Journal of Engineering and Thermal Sciences
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Study of experimental modal analysis method of machine tool spindle system
Get PDFDynamic properties of the machine tools especially the spindle systems contribute greatly to the reliability of the machine tools. The increasing use of modal analysis as a standard tool to estimate the dynamic modal parameters means that both experienced and inexperienced analysts are faced with new challenges: uncertainty about the accuracy of results. Therefore, the key requirement for experimental modal analysis is a reliable, efficient and accurate experimental method in spindle system analysis. Several processes, such as reference and response selection in modal test however would make the system identification process for structural dynamics inaccurate. To investigate the results accuracy when applying experimental modal analysis on machine tool spindle, this work hence further studied the experimental setup itself based on the reference and response selection. The reference selection and reference optimization method is developed for the accuracy and efficiency improving purpose. First, by comparing results from different reference quantity and direction test, the method to select reference points is studied. Then the modal parameters are verified by the complex mode indicator functions and finite element analysis to study the influence of the reference on the modal analysis accuracy. Next, improved algorithm of response points optimization is developed based on the MAC matrix to minimize the number and location of measuring response points. Lastly, the general standard and method to select the reference and response points are put forward. The approach setting-up the experimental impact test provides reliable and accurate results and can reduce the testing time at the same time
Numerical calculation of transmission noise for the magnesium alloy cylinder head cover
Get PDFTransmission noise of the magnesium alloy cylinder head cover was researched in this paper. Firstly, the numerical calculation mode of a cylinder head cover was compared with the experimental one. Results showed that the numerical calculation model had a relatively high accuracy, and it could be used in subsequent analysis. Secondly, sound pressure inside the cylinder head cover was extracted through the four-load method and taken as the sound source. Then, it was applied in a simulation model in order to simulate transmission noise of the actual situations. Afterwards, transmission noise of the magnesium alloy cylinder head cover was compared with the aluminum alloy one. It was shown that relatively low transmission noise was generated from the magnesium alloy cylinder head cover. Meanwhile, its mass was only 0.65 times of that of the aluminum alloy one. Therefore, the requirement for low noise and light weight was achieved by the magnesium alloy cylinder head cover. Then, dynamic stresses of cylinder head covers for two materials were compared. Results showed that dynamic stress of the magnesium alloy cylinder head cover was slightly smaller than that of the aluminum alloy one. The magnesium alloy cylinder head cover satisfied the requirement for strength and had a relatively prominent comprehensive performances. Finally, sound absorption coefficient of a porous material was calculated by using the numerical simulation technology. It was also laid inside the magnesium alloy cylinder head cover to constitute a composite cylinder head cover. Transmission noise of such composite cylinder head cover was much smaller than that of the original structure. This researches provided a method for low noise and light weight design of the cylinder head cover
Automated wavelet-based damage identification in sandwich structures using modal curvatures
Get PDFRecently, damage assessment of composite structures being in operation has been one of crucial problems in industries such as aircraft, aerospace, automotive, etc. Following this, rapid development of non-destructive testing methods has been observed over the last decades. One of the promising approaches is vibration-based one, which in general is based on identification of a damage using singularities in modal shapes of vibration. The identification procedure requires application of advanced signal processing techniques, where the wavelet transform is used the most commonly. Due to the high sensitivity of wavelet-based approach to changes of parameters of an analysis, e.g. a type of applied wavelet and its order, it was decided to develop an algorithm, which allows automating this process by using multi-objective meta-optimization of the mentioned parameters. The presented approach allows selecting optimal parameters for wavelet-based damage identification procedure without neither a priori knowledge on values of wavelet parameters, nor the parameters of an optimization algorithm. The proposed approach was tested on composite sandwich structures with damaged core as well as damaged face sheets. Obtained results confirm the effectiveness of automated damage identification mainly in the context of the high convergence to the optimal solution
A contrast between classical method and finite element method for calculating strength in impeller of centrifugal pump
Get PDFIn 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
Vortex signal detection method with stochastic resonance based on adaptive coupled feedback control
Get PDFThe control of stochastic resonance is the key to its application. A feedback method is proposed to control the generation of stochastic resonance with coupling, and then enhance resonance effect with the optimization of control parameters. The method is applied to detect vortex signal. Artificial fish swarm algorithm is used to adjust the control variables adaptively, thus the optimal control of the coupled bistable stochastic resonance is realized. Numerical simulation and experimental results manifest that by this means the resonance effect can be enhanced effectively, the signal-to-noise ratio (SNR) of vortex signal can be improved, and the vortex shedding frequency can be obtained accurately
Vibration signal simulation of planetary gearbox based on motion process modeling
Get PDFIn planetary gearbox, multiple gear pair meshing with each other and the vibration transmission paths from gear meshing points to the fixed sensors are time-varying. Therefore, fault diagnosis of the planetary gearbox is more difficult compared to that of fixed-axis gearbox, in which the vibration signal simulation models are very important. This paper constructs vibration signal models based on motion process modeling. This kind of modeling method is easier to understand compare with other methods which mainly based on the theory or physical laws behind the phenomena. The modeling process was presented in a step-by-step procedure according to the motion process of planetary gearbox. Frequency analysis was also implemented and comprehensive diagram was shown to help understand the result
Investigation of electrical conductivity of milk in robotic milking system and its relationship with milk somatic cell count and other quality traits
Get PDFThe scientific research was carried out at Lithuanian University of Health Sciences, Veterinary Academy, state enterprise “Pieno tyrimai”, as well as in dairy farms running automatic voluntary (robotic) milking systems in Lithuania. A total data set of 462574 cow milking records was assessed in the research. The objectives of this investigation were to evaluate the milk electrical conductivity indicator from robotic milking system and to assess the genetic correlation with the indices collected in a database of Lithuanian dairy cattle, to estimate heritability coefficient using multiple traits mixed linear model with permanent environment effects. The research has shown, that the electrical conductivity of milk ranged from 4.6 to 5.8 ms/cm in milk samples where somatic cell count did not exceed 200 thousand/ml and variation in electric conductivity of milk can be treated as one of the main parameters for cows’ health monitoring system. A high coefficient of heritability of electrical conductivity of milk (h2 = 0.512 ± 0.028; p < 0.001) and a very low coefficient of heritability of somatic cell count (h2 = 0.032 ± 0.014; p < 0.001) was determined. The results of the research have also revealed a positive genetic correlation of electrical conductivity with milk somatic cell count (rg = 0.332 ± 0.016; p < 0.001). Electrical conductivity of milk from robotic milking system can be introduced as an indicator of mastitis prevention in dairy cows and genetic selection based on this trait may be possible
A combined method of thermal and vibratory stress relief
Get PDFA combined method of thermal and vibratory stress relief (TVSR) to extend effects of vibratory stress relief (VSR) is presented. TVSR was implemented by imposing vibratory load on a workpiece at an assisted temperature. Residual stresses before and after treatment were measured using the modified layer removal method (MLRM) to evaluate the stress variations. A finite element (FE) model was developed to investigate and compare TVSR and VSR treatment on workpieces cut from a 7075 aluminum alloy plate. Thermal influence on TVSR equipment and vibratory treatment of the workpiece was analyzed using this model. Experiments were conducted to validate simulation results. Significant residual stress relief was observed in TVSR, however, effects of VSR were limited
Conversion of inhomogeneous robin boundary conditions into virtual sources for wave motions and heat conduction
Get PDFIn vibration engineering, the differential equations of wave motions and heat conduction are usually accompanied by inhomogeneous boundary conditions in practice. Boundary inhomogeneity makes the dynamics essentially nonlinear, which prevents Hilbert space from being applied for modal decomposition. To deal with this difficulty, this paper does not treat boundary inhomogeneity as a “condition”, but almost converts it into a virtual source in conjunction with homogeneous boundary. This conversion counts mostly on the Laplace-Galerkin transform, a functional tool developed in previous works. We also explore boundary topology of this virtual-source conversion, and find that its strategy is to zero the environment and simultaneously create a spatially impulsive source on the homogeneous boundary, yielding almost the same solution. In one-dimensional region, such a boundary source takes the form of Dirac delta function usually combined by its derivatives. In a sense, this paper catches how Nature really handles boundary conditions
Impact analysis of lateral damper on the ride quality of metro vehicle
Get PDFIn view of the lateral and vertical vibration problem of car body in actual operation, dynamic simulation and relevant line tests are carried out to study the impact of lateral damper on the ride quality. To facilitate comparative analysis, dynamic models of metro vehicle are set up and simulation results indicate that ride quality when using a single lateral damper is better than when using double dampers. On this basis, line comparison tests are conducted, with ride index in time domain as an indicator. Acceleration sensors are utilized to conduct lateral and vertical acceleration tests when using a single lateral damper and double dampers, respectively. Ride index of every 5 seconds at normal operating velocity is obtained after post-processing of data collected from the tests. Comparison of ride index of two adjacent stations obtained by statistics has found that, in actual operation, metro vehicle with a single lateral damper mounted on the bogie has a better ride quality both laterally and vertically than that with double dampers. Single lateral damper model can also effectively solve abnormal vibration problem of the metro vehicle