Journal of Engineering and Thermal Sciences
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Effective reduction of stiffness at peak frequency in hydraulic engine mounts by using magneto-rheological fluids
Get PDFHydraulic engine mounts are generally used in aerospace and automotive applications for the purpose of cabin noise and vibration reduction. By careful selection of hydraulic mount design parameters, at a certain frequency, namely the notch frequency, the dynamic stiffness will be smaller than the static stiffness and cabin vibration and noise reduction is provided at that frequency. Literature review indicates that in all previous designs of hydraulic engine mounts the dynamic stiffness increases after the notch frequency. This phenomenon undesirable because of the increase in the force transmitted to the cabin. This paper proposes a new hydraulic engine mount that uses two working fluids. The new design has two notch frequencies and two peak frequencies. In this study, effective reduction of the peak frequencies has been demonstrated by using a controllable fluid as one of the working fluids and a non-controllable fluid as the second working fluid. As a result, one can obtain a hydraulic engine mount design with only one notch frequency but having no peak frequency. The new hydraulic engine mount design and its mathematical model are presented in detail and some discussions on the simulation results are provided
Non-iterative mode shape expansion for three-dimensional structures based on coordinate decomposition
Get PDFThe direct mode shape expansion method is an iterative technique, one can conclude that the convergence performance maybe challenged when applied to three-dimensional structures. In addition, mode shape values at different DOFs (degrees-of-freedom) sometimes are not in a same order of magnitude, which will produce much error for the estimation of small values of unmeasured mode components. Therefore this paper proposed a non-iterative mode shape expansion method based on coordinate decomposition technique. The advantage of coordinate decomposition is that the unmeasured components of mode shape values could be estimated with different weighting coefficients, even in a physical meaningful interval. Numerical studies in this paper are conducted for a 30-DOF cantilever beam with multiple damaged elements, as the measured modes are synthesized from finite element models. The numerical results show that the approach can estimate unmeasured mode shape values at translational and rotational DOFs in x, y and z directions with different weighting coefficients, respectively; and better mode shape expansion results can be obtained when proper constraints are employed. A numerical three dimensional structure is also investigated, and results indicate that the estimation of unmeasured components can be improved by imposing reasonable constraints based on the coordinate decomposition technique, even only translational DOFs of two diagonal nodes of the first floor are measured
Tribological adhesion of particles in acoustic field
Get PDFThis paper investigates interaction between two particles in acoustic field. It is shown that additional oscillating movements of particles occur as a result of plain acoustic wave action. This sufficiently increases the probability of collisions between particles. Micro-displacements in the collision zone help to remove various pollutants, oxidation products and adsorbed gas molecules from surfaces of particles. Strong adhesive bonds are formed in the contact area between the particles
A survey of Hopf bifurcation analysis in nonlinear railway wheelset dynamics
Get PDFThis article attempts to analyze the Hopf bifurcation behavior of a railway wheelset in the presence of dead-zone and yaw damper nonlinearities. A model that is more precise than Yang and Ahmadian is investigated. Using Bogoliubov-Mitropolsky averaging method and critical speed, the amplitude of the limit cycle in the presence of the mentioned nonlinearities is taken into consideration. To solve these nonlinear equations analytically, the integration interval has been divided into three sub-domains. Two-dimensional bifurcation diagrams are provided to illustrate the mechanism of formation of Hopf bifurcation. These diagrams can be used for design of stable wheelset systems
Analysis of damage characteristics for cracked composite structures using spectral element method
Get PDFStructural health monitoring of composites, due to their wide use, has attracted more attention. It is essential to study variations of structural dynamic characteristics caused by the damage. A cracked spectral element model is developed to study dynamics of cracked composite structures. Taking crack location as a boundary, the cracked composite beam is separated into two parts, which are connected by a spring. The spring, whose flexibility can be obtained by laws of fracture mechanics, is used to model axial-flexural coupling effect due to asymmetry of the crack. Calculated natural characteristics are in good agreement with the results of conventional finite element method. Lamb wave reflection and transmission at the crack location are also analyzed to verify the model. Formulations are derived to calculate power reflection and transmission of wave modes. The results indicate that power reflection/transmission ratio of a single mode is monotonic, which may provide some quantitative foundations for structural health monitoring
A study of selected properties in high dispersion padding welds produced in machine elements
Get PDFThis paper presents selected laboratory research results concerning the production of high dispersion padding welds that were made from Castolin EnDOtec DO390N P pulverized nanowire on acid resistant 0Hl8N9 steel using laser technology. The analysis of the microstructure showed a high dispersion of the micro- and nano-structure where the phase particles of large volume carbide (MC), M23(BC) boron carbides, and M2B borides are distributed in the fine-grained iron matrix. The study found extensive differentiation of chemical composition in the micro-areas and extensive non-homogeneity of the microstructure due to repeated laser melting of the padding weld layer. Its surface hardness was 68-72 HRC and the cross-sectional microhardness was as high as 990 - ll00 HV0, l
Investigation of dissipative properties of liquid crystalline lubricant layer
Get PDFThis work aims to investigate vibration behavior of rotating roller - a fixed segment friction pair lubricated with pure motor oil and motor oil containing liquid crystal (cholesteryl oleate) additive. Experiments were performed under boundary friction conditions. Mechanical vibrations were registered through the processing and analysis of radial vibration data of the segment, obtained for each lubricant composition under constant roller speed. It is established that vibration level of the segment is reduced at the presence of liquid crystal additive. Theoretical investigations of load-carrying properties of individual layered liquid crystal in a lubricating gap of the film lubrication bearing show a strong increase in load as compared with the equivalent viscous lubricant
Correlation of shear-wave velocities and cone resistance of quaternary glacial sandy soils defined by Seismic Cone Penetration Test (SCPT)
Get PDFThe derivation of dynamic geotechnical parameters of soil are of primary importance in designing specific structures. Direct measurements are expensive and time-consuming. In this study the correlation between the seismic wave velocities and cone resistance was derived from seismic cone penetration testing (SCPT) of Quaternary glacial sandy soils in Lithuania. The close relationship was obtained for sandy soils indicating wide range of cone resistance and seismic wave velocities. The correlation is as high as R = 0.80. The derived regression equation could be reasonably used in assessing dynamic geotechnical and seismic parameters in Lithuania and other territories characterized by similar geological conditions using conventional cone penetration testing (CPT) method. It enables consistent geotechnical and seismic zoning of sandy soils
Experimental analysis of power harvesting on vehicle vibration using smart piezoelectric materials
Get PDFIn this paper the experimental analysis for power harvesting from mechanical vibration on a vehicle has been studied by using QuickPack smart materials with piezoelectric effect. The finite element ANSYS method (ANSYS FEM) was applied to explore the required mechanical structure, modal and harmonic analysis, and electrical feature, i.e., output voltage, admittance. The experimental platform consists of a shocker and a lever, which simulated a periodical oscillation on vehicle vibration, for evaluating conversion efficiency from mechanical energy to electrical energy. During loading experiments of power generation, the electromechanical coupling characteristics of smart materials were investigated via a proposed testing circuit. Also, various electrical output loadings were specified within resistance of 5~3000 kΩ. Through the experiment analysis, the power harvesting test with a buck converter at the output terminal was processed to obtain the spectrum analysis of output voltage within the vibrating frequencies below 200 Hz, controlled by the electromagnetic shaker. Based on the comparison between ANSYS FEM and spectrum analysis, the optimal results of mechanical oscillating quantities have been verified by the maximum output voltage for the QuickPack NQ45N material. Hence, the optimum power harvesting of the smart material has the maximum output power of 0.18 mW at 26-Hz-vibration on a vehicle
Efficient modeling and simulations of Lamb wave propagation in thin plates by using a new spectral plate element
Get PDFA new spectral plate element is presented for modeling selectively or simultaneously the symmetric and/or anti-symmetric modes of Lamb waves propagating in thin plate structures. The Legendre polynomials and the extended form of the displacement field are used in the formulation. The diagonal mass matrix is obtained by using a simple method with less computational effort. Detailed derivations are provided. Comparisons with existing results are performed to validate the formulations as well as the written programs. Numerical calculations have been carried out for thin aluminum plates with and without damages by using the proposed spectral plate element. Comparisons reveal that the proposed spectral plate element is more effective than the spectral plate element based on Chebyshev polynomials and the 3-D spectral finite elements with the same order of Legendre polynomials as the shape functions