• Title/Summary/Keyword: Unstable state

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Shape Finding of Unstable Link Structures (불안정(不安定) Link 구조물(構造物)의 형태해석(形態解析)에 관(關)한 연구(硏究))

  • Kim, Jae-Yeol
    • Journal of Korean Association for Spatial Structures
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    • v.3 no.2 s.8
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    • pp.101-107
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    • 2003
  • There exists a structural problem for link structures in the unstable state. The primary characteristics of this problem are in the existence of rigid body displacements without strain, and in the possibility of the introduction of prestressing to change an unstable state into a stable state. When we make local linearized incremental equations in order to obtain knowledge about these unstable structures, the determinant of the coefficient matrices is zero, so that we face a numerically unstable situation. This is similar to the situation in the stability problem. To avoid such a difficult situation, in this paper a simple and straightforward method was presented by means of the generalized inverse for the numerical analysis of stability problem.

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Analysis of Stabilizing Process for the Unstable Truss Structures using a Topology of Member Connection (구성부재의 위상을 이용한 불안정 트러스 구조물의 안정화 이행과정)

  • 권택진;김진우;김재열
    • Proceedings of the Computational Structural Engineering Institute Conference
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    • 2001.04a
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    • pp.251-258
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    • 2001
  • Cable and membrane structures can be classified as a unstable structure in the view point of shape determination process. An unstable stucture at the initial state generally cannot take a role as the resistance for the external force. Therefore, there should be a stabilizing process to get the stable state of a structure and it is necessary to visualize the shape finding from unstable state to stable state. In this paper, a numerical method of stabilizing procedure for the link structures is presented. The structures are assumed to have rigid movements and thus only changing of the topology of member is considered during the analysis. The generalized inverse matrix and the principle of minimum potential energy are used in the process. Illustrative examples are presented and the results show good convergence.

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The Time Correlation Function Near (and at) a Stable Steady State, When a Chemical System Relaxes from the Unstable Steady State$^*$

  • Lee, Dong-Jae;Ryu, Moon-Hee;Lee, Jong-Myung
    • Bulletin of the Korean Chemical Society
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    • v.6 no.2
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    • pp.91-95
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    • 1985
  • The dynamic properties near (and at) a stable steady state are discussed, when a chemical system relaxes from the unstable steady state. The time-dependent correlation length for the fluctuating variable near a stable steady state is explicitly obtained by introducing the probability average for the variable satisfying the rate equation. The study is carried out about the effect of nonlinearity on the correlation length near (and at) a stable steady state.

Difference in Muscle Activities According to Stability on Support Surface During Plank Exercise

  • Cho, Yong-Ho;Choi, Jin-Ho
    • Journal of the Korean Society of Physical Medicine
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    • v.12 no.3
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    • pp.73-77
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    • 2017
  • PURPOSE: The present study aimed to measure muscle activities in the pectoralis major, the erector spinae, and the quadriceps femoris according to support surface states of arms and legs during plank exercise. METHODS: The subjects of this study were 21 healthy males in their 20s and their muscle activities at three states were measured as follows: The first state was where the support surface of arms and legs was stable. The second state was where only arms were unstable, and the third state was where only legs were unstable. Electromyography (EMG) was used to measure muscle activities. Pectoralis major, quadriceps femoris, and elector spinae were measured for muscle activities. RESULTS: The muscle activities in the pectoralis major were statistically high when arms were unstable. The muscle activities in the quadriceps femoris were statistically high when legs were unstable. The muscle activities in the erector spinae were higher when arms and legs were unstable compared to that at the stable support surface. No significant difference was revealed statistically when arms and legs were unstable. CONCLUSION: If the instability of arms and legs is employed during plank exercise, exercise on the upper and lower bodies or the erector spinae is expected to be more effective.

State-Space Model Identification of Arago's Disk System (아라고 원판 시스템의 상태공간 모델 식별)

  • Kang, Ho-Kyun;Choi, Soo-Young;Choi, Goon-Ho;Park, Ki-Heon
    • Proceedings of the KIEE Conference
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    • 2000.07d
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    • pp.2687-2689
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    • 2000
  • In many cases the systems are so complex that it is not possible to obtain reasonable models using physical insight. Also a model based on physical insight contains a number of unknown parameters even if the structure is derived from physical laws. These problems can be solved by system identification. In this paper, Arago's disk system which has both stable and unstable regions is selected as an example for identification and a state-space model is identified using tailor-made model structure of this system. In stable region, a state-space model of Arago's disk system is identified through open loop experiment and a state-space model of unstable region is identified through closed loop experiment after using fuzzy controller to stabilize unstable system.

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Influence of Potassium on the Cement Clinker Formation I. Unstable Free Alkali in Clinker (시멘트 클린커 생성과정에 미치는 Potassium의 영향 I. 불안정 상태의 알칼리)

  • 서일영;최상홀
    • Journal of the Korean Ceramic Society
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    • v.22 no.1
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    • pp.25-34
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    • 1985
  • The states of alkali occuring in Portland cement clinker were studied. Potassium was added to raw mixture by there kinds ; $K_2SO_4$, $K_2CO_3$ and KOH. In case of $K_2CO_3$ and KOH addition the new state of unstable alkali was found when alkakli content is high and $SO_3$ content is low in the clinker. Unstable state of highly basic free 4K_2O$ causes lowering burnability much more than alkali sulfate especially at the early stage of burning. Lowered burnability by 4K_2O$ became more serious with higher LSF. Unstable free-4K_2O$ which is readily soluble with water reacts with gypsum to form $Ca(OH)_2$ and syngenite as soon as water is added. As a results the liberation rate of heat of hydration at the early hydration process(1st peak) was increased.

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CONSIDERATIONS CONCERNING IMPROVEMENT OF EMERGENCY EVASION PERFORMANCE

  • Nozaki, H.
    • International Journal of Automotive Technology
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    • v.7 no.2
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    • pp.187-193
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    • 2006
  • When emergency evasion during running is required, a driver sometimes causes a vehicle to drift, that is, a condition in which the rear wheels skid due to rapid steering. Under such conditions, the vehicle enters a very unstable state and often becomes uncontrollable. An unstable state of the vehicle induced by rapid steering was simulated and the effect of differential steering assistance was examined. Results indicate that, in emergency evasion while cornering and during which the vehicle begins to drift, unstable behavior like spins can be avoided by differential steering assistance and both the stability and control of the vehicle is improved remarkably. In addition, reduction of overshoot during spin evasion by the differential steering assistance has been shown to enable the vehicle to return to a state of stability in a short time in emergency evasion during straight-line running. Moreover, the effectiveness of differential steering assistance during emergency evasion was confirmed using a driving simulator.

Searching for the Steady State of Unstable Link Structures by using Reduced Dimension Technique (차원 저감화기법을 이용한 불안정 링크구조물의 안정경로 탐색)

  • Kim, Jae-Yeol
    • Journal of Korean Association for Spatial Structures
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    • v.4 no.1 s.11
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    • pp.39-48
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    • 2004
  • Generally, a structural system with large inextensional deformations, or in other words, non-strained deformation is called as 'Unstable Structure', Truss-linked structures, cable structures, membrane structures and movable structures as foldable space structures etc, are included in this category. In this paper, a dynamic analysis method for unstable structural systems is presented. Governing equations for dynamic analysis of unstable truss structures with inextensional displacements are derived. Because of singularity of inverse matrixin in practical analysis of unstable structure, the generalized inverse matrix is Introduced to resolve the singular problem. Also, the RREF technique is used to get the inextensional displacement mode. Two unstable truss structures are analyzed by using presented method. Damping is not considered. From the given results, it is known that proposed method is useful to figure out the dynamic behavior of unstable truss structures.

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Design of an Augmented State Feedback Controller for a Wheeled Inverted Pendulum Returning to the Origin (원점 복귀 가능한 차륜형 역진자 제어를 위한 확장 상태피드백 제어기 설계)

  • Lee, Se-Han
    • The Journal of Korea Robotics Society
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    • v.6 no.4
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    • pp.317-322
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    • 2011
  • An augmented state feedback controller for a Wheeled Inverted Pendulum (WIP) is proposed in this research. The augmented state feedback controller is able to keep the WIP returning to the origin. Generally, the WIP has both stable and unstable equilibrium points. To keep the WIP over the unstable equilibrium point, the WIP consistently is being controlled. A simple state feedback controller is letting the WIP out of the origin when the center of gravity of the WIP locates out of the schematic center line. In some case of applications, it may not be desirable that the WIP is drifting out of the initial location. The proposed augmented state feedback controller is able to keep the WIP at the initial location whether its center of gravity lies out of the center line or not. Numerical simulations are carried out to show the validation of the augmented sated feedback controller.

Dynamic stabilization for a nonlinear system with uncontrollable unstable linearization (제어불가능 불안정 선형화를 가지는 비선형 시스템에 대한 다이나믹 안정화)

  • Seo, Sang-Bo;Seo, Jin-Heon;Shim, Hyung-Bo
    • Proceedings of the IEEK Conference
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    • 2009.05a
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    • pp.79-81
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    • 2009
  • In this paper, we design a dynamic state feedback smooth stabilizer for a nonlinear system whose Jacobian linearization may have uncontrollable because its eigenvalues are on the right half-plane. After designing an augmented system, a dynamic exponent scaling and backstepping enable one to explicitly design a smooth stabilizer and a continuously differentiable Lyapunov function which is positive definite and proper.

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