• Wind and Structures
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• 제16권1호
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• pp.93-115
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• 2013

This paper describes a study of the influence of a dynamically flexible building structure on pressures inside and net pressures on the roof of low-rise buildings with a dominant opening. It is shown that dynamic interaction between the flexible roof and the internal pressure results in a coupled system that is similar to a two-degree-of-freedom mechanical system consisting of two mass-spring-damper systems with excitation forces acting on both the masses. Two resonant modes are present, the natural frequencies of which can readily be obtained from the model. As observed with quasi-static building flexibility, the effect of increased dynamic flexibility is to reduce the first natural frequency as well as the corresponding peak value of the admittance, the latter being the result of increased damping effects. Consequently, it is found that the internal and net roof pressure fluctuations (RMS coefficients) are also reduced with dynamic flexibility. This model has been validated from experiments conducted using a cylindrical model with a leeward end flexible diaphragm, whereby good match between predicted and measured natural frequencies, and trends in peak admittances and RMS responses with flexibility, were obtained. Furthermore, since significant differences exist between internal and net roof pressure responses obtained from the dynamic flexibility model and those obtained from the quasi-static flexibility model, it is concluded that the quasi-static flexibility assumption may not be applicable to dynamically flexible buildings. Additionally, since sensitivity analyses reveal that the responses are sensitive to both the opening loss coefficient and the roof damping ratio, careful estimates should therefore be made to these parameters first, if predictions from such models are to have significance to real buildings.

• 대한기계학회논문집A
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• 제38권11호
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• pp.1231-1237
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• 2014

군용 차량의 경우 야지 주행에 대한 성능 시험이 필수적인데 실차 시험의 경우 비용과 시간에 의한 제약을 받게 되므로, 시뮬레이션을 통한 성능 분석이 효율적이다. 본 연구에서는 상용 다물체 해석프로그램인 MSC.ADAMS 를 이용하여 차량 모델을 개발한다. 타이어 수직 강성 시험을 수행하고 FTire 모델에 반영하여 타이어 모델을 생성한다. 댐퍼의 경우 비선형 특성 시험을 통해 얻은 결과를 반영하여 댐퍼를 모델링 하였으며, 겹판 스프링은 빔 요소 모델로 차량 모델을 구성한다. 단순 장애물 통과 시험 및 파형로 통과 시험을 수행하고 가속도 응답 및 휠 하중 응답 분석을 통해 차량 모델의 신뢰성을 검증하였다.

• 한국자동차공학회논문집
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• 제3권1호
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• pp.33-44
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• 1995

As the occupant safety receives more attention from automobile industries. protection systems have been developed quite well. Developed protection systems must be evaluated through real tests in crash environment Since the real tests are extremely expensive. computer simulations are replaced for some prediction of the real test In the computer simulation. it is very crucial to express the real environment precisely in the modeling precess. The energy absorbing(EA) steering system has a very important rote in vehicle crashes because the occupant can hit the system directly. In this study. the EA steering system is modeled precisely. analyzed for the safely and designed by an optimization technology. First. the EA steering system is disassembled by parts and modeled by segments and joints. The segments are modeled by rigid bodies in motion and they have resistances in contact. Spring-damper elements and force-deflection curves are utilized to represent the joints. The body block test is cal lied out to validate. the modeling. When the test results are not enough for the detailed modeling. the differences between tests and simulations are minimized to calculate unknown parameters using optimization. The established model is applied to a crash simulation of a full-car model and tuned again. After the modeling is finished. components of the steering system are designed by an optimization algorithm. In the optimization process. the compound injury of a driver is defined and minimized to determine the chracteristics of the components. The second. order approximation algorithm has been adopted for the optimization.

• 한국소음진동공학회논문집
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• 제25권12호
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• pp.856-865
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• 2015

In a high-speed press, numerous moving links are interconnected and each link executes a constrained motion at high speed. As a consequence, high-level dynamic unbalance force and unbalance moment are transmitted to the main frame of the press, which results in unwanted vibration and significantly degrades manufacturing accuracy. Dynamic unbalance force and unbalance moment inevitably transmits high-level vibrational force to the foundation on which the press is installed. Minimizing the vibrational force transmitted to the foundation is critical for the protection of both the operators and the surrounding structures. The whole task should be carried out in two steps. The first step is to reduce dynamic unbalance based upon kinematic and dynamic analyses. The second step is to design and build an optimal vibration isolation system minimizing the vibrational force transmitted to the foundation. Firstly, the dynamic design method is presented to reduce dynamic unbalance force and moment. For this a 3D CAD software was utilized and a computer program was written to compute dynamic unbalance force and moment. Secondly, the design method for vibration isolation system is presented. The method for designing coil springs and viscous dampers are explained in detail.

• 한국소음진동공학회논문집
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• 제18권9호
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• pp.961-971
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• 2008

In the design of a rotor shaft, care should be taken to minimize vibration by taking into account the sources of vibration. In addition, the intensity critical speed, stability, and other related aspects of the system must be considered. especially when it is operated at a critical speed, it is important to address issues related to vibration, as an increase in the whirling response of the rotor shaft can cause damage to the shaft, destruction of the rotor parts, and detrimental abrasions on the bearings. In this thesis, the vibration characteristics of a rotor shaft are investigated through the use of the finite element method. Variations of the diameters and lengths were used to determine the effect of a rotor shaft using Beam No.188(3D linear strain beam) in ANSYS version 11.0 as a universal interpretation program for finite elements. Special care was taken to prevent excessive vibration, which can result from resonance at the initial stage, in the formulation of a dynamic design for a rotor shaft through calculations while changing the diameters and the lengths of the shaft. Moreover, the dynamic characteristics of the critical speed, total mass, D/L(diameter to length) ratio, and natural frequency were verified. Furthermore, the rotor shaft applied by bearing element was calculated and compared by using Combi No. 214(2-D spring-damper bearing).

• 한국군사과학기술학회지
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• 제10권4호
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• pp.5-11
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• 2007

The future combat system is likely to be studied and developed in terms of enhancing both firepower and mobility simultaneously. Increased firepower often necessitates a heavier firing system. In return, the body of the vehicle needs to be light-weight in order to improve the mobility of the whole system. For this reason, in the areas of weapons systems such as the tank and self-propelled artillery, a number of studies attempting to develop designs that reduce recoil force against the body of the vehicle are being conducted. The current study proposes a tank construction that has a mass-spring-damper system with two degrees of freedom. A tank structure mounted with a specific soft recoil system that was implemented using a soft recoil technique and another tank structure based on a general recoil technique were compared to each other in order to analyze the recoil forces, the displacements of recoil, and the firing intervals when they were firing. MATLAB-Simulink was used as a simulating tool. In addition, the relationship between the movement of the recoil parts and the positions of the recoil latches in each of the two structures were analyzed. The recoil impact power, recoil displacement, firing interval, and so on were derived as functional formulas based on the position of the recoil latch.

• 대한기계학회논문집A
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• 제38권6호
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• pp.619-627
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• 2014

본 논문은 등가정하중을 이용하여 제어시스템을 포함한 구조물의 설계를 위한 최적화 방법을 제안한다. 지난 연구는 구조물과 제어시스템 최적설계를 독립적으로 분리하여 수행하였고, 구조물과 제어시스템을 동시에 최적화하여도 제어시스템의 제어변수는 정상상태에서만 최적화하여 성능을 향상시켰다. 하지만 제어변수는 모든 시간영역에서 최적화해야 한다. 즉, 제어시스템의 해석은 과도상태에서 수행해야 한다. 본 연구에서는 새로운 등가정하중을 이용하여 제어변수를 포함하는 제어시스템 구조물의 최적설계를 위한 방법을 제시하였다. 등가정하중은 동적하중이 구조물에 작용할 때 발생하는 임의 시간에서의 변위장과 동일한 변위장을 만들어내는 정하중을 의미한다. 이렇게 계산된 등가정하중을 이용하여 설계영역에서 선형정적응답 최적설계를 진행한다. 몇 가지 예제를 통해 새로운 등가정하중을 적용한 동적응답 최적설계방법의 유용성을 확인하였다.

• Advances in biomechanics and applications
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• 제1권3호
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• pp.169-185
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• 2014

Computational multibody models of the elbow can provide a versatile tool to study joint mechanics, cartilage loading, ligament function and the effects of joint trauma and orthopaedic repair. An efficiently developed computational model can assist surgeons and other investigators in the design and evaluation of treatments for elbow injuries, and contribute to improvements in patient care. The purpose of this study was to develop an anatomically correct elbow joint model and validate the model against experimental data. The elbow model was constrained by multiple bundles of non-linear ligaments, three-dimensional deformable contacts between articulating geometries, and applied external loads. The developed anatomical computational models of the joint can then be incorporated into neuro-musculoskeletal models within a multibody framework. In the approach presented here, volume images of two cadaver elbows were generated by computed tomography (CT) and one elbow by magnetic resonance imaging (MRI) to construct the three-dimensional bone geometries for the model. The ligaments and triceps tendon were represented with non-linear spring-damper elements as a function of stiffness, ligament length and ligament zero-load length. Articular cartilage was represented as uniform thickness solids that allowed prediction of compliant contact forces. As a final step, the subject specific model was validated by comparing predicted kinematics and triceps tendon forces to experimentally obtained data of the identically loaded cadaver elbow. The maximum root mean square (RMS) error between the predicted and measured kinematics during the complete testing cycle was 4.9 mm medial-lateral translational of the radius relative to the humerus (for Specimen 2 in this study) and 5.30 internal-external rotation of the radius relative to the humerus (for Specimen 3 in this study). The maximum RMS error for triceps tendon force was 7.6 N (for Specimen 3).

• 한국정보과학회논문지:소프트웨어및응용
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• 제32권8호
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• pp.769-780
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• 2005

본 논문에서는 스프링-댐퍼 메쉬를 2차원 영상 패턴의 변형을 모델링 및 분석하는 데 응용하는 방법을 제안한다. 기존의 메쉬와 다르게 새롭게 제안된 메쉬 모형은 메쉬 노드와 영상 픽셀을 하전입자로 표현하고 둘 사이의 상호작용에 의하여 변형되는 메쉬를 다양한 기준함수에 의하여 분석하는 것이다. 메쉬의 변형 과정은 하전입자 사이의 상호작용에 의한 스트레스 완화 과정으로써 널리 알려진 간단한 수치적분법을 사용한다. 변형 메쉬평가함수로 네 가지를 제안하고 각각의 성능을 분석하였다. 훈련 메쉬로는 샘플 영상의 평균 패턴을 구하여 메쉬로 직접 변환한 것을 사용하였다. 실험 결과 각 함수는 국소 변형을 모두 제대로 평가하는 측도로서는 아직 부족하지만 앞으로 이에 대한 보완 또는 새로운 함수의 제안, 그리고 이완 과정의 개선이 뒤따른다면 보다 체계적인 분석 방법과 높은 성능을 제공할 것으로 판단된다.

• 한국지진공학회논문집
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• 제14권4호
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• pp.37-48
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• 2010

본 논문에서는 철근콘크리트 구조물과 같이 강성저감으로 인해 낮은 에너지 소산능력을 갖는 구조물의 제진성능을 비선형시간이력해석을 통해 조사하였다. 원구조물은 modified Takeda 이력모델을 갖는 단자유도시스템으로 이상화하였고, 완전탄소성 모델로 이력감쇠장치를 모델링하였다. 수치해석결과의 통계를 기초로 등가선형화에 의한 제진응답 평가의 적용성을 검증하였고, 제진보강 구조물의 응답예측을 위한 경험식을 제시하였다. 결과적으로 등가선형화를 통한 변위응답 평가보다는 본 연구에서 제시한 경험식을 이용하여 요구연성도를 추정하는 것이 더 정확하다. 경험식에서 얻어진 적정 감쇠기 항복강도는 완전탄소성시스템에 대한 최적 항복강도와는 상당한 차이를 가진다. 획득 가능한 연성도 저감효과는 원구조물의 고유주기가 짧을수록, 지진의 상대적 강도가 약할수록 우수한 것으로 나타났다.