Materials Science Forum Vols. 628-629

Abstract: Heat transfer enhancement is achieved by flow-induced vibration in planar elastic tube bundle heat exchangers. The optimum of structural parameters of tube bundle is of importance to the characteristic and control of flow-induced vibration. The influence of pipe structural parameters such as cross section diameter, thickness and connectors mass on vibration characteristic is studied in this paper with numerical simulation method. Based on the amplitude of flow-induced vibration and stress intensity, the characteristic of planar vibration and vertical vibration are compared, and the amplitude range of infinite fatigue life is predicted. The results show that the cross section diameter of pipe and the connectors mass have major influence on the vibration characteristic of tube bundle. Compare to the planar vibration of tube bundle, the vertical vibration has much advantage in the vibration amplitude and stress intensity distribution.

Abstract: This paper studies the frequency reliability of the main shaft system of Francis turbine-generator units based on nonlinear vibration. Taking the generator and turbine as an integrated system, the nonlinear coupling dynamic equations of the system are established by the finite element method. According to the dynamic equations, the frequent factors of system are obtained by the method of multiple scales. The criterion is used that the difference between the natural frequencies and driving frequencies including the frequent factors should be less than specific values. The reliability mode and the safety probability of the main shaft system of Francis turbine-generator units are defined as a series mode, and the frequency reliability analysis method for avoiding the resonance is proposed. Finally, an example is presented.

Abstract: According to poor computational accuracy at small to median sample sizes of Monte Carlo ( MC ) simulation techniques in estimating the probability failure of mechanical structures, the number theoretical net ( NT-net ) simulation method is proposed to reduce computing effort. Several key concepts, such as good point set, good-lattice point ( glp ), discrepancy and NT-net method, are defined. The sampling stategy is improved by introducing NT-net that can provide better convergent rate over MC. The new method is used to estimate failure probability of the side impact bar on the car door. Results indicate the computational effort needed by NT-net for the same accuracy is about 1/12 of that needed by the MC-based method, and the obtained results are more stable.

Abstract: In the early design phase of direct-drive hobbing machine, to allocate the reliability index scientifically and reasonably without the related reliability data, fuzzy analytic hierarchy process (fuzzy AHP) is used to allocate the reliability index of the main system units of direct-drive hobbing machine. This method is an effect way for multi-factor decision, which can consider the influence of the factors of every hierarchy on the machine maximatily and calculate the influence weights of the factors of every hierarchy quantitatively. Research on reliability allocation of direct-drive hobbing machine illustrate that this method is suitable for reliability allocation during innovative design phase.

Abstract: A new optimal technology and process of separating plastic from domestic waste was presented according to the recycling benefit. An optimal analysis modal was established and the recycling benefit was analyzed. The technique and process of plastic separation was studied. As a result, the investment is much less than that of the synthetic recycling treatment and the recycling benefit is also higher. Depending on optimal separating technique and process, it can reclaim plastic that has high recycling value to a maximum in 15 separating type. A mathematical model of the separating process was established, and the effect of some parameters such as wind speed, sloping angle of airflow on the separating rate was studied; with an optimal 15 m/s wind-speed horizontally and 14-degree blowing angle, so that the rate of separating plastic is over 85%. Therefore, the enterprises can realize persistent development for a long run without government allowances.

Abstract: The cutter head drive hydraulic system of φ1.8m simulate shield machine is introduced in this article, which has the variable speed pump control technique and the closed loop control method. The AMESim simulation model of the hydraulic system is built up, and the efficiency of the hydraulic system, speed control performance by open loop and closed loop control are analyzed. The result of the simulation shows that the variable speed pump control system has higher efficiency than the variable displacement pump control system about 4%-26% in the same condition when the cutter head speed is at the range of 0.5-4r/min, and the hydraulic system has good dynamic characteristics in closed-loop PID control.

Abstract: A new improved genetic algorithm (IGA) based on floating point encoding is proposed. Firstly, IGA uses information entropy to produce better initialized species population. Secondly, after synthetically studying the searching properties of crossover operator in GA, it designs a new crossover strategy that effectively increases searching efficiencies of IGA. Thirdly, to avoid searching being trapped in local minimum, it designs a chaos degenerate mutation operator that makes the searching fast converge to a global minimum. At last IGA is used to solve the problem of the optimal design to crane girder, which is a typical problem of mechanical optimal design. Compared with the traditional random direction method, neural network method, genetic-neural network method, hybrid genetic algorithm, chaos-GA, PSO algorithm, chaos-PSO algorithm and standard GA, IGA shows better performance at the aspect of solution precision and convergence speed than that of these algorithms.

Abstract: Take “Research on minitype universal autonomous docking mechanism” as an example, the paper studied on the platform of complex product’s cooperative design and simulation of mechanical field. The process of mechanical component design was introduced. The paper put forward the bottleneck problem in the design process of data transmission and gave the solution. A new method that uses HLA/RTI (High Level Architecture/Runtime Infrastructure) for function module communication was given. By using component technology and integrating all the function module of current commercial software based on the design process, this platform expands easily and the simulation sub-system can plug and play.

Abstract: The modelling method of dynamic flow path feature (DFPF) is proposed for the design process of hydraulic manifold block (HMB). In this method, temporary body model and B-Rep model are adopted to represent geometric model of DFPF; the former is used for showing flow path, checking connectivity and safe wall thickness, and the latter is used for saving the final results. A novel feature topological representation method based on solid adjacency graph (SAG) is provided, and then validity of feature semantics can be checked through SAG. Finally dynamic topological changeability of flow path feature is realized by constraint solution and knowledge driving. Object-oriented model of DFPF is given, and the design process of HMB based on DFPF is illustrated.

Abstract: In order to investigate the changing law of the film thickness caused by the deformation of hollow coaxial and drum-shaped lining and accurately calculate the stress of hollow coaxial and rum-shaped lining, the fluid-solid numerical simulatied model of a large-scale hydrostatic bearing was established. The stress and deformation of hollow coaxial and drum-shaped lining was obtained by indirect coupled methods. The typical impact factors and the deformation laws of the thinnest film were discussed. The simulation results indicate that the maximum stress locatioes on the drum-shaped lining and hollow coaxial; and the deformation of the hollow coaxial is 60.47 times that of the drum-shaped lining, and the oil film thinnest thickness decreases by 12.1% due to the deformation of the hollow coaxial and drum-shaped lining; and the stiffness of the hollow coaxial makes greatest impact on oil film deformation.