• Journal of the Society of Naval Architects of Korea
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• v.46 no.6
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• pp.667-674
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• 2009

The researches on the development of composite material underwater vehicle propeller have been actively attempted for the reduction of radiation noise with outstanding damping effects. Composite material propellers have almost been designed and produced by the foreign experts, and it is difficult to obtain the related informations about their flow, vibration, material characteristics because they are treated as the secrets with close relationship to the military technology, especially in the case of underwater vehicles. For the security of domestic manufacture of composite material propeller and the comparison and examination of its performance and radiation noise characteristics with those of German CONTUR composite material propeller, two propellers were self-produced according to the fiber weaving and array using compressible molding process and their self performances and radiation noise characteristics were measured. The mean fluctuations of blade tip of self-produced composite material propeller were increased and the radiation noises in the low frequency band were reduced compared to those of CONTUR, which could be estimated as the change of material characteristics and also be thought to be used for the future research informations.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 1998.03a
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• pp.209-213
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• 1998

This study considers flowshop scheduling problem related to flexible maufacturing cell in which consists of two machining centers, robots for loading/unloading, and an automated guided vehicle(AGV) for material handling between two machining centers. Because no machinng center has buffer storage for work in process, a machining center can not release a finished job until the empty AGV is available at that machining center. While the AGV cannot tranfer an unfinished job to a machining center until the machining center empty. In this paper, an new heuristic algorithm is given to find the sequence that minimize their makespan.

• Elastomers and Composites
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• v.58 no.1
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• pp.26-31
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• 2023

Aromatic diamine containing ortho catenation and methyl group was synthesized from 4-methyl catechol and 4-nitrobenzoyl chloride. Subsequently, a poly(amic acid) was prepared by reacting 4-methyl-1,2-phenylene bis(4-aminobenzoate) with 4,4'-hexafluoroisopropylidenediphthalic anhydride (6FDA). The resulting poly(amic acid) was transformed into a polyimide through chemical imidization. The polyimide formed was soluble in N-methyl-2-pyrrolidone (NMP) and could be cast into a flexible, transparent film. Furthermore, the polyimide exhibited a 5% weight loss at 380 ℃ in the nitrogen atmosphere.

• Elastomers and Composites
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• v.59 no.3
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• pp.91-96
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• 2024

A novel aromatic polyimide containing the 4-tert-butyl group was prepared from 4-tert-butyl-1,2-phenylene bis(4-aminobenzoate) and 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA). 4-tert-Butyl-1,2-phenylene bis(4-aminobenzoate) was synthesized from 4-tert-butyl catechol and 4-nitrobenzoyl chloride. The poly(amic acid) was transformed into a polyimide via chemical imidization. The polyimide was soluble in N-methyl-2-pyrrolidone (NMP) and could be cast into a flexible and transparent film. The thermal stability of the polyimide was decreased slightly due to the pendant tertbutyl group.

• The Journal of Korea Robotics Society
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• v.12 no.3
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• pp.263-269
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• 2017

Recently, soft robots using soft materials are presented. Thanks to soft materials, soft robots have flexible, highly-stretchable or adaptable features. However, due to the flexibility of soft material, it is hard for soft robots to control accurately or perform high force. To deal with these limitations, variable stiffness technology, which enables the stiffness control of structure, has been developed. In this research, a dual-stiffness structure that is actuated by the assembly of two flexible structures are presented. Each flexible structure consists of flexible film part and rigid parts placed at regular intervals. The flexibility of film between rigid parts allows each structure to move softly. On the other hand, by combining two structures rigid part of each part constrain the degrees of freedom of the other side part. And this causes the stiffness of whole structure to be increased. This paper will cover concepts, design, analysis and experiments of this structure.

• Journal of the Korean Society for Precision Engineering
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• v.31 no.8
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• pp.683-688
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• 2014

This paper presents a high-performance flexible tactile sensor based on inorganic silicon flexible electronics. We created 100 nm-thick semiconducting silicon ribbons equally distributed with 1 mm spacing and $8{\times}8$ arrays to sense the pressure distribution with high-sensitivity and repeatability. The organic silicon rubber substrate was used as a spring material to achieve both of mechanical flexibility and robustness. A thin copper layer was deposited and patterned on top of the pressure sensing layer to create a flexible temperature sensing layer. The fabricated tactile sensor was tested through a series of experiments. The results showed that the tactile sensor is capable of measuring pressure and temperature simultaneously and independently with high precision.

• International Journal of Aeronautical and Space Sciences
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• v.18 no.1
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• pp.70-81
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• 2017

Various components of an engine nozzle are modeled as flexible multi-body components that are operated under high temperature and pressure. In this paper, in order to predict complex behavior of an engine nozzle, thermo-fluid-flexible multi-body dynamics coupled analysis framework was developed. Temperature and pressure on the nozzle wall were obtained by the steady-state flow analysis for a two-dimensional nozzle. The pressure and temperature-dependent material properties were delivered to the flexible multi-body dynamics analysis. Then the deflection and strain distribution for a nozzle configuration was obtained. Heat conduction and thermal analyses were done using MSC.NASTRAN. The present framework was validated for a simple nozzle configuration by using a one-way coupled analysis. A two-way coupled analysis was also performed for the simple nozzle with an arbitrary joint clearance, and an asymmetric flow was observed. Finally, the total strain result for a realistic nozzle configuration was obtained using the one-way and two-way coupled analyses.

• Smart Structures and Systems
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• v.7 no.2
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• pp.103-116
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• 2011

This paper is concerned with the trajectory tracking and vibration suppression of a single-link flexible arm by using piezoelectric materials. The dynamics of a single flexible arm with PZT patches as sensor and actuator is derived using extended Hamilton's principle. Resulting equations show that the coupled beam dynamics including beam vibration and its rigid in-plane rotation takes place in two different time scales. By using singular perturbation theory, the system dynamics is divided into two subsystems. Then, a composite control scheme is elaborated that makes the orientation of the arm track a desired trajectory while suppressing its vibration. The proposed controller has two parts: one is a tracking controller designed for the slow (rigid) subsystem, and the other one is a stabilizing controller for the fast (flexible) subsystem. The outputs considered for the system are angular position of the hub and voltage of the sensor mounted on the structure. To avoid requiring further measurements of beam vibration and also angular velocity of the hub for the fast and slow control laws, respectively, two sliding mode observers for estimating the unknown states are also designed.

• Journal of the Society of Naval Architects of Korea
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• v.48 no.5
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• pp.445-450
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• 2011

In order to estimate a yacht sail performance, measuring system of aerodynamic forces acting on the yacht sail is constructed and experiments of flexible model sail are carried out at the medium-size subsonic wind tunnel of Chungnam National University. Experimental results for a flexible sail are compared with experimental and numerical results of fixed shape sail. In case of a fixed shape sail, lift and drag coefficients are rarely changed at all velocity conditions. However, those of the flexible sail are decreased as the incoming velocity is increased. These are understandably resulted from shape variations due to the flexible material. Therefore aero-elastic similarity should be more carefully considered in the model test rather than other similarities.

• Journal of Advanced Marine Engineering and Technology
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• v.31 no.6
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• pp.768-776
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• 2007

In this study, axial vibration analysis has been conducted on a propulsion and lift shafting system for an air cushion vehicle using ANSYS code. The shafting system is totally flexible multi-elements system including wood composite material of air propeller. aluminum alloy of lift fan and thin walled shaft with flexible coupling. The analysis calculated the axial natural frequencies and mode shapes of the shafting system taking into account an equivalent mass-elastic model for shafting system as well as the three-dimensional models for propeller blade and fan impeller. Such a flexible shafting system has very intricate vibrating characteristics and especially, axial natural frequencies of flexible components such as propeller blade and impeller of lift fan can be lower to the extent that causes a resonance in the range of operating revolution. The results for axial vibration analysis are presented and compared with the results of axial vibration test for lift fan conducted during Sea Trial.