旋转圆盘受均布压力作用时的摄动分析

本文对中心带轴匀速旋转圆盘在均布压力作用下的受力及变形问题进行了摄动分析，得到了受载条件为Ｊ＾２／ＪＨ＜＜１时，圆盘应力及形变的渐近解。其形变渐近解为Ｗｈｉｔａｋｅｒ函数形式比较表明，渐近解与Ｃｈｅｂｙｓｈｅｖ数值解有较好的一致性。     

用拉格朗日相关结构研究圆盘启动过程的流体输运

利用粒子成像测速(PIV)技术,得到了圆盘启动涡环流场的速度分布和涡量分布.圆盘启动涡环流场的有限时间李雅普诺夫指数场(Finit-time Lyapunov exponents,FTLE)以及拉格朗日相关结构(Lagrangian coherent structures,LCS)被计算出来.基于圆盘启动涡环流场的有限时间李雅普诺夫指数场以及拉格朗日相关结构,通过跟踪流体质点,对圆盘启动涡环流场的输运情况进行了分析.在圆盘启动涡环形成过程中,流体发现被圆盘和相互排斥的拉格朗日相关结构分成三部分.剪切流窗口(vorticity-flux window)被发现,涡量流通过剪切流窗口进入涡核.涡环的非定常边界被确定,它由相互排斥的拉格朗日相关结构背风面、圆盘以及剪切流窗口组成.     

Flow of micropolar fluid between two orthogonally moving porous disks

The unsteady,laminar,incompressible,and two-dimensional flow of a micropolar fluid between two orthogonally moving porous coaxial disks is considered.The extension of von Karman’s similarity transformations is used to reduce the governing partial differential equations(PDEs) to a set of non-linear coupled ordinary differential equations(ODEs) in the dimensionless form.The analytical solutions are obtained by employing the homotopy analysis method(HAM).The effects of various physical parameters such as the expansion ratio and the permeability Reynolds number on the velocity fields are discussed in detail.     

Extending Circle Mappings to the Annulus

We show that any monotone degree one C mapping of the circle can be realized as the induced mapping on the boundary by a C area preserving diffeomorphism of the open annulus. The circle mapping may have critical points, allowing the possibility of Denjoy behavior on the boundary.     

Closed-Loop Control of the Motion of a Disk–Rod System

This work deals with the guidance and control of a system which is composed of a rolling disk and a controlled slender rod that is pivoted, through its center of mass, about the disk center. There are given N points P _i, i=1, ..., N, in the horizontal plane, a set of angles _2i , i=1, ..., N, a finite-time interval [0, t _f], and a sequence of times ₁=0<₂<...< _N =t _f. Using the concept of path controllability, a closed-loop control law is derived to steer the system in such a manner that the disk center and the rod angle of rotation ₂ will pass through (P _i, _2i ) at the times _i , i=1,...,N, respectively. This system serves as a model for the motion of a simple mobile robot.     

Novel biodegradable poly(1,8-octanediol malate) for annulus fibrosus regeneration

A novel elastic scaffold that simulates the deformability of annulus fibrosus (AF) and has good biocompatibility was developed. The scaffold was formed of a malic acid-based polyester poly(1,8-octanediol malate) (POM), which was synthesized by direct polycondensation. The tensile strength of POM gradually increased with the extension of the polymerization time, while the degradation rate decreased. Rat AF cells proliferated on the POM films and maintained their phenotype. The 3D scaffold also supported the growth of the AF cells, as confirmed by Safranin-O and type II collagen staining. POM also demonstrated a good biocompatibility in an in vivo foreign body response assay, an important prerequisite for tissue engineering applications. This study suggests that elastic POM scaffold may be an ideal candidate for AF tissue engineering.     

Michelson干涉仪式光纤空气声传感器

介绍了一种用于直升机等低空目标探测的光纤空气声传感器.该传感器基于光纤Michelson干涉仪的原理,结合弹性盘片的应力应变理论分析和光纤粘接的工艺设计,采用相位载波解调技术进行信号解调.对比实验测试验证了这种声音探测技术可行性.传感器理论灵敏度为2.38 rad/Pa,实测灵敏度为1.5 rad/Pa,采用PGC相位解调理论最小可探测的最小声信号为6.7 μPa,即9.5 dB.传感器在20～300 Hz范围内响应基本平坦.结合声音传播规律分析并肯定其在实用中的可行性.     

Experimental study on the added mass and damping of a disk submerged in a partially fluid-filled tank with small radial confinement

The dynamic response of submerged and confined disk-like structures is of interest in engineering applications, such as in hydraulic turbine runners. This response is difficult to be estimated with accuracy due to the strong influence of the boundary conditions. Small radial gaps as well as short axial distances to rigid surfaces greatly modify the dynamic response because of the added mass and damping effects.In this paper, the influence of the axial nearby rigid distance on the dynamic response of a submerged disk is evaluated when the radial gap is very small. Moreover, the effects of the fluid depth and fluid viscosity on the natural frequencies and damping ratio of the submerged disk are studied. The study has been performed experimentally and numerically using structural–acoustic simulations.For the experimental investigation a test rig has been developed. It consists of a disk attached to a shaft and confined with a small radial gap inside a cylindrical container full of water. The disk can be moved up and down along the shaft to vary the axial distance to the nearby rigid surface. Piezoelectric patches are used to excite the disk and the response is measured with submersible accelerometers. Several excitation patterns can be used due to the disposition of these piezoelectric patches. For each configuration tested, the dynamic response of the structure is studied analyzing the natural frequencies and damping ratio of the disk attached to the shaft. The numerical results have been compared with the experimental results.     

Synchronous vibration parameters identification by tip timing measurements

The Blade Tip Timing (BTT) measurement system is a technique to measure vibration parameters of a rotating bladed disk. In particular for synchronous vibrations the BTT provides signals versus the rotation speed of the disk starting from the measurement of the time of arrival (TOA) of each blade under the tip timing probes. The signals must be post processed in order to obtain the interesting parameters of each blade vibration. The paper presents a method to extract the main parameters (amplitude and frequency) in resonance condition from the tip timing measurements. The proposed method is a revision of the already existing well known Two-Parameter Plot (2PP) method which requires a minimum of two probes. Improvements to the existing 2PP method are here suggested mainly in the part of engine order identification.The proposed method is then applied to the BTT measured signals coming from a rotating bladed disk excited at different engine orders. At the same time on the disk the vibration of one blade was detected by strain gauges. The strain gauges were calibrated and they provide the reference values of the vibration parameters. The vibration parameters derived by the proposed method are in agreement with those obtained by the strain gauges methodology.     

Capacitance of an elliptical disk on a semi-infinite dielectric material

Using an integral transform, the mixed boundary value problem of a conducting, elliptical disk on a dielectric half-space in an electric field is reduced to the solution of an integral equation. An analytical expression of the electric system capacitance is derived, which is a function of the eccentricity of the elliptical disk. The electric charge and electric stress distribute non-uniformly over the surface of the elliptical disk and display local singularities at the edge of the elliptical disk. The square root singularity of the electric field at the edge of the elliptical disk leads to the divergent of the resultant force on the elliptical disk, which is physically unrealistic. There likely exist geometrical constraint and/or field constraint to limit the presence of the square root singularity of the electric field. For any symmetric conductor in an infinite space that consists of air (vacuum) and a semi-infinite dielectric material with symmetric plane being in the interface between the air and the dielectric material, the electric potential in the space is independent of the dielectric constant of the dielectric material.