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CONTENTS
Volume 10, Number 6, December 2012
 

Abstract
We design and test a shape memory alloy (SMA)-based actuation system that can be used to propel a fish robot. The actuator in the system is composed of a 0.1 mm diameter SMA wire, a 0.5 mm-thick glass/epoxy composite strip, and a fixture frame. The SMA wire is installed in a pre-bent composite strip that provides initial tension to the SMA wire. The actuator can produce a blocking force of about 200 gram force (gf) and displacement of 3.5 mm at the center of the glass/epoxy strip for an 8 V application. The bending motion of the actuator is converted into the tail-beat motion of a fish robot through a linkage system. The fish robot is evaluated by measuring the tail-beat angle, swimming speed, and thrust produced by the tail-beat motion. The tail-beat angle is about 20o, the maximum swimming speed is about 1.6 cm/s, and the measured average thrust is about 0.4 gf when the fish robot is operated at 0.9 Hz.

Key Words
fish robot; SMA wire; bending actuator; biomimetics

Address
Chan Hoang Le, Quang Sang Nguyen and Hoon Cheol Park : Department of Advanced Technology Fusion, Konkuk University, Seoul 143-701, Korea

Abstract
In this paper, vibration-based methods to monitor damage in foundation-structure interface of harbor caisson structure are presented. The following approaches are implemented to achieve the objective. Firstly, vibration-based damage monitoring methods utilizing a variety of vibration features are selected for harbor caisson structure. Autoregressive (AR) model for time-series analysis and power spectral density (PSD) for frequency-domain analysis are selected to detect the change in the caisson structure. Also, the changes in modal parameters such as natural frequency and mode shape are examined for damage monitoring in the structure. Secondly, the feasibility of damage monitoring methods is experimentally examined on an unsubmerged lab-scaled mono-caisson. Finally, numerical analysis of un-submerged mono-caisson, submerged mono-caisson and un-submerged interlocked multiple-caissons are carried out to examine the effect of boundary-dependent parameters on the damage monitoring of harbor caisson structures.

Key Words
harbor caisson; foundation-structure interface; damage monitoring; autoregressive model; power spectral density; modal parameters

Address
So-Young Lee, Khac-Duy Nguyen, Thanh-Canh Huynh and Jeong-Tae Kim : Department of Ocean Eng., Pukyong National University, Busan, Korea
Jin-Hak Yi and Sang-Hun Han : Coastal Development & Ocean Energy Research Dept., Korea Institute of Ocean Science and Technology (KIOST), Ansan, Korea

Abstract
Measuring crack length in concrete fracture test is not a trivial problem due to high speed crack propagation. In this study, mechanoluminascent (ML) material, which emits visible light under stress condition, was employed to visualize crack propagation during concrete fracture test. Three-point bending test was conducted with a notched concrete beam specimen. The cracking images due to ML phenomenon were recorded by using a high speed camera as a function of time and external loadings. The experimental results successfully demonstrated the capability of ML material as a promising visualization tool for concrete crack propagation. In addition, an interesting cracking behavior of concrete bending fracture was observed in which the crack propagated fast while the load decreased slowly at early fracture stage.

Key Words
mechanoluminescence; concrete fracture; high speed crack detection; cracking images; threepoint bending test

Address
Wha-Jung Kim, Jae-Min Lee and Chang Joon Lee : School of Architecture and Civil Engineering, Kyungpook National University, Daegu, South Korea
Ji-Sik Kim : Department of Advanced Materials Engineering, Kyungpook National University, Sangju, South Korea

Abstract
This paper focuses on the vibration control of long-span reticulated steel structures under multidimensional earthquake excitation. The control system and strategy are constructed based on Magneto- Rheological (MR) dampers. The LQR and Hrovat controlling algorithm is adopted to determine optimal MR damping force, while the modified Bingham model (MBM) and inverse neural network (INN) is proposed to solve the real-time controlling current. Three typical long-span reticulated structural systems are detailedly analyzed, including the double-layer cylindrical reticulated shell, single-layer spherical reticulated shell, and cable suspended arch-truss structure. Results show that the proposed control strategy can reduce the displacement and acceleration effectively for three typical structural systems. The displacement control effect under the earthquake excitation with different PGA is similar, while for the cable suspended arch-truss, the acceleration control effect increase distinctly with the earthquake excitation intensity. Moreover, for the cable suspended arch-truss, the strand stress variation can also be effectively reduced by the MR dampers, which is very important for this kind of structure to ensure that the cable would not be destroyed or relaxed.

Key Words
vibration control; reticulated steel structure; MR damper; semi-active control; earthquake excitation

Address
Zhen Zhou, Shao-ping Meng, Jing Wu and Yong Zhao : Southeast University, Key Laboratory of Concrete and Prestressed Concrete Structures of the Ministry of Education, Nanjing, 210096, China

Abstract
In this study, a procedure to design an optimal LCVA that maximizes the equivalent damping ratio added to the primary structure subjected to along-wind excitation is proposed. That design procedure does not only consider the natural frequency and damping ratio of the LCVA, but also the proportion of the Ushaped liquid, which is closely related to the participation ratio of the liquid mass in inertial force. In addition, constraints to ensure the U-shape of the liquid are considered in the design process, so that suboptimal solutions that violate the optimal tuning law partly are adopted as a candidate of the optimal LCVA. The proposed design procedure of the LCVA is applied to the control of the 76-story benchmark building, and the optimal proportions of the liquid shape under various design conditions are compared.

Key Words
liquid column vibration absorber; vibration control; equivalent damping ratio

Address
Ji-Hun Park : Department of Architectural Engineering, University of Incheon, Incheon, South Korea
Kyung-Won Min : Department of Architectural Engineering, Dankook University, Yongin, South Korea


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