• The Journal of the Acoustical Society of Korea
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• v.37 no.4
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• pp.181-187
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• 2018

In this paper, sound absorption of micro-perforated elastic plates installed in an impedance tube of a circular cross-section is discussed using an analytic method. Vibration of the plates and sound pressure fields inside the duct are expressed in terms of an infinite series of modal functions, where modal functions in the radial direction is given in terms of the Bessel functions. Under the plane wave assumption, a low frequency approximation is derived by including the first few plate modes, and the sound absorption coefficient is given in terms of an equivalent impedance of a single surface. The sound absorption coefficient using the proposed formula is in excellent agreement with the result by the FEM (Finite Element Method), and shows dips and peaks at the natural frequencies of the plate. When the perforation ratio is very small, the sound absorption coefficient is dominated by the vibration effect. However, when the perforation ratio reaches a certain value, the sound absorption is mainly governed by the rigid MPP (Micro-Perforated Plate), while the vibration effect becomes very small.

• Proceeding of KASS Symposium
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• 2006.05a
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• pp.233-238
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• 2006

This paper provides a new topology optimization technique which is intended to maximize the fundamental frequency with simultaneous consideration of other natural frequencies in the form of multi-frequency problems. The modal strain energy is considered as the objective function to be minimized and the initial volume of structures is used as the constraint function. The resizing algorithm based on the optimality criteria is adopted to update the hole size existing inside the material. From numerical tests, the proposed technique is found to be very effective to maximize the fundamental frequency of the structure and it can also successfully consider several higher mode effects into the optimum topology of structure through the introduction of weights.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.22 no.2
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• pp.79-87
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• 2010

This is the first of the two papers dealing with reliability analyses for external and internal stability of a quay wall constructed on a special foundation. A new practical reliability analysis method is proposed in this paper to evaluate the quantitative risk associated with external stability of a quay wall constructed on the deep cement mixed ground. The method can consider uncertainties in various design variables. For the risk estimation to external stability of the improved soil-quay wall, three corresponding limit state functions of sliding, overturning and bearing capacity are fully defined by introducing concept of the secondary random variable. Three representative reliability methods, MVFOSM, FORM and MCS are then applied to evaluate the failure probabilities of the three limit state functions explicitly expressed in terms of the basic and secondary random variables. From the reliability analysis results, the failure probabilities obtained from the three approaches are very close to each other, and the sliding failure mode appears to be the most critical when the earthquake loading is under consideration.

• Journal of the KSME
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• v.33 no.12
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• pp.1043-1051
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• 1993

Nd:Yag 레이저의 제2고조파와 광대역 모드 없는 레이저를 광원으로 사용하고 이중회절발분광 기에 설치된 다채널광검출기로 분광된 CARS 스펙트럼을 레이저 펄스마다 측정 할 수 있는 광 대역 CARS 분광기를 제작하였다. CARS 온도측정 불확정도는 300K에서 1300K까지는 1.5% 이내였다. CARS 기술을 이용하여 분젠버너의 화염면에서의 온도 분포를 측정하였으며, 대향류 버너의 화염내부의 온도 분포 및 CO 농도분포를 측정하였다. 이러한 CARS 기술은 정상상태의 연소진단에 응용할 수 있을 뿐만 아니라 레이저 펄스마다 측정되는 온도의 분포함수를 조사하면 앞으로 난류연소의 진단에도 응용이 가능하며, 내연기관 등과 같이 연속폭발연소 상태의 기체의 온도나 농도 측정이 가능하다. 본 연구에서 연구된 CARS 기술의 온도 측정정확도는 약 2% 이 내이고 농도 측정은 측정기체의 농도가 상온에서는 약 0.1% 이상, 1500K 이상의 고온에서는 0.3%이상이면 가능하다.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.11 no.6
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• pp.939-945
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• 2000

A cylindrical object buried in the lossy half space is reconstructed from the measured scattered fields above the lossy half space. The position, the size and the medium parameters i.e. relative dielectric constants and conductivity of the buried object as well as the medium parameters of the background lossy half space are obtained from the scattered fields by using the iterative inversion method and the optimization hybrid algorithm combining the genetic algorithm and the Levenberg-Marquardt algorithm. Illposedness of the inversion due to the measurement errors in the scattered fields are regularized by filtering out the evanescent modes in the spatial frequency spectrum domain.

• The Transactions of the Korea Information Processing Society
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• v.4 no.10
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• pp.2521-2532
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• 1997

The next generation internet protocol, IPv6, have been developed by the IETF according to the requirements of enhancement of classic IP protocols to satisfy the lack of Internet address space as well as the support of multimedia applications. This paper presents an implementation of IPv6 protocols on the Windows NT kernel environment. In this work, we developed and also tested the basic functions, required for operating as an IPv6 host, such as IPv6 header processing, IPv6 address handling, control message processing, group membership processing and neighbor discovery functions. The implemented IPv6 protocol driver module is connected to the lower network interface card through NDIS, a standard network interface. And this driver module that operates within kernel, is implemented as it is connected to upper user applications and lower NDIS using dispatch and lower-edge functions. The developed IPv6 protocol driver can provide not only enhanced performance because it is implemented in kernel mode, but also convenience of usage to the application developers because it gives user interface as a dynamic link library.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.22 no.2
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• pp.88-94
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• 2010

A reliability analysis method is proposed in this paper to quantitatively evaluate the risk for internal stability of a quay wall constructed on the deep cement mixed ground, differentiating from the companion paper that mainly describes the external stability. Failure modes for toe pressure, shear strength of improved ground and extrusion of unimproved soft soil are investigated and compared in the risk estimation of internal stability using MVFOSM, FORM, and MCS. From the reliability analysis results for internal stability of a quay wall, the variance and distribution type of the compressive strength of Deep Mixed Soil-Cement appear to be very affective to the failure probability. On the other hand, other random variables seem to be relatively very insensitive to the probability of failure. It is therefore very important to rationally and accurately determine the probabilistic properties of the in-site compressive strength of Deep Mixed Soil-Cement.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.25 no.4
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• pp.293-300
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• 2012

In this study, the delamination analysis has been implemented to investigate the initiation and propagation of crack in composite laminates composed of orthotropic materials. A simple modeling was achieved by moving nodal technique without re-meshing work when crack propagation occurred. This paper aims at achieving two specific objectives. The first is to suggest a very simple modeling scheme compared with those applied to conventional h-FEM based models. To verify the performance of the proposed model, analysis of double cantilever beams with composite materials was implemented and then the results were compared with reference values in literatures. The second one is to investigate the behavior of interior delamination problems using the proposed model. To complete these objectives, the full-discrete-layer model based on Lobatto shape functions was considered and energy release rates were calculated using three-dimensional VCCT(virtual crack closure technique) based on linear elastic fracture mechanics.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.17 no.2
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• pp.83-92
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• 2007

In connectionless packet network, if a sender encrypts packets by block chaining mode and send it to receiver, the receiver should decrypt packets in encrypted order that is not received order. Therefore, the performance and efficiency are lowered for crypto communication system. To solve this problem, we propose packet encryption scheme for connectionless packet network that can decrypt the packets independently, even if the received order of packets are changed or packets are missed. The scheme makes new IV(Initial Vector) using IV that created by key exchange process and salt that made by random number. We propose extended Cryptoki API that added packet encryption/decryption functions and mechanism for improving convenience and performance. We implement the scheme and get result that the performance increased about $1.5{\sim}l5.6$ times compare with in case of implementing using Cryptoki API in the test environment.

• Journal of the Korean Applied Science and Technology
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• v.33 no.4
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• pp.836-847
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• 2016

Water soluble oil was obtained by pyrolysis of biomass. The characteristics of emulsified fuel by mixing water soluble oil and MDO(marine diesel oil) and engine emissions were studied with engine dynamometer. Saw dust was used as biomass. Water soluble oil was obtained by condensing of water and carbon content with pyrolysis of saw dust at $500^{\circ}C$. Emulsion fuel was obtained by emulsifying MDO and water soluble oil by the water soluble oil mixing ratio of 10 to 20% of MDO. Exhaust gas detection was performed with engine dynamometer. While combustion, micro-explosion took place in the combustion chamber by water in the emulsion fuel, emulsion fuel scattered to micro particles and it caused to smoke reduction. The heat produced from water vapour reduce the temperature of internal combustion chamber and it caused to inhibition of NOx production. It can be verified by the lower exhaust temperature of each ND-13 mode using emulsion fuel than that of MDO fuel. The NOx and smoke concentration were reduced by increasing water soluble oil content in the emulsion fuel. The power also decreased according to the increment of water soluble oil content of emulsion fuel because emulsion fuel has low calorific value due to high water content than MDO. As a result of ND-13 mode test with 20% bio oil content, it was achieved 25% reduction in NOx production, 60% reduction in smoke density, and 15% reduction in power loss.