• Title/Summary/Keyword: random loads

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Dynamic response analysis of closed loop control system for intelligent truss structures based on probability

  • Gao, W.;Chen, J.J.;Ma, H.B.;Ma, X.S.;Cui, M.T.
    • Structural Engineering and Mechanics
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    • v.15 no.2
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    • pp.239-248
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    • 2003
  • The dynamic response analysis of closed loop control system based on probability for the intelligent truss structures with random parameters is presented. The expressions of numerical characteristics of structural dynamic response of closed loop control system are derived by means of the mode superposition method, in which the randomness of physical parameters of structural materials, geometric dimensions of active bars and passive bars, applied loads and control forces are considered simultaneously. The influences of the randomness of them on structural dynamic response are inspected by several engineering examples and some significant conclusions are obtained.

A Study on the Effect of Overloading on Fatigue Life (과대하중이 피로수명에 미치는 영향에 관한 연구)

  • 김경수;신병천;심천식;박진영;조형민
    • Journal of the Society of Naval Architects of Korea
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    • v.40 no.3
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    • pp.45-53
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    • 2003
  • Ships and ocean structures are subjected to random loads caused by irregular waves. The irregularity of amplitude from random loading affects on fatigue crack growth and fatigue life. However the effects of irregularity of loading on fatigue including random loading have not been explained exactly. Therefore in this paper crack growth tests on DENT specimens under constant-amplitude loading including a single tensile overload are conducted to investigate the effect of overload on crack growth rate. The size of plastic zone and crack growth rate before and after a single tensile overloading are measured using ESPI system. Crack growth retardation model that is characterized by crack growth length and the size of plastic zone was proposed and compared with test result. From the research, the validity of proposed model is examined on crack growth retardation, and consequently fatigue life.

Aircraft wings dynamics suppression by optimal NESs designed through an Efficient stochastic linearisation approach

  • Navarra, Giacomo;Iacono, Francesco Lo;Oliva, Maria;Esposito, Antonio
    • Advances in aircraft and spacecraft science
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    • v.7 no.5
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    • pp.405-423
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    • 2020
  • Non-linear energy sink (NES) is an emerging passive absorber able to mitigate the dynamic response of structures without any external energy supply, resonating with all the modes of the primary structure to control. However, its inherent non-linearities hinder its large-scale use and leads to complicated design procedures. For this purpose, an approximate design approach is herein proposed in a stochastic framework. Since loads are random in nature, the stochastic analysis of non-linear systems may be performed by means of computational intensive techniques such as Monte Carlo simulations (MCS). Alternatively, the Stochastic Linearisation (SL) technique has proven to be an effective tool to investigate the performance of different passive control systems under random loads. Since controlled systems are generally non-classically damped and most of SL algorithms operate recursively, the computational burden required is still large for those problems that make intensive use of SL technique, as optimal design procedures. Herein, a procedure to speed up the Stochastic Linearisation technique is proposed by avoiding or strongly reducing numerical evaluations of response statistics. The ability of the proposed procedure to effectively reduce the computational effort and to reliably design the NES is showed through an application on a well-known case study related to the vibrations mitigation of an aircraft wing.

A Study on an Optimal Spot-weld Layout Design for a Shock Tower Structure Considering the Fatigue Life under Random Vibration Loads (불규칙 진동하중을 받는 쇽 타워의 피로수명을 고려한 점용접 위치 최적설계)

  • Lee, Yong-Hoon;Lee, Seung-Yoon;Bae, Bok-Soo;Lee, Sang-Beom;Yim, Hong-Jae
    • Transactions of the Korean Society for Noise and Vibration Engineering
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    • v.21 no.9
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    • pp.798-804
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    • 2011
  • In this paper, optimal spot weld layout design for a shock tower structure is presented. This design increases the fatigue life of the spot-welds thereby increasing the fatigue life of the shock tower itself. In order to predict the fatigue life, a quasi-static analysis has been conducted then a fatigue analysis was performed through the application of random vibration loads. In order to optimize the spot weld layout, the design variables that have an effect on the spot weld fatigue life were determined. A spot weld fatigue analysis was then conducted based on the experiment design. Finally, a response surface model was made using the fatigue analysis results and an optimized spot weld layout model, one that increases the fatigue life of the spot welds and thereby the fatigue life of the shock tower, was developed.

A Study of the Voltage drops computation program on multi-distributed random loads (다중 분산부하 전압강하산정 프로그램 연구)

  • Kang, Cha-Nyeong;Kwon, Sae-Hyuk;Cho, Sung-Pil
    • Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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    • 2006.05a
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    • pp.37-42
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    • 2006
  • The voltage drop in electrical circuits causes a heat accumulation of wiring. This heat could change the specific character of an insulator and deteriorate the dielectric strength so that it could affect an electric leakage, an electric ant a power failure and a fire caused by the short circuit. Therefore optimal design for voltage drop in electrical wiring became an important factor to ensure the safety and economical efficiency of electrical facilities. So in this paper, I analyzed consequences that voltage drop affects in electrical wiring in multi-distributed system used for low electrical system such as road lights, Building, subway station which needs securities for the public society. And I proposed voltage drops computation program and optimal design to ensure the safety and economical efficiency.

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System reliability assessment of hanger structure considering corrosion-fatigue coupling effect

  • Yang Ding;Chao-Dong Guan;Jian Zhou;Tian-Yun Chu;Xue-Song Zhang
    • Steel and Composite Structures
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    • v.53 no.2
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    • pp.145-153
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    • 2024
  • The bridge hanger is exposed to cyclic loads, such as wind and vehicle loads, which can induce fatigue failure, significantly reducing its operational lifespan. Additionally, the hanger is prone to corrosion throughout transportation, construction, and operation. Although corrosion fatigue curves are typically derived from individual steel wire experiments, the bridge hanger comprises multiple parallel steel wires. Consequently, a corrosion fatigue curve based on a single wire may not accurately portray the hanger's longevity, and data solely at the component level may not encompass the overall system-level condition. To tackle this challenge, this paper introduces a series system-level reliability assessment framework based on dynamic Bayesian Networks, accounting for the interdependence between variables. Specifically, the framework encompasses a time-varying reliability model featuring three random parameters (corroded number, equivalent structural stress, and the total cycles number of wires) and leverages seven numerical simulation studies to investigate the impacts of these random parameters on system reliability.

Self-organized Spectrum Access in Small-cell Networks with Dynamic Loads

  • Wu, Ducheng;Wu, Qihui;Xu, Yuhua
    • KSII Transactions on Internet and Information Systems (TIIS)
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    • v.10 no.5
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    • pp.1976-1997
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    • 2016
  • This paper investigates the problem of co-tier interference mitigation for dynamic small- cell networks, in which the load of each small-cell varies with the number of active associated small-cell users (SUs). Due to the fact that most small-cell base stations (SBSs) are deployed in an ad-hoc manner, the problem of reducing co-tier interference caused by dynamic loads in a distributed fashion is quite challenging. First, we propose a new distributed channel allocation method for small-cells with dynamic loads and define a dynamic interference graph. Based on this approach, we formulate the problem as a dynamic interference graph game and prove that the game is a potential game and has at least one pure strategy Nash equilibrium (NE) point. Moreover, we show that the best pure strategy NE point minimizes the expectation of the aggregate dynamic co-tier interference in the small-cell network. A distributed dynamic learning algorithm is then designed to achieve NE of the game, in which each SBS is unaware of the probability distributions of its own and other SBSs' dynamic loads. Simulation results show that the proposed approach can mitigate dynamic co-tier interference effectively and significantly outperform random channel selection.

Short-term fatigue analysis for tower base of a spar-type wind turbine under stochastic wind-wave loads

  • Li, Haoran;Hu, Zhiqiang;Wang, Jin;Meng, Xiangyin
    • International Journal of Naval Architecture and Ocean Engineering
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    • v.10 no.1
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    • pp.9-20
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    • 2018
  • Due to integrated stochastic wind and wave loads, the supporting platform of a Floating Offshore Wind Turbine (FOWT) has to bear six Degrees of Freedom (DOF) motion, which makes the random cyclic loads acting on the structural components, for instance the tower base, more complicated than those on bottom-fixed or land-based wind turbines. These cyclic loads may cause unexpected fatigue damages on a FOWT. This paper presents a study on short-term fatigue damage at the tower base of a 5 MW FOWT with a spar-type platform. Fully coupled time-domain simulations code FAST is used and realistic environment conditions are considered to obtain the loads and structural stresses at the tower base. Then the cumulative fatigue damage is calculated based on rainflow counting method and Miner's rule. Moreover, the effects of the simulation length, the wind-wave misalignment, the wind-only condition and the wave-only condition on the fatigue damage are investigated. It is found that the wind and wave induced loads affect the tower base's axial stress separately and in a decoupled way, and the wave-induced fatigue damage is greater than that induced by the wind loads. Under the environment conditions with rated wind speed, the tower base experiences the highest fatigue damage when the joint probability of the wind and wave is included in the calculation. Moreover, it is also found that 1 h simulation length is sufficient to give an appropriate fatigue damage estimated life for FOWT.

Amplitude dependency of damping of tall structures by the random decrement technique

  • Xu, An;Xie, Zhuangning;Gu, Ming;Wu, Jiurong
    • Wind and Structures
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    • v.21 no.2
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    • pp.159-182
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    • 2015
  • This study focuses on the amplitude dependency of damping of tall structures by the random decrement technique (RDT). Many researchers have adopted RDT to establish the amplitude dependency of damping ratios in super-tall buildings under strong wind loads. In this study, a series of simulated examples were analyzed to examine the reliability of this method. Results show that damping ratios increase as vibration amplitudes increase in several cases; however, the damping ratios in the simulated signals were preset as constants. This finding reveals that this method and the derived amplitude-dependent damping ratio characteristics are unreliable. Moreover, this method would obviously yield misleading results if the simulated signals contain Gaussian white noise. Full-scale measurements on a super-tall building were conducted during four typhoons, and the recorded data were analyzed to observe the amplitude dependency of damping ratio. Relatively wide scatter is observed in the resulting damping ratios, and the damping ratios do not appear to have an obvious nonlinear relationship with vibration amplitude. Numerical simulation and field measurement results indicate that the widely-used method for establishing the amplitude-dependent damping characteristics of super-tall buildings and the conclusions derived from it might be questionable at the least. More field-measured data must be collected under strong wind loads, and the damping characteristics of super-tall buildings should be investigated further.

The effect of random spectrum on the fatigue life of hybrid metal matrix composites (랜덤하중이 하이브리드 금속복합재료의 피로수명에 미치는 영향)

  • 김성훈;배성인;송정일
    • Composites Research
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    • v.16 no.6
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    • pp.48-55
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    • 2003
  • This research makes comparisons of empirical fatigue-lives between AC8A A1 alloy and the metal matrix composites(A1/A12O3, A1/A12O3/A12O3p), and also includes comparisons of fatigue-lives between empirical fatigue-lives and estimated fatigue-lives from regular-periodic load testing, AE method to predict fatigue-crack initiation before visible in sight and SEM(scanning electron microscope) photographs of each material. According to the test results of the notched specimen. the fatigue life of the hybrid metal matrix composites and the metal matrix composites, which are more brittle than the base matrix was shorter than that of the base matrix under both types of loads. In addition, the fatigue-life estimated from the damage summation method and that from experiments at random loads were fairly identical.