Field Of Vibration Research Articles

Uniqueness in the determination of vibration sources in rectangular Germain–Lagrange plates using displacement measurements over line segments with arbitrary small length

The theme of this work is related to the field of vibration and source detection, which is important in naval, aerospace and civil engineering industries. The detection of unexpected vibration sources, in general, signals malfunctioning, or even an undesired presence in the case of defense systems. The focus will be on thin plates, which are among the basic building blocks of large complex structures. Here, we consider loads acting on a rectangular plate R of the product form g(t)Q(x), where the function of time g has a continuous first derivative and the spatial load distribution Q is a square-integrable function over R. We prove that the observation of the displacement of a line segment with arbitrary length parallel to one of the sides of the plate is enough for the determination of Q, provided that the interval of time is long enough. We also prove that the normal derivative along a side of the rectangle measured for an arbitrarily small interval of time is sufficient to determine the spatial load distribution Q. The method used to obtain the results is based on the series decomposition of the dynamic response and an analysis of the almost periodic distribution that arises from it.

Prediction of Unmeasured Mode Shape Using Artificial Neural Network for Damage Detection

Artificial neural networks (ANNs) have received much attention in the field of vibration–based damage detection since the 1990s, due to their capability to predict damage from modal data. However, the accuracy of this method is highly dependent on the number of measurement points, especially when the mode shape is used as an indicator for damage detection. With a high number of measurement points, more information can be fed to the ANN to detect damage; therefore, more reliable results can be obtained. Nevertheless, in practice, it is uneconomical to install sensors on every part of a structure; thus the capability of ANNs to detect damage is quite limited. In this study, an ANN is applied to predict the unmeasured mode shape data based on a limited number of measured data. To demonstrate the accuracy of the proposed method, the results are compared with the Cubic Spline interpolation (CS) method. A parametric study is also conducted to investigate the sensitivity of the number of measurement points to the proposed method. The results show that the ANN provides more reliable results compared to the CS method as it is able to predict the magnitude of mode shapes at the unmeasured points with a limited number of measurement points. The application of a two–stage ANN showed results with a high potential for overcoming the issue of using a limited number of sensors in structural health monitoring.

In Memoriam: Shoei-Sheng Chen (January 26, 1940–February 11, 2012)

Shoei-Sheng Chen, or S.-S. or more affectionately “Sunshine” as he was commonly known to his close friends and colleagues, was born in Ko-Lin Village in Dong-Shan County of I-Lan, Taiwan. He was the first in his town to attend high school and eventually graduated at the top of the class in engineering at the National Taiwan University and was awarded a scholarship to study in the U.S. He received his Ph.D. at Princeton University in 1968. After that he took a job as a civil and mechanical engineer at the Argonne National Laboratory in Darien, Illinois—a position he held for 30 years until his retirement in 1998. S.-S. met his wife Ruth in the U.S. They were married in 1969 and settled down in Willowbrook, Illinois, with their three children Lyrice, Lisa, and Steve.Throughout his career at Argonne, S.-S. was a prolific researcher in the field of flow-induced vibration and fluid–structure interaction. He pioneered the highly complex area of analytical formulation of tube bundle fluid–elastic instability and earned numerous awards and recognitions for his publications. In 1987, he published the book “Flow-Induced Vibration of Circular Cylindrical Structures,” which has since become a classic treatise in this field.In addition to his research activities at Argonne, S.-S. was very active in professional societies. He was, for example, a Fellow of The American Society of Mechanical Engineers and the Chair of the Technical Committee on Fluid–Structure Interaction in the ASME Pressure Vessel and Piping (PVP) Division from 1987 to 1991. From 1991 to 1995, he served as the Honors and Awards Chair of the Division and in 1995 as the Chair of the PVP Conference in Hawaii. He was the Chair of the PVP Division from 1995 to 1996. For his contribution to ASME and to the engineering profession, S.-S. was awarded the Pressure Vessel and Piping Medal in 2001. In addition, The Division’s Outstanding Service Award now carries his name.After his retirement from Argonne National Laboratory, S.-S. and Ruth moved to Laguna Niguel in California, where he began the next chapter of his life devoting himself to Christianity, health and natural methods of disease prevention. He served as a deacon in the Chinese Christian Mandarin Church at Laguna Niguel.In addition to his wife Ruth and three children, S.-S. is survived by five grandchildren: Elizabeth, Jessica, Anna, Claire, and Isaac, with one more grandchild born by the time this message is printed.

The Modification Method of the Matlab Built-in Function PSD Using in the Field of Random Vibration

The process of calculating power spectrum density is introduced. The built fuction PSD in Matlab used in engineering field widely is analyzed in detail. Problems are found when built-in function psd is used to calculated power spectrum density of random signal. Based on such analysis a modification method is proposed.

Self-adaptive modal control for time-varying structures

For the past several years, modal controllers are widely studied and used in the field of vibration or vibro-acoustics control. They are efficient but not robust, because these methods involve a reconstructor based on a modal truncation. When the dynamic behavior of the structure change, the controller and reconstructor must be updated to cope with the changes in the structure behavior, in order to maintain both performance and robustness. A solution is adaptive control but this approach needs some specific information not generally available particularly in the case of undergone modifications. This paper deals with a self-adaptive modal control based on a real-time identifier, which avoid the need of specific information. The identifier permits to update the controller and the reconstructor according to the changes of modal characteristics of time-varying structures. A classical algorithm of identification is used to obtain a state space model with an unspecified state vector. Then, based on this model, a well adapted transformation is carried out to get the modal characteristics from the expression of complex modes, including the mode shapes. As a criterion of running identification, the value of “variance-accounted for” (VAF) is employed to carry out the identifier only when the initial or previous model is not enough exact. A Linear Quadratic Gaussian Algorithm is employed in such a way that the controller and observer can be optimized according to the updated modal model. By this way, a self-adaptive modal control is completed and can demonstrate some smart properties. The proposed methodology is carried out on a simple but representative time-varying mechanical discrete structure. An inertia modification leads not only to low modal frequency shifts but also to inversion of a mode shape which is shown to lead to unstable configuration when control system is not updated. The overall procedure will be described through simulations and performed for different operating conditions, which will prove that mode shapes have to be precisely determined and updated in the controller and observer to guarantee a robust modal control with high performance in spite of the changes of structure.

Final report on the key comparison EUROMET-AUV.V-K1.1

This report of the EUROMET.AUV.V-K1.1 comparison presents the final results of the second, follow-up EUROMET comparison in the area of vibration, in this case defined as sinusoidal acceleration. The relation between the results of the participants in this RMO comparison and the results of the first CIPM comparison in the field of vibration CCAUV.V-K1 is calculated via a procedure using one linking laboratory and is fully described. Using this linking, the results of the participants can be directly compared with the results of other comparisons, whether the CCAUV.V-K1 itself or others that are also linked such as the EUROMET.AUV.V-K1. The full uncertainty budgets are given in Appendix A and the Technical Protocol that was used is included as Appendix B.Main text.To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the CCAUV, according to the provisions of the CIPM Mutual Recognition Arrangement (MRA).

Final report on the key comparison CCAUV.V-K1.1

This report of the CCAUV.V-K1.1 key comparison (KC) presents the final results of the second, follow-up CIPM comparison in the area of vibration, in this case defined as sinusoidal acceleration. The relation between the results of the participants in this follow-up comparison and the results of the first CIPM comparison in the field of vibration CCAUV.V-K1 is calculated via a procedure using one linking laboratory and is fully described. Using this linking, the results of the participants can be directly compared with the results of other comparisons like CCAUV.V-K1.Supplementing the scope of the original CIPM comparison, the frequency range of the reported KC was extended up to 10 kHz and the measurand phase was included for some of the participants.The Technical Protocol that was used is included as Appendix A and the full uncertainty budgets are given in Appendix B.Main text.To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the CCAUV, according to the provisions of the CIPM Mutual Recognition Arrangement (MRA).

Study on Rheology of LLDPE under Compound Stress Field of Vibration and Shear in Extrusion Molding

In this article, a new equipment was self-developed to study the effect of compound stress field of vibration and shear on rheological properties. Using the special equipment, study on the rheological properties of LLDPE under single vibration field, single shear field and compound stress field was respectively carried out. The experimental results show that the changes of apparent viscosity of LLDPE melt is relative to vibration frequency, vibration amplitude, and mandrel rotary speed under the compound stress field. The apparent viscosity can be reduced much more sharply in compound stress field than in the single vibration or shear field.

Recent Developments and Selected Patents on Vibration Based Methods for the Elastic Characterization of Isotropic Materials

A detailed knowledge of the basic engineering material properties is of fundamental importance for fabrication purpose as well as for proper design and reliability estimation of any kind of engineering structure. In particular, knowledge of elastic properties, such as Youngs Modulus and Poissons Ratio allows to assess the static and/or dynamic performances of a structure and provides information on the quality achieved during the fabrication process. Various methodologies have been proposed through the years for the elastic characterization of engineering materials. Vibrationbased methods allow to determine the material properties combining experimentally measured natural frequencies of suitable samples to analytical or numerical models relating the natural frequencies to the geometrical dimensions, mass density and the unknown elastic properties. Vibration-based methods are today commonly employed because of the nondestructive nature of frequency measurements and the simple operating procedures involved. The efforts provided by research scientists and engineers in this field are currently enclosed in a huge number of meaningful journal papers and patents devoted to the subject. The aim of the present work is to review recent progresses and selected patents in the field of vibration based methods for the elastic characterization of isotropic materials. Keywords: Elastic constants, isotropic materials, dynamic tests, sonic resonance, &, NDT

Micropower energy harvesting

More than a decade of research in the field of thermal, motion, vibration and electromagnetic radiation energy harvesting has yielded increasing power output and smaller embodiments. Power management circuits for rectification and DC–DC conversion are becoming able to efficiently convert the power from these energy harvesters. This paper summarizes recent energy harvesting results and their power management circuits.

The Influence of PZT Actuators Positioning in Active Structural Acoustic Control

This paper deals with the effect of secondary actuator positioning in an active structural acoustics control (ASAC) experiment. The ASAC approach is based on minimizing the sound radiation from structures to the far field by controlling the structural vibrations. In this article a rectangular steel plate structure was assumed with one secondary actuator attached to it. As a secondary actuator, a specially designed piezoelectric stripe actuator was used. We studied the effect of the position of the actuator on the pattern and on the radiated sound field of the structural vibration, with and without active control. The total radiated power was also measured. The experimental data was confronted with the results obtained by a numerical solution of the mathematical model used. For the solution, the finite element method in the ANSYS software package was used.

Use of Frequency-Domain Concepts in the Analysis and Design of Mechanical Vibrating Systems

This paper investigates the frequency-domain approach for some useful types of analysis and design related to problems of mechanical vibration. First, some attractive features of the frequency-domain analysis are noted. The possibility of a unified approach to analysis is indicated through the existence of analogies between mechanical and non-mechanical systems. The uses of mechanical impedance and transmissibility functions in the modeling, analysis, and design of mechanical vibrating systems are illustrated. Applications in the design of vibration isolators and in the analysis of material damping are given to demonstrate the attractive characteristics of some frequency-domain techniques in the field of mechanical vibration. The manner in which the material presented in the paper may be incorporated into an undergraduate core course in mechanical vibration is indicated.

On Vortex Formation in the Wake Flows of Transonic Turbine Blades and Oscillating Airfoils

This paper demonstrates similarities between the vortex shedding from blunt trailing-edge transonic turbine nozzle blades and from oscillating airfoils and bluff bodies. Under subsonic conditions the turbine nozzle cascade shed wake vortices in a conventional von Kármán vortex street. This was linked with a depressed base pressure and associated energy separation in the wake. Under transonic conditions a variety of different shedding configurations was observed with vortices shedding and pairing in several different ways. Similarities are addressed between the observed structures and those from vortex shedding in some other physical situations, such as the vortex wakes shed from cylinders and airfoils in sinusoidal heaving motion in low-speed flow. The established field of vortex-induced vibration has provided a developed classification scheme for the phenomena observed. The paper has brought together three previously independent fields of investigation and, by showing that the three are essentially related, has provided the basis for a new synthesis.

Propagation of High Frequency Waves in Slender Engineering Structures

High-frequency vibration in complex engineering structures is challenging problem. Attempts to describe all of the details of real structures fail for many reasons. First, the existence of many inherently uncontrolled factors plays an essential role. In structural dynamics, uncertainties arise from stiffness, mass and damping fluctuations caused by variations in material properties as well as by variations resulting from manufacturing and assembly. The boundary conditions for each structural member also are not known precisely since the high frequency dynamic properties of joints between structural members are especially uncertain. Second, the essential heterogeneity and presence of secondary systems have to be taken into account. Third, the interpretation of the solution of an “exact” boundary-value problem presents great difficulty. The field of vibration of a complex structure (for instance, under a broad-band excitation) is a very complicated function of time and spatial coordinates because a great many modes are excited in the structure. Hence, new approaches are needed for an adequate modelling of structures at high frequencies since with the conventional methods, results become unreliable and can hardly be interpreted. There exist a great number of approaches, among which the Statistical Energy Analysis is the more celebrated one. However, it belongs to a class of discrete approaches, in which field is averaged within each structural member. Thus this approach is not applicable to problems of wave propagation. An alternative is the so-called continuous approach, the approach of high-frequency structural dynamics being utilised in the present paper. The basic substantiation for this approach is that the structures at high frequencies behave like a mechanical system with a continuous spectrum of natural frequencies. This result naturally leads to the representation of complex structures in the form of an elastic carrier structure, in which the primary structure is modelled with oscillators attached to it. The oscillators are introduced into the model to describe numerous secondary systems which comprise the major portion of the structural members of a unit. A number of investigations have been concerned with such a representation. One pioneering work dealt with a one-dimensional representation, whilst other papers were devoted to the three-dimensional analysis of isotropic and anisotropic carrier media, respectively. The present paper is devoted to the problem of propagation of high frequency vibration in such structures, which allows the application of one-dimensional models. It is shown that closed-form solutions are obtained for a rather general case of a structure with varying cross-sectional area, nonlinear energy absorption and secondary systems. The vibration field is shown to have an upper limit which does not depend on the intensity of external excitation.

Structural Health Monitoring Through Chaotic Interrogation

The field of vibration based structural health monitoring involves extracting a ‘feature’ which robustly quantifies damage induced changes to the structure in the presence of ambient variation, that is, changes in ambient temperature, varying moisture levels, etc. In this paper, we present an attractor-based feature derived from the field of nonlinear time-series analysis. Emphasis is placed on the use of chaos for the purposes of system interrogation. The structure is excited with the output of a chaotic oscillator providing a deterministic (low-dimensional) input. Use is made of the Kaplan–Yorke conjecture in order to ‘tune’ the Lyapunov exponents of the driving signal so that varying degrees of damage in the structure will alter the state space properties of the response attractor. The average local attractor variance ratio (ALAVR) is suggested as one possible means of quantifying the state space changes. Finite element results are presented for a thin aluminum cantilever beam subject to increasing damage, as specified by weld line separation, at the clamped end. Comparisons of the ALAVR to two modal features are evaluated through the use of a performance metric.

The current status of measurement standards for acoustics and vibration at INMETRO

The Division of Acoustics and Vibration of INMETRO (DIAVI) establishes, validates and maintains the Brazilian national measurement standards used for the realization of the units of physical quantities related to the field of acoustics and vibration. The basic vibration quantity realized by DIAVI is translational acceleration, from which the other motion quantities, i.e., velocity and displacement can be derived. Acoustics physical quantities include sound pressure and sound power. The national measurement standards comprise both absolute (primary) and comparison (secondary) calibration setups, which are used to cover the wide range of calibration and testing services demanded by the Brazilian society, trade, industry, and science. This paper outlines the current status of these measurement standards and presents the measurement capabilities of INMETRO in the field of acoustics and vibration.

Some recent advances in the theory of random vibration.

A brief introduction is first given of the history of the technical field of random vibration, tracing back to the works of physicists since the beginning of the twentieth century. This is then followed by an account of more recent developments, with emphasis on nonlinear and quasi-nonlinear systems, and on analytical solutions for the associated Fokker-Planck equation and the generalized Pontryagin equation. The governing equation of a quasi-nonlinear system is linear, but with one or more randomly varying coefficients. The techniques for finding exact probability solutions, approximate probability solutions, conditions for motion stability, and the failure probability and statistics of a system are discussed.

Current trends in the international standardization of mechanical vibration and shock

Current concerns on world trade (e.g., fair business practices, product quality, and reliability), the environment (e.g., the propagation and radiation of noise from structures), and public safety (e.g., the effects of shock and vibration on humans, civil structures, and vehicles) have placed increased international attention on the development of quality standards in the field of mechanical vibration and shock. Recognizing its importance, the International Organization for Standardization (ISO) has set up a Technical Committee to develop standards in the field of mechanical vibration, shock, and the condition monitoring of machines and structures, ISO/TC 108. Its scope includes the areas of mechanical vibration and shock pertaining to: terminology and nomenclature; actuators, sensors, and associated instrumentation; reduction and control methods; measurement and evaluation of the exposure of humans, stationary structures, vehicles, and machines. In addition, standardization in the field of vibration and shock for data processing, data acquisition, diagnostic measurement methods, transducer calibration, and condition monitoring are actively being developed. This presentation addresses topics on the broad issues of standardization in the field of mechanical vibration and shock with emphasis on (1) societal objectives, (2) economic stakes of diverse constituencies, and (3) structure, process, and future direction of ISO/TC 108.

BOUNDARY CONDITION IDENTIFICATION USING CONDENSATION AND INVERSION — APPLICATION TO OPERATING PIPING NETWORK

This paper deals with the experimental analysis of piping systems under operating conditions in the field of vibration and acoustic analysis. A new approach to identify the boundary conditions of a part of a curvilinear structure is presented. The basic concept consists of solving an inverse problem where the measured response of the system tested is combined with an incomplete analytical model in order to identify the boundary dynamical state in the frequency domain. As in finite element methods, the tested network is described using elements and nodes. An original technique using a transfer matrix of continuous elements provides a small-size analytical model. In addition, condensation procedure is used to eliminate all degrees of freedom (d.o.f.) having a modelled boundary condition and to reduce the size of the solved inverse problem. Since identification of boundary conditions is performed, the analysis of dynamic response of the tested network may be performed without further matrix computation. The validity and the feasibility of the approach are shown using actual test results. Examples concerning real applications are also presented.

Current state and trends of ensuring traceability for vibration and shock measurements

Recent and current activities at the level of national metrology institutes (NMIs) towards ensuring traceability of vibration and shock measurements to the International System of Units are mainly twofold: (i) initiating and contributing to new international standardization projects, within the International Organization for Standardization, ISO TC 108, to specify upgraded or new standard methods for the vibration and shock calibration of transducers; and (ii) improving the metrological base by developing upgraded or new standard equipment (e.g. national measurement standards) in compliance with up-to-date standard methods. Laser interferometry, which is the preferred primary vibration calibration method at NMI level, has been further developed at the Physikalisch-Technische Bundesanstalt (PTB) in recent years as a uniform methodology and technique for the primary measurement of translational motion quantities (e.g. acceleration) and rotational motion quantities (e.g. angular acceleration) at sinusoidal, shock-shaped and other, user-defined time histories. A traceability chain has been defined and developed which realizes and disseminates the units of the respective physical quantities at such time-dependencies which reproduce as closely as possible, during calibration of any transducer (e.g. accelerometer) or measuring instrument (e.g. laser vibrometer), the conditions of use after calibration (i.e. shock measurement in the peak acceleration range 1000 m/s2 to 50000 m/s2). A general account is given of the state of the art in transducer calibration, and an ensemble is presented of six national measurement standards (example from the PTB) with comparison results verifying the lowest measurement uncertainty achieved so far. From a survey of past comparisons, conclusions are drawn for key comparisons in the field of vibration and shock. Recommendations for future work areas are made.