• 대한기계학회논문집A
• /
• 제39권1호
• /
• pp.45-53
• /
• 2015

세탁기의 용량이 커지면서 세탁 및 탈수 시의 세탁물에 의한 질량 불균형 문제가 심해지고 있으며, 이러한 문제를 해결하기 위하여 세탁기에서도 다양한 형태의 서스펜션이 장착되고 있다. 본 연구에서는 마찰 서스펜션에서 발생하는 힘을 측정한 뒤, 물리적인 수식으로 마찰 서스펜션의 비선형 특성을 모델링 하였다. 최소 자승 해(least squares solution)를 구해 파라미터들을 추정하고, 시험과 동일한 조건의 시뮬레이션을 실시하여 개발된 마찰 서스펜션 모델링의 타당성을 검증하였다.

• 한국추진공학회지
• /
• 제16권5호
• /
• pp.29-36
• /
• 2012

연소시험을 통한 성공/실패 사례가 있는 FASTRAC 연소기에 대해, 효용성이 검증된 3차원 선형 음향해석을 수행하여 음향공의 물성치 변화에 따른 감쇠 특성을 파악하였다. 음향공의 동조주파수와 감쇠능력을 정량화하기 위해 음향 임피던스 개념을 도입하였다. 기하학적 형상이 주어진 상태에서, 음향공 내부의 음속 변화에 따라 최적의 동조가 가능한 음속을 파악하였다. 최적의 동조가 이루어지기 위한 음향공 내부의 음속 예측 방법을 제시하였다. 이를 통하여 여러 기하학적 형상을 가지는 음향공에 대하여 적용하여 감쇠능력을 정량화함으로써 연소안정성의 확보 여부에 대한 검토가 가능할 것이며, 안정성이 확보되지 못한 경우에 대해서는 그 이유를 명확하게 규명할 수 있을 것이다.

• 국제초고층학회논문집
• /
• 제5권1호
• /
• pp.21-30
• /
• 2016

The structural efficiency of tall buildings heavily depends on the lateral stiffness and resistance capacity. Among those structural systems for tall buildings, outrigger system is one of the most common and efficient systems especially for those with relatively regular floor plan. The use of outriggers in building structures can be traced back from early 50 from the concept of deep beams. With the rise of building height, deep beams become concrete walls or now in a form of at least one story high steel truss type of outriggers. Because of the widened choice in material to be adopted in outriggers, the form and even the objective of using outrigger system is also changing. In the past, outrigger systems is only used to provide additional stiffness to reduce drift and deflection. New applications for outrigger systems now move to provide additional damping to reduce wind load and acceleration, and also could be used as structural fuse to protect the building under a severe earthquake condition. Besides analysis and member design, construction issue of outrigger systems is somehow cannot be separated. Axial shortening effect between core and perimeter structure is unavoidable. This paper presents a state-of-the-art review on the outrigger system in tall buildings including development history and applications of outrigger systems in tall buildings. The concept of outrigger system, optimum topology, and design and construction consideration will also be discussed and presented.

• 한국콘크리트학회:학술대회논문집
• /
• 한국콘크리트학회 1998년도 봄 학술발표회논문집(II)
• /
• pp.433-438
• /
• 1998

Design lateral strength calculated by current seismic design code is prescribed to be much lower than the force level required for a structure to respond elastically during design level earthquake ground motion. Present procedures for calculating seismic design forces are based on the use of elastic spectra reduced by a strength reduction factor known as "response modification factor, R". This factor accounts for the inherent ductility, overstrength, redundancy, and damping of a structural system. This study considers ductility and overstrength of the wall-type structure for investigating R factor. This means that R factor is determined from the product of "ductility-based R factor($R_$\mu$$) and overstrength factor($R_s$). $R_$\mu$$ factor is calibrated to attain the targer ductility ratio (system ductility capacity) and produced in the from of $R_$\mu$$ spectra considering the influence of target ductility, natural period, and hysteretic model. On the other hand, $R_s$ is more difficult to quantify, since it depends on both material and system-dependent uncertain parameters. In this study Rs factor was determined from the result of push-over analysis.-over analysis.

• 한국소음진동공학회:학술대회논문집
• /
• 한국소음진동공학회 2008년도 추계학술대회논문집
• /
• pp.394-400
• /
• 2008

This paper presents an analytical method to investigate the stability of FDBs (fluid dynamic bearings) considering the tilting motion. The perturbed equations of motion are derived with respect to translational and tilting motion for the general rotor-bearing system with five degrees of freedom. The Reynolds equations and their perturbed equations are solved by using the FEM in order to calculate the pressure, load capacity, and the stiffness and damping coefficients. This research introduces the radius of gyration to the equations of notion in order to express the mass moment of interia with respect to the critical mass. Then the critical mass of FDBs is determined by solving the eigenvalue problem of the linear equations of motion. This research is numerically validated by comparing the stability chart of FDBs with the time response of the whirl radius obtained from the direct integration of the equations of motion. This research shows that the tilting motion is one of the major design considerations to determine the stability of rotating system. It also shows that the stability of FDBs considering only translation is overestimated in comparison with the stability of FDBs considering both translational and tilting motion.

• 터널과지하공간
• /
• 제6권2호
• /
• pp.144-156
• /
• 1996

The deformation behaviors under uniaxial compressive cyclic loading were investigated for fresh rocks and freeze-thaw cycled samples. The Pocheon granite which is one of the most popular building stone in Korea was selected for tests. 0.5 Hz and 50% of dynamic strength were used as test conditions for frequency and fatigue span, respectively. For freezethaw procedure, sample were frozen for 3 hours under the temperature of -2$0^{\circ}C$ and then followed 3 hours thawing under the temperature of +2$0^{\circ}C$. Twenty seven samples were used as untreated and seventy three for freeze-thaw samples. No failure occurred up to 15000 cycles at the stress level of 60% of dynamic strength, indicating that the lowest strees level for fatigue failure may be around 60% of dynamic strength. Permanent strain and damping capacity curves show that there were three stages when rock behaves like under creep. Young's moduli were increased and Possion's ratios were decreased with the increase of the number of cycles. Possion's ratios varied more rapidly than Young's moduli did with the increase of the number of cycles. This may represent that most microcracks developed by fatigue stress are parallel to the axis of loading. The deformation behavior of freeze-thaw cycled samples were almost the same as that of untreated samples. However, the result of freeze-thaw cycled samples showed lower regression constant, indicating that the physical durability of rock is much lowered because of cyclic temperature variation.

• Journal of Advanced Marine Engineering and Technology
• /
• 제13권1호
• /
• pp.57-68
• /
• 1989

This paper treats the analytical and experimental studies on the improvement of commutating circuit for the speed control of DC motor. A simple circuit composed of R, L and C elements is proposed here for switching off power SCR carrying the load current. The real important in this chopper circuit is to determine the reasonable values of commutating circuit constants. In this paper, the reasonable values of the commutating circuit constants are basically determined on a view point of commutating performances in the given circuit model and must satisfy the following conditions. The first, the peak commutating current should be larger than the anticipated maximum load current. The second, the circuit turn-off time (tc) must be longer than the SCR turn-off time (tq). The third, the resistor should be enough large to permit the current to be neglected in the analysis of the commutation circuit, as well as be enough small to permit to charge the capacity voltage (Ec) to the half the value of source voltage (E) before the next communication cycle is initiated. The last, the period of chopping signal must be the least possible multiple of the damping vibration period of commutating circuit. The improved chopper circuit used in the experiment under unloaded condition was composed to meet the reasonable conditions mentioned above, and a successful commuting performance was achieved without failure. Several types of microprocessor having a different value of CPU speed individually have been applied to the experiment under the loaded conditions. Also it shows that the faster the speed of CPU is, the more stable the commutation turns out.

• 한국강구조학회 논문집
• /
• 제20권2호
• /
• pp.215-226
• /
• 2008

강관이 삽입된 강합성 중공 기둥의 내진 성능 평가 실험을 수행하였다. 준정적 실험을 통하여 강합성 중공 기둥과 일반 중실 RC기둥의 내진 성능을 비교 평가 하였다. 각각의 기둥 시험체에 대해 최대 하중과 변위의 관계를 측정하였으며, 이를 바탕으로 연성도, 소산에너지, 등가 감쇠비, 손상 지수가 계산되었다. 실험 결과 강합성 중공 기둥은 중실 RC 기둥에 비해 약 2배의 모멘트에 저항을 하였으며, 에너지의 흡수와 소산에서도 2배 정도의 성능을 보여주어, 강합성 중공 기둥의 우수한 성능을 확인하였다.

• 한국전산구조공학회논문집
• /
• 제15권2호
• /
• pp.197-207
• /
• 2002

본 연구에서는 죄굴이 방지된 비부착 가새가 설치된 철골조 건물의 에너지 소산능력과 지진응답에 대하여 연구하였다. 먼저 조화하중을 받는 단자유도계 구조물을 대상으로 변수분석을 수행하고 가새의 최적항복강도를 구하였다. 다자 유도계 골조구조물의 비선형 시간이력 해석을 통하여 다양한 크기와 강도를 가진 가새가 설치된 구조물의 지진응답을 분석하고, 가새의 적당한 층별 분배방법을 찾기 위하여 여러 가지 분배방법을 적용하였다. 해석결과에 따르면 일반적으로 가새의 강성이 증가함에 따라 구조물의 최대변위는 감소하였다. 그러나 구조물의 고유주기 및 하중에 따라 가새의 강성이 커짐에 따라 구조물의 최대 변위와 누적된 손상이 증가하는 것으로 나타났다.

• 소성∙가공
• /
• 제23권8호
• /
• pp.495-500
• /
• 2014

Magnesium alloys are currently expected to be widely used for weight reduction of cars and as high efficient materials in the automotive and electronics industries. Although the specific strength of magnesium is excellent, it cannot be easily formed at room temperature due to its HCP structure. However in order to improve the formability of magnesium, it is necessary to investigate its formability in the warm temperature range. In the current study, the aim was to add to the magnesium property database so that the mass production of a magnesium car body can be accomplished. Warm tensile tests were conducted and the forming limit diagram was determined to confirm formability characteristics of magnesium AZ31B alloy sheet. In addition the bending formability and the magnesium damping capacity were evaluated for AZ31B and compared to SPRC440E which is a sheet steel used for car bodies.