• 수산해양기술연구
• /
• 제54권1호
• /
• pp.25-31
• /
• 2018

In this study, the differences of holding power according to the shape and weight distribution of concrete weight used in shellfish shell fishery were investigated through the experiments. To investigate the differences in shape, five bar-shaped concrete weights with the same length and different cross-sectional shapes were produced. The sectional shape of each weight was square, triangle, circle, small cross, and large cross (SQ, TR, CI, CR-S, CR-L). Ten rectangular parallelepiped weights with different bottom area and cross-sectional area were produced. To investigate the differences by the weight distribution, the holding power on the square model (SQ) with six 50 g weights at different positions was investigated. All the holding power was obtained by measuring the tensile force generated when the concrete weight was pulled at a constant speed on the sand. As a result, there were no differences in holding power between the ten rectangular weights. However, the experiment on weights with different cross-sectional shapes showed differences in holding power. The holding power was higher in the order of CR-L > CR-S > CI > TR > SQ. In the weight distribution test, the holding power was higher as the front side of the weight was heavier. Generally, the frictional force is the same even if the shape is different, when two objects have the same value in the weight and the roughness. On the other hand, it seems to have a large impact when the shape of the bottom is deformed in the course of pulling the object. Particularly, the larger the degree of protrusion like cruciform weights, the more the holding power increased while deeply digging the bottom. It is also likely that the holding power increases as the front weight increases.

• 동력기계공학회지
• /
• 제10권2호
• /
• pp.22-28
• /
• 2006

Computer simulation of the air flow over an automotive vehicle is now becoming a routine process in automotive industry to assess the aerodynamic characteristics of a medium-size vehicle such as $C_d\;and\;C_1$ and aslo to investigate the possibility of improving aerodynamic performance of the vehicle as a preliminary design for the production line. Mainly due to its contribution in saving time and cost in the development of new cars, computer simulation of the air flow over a vehicle is usually done well before a production car is introduced to the market and in gaining more and more attention as powerful computer resources are getting readily available nowadays. To aerodynamically design a car is mainly related with reducing a drag coefficient of car. A well designed car usually has a $C_d$ value in the range of $0.3{\sim}0.4$. It is understandable that automotive industry is rushing to reduce a drag coefficient as reducing even a small fraction of the $C_d$ value can have an enormous overall impact on many areas. Actually, the present research model was able to achieve a $C_d$ value in the range of $0.3{\sim}0.36$ for flow velocities of $60km/h{\sim}100km/h$ by strategically removing the possible factor hazardous to lower $C_d$ value. Prediction of the medium-size vehicle aerodynamics using CFD was performed when an actual car model was in the development stage and three-dimensional modeling was also performed to optimize it as the best model in terms of the best aerodynamic performance.

• 한국정보통신학회논문지
• /
• 제18권2호
• /
• pp.303-310
• /
• 2014

n개의 무선 노드가 랜덤하게 위치한 초 광 대역 애드 혹 네트워크에서의 개선된 용량 스케일링 법칙을 보인다. 먼저, 수정된 계층적 협력 기술이 사용되는 경우를 고려한다. 단위 면적의 밀집 네트워크에서, 유도한 용량 스케일링은 전력 제한된 성격 때문에 특정 동작 영역에서 경로손실 지수 ${\alpha}$에 의존함을 보인다. 또한, 계층적 협력 기술은 2 < ${\alpha}$ < 3에서 우월하지만 ${\alpha}{\geq}3$에 대해서는 다중 홉 라우팅을 사용하는 것이 더 높은 용량을 취득함이 밝혀진다. 둘째로, m개의 기지국이 초 광 대역 네트워크에 균일하게 분포한 경우, 인프라 구조의 영향 및 이득을 분석한다. 이때, 모든 동작 영역에 대해 전력 제한된 성격 때문에, 유도한 용량 스케일링은 ${\alpha}$에 의존한다. 게다가, 변수 m이 특정 레벨 이상일 때 전체 용량이 m과 함께 선형적으로 스케일함을 보인다. 그러므로 계층적 협력 또는 인프라 구조의 사용은 특정 조건에서 초 광 대역 네트워크의 용량을 개선하는데 도움이 된다.

• 한국기계가공학회지
• /
• 제20권8호
• /
• pp.42-51
• /
• 2021

Investigations of process parameters are essential when fabricating high-quality parts using additive manufacturing. This study investigates the change in the mechanical characteristics of a SUS316L specimen fabricated using selective laser melting based on the energy density and bead overlap ratio. The SUS316L powder particles were spherical and 35 ㎛ in size. Single-bead and hexahedral shape deposition experiments were performed sequentially. A single bead experiment was performed to obtain the bead overlap ratios for different laser parameters utilizing laser power and scan speed as experimental parameters. A hexahedral shape deposition experiment was also performed to observe the difference in mechanical properties, such as the internal porosity, surface roughness, and hardness, based on the energy density and bead overlap ratio of the three-dimensional printed part. Laser power, scan speed, overlap ratio, and layer thickness were chosen as parameters for the hexahedral shape deposition experiment. Accordingly, the energy density applied for three-dimensional printing, and the experimental parameters were calculated, and the energy density and bead overlap ratio for fabricating parts with good properties have been suggested.

• Geomechanics and Engineering
• /
• 제30권5호
• /
• pp.401-411
• /
• 2022

To obtain the dynamic mechanical properties, fracture modes, energy and brittleness characteristics of Furong Baijiao coal rock, the dynamic impact compression tests under 0, 4, 8 and 12 MPa confining pressure were carried out using the split Hopkinson pressure bar. The results show that failure mode of coal rock in uniaxial state is axial splitting failure, while it is mainly compression-shear failure with tensile failure in triaxial state. With strain rate and confining pressure increasing, compressive strength and peak strain increase, average fragmentation increases and fractal dimension decreases. Based on energy dissipation theory, the dissipated energy density of coal rock increases gradually with growing confining pressure, but it has little correlation with strain rate. Considering progressive destruction process of coal rock, damage variable was defined as the ratio of dissipated energy density to total absorbed energy density. The maximum damage rate was obtained by deriving damage variable to reflect its maximum failure severity, then a brittleness index BD was established based on the maximum damage rate. BD value declined gradually as confining pressure and strain rate increase, indicating the decrease of brittleness and destruction degree. When confining pressure rises to 12 MPa, brittleness index and average fragmentation gradually stabilize, which shows confining pressure growing cannot cause continuous damage. Finally, integrating dynamic deformation and destruction process of coal rock and according to its final failure characteristics under different confining pressures, BD value is used to classify the brittleness into four grades.

• 한국산업보건학회지
• /
• 제16권4호
• /
• pp.334-345
• /
• 2006

The objectives of this study were to analyze and compare 24 hrs personal exposure levels of MF at microenvironments such as home, school, educational institute, internet pc game room, transportation, and other places according to time activity patterns using various metrics for children attending the primary schools located near and away from the power lines, and to characterize the major microenvironments and impact factors attributed personal exposure level. The study was carried out for 44 children attending a primary school away from the lines(school A) and 125 children attending a school away from 154 kV power lines(school B), all who aged 12 years and were 6 grade, from July 2003 to December 2003. All participants filled in a questionnaire about characteristics, residence, use of electrical appliances and others. Children wore a small satchel in which EMDEX II and Lite (Enertech, Co. Ltd) and a diary of activity list for period of registration in 20 minutes blocks. All statistical calculations were made with the SAS System, Releas 6.12. The summary of results was presented below. First, about the characteristics of subjects, there no differences between two groups. The subject almost spent about 56 % of their time at home and about 20~25 % of their time at school. Fifty percent of children spent 2 hours at private educational institutes. Second, the personal exposure measurements of children in school B was statistically higher than those of children in school A by various metrics such as arithmetic mean, geometric mean, percentile(5, 25, 50, 75, 95), maximum, rate of change metric, constant field metric. The arithmetic and geometric mean magnetic fields during the time the children were at school B were 0.98 and $0.86{\mu}T$ and were about 23 times higher than those of children were at school A. In conclusion, the significant major determinants of personal exposure level is the distance from the power line to microenvironments.

• 한국수소및신에너지학회논문집
• /
• 제31권1호
• /
• pp.132-137
• /
• 2020

Lithium secondary batteries have become an important power source for portable electronic devices such as cellular phones, laptop computers. Presently, commercialized lithium-ion batteries use a LiCoO₂ cathode. However, due to the high cost and environmental problems resulting from cobalt, an intensive search for new electrode materials is being actively conducted. Recently, solid solution LiMn_1-xNi_xO₂ have become attractive because of high capacity and enhanced safety at high voltages over 4.5 V. The Li_1.6Ni_0.35Mn_0.65O₂ compounds were conventionally prepared by a sol-gel method, which can produce the layered Li-Ni-Mn-O compounds with a high homogeneity. And by adding a graphene 2wt% the first charge-discharge voltage profiles was increased over Li_1.6Ni_0.35Mn_0.65O₂ compound. Also, the variation s of the discharge capacities with cycling showed a higher capacity retention rater. In this study, material lifecycle evaluation was performed to analyze the environmental impact characteristics of Li_1.6Ni_0.35Mn_0.65O₂ & graphene 2wt% half-cell manufacturing process. The software of material life cycle assessment was Gabi. Through this, environmental impact assessment was performed for each process. The environmental loads induced by Li_1.6Ni_0.35Mn_0.65O₂ & graphene 2wt% synthesis process were quantified and analyzed, and the results showed that the amount of power had the greatest impact on the environment.

• 환경영향평가
• /
• 제31권1호
• /
• pp.47-62
• /
• 2022

풍력발전은 비용 효율적인 신재생에너지원으로 우리나라 뿐 아니라 전세계적으로 빠르게 보급이 확대되고 있다. 환경적 지속가능성을 보장하면서 지속가능한 에너지를 공급하기 위해서는 증거에 기반한 정책수립과 혁신적인 방안 마련이 필요하다. 본 논문은 풍력발전 환경영향평가서 58건의 분석을 통해 1) 국내 육상풍력의 주요 특징이 어떠한가? 2) 환경영향을 최소화하기 위한 사업별 환경적 지속가능성을 분석하는 방법이 있는가?에 대한 해답을 제시하고자 한다. 환경영향평가서에 제시된 개별 육상풍력사업의 환경적 지속가능성과 관련한 변수를 추출하여 이러한 환경변수에 대한 요인분석을 수행하고 개별 변수의 가중치를 계산하여 육상풍력발전의 환경적 지속가능성을 평가할 수 있는 지수를 개발하였다. 이러한 환경적 지속가능성지수는 육상풍력발전의 입지를 고려할 때 활용할 수 있는 유용한 증거에 기반한 의사결정도구로 활용될 수 있을 것이다. 58개 사업은 사업지역의 고도 및 자연성의 정도를 바탕으로 1) 산악형, 2) 목장형, 3) 해안형으로 구분하였다. 본 연구에서는 개별 풍력발전사업에 대한 환경적 지속가능성지수를 성공적으로 계산하였다. 가장 환경적 지속가능성이 큰 사업은 목장형으로 분류된 33번 사업이 1.04였고, 가장 낮은 사업은 산악형으로 분류된 55번 사업으로 -1.44였다. 둘째, 분석결과는 목장형이 환경지속가능성 지수가 평균 0.4551로 환경적 지속가능성이 가장 높고, 해안형이 평균 0.3712으로 중간이었으며, 산악형이 평균 -0.3457로 가장 낮은 것으로 나타났다. 이러한 결과는 육상풍력발전과 관련된 기존의 연구에서 제시된 결과를 보다 계량적으로 증명하고 있으며, 신재생에너지개발과 관련한 정책에 활용할 수 있는 중요한 함의를 제공하고 있다.

• 한국항공운항학회지
• /
• 제25권4호
• /
• pp.1-23
• /
• 2017

Organizational culture among flight crews has a profound impact on the individual attitude and behavior of member flight crews, and active training is conducted focusing on improving flight crews' Crew Resource Management(CRM) performance. However, adequate research and training on the relationships between flight crew's individual culture and CRM performance have not been conducted. Hence, this study examined the effect of individual cultural values on CRM performance and the moderation effect of psychological safety, with captains and first officers working for commercial airlines as participants. For the factors related to individual cultural value scale, power distance had no significant effect on CRM performance, uncertainty avoidance had a significant negative effect, and individualism had a significant positive effect. With regard to the moderation effect of psychological safety on the relationships between individual cultural values and CRM performance, a significant interaction was found between power distance and CRM performance, but not between uncertainty avoidance and CRM performance, or between individualism and CRM performance. Power distance and CRM performance exhibited a strong negative correlation in case of low psychological safety. Compared to existing research measuring the cultural characteristics of pilot groups on a national or organizational culture level, this study is uniquely valuable in that it also covers the relationship between individual cultural values of commercial airline flight crews and CRM performance.

• 한국의류산업학회지
• /
• 제15권6호
• /
• pp.971-976
• /
• 2013

This study provides insight into current social media influences and purchasing power of the young generation in that the size of both of these demographic groups will impact the apparel companies and retail market for the predictable future Denim apparel companies are aware of the discretionary spending power of the Y and Z Generations. The characteristics of current teens are so similar to college-age individuals in that they have grown up with digital technology and they prefer to communicate via social networking sites. Retailers have utilized these social media platforms in order to capture the attention of the generations. Traditionally marketing campaigns have differentiated between teens and the college-age population. However, the teens actually have larger spending power and more discretionary income. A survey consisted of 32 questions pertaining to Internet media influences, influence of people, and decision factors on decisionmaking related to purchasing selection. A random sampling of 163 females responded to a set of questionnaires. Teens, like college students desire to make their own decisions when they select and purchase denim jeans. Overall 40% of them wanted to make their own decisions when purchasing their jeans, however, a significant number are influenced by their friend's opinions (34%) and the opinions of family members (15%). However, celebrities (10%) had the least influence on their decisions. Teens, like colleges students make decisions based on the same decision factors: fit (63%), cost (23%), brand (10%) and color (2%). The most important factor in determining preference was "fit".