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To study the aerodynamic noise characteristics of alternators in vehicles, this paper established a computational model for the aerodynamic noise of an alternator based on computational fluid dynamics (CFD). The alternator adopted a non-scaling model and considered the detailed structure of collectors and other parts. Based on Lighthill acoustic theory, this paper adopted three-dimensional and large eddy simulation (LES) to conduct an unsteady numerical simulation for the flow field around the alternator, and Ffowcs Williams-Hawkings (FW-H) model was then adopted to conduct an unsteady computation for the aerodynamic noise of the alternator in the far field. When the rotational speed of the alternator was 10000 r/min, this paper obtained the aerodynamic noise characteristics of the alternator and the unsteady flow field structure around the alternator. Studied results showed: The main aerodynamic noise sources of the alternator were front fan, rear fan and stator structure; main influence orders of aerodynamic noises were the 6th, 8th, 10th, 12th, 18th, 24th, 30th and 36th orders. Similarly, this paper also conducted an experimental test on the noise of vehicle alternators. The main influence orders of aerodynamic noises of alternators were the 6th, 8th, 10th, 12th, 18th, 24th, 30th and 36th orders, which was consistent with the working condition of numerical simulation. It showed the correctness of computational results in this paper. In addition, this paper adopted the method of vector synthesis and the distribution of fan blades of the alternator to explain the cause of various orders and provided engineering application foundation for further reducing the noise of main orders. [ABSTRACT FROM AUTHOR]

Shells are important structural elements widely used in various engineering applications ranging from outer space to deep oceans such as rockets, aircrafts, missiles, submarines and automobiles etc. A huge amount of research efforts has been devoted to vibration analysis and dynamic behaviors of the shells. Furthermore, a large variety of shell theories and computational methods have been proposed and developed by researchers. For different cases different computational approaches have been used in literature to study the vibration characteristics of shells. This review is aimed to provide contemporarily relevant survey of papers on vibrational characteristics of shells and identification of various methods and approaches that have been used to study its vibration characteristics. Focus has been kept to important and prominent studies and its compilation in a single paper to help future researchers to identify relevant literature quickly and easily and also help them to apply these approaches to study vibration characteristics of other built up and coupled structures. [ABSTRACT FROM AUTHOR]

This paper presents the design and verification of a damping multi-model adaptive switching controller for electronic air suspension (EAS) system. In order to improve the convergence rate of identification algorithm of conventional adaptive controller, multiple local linear full-car vehicle models of EAS system with fixed parameters are established according to the actual damping control process of EAS for different vehicle driving conditions and an adaptive model whose initial value of parameters can be re-assigned is introduced to enhance the system control precision. The model switching control strategy based on minimum error is used to select the best matching model online and the optimum damping force is regulated by adaptive control algorithm, thus constituting the damping multi-model adaptive control for EAS. Simulation results show that the control method proposed in this paper can improve the damping regulating performance of EAS effectively in wide range driving conditions, especially for the case of sudden change in driving conditions. [ABSTRACT FROM AUTHOR]

This paper presents a technique for minimizing vibrations of the steering wheel from vibration transmission path based on the method of shift frequency vibration reduction. At first, a road experiment was conducted on a vehicle with brake judder. Transmission path and excitation frequency of the vibration were determined through analyzing the experimental data. Then, modal analysis on the whole structure of the steering wheel was carried out by the finite element method. In this way, its inherent frequencies and modes could be obtained. In order to verify the accuracy of the finite element model, the modal experiment was carried out and its results were compared with the simulated one. Sensitivity analysis and optimization design were carried out on the fixation support of the steering wheel by using Optistruct in Hyperworks. In this way, the inherent frequency of the whole structure could avoid the excitation frequency. Finally, an experimental verification was also carried out on the vehicle, and the results show that the vibration acceleration value of the steering wheel reached the allowable value. The technique for minimizing vibrations of the steering wheel is feasible in this paper. [ABSTRACT FROM AUTHOR]

In the paper a novel automatic seismic signal segmentation procedure is proposed. This procedure is motivated by analysis of real seismic vibration signals acquired in an underground mine. During regular mining activities in the underground mine one can expect some seismic events which appear just after the mining activity, e.g. blasting procedures, provoked relaxation of rock and some events that are unexpected, like natural rock burst. It often happens that, during one signal realization, several shocks (events) appear. Apart from two main sources of events (i.e. rock burst and blasting), other activities in the mine might also initiate seismic signal recording procedure (for example machine moving nearby the sensor). Obviously, significance of each type of recorded signal is very different, its shape in time domain, energy and frequency structure (i.e. spectrum of the signal) are different. In order to recognize these events automatically, recorded observation should be pre-processed in order to isolate a single event. The problem of signal segmentation is investigated in literature, several application domains might be found. Although, there are just a few works on seismic signal segmentation. In this paper we propose to use a time-frequency decomposition of the signal and model each sub-signal at every frequency bin using statistical methods. Narrowband components are much easier to search for so called structural breakpoint, i.e. time instance when properties of signal significantly change. It is obvious that simple energy-based methods applied to raw signal fail when one event begins before the previous one relaxed. In order to find beginning and end of a single event we propose to use measures based on empirical quantiles estimated for each sub-signal and, finally, aggregate 2D array into 1D probability vector which indicates location where statistical features has switched from one regime to another one. The proposed procedure can be applied in order to improve time domain isolation of single event for the case, when duration of signal acquisition is longer than duration of the event or to isolate single event from sequence of events (recorded for example during blasting). [ABSTRACT FROM AUTHOR]

Preventive maintenance (PM) and condition-based maintenance (CBM) are two dominant maintenance policies in industrial applications. Inspection activities are the foundation of PM and CBM policies as to provide the operating information of system through processing the collected vibration data. Age based replacement is one of the most used preventive maintenance policy aiming at avoiding unplanned downtime and higher failure loss. This paper proposes a joint optimal policy of inspection and age based replacement based on a three-stage failure process for a single component system. The three-stage failure process, which is closer to reality, divides the failure process of system into three stages: namely normal, minor defective and severe defective. When the severe defective stage is identified, maintenance action is carried out immediately. The system is replaced once it reaches certain age. However, two potential actions are considered and analyzed in this paper when the minor defective stage is identified: halving the subsequent inspection interval or replacing the item immediately. As inspection may not be perfect because of the complexity of plant items, both perfect and imperfect inspection cases are considered. Finally, a case study is presented to demonstrate the efficiency of the proposed models. [ABSTRACT FROM AUTHOR]

Roller bearings are widely used elements in rotary machines. How to monitor the working conditions of roller bearings are focus study in the world. Monitoring the vibration signals of roller bearings is important indirect mean for that they reveal the characteristics and feature of roller bearing faults. Therefore, monitor the vibration signals and diagnose the working states of roller bearings are widely used to ensure the safety operation of the machines. This paper studies a novel roller bearing faults discrimination method with harmonic wavelet packet and Multi-classification Relevance Vector Machine (MRVM). Indeed, the fault discrimination is a pattern recognition process including feature extraction and faulty patterns recognition. Therefore, this paper collects vibration signals and decomposes them with harmonic wavelet packet. After the wavelet coefficients of each node are available, compute the vector energy by corresponding coefficients. The feature vector is prepared after the vector energy has been standardized. With MRVM, the paper proposes three fault discrimination methods in order to identify good bearing, bearing with inner race fault, bearing with outer race fault and bearing with roller fault. The Decision Tree (DT) model, One Against Rest (OAR) model and One Against One (OAO) model are used to propose the classification methods respectively. The proposed OAO model is simplified in order to improve the computation efficiency and simplify the architecture of the model. Finally, capture the vibration signal from the roller bearing stand of electric engineering lab and the roller bearing fault simulation stand QPZZ-II to illustrate the proposed methods. The proposed feature extraction method with harmonic wavelet packet is compared with conventional wavelet packet. With the previous feature vectors, the accuracy and efficiency of the three fault discrimination methods are compared. The accuracy and efficiency of three fault discrimination methods are compared under different conditions including developing faults, noise involving and several faults developing simultaneously. Experiment results show that the proposed feature extraction method is more effective than conventional method and the simplified OAO-RVM model possess the best fault discrimination accuracy and DT-RVM model possesses the better computation efficiency. [ABSTRACT FROM AUTHOR]

This paper concerns a global stabilization problem for an n-TORA (Translational Oscillator with a Rotational Actuator) system which consists of n carts connected to the fixed walls and each other by n+1 linear springs with each cart having an eccentric rotational proof-mass actuator moving in the horizontal plane. First, this paper derives the motion equation of the n-TORA system. Then, by using Lyapunov stability theory and physical properties of mechanical parameters of the n-TORA system, this paper proves that the global stabilization of the n-TORA system can be achieved by the PD control of the angle of the rotational proof-mass of each TORA. This paper presents numerical simulation results for 2- and 3-TORA systems to validate the result of the global stabilization. [ABSTRACT FROM AUTHOR]

Temperature field has serious effects on the accuracy of rubbing acoustic emission (AE) source localization in a thin-walled cylinder structure, but it is difficult to explore the functioning mechanism through experiments. This paper aims to propose a thermos-elastic coupling simulation procedure to reveal the effect of the uniform temperature and non-uniform temperature field on the propagation characteristics of AE waves. To obtain the behaviors of guiding wave in the thin-walled cylinder, an efficient numerical simulation tool for AE wave propagation modeling is explored. The numerical results of AE propagation in a plate are compared with the experimental data. Then the semi-analytical finite element method is introduced to calculate the characteristics of multi-modal and dispersion. To remove the unwanted reflections from boundaries generated by the numerical simulation, a methodology combined with the infinite element and Rayleigh damping is presented. Consequently, several AE wave propagation simulations are carried out respectively, including the model with the uniform temperature in a range of 20-700 °C, and the non-uniform temperature field with the temperature of the central region, 649 °C. On the basis of the modeling and evaluation results, both the peak-to-peak amplitude and arrival time versus temperatures are summarized and analyzed. The validation results demonstrate that the proposed approach could be used efficiently to research rubbing AE source localization applications with a high degree of accuracy. [ABSTRACT FROM AUTHOR]

The sensitivity of human hearth's rhythm to the fluctuations of Earth's local magnetic field is analyzed in this paper. Data collected during the long-term project of heart-rate variability (HRV) data from 17 female volunteers were used to correlate to measured fluctuations of Earth magnetic signals. Magnetic signals are collected utilizing the first global network of GPS time stamped detectors designed to continuously measure magnetic signals that occur in the same range as human physiological frequencies such as the brain and cardiovascular systems. [ABSTRACT FROM AUTHOR]

In order to calculate accurately the stress and the deformation conditions of the closed impeller of centrifugal pumps in the flow field, "direct-calculation method" and the ANSYS Workbench-based finite element method are separately used to calculate the maximum stress that the impeller bears and the strength check of it have been proceed. This paper has made a comparative analysis between the two methods, and it is shown that the finite element analysis method can more comprehensively show the stress concentration, whereas the traditional method is more focused on the average of checking. Therefore, in terms of the results, it is suggested that in addition to the traditional direct-calculation method, modern simulation software such as the finite element method should be used for the proofread of the impeller in the industry, in order to improve the running safety and the reliability of the closed impeller of centrifugal pumps. [ABSTRACT FROM AUTHOR]

Structural vibration control technique is an appropriate and acceptable method to control structural vibration condition and dissipate structural vibration energy during severe earthquakes and violent winds. Metallic dampers are verified to be stable and effective for passive control by many scholars and engineers. Low-yield-point (LYP) steel provides a promising prospect for energy dissipation dampers widely applied in structural engineering practice. Experimental study was conducted on a novel rhombic steel plate damper in former research and numerical simulation of the hysteretic behavior of rhombic dampers was performed in this study. Mechanical performance and implementation of the novel rhombic steel plate damper is briefly introduced in this paper. The hysteretic behavior of the novel rhombic steel plate dampers made of three types of steel was investigated by testing and finite element method. It is concluded that the yield strength enhancement of the rhombic steel damper made of LYP steel is substantial. The numerical simulation results of the hysteretic behavior of the rhombic steel plate damper are similar to the experimental results for these three types of steel. The energy dissipation capability of rhombic LYP steel dampers is excellent and adequate to be used in passive control strategy for civil engineering structures. [ABSTRACT FROM AUTHOR]

This paper proposes a method of analyzing distinct modal characteristics to obtain accurate sensitivity of natural frequencies and coupled modes to system parameters of multi-stage planetary gears. A purely rotational dynamic model of multi-stage planetary gear system with general descriptions is established based on the lumped mass method. The vibration modes of multi-stage planetary gears are classified into overall and planet modes with unique properties. According to the modal energy distributions in multi-stage planetary gears, the natural frequencies are clustered by each dominant vibration stage. The modal properties of each cluster in the multi-stage planetary system are similar to the single-stage planetary gear system established by the associated dominant vibration stage. It is shown that, variation of gear parameters in one planet stage mainly affects the natural frequencies in the cluster associated with the same stage, while the coupling shaft parameters significantly impact the natural frequencies corresponding to the planet stage which contains the connected sun gear. [ABSTRACT FROM AUTHOR]

This paper proposed an improved virtual reference model for semi-active suspension to coordinate the ride comfort and handling stability of a vehicle. The reference model combines the virtues of sky-hook and ground-hook control logic, and the hybrid coefficient is tuned according to the longitudinal and lateral acceleration so as to improve the handling stability especially in high speed condition. The full scale vehicle model considering the heave-pitch-roll motion is presented, and the theory of hydro-pneumatic suspension with continuous adjustable damper is also illustrated. A sliding mode controller is designed to track the states of the reference model. The stability of the sliding mode control strategy is analyzed by means of Lyapunov function approach taking into account of the nonlinear damper characteristics and sprung mass variation of the vehicle. Finally, the performances of the controller are validated under three typical working conditions: the random road, speed bump road and sharp acceleration and braking. The simulation results indicated that, compared with the traditional passive suspension, the proposed control algorithm can offer a good coordination between ride comfort and handling stability of a vehicle. The designed controller could be commercially implemented in semi-active suspension systems. [ABSTRACT FROM AUTHOR]

Permanent magnet synchronous motor field oriented control system often uses dual-loop (speed and current) cascade structure, and the dynamics speeds of the two loops mismatch. The motor's mechanical and electrical subsystems have the typical multirate characteristics. Based on the multirate control theory, this paper proposes multirate input quasi-sliding mode algorithm for the speed control loop. Under the situation of the output data loss, the proposed algorithm builds the extended input vector with the output prediction information. Due to the extended input vector, the proposed algorithm reduces the system steady state chatterring, and then improves the performance of the whole system. Simulation and experimental results demonstrate the effectiveness of the proposed algorithm. [ABSTRACT FROM AUTHOR]

Amongst the robotics and autonomous systems, robot manipulators have proven themselves to be of increasing importance and are widely adopted to substitute for human in repetitive and/or hazardous tasks. In this paper, the purpose is to research on dynamic performance and motion control of robot manipulator for the more precise, crucial and critical tasks in industry. Firstly, the forward and inverse kinematics was accurately described by obtaining the link transformation matrices from each joint in robot manipulator. To find admissible solutions along the path, the workspace of the manipulator was determined by joint limit condition and validated by actual measurement. And then, the dynamic performance of robot manipulator is researched by using the forming flexible multi-body system. Furthermore, the frequency response curves are obtained by exciting vibration simulation based on vibration model, which the predicted method was validated by comparing simulation and experimental results. Finally, the control system architecture was given and the grasping process was conducted by gripper based on motion trajectory control in the workspace. [ABSTRACT FROM AUTHOR]

In this paper a novel method for informative frequency band selection for local damage detection is presented. Local damage in bearings/gearbox provides specific vibration signature, i.e. train of impulses with cycle related to fault frequency. The proposed approach is based on the α-stable distribution, which is an extension of the Gaussian one. The choice of this distribution is motivated by its superiority towards other distributions when modeling impulsive data. We introduce here the new selector (to select informative frequency band) which is based on the stability parameter α. Moreover we propose also the new time-frequency maps based on the measures of dependence adequate for α-stable distribution, namely autocodifference and autocovariation maps. The introduced methodology is illustrated by analysis of simulated and real vibration signals from heavy-duty rotating machinery. The results prove that proposed approach allows detection of multiple damages in signal and location of informative frequency band related to these damages. Moreover the analyzed examples indicate the α-stable distribution approach for some cases can give better results in contrast to the classical methodology based on the spectral kurtosis. [ABSTRACT FROM AUTHOR]

This paper considers the longitudinal coupled vibration of an elastic bearing concrete pipe pile with the saturated soil. The outer and inner saturated soil are governed by the dynamic consolidation theory originally presented by Biot. The governing equations of soil are transferred to ordinary differential equations by Laplace transform. The volumetric strain and pore pressure of soil are obtained by directly solving the coupling equations of soil without introducing potential functions. The analytical expressions of the displacements and shear stresses of the soil are then obtained. The pile response is derived on the basis of 1D elastic theory and the perfect contacts between the pile and soils. The displacement and velocity of the pile in time domain are obtained by using numerical inverse transformation. Selected numerical results are presented to portray the influence of the existences of soils, pile geometry and dynamic permeability coefficients of soils on the vibration characteristics of the pipe pile. At last, the displacement response between a pipe pile and solid pile are compared. [ABSTRACT FROM AUTHOR]

This paper presents a topology optimization method to design the optimal layout of Constrained Layer Damping (CLD) material in structures subjected to harmonic excitations or stationary random excitations. A finite element model is used to describe the dynamic performances of the CLD structure. Since energy dissipation arises only from the viscoelastic (VEM) layer, the modulus of elasticity of the VEM layer is complex. The complex mode superposition method is employed to calculate the steady-state response of the CLD structure under harmonic excitations. According to Pseudo-Excitation Method (PEM), the vibration analysis of stationary stochastic excitations can be transformed to the analysis of harmonic excitations. The minimization of frequency response at specified one point or several points in structures are selected as optimization objective. The Solid Isotropic Material with Penalization (SIMP) method is adopted to interpolate the CLD material. The sensitivity is derived by means of the adjoint variable method which is more efficient than the direct variable method. The Method of Moving Asymptote (MMA) is used to search the optimal layout of CLD material on structures. Numerical examples are given to illustrate the efficiency and verification of the proposed approach. [ABSTRACT FROM AUTHOR]

Regenerative chatter is an unstable form of self-excited vibration in the machining process, and it is one of the main obstacles which limit the productivity and the surface quality of the component. This paper investigates the effect of 2-D vibration assistance on high frequency regenerative chatter in the micro milling process. External vibration is applied on the workpiece in a range of frequencies and amplitudes using the piezoelectric actuators. The chatter vibration is monitored using the sound pressure signal measured by the microphone. The chatter amplitude with vibration assistance in 1-D (feed or normal direction) and 2-D is studied. The effect of the frequency and amplitude of the vibration assistance on chatter amplitude is analyzed. It is concluded that the vibration assistance is able to effectively attenuate the high frequency chatter by modifying the dynamic chip thickness and adding process damping in the micro milling process. [ABSTRACT FROM AUTHOR]