• Title, Summary, Keyword: Modified Boundary Layer Formulation

Search Result 8, Processing Time 0.072 seconds

Efficient and accurate domain-truncation techniques for seismic soil-structure interaction

  • Guddati, Murthy;Savadatti, Siddharth
    • Earthquakes and Structures
    • /
    • v.3 no.3_4
    • /
    • pp.563-580
    • /
    • 2012
  • We modify the formulation of a recently developed absorbing boundary condition (ABC), the perfectly matched discrete layers (PMDL), to incorporate the excitation coming from the exterior such as earthquake waves. The modified formulation indicates that the effect of the exterior excitation can be incorporated into PMDL ABCs (traditionally designed to treat only interior excitation) simply by applying appropriate forces on the nodes connected to the first PMDL layer. Numerical results are presented to clearly illustrate the effectiveness of the proposed method.

Application of ADE-PML Boundary Condition to SEM using Variational Formulation of Velocity-Stress 3D Wave Equation (속도-응력 변분식을 이용한 3차원 SEM 탄성파 수치 모사에 대한 ADE-PML경계조건의 적용)

  • Cho, Chang-Soo;Son, Min-Kyung
    • Geophysics and Geophysical Exploration
    • /
    • v.15 no.2
    • /
    • pp.57-65
    • /
    • 2012
  • Various numerical methods in simulation of seismic wave propagation have been developed. Recently an innovative numerical method called as the Spectral Element Method (SEM) has been developed and used in wave propagation in 3-D elastic media. The SEM that easily implements the free surface of topography combines the flexibility of a finite element method with the accuracy of a spectral method. It is generally used a weak formulation of the equation of motion which are solved on a mesh of hexahedral elements based on the Gauss-Lobatto-Legendre integration rule. Variational formulations of velocity-stress motion are newly modified in order to implement ADE-PML (Auxiliary Differential Equation of Perfectly Matched Layer) in wave propagation in 3-D elastic media, because a general weak formulation has a difficulty in adapting CFS (Complex Frequency Shifted) PML (Perfectly Matched Layer). SEM of Velocity-Stress motion having ADE-PML that is very efficient in absorbing waves reflected from finite boundary is verified with simulation of 1-D and 3-D wave propagation.

Validation of Numerical Model for the Wind Flow over Real Terrain (실지형을 지나는 대기유동에 대한 수치모델의 검증)

  • Kim, Hyeon-Gu;Lee, Jeong-Muk;No, Yu-Jeong
    • Journal of Korean Society for Atmospheric Environment
    • /
    • v.14 no.3
    • /
    • pp.219-228
    • /
    • 1998
  • In the present investigation, a numerical model developed for the prediction of the wind flow over complex terrain is validated by comparing with the field experiments. For the solution of the Reynolds - Averaged Clavier- stokes equations which are the governing equations of the microscale atmospheric flow, the model is constructed based on the finite-volume formulation and the SIMPLEC pressure-correction algorithm for the hydrodynamic computation. The boundary- fitted coordinate system is employed for the detailed depiction of topography. The boundary conditions and the modified turbulence constants suitable for an atmospheric boundary- layer are applied together with the k- s turbulence model. The full- scale experiments of Cooper's Ridge, Kettles Hill and Askervein Hill are chosen as the validation cases . Comparisons of the mean flow field between the field measurements and the predicted results show good agreement. In the simulation of the wind flow over Askervein Hill , the numerical model predicts the three dimensional flow separation in the downslope of the hill including the blockage effect due to neighboring hills . Such a flow behavior has not been simulated by the theoretical predictions. Therefore, the present model may offer the most accurate prediction of flow behavior in the leeside of the hill among the existing theoretical and numerical predictions.

  • PDF

Interfacial Crack-tip Constraints and J-integrals in Plastically Hardening Bimaterials under Full Yielding (완전소성하 변형경화 이종접합재의 계면균열선단 구속상태 및 J-적분)

  • Lee, Hyung-Yil;Kim, Yong-Bom
    • Transactions of the Korean Society of Mechanical Engineers A
    • /
    • v.27 no.7
    • /
    • pp.1159-1169
    • /
    • 2003
  • This paper investigates the effects of T-stress and plastic hardening mismatch on the interfacial crack-tip stress field via finite element analyses. Plane strain elastic-plastic crack-tip fields are modeled with both MBL formulation and a full SEC specimen under pure bending. Modified Prandtl slip line fields illustrate the effects of T-stress on crack-tip constraint in homogeneous material. Compressive T-stress substantially reduces the interfacial crack-tip constraint, but increases the J-contribution by lower hardening material, J$\_$L/. For bimaterials with two elastic-plastic materials, increasing plastic hardening mismatch increases both crack-tip stress constraint in the lower hardening material and J$\_$L/. The fracture toughness for bimaterial joints would consequently be much lower than that of lower hardening homogeneous material. The implication of unbalanced J-integral in bimaterials is also discussed.

A Simple Calculational Method by using Modified Von Mises Transformation applied to the Coaxial Turbulent Jet Mixing (유동함수를 이용한 난류제트혼합유동 계산에 관한 연구)

  • Choi Dong-Whan
    • Journal of the Korean Society of Propulsion Engineers
    • /
    • v.9 no.2
    • /
    • pp.97-104
    • /
    • 2005
  • A simple but efficient grid generation technique by using the modified compressible form of stream function has been formulated. Transformation of a physical plane to a streamline plane, the Von Mises Transformation, has been widely used to solve the differential equations governing flow phenomena, however, limitation arises in low velocity region of boundary layer, mixing layer and wake region where the relatively large grid spacing is inevitable. Modified Von Mises Transformation with simple mathematical adjustment for the stream function is suggested and applied to solve the confined coaxial turbulent jet mixing with simple $\kappa-\epsilon$ turbulence model. Comparison with several experimental data of axial mean velocity, turbulent kinetic energy, and Reynolds shear stress distribution shows quite good agreement in the mixing layer except in the centerline where the turbulent kinetic energy distributions were somewhat under estimated. This formulation is strongly suggested to be utilized specially for free turbulent mixing layers in axisymmetric flow conditions such as the investigation of mixing behavior, jet noise production and reduction for Turbofan engines.

Relationship between Side-Necked Volume in a SENB specimen and Plastic Deformation Volume (SENB 시험편의 측면함몰과 소성영역관계)

  • Lee, Jeong-Hyun;Kim, Do-Hyung;Kim, Dong-Hak;Kang, Ki-Ju
    • Proceedings of the KSME Conference
    • /
    • /
    • pp.420-425
    • /
    • 2004
  • Lee and Kang measured side-necking deformation near a crack-tip for CT specimen using Stereoscopic Digital Speckle Photography and Digital Image Correlation. In this work the same technique was applied to SENB specimen. We happened to find that the deformation shape of the side-necking is similar to the one of plastic region estimated by McClictock using slip line theory. Based on volume constancy of plastic deformation as well as this finding, it is expected that a linear relationship holds between the volume of plastic deformation region and the one of side-necking upon the lateral surface of a specimen. To prove the idea, a preliminary study has been performed using 3-D finite element method on a model with modified boundary layer formulation. As the result, it is shown that the idea works well with acceptable error.

  • PDF

Free vibration of FG-GPLRC conical panel on elastic foundation

  • Eyvazian, Arameh;Musharavati, Farayi;Tarlochan, Faris;Pasharavesh, Abdolreza;Rajak, Dipen Kumar;Husain, Mohammed Bakr;Tran, Tron Nhan
    • Structural Engineering and Mechanics
    • /
    • v.75 no.1
    • /
    • pp.1-18
    • /
    • 2020
  • Present research is aimed to investigate the free vibration behavior of functionally graded (FG) nanocomposite conical panel reinforced by graphene platelets (GPLs) on the elastic foundation. Winkler-Pasternak elastic foundation surrounds the mentioned shell. For each ply, graphaene platelets are randomly oriented and uniformly dispersed in an isotropic matrix. It is assumed that the Volume fraction of GPLs reainforcement could be different from layer to layer according to a functionally graded pattern. The effective elastic modulus of the conical panel is estimated according to the modified Halpin-Tsai rule in this manuscript. Cone is modeled based on the first order shear deformation theory (FSDT). Hamilton's principle and generalized differential quadrature (GDQ) approach are also used to derive and discrete the equations of motion. Some evaluations are provided to compare the natural frequencies between current study and some experimental and theoretical investigations. After validation of the accuracy of the present formulation and method, natural frequencies and the corresponding mode shapes of FG-GPLRC conical panel are developed for different parameters such as boundary conditions, GPLs volume fraction, types of functionally graded and elastic foundation coefficients.

Development of Cleavage Fracture Toughness Locus Considering Constraint Effects

  • Chang, Yoon-Suk;Kim, Young-Jin;Ludwig Stumpfrock
    • Journal of Mechanical Science and Technology
    • /
    • v.18 no.12
    • /
    • pp.2158-2173
    • /
    • 2004
  • In this paper, the higher order terms in the crack tip stress fields are investigated macroscopically for more realistic assessment of structural material behaviors. For reactor pressure vessel material of A533B ferritic steel, effects of crack size and temperature have been evaluated using 3-point SENB specimens through a series of finite element analyses, tensile tests and fracture toughness tests. The T-stress, Q-parameter and q-parameter as well as the K and J-integral are calculated and mutual relationships are investigated also. Based on the evaluation, it has proven that the effect of crack size from standard length (a/W=0.53) to shallow length (a/W=0.11) is remarkable whilst the effect of temperature from -20$^{\circ}C$ to -60$^{\circ}C$ is negligible. Finally, the cleavage fracture toughness loci as a function of the promising Q-parameter or q-parameter are developed using specific test results as well as finite element analysis results, which can be applicable for structural integrity evaluation considering constraint effects.