• Tribology and Lubricants
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• v.39 no.3
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• pp.102-110
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• 2023

This study aims to quantify the variation in the performance of a tilting pad journal bearing (TPJB) owing to the elastic deformation of its pad. To this end, we first defined a parameter, "elastic preload", and predicted the changes in the performance of the TPJB, as a function of the preload amount. We used the iso-viscosity Reynolds equation, which ignores the temperature rise due to viscous shear in thin films, and the resultant thermal deformation of the bearing structure. We employed a three-dimensional finite element model to predict the elastic deformation of the bearing pad, and a transient analysis, to converge to a static equilibrium condition of the flexible pads and journal. Conducting a modal coordinate transformation helped us avoid heavy computational issues arising from a mesh refinement in the three-dimensional finite element pad model. Moreover, we adopted the Hertzian contact model to predict the elastic deformation at the pivot location. With the aforementioned overall strategy, we predicted the performance changes owing to the elastic deformation of the pad under varying load conditions. From the results, we observed an increase in the preload due to the pad elastic deformation.

• Tribology and Lubricants
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• v.5 no.1
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• pp.64-68
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• 1989

The dynamic characteristics of the annular pressure seal employed in pump have been theoretically deduced with consideration of the effects of elastic deformation due to the centrifugal stress. The deformation of the shaft is governed by the linear theory of elasticity. The results derived herein considering the elastic deformation are compared with the previously published author's results in the stiffness and damping coefficients.

• Journal of the Earthquake Engineering Society of Korea
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• v.3 no.4
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• pp.95-100
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• 1999

Dynamic measurements are used rather sparingly to determine the elastic modull of rock cores and modulus values are not much utilized in design practice. The reason seems to result from the general perception that values obtained by dynamic measurement are much higher (about 10 times) than those determined statically. This paper presents results from dynamic and static tests on rock cores. The findings are: 1) elastic modull can be consistently determined by laboratory seismic testing. 2) nonlinear deformation characteristics of rock cores was tentatively proposed with variation in elastic modulus with strain.

• Journal of Welding and Joining
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• v.21 no.3
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• pp.68-77
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• 2003

It is important to understand the characteristics of material strength and fracture under the dynamic loading like as earthquakes to assure the integrity of welded structures. The characteristics of dynamic strength and fracture in structural steels and their welded joints should be evaluated based on the effects of the strain rate and the service temperature. It is difficult to predict or measure temperature rise history with the corresponding stress-strain behavior. In particular, material behaviors beyond the uniform elongation can not be precisely evaluated, though the behavior at large strain region after the maximum loading point is much important for the evaluation of fracture. In this paper, the coupling phenomena of temperature and stress-strain fields under the dynamic loading was simulated by using the finite element method. The modified rate-temperature parameter was defined by accounting for the effect of temperature rise under the dynamic deformation, and it was applied to the fully-coupled analysis between heat conduction and thermal elastic-plastic behavior. Temperature rise and stress-strain behavior including complicated phenomena were studies after the maximum loading point in structural steels and their undermatched joints and compared with the measured values.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 1998.10a
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• pp.353-360
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• 1998

Dynamic measurements are used rather sparingly to determine the elastic moduli of rock cores and modulus values are not much utilized in design practice. The reason seems to result from the general perception that values obtained by dynamic measurement are much higher (about 10 times) than those determined statically. This paper presents results from dynamic and static tests on rock cores. The findings are : 1) elastic moduli can be consistently determined by laboratory seismic testing. 2) nonlear deformation characteristic of rock cores was tentatively proposed with variation in elastic modulus with strain.

• Journal of the Korean Society for Precision Engineering
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• v.10 no.3
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• pp.107-116
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• 1993

In the design and operation of robitic arm with flexible links, the equation of motion are required to exactly model the interaction between rigid body motion and elastic motion and to be formulated efficientlyl. In this paper, the flexible link is represented by applying the D-H rigid link representation method to measure the elestic deformation. And the equations of motion of robotic arm, which are configured by the generalized coordinates of elastic and rigid degrees of freedom, are formulated from the principle of virtual power. Dynamic characteristics due to elastic deformation of each link are obtained by using F. E. M to model complex shaped link acurately and by eliminating elastic modes of higher order that do not largely affect motion to reduce the number of elastic degrees of freedom. Also presented is the result of simulation of flexible robotic arms whose joints are controlled by direct or PD control.

• Structural Engineering and Mechanics
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• v.60 no.3
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• pp.489-505
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• 2016

Sinusoidal shear deformation theory (SSDT) is developed here for dynamic buckling of functionally graded (FG) nano-plates. The material properties of plate are assumed to vary according to power law distribution of the volume fraction of the constituents. In order to present a realistic model, the structural damping of nano-structure is considered using Kelvin-Voigt model. The surrounding elastic medium is modeled with a novel foundation namely as orthotropic visco-Pasternak medium. Size effects are incorporated based on Eringen'n nonlocal theory. Equations of motion are derived from the Hamilton's principle. The differential quadrature method (DQM) in conjunction with Bolotin method is applied for obtaining the dynamic instability region (DIR). The detailed parametric study is conducted, focusing on the combined effects of the nonlocal parameter, orthotropic visco-Pasternak foundation, power index of FG plate, structural damping and boundary conditions on the dynamic instability of system. The results are compared with those of first order shear deformation theory and higher-order shear deformation theory. It can be concluded that the proposed theory is accurate and efficient in predicting the dynamic buckling responses of system.

• Tribology and Lubricants
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• v.12 no.3
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• pp.63-71
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• 1996

The connecting rod bearing, which is subjected to periodical dynamic loading, is an impoRant component of the reciprocating engine. In the operation of this bearing, significant parameters are the oil film thickness and the film pressure. Peak film pressures of 20-30 MPa are not uncommon. So the elastic deformation of the bearing housing can have a significant effect on the bearing performance. In this study, a numerical analysis of connecting rod bearing is investigated. Elastic deformation of the bearing housing is considered in the analysis. Separate hydrodynamic and structural analysis are coupled through a direct iterative process. It is shown that as the result of the elastic deformation of the bearing housing, the eccentricity ratio is increased, and the minimum value of the minimum film thickness and the maximum value of the maximum film pressure are decreased. The variations of rotational speed and cylinder pressure affect the minimum film thickness and the maximum film pressure variations of the connecting rod bearing.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.4
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• pp.737-752
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• 1992

Analysis of elasto-dynamic deformation of flexible linkage mechanism is conducted using the finite element method. The equations of motion of the system are derived from the static structural problem in which dynamic inertia, gravitational and driving forces are treated as external loads. Linear spring model is included in the formulation of equation of motions to represent the effects of deformation of elastic bearings of revolute joints on the system behavior. A computer program is constructed and applied to analyze a specific crank-lever 4-bar mechanism. The algorithm of the program is as follows. First, the natural frequencies and the mode shapes of the system are calculated by solving the eigenproblem of the mechanism system which can be considered as a static structure by assuming the input shaft (crank shaft) to be fixed at any given configuration of mechanism. And finally, the elasto-dynamic deformation of the whole system is obtained using mode superposition method for the case of constant input speed. The effect of geometric stiffness on the mechamism is included in the program with the axial forces of links obtained through the quasi-static displacement analysis. It is found that the geometric stiffness exerts an important effect upon the elasto-dynamic behavior of the flexible linkage mechanism. Elastic deformation of bearing lowers the natural frequencies of the system, resulting smaller elastic displacement at the mid-point of the links and bigger elestic displacement at the ends of the links than rigid bearing. The above investigation of flexible linkage mechanism shows that the effects of the elastic deformation of bearing on the mechanism should be considered to design the mechanism which satisfies more preciously the purpose and the condition of design.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.1
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• pp.79-88
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• 2014

Enhancing the working speed and positional accuracy of high-speed press machines is essential for improving the parts accuracy and productivity. However it is known that the positional accuracy decreases and the risk of parts failure increases as the working speed of press machine increases. Therefore predicting such problems during the stage of press structure design is necessary for precise design of high-speed press machines. In the present investigation, the dynamic-elastic deformation of press drive module parts with eccentric masses was examined by finite element analysis and experiment. Then the positional accuracy and parts failure of high-speed press machines was evaluated.