Theoretical Analysis and Numerical Simulation of the Static and Dynamic Characteristics of Hydrostatic Guides Based on Progressive Mengen Flow Controller

The oil film thickness of oil hydrostatic guide with constant pressure supply based on capillary restrictor is greatly affected by load, and this kind of hydrostatic guide is usually applied to the machine tools with moderate load. The static and dynamic characteristics of the guide have been studied by using some theoretical, numerical and experimental approaches, and some methods and measures have been proposed to improve its performances. The hydrostatic guide based on progressive mengen（PM） flow controller is especially suitable for the heavy numerical control（NC） machine tools. However, few literatures about the research on the static and dynamic characteristics of the hydrostatic guides based on PM flow controller are reported. In this paper, the formulae are derived for analyzing the static and dynamic characteristics of hydrostatic guides with rectangle pockets and PM flow controller according to the theory of hydrostatic bearing. On the basis of the analysis of hydrostatic bearing with circular pocket, some equations are derived for solving the static pressure, volume pressure and squeezing pressure which influence the dynamic characteristics of hydrostatic guides with rectangle pocket. The function and the influencing factors of three pressures are clarified. The formulae of amplitude-frequency characteristics and dynamic stiffness of the hydrostatic guide system are derived. With the help of software MATLAB, programs are coded with C＋＋ language to simulate numerically the static and dynamic characteristics of the hydrostatic guide based on PM flow controller. The simulation results indicate that the sensitive oil volume between the outlet of the PM flow controller and the guide pocket has the greatest influence on the characteristics of the guide, and it should be reduced as small as possible when the field working condition is met. Choosing the oil with a greater viscosity is also helpful in improving the dynamic performance of hydrostatic guides. The research work has instructing significance for analyzing and designing the guide with PM flow controller.

Static Characteristics of the New Type Nozzle Flapper Amplifier for Double Nozzle Flapper Electro-Hydraulic Servo Valve

A new type nozzle flapper amplifier for double nozzle flapper electro-hydraulic servo valve is proposed in the paper.The electro-mechanical converter of new type nozzle flapper amplifier is designed by using the piezoelectric bimorph and beryllium-bronze materials.The structure and working principle of the new type nozzle flapper amplifier are introduced.Pressure characteristic and flowrate characteristic are analyzed by experimental method.The research results show that pressure characteristic has large amplification factor and output pressure;flowrate characteristic has large linear range and output flowrate.

Nonlinear Static and Dynamic Stiffness Characteristics of Support Hydraulic System of TBM

Full-face hard rock tunnel boring machines(TBM)are essential equipment in highway and railway tunnel engineering construction.During the tunneling process,TBM have serious vibrations,which can damage some of its key components.The support system,an important part of TBM,is one path through which vibrational energy from the cutter head is transmitted.To reduce the vibration of support systems of TBM during the excavation process,based on the structural features of the support hydraulic system,a nonlinear dynamical model of support hydraulic systems of TBM is established.The influences of the component structure parameters and operating conditions parameters on the stiffness characteristics of the support hydraulic system are analyzed.The analysis results indicate that the static stiffness of the support hydraulic system consists of an increase stage,stable stage and decrease stage.The static stiffness value increases with an increase in the clearances.The pre-compression length of the spring in the relief valve a ects the range of the stable stage of the static stiffness,and it does not a ect the static stiffness value.The dynamic stiffness of the support hydraulic system consists of a U-shape and reverse U-shape.The bottom value of the U-shape increases with the amplitude and frequency of the external force acting on the cylinder body,however,the top value of the reverse U-shape remains constant.This study instructs how to design the support hydraulic system of TBM.

High-temperature characteristics of SiC module and 100 kW SiC AC–DC converter at a junction temperature of 180 ℃

High-temperature,high-power converters have gained importance in industrial applications given their ability to operate in adverse environments,such as in petroleum exploration,multi-electric aircrafts,and electric vehicles.SiC metaloxide-semiconductor field-effect transistor(MOSFET),a new,wide bandgap,high-temperature device,is the key component of these converters.In this study,the static and dynamic characteristics of the SiC MOSFET,half-bridge module,are investigated at the junction temperature of 180℃.A simplified experimental method is then proposed pertaining to the power operation of the SiC module at 180℃.This method is based on the use of a thermal resistance test platform and is proven convenient for the study of heat dissipation characteristics.The high-temperature characteristics of the module are verified based on the conducted experiments.Accordingly,a 100 kW high-temperature converter is built,and the test results show that the SiC converter can operate at a junction temperature of 180℃in a stable manner in compliance with the requirements of high-temperature,high-power applications.

DESIGN THEORY FOR G-π BRIDGE RELIEF VALVE WITH ZERO OVERRIDE

A new construction of the relief valve is presented with pilot G-pi bridghydraulic resistances network. The design theory of G-pi bridge relief valve is studied and theformulas for designing the relief valve with zero static pressure override are obtained. The staticperformances of the relief valve are experimentally investigated. The theoretical and experimentalresults show that the static pressure override of the developed relief valve can be zero, i.e. whenthe overflow increases the control pressure is kept constant.

ESTIMATION OF FATIGUE LIFE UNDER RANDOM LOADING WITH PLASTIC HYSTERESIS ENERGY THEOREM

Fatigue damage of materials includes static damage and cyclic damage.Static damage is a ratio of the plastic energy in first static loading to the statictoughness, while cyclic damage is the ratio of the cyclic plastic hysteresis energy to thefatigue toughness. In the calculation, cyclic hardening (or softening) of a material istaken into account, which results in the increase (or decrease) of the yield stress. Forsimplification, it is assumed that stress and strain in cyclic loading vary in accordancewith the hysteresis loop. Fatigue toughness of a material can be detennined bysymmetric cyclic stress controlled fatigue test. A method, rational and convenient forengineering, is proposed to estimate the fatigue life under random loading based onplastic hysteresis energy theorem. Preliminary verification by test is satisfactory.

Effects of coefficient of friction and coefficient of restitution on static packing characteristics of polydisperse spherical pebble bed

The effects of the coefficient of friction and coefficient of restitution on the static packing characteristics of a polydisperse spherical pebble bed are numerically investigated using the discrete element method.Several important static packing characteristics under different coefficients of friction and restitution are presented and discussed.The results show that the coefficients of friction and restitution impose opposite effects on the packing heights and global packing factor.Neither the coefficient of friction nor restitution affected the oscillation width of the wall,whereas their effects are primarily reflected in the oscillation amplitude of the radial local packing factor and the axial local packing factor distribution at the top of the pebble bed.In both the contact force distribution and coordination number distribution,a left-shifted phenomenon appearing as the coefficient of friction occurred,and only the magnitude of the maximum frequency is affected when the coefficient of restitution changed from 0.1 to 0.9.In all simulation cases,the effects of the coefficients of friction and restitution are similar to that of cross-impact.

Design of flying vehicle control system by signal to noise ratio

Presents the new concept of ″Desired to be small″ based on the basic function of vehicle flight control system for an optimal design of flying vehicle control system, and the definition of S/N ratio and calculation formula for ″Desired to be small″ dynamic characteristics, and the S/N ratio method established for design of velicle flight control systems, by which, an orthogrnal table is used to arrange test schemes, and error facters are used to simulate various interferences, and the use of S/N ratio as a design criterion to synthesise the design of dynamic and static characteristics for definition of an optimal scheme, the application of S/N ratio method to the design of a type of vehicle control system and the single run success abtained in design of control system, technical evaluation test and design finalization flight test.

Static recording characteristics of new type super-resolution near-field structure

A novel super-resolution near-field optical structure （super-RENS） with bismuth （Bi） mask layer is proposed in this paper. Static optical recording tests with and without super-RENS are carried out using a 650-nm semiconductor laser at recording powers of 14 and 7 mW with pulse duration of 100 ns. The recording marks are observed by high-resolution optical microscopy with a charge-coupled device （CCD） camera. The results show that the Bi mask layer can also concentrate energy into the center of a laser beam at low laser power similar to the traditional Sb mask layer. The results above are further confirmed by another Ar;laser system. The third-order nonlinear response induced by the plasma oscillation at the Bi/SiN interface during laser irradiation can be used to explain the phenomenon. The calculation results are basically consistent with our experimental results.

Three-dimensional flow field mathematical model inside the pilot stage of the deflector jet servo valve

A new flow field mathematical model is proposed to describe accurately the flow field structure and calculate the static characteristics of the pilot stage in a deflector jet servo valve(DJSV). The flow field is divided into five regions, a 3D turbulent jet is adopted to describe the free jet region, and a velocity distribution expression of the jet is proposed. The jet entrainment model is put forward in the pressure recovery region to describe the coupling relationship between the pressure in the receiving chamber and the jet flow. The static characteristics, including pressure-flow characteristics, pressure characteristics,and flow characteristics of the pilot stage are obtained. The flow field structure and the static characteristics are verified by finite element analysis(FEA) and experiment, respectively, and the mathematical model results are in good agreement with the experimental and simulation results.