Nonlinear Modeling and Identification of Structural Joint by Response Control Vibration Test

Components of mechanical product are assembled by structural joints,such as bolting,riveting,welding,etc.Structural joints introduce nonlinearity to some engineering structures,and the nonlinearity need to be modeled precisely.To meet serious quality requirements,it is necessary to detect and identify nonlinearity of mechanical products for structural optimization.Modal test to acquire a dynamic response has been applied for decades,which provides reliable results for finite element(FE)model updating.Here response control vibration test for identification of nonlinearity is presented.A nonlinear system can be regarded as linearity for particular steady state response,and classical linear analysis tool is applicable to extract modal data for particular response.First,its applicability is illustrated by some numerical simulations.Subsequently,it is implemented on experimental setup with structural joints by shaking table.The stiffness and damping function dependent of relative displacement are fitted to describe its inherent nonlinearity.The spring and damping forces are identified by harmonic balance method(HBM)to predict output response.Based on the identified results,the procedure is recommended that it allows a reliable measurement of nonlinearity with a certain accuracy.

Vibration Test Measures for Pump Fault Diagnosis

p;Calculation;Diagnosis The vibration measuring standard for compound machinery utilized in modern industrial production will be employed for the application of detecting technologies.The vibration intensity can be obtained by selecting the detecting method to obtain the speed of mechanical vibration,and technicians can examine whether the vibrating machinery is in a proper functioning state based on the value of vibration intensity,allowing for thorough fault diagnosis.In order to provide useful diagnosis ideas for technicians,this study examines the measurement of mechanical vibration and investigates the calculating method of mechanical vibration intensity.

Analysis of the track system in bumpy unstructured hard road environment by vibration test

The complex terrain environment in the hilly land directly affects the operational reliability of agricultural robots.In order to study the impact of road irregularity on walking chassis vibration,the 3CYLZ-750 remote-controlled weeding machine which is applied to orchards was taken as the object of study,and the rear roller was selected as the object of observation to reveal the rules under which the vibration of the track chassis changes as there is a sudden change in road surface elevation.A column-type test-to-pass method based on unit excitation was proposed in this study.The excitation behavior and action process were analyzed by category.A critical acceleration prediction model was built and verified by virtual simulation and hard road surface excitation testing.The results showed that at the forward velocity of 0-2.5 km/h and exciter height of 20-100 mm,the vertical vibration acceleration of the target roller was significantly affected by Track Contact Point Centrifugal Acceleration(TCPCA).As TCPCA increased,the change rate of vertical vibration acceleration decreased,reaching a minimum of[−13.8,28.8];as TCPCA decreased,the vertical vibration acceleration tended to increase positively at a maximum variation range of[−13.3,42.2].The measured and simulated macroscopic change rules were consistent with the theoretical analysis,further verifying the correctness of variable extraction,and providing a research basis for the accurate modification and improvement of the model.The research conclusions can lay a theoretical foundation for analyzing the walking reliability of the track chassis,and provide a design basis and technical support for the development of a tracked agricultural robot chassis for the hilly land in the future.

Wavelet-based iterative data enhancement for implementation in purification of modal frequency for extremely noisy ambient vibration tests in Shiraz-Iran

The main purpose of the present study is to enhance high-level noisy data by a wavelet-based iterative filtering algorithm for identification of natural frequencies during ambient wind vibrational tests on a petrochemical process tower.Most of denoising methods fail to filter such noise properly.Both the signal-to-noise ratio and the peak signal-to-noise ratio are small.Multiresolution-based one-step and variational-based filtering methods fail to denoise properly with thresholds obtained by theoretical or empirical method.Duc to the fact that it is impossible to completely denoise such high-level noisy data,the enhancing approach is used to improve the data quality,which is the main novelty from the application point of view here.For this iterative method,a simple computational approach is proposed to estimate the dynamic threshold values.Hence,different thresholds can be obtained for different recorded signals in one ambient test.This is in contrast to commonly used approaches recommending one global threshold estimated mainly by an empirical method.After the enhancements,modal frequencies are directly detected by the cross wavelet transform(XWT),the spectral power density and autocorrelation of wavelet coefficients.Estimated frequencies are then compared with those of an undamaged-model,simulated by the finite element method.

Vibration test and analysis of mini-tiller

Intense vibration happens at the handle of the mini-tillers that abundantly used in mountainous and hilly areas of southwest China.It is absolutely essential to probe into the vibration characteristics and factors why handle of the tiller vibrates violently.Therefore,the vibration acceleration signals of a mini-tiller’s handle and engine cover were tested under the following four conditions:the engine being idle,racing at medium and high speeds,and the tiller working in the field with high engine speed.The signals were processed by means of the time domain eigenvalue analysis and the frequency spectrum analysis.The results showed that when the tiller was under static condition,with increase of the engine speed,the handle vibration decreased in the vertical direction,increased in the fore-and-aft direction and had marginal changes in the left-to-right direction.When the tiller worked at high engine speed,the handle vibrated most violently in the fore-and-aft direction,while the vibrations at the engine cover and handle decreased substantially in each direction,compared with the static conditions.Rotary blades cutting soil increased the damping of the whole machine so as to reduce the vibration at the handle and the engine cover,but the handle vibration was still violent.When the tiller worked,that soil absorbing energies of some frequencies led to the first order unbalanced inertia force of the engine becoming the main reason why handle vibrated intensely.

Ambient vibration testing and updating of the finite element model of a simply supported beam bridge

An ambient vibration test on a concrete bridge constructed in 1971 and calibration of its finite element model are presented.The bridge is characterized by a system of post-tensioned and simply supported beams.The dynamic characteristics of the bridge,i.e.natural frequencies,mode shapes and damping ratios were computed from the ambient vibration tests by using the Eigensystem Realization Algorithm(ERA).Then,these characteristics were used to update the finite element model of the bridge by formulating an optimization problem and then using Genetic Algorithms(GA)to solve it.From the results of the ambient vibration test of this type of bridge,it is concluded that two-dimensional mode shapes exist:in the longitudinal and transverse;and these experimentally obtained dynamic characteristics were also achieved in the analytical model through updating.The application of GAs as optimization techniques showed great versatility to optimize any number and type of variables in the model.

Structural Model Updating of Jacket Platform by Control Theory Using Vibration Measurement Approach

The identification of variations in the dynamic behavior of structures is an important subject in structural integrity assessment.Improvement and servicing of offshore platforms in the marine environment with constant changing,requires understanding the real behavior of these structures to prevent possible failure.In this work,empirical and numerical models of jacket structure are investigated.A test on experimental modal analysis is accomplished to acquire the response of structure and a mathematical model of the jacket structure is also performed.Then,based on the control theory using developed reduction system,the matrices of the platform model is calibrated and updated.The current methodology can be applied to prepare the finite element model to be more adaptable to the empirical model.Calibrated results with the proposed approach in this paper are very close to those of the actual model and also this technique leads to a reduction in the amount of calculations and expenses.The research clearly confirms that the dynamic behavior of fixed marine structures should be designed and assessed considering the calibrated analytical models for the safety of these structures.

Field measurements for calibration of simplified models of the stiffening effect of infill masonry walls in high-rise RC framed and shear-wall buildings

As a type of nonstructural component, infill walls play a significant role in the seismic behavior of high-rise buildings. However, the stiffness of the infill wall is generally either ignored or considered by simplified empirical criteria that lead to a period shortening. The difference can be greatly decreased by using a structural identification methodology. In this study, an ambient vibration test was performed on four on-site reinforced concrete high-rise buildings, and the design results were compared with the PKPM models using corresponding finite element(FE) models. A diagonal strut model was used to simulate the behavior of the infill wall, and the identified modal parameters measured from the on-site test were employed to calibrate the parameters of the diagonal strut in the FE models. The SAP2000 models with calibrated elastic modulus were used to evaluate the seismic response in the elastic state. Based on the load-displacement relationship of the infill wall, nonlinear dynamic analysis models were built in PERFORM-3 D and calibrated using the measured modal periods. The analysis results revealed that the structural performance under small/large earthquake records were both strengthened by infill walls, and the contribution of infill walls should be considered for better accuracy in the design process.

Frequencies Prediction of Laminated Timber Plates Using ANN Approach

Cross laminated timber(CLT)panels,which are used as load bearing plates and shear panels in timber structures,can serve as roofs,walls and floors.Since timber is construction material with relatively less stiffness,the design of such structures is often driven by serviceability criteria,such as deflection and vibration.Therefore,accurate vibration and elastic properties are vital for engineered CLT products.The objective of this research is to explore a method to determine the natural frequencies of orthotropic wood plates efficiently and fast.The method was developed based on vibration signal processing by wavelet to acquire the effective sample data,and a model developed by artificial neural network(ANN)to achieve the prediction of nature frequencies.First,experiments were performed to obtain vibration signals of single-layer plates.The vibration signals were then processed by wavelet packet transform to extract the eigenvectors,which served as the samples to train the ANN model.The trained model was employed to predict three nature frequencies of other test specimens.The results showed that the proposed method can produce predicted frequencies fast and efficiently within 10%of the measured values.

Finite Element Model Updating for Structural Health Monitoring

This paper provides a model updating approach to detect,locate,and char-acterize damage in structural and mechanical systems by examining changes in mea-sured vibration responses.Research in vibration-based damage identification has been rapidly expanding over the last few decades.The basic idea behind this technology is that modal parameters(notably frequencies,mode shapes,and modal damping)are functions of the physical properties of the structure(mass,damping,and sifies).Therefore,changes in the physical properties will cause changes in the modal proper-ties which could be obtained by structural health monitoring(SHM).Updating is a process fraught with numerical difficulties.These arise from inaccuracy in the model and imprecision and lack of information in the measurements,mainly taken place in joints and critical points.The motivation for the development of this technology is.presented,methods are categorized according to various criteria such as the level of damage detection provided from vibration testing,natural frequency and mode shape readings are then obtained by using modal analysis techniques,which are used for updating structural parameters of the associated finite element model The experi-mental studies for the laboratory tested bridge model show that the proposed model.updating using ME scope technique can provide reasonable model updating results.

System Identification of Heritage Structures Through AVT and OMA:A Review

In this review article,the past investigations carried out on heritage structures using Ambient Vibration Test(AVT)and Operational Modal Analysis(OMA)for system identification(determination of dynamic properties like frequency,mode shape and damping ratios)and associated applications are summarized.A total of 68 major research studies on heritage structures around the world that are available in literature are surveyed for this purpose.At first,field investigations carried out on heritage structures prior to conducting AVT are explained in detail.Next,specifications of accelerometers,location of accelerometers and optimization of accelerometer networks have been elaborated with respect to the geometry of the heritage structures.In addition to this,ambient vibration loads and data acquisition procedures are also discussed.Further,the state of art of performing OMA techniques for heritage structures is explained briefly.Furthermore,various applications of system identification for heritage structures are documented.Finally,conclusions are made towards errorless system identification of heritage structures through AVT and OMA.

Time-domain and frequency-domain approaches to identification of bridge flutter derivatives

Flutter derivatives are essential for flutter analysis of long-span bridges,and they are generally identified from the vibration testing data of a sectional model suspended in a wind tunnel.Making use of the forced vibration testing data of three sectional models,namely,a thin-plate model,a nearly streamlined model,and a bluff-body model,a comparative study was made to identify the flutter derivatives of each model by using a time-domain method and a frequency-domain method.It was shown that all the flutter derivatives of the thin-plate model identified with the frequency-domain method and time-domain method,respectively,agree very well.Moreover,some of the flutter derivatives of each of the other two models identified with the two methods deviate to some extent.More precisely,the frequency-domain method usually results in smooth curves of the flutter derivatives.The formulation of time-domain method makes the identification results of flutter derivatives relatively sensitive to the signal phase lag between vibration state vector and aerodynamic forces and also prone to be disturbed by noise and nonlinearity.