• Journal of the Korean Society of Marine Environment & Safety
• /
• v.28 no.7
• /
• pp.1259-1266
• /
• 2022

Recently, due to the specialization of structural design standards and evaluation methods, the classification rules are being integrated. A good example is the common international rules (CSR). However, detailed regulations are presented only for the cargo hold area where the longitudinal load is greatly applied, and no specific evaluation guidelines exist for the bow and stern structures. Structural design of the mentioned area is carried out depending on the design experience of the shipbuilder, and because no clear standard exists even in the classification, determining the root cause is difficult even if a structural damage problem occurs. In this study, an engineering-based solution was presented to identify the root cause of representative cases of buckling damage that occurs mainly in the stern. Buckling may occur at the panel wall owing to hull girder bending moment acting on the stern structure, and the plate thickness must be increased or vertical stiffeners must be added to increase the buckling rigidity. For structural strength verification based on finite element analysis modeling, reasonable solutions for load conditions, boundary conditions, modeling methods, and evaluation criteria were presented. This result is expected to be helpful in examining the structural strength of the stern part of similar carriers in the future.

• The Journal of the Acoustical Society of Korea
• /
• v.42 no.3
• /
• pp.243-249
• /
• 2023

The occurrence of cavitation on the propeller is directly linked to the naval ship's survivability, and it is necessary to design a propeller shape that delays the cavitation inception. However, the propeller cavitation can occur under various operating conditions, thus it is important to identify whether the propeller cavitation exists during operation as well as in the design phase. To this end, it is necessary to use noise or vibration signals on board to monitor the cavitation inception. In this study, a hydrophone and an accelerometer were installed on the ship hull right above the propeller to compare the performance of analyzing cavitation inception between acoustic and vibration signals. Also, a high speed camera was used to visually observe the occurrence of cavitation through an observation window. The measured results showed that the spectral shapes between acoustic and vibration signals were different, but the level increases at each frequency band and the overall level of the frequency band from 1 kHz to 10 kHz showed a similar tendency. The Detection of Envelope Modulation On Noise (DEMON) analysis also showed similar results for both acoustic and vibration signals, confirming that both hydrophones and accelerometers can be utilized in the analysis of cavitation inception.

• The Journal of the Acoustical Society of Korea
• /
• v.42 no.3
• /
• pp.250-261
• /
• 2023

In this study, the noise contributions by the duct, stator and rotor, which are the propulsor components, are evaluated to identify the flow noise source in cavitation and non-cavitation conditions on pumpjet propulsion and the noise levels in both conditions are compared. The unsteady incompressible Reynolds averaged Navier-Stokes (RANS) equation based on the homogeneous mixture assumption is applied on the suboff submarine hull and pumpjet propeller in the cavitation tunnel, and the Volume of Fluid (VOF) method and Schnerr-Sauer cavitation model are used to describe the two-phase flow. Based on the flow simulation results, the acoustic analogy formulated by Ffowcs Williams and Hawkings (FW-H) equation is applied to predict the underwater radiated noise. The noise contributions are evaluated by using the three types of impermeable integral surface on the duct, stator and rotor, and the two types of permeable integral surface surrounding the propulsor. As a result of noise prediction, the contribution by the stator is insignificant, but it affects the generation of flow noise source due to flow separation in the duct and rotor, and the noise is predominantly radiated into the upward and right where the flow separations are. Also, the noise is radiated into the thrust direction due to pressure fluctuation between suction and pressure sides on the rotor blades, and the it can be seen that the cavitation effect into the noise can be considered through the permeable integral surface.

• Journal of the Korean Society of Marine Environment & Safety
• /
• v.29 no.2
• /
• pp.139-146
• /
• 2023

Maritime object detection systems, which detects small maritime obstacles such as fish farm buoys and visualizes distance and direction, is equipped with a 3-axis gimbal to compensate for errors caused by hull motion, but there is a limit to distance error corrections necessitated by the vertical movement of the camera and the maritime object due to wave motions. Therefore, in this study, the distance error of maritime object detection systems caused by the movement of the water surface according to the external environment is analyzed and corrected using average filter and moving average filter. Random numbers following a Gaussian standard normal distribution were added to or subtracted from the image coordinates to reproduce the rise or fall of the buoy under irregular waves. The distance calculated according to the change of image coordinates, the predicted distance through the average filter and the moving average filter, and the actual distance measured by laser distance meter were compared. In phases 1 and 2, the error rate increased to a maximum of 98.5% due to the changes of image coordinates due to irregular waves, but the error rate decreased to 16.3% with the moving average filter. This error correction capability was better than with the average filter, but there was a limit due to failure to respond to the distance change. Therefore, it is considered that use of the moving average filter to correct the distance error of the maritime object detection system will enhance responses to the real-time distance change and greatly improve the error rate.

• Journal of the Society of Naval Architects of Korea
• /
• v.60 no.4
• /
• pp.222-230
• /
• 2023

In the present work, the scale effect on the Boil-Off Rate (BOR) was investigated based on an analytical method to systematically evaluate the thermal performance of a Liquefied Natural Gas (LNG) Cargo Containment System (CCS). A two-dimensional thermal resistance network model was developed to accurately estimate the heat ingress into the CCS from the outside. The analysis was performed for the KC-1 LNG membrane tank under the IGC and USCG design conditions. The ballast compartment of both the LNG tank and cofferdam was divided into six sections and a thermal resistance network model was made for each section. To check the validity of the developed model, the analysis results were compared with those from existing literature. It was shown that the BOR values under the IGC and USCG design conditions were agreed well with previous numerical results with a maximum error of 1.03% and 0.60%, respectively. A SDR, the scale factor of the LNG CCS was introduced and the BOR, air temperature of the ballast compartment, and the surface temperature of the inner hull were obtained to examine the influence of the SDR on the thermal performance. Finally, a correlation for the BOR was proposed, which could be expressed as a simple formula inversely proportional to the SDR. The proposed correlation could be utilized for predicting the BOR of a full-scale LNG tank based on the BOR measurement data of lab-scale model tanks.

• Asia Marketing Journal
• /
• v.16 no.1
• /
• pp.1-12
• /
• 2014

The goal-gradient hypothesis states that the tendency to approach a goal increases with the increasing proximity of the goal (Hull 1932). It was initially supported with an evidence of animal experiments and since then, several papers have investigated the goal-gradient hypothesis in humans. Although there are some evidences related to the goal-gradient hypothesis in human behaviors, none of previous studies can properly explain its underlying mechanism, and what's more, they were not able to suggest useful managerial applications in human behaviors. From these perspectives, this work points out that there are some theoretical weaknesses to apply the goal-gradient hypothesis into the complicated human decision-making behaviors and proposes an alternative theoretical mechanismthat underlies the goal-gradient hypothesis in human. Finally, it offers insights into managerial implications of the goal-gradient hypothesis in the marketing field. This study focuses on the changes in motivations for achieving goals, in terms of how approaches to goals vary according to temporal distance from those goals. Specifically, the temporal construal theory (Liberman and Trope 1998) is considered as the underlying mechanism of the goal-gradient in that the temporal construal theory argues how the temporal distance from a goal makes people change their associated values regarding to that goal. According to the temporal construal theory, the value of distant future outcomes (near future outcomes) is construed on the basis of abstract and central features (concrete and peripheral features), and it argues that distant future situations are construed on a higher level than near future situations. This means that the value associated with the high-level construal is enhanced over delay, whereas the value associated with the low-level construal is discounted over delay. Our propositions suggest that the goal-gradient behavior in human can be motivated by the different aspects or characteristics of the goal as time changes based on the temporal construal theory. Thus, the following propositions are proposed. P 1-1: If the goal is far away, consumers put more value on the central features that are more associated with the desirability of the goal. P 1-2: If the goal is far away, consumers put more effort into accomplishing the goal that has more central features, regardless of its peripheral features. P 2-1: If a goal is near, consumers put more value on the peripheral features that are more associated with the feasibility of the goal. P 2-2: If a goal is near, consumers put more effort into accomplishing the goal that has more peripheral features, regardless of its central features. We hope to provide sufficient managerial implications for the companies as our research aims to show how consumers react differently as they progress toward the goal. Proposed propositions may provide guidance for companies developing a loyalty program, enabling them to understand what kinds of benefits or services they should provide or emphasize to consumers in loyalty programs on the basis of the time-dependent changes in outcome values (such as gifts, reward coupons). The effects of temporal distance from a goal should inform companies' marketing activities and help themto determine where emphasis should be placed in designing the benefits of their loyalty program.

• Journal of Practical Agriculture & Fisheries Research
• /
• v.21 no.1
• /
• pp.81-87
• /
• 2019

The investigation of mycelial growth for artificial cultivation in T. albuminosus determined that within PDA, YM, MEA medium, both KNCAF 9001 and 9002 strains showed the highest mycelial growth in MEA media with 89, 81 mm, respectively, followed by YM, PDA in respected order. Furthermore, optimal mycelial growth of 89 and 77 mm in 9001 and 9002, respectively, at 25 ℃. Mycelial growth rapidly decreased at 30 ℃, but it was confirmed that it survived at 40 ℃. At pH 6, mycelial growth was fast with growth of 89 and 88 mm for both 9001 and 9002, respectively. In the case of 9001, the addition of with cotton seed hull(80%) and rice bran (20%) each other resulted in maximum productivity of 99 mm/10 days. The result differed in order of corn cob(97 mm), oak sawdust(96 mm) and poplar sawdust(93 mm). Ultimately, the result confirmed that addition of rice bran in comparison to bran resulted in higher yield. Even with identical medium component, 9002 showed the same tendency as 9001 but its growth was relatively slower than 9001. The effect of mycelial growth on the moisture content of the medium was best at 101. 94 mm/10 days when the moisture content of 9001 and 9002 was 65%. Mycelial growth rate tended to be slower when the moisture content was higher or lower than 65%.

• Journal of the Korean Society of Marine Environment & Safety
• /
• v.29 no.7
• /
• pp.950-957
• /
• 2023

For safe mooring and towing between the ship and port, the equipment must be designed in accordance with the relevant international regulations. However, some small shipyards and engineering companies often do not fully comprehend the core contents. Therefore, the international regulations regarding towing and mooring equipment are reviewed and the bollard and chock are newly developed based on the Mooring Equipment Guideline 4 (MEG4) standards. A bollard is a mooring equipment used to fix a mooring rope to the hull. It has two columns and is mostly used in a figure eight pattern knots under the mooring condition. The chock, which is used to change the mooring rope direction coming into the ship from outside, is manufactured using a casting with curvature. The two mooring equipment are widely used in the stern, bow, and mid-side. Owing to the increase in the size of container vessels and LNG ships, the mooring rope load has increased and the safe working load of the mooring equipment must be revised. This study summarizes and examines the results of the allowable stress method obtained using finite element analysis modelling. To consider the mesh size effect, a reasonable criteria was suggested by referring the existing class guidance. Additionally, the safe working load was verified through nonlinear collapse analysis, and the elastic region against load increments was confirmed. Furthermore, the proposed evaluation method can be used to develop similar equipment in the near future.

• Journal of the Korean Society of Marine Environment & Safety
• /
• v.29 no.7
• /
• pp.857-862
• /
• 2023

In order for an autonomous ship to arrive near the pier and automatically berth without the help of a tugboat or pilot, it is necessary to recognize the pier and calculate the thruster output and output angle for berthing to the pier at a fixed berthing speed under given external force conditions. Therefore, in this study, the external force and moment acting on the ship while berthing were analyzed, and the thruster output calculation for automatic berthing was designed and the basic concept for the development of the automatic berthing program was designed. The wind pressure applied to the hull by the wind while the ship is berthing was calculated based on the wind pressure area and the wind direction angle and the turning moment to rotate the ship according to the transverse force of the ship was calculated. Considering the force acting on the ship and the turning moment during berthing, a theoretical formula was presented to calculate the thruster output and output angle for berthing parallel to the pier, and the turning due to other variables was controlled by the PID controller. In addition, the basic concept for program development was presented by analyzing the input elements necessary for the theoretical formula.

• Journal of the Korean Society of Marine Environment & Safety
• /
• v.30 no.4
• /
• pp.348-357
• /
• 2024

Maneuvering performance is crucial for fishing vessels, especially under operational conditions that involve frequent course changes and weight variations due to catch. Small vessel accidents account for approximately 60% of maritime incidents as of 2022, mainly attributed to collisions and stranding accidents due to insufficient maneuvering performance. Especially, accidents that occur on small vessels less than 10 tons account for about 65% of all accidents. The absence of international standards presents challenges in accurately evaluating the maneuvering performance of small vessels. In this study, a 4.99-ton small fishing vessel was selected as the target, and a 3d-cad model was created. The commercial numerical analysis program STAR-CCM+ was employed to establish a simulation environment for the vessel's maneuvring motion. Based on this standard loading conditions and weight distribution were considered, 10° / 10°, 20° / 20° zigzag tests and 35° turning test were conducted. The results revealed a tendency for decreased yaw and course-keeping performance and improved turning performance as the hull weight increased. However, in partial arrival and full load departure condition, the manoeuvering performance were relatively poor. Based on this, the need for evaluation of maneuvering and standardized criteria of maneuvering performance for safe navigation of small vessels is presented. Furthermore, it is expected that the evaluation results of maneuvering performance in this study can serve as fundamental data for establishing criteria for evaluating the maneuvering performance of small vessels.