|Measurement of Sea Bed Scour around a Pile - Simplified Instrumentation|| This paper outlines a simplified experimental measurement technique for the measurement of scour around pile foundation in laboratories. A suitable instrumentation system has been developed and adopted. Based on the measurements, a relationship for the scour depth in terms of properties of soil, model characteristics and fluid parameters has been proposed. |
Local scouring around any obstruction placed in the ocean bed is a result of the interaction of the local flow field with the sediment particles. The inevitable result "under scour" occurs when fluid flow induced shearing stresses on the sea bed surface reach values exceeding the shearing strength of the soil. There are certain difficulties in predicting the scour depth as the particulate movement is time dependent. Considering the complexity of the problem, an elaborate instrumentation system for measuring scour depth was adopted and used for monitoring the scour with time till the equilibrium profile of the soil bed is attained. A detailed laboratory testing programme on model piles of diameters 50mm to 110mm was carried out in a wave flume of 30m length in 2.0m width in which waves as well as waves superimposed on following current can be generated. Waves of heights from 0.15m to 0.25m and periods from 1.0 to 2.0 sec were generated and the results are analyzed following the standard model laws.
The instrumentation employs wave monitor (Churchill wave monitor) to measure the output which gives the developed scour depth at any instant. The stainless steel probe wires are embedded in the specially made grooves on the model and connected to the wave monitor. The instrument works on the principle of measuring the current flowing through a pair of probe wires of 2.5mm diameter with 10mm apart. Scour caused around the model removes the soil around the probe elements that in turn changes the current flow between the probe elements. Measurement by wave monitor at a particular instant gives output in terms of voltage proportional to the scour developed at that time. The assessment of scour is truly based on the prepared calibration chart showing the relationship between scour depth and voltage.
|A Method to Study Ship's UEF Signatures by Scale-Model Experiment|| Ship's underwater electric field (UEF) signatures are generated by corrosion-protecting equipment on the hull such as impressed current corrosion protection (ICCP) and sacrificial metallic plates (SMP). These signatures are mainly dependent on materials, positions and areas of the metallic plates which constitute anodes and cathodes on the hull. They are also affected by electric polarization on the surface of the metallic plates in the water, which is caused by electro-chemical reaction and related to elapsed time. They are usually measured with UEF sensors installed on the seafloor while letting actual ships cruise on them|
What is suitable and cost-effective to study the dependence of these signatures on metallic plates is to experiment with a use of physical scale models.
We made a physical scale model of s ship with 1/100 contraction and measured its UEF signatures in the water tank. Our originality was to use fresh water instead of seawater in measuring signatures with saturated mercury chloride sensors. As fresh water decelerated the reaction of polarization on the metallic plates, the changes in signatures were observed with various positions on the metallic plates.
|Design and Construction of Marine Structures in Deep and Rough Seas|| The deepest breakwater in Japan is under construction at the mouth of|
Kamaishi Bay, to protect the port area from tsunamis. The Kamaishi Tsunami Protection Breakwater is a unique breakwater that reduces the bay-mouth opening to lessen tsunami run-up height as well as wind waves and swell. This breakwater is also attracting great interest around the world as its 63-meter depth will make it the world's deepest.
After the construction of the breakwater, the opening sectional area of the bay will become only 5% of the original one, consequently, strong currents are generated here when tsunami attacks. Detailed information on the tsunami flow around the opening section is difficult to predict, therefore, experimental studies have been conducted to determine the breakwater design, as well as the method to protect the rubble mound from scouring.
A host of proper technologies to overcome the great depths has been also developed. For example, ĊJRubble-Mound Leveling EquipmentĊJ was developed to replace the leveling work that is conventionally done manually by divers. The combination of this equipment with ĊJRubble-Mound Supply EquipmentĊJ can ensure better safety and improve operational efficiency.
Recent studies have confirmed that the tsunami protection breakwater is effective in protecting the large bay from tsunami attack. In addition, the studies are successful for the estimation of the effective weight and coverage area of the armor blocks to protect the rubble mound foundation against the strong tsunami currents.
It is confirmed that this breakwater will ensure safe navigation for vessels, shelter for commercial fishing, and provide space for marine recreational activities. It is thus expected to contribute greatly to economic growth in the area.
|An Acoustico-Hydrophysical Track of the Shelf Zone of the Japan Sea|| For investigations of the influence of thermoclyne and internal waves on the modal structure of low-frequency acoustic field, at the shelf zone of the Japan Sea near the Gamov peninsula an experimental track was created. The track is equipped by the stationary acoustic source, situated at a depth of 26m, and two vertical acoustico-hydrophysical arrays, installed at the distance 250m (bottom depth is 38m) and 400m (bottom depth is 40m) from the source. The arrays provide for synchronous measurements of acoustic pressure at 8 levels and temperature of water at 5 and 8 levels. The second array is also equipped by 7 distributed temperature sensors, installed between successive thermistors, and near the first array two distributed temperature sensors of the 20m length each are installed. The temporal and digital systems of condensing and transfer of data and used. Decoding, processing and storing of data are performed at a coastal post (the Pacific Oceanological Institute FEBRAS expedition base at the Schultz cape).|
The processing of array data includes its decompositions into the sum of internal wave normal modes (temperature data), computed in long-wave limit without any approximations of the Bussinesq type, and acoustic normal modes (acoustic pressure data). A perturbative approach to the problem of intermittency of temperature data is used in internal wave normal modes calculations. Possible applications to some inverse problems are discussed.
|Liquid-Solid Two-Phase Flow Theory and Its Application|| By using liquid-solid particles tow-phase flow theory and computational fluid dynamics method SIMPLE, a mathematical model is established to investigate dynamic behaviors of two-phase flow, such as, implosion phenomena of a hollow body in a high pressure chamber, and transportation of liquid-solid two-phase flow in pipelines, etc. The flow is considered to be a mixture of a liquid and pseudofluid of solid particles. Furthermore, a computer program is provided to calculate and predict above-mentioned phenomena, and extensive calculations for predicting implosion phenomena are performed under various conditions, the results are shown in a series of plots. Besides, a comparison and analysis with other research results are carried out, and satisfying conclusions are obtained. It is shown that the results of this research can also be used to investigate other specified cases, such as the sedimentation phenomena in hydraulic engineering.|
|Construction of Immersed-Tube Tunnel at Port of Osaka|| The port of Osaka is located at the inner part of the Osaka bay and is developing as an international trade port in Japan. Osakako Sakishima Tunnel was planned in 1985 by City of Osaka and the construction work of the immersed-tube tunnel was executed by the Third District Port Construction Bureau of the Ministry of Transport and opened in October 1997. The tunnel is composed of land tunnel part, immersed-tube tunnel part at the center and ventilation towers at both ends of immersed-tube tunnel part. The total length is 2,200m, and immersed tunnel section is 1,025m. The route of the tunnels passes through the main waterway of port of Osaka, so the space of 400m width and 13m depth had to be secured under the sea for navigational clearance of large sized vessels. Sectional part of immersed-tube is composed of three tubes. The central part includes tracks for subway, while the remaining two tubes are for motor vehicles with two lanes each. The shape of tunnel element is 35.2m width, 8.6m height and 103m length and its weight is approximately 30,000t.|
The tunnel was constructed adopting the following advanced technologies. Steal sheet is used in place of the main reinforcing bar on the outside of the tunnel elements and is integrated with concrete by means of stud dowel. It also discharges the function of waterproofing at the same time. In a tunnel join, the flexible joint system was adopted for resisting against earthquake. In the system the rubber gaskets work as resistance against compressive force and connecting cable against tensile force. Horizontal shear keys on the bottom board work against horizontal shear, and vertical shear keys on the partition walls against vertical shear.
The V-Block system has been newly developed and adopted to this tunnel at first. The system consists in inserting wedge shaped block called V-Block in the final joint of immersed-tube tunnel and putting the caisson in close contact with the existing box by water-pressure joining by rationally utilizing the differential water pressure acting on the top and bottom of the block and the dead weight of the caisson itself.
Facilities for ventilation, lighting and disaster prevention and safety inside the tunnel have been provided; for example, ventilation system (exhauster 3,150mm dia x 4 units x 2 towers) controlled by fuzzy theory, ventilation facilities with dust collector system, power supply system using private power generator in combination with batteries without power failure, monitoring system by color industrial TV camera for monitoring and high-pressure atrium lamp.