• Transactions of the Korean Society of Mechanical Engineers A
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• v.25 no.1
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• pp.153-160
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• 2001

A general procedure for the design sensitivity analysis of structural dynamic problems has been presented in frame of the FRF-based substructuring formulation. For a system response function, the proposed method gives a parametric design sensitivity formula in terms of the partial derivatives of the connection element properties and the transfer matrix of the subsystems. The derived design sensitivity formula is applied to an engine mount system. An interior noise problem in the passenger car is analyzed using the FRF-based substructuring method and the proposed formulation is adopted to study the response variations with respect to the dynamic characteristics of the engine mounts and the bushes. To obtain the FRFs, a finite element model is built for the engine mount structures, and test data is used for the trimmed body including cabin cavity. The comparison of sensitivities derived by the proposed method and the finite difference method shows that the proposed method is efficient and accurate. The proposed sensitivity analysis method indicates effectively the most sensitive location to the interior noise among the engine mounts and the bushes.

• Wind and Structures
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• v.24 no.4
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• pp.351-365
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• 2017

The minimization method is widely used to predict the dynamic characteristics of a system. Generally, data recorded by experiment (for example displacement) tends to contain noise, and the error in the properties of the system is proportional to the noise level (NL). In addition, the accuracy of the results depends on various factors such as the signal character, filtering method or cut off frequency. In particular, coupled terms in multimode systems show larger differences compared to the true value when measured in an environment with a high NL. The iterative least square (ILS) method was proposed to reduce these errors that occur under a high NL, and has been verified in previous research. However, the ILS method might be sensitive to the signal processing, including the determination of cutoff frequency. This paper focused on improving the accuracy of the ILS method, and proposed the modified ILS (MILS) method, which differs from the ILS method by the addition of a new calculation process based on correlation coefficients for each degree of freedom. Comparing the results of these systems with those of a numerical simulation revealed that both ILS and the proposed MILS method provided good prediction of the dynamic properties of the system under investigation (in this case, the damping ratio and damped frequency). Moreover, the proposed MILS method provided even better prediction results for the coupling terms of stiffness and damping coefficient matrix.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.05a
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• pp.796-801
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• 2002

The goal of this research is the shape design of the valve using a computer simulation. For an analysis a basic mathematical model describing compression cycle is considered as consisting of five sets of coupled equations. These are the volume equation (kinematics), valve dynamic equation (dynamics), ideal gas equation (thermodynamics), Bernoulli equation (fluid dynamics), and dynamic equation of fluid particle based on Helmholtz equation (acoustics). Valve motion is made by the superposition of free vibration modes obtained by the finite element method. That is, the eigenvalues and eigenvectors are the sufficient modeling factors fur the valve in the simulation program. Thus, to design a shape of the valve, shape design sensitivity through chain-ruled derivatives is considered from two sensitivity coefficients, one is the design sensitivity of the capability of compressor with respect to the eigenvalues of the valve, and the other is the design sensitivity of the eigenvalue with respect to the shape change of the valve. In this research, the continuum design sensitivity analysis concepts are used for the latter.

• Proceedings of the SCSK Conference
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• 2003.09b
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• pp.319-329
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• 2003

Ursolic acid (UA) and oleanolic acid (OA) are pentacyclic triterpenoids which are widely distributed in plants, and their derivatives are aglycones of many naturally occurring saponins. It is known that pentacyclic acids may possibly enhance the mechanical barrier functions of cell membranes in plants. Recently, it has been reported that OA and UA have interesting biological activities on skin, such as anti-inflammatory and anti-wrinkle activities. Since triterpenoids are extremely insoluble and their solubility problem limits skin-care application, OA and UA were encapsulated in liposomes via micelle-to-vesicle transition to overcome poorly soluble property and enhance biological efficacy. Optimal molar ratio of OA to lecithin was found to exist for producing liposomes of small hydrodynamic size and liposomal suspensions without recrystallized precipitation of OA. From electron micrograph and dynamic light scattering studies, reconstituted OA-containing liposomes without severe mechanical treatment showed small hydrodynamic size about 150 nm. Wide-angle X-ray diffraction coupled with dynamic light scattering revealed that optimal amount of OA in liposome was 25.4 mole %. In biological evaluation, OA-containing liposome significantly increased filaggrin and transglutaminase as markers of keratinocyte differentiation in epidermal layer of hairless mouse, whereas ursolic acid-containing liposome did not show noticeable increase of filaggrin and transglutaminase compared to empty liposome. It is concluded that nano-scaled liposomes containing triterpenoids were spontaneously prepared by vesicular transition from mixed micelle and liposomal triterpenoids can enhance skin absorption of triterpenoid and biological efficacy.

• International Journal of Aeronautical and Space Sciences
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• v.3 no.1
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• pp.74-85
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• 2002

The numerical experiment has been conducted to investigate the unsteady shock wave reflecting phenomena. The cell-vertex finite-volume, Roe's upwind flux difference splitting method with unstructured grid is implemented to solve unsteady Euler equations. The $4^{th}$-order Runge-Kutta method is applied for time integration. A linear reconstruction of the flux vector using the least-square method is applied to obtain the $2^{nd}$-order accuracy for the spatial derivatives. For a better resolution of the shock wave and slipline, the dynamic grid adaptation technique is adopted. The new concept of grid adaptation technique, which is much simpler than that of conventional techniques, is introduced for the current study. Three error indicators (divergence and curl of velocity, and gradient of density) are used for the grid adaptation procedure. Considering the quality of the solution and the numerical efficiency, the grid adaptation procedure was updated up to $2^{nd}$ level at every 20 time steps. For the convenience of comparison with other experimental and analytical results, the case of interaction between the straight incoming shock wave and a sharp wedge is simulated for various flow conditions. The numerical results show good agreement with other experimental and analytical results, in the shock wave reflecting structure, slipline, and the trajectory of the triple points. Some critical cases show disagreement with the analytical results, but these cases also have been proven to show hysteresis phenomena.

• Journal of the Korean Society for Railway
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• v.20 no.2
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• pp.234-240
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• 2017

In this study, the influences of rail surface roughness on dynamic wheel-rail forces currently employed in conventional lines were assessed by performing field measurements according to grinding of rail surface roughness. The influence of the grinding effect was evaluated using a previous empirical prediction model for dynamic wheel-rail forces; model includes first-order derivatives of QI (Quality Index) and vehicle velocity. The theoretical dynamic wheel-rail force determined using the previous prediction equation was analyzed using the QI, which decreased due to rail grinding as determined through field measurements. At a constant track support stiffness, an increase in the QI caused an increase in dynamic wheel-rail forces. Further, it can be inferred that the results of dynamic wheel-rail analysis obtained using the measured data, such as the variation of QI due to rail grinding, can be used to predict the peak dynamic forces. Therefore, it is obvious that the optimum amount of rail grinding can be determined by considering the QI, that was regarding an operation characteristics of the target track (vehicle velocity and wheel load).

• Coupled systems mechanics
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• v.1 no.2
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• pp.133-154
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• 2012

In this paper a bridge flutter prediction is performed by using advanced numerical simulation. Two novel approaches were developed simultaneously by utilizing the ANSYS v12.1 commercial software package. The first one is a fluid-structure interaction simulation involving the three-dimensional elastic motion of a bridge deck and the fluid flow around it. The second one is an updated forced oscillation technique based on the dynamic mode shapes of the bridge. An aeroelastic wind tunnel model was constructed in order to validate the numerical results. Good agreement between the numerical results and the measurements proves the applicability of the novel methods in bridge flutter assessment.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2000.04b
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• pp.177-186
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• 2000

An improved multi-level（IML) optimization algorithm using automatic differentiation (AD) for multi-objective optimum design of framed structures is proposed in this paper. In order to optimize the steel frames under seismic load, two main objective functions need to be considered for minimizing the structural weight and maximizing the strain energy. For the efficiency of the proposed algorithm, multi-level optimization techniques using decomposition method that separately utilizes both system-level and element-level optimizations and an artificial constraint deletion technique are incorporated in the algorithm. And also to save the numerical efforts, an efficient reanalysis technique through approximated structural responses such as moments, frequencies, and strain energy with respect to intermediate variables is proposed in the paper. Sensitivity analysis of dynamic structural response is executed by AD that is a powerful technique for computing complex or implicit derivatives accurately and efficiently with minimal human effort. The efficiency and robustness of the IML algorithm, compared with a plain multi-level (PML) algorithm, is successfully demonstrated in the numerical examples.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.9 no.2
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• pp.112-118
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• 2000

This paper deals with the application of sensitivity method to the parameter estimation for the dynamic analysis of gener-al mechanical system. In this procedure we take the derivatives of the given system with respect to a certain parameter and use this information to implement the steepest descent method. This paper will give two examples of this technique applied to simple vehicle models. This paper will give two examples of this technique applied to simple vehicle models. Simulation results show excellent convergence and accuracy of parameter estimates.

• International Journal of Automotive Technology
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• v.6 no.6
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• pp.599-604
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• 2005

A functional suspension model is proposed as a kinematic describing function of the suspension, that represents the relative wheel displacement in polynomial form in terms of the vertical displacement of the wheel center and steering rack displacement. The relative velocity and acceleration of the wheel is represented in terms of first and second derivatives of the kinematic describing function. The system equations of motion for the full vehicle dynamic model are systematically derived by using velocity transformation method of multi-body dynamics. The comparison of test and simulation results demonstrates the validity of the proposed functional suspension modeling method. The model is computationally very efficient to achieve real-time simulation on TMS 320C6711 150 MHz DSP board of HILS (hardware-in-the-loop simulation) system for ECU (electronic control unit) evaluation of semi-active suspension.