantity converges almost to the saturated situation, where the predator is absent at an exponential rate. Under the condition of permanence, the unique stationary distribution converges weakly to the degenerate measure concentrated at the unique limit cycle or at the globally asymptotic equilibrium when the diffusion term tends to 0.

Motion cueing algorithms are used to produce a motion which feels as realistic as possible while remaining in the limited workspace of driving simulators. Several optimal motion cueing algorithms were developed to improve both the exploitation of the workspace of a driving simulator and the realistic of the simulated motion. In the dynamics model of the optimal motion cueing algorithms, several kinds of motion-sensory systems are integrated to optimize the simulated motion sensation. However, most previous works have just focused on the visual and vestibular system. The mathematical model of the proprioceptive system, that also senses the non-visual motion, has rarely been concerned. In this paper, a novel optimal motion cueing algorithm, which integrates model of the proprioceptive system, is developed to reduce the false cues from muscle spindle of head/neck system sensing lateral tilted angle. The optimal motion cueing algorithm has a significant effect on the pilot's perception when the tilted angle is rather large. An example of the simulation of a roller coaster running along a planar S-curve trajectory with only lateral acceleration is investigated with current motion cueing algorithms and optimal motion cueing algorithm. Several objective criteria were introduced to evaluate the simulated perception of all investigated motion cueing algorithms. The results demonstrate that optimal motion cueing algorithm is better than current motion cueing algorithms in most criteria and also sub-criteria.

The aim of this study involved evaluating and predicting forming limit curves of boron steel 22MnB5 sheet at elevated temperatures. A finite-element method simulation was adopted based on ductile fracture criteria and simple experiments at elevated temperatures. First, tensile experimental data and ductile fracture criterions of Johnson–Cook and ductile void growth models were input to ABAQUS/Explicit software to predict and compare the same with fracture occurrence in experiments performed via Hecker’s punch stretching tests at room temperature. Subsequently, punch stretching test data at room temperature were added to correct the fracture strain locus in the space of the stress triaxiality and the equivalent strain following the ductile void growth model. After confirming the accuracy of the forming limit curve prediction at room temperature, fracture strain loci at high temperatures using ductile void growth model were determined based on the average ratio between the fracture equivalent plastic strains at room temperature as well as higher temperatures. Finally, Hecker’s punch stretching tests were numerically simulated to predict forming limit curve(s) of boron steel 22MnB5 sheet at high temperatures.

In the traditional mold manufacturing process, manual methods are mostly used to design, fabricate and then perform forming test to find out the reasonable processing mode for the product. Thanks to the development of technology, the forming design can be greatly reduced by using commercial software. This study uses a combination of ABAQUS software and TAGUCHI algorithms to calculate and design products. By using simulation tool, the fracture, safety, wrinkles as well as stress and strain on the surface of the product can be easily predicted after forming process. So that, the forming process were firstly simulated and executed on the software to find out important parameters. The variance analysis (ANOVA) was then performed to assess the effect of each parameter. Finally, the optimum solution for the product was selected based on ranking levels of each parameter.

This paper presents experimental studied results about surface roughness during end milling SKD11 steel under room temperature and work-piece preheated condition. Conventional samples were first performed. The samples which are same technical parameters were then performed at elevated temperatures to evaluate effective of heating process on the surface roughness. Orthogonal array Taguchi method was used to experimental design. The results showed that the surface quality of product was significantly improved under thermal - assisted milling. The surface roughness model during machining at room and elevated temperatures were evaluated and showed a good agreement with result of experiments.

Nowadays, increasing the productivity and the quality of machining become major challenges of the metal cutting process. Due to the complexity of the chip formation process, in particular, at high cutting speeds, finite element model (FEM) has been frequently used as an alternative solution. Chip shrinkage coefficient and cutting force are the two basic parameters of the cutting process, which determines the productivity and quality of the workpiece. This study uses a Grey correlation relationship to analyze and select the common set of parameters for cutting force and chip shrinkage coefficient of the chip. Simulation of the A6061 aluminum alloy high-speed milling is done by Bao-Wierzbicki's (B-W) model. The optimal parameters are determined cutting depth 1 mm, clearance angle 6o and rake angle 10o. This parameter set adjusts the cut parameters so that the cutting process achieves the highest machining efficiency.

This paper presents the experimental test results on mechanical properties of steel plate grade SS400 at elevated temperatures. The steel is often used as structural steel due to its weldability and machinability. The steel plates were heated by a high frequency heating system to reach specific temperatures before being tested on a tensile testing machine. Five different temperature conditions were used, namely room temperature, 100°C, 300°C, 500°C and 600°C. The data of mechanical properties measured for SS400 steel plates at various temperature conditions were recorded and analysed. The research showed that when the temperature is increased, the force in tensile test is decreased while the strain is increased. The observation and the data were then used to setup the stress – strain – temperature relation for formability study of SS400 steel plates. The same method can be used to establish the mechanical properties at elevated temperatures.

In order to predict correctly stress-strain curve for tensile tests at elevated and cooling temperatures, a modification of a Johnson–Cook (J-C) model and a new method to determine (J-C) material parameters are proposed. A MATLAB tool is used to determine material parameters by fitting a curve to follow Ludwick and Voce's hardening law at various elevated temperatures. Those hardening law parameters are then utilized to determine modified (J-C) model material parameters. The modified (J-C) model shows the better prediction compared to the conventional one. An FEM tensile test simulation based on the isotropic hardening model for metal sheet at elevated temperatures was carried out via a user-material subroutine, using an explicit finite element code. The simulation results at elevated temperatures were firstly presented and then compared with the measurements. The temperature decrease of all elements due to the air cooling process was then calculated when considering the modified (J-C) model and coded to VUMAT subroutine for tensile test simulation. The modified (J-C) model showed the good comparability between the simulation results and the corresponding experiments.