Seakeeping Criteria Research Articles

Seakeeping criteria of a moored and articulated multibody floating platform in head seas

Within the Space@Sea project, a multi-use floating concept was proposed by following the analogy of standardization to enlarge a floating platform using a multitude of smaller structures. An operability analysis must be performed to identify its seakeeping criteria and how the criteria limit its functionality. A two-step strategy is proposed to calculate the responses of the target floating concept in head waves, where nonlinearities of the mooring lines and mechanical joints are taken into account. The weakly nonlinear time-domain procedure relies on a diffraction-radiation model in the frequency domain. The motions of floating bodies are solved in the time domain, in which nonlinear Froude-Krylov and hydrostatic forces are estimated under instantaneous incident wave surface. Multibody interactions are resolved under consideration of catenary mooring lines and hinged joints. Wave-induced motions and loads are expressed in terms of transfer function for determining the limiting criteria, including the translational and rotational motions velocities and accelerations; relative motions, velocities and accelerations between module floaters; mooring tensions; as well as hinge forces. Assessments are carried out for various sea conditions against the prescribed values, for the chosen criteria, to address safety issues due to sever platform responses. Different operational requirements for trained workers and untrained passengers of motions and accelerations are taken into consideration. Results show that rotational motions have a significant influence on the platform’s seakeeping performance. Nevertheless, the root mean square (RMS) value of vertical acceleration dominates the comfort of persons onboard, defining the final limiting criterion of the entire platform.

OPERATIONAL BEHAVIOUR OF AN OFFSHORE MULTIPURPOSE SUPPORT VESSEL IN THE EASTERN MEDITERRANEAN SEA

The objective of this work is to analyse the operational behaviour of an offshore multipurpose support vessel designed to operate in the Eastern Mediterranean Sea. First, the seakeeping analysis is performed in a regular wave condition for different heading angles estimating heave and pitch motions through the strip theory. After that, the effects of the vertical acceleration on the bow, occurrence of slamming or hydrodynamic impact of the hull on the surface of the water; wetted deck, occurrence or invasion of water on the deck of the vessel and propeller emersion, motion sickness and wave-induced additional resistance are analysed. The present analysis is extended in an irregular sea condition, and the estimated seakeeping criteria are compared to the acceptable levels. In defining the most suitable operational mode of the offshore support vessels, multi-criteria decision techniques and probabilistic approach are employed to perform an adequate evaluation of the seakeeping performance accounting for different hazardous events through the service life.

Resistance Analysis of Rescue Boat in Calm Water Condition

Search and rescue operations, especially in ship accidents, require speed and reliability from the rescue vessels in facing the challenges of extreme weather and sea waves. A rescue boat hydrodynamic performance study is very important to be carried out in order to determine the ship’s ability to withstand dangerous conditions while in operation. A combination of using Maxsurf and CFD method are implemented to estimate the resistance of 3 (three) selected designs of crew boat, which demonstrated a good agreement between the two techniques. Selection of the final design also uses seakeeping criteria, i.e. having lower pitching and rolling responses. The final model is further tested in a towing tank belongs to the Institut Teknologi Sepuluh Nopember (ITS) and agrees well with Maxsurf and CFD calculation.

Review of the seakeeping criteria for the study of a passenger ship criteria in Indonesian water

The human sickness of the ship’s crews and passengers is considered as main requirements to be fulfilled in ship design stages which is related to the performance of ship motion when operating in seaway. This paper describe review some seakeeping criteria which are published by several institutions for the purpose of ship safety and comfort. Since these criteria were initially issued based on extreme sea conditions, it is necessary to study if they are applied to relatively moderate sea conditions in Indonesian. For this reason, a new approach is proposed to deal with a new criteria by measuring motions directly on the ship in operation. Briefly method is described as first, the ship motion in 6 degrees of freedom is measured by sensors which is installed in a particular place on the ship’s board, for which the data generated include an angular velocity, a vertical and a tranversal accelerations of motions. Second, Fast Fourier Transform (FFT) algorithm is adopted to process the measured data which are presented in the form of time series and spectrum diagrams, and the Power Spectral Density (PSD) method is also used to eliminate nois data. Third, the ship motion criteria for the case of the passenger ship is determined and it compare to the existing criteria.

Determination of a DP operability index for an offshore vessel in early design stage

For an offshore vessel, it is common practice to evaluate the ship's operability considering working criteria inherent to motions/accelerations in several operative conditions. However, to an offshore vessel, it is also required to keep an assigned position and heading during operations or in a rough sea. Station keeping and seakeeping problems are not usually considered as part of the same analysis, mainly because the station keeping issues are mostly related to surge, sway and yaw, while seakeeping deals more with heave, roll and pitch. It is also possible to perform combined analysis, determining seakeeping criteria for dynamic positioning (DP) due to ship motions, and use it as effective limiting environmental criteria for capability plots. In any case, even though seakeeping operational criteria are probably more restrictive than DP ones, it can be useful to investigate the effective operability of the DP system, considering all the possible wind wave combinations, the vessel can encounter during his operational life, together with the sea current. For this purpose, an enhanced and innovative procedure to establish the effective DP operability of an offshore vessel has been developed, by explicitly considering the vessel geographic operational area. The procedure has been tested on a pipe-lay vessel (PLV) and compared with the standard DP calculations, considering all the possible failures requested by regulations. Differences obtained from the comparison are significant and constitute a matter for further discussions.

On operation capabilities analysis of a 100000 tdw tanker by seakeeping criteria

The operation capabilities of a maritime ship have to be assessed during the design, including the seakeeping criteria. In this study a 100000 tdw tanker is considered, with two loading conditions, cargo and ballast. The numerical analyses are developed with our own software DYN, module OSC, based on a linear hydrodynamic strip theory. The main oscillation components, heave, pitch and roll, are considered. The analysis includes an extended parametric study for the tanker speed up to 15 knots, different vertical positions of the gravity centre, a heading angle full range and irregular waves significant height up to 12m. Also the seakeeping limits have two sets of criteria. The results are pointing out the operation limits of the tanker on combined navigation parameters in irregular waves, by motions and acceleration short term seakeeping criteria.

Operational Behaviour of an Offshore Multipurpose Support Vessel in the Eastern Mediterranean Sea

The objective of this work is to analyse the operational behaviour of an offshore multipurpose support vessel designed to operate in the Eastern Mediterranean Sea. First, the seakeeping analysis is performed in a regular wave condition for different heading angles estimating heave and pitch motions through the strip theory. After that, the effects of the vertical acceleration on the bow, occurrence of slamming or hydrodynamic impact of the hull on the surface of the water; wetted deck, occurrence or invasion of water on the deck of the vessel and propeller emersion, motion sickness and wave-induced additional resistance are analysed. The present analysis is extended in an irregular sea condition, and the estimated seakeeping criteria are compared to the acceptable levels. In defining the most suitable operational mode of the offshore support vessels, multi-criteria decision techniques and probabilistic approach are employed to perform an adequate evaluation of the seakeeping performance accounting for different hazardous events through the service life.

Dynamic response investigation of a small size floating dock unit in irregular oblique waves

The floating dock units, according to the operation schedules, from time to time have to be relocated to different shipyards, involving river or costal routes. In this study, the dynamic behaviour of a small size floating dock during relocation is analyzed, with two constructive types of the floating structure above the dock pontoon deck and a maximum length of 60 m. By the floating dock and tug ship system resistance prediction, results a maximum towing speed around 18 km/h (9.72 kn). So, the numerical analysis is carried on for a set of five speed values, between 0 and 18 km/h. The dynamic response in irregular waves of the floating dock, full heading angle set, is computed by own program code. The irregular waves intensity is prescribed in terms of statistical wave significant height, with the maximum values corresponding to the Lower Danube River way and the Black Sea Coastal on Romanian area. The statistical dynamic responses, in terms of motion and acceleration significant amplitudes, are checked out against the short-term seakeeping criteria, in order not flood the dock pontoon deck. The study results are pointing out the limit navigation conditions for safety during the small size floating dock relocation operation.

Seakeeping Performance Estimation of the Container Ship under Irregular Wave Condition Using Artificial Neural Network

In the current study, sea keeping performance of the S-175 container ship is estimated under irregular wave conditions by using numerical calculation and artificial neural networks (ANNs). For this purpose, strip theory is employed to calculate of the response amplitude operator (RAO) and wave resistance. Then, the RAO of heave, pitch, and roll motions and added resistance are used in the considered ANN. In our calculation, the ship dimensions are changed at the same displacement and body form. By comparing the RAO diagrams and according to survey seakeeping criteria, optimum hull is determined for seakeeping performance. In addition, predictive equations based on length of vessel (L), the breadth (B), draft (T) and wave encounter angle (μ), are presented to estimated of seakeeping performance by using ANN.

Optimizing Trimaran Yacht Hull Configuration Based on Resistance and Seakeeping Criteria

An investigation into the optimization of a trimaran yacht, which is equipped with axebow, was carried out numerically. The study was focused on the analysis of resistance and seakeeping which can provide the best performance to the yacht, based on those two criteria. The numerical study used Ansys Fluent code for resistance analysis and seakeeper from Maxsurf for seakeeping analysis. The overall results were compared with published data for validation purposes. The results are believed to be useful for the development of the marine-tourism, which is now growing quite rapidly in Indonesia.

Prediction of the dynamic responses for two containerships operating in the black sea

This work presents a methodology for the evaluation of the vessels operability in the basin of the Black Sea. The approach proposed is based on the results provided by a wave prediction system that was implemented and validated in the Black Sea. This offers a meaningful framework in the assessment of the seakeeping performance for ships operating in different conditions. The aim of the work is to improve the seakeeping performances for various types of ships that sail in the Romanian coastal zones. Two containerships are considered, of 1300TEU and 800TEU respectively, which have however the same displacement. For predicting the ship motions induced by the various wave conditions encountered in the operational area, it is necessary to know the transfer functions for different ship speeds and heading angles. These are computed with a numerical code based on the strip theory. The predicted motions are then compared with the limit values of the relevant seakeeping criteria, considered as the criteria for checking the operability of the ship. By defining the acceptable operating boundaries, the ship behavior in waves can be quantified. The vessel meets the criteria for those combinations wave height-wave period that are below the limit curves. The results are presented as operational maps for the Black Sea basin, allowing the identification of the areas that should be avoided due to unfavorable weather conditions. The methodology proposed herewith can be extended and applied to various marine environments and types of ships.DOI: http://dx.doi.org/10.3329/jname.v11i1.17289

Forecasting fishing vessel responses in coastal areas

A system for forecasting the operability of ships was developed by extending a wave forecasting system with the ship responses to the forecast sea states. The system produces 4-day wave forecasts in an implementation for the Portuguese Exclusive Economic Zone, where the vessels’ seakeeping performance is forecast, although the method presented could well be applied to any other coastal region. The proposed procedure requires the knowledge of the transfer functions for different ship speeds and headings. The computations are made for two different types of fishing vessels that currently operate in the Portuguese coast. Ship motions and derived responses are evaluated with a strip theory code and compared with the prescribed values of relevant seakeeping criteria that represent the limit conditions that still allow standard operational conditions for those vessels. For each forecast sea state at each grid point at a given time, the response spectrum is calculated and operability indexes are computed and compared with the maximum allowed values for a specific operation criterion. The results are presented as operational index maps for various areas of the Portuguese coast, and the information provided by system will help ship masters to plan the operation of their ships, namely to decide the areas to operate in anticipation. In this way, they can identify areas in which the level of operationally of their ships will be degraded due to weather conditions and avoid them.

Minimum ship size for seakeeping

This paper describes a computational procedure to determine the minimum ship size to achieve the required seakeeping performance for a given design speed in a specified sea state. The procedure contains four basic elements: a procedure for representing alternative hull form designs with various sizes, a procedure for predicting the seakeeping performance of a given design, a non-linear direct search procedure and a user interface to provide the objectives and the constraints of the problem. The seakeeping performance of the ship in a specified sea area is expressed as a function of the ship size. A non-linear optimization problem is then formulated and solved by using non-linear direct search techniques. The objective is to find the minimum ship size satisfying given seakeeping criteria for a given design speed in a specified sea state. A typical example of determining the minimum dimensions for a patrol boat design is presented. The resultant design is shown to be the smallest vessel that could operate without violating the given set of seakeeping criteria.

Seakeeping performance of fishing vessels in irregular waves

A study of the seakeeping performance of a set of fishing vessels is carried out aiming to identify the seakeeping criteria, and vessel conditions that limit the operability of the fishing vessels in certain sea states. Ship motions and derived responses are obtained in fully developed sea states using the transfer functions of the hull forms. Those responses are assessed against the prescribed values, for the chosen criteria, to determine the vessels operational conditions that might result in hazards or seasickness. For the purpose of this study, each fishing vessel is considered operating in sea states 5 and 6, with different Froude numbers and heading angles, and their short term responses are assessed against the most relevant criteria related with the absolute and relative motions, accelerations, slamming and green water on deck. The results obtained show that roll and pitch criteria are most critical for seakeeping performance, and there is a significant influence of the transverse metacentric height, GMt, and the location of the reference checking points in the seakeeping performance of these fishing vessels.

실습선 한바다호의 운항성능에 관한 연구(I) -선체감시장치(HMS) 계측 데이터를 이용한 내항성능 평가-

최근에 선박이 대형화, 고속화되면서 선수 충격파 영향으로 인하여 선체 또는 화물에 잦은 손상을 초래하기도 하고, 극판적인 상황에서는 선박이 절단되기도 한다. 본 논문에서는 내항성능 평가요소 중 하나인 상하가속도 값을 선교에 설치된 선체감시장치를 이용하여 해상상태별 변화량을 계측하고, 이를 모형시험 및 이론계산 결과와 상호 비교하였다. 또한 ITTC에서 제시하는 내항성능 기준치와도 비교함으로써 실습선 한바다호의 내항성능을 확인하였다. 이러한 결과는 앞으로 경험할 수 있는 다양한 해상상태에서의 작업가능성 및 위험성 정도의 예측을 가능하게 함으로써 선박의 안전운항에 큰 도움이 될 것으로 판단되며, 또한 다양한 실선계측 자료를 통하여 조선소에서는 보다 우수한 성능의 선박 건조가 가능하리라 본다. As the ship is getting bigger and faster lately, ship's structure or cargoes might be often damaged and the ship might be cut in two in extreme conditions by a wave impact on its bow. In this paper, the vertical acceleration, which is one of factors for evaluating seakeeping performance, was measured under the various sea states by the hull stress monitoring system(HMS) on the bridge, and the result was compared with those of model test and theoretical studies. Then, we confirmed the seakeeping performance of T.S. HANBADA by comparing it with ITTC seakeeping criteria This result will be a great help for the safe navigation by making it possible to estimate the possibility of work and the amount of risk under the various sea conditions with which may be confronted, and the shipbuilding yard can be possible to construct the vessel with superior performance through these data measured on the actual ship.

ON THE DEVELOPMENT OF SEAKEEPING CRITERIA

In order to determine the effects of ship motion on operational performance, quantitative seakeeping criteria are required. In this paper, it is proposed that seakeeping criteria should be presented in terms of limits on the incidence of whatever degrading event is determined to curtail the operation of interest, rather than limits on the underlying ship motions. For personnel operating on deck, the degrading events of most interest are the onset of loss-of-balance incidents, termed motion-induced interruptions, due to tipping or sliding. For unsecured helicopter operations, the most important degrading event is the helicopter sliding. The authors present a frequency-domain method of predicting the incidence of personnel or of equipment sliding which includes the forces due to roll, pitch, longitudinal, lateral and vertical accelerations, and also the effects of non-zero mean heel angles. They then present a method for predicting the incidence of personnel experiencing motion-induced interruptions due to loss of balance which includes the above forces and also the effects of steady and unsteady winds. In order to work in the frequency-domain, all of the forces are linearised and we consider only the linear turbulent wind force, and neglect the nonlinear term. Two main applications of the methods are anticipated. The first application is to design. The seakeeping criteria presented here are closely linked with the physical phenomena that are causing performance to be degraded, and are equally applicable to all ship types. The second application is to active operational guidance systems which provide real time information to the operators of naval vessels on the effects of changes in speed or heading on operations. Developing criteria in terms of the degrading events of most interest to the operator should result in an immediate improvement in the quality of the guidance.

On the Development of Seakeeping Criteria

ABSTRACTIn order to determine the effects of ship motion on operational performance, quantitative seakeeping criteria are required. In this paper, we propose that seakeeping criteria should be presented in terms of limits on the incidence of whatever degrading event is determined to curtail the operation of interest, rather than limits on the underlying ship motions. For personnel operating on deck, the degrading events of most interest are the onset of loss‐of‐balance incidents, termed motion‐induced interruptions, due to tipping or sliding. For unsecured helicopter operations, the most important degrading event is the helicopter sliding.We present a frequency‐domain method of predicting the incidence of personnel or of equipment sliding which includes the forces due to roll, pitch, longitudinal, lateral and vertical accelerations, and also the effects of non‐zero mean heel angles. We then present a method for predicting the incidence of personnel experiencing motion‐induced interruptions due to loss of balance which includes the above forces and also the effects of steady and unsteady winds. In order to work in the frequency‐domain, all of the forces are linearized and we consider only the linear turbulent wind force, and neglect the nonlinear term.Two main applications of the method are anticipated. The first application is to design. The seakeeping criteria presented here are closely linked with the physical phenomena that are causing performance to be degraded, and are equally applicable to all ship types. The second application is to active operational guidance systems which provide real time information to the operators of naval vessels on the effects of changes in speed or heading on operations. Developing criteria in terms of the degrading events of most interest to the operator should result in an immediate improvement in the quality of the guidance.

Motion‐Induced Interruptions as Ship Operability Criteria

ABSTRACTAn important goal of operability research is the development of quantitative seakeeping criteria to permit the effects of ship motions on operations to be assessed. This paper examines the problem of developing seakeeping criteria for deck operations. The lateral force estimator is generalized to permit frequency‐domain computation of the incidence of personnel losing balance in the presence of non‐zero vertical acceleration.The inadequacy of roll‐angle based seakeeping criteria for deck operations is shown. Other possible criteria for deck operations are discussed, and it is concluded that a limit on the number of motion‐induced interruptions during deck operations is most suitable, since it is platform‐independent, and may now be computed in the frequency‐domain.

ASSESSMENT OF THE ACW-400 OIL SKIMMER BY THE CANADIAN COAST GUARD FOR OIL SPILL COUNTERMEASURE OPERATIONS

ABSTRACT Early in 1978, the Canadian Coast Guard acquired a diesel-powered vessel-mounted ACW-400 oil skimmer developed by Frank Mohn A/S of Norway. The skimmer was landed in St. John's, Newfoundland, where a series of static and field trials were undertaken preparatory to its addition to the hardware countermeasures inventory of the marine emergency organization of the Canadian Coast Guard. The results of these acceptance trials are described hereunder with an evaluation of the unit with respect to the specific requirements of the Canadian Coast Guard. Following this deployment, the ACW-400 was shipped to Tuktoyaktuk on the Beaufort Sea where it became a component of the Canadian Coast Guard contingency plan for offshore petroleum exploration in that theatre. From this experience it was apparent that the ACW-400 was well designed and met the safety, transportability, flexibility, sea-keeping, and oil recovery criteria required to fulfill the specific countermeasures obligations of the marine emergency organization of the Canadian Coast Guard.