• Computational Structural Engineering
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• v.8 no.4
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• pp.189-198
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• 1995

The conventional finite element formulations for incompressible materials show pressure oscillations or pressure modes in four-node quadrilateral elements of commonly used displacement and pressure interpolations. The criterion for the stability in the pressure solution is the so-called Babugka-Brezzi stability condition, and the above elements do not satisfy this condition. In this study, a pressure continuity residual based on the pressure discontinuity at element interfaces is used to study the stabilization of pressure solutions in bilinear displacement-constant pressure four-node quadrilateral elements. This pressure residual is implemented in Q1P0 element derived from the conventional incompressible elasticity. The pressure solutions can be stable with the pressure residual though they exhibit sensitivity to the stabilization parameters. Parametric study for the solution stabilization is also discussed.

• Journal of the Korean Society for Nondestructive Testing
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• v.13 no.4
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• pp.32-41
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• 1994

The stabilized Michelson interferometer was developed in order to measure micro dynamic displacement at the surface of solids due to elastic wave propagation. The stabilizer was designed to compensate light path disturbances using a reference mirror driven by piezoelectric actuator. Using stabilizer, the effect of external vibration was reduced and the quadrature condition was satisifed. As the results, the output of photodetector had maximum sensitivity and linearity. The minimum detectable displacement was 0.3nm at the band width of 10 MHz. The epicentral displacements due to the glass capillary breaks and the steel ball drop impact were measured using the developed interferometer and the results were compared with the calculated one.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.18 no.4
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• pp.337-347
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• 2009

Generally, finite element models used in structural analysis have some uncertainties of the geometric dimensions, applied loads and boundary conditions, as well as in material properties due to the manufacturability of aluminum intensive body. Therefore, it is very important to refine or update a finite element model by correlating it with dynamic and static tests. The structural optimization problems of automotive body are considered for mechanical structures with initial stiffness due to preloading and in operation condition or manufacturing. As the mean compliance and deflection under preloading are chosen as the objective function and constraints, their sensitivities must be derived. The optimization problem is iteratively solved by a sequential convex approximation method in the commercial software. The design variables are corrected by the strain energy scale factor in the element levels. This paper presents an updated method based on the sensitivities of structural responses and the residual error vectors between experimental and simulation models.

• Transactions of the Korean Society of Mechanical Engineers
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• v.13 no.1
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• pp.29-39
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• 1989

In this work, a numerical and experimental study was done to get an optimum cam profile considering dynamic characteristics of a cam-valve system. First of all, a four degree of freedom dynamic model was set up for an OHV type cam-valve acceleration while not modifying original cam shape greatly. Also another optimization which aims to enlarge the valve displacement area while reducing the peak valve acceleration, was tried. The optimized cam profile was tested experimentally and found that the measured valve displacement and pushrod force show only very small error from the analytically predicted model simulation results.

• International Journal of CAD/CAM
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• v.8 no.1
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• pp.1-10
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• 2009

This paper presents a topology optimization approach using element-free Galerkin method (EFGM) for the optimal design of compliant mechanisms with geometrically non-linearity. Meshless method has an advantage over the finite element method(FEM) because it is more capable of handling large deformation resulted from geometrical nonlinearity. Therefore, in this paper, EFGM is employed to discretize the governing equations and the bulk density field. The sensitivity analysis of the optimization problem is performed by incorporating the adjoint approach with the meshless method. The Lagrange multipliers method adjusted for imposition of both the concentrated and continuous essential boundary conditions in the EFGM is proposed in details. The optimization mathematical formulation is developed to convert the multi-criteria problem to an equivalent single-objective problem. The popularly applied interpolation scheme, solid isotropic material with penalization (SIMP), is used to indicate the dependence of material property upon on pseudo densities discretized to the integration points. A well studied numerical example has been applied to demonstrate the proposed approach works very well and the non-linear EFGM can obtain the better topologies than the linear EFGM to design large-displacement compliant mechanisms.

• Structural Engineering and Mechanics
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• v.77 no.2
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• pp.231-243
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• 2021

In this paper, a dynamic response mapping model of the wheel-rail system is established by using the support vector regression (SVR) method, and the hierarchical safety thresholds of the subgrade void are proposed based on the reliability theory. Firstly, the vehicle-track coupling dynamic model considering the subgrade void is constructed. Secondly, the subgrade void area, the subgrade compaction index K30 and the fastener stiffness are selected as random variables, and the mapping model between these three random parameters and the dynamic response of the wheel-rail system is built by using the orthogonal test and the SVR. The sensitivity analysis is carried out by the range analysis method. Finally, the hierarchical safety thresholds for the subgrade void are proposed. The results show that the subgrade void has the most significant influence on the carbody vertical acceleration, the rail vertical displacement, the vertical displacement and the slab tensile stress. From the range analysis, the subgrade void area has the largest effect on the dynamic response of the wheel-rail system, followed by the fastener stiffness and the subgrade compaction index K30. The recommended safety thresholds for the subgrade void of level I, II and III are 4.01㎡, 6.81㎡ and 9.79㎡, respectively.

• Computers and Concrete
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• v.32 no.5
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• pp.499-511
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• 2023

Anchor channels are commonly used for façade, tunnel, and structural connections. These connections encounter various types of loadings during their service life, including high rate or impact loading. For anchor channels that are placed close and parallel to an edge and loaded in shear perpendicular to and towards the edge, the failure is often governed by concrete edge breakout. This study investigates the transverse shear behavior of the anchor channels under quasi-static and high rate loadings using a numerical approach (3D finite element analysis) utilizing a rate-sensitive microplane model for concrete as constitutive law. Following the validation of the numerical model against a test performed under quasi-static loading, the rate-sensitive static, and rate-sensitive dynamic analyses are performed for various displacement loading rates varying from moderately high to impact. The increment in resistance due to the high loading rate is evaluated using the dynamic increase factor (DIF). Furthermore, it is shown that the failure mode of the anchor channel changes from global concrete edge failure to local concrete crushing due to the activation of structural inertia at high displacement loading rates. The research outcomes could be valuable for application in various types of connection systems where a high rate of loading is expected.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.5
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• pp.82-88
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• 2018

This study investigated the structure of an 8-pole 8-slot linear generator, which acts as an electromagnetic damper by combining the structure of an electromagnetic suspension device capable of generating electrical energy through energy harvesting by absorbing the vibration energy from the road surface while driving. To compare the energy harvesting effect of the electromagnetic suspension according to the actual road surface, a driving road test was simulated for two actual road conditions, an asphalt road surface and unpacked road surface condition, using a civilian combined vehicle model in conjunction with a vehicle simulation program, Carsim and Simulink. As a result, the relative displacements of the suspensions on the asphalt road surface and the unpaved road were 8 mm and 13 mm, respectively. By applying the suspension displacement value derived by modeling the linear generator coupled to the electromagnetic suspension, the simulation was then performed for an analysis time of 0.3s by applying the same analytical conditions using the commercial electromagnetic analysis program, ANSYS MAXWELL, The average power generation on the unpacked roads and asphalt roads was 198.6W and 98.7W respectively, which was 103.7% higher for unpackaged roads. Finally, to compare the sensitivity of the road surface frequency and the suspension input displacement to the power generation output, the sensitivity of the two variables was 1.725 and 1.283, respectively, and the road surface frequency had a 34.5% higher effect on the average power generation.

• Journal of Biomedical Engineering Research
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• v.21 no.3 s.61
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• pp.295-301
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• 2000

It is known that among many factors, relative micromotion at bone/implant interfaces can hinder bone ingrowth into surface pores of an implant. Loading conditions, mechanical properties of spinal materials, friction coefficients at the interfaces and geometry of spinal segments would affect the relative micromotion and spinal stability. A finite clement model of the human lumbar spine segments (L4-L5) was constructed to investigate the mechanical sensitivity at the interfaces between bone and cage. Relative micromotion. Posterior axial displacement. bone stress, cage stress and friction force were predicted in changes of friction coefficients, loading conditions. bone density and age-related material/geometric properties of the spinal segments. Relative micromotion (slip distance in a static loading means relative micromotion in routine activity) at the interfaces increased significantly as the mechanical properties of cancellous bone, annulus fibers or/and ligaments decrease or/and as the friction coefficient at the interfaces decreases. The contact normal force at the interfaces decreased as cancellous bone density decreases or/and as the friction coefficient increases A significant increase of slip distance at anterior annulus occurred with an addition of torsion to compressive preload. Relative micromotion decreased with an increase of disc area. In conclusion. relative micromotion, stress response. Posterior axial displacement and contact normal force are sensitive to the friction coefficient of the interfaces, bone density, loading conditions and age-related geometric/material changes.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.9
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• pp.2172-2180
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• 1993

Under general loadings, including body forces, crack-face tractions and thermal loading, the energy release rate equation for a two-dimensional cracked body is presented. Defining the virtual crack extension as the variation of the geometry, the equation is directly derived by a shape design sensitivity of the potential energy. Although the form of the derived energy release rate equation is different from other researchers's results, the three example show that the former is exactly the same as the latter. However, the final integral equation do not involve the derivative of the displacement on the crack surface and crack tip region, thereby improving the numerical accuracy in the computation of the energy relase rate. Moreover, as it was derived from the governing equation including non-linear elasticity without special assumptions, the energy release rate of a elasto-plastic fracture can be obtained and any numerical stress analysis method can be applied.