Ship Research Institute Research Articles

Forecasting a water-surface wave train with artificial intelligence (Part 2) – Can the occurrence of freak waves be predicted with AI?

In the author's previous paper published under the same title, the author showed that in a water-surface wave train, the peak height of a next-coming wave can be forecasted fairly well with recurrent neural networks (RNN). It has been also shown that the motion peak heights of a floating body in a wave train can be forecasted even better than the forecasting of wave peak heights. As the Part-2 paper, freak events such as extremely large waves or motions that are being reported taking place more often than previously thought are dealt with to investigate if such extreme events could be forecasted in advance with artificial intelligence. Two kinds of wave time series were submitted to the present work. One is that numerically produced in a computer while linearly superposing a certain number of regular waves of different frequencies and amplitudes, in which freak-like waves appeared. The other one is that measured in a real sea collected in a 4-year project conducted by Ship Research Institute (currently National Maritime Research Institute), Japan. By courtesy of the institute, the author could access quite a large amount of digitized raw data of measured wave time series and analyze them in the present study. Quite a few freak-like waves appeared in the data. As the result of the analyses conducted in the present work using the numerically produced wave time series, it has been found that the occurrence timing of freak-like waves as well as their heights could be forecasted well with RNN. On the other hand, the results of the analyses obtained using the wave data actually measured in a real sea suggest the occurrence timing of freak-like waves could be forecasted fairly well with RNN, while the peak heights of freak-like waves predicted with RNN are noticeably lower than their actual heights.

해양플랜트 설비 Corrugated Blast Wall의 폭발 충격응답 인자 특성에 관한 파라메트릭 연구

*The Ship and Offshore Research Institute Pusan National Univer sity, Busan, KoreaKEY WORDS: Explosion 폭발, Corrugated blast wall 파형 방폭벽, Impact response characteristics 충격응답특성.ABSTRACT: More than 70% of the accidents that occur on offshore installat ions stem from hydrocarbon explosions and fires, which, because they involve blast effects and heat, are extremely hazardous and hav e serious consequences in terms of human health, structural saf ety,and the surrounding environment. Blast barriers are integral structures in a typical offshore topside module to protect personnel and safety critical equipment by preventing the escalation of events caused by hydr ocarbon explosions. Many researchers have shown the adequacy of the simple design tool commonly used by the offshore industry for the analysis an d design of blast walls. However, limited information is availa ble for corrugated blast wall design with explosion impact response characteristic s. Therefore, this paper presents a parametric study on the exp losion impact response characteristics of an offshore installation’s stainless steel c orrugated blast wall. This paperalso investigates and recommend s design parameters for the structural design of a corrugated blast wall based on a nonlinear structural analysis of experiential results.교신저자 서정관: 부산광역시 금정구 부산대학로 63번길, 051-510-2415, seojk@pusan.ac.kr본 연구는 2011년 부산에서 개최된 한국해양과학기술협의회 공동학술대회에 발표된 논문을 근간으로 하고 있음을 밝힙니다 .

Slamming of ships: where are we now?

Literature published on the problem of ship slamming in waves is reviewed from the point of view of someone working at a ship research institute. Such an institute is confronted with rather practical questions regarding the acceptability of certain design parameters such as the acceptable amount of bow flare angle for use at sea. The importance of these questions is illustrated by noting that actual slamming or the presumed danger of slamming is the main reason for ship operators to reduce speed or to change heading. The review shows that such questions cannot yet be answered. The problem of the local effect of the impact is very complicated owing to the importance of air inclusions, bubbles in the water, compressibility of water and cavitation effects. Only a computational method properly including all these effects will give an accurate answer; also model tests will not be capable of doing this, if only because the methods to extrapolate the results of models to full scale are not yet developed. The problem of the global response of the ship to a wave impact is closer to being solved. A two-stage approach is proposed, consisting of a computational fluid dynamics method for individual impacts and an approximate method to be included in long-term simulations. However, to arrive at a realistic long-term distribution, one has to account for the seamanship of the captain; avoiding the worst conditions or adapting the ship speed and course has a large effect on the actual extremes. Research on this topic has hardly begun.

Methods for probabilistic safety assessments of ships

At the 62nd MSC conference (MSC62) in 1993, the UK proposed a new methodology for the consideration of safety regulations. This method is called formal safety assessment (FSA). FSA is an application of probabilistic safety assessment (PSA). Risk is used as an index of safety. One of the most important parts of FSA is to evaluate the risk to a ship when it is equipped with the safety measures recommended by the proposed safety regulations. The National Maritime Research Institute (NMRI, formerly the Ship Research Institute) has been developing a method which allows the risk to be obtained holistically by utilizing a scientific method. To obtain the risk, the probability and consequences of every accident must be evaluated. This paper examines the following points: (a) a holistic methodology for risk evaluation; (b) a method used in the process of estimating the probability of collision; (c) a method to reduce the numbers of fire escalation scenarios; (d) a trial risk evaluation of cabin fire.

Analysis of freak wave measurements in the Sea of Japan

This paper presents an analysis of a set of available freak wave measurements gathered from several periods of continuous wave recordings made in the Sea of Japan during 1986–1990 by the Ship Research Institute of Japan. The analysis provides an ideal opportunity to catch a glimpse of the statistics of freak waves in the ocean. The results show that a well-defined freak wave may occur in the developed wind–wave condition: S( f)∝ f −4, with single-peak directional spectra. The crest and trough amplitude distributions of the observed sea waves including freak waves are different from the Rayleigh distribution, although the wave height distribution tends to agree with the Rayleigh distribution. Freak waves can be readily identified from the wavelet spectrum where a strong energy density occurs in the spectrum, and is instantly surged and seemingly carried over to the high-frequency components at the instant the freak wave occurs.

Study of Interaction between Ship Hull and Rudder by Computation

Accurate estimation of not only hydrodynamic forces acting on a ship hull, but also interaction among ship hull and propeller, rudder is essential for the mathematical model of ship maneuverability.In the present paper, the Navier-Stokes code NEPTUNE developed at Ship Research Institute has been extended to compute flows around a ship with a rudder in a maneuvering motion.Brief description of the numerical method is given followed by the comparisons of the computational results with experimental values.Since both the hydrodynamic forces and the interaction between ship hull and rudder show good agreement between the simulations and the measurements, the practical usefulness of the present method has been demonstrated

The performance of buffer bow structures against collision

In order to prevent a disastrous damage induced by collision accident which might cause cargo oil spill from a struck oil tanker, the double hull system in side hull of oil tanker has been recognized as an effective countermeasures. However, when considering that ocean-going vessels are increasing not only in size but also in speed, the threat of disastrous collision accident should be further mitigated also on the responsibility of striking ships. The concepts of buffer bow have been proposed supposing its installation to fast passenger ships in the late 1960s and to large cargo vessels equipped with bulbous bow in the 1990s. RR76 panel of Shipbuilding Research Association of Japan and Ship Research Institute have started, as a joint work, to study the necessary items for the buffer bow structure since 1998.SRI has conducted a series of crush test using three kinds of simplified scale models of the buffer bow. A simple analysis method has been developed to evaluate the crashworthiness of buffer bow structure and its accuracy has been verified by comparing the results with the test and FEM calculation as well. The paper describes the performance of the buffer bow focusing on the collapse mechanism and the P/δ relation, then demonstrates the effectiveness of the present analysis method.

A time-domain mode-expansion method for calculating transient elastic responses of a pontoon-type VLFS

A time-domain calculation method is described for elastic responses to arbitrary time-dependent external loads, on the basis of a general differential equation of second order including the convolution integral related to memory effects in the hydrodynamic forces. The time-dependent elastic deflection of a structure is represented by a superposition of mathematical modal functions, and a Galerkin scheme is employed to obtain a linear system of simultaneous differential equations for the amplitude of modal functions assumed. Special care is paid to numerical accuracy in computing the memory-effect function and the added mass at infinite frequency. The validity of the numerical results was confirmed through a comparison with time histories of the vertical deflection measured in an impulsive weight-drop test conducted at the Ship Research Institute and a comparison with existing numerical results for the same problem. To check the necessity of memory-effect terms, computations using a constant value for the hydrodynamic damping coefficient were also performed, and practical measures for reducing the computation time are discussed.

原子力プラント状態の自動分類機能の開発

For the future autonomous plant, automatic control and diagnostics are being incorporated and operators are mainly engaged in the high levels of diagnosis and decision-making in emergencies. Therefore these matters will be performed through the Man-Machine Interface (MMI). Ship Research Institute has been carrying out the research on the MMI system for autonomous power plants. The automatic classification system of plant states is one of the functions of this MMI and the system utilizes COBWEB, which is known as a way of clustering data to acquire concepts. In this paper, many plant states produced by a plant simulator we examined in order to confirm the effectiveness of this system. The system has well classified plant states produced by a plant simulator.

Interrelationship Among the Long-Term Wave Data Bases

For the design of ships or offshore structures, a reliable database of long-term wave is very import. Nowadays this valuable information is mainly available in three forms : (1) based on visual observation (ship data); (2) hindcast data, such as provided by Ship Research Institute (SRI) and (3) based on wind data, such as provided by Global Wave Statistics (GWS) system developed by N. Hogben et al. in UK. Those different approaches to create the statistical database presents significant differences for the same sea area subdivision and the designer must choose the convenient database for each area. In this work, the long-term prediction and mutual transformation were considered to give the basic information aiming at the unification of those different databases.

Computation of Hydrodynamic Forces acting on a Ship in Manoeuvring Motion

Accurate estimation of hydrodynamic forces acting on a ship hull is essential for the evaluation of ship maneuverability.In the present paper, the Navier-Stokes code NEPTUNE developed at Ship Research Institute has been extended to compute flows around a ship with/without a rudder in a maneuvering motion.Brief description of the numerical method is given followed by the comparisons of the computational results with experimental values.Since both the hydrodynamic forces and the wake flow fields show good agreement between the simulations and the measurements, the practical usefulness of the present method has been demonstrated.

MECHANICAL PROPERTIES OF MODEL ICE

Model testing at an ice tank is an indispensable tool for the design of offshore structures or ships to be used in ice. Model ice is used to represent sea ice at model scale. Mechanical properties of model ice should be properly scaled down from those of sea ice so that results of model testing in ice are of significance. This paper discusses mechanical properties of model ice based on data obtained at the ice tank of Ship Research Institute.

音声入出力を用いた一名当直時の人間を含むシステムの異常対策について

Nowadays, because of the reduction of active sailors and their aging, a navigation support for one person bridge operation (OPBO) is demanded. From 1993, Japan Coastal Tanker Association and Ship Research Institute started to study a navigation support system (NSS) for OPBO. Based on the results of the study, the navigation support system was developed by Mitsubishi Heavy Industries Ltd. In the design and development of the navigation support system, countermeasures for malfunctions of both human and NSS were considered as one of the most important function. In this paper, the systematic countermeasures against malfunctions of both human and the NSS by using speech communication as human machine interface are described.

実験参与船員の意見に見られるTSL飛翔の安全な航行方法

A project of a high speed craft, Techno-Super-Liner had been held and a prototype ship "Hishou" was constructed. A part of final experiment of "Hishou" had been executed to investigate the way of safety navigation of a high speed craft encountering with an ordinary speed ship by Ship Research Institute in 1995. The experiment was done both at sea and on our simulator. We got some subjective evaluation results for safety navigation from participants who had evaluated Hishou's safety on the experiment. Based on their subjective evaluation results, we investigated the way of safety navigation for Hishou in congested sea area and reported it in our last paper of the Japan Institute of Navigation. In this paper we carried out more detailed investigation of the subjective evaluation results. The participant mariners were classified into 3 classes which were ordinary ship's captain, officer and Hishou classes. Their subjective evaluation results were compared among 3 classes. Then it was found that Hishou and the captain classes determined their recognition of the encountering situation severer than the officer's one. As the items which had been used on their judgement of collision danger were examined by Principal Components Analysis, we found differences between captain class and officer class. By comparison between the onboard experiments and the simulators', a simulator was conceded to be an effective tool getting mariner's characteristics. Finally we offered basic criteria of Hishou's safety navigation.

238 自由航走模型船の水中超音波による位置計測システム

Ultrasonic positioning system for free running model ships at the 80m square basin in Ship Research Institute has recently been enhanced with a newly developed signal processing code on personal computer. This positioning system visualizes the trajectory of radio controlled model ship together with time history of her speed, direction, drift angle and turning rate. in time. The accuracy of the positioning is confirmed to be enough for the analyses of model ship motion.

Performance of the Patrol Icebreaker “TESHIO” in Ice-Covered Waters

The patrol icebreaker “TESHIO” was built and delivered to the Japan Maritime Safety Agency in Autumn 1995. Full-scale trials in ice were conducted at the Sea of Okhotsk in February, 1996. Several kinds of test were performed in order to confirm her performance such as continuous ice-breaking, ramming and stopping performance, turning capability and zigzag course manoeuvrability, and coordinated ice-breaking operation together with the patrol icebreaker “SOYA”.While her design and construction were in process, series of model test were carried out both in ice and in ice-free water as the joint research project between Ship Research Institute, Ministry of Transport and NKK Corporation. At the ice model basins of the two organizations, comprehensive model tests in ice were conducted which included resistance and self-propulsion tests in various ice conditions, ramming and turning tests in level ice.This paper describes the results of model and full-scale tests of “TESHIO” and their correlation for both continuous ice-breaking and ramming performance.In order to predict the required BHP for the continuous ice-breaking in level ice, the propulsion coefficient was decomposed into three parts which denote effects of open water characteristics, overload and propulsor/ice interaction, respectively. The thrust deduction coefficient obtained from towed propulsion tests in ice showed very good agreement with that from overload tests in ice-free water. The predicted BHP showed good agreement with the full-scale results when the effect of propulsor/ice interaction was taken into consideration.A prediction formula for ramming penetration distance was devised using an energy-based method. Correlation of both the model and full scale data to the prediction results showed that thrust loss due to the propulsor/ice interaction and the automatic overload protection control of the main engine had much influence on the prediction of ramming performance.

Hot salt corrosion tests results: Report on interim findings

AbstractA series of hot salt corrosion burner rig tests has been carried out at the Ship Research Institute under the sponsorship of VAMAS. The test rig was of ducted type and operated at atmospheric pressure. Three specimens of diameter 10 mm and length 120 mm were mounted at 128 mm intervals along the gas stream. Twenty-four pins were exposed to two different temperatures. The tests were shut down every 7 h for about 24 h and this operation was repeated 15 times. A unique grainy hot salt deposition has been observed to occur within CoCrAlY-coated Rene 80 and alumina pins exposed at 700°C.

Study on the Tension Mooring of the Floating Ocean Structure (4th Report)

Japan Marine Science and Technology Center plans the TLP sea test using a prototype floating offshore structure which has been designed by Ship Research Institute, Japan Ministry of Transport, for the joint at-sea experiments.The TLP sea tests will be excuted in this and next years. The test will be performed to evaluate the performance and reliability of the tension mooring system in the real ocean environment. The site is 40m deep and 3km offshore facing the Japan Sea. The environmental condition is favorable in summer, which allows us very easy installation work. It becomes, however, severe in winter. The prototype floating ocean structure is not originally designed for TLP. Moreover this test structure is made as small as the motions of the structure and the mooring line tensions can be measured in relatively severe sea conditions upon keeping enough stability.The air draft is only 5.5m. Consequently the great waves will crash the upper structure causing shock loads in the tension mooring line. By the 1/40 scale model test the critical wave heigh is proved to be 7.2m. Therefore, the test period during which the sea test can be excuted safely is decided from May till October. The stress check for yielding and buckling is proved that the working stresses under the critical environmental conditions are much less than the allowable stresses.

舶用機関故障のデータバンクとアベイラビリティ向上に関する応用

The basis of all approaches to improving reliable marine engines is to analyze the field data of troubles and failures on marine engines. To this end, a data bank system is developed at Ship Research Institute. The data bank system contains data on ships and their engine failures and troubles. The total number of ships dealt with is 1029 vessel × year. The details of the data bank are described in this paper.Two examples of application of the data bank are stated here. One of them is factor analysis of diesel engine failures by the Irincipal Component Analysis Method. Especially, detecting methods of abnormal states and initial judgments by operators are carefully analyzed as failure factors. The other is a failure map as an engine trouble diagnostic system.

Optimization problems on the reactor shields Part 1: Optimization techniques and models: Kanai, Y. and Ito, Y. (in Japanese) Report of Ship Research Institute of Japan vol 10, no 5 (September 1973) pp 27–48

Optimization problems on the reactor shields Part 1: Optimization techniques and models: Kanai, Y. and Ito, Y. (in Japanese) Report of Ship Research Institute of Japan vol 10, no 5 (September 1973) pp 27–48