• 한국철도학회:학술대회논문집
• /
• 한국철도학회 2005년도 춘계학술대회 논문집
• /
• pp.385-390
• /
• 2005

A specimen with residual stress due to welding was analyzed by three-dimensional cohesive zone model. The residual stress distribution was calculated by simulating welding process, and cohesive elements were located along crack propagation planes. Crack growth is possible since two planes of the cohesive element are separated beyond a maximum load carrying capacity. Stress fields around a crack tip are compared for specimens with and without residual stresses. Load-displacement curves and crack growth behaviors are also examined.

• Geomechanics and Engineering
• /
• 제7권3호
• /
• pp.233-246
• /
• 2014

Estimation of fracture initiation pressure is one of the most difficult technical challenges in hydraulic fracturing treatment of vertical or horizontal oil wells. In this study, the influence of in-situ stresses and pore pressure values on fracture initiation pressure and its profile in vertical and horizontal oil wells in a normal stress regime have been investigated. Cohesive elements with traction-separation law (XFEM-based cohesive law) are used for simulating the fracturing process in a fluid-solid coupling finite element model. The maximum nominal stress criterion is selected for initiation of damage in the cohesive elements. The stress intensity factors are verified for both XFEM-based cohesive law and analytical solution to show the validation of the cohesive law in fracture modeling where the compared results are in a very good agreement with less than 1% error. The results showed that, generally by increasing the difference between the maximum and minimum horizontal stress, the fracture pressure and its profile has been strongly changed in the vertical wells. Also, it's been clearly observed that in a horizontal well drilled in the direction of minimum horizontal stress, the values of fracture pressure have been significantly affected by the difference between overburden pressure and maximum horizontal stress. Additionally, increasing pore pressure from under-pressure regime to over-pressure state has made a considerable fall on fracture pressure in both vertical and horizontal oil wells.

• 한국해안해양공학회지
• /
• 제1권1호
• /
• pp.44-49
• /
• 1989

점성토의 퇴적현상에는 여러가지 물리화학적 인자가 작용하기 때문에 최근까지의 연구경향은 주로 현장관측이나 수리실험에 의존하고 있는 실정이다. 본 연구에서는 금강하구에서 채취한 시료를 사용하여 정성토의 침식 및 퇴적에 관한 개수로 실험을 하였다. 침식에 대한 실험에서는 여러가지 수리조건에서의 시간에 따른 부유농도 변화를 측정하여 침식률 및 침식계수를 구하여 침식에 대한 한계소류력을 결정하였으며, 퇴적에 대한 실험에서는 수리조건을 변화시키면서 각 소류력에 대한 평형농도를 결정하여 평형농도와 초기농도와의 비와 소류력과의 관계를 얻었다. 본 연구의 결과를 다른 자료와 비교 검토하여 정상적으로 유사한 경향을 나타내고 있음을 알 수 있었다.

• 소성∙가공
• /
• 제19권4호
• /
• pp.217-223
• /
• 2010

The objective of this study is to propose the FE model for mechanical clinched joint using cohesive zone model to analyze its failure behavior under impact loading. Cohesive zone model (CZM) is two-parameter failure criteria approach, which could describe the failure behavior of joint using critical stress and fracture toughness. In this study, the relationship between failure behavior of mechanical clinched joint and fracture parameters is investigated by FE analysis with CZM. Using this relationship, the critical stress and fracture toughness for tensile and shear mode are determined by H-type tensile test and lap shear test, which were made of 5052 aluminum alloy. The fracture parameters were applied to the tophat impact test to evaluate the crashworthiness. Compared penetration depth and energy absorption at the point where 50% of total displacement in result of FE analysis and experiment test for impact test, those has shown similar crashworthiness.

• 한국수자원학회:학술대회논문집
• /
• 한국수자원학회 2023년도 학술발표회
• /
• pp.319-319
• /
• 2023

Flows of water in the environment (e.g. in a river or estuary) generally occur in complex conditions. This complexity can hinder a general understanding of flows and their related sedimentary processes, such as erosion and deposition. To gain insight in simplified, controlled conditions, hydraulic flumes are a popular type of laboratory research equipment. Linear flumes use pumps to recirculation water. This isn't appropriate for the investigation of cohesive sediments as pumps can break fragile cohesive sediment flocs. To overcome this limitation, the rotating annular flume (RAF) was developed. While not having pumps, a side-effect is that unwanted secondary circulations can occur. To counteract this, the top and bottom lid rotate in opposite directions. Furthermore, a larger flume is considered better as it has less curvature and secondary circulation. While only a few RAFs exist, they are important for theoretical research which often underlies numerical models. Many of the first-generation of RAFs have come into disrepair. As new measurement techniques and models become available, there is still a need to research cohesive sediment erosion and deposition in facilities such as a RAF. New RAFs also can have the advantage of being automatic instead of manually operated, thus improving data quality. To further advance our understanding of cohesive sediment erosion and deposition processes, a large, automatic RAF (1.72 m radius, 0.495 m channel depth, 0.275 m channel width) has been constructed at the Hydraulic Laboratory at Chungnam National University (CNU), Korea. The RAF has the ability to simulate both unidirectional (river) and bidirectional (tide) flows with supporting instrumentation for measuring turbulence, bed shear stress, suspended sediment concentraiton, floc size, bed level, and bed density. Here we present the current status and future prospect of the CNU RAF. In the future, calibration of the rotation rate with bed shear stress and experiments with unidirectional and bidirectional flow using cohesive kaolinite are expected. Preliminary results indicate that the CNU RAF is a valuable tool for fundamental cohesive sediment transport research.

• 한국지반공학회:학술대회논문집
• /
• 한국지반공학회 1994년도 연약지반처리위원회 봄 학술발표회 논문집 연약지반처리
• /
• pp.3-12
• /
• 1994

Based on the shear failure mechanism, hydraulic fracturing criteria are extended to three dimensional stress state. According to the situation of the directions of borehole and major principal stress axes, three equations can be derived for three dimensional hydraulic fracturing problems. By comparing these equations, a single criterion is selected for hydraulic fracturing pressure in cohesive soils. The criterion is a function of maximum principal stress, minimum principal stress and soil parameters in UU conditions. The equation indicates that with any increase in maximim principal stress, hydraulic fracturing pressure decreases. In order to prove the integrity of the criteria, laboratory tests are performed on compacted cubical specimens using true a triaxial apparatus. The shape and direction of fractures are determined by injecting colored water after fracture initiation. It is found that the direction of fractures are perpendicular to the o1 plane.

• 대한기계학회논문집A
• /
• 제32권5호
• /
• pp.387-395
• /
• 2008

Stress distribution and interfacial debonding process at the interface between a rubber mold and a powder compact were analyzed during unloading under cold isostatic pressing. The Cap model proposed by Lee and Kim was used for densification behavior of powder based on the parameters involved in the yield function of general Cap model and volumetric strain evolution. Cohesive elements incorporating a bilinear cohesive zone model were also used to simulate interfacial debonding process. The Cap model and the cohesive zone model were implemented into a finite element program (ABAQUS). Densification behavior of powder was investigated under various interface conditions between a rubber mold and a powder compact during loading. The residual tensile stress at the interface was investigated for rubber molds with various elastic moduli under perfect bonding condition. The variations of the elastic energy density of a rubber mold and the maximum principal stress of a powder compact were calculated for several interfacial strengths at the interface during unloading.

• Ocean and Polar Research
• /
• 제26권2호
• /
• pp.323-332
• /
• 2004

This paper concerns about a study on dynamic responses of tracked vehicle on soft cohesive soil. For dynamic analyses of tracked vehicle, two different models were adopted, i.e. a single-body model and a multi-body model. The single-body vehicle model was assumed as a rigid body with 6-dof. The multi-body vehicle was modeled by using a commercial software, RecurDyn-LM. For the both models properties of cohesive soft soil were modeled by means of three relationships: pressure to sinkage, shear displacement to shear stress, and shear displacement to dynamic sinkage. Traveling performances of the two tracked vehicle models were compared through dynamic analyses in time domain.

• 한국해양공학회지
• /
• 제25권1호
• /
• pp.14-21
• /
• 2011

The purpose of this study is to quantify the erosional parameters, such as the critical shear stress for erosion and the erosion rate coefficient for cohesive sediments from the Mokpo coast. Using Chonbuk annular flume, five erosion tests were conducted under the uniform bed condition but a different bed density respectively. Erosion test results for Mokpo sediments have shown increases in the range of $0.16{\sim}0.43\;N/m^2$ but decreases exponentially in the range of $272{\sim}4.64\;mg/cm^2{\cdot}hr$ for the given bed shear stress of $1.14{\sim}1.34\;g/cm^3$. The erosional parameters of Mokpo sediments are found to vary remarkably in quantity compared with those for cohesive sediments from other sites. On the whole, the value of Mokpo coast sediments appears to be similar to Kunsan sediments but smaller than Saemankeum and Okeechobee sediments. On the other hand, Mokpo sediments have been shown to be larger than Saemankeum and Okeechobee sediments but smaller than Kunsan sediments.

• 한국해안·해양공학회논문집
• /
• 제24권3호
• /
• pp.159-165
• /
• 2012

본 연구에서는 환형수조를 이용한 일련의 퇴적실험을 수행하여, 국내 최초로 자연 점착성 퇴적물 시료에 대한 퇴적 매개변수가 정량적으로 산정되었다. 퇴적실험을 위해 광양만이 대표 해역으로 선정되어 시료가 채취되었으며, 퇴적실험은 초기농도가 동일한 조건에서 바닥전단응력의 크기만을 변화시키면서 총 18회의 실험이 수행되었다. 퇴적실험결과, 광양만 갯벌 점착성 퇴적물의 최소전단응력 ${\tau}_{bmin}$과 퇴적률 매개변수들 ${\sigma}_1$, $({\tau}_b^*-1)_{50}$은 각각 $0.11N/m^2$, 0.68, 0.85로 산정되었으며, 과거 타 연구결과와의 비교검토를 통하여 본 실험에서 도출된 결과의 타당성이 입증되었다.