基于线性压机驱动的高频同轴脉管制冷机研究

介绍了基于线性压机驱动的高频同轴脉管制冷机的特点及同轴脉管制冷机与线性压机匹配时的设计思路,通过数值计算模拟了同轴脉管制冷机制冷性能和动态参数的关系。搭建了脉管制冷机试验台并介绍了测试系统的组成,最后对所设计的高频同轴脉管制冷机进行了初步试验研究。试验结果对进一步改进脉管制冷机的设计提供了有益的参考。

Low power linear actuator for direct drive electrohydraulic valves

This paper presents a bi-directional permanent-magnet linear actuator for directly driving electrohydraulic valves with low power consumption. Its static and dynamic performances were analyzed using the 2D finite element method,taking into account the nonlinear characterization and the eddy current loss of the magnetic material. The experiment and simulation results agree well and show that the prototype actuator can produce a force of ±100 N with the maximum power being 7 W and has linear characteristics with a positive magnetic stiffness within a stroke of ±1 mm. Its non-linearity is less than 1.5% and the hysteresis less than 1.5%. The actuator's frequency response(-3 dB) of the displacement reaches about 15 Hz,and the most significant factor affecting the dynamic performance is identified as the eddy current loss of the magnetic material.

Nonlinear Modeling of a High Precision Servo Injection Molding Machine Including Novel Molding Approach

A nonlinear mathematical model of the injection molding process for electrohydraulic servo injection molding machine (IMM) is developed.It was found necessary to consider the characteristics of asymmetric cylinder for electrohydraulic servo IMM.The model is based on the dynamics of the machine including servo valve,asymmetric cylinder and screw,and the non-Newtonian flow behavior of polymer melt in injection molding is also considered.The performance of the model was evaluated based on novel approach of molding - injection and compress molding,and the results of simulation and experimental data demonstrate the effectiveness of the model.

Sliding Mode Control Approach for Electrically Controllable Clutch of AMT Based on the Feedback Linearization

A sliding mode control approach based on the feedback linearization is proposed for the electrically controllable clutch of AMT vehicles. The nonlinear dynamic model for the hydraulic actuator associated with clutch is established. By means of the exact feedback linearization procedure of differential geometry, an equivalent, fully controllable and linear model is derived via a homomorphic transformation for the AMT clutch system.Furthermore, a sliding mode control is introduced to improve robustness. The tracking tests are performed using the sliding mode control on a Santana LX passenger car, and the experimental results prove that this nonlinear controller is of fine robustness and high degree of tracking accuracy.

Transient reliability optimization for turbine disk radial deformation

The radial deformation design of turbine disk seriously influences the control of gas turbine high pressure turbine(HPT) blade-tip radial running clearance(BTRRC). To improve the design of BTRRC under continuous operation, the nonlinear dynamic reliability optimization of disk radial deformation was implemented based on extremum response surface method(ERSM), including ERSM-based quadratic function(QF-ERSM) and ERSM-based support vector machine of regression(SR-ERSM). The mathematical models of the two methods were established and the framework of reliability-based dynamic design optimization was developed. The numerical experiments demonstrate that the proposed optimization methods have the promising potential in reducing additional design samples and improving computational efficiency with acceptable precision, in which the SR-ERSM emerges more obviously. Through the case study, we find that disk radial deformation is reduced by about 6.5×10–5 m; δ=1.31×10–3 m is optimal for turbine disk radial deformation design and the proposed methods are verified again. The presented efforts provide an effective optimization method for the nonlinear transient design of motion structures for further research, and enrich mechanical reliability design theory.

Design and Guideline Rules for the Performance Improvement of Vertically Integrated Nanogenerator

Piezoelectric nanowires have attracted much scientific interest in the last few years because of their enhanced piezoelectric coefficients at nanometer scale, with promises of efficient mechanical energy harvesters for autonomous integrated systems. This paper presents the design and, for the first time, guideline rules, based on simple analytical expressions, to improve the performance of a mechanical energy harvester integrating vertical ZnO piezoelectric nanowires. Additional simulations were carried out to account more realistically for device geometry. The authors discuss the prospects of such an approach, based on design and material improvement.

Nonlinear static response of piezoelectric plates considering electro-mechanical coupling

Nonlinear static analysis of piezoelectric plates has been carried out using nonlinear finite element method considering electro-mechanical coupling,The geometrical nonlinearity has been taken into account and electric potential is assumed to be quadratic across the plate thickness,The governing equations are obtained using potential energy and Hamilton's principle that includes elastic and piezoelectric effects.The finite element model is derived based on constitutive equation of piezoelectric material accounting for coupling between elasticity and electric effect using higher order plate elements,Results are presented for piezoelectric plate under different mechanical boundary conditions,Numerical results for the plate are given in dimensionless graphical forms.Effects of boundary conditions on linear and nonlinear response of the plate are also studied.The numerical results obtained by the present model are in good agreement with the available solutions reported in the literature.

Assessing Micro-generation＇s and Non-linear Loads＇ Impact in the Power Quality of Low Voltage Distribution Networks

Distribution networks face an increasing penetration of solar PV （photovoltaic） and small WTG （wind turbine generator） as well as other forms of micro-generation. To this scenario, one must add the dissemination of non-linear loads such as EV （electric vehicles）. There is something in common between those loads and sources： the extensive use of power electronic converters with commutated switches. These devices may be a source of medium-to-high frequency harmonic distortion and their impact on the local distribution grid must be carefully assessed in order to evaluate their negative impacts on the network, on the existing conventional loads and also on other active devices. In this paper, methodologies to characterize effects such as： harmonics, network unbalances, damaging power line resonance conditions, and over/under voltages are described and applied to a real local grid configuration.

Simulation of Reciprocating Compressor Start-up and Shut-down under Loaded and Unloaded Conditions

During the start-up and shut-down phase of reciprocating compressors, the loads on all components of driven train system are very high. In this paper a method for calculating the forces on coupling, e-motor, crank shaft as well other components of the system will be described. The modelling of the electrical induction motor, coupling, crank shaft, damper as well as the compressor resistance torque are extremely important in simulating start-up and shut-down of reciprocating compressor. Furthermore the switching torque of the electrical motor and the instantaneous moment of inertia of the reciprocating compressor crank gear are important as well. The transient start-up and shut-down process under loaded and unloaded conditions is described using a non-linear differential equation for driven train system： E-motor--coupling--flywheel--reciprocating compressor--damper. Shaft torsional moments on the drive train and especially on the coupling, whether elastic or stiff, can then only be calculated using numerical simulation. This paper will describe some of the key elements in modelling, simulating and measurements of drive train start-up and shut-down carried out on already operational piston compressor units.

Modified k-ω model using kinematic vorticity for corner separation in compressor cascades

A new method of modifying the conventional k-w turbulence model for comer separation is proposed in this paper. The production term in the w equation is modified using kinematic vorticity considering fluid rotation and deformation in complex geometric boundary conditions. The corner separation flow in linear compressor cascades is calculated using the original k-w model, the modified k-w model and the Reynolds stress model （RSM）. The numerical results of the modified model are compared with the available experimental data, as well as the corresponding results of the original k-w model and RSM. In terms of accuracy, the modified model, which significantly improves the performance of the original k-w model for predicting comer separation, is quite competitive with the RSM. However, the modified model, which has considerably lower computational cost is more robust than the RSM.

Development of a linear compressor for two-stage pulse tube cryocoolers

A valveless linear compressor was built up to drive a self-made two-stage pulse tube cryocooler. With a designed maximum swept volume of 60 cm3, the compressor can provide the cryocooler with a pressure volume (PV) power of 400 W. Preliminary measurements of the compressor indicated that both an efficiency of 35%～55% and a pressure ratio of 1.3～1.4 could be obtained. The two-stage pulse tube cryocooler driven by this compressor achieved the lowest temperature of 14.2 K.

Review of cavity optomechanics in the weak-coupling regime: from linearization to intrinsic nonlinear interactions

Recently, cavity optomechanics has become a rapidly developing research field exploring the coupling between the optical field and mechanical oscillation. Cavity optomechanical systems were predicted to exhibit rich and nontrivial effects due to the nonlinear optomechanical interaction. However, most progress during the past years have focused on the linearization of the optomechanical interaction, which ignored the intrinsic nonlinear nature of the optomechanical coupling. Exploring nonlinear optomechanical interaction is of growing interest in both classical and quantum mechanisms, and nonlinear optomechanical interaction has emerged as an important new frontier in cavity optomechanics. It enables many applications ranging from single-photon sources to generation of nonclassical states. Here, we give a brief review of these developments and discuss some of the current challenges in this field.