Browsing by Author "Liao, WH"

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A multi-path QoS routing protocol in a wireless mobile ad hoc network
(2002)
Liao, WH
;
Wang, SL
;
Sheu, JP
;
Tseng, YC
;
資訊工程學系
A mobile ad hoc network (MANET) is one composed of a set of mobile hosts capable of communicating with each other without the assistance of base stations. This paper considers the QoS (quality-of-service) routing problem in a MANET, which is important for many real-time multimedia applications. We propose an on-demand protocol for searching for a multi-path QoS route from a source host to a destination host in a MANET, where a multi-path is a network with a source and a sink satisfying certain bandwidth requirement. Existing works all try to find a uni-path to the destination. The basic idea is to distribute a number of tickets from the source, which can be further partitioned into subtickets to search for a satisfactory multi-path. Through simulations, we justify that the value of our multi-path protocol is in its flexibility: (i) when the network bandwidth is very limited, it can offer a higher success rate to find a satisfactory QoS route than those protocols which try to find a uni-path, and (ii) when the network bandwidth is sufficient, it can perform almost the same as those protocols which try to find a uni-path (in both routing overhead and success rate).
A multi-path QoS routing protocol in a wireless mobile ad hoc network
(2001)
Liao, WH
;
Tseng, YC
;
Wang, SL
;
Sheu, JP
;
資訊工程學系
A mobile ad hoc network (MANET) is one consisting of a set of mobile hosts capable of communicating with each other without the assistance of base stations, This paper considers the QoS (quality-of-service) routing problem in a MANET. We propose an on-demand protocol for searching for a multi-path QoS route from a source host to a destination host in a MANET, where a multi-path is a network with a source and a sink satisfying certain bandwidth requirement. Existing works all try to find a uni-path to the destination. The basic idea is to distribute a number of tickets from the source, which can be further partitioned into sub-tickets to search for a satisfactory multi-path. Through simulations, we justify that the value of our multi-path protocol is on its flexibility: (i) when the network bandwidth is very limited, it can offer a higher success rate to find a satisfactory QoS route than those protocols which try to find a uni-path, and (ii) when the network bandwidth is sufficient, it can perform almost the same as those protocols which try to find a uni-path (in both routing overhead and success rate).
A state-space approach for dynamic analysis of sliding structures
(2001-07-01)
Wang, YP
;
Liao, WH
;
Lee, CL
;
土木工程學系
;
Department of Civil Engineering
This study presents a numerical algorithm based on a state-space approach for the dynamic analysis of sliding systems. According to the proposed scheme, the equations of motion for the base-isolated structure in both the stick and slip phases are integrated into a single set of equations by treating the friction force as a Lagrange multiplier. The Lagrange multiplier is determined, with additional conditions of equilibrium and kinematic compatibility at the sliding interfaces, via a simple matrix algebraic calculation within the framework of state-space formulations. The responses can thus be obtained recursively from the discrete-time state-space equation using a one-step correction procedure. In addition, the integration step size is maintained constant throughout the analysis. The effectiveness of the proposed scheme is confirmed through tramples of sliding systems, under conditions of either free vibration or harmonic excitations, for which analytical solutions are available. Additionally, the novel algorithm is compared with a corrective psuedo-force iterative procedure for seismic response analysis of a FPS-supported five-story building. The novel algorithm is more systematic and easy to implement than conventional approaches. Moreover, by simplifying the task, the proposed algorithm also enhances accuracy and efficiency. (C) 2001 Elsevier Science Ltd. All rights reserved.
A study on seismic retrofit of multi-fab plants in Taiwan's hi-tech industry
(2004)
Wang, YP
;
Liao, WH
;
Lee, CL
;
土木工程學系
;
Department of Civil Engineering
This study investigates the seismic hazard potential of multiple-fab plants increasingly adopted by Taiwan's hi-tech industry. A typical double-fab plant for wafer foundry in Hsinchu Science-Based Industrial Park (HSBIP) is considered for case study. Dynamic analysis of the objective double-fab plant using the ground excitation recorded near the HSBIP during the 1999 Chi-Chi earthquake has been carried out. Analysis indicates that large story drifts and damages are concentrated in the soft stories where the clean-rooms are located. Seismic retrofit of the wafer foundry plant with soft-and-weak stories using a displacement-dependent metallic yielding damper is proposed to increase the stiffness and damping of the structure. Analysis shows that the peak reductions of the story drift can reach as high as 70 percent if properly designed. The proposed retrofit strategy using metallic yielding dampers proves to be effective and sufficient.
Data broadcasting and seamless channel transition for highly demanded videos
(2001-05-01)
Tseng, YC
;
Yang, MH
;
Hsieh, CM
;
Liao, WH
;
Sheu, JP
One way to broadcast a popular video is to use a number of dedicated channels, each responsible for broadcasting some portion of the video periodically in a predefined way. The stress on channels can be alleviated, and new viewers do not have to wait long to start their playback, Many approaches falling in this category have been proposed, One such scheme that interests us is the fast broadcasting (FB) scheme, which can broadcast a video using k channels by incurring at most O(D/2(k)) waiting time on new-coming viewers, where D is the length of the video. In this paper, we consider a set of videos, each being broadcast by the FB scheme, Since the levels of demands on these videos may change by time, it is sometimes inevitable to change the numbers of channels assigned to some videos. We propose a novel seamless channel transition enhancement on top of the FB scheme to dynamically change the number of channels assigned to a video on-the-fly. Clients currently viewing this video will not experience any disruption because of the transition. A channel allocation scheme is also proposed based on the arrival rates of videos to minimize the average waiting experienced by all viewers, From the system manager's point of view, the enhancement will make the FB scheme more attractive.
Dynamic analysis of sliding structures with unsynchronized support motions
(2000-03-01)
Wang, YP
;
Liao, WH
;
土木工程學系
;
Department of Civil Engineering
The dynamic analysis of sliding structures is complicated due to the presence of friction. Synchronization of the kinematics of all the isolation bearings is often granted to simplify the task. This, however, may lead to inaccurate prediction of the structural responses under certain circumstances. Stepped structures or continuous bridges with seismic isolation are notable examples where unsynchronized bearing motions are expected. In this paper, a logically simple and numerically efficient procedure is proposed to solve the dynamic problem of sliding systems with unsynchronized support motions. The motion equations for the sliding and non-sliding modes of the isolated structure are unified into a single equation that is represented as a difference equation in a discrete-time state-space form and the base shear forces between the sliding interfaces can be determined through simple matrix algebraic analysis. The responses of the sliding structure can be obtained recursively from the discrete-time version of the motion equation with constant integration time step even during the transitions between the non-sliding and sliding phases. Therefore, both accuracy and efficiency in the dynamic analysis of the highly non-linear system can be enhanced to a large extent. Rigorous assessment of seismic structures with unsynchronized support motions has been carried out for both a stepped structure and a continuous bridge. Effectiveness of friction pendulum bearings for earthquake protection of such structures has been verified. Moreover, evident unsynchronized sliding motions of the friction bearings have been observed, confirming the necessity to deal with each of the bearings independently in the analytical model. Copyright (C) 2000 John Wiley & Sons, Ltd.
GRID: A fully location-aware routing protocol for mobile ad hoc networks
(2001)
Liao, WH
;
Sheu, JP
;
Tseng, YC
;
資訊工程學系
;
Department of Computer Science
A mobile ad hoc network (MANET) is one consisting of a set of mobile hosts capable of communicating with each other without the assistance of base stations. One prospective direction to assist routing in such an environment is to use location information provided by positioning devices such as global positioning systems (GPS). In this paper, we propose a new routing protocol called GRID. which tries to exploit location information in route discovery, packet relay, and route maintenance. Existing protocols, as compared to ours, are either not location-aware or partially location-aware in that location knowledge is not fully exploited in all these three aspects. One attractive feature of our protocol is its strong route maintenance capability - the intermediate hosts of a route can perform a "handoff" operation similar to that in cellular systems when it roams away to keep a route alive. This makes routes in the MANET more stable and insensitive to host mobility. Simulation results show that our GRID routing protocol can reduce the probability of route breakage, reduce the number of route discovery packets used, and lengthen routes' lifetime.
Location awareness in ad hoc wireless mobile networks
(2001-06-01)
Tseng, YC
;
Wu, SL
;
Liao, WH
;
Chao, CM
;
交大名義發表
Networks composed of dynamically repositioning mobile hosts require location awareness to provide new geographic services and to maximize routing efficiency and quality of service.
Seismic isolation of viaduct piers by means of a rocking mechanism
(2006-05-01)
Chen, YH
;
Liao, WH
;
Lee, CL
;
Wang, YP
;
土木工程學系
Rocking mechanism can be an effective means of seismic isolation, despite the fact that it is rarely conceived a possible alternative. In this study, the feasibility of utilizing a rocking mechanism for earthquake protection of slender viaduct pier structures is explored both analytically and experimentally. With a discontinuous interface between the pier footings and the underlying pile caps, a rocking system is designed to rock intermittently as the seismic overturning moment exceeds the restoring moment provided by gravity. During the rock mode, the resisting flexural moment in the pier is released while the earthquake load is counteracted by the rotational inertia with respect to the supporting foot, thus preventing the Columns from yielding. Analytical modelling of this non-linear dynamic system is derived with a numerical procedure developed based on the fourth-order Runge-Kutta-Nystrom method. A series of tests including the free rocking and seismic performance test, has been conducted using a 1:50 scaled-down model structure of a typical viaduct pier system. Both analytical and experimental results show that the rocking pier system (RPS) for seismic protection of viaduct pier structures is effective and stable, and the stronger the earthquake intensity the more pronounced the control efficiency. The concept of using rocking mechanism for seismic isolation of viaduct pier structures has been demonstrated feasible and promising. Nevertheless, practical issues such as prevention of overturning, foot damage due to impact, or possible sliding of the pier following impact need to be carefully dealt with in the design aspect. Copyright (C) 2006 John Wiley & Sons, Ltd.
Seismic response analysis of bridges isolated with friction pendulum bearings
(1998-10-01)
Wang, YP
;
Chung, LL
;
Liao, WH
;
土木工程學系
;
Department of Civil Engineering
A systematic method is developed for the dynamic analysis of the structures with sliding isolation which is a highly non-linear dynamic problem. According to the proposed method, a unified motion equation can be adapted for both stick and slip modes of the system, Unlike the traditional methods by which the integration interval has to be chopped into infinitesimal pieces during the transition of sliding and non-sliding modes, the integration interval remains constant throughout the whole process of the dynamic analysis by the proposed method so that accuracy and efficiency in the analysis of the non-linear system can be enhanced to a large extent. Moreover, the proposed method is general enough to be adapted for the analysis of the structures with multiple sliding isolators undergoing independent motion conditions simultaneously. The superiority of the proposed method for the analysis of sliding supported structures is verified by a three-span continuous bridge subjected to harmonic motions and real earthquakes. In addition, the side effect of excessive displacement of the superstructure induced by the sliding isolation is eliminated by replacing one of the roller supports on the abutments with hinge support. Therefore, both reductions in the forces of the substructure and the displacements of the superstructure can be achieved simultaneously. (C) 1998 John Wiley & Sons, Ltd.
Seismic response analysis of bridges isolated with friction pendulum bearings
(1998-10-01)
Wang, YP
;
Chung, LL
;
Liao, WH
;
土木工程學系
;
Department of Civil Engineering
A systematic method is developed for the dynamic analysis of the structures with sliding isolation which is a highly non-linear dynamic problem. According to the proposed method, a unified motion equation can be adapted for both stick and slip modes of the system, Unlike the traditional methods by which the integration interval has to be chopped into infinitesimal pieces during the transition of sliding and non-sliding modes, the integration interval remains constant throughout the whole process of the dynamic analysis by the proposed method so that accuracy and efficiency in the analysis of the non-linear system can be enhanced to a large extent. Moreover, the proposed method is general enough to be adapted for the analysis of the structures with multiple sliding isolators undergoing independent motion conditions simultaneously. The superiority of the proposed method for the analysis of sliding supported structures is verified by a three-span continuous bridge subjected to harmonic motions and real earthquakes. In addition, the side effect of excessive displacement of the superstructure induced by the sliding isolation is eliminated by replacing one of the roller supports on the abutments with hinge support. Therefore, both reductions in the forces of the substructure and the displacements of the superstructure can be achieved simultaneously. (C) 1998 John Wiley & Sons, Ltd.