Journal of Engineering and Thermal Sciences
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Rapid optimization of the sound insulation performance of magnesium alloy dash panel based on periodic sound-package structure
Get PDFIn order to improve the sound insulation performance of the magnesium alloy dash panel at medium and low frequency, the FE-SEA hybrid method was employed to numerically calculate the sound transmission loss of the dash panel, which was subsequently compared with the experimental result and eventually proved the feasibility of this numerical method. Subsequently, through analysis on the modal contribution, the speed vibration modes at the natural frequencies were extracted, and the key sound-transmission areas were identified. Through combined considerations of both the vibration-isolating and the sound-absorbing characteristics, the parallel periodic sound-package structure was proposed, whose basic theory was deduced by reference to phononic crystals. Moreover, a reverberation box was designed and manufactured so as to test the sound transmission loss of specimens with small sectional dimensions, such as the periodic sound-package structure, and the reliability of the predicting method was simultaneously verified. Additionally, manually weaving the parameters of the periodic sound-package structure could maximally improve its sound insulation characteristic, and changing the traditional parallel structure into the staggered and skewed laying manner could upgrade the vibration-isolating and sound-absorbing effect. Finally, this noise-reducing scheme was applied to the magnesium alloy dash panel, where in the medium and low frequency noise was rapidly optimized
Nonlinear dynamics modeling and analysis of disc brake squeal considering acting process of brake force
Get PDFDisc brake squeal of automobile is one of the hottest and most difficult issues concerned by automobile manufacturers and researchers. Considering the acting process of brake force, a simplified nonlinear dynamics model is developed in this paper. The nonlinear dynamics equations are set up and solved by theoretical method and numerical calculation. By studying the effects of key parameters on the system’s behavior, the mechanism of brake squeal are analyzed and discussed. The results indicate that the state of system is more sensitive to the fluctuation of brake force than the variation of the negative slope of friction coefficient against the relative velocity between pad and disc. The dynamic characteristics of brake system are greatly connected with the components stiffness. The brake system may become weakly stable and easily produce brake squeal when tangential contact stiffness, normal contact stiffness and connection stiffness satisfy a certain relationship
Modal analysis of cable-tower system of twin-span suspension bridge
Get PDFA three-dimensional finite element model is developed in order to analyze the free vibration characteristics of the tower-cable system of a triple-tower twin-span suspension bridge during the construction phase and right after the erection of the main cable. The dynamic characteristics of each component in the tower-cable system, the isolated side span, main span cables and free-standing towers, are first analyzed separately. The natural frequencies and the vibration modes of the isolated side span and the main span cables obtained from the finite element analysis closely matched the analytical solution from the linear free vibration analysis and verified the validity of the finite element model. The local natural frequency and global natural frequency were defined to categorize the characteristics of the free vibration. The calculation results show that not only does the tower-cable system maintains the information on the modal characteristics of each component in the system, but it also contains its own unique modal characteristics and other important information about the dynamics characteristics of the system. At lower natural frequency range, the swinging motion and in-plane motion are uncoupled. The coupled modal information of the towers and the cables are separated into two groups based on the natural frequencies of the vibration of the main component of the tower-cable system. Some additional natural frequencies and vibration modes are obtained from the finite element analysis depicting the dynamic interaction between the towers and the cables. Furthermore, it is observed that the lower order modes of side span cables couple with the higher order modes of the main span cables. Either in phase or out of phase, local or global modes, the tower-cable system exhibits many new coupled mode combinations that reveal useful information
Earthquake response and effect of adjacent structures founded at different depths
Get PDFThis paper deals with the earthquake response and effect of adjacent structures founded at different depths. In this paper, the dynamic time history analyses were performed using structural analysis program developed in this research, both the structure and the soil were represented by plane stress or plane strain elements, with response quantities to be interpreted from the stresses obtained at element centers. The elasticity modulus of the ground is varied. Just like the modification of elasticity modulus, the varying relations of inertia have a strong influence on the section forces within the structures. Two structures with different foundation depths and the same foundation levels were represented by the three different systems. The interaction of the proposed method and programs was demonstrated and discussed with numerical examples. As a result, the greatest difference between two structures could be observed in the shallow and deep foundations. Concerning the plane stress model, the calculation of section forces reveals that the greatest difference was also in the shallow and deep foundations. If case of both structures having shallow foundations, the interaction was small and negligible. If one structure is shallow and the other one deep, then the interaction renders the forces in one structure 20 % smaller than those in a single shallow structure, If the adjacent structures have the same deep foundation level, then due to interaction the forces in one structure are 25 % larger than those in a single deep structure
Fracture toughness prediction of eutectic ceramic composite considering damage effect and transformation toughening
Get PDFThe toughness of eutectic ceramic composites is obtained by multiple toughening mechanisms involving crack-bridging and pull-out of rod-shaped eutectics, as well as stress-induced transformation toughening. In the loading procedure, damage will emerge in the rod-shaped eutectic. Firstly, the damage variables are defined by the microstructure of rod-shaped eutectic with aligned nano/micro- fibers. The maximum strain criterion is used for determining the loading function. According to the attenuation characteristic of eutectic rigidity, the critical fracture stress of the damage rod-shaped eutectic is obtained by damage variable maximizing. Secondly, we imagine the bridging load carried by the damage rod-shaped eutectics in the crack wake to produce a crack-closing force. The latter reduces the stress intensity in front of the crack. The pull-out work is given by the integral of the frictional force over the pull-out length. Bridging toughening mechanism and pull-out toughening mechanism of damage rod-shaped eutectics are constructed. Thirdly, defining a parabola transformation yield function, the transformation plastic strain increment is gotten by transformation plastic potential function. The screening impact of transformation particles for mixed-mode I-II crack is gained. And lastly, based on the crack-bridging and pull-out of rod-shaped eutectics, as well as stress-induced transformation toughening mechanisms, the added toughness scale with the inherent matrix toughness, the theoretical formula of fracture toughness of the eutectic ceramics composite is determined. The result shows that the fracture toughness is dependent on the aspect ratio of rod-shaped eutectic: the fracture toughness is minimum as the aspect ratio is equal to 0.3 and maximizing when the aspect ratio is equal to 14. The damages inside eutectics enlarge the incremental range of variation of the fracture toughness. The transformation particles exert a slight influence on the fracture toughness due to its less content
A well-balanced unsplit finite volume model with geometric flexibility
Get PDFA two-dimensional finite volume model is developed for the unsteady, and shallow water equations on arbitrary topography. The equations are discretized on quadrilateral control volumes in an unstructured arrangement. The HLLC Riemann approximate solver is used to compute the interface fluxes and the MUSCL-Hancock scheme with the surface gradient method is employed for second-order accuracy. This study presents a new method for translation of discretization technique from a structured grid description based on the traditional (i, j) duplet to an unstructured grid arrangement based on a single index, and efficiency of proposed technique for unsplit finite volume method. In addition, a simple but robust well-balanced technique between fluxes and source terms is suggested. The model is validated by comparing the predictions with analytical solutions, experimental data and field data including the following cases: steady transcritical flow over a bump, dam-break flow in an adverse slope channel and the Malpasset dam-break in France
Improving pitch and yaw motion control of twin rotor MIMO system
Get PDFIn this paper, a fuzzy logic controller approach is presented for twin rotor multi-input-multi-output (MIMO) system in order to improve the control of pitch and yaw motions under hovering conditions. Twin rotor MIMO system resembles a helicopter model in some common aspects like cross coupling of pitch and yaw motions. The proposed approach is compared with another control strategy by simulations for a nonlinear two degrees of freedom twin rotor model. Set point reaching and trajectory tracking behaviours of the TRMS are analysed by time and step response characteristics. Results of time and step responses indicate that fuzzy logic controller improves set point reaching and trajectory tracking performance of the closed loop system
Development of nanostructured Al/SiO2 composite film for vibroisolation applications
Get PDFThis paper presents the investigation of surface morphology, wetting and chemical properties of the nanocomposite Al/SiO2 film, which can be used as a shock generated vibration isolator for microelectromechanical devices. AFM analysis shows that two-step prepared Al/SiO2 composite film has regular nanoisland type surface topography provided by SiO2 nanospheres. EDS analysis confirms that SiO2 nanospheres are well distributed on the substrate. Carbon found in the composition of composite film can be attributed to the residuals of organic compounds used for the preparation of SiO2 nanospheres. FTIR analysis confirms formation of the Si-O and Si-OH functional groups and the presence of –CH3 stretching group can be related to the improved non-wetting behavior of the composite
Noise and vibration assessment of permanent-magnet synchronous motors based on matching pursuit
Get PDFThis paper presents a noise and vibration assessment scheme for the elevator permanent-magnet synchronous motors (PMSMs) based on matching pursuit (MP) with carefully selected atoms. The atomic dictionary is developed by considering of the complication of electromagnetic noise and vibration of the elevator PMSMs. After identifying the natural frequencies by modal testing and computing the characteristic electromagnetic frequencies of the PMSMs, the impulse energy ratio based on transient components, which are extracted by projecting on the selected atoms based on the MP method, are computed and used to assess the machines. The assessing results indicate that the transient components can accurately represent the electromagnetic impulse since the distorted magnetic fields and the features are robust for quality inspection of the elevator PMSMs
An analysis of the equipotential surface waves of the Earth’s gravity field
Get PDFA detailed analysis is performed on the influence that the celestial bodies have on the equipotential surface of the Earth’s gravity field. The necessary background is developed in order to progress a new more intelligent methodology of estimating the influence that the celestial bodies have on the geodetic measurements. Previous studies demonstrate that this impact strongly depends on the elasticity of the solid Earth. It is also unequal on different equipotential surface waves. Some results of current investigations are presented, which demonstrate the waves of the Earth’s gravity field influenced by the celestial bodies. The assessment of changes in an equipotential surface is required when reducing the measurement data into a common coordinate system of a definite epoch