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To excite sufficient vibrations of bridges for more effective modal experiments to take place, traveling vehicles were utilized in many bridge field inspection campaigns in history. However, the dynamics of a bridge subjected to the traveling vehicles are of changed resonant properties compared with those of the same structure with the ambient excitation in nature. Therefore, the field modal experiments employing vehicle excitations might unfavorably lead to shifted measurement results of low-order natural frequencies for long-span bridges of large mass. Using Xinjiang Bridge (a single-tower pre-stressed concrete cable-stayed bridge with spans 40m + 150m + 150m + 40m) as the engineering background, this paper validates this technical notion based on reliable physical experiments and numerical simulations and seeks a practical approach to deal with the issue. It is found that the maximum deviation between the low-order modal frequencies measured on Xinjiang Bridge for the vehicle excitation case and those measured for the ambient excitation case (the accurate values) reaches 0.65Hz, and the deviation between the lower limit of the usual vehicle excitation’s energy band and the modal frequency measured (factor 1) and the traveling vehicles’ speed (factor 2) are the two key factors influencing the modal frequency shifts. An empirical model to compensate for modal frequencies’ deviations is formulated considering the two key factors accordingly, which is of high-practical significance in future applications of the modal experiments using vehicle excitations to other long-span bridges. [ABSTRACT FROM AUTHOR]

Abstract In addressing the finite element model and actual structural error of the sprayer boom truss, this study aims to achieve high-precision dynamic characteristics, enhance simulation credibility, make informed optimization decisions, and reduce testing costs. The research investigates the dynamic behavior of the sprayer boom truss through modal experiments and finite element simulations. Initially, modal parameters of the sprayer boom are obtained through experimental testing, validating their reasonableness and reliability. Subsequently, Ansys Workbench18.0 simulation software was employed to analyze the finite element model of the sprayer boom, revealing a maximum relative error of 11.93% compared to experimental results. To improve accuracy, a kriging-based response surface model was constructed, and multi-objective parameter adjustments using the MOGA algorithm reduce the maximum relative error to 4.6%. Sensitivity analysis further refines the model by optimizing target parameters, resulting in a maximum relative error of 4.96%. These findings demonstrate the effective enhancement of the corrected finite element model’s precision, with the response surface method outperforming sensitivity analysis the maximum relative error between the updated finite element model and experimental results was within the engineering allowable range, confirming the effectiveness of the updated model.

Abstract A wealth of practical cases indicates that the fatigue failure of subway bogies primarily stems from the modal resonance of the structure. If the modal characteristics of the entire vehicle, including equipment and bogies, are mismatched, rail vehicles may experience abnormal vibrations and noise. Therefore, it is imperative to conduct modal analysis and matching design for subway vehicle bogies to ensure smooth operation, reduce structural vibrations and noise, and enhance vehicle safety and ride comfort. Modal identification methods under the ambient l excitations during vehicle operation were employed to identify the modal parameters of the bogie structure before and after wheel reprofiling and under different load conditions. According to the test results, wheel reprofiling has minimal impact on the modal parameters of the structure, but with an increase in load, the modal frequencies of each order generally increase. This is associated with boundary constraint states, such as the increased stiffness of the bogie air spring with an increase in vehicle load. By comparing the test results with simulation analysis results of the bogie structure under free and constrained states, it is evident that simulating realistic boundary constraint conditions is crucial to ensure the accuracy of the finite element model. Based on frequency isolation criteria and vibration isolation theory, a frequency planning basis for the bogie structure was established. The study found that as the vehicle load increases, changes in the boundary conditions of the bogie affecting the elastic modal frequencies of the structure may have a certain impact on matching design, and may even better comply with the requirements of frequency management equations. This provides a new direction for subsequent scholars researching modal matching design.

A wealth of practical cases indicates that the fatigue failure of subway bogies primarily stems from the modal resonance of the structure. If the modal characteristics of the entire vehicle, including equipment and bogies, are mismatched, rail vehicles may experience abnormal vibrations and noise. Therefore, it is imperative to conduct modal analysis and matching design for subway vehicle bogies to ensure smooth operation, reduce structural vibrations and noise, and enhance vehicle safety and ride comfort. Modal identification methods under the ambient l excitations during vehicle operation were employed to identify the modal parameters of the bogie structure before and after wheel reprofiling and under different load conditions. According to the test results, wheel reprofiling has minimal impact on the modal parameters of the structure, but with an increase in load, the modal frequencies of each order generally increase. This is associated with boundary constraint states, such as the increased stiffness of the bogie air spring with an increase in vehicle load. By comparing the test results with simulation analysis results of the bogie structure under free and constrained states, it is evident that simulating realistic boundary constraint conditions is crucial to ensure the accuracy of the finite element model. Based on frequency isolation criteria and vibration isolation theory, a frequency planning basis for the bogie structure was established. The study found that as the vehicle load increases, changes in the boundary conditions of the bogie affecting the elastic modal frequencies of the structure may have a certain impact on matching design, and may even better comply with the requirements of frequency management equations. This provides a new direction for subsequent scholars researching modal matching design. [ABSTRACT FROM AUTHOR]

Gantry five-axis machine tools have garnered acclaim for their robustness, cost-effectiveness, and accuracy in fabricating intricate workpieces. In the era of Industry 4.0, these tools necessitate heightened flexibility, precision, and cognitive capabilities to meet contemporary industrial requisites and accommodate escalating processing demands. This study delved into a comprehensive analysis of a gantry five-axis machine tool via the finite element method, encompassing static, modal, spatial accuracy analysis, and topological optimization, to grasp the structural attributes of the entire apparatus. Modal experiments were conducted to validate the numerical findings, with experimental and analytical errors falling within an acceptable range, ranging from 11 to 2.5% respectively. The analysis outcomes facilitated the identification of structural vulnerabilities and resonance frequencies, enabling the avoidance of these frequencies during machining, thereby enhancing machining precision and work piece value. Utilizing ANSYS mechanical, topology optimization of the column was executed, achieving objectives such as weight reduction, augmented rigidity, and enhanced natural frequencies in contrast to the original design. Lattice optimization was applied to the spindle, aiming to elevate the fundamental frequency and diminish mass. This approach yielded a notable frequency increase from 580 to 736 Hz and nearly halved the mass. Spatial accuracy analysis facilitated the detection of component errors at various machine positions, enabling input to the machine tool's controller for error compensation, thereby enhancing precision. This comprehensive investigation underscores the significance of advanced analytical techniques and optimization strategies in fortifying the performance and efficacy of gantry five-axis machine tools in modern industrial settings. [ABSTRACT FROM AUTHOR]

As the core component of electronic equipment, vibration load has an important effect on the reliability of circuit boards. However, construction machinery has high requirements for construction efficiency and safety performance, and also has high maintenance costs. In this paper, a vibration reliability analysis and structural optimization of the control circuit board of a drilling rig are conducted. First, Failure Mode, Effects and Criticality Analysis (FMECA) and Fault Tree Analysis (FTA) qualitative and quantitative analysis were used to find the weak links in the circuit board. The quantitative and qualitative analysis results of FMECA and FTA show that the critical probability importance values of the chip inductor and TVS diode short circuit are the highest, at 0.249 and 0.173, respectively. They are up to 0.239 higher than those of the other components. Then, according to the analysis results, a precise simplified model is established for the core components, including the weak links, and modal simulations and modal tests are carried out. The key influencing parameters are obtained through comparative analysis and research on natural frequency and frequency response curves. Finally, the position of the stress–strain sensitive source in the real working environment is determined by a dynamic simulation analysis of the random vibration performance of the finite element model. The results can provide an optimization basis for an anti-vibration design of circuit boards. [ABSTRACT FROM AUTHOR]

The double stator high-temperature superconducting field modulated (DS-HTS-FM) machine with a dual-stator configuration and high-temperature superconducting materials includes numerous cryogenic components that establish the required operating temperature for superconducting magnets. This abundance of cryogenic elements introduces complexity to the process of conducting a modal analysis of the entire machine. However, the conventional trial-and-error approach employed to achieve precise modal analysis results for the entire-machine suffers from the drawback of lacking a clear direction for adjustment elastic modulus which has a great influence on the modal analysis results. Therefore, it is difficult to obtain accurate modal analysis results of the entire-machine. In response to this challenge, this study focuses on a 10 kW DS-HTS-FM machine as its subject and presents an elastic modulus adjustment method based on the entire-machine modal analysis, aiming to obtain accurate finite element (FE) modal analysis results of the entire-machine. Initially, the FE method is used to find the components that have a great influence on the outer stator modals while the components that have less influence on the outer stator modal are equivalent to the front and rear end cover in the form of additional mass, thus establishing an entire-machine equivalent model for elastic modulus adjustment. Subsequently, an examination is conducted to ascertain the relative impact proportions of the elastic modulus associated with the outer stator, casing, end cover, and armature windings on the natural frequencies of the outer stator, which can lead to a precise determination of the optimal direction for adjusting the elastic modulus parameters. Lastly, based on the entire-machine modal experiment, the elastic modulus of the equivalent model is modified in a definite direction. Consequently, the elastic modulus values for various components of the DS-HTS-FM machine can be accurately identified. Experimental outcomes affirm the efficacy of this approach in attaining precise FE modal results for the DS-HTS-FM machine and reducing the computational time required for FE analysis.

This paper proposes a novel method to design the internal stiffeners layout of the supporting parts of a machine tool. This method skillfully adopts the natural growth law of leaf veins. Firstly, the similarity between the growth law of leaf veins and the layout of stiffeners in the supporting parts is dealt with in detail. The mechanical properties of different growth types of leaf veins are compared and analyzed by the finite element simulation. In addition, the optimality of the adaptive growth law of leaf veins is also analyzed. Then, a parameter optimization method of stiffeners layout based on a variable cross-section structure is proposed. Distinct from the traditional design of stiffeners layout, the method proposed in this paper not only adopts the idea of a variable cross-section structure, but also simulates the adaptive growth law of leaf veins through a parametric method. In the process of establishing a meta model, three modeling methods are compared, and the excellent performance of the genetic algorithm and BP neural network (GABPNN) method in meta model accuracy is determined. And a marine predator algorithm is implemented to optimize the meta model. Finally, the method proposed in this paper is applied to the design of the column part of a machine tool, and the effectiveness of the proposed method is verified by simulation and experiments, which provides a good idea for the design of stiffeners layout of the supporting parts of a machine tool. [ABSTRACT FROM AUTHOR]

Measurement of thermal forces is an important process that aids in reducing the maintenance cost of continuous welded rails (CWRs). But it is still a very challenging problem. Axial force can be measured through vibration modal changes, and vibration measurement methods have several merits compared to conventional measurement methods using piles, strain sensors, magnetoelastic and acoustoelastic effect sensors, and X-rays. Vibration measurement methods have the ability to measure the absolute thermal force in a local interval and are robust against abrasion, surface residual stress, and material grains. However, they are affected by both axial force and track parameters, thereby restricting their engineering applications. To address these limitations, this study proposes a novel method called 'modal utilization method of periodic structure' (MUMPS). Its novelty lies in proving that variations in frequency constitute a random sequence satisfying the constraints of Chebyshev's law of large numbers. It can determine the influence of track parameters on the vibration modes by averaging across different eigenfrequencies without investigating what they correspond to respectively. First, MUMPS is introduced through a hypothesis that the mean value of the natural frequency variations caused by the track parameter variations approaches a stable value. Second, MUMPS is validated using finite element simulation results, which show that the probability density function of the measurement error of the neutral temperature obey N(0.5,2.6). Finally, the accuracy of MUMPS is investigated through experiments, the results are compared with the strain-gauge method results, and they show good agreement. The experimental results show that as the number of the eigenfrequencies reaches 12, the mean value becomes stable, and the measurement error of neutral temperature is less than 4 ∘ C . Engineering applicability of MUMPS is demonstrated by conducting real-time measurements on railway tracks. The results show that the proposed method is simple, as sophisticated instruments are not employed to determine the axial forces on railway tracks. [ABSTRACT FROM AUTHOR]

The vibration problem during the operation of rice transplanter is the most common phenomenon. In order that the static and dynamic characteristics of the rice transplanter chassis can meet the requirements of more stable operation, the research took the 2ZG-6DK rice transplanter as the research object to carry out a vibration reduction optimization study. In the research, the Pro/Engineer 5.0 software was first used to model the chassis of the rice transplanter. The constructed finite element model was revised by using the structural parameter revision method and the mixed penalty function method. The model was imported into ANSYS Workbench to solve the modal frequency and vibration shape of the rice transplanter chassis. Based on the MAC (modal assurance criterion) criterion, modal tests were carried out to verify the accuracy of the finite element theoretical analysis. Through the analysis of the characteristics of the external excitation frequency, the chassis is structurally optimized to avoid resonance caused by the natural frequency of the chassis falling within the road excitation frequency range. The final optimization results showed that the first four orders of modal frequencies of the chassis were adjusted to 32.083 Hz, 33.751 Hz, 42.517 Hz, and 50.362 Hz, respectively, in the case that the chassis mass was increased by 6.714 kg (8.8%). They all avoid the range of road excitation frequency (10-30 Hz) so that the rice transplanter can effectively avoid the resonance phenomenon during operation. This study can provide a reference for the design and optimization of chassis structure of transplanter. [ABSTRACT FROM AUTHOR]

The inaccurate prediction of vibrations in blade-disk structures leads to frequent occurrences of failures in rotating machinery, such as air-engines. Existing methods often empirically treat the contact parameters of interfaces as globally constant and rarely consider manufacturing and assembly deviations, resulting in a deviation of prediction models from reality. This work presents a model for complex assembly structures that includes non-uniform distributions of normal contact stiffness and tangential friction coefficients at rough interfaces, while also introducing experimentally measured geometric deviations to enhance alignment with real-world conditions. Taking fir-tree blade-disk structure as an example, the accuracy of the proposed method is comprehensively verified by four measurement experiments and one modal experiment. Subsequently, the combined influence of rough interfaces and three experimentally measured geometric deviations on the overall modal characteristics of blade-disk structure are investigated, and their influencing mechanisms are revealed. The results indicate that ignoring the interface roughness and geometric deviations may significantly affect the prediction accuracy of the modal characteristics. The proposed method has great potential in the field of predicting the modal characteristics for complex assembly structures and optimizing the design of their machining and assembly processes. [Display omitted] • A model including distributions of stiffness and friction coefficient is proposed. • Various experiments are carried out to verify the proposed model. • Combined influence of contact parameters between rough interfaces is obtained. • The necessity of experimentally measuring geometric deviations is explored. • Influence mechanisms of roughness and geometric deviations on the mode are revealed. [ABSTRACT FROM AUTHOR]

The development of cybernetics conditioned the appearance of the modelling method as general scientific model and made the unity of theory and practice become by far more qualitative from, until then, ruling statistic method. This method appears in social sciences as modal experiment. By using of this fundamental experiences, the authors in this paper are firstly theoretically analysing the concept and structure of modelling including the concept and kinds of modelling, the concept and kinds of experiment, thus, its basic model in modal experiment and, finally, as the essential part of the paper, conceptual model of the security system of the Republic of Serbia and variables of modal experiment. Generally speaking, the model is considered from strategic, doctrinaire, legal-normative and organisastional-functional aspect adequate to contemporary security movements in the world, our needs and objective possibilities as well. Its application is, of course, possible in the local self-management, which is becoming increasingly important factor of the state security system.

TiBw / TC4 composite material was used as the machining object of Ultrasonic vibration assisted drilling (UVAD), the single directional three-degree-of-freedom dynamical system model was established. The dynamic signal test and analysis system was used for modal experiment to identify the parameters in the model. Under the condition of dry cutting, the drilling axial force and tool vibration in the drilling process are studied. The results showed that the maximum values of the predicted and measured axial drilling force were 412.5N and 439.6N respectively, and the error rate was 6.165%, which verified the reliability of the predicted axial drilling force model. For cutting tools, the average amplitudes of simulated vibration and measured vibration were 0.1124mm and 0.1151mm respectively, with a difference of 2.402%, and the overall trends were the same, which verifies the reliability of the dynamical model. Finally, the stability of drilling process was analyzed, and the frequency and amplitude of ultrasonic vibration were analyzed. The results show that in order to expand the unconditional stability region, it is more efficient to increase the amplitude than to increase the frequency. [ABSTRACT FROM AUTHOR]

Highlights • The nonlinear dynamics of Z-shaped folded plates with inner resonance are investigated. • The nonlinear dynamical behaviors of the Z-shaped folded plate are conducted by numerical simulation and compared with the results obtained by experiment. • The middle plate yielded more complex vibration forms than the other two plates with increasing transverse excitations. Abstract As one of the classical complex multibody structures, Z-shaped folded plates are widely applied in several engineering structures. In the present paper, the nonlinear vibration characteristics of a Z-shaped folded plate composed of three carbon-fiber composite plates were analyzed through theoretical and experimental investigation. The nonlinear dynamic model of the Z-shaped plate was developed based on the Hamilton principle, von Kármán equations, and the classical laminate plate theory, and the vibration mode shape functions of the system were calculated in ANSYS. Further, the Galerkin approach was employed to discretize the partial differential equations into a two-degrees-of-freedom nonlinear system, and the effects of transverse excitations on the nonlinear dynamic behavior of the Z-shaped folded plate were investigated through a comprehensive numerical simulation. Moreover, the obtained theoretical results were verified by experimental analysis. In addition, the vibration mode shapes of the Z-shaped folded plate were obtained by operational modal analysis (OMA). The modal parameters were first identified successfully using the PolyMAX method and then validated by modal assurance criterion (MAC). Finally, an excitation-measurement test was designed to measure the nonlinear vibration characteristics of the Z-shaped folded plate. [ABSTRACT FROM AUTHOR]

Rods fastened rotor system are widely used in heavy-duty gas turbines. The contact nonlinearity and discontinuity induced by bolted rotor structures, make it difficult to design a scaled rotor system accurately. Thus, a dynamic scaling design strategy for discontinuous bolted rotor systems is proposed in this paper. An improved continuous modeling method considering rods deformation based on equivalent material layer (EML) is introduced to reflect the weakening effect of the rotor stiffness with bolted structure, and the parameter mapping relationships between the continuous and the discontinuous structure are constructed. The scaling factors of each element of the rotor system are derived by the similarity theory. Through this approach, a discontinuous rotor system can be scaled, demonstrating a high level of consistency with the prototype in terms of natural frequencies, critical speeds as well as frequency response. In addition, modal experiments under different preloads and dynamic acceleration experiment are carried out to verify of the proposed modeling method for discontinuous rotor structures. The testing and simulation results prove that the introduced equivalent material layer reflects the contact effect of prototype accurately. Compared with the experimental results, the maximum deviation of the first two natural frequencies is 4.06%, and the maximum deviation of the critical speeds is 1.36%, demonstrating the potential of small size, low-cost scaled models for predicting the complex dynamic characteristics of the prototype rotor system. Overall, the proposed scaling design strategy provides practical guidance for the design and manufacture of the discontinuous scaled rotor systems, which has broad application in testing, fault prediction and dynamic design of prototypes. [ABSTRACT FROM AUTHOR]

Aiming at the modal problem of fluid-filled pipeline under fluid-structure interaction. At first, from the view of simulation, the modal characteristics of the simplified U-shaped pipeline structure under fluid-structure interaction were analyzed by ANSYS Workbench software. Then, from the view of experimental, the experimental modal analysis of the liquid-filled pipeline was carried out by means of frequency sweeping and hammering. Finally, the simulation model was modified based on the results of the experiment. The experimental results verified that the modified simulation model and the boundary conditions were correct. It provides a basis for the dynamic simulation and experimental analysis of the liquid-filled pipeline under fluid-structure interaction. [ABSTRACT FROM AUTHOR]

Abstract In this study, a multi-objective optimization method that combines the compromise programming approach with the mean frequency method is proposed. The proposed method is used to optimize a machine tool column for three objectives: compliance, deformation, and natural frequency. From this optimization, the following conclusions can be drawn: 1) the static stiffness of the vertical machining center is increased by 21.53%; 2) the tool tip static deformation is decreased by 13.69%; and 3) the shapes of the first four modes for the whole machine remain unchanged, but their natural frequencies are increased by 5.09%, 7.66%, 4.16%, and 5.45%, respectively. [ABSTRACT FROM AUTHOR]

An approach to calculating vibration modal characteristics of a marine gear system featuring confluence transmission based on the theoretical and the experimental modal analysis is given in view of the fact that it is difficult to accurately determine the modal data of the system because of its complex vibration mechanism. Firstly, a dynamic finite element model of a coupled gear-rotor-bearing-housing system is developed by combining the gearbox transmission model with the gearbox housing model using the modal parameter identification data. Then, the modal frequency and the mode of vibration can be obtained. In fact, the proposed model can provide a faster approach to analysing the mode of the gear system vibration. Finally, experimental testing of the mode of vibration is performed on the experimental prototype to verify the rationality of the theoretical analysis. A comparison of the two sets of results shows that the experimental results are in good agreement with the computational results, with a maximum error of 6.3%. [ABSTRACT FROM AUTHOR]

Composite sandwich structures with a grid-stiffened core (SSGSC) are one of the new structural configurations employed in advanced industries, and therefore the knowledge of their dynamic characteristics is very important. Hence, in the present study, three composite SSGSC samples of glass/epoxy and carbon/epoxy were fabricated by the hand lay-up method using a silicon rubber die. Also, two metallic samples — a monolithic one and a SSGSC, made of Aluminum 1050, were fabricated. The core of the aluminum SSGSC was produced using the wire cutting process, and the face sheets were attached using a high-grade adhesive. Modal experiments were carried out on all the samples using B&K vibration equipment. The frequency, mode shape, and damping coefficients were obtained from each experiment. Finally, a numerical modal analysis was performed, and good agreement between experimental and numerical results was obtained. [ABSTRACT FROM AUTHOR]

To improve the dynamic performance and reduce the weight of the planet carrier in wind turbine gearbox, a multi-objective optimization method, which is driven by the maximum deformation, the maximum stress and the minimum mass of the studied part, is proposed by combining the response surface method and genetic algorithms in this paper. Firstly, the design points' distribution for the design variables of the planet carrier is established with the central composite design (CCD) method. Then, based on the computing results of finite element analysis (FEA), the response surface analysis is conducted to find out the proper sets of design variable values. And a multi-objective genetic algorithm (MOGA) is applied to determine the direction of optimization. As well, this method is applied to design and optimize the planet carrier in a 1.5MW wind turbine gearbox, the results of which are validated by an experimental modal test. Compared with the original design, the mass and the stress of the optimized planet carrier are respectively reduced by 9.3% and 40%. Consequently, the cost of planet carrier is greatly reduced and its stability is also improved. [ABSTRACT FROM AUTHOR]

The vibration method is one of the most effective methods for nondestructively testing the elasticity modulus of wood. But the past research was mostly concentrated in the small size specimens. In order to better prepare for the nondestructive testing of the elasticity modulus of full-size artificial board, here tests and analyzes its vibration modal. In order to solve the modal parameters of full-size artificial board in free vibration, it uses 6 full-scale artificial boards of two kinds of materials, and for each kind there are 3 kinds of thicknesses, in which including the particle board and medium density fiberboard as the test objects. Then it props them at the first order pitch line of free vibration, namely the 22.4% and 77.6% of the full-length of the full-size artificial board. After exciting by the pulse hammer and vibration picking by the acceleration sensor, it can measure the vibration mode, the vibration frequency and the damping ratio of the full-size artificial boards at each order. It obtains the vibration mode, the frequency and the damping ratio of the full-size artificial board at the first 3 orders in the free vibration form. The results show that: 1) for the three materials of full-size artificial boards with all thicknesses, their vibration modes at the first order are bending along with the length direction; 2) the vibration modes of the full-size artificial boards with the same thickness are the same at the same order, and are all bending vibration. [ABSTRACT FROM AUTHOR]

The development of cybernetics resulted in the birth of modeling method as a general scientific method, and made unity of theory and practice become, by far, more qualitative than, until then, governing statistical method. In the field of social science, the method has appeared as the modal experiment. Using these fundamental experiences, in this work, the authors firstly explain the concept, structure and types of modeling, and then the concept and types of experiments, that is, the basic model in modal experiment. In the end, the authors elaborate a possible conceptual model of security system of the Republic of Serbia and modal experiment variables. In this model, it is possible to vary and change the quality, intensity, dynamics and quantity factors. With the help of this model, it is possible to determine the power of accomplishment and tendencies. To achieve this simulation the research prognostic technique has been applied. Conceptual model has been seen from the doctrinal, legal and organizational perspectives, having been in compliance with security movements in the world, needs and objective possibilities of the Republic of Serbia. [ABSTRACT FROM AUTHOR]

Abstract: This article investigates the role of bearing preloads on the modal characteristics of a shaft-bearing assembly with a double row angular contact ball bearing. First, an analytical model is developed to comparatively evaluate the effects of axial bearing preloads on the vibratory responses of alternate double row configurations. The analytical model includes bearings via a five dimensional stiffness matrix. Changes in the resonant amplitudes with respect to the bearing preloads are examined for preload-independent and preload-dependent viscous damping models. The bearing preloads significantly affect the vibration characteristics of the shaft-bearing assembly due to major changes in both diagonal and off-diagonal elements of the stiffness matrix, and such effects depend on the bearing configuration. Second, a new experiment consisting of a vehicle wheel bearing assembly with a double row angular contact ball bearing in a back-to-back arrangement is designed. The bearing is subjected to axial or radial preloads in a controlled manner. Experiments with two preloading mechanisms show that the nature and extent of the bearing preloads considerably affect the natural frequencies and resonant amplitudes, thus influencing the vibration behavior of the bearing assembly. Finally, the new bearing stiffness model is validated using measurements from the modal experiment. Suggestions for further work are briefly discussed. [Copyright &y& Elsevier]

Abstract: This paper presents an approach to investigate the dynamic characteristic of a 3-DOF stage. The stage is levitated by high-stiffness air bearing and the positioning accuracy can reach nanometer level. The mover of the stage, whose lowest order nature frequency is much higher than control bandwidth, is regarded as rigid body. The air bearing is equivalent to a series of linear and torsion springs, so that the dynamic performance of air bearing can be simulated and the impact to the positioning accuracy caused by air bearing can be studied. Then, an analytical modeling method of the stage based on analysis of rigid body finite rotation is proposed, and the general equation of dynamics with virtual power form is obtained. By using method, the vibration characteristics of the stage when positioning are obtained. The modal experiment is performed on the stage. The experiment results are in good agreement with analysis results, which has verified the equivalence method of the air bearing and the dynamic modeling method of the stage. [Copyright &y& Elsevier]

In this paper, the simple genetic algorithm (SGA) is improved by combining with the simulated annealing algorithm (SAA) for the parameter identification of a reinforced concrete (RC) frame on elastic foundation. SGA adopts parallel search strategy, which is based on the concept of "survival of the fittest" in optimization while SAA adopts a serial form and the process is endowed with time-variety probable jumping property so that local optimization could be prevented. The global searching ability is developed by combining the two methods and the new algorithm is named genetic annealing hybrid algorithm (GAHA). Modal experiments were carried out on a four-storey RC frame structural model with isolated embedded footings in laboratory. The measured natural frequencies and mode shapes have been utilized to identify the physical parameters of the frame by the proposed method. Four cases of concrete elastic modulus and foundation dynamic shear modulus are identified, and the results are compared with the usual sensitivity methods (SM). By model updating, the results show that the elastic modulus of concrete increases with respect to the storey. The identified elastic modulus of the concrete is generally larger than that found by compressive testing because the dynamic modulus of concrete is larger than the static modulus of concrete. The identified soil dynamic shear modulus also increases with the storey since the soil property depends on the pressure exerted on the soil. It is also shown that the identified results by GAHA are better than that of SM. [ABSTRACT FROM AUTHOR]

Firstly, based on modal experiment, this paper analyses composite fiber curve laminates, which includes [<0|15>] 8 , [<15|30>] 8 , [<30|45>] 8 , [<45|60>] 8 , [<60|75>] 8 , [<75|90>] 8 , and then gets damping ratio of each laminated plate. After analysis, the results showed that the curve of fiber layer for <30|45> composite laminated plate damping ratio is the maximum, however, the curve of fiber layer for <60|75> composite laminated plate damping ratio is the maximum. Secondly, the simple harmonic test of laminated plates with curved layers was carried out. Those plates includes [0/45/<0|15>/−45] s , [0/45/<15|30>/−45] s , [0/45/<30|45>/−45] s , [0/45/<45|60>/−45] s , [0/45/<60|75>/−45] s , [0/45/<75|90>/−45] s. It is easy to get the acceleration response maps of each laminated plate. The above simple harmonic test results showed that larger the damping ratio, the better the damping effect and the smaller the amplitude of acceleration. The amplitude of acceleration changes inversely with the change of damping ratio. Finally, the conclusion is that the laminated plate with the best vibration damping effect is [<30|45>] 8 , and the laminated plate with the worst vibration damping effect is [<60|75>] 8. [ABSTRACT FROM AUTHOR]

Firstly, based on modal experiment, this paper analyses composite fiber curve laminates, which includes [〈0|15〉] 8 , [〈15|30〉] 8 , [〈30|45〉] 8 , [〈45|60〉] 8 , [〈60|75〉] 8 , [〈75|90〉] 8 , and then gets damping ratio of each laminated plate. After analysis, the results showed that the curve of fiber layer for 〈30|45〉 composite laminated plate damping ratio is the maximum, however, the curve of fiber layer for 〈60|75〉 composite laminated plate damping ratio is the maximum. Secondly, the simple harmonic test of laminated plates with curved layers was carried out. Those plates includes [0/45/〈0|15〉/−45] s , [0/45/〈15|30〉/−45] s , [0/45/〈30|45〉/−45] s , [0/45/〈45|60〉/−45] s , [0/45/〈60|75〉/−45] s , [0/45/〈75|90〉/−45] s. It is easy to get the acceleration response maps of each laminated plate. The above simple harmonic test results showed that larger the damping ratio, the better the damping effect and the smaller the amplitude of acceleration. The amplitude of acceleration changes inversely with the change of damping ratio. Finally, the conclusion is that the laminated plate with the best vibration damping effect is [〈30|45〉] 8 , and the laminated plate with the worst vibration damping effect is [〈60|75〉] 8. [ABSTRACT FROM AUTHOR]

In order to effectively improve the dynamic characteristics of the fixed metal joint interface, it is important to establish a correct equivalent model of the metal joint interface. In this paper, three equivalent methods for simulating the metal joint interface are analyzed, including the virtual material method, spring damping method, finite element method, and verification by modal experiment. First, according to the contact mechanics model of the constructed metal joint interface, the physical properties of the three-dimensional models of the fixed joint interface are assigned in the ANSYS software. Then, three methods are used for the modal analysis and compared with a modal experiment. The results show that the modal shapes of the three theoretical methods are consistent with those of the experimental modes. The first five natural frequencies obtained by the virtual material method are closest to the experimental natural frequencies, and the errors are within 10%. The errors of the other two methods are between 9% and 39%. Therefore, the virtual material method is a better equivalent method of the metal joint interface. [ABSTRACT FROM AUTHOR]