Kanmon Strait Research Articles

Abnormal surges and the effects of the Seto Inland Sea circulation in Hiroshima Bay, Japan

The Seto Inland Sea (SIS) is the largest semienclosed coastal sea in Japan and has three connections with the outer seas. When a typhoon approached the SIS in September 2011, spatial variations of sea level elevation were observed across the SIS. Additionally, an unusual sea level rise (abnormal surge) occurred in Hiroshima Bay approximately 8 days after the typhoon passed, with the Itsukushima Shrine in the bay flooded by the surge. To understand the mechanism of the abnormal surge in the bay and the relationship between sea level variations and circulation in the SIS, we investigated the 2011 event by applying a high-resolution numerical ocean circulation model using SCHISM with bias correction for sea surface heights (SSHs) at the open boundary. The overall easterly throughflow due to the west-high east-low SSH pattern in the SIS and temporary SSH disturbances due to typhoons were well reproduced in the model results. Among the three connections, the Bungo Channel mainly determined the overall net flux into the SIS and contributed significantly to sea level variations within the SIS. Additionally, the Kii Channel played more crucial roles in shaping the circulation and local sea level variations. The Kanmon Strait exhibited minor impacts. The abnormal tide in Hiroshima Bay was mainly attributed to seawater flux input from the outer seas, in conjunction with the subtidal internal seiche with the bay. The results will help us to further understand the physical processes of the ocean and establish evidence-based safety plans for reducing natural hazard damage.

Characteristics of Twin-Runner Darreus Water-Turbines for Tidal Current Power Generation

In order to make the electrical-power generation feasible under the lower tidal-current condition the twin-runner Darreus water-turbine was developed. The counter rotations of twin runners are expected to increase the power output. In order to find out the best distance between the runners the wind-tunnel tests using the subscale model were carried out. At the dimensionless distance of 0.18 the rotational numbers were increased up to 156 percent of those at the single-runner configuration. With this distance the water-channel test was also conducted. It was confirmed that the revolution numbers of the twin runners were increased by 20 percents of those in the single-runner configuration. The increasing effect of speed by a diffuser was investigated. At the stand-alone test of a diffuser in the wind tunnel the velocity of the current passing through the diffuser was accelerated by 1.1 of the free-stream velocity, however, in the water-channel test the subscale Darreus model with the shorter diffuser showed no increasing effect. This was primarily because of the short length of the diffuser to the mouth distance, which was determined from the standpoint of the structural efficiency. The demonstrative power generation test is planned at the Kanmon strait in March, 2012.

Detection of Ship Fuel Sulfur Contents in Exhaust Plumes at the Kanmon Straits, Japan, before and after the Global Sulfur Limit 2020

The global limit on the sulfur content of ship fuel was reduced from 3.50% to 0.50% in January 2020 to reduce ship emissions of SO2 and particulate matter. We conducted observational campaigns before and after the new global limit was introduced to detect changes in coastal air quality. We measured ambient concentrations of SO2 and CO2 ship plumes on shore with the sniffing method under the Kanmon Bridge over the Kanmon Straits between Honshu and Kyusyu Islands, Japan, for several weeks in August to September in 2019 and 2020. The fuel sulfur content (FSC) estimated from our measurements mainly varied from 0.50% to 3.00% in 2019, whereas the range narrowed to 0.10% to 0.40% in 2020, showing that all the ships complied. The mean FSC in 2020 was reduced to 16% of that in 2019, which was consistent with the reduction in the ambient SO2 concentration. Sakurai et al.(2021) estimated that after the 2020 global limit was brought in, SO2 emissions from ships were reduced to 24% of their previous values by assuming that all ships have a FSC of 0.50%. Our results indicate the 2020 global limit led to much greater reductions in SO2 emissions from ships than expected.

NUMERICAL SIMULATIONS ON INFLUENCE OF LONG-TERM FLUCTUATION OF MEAN WATER LEVEL ON SAND WAVES IN THE KANMON WATERWAY, JAPAN

In this study, the numerical simulation of tidal current and sediment transport in the Kanmon Waterway were performed by using a numerical simulation model FVCOM (Finite Volume Community Ocean Model (Chen et al. 2003)), in order to discuss the influence of the long-term fluctuation of mean water level on the sand waves. The numerical simulation results suggested that the spatial difference of the long-term fluctuation of mean water level in the Kanmon Straits slightly changes the tidal current around Tanoura Area, and consequently affects the development of sand waves.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/kfMfIVGiLKM

STUDY ON CHARACTERISTICS AND CAUSE OF SAND WAVES IN THE KANMON WATERWAY

The Kanmon waterway is one of the most important international routes in Japan. The waterway is in the Kanmon Strait, which is remarkably narrow and meandering considerably, and the tidal current is rapid and complicated in several places. In the waterway, sand waves, which may hamper the ship navigation, develop on the bottom at some places. The dredging is indispensable to the maintenance of required water depth in the waterway. In this study, for the purpose of accumulating useful knowledge for the efficient maintenance of the Kanmon waterway, the characteristics and cause of the sand waves in the waterway were investigated.

Tidal Power Generation System with Counter-rotating

This paper describes a tidal power generation system with counter-rotating generator. The method of charging is charging current control. The demonstration experiment was conducted by the method using counter-rotating generator and the usual method at Kanmon Straits. They realized following maximum efficiency. However the mechanical loss of the generator’s stator was 3 times larger than rotor loss. Also, in counter-rotating, the stator loss was about 2.5 times the usual. Therefore in order to increase the power generation capacity, selecting a generator that the stator loss is smaller is important in counter-rotating.

日本周辺主要海域のAISデータの現状 : 関門海峡および周辺海域( AISデータの利用と実際)

日本周辺主要海域のAISデータの現状 : 関門海峡および周辺海域( AISデータの利用と実際)

Battery Charging System for Tidal Power Generation

This paper describes a charging system to follow maximum efficiency of the water turbine. It charges a battery with electric power by tidal power generation at Kanmon Straits. The generator is counter-rotating three-phase one and is driven by Darrieus turbine in parallel. The generator output is converted to direct current and the battery is charged. The methods of charging are floating charge and charging current control. We confirmed that floating charge of simple equipment charged 2.7 kWh at a large tidal range period. The charging current control was able to follow the maximum efficiency under more than 0.8 m/s current speed.

Isolation of Lactic Acid Bacteria from Kuruma Shrimp (Marsupenaeus japonicus) Intestine and Assessment of Immunomodulatory Role of a Selected Strain as Probiotic

Fifty-one lactic acid bacteria (LAB) strains were isolated and identified based on 16S ribosomal DNA sequence from the intestinal tracts of 142 kuruma shrimps (Marsupenaeus japonicus) collected from Kanmon Strait, Fukuoka and Tachibana Bay, Nagasaki, Japan. Cellular immunomodulatory function of 51 isolated LAB strains was assessed by measuring the level of interferon (IFN)-γ induction in mouse spleen cell culture. The strain Lactococcus lactis D1813 exhibited the highest amount of IFN-γ production and also bactericidal activity and was selected for testing its immunomodulatory role as a probiotic in kuruma shrimp. We also assessed the effect of dietary incorporation of this probiotic on resistance to Vibrio penaeicida infection in the kuruma shrimp. Our results demonstrate that probiotic L. lactis D1813-containing diet-fed (10⁵ cfu g⁻¹) shrimps displayed a significant up-regulation of lysozyme gene expressions in the intestine and hepatopancreas. However, insignificantly higher expression of anti-lipopolysaccharide factor, super oxide dismutase, prophenoloxidase, and toll-like receptor 1 was recorded in the intestine of shrimps fed the probiotic diet. Moreover, significantly increased (P < 0.01) resistance to the bacterial pathogen in term of better post-infection survival (61.7 %) was observed in the shrimps fed with the probiotic-incorporated diet compared with the control diet-fed group (28.3 %). The present study indicates the immunomodulatory role of the LAB L. lactis D1813 on the kuruma shrimp immune system and supports its potential use as an effective probiotic in shrimp aquaculture.

Acoustic wave propagation and scattering in turbulence and internal waves.

Acoustic wave propagation and scattering in turbulence and internal waves in Kanmon Strait and the outer New Jersey shelf are measured in a bistatic source-receiver configuration at frequency 5500 Hz. While internal wave dominates on the open New Jersey shelf, the turbulence dominates in the Kanmon Strait channel. Initially strong internal wave scattering is reduced rapidly due to strong mixing in the shallow strait. On the flat and open continental shelf, internal wave and warm water intrusion dominate while turbulence is near absent. The parabolic equation code predictions agree with data very well. The bistatic scattering data are processed for bistatic angles and the effects of Doppler shift on the mean flow and the broadening of peek spectra on the turbulent fluctuations. The mean flow and turbulence fluctuation obtained from the Doppler shift agreed with the two parameters obtained by the reciprocal acoustic transmission.

Case Study of the Storm Surges in the Seto Inland Sea Caused by Typhoon Chaba

Typhoon Chaba hit southeastern Kyushu and passed through Chugoku (western part of Japan's main island) on August 30, 2004, causing large storm surges in the Seto Inland Sea (SIS). Record-high storm tides were recorded at tide stations in Takamatsu and Uno Ports. We analyzed the tidal data and simulated this case with numerical storm surge models. The results revealed that the wind setup basically played a key role in causing the large storm surges. Since the time of the maximum storm surge (MSS) approximately corresponded to the time of high spring tide in Takamatsu, a record-breaking storm tide was observed there. However, the MSS occurred not when the typhoon was closest to the city but two hours later. We also investigated the mechanism and the degrees of contribution of the two main factors of storm surges, the inverse barometer effect and the wind setup, in each local area. The results revealed that the peak time of each effect was influenced by geographical features, as well as the wind field and the typhoon position, and had different characteristics in these areas. They also revealed that the Kanmon Strait, which is very narrow and supposed to be negligible in effect, had an important role in sea water inflow into the SIS.

Acoustic wave scattering in turbulence and in internal waves.

Analytical solutions of acoustic wave scattering have been obtained for turbulent currents and for shallow water internal waves. The scattering characteristics of the two are quit different. The most striking difference is that the maximum scattering is in only one direction by turbulence. Whereas there are two directions of maximum scattering in internal waves. In turbulence, acoustic waves scatter quite strongly while internal waves acoustic waves scatter very weakly. Therefore, turbulence changes acoustic wave (coherent) energy rapidly into (incoherent) scattered acoustic energy. The scattering of acoustic energy by internal waves is weak, on the order of 0.001 of that of turbulence. The theoretical results are verified with transmission loss measured in Kanmon Strait and at New Jersey Shelf with good agreements. [Work supported by ONR Code 322 OA.]

Numerical Simulations of Wind Wave Growth under a Coastal Wind Jet through the Kanmon Strait

Abstract The development of a coastal wind jet flowing through the Kanmon Strait and the associated wind wave growth are investigated from a case study on 24–26 July 1999. This study presents a realistic example of fetch-limited wave growth under a developing wind jet outflowing from a terrestrial gap of a coast. A series of numerical simulations are used by one-way coupling between a mesoscale meteorological model and a shallow-water wave model with high spatiotemporal resolutions of 2 km and 1 h. The simulated fields of wind and wave are compared with satellite and in situ observations and it is confirmed that they coincide with observations. A complete picture of the wind jet is obtained from the wind simulations, and wave simulations demonstrate the areal extent of higher waves growing with the development of the wind jet. The wind maximum region is localized and extends downwind. The maximum wave height region is highly localized but located more downwind of the wind speed maximum. The high wave region completely reaches the southern coast of the Korean Peninsula before the strong wind. In the lee of the islands, waves are blocked. The conventional fetch growth of waves holds in waves at the more upwind locations than the highest wave region. The forecasting of localized waves under a coastal wind jet is a case in which adequately high spatiotemporal resolution is required for both the wave simulation and wind input.

Evidence of nighttime movement of finless porpoises through Kanmon Strait monitored using a stationary acoustic recording device

From March 2005 to March 2006, the presence of the finless porpoise Neophocaena phocaenoides in the Kanmon Strait, Japan was monitored using a stationary acoustic event recording device. A stereo acoustic event recorder (A-tag) recorded biosonar signals as well as sound source directions, which can be used to count the number of echolocating porpoises within a distance of 126m. During 75 days of effective observation, 37 porpoises were detected acoustically. On average, one individual was detected every two days. Most of the finless porpoises appeared at night, and no porpoises were observed from 12:00 to 18:00 hours. Shipping traffic observed using the same acoustic system showed trends opposite to that of finless porpoise during the daytime. The tidal current did not affect the presence of the animals. (up to 5.2 knots). However, porpoises were suggested to swim along the current direction. Finless porpoise appeared to be isolated and used relatively long-range sonar during the observations, suggesting that the porpoises passed through the Kanmon Strait rather than searched for prey.

Current structure measurements by the coastal acoustic tomography

The coastal acoustic tomography (CAT), coastal-sea application of deep-sea acoustic tomography (Munk and Wunsch, 1978), is proposed as an advanced technology to map current structures in the coastal sea. A sequence of successful experiments was recently carried out in the coastal seas with various oceanographic conditions around Japan (Yamaguchi et al., 2005; Kaneko et al., 2005; Lin et al., 2005). In the Tokyo Bay experiment of November 2002, the 2-D tidal currents inducing a clockwise residual circulation were mapped by eight CAT systems, located at both the eastern and western coasts of the bay. The vortex-embedded tidal currents with a maximum velocity of 5 ms−1 were targets in the Kanmon Strait experiment of March 2003. In the Hiroshima Bay experiment of September 2003, the stratified sea was shifted to the homogenized sea after the passage of a typhoon. The transition of tidal current structures before and after the typhoon was well measured by seven CAT systems, located at the northern coast and on the southern oyster rafts. The procedure of 2-D current mapping for the coastal seas with depths shallower than about 30 m is well established through a sequence of CAT experiments mentioned above.

Accurate imaging and prediction of Kanmon Strait tidal current structures by the coastal acoustic tomography data

The Kanmon Strait acoustic tomography data acquired at a 5‐min interval are assimilated sequentially into a 2D ocean model on the basis of the ensemble Kalman filter scheme to image strong tidal current structures occurring in the strait. When the accurate range‐averaged currents obtained for the sound transmission lines connecting eight tomography stations are used as assimilation data, the complicated vortex‐imbedded currents are imaged with horizontal resolution and accuracy much better than the result of tomographic inversion. The assimilated currents are well compared to the shipboard ADCP data with a RMS difference of about 24 cm s−1 for both the horizontal velocity components. The assimilated volume transport across the strait also shows a good agreement with the transport estimated from the range‐averaged current on a pair of transmission lines crossing the strait, making a RMS difference of 3700 m3 s−1.

A Continuous Mapping of Tidal Current Structures in the Kanmon Strait

Tidal current structures at the Hayatomono-Seto of the Kanmon Strait are mapped continuously during March 17 to 20, 2003, including a spring tide, by the eight coastal acoustic tomography (CAT) systems distributed on both the sides of the strait. Detailed structures of strong tidal currents and their associated vortices are well reconstructed by the inverse analysis of travel-time difference data obtained from the reciprocal sound transmission between the paired CAT systems located at both sides of the strait mainly. The results are well compared to the shipboard acoustic Doppler current profiler (ADCP) data at the correlation rate of 0.84/0.82 and the RMS difference of 0.47/0.48 ms−1 for the east-west/north-south current after the selection of good data. During the observation period, the maximum hourly mean volume transport for the upper 7 m layer across the strait reached 13,314 m3 s−1 for the eastward and 5,547 m3 s−1 for the westward. The daily mean transport is directed to the eastward and estimated 1,470 m3 s−1 and 2,140 m3 s−1 for March 18 and 19, respectively, when a spring tide occurs.

A Historical Study on Landscape Structures Experienced in Kanmon Straits Region

A Historical Study on Landscape Structures Experienced in Kanmon Straits Region

Current and turbidity variations in the Western part of Suo-Nada, the Seto Inland sea, Japan: A hypothesis on the oxygen-deficient water mass formation

A hydrographic survey and a 25-hour stationary observation were carried out in the western part of Suo-Nada in the summer of 1998 to elucidate the formation mechanism of the oxygen-deficient water mass. A steep thermocline and halocline separated the upper layer water from the bottom water over the observational area except for near the Kanmon Strait. The bottom water, in comparison with the upper layer water, indicated lower temperature, higher salinity, lower dissolved oxygen, higher turbidity, and higher chlorophyll a. Turbidity in the upper layer water changed with semi-diurnal period while the bottom water turbidity showed a quarter-diurnal variation, though the M2 tidal current prevailed in both waters. From the turbidity distribution and the current variation, it is revealed that the turbidity in the upper layer water is controlled by the advection due to the M2 tidal current. On the other hand, the quarter-diurnal variation in the bottom water turbidity is caused by the resuspension of bottom sediments due to the M2 tidal current. The steep thermocline and halocline were maintained throughout the observation period in spite of the rather strong tidal currents. This implies an active intrusion of the low temperature and high salinity water from the east to the bottom of Suo-Nada. Based on the observational results, a hypothesis on the oxygen-deficient water mass formation was proposed; the periodical turbidity variation in the bottom water quickly modifies the oxygen-rich water in the east to the oxygen-deficient bottom water in Suo-Nada in a course of circulation.

船舶間の相対位置の解析

This paper is intended as an investigation of the evasive area around a ship which a navigator would like to keep free with respect to other ships as defined by Ms. Goodwin. Authors assume that the boundary of the evasive area is an ellipse around a certain ship and the distribution of ship's paths is a normal distribution. From both of the theoretical considerations for the evasive area and the radar observations in the KANMON Strait and the KURUSHIMA Strait, it was confirmed that the density distribution of the relative positions of the following ships was represented in the normal distribution with changing σ according to the distance from the preceding ships. Furthermore, it became clear that there was a difference in the size and the shape of the evasive area between the above two observation areas.