• Smart Structures and Systems
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• 제24권1호
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• pp.83-94
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• 2019

Passive negative stiffness dampers (NSDs) that possess superior energy dissipation abilities, have been proved to be more efficient than commonly adopted passive viscous dampers in controlling stay cable vibrations. Recently, inertial mass dampers (IMDs) have attracted extensive attentions since their properties are similar to NSDs. It has been theoretically predicted that superior supplemental damping can be generated for a taut cable with an IMD. This paper aims to theoretically investigate the impact of the cable sag on the efficiency of an IMD in controlling stay cable vibrations, and experimentally validate superior vibration mitigation performance of the IMD. Both the numerical and asymptotic solutions were obtained for an inclined sag cable with an IMD installed close to the cable end. Based on the asymptotic solution, the cable attainable maximum modal damping ratio and the corresponding optimal damping coefficient of the IMD were derived for a given inertial mass. An electromagnetic IMD (EIMD) with adjustable inertial mass was developed to investigate the effects of inertial mass and cable sag on the vibration mitigation performance of two model cables with different sags through series of first modal free vibration tests. The results show that the sag generally reduces the attainable first modal damping ratio of the cable with a passive viscous damper, while tends to increase the cable maximum attainable modal damping ratio provided by the IMD. The cable sag also decreases the optimum damping coefficient of the IMD when the inertial mass is less than its optimal value. The theoretically predicted first modal damping ratio of the cable with an IMD, taking into account the sag generally, agrees well with that identified from experimental results, while it will be significantly overestimated with a taut-cable model, especially for the cable with large sag.

• International Journal of Ocean Engineering and Technology Speciallssue:Selected Papers
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• 제6권1호
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• pp.38-43
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• 2003

This paper presents the results of a post-tensioning test and analysis of a pyramidal unit structure that is basic element for space structures. The behavior characteristics was analyzed and compared with the numerical analysis and the mechanism in test model was confirmed with geometrical analysis. The results of this paper show that the behaviors of space structures can be predicted in multi-directional Mero joint system. And the authors suggest the possibility of erection and shaping formation with comparatively small post-tensioning, and space structure with the mechanism should consider the nonlinear behavior due to large deformation.

• International Journal of Control, Automation, and Systems
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• 제6권1호
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• pp.76-85
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• 2008

Motivated by the fact that in many industrial robots the joint velocity is estimated from position measurements, the trajectory tracking of robot manipulators with output feedback is addressed in this paper. The fact that robot actuators have limited power is also taken into account. Let us notice that few solutions for the torque-bounded output feedback tracking control problem have been proposed. In this paper we contribute to this subject by presenting a theoretical reexamination of a known controller, by using the theory of singularly perturbed systems. Motivated by this analysis, a redesign of that controller is introduced. As another contribution, we present an experimental evaluation in a two degrees-of-freedom revolute-joint direct-drive robot, confirming the practical feasibility of the proposed approach.

• Educational Technology International
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• 제8권1호
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• pp.57-69
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• 2007

The advantages of the Internet enable teachers in the world to break the communication barriers between their schools and collaborate with each other, giving them opportunities for richer educational practices than ever accomplished. I assume that collaborative learning like an international exchange naturally lead the students to acquire the knowledge to communicate with their peers using ICT skills. In this paper, two international exchange projects that have years of practice are reported, i.e., new types of collaborative education projects that the development of the Internet has enabled us to carry out. The international exchanges reported here have been possible because both students and teachers have effectively used the various functions of the Internet. To use English as a "common international communication language" is particularly important for the youth in Asia, and the students have come to realize the importance of English as a communication language through these projects. Also, since these practices are based on the infrastructure of the Internet, they have elucidated what kind of Internet use produces richer educational results .At the final stage of the exchanges, "joint presentation in English" is designed. Students communicate and collaborate over the network, and finally meet with each other and try to give a presentation as a product of their collaborative work. The files and scenes of their presentations are stored on the network and used as educational materials in Asia as well as models for the activities in the following years. We will report how to design international exchange education in this Internet age.

• International Journal of Naval Architecture and Ocean Engineering
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• 제6권2호
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• pp.245-256
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• 2014

I-core sandwich panel that has been used more widely is assembled using high power $CO_2$ laser welding. Kim et al. (2013) proposed a circular cone type heat source model for the T-joint laser welding between face plate and core. It can cover the negative defocus which is commonly adopted in T-joint laser welding to provide deeper penetration. In part I, a volumetric heat source model is proposed and it is verified thorough a comparison of melting zone on the cross section with experiment results. The proposed model can be used for heat transfer analysis and thermal elasto-plastic analysis to predict welding deformation that occurs during laser welding. In terms of computational time, since the thermal elasto-plastic analysis using 3D solid elements is quite time consuming, shell element model with multi-layers have been employed instead. However, the conventional layered approach is not appropriate for the application of heat load at T-Joint. This paper, Part II, suggests a new method to arrange different number of layers for face plate and core in order to impose heat load only to the face plate.

• International Journal of Aeronautical and Space Sciences
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• 제18권1호
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• pp.56-62
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• 2017

Because adhesively bonded joints are used in many structural systems, it is important to predict accurate adhesive strengths. Composite aircraft with many joints are easily exposed to low temperatures and high relative humidity. This paper presents a humidity aging effect on the adhesive strength of a composite single-lap joint (SLJ). The adhesive strength of the SLJ is predicted using a finite element analysis with a cohesive zone model (CZM) technique. The humidity aging effect is evaluated based on the adhesive strength and CZM parameters. A lap joint test is carried out on the composite SLJ specimens, which are exposed for four months of 100% R.H. at $25^{\circ}C$. The predicted strengths are in good agreement with experimental data, and the actual crack propagation is satisfactorily simulated using the local CZM technique.

• International Journal of Control, Automation, and Systems
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• 제5권5호
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• pp.559-569
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• 2007

In this paper, the dynamic controller design problem of a redundant planar 2-dof parallel manipulator is studied. Using the Euler-Lagrange equation, we formulate the dynamic model of the parallel manipulator in the joint space and propose an augmented PD controller with forward dynamic compensation for the parallel manipulator. By formulating the controller in the joint space, we eliminate the complex computation of the Jacobian matrix of joint angles with end-effector coordinate. So with less computation, our controller is easier to implement, and a shorter sampling period can be achieved, which makes the controller more suitable for high-speed motion control. Furthermore, with the combination of static friction model and viscous friction model, the active joint friction of the parallel manipulator is studied and compensated in the controller. Based on the dynamic parameters of the parallel manipulator evaluated by direct measurement and identification, motion control experiments are implemented. With the experiments, the validity of the dynamic model is proved and the performance of the controller is evaluated. Experiment results show that, with forward dynamic compensation, the augmented PD controller can improve the tracking performance of the parallel manipulator over the simple PD controller.

• International Journal of Aeronautical and Space Sciences
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• 제16권1호
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• pp.28-40
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• 2015

This paper aims to address the intelligent active vibration control problem of a flexible rectangular plate vibration involving parameter variation and external disturbance. An adaptive sliding mode (ASM) MIMO control strategy and smart piezoelectric materials are proposed as a solution, where the controller design can deal with problems of an external disturbance and parametric uncertainty in system. Compared with the current 'classical' control design, the proposed ASM MIMO control strategy design has two advantages. First, unlike existing classical control algorithms, where only low intelligence of the vibration control system is achieved, this paper shows that high intelligent of the vibration control system can be realized by the ASM MIMO control strategy and smart piezoelectric materials. Second, the system performance is improved due to two additional terms obtained in the active vibration control system. Detailed design principle and rigorous stability analysis are provided. Finally, experiments and simulations were used to verify the effectiveness of the proposed strategy using a hardware prototype based on NI instruments, a MATLAB/SIMULINK platform, and smart piezoelectric materials.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제11권1호
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• pp.146-170
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• 2017

Joint channel assignment and routing is a well-known problem in multi-radio wireless mesh networks for which optimal configurations is required to optimize the overall throughput and fairness. However, other objectives need to be considered in order to provide a high quality service to network users when it deployed with high traffic dynamic. In this paper, we propose a re-configuration optimization model that optimizes the network throughput in addition to reducing the disruption to the mesh clients' traffic due to the re-configuration process. In this multi-objective optimization model, four objective functions are proposed to be minimized namely maximum link-channel utilization, network average contention, channel re-assignment cost, and re-routing cost. The latter two objectives focus on reducing the re-configuration overhead. This is to reduce the amount of disrupted traffic due to the channel switching and path re-routing resulted from applying the new configuration. In order to adapt to traffic dynamics in the network which might be caused by many factors i.e. users' mobility, a centralized heuristic re-configuration algorithm called State-Aware Joint Routing and Channel Assignment (SA-JRCA) is proposed in this research based on our re-configuration model. The proposed algorithm re-assigns channels to radios and re-configures flows' routes with aim of achieving a tradeoff between maximizing the network throughput and minimizing the re-configuration overhead. The ns-2 simulator is used as simulation tool and various metrics are evaluated. These metrics include channel-link utilization, channel re-assignment cost, re-routing cost, throughput, and delay. Simulation results show the good performance of SA-JRCA in term of packet delivery ratio, aggregated throughput and re-configuration overhead. It also shows higher stability to the traffic variation in comparison with other compared algorithms which suffer from performance degradation when high traffic dynamics is applied.

• 통상정보연구
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• 제6권2호
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• pp.3-12
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• 2004

A large number of Chinese trade marks and domain names have been registered improperly or illegally by foreign companies or businessmen. Additionally, a large number of famous Chinese brands have vanished through joint ventures, mergers and acquisitions since foreign direct investment (FDI) came to China more than two decades ago because some Chinese managers have not been fully aware of the value of trade marks and domain names. Consequently, the number of China's registered trade marks and famous brands does not match China's export volume and its Number four trade status in the world. China's enterprises have yet to realize the effects of these events. It is very important for China to protect and cultivate its own famous brands. This paper discusses Chinese companies' neglect of the value of their trade marks and domain names, and the possible consequences. Additionally, this paper puts forward suggestions concerning the protection and cultivation of China's famous brands.