• The Journal of the Acoustical Society of Korea
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• v.39 no.1
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• pp.1-7
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• 2020

The acoustic parabolic equation method in the ocean is an efficient technique to calculate the acoustic field in the range-dependent environment, emanating from a point source. However, we often need to use the directional source with a main beam in the practical problem. In this paper, we present two methods to implement the directional source in the acoustic parabolic equation code easily. One is simply to filter the Delta function idealized as an omni-directional point source. Another method is based on the rational filtering of the self-starter solution. It has a limitation not to separate the up-going and the down-going wave for the depth, but would be useful in implementing the mode propagation. Numerical examples for validation are given in the Pekeris environment and the deep sea environment.

• Journal of the Korea Organic Resources Recycling Association
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• v.23 no.1
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• pp.38-44
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• 2015

We have investigated the productivity of microalgae, Nannochloropsis sp., using highly efficient vertical photobioreactor which has been developed by the company IMBiz. This experiment was performed in the field for one month with 2 sets of 2 tons of media under autotrophic cultural mode. In the culture with 0.1% of $CO_2$, the average daily productivity was shown to be up to 0.953g per liter, and 0.574g per liter in the culture with only ambient air. The temperature ranged from $20^{\circ}C$ to $31^{\circ}C$, and it didn't make any differences on the productivity. The light intensity ranged from 5,000 Lux to 40,000 Lux. The light has been appeared to have a very close relationship with the productivity of microalgae. Meanwhile, the harvesting method of pressurefloating attempted in this photobioreactor was found to be very effective.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.20 no.9
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• pp.1633-1640
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• 2016

In this paper, we propose a open-ended rectangular microstirp patch antenna with fork-shaped feeding structure. This antenna extends the effective bandwidth by transforming single or multi resonant frequency and is designed planar monopole structure with microstrip line to satisfy the WLAN bands (2.4 - 2.484, 5.15 - 5.35, 5.25-5.825 GHz). The substrate is printed in 0.8 mm thickness on an FR-4 board. A commercial 3D simulation tool was used to analyze surface current and electromagnetic field distribution in order to analyze the operation mode and reconfiguration principle of antenna. According to the lengths of individual patches, simulated reflection loss was compared to obtain optimized values. When it was designed with the optimized values, it satisfied WLAN bands (2.380 - 2.710, 4.900 - 5.950 GHz), if the switch is off, and 2.4 WLAN band (2.380 - 2.710 GHz). From the fabricated and measured results, measured results of return loss, gain and radiation patterns characteristics displayed for operating bands.

• Computers and Concrete
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• v.16 no.6
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• pp.933-961
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• 2015

Damage by high-speed impact fracture is a dominant mode of failure in several applications of concrete structures. Numerical modelling can play a crucial role in understanding and predicting complex fracture processes. The commonly used mesh-based Finite Element Method has difficulties in accurately modelling the high deformation and disintegration associated with fracture, as this often distorts the mesh. Even with careful re-meshing FEM often fails to handle extreme deformations and results in poor accuracy. Moreover, simulating the mechanism of fragmentation requires detachment of elements along their boundaries, and this needs a fine mesh to allow the natural propagation of damage/cracks. Smoothed Particle Hydrodynamics (SPH) is an alternative particle based (mesh-less) Lagrangian method that is particularly suitable for analysing fracture because of its capability to model large deformation and to track free surfaces generated due to fracturing. Here we demonstrate the capabilities of SPH for predicting brittle fracture by studying a slender concrete structure (column) under the impact of a high-speed projectile. To explore the effect of the projectile material behaviour on the fracture process, the projectile is assumed to be either perfectly-elastic or elastoplastic in two separate cases. The transient stress field and the resulting evolution of damage under impact are investigated. The nature of the collision and the constitutive behaviour are found to considerably affect the fracture process for the structure including the crack propagation rates, and the size and motion of the fragments. The progress of fracture is tracked by measuring the average damage level of the structure and the extent of energy dissipation, which depend strongly on the type of collision. The effect of fracture property (failure strain) of the concrete due to its various compositions is found to have a profound effect on the damage and fragmentation pattern of the structure.

• Archives of design research
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• v.19 no.1 s.63
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• pp.191-200
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• 2006

A design representation is reflected in the typicality of branch representation as a syntagm in combination with design factors. And the design factors form up paradigm as an attributive category which is reflected object and value of branch representations, and they are consisted of selection and combination in representative process. Selection and combination of the design attributive category also reflect the representation consciousness of operating in representative process, and they imply a cognizance about object and value of the representation. Therefore, branch representation appears an attributive structure which is required of a given field by means of the representative object and value. This is made up of the divided differentiation according to a combined mode. This study is to investigate the fact verification between typicality of attributive structure and each divided differentiation to measure consideration degree of attributive category which is consisted in the design representation. The attributive structure of representation which is affected the industrial design, the visual communication design, and the environmental design fields identifies to take the typical differentiation by means of evaluations and results of this study.

• The Research Journal of the Costume Culture
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• v.7 no.6
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• pp.98-115
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• 1999

As sports infiltrates each field of modern society and becomes familiar, sports wear was changed functionally and was introduced and enveloped into everyday dress. Modern sports wear has been the settled in everyday life deeply and become the clothes of life which are worn regardless of place, time and age. The aim of this paper was to clarify what kind of fashion of sports style would be given to the modern people. In this study, sports wear which has become everyday dress classified from a gender point of view. It was divided into masculine image, feminine image, and neutral image. Sports wear of masculine image generated a silhouette which emphasized the shoulder with the aspiration for youth and health. Wide shoulder was considered as the symbol of masculine beauty and the expression of healthy beauty. It was reflected well in body conscious look. And owing to the development of up-to-data materials, innovation of design, and the study of human body technology, the functional character was settled in the sports wear which showed masculine image. Sports wear of feminine image was represented fashion of body exposure, body feet with body conscious look, and romantic mode. This image was expressed fashion as comforts, pleasant, active design, materials, color, and romantic feminine beauty. Sports wear of neutral image was expressed into unisex clothes. This cloths have no difference in gender, age, and class. It was used as casual sports wear. In the 1960s, young generation participated in such street sports as street basketball and skate. They usually sore the sports wears of neutral image such as cycling, skating, and ski. In the materials of sports, the development of up-to-data material like lycra made the sayings lifelike, “up-to-data material is the second skin” It show that glamorous feminine image and strong masculine image coexisted. The contemporary concept of sportswear is no longer limited to those clothes for sports found in such places like tennis court or swimming pool. Now, the sports wear become more like casual activity wear all classes of people can enjoy in their life regardless of where they are, when they wear, and even how old they are.

• Aerospace Engineering and Technology
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• v.6 no.1
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• pp.83-91
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• 2007

An experimental verification of multipactor(MP) discharge for S-band diplexer as a sample DUT for space application by an in-house MP test facility is proposed. The designed diplexer having two BPFs for Rx and Tx is applied to a design of five pole inter-digital cavity type band pass filter with chebyshev response, it has 2.7 % bandwidth centered at 2.232 and 2.055 GHz for Rx, Tx, respectively. To avoid the MP discharge, the accurate design and analysis methods based on 3D EM field analysis are considered. The proposed in-house MP test facility consists of a phase detecting system using a doubly balanced mixer as a simple, low cost and real time MP test method compared with results of previously well-known MP detection systems as cross reference methods. The calculated MP threshold RF input power is 43.13 dBm. The measured one is 43 dBm and 44 dBm for CW, pulsed mode test, respectively.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.16 no.2
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• pp.49-52
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• 2006

Periodic electric field assisted poling low loss (${\sim}0.1dB/cm$) single-mode Ti-diffused waveguides in $LiNbO_3$ has been achieved using a periodically patterned electrode on the +Z surface of Ti : $LiNbO_3$ crystal and homogeneous LiCl solution. Using selective chemical etching, we confirmed the periodic (${\sim}16{\mu}m$) domain inverted structure and measured SH (second harmonic) properties of fabricated periodically poled Ti : $LiNbO_3$ waveguides.

• Journal of the Korea institute for structural maintenance and inspection
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• v.8 no.2
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• pp.147-158
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• 2004

For stiffened plates composed of composite materials, many researchers have used a finite element method which connected isoparametric plate elements and beam elements. However, the finite element method is difficult to reflect local behavior of stiffener because beam elements are transferred stiffness for nodal point of plate elements, especially the application is limited in case of laminated composite structures. In this paper, for analysis of laminated composite stiffened plates, 3D shell elements for stiffener and plate are employed. Reissner-Mindlin's first order shear deformation theory is considered in this study. But when thickness will be thin, isoparamatric plate bending element based on the theory of Reissner-Mindlin is generated by transverse shear locking. To eliminate the shear locking and virtual zero energy mode, the substitute shear strain field is used. A deflection distribution is investigated for simple supported rectangular and skew stiffened laminated composite plates with arbitrary orientation stiffener as not only variation of slenderness and aspect ratio of the plate but also variation of skew angle of skew stiffened plates.

• Transactions of the Korean Society of Automotive Engineers
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• v.6 no.2
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• pp.12-20
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• 1998

Exter ballistics of a typical high-speed projectile is studied through a flow-visualization experiment and an unstructured grid Navier-Srokes computation. Experiment produced a schlieren photograph that adequately shows the characteristic features of this complex flow, namely two kinds of oblique cone shocks and turbulent wake developing into the downstream. A hybrid scheme of finite volume-element method is used to simulate the compressible Reynolds-Averaged Navier-Stok- es solution on unstructured grids. Osher's approximate Riemann solver is used to discretize the cinvection term. Higher-order spatial accuracy is obtained by MUSCL extension and van Albada ty- pe flux limiter is used to stabilize the numerical oscillation near the solution discontinuity. Accurate Gakerkin method is used to discretize the viscous term. Explict fourth-order Runge-Kutta method is used for the time-stepping, which simplifies the application of MUSCL extension. A two-layer k-$\varepsilon$ turbulence model is used to simulate the turbulent wakes accurately. Axisymmetric folw and two-dimensional flow with an angle of attack have been computed. Grid-dependency is also checked by carrying out the computation with doubled meshes. 2-D calculation shows that effect of angle of attack on the flow field is negligible. Axi-symmetric results of the computation agrees well with the flow visualization. Primary oblique shock is represented within 2-3 meshes in numerical results, and the varicose mode of the vortex shedding is clearly captured in the turbulent wake region.