• Title, Summary, Keyword: Dynamic Stability

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Analysis of the Static and Dynamic Stability Properties of the Unmaned Airship

  • Lee, Hae Chang
    • International Journal of Aeronautical and Space Sciences
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    • v.2 no.2
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    • pp.82-94
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    • 2001
  • The purpose of this paper is to analyze the static and dynamic stability-of the unmanned airship under development ; the target airship's over-all length of hull is 50m and the maximum diameter is 12.5m. For the analysis, the dynamic model of an airship was defined and both the nonlinear and linear dynamic equations of motion were derived. Two different configuration models (KA002Y and KA003Y) of the airship were used for the target model of the static stability analysis and the dynamic stability analysis. From the result of analyses, though the airship is unstable in static stability, dynamic characteristics of the airship can provide the stable dynamic stability. All of the results, airship models and dynamic flight equations will be an important basement and basic information for the next step of developing the automatic flight control system(AFCS) and the stability augmentation system(SAS) for the unmanned airship as well as for the stratospheric airship in the future.

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The dynamic stability analysis of guyed masts under random wind loads

  • He, Yan-Li;Chen, Wu-Jun;Dong, Shi-Lin;Wang, Zhao-Min
    • Wind and Structures
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    • v.6 no.2
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    • pp.151-164
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    • 2003
  • On the basis of the first Lyapunov stability theory, this paper develops a dynamic stability criterion for elastic structural systems under arbitrary dynamic loads, and shows the stability criterion using energy variation. After the dynamic stability criterion is validated through a classic example, it is used for the dynamic stability investigation of practical guyed masts under random wind loads. The criterion is reliable, simple and of advantage for structures with large number of elements and nodes. The slack guys and internal resonance between guys and mast are two main factors which induces the dynamic instability of guyed masts, at the same time, some dynamic stability characteristics of guyed masts are found.

Local Dynamic Stability Associated with Load Carrying

  • Liu, Jian;Lockhart, Thurmon E.
    • Safety and Health at Work
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    • v.4 no.1
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    • pp.46-51
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    • 2013
  • Objectives: Load carrying tasks are recognized as one of the primary occupational factors leading to slip and fall injuries. Nevertheless, the mechanisms associated with load carrying and walking stability remain illusive. The objective of the current study was to apply local dynamic stability measure in walking while carrying a load, and to investigate the possible adaptive gait stability changes. Methods: Current study involved 25 young adults in a biomechanics research laboratory. One tri-axial accelerometer was used to measure three-dimensional low back acceleration during continuous treadmill walking. Local dynamic stability was quantified by the maximum Lyapunov exponent (maxLE) from a nonlinear dynamics approach. Results: Long term maxLE was found to be significant higher under load condition than no-load condition in all three reference axes, indicating the declined local dynamic stability associated with load carrying. Conclusion: Current study confirmed the sensitivity of local dynamic stability measure in load carrying situation. It was concluded that load carrying tasks were associated with declined local dynamic stability, which may result in increased risk of fall accident. This finding has implications in preventing fall accidents associated with occupational load carrying.

Comparison of the Effects of Dynamic Postural Stability Training Versus Soft Ankle Bracing on Multiple Hop Performance in Participants With Functional Ankle Instability (기능적 발목 불안정성을 가진 대상자에게 동적 자세 안정성 훈련과 연성 발목 보조기가 다중 한발 뛰기 수행에 미치는 효과 비교)

  • Cha, Youn-sang;Park, Kyue-nam
    • Physical Therapy Korea
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    • v.24 no.1
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    • pp.1-8
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    • 2017
  • Background: The multiple hop test is an active performance test that has been commonly used to assess individuals with functional ankle instability. Previous studies have suggested that insufficiency of dynamic postural stability and passive stability during dynamic activities can have an influence on performance in the multiple hop test. However, no study has investigated the effects of dynamic postural stability training and ankle bracing on multiple hop test performance in individuals with functional ankle instability. Objects: The purpose of this study was to compare the immediate effects of dynamic postural stability training versus ankle bracing in the performance of the multiple hop test for participants with functional ankle instability. Methods: Twenty-nine participants with functional ankle instability who scored below 24 in the Cumberland Ankle Instability Tool were selected. The participants were randomly divided into two groups: a dynamic postural stability training group (n1=14) and an ankle bracing control group ($n_2=15$). The multiple hop tests were performed before and after applying each intervention. Dynamic postural stability training was performed using visual-feedback-based balance-training equipment; participants in this group were asked to perform a heel raise in a standing position while watching the centering of their forefoot pressure to prevent excessive ankle inversion. Ankle bracing was applied in the control group. Results: When comparing the pre- and post-intervention period for both groups, both methods significantly improved the results of the multiple hop test (p<.05). However, no significant differences were shown between the dynamic postural stability training and ankle bracing groups (p>.05). Conclusion: Both dynamic postural stability training and ankle bracing showed significant improvement (2.85 seconds and 2.05 seconds, respectively) in test performance. Further study is needed to determine the long-term effects of dynamic postural stability training and to determine whether insufficient dynamic postural stability is a causative factor for functional ankle instability.

Fall Risk Assessments Based on Postural and Dynamic Stability Using Inertial Measurement Unit

  • Liu, Jian;Zhang, Xiaoyue;Lockhart, Thurmon E.
    • Safety and Health at Work
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    • v.3 no.3
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    • pp.192-198
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    • 2012
  • Objectives: Slip and fall accidents in the workplace are one of the top causes of work related fatalities and injuries. Previous studies have indicated that fall risk was related to postural and dynamic stability. However, the usage of this theoretical relationship was limited by laboratory based measuring instruments. The current study proposed a new method for stability assessment by use of inertial measurement units (IMUs). Methods: Accelerations at different body parts were recorded by the IMUs. Postural and local dynamic stability was assessed from these measures and compared with that computed from the traditional method. Results: The results demonstrated: 1) significant differences between fall prone and healthy groups in IMU assessed dynamic stability; and 2) better power of discrimination with multi stability index assessed by IMUs. Conclusion: The findings can be utilized in the design of a portable screening or monitoring tool for fall risk assessment in various industrial settings.

A Study on Changes in Appendage Design for Improvement of Dynamic Stability of Manta-type Unmanned Undersea Vehicle (Manta형 무인잠수정의 동안정성 향상을 위한 부가물의 설계 변경에 관한 연구)

  • Bae, Jun-Young;Sohn, Kyoung-Ho;Kwon, Hyeong-Ki;Lee, Seung-Keon
    • Journal of the Society of Naval Architects of Korea
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    • v.44 no.3
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    • pp.323-331
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    • 2007
  • Proposed Manta-type Unmanned Undersea Vehicle(UUV) turned out to have the tendency of dynamic instability in vertical plane, and moreover to have that of so strong dynamic stability in horizontal plane as to cause another problem in turning motion due to negative value of sway damping lever. The authors discussed the changes in appendage design for improvement of dynamic stability of UUV in vertical and horizontal planes. As a result, the dynamic stability in vertical plane was improved by increasing the area of horizontal stern planes. and the dynamic stability in horizontal plane was also improved by removal of lower vertical plate and by adjusting the area and position of upper vertical plate simultaneously.

Effects of Lumbar Stability Exercise Program on Trunk, Lower Extremity of Muscle Activity and Balance in Soccer Player (요부 안정화 운동 프로그램이 축구선수의 체간 및 하지 근활성도와 균형에 미치는 영향)

  • Kim, Je-Ho;Park, Seung-Kyu;Kang, Jeong-Il;Yang, Dea-Jung
    • The Journal of Korean Physical Therapy
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    • v.22 no.5
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    • pp.25-31
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    • 2010
  • Purpose: The purpose of this study is to provide an efficient and scientific basis for muscle activity (%MVIC) of RA, EO, VL, HS muscles and balance in soccer players through dynamic lumbar stability exercise and static lumbar stability exercise. Methods: This study included 23 soccer players belonging to D University of J province who attended the program for 30 minutes at a time and three times a week for 4 weeks. Of these 13 attended the dynamic lumbar stability exercise (DLSE) program and 10 the static lumbar stability exercise (SLSE) program. The differences between the effects of the dynamic lumbar stability exercise program and static lumbar stability exercise program were analyzed. Results: To increase muscle activity (%MVIC) and balance (WPL), the dynamic lumbar stability exercise program was more effective than was the static lumbar stability exercise program. 1) The %MVIC of trunk muscle (RA &EO) and lower extremitys muscle (VL & HS) increased from before training to after training in the case of the participants who performed the dynamic lumbar stability exercise. 2) The whole path length (WPL) decreased from before the training to after the training. The 2 groups significantly differed in this regard. Conclusion: Dynamic lumbar stability exercise program helps to improve the balancing ability and muscle activity in a soccer players who requires both muscle activity and balance than does any other players.

A Study on the Walking Stability of the Quadruped Robot with WBO (균형추를 장착한 4족 로봇의 보행 안정성에 관한 연구)

  • Choi Gi Hun;Kim Young Tark;Yoo Jae Myung
    • Journal of the Korean Society for Precision Engineering
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    • v.22 no.6
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    • pp.118-126
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    • 2005
  • There are many types of walking robots in the world. For dynamic walking of the robots it is necessary to keep its dynamic stability. The dynamic stability is influenced by the position of ZMP (zero moment point). In this paper we study the control of the ZMP position of walking robot. For experiment we developed a quadruped robot and analyzed the dynamic stability of the robot. Developed robot has 2 joints at each leg and WBO (weight balancing oscillator) on the body of the robot. The WBO is designed to move linearly from side to side when the robot walks dynamically. Walking test was performed to verify the validity of the proposed methods. Especially we showed that the dynamic stability of the robot can be improved without sacrifice of the walking speed by control the WBO.

Dynamic Characteristics and Stability of an Infrared Search and Track (적외선 탐색 및 추적장비의 동적 특성 및 안정화)

  • Choi, Jong-Ho;Park, Yong-Chan;Lee, Joo-Hyoung;Choi, Young-Soo
    • Journal of the Korea Institute of Military Science and Technology
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    • v.11 no.2
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    • pp.116-124
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    • 2008
  • Current paper investigates the dynamic behavior and stability of an infrared search and track subjected to external disturbance having gimbal structure with three rotating axes keeping constant angular velocity in the azimuth direction. Euler-Lagrange equation is applied to derive the coupled nonlinear dynamic equation of motion of infrared search and track and the characteristics of dynamic coupling are investigated. Two equilibrium points with small variations from the nonlinear coupling system are derived and the specific condition from which a coupled equation can be three independent equations is derived. Finally, to examine the stability of system, Lyapunov direct method was used and system stability and stability boundaries are investigated.

Static and dynamic stability of cracked multi-storey steel frames

  • Sabuncu, Mustafa;Ozturk, Hasan;Yashar, Ahmed
    • Structural Engineering and Mechanics
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    • v.58 no.1
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    • pp.103-119
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    • 2016
  • Multi-storey frame structures are frequently exposed to static and dynamic forces. Therefore analyses of static (buckling) and dynamic stability come into prominence for these structures. In this study, the effects of number of storey, static and dynamic load parameters, crack depth and crack location on the in-plane static and dynamic stability of cracked multi-storey frame structures subjected to periodic loading have been investigated numerically by using the Finite Element Method. A crack element based on the Euler beam theory is developed by using the principles of fracture mechanics. The equation of motion for the cracked multi-storey frame subjected to periodic loading is achieved by Lagrange's equation. The results obtained from the stability analysis are presented in three dimensional graphs and tables.