The approximate conserved quantity of the weakly nonholonomic mechanical-electrical system

We study the approximate conserved quantity of the weakly nonholonomic mechanical-electrical system. By means of the Lagrange-Maxwell equation, the Noether equality of the weakly nonholonomic mechanical-electrical system is obtained. The multiple powers-series expansion of the parameter of the generators of infinitesimal transformations and the gauge function is put into a generalized Noether identity. Using the Noether theorem, we obtain an approximate conserved quantity. An example is provided to prove the existence of the approximate conserved quantity.

Morphological stability analysis of vesicles with mechanical-electrical coupling effects

Using a recently established liquid crystal model for vesicles, we present a theoretical method to analyze the morphological stability of liquid crystal vesicles in an electric field. The coupled mechanical-electrical effects associated with elastic bending, osmotic pressure, surface tension, Max- well pressure, as well as flexoelectric and dielectric proper- ties of the membrane are taken into account. The first and second variations of the free energy are derived in a com- pact form by virtue of the surface variational principle. The former leads to the shape equation of a vesicle embedded in an electric field, and the latter allows us to examine the stabil- ity of a given vesicle morphology. As an illustrative exam- ple, we analyze the stability of a spherical vesicle under a uniform electric field. This study is helpful for understanding and revealing the morphological evolution mechanisms of vesicles in electric fields and some associated phenomena of cells.

Mechanical-electrical synergy damage effect on GaN HEMT under high-power microwave

High-power microwave damage to enhanced-mode Ga N high electron mobility transistors(HEMT)is studied considering the mechanical-electrical synergy effect due to the strong piezoelectric properties of Ga N,which has a wurtzite crystal structure.Based on the piezoelectric constitutive equation,the mechanical and electrical energies were equivalently coupled,and the effective numerical model was built in the simulation software.The results indicated that a part of the electrical energy was stored in the device as a form of elastic energy,causing the burnout time of Ga N HEMT to be extended.The effects of different injection voltages and frequencies were analyzed,and the results revealed that elastic energy plays a different role during the process of device damage.These results are of great significance for the design of Ga N HEMTs with better reliability in harsh electromagnetic environments and for improving their protection design.

MECHANICAL-ELECTRIC COUPLING DYNAMICAL CHARACTERISTICS OF AN ULTRA-HIGH SPEED GRINDING MOTORIZED SPINDLE SYSTEM

On the basis of the traditional mechanical model of a grinding wheel rotor and the mechanical-electric coupling model with ideal sinusoidal supply, taking high-frequency converting current of inverter power switches into further consideration, a modified mechanical-electric coupling model is created. The created model consists of an inverter, a motorized spindle, a grinding wheel and grinding loads. Some typical non-stationary processes of the grinding system with two different supplies, including the starting, the speed rising and the break in grinding loads, are compared by making use of the created model. One supply is an ideal sinusoidal voltage source, the other is an inverter. The theoretical analysis of the high-order harmonic is also compared with the experimental result. The material strategy of suppressing high-order harmonic mechanical-electric coupling vibration by optimizing inverter operating parameters is proposed.

《微机控制技术》课程的教学探讨

通过对机械专业《微机控制技术》课程教学情况进行分析,从课程内容安排、讲课形式与方法以及教学计划与教学要求等几方面,就改进与提高敦学质量的措施和方案进行了探讨。

Flow aeroacoustic damping using coupled mechanical electrical impedance in lined pipeline

We report a new noise-damping concept which utilizes a coupled mechanical-electrical acoustic impedance to attenuate an aeroacoustic wave propagating in a moving gas confined by a cylindrical pipeline. An electrical damper is incorporated to the mechanical impedance, either through the piezoelectric, electrostatic, or electro-magnetic principles. Our numerical study shows the advantage of the proposed methodology on wave attenuation. With the development of the micro-electro-mechanical system and material engineering, the proposed configuration may be promising for noise reduction.

A GENERAL SOLUTION AND THE APPLICATION OF SPACE AXISYMMETRIC PROBLEM IN PIEZOELECTRIC MATERIAL

According to the structure feature of the governing equations of spaceaxisymmetric problem in transversely, isotropic piezoelectric material. using the methodof introducing potential .function one by. one, in this paper we obtain the so-calledgeneral solution of displacement and eleclric potential function denoied by uniquepoiential.function which satisfies specific partiality equations. As an applying exampleof the general solution, we solve problem of semi-infinile boodt. made of piezoelectricmaterial, on the surface of the semi-infinite body a concentrative .force is applied, andget the analytic .formulations of stress and electric displacement comiponenis. Thegeneral solution provided by this paper can be used as a tool to analyse the mechanical-electrical coupling behavior of piezoelecrtic material which conlains defects such ascavity inclusion. penny-shape crack. and so on. The result of the solved problem canbe used directly to analyse contact problems which take place between twopiezoelectric bodies or piezoelectric body. and elastic body .

PENNY-SHAPED CRACK IN TRANSVERSELY ISOTROPIC PIEZOELECTRIC MATERIALS

Using a method of potential functions introduced successively to integrate the field equations of three-dimensional problems for transversely isotropic piezoelectric materials, we obtain the so-called general solution in which the dis- placement components and electric potential functions are represented by a singular function satisfying some special partial differential equations of 6th order. In order to analyse the mechanical-electric coupling behaviour of penny-shaped crack for above materials, another form of the general solution is obtained under cylindrical coordi- nate system by introducing three quasi-harmonic functions into the general equations obtained above. It is shown that both the two forms of the general solutions are complete. Furthermore, the mechanical-electric coupling behaviour of penny-shaped crack in transversely isotropic piezoelectric media is analysed under axisymmetric tensile loading case, and the crack-tip stress field and electric displacement field are obtained. The results show that the stress and the electric displacement components near the crack tip have (r^(-1/2)) singularity.

OPTIMUM DESIGN AND SENSITIVITY ANALYSIS OF PIEZOELECTRIC TRUSS STRUCTURES

This paper is concerned with the optimum design and sensitivityanalysis methods of piezo- electric intelligent trusses on thestructural stiffness and free-vibration frequency. On the basis ofthe finite el- ement emthod and taking into account themechanical-electric coupling effect under electric load and me-chanical load, the computational formula of sensitivities ofstructural displacement and free -vibration frequen- cy with respectto the size and shape design variables are proposed.

Theoretical study on two-dimensional MoS2 piezoelectric nanogenerators

Recent experiments have demonstrated that nanogenerators fabricated using two-dimensional MoS2 flakes may find potential applications in electromechanical sensing, wearable technology, pervasive computing, and implanted devices. In the present study, we theoretically examined the effect of the number of atomic layers in MoS2 flakes on the nanogenerator output. Under a square-wave applied strain, MoS2 flakes with an even number of atomic layers did not exhibit a piezoelectric output, owing to the presence of a projected inversion symmetry. On the other hand, for MoS2 flakes with an odd number of layers, owing to the lack of inversion symmetry, piezoelectric output voltage and current were generated, and decreased with the increase of the number of layers. Furthermore, as MoS2 flakes were only a few atoms thick, the capacitance of the MoS2 nanogenerators was at least an order of magnitude smaller than that of the nanowire- and nanofilm-based nanogenerators, enabling the use of MoS2 nano- generators in high-frequency applications. Our results explain the experimental observations and provide guidance on optimizing and designing two-dimensional nanogenerators.

Study of Longitudinal-Vertical Dynamics for In-Wheel Motor-Driven Electric Vehicles

The in-wheel motor(IWM)-driven electric vehicles(EVs)attract increasing attention due to their advantages in dimensions and controllability.The majority of the current studies on IWM are carried out with the assumption of an ideal actuator,in which the coupling effects between the non-ideal IWM and vehicle are ignored.This paper uses the braking process as an example to investigate the longitudinal-vertical dynamics of IWM-driven EVs while considering the mechanical-electrical coupling effect.First,a nonlinear switched reluctance motor model is developed,and the unbalanced electric magnetic force(UEMF)induced by static and dynamic mixed eccentricity is analyzed.Then,the UEMF is decomposed into longitudinal and vertical directions and included in the longitudinal-vertical vehicle dynamics.The coupling dynamics are demonstrated under different vehicle braking scenarios;numerical simulations are carried out for various road grades,road friction,and vehicle velocities.A novel dynamics vibration absorbing system is adopted to improve the vehicle dynamics.Finally,the simulation results show that vehicle vertical dynamic performance is enhanced.