In the previous study, a shooting trajectory assuming that the purse seine shooting trajectory is a circle was proposed based on the speed and direction of the movement of the fish school. However, in practice, a trajectory that is closer to an elliptical shape than a circular one is often formed. In this study, the existing circular trajectory and the elliptical trajectory methods were compared under the same conditions to confirm the effectiveness of elliptical shooting trajectory. In addition, changes in the eccentricity of ellipses were derived to assess which type of ellipse was appropriate as a shooting trajectory. When a high-speed fish school moves in a straight line, an elliptical shooting trajectory with the eccentricity of 0.7 to 0.9 will be reasonable, and for middle-low speed fish school, an elliptical shooting trajectory with the eccentricity of 0.4 to 0.6 will be more useful than a circle shooting trajectory.
The occurrence of eggs of hairtail, Trichiurus japonicus was examined in the coastal waters of Jeju Island, Korea in spring from May to June in 2014, April to May in 2015, and April to in 2016. As a whole, hairtail eggs occurred abundantly in May, 2014. Especially, high densities over 300 ind./1,000 m3 of eggs abundances in May and June, 2014 occurred in the north-western area of Jeju Island where is upwelling phenomenon occurred throughout the year. In the relationship between T-S and the hairtail eggs abundances, high densities over 100 ind./1,000 m3 of eggs abundances occurred in temperature of 18.1-18.7℃ and salinity of 33.92-34.87‰ in May when hairtail eggs occurred abundantly.
Monthly fluctuation in abundance and species composition of fish in coastal waters off Oenaro island, Goheung were investigated using seasonal samples collected by a shrimp beam trawl in 2018. A total of 5,981 fishes were sampled and classified into 48 species, 32 families, and 9 orders. The dominant species was Engraulis japonicus (993 individuals, 16.60%), Amblychaeturichthys hexanema (844 individuals, 14.11%), and Thryssa kammalensis (674 individuals, 11.27%). The highest number of individuals was found in August (958 individuals), while the lowest number of individuals was found in January (136 individuals). The diversity index was the highest in November (H’ = 2.37) and the lowest in January (H’ = 1.77).
Thousands of pelagic and demersal fishes inhabit the waters around Korea and many of them are overexploited. One of the reasons is technological development, which increases the efficiency of the vessels continuously. The analysis was conducted to identify the change of fishing power index to develop the vessel and gear technology that may have improved the fishing efficiency of the otter trawl fishery from 1960s to 2010s. Gross tonnage was decreased stably, but horse power was increased annually. The perimeter of net mouth was somewhat longer, but little changed. Color fish finder was utilized from the mid-1960s. Hydraulic net drum were introduced in the early 1990s, and supply rate was gradually increased. Surveys on the supply and upgrading of fishing equipment utilized visiting research. Therefore, the relative fishing power index in the trawl fishery increased about two to three times in the 2010s compared to the 1980s. The results are expected to contribute to reasonable fisheries stock management.
The change of fishing power index was analyzed to identify the development of the vessel and gear technology that may improve the fishing efficiency of the offshore conger eel pot fishery from 1980s to 2015. Gross tonnage per fishing vessel was rapidly increased annually. The standard of pot was maintained, but the number of pot used rapidly increased by using conger eel pot hauling devices, carrying and loading devices, main line hauler, casting devices and slide type pot. Fish finder system to identify fishing ground information and the conger eel pot hauling devices were modernized, and supply rate was also increased. Therefore, the relative fishing power index in the offshore conger eel pot fishery increased from 1.0 in 1980 to 1.3 in 1990, to 1.8 in 2000 and to 2.0 in 2015. The results are expected to contribute to reasonable fisheries stock management of the offshore conger eel pot fishery.
In this study, an automatic system for improving the working environment and increasing production efficiency of a laver aquaculture industry in Korea was developed by combining a hydraulic control system and a load cell in a current landing work of the laver. The improved gathering laver system allowed the automatic gathering process of the laver in the sea with the hydraulic control system connected to a cutting machine of the laver on the operating ship, which has been used for gathering the laver semi-automatically in a form of the traditional farming method. The transporting process of the laver from an operating ship to the land was improved as follows. A frame installed on the operating ship and the bag nets were designed and made to hold about 1,000 kg of the laver inside. The bag nets contain the laver on the improved operating ship were tied in knots and hooked on a crane using a load cell. The weight is measured immediately by lifting the bag nets through the load cell system. Weight information is communicated to the fishermen and successful bidders through the application. The advantages of the improved system can help fishermen to fish by improving their working environment and increasing production efficiency. The field survey to improve the landing operation of the laver aquaculture was conducted in Gangjin, Goheung, Shinan, Wando, Jindo, and Haenam in South Jeonnam Province. A total of 10 sites including Gunsan in Jeonbuk Province, Daebu Island in Ansan City, Jebu Island in Hwaseong City in Gyeonggi Province, and Seocheon in Chungnam Province were searched to collect data. Prototypes of the system were tested at the auction house of laver located in Goheung, where laver collection using hydraulic control and landing using road cell could be improved.
In this study, the authors introduce a newly developed flatfish grading system. Owing to the features of flatfish with and wide body, the general types of grading system are not easy to apply for it. Furthermore, the flatfish to be graded is alive such that the existing measurement and grading systems cannot be used for it as well. This study gives a solution for measuring and grading the flatfish with high speed and good accuracy. For this object, the authors developed flatfish measurement and grading system. This system consist of the feeding, conveying, measurement part and sorting part. Especially, the measurement part is made by vision based measuring technique which satisfies the given specification. The result from the experiment shows that the developed system is applicable for measuring and grading the flatfish sizes in variety.
In this study, system modeling and dynamic analysis of crane are conducted. Especially, among many different kinds of a crane system, the issues on crane operating problems installed on the vessel are considered. As well known, marine systems including cranes are exposed to various disturbances such as vessel motions, hydrodynamic forces, wave and wind attack, etc. In order to analysis the system dynamic with environmental conditions, the authors derived the nonlinear dynamic model of offshore crane and derived a linear model which is used for designing the control system. Using the obtained nonlinear and linear models, simulations were conducted to evaluate the usefulness of the obtained models. By simulation and result evaluation, the usefulness of the linear model, which presents the dynamics, is effectively verified.
This paper proposes a possibility of using active front-end rectifier with the SVPWM method for induction motor speed control, which is applicable to small electric propulsion boats. The proposed method can produce a more precise sinusoidal input current waveform and a higher power factor than conventional methods. Its speed, torque, input current, DC voltage, and load current control performance are similar to or better than those of conventional methods. Through computer simulations using the PSIM program, the validity of the proposed method was verified by comparing and analyzing the characteristics of the conventional methods and the proposed method.