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CONTENTS
Volume 13, Number 3, March 2014
 

Abstract
Given a body undergoing a stress-strain status as consequence of external excitations, sensors can be deployed on the accessible lateral surface of the body. The sensor readings are regarded as input of a numerical model of reduced order (i.e., the number of sensors is lower than the number of the state variables the full model would require). The goal is to locate the sensors in such a way to minimize the deviations from the response of the true (full) model. One adopts either accelerometers as sensors or devices reading relative displacements. Two applications are studied: a plane frame is first investigated; the focus is eventually on a 3D body.

Key Words
model order reduction (MOR); numerical model; sensor placement; state variables; truncation

Address
Fabio Casciati and Lucia Faravelli :Department DICAR, University of Pavia, Via Ferrata 1, 27100 Pavia, Italy

Abstract
Recent studies were dedicated to the realization of measurements on stay-cable samples of different geometry and static conditions as available at several facilities. The elaboration of the acquired data showed a a satisfactory efficacy of the dampers made of NiTi wires in smoothing the cable oscillations. A further attempt to investigate the applicability of the achieved results beyond the specific case-studies represented by the tested cable-stayed samples is herein pursued. Comparative studies are carried out by varying the diameter of the NiTi wire so that similar measurements can be taken also from laboratory steel cables of reduced size. Details of the preparation of the Ni-Ti wires are discussed with particular attention being paid to the suppression of the creep phenomenon. The resulting shape of the hysteretic cycle differs according to the wire diameter, which affects the order of the fitting polynomial to be used when trying to retrieve the experimental results by numerical analyses. For a NiTi wire of given diameter, an estimate of the amount of dissipated energy per cycle is given at low levels of maximum strain, which correspond to a fatigue fracture life of the order of millions of cycles. The dissipative capability is affected by both the temperature and the cycling frequency at which the tests are performed. Such effects are quantified and an ageing process is proposed in order to extend the working temperature range of the damper to cold weathers typical of the winter season in Northern Europe and Canada. A procedure for the simulation of the shape memory alloy behavior in lengthy cables by finite element analysis is eventually outlined.

Key Words
cables-stayed; damping; fatigue; finite element analysis; hysteresis; martensitic transformations;shape memory alloy

Address
Vicenç Torra and Guillem Carreras : 1UPC (retired) PRG, Villarroel 162, E-08036 Barcelona, Catalonia, Spain
Sara Casciati: Department of DICA, University of Catania, Italy
Patrick Terriault: Department of Mech. Eng. ETS, Quebec University, H3C 1K3 Montréal, Canada

Abstract
The effectiveness of using the advanced seismic protection technology based on shape memory alloy (SMA) dampers to preserve a historical minaret is investigated. The proposed studied case, the minaret of Mansourah, is a seven century old minaret located in Tlemcen, Algeria. Its original height was of 47m, while nowadays, the monument is half destructed and its current height reaches the 40m. The proposed seismic retrofit is based on the technique that utilizes SMA wires as dampers for the upper flexible part of the minaret. The effectiveness of the proposed technique is numerically evaluated via non-linear finite element analysis using the structural software ANSYS. The effectiveness of the proposed device in mitigating the seismic hazard is demonstrated by the effective reduction in its dynamic response.

Key Words
minarets; historical monument; shape memory alloys; dynamic analysis

Address
Karim Hamdaoui and Zahira Benadla: Department of Civil Engineering, Faculty of Technology, University of Tlemcen,
B.P. 230, 13000, Tlemcen, Algeria

Abstract
Optimal sensor placement techniques play a significant role in enhancing the quality of modal data during the vibration based health monitoring of civil structures, where many degrees of freedom are available despite a limited number of sensors. The literature has shown a shift in the trends for solving such problems, from expansion or elimination approach to the employment of heuristic algorithms. Although these heuristic algorithms are capable of providing a global optimal solution, their greatest drawback is the requirement of high computational effort. Because a highly efficient optimisation method is crucial for better accuracy and wider use, this paper presents an improved simulated annealing (SA) algorithm to solve the sensor placement problem. The algorithm is developed based on the sensor locations‟ coordinate system to allow for the searching in additional dimensions and to increase SA‟s random search performance while minimising the computation efforts. The proposed method is tested on a numerical slab model that consists of two hundred sensor location candidates using three types of objective functions; the determinant of the Fisher information matrix (FIM), modal assurance criterion (MAC), and mean square error (MSE) of mode shapes. Detailed study on the effects of the sensor numbers and cooling factors on the performance of the algorithm are also investigated. The results indicate that the proposed method outperforms conventional SA and Genetic Algorithm (GA) in the search for optimal sensor placement.

Key Words
optimal sensor placement; simulated annealing; coordinate-based solution coding

Address
K.H. Tong, Norhisham Bakhary and A.Y. Mohd Yassin: Faculty of Civil Engineering, Universiti Teknologi, Malaysia, 81310 Skudai, Johor, Malaysia
A.B.H. Kueh: Construction Research Centre, Universiti Teknologi, Malaysia, 81310 Skudai, Johor, Malaysia

Abstract
The purpose of this paper is to present an Integrated Life Cycle Bridge Information Modeling that can be used throughout different phases of the bridge life cycle including: design, construction, and operation and maintenance phases. Bridge Information Modeling (BrIM) has become an effective tool in bridge engineering and construction. It has been used in obtaining accurate shop drawings, cost estimation, and visualization. In this paper, BrIM is used as an integrated tool for bridges life cycle information modeling. In the design phase, BrIM model can be used in obtaining optimum construction methods and performing structural advanced analysis. During construction phase, the model selects the appropriate locations for mobile cranes, monitors the status of precast components, and controls documents. Whereas, it acts as a tool for bridge management system in operation and maintenance phase. The paper provides a detailed description for each use of BrIM model in design, construction, and operation and maintenance phases of bridges. It is proven that BrIM is an effective tool for bridge management systems throughout their life phases.

Key Words
project management; bridges construction; Building information modeling; bridge life cycle phases

Address
Mohamed M. Marzouk and Mohamed Hisham :Department of Structural Engineering, Faculty of Engineering, Cairo University, Egypt
Khalid Al-Gahtani: Department of Civil Engineering, King Saud University, Kingdom of Saudi Arabia

Abstract
In this paper, the electromagnetic damper (EMD), which is composed of a permanent-magnet rotary DC motor, a ball screw and a nut, is considered to be analyzed as a semi-active damper. The main objective pursued in the paper is to study the two degrees of freedom (DOF) model of the semi-active electromagnetic suspension system (SAEMSS) performance and energy regeneration controlled by on-off and continuous damping control strategies. The nonlinear equations of the SAEMSS must therefore be extracted. The effects of the EMD characteristics on ride comfort, handling performance and road holding for the passive electromagnetic suspension system (PEMSS) are first analyzed and damping control strategies effects on the SAEMSS performance and energy regeneration are investigated next. The results obtained from the simulation show that the SAEMSS provides better performance and more energy regeneration than the PEMSS. Moreover, the results reveal that the on-off hybrid control strategy leads to better performance in comparison with the continuous skyhook control strategy, however, the energy regeneration of the continuous skyhook control strategy is more than that of the on-off hybrid control strategy (except for on-off skyhook control strategy).

Key Words
semi-active electromagnetic suspension system; electromagnetic damper; ball screw shock absorber; energy regeneration

Address
Morteza Montazeri-Gh and Omid Kavianipour:Department of mechanical engineering, systems simulation and control laboratory, IUST, Narmak,Tehran 16844, Iran

Abstract
In this paper, we investigate the vibration control of multimodal structures and present an efficient control law that requires less energy supply than active strategies. This strategy is called modal global semi-active control and is designed to work as effectively as the active control and consume less power which represents its major limitation. The proposed law is based on an energetic management of the optimal law such that the controller follows this latter only if there is sufficient energy which will be extracted directly from the system vibrations itself. The control algorithm is presented and validated for a cantilever beam structure subjected to external perturbations. Comparisons between the proposed law performances and those obtained by independent modal space control (IMSC) and semi-active control schemes are offered.

Key Words
multimodal structures; control; energy; IMSC; accumulator; actuator; semi-active

Address
Thamina Loukil:LTDS, Ecole Centrale de Lyon, 36 Avenue Guy de Collongue, F-69134 Ecully, France;
U2MP, Ecole Nationale d\'Ingenieurs de Sfax, Route sokra Km 4.5 BP 1173 Sfax, Tunisie
Mohamed Ichchou and Olivier Bareille :LTDS, Ecole Centrale de Lyon, 36 Avenue Guy de Collongue, F-69134 Ecully, France
Mohamed Haddar: U2MP, Ecole Nationale d\'Ingenieurs de Sfax, Route sokra Km 4.5 BP 1173 Sfax, Tunisie

Abstract
The fault diagnosis of rolling element bearings has drawn considerable research attention in recent years because these fundamental elements frequently suffer failures that could result in unexpected machine breakdowns. Artificial intelligence algorithms such as artificial neural networks (ANNs) and support vector machines (SVMs) have been widely investigated to identify various faults. However, as the useful life of a bearing deteriorates, identifying early bearing faults and evaluating their sizes of development are necessary for timely maintenance actions to prevent accidents. This study proposes a new two-layer structure consisting of support vector regression machines (SVRMs) to recognize bearing fault patterns and track the fault sizes. The statistical parameters used to track the fault evolutions are first extracted to condense original vibration signals into a few compact features. The extracted features are then used to train the proposed two-layer SVRMs structure. Once these parameters of the proposed two-layer SVRMs structure are determined, the features extracted from other vibration signals can be used to predict the unknown bearing health conditions. The effectiveness of the proposed method is validated by experimental datasets collected from a test rig. The results demonstrate that the proposed method is highly accurate in differentiating between fault patterns and determining their fault severities. Further, comparisons are performed to show that the proposed method is better than some existing methods.

Key Words
statistical parameters; bearing fault diagnosis; deterioration evaluation; a two-layer structure; support vector regression machine

Address
Changqing Shen : Department of Systems Engineering & Engineering Management, City University of Hong Kong, China;
School of Engineering Science, University of Science and Technology of China, Hefei 230026, China
Dong Wang and Peter W. Tse : Department of Systems Engineering & Engineering Management, City University of Hong Kong, China
Yongbin Liu and Fanrang Kong: School of Engineering Science, University of Science and Technology of China, Hefei 230026, China

Abstract
Tuned mass dampers (TMDs) have been installed in many high-rise buildings, to improve their resiliency under dynamic loads. However, high-rise buildings may experience natural frequency changes under ambient temperature fluctuations, extreme wind loads and relative humidity variations. This makes the design of a TMD challenging and may lead to a detuned scenario, which can reduce significantly the performance. To alleviate this problem, the current paper presents a proposed approach for the design of a robust and efficient TMD. The approach accounts for the uncertain natural frequency, the optimization objective and the input excitation. The study shows that robust design parameters can be different from the optimal parameters. Nevertheless, predetermined optimal parameters are useful to attain design robustness. A case study of a high-rise building is executed. The TMD designed with the proposed approach showed its robustness and effectiveness in reducing the responses of high-rise buildings under multidirectional wind. The case study represents an engineered design that is instructive. The results show that shear buildings may be controlled with less effort than cantilever buildings. Structural control performance in high-rise buildings may depend on the shape of the building, hence the flow patterns, as well as the wind direction angle. To further increase the performance of the robust TMD in one lateral direction, active control using LQG and fuzzy logic controllers was carried out. The performance of the controllers is remarkable in enhancing the response reduction. In addition, the fuzzy logic controller may be more robust than the LQG controller.

Key Words
high-rise buildings; wind-induced vibration; robust control; tuned mass damper; optimal design; white-noise; LQG controller; fuzzy logic controller

Address
Aly Mousaad Aly :Department of Civil and Environmental Engineering, Louisiana State University, 3513D Patrick F. Taylor Hall, Baton Rouge, LA 70803, USA


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