• Special Issue of the Society of Naval Architects of Korea
• /
• 2007.09a
• /
• pp.107-117
• /
• 2007

A surface piercing propeller (SPP) in tunnel has been proposed recently as a new propulsion system for a high speed air cavity ship. The purpose of the present study is to investigate the characteristics of the SPP in tunnel through a series of model tests. A model propulsion system is placed on a dummy body made of Acrylics. The tunnel is divided into two regions by a guide vane extending from the inlet to the center of the propeller shaft. Air has been supplied from an air nozzle placed at the bottom of the dummy body and the changes in propeller performances caused by the air flow are investigated. The measurements are done for open water and in-tunnel conditions, both for fully and partially submerged propeller. The influence of the guide vane configurations on the propeller performance is also studied. The experiments are performed at the variable pressure circulation water channel of Inha University.

• Journal of Ocean Engineering and Technology
• /
• v.20 no.2 s.69
• /
• pp.46-51
• /
• 2006

Moonpool characteristics of a cleaning skip related with the performance of a skip are experimentally investigated. Resistance performances of the ship and flow patterns in the moonpool are observed, in order to determine the effect of different shaped moonpool. The ways to reduce ship pithing motion caused by force in the moonpool are examined. Experimental results, using a scale model of cleaning ship with moonpool, show that the step arranged in tier under water leads to significant improvements in performance, such us resistance and ship pithing motion. Depending upon the shape of step in the moonpool, the results indicate that the increment of resistance performance may be up to 35%, especially in the case of no step or high step.

• Korean Journal of Fisheries and Aquatic Sciences
• /
• v.12 no.4
• /
• pp.201-207
• /
• 1979

The stow net now used in the Yellow Sea, are traditional bag net with the opening held by a lighter upper and a weighted lower beams standing against the current. Such bag net anchored at the bottom are known in many countries, particularly in the estuaries of large rivers, but more rarely in sea fisheries, because they are too much affected by the weather, moreover a permanent strong current is necessary. Some scientists intended to improve this fishing gear, using the shearing devices instead of a lighter upper and a weighted lower beams in order to widen mouth of the stow net however they are unsuccessful. One-fortieth scale model net of the stow net was tested in a circular water tank with an effective volume of $5.67m\times1.76m\times1.00m$ of observing the configuration and tension of the net. Experiments were carried out under the various combination including water velocity, spherical floats and elevating floats with the shearing hoods instead of the upper beam. We found those devices offered a very low resistance per net area to current compared with the spherical floats or upper beam, and had a fairly good shearing power at any velocity and direction of the current. The total resistance (R) of the model net to which shearing hoods and floats are attached can be induced by the following formula under the condition of 0.25m/sec to 0.5m/sec, $$R(kg)=3.11V^{1.54}$$ The height (h) of the improved model net (m-B) is higher than traditional model net(m-A) with upper and lower beams, m-A: h(cm)=89.22-2.42(V-15). $V\geqq15,\;cm/sec$ m-B: h(cm)=89.20-0.78V (V:cm/sec) The catch efficiency of improved model net is 1.5 times traditional model net.

• Journal of the Korean Society of Fisheries and Ocean Technology
• /
• v.40 no.3
• /
• pp.214-224
• /
• 2004

A large cage system for the purpose of fishes farming in the open sea was influenced by various forces from the ocean environment. The deformation of the cage by these forces affects the safety of the cage itself, as well as that of the cultivated creatures. In this research, theoretical model was established to analyzing dynamic movement influenced by current for cage. Also, to increase the accuracy of calculations, the reduction ratio of flow speed acquired using the flume tank experiment. Applying the reduction ratio of flow speed to the numerical calculation, the calculation values were compared with the measured values in the flume tank experiment using cage model. The results were as follows ; 1. When the flow speed of the flume tank is fixed, the decrease of the velocity of flow which is passed the upper panel side is proportion to the increase of porosity ratio of netting. 2. When the porosity ratio is fixed, the increase of the velocity of flow which is passed the upper panel side is proportion to the increase of velocity of flow. 3. When the porosity ratio and the flow speed of the flume tank are fixed, the decrease of the velocity of flow which is passed the upper panel side is proportion to the increase of attack angle. 4. As a result of comparison between the underwater shape by simulation which is applying the reduction ratio of flow speed from the experiment using plane netting and that by model experiment, it was found out that the result of the simulation was very close to that of model gear within ${\pm}$ 5 % error range.

• Journal of the Society of Naval Architects of Korea
• /
• v.47 no.3
• /
• pp.328-341
• /
• 2010

The authors adopt the Unmanned Undersea Vehicle(UUV), which has taken the shape of manta(Sohn et al. 2006). They call here it Manta-type Unmanned Undersea Test Vehicle(MUUTV). MUUTV is designed with the similar concept of UUV called Manta Test Vehicle(MTV), which was originally built by the Naval Undersea Warfare Center, USA(Lisiewicz and French 2000, Sirmalis et al. 2001, U.S. Navy 2004). The present study deals with evaluation of extreme motion of MUUTV at large attack angles. Extreme motion contains, for example, rising and depth change due to operation of hovering thrusters attached to MUUTV, lateral motion due to ocean current applied to MUUTV at low advance velocity, and so on. Numerical simulation technique has been utilized. The previous mathematical model on manoeuvring motion of MUUTV(Bae et al. 2009a) is basically adopted. Based on the results of present model experiment on extreme motion, the mathematical model is revised and supplemented in order to describe extreme motion. The hydrodynamic derivatives related to extreme motion are obtained from present model experiment and the other derivatives are referred to previous work(Bae et al. 2009a).

• Journal of Ocean Engineering and Technology
• /
• v.25 no.1
• /
• pp.49-55
• /
• 2011

The EG/AD/S model ice, originally developed by Timco (1986), was selected as the primary model ice material for the newly built MOERI Ice Model Basin in Korea. However, the existence of a sugar component in the EG/AD/S mixture may cause a serious maintenance problem, as described in certain references. This study focuses on the tests of the mechanical properties of the EG/AD/S and the EG/AD model ice. In order to understand the influence of sugar in the original EG/AD/S model ice and to find a possible substitute for sugar, a series of tests with the EG/AD model ice were performed, and the results were compared to those of the EG/AD/S model ice. The relatively large size of the MOERI Ice Model Basin made it difficult to control the initial strength of model ice, so it took a much longer time to achieve the target strength. In order to obtain a lower strength and stiffness for the model ice, the amount of chemical additives may be varied to achieve the desired strength level. This paper is a preliminary study aimed at seeking a possible substitute for the original EG/AD/S model ice for utilization in a large-scale ice tank. To understand the influence of sugar in the original EG/AD/S model ice, the mechanical properties of the EG/AD/S and EG/AD model ice, such as flexural strength, compressive strength, and elastic modulus, were tested in the laboratory condition and compared to each other. The warm-up procedure seems to be an important factor to reduce ice strength in the tests, so it is discussed in detail.

• Journal of the Society of Naval Architects of Korea
• /
• v.36 no.3
• /
• pp.1-7
• /
• 1999

This paper describes the modification of hull bottom for the air lubrication technique to the passenger boat in service at the Chung-Ju lake, which has a large beam-draft ratio. From numerical analysis of 2-D cavity problem by potential theory, the cavity shape, length and the pressure in cavity are estimated for the simplified geometry of hull bottom, and the non-dimensional parameters affecting air cavity phenomena are investigated. Extensive resistance tests for the model ship which has variation of step height and side strip have been performed to investigate the formation of air cavity and the drag reduction effectiveness. And also, the development of attached cavity to the bottom were observed from the flat bottom made by transparent acrylic plate. From this survey on the modification of bottom shape and the air lubrication technique, the total resistance of model ship could be reduced by about 25% at the design speed compared to the proto type hull form.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.13 no.2
• /
• pp.89-99
• /
• 2001

In the present paper, Helmholtz resonator, which is widely used as a sound-amplification device, is applied to the development of seawater-exchanging breakwater. The incident waves can induce a large response in the resonator when incident wave frequency is close to one of natural modes of the resonator. Largely amplified potential energy due to the resonance supplies clean seawater into the harbor side throughout the channel. Flow supplied by the resonator circulates the seawater of harbor and helps to improve water quality. Within the framework of linear potential theory, matched asymptotic expansion method is employed to analyze the wave responses in a resonator. The semi-circular shape of the resonator has been chosen as an analytic model for mathematical simplicity. The wave responses of both single and arrays of Helmholtz resonator are investi¬gated. To validate an analytic solution, model test is conducted at 2-dimensional wave tanle Wave hcights in the resonator and velocity at the channel are measured for the state of valve-on and valve-off.

• Journal of the Society of Naval Architects of Korea
• /
• v.31 no.3
• /
• pp.65-79
• /
• 1994

In the present paper, An emphasis is laid upon effects of stern bulb on hydrodynamic property and manoeuvring performance. We carried out captive model tests in circulating water channel with two ship models of which the frame lines of aft bodies are different. such as normal stern form and stern form with bulb, but of which the other parts are exactly same. The tests conducted consist of hull resistance test, effective thrust measurement, oblique tow test, and measurements of factors related to rudder force. From the results of model tests, we discussed effects of stern bulb on hull forces and on hull-propeller-rudder interactions, comparing with normal stern form. Furthermore, we also discussed effects of stern bulb on course stability. turning ability. spiral characteristics and zig-zag manoeuvre by computer simulation. As a result, it is clarified that the adoption of stern bulb makes course stability the worse and turning ability the better. The difference of the hydrodynamic derivatives of naked hull between two ship forms cause the worse course stability of the ship with stern bulb. The differences of the effective inflow velocity to rudder and hull forces induced by steered rudder cause the better turning ability of the ship with stern bulb.

• Journal of the Society of Naval Architects of Korea
• /
• v.29 no.1
• /
• pp.71-80
• /
• 1992

The Seakeeping committee of Korea Towing Tank Conference executed the cooperative experimental study on deck wetting phenomena using S-175 contatiner model ships. Two members, Korea Research Institute of Ships and Ocean Engineering(KRISO) and Hyundai Maritime Research Institute(HMRI) participated in the study. This study was initiated by the ITTC(International Towing Tank Conference) Seakeeping Committee as the cooperative study of the 19th ITTC aiming at the establishement of the model test procedure on the deck wetting phenomena. Special emphasis was made on the determination of reliable record length for experimental measurement on rarely occurring events(such as deck wetness, slamming etc). Comparisons were made on both the test results and the test procedrues in this research. The measured frequencies of deck wetting show remarkable deviations between the runs. This fart implies that sufficiently long record length is required in the deck wetness measurement compared to the conventional ship motion tests. Careful considerations were made on the physical interpretation of the deck wetting phenomena, the correlation between the measured relative motion at stemhead and the measured deck wetness, and the estimation of deck wetting frequencies by Poisson process.