Advanced Materials Research Vols. 44-46

Abstract: In order to eliminate the disadvantages of the traditional electro-hydraulic converters in the turbine governor, a new electro-hydraulic converter with strong restoring-motion was studied in this paper. The basic structure and working principal were analyzed, and the basic characteristics were described in detail. The simulation analysis of its dynamic characteristics was made by using Simulink software and the methods for improvement of the performances were suggested. The results of field tests indicated that the performance indexes of the hydro-turbine governors with this new technology were conformable to or higher than GB. It is concluded that the new electro-hydraulic converter has a promising future in engineering applications, especially in turbine governing systems that suffer from jam fault.

Abstract: In this paper, a two-dimensional mathematical model of a processor for fuel cell vehicles was presented in order to predict the effect of the parameters on the hydrogen content of the processor. The structure of the processor and the operating parameters were taken into account in the model. The complex physical and chemical process in the processor of dimethyl ether partial oxidation was well described by this model. The mathematical model was introduced into the commercial software star-cd, and then numerical simulations were also performed based on this model. In order to accounting for the effect of the processor temperature and volume fraction field, TGrid mesh method and laminar flow model were selected. Experimental verification of the two-dimensional mathematical model was implemented on self-designed equipment. The result indicates that the computed data is in good agreement with the experiment one. Finally, on the basis of the mathematical model, the effect of the parameters on the hydrogen content of the processor were investigated.

Abstract: On the basis of the Bouc-Wen hysteretic model, a numerical method for the reliability analysis of stochastic multi-degree-of-freedom hysteretic system with correlated failure modes is presented. Under the first passage model, considering the random caused by hysteretic loop itself, the theory of incomplete probability information and the fourth-moment technique and Gram Charlier series are employed to develop a numerical reliability analysis method systematically. The numerical example reveals that in most of cases, though system is characterized by a set of independent random parameters, the responses are strongly correlated, and correlation coefficient between the responses is fluctuated with time. The system reliability with correlated failure modes is evaluated with proposed method, and the result obtained by this method is compared well with the Monte-Carlo simulations.

Abstract: A fatigue life prediction method was introduced. The method was based on the combination of time domain and frequency domain method. Dynamic model of a complete railway locomotive system was established using SIMPACK software. The dynamic load histories acting on the bogie frame can be obtained by the Multi-Body System (MBS) analysis technique with time integration. FEM model of the bogie frame was established by applying ANSYS software. The natural frequencies and mode shapes of the frame were calculated and the dangerous nodes in the critical location were determined using the modal analysis technique. The stresses in dangerous nodes were calculated with the quasi-static stress/strain technology. PSD of the stresses was generated using the Fast Fourier Transformation (FFT). Fatigue life of the bogie frame was evaluated with the Dirlik’s formulation. Results showed that the calculated life of the analyzed bogie frame could meet the design requirement.

Abstract: Zirconium tube is widely used in heat exchanger equipments in petrochemical process for significant corrosion resistance. The connection joint of tube-tubesheet is the weakest parts in a heat exchanger. The experiment and numerical analysis of different materials (zirconium tubes, titanium tubes and 16MnR tubesheets, 316L tubesheet) joints were performed in this paper. The expansion joints specimens were prepared at the pressure ranging from 28MPa to 38MPa. And pulling out test was performed from 20°C to 300°C. The finite element model of tube-tubesheet joint was established. The effect of expansion pressure, temperature and groove on the pulling out strength of joints was analyzed. Both the experiments and the finite element analysis show that the pull-out strength increases with the increasing expansion pressures. Working temperature also has a great effect on the connection strength of tube-to-tubesheet joints, especially for the zirconium and 316L joints, which have the most significant difference of thermal expansion coefficient between tube and tubesheet. The residual contacting pressure on the contact surface between tubes and the tubesheet is not uniformly distributed and two tightness bands are found near the surfaces of the tubesheet or at the two brinks of the groove on the tubesheet hole. Compared with the ungrooved joint, the residual contacting pressure on the tightness bands for the grooved joint is much higher, indicating a grooved joint has better tightness.

Abstract: The quantitative analysis of “domino” effects is one of the main aspects of hazard assessment in chemical industrial park. This paper demonstrates the application of heterogeneous stochastic Petri net modeling techniques to the quantitative assessment of the probabilities of domino effects of major accidents in chemical industrial park. First, five events are included in the domino effect models of major accidents: pool fire, explosion, boiling liquid expanding vapour explosion (BLEVE) giving rise to a fragment, jet fire and delayed explosion of a vapour cloud. Then, the domino effect models are converted into Generalized Stochastic Petri net (GSPN) in which the probability of the domino effect is calculated automatically. The Stochastic Petri nets’ models, which are state-space based ones, increase the modeling flexibility but create the state-space explosion problems. Finally, in order to alleviate the state-space explosion problems of GSPN models, this paper employs Stochastic Wellformed Net (SWN), a particular class of High-Level (colored) SPN. To conduct a case study on a chemical industrial park, the probability of domino effects of major accidents is calculated by using the GSPN model and SWN model in this paper.

Abstract: 300MN forging hydraulic press is the essential equipment in our country national defense and the infrastructure, and the primary work cylinder is one important part of the hydraulic press. In view of the judgment on the Working States of the primary work cylinder whether safe existence fuzziness, which has carried on the fuzzy reliability analysis and computation to the primary work cylinder probability law design result and the method of safety coefficient design result, the computed result indicated that, the design result with traditional safety coefficient is conservative, but based on probability design result is not safe enough. At the same time, under the condition that don’t reduce the fuzzy reliability, which has carried on the optimal design based on the finite element software to the thickness of the primary work cylinder.

Abstract: Many data in practical projects belong to incomplete data distribution. An approach for treat the data is investigated from chi-square optimization to measure the parameters. The statistical reference is also performed in the measuring process. Availability has been indicated by an example.

Abstract: Experimental study is performed on the probabilistic cyclic stress-strain responses of grade B cast steel, which is utilized in the manufacture of Chinese K6 type bogie. Fatigue test is carried out by an incremental strain-controlled method with 8 strain levels. Analysis of test data and observation on fatigue fracture surfaces of test specimens indicate that difference and evolution of local conditions are basic causes of the random fatigue damage behavior. So it is verified again that the random character of stress-strain responses is an intrinsic fatigue behavior of engineering materials. Taking the scattering regularity and the size of specimens into account, cyclic constitutive models of present test data with arbitrary probability and confidence are obtained. The analysis reveals that these models can reflect the random responses of material correctly.

Abstract: The diesel generator sets digital control system based on DSP is studied in this paper. The principles of voltage and speed control are analyzed. The main DSP chip is 16-bit fixed-point TMS320LF2407A. The hardware design, the former channels, the after channels and the CAN controller are accomplished in this paper. The simulation results indicate the controller has high-performance processing capabilities and it can meet the need of Generator Sets' real-time control and performance requirements.