Toshihiko Nagai

EXTENSION OF THE MAXIMUM ENTROPY PRINCIPLE METHOD FOR DIRECTIONAL WAVE SPECTRUM ESTIMATION

A special reflecting wall 12 m long and 2.1 m high was built off the beach at Reggio Calabria, and 30 wave gauges were assembled before the wall and were connected to an electronic station on land. It was possible to observe the reflection of wind waves generated by a very stable wind over a fetch of 10 Km. The experiment aimed to verify the general closed solution for the wave group mechanics (Boccotti, 1988, 1989), for the special case of the wave reflection.Significant features on Wadden Sea wave climate are evaluated in respect of the state of the art. Main emphasis was laid on an analysis of the governing boundary conditions of local wave climate in island sheltered Wadden Sea areas with extensions being sufficient for local wind wave growth. Explanatory for significant wave heights a reliable parametrization of local wave climate has been evaluated by using generally available data of water level and wind measurements.

Experiments on wave-soil interaction and wave-driven soil transport in clay beds

Abstract Wavelength and wave damping of water waves propagating over soft clay beds are measured in a soil-wave tank. Mudline motion and wave-induced mass transport in the clay beds are also measured. It is confirmed experimentally that the wave dispersion is uniquely governed by the mudline motion. Mass transport develops in a clay bed when shear strain amplitude exceeds the limit shear strain of about 5%. The rate of wave-induced mass transport in a clay bed is found to be proportional to the rate of wave energy dissipation in the clay bed. This paper presents a complete report of the measurements and data.

OFFSHORE TSUNAMI PROFILES OBSERVED AT THE COASTAL WAVE STATIONS

A study of alternatives including a shoreline evolution numerical modelization has been carried out in order to both diagnose the erosion problem at the beaches located between Cambrils Harbour and Pixerota delta (Tarragona, Spain) and select nourishment alternatives.

Recent Developments of GPS Tsunami Meter foraFar Offshore Observations

A new tsunami observation system using GPS buoys has been developed, which employs the RTK-GPS technique to detect and monitor tsunamis in real-time before they reach the coast. A series of experimental GPS buoys succeeded in detecting three tsunamis with amplitudes of about 10 cm. Following this success, since 2007, the Japanese government has established GPS buoy systems for monitoring sea waves at 19 sites around the Japanese coast. These systems succeeded to detect 11th March 2011 Tohoku-Oki earthquake tsunami. Through these experiences, we recognized two problems that need to be solved in order to deploy buoys at farther distances from the coast: one is that positioning accuracy decreases as the distance increases and the data transmission by radio becomes difficult for a long distance. In order to overcome these difficulties, first, a new algorithm of PPP-AR for real-time application was employed. The test analysis showed that the positioning accuracy may attain a few centimeters even if the reference GPS network that generates precise orbits and clocks is farther than 1,000 km. Then, a satellite communication system was experimentally used to send data in both directions between the land base and buoy. The data that was obtained on the buoy was transmitted to the land base and was shown on a webpage in real-time, successfully. This kind of system may have further applications of earth science; for example, we are trying to implement GPS/acoustic apparatus for continuous monitoring of ocean floor crustal deformations.

DEVELOPMENT OF A SUBMERGED DOPPLER-TYPE DIRECTIONAL WAVE METER

A special reflecting wall 12 m long and 2.1 m high was built off the beach at Reggio Calabria, and 30 wave gauges were assembled before the wall and were connected to an electronic station on land. It was possible to observe the reflection of wind waves generated by a very stable wind over a fetch of 10 Km. The experiment aimed to verify the general closed solution for the wave group mechanics (Boccotti, 1988, 1989), for the special case of the wave reflection.Significant features on Wadden Sea wave climate are evaluated in respect of the state of the art. Main emphasis was laid on an analysis of the governing boundary conditions of local wave climate in island sheltered Wadden Sea areas with extensions being sufficient for local wind wave growth. Explanatory for significant wave heights a reliable parametrization of local wave climate has been evaluated by using generally available data of water level and wind measurements.

ESTIMATION ON THE WHARF OPERATION RATIO OF SHIPS MOORED TO QUAYWALL BY USE OF CONTINOUS OBSERVED WAVE DATA

This paper discusses the wharf operation ratio in a port by use of wave data obtained by Nationwide Wave information network for Ports and HAabourS (NOWPHAS). The observed interval of wave data was twenty minuets of every two hours due to the limitation of data transformation during about thirty years after starting the wave observation in 1970. In recent years, continuous wave data have been observed in the remarkable progress of information processing and communication technology. However, the effect on the wharf operation ratio depending on the difference of wave observation interval was not discussed. This paper thus examines the differences of wharf operation ratio estimated when discontinuous or continuous data were applied, respectively.

DEVELOPMENT OF THE OFFSHORE WIND AND POWER-GENERATION RATE ESTIMATION SYSTEM BASED ON FIELD DATA

A new system was developed to estimate wind velocity distribution around the offshore wind-power generators, by assuming the wind energy conservation equation. Based on the long-term wind and power-generation observed data at the offshore and on-land stations, applicability of the tri-dimensional numerical wind simulation based on the k-e model was confirmed. Interactions among the wind-power generators were estimated by using the numerical simulation, and example of the estimated power generation rate distribution around the existing generators was introduced. It was concluded that wind power generators reduce the wind velocity and wind-power potential of the surrounding sea-surface in the large area more than 5 times of the wind generators diameter.

EVALUATION ON THE WIND SPEED DISTRIBUTION BEHIND THE OFFSHORE WIND POWER GENERATION USED FIELD DATA OBTAINED AT THE PORT OF SETANA

This paper described on the wind speed distribution behind the offshore wind generation by use of the filed observation carried out at the port of Setana and the result of numerical simulation on the wind speed distribution by means of kE model. The profiles of vertical wind speed distribution at the offshore site are examined by use of observed data. And also the numerical simulation model and its parameter n on the ratio of sheltering effect by the wind power generation are examined.

NATIONWIDE COASTAL INFRA-GRAVITY WAVE OBSERVATION NETWORK BASED ON CONTINUOUS DATA SAMPLING AND FREQUENCY BANDED SPECTRUM EXPRESSION

This paper introduces Japanese Nationwide Ocean Wave information network for Ports and HArbourS (NOWPHAS) system, which recently improved for the directional and infra-gravity wave observation with continuous data aquisition. New concept of frequency banded expression has been introduced in the data analysis of directional and infra-gravity waves. Examples are demonstrated as the time series and annual statistics forms observed by the Japanese NOWPHAS system.The NOWPHAS new wave data acquisition and analysis system clarified the characteristics of the long period swells originated from typhoons and low pressures, and the 2001 Peru Earthquake Tsunami.

STATISTICAL WAVE FORECASTING THROUGH KALMAN FILTERING COMBINED WITH PRINCIPAL COMPONENT ANALYSIS

Detailed studies have been undertaken to assist in the design of major extensions to the port of Haifa. Both numerical and physical model studies were done to optimise the mooring conditions vis a vis the harbour approach and entrance layout. The adopted layout deviates from the normal straight approach to the harbour entrance. This layout, together with suitable aids to navigation, was found to be nautically acceptable, and generally better with regard to mooring conditions, on the basis of extensive nautical design studies.Hwa-Lian Harbour is located at the north-eastern coast of Taiwan, where is relatively exposed to the threat of typhoon waves from the Pacific Ocean. In the summer season, harbour resonance caused by typhoon waves which generated at the eastern ocean of the Philippine. In order to obtain a better understanding of the existing problem and find out a feasible solution to improve harbour instability. Typhoon waves measurement, wave characteristics analysis, down-time evaluation for harbour operation, hydraulic model tests are carried out in this program. Under the action of typhoon waves, the wave spectra show that inside the harbors short period energy component has been damped by breakwater, but the long period energy increased by resonance hundred times. The hydraulic model test can reproduce the prototype phenomena successfully. The result of model tests indicate that by constructing a jetty at the harbour entrance or building a short groin at the corner of terminal #25, the long period wave height amplification agitated by typhoon waves can be eliminated about 50%. The width of harbour basin 800m is about one half of wave length in the basin for period 140sec which occurs the maximum wave amplification.Two-stage methodology of shoreline prediction for long coastal segments is presented in the study. About 30-km stretch of seaward coast of the Hel Peninsula was selected for the analysis. In 1st stage the shoreline evolution was assessed ignoring local effects of man-made structures. Those calculations allowed the identification of potentially eroding spots and the explanation of causes of erosion. In 2nd stage a 2-km eroding sub-segment of the Peninsula in the vicinity of existing harbour was thoroughly examined including local man-induced effects. The computations properly reproduced the shoreline evolution along this sub-segment over a long period between 1934 and 1997.In connection with the dredging and reclamation works at the Oresund Link Project between Denmark and Sweden carried out by the Contractor, Oresund Marine Joint Venture (OMJV), an intensive spill monitoring campaign has been performed in order to fulfil the environmental requirements set by the Danish and Swedish Authorities. Spill in this context is defined as the overall amount of suspended sediment originating from dredging and reclamation activities leaving the working zone. The maximum spill limit is set to 5% of the dredged material, which has to be monitored, analysed and calculated within 25% accuracy. Velocity data are measured by means of a broad band ADCP and turbidity data by four OBS probes (output in FTU). The FTUs are converted into sediment content in mg/1 by water samples. The analyses carried out, results in high acceptance levels for the conversion to be implemented as a linear relation which can be forced through the origin. Furthermore analyses verifies that the applied setup with a 4-point turbidity profile is a reasonable approximation to the true turbidity profile. Finally the maximum turbidity is on average located at a distance 30-40% from the seabed.