A QUANTITATIVE EVALUATION OF ELASTIC WAVE IN SOLID BY STROBOSCOPIC PHOTOELASTICITY

We have developed a method for visually measuring and evaluating stresses emitted from an ultrasonic probe into a model solid similar to the actual material, by using image-processing techniques and stroboscopic photoelasticity. The visualization of wave stress (sound pressure) distribution can be achieved by synthesizing two photoelastic pictures, in which the directions of the principal axes of linear polariscopes are different by 45 degrees. The sound pressure field generated by commercial ultrasonic probes was measured by using the proposed method.     

The effects of external optical feedback on the power penalty of DFB-LD modules for 2.5Gbs−1 optical transmission systems

We report the effects of external optical feedback on the power penalty of commercial distributed feedback laser diode (DFB-LD) modules for 2.5Gbs–1 optical transmission systems. External optical feedback presented to the DFB-LD modules causes the excitation of external cavity modes, resulting in increased relative intensity noise (RIN) and intensity noise ripples at low frequency region below 500MHz. For a 10–10 bit error rate (BER), the minimum power penalty is as much as 1.25dB for a feedback ratio of –8.8dB. An excess power penalty of 0.5dB per 3dB increase in the feedback ratio was also empirically obtained. We suggest that optical isolators in 2.5Gbs–1 DFB-LD modules used in conventional optical transmission systems or WDM systems must have a peak isolation ratio of better than 54.5dB, instead of the previously recommended 30dB, for negligible power penalty induced by external optical feedback.     

ABO3型晶体中氧的电子自发极化

计算O^-2在晶体场中出现的Jahn-Teller效应,得到具有电矩的2p_π3s3d₀杂化原子轨道。BO₆八面体共价性质决定了ABO₃晶体的各种极化相。理论给出P_s比值、钛位移大小和热力学参数ξ′,ζ′均接近于实验结果。统一解释了钛酸钡的三个相转变。相变条件给出七种晶体中氧的屏蔽常数平均值与Slater的值一致。     

晶体管杂系参数与自然等效线路

本文研究面结合型晶体管共发射极线路的小讯号h参数与自然等效线路中元件的关系。根据两种合金管(2N104及Ⅱ-6晶体管)h参数的实验结果求出h参数与自然等效线路元件随频率及随直流运用状态(直流发射极电流及直流集电极电压)的相互关系。对实验结果与根据晶体管物理构造分析计算的结果进行了比较。对开路反向电压放大系数μ_bc的现象给予详细分析,并求出μ_bc与开路输出导纳h₂₂的相互关系。两套晶体管的h参数及自然等效线路的完整资料可供晶体管器件设计及线路研究者的使用。     

PARAMETRIC STUDY FOR AN EFFICIENT MESHLESS METHOD IN VIBRATION ANALYSIS

Based on the moving least-squares (MLS) approach, an efficient meshless method is employed to generate the displacement functions for vibration analysis of elastic bodies. The equation of motion is established by following the standard procedure and the boundary conditions are imposed by applying penalty functions. As the displacement functions are expressed in terms of weight functions, the accuracy will depend on the parameters of the weight functions. Therefore, a parametric study is carried out to determine the best values for these parameters. To demonstrate the accuracy, modal analyses of the beams and plates with different boundaries have been carried out. In addition, the responses of these structures under dynamic excitation have been analyzed. The examples include simply supported beams subjected to sudden excitations and simply supported plates subjected to initial displacements.     

FREE VIBRATION ANALYSIS OF A SPINNING FLEXIBLE DISK-SPINDLE SYSTEM SUPPORTED BY BALL BEARING AND FLEXIBLE SHAFT USING THE FINITE ELEMENT METHOD AND SUBSTRUCTURE SYNTHESIS

Free vibration of a spinning flexible disk-spindle system supported by ball bearing and flexible shaft is analyzed by using Hamilton's principle, FEM and substructure synthesis. The spinning disk is described by using the Kirchhoff plate theory and von Karman non-linear strain. The rotating spindle and stationary shaft are modelled by Rayleigh beam and Euler beam respectively. Using Hamilton's principle and including the rigid body translation and tilting motion, partial differential equations of motion of the spinning flexible disk and spindle are derived consistently to satisfy the geometric compatibility in the internal boundary between substructures. FEM is used to discretize the derived governing equations, and substructure synthesis is introduced to assemble each component of the disk-spindle-bearing-shaft system. The developed method is applied to the spindle system of a computer hard disk drive with three disks, and modal testing is performed to verify the simulation results. The simulation result agrees very well with the experimental one. This research investigates critical design parameters in an HDD spindle system, i.e., the non-linearity of a spinning disk and the flexibility and boundary condition of a stationary shaft, to predict the free vibration characteristics accurately. The proposed method may be effectively applied to predict the vibration characteristics of a spinning flexible disk-spindle system supported by ball bearing and flexible shaft in the various forms of computer storage device, i.e., FDD, CD, HDD and DVD.     

PREDICTION OF NON-CAVITATING UNDERWATER PROPELLER NOISE

Non-cavitation noise of underwater propeller is numerically investigated. The main purpose is to analyze non-cavitation noise in various operating conditions with different configurations. The noise is predicted using time-domain acoustic analogy and boundary element method. The flow field is analyzed with potential-based panel method, and then the time-dependent pressure data are used as the input for Ffowcs Williams-Hawkings formulation to predict the farfield acoustics. Boundary integral equation method is also considered to investigate the effect of ducted propeller. Sound deflection and scattering effect on the duct is considered with the BEM. The governing equations are based on the assumption that all acoustic pressure is linear. A scattering approach is applied in which the acoustic pressure field is split into the known incident component and the unknown scattered component. Noise prediction results are presented for single propeller and ducted propeller in non-uniform flow conditions similar to real situation. The investigation reveals that the effect of a duct on the acoustic performance propeller is small in the far field under non-cavitating situations since the noise directivities of single and ducted propellers are almost the same. Only the high order BPFs are influenced by the existence of the duct.