A model net experiment of the gape net for anchovy in Jindo, Jeollanam-do was carried out to investigate the net shape and hydrodynamic resistance using circulating water channel. The model net was made 1/33 down scale by Tauti’s similarity method and the range of experimental current speed was from 0.5 knot to 3.5 knot (increasing 0.5 knot interval). The net mouth height in 0.5 knot of the minimum experiment current speed was shown 26.0 cm (full-scale conversion value 8.58 m). The net mouth height and mouth area in 1.5 knot of the same current speed with a gape net fishing ground were shown 20.0 cm (full-scale conversion value : 6.60 m) and about 507.9 cm2 (full-scale conversion value : 55.31 m2). The net mouth height and area were decreased with increase the experimental current speed. The hydrodynamic resistance of the model net in 1.5 knot current speed was shown 1.11 kgf and the value of full-scale conversion by Tauti’s method was shown 3.996 ton.

An experiment to acoustically analyze the shape of gill-net in the current was conducted in Jaran Bay, Gosung, Korea on the 9th to 10th September(spring tide) and 28th to 29th September(neap tide) 2006. It was measured by a 3D underwater positioning system with a radio-acoustic linked positioning buoys. Six of 7 acoustic transmitters used in the experiment were attached on the float line of the gill-net and the other was fixed on the sea bed. During spring tide, the maximum movement of the gill-net was 27.0m(22:00) in the west(4.4cm/s, 311.9˚) and 20.6m(04:00) in the east(3.9cm/s, 66.5˚). The maximum extension of the gill-net(the distance between P1 and P6) was 119.8m(21:00, 11.6cm/s, 321.9˚) and the minimum was 109.9m(23:00, 16.1cm/s, 88.5˚). During neap tide, the maximum movement was 38.0m(20:00) in the east(9.6cm/s, 278.2˚) and 11.0m(12:00) in the west(1.9cm/s, 232.1˚). The maximum extension was 99.6m(14:00, 12.5cm/s, 94.7˚) and the minimum was 85.0m(06:00, 9.0cm/s, 265.8˚). During spring tide, the maximum height of the gill-net from the sea bed was 3.7m(02:00, 7.4cm/s, 151.6˚) and the minimum was produced the three times as 1.5m. At that time, the current speed and direction was 17.9cm/s and 85.3˚(23:30), 16.1cm/s and 249.4˚(05:00), and 13.7cm/s and 291.4˚(06:30), respectively. During neap tide, the maximum height was 3.6m(12:30, 2.1cm/s, 242.3˚) and the minimum was 1.5m(14:00, 12.5cm/s, 94.7˚).

The pound net fishery is very important one in Korean coastal fishery and it need to grasp the characteristics of the net affected by many factors. It is considered that the structure and the shape of the pound net can be changed by the direction and speed of current, wave height, depth and conditions of sea bed. However, most of all, the speed of current and wave height influence more upon the pound net than any other factors to deform and flutter. In this study, author carried out the experiments with a model of double one-side pound net made by the similarity law as 1:100 scales at a real experimental area, and additionally the model net experiments were conducted in the circulating water channel in Pukyong National University. The author analyzed the data of transformation of shape and tension of the model pound net to recognize the characteristics of the current and wave acting on it. Regardless of the direction of flow affecting on the fish court net or bag net, the deformed angle and depth to the side panel and bottom of box nets becomes bigger as the wave gets higher and the period of wave is faster. The tension in both upward or downward tends to be changed by the speed of wave. Those value of changes occurred similarly in either fish court net or bag net. Generally, when bag net is located at upward of flow, the value of tension was bigger 10% than any other location or nets. Regardless of the setting direction, the tension of the pound net is increased in proportion to flow speed, wave height and period of wave, and it becomes bigger about 15-30% at upward to flow than downward. Where the flow is upward in the court net, the tension in the wave increased to 37% compared to the one in the flow only in the condition of flow of 0.1-0.3m/s. Where the flow is upward in the bag net, the tension in the wave increased to 52% in the flow of 0.1m/s, and the tension increased to 48% in the flow of 0.2-0.3m/s.

Several practical applications of melt-textured bulk superconductors require the complex-shaped products such as curved, ring-shaped, and drilled blocks rather than simple shaped pellets. However, melt-textured bulk superconductors are often damaged when they are cut, grinded, or drilled. With the aim of reducing such damages, we have investigated the preparation of the complex-shaped bulk superconductors by previously machining binder-added precursors and pre-sintered precursors. We could produce various complex-shaped bulk superconductors without cracking from these machined precursors

A model experiment using circulation water channel was carried out to investigate the dynamic characteristics of bottom trawl net which can be used in sea mount of North Pacific. Hydrodynamic resistance and shape variation according to the flow velocity and angle of hand rope transformation for net were measured, and experimental value was analyzed as the value of full-scale bottom trawl net. The results summarized are as follows; At the 30˚ of angle of hand rope to net, hydrodynamic resistance varied from 0.5kgf to 2.68kgf as the flow velocity increased between 0.31m/s and 0.92m/s, and formula of hydrodynamic resistance for the model net was Fm=3.04 · r1.53. At the fixed angle of hand rope, Net height was low and Net width was high according to the increase of flow velocity, and in addition, vertical opening was low and Net width was high by the increase of angle of hand rope at the fixed flow velocity. At the 30˚ of angle of hand rope to net, net opening area was 0.214m2 as flow velocity was 0.61m/s, and formula of net opening area for the model net was Sm=-0.22r+0.35. At the 30˚ of angle of hand rope to net, catch efficiency seemed to be highest as 0.319m3/s of filtering volume at the 0.76m/s(51kt's) of flow velocity. Shape variation of net showed the gradual laminar transform for the variation of flow velocity but there needed some improvements due to the occurrence of shortening at the ahead of wing net.

A novel production method for porous metal components has been developed by applying powder space holder (PSH) method to metal powder injection molding (MIM) process. The PSH-MIM method has an industrial competitive advantage that is capable of net-shape manufacturing the micro-sized porous metal products with complicated shapes and controlled porosity and pore size. In this study, the small impeller with homogeneous micro-porous structure was manufactured by the PSH-MIM method. The effects of combinations in size and fraction of PMMA particle on dimensional tolerance and variation of sintered porous specimens were investigated. It was concluded that the PSH-MIM method could manufacture commercially microporous metal components with high dimensional accuracy.

In this study, the 'force density method' for shape finding of cable net structures is presented. This concept is based on the force-length ratios or force densities which are defined for each branch of the net structures. This method renders a simple linear 'analytical form finding' possible. If the free choice of the force densities is restricted by further condition, the linear method is extended to a nonlinear one. The nonlinear one can be applied to the detailed computation of networks. In this paper, the general inverse matrix is introduced to solve the nonlinear equilibrium equation including Jacobian matrix which is rectangular matrix. Several examples for linear and nonlinear analysis applied additional constraints are presented. It is shown that the force density method is suitable for form finding of cable net and the general inverse matrix can be applied to solve the nonlinear equation without Lagrangian factors.

저층트롤 실물 어구를 이용한 해상 실험을 통하여 예망 중인 어구의 망구 형태에 관련되는 전개판의 간격 및 망고 등을 예망 속도별, 끌줄의 길이별로 측정하고, 이론적인 수치 해석 결과와 비교하여 실물어구의 수중 현황을 해석함으로서 어구의 효율적인 운용과 어획효과의 증대를 위한 기초자료를 제공하고자 한다. 수중 현황을 해석한 결과를 요약하면 다음과 같다. 1. 전개판의 전개간격은 예망 속도와 끌줄길이의 증가에 따라 직선적으로 증가하며 끌줄 길이에 의한 증가율이 예망 속도에 의한 증가율보다 현저히 크게 나타났으며, 그 간격의 변화는 57.0∼82.8m로서 후릿줄과 그물목줄 및 그물길이 전체의 43∼62%를 차지하였다. 2. 망구의 높이는 예망 속도와 끌줄길이의 증가에 따라 직선적으로 감소하며, 예망 속도에 의한 감소율이 끌줄 길이에 의한 감소율보다 현저히 크게 나타났는데 그 높이의 변화는 3.1∼4.0m로 나타났다. 3. 양 날개끝의 간격이 커지면 망고는 낮아지나 끌줄 길이가 증가할수록 날개 끝 간격의 증가에 대한 망구 높이 감소율의 비는 점차 작아졌다. 4. 망고에 대한 양 날개 끝 간격의 비는 예망속도와 끌줄 길이의 증가에 따라 점차 커졌는데, 그 비는 4.17∼7.81로 나타났다.

본 연구에서는 실물 어구를 이용한 해상실험을 통하여 예망 중인 어구의 망구 형상을 해석하기 위해서 예망 속도, 어구의 저항, 전개판의 간격, 망고 등을 계측ㆍ분석하였다. 또한 망구 형상을 이론적으로 계산하기 위해서 망구의 형상을 지배하는 뜸줄, 발줄 및 옆줄의 모양을 현수곡선으로 간주하고 수학모텔을 기술하여 수치해석 하였고, 이 결과를 실제 측정된 값과 비교하여 모텔의 타당성을 검토하였다. 본 실험에 대한결과를 요약하면 다음과 같다. 1. 선속의 변화에 따라 크게 변하는 요소로는 장력과 망고였고, 끌줄 길이의 변화에 민감하게 반응한 것은 어구 수심과 전개판의 간격이었다. 2. 계측된 트롤 어구의 상태량을 토대로 뜸줄 및 옆줄의 형상을 수치해석한 결과, 선속이 증가함에 따라 뜸줄 및 발줄의 폭과 옆줄의 높이는 감소하였고, 뜸풀 및 옆줄 중앙부의 처짐 정도는 증가하였다. 3. 예망속도에 따른 망고변화에 대하여 수치해석한 결과와 실제 실험에서 얻은 데이터를 비교한 결과, 비교적 양호한 결과를 얻을 수 있었다. 4. 수치해석한 결과로부터 망구의 형상을 추정한 결과, 선속이 증가함에 따라 횡축으로 긴 직사각형의 형상이 나타났으며, 횡축 및 종축 모두 크기가 감소하였다.

In order to investigate the performance for the mackerel purse seine of one boat purse seiner using in the sea area of Cheju Island, a model net is made of the scale of 1/400 of its full scale, and model test on the shape of net and the tension of purse line is carried out in the stagnant water channel of the circulating water tank. Designing and testing for the model net are based on the Tauti's law. The obtained results are as follows; 1. The sinking rate of net is maximized the value of 6.40 m/min from 5 to 10 minutes after shooting net, and the mean value is 6.13 m/min. 2. The enclosed area formed with the float line after pursing operation is 76-84% of the area which is formed immediately after the shooting operation. At that time, purse seine is pulled inward the circle of surrounding net about 26.5% of the diameter. 3. In operating, when longitudinal section area of the central part of the net is maximized, the split area of both the wing-ends is 31-32% of the former. 4. When the time for the completing of pursing is 20 minutes, the maximum tension of the purse line is about 10.2 tons.

As a primary step in studying the effects of the netting porosity on the net-shape in the four-seam trawling net, a series of experiments were performed changing the porosity of each panel, with the simplified mo:iel of the bag net made of porous vinyl film and that ma:ie of net webbing. These models were suspended horizontally in circularly flowing water, with two pairs of susp~nding threais to four points of symetry at the border of the bag mouth in place of both wing nets. And then, the section shape of the bag mouth photographed and the tensions on both pairs of suspending threads were measured with two load cells in circularly flowing water. From the results, the auther estimated an experimental equation from the relationship between the porosity of each panel in the bag net and the section shape of the bag mouth, h/w=k (l-Pr_u/lPr_s)<r, where h is the central height of the bag mouth, w is the lateral width of that, Pr-u and Pr-s indicate the porosity of the upper panel and that of the side panel individually.