Sine Sweep Excitation Research Articles

Dynamic testing of shock absorbers under non-sinusoidal conditions

This paper deals with the dynamic characterization of an automotive shock absorber, the continuation of an earlier work [1]. The objective of this ongoing research is to develop a testing and analysis methodology for obtaining dynamic properties of automotive shock absorbers for use in CAE-NVH low-to-mid-frequency chassis models. Stepped sine sweep excitation is currently used in industry to obtain shock absorber parameters along with their frequency and amplitude dependence. Sine-on-sine testing, which involves excitation using two different sine waves, has been done in this study to understand the effects of the presence of multiple sine waves on the estimated dynamic properties. In an effort to obtain all frequency dependent parameters simultaneously, different types of broadband random excitation have also been studied. Results are compared with stepped sine sweep tests. Additionally, actual road data measured on different road profiles have been used as input excitation to obtain the shock absorber parameters for broad frequency bands under realistic amplitude and frequency conditions. These results are compared with both simulated random excitation and stepped sine sweep test results.

STRUCTURAL IDENTIFICATION USING A COMBINATION OF SUBSPACE ANALYSIS AND BLOCK SUM TRANSFORMATION

In this article a combination of the subspace method with the block sum transformation is presented. Applying the block sum transformation a measuring window of the length T can be subdivided into intervalsT* where T*is an integer part of T. The data of all subwindows are added up to only one, which can then be analysed with the subspace method. Without a loss of accuracy the number of sample points can be reduced substantially and the computing effort is minimised. Sine sweep excitation is extremely useful for the analysis of structures with neighbouring eigenfrequencies or with high damping. The application of the proposed structural identification routine is numerically and experimentally validated.

Experimental characterization of nonlinear rubber isolators in a multi-degree-of-freedom system configuration

Experimental characterization has been investigated for three rubber isolators placed in a multi-degree-of-freedom system configuration. The configuration consisted of a rigid mass mounted to a flexible support beam via each of the rubber isolators. Random, sinusoidal, and sine sweep excitations were applied to the rigid mass and accelerations were measured. Data revealed the dependence of the isolators’ properties on amplitude and type of excitation. Modeling based on the continuous system theory resulted in quasi-linear representations of the experimental system. Discrete system models consisting of nonlinear polynomial equations for describing the nonlinearities of the isolators were also developed. In addition, sound pressure levels were measured during sine sweep excitation for one of the isolators. Increased sound levels were observed at off-resonant regions of the vibration response. Finally, single-degree-of-freedom static and dynamic experiments were conducted. Discrepancies in the isolators’ properties were found between the single- and multi-degree-of-freedom experimental results.

Harmonic Balance Vibration Analysis of Turbine Blades With Friction Dampers

Although considerable effort has been devoted to the formulation of predictive models of friction damper behavior in turbomachinery applications, especially for turbine blades, the problem is far from being solved due to the complex nonlinear behavior of the contact surfaces. This paper primarily focuses on analytical and numerical aspects of the problem and addresses the problem in the frequency domain while exploring the viability of equivalent time-domain alternatives. The distinct features of this work are: (i) the modelling of nonlinear friction damper behavior as an equivalent amplitude-dependent complex stiffness via a first-order harmonic balance method (HBM), (ii) the use of sine sweep excitation in time-marching analysis, (iii) the application of the methodology to numerical test cases, including an idealised 3D turbine blade model with several friction dampers, (iv) the verification of the numerical findings using experimental data, and (v) a detailed assessment of the suitability of HBM for the analysis of structures with friction dampers.

Effect of disk drive actuator unbalance on track following response to external vibration and shock

A two-disk, 2 1/2" drive with a multirate observer-based controller is tested for operating vibration and shock, and the off-track performance of the servo system is measured. Measured data are compared to analytical predictions in each case. Actuator pivot unbalance is computed by comparing analysis results to measurement for 0.5 G sine sweep excitation. Four shock excitations are considered from 20 G to 100 G in amplitude, with 11 ms and 2 ms durations. Predicted off-track displacements are converted to corresponding position error quadrature signals for comparison to measurement. Measured acceleration excitation is also used as input to the analysis. Predicted response compares favorably with measurement for operating vibration, as well as for shock excitations of 20 G (11 ms), 50 G (11 ms), and 25 G (2 ms). For 100 G (2 ms) shock, predicted response varies significantly from measurement. The paper also includes a discussion of the control algorithm typically used for head positioning in Seagate small disk drives.

On the use of neural networks for identification of linear and nonlinear systems

A procedure based on neural networks for the classification of linear and nonlinear systems is presented, using excitation and response data under swept sine excitation. Special attention is paid to the classification and identification of linear and bilinear systems, the latter being considered since they exhibit typical characteristics of cracked systems. The computer simulations show that: (1) using the procedure presented in this paper the trained classification network can reliably classify a linear system and different nonlinear systems; (2) the output of the trained identification neural network for a linear system and a bilinear system can be used as a quantitative indicator of characteristics of bilinear systems having different stiffness ratios (k(x>0)/k(x<0)) with respect to the bilinear system used in the training stage; (3) for two-degree-of-freedom systems, the trained network can not only determine the existence of a bilinear stiffness and the magnitude of its stiffness ratio, but also specify which stiffness is bilinear, i.e. indicate its position. These results provide a possibility of using the trained neural networks to detect and locate structural cracks which have the characteristics of bilinear systems.

歯周組織支持構造の動特性解析

The pourpose of this study is to develop a more scientific system which can objectively catch the biophysical qualities of the tooth supporting structures, for the proper evaluation of the actual conditions of the structures.The experimental tests have been started by bonding a force transducer and an accelerometer onto a maxillary central incisor. A certain amount of impact force has been applied by a spring-driven impactor to the force transducer to vibrate the tooth and its supporting structures, and then the force signal and the acceleration signal have been recorded simultaneously.In the next experimental stage, a new analysis system has been developed and improved for easier application in the clinic, and put to the test on the subjects with teeth of different degree of clinical mobility.The following results were obtained by this study:(1) The behavior of the impact force has been caught by the piezo-plastic-film force transducer.(2) It has been found that the analysis of the vibration response obtained from the tooth and its supportingstructures under the impact force requires special consideration of the influence from the time duration of the impact force.(3) There have been some differences in the results of the frequency analyses between the case where the whole acceleration response was taken as the object of the analysis and the case where only the free vibration was taken, in vivo.(4) Both results obtained by the new analysis system and by the forced excitations (random excitation and swept-sine excitation) agree with each other.(5) In the normal teeth tested, three peaks on the Fourier spectrum have been observed.(6) It has been also observed that the peaks shown in the cases of the abnormal teeth move toward the lower area, compared with the cases of normal teeth.From the above test results, it is obvious that the application of this new analysis system makes possible more objective evaluation of the tooth supporting structures.

Response of Two Nuclear Power Plant Valves to Dynamic Excitation

To formulate more suitable testing criteria for safety-related equipment in nuclear power plants, new investigations of equipment behavior under dynamic loading are required. Currently used guidelines and their applicability are summarized and several major problems to be solved by new investigations are described. Experimental and analytical studies conducted on two typical valves exemplify the type of investigation required. A 4-in. and 6-in. globe valve were investigated to determine characteristic structural dynamic-response relationships among various magnitudes of swept-sine, sine-dwell, random, and shock excitation. Different directions of acceleration were applied to each type of excitation. Finite element models of the valves were used to determine the dominant eigenvalues and eigenvectors. The experimental measurements were analyzed by the introduction of suitable dimensionless response parameters and appropriate excitation intensity measures that clearly indicate the presence of nonlinear response phenomena. Some guidelines are given for the qualifications testing of similar equipment and some areas of concern are pointed out.

Acoustic impedance measurement using sine sweep excitation and known volume velocity technique

The direct determination of acoustic impedance requires the measurements of both pressure and volume velocity, but the latter in general cannot be measured directly. Thus, other means must be adopted to bypass this measurement problem. This paper presents two methods which utilize excitation of a system with known volume velocity. This, along with measured pressure response, provides both magnitude and phase of impedance as continuous functions of frequency. The first method uses a convertible acoustic horn driver for excitation. Its volume velocity is determined by measuring calibrated pressure in a fixed cavity at the back of the driver. The second method uses for excitation an electrodynamic shaker driven piston which carriers an accelerometer. This signal is integrated to yield input acoustic velocity information. The two-channel analog signal processing setup includes the following instruments: sine sweep oscillator, tracking filters, log converters, phase meter, etc. In order to establish the validity of the proposed experimental techniques, several example cases have been evaluated. Excellent agreement between theory and measurements are obtained for driving point and transfer impedances over the plane wave frequency regime. The advantages of the methods proposed here over some other established techniques are as follows: (1) our methods are easier to use, (2) continuous impedance spectra are obtained quickly, (3) excellent dynamic range is achieved, and (4) complications of digital systems are not involved.