Journal of Vibroengineering
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Research on the radiation characteristics of aerodynamic noises of a simplified bogie of the high-speed train
Get PDFThis paper built a simplified bogie model including 2 axles, 2 wheel-sets and frames, and it was then installed on the high-speed train to compute the aerodynamic noise. The computational result showed that bogies made the noise of the high-speed train obviously serious, the noise near the bogie increased obviously, and the maximum sound pressure level increased by 1.3dBA. Based on Lighthill acoustic theories, this paper adopted large eddy simulation (LES) and FW-H (Ffowcs Williams-Hawking) acoustic model to compute numerical solution for the aerodynamic noise of the bogie. The aerodynamic flow behavior of the bogie and the distribution of aerodynamic noises in the far field were analyzed. Fluctuating pressure at the surface of the bogie was obtained and then combined with boundary element method (BEM) to study the aerodynamic noise sources and acoustic propagation characteristics of the bogie. Computational results showed that large eddies were in axles and wheel-sets, and axles mainly caused the phenomenon of Karman Vortex Street. When the bogie ran at the speed of 30 m/s, main frequencies were 278 Hz and 556 Hz, and the main frequency of aerodynamic drag was twice that of aerodynamic lift. In the vertical plane, longitudinal plane and lateral plane, the aerodynamic noise of the bogie had the characteristics of dipole noises. The main directions of radiation were 90° and 270°. The maximum sound pressure level was 57.3 dBA. The main direction of propagation for the aerodynamic noise of the bogie was right above and below the bogie rather than the left side and the right side of the bogie. The aerodynamic noise sources of the bogie were mainly at the second end axle and the surface of wheel-sets close to axles
Seismic fragility curves for highly skewed highway bridges
Get PDFIn this paper, a multi span concrete girder highway bridge with a 60 degree skewness is used for developing seismic analytical fragility curves for different performance level of the bridge. A detailed finite element modeling of the bridge is presented. Incremental dynamic analysis (IDA) is applied to the bridge in longitudinal direction of the bridge to capture the seismic response of the bridge incrementally. A suite of 14 earthquake ground motions with different range of PGAs are used in nonlinear dynamic analysis of the bridge. Different spectral intensity measures and PGA are studied to find the proficient intensity measure to figure out the analytical fragility curves. The results show that the Sa (1.2 T1,5 %) is the most proficient intensity measure for the current study
The impact of different processing techniques on foot parameters in adults
Get PDFThis study presents data on the application of two different processing techniques of foot parameters and the comparison of their validity and reliability in adults. Twenty-four healthy participants volunteered took part in the study. Three digital scans were obtained from each participant by one experienced investigator. The foot parameters were: Clarke index, ‘KY’ index of Sztriter-Godunov, heel angle and Wejsflog index. The parameters were identified into two ways: manually using software SolidWorks and by a new computer-aided system. The results of the Spearman's rank correlation suggest a strong positive relationship between parameters obtained from the computer-aided system and manually counted (R> 0.9). The current study suggests that computer-aided system is a practical tool for foot type assessment in adults and could be recommended for both research and clinical applications
Numerical optimization of sound pressure responses for the dash panel based on automatically matched layer and genetic algorithm
Get PDFThe sound insulation performance of the dash panel has a direct influence on the level of sound absorption of the whole vehicle. Therefore, it is necessary to adopt proper optimization strategies to optimize the dash panel and interior sound pressure response. Firstly, damping loss factor was imported into the dash panel and the coupling model of interior acoustic cavity to compute the sound pressure response of the driver. Sound pressure response had multiple peak noises in the analyzed frequency band. With the increase of the analyzed frequency, Contours for the noise of interior acoustic cavity became increasingly dispersed. Secondly, reverberation chambers on both sides were coupled with the dash panel respectively to establish AML model. In this way, the computational transmission loss would be more consistent with the actual situation. AML method can directly obtain transmission loss without extracting the transmission sound power to compute transmission loss through relevant formulas. In reported papers, there are big differences between simulation and experiment in the low frequency because it is difficult to simulate the real boundary conditions. The computational results of this paper were more consistent with experimental results in the whole frequency band, which indicated that it was more effective to use AML method to compute the transmission loss of the dash panel. Then, a sound package was applied to the dash panel to conduct parametric analysis. Results showed that the thickness of the sound-absorption layer could effectively improve transmission loss over 250 Hz. When the thickness of the sound-absorption layer was 15 mm, transmission loss was relatively optimal. In addition, the thickness of the air layer had little influence on transmission loss. Finally, genetic algorithm was also used to optimize the parameters of sound package of the dash panel. Results showed that the optimized dash panel had a higher average transmission loss and total mass, and the average sound pressure response of the driver also decreased. Additionally, the transmission loss and sound pressure response of the driver optimized by genetic algorithm at each frequency point were improved in the analyzed frequency band to obtain a low-noise and lightweight dash panel
Numerical research on aerodynamic radiation noises of alternators in vehicles
Get PDFTo 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
Numerical simulation and optimization for the vibration of the seed metering device based on a novel ML-IGA method
Get PDFThe reported researches only analyze vibration parameters of the seed-metering device. However, they do not adopt any algorithm to conduct a multi-objective optimization for the vibration performance of the seed-metering device. In this paper, the vibration of the seed-metering device is numerically computed firstly, and the correctness of the computational model is validated by experimental test. Then, some parameters including the plate thickness, inclination angle, excitation source position and supporting leg thickness of the seed-metering device are studied. In this way, those parameters which have serious impacts on the vibration are obtained. Therefore, the vibration performance is tried to optimize using these parameters as the design variables. This paper proposes a novel multi-layer immune algorithm based on genetic algorithms (ML-IGA). In order to further verify validity of the novel ML-IGA model for optimizing the vibration of the seed-metering device, it is compared with the traditional GA model and PSO-GA model. When the iteration of ML-IGA model was conducted to the 156th generation, the predicted error is smaller than the set critical error. Compared with other two kinds of algorithms, the optimized time is reduced. Regarding optimization of the GA model, the vibration amplitudes are increased by 2.49 % and 4.22 % respectively. Regarding optimization of the PSO-GA model, the vibration amplitudes are increased by 9.74 % and 6.024 % respectively. Regarding optimization of the ML-IGA model, the vibration amplitudes are increased by 17.34 % and 6.78 % respectively. Obviously, structures with better performance can be obtained through using the novel ML-IGA model
Response analysis of cracked structure subjected to transit mass – a parametric study
Get PDFThis work is focused on determining the response of a multi-cracked structure in the presence of different types of cracks vibrated due to a transit mass. The open transverse and inclined edge cracks of random crack depth are present at various locations of the cracked structure. The mass is moving on the beam at the different critical speeds of the structure. Runge-Kutta fourth order method is employed to evaluate the response of the structure numerically. The significance of different factors like the magnitude of the moving mass, moving speed, crack depth, crack inclination angle and their effects on the response of the deteriorated structure are investigated. Numerical analyses with numerous examples are carried out and validated the results with finite element analysis (FEA) and experimental investigations
Structural multi-damage identification based on strain energy and micro-search artificial fish swarm algorithm
Get PDFA two-stage damage detection method based on strain energy and micro-search artificial fish swarm algorithm (MSAFSA) is presented for solving structural multi-damage problem. First, structural modal strain energy and energy dissipation process are analyzed and an improved modal strain energy dissipation ration index (IMSEDRI) is proposed to preliminarily detect suspected damage elements. Then, artificial fish swarm algorithm (AFSA) is used to identify damage extent of suspected damage elements. In general, the search efficiency of a basic AFSA isn’t very efficient for the search procedure. So, a micro-search artificial fish swarm algorithm is presented in this paper. The simulation results demonstrate that the damage detection method can estimate the damage locations and extent with good accuracy, and the calculated results of the proposed MSAFSA are obviously superior to those of both the basic AFSA and the AFSA with visual-step change strategy
Chatter suppression in boring with tool position feedback control
Get PDFRegenerative self-excited vibrations (chatter) often occur in boring operation due to low stiffness of a slender cantilever holder of a tool. These vibrations lead to significant defects of a machined surface and cutting tool damages. The new chatter suppression method is proposed in the paper. Displacement signal measured in the direction which is orthogonal to machined surface is used for generating a control action in the feed direction. Linear proportional control law is applied. Mathematical model of boring process dynamics with control has been developed for validation of the proposed method efficiency and searching better values of feedback gain
Structural response and optimization of airtight blast door under gas explosion load
Get PDFAirtight blast door, as one of the key components of a rescue device or a ventilating device in underground coal mine, which can not only guarantee the normal operation ventilation system, but also can prevent the propagation of shock wave and invasion of toxic gases. Therefore, high structural stability and safety is fundamental when designing a door. An airtight blast door was developed and optimized based on static analysis and topological optimization, and dynamic response analysis of the optimized airtight blast door subjected to gas explosion load was conducted using a novel approach proposed in this paper-the FEM-SPH contact algorithm. Results showed that the main component weight of this kind of door is 27.4 % smaller than the original one without reducing the blast and impact behavior, the maximum displacement and stress of the optimization door obtained by FEM-SPH contact algorithm (dynamic response) are much larger than those using static mechanical analysis. The FEM-SPH contact algorithm and typical optimization method as well as the example presented in this paper are helpful for the original design and optimization of other products. Some conducive suggestions were recommended based on the simulation results