• 한국소음진동공학회논문집
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• 제15권7호
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• pp.788-798
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• 2005

The monopole theory has long been used to model air-pumped effect from the elastic cavities in car tire. This approach models the change of an air as a Piston moving backward and forward on a spring and equates local air movements exactly with the volume changes of the system. Thus, the monopole theory has a restricted domain of applicability due to the usual assumption of a small amplitude acoustic wave equation and acoustic monopole theory This paper describes an approach to predict the air-pumping noise of a car tyre with CFD/Kirchhoff integral method. The tyre groove is simply modeled as piston-cavity-sliding door geometry and with the aid of CFD technique flow properties in the groove of rolling car tyre are acquired.'rhese unsteady flow data are used as a air-pumping source in the next CFD calculation of full tyre-road geometry. Acoustic far field is predicted from Kirchhoff integral method by using unsteady flow data in space and time which is provided by the CFD calculation of full tyre-road domain. This approach can cover the non-linearity of acoustic monopole theory with the aid of Non-linear governing equation in CFD calculation. The method proposed in this paper is applied to the prediction of air-pumping noise of simply modeled car tyre and through the predicted results, the influence of nonlinear effect on air-pumping noise propagation is investigated.

• Journal of Mechanical Science and Technology
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• 제20권12호
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• pp.2218-2229
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• 2006

A conservative finite-volume numerical method for unstructured grids with the cell-centered method has been developed for computing flow and heat transfer by combining the attractive features of the existing pressure-based procedures with the advances made in unstructured grid techniques. This method uses an integral form of governing equations for arbitrary convex polyhedra. Care is taken in the discretization and solution procedure to avoid formulations that are cell-shape-specific. A collocated variable arrangement formulation is developed, i.e. all dependent variables such as pressure and velocity are stored at cell centers. For both convective and diffusive fluxes the forms superior to both accuracy and stability are particularly adopted and formulated through a systematic study on the existing approximation ones. Gradients required for the evaluation of diffusion fluxes and for second-order-accurate convective operators are computed by using a linear reconstruction based on the divergence theorem. Momentum interpolation is used to prevent the pressure checkerboarding and a segregated solution strategy is adopted to minimize the storage requirements with the pressure-velocity coupling by the SIMPLE algorithm. An algebraic solver using iterative preconditioned conjugate gradient method is used for the solution of linearized equations. The flow analysis code (PowerCFD) developed by the present method is evaluated for its application to several 2-D structured-mesh benchmark problems using a variety of unstructured quadrilateral and triangular meshes. The present flow analysis code by using unstructured grids with the cell-centered method clearly demonstrate the same accuracy and robustness as that for a typical structured mesh.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2003년도 춘계학술대회논문집
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• pp.443-447
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• 2003

The BEM (Boundary Element Method) is a computational technique for the approximate solution of problems in continuum mechanics. In the BEM both volume and surface integrals transformed into boundary integral equations. So, we applied the ECM (Electrochemical Machining) process to boundary problem, because our focus is only deformed shape. The ECM process is modeled as a two-dimensional problem assuming constant properties of electrolyte, and an incremental formulation is used with automatic mesh regeneration. As a result the final shape is roughly agreed with experimental shape. But, it has an error of exact shape, because a chemically factor is not considered

• Steel and Composite Structures
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• 제44권6호
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• pp.829-843
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• 2022

This manuscript work presents a comprehensive continuum model capable to investigate the effect of porosity on vibro-acoustic behaviour of functionally graded (FG) beams resting on an elastic foundation subjected to thermal and mechanical loadings. Effects of uniform temperature rise and edge compressive load on the sound radiation characteristics are studied in a comparative manner. The numerical analysis is carried out by combining finite element method with Rayleigh's integral. Detailed parametric studies are accomplished, and influences of power law index, porosity volume, porosity distribution and boundary conditions on the vibro-acoustic response characteristics are analyzed. It is found that the vibro-acoustic response under mechanical edge compression is entirely different compared to from that under the thermal load. Furthermore, nature of grading of porosity affects the sound radiation behaviour for both the loads. The proposed model can be used to obtain the suppression performance of vibration and noise FG porous beams under thermal and mechanical loads.

• 대한토목학회논문집
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• 제29권5B호
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• pp.429-439
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• 2009

댐 붕괴로 인한 극한홍수가 발생하였을 경우, 홍수경보에 대한 대응시간은 일반적인 홍수의 경우보다 훨씬 짧다. 수치모형은 홍수파의 전파양상을 예측하고, 범람지역, 홍수파 도달시간 그리고 침수심 등에 관한 정보를 제공하는데 있어 강력한 도구가 될 수 있다. 그러나 댐 붕괴로 인한 홍수파의 전파는 불연속 흐름이나 마른하도의 전파를 포함하고 있으므로, 수학적으로 표현하기 어려운 경우가 많다. 그럼에도 불구하고 최근에 유한체적기법을 이용하여 댐 붕괴로 인한 홍수범람을 모의하기 위한 수치모형의 개발이 많이 이루어졌다. 유한체적기법은 적분보존형 방정식을 기본으로 하고 있으므로, 불연속 흐름이나 충격파의 해석에 용이하다. 따라서, 본 연구에서는 2차원 보존형 천수방정식의 해석을 위해 유한체적기법과 Riemann 근사해법을 이용한 수치모형을 개발하였다. 그리고 예측단계와 수정단계에서 연속방정식과 운동량 방정식의 보존변수 재구성을 위해 수면경사법과 연계한 MUSCL 기법을 적용하여 시간과 공간에서 2차정확도를 얻었다. 개발한 유한체적모형을 2차원 부분적 댐 붕괴 해석 및 삼각형 융기를 가진 하도에 대한 댐 붕괴 해석에 적용하고, 적용결과를 실험자료 및 기존 연구자의 계산결과와 비교하여 개발모형을 검증하였다.

• Advances in concrete construction
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• 제9권3호
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• pp.327-335
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• 2020

Concrete pipes are considered important structures playing integral role in spread of cities besides transportation of gas as well as oil for far distances. Further, concrete structures under seismic load, show behaviors which require to be investigated and improved. Therefore, present research concerns dynamic stress and strain alongside deflection assessment of a concrete pipe carrying water-based nanofluid subjected to seismic loads. This pipe placed in soil is modeled through spring as well as damper. Navier-Stokes equation is utilized in order to gain force created via fluid and, moreover, mixture rule is applied to regard the influences related to nanoparticles. So as to model the structure mathematically, higher order refined shear deformation theory is exercised and with respect to energy method, the motion equations are obtained eventually. The obtained motion equations will be solved with Galerkin and Newmark procedures and consequently, the concrete pipe's dynamic stress, strain as well as deflection can be evaluated. Further, various parameters containing volume percent of nanoparticles, internal fluid, soil foundation, damping and length to diameter proportion of the pipe and their influences upon dynamic stress and strain besides displacement will be analyzed. According to conclusions, increase in volume percent of nanoparticles leads to decrease in dynamic stress, strain as well as displacement of structure.

• 한국음향학회지
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• 제42권3호
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• pp.250-261
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• 2023

본 연구에서는 펌프젯 추진기를 대상으로 공동, 비공동 조건에서의 유동 소음원을 규명하기 위하여 추진기의 각 구성품인 덕트와 스테이터, 로터에 의한 소음 기여도를 평가하였으며, 공동과 비공동 조건에서의 소음 수준을 비교하였다. 대형 캐비테이션 터널 내 Suboff 잠수함 선형과 펌프젯 추진기를 대상으로 균일혼상류 가정의 비정상 비압축성 Reynolds averaged Navier-Stokes(RANS) 방정식을 적용하였으며, 이상 유동을 모사하기 위해 Volume of Fluid(VOF) 기법과 Schnerr-Sauer 공동 모델을 적용하였다. 유동해석 결과를 기반으로 수중방사소음을 예측하기 위해 Ffowcs Williams and Hawkings(FW-H) 방정식 기반의 음향상사법을 적용하였으며, 덕트와 스테이터, 로터로 구성된 3개의 비투과성 적분면과 추진기를 감싸는 형태의 2가지 투과성 적분면을 선정하여 소음 기여도를 평가하였다. 소음 예측결과로부터 스테이터는 전체 소음에 대한 직접적인 기여도는 낮으나 덕트와 로터에서의 유동 박리에 의한 소음원 형성에는 영향을 미치는 것을 확인하였으며, 유동이 박리되는 연직상방과 우측방향으로 소음이 크게 방사되었다. 또한 로터에서는 날개의 흡입면과 압력면 간의 압력 섭동에 의해 추진방향으로 소음이 크게 방사되었으며, 투과성적분면을 통해 체적 소음원인 공동의 효과를 반영할 수 있음을 확인하였다.

• Steel and Composite Structures
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• 제17권5호
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• pp.753-776
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• 2014

In this paper, nonlinear vibration and post-buckling analysis of beams made of functionally graded materials (FGMs) resting on nonlinear elastic foundation subjected to thermo-mechanical loading are studied. The thermo-mechanical material properties of the beams are assumed to be graded in the thickness direction according to a simple power law distribution in terms of the volume fractions of the constituents, and to be temperature-dependent. The assumption of a small strain, moderate deformation is used. Based on Euler-Bernoulli beam theory and von-Karman geometric nonlinearity, the integral partial differential equation of motion is derived. Then this PDE problem which has quadratic and cubic nonlinearities is simplified into an ODE problem by using the Galerkin method. Finally, the governing equation is solved analytically using the variational iteration method (VIM). Some new results for the nonlinear natural frequencies and buckling load of the FG beams such as the influences of thermal effect, the effect of vibration amplitude, elastic coefficients of foundation, axial force, end supports and material inhomogenity are presented for future references. Results show that the thermal loading has a significant effect on the vibration and post-buckling response of FG beams.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2008년도 정기 학술대회
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• pp.27-32
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• 2008

The laminated composite materials have been applied to various mechanical structures due to their high performance to weight ratios. In this study, we suggest a stochastic finite element scheme for the probabilistic analysis of the composite laminated plates. The composite materials consist of two different materials which constitute the matrix and fiber. The material properties in the major and minor directions are determined depending on the volume fraction of these two materials. In this study, the elastic modulus and shear modulus are considered as random and the effect of these random properties on the behavior of the composite plate is investigated. We adopt the weighted integral scheme in the formulation, which has been recognized as the most accurate method in the statistical methodologies. For verification of the proposed scheme, Monte Carlo analysis is also performed for the comparison with the proposed scheme.

• International Journal of Automotive Technology
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• 제8권5호
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• pp.563-573
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• 2007

Optimal design of an automotive catalytic converter for minimization of cold-start emissions is numerically performed using a micro genetic algorithm for two optimization problems: optimal geometry design of the monolith for various operating conditions and optimal axial catalyst distribution. The optimal design process considered in this study consists of three modules: analysis, optimization, and control. The analysis module is used to evaluate the objective functions with a one-dimensional single channel model and the Romberg integration method. It obtains new design variables from the control module, produces the CO cumulative emissions and the integral value of a catalyst distribution function over the monolith volume, and provides objective function values to the control module. The optimal design variables for minimizing the objective functions are determined by the optimization module using a micro genetic algorithm. The control module manages the optimal design process that mainly takes place in both the analysis and optimization modules.