Applied Mechanics and Materials Vols. 121-126

Abstract: Servo presses are widely used in high-precision, complicated forming process fields and promoted around the world in recent years. It is the trend of forging machinery for its servo motor-based digital heavy haul driven technology. At present, it becomes the hot research field. The structure characteristics of triangular elbow servo press were firstly introduced in the paper. And then the kinematics mathematical model of triangular elbow transmission mechanism was deduced and given. Based on it, this paper provides the slider kinematics analysis by Matlab. The slider motion law under various parameters can be analyzed and compared. The results would be useful reference for optimization design of transmission mechanism. The case study provides more visual and reliable decision basis for designer.

Abstract: Based on the product integrated design theory, the key part of large-scale centrifugal compressor — the impeller is researched. Structural optimization design and analysis on the conventional impeller is completed by the finite element method, and then the strength characteristic and the distortion tendency of the impeller under the action of the inertial force are obtained, the stress distribution of the impeller assembly structure after reaching stability in the assembly process is also obtained. The correctness and effectiveness of structural optimization design of the impeller are verified by the analysis results, and the comprehensive performance of the impeller has been greatly improved. The results above are also laid the foundation for optimization design and innovative design for other mechanical key components.

Abstract: A magnetorheological digital flow control valve is designed using magnetorheological fluid (MRF) magnetorheological characteristics. The paper gives the magnetorheological digital flow control valve’s structure and mathematical model, and according to the working condition, proposes using the pulse width modulation (PWM) control mode which is one of the digital valve control modes to realize the flow control. Simulation analysis has been done and the results show that the magnetorheological digital flow control valve has good static performance, high frequency switching speed and response，easy to realize intelligent control.

Abstract: The mathematical physical model of the heat and moisture transfer in the single-U-tube heat exchanger of a ground source heat pump (GSHP) is validated using observed data from the practical rock-soil thermal response test on a resident district in Taiyuan, the soil is layered according to the geological structure of an actual drill in the depth direction in this model. Inputting the dynamic design cooling and heating load of the district into the Realizable turbulent model in Fluent, the temperature fields of a single well in the GSHP project running for 1 year in 2 conditions in which convalescence is considered and not, are simulated numerically. It shows that it rather necessary to take the influence of convalescence into consideration while predicting the soil temperature field of a GSHP system running for a long term, or may not correspond to the reality and make a wrong theory guide to the practical engineering.

Abstract: A three-dimensional mechanical model and a transcalent model of flange bolt joint were built, considering the nonlinearity of gasket and the contact problem, the effect of inhomogeneous temperature field and its variation to pressure of bolt and gasket was studied, and the joint parameters of two schemes were compared; based on the orthogonal text, two bolt system schemes, adding disc spring and adding sleeve, were experimentally studied. The investigation showed that the sealability of different parts of the gaskets is different, owing to the difference of each bolt in radial and axial displacement under the influence of inhomogeneous temperature field, and the fatigue of gasket and bolt is easily caused; the scheme of disc spring is better than sleeve, and the disc spring, whose thickness is 0.9mm, was selected to improve the mechanical performance of bolt system.

Abstract: This paper analyzes the working principle of the electromagnetic damper and proves the characteristic of linear damping. Basing on the characteristic, a method of controlling the magnetic damping is proposed that the oscillating time can be reduced by using the sectional damping coefficients in second-order oscillating system. Using Matlab, the results of decreasing time are compared under the sectional damping consisting of two-segment or more segment with various coefficients.

Abstract: In the paper, a non-API tubing connection’s sealing structure is analyzed through numerical simulation. It is very important for sealing integrity to maintain intimate and usually high contact stress of mating metal surfaces under different loading. First, the contact pressure of main sealing surface and torque shoulder surface generated by interference fit after make-up procedure is analyzed. Then, the variation of contact pressure of sealing system during the load envelope test consisting of the axial loads and internal pressure is analyzed. The analysis results can be used to optimum design and operational suitability test of non-API tubing connections.

Abstract: Through research on the importance of power equilibrium in multi-motored starting of belt conveyor, this paper concluded that the factors which influenced the power equilibrium and how to achieve power equilibrium. With the example of hydro-viscous soft start device, this paper introduced the principles of hydro-viscous transmission and put forward concrete adjusting methods of staring power equilibrium in multi-motored belt conveyor. Based on the analysis and design above, finally power equilibrium controlling system in starting progress was designed.

Abstract: The dry mica tape and impregnation resin were introduced in this paper, which were main insulation materials of 200MW air-cooled turbo-generator stator bar manufactured by VPI (vacuum pressure impregnation) technology. The insulation manufacture technology, corona protection technology and properties of real products also were introduced in this paper. The results show that the electrical properties of the stator bars made by this kind of VPI technology reached the top level of the world which could be seen as follows: there is no discharge appeared during the AC high voltage potential test when the test voltage was 3UN, the dissipation factor tgδ under 0.2UN is lower than 1%, and the increment Δtgδ=tgδ0.6UN- tgδ0.2UN is lower than 0.5%, when the voltage applied is from 0.2UN to 1.2UN. The magnitude of maximum partial discharge is only 90pc to 110pc, the instantaneous breakdown strength of the bars are all higher than 34kV/mm, under the field of 8.73 kV/mm, the lest enduring time of the test bar is 1500h.

Abstract: This work studies a numerical research undertaken to investigate the dynamic behaviors of porous squeeze film damper mounted a rotor considering longitudinal and transverse roughness effect under nonlinear suspension. The dynamic response of the rotor center and bearing center are studied. The analysis methods employed in this study are inclusive of the dynamic trajectories of the rotor center and bearing center, Poincaré maps and bifurcation diagrams. The maximum Lyapunov exponent analysis is also used to identify the onset of chaotic motion. The modeling results provide some useful insights into the design and development of rotor-bearing system for rotating machinery that operate in highly rotational speed and highly nonlinear regimes.