A biaxial stress transducer for fabrics

A transducer^* is developed for measurement of biaxial stresses in fabrics and other flexible sheet materials. The stress transducer responds directly to the far-field stresses by means of strains induced in an elastic inclusion which are monitored by strain gages. Design of the transducer is based on the analytical solution for such inclusions in linear-anisotropic materials, but the concept is applied and tested in nonlinear-orthotropic structural fabrics. Calibration and verification tests are conducted for principal far-field stresses in the yarn directions in vinyl-coated polyester and tefloncoated fiberglass.     

A shear stress transducer for molten polymers

Present rheometrical techniques are inadequate for the measurement of viscoelastic properties associated with shearing at high rates. A possible solution to this problem is to use a sliding plate rheometer together with a device for measuring the local wall shear stress away from the ends and edges of the plates. Such a device has been constructed, and the results of preliminary tests are encouraging.     

A Volterra-PEM approach for random vibration spectrum analysis of nonlinear systems

In this paper, the Volterra series and the pseudo-excitation method (PEM) are combined to establish a frequency domain method for the power spectral density (PSD) analysis of random vibration of nonlinear systems. The explicit expression of the multi-dimensional power spectral density (MPSD) of the random vibration response is derived analytically. Furthermore, a fast calculation strategy from MPSD to physical PSD is given. The PSD characteristics analysis of the random vibration response of nonlinear systems is effectively achieved. First, within the framework of Volterra series theory, an improved PEM is established for MPSD analysis of nonlinear systems. As a generalized PEM for nonlinear random vibration analysis, the Volterra-PEM is used to analyse the response MPSD, which also has a very concise expression. Second, in the case of computation difficulties with multi-dimensional integration from MPSD to PSD, the computational efficiency is improved by converting the multi-dimensional integral into a matrix operation. Finally, as numerical examples, the Volterra-PEM is used to estimate the response PSD for stationary random vibration of a nonlinear spring-damped oscillator and a non-ideal boundary beam with geometrical nonlinearity. Compared with Monte Carlo simulation, the results show that by constructing generalized pseudo-excitation and matrix operation methods, Volterra-PEM can be used for input PSD with arbitrary energy distribution, not only restricted to broadband white noise excitation, and accurately predict the secondary resonance phenomenon of the random vibration response of nonlinear systems in the frequency domain.

     

一种基于相关分析的平面振源探测方法

相关分析在信号处理，振动测试等领域内得到广泛应用。本基于相关分析技术，提出一种探测平面横向振源的方法，并设计了一组实验来检验该方法的有效性。通过对实验结果的分析，找出了利用该方法探测振源时振源时所应满足的条件和需要解决的问题。实验证明，在一定条件下，该方法可以成功地探测出震源位置。     

舰船尾部振动水弹性分析软件系统HDSS

介绍一个实用的舰船尾部振动水弹性分析软件系统,该系统基于流固耦合理论,针对舰船尾部结构特征,可以准确方便地预报出舰船尾部振动特性。系统还配有较强的后处理图形生成模块,可以形象逼真地绘制出振型图。     

密集建筑物下隧道开挖微振控制爆破方法与振动分析

为适应城市密集建筑物下隧道爆破对振动的高安全要求, 研究用普通爆破器材进行振速精确控制的爆破技术和参数确定方法。以渝中隧道为研究背景, 在开发准确延时非电雷管的基础上, 利用傅立叶函数和MATLAB软件拟合了不同药量单孔爆破振动波形, 分析了1~50 ms不同间隔下振动叠加的量化数据; 讨论了各微差间隔时间的降振效果; 在指定振速的情况下, 确定单孔药量和微差起爆时间; 实测并分析了现场使用雷管各段微差间隔特点, 据此进行针对性的爆破设计和采用逐孔掏槽爆破进行振速控制。现场应用表明:隧道爆破振速始终小于1.00 cm/s, 在此振速下避免振动叠加的最优单孔药量为1.2 kg, 爆破振速峰值位于主掏槽的第1段或第2段雷管起爆后, 且与理论分析结果吻合较好; 逐孔起爆60 ms后振速下降50%以上。研究表明:在高安全指标下, 以非电雷管实施精确控制爆破是可以实现的。     

Moiré interferometry for vibration analysis of plates

Moiré interferometry is used to locate nodal regions and measure vibration amplitudes of sinusoidally vibrating square plates. The high sensitivity afforded by this technique makes possible the study of plate vibrations at high frequencies and low amplitudes. The initial pattern is modulated by the zero-order Bessel function representing the vibratory motion. The fringe (or fringes) with best contrast indicate the nodal regions, while the higher order fringes, describing loci of points vibrating with the same amplitude, have decreasing contrast which is improved by spatial filtering.     

A reusable biaxial strain transducer

This paper describles a transducer which is, in effect, a reusable strain-gage rosette. The sensitive member of the instrument is a flat element shaped in the form of a hollow equilateral triangle. At the corners of the triangle are styli mounted perpendicular to the plane of the triangular element. On each side of each arm, an electric-resistance strain gage is centrally mounted parallel to the edges of the arm. The two gages on an arm form a temperature-compensated pair. In operation, the styli are pressed into the test surface, and subsequent straining of the surface induces bending and twisting strains in the arms of the element. The bending strain in an arm is detected by the strain gages mounted thereon and is proportional to the strain in the test surface in the direction parallel to the arm. The bending strain in a particular arm is unaffected by the forces in the other two arms. The theory of the transducer is discussed and experimental evidence which supports the theory is provided.     

A traceable dynamic force transducer

A traceable dynamic force measurement system built at the National Physical Laboratory (NPL) for the frequency range of 0.1 to 100 Hz, is described. The strain on a load-cell element was measured by two independent methods, both calibrated in the static force standard at the NPL. All instrumentation and the measurement system for determination of the dynamic amplitudes were calibrated dynamically against reference sine waves. The load cell was then tested dynamically in a servohydraulic machine and the two force outputs compared. The two methods of strain measurement chosen were the strain gage and a capacitance gage, designed to measure the strain in as diverse a way as possible from the strain gages. Two load cells were built, with steel and aluminum elements. The strain-gage bridge was d-c excited, amplified, filtered and digitally sampled. The capacitance gage was a-c excited from a commercial capacitance bridge, which was calibrated by the injection of reference signals at the sideband frequencies. This technique is in principle applicable to any a-c excited instrumentation. The measurement system consisted of a digital storage oscilloscope, coupled to a computer. The force amplitudes were measured by cross correlation against sine waves generated in software at the frequency of the applied force. Comparison of the two methods of strain measurement and detection of systematic errors caused by the dynamic response of the capacitance electrodes lead to the determination of the uncertainty of dynamic force measurement. This was calculated to be ±0.4 percent over the frequency range of 0.001 to 100 Hz. The thermoelastic effect was also visible at frequencies below 0.1 Hz. Paper was presented at the 1989 SEM Spring Conference on Experimental Mechanics held in Cambridge, MA on May 28–June 1.     

A simple transducer for detecting projectiles in gun barrels

Strain gages were cemented on an adjustable hose clamp. The strain-gaged hose clamp was used as a simple transducer on gun barrels to detect projectiles during firing in order to synchronize other instrumentation, such as high-speed flash X rays and a pulsed-laser holographic camera, with a reproducibility of the order of one microsecond.     

A vibration absorber for motorcycle handles

This paper describes the application of a vibration absorber to ameliorate the comfort of motorcycle handles. The concept of dynamical absorber is briefly summarised and a frequency response function is expressed as the ratio of vibration amplitudes (transmissibility). Some practical hints on the tuning strategy are also suggested in order to correctly define the absorber and then achieve the most effective vibration reduction. A specifically designed item is presented, with the peculiar characteristic of taking advantage of the damping properties of viscoelastic material undergoing shear deformations. An experimental verification of the good performances of the absorber is eventually given on the basis of both a modal analysis of a motorbike and the testing of its handle on an electrodynamical shaker.     

A nth-order shear deformation theory for the free vibration analysis on the isotropic plates

In the present paper, a nth-order shear deformation theory is used to perform the free vibration analysis of the isotropic plates. The present nth-order shear deformation theory satisfies the zero transverse shear stress boundary conditions on the top and bottom surface of the plate. Reddy??s third order theory can be considered as a special case of present nth-order theory (n=3). The governing equations and boundary conditions are derived by the principle of virtual work. The governing differential equations of the isotropic plates are solved by the meshless radial point collocation method based on the thin plate spline radial basis function. The effectiveness of the present theory is demonstrated by applying it to free vibration problem of the square and circular isotropic plate.     

A rapidly converging technique for vibration analysis of plates with a discrete mass distribution

Summary A technique based on the Galerkin approach has been developed for determination of the natural frequencies of rectangular plates with discrete masses added. The technique is applied to the rectangular plates with simply supported and clamped boundary conditions, but no difficulty exists in applying the same method to the plates of various forms with different boundary conditions. The results of this technique applied to one particular case are compared to a solution obtained by an exact method; the comparison shows the two methods to be in excellent agreement.

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Übersicht Es wird eine auf dem Galerkin-Verfahren basierende Methode zur Berechnung der Eigenfrequenzen rechteckiger Platten mit diskreten Einzel-Massen angegeben. Es werden einfach aufgelagerte und eingespannte rechteckige Platten untersucht, jedoch ergeben sich keine Schwierigkeiten bei der Anwendung derselben Methode auf Platten anderer Formen mit anderen Randbedingungen. Für einen Sonderfall werden die Ergebnisse der Berechnungen mit exakten Lösungen verglichen, wobei eine ausgezeichnete Übereinstimmung festgestellt werden kann.

     

A modeling and vibration analysis of a piezoelectric micro-pump diaphragm

The vibration analysis of a micro-pump diaphragm is presented. A piezoelectric micro-pump is studied. For this purpose, a dynamic model of the micro-pump is derived. The micro-pump diaphragm is modeled as circular double membranes, a piezoelectric one as actuator and a silicon one for representing the membrane for pumping action. The damping effect of the fluid is introduced into the equations. Vibration analysis is established by explicitly solving the dynamic model. The natural frequencies and mode shapes are calculated. The orthogonality conditions of the system are discussed. To verify the results, the finite-element micro-pump model is developed in ANSYS software package. The results show that the two methods are well comparable.     

Comparison of methods for vibration analysis of electrostatic precipitators

The paper presents two methods for the formulation of free vibration analysis of collecting electrodes of precipitators.The first,called the hybrid finite element method, combines the finit element method used for calculations of spring deformations with the rigid finite element method used to reflect mass and geometrical features,which is called the hybrid finite element method.As a result,a model with a diagonal mass matrix is obtained.Due to a specific geometry of the electrodes,which are long plates of complicated shapes,the second method proposed is the strip method which is a semi-analytical method.The strip method allows us to formulate the equations of motion with a considerably smaller number of generalized coordinates.Results of numerical calculations obtained by both methods are compared with those obtained using commercial software like ANSYS and ABAQUS.Good compatibility of results is achieved.     

圆柱壳自由振动特性分析方法研究

对传统解析法进行了改进,直接将复特征根代入边界条件构造了特征方阵;并基于圆柱壳Flügge 模型推导了位移形式的传递函数矩阵.在此基础上对比了改进的解析法、传递函数法、有限元法和实验方法获得的两端自由边界条件下圆柱壳的固有频率和模态.研究结果表明:改进的解析方法其特征方阵表达式简单且易于实现;同时通过与有限元和实验方法的对比,验证了改进解析法和位移形式传递函数矩阵的正确性;传递函数法相对于传统解析法对舍入误差敏感,可以通过增加字长的方式进行改善.     

Boundary element analysis for dynamic response of vibration foundation

The boundary elament method (BEM) for numerical solution to dynamic response of vibration fundation in plane, elastic domains are presented. The dynamic boundary integral equation is derived from the Laplace integral transform of the elestodynamic differential equation. Numerical solution can then be completed by the discrete boundary element in the transform space. Finally, dynamic responsed in time domain will be inverted back from the transform space with the numerical method. Excited harmonic load responses of dynamic rigid foundation are calculated and discussed for different frequencies, Layer depths and foundation embedments. Again, screening of exciting wave is also studied.The support of the ressarch project part in this work by Dr. O. Tullberg, Goteborg Universities' Computing Centre, Sweden, is gratefully acknwledged.     

A new reusable quadriaxial strain transducer

The reusable quadriaxial strain transducer consists of an eight-arm (at 45 degrees from one another) star-shaped plane-sensitive element. Two strain gages are mounted to the inner and outer sides of each arm in the neighborhood of the extremity where hard oblique pins are fixed. The pins are impressed into the surface of the material so the strains on the surface induce bending and torsional displacements of the arms. The paper describes the transducer design and the calibration procedure. Experimental results obtained on wood materials are analyzed.