• Title/Summary/Keyword: Boundary Layer Behavior

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Computational Validation of Supersonic Combustion Phenomena associated with Hypersonic Propulsion (극초음속 추진과 관련된 초음속 연소 현상의 수치적 검증)

  • Choi Jeong-Yeol;Jeung In-Seuck;Yoon Youngbin
    • 한국전산유체공학회:학술대회논문집
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    • 1998.05a
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    • pp.117-122
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    • 1998
  • A numerical study is carried out to investigate the transient process of combustion phenomena associated with hypersonic propulsion devices. Reynolds averaged Navier-Stokes equations for reactive flows are used as governing equations with a detailed chemistry mechanism of hydrogen-air mixture and two-equation SST turbulence modeling. The governing equations are discretized by a high order accurate upwind scheme and solved in a fully coupled manner with a fully implicit time accurate method. At first, oscillating shock-induced combustion is analyzed and the comparison with experimental result gives the validity of present computational modeling. Secondly, the model ram accelerator experiment was simulated and the results show the detailed transient combustion mechanisms. Thirdly, the evolution of oblique detonation wave is simulated and the result shows transient and final steady state behavior at off-stability condition. Finally, shock wave/boundary layer interaction in combustible mixture is studied and the criterion of boundary layer flame and oblique detonation wave is identified.

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Cutting Force Regulation in Turning Using Sliding Mode Control (슬라이딩 모드 제어기를 응용한 선삭공정 절삭력 제어)

  • 박영빈;김종원
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • 1996.11a
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    • pp.605-609
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    • 1996
  • Continuous sliding mode control is applied to turning process for cutting force regulation. The highest feedrate compatible with the allowable cutting force is applied in rough cutting process such that maximum productivity is ensured and tool breakage is avoided. The programmed feedrate is overridden after the control algorithm is carried out. However, most CNC lathe manufacturers offer limited number of data bits far feedrate override, thus resulting in nonlinear behavior of the machine tools. Such nonlinearity brings “quantized” effect, and the optimal faedrate is rounded off before being fed into the CNC system. To compensate for this problem, continuous sliding mode control is applied. Conventional switching control law at a sliding surface is replaced by a smooth control interpolation in a selected boundary layer to avoid the excitation of high-frequency dynamics. Simulation results are presented in comparison with those obtained by applying adaptive control.

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The strongest control of thermophoresis coefficient on nanoparticle profile at intermediate gaps: A spinning sphere

  • Sharif, Humaira;Naeem, Muhammad Nawaz;Khadimallah, Mohamed A.;Ayed, Hamdi;Hussain, Muzamal;Alshoaibi, Adil
    • Computers and Concrete
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    • v.29 no.3
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    • pp.201-207
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    • 2022
  • The evaluation of velocity profile for large values of buoyancy parameter and Bioconvected Rayleigh number is examined. The non-linear problem has been tackled numerically by shooting technique. Nanofluid temperature and nanoparticle concentration slightly elevates for increasing values of thermophoresis coefficient. Thickness of thermal boundary layer is significantly increased with thermophoresis coefficient whereas thickness of concentration boundary layer is more slightly enhanced. The response of temperature and nanoparticles concentration is observed due to change in Brownian motion parameter. As Brownian motion parameter increased temperature distribution is slightly enhanced. The reverse behavior is observed in case of nanoparticles concentration. Comparison of numerical technique with the extant literature is made and an acceptable agreement is attained.

Stress Analysis in Polymeric Coating Layer Deposited on Rigid Substrate

  • Lee, Sang Soon
    • Corrosion Science and Technology
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    • v.14 no.4
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    • pp.161-165
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    • 2015
  • This paper presents an analysis of thermal stress induced along the interface between a polymeric coating layer and a steel substrate as a result of uniform temperature change. The epoxy layer is assumed to be a linear viscoelastic material and to be theromorheologically simple. The viscoelastic boundary element method is employed to investigate the behavior of interface stresses. The numerical results exhibit relaxation of interface stresses and large stress gradients, which are observed in the vicinity of the free surface. Since the exceedingly large stresses cannot be borne by the polymeric coating layer, local cracking or delamination can occur at the interface corner.

Analysis of Lamb wave propagation on a plate using the spectral element method (스펙트럼 요소법을 이용한 판 구조물의 램파 전달 해석)

  • Lim, Ki-Lyong;Kim, Eun-Jin;Choi, Kwang-Kyu;Park, Hyun-Woo
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2008.11a
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    • pp.71-81
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    • 2008
  • This paper proposes a spectral element which can represent dynamic responses in high frequency domain such as Lamb waves on a thin plate. A two layer beam model under 2-D plane strain condition is introduced to simulate high-frequency dynamic responses induced by piezoelectric layer (PZT layer) bonded on a base plate. In the two layer beam model, a PZT layer is assumed to be rigidly bonded on a base beam. Mindlin-Herrmann and Timoshenko beam theories are employed to represent the first symmetric and anti-symmetric Lamb wave modes on a base plate, respectively. The Bernoulli beam theory and 1-D linear piezoelectricity are used to model the electro-mechanical behavior of a PZT layer. The equations of motions of a two layer beam model are derived through Hamilton's principle. The necessary boundary conditions associated with electro mechanical properties of a PZT layer are formulated in the context of dual functions of a PZT layer as an actuator and a sensor. General spectral shape functions of response field and the associated boundary conditions are formulated through equations of motions converted into frequency domain. A detailed spectrum element formulation for composing the dynamic stiffness matrix of a two layer beam model is presented as well. The validity of the proposed spectral element is demonstrated through comparison results with the conventional 2-D FEM and the previously developed spectral elements.

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Viscoelastic Analysis for Behavior of Edge Cracks at the Bonding Interface of Semiconductor Chip (반도체 칩 접착 계면에 존재하는 모서리 균열 거동에 대한 점탄성 해석)

  • 이상순
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.14 no.3
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    • pp.309-315
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    • 2001
  • The Stress intensity factors for edge cracks located at the bonding interface between the elastic semiconductor chip and the viscoelastic adhesive layer have been investigated. Such cracks might be generated due to stress singularity in the vicinity of the free surface. The domain boundary element method(BEM) has been employed to investigate the behavior of interface stresses. The overall stress intensity factor for the case of a small interfacial edge crack has been computed. The magnitude of stress intensity factors decrease with time due to viscoelastic relaxation.

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Spectral Element Formulation for Analysis of Lamb Wave Propagation on a Plate Induced by Surface Bonded PZT Transducers (표면 부착형 PZT소자에 의해 유발된 판 구조물의 램파 전달 해석을 위한 스펙트럼 요소 정식화)

  • Lim, Ki-Lyong;Kim, Eun-Jin;Kang, Joo-Sung;Park, Hyun-Woo
    • Transactions of the Korean Society for Noise and Vibration Engineering
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    • v.18 no.11
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    • pp.1157-1169
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    • 2008
  • This paper presents spectral element formulation which approximates Lamb wave propagation by PZT transducers bonded on a thin plate. A two layer beam model under 2-D plane strain condition is introduced to simulate high-frequency dynamic responses induced by a piezoelectric (PZT) layer rigidly bonded on a base plate. Mindlin-Herrmann and Timoshenko beam theories are employed to represent the first symmetric and anti-symmetric Lamb wave modes on a base plate, respectively. The Euler-Bernoulli beam theory and 1-D linear piezoelectricity are used to model the electro-mechanical behavior of a PZT layer. The equations of motions of a two layer beam model are derived through Hamilton's principle. The necessary boundary conditions associated with the electro-mechanical properties of a PZT layer are formulated in the context of dual functions of a PZT layer as an actuator and a sensor. General spectral shape functions of response field and the associated boundary conditions are obtained through equations of motions converted into frequency domain. Detailed spectrum element formulation for composing the dynamic stiffness matrix of a two layer beam model is presented as well. The validity of the proposed spectral element is demonstrated through numerical examples.

Bearing Capacity of Strip Footing on Geogrid-Reinforced Soft Ground (지오그리드로 보강된 연약지반 위에 위치한 연속기초의 극한 지지력)

  • 유충식;신승우
    • Proceedings of the Korean Geotechical Society Conference
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    • 1994.09a
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    • pp.169-174
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    • 1994
  • This paper presents the results of a parametric study on the bearing capacity behavior of a footing located above geogrid-reinforced ground using the finite element method of analysis. A wide range of boundary conditions were analyzed, with varing geogrid design parameters such as depth of geogrid layer, length and siffness of geogrid, and number of geogrid layer, were analyzed. Based on the results of analysis, the optimum geogrid design parameters were determined, which maximize the reinforcing effect of geogrid reinforcement for a given conidition. Furthermore, the mechanistic behavior of a geogrid-reinforced ground subjected to a footing load was discussed using the results of analysis such as stress distribution, propagation of plastic yielding, displacement vector among others.

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Dynamic behavior of piezoelectric bimorph beams with a delamination zone

  • Zemirline, Adel;Ouali, Mohammed;Mahieddine, Ali
    • Steel and Composite Structures
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    • v.19 no.3
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    • pp.759-776
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    • 2015
  • The First Order Shear Deformation Theory (FOSDT) is considered to study the dynamic behavior of a bimorph beam. A delamination zone between the upper and the lower layer has been taken into consideration; the beam is discretised using the finite elements method (FEM). Several parameters are taken into consideration like structural damping, the geometry, the load nature and the configurations of the boundary conditions. Results show that the delamination between the upper and the lower layer affects considerably the actuation.

Buckling analysis of noncontinuous linear and quadratic axially graded Euler beam subjected to axial span-load in the presence of shear layer

  • Heydari, Abbas
    • Advances in Computational Design
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    • v.5 no.4
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    • pp.397-416
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    • 2020
  • Functionally graded material (FGM) illustrates a novel class of composites that consists of a graded pattern of material composition. FGM is engineered to have a continuously varying spatial composition profile. Current work focused on buckling analysis of beam made of stepwise linear and quadratic graded material in axial direction subjected to axial span-load with piecewise function and rested on shear layer based on classical beam theory. The various boundary and natural conditions including simply supported (S-S), pinned - clamped (P-C), axial hinge - pinned (AH-P), axial hinge - clamped (AH-C), pinned - shear hinge (P-SHH), pinned - shear force released (P-SHR), axial hinge - shear force released (AH-SHR) and axial hinge - shear hinge (AH-SHH) are considered. To the best of the author's knowledge, buckling behavior of this kind of Euler-Bernoulli beams has not been studied yet. The equilibrium differential equation is derived by minimizing total potential energy via variational calculus and solved analytically. The boundary conditions, natural conditions and deformation continuity at concentrated load insertion point are expressed in matrix form and nontrivial solution is employed to calculate first buckling loads and corresponding mode shapes. By increasing truncation order, the relative error reduction and convergence of solution are observed. Fast convergence and good compatibility with various conditions are advantages of the proposed method. A MATLAB code is provided in appendix to employ the numerical procedure based on proposed method.