Akihiko Matsuda

Model Experiment on Heel-Induced Hydrodynamic Forces in Waves for Realising Quantitative Prediction of Broaching

Mathematical models for capsizing due to broaching, one of the great threat to ships running in following and quartering seas, have been developed by many researchers. However these models can predict it only qualitatively. For realising quantitative prediction, we conduct the systematic captive model experiments with the large heel angles up to 50 degrees in severe following waves. As a result, the details of nonlinear heel-induced hydrodynamic forces with respect to heel angle in waves are presented. Then the comparisons between a free running model experiment and the numerical simulation with direct use of the measured heel15 induced hydrodynamic forces are carried out. As a result, the mathematical model for realising quantitative prediction of broaching in severe following and quartering seas is presented. Finally the simplified mathematical model is also proposed for more practical uses with less experimental efforts.

Experimental Study on Parametric Roll of a Post-Panamax Containership in Short-Crested Irregular Waves

Free running model experiments of a post-Panamax containership were conducted to examine the danger of parametric roll in regular waves, long-crested and short10 crested irregular waves. As a result, parametric roll in head and bow waves were clearly recorded even in long-crested and short-crested irregular waves. From the experimental results, the effects of wave steepness, forward velocity, heading angle, irregularity of waves on parametric roll were systematically examined.

Spatial and Temporal Variation of the Fish Assemblage on a Large Artificial Reef Assessed Using Multiple-Point Stationary Observations

Over the past decade, the sizes of artificial reefs in Japan have increased, with heights reaching 30 m or more. However, there are few studies about the efficiency of the high-rise artificial reefs, and it is not clear how effectively these reefs gather and nurse fish resources. In these large artificial reefs, it is difficult for divers to view entire schools of fish. We developed a stationary observation system called FISCHOM (fish school monitoring system) to replace or complement visual censuses conducted by divers. FISCHOM consists of a stereo camera, a programmable timer, and a battery in a stainless steel pressure-resistant housing with transparent acrylic glass rated to a depth of 80 m. FISCHOM takes periodic underwater stereo images, and its maximum duration of operation is approximately 2 months when the photographing interval is set to 1 h. By using multiple FISCHOM systems around an artificial reef, researchers can obtain quantitative data on fauna and body size compositions of the reef fish assemblages and their trends. In this study, we will try to describe the possibilities offered by FISCHOM to study the artificial reef fish assemblages. Then, we will show the survey results conducted at a high-rise artificial reef in the Sea of Japan. We describe the advantages and limitations of FISCHOM for observing artificial reef fish assemblages based on the results of the survey.

Quantitative Surveys of Fish Assemblage at a High-rise Artificial Fish Reef by Stationary Underwater Cameras

Stationary underwater cameras were deployed to evaluate spatial and temporal distribution of fish assemblage inhabiting a high-rise artificial reef. The camera named FISCHOM has a stereo camera or a monaural camera on board and it can operate periodically by an arbitrary interval. We can acquire the information about fish fauna and fish size distribution and their time series of reef fish assemblages by the assessment using the FISCHOMs. Two surveys were conducted in the early summer and fall of 2005 at a high-rise artificial fish reef in the Sea of Japan. In both surveys, five FISCHOMs were fixed dispersedly on the reef and operated in an hour interval. As a result, we could evaluate the spatial and temporal distribution of the fish assemblage and their seasonal variations around the reef about 20 days. In total, 48 thousands of fish were counted in both surveys. Pearl-spot chromis Chromis notata notata, jack mackerel Trachurus japonicus, and rockfish Sebastes spp. were mainly observed. We confirmed these major species had stable diurnal cycles; they were observed in daytime and rarely observed in midnight The differences of the spatial distributions of the major species were found by comparing the results of each FISCHOMs. The folk lengths of the major species were estimated by stereo measurements.