• 한국정밀공학회:학술대회논문집
• /
• 한국정밀공학회 2011년도 춘계학술대회 논문집
• /
• pp.1087-1088
• /
• 2011

• 생물환경조절학회지
• /
• 제7권3호
• /
• pp.181-190
• /
• 1998

현재 제주도 서귀포시 제주감귤연구소에서 개발중인 내풍형 2중 아치 비닐하우스에 풍하중을 재하하여 탄성수치해석을 시도한 결과, 풍동실험에 의하면 파풍망의 효과는 풍속이 5∼25m/s 일 때 파풍망을 통과한 유출속도가 86∼98%까지 감소하여 매우 효과적임을 알 수 있었다. 본 연구에서는 일반적으로 사용하고 있는 파이프를 지반에 고정시키는 경계조건을 주지 않고 설치한 피라미드형 콘크리트 지지대의 사하중을 지점에 재하하여 경계조건을 준 결과, 하우스가 풍하중의 양력에 의하여 위로 들리는 거동을 나타내고 있었다. 이러한 거동은 현장에서 목격되는 파괴형상이 기초 전체가 인발되고 파이프가 콘크리트 기초로부터 인발됨으로써 야기되는 파괴요인이 된다. 본 연구에서 재하한 45m/s의 풍하중은 재현기간이 100년에 대한 값으로 반영구적인 구조물에 기준으로 비닐하우스의 내구수명이 상대적으로 짧으므로 이 풍하중을 감소시켜서 설계할 수 있었다. 또한 본 연구에서는 지붕아치가 연결되는 Y-형 접속장치를 내부힌지로 모델링한 것을 제외하고는 모든 연결을 고정연결로 보아 해석하였다.

• 소성∙가공
• /
• 제12권1호
• /
• pp.34-42
• /
• 2003

This paper presents a rigid-plastic finite element method to handle the frictional contact problem between two deformable bodies experiencing large deformation. The variational formulation combined with incremental quasi-static model is employed for treating the contact boundary condition. The frictional behavior of the model obeys Coulomb's law of friction. The proposed contact algorithms are classified into two categories, one for searching contacting nodes and the other for calculating contact forces at the contact surface. A slave node and master contact segment are defined using the geometric condition of finite elements on the contact interface. The penalty parameter is used to limit the penetration between contacting bodies, and the finite elements are coupled with contact boundary elements.us gates and cavity thicknesses. Through this study we have observed that the jetting is related to the die swell of material. This means that the jotting is strongly affected by the elastic flow property rather than the viscous flow property in viscoelastic characteristics of molten polymer. Different resins have different elastic properties, and elastic flow behavior depends on the shear rate of flow, i.e. injection speed. Large die swell would eliminate jetting however, the retardation of die swell would stimulate jetting. In the point of mole design, reducing the thickness ratio of cavity to gate can reduce or eliminate jetting regardless of amount of elasticity of polymer melt.

• Geomechanics and Engineering
• /
• 제8권3호
• /
• pp.323-359
• /
• 2015

This paper presents an elasto-plastic model for determination of the ground response curve of a circular underwater tunnel excavated in elastic-strain softening rock mass compatible with a nonlinear Hoek-Brown yield criterion. The finite difference method (FDM) was used to propose a new solution to calculate pore water pressure, stress, and strain distributions on periphery of circular tunnels in axisymmetric and plain strain conditions. In the proposed solution, a modified non-radial flow pattern, for the hydraulic analysis, is utilized. To evaluate the effect of gravitational loads and variations of pore water pressure, the equations concerning different directions around the tunnel (crown, wall, and floor) are derived. Regarding the strain-softening behavior of the rock mass, the stepwise method is executed for the plastic zone in which parameters of strength, dilatancy, stresses, strains, and deformation are different from their elasto-plastic boundary values as compared to the tunnel boundary values. Besides, the analytical equations are developed for the elastic zone. The accuracy and application of the proposed method is demonstrated by a number of examples. The results present the effects of seepage body forces, gravitational loads and dilatancy angle on ground response curve appropriately.

• Geomechanics and Engineering
• /
• 제22권1호
• /
• pp.11-23
• /
• 2020

In this study, a new analytical-numerical procedure is developed to give the stresses and strains around a circular tunnel in rock masses exhibiting different stress-strain behavior. The calculation starts from the tunnel wall and continues toward the unknown elastic-plastic boundary by a finite difference method in the annular discretized plastic zone. From the known stresses in the tunnel boundary, the strains are calculated using the elastic-plastic stiffness matrix in which three dimensional Hoek-Brown failure criterion (Jiang and Zhao 2015) and Mohr-Coulomb potential function with proper dilation angle (i.e., non-associated flow rule) are employed in terms of stress invariants. The illustrative examples give ground response curve and show correctness of the proposed approach. Finally, from the results of a great number of analyses, a simple relationship is presented to find out the closure of circular tunnel in terms of rock mass strength and tunnel depth. It can be valuable for the preliminary decision of tunnel support and for prediction of tunnel problems.

• Journal of Welding and Joining
• /
• 제29권4호
• /
• pp.48-53
• /
• 2011

A thermal distortion analysis which takes strains directly as boundary conditions removed barrier of analysis time for the evaluation of welding distortion in a large shell structure like ship block. If the FE analysis time is dramatically reduced, the structure modeling time or the input-value calculating time will become a new issue. On the contrary to this, if the calculation time of analysis input-value is dramatically reduced and its results also are more meaningful, a little longer analysis time could be affirmative. In this study, instead of using inherent strain based on elastic analysis, a thermal strain based on elasto-plastic analysis is used as the boundary condition of weldments in order to evaluate the welding distortion. Here, the thermal strain at the weldment was established by using a stress-strain curve established from the test results. It is possible to automatically recognize the modeling induced-stiffness in the shrinkage direction of welded or heated region. The validity of elasto-plastic thermal distortion analysis was verified through the experiment results with various welding sequence.

• 소성∙가공
• /
• 제11권6호
• /
• pp.513-518
• /
• 2002

The equivalent boundary conditions have been applied to the front door panel forming process, in order to demonstrate its reliability and validity. The elongation in the bead forming process is applied to the binder wrap process as the equivalent displacement boundary condition and the restraining force in the drawing process is applied to stamping process as the equivalent force boundary condition. The result calculated with the equivalent boundary conditions shows closer coincidence with the experimental result than simulation with different boundary conditions. The numerical result fully demonstrates that drawbead forming simulation for calculation of equivalent boundary conditions is necessary and effective.

• 대한기계학회논문집A
• /
• 제27권7호
• /
• 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.

• Steel and Composite Structures
• /
• 제14권6호
• /
• pp.571-586
• /
• 2013

This paper focuses on the buckling capacity of a hybrid grid shell. The eigenvalue buckling, geometrical non-linear elastic buckling and elasto-plastic buckling analyses of the hybrid structure were carried out. Then the influences of the shape and scale of imperfections on the elasto-plastic buckling loads were discussed. Also, the effects of different structural parameters, such as the rise-to-span ratio, beam section, area and pre-stress of cables and boundary conditions, on the failure load were investigated. Based on the comparison between elastic and elasto-plastic buckling loads, the effect of material non-linearity on the stability of the hybrid barrel vault is found significant. Furthermore, the stability of a hybrid barrel vault is sensitive to the anti-symmetrical distribution of loads. It is also shown that the structures are highly imperfection sensitive which can greatly reduce their failure loads. The results also show that the support conditions pose significant effect on the elasto-plastic buckling load of a perfect hybrid structure.

• 한국정밀공학회:학술대회논문집
• /
• 한국정밀공학회 2011년도 춘계학술대회 논문집
• /
• pp.1309-1310
• /
• 2011