Wyniki wyszukiwania - BazTech

1

Numerical simulation of the seakeeping of a military trimaran hull by a novel overset mesh method in regular and irregular waves

Ghadimi Parviz, Karami Saeid, Nazemian Amin

Zeszyty Naukowe Akademii Morskiej w Szczecinie

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2021

|

nr 65 (137)

38--50

EN

The hydrodynamic performance of trimaran hulls has been previously investigated for optimum performance in calm water, but there is still a limited understanding of its motion response; therefore, a CFD-based numerical approach was developed and applied on a trimaran hull in the presence of regular and irregular waves. To validate the CFD method, a comparison was conducted using both experimental and 3D panel method data. In this study, two different turbulence models were surveyed, and the SST Menter k-Omega (k-ω) turbulence model was shown to be a more accurate model than the realizable k-Epsilon (k-ε) model. The different features of the proposed numerical model include the implementation of an overset mesh method, unique mesh plan refinement, and wave-damping region. The discrepancy between the experimental data and the results of other seakeeping calculation methods have always been problematic, especially for low-speed strip theory and 3D panel methods, but good consistency was observed between the proposed CFD model and experimental data. Unlike potential-based or conformal mapping seakeeping analysis methods, the effect of nonlinear waves, hull shape above the waterline, and other ship dynamic phenomena were considered in this CFD application. The proposed CFD method reduces the simulation time and computational efforts for ship motion calculations.

2

Comparison of safety levels required by adequate regulations for cargo ships of different types

Szulczewski Piotr

Zeszyty Naukowe Akademii Morskiej w Szczecinie

|

2021

|

nr 68 (140)

38--46

EN

During the currently ongoing development of methods for assessing the safety of ships, it is imperative that a compromise between the accuracy of the results and the accessibility of obtaining results is reached. This paper shows the calculations of a theoretical hull against damage stability regulations as included in SOLAS 2020, ICLL 66/88 as amended in 2003 and MARPOL 78. The rules included in the currently valid regulations require certain righting arm curve properties from vessels before and after potential damage, which does not pose a high difficulty level to engineers. However, for many engineers and scientists working with these rules, it is unclear what kind of behavior (particularly roll motion) these righting arm curve parameters correspond. In this paper, a correlation between the required GZ properties and the actual roll motion of a ship in waves, as calculated with the well-established method proposed by the ITTC, is revealed, and a comparison of the results to the currently in use regulations as well as comparison between the methods themselves is made. The comparison reveals the impact of GZ curve parameters on the roll motion of the ship.

3

Prediction of ship motions in irregular waves based on response amplitude operators evaluated experimentally in noise waves

Bielicki Sebastian

Polish Maritime Research

|

2021

|

nr 1

16--27

EN

The most common methods for predicting ship roll motions in a specified sea state are direct measurements of motions in a representative irregular wave realisation (time domain) or calculations of motions from response amplitude operators (RAOs) in the frequency domain. The result of the first method is valid only for the tested sea state, whilst the second method is more flexible but less accurate. RAO-based predictions are calculated assuming a linear model of ship motions in waves. RAO functions are usually evaluated by means of tests in regular waves for a limited number of frequencies and a constant wave amplitude. This approach is time-consuming and the discrete form of the RAO functions obtained for a limited number of frequencies may lead to discrepancies in the prediction of seakeeping and often does not allow the actual amplitude of the response in resonant frequency to be determined. Another challenge is the appropriate selection of wave amplitude for tests due to the considerable influence of viscous damping on roll response in irregular sea waves. There are alternative methods for the experimental determination of RAO functions and one of them is presented in this study. The presented approach allows RAO functions to be evaluated in one run by the generation of irregular waves characterised by a white or coloured noise spectrum. This method reduces the experiment duration, with almost continuous RAO characteristics obtained. The flat (white noise) and linear (coloured noise) wave spectral energy characteristics are considered in the experiment and the obtained predictions are compared with the results of accurate measurements in irregular waves.

4

Determination of seakeeping performance for a case study vessel by the strip theory method

Niklas Karol, Karczewski Artur

Polish Maritime Research

|

2020

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nr 4

4--16

EN

The increase of seakeeping performance is of particular importance for car and passenger ferries, service ships in the gas and oil extraction industry and offshore wind power farm industry, as well as for special purpose ships (including military applications). In the water areas of the Baltic Sea, North Sea, and Mediterranean Sea, which are characterised by a short and steep wave, the hull shape has a substantial impact on the operational capacity and propulsion efficiency of the ship, as well as on comfort and safety of navigation. The article analyses selected aspects of seakeeping for four variants of a selected case study vessel, indicating practical limitations of the strip method. The analysed aspects included hull heaving and pitching, added resistance, Motion Thickness Indicator (MSI), and Subjective Magnitude (SM). Experimental tests were also performed in the towing tank. Their comparison with the numerical results has indicated high inaccuracy of the strip method. What is more, the simplified representation of hull shape used in the strip method makes it impossible to analyse the effect of hull shape changes on the predicted seakeeping characteristics. Especially for the case of head wave, neglecting highly non-linear phenomena, such as slamming or head wave breaking, in strip method-based computer simulations will significantly decrease the reliability of the obtained results. When using the strip method, the seakeeping analysis should be complemented with model tests in a towing tank, or by another more complex numerical analysis, such as CFD for instance.

5

An underwater spoiler on a warship: why, when and how?

Bouckaert B.

Zeszyty Naukowe Akademii Marynarki Wojennej

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2018

|

R. 59 nr 3 (214)

5--23

EN

There are a lot of energy saving devices for ships on the market, but few have seen wide adoption on naval ships, with one exception: the bulbous bow. The bulbous bow was developed for naval ships in the early 20th century and is now widespread on a variety of ship designs. Many have wondered if the effect of the bulbous bow — reducing the resistance of a ship by reducing the bow wave — could be replicated somehow at the stern — by reducing the stern wave. This is exactly what is done by a novel and patented energy saving device called Hull Vane. Invented by Dutch hydrodynamicist Dr Peter van Oossanen for an America’s Cup sailing yacht in the early 21st century, research over the years has shown that this wing-shaped appendage works best on ships that combine a relatively high displacement with a relatively high top speed requirement — even if most sailing hours are done at half speed. Examples are certain offshore vessels, superyachts, patrol vessels and naval ships. On offshore patrol vessels, the resistance reduction from the Hull Vane ranges typically from 10 to 20% over the entire useful speed range. In this paper, the working principles of the Hull Vane will be described to give a better understanding of the device. An overview will be given of the work carried out on naval ships and coastguard ships (25 to 142 m), based on Computational Fluid Dynamics studies, model tests and full-scale applications. The question ‘Why?’ will be answered by translating the hydrodynamic effects to concrete capability improvements for naval ships: a lower fuel consumption, a longer range, reduced signature, a higher top speed and improved seakeeping. The question ‘When?’ will zoom in on whether a Hull Vane® is something to be included in a newbuild or if it is something to be retrofitted to an existing ship. Finally the answer to the question ‘How?’ will explain the process of either integrating a Hull Vane in a newbuild project or retrofitting it during a midlife upgrade of an existing ship.

PL

Istnieje wiele urządzeń energooszczędnych dla statków dostępnych na rynku, ale niewiele z nich znalazło szerokie zastosowanie na okrętach wojennych, z jednym wyjątkiem: bulwiastym dziobem. Bulwiasty dziób został opracowany dla okrętów na początku XX wieku i obecnie jest szeroko rozpowszechniony na różnych konstrukcjach statków. Wiele osób zastanawiało się, czy efekt bulwiastego dzioba — zmniejszający opór statku przez zmniejszenie fali dziobowej — mógłby zostać w jakiś sposób zreplikowany na rufie — poprzez zmniejszenie fali rufowej. Dokładnie tak jest to wykonywane przez nowe, opatentowane urządzenie energooszczędne o nazwie Hull Vane. Skonstruowane ono zostało przez holenderskiego hydrodynamika dr. Petera van Oossanena dla jachtu biorącego udział w America’s Cup na początku XXI wieku. Badania z ostatnich lat wykazały, że występ w kształcie skrzydła najlepiej sprawdza się na statkach, które łączą stosunkowo dużą wyporność z wysokim zapotrzebowaniem na maksymalną prędkość — nawet jeśli większość godzin żeglarskich odbywa się z połową maksymalnej prędkości. Przykładami są niektóre jednostki przybrzeżne, superjachty, jednostki patrolowe i okręty marynarki wojennej. Na przybrzeżnych jednostkach patrolowych redukcja oporu z Hull Vane® waha się zwykle od 10 do 20% w całym zakresie użytecznych prędkości. W artykule zostaną opisane zasady działania Hull Vane® w celu lepszego zrozumienia urządzenia. Dokonany będzie przegląd pracy wykonywanej na okrętach i jednostkach straży przybrzeżnej (od 25 do 142 m) w oparciu o badania Computational Fluid Dynamics, testy modelowe i aplikacje na pełną skalę. Udzielona zostanie odpowiedź na pytanie „dlaczego?” poprzez wytłumaczenie oddziaływań hydrodynamicznych na udoskonalenia konkretnych zdolności okrętów wojennych: mniejsze zużycie paliwa, większy zasięg, zmniejszone pole magnetyczne, wyższą prędkość maksymalną i udoskonaloną dzielność. Pytanie „kiedy?” skupi się na tym, czy kadłub Hana Vane ma być częścią nowej konstrukcji, czy też jest czymś, co należy zmodernizować na istniejącym statku. Na koniec odpowiedź na pytanie „jak?” wyjaśni proces integracji Hull Vane® w nowo budowanym projekcie lub modernizacji w trakcie zmian w połowie eksploatacyjnego życia istniejącego statku.

6

Development of Solution for Safe Ship Considering Seakeeping PERformance

Yoon H.K., Nguyen V.M., Nguyen T.T.

TransNav : International Journal on Marine Navigation and Safety of Sea Transportation

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2018

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Vol. 12, no. 3

517--525

EN

In recent years, safety of a ships has become one important issues needed to solved as soon as possible in ship navigation. Optimal weather routing is one of best solution for ensuring safe operation of a ship with a with short passage time or minimum energy to avoid a certain excessive motion. This paper introduced the development of solution for safety and optimal weather routing a ship considering seakeeping performance based on model test result. This study introduced how to apply A* algorithm based on result of the seakeeping model test for determining the optimal ship routes. Seakeeping model test of 8600 TEU container ship was carried out in Changwon National University's seakeeping basin and its RAOs at various frequencies were used to predict the RMS motion values in irregular waves. The specially modelled path-cost function and the safety constraints were proposed for finding the optimal path of the ship. The comparison of ship performances estimated by great circle’s path and estimated optimal route during the voyage of the ship was investigated.

7

Analiza wybranych metod obliczeniowych i eksperymentalnych wyznaczania charakterystyk amplitudowych jachtu żaglowego na fali regularnej

Karczewski A., Szmagliński R.

Prace Wydziału Nawigacyjnego Akademii Morskiej w Gdyni

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2018

|

Z. 33

21--32

PL

W artykule zaprezentowano wyniki analizy porównawczej charakterystyk amplitudowych właściwości morskich kadłuba jachtu żaglowego na fali regularnej, uzyskanych trzema metodami. Dwie z nich opierały się na podejściu obliczeniowym, trzecia zaś na klasycznym eksperymencie, przeprowadzonym na basenie modelowym. Zrewidowano użyteczność formuł empirycznych, opracowanych na bazie badań kadłubów jachtowych serii Delft. Wykonano symulacje komputerowe przy użyciu modelu numerycznego według teorii paskowej oraz wykonano badania modelowe w celu walidacji obu metod. Dla wybranych warunków falowania porównano zachowania jachtu, które są charakterystyczne dla jego pływania w warunkach sfalowanej powierzchni akwenu wodnego, czyli nurzanie i kiwanie. Zbadano również przyrost oporu kadłuba od falowania.

EN

This paper presents the results of a comparison analysis for seakeeping performance in regular waves obtained by three methods. Two of them were based on a computational approach, the third was based on an experiment carried out in a model pool. The usefulness of empirical formulas developed on the basis of the Delft yacht hulls has been revised. Computer simulations were performed using a numerical model according to strip theory, and model tests were performed to validate both methods. For selected wave characteristics, heave and pitch motions was compared. The added resistance in waves was also examined.

8

Numerical and experimental analysis of the wave induced forces on the tripod support structure. Laboratory study

Kraskowski M., Pastwa K., Kowalczyk S., Marcinkowski T.

Biuletyn Instytutu Morskiego w Gdańsku

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2017

|

Vol. 32, No. 1

21--29

EN

The presented work was realized within the framework of the AQUILO project, aiming to create the base of knowledge for prospective future investments in offshore wind energy on the Baltic Sea. The presented part of the work is focused on the experimental validation of numerical method of evaluation of the wave-induced forces on the bottom-mounted support structure of the offshore wind turbine. The experimental setup and measurement equipment, including in-house developed 6-DOF (six freedom) dynamometer, are described. Comparison of performance of different methods of evaluation of wave loads for wide range of parameters is presented. The results of experiments and numerical analyses are consistent; the largest discrepancy occurred at lowest wave frequencies, i.e., largest wave lengths. This may result from increased relative error of measurements for long waves in a relatively short tank.

PL

Prezentowana praca została wykonana w ramach projektu AQUILO, mającego na celu stworzenie bazy wiedzy dla przyszłych, potencjalnych inwestycji w energetykę wiatrową na akwenach Morza Bałtyckiego. W prezentowanej pracy wykonano empiryczną walidację numerycznej metody wyznaczania obciążeń falowych działających na konstrukcję wsporczą morskiej elektrowni wiatrowej. Przedstawiono i opisano fizyczny model doświadczalny oraz urządzenia pomiarowe, włącznie z wykonanym dla tego zadania dynamometrem o sześciu stopniach swobody (6 DOF). Zaprezentowano porównanie wyników obciążeń wywołanych falowaniem, otrzymanych różnymi metodami, dla szerokiego zakresu zmienności parametrów falowania. Wyniki uzyskane z przeprowadzonych doświadczeń oraz wyniki otrzymane z modelu numerycznego wykazują zadowalającą zgodność; największe rozbieżności wystąpiły dla częstotliwości najniższych, tj. dla fal najdłuższych. Przyczynę tych rozbieżności można tłumaczyć wzrostem względnego błędu pomiarowego dla bardzo długich fal w stosunkowo krótkim basenie.

9

On scaling of ship seakeeping

Artyszuk J.

Prace Naukowe Politechniki Warszawskiej. Transport

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2016

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z. 112

9--24

EN

The widely accepted linear model of ship motions in waves is considered in frequencydomain, where the steady-state harmonic motions as response to harmonic waves are of interest. The solution of motion transfer functions is presented in dimensionless form with special concern about the dimensionless wave frequency as independent variable. Though some facts are known within ship model testing methodology, this detailed and careful derivation is aimed to enhance in-depth understanding of the seakeeping characteristics of a ship. It is also expected that a transfer functions data exchange between one full-scale ship and another of close geometry yet of different size will be more encouraged.

PL

Na bazie liniowego modelu dynamiki wyprowadzono funkcje przenoszenia sprzężonych kołysań statku na fali harmonicznej. Szczególny nacisk położono na pełne ujęcie bezwymiarowe, z istotną rolą bezwymiarowej częstości fali. Mimo że ta ostatnia jest szeroko stosowana w okrętowych badaniach modelowych, to jest stosunkowo rzadko wykorzystywana w przeliczaniu funkcji przenoszenia między statkami rzeczywistymi o różnych wielkościach, gdy takie charakterystyki są znane. Ma to znaczenie np. w szybkim modelowaniu większej klasy statków i oceny ryzyka eksploatacji, m.in. w systemach nadzoru ruchu. Zarówno sam sposób niniejszego wywodu, jak i dyskusja poszczególnych założeń i kroków ma stanowić przyczynek do lepszego rozumienia analizy bezwymiarowej ('bezwymiarowania') w odniesieniu do kołysań statku, i tym samym służyć zwiększeniu świadomości użytkowników narzędzi analitycznych i decydentów.

10

Seakeeping software for the analysis of a ship’s seaworthiness

Cepowska Ż., Cepowski T.

Zeszyty Naukowe Akademii Morskiej w Szczecinie

|

2015

|

nr 42 (114)

95--100

EN

The article presents the Seakeeping research software, developed for the computation of a ship’s motions in regular and irregular waves on the basis of the following ship parameters: length between perpendiculars, beam, draught, block coefficient and transverse initial metacentric height. The software implements approximating functions of amplitude-phase characteristics of rolling, heaving, and pitching, developed by the author by means of artificial neural networks. The software determines transfer functions for the phenomena accompanying the rolling motion, such as slamming, green water, propeller surfacing, vertical acceleration forward and on the bridge. The article discusses possible uses of the software in scientific research, ship design and operation, and for educational purposes.

11

Test studies of the resistance and seakeeping performance of a trimaran planing hull

Ma W., Sun H., Sun H., Zou J., Zhuang J.

Polish Maritime Research

|

2015

|

nr 1

22—27

EN

Towing tank tests in calm water were performed on a trimaran planing hull to verify its navigational properties with different displacements and centres of gravity, as well as to assess the effects of air jets and bilge keels on the hull’s planing capabilities, and to increase the longitudinal stability of the hull. Hydrostatic roll tests, zero speed tests, and sea trials in the presence of regular waves were conducted to investigate the hull’s seakeeping ability. The test results indicate that the influence of the location of the centre of gravity on the hull resistance is similar to that of a normal trimaran planing hull; namely, moving the centre of gravity backward will reduce the resistance but lower the stability. Bilge keels improve the longitudinal stability but slightly affect the resistance, and the presence of air jets in the hull’s channels decreases the trim angle and increases heaving but has little effect on the resistance. Frequent small-angle rolling occurs in waves. The heaving and pitching motions peak at the encounter frequency of , and the peaks increase with velocity and move towards greater encounter frequencies. When the encounter frequency exceeds, the hull motion decreases, which leads to changes in the navigation speed and frequency.

12

Open water seakeeping model tests in the research work of the Gdansk University of Technology Shipbuilding Institute in the 1960s

Dudziak J.

Polish Maritime Research

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2007

|

S 2

13--17

EN

The paper discusses technical facilities and methodological foundations for the seakeeping model tests of ships carried out on Jeziorak Lake in the 1960s by the Ship Hydromechanics Department, Shipbuilding Institute, Technology University of Gdansk. Major achievements in the research programmes performed then are also mentioned.

13

Nonlinear time domain analysis of vertical ship motions

Bruzzone D., Grasso A.

Archives of Civil and Mechanical Engineering

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2007

|

Vol. 7, no 4

27-37

EN

A nonlinear time domain seakeeping analysis has been performed for ships advancing in head seas with regular waves. A hybrid approach has been employed, solving the unsteady hydrodynamic problem in the frequency domain and the equations of motion in the time domain. This procedure transfers radiation and diffraction forces, supposed linear, from frequency to time domain, where nonlinear FroudeKrylov and hydrostatic forces are computed considering the actual hull wetted surface at each time step. In a first test case, a monohull, both a strip theory and a three-dimensional Rankine panel method have been used for the frequency domain analysis, while for another test case, a trimaran, only the three-dimensional methodology has been applied. A comparison of the results shows a good agreement with experimental data and the hybrid approach appears to be actually independent of the technique used in the frequency domain, even if the reliability of the results is strongly related with the accuracy of the evaluation of the hydrodynamic terms.

PL

Przedstawiona została nieliniowa analiza właściwości morskich statku w dziedzinie czasu dla statków poruszających się przy regularnej fali przeciwnej. Zastosowana została metoda hybrydowa polegająca na rozwiązywaniu nieustalonego zagadnienia hydrodynamicznego w dziedzinie częstotliwości i równań ruchu w dziedzinie czasu. Siły radiacyjne i dyfrakcyjne, z założenia liniowe, są przekazywane z dziedziny częstotliwości do dziedziny czasu, gdzie w każdym kroku czasowym obliczane są nieliniowe siły Froude'a-Kryłowa i siły hydrostatyczne z uwzględnieniem rzeczywistej powierzchni zwilżonej kadłuba. W pierwszym prezentowanym przypadku - statku jednokadłubowego, do analizy w dziedzinie częstotliwości została zastosowana zarówno metoda paskowa (strip theory), jak i trójwymiarowa metoda panelowa Rankine'a, natomiast w drugim przypadku - trimarana, zastosowano tylko metodę trójwymiarową. Porównanie wyników pokazuje dobrą zgodność z danymi doświadczalnymi. Metoda hybrydowa okazała się rzeczywiście niezależna od metody zastosowanej w dziedzinie częstotliwości nawet, jeżeli wiarygodność wyników jest silnie zależna od dokładności wyznaczania członów hydrodynamicznych.

14

Aproksymacja kołysań bocznych kontenerowca S-175 na fali nieregularnej oparta na parametrach eksploatacyjnych statku

Cepowski T.

Zeszyty Naukowe / Akademia Morska w Szczecinie

|

2005

|

nr 6 (78)

65-75

PL

Przedstawiono aproksymację kołysań bocznych kontenerowca S-175 na fali nieregularnej opartą na parametrach eksploatacyjnych statku. Wartości wzorcowe kołysań bocznych obliczono dokładnymi metodami numerycznymi za pomocą programu SEAWAY. Funkcję aproksymacyjną opracowano za pomocą sztucznych sieci neuronowych i przedstawiono w postaci analitycznej. Prezentowana metodyka może pozwolić na prognozowanie rzeczywistych wartości kołysań bocznych, opartych na danych zarejestrowanych na statku.

EN

The paper presents approximations of roll amplitudes of a S-175 containershipoccurring in irregular waves on the basis of main service parameters. Standard values of ship's roll were determined by means of exact numerical methods by using the SEAWAY software. The relationships were elaborated by means of artificial neural networks and presented as an analytical function. The proposed approach may be used to approximate real values of roll angle amplitude on the basis of data recorded onboard the ship during its service.

15

An approach to optimization of ship design parameters with accounting for seakeeping ability

Szelangiewicz T., Cepowski T.

Polish Maritime Research

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2002

|

Vol. 9, nr 4

8-16

EN

In the paper a method, using a genetic algorithm, of searching optimum ship design parameters which satisfy economical and technical criteria with accounting for seakeeping ability, was presented. To assess seakeeping ability of a ship in waves the ship operational effectiveness factor E was applied. An example of application of the approach is attached and discussed.

16

Application of Artificial Neural Networks to investigations of ship seakeeping ability. Part II

Cepowski T., Szelangiewicz T.

Polish Maritime Research

|

2001

|

Vol. 8, nr 4

26-29

EN

In order to optimize the ship design at its conceptual and preliminary stages with taking into account also seakeeping criteria, simple and simultaneously exact relationships between the basic ship design parameters and seakeeping ability are necessary. The wave-induced motions of the ship in irregular waves as well as phenomena accompanying the motions, are determined on the basisi of the frequency transfer functions of the ship motions in regular waves. in this paper an approximation method is presented for determinational of such transfer functions with the use of the Artificial Neural Networks (ANNs). The attached results of numerical calculations show that the method provides exact data for ships of very different sizes, within wide ranges of ship velocity and direction of wave relative to the ship.

17

Application of Artificial Neural Networks to investigations of ship seakeeping ability. Part I

Cepowski T., Szelangiewicz T.

Polish Maritime Research

|

2001

|

Vol. 8, nr 3

11-15

EN

In order to optimize the ship design at its conceptual and preliminary stages with taking into account also seakeeping criteria, simple and simultaneously exact relationships between the basic ship design parameters and seakeeping ability are necessary. The wave-induced motions of the ship in irregular waves as well as phenomena accompanying the moations, are determined on the basis of the frequency transfer functions of the ship motions in regular waves. In this paper an approximation method is presented for determination of such transfer functions with the use of the Artificial Neural Networks (ANNs). The attached results of numerical calculations show that the method provides exact data for ships of very different sizes, within wide ranges of ship velocity and direction of wave relative to the ship.