造船，海洋工学

Flows around ships have various kinds of multiphase flows because ships move at the interface between air and water. The first example is free-surface waves generated by an advancing ship. The phenomenon can be simulated using CFD based on NS solvers, and the comuted wave pattern and the wavemaking resistance agree well with measurements. The second example is wave impact generated at the bow of a ship running in waves. In this example, the flow becomes a multiphase flow type with foams or bubbles. The third example is propeller cavitation, which is an evaporation process at normal temperature. On a full-scale propeller, the cavitation consists of bubbles, which cause erosion in the collapsing stage. The last example is microbubbles for the reduction of frictional drag, the major part of ship's drag. The microbubbles are quite effective in the reduction, but further study is needed for its practical use.

Past tsunami disasters showed us that tsunamis caused various types of damage to wide coastal areas, which were not only inundation but also destruction of houses, drift of vessels and cars, erosion of beach and others. To estimate and understand possible tsunami damage is essential to mitigate tsunami disasters and develop resilient areas and communities. The numerical simulation system named STOC has been developed to estimate tsunami damage to coastal areas in which there are a lot of structures. STOC consists of two fluid models of STOC-IC and STOC-ML and a floating body model of STOM-DM. STOC-IC is a three-dimensional and non-hydrostatic model to calculate the tsunami interacting with structures, and STOC-ML is a multi-layer model with the hydrostatic pressure assumption to calculate the tsunami propagating in the open sea. STOC-DM calculates motion of numerous floating bodies excited by drag, inertia and buoyancy forces, using data of water surface elevation and fluid velocity calculated by STOC-IC and STOC-ML. STOC has been validated in comparison with physical model tests. Furthermore, STOC is applied to an actual port area to estimate what the expected tsunami causes. The estimation results are indicated by a visualization tool developed to present the calculation results for general people in a way easy to understand.

A undersea earthquake with a magnitude of 9.0 "The 2011 off the Pacific Coast of Tohoku earthquake" took place off the Pacific coast of Japan at 14:46 JST (5:46 UTC) on March 11, 2011. A massive tsunami caused by the earthquake struck the Pacific side of Japan, especially the coasts of Aomori, Iwate and Miyagi prefectures, resulting in a cataclysmic disaster "East Japan Great Earthquake Disaster (Higashi Nihon Daishinsai in Japanese)". This paper describes the fundamental characteristics of Tsunami and the brief overview of the past huge tsunami disasters in Sanriku area. The tsunami damages of the East Japan Great Earthquake Disaster are, furthermore, reported on the base of the field survey, which was conducted from April 4 to 9, 2011 as a group of the 2011 Tohoku Earthquake Tsunami Joint Survey Group of Japan.

At 14:46 local time on March 11, 2011, a magnitude 9.0 earthquake occurred off the coast of northeast Japan. This earthquake generated a tsunami that struck Japan as well as various locations around the Pacific Ocean. With the participation of about 300 researchers from throughout Japan, joint research groups conducted a tsunami survey along a 2,000 km stretch of the Japanese coast. The inundation height and run-up height were surveyed by laser, GPS and other instruments. Based on the survey dataset, the regional and local scale analyses were conducted to understand the basic characteristics of this event. The survey data are shown with photograph and are discussed about magnitude of damage and tsunami event.

On March 11, 2011, at 14:46 local time, a powerful earthquake occurred off the Sanriku coast of northeastern Japan. It was immediately apparent that this was the strongest earthquake on the historical record, and the resulting series of tsunami ravaged the Tohoku region. In Iwate Prefecture, the tsunami height generally exceeded the design tsunami level for safety, which had been determined on the basis of the Meiji-Sanriku tsunami (1896), the Showa-Sanriku tsunami (1933), and the Chile tsunami (1960). As of Jan. 30, the number of dead and missing in Iwate rose to 5993. Over 24,000 buildings had been destroyed. After the Showa-Sanriku, disaster prevention facilities were built along the coast. However, many tsunami seawalls and water gates suffered enormous damage from the impact of the 2011 Tohoku Tsunami. This paper sketches out the characteristics and scope of the damage in the coastal areas of Iwate Prefecture.

Recently an air lubrication method (ALM) has been recognized as one of promising techniques to save energy in naval engineering. In the present article, a brief introduction of ALM in naval architecture is presented. Since ALM requires the additional power to inject air bubble beneath the ship bottom, an air supply method with much less energy consumption should be a key technology to make ALM be promising method for large ships. A scavenge gas bypass method is proposed as one of breakthrough technologies. In the article, recent application of ALM to large commercial ships, including the scavenge gas bypass system, is introduced.

Developments of natural resources in the Arctic region are becoming active in the recent years. Commercial use of the northern sea route is taking on realness with a decrease of sea ice area along the Arctic coast. Also Arctic and Antarctic observation is important to clarify a global climatic change. Icebreakers are indispensable to the support for the development, the escort for cargo ships and the polar observation in ice-covered waters. The technology on icebreaker's performance is improving steadily, responding to those missions. This paper shows the typical characteristics of icebreaker and introduces several technologies to improve the performance.

This introduction contains the history of building very large crude-oil carrier (VLCC) at IHI Marine United Inc. (IHIMU), the outline of present VLCC “Idemitsumaru” and environmentally friendly ship of “eFuture 310T” developed by IHIMU. The “eFuture 310T” was developed so that 30% reduction of GHG is attained by integrating the technology of IHIMU such as advanced contra rotating propeller, tip raked propeller, rudder bulb and semicircular duct, waste heat recovery system, whaleback bow and air resistance reducing vane.

Applications of multi-phase flow technologies to clean marine engineering are introduced. Large efforts have been made to reduce CO2, SOx, NOx and Particulate matter (PM) emissions from marine diesel engines. Urea Selective Catalytic Reduction (SCR) system is one of the most promising technology to largely reduce NOx emission. PM in exhaust gas may deposit on a honeycomb SCR catalyst, which increases pressure drop, blocks the flow area and decreases NOx reduction performance. Air blow (soot blow) can be effective for removing PM on a catalyst. An experimental investigation confirms that (1) large pore diameter of SCR catalyst and optimum exhaust gas velocity prevent PM accumulation, (2) PM accumulates mainly at the inlet and exit of the catalyst, and (3) high pressure soot blow removes PM.

The authors have created new type of electric boat “RAICHO-S” in 2011. The craft has some special and unique features that set it apart from existing electric boats or battery-powered boats. First, she utilizes a lithium-ion battery with plug-in system or a rapid charging system. A dockside-mounted rapid charger can bring the boat’s battery up to 80% of full charge within 30 minutes, which is a much shorter time than is possible under conventional charging systems. The boat can operate for 45 minutes and berth for 30 minutes in a cyclic operation. The powerful lithium-ion battery gives the boat a running speed capability of around 10 knots, enabling it to navigate not only in flat-surface waters but also in open sea conditions where wind and waves prevent operation by conventional battery-powered craft. “RAICHO-S” utilizes a water jet propulsion system driven by electric motor whose advantages are safety for the diver, passing floating rope on fish preserve, environmental reservation (no-damage on leafs, fishes, and aquatic plants) and causing no cavitation. The disadvantage of water jet driven by combustion engine in low efficiency and low maneuverability at low speed can be overcome by use of electric motor.

The present paper reports the fundamental research for the sterilization treatment of marine bacteria contained in ships’ ballast water. In the field of maritime sciences, destruction of marine ecosystem caused by sea creatures carried in ships’ ballast water to different seas is a serious international problem. In order to solve the problem, a new sterilization technique using shock wave and microbubble is proposed to develop more secure and environmentally friendly treatment method for ships’ ballast water. This method applies mechanical and chemical effects of shock pressures and free radicals generated by contraction and collapse of microbubbles to marine bacteria. Our previous and ongoing works are presented and prospective approaches that need to be solved the problems are described.

East coasts of Hokkaido, facing Okhotsk Sea and Pacific Ocean, are covered by sea ice drifted from northern Okhotsk Sea in late January through early of March. When tsunami occurs during the term and arrives at the ice-covered coasts, the disaster risks are significantly increased since ice floes carried by run-up tsunami can extend the possible damages through distinct dynamic behaviors occurring in ice-floe-laden flows; that is, forming pile-ups and jams of the ice floes, and enhancing ice and hydraulic forces. In this paper, features of the previous damages to residences and infrastructures by sea ice for the 1952 Tokachi-oki tsunami and the 2011 Tohoku tsunami are firstly discussed for charactering the ice-structure interactions. The fracture mechanisms of the ice floes colliding to structures during jamming and piling-up processes are identified on the basis of model experiments as well as numerical computations using a 3D Distinct Element Method. We also find structures with openings, such as windows and space between columns, induce ice jams and pile-ups and dam up the run-up flows, resulting in downstream water level rise and thus significant increase of hydraulic pressure acting on the structure, which indicates the increased risks expected in urban area.

Tsunami-induced local scouring at the landward toe of a coastal dike and the effectiveness of countermeasures to improve its tenacity are investigated using a numerical model that considers fluid-sediment-seabed interactions. From a comparison between experimental data and numerical results, the predictive capability of the model is demonstrated in terms of water surface elevations and final scour profiles. From the numerical results, it is found that armor blocks below the crown and berm of the landward slope of the dike receive large landward and upward force because of an increase in air pressure inside the dike and a decrease in water pressure induced by flow separation, suggesting that these blocks would be vulnerable against tsunami overflow. The numerical results also show that protection blocks covering the landward side of the dike move the scouring area landward and reduce its maximum depth, suggesting that they would be effective to extend the time before beginning the damage of the body of the dike.

Drag reduction using bubbles are now in operation for marine vessels, and recorded significant fuel saving. Beside it, fluid mechanics inside high-speed bubbly turbulent boundary layer is highly complex. Efforts by scientists and engineers in Japan straggled in the last 30 years and recently reached the goal. They found further potential of technical improvement with recent experimental discovery on bubbles’ organizing behaviors.

Breaking waves entrains huge amounts of air bubbles into bulk seawater, which is involved in turbulence produced in splash-up breaking processes. Buoyant bubbles arriving wave surfaces aggregate to form clusters behind the wave front (so-called whitecap). While a series of the bubble dynamics are believed to be relevant to air-sea momentum transfers and gas exchanges, microscopic bubble behaviors on whitecap water surface in wave breaking turbulence have not been understood. This article introduces previous research progress on mechanical interactions between bubble and turbulence in bulk water under breaking waves, interactions of rising bubble with water surface in addition to interactions among bubbles floating on surface resulting in formation of whitecap water.