Bu-Geun Paik

An Experimental Research on Gap Cavitation Erosion of Semi-spade Rudder

Cavitation related erosion damages on semi-spade rudder generally occur at around leading edge of lower-face and behind gap of lower pintle. To get the idea of gap entrance profile for the latter case, a series of tests with large models has been carried out at MOERI. In the tests, the flow pattern around lower pintle have been investigated and visualized by high speed camera. Additionally, cavitation inception tests and pressure measurements have also been conducted for better comparison. As a result a new model (F rudder) has been developed. The new model turned out to have stable pressure distribution along the surface and so the cavitation inception speeds within of rudder angle were delayed approx. 4 knots in average.

Self-cleaning features of plasma-treated surfaces with self-assembled monolayer coating

A biomimic surface was coated onto a poly(tetrafluoroethylene) (PTFE) substrate. The coated PTFE surface was found to have nanoscale roughness and high hydrophobicity. In the first preparation step, the PTFE surface was modified by plasma etching. A self-assembled monolayer (SAM) of octadecyltrichlorosilane (ODTS) was then deposited onto the modified surface with a thickness of a 2–3 nm. This surface was found to have self-cleaning features similar to those of a lotus leaf. The self-cleaning features were confirmed by comparing the contact and sliding angles of the original PTFE surface, a PTFE surface plasma treated, and a PTFE surface plasma treated and SAM coated. The PTFE surface treated with plasma and SAM coated had an increased contact angle and a decreased sliding angle compared with the other surfaces. It also exhibited increased stability and slow aging. The quantity of oxygen-containing groups that can be greatly influenced by plasma treatment, SAM coating, and aging, seems to play an important role in surface modification.

Cavitation Observation and Visualization of the Gap Flows on a Rudder Influenced by Propeller Slipstream and Hull Wakes

In the present study, the influences on the gap cavitaiton of the semi-spade rudder are investigated experimentally in the condition with propeller and hull wakes. To reduce the scale effect in the given experimental conditions, 1/28.5-scale-down models of propeller and rudder are manufactured. We have the propeller rotate ahead of the rudder, inducing the three dimensional effects originated from the propeller action. Experimental methods are composed of the cavitation observation using high speed camera, PIV (particle image velocimetry) measurements to visualize the cavitaition and flows around the gap. The propeller slipstream affects both of the gap flows and cavitation of the rudder.

Experimental Tests on the Wireless Sensor Network and the Power-line Communication in a Real Ship and Laboratory

Abstract Basic performances of wireless sensor network (WSN) and power line communication (PLC) confirmed in the test bed ashore are investigated in the 3000-ton class training ship of Korea Maritime University. The ubiquitous technologies can be considered for the provision of safety and convenience in a ship. We employed WSN and PLC, as the ubiquitous technologies, at the two areas within the training s hip to estimate the realization of the ubiquitous environments in a ship. The experiments show rather good results in terms of data transfer rate. However, more detailed studies concerning the connection between WSN and PLC, noises induced to power line and fading ef fects are required to improve the quality and the stability of the communication for the ubiquitous environments. ※Keywords: Ship(선박), Wireless senor network(무선센서통신망), Zigbee(지그비), Power line communication(전력선 통신), Ubiquitous(유비쿼터스) 1. 서 론 언제 어디서나 필요한 정보를 얻어 필요한 서비 접수일: 2007년 12월 3일, 승인일: 2008년 5월 6일 †교신저자: ppaik@moeri.re.kr, 019-358-0255

A Study on USN Technologies for Ships

This paper describes the ubiquitous computing technologies for ship, which is produced and assembled by many steel blocks. It particularly describes the testing of a 2.4 GHz wireless communications platform, especially zigbee, on a number of intelligent devices, with the blocks disturbing the wireless communication. The power line communication that is established in a ship already is also experimented for some data transfer. At last, the RFID technology is applied at the test bed that is composed of three steel containers. In this paper, we implemented some USN technologies in the test bed simulating a ship environment and investigated the basic characteristics of ubiquitous computing technologies. Possible applications of such ubiquitous computing technologies to ships are also introduced here in.

Study on the Three Dimensional Flow Characteristics of the Propeller Wake Using PIV Techniques

A stereo-PIV (particle image velocimetry) technique is used to investigate the vortical structure of the wake behind a rotating propeller in the present study. A four bladed propeller is tested in a cavitaion tunnel without any wake screen. Hundreds of instantaneous velocity fields are phase-averaged to reveal the three dimensional spatial evolution of the flow behind the propeller. The results of conventional 2-D PIV are also compared with those of the stereo-PIV to understand the vortical structure of propeller wake deeply. The variations of radial and axial velocities in the 2-D PIV results seem to be affected by the out-of-plane motion. generating a little perspective error in the in-plane velocity components of the slipstream. The strong out-of-plane motion around the hub vortex also causes the perspective error to vary the axial velocity component a little at the near wake region. The out-of-plane velocity component had the maximum value of about 0.3U0 in the tip vortices and continued its magnitude in the wake region.

Stereoscopic PIV Measurements of Flow around a Marine Propeller

A stereoscopic PIV (Particle Image Velocimetry) technique has been employed to measure the 3 dimensional flow structure of turbulent wake behind a marine propeller with 5 blades. The out-of-plane velocity component was measured using particle images captured simultaneously by two CCD cameras installed in the angular displacement configuration. 400 instantaneous velocity fields were acquired for each of four different blade phases of 0°, 18°, 36° and 54°. They were ensemble averaged to investigate the spatial evolution of propeller wake in the near wake region up to one propeller diameter (D) downstream. The phase-averaged velocity fields show clearly the viscous wake formed by the boundary layers developed along both surfaces of the blade. Tip vortices were generated periodically and the slipstream contraction occurs in the near-wake region. The out-of-plane velocity component has large values at the locations of tip and trailing vortices. With going downstream, the axial turbulence intensity and the strength of tip vortices were decreased due to the viscous dissipation, turbulence diffusion and blade-to-blade interaction. The difference in the mean velocity fields measured by SPIV and 2-D PIV methods was about 5% ≈ 10%. However, the 2-D PIV results also give sufficient information on propeller wake beyond the region of X/D=0.2.

Production & Performance Assessment of Composite Material Flexible Propeller

The researches on the development of composite material underwater vehicle propeller have been actively attempted for the reduction of radiation noise with outstanding damping effects. Composite material propellers have almost been designed and produced by the foreign experts, and it is difficult to obtain the related info rmations about their flow, vibration, material characteristics because they are treated as the secrets with close relationship to the military technology, especially in the case of underwater vehicles. For the security of domestic manufacture of composite material propeller and the comparison and examination of its performance and radiation noise characteristics with those of German CONTUR composite material propeller, two propellers were self-produced according to the fiber weaving and array using compressible molding process and their self performances and radiation noise characteristics were measured. The mean fluctuations of blade tip of self-produced composite material propeller were increased and the radiation noises in the low frequency band were reduced compared to those of CONTUR, which could be estimated as the change of material characteristics and also be thought to be used for the future research informations.

PIV Aanalysis of Vortical Flow behind a Rotating Propeller in a Cavitation Tunnel

A two-frame PIV (Particle Image Velocimetry) technique is used to investigate the wake characteristics behind a marine propeller with 4 blades at high Reynolds number. For each of 9 different blade phases from to , one hundred and fifty instantaneous velocity fields are measured. They are ensemble averaged to study the spatial evolution of the propeller wake in the region ranging from the trailing edge to one propeller diameter (D) downstream location. The phase-averaged mean velocity shows that the trailing vorticity is related to radial velocity jump, and the viscous wake is affected by boundary layers developed on the blade surfaces and centrifugal force. Both Galilean decomposition method and vortex identification method using swirling strength calculation are very useful for the study of vortex behaviors En the propeller wake legion. The slipstream contraction occurs in the near-wake region up to about X/D : 0.53 downstream. Thereafter, unstable oscillation occurs because of the reduction of interaction between the tip vortex and the wake sheet behind the maximum contraction point

Study on the Drag Reduction of 2-D Dimpled-Plates

The main objective of the present study is to investigate the roles of the micro-dimpled surface on the drag reduction. To investigate the effectiveness of the micro-dimpled surface, the flat plates are prepared. The micro-size dimples are directly carved on the metal surface by ultrasonic nano-crystal surface modification (UNSM) method. Momentum of the main flow is increased by the dimple patterns within the turbulent boundary layer (TBL), however, there is no significant change in the turbulence intensity in the TBL. The influence of dimple patterns is examined through the flow field survey near the flat plate trailing edge in terms of the profile drag. The wake flow velocities in the flat plate are measured by PIV technique. The maximum drag reduction rate is 4.6% at the Reynolds number of . The dimples tend to increase the drag reduction rate consistently even at high Reynolds number range.