In order to improve the kinematic reliability, it is crucial to find out the influence of each error source on the kinematic reliability of the mechanism. Reliability sensitivity analysis is used to find the changing rate in the probability of reliability in relation to the changes in distribution parameters. Based on the structural response surface function method, the functional relation between the kinematic reliability of a modified Delta parallel mechanism and the original input-error vectors is described using the quadratic function with cross terms. Moreover, the partial derivatives of the functional relation with respect to the means and variances of the original input errors are derived, which can efficiently evaluate kinematic reliability sensitivity of the mechanism. The advantages of this method are as follows: First, the response surface function, which can be easily set up by the position-error model of the mechanism, is convenient for calculating the variance, partial derivative, and reliability sensitivity. Second, in this case (unlike in the traditional error-mapping model), although the input-error values are unknown, pseudorandom variables used as random input-error sources can be generated by MATLAB software. Furthermore, the kinematic reliability of the mechanism can be assessed using the Monte Carlo method.
To solve the problem of valve noise, a multi-hole sleeve valve with secondary pressure-reducing function is presented in this paper. During the flow design of the valve, the flow resistance coefficient of the valve served as an important parameter. Because of two pressure-reducing components assembled to a multi-hole sleeve valve, the flow resistance coefficient of the valve changed. Thus, correction of the flow resistance coefficient had to be affected. In this paper, the relationship between the flow rate and flow resistance coefficient of the valve was first mapped and established. Then, the flow rate of the sleeve was obtained using SolidWorks simulation software. Locally refined finite element mesh technology was applied to the simulation to improve simulation accuracy. A parallel flow test platform for the regulating valve was established, and the flow rate of the multi-hole sleeve valve was detected at different openings, thus, verifying the reliability of the numerical simulation results. Finally, the simulation flow rate of the valve at different openings was substituted into the mapping relationship formula, in this way, the flow resistance coefficient of the sleeve valve was obtained. By using the modified flow resistance coefficient, the flow rate characteristics of the multi-hole, secondary pressure-reducing sleeve valve were efficiently and accurately established.
Introduction The applications of the modified domain decomposition method in nonlinear vibration analysis of the composite hard-coating cylindrical shells are still at a relatively superficial level, owing to the fact that its performance under different decomposition parameters has not been thoroughly investigated for achieving sufficient precision. Methods A parametric domain decomposition method is developed to facilitate self-performance evaluation in nonlinear vibration analysis of the shell. Correspondingly, in order to avoid a mass of redundant computation of the segment stiffness and material damping matrices during iterations, a specialized preprocessing scheme is designed by pre-establishing the parametric analytical expressions and matrix databases. Results The resonant response is sensitive to the circumferential segment number, but weakly affected by the axial segment number. The optimum circumferential segment number in the present study is suggested to be Nθ = 70, which can achieve good calculation accuracy and efficiency. Highly consistency is shown for the distributions of axial equivalent strain under different axial segment numbers. Smaller circumferential segment numbers would result in larger equivalent strain and bad solution accuracy. Conclusions The sufficient solution accuracy of nonlinear vibration of the composite hard-coating cylindrical shell can't be achieved by increasing the axial segment number with constant segment width, but only by enough circumferential segment number, which is fundamentally determined by its equivalent strain distributions and gradients, and is with close relation to the axial and circumferential wave numbers of the shell.
Vortex-induced vibration of a regulating valve not only wastes the energy of the control system, but also causes serious damage to the valve trims. It is very important to suppress vortex-induced vibration of the flow field in a valve by optimizing the valve trim structure. In this paper, a multistage pressure-reducing valve is proposed, and the flow fields in the valve with the lightweight, flat bottom, circular truncated cone and cylinder valve plug are simulated using the ANSYS Workbench. To verify the reliability of the simulation, a flow test device for the valve is established and the flow rates at different openings are measured. The test result shows that the valve designed by simulation conforms to the specified flow characteristics. By monitoring the lift coefficient of the vortex cross flow, the amplitude and main frequency of vortex-induced vibration are evaluated. The effect of the valve plug shapes on the vortex-induced vibration characteristics is studied. The results show that the shape of the valve plug has an obvious effect on the amplitude of vortex-induced vibration. The conical valve plugs can play the role of flow guiding, the amplitude of vortex-induced vibration of the valve is smallest, it is about 1/4 of that of other valve plugs at medium and high openings. This work is of significance for suppressing the vortex-induced vibration of the multistage pressure-reducing valve.
A multistage pressure reducing valve is presented in this paper. The pressure reducing components are specially designed to not only control the flow rate but also effectively prevent the cavitation vibration. However, when the fluid flows through the pressure reducing components, the divergence and shedding of the vortices in the flow field seriously affect the stability of the valve and cause vortex-induced vibration. Especially, the main frequency of the vortex shedding is in the same frequency range as the modal frequency of the valve, the vortex-induced resonance of the valve occurs. It seriously affects the safety of a control system. In this paper, by monitoring the lift coefficient of the vortex cross flow in the valve, the frequency spectrum information of the lift coefficient is used as the novelty indexes to indicate vortex-induced vibration of the fluid in the valve. The main frequency and amplitude of vortex-induced vibration are obtained. The factors affecting the vortex-induced vibration of the fluid are analyzed. The results indicate that vortex-induced vibration is the most serious when the valve is opened or closed. The variation of the flow velocity and the pressure difference have obvious effects on vortex-induced vibration of the valve. The intensity of the variation affects the main frequency and amplitude of vortex-induced vibration. Using thermal-fluid-solid coupling modal analysis instead of traditional modal analysis, the modal frequency under the working state of the valve is obtained. It is compared with the main frequency of vortex shedding, and vortex-induced resonance does not occur in the multistage pressure reducing valve.
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