Random Vibration

At present, the linear fatigue accumulation theory proposed by Miner is used to calculate the fatigue problem of random vibration. In this process, the loading order of the loads is ignored, so that the results obtained are riskier. The nonlinear fatigue cumulative damage theory takes into account the effects of the load loading sequence, but the calculation becomes more complicated. Many scholars have shown that the fatigue calculation of alternating loads is not strictly linear, and the high and low order will affect the damage index. This phenomenon will be more obvious in the random vibration process. In this paper, the effects of loading sequence on the calculation of non-Gaussian random vibration fatigue damage are studied by virtual experiments. Through the phase selection method, 7 sets of excitations with different kurtosis were loaded onto the notched specimen. Through the calculation results of fatigue damage in the notch sensitive area, it was confirmed that the damage calculated by linear and nonlinear cumulative damage formula was improved with the increase of kurtosis. The results can make a significant difference.

W pracy rozpatrywane są stochastyczne drgania belki sandwiczowej swobodnie podpartej wywołane stochastyczną siłą poruszającą się ze stałą prędkością. Korzystając z podstawowych technik analitycznych przeprowadzono analizę korelacyjną dla stochastycznych drgań belki. Przedstawiono dla wariancji rozwiązanie częściowo w formie zamkniętej. Rezultatem pracy jest zaprezentowanie wpływu prędkości z jaką porusza się siła na losową charakterystykę drgań, m.in. wariancji przemieszczeń pionowych i obrotu belki sandwiczowej. Wyprowadzono również zależność na dynamiczny współczynnik dla obciążeń stochastycznych.

W pracy rozpatrywane są stochastyczne drgania belki sandwiczowej swobodnie podpartej wywołane stochastyczną siłą poruszającą się ze stałą prędkością. Korzystając z podstawowych technik analitycznych przeprowadzono analizę korelacyjną dla stochastycznych drgań belki. Przedstawiono dla wariancji rozwiązanie częściowo w formie zamkniętej. Rezultatem pracy jest zaprezentowanie wpływu prędkości z jaką porusza się siła na losową charakterystykę drgań, m.in. wariancji przemieszczeń pionowych i obrotu belki sandwiczowej. Wyprowadzono również zależność na dynamiczny współczynnik dla obciążeń stochastycznych.

Very low failure rates, down to 10 FIT are now currently expected by electronic system manufacturers. In the same time, severe conditions of utili sation are common in most of industrial and commercial applications, li ke automotive sector for example. In order to assess this reliabilit y “ challenge” , process control, design and technological solutions have to be optimised to guarantee almost no defect during the operating life time. Reliabilit y testing strategy must also strongly evolve from the classical accelerated ageing statistical median life testing to the use of more sophisticated degradation laws, based on physics of failure, and in many cases computer assisted.

In this work, the analysis the response to vibrations of a small building equipped with an electromechanical vibration absorber is investigated. In the first part, the case of harmonic excitation with constant or time dependent frequencies is considered, and in the second part, the case of random earthquakes, respectively. The cross correlation functions and the mean square displacements are calculated for the structure when it is equipped with an electromechanical vibration absorber. The stochastic process which characterizes the earth movements is coupled to the cnoidal method which delivers the analytical solutions of the nonlinear problem. The interaction between the structure and the energy source is analyzed via the Sommerfeld effect inside the resonance region. The resonance capture and the vibration reduction are displayed by the time history responses of the displacement and angular velocities above the resonance.

At the end of the XIX and the beginning of the XX century there was a considerable industrial development in Portugal, characterized by the flourishing of several industrial plants. Brick masonry chimneys represent some of the most interesting examples of the industrial architectural heritage. The paper shows the case study of a chimney from a former ceramic factory near Porto city and that now is part of a cultural and leisure public park. With the main goal of evaluating the seismic vulnerability of existing structures, numerical models are often used without the proper knowledge of their mechanical characteristics. The focus on this paper is given on the construction of a realistic numerical model based on a detailed in-situ survey of the chimney, involving: geometrical characterization; visual inspection, with damage registration; structural/material assessment, based on in situ dynamic tests. Two different approaches regarding the chimney damage state were followed for the calibration of the numerical model. The models from both approaches were then subjected to accelerograms matching the chimney site conditions and the responses were compared, underlining the importance of a good mechanical characterization of the materials involved.

The principal goal of this research is developing physics-based, reduced-order, analytical models of nonlinear fluid-structure interactions associated with offshore structures. Our primary focus is to generalize the Hamilton's variational framework so that systems of flow-oscillator equations can be derived from first principles. This is an extension of earlier work that led to a single energy equation describing the fluid-structure interaction. It is demonstrated here that flow-oscillator models are a subclass of the general, physical-based framework. A flow-oscillator model is a reduced-order mechanical model, generally comprising two mechanical oscillators, one modelling the structural oscillation and the other a nonlinear oscillator representing the fluid behaviour coupled to the structural motion.Reduced-order analytical model development continues to be carried out using a Hamilton's principle-based variational approach. This provides flexibility in the long run for ge...

In earthquake engineering problems, uncertainty exists not only in the seismic excitations but also in the structure's parameters. This study investigates the influence of structural geometry, elastic modulus, mass density, and section dimension uncertainty on the stochastic earthquake response of a multi-story moment resisting frame subjected to random ground motion. The North-south component of the Ali Gharbi earthquake in 2012, Iraq, is selected as ground excitation. Using the power spectral density function (PSD), the two-dimensional finite element model of the moment resisting frame's base motion is modified to account for random ground motion. The probabilistic study of the moment resisting frame structure using stochastic finite element utilizing Monte Carlo simulation was presented using the finite element program ABAQUS. The dynamic reliability and probability of failure of the stochastic and deterministic structure based on the first passage failure were checked and evaluated. Results revealed that the probability of failure increased due to randomness in stiffness and mass of the structure. Generally, natural frequencies for the lower modes of vibration and relative displacements for the lower stories were more sensitive to the randomness in system parameters.

Historic Cairo has been a UNESCO World Heritage Site since 1979. It has more than 600 historic structures, which require extensive studies to sustain their cultural, religious, and economic values. The main aim of this paper is to undertake dynamic investigation tests for the dome of Fatima Khatun, a historic mausoleum in Historic Cairo dating back to the 13th century and consisting of mainly bricks and stones. The challenge was that the structure was difficult to access, and only a small portion of the top was accessible for the attachment of accelerometers. Current dynamic identification procedures typically adopt methods in which the sensors are arranged at optimal locations and permit direct assessment of the natural frequencies, mode shapes, and damping ratios of a structure. Approaches that allow for the evaluation of dynamic response for structures with limited accessibility are lacking. To this end, in addition to in situ dynamic investigation tests, a numerical model was cr...

Historic Cairo has been a UNESCO World Heritage Site since 1979. It has more than 600 historic structures, which require extensive studies to sustain their cultural, religious, and economic values. The main aim of this paper is to undertake dynamic investigation tests for the dome of Fatima Khatun, a historic mausoleum in Historic Cairo dating back to the 13th century and consisting of mainly bricks and stones. The challenge was that the structure was difficult to access, and only a small portion of the top was accessible for the attachment of accelerometers. Current dynamic identification procedures typically adopt methods in which the sensors are arranged at optimal locations and permit direct assessment of the natural frequencies, mode shapes, and damping ratios of a structure. Approaches that allow for the evaluation of dynamic response for structures with limited accessibility are lacking. To this end, in addition to in situ dynamic investigation tests, a numerical model was cr...

This article compares for the first time three well-known procedures for characterizing the noise temperature and conversion loss of a millimeter wave mixer. To carry out this study, a 183 GHz subharmonic mixer has been measured using three common procedures, that is, the "attenuator," the "gain," and the "noise injection" procedures. Furthermore, for every measurement procedure, three different detection methods have been used; a broadband power meter, a yttrium iron garnet filter working together with a broadband power meter, and a spectrum analyzer. The "gain procedure" has turned out to be the most stable one in terms of less variation between consecutive values and flatter results along all the frequency range. Results obtained with every detection method are consistent with each other, showing a similar performance of the mixer independent of the detection method used. In addition, the effect of the inclusion or omission of an isolator between mixer and intermediate frequency pre-amplifier has also been evaluated. For the first time, clear conclusions about its influence are driven. The inclusion of the isolator has culminated in more reliable results, although the measured NT values are increased.

Random and single frequency vibration tests were used to investigate vibration behaviors and thresholds of the fretting corrosion of connector samples with different wiring tie-off lengths. Multiple vibration modes and the rocking style motion of the connector systems were observed. Through experimental threshold tests, the threshold behavior at various frequencies for the onset of fretting degradation was identified. Typically the micrometer-scale axial vibration was able to trigger the fretting corrosion of the connector samples. It is also found that the threshold amplitude at the natural frequency of one of the modes was the lowest. Thresholds at this mode of the connectors with different wiring tie-off lengths were also tested. In addition, a discrete vibration model was developed to explain and predict the threshold behavior. Through a parametric "best fit" of the vibration transfer functions, the thresholds predicted by the model correlated well with the experimental results. The analysis demonstrated that the thresholds are greatly affected by the stiffness and damping as a result of the tie-off configurations. Consequently, it is concluded that the dynamic response of the mechanical system under various tie-off configurations can greatly influence the performance of the vibration induced fretting corrosion of a connector system.

A stochastic variational inequality is proposed to model an elasto-plastic oscillator excited by a filtered white noise. We prove the ergodic properties of the process and characterize the corresponding invariant measure. This extends Bensoussan-Turi's method (Degenerate Dirichlet Problems Related to the Invariant Measure of Elasto-Plastic Oscillators, AMO, 2008) with a significant additional difficulty of increasing the dimension. Two points boundary value problem in dimension 1 is replaced by elliptic equations in dimension 2. In the present context, Khasminskii's method (Stochastic Stability of Differential Equations, Sijthoff and Noordhof,1980) leads to the study of degenerate Dirichlet problems with partial differential equations and nonlocal boundary conditions.

spécifier aussi précisément que possible l'environnement mécanique, et en particulier vibratoire, dans lequel ils seront amenés à fonctionner. C'est à cette condition que l'on pourra par la suite optimiser ces constituants vis-à-vis de leur résistance aux sollicitations liées au fonctionnement du moteur d'une part, ainsi qu'à celles issues du profil routier d'autre part, tout en limitant les coûts et les délais de développement. L'article présente une méthodologie permettant de combiner simultanément un sinus balayé et une densité spectrale de puissance d'accélération pour s'assurer de la tenue mécanique des composants montés soit sur le moteur soit sur la boîte de vitesse. La première partie traite de la séparation des composantes harmoniques et aléatoires par le biais d'une extraction d'ordre sous forme de signaux temporels. La seconde partie présente une méthode permettant d'estimer le spectre de réponses extrêmes et le spectre de dommage par fatigue d'un profil combinant un sinus balayé et une densité spectrale de puissance. Dans la troisième partie, axée sur la démarche de personnalisation des essais, ces deux composantes sont traitées indépendamment l'une de l'autre puis combinées pour définir une sollicitation de type sinus balayé sur bruit intégrant un usage client. Enfin, des applications de cette démarche sur des cas industriels relatifs à des moteurs automobiles sont décrites.

This paper proposes a new subparticle reassembly theory by decomposing quarks into rhythm units through "knoton-based phase response." Based on the "Knot of Light" framework, it assumes that as the essential light decays, a phase-responsive field emerges and particles align within it. 본 논문은 '결소자 기반 위상 응답'을 통해 쿼크를 리듬 단위로 분해하고, 각 위상 응답을 바탕으로 미립자를 재조립하는 새로운 이론을 제안한다. 이 이론은 '빛의 매듭' 프레임워크에 기반하여, 본질적 광속의 감쇠 속에서 위상 응답 필드가 형성되고 그 안에서 입자가 정렬된다는 전제를 따른다.

Alstom developed a reliable, elegant and efficient way of considering the complex substructure dynamics in rotordynamic analyses. With the presented approach the accuracy of rotordynamic predictions has been significantly increased. Usually substructures are represented by lumped mass systems (single-degree-of-freedom, SDOF). This representation is easy to implement using standard rotordynamic tools. However, in reality the dynamic behavior of the substructure (e.g. pedestals, casings, foundations) can be much more complex. Only a multi-degree-of-freedom (MDOF) representation provides modelling close to reality. Usually the substructure consists of several components which are designed, assessed and modelled by the individual departments and/or disciplines. For many applications the dynamic behavior of the substructure significantly influences the rotordynamic chararcteristics of the shaft train and therefore needs to be included in the assessment. Numerous theoretical approaches ex...

In engineering, the study of the dynamic response of structures subjected to nondeterministically variable loads is particularly important, especially when considering the damage that such loads can cause due to fatigue phenomena. This is the case, for example, of the vibrations that a satellite must withstand during the launch phase. In the preliminary design phases, it is very useful to have semi-analytical calculation methodologies that are sufficiently reliable but, at the same time, simple. In the technical literature, there are numerous publications that deal with the study of the random dynamic response of beam models. In general, the presented studies are rather complex, and the dynamic solutions are often obtained in the time domain. The case of a linear elastic uniform cantilever beam model is considered here, for which the analytical expressions of the transfer functions for acceleration, displacement, bending moment, and bending stress are calculated, taking as input the acceleration assigned to the root section or an external lateral load. Knowing the spectral density of the input loads, the spectral densities of all the above-mentioned variables are calculated along the beam axis, assuming stationary and ergodic random processes. Using the spectral density of each output variable, the effective value (RMS) is obtained via integration, which allows for a preliminary estimate of the severity of the working conditions of the beam. The spectral density of the responses also allows us to quickly highlight the contribution of each natural vibration mode as the spectrum of the load varies. The results were obtained using simple spreadsheets available to the reader.

This research is developed in collaboration with the Istituto di Radioastronomia, Istituto Nazionale di Astrofisica (IRA-INAF) located at Medicina (Bologna), in the context of the BEST (Basic Element for SKA Training) project. SKA is the name given to a new generation radio-telescope that will have 1 km 2 of effective collecting area. SKA will be the most sensitive radio-telescope ever built that allows a deeper knowledge of the universe. After a reliability analysis we estimated the MTBF of the two approaches so we suggested the most reliable solution to implement. This work considers the most reliable solution for the radio astronomical signal receiver chains, the solution that conveys the analog signal through optical fibre. Since the reliability prediction indicated the front-end, installed on the focal line of the antenna, as the more stressed block by environmental and climatic factors, we recommended to perform the environmental tests on it. The whole tests plan has been char...

In this paper, the results of reliability measurements and tests are presented. The systems taken into account concern two different architectures of a receiver chain for implementation in the Northern Cross Radiotelescope. A reliability analysis of the circuit and reliability tests implemented on critical parts of a fiber receiver chain were performed. The target was to chose the receiver chain with the highest value of mean time between failures and minimize faults in the structure. Moreover, since the reliability prediction indicated the front end, which was installed on the focal line of the antenna, as the more stressed block of the entire radioreceiver chain by environmental and climatic factors, we proposed specific development tests. The whole test plan has been characterized, and some results after a combination of temperature and humidity cycles, as well as random vibrations tests, are reported in this paper. The measurement and tests implemented in this paper for the solution of the receiver chain in the Northern Cross Radiotelescope can represent a useful aid for the new design of the international SKA project.

In the coming years, biomedical instrument manufacturers will have to inform the Notified Body of RoHS conformity assessment of the new medical instruments. In particular, in the case of lead-free solders, the Notified Body will require evidence that such solders are equally reliable as tin-lead, for the proposed use and lifetime of the product. So, biomedical instrument manufacturers are strongly interested in evaluating the performance of new soldering lead-free material used for the implementation of electronic parts. In order to support them and fill the technology knowledge gap, this paper presents a novel 128-channel phased-array probe for echocardiograph applications realized by new soldering technique where isotropic silver electrically conductive adhesive is used. In particular, the new soldering material is taken into consideration in the design phase of ultrasound array transducer, which is the core of a linear phased-array probe that is able to monitor the cardiac muscle. Being such material innovative in the application, a detailed study of the failure condition regarding the phased-array probe by means of accelerated qualification testing is proposed in order to assure its performances under stress and over time. A comparison of the electroacoustic measurement results with respect to the conventional probe, soldered with Sn-Pb, is also presented in this paper.

-induced vibration and ignition overpressure response environments are predicted in the low-frequency (5 to 200 hertz) range. The predictions are necessary to evaluate their impact on critical components, structures, and facilities in the immediate vicinity of the rocket launch pad.

This paper presents a deterministic theory for the random vibration problem for predicting the response of structures in the low-frequency range (0 to 20 hertz) of launch transients. Also presented are some innovative ways to characterize noise and highlights of ongoing test-analysis correlation efforts titled the Verification Test Article (VETA) project.

The design of launch pad structures, particularly those having a large area-to-mass ratio, is governed by launch-induced acoustics, a relatively short transient with random pressure amplitudes having a non-Gaussian distribution. The factors influencing the acoustic excitation and resulting structural responses are numerous and cannot be predicted precisely. Two solutions (probabilistic and deterministic) for the random vibration problem are presented in this article from the standpoint of their applicability to predict the response of ground structures exposed to rocket noise. Deficiencies of the probabilistic method, especially to predict response in the low-frequency range of launch transients (below 20 Hz), prompted the development of the deterministic analysis. The relationship between the two solutions is clarified for future implementation in a finite element method (FEM) code.

Consistently achieving acceptable wave solder through-hole fill on thick boards is a well-known process challenge, but the introduction of lead free solders has created additional difficulties. There are many reasons why one might achieve lower fill with lead free solders and there is much room for improvement in flux materials and process development, but unnecessary scrap and rework may be avoided by allowing lower barrel fill in some cases. Most OEMs have a waiver process to allow lower barrel fill than required by IPC-A-610D Acceptability of Electronic Assemblies for individual holes, but it seemed critical to gather more information for lead free solders in order to support the possibility of lowering the fill requirements for more boards and components by class. This study updated the previous work that had been done on through-hole reliability by considering joints made with Sn-3.0Ag-0.5Cu (SAC305) solder and a range of fill percents, including lower fill percents than are required by IPC-A-610D. SAC305 through-hole joints (with components loaded) were soldered on 0.062", 0.097", and 0.130" thick boards, with fill percents between 10% and 100%. These boards were subjected to thermal cycling, shock or vibration. After the stress exposure, the pull strengths of the joints were measured. The data showed that pin wetted length correlates well with the pull strengths of through-hole joints for different PCB thicknesses. Shock and vibration were the most detrimental stressors in the range tested. Minimum fill requirements were determined, based on board thicknesses and load per pin. This work has shown that lower fill levels than are sometimes required by IPC-A-610D will produce reliable SAC solder joints.

Abstract: This paper introduces a voltage multiplier (VM) circuit which can step up a minimum voltage of 150 mV (peak). The operation and characteristics of this converter circuit are described. The voltage multiplier circuit is also tested with micro and macro scale ...

Historic Cairo has been a UNESCO World Heritage Site since 1979. It has more than 600 historic structures, which require extensive studies to sustain their cultural, religious, and economic values. The main aim of this paper is to undertake dynamic investigation tests for the dome of Fatima Khatun, a historic mausoleum in Historic Cairo dating back to the 13th century and consisting of mainly bricks and stones. The challenge was that the structure was difficult to access, and only a small portion of the top was accessible for the attachment of accelerometers. Current dynamic identification procedures typically adopt methods in which the sensors are arranged at optimal locations and permit direct assessment of the natural frequencies, mode shapes, and damping ratios of a structure. Approaches that allow for the evaluation of dynamic response for structures with limited accessibility are lacking. To this end, in addition to in situ dynamic investigation tests, a numerical model was created based on available architectural, structural, and material documentation to obtain detailed insight into the dominant modes of vibration. The free vibration analysis of the numerical model identified the dynamic properties of the structure using reasonable assumptions on boundary conditions. System identification, which was carried out using in situ dynamic investigation tests and input from modelling, captured three experimental natural frequencies of the structure with their mode shapes and damping ratios. The approach proposed in this study informs and directs structural restoration for the mausoleum and can be used for other heritage structures located in congested historic sites.

During the Iasrthree decades ， the cntica ］ exc 圃tatlon methods have been developed extens 且 vely to account fbr mherent uncertaintles ln predlcting fbrthcoming earthquake events and to construct design earthquake ground motlons i n areasona り 1e way ． 「 In contrast to the conventlonal methods ， a litochastic response index is treated as the obJective 負mctlon to be maximized ， lhe power and the mtensity are fixed and the critical excltat 且on ls fbund under these restrlctlons ． It且s shown that the original ldea fbr statlonary random lnputs can be utll 聖 zed effectiv 璽 ly ln the procedure fbr ド finding a critlcal excitatlon for nbnstationary random vibrations of nonproportlonally

Interlayer swelling of clays has been studied. Hydration isotherms and X-ray diffraction patterns were obtained for Na-Ca, Na-, and Ca-montmorillonites, black cotton soil and kaolinite. Behaviour of Na-Ca montmorillonite is similar to that of black cotton soil but different from that of homoionic species. All hydrated water in Na-Ca montmoriUonite is interlayer water, and its texture changes with humidity.

Abstract: The dynamic responses of human standing postural control were investigated when subjects were exposed to long-term horizontal vibration. It was hypothesized that the motion of standing posture complexity mainly occurs in the mid-sagittal plane. The motor-driven ...

We present a Nyström method capable of producing high-order convergence of solutions of two-dimensional acoustic scattering problems with Neumann boundary conditions in domains with corners. Our approach is based on our recently introduced Direct Regularized ...

This paper deals with the generation of artificial spectrum compatible ground motion complying with different goals. In particular, three distinct objectives that may emerge in performance-based seismic analysis and design are discussed: • Conservative design analysis based on only few spectrum-compatible accelerograms • Performance-based earthquake engineering approaches for risk studies, in general less than 30 accelerograms are used. • Full " best-estimate " analysis for probabilistic and reliability analysis of structures subject to seismic random excitation. The ground motion time-histories have to be in agreement with these goals. Different methods and ground motion models are available in literature. Vanmarcke was among the first to implement these approaches to be used for engineering design (SIMQKE [9]), later models introduced non stationary features e.g. Preumont [1]. More recently, a module for the generation of artificial ground motion has been introduced in C...

The turbulent flow of a micropolar fluid downwards on an inclined open channel is studied. The wave profile moves downstream as a linear superposition of solitons at a constant speed and without distortion. The model parameters are determined by using a genetic algorithm.

In the course of reassessing seismic hazards at the Idaho National Engineering Laboratory (INEL), several key issues have been raised concerning the effects of the earthquake source and site geology on potential strong ground motions that might be generated by a large ...

The paper examines the effects of soil-structure interaction on the dynamic behavior of the historical Carmine bell tower in Naples, damaged by the Sannio earthquake in 1456. The brickwork structure is 68m tall, endowed with direct foundations on a deformable deposit of man-made ground and alluvial sands, overlying volcanic tuff. The structural model was calibrated on existing data, the foundation and the geotechnical subsoil model were reconstructed according to recent investigations. Soil-structure interaction was simulated by simplified and advanced approaches, considering the input motion determined through seismic response analyses. The seismic action on the rock outcrop was defined, simulating the 1456 earthquake. Comparing the results of the analyses on the fixed based structure with those of soil–structure system, the effects of the interaction was recognized in terms of elongation of the period, reduction of the damping and increase of structural displacements due to the ri...

Ship hull vibration is a major contributor to fatigue crack growth and main engine excitation is identified as an important vibration source. A general method to solve any vibration problem arising onboard a ship does not exist, which encourages the use of a reliability-based framework for assessing ship vibration and its consequences. A stochastic model of vibration response is developed for the probabilistic formulation of the failure probability of the occurrence of crack propagation of a secondary structural hull component. The secondary structural component considered is a pipe stack support. The pipe stack support connects a cargo pump pipe stack to the wall inside the cargo tank, and the support is welded directly onto this wall. First, a generic cargo hold model is analysed with engine speed and the relative distance between the engine and the structural component under consideration as stochastic variables. Then, submodels are used to investigate the local vibration of the ...

Earth dams are 3-Dimensional, huge and inhomogeneous structures that interact with water and soil. They are the most common type of dams used in the world and developing countries like Iran. Seismic analysis of earth dam is very important in regions which have been subjected with earthquake impaction several times. Calculating the natural frequency of dams is the essential part for its seismic behavior analysis. So it is very important to present an appropriate solution for calculation of natural frequency. Natural frequency of earth dams is usually calculated by means of experimental correlations, shear beam analysis (base on the height of dam and shear wave velocity) and time historical dynamic analysis. The present study concerns a new formulation for natural frequency of earth dams by means of analytical method. In this method, shear wave velocity and height of dam are two parameters which are used for obtaining natural frequency. Geometry of dam body, rigidity of foundation, modulus of elasticity and Poisson's ratio are essential in calculating process. Results from proposed method are compared with case histories, numerical method and other formulations. Comparison shows that there is no significant difference in dams with various heights up to 100m.

The functional model-based method is a unique vibration-based approach to damage localization and magnitude estimation in structures under normal operation, capable of operating on naturally arising random vibration signals without human intervention. It employs an innovative data-based stochastic functional model representing the partial dynamics under various damage scenarios, estimation techniques, and statistical hypothesis testing. Unlike alternative vibration methods employing data-based models but treat the localization and magnitude estimation approximately, as classification problems, it handles them properly as estimation problems. Among its remarkable properties is its ability to operate with a low number of vibration response sensors and low-and limited-frequency bandwidth, characteristics important in many applications. In this article, an overview of the method and its principles are presented, along with three validation case studies.

Vibration-based damage diagnosis Structural health monitoring Uncertainties Gaussian mixture model random coefficient approach Time-dependent ARMA models Linear parameter varying ARMA models Wind turbines the indicated quantity; for instance b h is an estimator/estimate of h.

In many vibration-based structural damage detection cases where the excitation is user specified, stationary random signals (typically white noise) are chosen as excitation. The question explored in this study is whether or not the use of non-stationary random excitation may lead to improved damage detectability. The latter is expressed as a distance, in the space defined via the detection method's characteristic quantity, between the damaged and healthy structural states. For exploring this issue, a parametric statistical damage detection method is employed, with the model's Power Spectral Density (PSD) constituting the characteristic quantity. The use of conventional stationary white noise excitation is contrasted to non-stationary excitation produced via a Time -dependent AutoRegressive Moving Average (TARMA) model. A simulated structure, derived from experimental signals obtained from a laboratory composite beam, is employed under two structural states: healthy and damag...

This paper addresses the stochastic modeling of recorded Times Between Failures (TBF) of electric rail vehicles, taking into account scheduled maintenance actions these vehicles undergo. The study is based upon historical data from the Athens Electric Railways and a novel non-stationary Functional Series (FS) modeling framework, which allows for the modeling, scheduled maintenance actions incorporation, analysis, as well as failure time prediction. Modeling of TBF series using square root and logarithmic transformations is considered as a simple means of accounting for non-Gaussianity and positiveness. The results of the study indicate that FS models incorporating scheduled maintenance actions are signican tly better than models not accounting for them. It is specically shown that knowledge of the maintenance actions signican tly improves prediction of the next Time to Failure.

he von >fises stress is often used as the metric for evaluating design margins. particularly for "a structures made of ductiie materials. While computing the von Mises stress distrilmion in a structural system due to a deterministic load condition may be straightforward, difficulties arise when considering random vibration environments. As a result, alternate methods are used in practice. One such method involves resolving the random vibration environment to an equivalent static load. This technique. however, is only appropriate for a very small class of problems and can easily be used incomectly. Monte Carlo sampling of numerical realizations that reproduce the second order statistics of the input is another method used to address this problem. This technique proves cornpumtionally inefficient and provides no insight as to the character of the distribution of von Ylises stress. This tutorial describes a new methodology to investigate the design reliability of st.mctural systems in a random vibration environment. The method provides analytic expressions for root mean square (R\lS) von Mises stress and for the probability distributions of von Mises stress \vhich can be evaluated efficiently and with good numerical precision. Further, this new approach has the important advantage of providing the asymptotic propetiies of the probability distribution. A brief ovemie~vof the theoretical development of the methodology is presented, foI1owedby detaiIed instructions on how to impIement the technique on engineering applications. As an exampIe, the method is applied to a complex finite element model of a Global Positioning Satellite (GPS) system. This tutorial presents an efficient and accurate methodology for correctly applying the von Mises stress criterion to complex computational models. The von Mises criterion is the traditional, method for determination of structural reliability issues in industry.

Many engineering structural elements are subjected during manufacture process or service to step excitation field. Vibration analysis of structural systems to step perturbation field has then become a vital requirement for modern structural engineering. The objective in this paper is to demonstrate that the hardening or softening nonlinearity affects some properties of viscoelastic dynamical systems under step loading field. The accuracy and reliability of the predicted performance is verified by comparison with numerical results. Phase diagrams are simulated to also verify the linear stability analysis according to the Lyapunov theory. Analytical and numerical results are found to be in satisfactory agreement. It is again found that the steady state forced response follows a power function of excitation rather than the linear law predicted by the viscously damped linear harmonic oscillator. So, it is shown that the stiffening or softening nonlinearity affects not only the transient...

Site response analysis, namely the analysis of the wave propagation of shear waves through a soil deposit, requires the specification of the input ground motion and the dynamic characterization of the soil deposit. While the stochastic approach is commonly used for modelling seismic excitation, the use of probability density functions for describing the soil properties is consistent only when precise informations based on a large amount of data from soil surveys are available. Conversely, a non-probabilistic approach based on fuzzy set theory would be more appropriate for dealing with uncertainties that are just expressed by vague, imprecise, qualitative, or incomplete information and supplied by engineering judgement. In this paper, a hybrid fuzzy-stochastic 1D site response analysis approach for dealing with soil uncertainties defined as convex normal fuzzy sets is addressed. Zadeh's extension principle, in combination with an efficient implementation of the Differential Evolution Algorithm is used for global minimization and maximization. Results are presented as fuzzy median value of the largest peaks of the peak ground acceleration at the surface by considering four types of soil classified in accordance with the European seismic building code.

In contemporary engineering practice, the investigation of the dynamic response of structures through time-history analysis requires the use of suites of acceleration ground motions. The paper studies the response of structures subjected to a novel methodology for the generation of target spectrum compatible artificial accelerograms. Existing spectrum-based models are used for the ground motion generation, whereas hazard consistency is achieved by matching these records either to a design spectrum or to a ground motion model. The obtained suites are used for the non-linear response history analysis (NRHA) of a benchmark multi-degree-of-freedom structure. Two study examples are presented. In the first example the generated suite matches only a spectral mean and in the second example the suite matches both the target spectral mean and variability. The results indicate that using the generated ground motion suites for the target NRHAs produces results that are consistent with record selection algorithms, thus confirming the efficiency of the proposed methodology.

A new stochastic methodology is proposed for the generation of bidirectional horizontal components of artificial, fully nonstationary, site-and spectrum-compatible seismic accelerograms through a nonseparable process. The model operates in the time-frequency domain and combines spectral representation techniques with signal processing tools. The basis of the methodology involves the generation of spectrum-compatible stationary artificial accelerogram signals whose nonstationarity is then modeled with a time-frequency modulating function that is based on a seed ground motion record. At the core of the proposed methodology lies the use of the Continuous Wavelet Transform (CWT). Specifically, the CWT method is used to perform time-frequency analysis and to define the nonstationary component. The proposed methodology provides any required number of seismic accelerograms whose temporal and spectral modulation is consistent with the characteristics of the site of interest. Furthermore, the model is extended to the case of pairs of bidirectional horizontal components. This is accomplished by probabilistically generating two orthogonal spectra whose geometric mean spectrum is compatible with a target spectrum. This procedure also takes into account the correlation structure of spectral acceleration pairs in orthogonal directions at different periods based on empirical models. The bidirectional components are then generated with the proposed site and spectrum-based methodology. An online tool that implements the proposed methodology is freely provided.