• International Journal of Railway
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• 제3권3호
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• pp.83-89
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• 2010

This paper attempts to extract the fundamental dynamic properties, i.e. natural frequencies, damping ratios of the 48 m-long, $20^{\circ}$ skewed real bridge with PSC girders wrapped by a steel plate. The forced vibration test is achieved by mounting 12 Hz-capacity of artificial oscillator on the top of bridge deck. The acceleration histories at the 9 different locations of deck surface are recorded using accelerometors. From this full-scaled vibration test, the two possible resonance frequencies are detected at 2.38 Hz and 9.86 Hz of the skewed bridge deck by sweeping a beating frequency up to 12 Hz. The absolute acceleration/energy exhibits much higher in case of higher-order twist mode, 9.86 Hz due to the skewness of bridge deck which leads asymmetric situation of vibration. This implies the test bridge is under swinging vertically in fundamental flexure mode while the bridge is also flickered up and down laterally at 9.86 Hz. This is probably by asymmetric geometry of skewed deck. A detailed 3D beam-shell bridge models using finite elements are performed under a series of train loads for modal dynamic analyses. Thereby, the effect of skewness is examined to clarify the lateral flickering caused by asymmetrical geometry of bridge deck.

• 공업화학
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• 제34권6호
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• pp.633-639
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• 2023

We synthesized 2-(10-methyl-10H-phenothiazin-3-yl)-5-phenyl-1,3,4-oxadiazole (MPPO) and 5,5-(10-methyl-10H-phenothiazin-3,7-diyl)-bis-(2-phenyl-1,3,4-oxadiazole) (DPPO). MPPO has both electron-donating and electron-accepting substituents with asymmetric molecular geometry. By incorporating one extra electron-accepting group into MPPO, we created a symmetric molecule, which is DPPO. The optical and electrochemical properties of these compounds were measured. The lowest unoccupied molecular orbital (LUMO) level of DPPO was lower than that of MPPO. The excited-state dipole moment of DPPO, with symmetric geometry, was calculated to be 4.1 Debye, whereas MPPO, with asymmetric geometry, had a value of 7.0 Debye. The charge-carrier mobility of both compounds was similar. We fabricated non-doped organic light-emitting diodes (OLEDs) using D-A type molecules as an emitting layer. The current efficiency of the DPPO-based device was 7.8 cd/A, and the external quantum efficiency was 2.4% at 100 cd/m², demonstrating significantly improved performance compared to the MPPO-based device. The photophysical and electroluminescence (EL) characteristics of the two D-A type molecules showed that molecular symmetry, as well as the lowered LUMO level of DPPO, played critical roles in the enhancement of EL performance.

• 한국소음진동공학회논문집
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• 제27권2호
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• pp.234-242
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• 2017

단순지지-자유 경계조건과 좁은 슬롯을 포함한 짧은 후판 실린더의 음향방사 특성을 검토하였다. 유한요소 해석을 통해 얻어진 샘플 실린더(슬롯 포함)의 진동 모드를 동일한 치수의 슬롯이 없는 균일 실린더의 진동 모드들의 선형 합으로 근사화하였다. 이렇게 얻어진 근사적인 진동 모드를 기준으로 (1) 레일리 적분을 이용한 직접 계산, (2) 균일 실린더의 음향 모드들을 이용한 모드전개법 등 두 방법을 적용하여 샘플 실린더의 음향 모드들을 정의하였다. 이 결과를 이용하여 음향파워, 최대음압, 지향성 선도 등 부가적인 특성을 계산한 다음, 전체 결과를 경계요소법을 이용한 수치해석 결과와 비교하여 검증하였다. 이 결과를 바탕으로, 제시된 두 가지 방법을 이용하여 짧은 비대칭 후판 실린더의 음향방사 특성을 비교적 정확하게 예측할 수 있음을 알 수 있다. 이 방법들은 다른 형태의 비대칭성 및 경계조건을 가진 실린더에도 확대 적용 가능할 것으로 판단되며 이를 통해 실린더 형태의 실제 부품들에서 방사되는 소음을 저감방안 도출도 가능할 것으로 기대된다.

• International Journal of Fluid Machinery and Systems
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• 제2권1호
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• pp.72-79
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• 2009

The effect of symmetric and asymmetric micro regenerative pump impellers on their pressure performance was studied. The shut off head of the pump with the symmetric impeller was about 2.5 times as that with the asymmetric impeller. The computation of the internal flow was performed to clarify the cause of the increase of the head. It was found that the contribution of the angular momentum supply was larger than that of shear stress for the head development in both cases. The larger head and momentum supply in the case of the symmetric impeller were caused by larger recirculated flow rate and larger angular momentum difference between the inlet and outlet to the impeller. The larger recirculated flow rate was caused by smaller pressure gradient in the direction of recirculated flow. The decrease of the circumferential velocity in the casing was attributed to the smaller local flow rate in the casing.

• Structural Engineering and Mechanics
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• 제34권1호
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• pp.61-84
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• 2010

Presented in this paper is the behaviour of asymmetric building isolated by the double variable frequency pendulum isolator (DVFPI). The DVFPI is an adoption of single variable frequency pendulum isolator (VFPI). The geometry and coefficient of friction of top and bottom sliding surfaces can be unequal. The governing equations of motion of the building-isolation system are derived and solved in incremental form. The analysis duly considers the interaction of frictional forces in the two principal directions developed at each sliding surface of the DVFPI. In order to investigate the behaviour of the base isolation using the DVFPI, the coupled lateral-torsional response is obtained under different parametric variations for a set of six far-fault earthquake ground motions and criterion to optimize its performance is proposed. Further, influences of the initial time period, coefficient of friction and frequency variation factors at the two sliding surfaces are investigated. The numerical results of the extensive parametric study help in understanding the torsional behaviour of the structure isolated with the double sliding surfaces as in the DVFPI. It is found that the performance of the DVFPI can be optimized by designing the top sliding surface initially softer and smoother relative to the bottom one.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 1996년도 춘계 학술대회논문집
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• pp.68-73
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• 1996

The full incompressible Navier-Stokes equations are numerically integrated to solve the unsteady channel flow using a new numerical scheme of second-order accuracy developed by the authors. It is well known that in spite of the symmetry in the boundary condition and geometry, asymmetry can develop with time-dependency in a channel with sudden expansion. The instability of the shear flow and the cross-channel pressure contribute to such asymmetric flow. In this paper, we successfully generated a channel flow in which vortex waves were propagated downstream due to the harmonically oscillating inlet flow. The structure of the eddies and wall vorticity are parametrically investigated.

• Advances in Computational Design
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• 제4권4호
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• pp.397-413
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• 2019

In this paper, static nonlinear analysis of gable frame is performed using OpenSees software. Both geometric and material nonlinearities are considered in analyses. To consider large displacements, co-rotational coordinate transformation is used in software. The effects of symmetric and asymmetric support conditions including clamped and simple supports are studied. On the other hand, the material nonlinearity is reflected on analyses using Giuffre-Menegotto-Pinto steel material. Note that strain hardening characteristics are also considered in this model. Moreover, I-shaped cross-section is assumed for all members. The results are provided for different geometry properties of gable frame including shallow and deep inclined roof. It should be added that buckling and post-buckling behaviors of gable frame are investigated using related equilibrium paths. A comparison study is also implemented on the responses of buckling loads obtained for different support and geometry conditions. To trace snap-through paths completely, a displacement control method entitled arc-length is utilized. Findings show the capability of proposed model in nonlinear analysis of gable frames.

• 복식
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• 제60권5호
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• pp.117-127
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• 2010

In this study, hyperspace is a result of imagination created by means of facts and fiction, represents a transfer to determination and indetermination, and means an extension to an open form. In other words, hyperspace is a high dimensional space expanded to imagination through the combination of the viewpoint on facts in this dimension and fiction. When the 2D plane surface or 3D symmetry is destroyed, or when the frame is twisted or entangled, the non-Euclidean geometry is created eventually. And when the twisting leads to transmutation and the destruction of the form reaches the extreme; this in turn became the twisting like Mbius band. Likewise, the non-Euclidean geometry is co-related to the asymmetry of the Higgs mechanism. When the 'destruction of symmetry' is considered, symmetric theory and asymmetric world can be connected. The asymmetry in turn can maintain balance by arranging the uneven weights at different distances from the shaft. Moreover, at this the concept of the upper, lower, left and right, which was included in the original form, may be crumbled down. The destruction of the symmetry is essential in order to present forecast that coincides with the phenomenon of the real world. Non-Euclidean geometry characteristic is expressed by asymmetry, twists, and deconstruction and its representative characteristic is ambiguity. The boundary between the front, back, upper, lower, inner and outer is unclear, and it is difficult and vague to pinpoint specific location. The design that does not clearly define or determine the direction of wearing costume is indeed the non-oriented design that can be worn without getting restricted by specific direction such as front and back. Non-Euclidean geometry characteristic of hyperspace have been applied to create new shapes through the modification of the substance from traditional clothing of the eastern world to modern fashion. The way of thinking in the 'hyperspace' that used to be expressed in the costumes of the east and the west in the past became the forum for unlimited creation.

• 대한조선학회논문집
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• 제47권6호
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• pp.843-849
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• 2010

This paper presents definition of symmetry of a ship section where three symmetries are proposed: material, geometric, and load symmetries. Precise terminologies of centroid, moment plane, and neutral axis plane are also defined. It is suggested that force vector equilibrium as well as force equilibrium are necessary condition to determine new position of neutral axis due to translational and rotational mobility. It is also stated that new reference datum of ENMP(elastic neutral moment plane), PNMP(fully plastic moment plane), ENAP(elastic neutral axis plane), and INAP(inelastic neutral moment plane) are required to define asymmetric section properties such as second moment of area, elastic section modulus, yield moment, fully plastic moment, and ultimate moment. Since collision-induced damage and flooding-induced biaxial bending moment produce typical asymmetry of section, the section properties are calculated for a typical VLCC. Geometry asymmetry is determined from ABS and DNV rules and two moment planes of 0/30 degs are assumed for load asymmetry. It is proved that the property reduction ratios directly calculated from second moment of area are usually larger than area reduction ratio. Reduction ratio of ultimate moment capacity shows almost linearly proportional to area reduction ratio. Mobility of elastic and inelastic neutral axis planes is visually provided.

• Nuclear Engineering and Technology
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• 제52권11호
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• pp.2601-2606
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• 2020

In this study, we expanded the performance of the existing EXVol code and performed empirical experiments and calculations. A high-resolution gamma spectroscopy system was constructed, and a standard point source and a standard volume source were measured with an HPGe detector with 43.1% relative efficiency. EXVol was verified by quantitative comparison of the detection efficiencies determined by measurements and calculations. To introduce the concept of the detector scanning that occurs in the actual measurement into the EXVol code, a collimator was placed between the source and detector. The detection efficiency was determined in the asymmetric arrangement of the source and detector with a collimator. A collimator made of lead with a diameter of 15 mm and a thickness of 50 mm was installed between the source and the detector to determine the detection efficiency at a specific location. The calculation result was contour plotted so that the distribution of detection efficiency could be visually confirmed. The relative deviation between the measurements and calculations for the coaxial and asymmetric structures was 10%, and that for the collimation structure was 20%. The results of this study can be applied to research using γ-ray measurements.