• ALGAE
• /
• 제34권2호
• /
• pp.153-162
• /
• 2019

Anthropogenic disturbances, including coastal habitat modification and climate change are threatening the stability of kelp beds, one of the most diverse and productive marine ecosystems. To test the effect of temperature and irradiance on the microscopic gametophyte and juvenile sporophyte stages of the rare kelp, Saccharina angustissima, from Casco Bay, Maine, USA, we carried out two sets of experiments using a temperature gradient table. The first set of experiments combined temperatures between $7-18^{\circ}C$ with irradiance at 20, 40, and $80{\mu}mol\;photons\;m^{-2}\;s^{-1}$. The second set combined temperatures of $3-13^{\circ}C$ with irradiance of 10, 100, and $200{\mu}mol\;photons\;m^{-2}\;s^{-1}$. Over two separate 4-week trials, in 2014 and again in 2015, we monitored gametogenesis, the early growth stages of the gametophytes, and early sporophyte development of this kelp. Gametophytes grew best at temperatures of $8-13^{\circ}C$ at the lowest irradiance of $10-{\mu}mol\;photons\;m^{-2}\;s^{-1}$. Light had a significant effect on both male and female gametophyte growth only at the higher temperatures. Temperatures of $8-15^{\circ}C$ and irradiance levels of $10-100{\mu}mol\;photons\;m^{-2}\;s^{-1}$ were conditions for the highest sporophyte growth. Sporophyte and male gametophyte growth was reduced at both temperature extremes-the hottest and coldest temperatures tested. S. angustissima is a unique kelp species known only from a very narrow geographic region along the coast of Maine, USA. The coupling of global warming with high light intensity effects might pose stress on the early life-history stages of this kelp, although, as an intertidal species, it could also be better adapted to temperature and light extremes than its subtidal counterpart, Saccharina latissima.

• 한국컴퓨터그래픽스학회논문지
• /
• 제26권5호
• /
• pp.1-13
• /
• 2020

본 논문에서는 흐르는 물에 의해 빙결 시뮬레이션 되어 방향성이 있는 얼음 형태를 안정적으로 모델링 할 수 있는 새로운 방법을 제시한다. 제안하는 얼음 모델링 프레임워크는 빙결 시뮬레이션에서 중요한 얼음의 성장 방향에 점성이 있는 유체의 흐름을 고려한다. 물 시뮬레이션 해법은 암시적 비압축성 유체 시뮬레이션에 새로운 점성 기법을 적용한 방법을 이용하고, 얼음의 방향과 글레이즈(Glaze) 효과는 제안하는 비등방성한 빙결 해법을 이용한다. 물 입자가 얼음 입자로 상태변화하는 조건은 습도와 물의 흐름에 따른 새로운 에너지 함수에 따라 계산된다. 습도는 오브젝트 표면의 가상 수막(Virtual water film)으로 근사되며, 유체의 흐름은 얼음의 성장 방향을 가이드하기 위해 우리의 비등방성한 빙결 해법에 통합된다. 결과적으로 점성이 있는 물의 흐름 방향에 따라 글레이즈와 방향성 있는 빙결 시뮬레이션 결과를 안정적으로 보여준다.

• Coupled systems mechanics
• /
• 제11권4호
• /
• pp.315-333
• /
• 2022

Fluid-Structure Interaction (FSI) modeling is highly effective to reveal deformations, fatigue failures, and stresses on a solid domain caused by the fluid flow. Mechanical properties of the solid structures and the thermophysical properties of fluids can change under different operating conditions. In this study, we investigated the interaction of [45/-45]₂ wounded composite tubes with the fluid flows suddenly pressurized to 5 Bar, 10 Bar, and 15 Bar at the ambient temperatures of 24℃, 66℃, and 82℃, respectively. Numerical analyzes were performed under each temperature and pressure condition and the results were compared depending on the time in a period and along the length of the tube. The main purpose of this study is to present the effects of the variations in fluid characteristics by temperature and pressure on the structural response. The variation of the thermophysical properties of the fluid directly affects the deformation and stress in the material due to the Wall Shear Stress (WSS) generated by the fluid flow. The increase or decrease in WSS directly affected the deformations. Results show that the increase in deformation is more than 50% between 5 Bar and 10 Bar for the same operating condition and it is more than 100% between 5 Bar and 15 Bar by the increase in pressure, as expected in terms of the solid mechanics. In the case of the increase in the temperature of fluid and ambient, the WSS and Von Mises stress decrease while the slight increases of deformations take place on the tube. On the other hand, two-way FSI modeling is needed to observe the effects of hydraulic shock and developing flow on the structural response of composite tubes.

• Wind and Structures
• /
• 제34권2호
• /
• pp.185-197
• /
• 2022

This study aimed to analyze the wind-induced mechanical energy (WME) of a proposed super high-rise and long-span transmission tower-line system (SHLTTS), which, in 2021, is the tallest tower-line system with the longest span. Anew index - the WME, accounting for the wind-induced vibration behavior of the whole system rather than the local part, was first proposed. The occurrence of the maximum WME for a transmission tower, with or without conductors, under synoptic winds, was analyzed, and the corresponding formulae were derived based on stochastic vibration theory. Some calculation data, such as the drag coefficient, dynamic parameters, windshielding areas, mass, calculation point coordinates, mode shape and influence function, derived from wind tunnel testing on reducedscale models and finite element software were used in calculating the maximum WME of the transmission tower under three cases. Then, the influence of conductors, wind speed, gradient wind height and wind yaw angle on WME components and the energy transfer relationship between substructures (transmission tower and conductor) were analyzed. The study showed that the presence of conductors increases the WME of transmission towers and changes the proportion of the mean component (MC), background component (BC) and resonant component (RC) for WME; The RC of WME is more susceptible to the wind speed change. Affected by the gradient wind height, the WME components decrease. With the RC decreasing the fastest and the MC decreasing the slowest; The WME reaches the its maximum value at the wind yaw angle of 30°. Due to the influence of three factors, namely: the long span of the conductors, the gradient wind height and the complex geometrical profile, it is important that the tower-line coupling effect, the potential for fatigue damage and the most unfavorable wind yaw angle should be given particular attention in the wind-resistant design of SHLTTSs

• Wind and Structures
• /
• 제38권1호
• /
• pp.43-58
• /
• 2024

To ensure the flutter stability of three-tower suspension bridges under skew wind, by using the computational procedure of 3D refined flutter analysis of long-span bridges under skew wind, in which structural nonlinearity, the static wind action(also known as the aerostatic effect) and the full-mode coupling effect etc., are fully considered, the flutter stability of a three-tower suspension bridge-the Taizhou Bridge over the Yangtze River in completion and during the deck erection is numerically investigated under the constant uniform skew wind, and the influences of skew wind and aerostatic effects on the flutter stability of the bridge under the service and construction conditions are assessed. The results show that the flutter critical wind speeds of three-tower suspension bridge under service and construction conditions fluctuate with the increase of wind yaw angle instead of a monotonous cosine rule as the decomposition method proposed, and reach the minimum mostly in the case of skew wind. Both the skew wind and aerostatic effects significantly reduce the flutter stability of three-tower suspension bridge under the service and construction conditions, and the combined skew wind and aerostatic effects further deteriorate the flutter stability. Both the skew wind and aerostatic effects do not change the evolution of flutter stability of the bridge during the deck erection, and compared to the service condition, they lead to a greater decrease of flutter critical wind speed of the bridge during deck erection, and the influence of the combined skew wind and aerostatic effects is more prominent. Therefore, the skew wind and aerostatic effects must be considered accurately in the flutter analysis of three-tower suspension bridges.

• Geomechanics and Engineering
• /
• 제38권2호
• /
• pp.125-137
• /
• 2024

In paste backfill mining, cemented coal gangue-fly ash backfill (CGFB) can effectively utilize coal-based solid waste, such as gangue, to control surface subsidence. However, given the pressurized water accumulation environment in goafs, CGFB is subject to coupling effects from water pressure and chloride ions. Therefore, studying the influence of pressurized water on the chlorine salt erosion of CGFB to ensure green mining safety is important. In this study, CGFB samples were soaked in a chloride salt solution at different pressures (0, 0.5, 1.5, and 3.0 MPa) to investigate the chloride ion transport characteristics, hydration products, micromorphology, pore characteristics, and mechanical properties of CGFB. Water pressure was found to promote chloride ion transfer to the CGFB interior and the material hydration reaction; enhance the internal CGFB pore structure, penetration depth, and chloride ion content; and fill the pores between the material to reduce its porosity. Furthermore, the CGFB peak uniaxial compression strain gradually decreased with increasing soaking pressure, whereas the uniaxial compressive strength first increased and then decreased. The resulting effects on the stability of the CGFB solid-phase hydration products can change the overall CGFB mechanical properties. These findings are significant for further improving the adaptability of CGFB for coal mine engineering.

• 터널과지하공간
• /
• 제26권2호
• /
• pp.59-67
• /
• 2016

본 논문에서는 해저 하이드레이트 퇴적층에서의 메탄가스 생산 과정에서 발생 가능한 생산정 주변 단층의 재활성화 가능성을 수치해석을 통해 평가하고 재활성화에 따른 미소지진 규모를 예측한 결과를 소개하였다. 가스 생산에 의한 하이드레이트 퇴적층의 유효응력 변화 및 역학적 변형은 TOUGH+Hydrate 코드와 FLAC3D 코드를 순차적으로 연계해석함으로써 시뮬레이션하였다. 단층면 재활성화 기준은 모어쿨롱(Mohr-Coulomb)법칙이 유효한 것으로 가정하였다. 30일간의 시험생산 해석 결과, 감압에 의한 공극압력 감소 및 유효응력의 증가가 주변 단층의 활성화를 일으킬 가능성은 크지 않은 것으로 나타났다. 초기응력 조건에 따른 활성화 가능성을 활동마찰각으로 평가한 결과로부터 수평응력에 비해 수직응력이 상대적으로 큰 정단층 응력조건(normal fault stress regime)에서 단층 재활성화 가능성이 상대적으로 큰 것으로 파악되었다. 또한, 정단층 응력조건에서 단층 재활성화에 기인한 유도지진 발생규모를 모멘트 크기(moment magnitude)로 추정할 경우, 모두 음(-)의 값을 보여 인간이 감지하지 어려운 수준의 미소지진에 해당하는 결과를 보였다. 다만, 본 해석은 하이드레이트 생산과정에서의 단층재활성화 가능성 평가를 목적으로 한 해석기법 구축 및 그 적용성을 소개할 목적으로 상당히 단순화된 지질구조 모델을 가정한 결과이므로, 향후 하이드레이트 시험 생산 및 상업 생산 지역에서의 상세 지질구조, 입력 물성 및 생산 설계조건을 반영한 해석에서는 상이한 결과를 보일 수 있을 것이다.

• 한국전자파학회논문지
• /
• 제16권11호
• /
• pp.1059-1066
• /
• 2005

본 논문은 피드포워드 전력 증폭기의 효율 개선을 위한 도허티 증폭기의 적용에 관한 연구이다. 성능 분석을 위하여 중심 주파수 2.14 GHz의 WCDMA 4FA신호를 인가하여 평균 출력 전력 15 W에서 측정하였다. 적용한 도허티 증폭기는 동급 class AB 증폭기와 비교하여 고효율 저선형성의 특성을 나타내며 효율 개선을 위하여 피드포워드 전력 증폭기(FPA)의 주 증폭기로 사용되었다. 특성 변화를 분석하기 위해 선형성과 효율 특성이 다른 2가지 종류의 도허티 증폭기를 적용하였으며 각각의 FPA들은 평균 출력 15 W에서 효율은 $2\%$ 이상의 개선을 보였지만 선형성은 1.5 dBc 이상 저하되는 특성을 나타냈다. 저하된 선형성을 개선하기 위하여 부가적으로 오차 루프의 결합 계수(CF)와 오차 증폭기의 용량을 변화시켰다. CF와 오차 증폭기의 용량 변화로 효율 개선과 높은 선형성을 얻을 수 있었고 도허티 증폭기가 35 dBc 이상의 선형성을 유지하면 부가적인 변화 없이 평균 출력 전력 15 W에서 $2\%$ 이상의 효율 개선과 충분한 선형성을 얻을 수 있다.

• 한국작물학회:학술대회논문집
• /
• 한국작물학회 2017년도 9th Asian Crop Science Association conference
• /
• pp.308-308
• /
• 2017

The low and unstable yield of soybean has been a major problem in Japan. Excess soil moisture conditions are one of the major factors to restrict soybean productivity. More than 80 % of soybean crops are cultivated in converted paddy fields which often have poor drainage. In central and eastern regions of Japan, the early vegetative growth of soybean tends to be restricted by the flooding damage because the early growth period is overlapped with the rainy season. Field observation shows that induced excess water stress in early vegetative stage reduces dry matter production by decreasing intercepted radiation by leaf and radiation use efficiency (RUE) (Bajgain et al., 2015). Therefore, it is necessary to evaluate the responses of soybean growth for excess water conditions to assess these effects on soybean productions. In this study, we aim to modify the soybean crop model (Sinclair et al., 2003) by adding the components of the restriction of leaf area development and RUE for adaptable to excess water conditions. This model was consist of five components, phenological model, leaf area development model, dry matter production model, plant nitrogen model and soil water balance model. The model structures and parameters were estimated from the data obtained from the field experiment in Tsukuba. The excess water effects on the leaf area development were modeled with consideration of decrease of blanch emergence and individual leaf expansion as a function of temperature and ground water level from pot experiments. The nitrogen fixation and nitrogen absorption from soil were assumed to be inhibited by excess water stress and the RUE was assumed to be decreasing according to the decline of leaf nitrogen concentration. The results of the modified model were better agreement with the field observations of the induced excess water stress in paddy field. By coupling the crop model and the ground water level model, it may be possible to assess the impact of excess water conditions for soybean production quantitatively.

• 한국진공학회:학술대회논문집
• /
• 한국진공학회 2013년도 제45회 하계 정기학술대회 초록집
• /
• pp.298-298
• /
• 2013

Finding renewable and clean energy resources is essential research to solve global warming and depletion of fossil fuels in modern society. Recently, complex harvesting of energy from multiple sources is available in our living environments using a single device has become highly desirable, representing a new trend in energy technologies. We report that when simultaneously driving the fusion and composite cells of two or more types, it is possible to make an affect the other cells to obtain a greater synergistic effect. To understand the coupling effect of photovoltaic and piezoelectric device, we fabricate the serially integrated hybrid cell (s-HC) based on organic solar cell (OSC) and piezoelectric nanogenerator (PNG). The size of increased voltage peaks when OSC and PNG are working on is larger than the case when only PNG is working. This voltage difference is the Voc change of OSC, not the voltage change of PNG and current density difference between these two cases is manifested more clearly. When the OSC and PNG are working in s-HC at the same time, piezoelectric potential (VPNG) is generated in ZnO and theoretical total voltage is sum of voltage of an OSC (VOSC) and VPNG. However, electrons from OSC are influenced by piezoelectric potential in ZnO and current loss of OSC in whole circuit decreases. As a result, VOSC increases temporarily. Current shows the similar behavior. PNG acts a resistance in the whole circuit and current loss occurs when the electrons from OSC pass through the PNG. But piezoelectric potential recover current loss and decrease the resistance of PNG. Our PNG can maintain piezoelectric potential when the strain is held owing to the LDH layer while general PNG cannot maintain piezoelectric potential. During the section that strain is held, voltage enhancement effect is maintained and same effect appeared even turn off the light. Actually at this time, electrons in ZnO nanosheets move to LDH and trapped by the positive charges in this layer. After this strain is held, piezoelectric potential of ZnO nanosheets is disappeared but potential difference which is developed by negative charge dominant LDH layer is remained. This potential acts similar role like piezoelectric potential in ZnO. Electrons from the OSC also are influenced by this potential and the more current flows.