¹MCA Engineers, Inc. Costa Mesa, California, USA

Mcheung@mcaengineers.com

　

²Marathon Oil Company Houston, Texas, USA

MJHiggins@MarathonOil.com

　

The two sister LNG tankers built by Ishikawajima-Harima Heavy Industries Co. Ltd. for Marathon Oil Company in 1993 were retrofitted with MCA's Hull Monitoring System (HMS) in 1996. These identical tankers have an overall length of 239 m with full load displacement in excess of 72,000 MT. They take turns carrying LNG from Nikiski, Alaska for delivery at Tokyo Bay, Japan. Annually, each ship makes about 34 one-way trips. Each one-way trip takes about 8 to 9 days for crossing and one day for cargo transfer. Since they trade along the Northern Pacific route, it is very treacherous in the winter months. The motion sensors from the HMS alert the deck officers about bow slamming, which can be detrimental to the ship's structure. The stress sensors allow the engineers to reconstruct the material fatigue damage experience in each trip. As a whole, the HMS gives the deck officers some scientific tools to navigate the ships safely, expeditiously and with minimal structural damages. The HMS also gives the engineers in the office more accurate information when performing finite element analysis of the ship structure.

　

In recent years, the software of the HMS was improved to monitor performance. Coupling the motion sensing with the pressure reading at the bottom of the bow, the instantaneous wave height can be determined. Every five minutes, a statistical Sea State is calculated. This has been proven to be accurate and consistent as observed by the crew. More importantly, we can re-construct the statistical wave properties for the past years. This helps define the level of fatigue resistant requirement for future ship designs that trade in this territory. The HMS further calculates the hull resistance, the total Power Consumption and Unit Power Consumption. It was discovered over the three years span, that one ship used significantly more fuel than the other, although these vessels have the same design, carry the same load and travel the same route. With this new tool, we hope to find a reasonable explanation. At the very least, we anticipate we will be able to use the HMS to trim off a little percentage of fuel consumption without sacrificing the safety and expedience of the operation.

　

　

Offshore Structures Division, Port and Airport Research Institute Yokosuka, Kanagawa, JAPAN

iijima@pari.go.jp

　

Drift force on floating structure is one of the important factors from the viewpoint of structural design of moorings. In this study, drift forces on large semi-submersibles both in regular waves and in irregular waves are numerically studied. Characteristics of drift force on multiple columns of various numbers are investigated. Starting from normal size semi-submersible supported on four columns, the number of columns is increased up to 320. First, the characteristics in regular waves are clarified. Then, the drift force on multiple columns in irregular waves is investigated. So far, approximate methods such as Hsu's method or Newman's method has been used for estimation of slowly varying drift force on floating structure in irregular waves due to their simplicity. However, there remains a question if these methods can be extended to large semi-submersible case. The author proposes an alternative direct method in which the second order terms of the pressure are directly integrated on the wetted surface of the columns under irregular wave condition. It is shown that Hsu's method, Newman's method and the direct method give almost the same results for the normal size semi-submersible. The direct method is extended to large semi-submersible case. It is shown that Hsu's method and Newman's method overestimate the slowly varying drift force on large semi-submersibles in irregular waves although they coincide as for the steady drift force term. For example, Newman's method estimates slowly varying drift force on 320 columns approximately five times as much in amplitude as the direct method does.

　

　

Department of Oceanic Architecture & Engineering College of Science & Technology, Nihon University Funabashi, Chiba, JAPAN

yasu@post.ocean.cst.nihon-u.ac.jp

　

For the structural design of floating architectural buildings on that various kinds of environmental loads, the design has to be done so as to save structural safety for dynamic response concerning to stress, deformation and motion as well. Even if structural safety of buildings was saved, there is possibility that the exceeding oscillation or vibration of the buildings caused by environmental loads which is uncomfortable to human, will lose the habitability and workability. Therefore, the structural design to be considered the physiological and psychological influence giving to human body becomes necessary in the vertical/horizontal motion of floating structure in particular.

　

The object of this paper is to study evaluation of habitability for floating-type oceanic architectural buildings. After having reviewed several standards such as ISO (International Standard Organization) describing about vibration and vertical motion, guideline for buildings vibration in Architectural Institute of Japan and others, we will propose evaluation method of habitability in vertical motion for floating-type oceanic architecture building. Using acceleration and frequency, three comfortable states of living level, office work level and work level in the evaluation of habitability has been set. Furthermore, we calculated acceleration response of floating structural model by significant average wave in Tokyo Bay, and plotted those results into the obtained figure in order to examine the validity of calculation process and evaluation by three states.

　

　

¹Department of Oceanic Architecture and Engineering, Nihon University Funabashi, Chiba, JAPAN

kshingu@shinguu2.cs.cst.nihon-u.ac.jp

　

²Graduate School of Science and Technology Department of Oceanic Architecture and Engineering Nihon University, Funabashi, Chiba, JAPAN

　

³Nihon University Tokyo, JAPAN

　

This study is on second drawing and fixing technique in the construction of large floating structures represented by the Mega Float. Constructing a large floating structure, many units are made in dock and towed to the settle region first. Under the influence of waves at sea, the units are jointed and combined to become a large floating structure. Existing methods of second drawing and fixing include some problems: for instance, "horizontal induction and mechanical combination method" includes two operations, i.e., drawing by using jacks and wires and fixing using distribution plates. This method needs large-scale steel pipes, which makes operations complicated. "Draft difference method" takes much time in arranging draft to be in a right condition. Waves may cause damage by the collision of decks and floating bodies' bottoms in second drawing. As to "hinged method", once hinges are welded they cannot be reused and be wastes.

　

To solve these problems and improve safety and construction efficiency, a new technique of joint device and joint method on sea using shape memory alloys are proposed in this study. Shape memory alloys have, distinct from ordinary metals, characteristics of shape memory effect and super-elasticity controllable by temperature.

　

This paper reports the results of joint experiment using floating body models with joint devices that make it possible to combine two remote floating bodies by drawing each other against disturbance of waves, controlling stiffness and transformation of shape memory alloys continuously by Joule heat of electric conduction in the alloys.

　

　

¹Institute of Oceanic Research and Development, Tokai University Tokai, JAPAN

tsuruya@scc.u-tokai.ac.jp

　

²Yokohama Research and Engineering Office for Port and Airport Kanto Regional Bureau Ministry of Land, Infrastructure and Transport Yokohama, Kanagawa, JAPAN

　

³Coastal Development Institute of Technology Chiyoda-ku, Tokyo, JAPAN

d_furuta@cdit.or.jp

　

⁴Kobe Research and Engineering Office for Port and Airport. Kinki Regional Development Bureau, Ministry of Land, Infrastructure and Transport

　

⁵Nagoya Research and Engineering Office for Port and Airport. Chubu Regional Development Bureau, Ministry of Land. Infrastructure and Transport

　

During assistance and restoration activities following the Hyogoken-Nanbu Earthquake Disaster, marine transportation and ports played an extremely important role as ships delivered cargo and personnel to the devastated region. The Ministry of Transport has applied this lesson to provide floating disaster prevention bases in three bays: Tokyo Bay, Ise Bay, and Osaka Bay.

　

A floating disaster prevention base is a marine structure used as a disaster prevention base by taking advantage of the merits of its floating structure: its earthquake resistance and the fact that it can be easily moved from place to place. At normal times, it is used as a floating pier, and when a disaster has occurred, it is towed to the disaster region to be used to unload cargo and personnel. For this reason the three constructed provide 4 functions: [1] mooring for a 1,000 DW class cargo ship, [2] a heliport, [3] interior storage space for cargo, and [4] a mooring structure that can be attached to and detached from the base.

　

This report is an outline of the design condition organization procedure and the structures and functions of each floating disaster prevention base.