• Journal of Navigation and Port Research
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• v.47 no.4
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• pp.256-270
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• 2023

In this study, a sliding mode (SM) controller for dynamic positioning (DP) was specifically designed for a turret connection operation of a ship or an offshore structure in which an arbitrary point on the structure could be controlled as the motion center instead of the center of mass. The SM controller allows control of the arbitrary point and provides capability to manage uncertainties in the dynamics of ships and offshore structures, external forces caused by unknown changing marine environments, and transient performance of DP systems. The Jacobian matrix included in kinematic equations of the controlled object was modified to design the SM controller to control based on an arbitrary point of ships or offshore structures. To ensure robustness of the controller, the Lyapunov stability theory was applied in the design of the SM controller. In general, for robustness in DP control, gain scheduling based on a proportional-derivative (PD) control algorithm is employed. However, finding appropriate gains for gain scheduling complicates the application of DP systems. Therefore, in this study, the SM control algorithm was considered to mitigate the complexity of the DP controller for ships and offshore structures. To validate the proposed SM control algorithm, time-domain simulations were conducted and utilized to evaluate the performance of the control algorithm. The effectiveness of the proposed SM controller was assessed by comparing simulation results with results of a conventional PD control algorithm applied in DP control.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.34 no.5
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• pp.445-456
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• 2001

In the 1990s, Cochlodinium polykikoides red tide has been annually occurred in the southern coast of Korea and caused the mass damage to the fisheries with a huge amount of economic loss. The present study was done to establish the biological foundation for the elucidation of the mechanism of C. polykikoiaes red tide. The growth response of C. polykikoides to physico-chemical factors such as temperature, salinity, pH, and light intensity were examined using axenic cultures to evaluate the relative importance of these factors on the dynamics of natural populations, It was found that the highest growth conditions were $25^{\circ}C,\;40\%_{\circ}$, pH 7.5, and 7,500 lux, respectively. The tolerable salinity range of growth was relatively wide at an optimum temperature and was reduced to a much narrower range at a sub-optimum temperature. These findings indicate that C. polykikoides is an eurythermal and euryhaline organism. The organism demanded higher light intensity and oceanic pH narrow in its growth. C. polykikoides utilize inorganic nutrients, such as nitrate and ammonium as N, and phosphate as P. The nutritional requirements of C. polykikoides were $40{\mu}M$ for nitrate, $50{\mu}M$ for ammonium, and $5{\mu}M$ for phosphate. The half saturation constant (Ks) for growth was $2.10{\mu}M$ for nitrate, $1.03{\mu}M$ for ammonium, and $0.57{\mu}M$ for phosphate. These values were comparatively smaller than those of other dinoflagellates reported previously. We confirmed that the organism is characterized as an eutrophic species. However, ammonium Ks value is smaller than that of other eutrophic species, This result indicates that C. polykikoides red tide may outbreak in the waters which eutrophication is in progress rather than eutrophicated waters. C. polykikoides preferred ammonium better than nitrate as a nitrogen source when in a growth stage, Therefore, our results indicate that ammonium is more important nutrient on the growth of the organism in comparison with other inorganic nutrients and C. polykikoides red tide is related with the increased ammonium concentration in the coastal waters.