• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.21 no.1
• /
• pp.45-53
• /
• 2009

A possibility of the drag coefficient estimation in numerical water basins was discussed where the numerical solution were calculated by the 3-dimensional hydro-dynamical model (FLOW-$3D^{(R)}$) with the RNG $k-{\varepsilon}$ turbulence model. On the known cases of the drag coefficients for a rectangle, the numerical drag coefficients got $1.34{\sim}1.52$ and the wind tunnel values were $1.3{\sim}1.5$. For a cylinder, the numerical values were calculated as $0.75{\sim}0.78$ in the range of 0.5

• Journal of the Society of Naval Architects of Korea
• /
• v.42 no.4 s.142
• /
• pp.368-378
• /
• 2005

The effects of rotary oscillation on the unsteady laminar flow past a circular cylinder. are numerically investigated in the present study. The numerical solutions for the 20 Wavier-Stokes equation are obtained using a finite volume method Tn the framework of an overlapping grid system. The vortex formation behind a circular cylinder and the hydrodynamics of wake flows for different rotary oscillation conditions are analyzed from the results of numerical simulation. The lock-on region is defined as the region that the natural shedding frequency due to the Karmann Vortex shedding and the forcing frequency due to the forced oscillating a cylinder are nearly same, and the quasi-periodic states are observed around that region. At the intersection between lock-on and non-lock-on region the shedding frequency is bifurcated. After the bifurcation, one frequency fellows the forcing frequency($S_f$) and the other returns to the natural shedding frequency($St_0$). in the quasi-periodic states, the variation of magnitudes and relevant phase changes of $C_L$ with forcing phase are examined.

• Journal of Advanced Marine Engineering and Technology
• /
• v.37 no.1
• /
• pp.114-120
• /
• 2013

Recently, navigation systems based on wireless communication have been applied to the internal structures such as building or ship. If a stable azimuth information is obtained, these systems can effectively guide the direction of the user's progress through the information and then can improve the performance of guidance. Since conventional method which has acquired an azimuth information using geomagnetic and acceleration sensor(azimuth sensor hereafter) is sensitive to the effects of the magnetic field, it has unstable error range according to the surrounding environment. In order to improve these problems, this paper presents a new relative azimuth estimation algorithm using the displacement of a mobile node and its rotation angle based on Wireless communication. For the performance assessment of the proposed algorithm, experiments using rotating arm are performed and the results are confirmed that the proposed system can estimate the relative azimuth without using additional sensors.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.34 no.10
• /
• pp.1507-1512
• /
• 2010

In this study, the plasma induced by $CO_2$ laser lap welding of 6t Zn coated steel used for ship building was measured using photodiodes and a microphone. Then, the welding phenomenon with gap clearance of lap joint was compared with RMS-treated signal. Thus, we found that intensity of the RMS-treated signal increased with Zn vaporization; further, the presence of defects results in rapid variations with the RMS value as a function of lap-joint parameters. Besides, the FFT value of the raw signal with variations of changing welding parameters was calculated, and then the calculated FFT frequency value was set as the bandwidth of digital filter for a more accurate in-process monitoring. The RMS values were acquired by filtering the raw signal. By matching the weld beads and the calculated RMS values, we confirmed that there is a strong relationship between the signals and the defects.

• Journal of the Korean Society for Marine Environment & Energy
• /
• v.11 no.4
• /
• pp.221-226
• /
• 2008

Air pollution associated with the SOx emission from the shipboard propulsion and generation engines is becoming one of the major environmental concerns these days. Lead by the international organizations including IMO and European Union, a significantly strengthened air pollution related regulations have been introduced and they are becoming in practice as scheduled. Such rules are basically giving the guidelines for permissible SOx emission which can be only met by using high quality fuel oils with less sulfur content or operating scrubbing systems aiming at reducing SOx at the engine exhaust. Since both countermeasures can lead to the cost increase in ship building and operation, Korean shipbuilding industries, leading the world's market, need to be well aware of the ever changing regulations and be prepared with proper solutions. Here, we briefly summarize such latest rules and regulations on the air pollution at sea, and review some technical issues on the scrubbing systems available with some suggestions.

• Journal of the Korean Society of Marine Environment & Safety
• /
• v.14 no.4
• /
• pp.325-331
• /
• 2008

Recently, new shipbuilding yards with medium capacity are established due to influence of prosperous condition no shipbuilding industry in Korea. These shipbuilding yards have characteristics such as high capacity facilities and followed system of dock launching just like major shipbuilding yards. The present paper explains the dry dock design and structural strength analysis by using FEM. The design stage used TRIBON M3 system while the estimation of structural strength used ANSYS Multiphysics module. The dry dock gate did not frequently open and close, it had to sustain against external wave load during building a ship. Moreover, documents related to design of dry dock gate have no guidelines about design criterion and process of structural strength calculation. It is necessary to make the guidelines about design of dry dock gate. It is expected that this paper will be a good reference to the design of dry dock gate.

• Structural Monitoring and Maintenance
• /
• v.5 no.2
• /
• pp.297-311
• /
• 2018

Plate and shell structure is widely applied in engineering, i.e. building roofs, aircraft wings, ship platforms, and satellite solar arrays. Its vibration problem has become increasingly prominent due to the tendency of lightening, upsizing and flexibility. As a new smart material with great actuating force and toughness, macro-fiber composite (MFC) is composed of piezoelectric fiber and epoxy resin basal body, which can be directly pasted onto the surface of plate and shell and is suitable for vibration control. This paper deduces the actuation equation of MFC coupled plate in different boundary conditions, an equivalent finite element modeling method is proposed which uses MFC actuating force as the applied excitation, and on this basis the active control simulation and experiment of MFC over plate and shell structure vibration are accomplished. The results indicate that MFC is able to implement effective control over plate and shell structure vibration in multi-band range. The comparison between experiment and simulation proves that the actuation equation deduced herein, effective and practicable, can be applied into the simulation calculation of MFC vibration control over plate and shell structure.

• Journal of the Korean Society for Marine Environment & Energy
• /
• v.9 no.2
• /
• pp.92-97
• /
• 2006

Hull forms of a high speed small boat have been developed through numerical studies. A round bilge type hull form has been drived form a using chine hull form with HCAD, a hull form variation software. Wave resistance and the flow fields around the ships have been computed using well-known software, WAVIS. This software employs Rankine source method with non-linear tree surface condition as well as dry transom boundary conditions. The round bilge hull form showed better resistance performance than to the chine hull form for the whole speed range. However, considering the building and labor costs of the small shipyard, the chine hull form has been selected and its wave resistance characteristics has been improved by modifying the bow regions and applying the stem wedge. It is found that the effect of stem wedge is quite satisfactory to improve the resistance characteristics of high speed chine hull form.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.39C no.12
• /
• pp.1307-1313
• /
• 2014

In this paper, we have proposed a tapered slot antenna for IR-UWB communication system suitable of indoor positioning in the building. The designed tapered slot antenna is designed using Ansys Inc. HFSS and its standing wave ratio, return loss, and radiation pattern is analyzed. In 2.36 GHz ~ 5.51 GHz and, the designed antenna shows satisfactory return loss at -10 dB and meets the requirement of $VSWR{\leq}2$. The presented designed showed a higher sensitivity for the end-fire propagation characteristics in a specific direction across all bands of the radiation pattern.

• Journal of Advanced Marine Engineering and Technology
• /
• v.36 no.6
• /
• pp.850-856
• /
• 2012

Bilateration using two fixed nodes has been used in the field of the real time indoor location system in the narrow space such as building or ship passage. However, as the distance between the fixed nodes increases or any obstructions exist in their zone, it is difficult to detect the location of mobile node(user) due to the degradation of its reception ratio. In order to compensate for these problems, this paper presents, based on IEEE 802.15.4a chirp signal, a new real time indoor location system using stride measurement algorithm which can calculate the location through sensors attached to user. The proposed system consists of an ultrasonic sensor to measure the leg length, a geomagnetic sensor to recognize the user's orientation, and an inertial sensor to obtain the angle between the legs. The experimental results are shown that the proposed system has twice or more accurate output compared with conventional indoor location method in the section which is partially out of communication reachability.