• Journal of Theoretical and Applied Mechanics
• /
• 제2권1호
• /
• pp.31-50
• /
• 1996

In this paper, a finite element analysis based on the local approach concept to fracture in the continuum damage mechanics is performed to analyze ductile fracture in two dimensional quasi-static state. First an isotropic damage model based on the generalized concept of effective stress is proposed for structural materials in the context of large deformation. In this model, the stiffness degradation is taken as a measure of damage and so, the fracture phenomenon can be explained as the critical deterioration of stiffness at a material point. The modified Riks' continuation technique is used to solve incremental iterative equations. Crack propagation is achieved by removing critically damaged elements. The mesh size sensitivity analysis and the simulation of the well known shearing mode failure in plane strain state are carried out to verify the present formulation. As numerical examples, an edge cracked plate and the specimen with a circular hole under plane stress are taken. Load-displacement curves and successively fractured shapes are shown. From the results, it can be concluded that the proposed model based on the local approach concept in the continuum damage mechanics may be stated as a reasonable tool to explain ductile fracture initiation and crack propagation.

• Structural Engineering and Mechanics
• /
• 제58권5호
• /
• pp.905-929
• /
• 2016

This paper assesses efficiency of the continuum method as the idealized system of building structures. A modified Coupled Two-Beam (CTB) model equipped with classical and non-classical damping has been proposed and solved analytically. In this system, complementary (non-classical) damping models composed of bending and shear mechanisms have been defined. A spatial shear damping model which is non-homogeneously distributed has been adopted in the CTB formulation and used to equivalently model passive dampers, viscous and viscoelastic devices, embedded in building systems. The application of continuum-based models for the dynamic analysis of shear wall systems has been further discussed. A reference example has been numerically analyzed to evaluate the efficiency of the presented CTB, and the optimization problems of the shear damping have been finally ascertained using local and global performance indices. The results reveal the superior performance of non-classical damping models against the classical damping. They show that the critical position of the first modal rotation in the CTB is reliable as the optimum placement of the shear damping. The results also prove the good efficiency of such a continuum model, in addition to its simplicity, for the fast estimation of dynamic responses and damping optimization issues in building systems.

• 음성과학
• /
• 제12권4호
• /
• pp.247-254
• /
• 2005

This study aimed at clarifing clinical effects of eight-step continuum treatment in a patient who showed apraxia of speech after stroke. The eight-step continuum treatment consisted of 8 steps and its clinical efficacy has been proven with American apraxic patients. However, it has not been clinically proven to be effective in Korean patients with apraxia of speech as of yet. Therefore, this study was conducted in an effort to provide preliminary clinical evidence regarding its effectiveness regardless of the linguistic differences between Korean and English. The therapy took place twice a week for 6 months, a total of 48 times. The results showed that the patient's receptive language was improved from 83% to 89% and 37% in accuracy, and expressive language from 15% to 37%. It seemed that spontaneous recovery did not playa role in his improvement since the study was conducted 2 years after the stroke. In addition, the improvement of expressive language was much greater(22%) than that of receptive language(6%), which implied that the therapy was effective in apraxia of speech because apraxia of speech is relatively confined to expressive ability, more specifically motor programming and sequencing.

• 천문학논총
• /
• 제21권2호
• /
• pp.101-112
• /
• 2006

We developed a new program for automatic continuum normalization of Echelle spectrographic data. Using this algorithm, we have determined spectral continuum of almost BOES data. The first advantage of this algorithm is that we can save much time for continuum determination and normalization. The second advantage is that the result of this algorithm is very reliable for almost spectral type of spectrum. But this algorithm cannot be applied directly to the spectrum which has very strong and broad emission lines, for example Wolf-Rayet type spectrum. We implanted this algorithm to the program which was developed in the previous study. And we introduced more upgraded BOES data reduction program. This program has more convenient graphical user interface environment, so users can easily reduce BOES data. Lastly, we presented the result of study on line profile variation of magnetic Ap/Bp stars analyzed using this program.

• Interaction and multiscale mechanics
• /
• 제7권1호
• /
• pp.543-561
• /
• 2014

We present a full energy and force formulation of the quasicontinuum method with non-local and local transition elements. Non-local transition elements are developed to transmit inhomogeneity from the atomistic to the continuum regions. Local transition elements are developed to resolve the mathematical mismatch between non-local atoms and the local continuum. The rationale behind these transition elements is provided by analyzing the energy and force transitions between atoms and continuum under the Cauchy-Born rule. We show that breakdown of the Cauchy-Born rule occurs for slaved atoms of local elements within the cutoff of non-local atoms. The inadequacy of the Cauchy-Born rule at the transition region naturally leads to the need of atomistic treatment of transition slaved and transition representative atoms. Such an atomistic treatment together with a full or cutoff sampling allows non-local transition elements containing these transition entities to transmit inhomogeneity. Different force formulations for transition representative atoms and pure local representative atoms allow the local transition elements to resolve non-local and local mismatches. The method presented herein is validated by force calculations in an unstressed perfect crystal as well as an unrelaxed grain boundary model. A nanoindentation simulation in 3D is conducted to demonstrate the accuracy and efficiency of the proposed method.

• Journal of Theoretical and Applied Mechanics
• /
• 제1권1호
• /
• pp.97-109
• /
• 1995

In this paper, a finite viscoelastic continuum model for rubber and its finite element analysis are presented. This finite viscoelatic model based on continuum mechanics is an extended model of Johnson and Wuigley's 1-D model. In this extended model, continuum based kinematic measures are rigorously defied and by using this kinematic measures, elastic stage law and flow rule are introduced. In kinematics, three configuration are introduced. In kinematics, three configuration are introduced. They are reference, current and virtual visco configurations. In elastic state law, it is assumed that at a certain time, there exists an elastic potential which describes the recoverable elastic energy. From this elastic potential, elastic state law is derived. The proposed flow rule is based on phenomenological observation. The flow rule gives precise relaxation response. In finite element approximation, mixed Lagrangian description is used, where total and similar method of updated Lagrangian descriptions are used together. This approach reduces the numerical job and gives simple nonlinear syatem of equations. To satisfy the incompressible condition, penalty-type modified Mooney-Rivlin energy function is adopted. By this method nearly incompressible condition is obtain the virtual visco configuration. For verification, uniaxial stretch tests are simulated for various stretch rates. The simulated results show good agreement with experiments. As a practical experiments. As a preactical example, pressurized rubber plate is simulated. The result shows finite viscoelastic effects clearly.

• Structural Engineering and Mechanics
• /
• 제57권5호
• /
• pp.809-821
• /
• 2016

Concentric-tube continuum robots have formed an active field of research in robotics because of their manipulative exquisiteness essential to facilitate delicate surgical procedures. A set of concentric tubes with designed initial curvatures comprises a robot whose workspace can be controlled by relative translations and rotations of the tubes. Kinematic models have been widely used to predict the movement of the robot, but they are incapable of describing its time-dependent hysteretic behaviors accurately particularly when snapping occurs. To overcome this limitation, here we present a finite element modeling approach to investigating the dynamics of concentric-tube continuum robots. In our model, each tube is discretized using MITC shell elements and its transient responses are computed implicitly using the Bathe time integration method. Inter-tube contacts, the key actuation mechanism of this robot, are modeled using the constraint function method with contact damping to capture the hysteresis in robot trajectories. Performance of the proposed method is demonstrated by analyzing three specifications of two-tube robots including the one exhibiting snapping phenomena while the method can be applied to multiple-tube robots as well.

• Membrane and Water Treatment
• /
• 제15권1호
• /
• pp.31-39
• /
• 2024

The flow in a nanopore of filtration membrane is often multiscale and consists of both the adsorbed layer flow and the intermediate continuum fluid flow. There is a controversy on which interface the slippage should occur in the nanopore filtration: On the adsorbed layer-pore wall interface or on the adsorbed layer-continuum fluid interface? What is the difference between these two slippage effects? We address these subjects in the present study by using the multiscale flow equations incorporating the slippage on different interfaces. Based on the limiting shear strength model for the slippage, it was found from the calculation results that for the hydrophobic pore wall the slippage surely occurs on the adsorbed layer-pore wall interface, however for the hydrophilic pore wall, the slippage can occur on either of the two interfaces, dependent on the competition between the interfacial shear strength on the adsorbed layer-pore wall interface and that on the adsorbed layer-continuum fluid interface. Since the slippage on the adsorbed layer-pore wall interface can be designed while that on the adsorbed layer-continuum fluid interface can not, the former slippage can result in the flux through the nanopore much higher than the latter slippage by designing a highly hydrophobic pore wall surface. The obtained results are of significant interest to the design and application of the interfacial slippage in nanoporous filtration membranes for both improving the flux and conserving the energy cost.

• 대한기계학회논문집B
• /
• 제41권6호
• /
• pp.429-434
• /
• 2017

분자-연속체 하이브리드 기법은 연속체 유체역학으로 예측하기 어려운 마이크로/나노 스케일 유동에 대해 개발되고 발전해 왔다. 분자동역학은 고체표면 주변 영역에서 사용되고, 나머지 영역에서는 나비아스톡스 방정식이 사용된다. 본 연구에서는 나노채널에서 고체-액체 상호작용과 표면 거칠기의 영향을 연구하기 위해 분자-연속체 하이브리드 기법을 이용하여 쿠에트 유동을 해석하였다. 우리는 고체-액체 상호작용 힘인 표면 에너지와 표면 거칠기가 유동의 표면 경계조건에 영향을 주는 것을 발견하였다. 표면 에너지가 낮을 때에는 유동이 고체 표면에서 미끄러짐이 발생하였고, 표면 에너지가 증가함에 따라 미끄러짐의 크기가 감소하였다. 표면 에너지가 높을 때에는 로킹(locking) 경계조건이 형성되었다. 또한 표면 거칠기는 유동이 고체 표면에서 미끄러지는 것을 방해하여 로킹 경계조건이 잘 형성되도록 영향을 주었다.

• 대한교통학회지
• /
• 제20권2호
• /
• pp.93-104
• /
• 2002

본 연구는 거시적 교통류 모형 중 고차연속교통류모형(high-order continuum model)의 개발을 목적으로 한다. 이 모형은 연속류 구간을 대상으로 수행되었고, 그 첫 번째 단계로 유·출입 구간이 없는 차로감소구간에서의 교통류를 묘사하였다. 개발된 모형은 차로변경율을 고려하였으며, 짧은 구간에서, 단기간동안의 교통류 행태에 대한 묘사를 가능하도록 하였다. 본 연구에서 개발된 모형은 우리나라 연속류 시설의 기하구조조건과 운전자들의 운전행태를 고려하여 우리나라 실정에 맞도록 새롭게 적용하였다. 이를 통해 장래에 연속류 시설에 대한 교통제어 전략 수립이나 운영 체계 개선과 같은 교통공학적 관리를 할 수 있을 것으로 기대된다. 모형의 현장적용성을 알아보기 위해, 현장에서 관측한 자료를 가지고 모의실험을 하였다. 그 결과, 교통량, 밀도, 속도의 시간대별 변동을 비교적 충실히 구현해 낸 것으로 판단된다.