• Computers and Concrete
• /
• 제3권4호
• /
• pp.213-233
• /
• 2006

Over the past years techniques for non-linear analysis have been enhanced significantly via improved solution procedures, extended finite element techniques and increased robustness of constitutive models. Nevertheless, problems remain, especially for real world structures of softening materials like concrete. The softening gives negative stiffness and risk of bifurcations due to multiple cracks that compete to survive. Incremental-iterative techniques have difficulties in selecting and handling the local peaks and snap-backs. In this contribution, an alternative method is proposed. The softening diagram of negative slope is replaced by a saw-tooth diagram of positive slopes. The incremental-iterative Newton method is replaced by a series of linear analyses using a special scaling technique with subsequent stiffness/strength reduction per critical element. It is shown that this event-by-event strategy is robust and reliable. First, the model is shown to be objective with respect to mesh refinement. Next, the example of a large-scale dog-bone specimen in direct tension is analyzed using an isotropic version of the saw-tooth model. The model is capable of automatically providing the snap-back response. Subsequently, the saw-tooth model is extended to include anisotropy for fixed crack directions to accommodate both tensile cracking and compression strut action for reinforced concrete. Three different reinforced concrete structures are analyzed, a tension-pull specimen, a slender beam and a slab. In all cases, the model naturally provides the local peaks and snap-backs associated with the subsequent development of primary cracks starting from the rebar. The secant saw-tooth stiffness is always positive and the analysis always 'converges'. Bifurcations are prevented due to the scaling technique.

• Structural Engineering and Mechanics
• /
• 제48권6호
• /
• pp.879-914
• /
• 2013

In part I of the article, formulation and characteristics of the several well-known structural geometrical nonlinear solution techniques were studied. In the present paper, the efficiencies and capabilities of residual load minimization, normal plane, updated normal plane, cylindrical arc length, work control, residual displacement minimization, generalized displacement control and modified normal flow will be evaluated. To achieve this goal, a comprehensive comparison of these solution methods will be performed. Due to limit page of the article, only the findings of 17 numerical problems, including 2-D and 3-D trusses, 2-D and 3-D frames, and shells, will be presented. Performance of the solution strategies will be considered by doing more than 12500 nonlinear analyses, and conclusions will be drawn based on the outcomes. Most of the mentioned structures have complex nonlinear behavior, including load limit and snap-back points. In this investigation, criteria like number of diverged and complete analyses, the ability of passing load limit and snap-back points, the total number of steps and analysis iterations, the analysis running time and divergence points will be examined. Numerical properties of each problem, like, maximum allowed iteration, divergence tolerance, maximum and minimum size of the load factor, load increment changes and the target point will be selected in such a way that comparison result to be highly reliable. Following this, capabilities and deficiencies of each solution technique will be surveyed in comparison with the other ones, and superior solution schemes will be introduced.

• 대한기계학회논문집
• /
• 제14권3호
• /
• pp.503-512
• /
• 1990

본 연구에서는 하중작용점(혹은 변위제어점)이 일점이고 스탭 백 현상이 없는 문제에 유용한 페널티 방법(penalty method)을 제안하고, 스냅 백 현상이 수반되는 경 우에는 페널티 방법과 Riks 방법을 선택적으로 취할 수 있도록 한다. 그리고 하중 작용점이 일점 혹은 그 이상의 점일 경우에 대해서는 Riks 방법을 기준으로 하되 일정 조건하에서는 새로운 증분하중 파라미터를 선택할 수 있게 하여, 순수한 Riks 방법으 로만 계산할 때에 일어날 수 있는 발산을 없앨 수 있게 한다. 끝으로 변위제어점이 일점 혹은 그 이상의 점인 경우에 대해 'Riks형 방법(Riks' type method)'을 제안하고, 이때에도 Riks형 방법을 기준으로 게산하되 일정한 조건하에서는 새로운 증분변위 파 라미터를 선택적으로 취할 수 있게 한다.

• 대한두개안면성형외과학회지
• /
• 제10권1호
• /
• pp.19-22
• /
• 2009

Purpose: There are various approaches for open reduction surgery for orbitozygomatic fractures. After the incisions are performed, patients might have various complications. In this point of view, we conducted a retrospective study of the usability of infraorbital incision on elderly patients, generally more vulnerable to scleral show and ectropion. Methods: In this study, 20 patients who are relatively more vulnerable to scleral show and ectropion through snap-back test having infraorbital incision were reviewed. We monitored the duration of the surgery, and complications resulted from the incision. We evaluated the scars with the researcher's observations and with the patient's level of satisfaction on a scale of 1 to 5. Results: On average, 5 minutes was spent between the skin incision and the fracture exposure. No case of scleral show and ectropion occurred. One year follow-up observation revealed 4 cases of visible scars, 9 cases of barely visible scars, and 7 cases of invisible scars. The subjective satisfaction level of the patients' scar is an average of 4.0. Conclusion: Infraorbital incision has many advantages. First, it can reduce the complications such as scleral show and ectropion. Second, it can shorten the operation time. Third, it can diminish incision-related scars.

• 대한토목학회논문집
• /
• 제10권2호
• /
• pp.11-22
• /
• 1990

본(本) 논문(論文)에서는 보존력(保存力) 및 비보존력(非保存力)을 받는 구조물(構造物)의 비선형(非線形) 유한요소해석(有限要素解析)을 수행(遂行)하기 위하여 기존의 하중증분법(荷重增分法)과 변위증분법(變位增分法)을 효율적(效率的)으로 결합(結合)시킨 수치적(數値的)인 해석(解析)알고리즘을 제시(提示)하였다. 제안(提案)한 알고리즘은 하중증분(荷重增分)과 변위증분(變位增分)이 자동(自動) 생성되도록 하므로써 Snap-Through, Turning-Back과 같은 비선형(非線形) 거동(擧動)을 포함(包含)하는 다양(多樣)한 평형경로(平衡經路)들을 추적(追跡)할 수 있었다.

• Structural Engineering and Mechanics
• /
• 제36권5호
• /
• pp.529-544
• /
• 2010

Nonlinear equations of structures are generally solved numerically by the iterative solution of linear equations. However, this iterative procedure diverges when the tangent stiffness is ill-conditioned which occurs near limit points. In other words, a major challenge with simple iterative methods is failure caused by a singular or near singular Jacobian matrix. In this paper, using the Newton-Raphson algorithm based on Davidenko's equations, the iterations can traverse the limit point without difficulty. It is argued that the propose algorithm may be both more computationally efficient and more robust compared to the other algorithm when tracing path through severe nonlinearities such as those associated with structural collapse. Two frames are analyzed using the proposed algorithm and the results are compared with the previous methods. The ability of the proposed method, particularly for tracing the limit points, is demonstrated by those numerical examples.

• 대한토목학회논문집
• /
• 제10권1호
• /
• pp.17-26
• /
• 1990

보존력(保存力) 및 비보존력(非保存力)을 받는 평면(平面) 뼈대 구조물(構造物)의 기하적(幾何的) 비선형(非線形) 거동(擧動)을 파악하기 위하여 기존의 하중증분법(荷重增分法)과 변위증분법(變位增分法)을 효율적으로 결합시킨 기하적(幾何的)인 비선형(非線形) 유한요소법(有限要素法)을 제시한다. 본(本) 논문(論文)에서 제안한 알고리즘은 보존력(保存力)뿐만 아니라 비보존력(非保存力)을 받는 경우에도 평면(平面) 뼈대의 Snap-Through, Turning-Back과 같은 강한 비선형(非線形) 거동(擧動)을 추적할 수 있다. 여러가지 예제(例題)들을 통하여 다른 문헌(文獻)들의 결과(結果)와 본(本) 연구(硏究)에 의한 결과(結果)를 비교 분석하므로써 제시된 이론(理論)의 정당성(正當性)을 입증(立證)한다.

• Steel and Composite Structures
• /
• 제27권1호
• /
• pp.13-25
• /
• 2018

The main objective of this study is to develop a dual approach for geometrically nonlinear finite element analysis of plane truss structures. The geometric nonlinearity is considered using the Total Lagrangian formulation. The nonlinear solution is obtained by introducing and minimizing an objective function subjected to displacement-type constraints. The proposed method can fully trace the whole equilibrium path of geometrically nonlinear plane truss structures not only before the limit point but also after it. No stiffness matrix is used in the main approach and the solution is acquired only based on the direct classical stress-strain formulations. As a result, produced errors caused by linearization and approximation of the main equilibrium equation will be eliminated. The suggested algorithm can predict both pre- and post-buckling behavior of the steel plane truss structures as well as any arbitrary point of equilibrium path. In addition, an equilibrium path with multiple limit points and snap-back phenomenon can be followed in this approach. To demonstrate the accuracy, efficiency and robustness of the proposed procedure, numerical results of the suggested approach are compared with theoretical solution, modified arc-length method, and those of reported in the literature.

• 한국의류학회지
• /
• 제27권8호
• /
• pp.873-882
• /
• 2003

The purpose of the study is altering ready-made garments for the wheelchair users. Some alterations ready-made garments suggested for the wheelchair users are applicable to the physical conditions using the wheelchair, which create limitations in the use of clothing. Alterations ready-made garments were suggested 3 parts of the altering on the tops and 3 parts of the pants. Detachable sleeves at the elbow, adding the action pleats on the shoulder and back openings with zipper were adapted on the tops. The altering crotch length from the center back, changing position of the pocket and adding the pleats at the knee were adapted on the pants. The snap-tapes, zipper and hook & eye were used for the altering the ready-made garments.

• 패션비즈니스
• /
• 제16권1호
• /
• pp.103-120
• /
• 2012

The study aimed to evaluate the appearance of the men's work clothes jumpers developed to suggest the prototype work clothes jumper patterns by using the 3-D clothing simulation technology. The 3-D simulated clothing images considered the upper body features of men in the age range between 20 and 59 in South Korea. A questionnaire survey conducted previously suggested a basic jumper style with shirt collar and snap opening cuffs for the heavy industry workers; and discomforting parts of the work clothes jumper of the subject workers have been referred to for the experimental jumper appearance test. Besides, defining the measurements of men's upper bodies enabled to generate the men's 3-D virtual models representing each age group's average body feature. The significant body measurement factors for men's 3-D body modeling and jumper pattern-making were stature for the height factor; chest, waist and hip circumferences for the circumference factor; waist back, hip and arm lengths and interscye front/back for the length factor; and back neck breadth for the breadth factor and armscye and scye depths for the depth factor. The men's body measurements of 30's were implemented to three experimental jumper pattern-making methods, i.e. the 1st method using the relations based on stature and chest circumference; the 2nd method using the direct body measurements; and the 3rd method adopting the maximum ease amount of given body measurements whether relations or direct measurements except the direct measurement of scye depth. A comparison among the three experimental jumpers' simulated images highlighted that the appropriate ease amount of the jumper gained higher scores in terms of the jumpers' front, side, back and sleeve parts and the total silhouettes. Therefore the 3rd experimental jumper was finally selected for the heavy industry workers.