Applied Mechanics and Materials Vols. 34-35

Abstract: Efficient and exact collision detection is important to improve reality and enhance immersion of virtual environment of NC(numerical control) lathe system. We introduce two techniques to improve efficiency and speed up the collision detection process. First, we adopt a spatial partitioning system and bounding volumes hierarchies to reduce the number of potential colliding polygons. Octree structure has been adopted to describe the partitioned object. Second, according to the feature of NC lathe system ,we exploit cylinders to simulate the workpieces. The experiments testify that the algorithm accelerates the velocity of collision detection and ensures the real_time requirement of collision detection in virtual dynamic processing environment.

Abstract: A hybrid particle swarm optimization (HPSO) approach is proposed to solve the optimization problem of the maximum entropy model oriented to Bayesian prior distribution. HPSO introduces chaos mechanism to create better initial species population, and the power-function carrier is adopted to improve the ergodicity and the sufficiency of the chaos mechanism. Then HPSO uses an inertia weight, which can balance global and local searching capability and fasten convergence speed. A nonlinear constrained optimization model of prior distribution based on the principle of maximum entropy is set up. By using Lagrange multiplier this constrained optimization problem is transformed to a non-constrained optimal one, which is solved by PSO and HPSO algorithm. The simulation example shows that HPSO not only has a better performance at the aspect of solution precision but also converges more quickly.

Abstract: Thermal induced errors are significant factors that affect machine tool accuracy. The deformation of spindle is the main contributor to thermal error. In this paper, the thermal characteristics of the spindle system are investigated. Taking into account the coupling of elastic deformation and temperature, the heat conduction of the spindle system is modeled. The heat of bearings and heat transfer coefficient, and boundary conditions of the spindle are determined. Based on the numerical results, an iterative model of spindle's temperature and thermal deformation are acquired under the actions of thermal loads using the finite element method. Taking the spindle of precision boring machine with some reasonable assumptions and simplicities as an example, the finite element analysis model of spindle thermal characteristics is analyzed with virtual prototyping, and the static/transient temperature field and thermal-structure field are calculated using ABAQUS software. The characteristics of heat flow and thermal deformation within the spindle are analyzed according to the simulation results. The research results provide a theoretical foundation for reasonable arrangement and optimal design to reduce radial and axial deformation of the spindle head, temperature controlling, and the error compensation to the precision machining tool.

Abstract: Pedestrian-vehicle accident without road marks has long been a headache to accident investigators. This paper suggested a new method with the application of fracture mechanics to estimate impact speed in pedestrian-vehicle. Firstly, a windshield crack propagation model based on the crack initiation model put forward by Freund [1] is established. In the model, crack bluntness coefficient is an unknown parameter, depending on various factors, so speed domain is then divided into five intervals and sample real-world accident cases are employed to the calibrate crack bluntness coefficient in different speed intervals. Further, fourth-order Runge Kutta’s method is used to solve the differential equation. Five additional real-world accident cases are then employed to verify the accuracy of the model. Results show good agreement between the model results and the real impact speeds. Finally, the advantages and limitations of this method are discussed.

Abstract: A new integrated child safety seat is presented in this paper. The seat is a two-mode seat for a motor vehicle cooperable with an adult seat belt assembly to provide two modes operation including an adult seat mode and a child seat mode. The seat locates in the center of the rear seat. The structure of the seat was designed in detail. The height of the booster of the seat can be adjusted continuously according to the seated shoulder height of the child passenger. The depth of booster cushion also can be changed according to the size of the passenger. The sled test with the seat was conducted. The seat simulation models with different booster heights were developed using MADYMO software and validated. Then, these models were used to study the performance of the seat in frontal impact. Some key parameters of the seat were studied in simulation test. The results of the test and simulation show that the seat can provide effective protection for the children aged from 3 to 10 years in frontal impact.

Abstract: Regarding 1100mm rolling mill hydraulic AGC system as the research object, on the basis of considering the pipeline dynamic characteristics and adopting position-pressure compound control method, the mathematical model of the hydraulic system is established. This paper analyzes the system dynamic characteristics in different conditions and studies the various static and dynamic error compensation methods.

Abstract: Improving reliability of the machining center (MC) has great significance for raising the manufacturing level of machine building industry and enhancing the international competitiveness of products. Based on the current situation of researches on the reliability of machining center, this paper presents a systematic discussion of MC from the perspectives of the reliability design, the test and assessment and reliability management respectively, aiming to improving reliability of the MC. Relevant methods and approaches, which form a theoretical system of reliability researches on the MC and serve as a scientific and systematic reference basis for them, are proposed. The study of it has an active meaning to raising the level of researches on the reliability of MC.

Abstract: Serpentine belt is widely used in the front end accessory drive (FEAD) system of automotive engine. Experimental setup and dynamic behaviors of a FEAD system are demonstrated in this paper. Some dynamic characteristics are investigated, subjected to multifrequency excitations and different crankshaft (CRK) loads. Experimental results show that the parametric instability of belt transverse vibration occurs mainly in the frequency regions of secondary resonance, and the instability regions are shifted to lower frequencies according to the increasing of CRK speed. With the same CRK load and speed, the rotational angle of tensioner arm, the hubload of tensioner pulley and the slip rate of ALT pulley in the short-belt system are smaller than that in the long-belt system. But with the increase of CRK loads, the parametric instability of belt transverse vibration in the short-belt system is stronger than that in the long-belt system, the higher CRK speed, the greater belt transverse displacement.

Abstract: The wheel-loader is modeled as a linear 12-DOF system in this paper for researching its ride comfort under typical working situations. The pseudo-excitation method is introduced for vibration analysis, which accuracy has been validated. By using this method and taking a certain type of wheel-loader as a representative example, the spectral density of real response of wheel-loader such as the vertical acceleration of driver, the for-and-aft angular acceleration of bucket and the wheel relative dynamic force due to different carrying capacity, speed and the road surface level are obtained. The results offer the theoretical evidence for the farther wheel-loader vibration reduction research.

Abstract: The dynamic behavior of roller system of a "1+4" hot strip rolling tandem mill were analyzed. The stochastic vertical vibration and the optimum mathematical model were established based on the reliability after the system simplified to some extent. Stochastic optimum has been done to the system according to the optimum mathematical model of the roller system. Its best natural frequency and damping coefficient are obtained by computer simulation under the situation of minimum response of the rollers stationary acceleration when chatter occurs. The results indicate that by optimizing the natural frequency and damping coefficient of the system can greatly improve the dynamic behavior of rollers system and equality of the strip, and are useful to the new design of the rolling mill and the setting up of the rolling parameters.