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CONTENTS
Volume 37, Number 4, February25 2011
 

Abstract
This study proposes an inverse estimation method for the input forces of a fixed beam structural system. The estimator includes the fuzzy Kalman Filter (FKF) technology and the fuzzy weighted recursive least square method (FWRLSM). In the estimation method, the effective estimator are accelerated and weighted by the fuzzy accelerating and weighting factors proposed based on the fuzzy logic inference system. By directly synthesizing the robust filter technology with the estimator, this study presents an efficient robust forgetting zone, which is capable of providing a reasonable trade-off between the tracking capability and the flexibility against noises. The period input of the fixed beam structure system can be effectively estimated by using this method to promote the reliability of the dynamic performance analysis. The simulation results are compared by alternating between the constant and adaptive and fuzzy weighting factors. The results demonstrate that the application of the presented method to the fixed beam structure system is successful.

Key Words
inverse estimation method; fuzzy kalman filter; least square method; fuzzy logic.

Address
Ming-Hui Lee: Department of Civil Engineering, Chinese Military Academy, Fengshan, Kaohsiung, Taiwan, R.O.C.

Abstract
In this paper, nonlinear partial differential equations of motion for a hybrid composite plate subjected to initial stresses on elastic foundations are established to investigate its nonlinear vibration behavior. Pasternak foundation and Winkler foundations are used to represent the plate-foundation interaction. The initial stress is taken to be a combination of pure bending stress plus an extensional stress in the example problems. The governing equations of motion are reduced to the time-dependent ordinary differential equations by the Galerkin\'s method. Then, the Runge-Kutta method is used to evaluate the nonlinear vibration frequency and frequency ratio of hybrid composite plates. The nonlinear vibration behavior is affected by foundation stiffness, initial stress, vibration amplitude and the thickness ratio of layer. The effects of various parameters on the nonlinear vibration of hybrid laminated plate are investigated and discussed.

Key Words
initial stress; Winkler foundation; Pasternak foundation; hybrid composite plate.

Address
Wei-Ren Chen: Department of Mechanical Engineering, Chinese Culture University, Taipei 11114, Taiwan
Chun-Sheng Chen: 2Department of Mechanical Engineering, Lunghwa University of Science and Technology, Guishan Shiang 33306, Taiwan
Szu-Ying Yu: Department of Electrical Engineering, Lee Ming Institute of Technology, Taishan 24305, Taiwan

Abstract
The aim of this research is to model the behaviour of recently developed high force to volume (HF2V) passive energy dissipation devices using a simple finite element (FE) model. Thus, the end result will be suitable for use in a standard FE code to enable computationally fast and efficient analysis and design. Two models are developed. First, a detailed axial model that models an experimental setup is created to validate the approach versus experimental results. Second, a computationally and geometrically simpler equivalent rotational hinge element model is presented. Both models are created in ABAQUS, a standard nonlinear FE code. The elastic, plastic and damping properties of the elements used to model the HF2V devices are based on results from a series of quasi-static force-displacement loops and velocity based tests of these HF2V devices. Comparison of the FE model results with the experimental results from a half scale steel beam-column sub-assembly are within 10% error. The rotational model matches the output of the more complex and computationally expensive axial element model. The simpler model will allow computationally efficient non-linear analysis of large structures with many degrees of freedom, while the more complex and physically accurate axial model will allow detailed analysis of joint connection architecture. Their high correlation to experimental results helps better guarantee the fidelity of the results of such investigations.

Key Words
damage avoidance design; DAD; HF2V; damping; high-force-to-volume; finite element analysis; supplemental damping; experimental; energy dissipation.

Address
Jonathan Desombre: Department of Mechanical Engineering, University of Canterbury, Private Bag 4800, Christchurch 8140, New Zealand
Geoffrey W. Rodgers: Department of Mechanical Engineering, University of Canterbury, Private Bag 4800, Christchurch 8140, New Zealand
Gregory A. MacRae: Department of Civil Engineering, University of Canterbury, Private Bag 4800, Christchurch 8140, New Zealand
Timon Rabczuk: Department of Mechanical Engineering, University of Canterbury, Private Bag 4800, Christchurch 8140, New Zealand
Rajesh P. Dhakal: Department of Civil Engineering, University of Canterbury, Private Bag 4800, Christchurch 8140, New Zealand
J. Geoffrey Chase: Department of Mechanical Engineering, University of Canterbury, Private Bag 4800, Christchurch 8140, New Zealand

Abstract
The aerodynamic stability of orthotropic tensioned membrane structures with rectangular plane is theoretically studied under the uniform ideal potential flow. The aerodynamic force acting on the membrane surface is determined by the potential flow theory in fluid mechanics and the thin airfoil theory in aerodynamics. Then, based on the large amplitude theory and the D\'Alembert\'s principle, the interaction governing equation of wind-structure is established. Under the circumstances of single mode response, the Bubnov-Galerkin approximate method is applied to transform the complicated interaction equation into a system of second order nonlinear differential equation with constant coefficients. Through judging the stability of the system characteristic equation, the critical divergence instability wind velocity is determined. Finally, from different parametric analysis, we can conclude that it has positive significance to consider the characteristics of orthotropic and large amplitude for preventing the instability destruction of structures.

Key Words
membrane structures; orthotropic; large amplitude; wind-structure interaction; critical instability wind velocity.

Address
Zhoulian Zheng: College of Civil Engineering, Chongqing University, Chongqing 400045, P.R. China; Key Laboratory of New Technology for Construction of China in Mountainous Area, Chongqing University, Chongqing 400045, P.R. China
Yunping Xu: College of Civil Engineering, Chongqing University, Chongqing 400045, P.R. China
Changjiang Liu: College of Civil Engineering, Chongqing University, Chongqing 400045, P.R. China
Xiaoting He: College of Civil Engineering, Chongqing University, Chongqing 400045, P.R. China
Weiju Song: College of Civil Engineering, Chongqing University, Chongqing 400045, P.R. China

Abstract
In this study, the homotopy perturbation method (HPM) is applied to free vibration analysis of beam on elastic foundation. This numerical method is applied on three different axially loaded cases, namely: 1) one end fixed, the other end simply supported; 2) both ends fixed and 3) both ends simply supported cases. Analytical solutions and frequency factors are evaluated for different ratios of axial load N acting on the beam to Euler buckling load, Nr. The application of HPM for the particular problem in this study gives results which are in excellent agreement with both analytical solutions and the variational iteration method (VIM) solutions for all the cases considered in this study and the differential transform method (DTM) results available in the literature for the fixed-pinned case.

Key Words
homotopy perturbation method; beam on elastic foundation; free vibration analysis.

Address
Baki Ozturk: Department of Civil Engineering, Faculty of Engineering and Architecture, Nigde University, 51100 Nigde, Turkey
Safa Bozkurt Coskun: Department of Civil Engineering, Faculty of Engineering, Kocaeli University, 41380 Kocaeli, Turkey

Abstract
In fatigue life design of mechanical components, uncertainties arising from materials and manufacturing processes should be taken into account for ensuring reliability. A common practice is to apply a safety factor in conjunction with a physics model for evaluating the lifecycle, which most likely relies on the designer\'s experience. Due to conservative design, predictions are often in disagreement with field observations, which makes it difficult to schedule maintenance. In this paper, the Bayesian technique, which incorporates the field failure data into prior knowledge, is used to obtain a more dependable prediction of fatigue life. The effects of prior knowledge, noise in data, and bias in measurements on the distribution of fatigue life are discussed in detail. By assuming a distribution type of fatigue life, its parameters are identified first, followed by estimating the distribution of fatigue life, which represents the degree of belief of the fatigue life conditional to the observed data. As more data are provided, the values will be updated to reduce the credible interval. The results can be used in various needs such as a risk analysis, reliability based design optimization, maintenance scheduling, or validation of reliability analysis codes. In order to obtain the posterior distribution, the Markov Chain Monte Carlo technique is employed, which is a modern statistical computational method which effectively draws the samples of the given distribution. Field data of turbine components are exploited to illustrate our approach, which counts as a regular inspection of the number of failed blades in a turbine disk.

Key Words
fatigue life; prior distribution; posterior distribution; Bayesian approach; Markov Chain Monte Carlo Technique; field inspection; turbine blade.

Address
Dawn An: School of Aerospace & Mechanical Engineering, Korea Aerospace University, Goyang-City, Korea
Joo-Ho Choi: School of Aerospace & Mechanical Engineering, Korea Aerospace University, Goyang-City, Korea
Nam H. Kim: Dept. of Mechanical & Aerospace Engineering, University of Florida, Gainesville, FL, USA
Sriram Pattabhiraman: Dept. of Mechanical & Aerospace Engineering, University of Florida, Gainesville, FL, USA

Abstract
An extensive numerical investigation on the magnetorheological (MR) damper-based smart passive control system for mitigating vibration of stay cables under wind loads has been conducted. The smart passive system is incorporated with an electromagnetic induction (EMI) device for reducing complexity of the conventional MR damper based semi-active control system by eliminating an external power supply part and a feedback control part (i.e., sensors and controller). In this study, the control performance of the smart passive system has been evaluated by using a cable structure model extracted from a full-scale long stay cable with high tension. Numerical simulation results of the proposed smart damping system are compared with those of the passive and semi-active control systems employing MR dampers. It is demonstrated from the results that the control performance of the smart passive control system is better than those of the passive control cases and comparable to those of the semi-active control systems in the forced vibration analysis as well as the free vibration analysis, even though there is no external power source in the smart passive system.

Key Words
cable vibration; smart passive control system; MR damper; electromagnetic induction.

Address
In-Ho Kim: Department of Civil and Environmental Engineering, KAIST, Daejeon 305-701, Korea
Hyung-Jo Jung: Department of Civil and Environmental Engineering, KAIST, Daejeon 305-701, Korea
Jeong-Tae Kim: Department of Ocean Engineering, Pukyong National University, Busan 608-739, Korea


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