• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.36 no.9
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• pp.825-834
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• 2008

Nose chine shape optimization study has been performed to maximize the directional stability at high angle of attack supersonic flow. Various chine shapes are generated using super ellipse equation. By numerically investigating the directional stability characteristics of those shapes, the baseline configuration for the shape optimization has been selected using the three-dimensional Navier-Stokes equations. The configuration is represented by the NURBS curves which can adjust the surface geometry by the control points. The response surfaces are constructed to obtain optimum shape which has high directional stability characteristics and lift-to-drag ratio. From this study, an efficient configuration design and optimization process which utilizes the parameter-based configuration generation techniques and approximation method has been established, then 29% improvement of the directional stability by strong vortexes from chine nose is accomplished.

• Journal of Korean Society of Steel Construction
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• v.12 no.2 s.45
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• pp.187-196
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• 2000

In this paper, stability analysis is carried out for the out of plane behaviors under compressive loads to the direction of the generator in anisotropic cylindrical shells. It is not easy to obtain the analytic solutions about the stability analysis of anisotropic cylindrical shells consisted of composite materials. For solving this problems, this paper used the finite difference method which is one of the numerical methods. Geometrical property of cylindrical shells transforms the compressive loads into the inplane behaviors. This paper studied the change of stiffness in the direction of the circumferential and stability of shells according to change of fiber angle, curvature, subtended angle and aspect ratio. From result of this study, anisotropic cylindrical shells under compressive loads to the direction of the generator vary greatly with respect to the change of the circumferential stiffness. Therefore, it will be more safe to strengthen the circumferential stiffness of anisotropic cylindrical shells under compressive loads.

• Transactions of the Korean Society of Mechanical Engineers
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• v.5 no.3
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• pp.178-182
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• 1981

쉘이 복합재로 제작되었거나 보강재를 사용하였을때에는 쉘요소의 역학적 특성은 방향성을 가지게 된다. 이 논문에서는 선형관계식을 사용하여 동적 표면가동을 받는 이방성원통쉘의 안정성을 고려하여 다루었다. 재료의 이방성을 고려하여 3방향 즉, 축방향, 둘레방향 및 반경향의 실성항이 포함된 운동방장실을 유도하였다. 동적 안전성의 해석은 Bolotin 의 방법을 따랐으며 근사해를 행렬식행으로 제시하였다. 수직열로 외압을 받는 원통쉘의 좌단을 다루었으며 본 이론과 고전이론 사이의 차이점을 검토하였다.

• Journal of the Korean Society of Marine Environment & Safety
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• v.20 no.4
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• pp.443-450
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• 2014

In this study, we have discussed about the effect of hydrofoil arrangement and longitudinal moment characteristic on longitudinal motion stability of fully-submerged hydrofoil by the experiment of tandem hydrofoil model. First of all, tandem hydrofoil model that has canard wing arrangement has been made and characteristics of lift force and drag force by performing the lift force and drag force measuring experiment has also been estimated. Besides, tandem hydrofoil model's wing arrangement which has the initial stability and self stability of longitudinal motion has also been determined. In longitudinal stability experiment of tandem hydrofoil model, the motion characteristic of pitch and heave and the longitudinal stability of foil borne condition by variation of self stability of longitudinal moment and longitudinal distance are estimated. The result from the experiment and it's important conclusion can be described as below; Increase the self stability for longitudinal moment, the higher self stability for pitch motions in a constant pitch angles. By increasing the self stability for longitudinal moment, the range of fluctuation of pitch motion and heave motion for pitch angle also will change relatively small and longitudinal stability is excellent. Lastly, when the lift force of hydrofoil is remain constants, we can conclude that securing the enough self stability for longitudinal moment is essential for stable foil borne condition of tandem hydrofoil.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.13 no.2
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• pp.139-148
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• 2001

Phenomena induced by waves, such as overtopping, sediment transport, vibration/fluctuation and destruction of structures are highly influenced by the directionality of wave propagation. These phenomena are often dominated by non-linearity, and so hydraulic model experiments are widely adopted for stability analysis rather than numerical modeling, Thus, stability ofrubblc mound breakwaters(RMB) due to wavc directionality was experimentally investigated in this study. The incident wave angle $30^{\circ}$ was found more risky on the damage rate of RMB under directional regular waves, and the incident wave angle $40^{\circ}$ was found relatively risky under directional irregular waves. These results clarified the wave directionality effect on the stability ofRMB, These facts were found correspondent to the occurrence of the peak between $20^{\circ}$-$40^{\circ}$ with the directional frequency distribution of lIlO maximum water particle velocity.

• Proceedings of the Korean Society for Rock Mechanics Conference
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• 2001.03a
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• pp.177-187
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• 2001

암반사면의 안정성은 암반 내에 발달한 불연속면의 방향성과 파괴특성에 지대한 영향을 받는다. 두 조의 연속성이 좋은 절리가 발달한 암반의 거동을 해석하기 위해 FLAC의 FISH 언어로 작성된 편재 절리모델을 사용하여 절리암반사면의 안정성을 평가하였다. 해석 결과는 절리의 간격과 방향성을 달리하면서 수행된 UDEC 해석과 저면 마찰 모델 시험결과와 비교하였다. UDEC 해석과 저면 마찰 모형시험 의해 발생된 파괴면의 형상은 유사하였으며, 이 결과로부터 편재절리모델에 의한 FLAC 해석에서의 파괴면은 두 조의 교차하는 절리를 따라 계단식으로 파괴면이 발생함을 추정할 수 있었다.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.40 no.11
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• pp.948-956
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• 2012

This paper presents the computations of the longitudinal and directional stability derivatives for the SDM(Standard Dynamic Model). The static and dynamic derivatives are evaluated at once using forced harmonic oscillations in the pitch and yaw directions. For the numerical simulations, a 3-D Euler solver that uses a dual time stepping method for unsteady time accurate simulations is applied. This work investigates the variation of the derivatives in terms of the Mach number and the several motion parameters. Good agreement of the pitch and yaw stability derivatives with previously published numerical results and experimental results are observed.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2004.05a
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• pp.21-21
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• 2004

본 논문은 수동 힘반영 기구의 안정성을 제어하기 위한 방법으로 수동성 제어기를 제안한다. 수동 힘반영 기구는 브레이크와 같은 수동 엑츄에이터를 사용함으로써 힘을 반영하게 되는데, 여기에 사용되는 수동 엑츄에이터는 사용자가 움직이고자 하는 방향의 반대방향으로만 힘을 생성할 수 있기 때문에, 힘을 생성할 수 있는 방향에 제한이 있다. 따라서 가상의 벽면을 나타내는 데에도 정확히 원하는 방향의 힘을 제시하지 못하고, 힘의 근사화를 통하여 가장 근접한 방향의 힘을 생성해낸다. 이는 이상적인 수동 힘반영 기구의 연구에서도 나타나며, FME(Force Manipulability Ellipsoid)에 의해 명확하게 설명이 되는 현상이다.(중략)

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.3
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• pp.310-316
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• 2016

We propose a novel contact-free transportation system in which an axial electrodynamic wheel is applied as an actuator. When the electrodynamic wheel is partially overlapped by a fixed conductive plate and rotates over it, three-axis magnetic forces are generated on the wheel. Among these forces, those in the gravitational direction and the lateral direction are inherently stable. Therefore, only the force in the longitudinal direction needs to be controlled to guarantee spatial stability of the wheel. The electrodynamic wheel consists of permanent magnets that are repeated and polarized periodically along the circumferential direction. The basic geometric configuration and the pole number of the wheel influence the stability margin of a transportation system, which would include several wheels. The overlap region between the wheel and the conductive plate is a dominant factor affecting the stiffness in the lateral direction. Therefore, sensitivity analysis for the major parameters of the wheel mechanism was performed using a finite element tool. The system was manufactured based on the obtained design values, and the passive stability of a moving object with the wheels was verified experimentally.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.40 no.1
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• pp.103-111
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• 2016

This paper presents an adaptive variable weights tuning system for an integrated chassis control with electronic stability control (ESC) and active front steering (AFS) for lateral stability enhancement. After calculating the control yaw moment needed to stabilize a vehicle with a controller design method, it is distributed into the tire forces generated by ESC and AFS using weighted pseudo-inverse-based control allocation (WPCA). On a low friction road, lateral stability can deteriorate due to high vehicle speed. To cope with the problem, adaptive tuning rules on variable weights of the WPCA are proposed. To check the effectiveness of the proposed method, a simulation was performed on the vehicle simulation package, CarSim.