• 한국해안·해양공학회논문집
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• 제32권1호
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• pp.11-16
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• 2020

인터로킹 케이슨에 의한 장대화된 방파제의 회전 안정성에 대해서 연구하였다. 무한 방파제에 경사지게 입사하는 선형파에 대한 해석해를 이용하여 방파제 기준선 방향으로의 파압 위상차 효과를 고려하였으며, 설계파의 비선형 특성을 고려하기 위하여 설계 기준 Goda 파압식을 차용하였다. 방파제의 회전 안전율을 케이슨 자중에 의한 회전 마찰저항모멘트와 수평 및 수직 파력에 의한 작용 회전모멘트의 비로 정의하고 최소 안전율을 보이는 회전 중심점 위치와 최소 안전율에 대한 해석해를 제시하였다. 규칙파, 불규칙파 및 다방향 불규칙파 등 현행 항만구조물 설계에 사용되고 있는 모든 설계파 조건에 대해서 적용 가능하도록 각 조건에 대한 평가식을 제안하였다.

• 한국산학기술학회논문지
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• 제18권2호
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• pp.31-37
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• 2017

본 연구는 오존 방식 선박평형수 처리의 주요 장치인 기체-액체 이젝터에 대하여 구동 노즐의 유입부에 회전 운동 유도 장치에 의해 발생되는 구동 유체의 회전 운동이 이젝터 효율에 미치는 영향에 관한 연구이다. 먼저 배압에 따른 이젝터의 각 포트별 압력과 흡입 유량을 확인하기 위하여 실험 장치를 구성하고, 회전 운동이 없는 이젝터에 대한 실험 수행 및 데이터를 획득한다. 실험의 데이터를 바탕으로 격자 사이즈 비교를 통해 기체-액체 이젝터에 적합한 유한요소모델을 선정하였으며, 도출된 CFD 모델을 이용하여 구동 유체의 회전 운동이 이젝터의 흡입 효율을 향상시킬 수 있음을 확인하였다. 이를 바탕으로 이젝터의 흡입 유량을 높이기 위하여, 메타 모델을 이용한 크리깅 기법을 사용하여 회전 유도 장치의 내부 형상 인자인 전체 길이 l, 내부 직경 d, 날개 개수 n에 대한 구조 최적화를 수행한다. 최적화된 회전 유도 장치를 적용한 결과 구동 유체의 회전 운동이 없는 이젝터에 비해 이젝터 효율이 약 3% 가량 개선됨을 확인하였다.

• 복합신소재구조학회 논문집
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• 제4권2호
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• pp.39-44
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• 2013

This study is aimed to examine the influence of the rotational stiffness of U-shaped ribs on the local buckling behaviors of laminated composite plates. Applying the orthotropic plates with eight layers of the layup $[(0^{\circ})4]s$ and $[(0^{\circ}/90^{\circ})2]s$, 3-dimensional finite element models for the U-rib stiffened plates were setup by using ABAQUS and then a series of eigenvalue analyses were conducted. There is a need to develope a simple design equation to establish the rotational stiffness effect, which could be easily quantified by comparing the theoretical critical stress equation for laminated composite plates with elastic restraints based on the Classical laminated plate theory. Through the parametric numerical studies, it is confirmed that there should clearly exist an increasing effect of local plate buckling strength due to the rotational stiffness by closed-section ribs. An applicable coefficient for practical design should be verified and proposed for future study. This study will contribute to the future study for establishing an increasing coefficient for the design strength and optimum design of U-rib stiffened plates.

• Geomechanics and Engineering
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• 제29권4호
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• pp.471-486
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• 2022

The effect of segmental joints is one of main importance for the segmental lining design when tunnels are excavated by a mechanized process. In this paper, segmental tunnel linings are analyzed by two numerical methods, namely the Beam-Spring Method (BSM) and the Solid-Interface Method (SIM). For this purpose, the Tehran Subway Line 6 Tunnel is considered to be the reference case. Comprehensive 2D numerical simulations are performed considering the soil's calibrated plastic hardening model (PH). Also, an advanced 3D numerical model was used to obtain the stress relaxation value. The SIM numerical model is conducted to calculate the average rotational stiffness of the longitudinal joints considering the joints bending moment distribution and joints openings. Then, based on the BSM, a sensitivity analysis was performed to investigate the influence of the ground rigidity, depth to diameter ratios, slippage between the segment and ground, segment thickness, number of segments and pattern of joints. The findings indicate that when the longitudinal joints are flexible, the soil-segment interaction effect is significant. The joint rotational stiffness effect becomes remarkable with increasing the segment thickness, segment number, and tunnel depth. The pattern of longitudinal joints, in addition to the joint stiffness ratio and number of segments, also depends on the placement of longitudinal joints of the key segment in the tunnel crown (similar to patterns B and B').

• 한국운동역학회지
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• 제13권3호
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• pp.81-98
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• 2003

The purpose of this study is to closely examine kinematic characteristics by jump phase of Li Xiaopeng motion in horse vaulting and provide the training data. In doing so, as a result of analyzing kinematic variables through 3-dimensional cinematographic using the high-speed video camera to Li Xiaopeng motion first performed at the men's vault competition at the 14th Busan Asian Games, the following conclusion was obtained. 1. It was indicated that at the post-flight, the increase of flight time and height and twisting rotational velocity has a decisive effect on the increase of twist displacement. And Li Xiaopeng motion showed longer flight time and higher flight height than Ropez motion with the same twist displacement of entire movement. Also the rotational displacement of the trunk at peak of COG was much short of $360^{\circ}$(one rotation) but twist displacement showed $606^{\circ}$. Likewise, Li Xiaopeng motion was indicated to concentrate on twist movement in the early flight. 2. It was indicated that at the landing, Li Xiaopeng motion gets the hip to move back, the trunk to stand up and the horizontal velocity of COG to slow down. This is thought to be the performance of sufficient landing, resulting from large security of rotational displacement of airborne and twist displacement. 3. It was indicated that at the board contact, Li Xiaopeng motion made a rapid rotation uprighting the trunk to recover slowing velocity caused by jumping with the horse in the back, and has already twisted the trunk nearly close to $40^{\circ}$ at board contact. Under the premise that elasticity is generated without the change of the feet contacting the board, it will give an aid to the rotation and twist of pre-flight. Thus, in the round-oH phase, the tap of waist according to the fraction and extension of hip joint and arm push is thought to be very important. 4. It was indicated that at the pre-flight, Li Xiaopeng motion showed bigger movement than the techniques of precedented studies rushing to the horse, and overcomes the concern of relatively low power of jump through the rapid rotation of the trunk. Li Xiaopeng motion secured much twist distance, increased rotational distance with the trunk bent forward, resulting in the effect of rushing to the horse. 5. At horse contact, Li Xiaopeng motion makes a short-time contact, and maintains horse take-off angle close to vertical, contributing to the increase of post-flight time and height. This is thought to be resulted from rapid move toward movement direction along with the rotational velocity of trunk rapidly earned prior to horse contact, and little shave of rotation axis according to twist motion because of effective twist in the same direction.

• 한국운동역학회지
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• 제24권1호
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• pp.1-9
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• 2014

The purpose of this study was to investigate the muscle mechanical properties of the pelvic axial pre-rotational movement for the Jireugi in the Taekwondo Juchumseogi stance. Eleven elite Taekwondo Poomsae athletes participated. Each participant performed 5 right hand Jireugi in Juchumseogi stance as fast and strong as possible while their motion was recorded by a 3D motion analysis system and the ground reaction forces by two force plates. The power and work of the muscular group surrounding the waist were analyzed to verify the effect of the stretch-shortening cycle (SSC) theory. The cause of the greater power seems to be the application of the SSC by the muscles surrounding the waist during the preparation phase of the pre-rotation group. For the none pre-rotation group, they only used the concentric contraction of the muscles surrounding the waist. Because the pre-rotation group used the SSC theory, they had the effect of shortening of the range of movement, creating a fast and more powerful rotation, thus anticipating the increase the magnitude of impact.

• Nuclear Engineering and Technology
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• 제54권6호
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• pp.2173-2187
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• 2022

A 3D thermo-elasto-hydrodynamic model is developed to analyze the sealing performance of a notched mechanical seal applied in the reactor coolant pump. In the model, the generalized Reynolds equation, the energy equation coupled with notch heat balance equation, the heat conduction equations, and the deformation equations of the sealing rings are iteratively solved by the finite element method. The film pressure and temperature distribution are obtained, and the deformation of the sealing rings is revealed to study the mechanism of the notched mechanical seals. A parameterized study is conducted to analyze the sealing performance under different operating conditions. As a comparison, the sealing performance of non-notched seals is also studied. The results show that the hydrostatic effect is dominant in the load-carrying capacity of the fluid film due to the radial mechanical and thermal deformations. The notch can cool the fluid film and influence the thermal deformation of seal rings. The sealing performance is sensitive to the pressure difference, ambient temperature, and rotational speed. It is suggested to set the notches on the softer sealing rings to acquire the greater hydrodynamic effect. Compared with the non-notched, the notched end face holds a better lubrication performance, especially under lower rotational speed.

• Tribology and Lubricants
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• 제14권2호
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• pp.42-48
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• 1998

Electro-Rheological (ER) fluid is a class of functional fluid whose apparent viscosity can be varied by the applied electric field strength. The ER fluid is classified into two types; one is a dispersive fluid and the other is a homogeneous. Dispersive ER fluid is a colloidal suspension of fine semiconducting particles in a dielectric liquid and liquid crystal (LC) is classed as homogeneous type ER fluid. LC has been originally developed for some electronic display devices. Various mechanical components applying ER fluid have been developed, and the their performance typically depends on the characteristics of ER fluid which have generally been evaluated by a rotational viscometer. However, the ER fluid introduced into various mechanical components undergoes not only simple shear flow but press flow or oscillating flow. For the evaluation of ER fluid, the authors developed an reciprocating type viscometer. The amplitude is controlled on 5 mm at the frequency from 50 to 1000 Hz. In the present paper, the performance of several types of ER fluid is evaluated by the reciprocating type viscometer and compared with those evaluated by a rotational viscometer.

• 한국가시화정보학회지
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• 제3권2호
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• pp.63-70
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• 2005

Birds and insects flap their wings to fly in the air and they can change their wing motions to do steering and maneuvering. Therefore, we created various wing motions with the parameters which affected flapping motion and evaluated the aerodynamic characteristics about those cases in this study. As the wing rotational velocity was fast and the rotational timing was advanced, the measured aerodynamic forces showed drastic increase near the end of stroke. The mean lift coefficient was increased until angle of attack of $50^{\circ}$ and showed the maximum value of 1.0. The maximum mean lift to drag ratio took place at angle of attack of $20^{\circ}$. Flow fields were also visualized around the wing using particle image velocimetry (PIV). From the flow visualization, leading-edge vortex was not shed at mid-stroke until angle of attack of $50^{\circ}$. But it was begun to shed at angle of attack of $60^{\circ}$.

• Earthquakes and Structures
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• 제10권4호
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• pp.867-891
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• 2016

This paper addresses numerically the behavior of steel structures under Fire-after-Earthquake (FAE) loading. The study is focused on a four-storey library building and takes into account the damage that is induced in structural members due to earthquake. The basic objective is the assessment of both the fire-behavior and the fire-resistance of the structure in the case where the structure is damaged due to earthquake. The combined FAE scenarios involve two different stages: during the first stage, the structure is subjected to the ground motion record, while in the second stage the fire occurs. Different time-acceleration records are examined, each scaled to multiple levels of the Peak Ground Acceleration (PGA) in order to represent more severe earthquakes with lower probability of occurrence. In order to study in a systematic manner the behavior of the structure for the various FAE scenarios, a two-dimensional beam finite element model is developed, using the non-linear finite element analysis code MSC-MARC. The fire resistance of the structure is determined using rotational limits based on the ductility of structural members that are subjected to fire. These limits are temperature dependent and take into account the level of the structural damage at the end of the earthquake and the effect of geometric initial imperfections of structural members.