• Composites Research
• /
• v.36 no.2
• /
• pp.132-139
• /
• 2023

A linerless composite propellant tank was designed and manufactured by using the carbon fiber-reinforced composite materials which have superior strength-to-weight ratio in order to reduce weight of the tank. In this research, we designed a sub-scale composite propellant tank with a diameter of 800 mm to withstand an MEOP of 1.7 MPa. We manufactured the boss of the tank by using the same composite materials to reduce the thermal expansion difference between the boss and the secondary-bonded composite layers of the barrel in the cryogenic environment. We used the collapsible mandrel to manufacture the tank without any liner. The mandrel was made from epoxy-based composite tooling prepregs to reduce weight of the mandrel. We manufactured the test tanks by laying up the carbon fiber fabric prepregs manually on the mandrel and then applying the autoclave cure process. We performed a proof test, a helium tightness test, a repeated pressurization test, and a burst test in room temperature. The test results demonstrate that the proposed design and manufacture process satisfies all strength requirements as well as an anti-leakage requirement.

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 2009.10a
• /
• pp.332-337
• /
• 2009

Recently, boss and rib test based on backward extrusion process was proposed to quantitative evaluate the interfacial friction condition in bulk forming process. In this test, the tube-shaped punch with hole pressurizes the workpiece so that the boss and rib are formed along the hole and outer surface of the punch. It was experimentally and numerically revealed that the height of boss is higher than that of the rib under the severe friction condition. This work is focused on the effect of the punch design and friction condition on deformation pattern in boss and rib test. From the boss and rib test simulations, it was found that there is slight variation in both the heights of boss and rib according to the length of punch land, nose radius, and face angle. However the hole diameter of the punch and the clearance between the punch and die have a significant influence on the heights of the boss and rib. In addition, the effect of flow stress was also investigated on the deformation patterns through FE simulations.

• The Proceeding of the Korean Institute of Electromagnetic Engineering and Science
• /
• v.4 no.2
• /
• pp.34-40
• /
• 1993

A microstrip antenna for mobile system are designed at the resont frequency 0.88 GHz. The microstrip array antenna are designed to depend on the size of rectanular microstrip path for the relative current distribution to be 1:4.69:1 using Tchebyscheff polynominals. Gain difference between the main lobe and sidelobe is calculated for theoritical values of 20 dB. The designed microstrip array antenna are mesureed various characteristics, such as return loss, radiation pattern, V.S.W.R, bandwidth, and agreed with each other and theoretical value. Also it is presented a process of phase variation of patch array antenna depend on relative current distribution for beam scanning.

• Tribology and Lubricants
• /
• v.24 no.4
• /
• pp.196-204
• /
• 2008

In this study, the pressure distributions on the oil film of piston pin bearings are found by two-dimensional lubrication analysis in order to help the optimum design of the bearings of piston pin. The lubrication analysis is carried out together with an equation related with the oil pressure-viscosity index. The oil film pressure distribution is used as an input data for pressure boundary conditions at the piston pin-boss surface. Finally, the piston pin-boss stress distribution coupled with the thermal stress is calculated, and then compared with the results of the stress analysis which is not counted with the oil film pressure boundary condition.

• Applied Chemistry for Engineering
• /
• v.16 no.1
• /
• pp.150-152
• /
• 2005

$La_{0.2}Ca_{0.8}MnO_3$ colossal magnetoresistance (CMR) powders and pellets were synthesized by sol-gel process involving a stable metal chelate complex with acetylacetone. The structural changes of reaction mixture were monitored by FT-IR spectroscopy and X-ray diffractometry. The microstructure of sintered samples and the cation composition of gel powder were studied by FE-SEM/EDS and ICP-AES. The magnetic property was investigated as a function of temperature.

• Journal of Korean Library and Information Science Society
• /
• v.35 no.2
• /
• pp.393-414
• /
• 2004

Traditional role of library is focused on the book collection and its reference service. However, library should be stressed the need of educational activity in the future. This study described to classify the roles of public library, which are book collecting and its reference services, educational activities, event place service for region community. Observation survey on the public libraries in Boston and its Vicinity shows that public libraries have various children's programs and they are getting more important roles. Public libraries of case study have done not only the roles for reference service space but also the informal lifelong education institute for region community. Library as the informal lifelong education institute deserve special emphasis on the development of education program.

• Korean Journal of Computational Design and Engineering
• /
• v.11 no.2
• /
• pp.77-87
• /
• 2006

It is necessary to change the existing design process to cope with a short life-cycle product and various customer's demands. Also a frequent design change may delay the whole design process and it will increase the unit cost of the production. New alternatives or techniques have emerged to solve the existing design problems, such as a knowledge based engineering, an intelligent CAD, a function based design, and so on. In this paper, we propose a hybrid design system with a knowledge based design methodology and a function based design technique. The knowledge based design is good at a frequent design change and the function based design is effective to extract a core design behavior. In an early design process, the system utilizes a core design behavior through the function based design process. On the other hand, the system manages complicated design issues with the knowledge based design technique in the detailed design process. We conclude that the hybrid design system can bring fair effects on implementing an efficient design environment in aspect of time and expense.

• The Journal of Society for e-Business Studies
• /
• v.12 no.4
• /
• pp.29-36
• /
• 2007

Recently, Jaiswal et al. proposed a protocol to improve the multi-agent negotiation test-bed which was proposed by Collins et al. Using publish/subscribe system, time-release cryptography and anonymous communication, their protocol gives an improvement on the old one. However, it is shown that the protocol also has some security weaknesses: such as replay data attack and DOS (denial-of-service) attack, anonymity disclosure, collusion between customers and a certain supplier. So proposed protocol reduces DOS attack and avoids replay data attack by providing ticket token and deal sequence number to the supplier. And it is proved that the way that market generates random number to the supplier is better than the supplier do by himself in guaranteeing anonymity. Market publishes interpolating polynomial for sharing the determination process data. It avoids collusion between customer and a certain supplie

• The Journal of Society for e-Business Studies
• /
• v.12 no.4
• /
• pp.17-27
• /
• 2007

This paper proposes a key distribution and authentication protocol between user, service provider and key distribution center (KDC). This protocol is based on symmetric cryptosystem, challenge-response, Diffie-Hellman component and hash function. In the proposed protocol, user and server update the session key under token-update operation, and user can process repeated efficient authentications by using updated session keys. And another merit is that KDC needs not to totally control the session key between user and server in proposed protocol. Even an attacker steals the parameters from the KDC, the attacker still can not calculate session key. According to the comparison and analysis with other protocols, our proposed protocol provides good efficiency and forward secure session key.

• Journal of the Korean Society of Costume
• /
• v.52 no.2
• /
• pp.45-57
• /
• 2002

21th century is evolving from physical to brain-oriented society, and from class oriented society to network society. In the midst of it, bobos is the new enlightened elite group. In depth analyzationon of the beat generation from the 1950's and hippies from the 1960's, which had influenced the bobos, were done to study on such new and core elite group. According to the research, the emerging of bobos was originated and created from the long gone conflict between the beat and bourgeois, and the hippie and the conservative. And this mixed culture of both free-spirited hippie and materialistic yuppies from the 80's is rapidly growing, and they are easily seem from various commercial advertisements, accessories and fashion designs. In addition, the bobo's were targeted by the main designers, and expressed through bohemian luxury and romantic hippie mood. Naive and childish floral prints, paisley prints that were influenced by the hippies, the hair styles from the 80's and washed denims were seen at the collections. However, the symbolism of the 60's defiant fashion styles seem to fade away but remains only as a style. The comparison and analyzation between the fashion of bobos, hidden meaning of those defiant fashion styles and the aesthetics of it are arranged in the following conclusions.