Ship Hydrodynamics

A multi-fidelity global metamodel is presented for uncertainty quantification of computationally expensive simulations. The multi-fidelity approximation is built as the sum of a low-fidelity-trained metamodel and the metamodel of the difference (error) between high-and low-fidelity simulations. The metamodel is based on dynamic stochastic radial basis functions, which provide the prediction along with the associated uncertainty. New training points are added where the prediction uncertainty is largest, according to an adaptive sampling procedure. The prediction uncertainty of both the low-fidelity and the error metamodel are considered for the adaptive training of the low-and high-fidelity metamodels, respectively. The method is applied to a steady fluid-structure interaction (FSI) problem of a 3D NACA 0009 stainless steel hydrofoil. Two functions are considered simultaneously, namely lift and drag coefficients, versus angle of attack and Reynolds number. Two problems are presented: in the first problem the high-fidelity evaluations are obtained through steady FSI computer simulations, whereas in the second problem they are given by available experimental data from literature. Low-fidelity evaluations are provided in both cases by steady hydrodynamic simulations. The overall uncertainty of the multi-fidelity metamodel is used as a convergence criterion.

A one-dimensional non-intrusive Polynomial Chaos (PC) method is applied in Uncertainty Quantification (UQ) studies for CFD-based ship performances simulations. The uncertainty properties of Expected Value (EV) and Standard Deviation (SD) are evaluated by solving the PC coefficients from a linear system of algebraic equations. The one-dimensional PC with the Legendre polynomials is applied to: (1) stochastic input domain and (2) Cumulative Distribution Function (CDF) image domain, allowing for more flexibility. The PC method is validated with the Monte-Carlo benchmark results in several high-fidelity, CFD-based, ship UQ problems, evaluating the geometrical, operational and environmental uncertainties for the Delft Catamaran 372. Convergence is studied versus PC order P for both EV and SD, showing that high order PC is not necessary for present applications. Comparison is carried out for PC with/without the least square minimization when solving the PC coefficients. The least square minimization, using larger number of CFD samples, is recommended for current test cases. The study shows the potentials of PC method in Robust Design Optimization (RDO) and Reliability-Based Design Optimization (RBDO) of ship hydrodynamic performances.

The importance of wave data in engineering design of offshore structures cannot be overemphasised. Besides good and reliable data regarding frequency of occurrence wave heights and period, there is also a need to identify the spectral distribution of wave energy. With such information, wave loading on fixed and floating marine structures can be determined with greater accuracy. This paper presents the results of a full-scale measurement of wave and vessel motions taken from a research vessel operating off the East Coast of Peninsular Malaysia. The Vessel Motion Monitoring System (VMMS) used in the study basically composed of a wave radar that is installed at the bow of the vessel to measure wave amplitudes; a set of accelerometers and gyroscopes to measure vessel motions and computer for acquisition, storage and analysis of data. The main analysis of the results obtained is in the form of spectral analysis of wave and vessel motions.

In recent years, the IMO has introduced new regulations to reduce the negative impact of ships on the natural environment. A particularly important step forcing technological innovations is the increasing requirement of ship energy efficiency. It is expressed by the Energy Efficiency Design Index (EEDI). Another important step towards green shipping is raising the required quality of fuel used for propulsion, the so-called Tier limits. Higher demand of Low Sulfur Fuel Oil resulted in its price rising up by 200% in the past two years. All these aspects increase the importance of ship fuel economy. As a result, the hull resistance reduction plays a significant role in the design process of new vessels. For vessels operating at sites with moderate and rough waves, the shape of the hull and, in particular, the bow section plays an important role. The paper presents results of some of the research carried out as a part of the "Smart Propulsion System" research project. The pres...

در حل مسئله های هیدرودینامیکی سازه های شناور بزرگ، در قسمتی از روش المان مرزی نیازمند محاسبه انتگرال تابع گرین و مشتقات آن یعنی ماتریس های موثر می باشد که جزء پیچیده ترین و حساس ترین قسمت آن می باشد و به گونه ای حساسیت درستی جواب ها به این مرحله وابسته است. در صورتی که از تابع گرین ساده استفاده شود، نیاز به بررسی میدان دوردست خواهد بود که زمان حل را زیاد و پر هزینه می کند و اگر از گرین های پیچیده تر استفاده کرد، میدان دوردست حذف و روند حل مسئله پیچیده تر ولی در زمانی به مراتب کمتر حالت از قبل حل خواهد شد. در این مقاله توابع گرین مختلف که در پروژه های کد نویسی فراساحلی استفاده می شوند بررسی شده است. در این تحقیق به حساسیت انتخاب تابع گرین توجه خاصی می گردد و صحت سنجی ای برای روش تصویر نیز ارائه می گردد. در نهایت بیان خواهد شد که برای پروژه های دریایی نیازی نیست که به روش های پیچیده ی مذکور مراجعه کرد، بلکه با ساده سازی های منطقی تر می توان از محاسبات پیچیده تر صرف نظر کرده و  در عین حال به نتایج با دقت های قابل قبولی دست یافت. اکثر تفاوت ها در نتایج گرین های مختلف مربوط به نقاط بحرانی و اکسترمم است. که این مسئله در پاسخ RAO بیشتر نمود پیدا می کند.

This paper presents the results of an investigation on manoeuvring of an LNG vessel in shallow water with ship-bank interaction effects due to restricted water. Experiments were conducted to obtain the hydrodynamic coefficients of the vessel in shallow water using a Planar Motion Mechanism (PMM). The ship bank interaction effects were calculated using empirical formula. A time domain simulation program has been developed, included hydrodynamic coefficients and the ship-bank interaction effect to determine the manoeuvring of the vessel. The comparison of ship manoeuvring with bank effect in two banks contours has been conducted. The results show the strong effect on lateral force and yaw moment of the vessel for the non-symmetry bank contour.

This paper reports a quantitative method for comparing race kayak (K1) and surfski performance using a Kayak Power Meter. Comparisons are made between two Nelo K1s and between two Epic surfskis. The effect of rudder type on performance is also measured. A mathematical model is developed to investigate the effects of wind and current on performance measurements.

Water jets are common place in vessels needing to achieve speeds of 30+ knots where conventional propeller solutions are unable to overcome the associated issues of cavitation, which in turn can lead to thrust breakdown and material failure. Any vessel designed for high speed requires a low resistance and corresponding slender hull. The propulsor needs to also be capable of accepting a high level of power and hence for a given diameter a high power density. There is a very few papers about the application of water jet propulsion of different type of ship. Water jet propulsion is widely applied in small ship as well as different kinds of big ships which are elaborately discussed in this paper. Here is also discussed the mathematical analysis of different types of water jet inlet as well as over all view of water jet propulsion from early to present as. In this analytical study, the important design variables for water jet propulsion system are established and the theoretical relationships between these variables are derived. Bottom mounted water jet has additional sinkage of stern which is consequence of waterjet hull interaction effect and this effect discussed by various mathematical parameters as well as with graphical presentation. Key Words: Water jet propulsion, waterjet-hull interaction, hydrofoil, T-craft, SES (surface effect ship). Nomenclatures: A j jet cross sectional area A P Propeller blade projected area C T coefficient of thrust C Tcr critical thrust coefficient dE Energy difference between jet and ship dE` Energy difference between jet and ship with ξ IVR inlet velocity ratio V i /V or V i /V s m mass of water flowing per second P C propulsive coefficient P E effective horsepower P I energy input, P i pressure infront of the inlet P o water pressure below water line P T V thrust horsepower T propelling force or thrust V free stream velocity cr the critical velocity V A the speed of advance, V I the velocity of water at the inlet V J the velocity of the jet at the nozzle exit V S the velocity of the ship ω the wake fraction() ν the velocity ratio() α the velocity ratio () η H the hull efficiency () η t transmission efficiency, shp/bhp η P pump hydraulic efficiency η i propeller efficiency η J the efficiency of the water jet η Jmax ξ loss coefficient

This report describes the modelling of an appended yacht hull that is free to heave and pitch with CFX v15.0, a finite volume Reynolds Averaged Navier-Stokes (RANS) code developed by ANSYS. The model is validated against experimental towing tank data, and is compared with predictions made using the Delft Systematic Yacht Hull Series (DSYHS) regression equations, and the results of a panel code.

This paper reports an analysis of the forces on a surfski as the paddler surfs, or attempts to surf a trochoidal ocean wave.  The wave conditions necessary to produce sustained, effortless ‘paddle-in-the-air’ runs are determined, and a prediction of the maximum possible speed of a surfski for the idealised wave model is made (53.5 km/h). Results are presented as a series of charts, which can be used to predict if a wave of a given height and period, travelling in water of a given depth, can be surfed effortlessly or not.

Table of Contents and Preface
of
L. Birk (2019). Fundamentals of ship hydrodynamics: fluid mechanics, ship resistance and propulsion. Wiley, first edition. ISBN: 978-1-118-85551-5

Fundamentals of Ship Hydrodynamics is designed as a textbook for undergraduate education in ship resistance and propulsion. The book provides connections between basic training in calculus and fluid mechanics and the application of hydrodynamics in daily ship design practice. Based on a foundation in fluid mechanics, the origin, use, and limitations of experimental and computational procedures for resistance and propulsion estimates are explained.

The book is subdivided into fifty-one chapters, providing background material for individual lectures.  The unabridged treatment of equations and the extensive use of figures and examples enable students to study details at their own pace.

Key features:
  •  Covers the range from basic fluid mechanics to applied ship hydrodynamics.
  •  Subdivided into 51 succinct chapters.
  •  In-depth coverage of material enables self-study.
  •  Around 300 figures and tables.

Fundamentals of Ship Hydrodynamics is essential reading for students and staff of naval architecture, ocean engineering, and applied physics. The book is also useful for practicing naval architects and engineers who wish to brush up on the basics, prepare for a licensing exam, or expand their knowledge.

A near-optimal flapping propulsor was designed for a container-feeder ship, in order to assess possible efficiency gains within practical constraints. Performance of this flapping propulsor was measured in open water conditions at scale 1/12th by varying systematically Loading, Pitching amplitude, Chordlength, Chord-wise flexibility and Fin-spacing. A large improvement was measured resulting in an efficiency of 81% for the flapping propulsor at proper loading compared to 63% for the design screw-propeller. The efficiency gain due to chord-wise flexibility was smaller than expected, and the sensitivity of efficiency to chord-length was much larger than expected. This results in an optimal configuration from the point of view of hydrodynamics that yields fins with short chords operating at high transverse acceleration. Detailed data is made available on the performance of flapping fins in the selected range of parameters.

Resistance reduction is the most important goal in ship design that causes higher speed and lower fuel consumption. Hydrodynamic optimization is an effective and robust design method that plays an indispensable role in ship hull form optimization. Designers and shipyards are required to produce vessels according to draft and speed specifications which have superior hydrodynamic performance under calm water conditions (the contract condition), and the optimization of ship hull designs is a vital part of achieving this goal. Resistance value of DTMB 5415 model has been measured by Maxsurf software and compared with CD Adabco Stare-CCM+ CFD based software results. These methods are used to compare the calm-water drags of several bow and aft forms and to define optimized hull for which the total (friction + wave) calm-water drag is minimized. The total drag is estimated using Holtrop method in Maxsurf. Comparisons of CFD calculations and experimental measurements for DTMB 5415 hull form show that CFD calculations are reliable. Bow type has been replaced with bulb and few changes have been done on aft that has better behavior than other types of aft on resistance and total resistance on hull has been decreased with replaced bulb and modified aft.

A submarine is capable of executing unsteady maneuvers in six degrees of freedom. The analysis of such motion is very complicated. In order to correctly predict the performance of a submarine during such conditions, there is a need to develop mathematical models and computational tools to investigate the effects. For development of reliable numerical tools, model tests are used to replicate full-scale behavior using scaling formulas. In model testing, the primary requirement to match Reynolds, Froude and Strouhal scale simultaneously presents conflicting demands on the relationship between velocity and characteristic length of the model. The objective of this paper is to satisfy dynamic scaling similarity at every instant of time and mathematically develop a procedure by first principle approach such that the hydrodynamic forces and moments acting on the full scale are correctly represented on the model for the entire range of maneuver. Then from the response equations, scaling formulas are derived to accurately predict the full scale motion from model measurements.

A composite investigation with panel code and Reynolds-Averaged Navier-Stokes (RANS) meth- ods is conducted on 3D and 2D hydrofoil geometries and NACA sections to quantify the forces and the performance of these structures. This methodology is aimed to prove that it is possible to combine different numerical methods for a time-effective hydrofoil design approach. This combination will use panel method and thinship theory to investigate 3D NACRA F20 C-foil geometries. RANS, with k - ω SST as turbulent model, is used to analyse 2D NACA 0012 sections. The results will be compared between the two methods and with the experimental data available. Results proved to be satisfactory being able to encompass in the study many different performance criteria of hydrofoil design. The data between the codes showed similar trends although some differences were encountered. A design methodology has been presented to show how each code is adapt to study which part of the physics involved with this flow prob- lem. Time proved to be a major restriction but the main objectives of the project have been met. A consideration on future works was proposed based on the outcomes of the research.

В книге рассматриваются вопросы выбора обводов корпуса и внешней архитектуры корабля с позиций наилучшей штормовой мореходности и безопасности в сложных условиях плавания. Проектирование океанского корабля, являющегося сложным инженерным сооружением, требует всестороннего изучения множества технологических и эксплуатационных факторов. Совместное использование исторического опыта хорошей морской практики, аналитических и экспериментальных исследований позволило определить непротиворечивые подходы к оптимизации основных элементов формы корпуса и общекорабельной архитектуры, и согласовать принципиальные технические решения для достижения наилучшей мореходности некоторых классов кораблей и судов. Эти вопросы последовательно обсуждаются в книге в форме технико-исторического анализа мореходности, физико-геометрического представления о корабельном волнообразовании и взаимодействии корпуса с морским волнением, с последующей интерпретацией сравнительных экспериментов с опытовыми моделями гипотетических и перспективных проектов кораблей и судов. Комплексный подход к рассмотрению вопросов морского инженерного дела позволил дополнить настоящее исследование материалами о гидротехнических особенностях гаваней морских портов, а также о вовлечении творческой молодежи к освоению морских наук. Изложение материалов ведется в краткой форме, достаточной для повторения и проверки основных результатов расчетов и экспериментов. Книга представляет интерес для судоводителей, корабельных инженеров, студентов морских институтов и всех интересующихся историей флота, мореходностью корабля и вопросами проектирования формы корпуса и общекорабельной архитектуры. Проектирование океанского корабля, являющегося сложным инженерным сооружением, требует всестороннего изучения множества технологических и эксплуатационных факторов. Совместное использование исторического опыта хорошей морской практики, аналитических и экспериментальных наук в области корабельной гидромеханики, позволило лишь коснуться непротиворечивых подходов к достижению наилучшей мореходности некоторых классов кораблей и судов. Новые проектные построения последовательно обсуждаются в книге в форме технико-исторического анализа мореходности, физико-геометрического представления о корабельном волнообразовании и взаимодействии корпуса с морским волнением, с последующей интерпретацией сравнительных экспериментов с опытовыми моделями гипотетических и перспективных проектов кораблей и судов. Комплексный подход к рассмотрению вопросов морского инженерного дела позволил дополнить настоящее исследование материалами о гидротехнических особенностях гаваней морских портов, а также о вовлечении творческой молодежи к освоению морских наук. Изложение ведется в краткой форме, достаточной для поверки основных результатов и воплощения всех проектных решений.

SUMMARY This paper deals with the hydrodynamic sideforce production of a wind-assisted ship. The subject is introduced in physical terms, and the importance of the hydrodynamic sideforce is established, before classical models are reviewed. Finally, the complications arising from diverse appendage topologies are discussed, and a theory for zero-aspect ratio lifting surfaces is discussed. The paper concludes with a short summary of ongoing work.

The energy control and efficiency of ships has been and
will continue to be a matter of increasing importance in
the years to come. Due to the large number of energy efficiency
measures available, the current paper focuses on
the measures which improve the hydrodynamic efficiency
of ships. The systems that are examined are divided into
two groups: hull systems (e.g. bow bulbs, stern flaps, and
appendages) and Energy Saving Devices (ESDs). Specifically,
the latter are defined mainly as systems that are
installed in the vicinity of the propeller-rudder zone. In
this context, alternative propeller configurations are also
examined. State-of-the-art systems from each category
are presented along with working principles, as well as
the savings quoted by the manufacturers.

In present work, two propeller analysis tools, namely a panel code and a RANS solver, are applied for the evaluation of mechanical characteristics and cavitation behavior of two CP thrusters in axial cylinder, for which experimental results are available, in terms of propeller mechanical characteristics in absence of cavitation and of cavitation behavior (cavitation extension and thrust and torque breakdown). The comparison of numerical results allow to underline merits and shortcomings of the two approaches and to define possible ways for their improvement, in view of their possible applications in the design loop.

Henk J.J. van den Boom 1 (Membership; V), Thijs W.F. Hasselaar 1 (Membership; V) 1 MARIN, Trials & Monitoring department The speed/power characteristics of ships have always been at the core of ship design. To prove contractually agreed values, speed trials are conducted by the yard prior to delivery of the ship to the owner. In the past schedule integrity of the vessel was often the most important factor for the speed requirement. Today, owners and operators are keen to reduce fuel consumption to decrease operational costs. So far a variety of methods for conducting and analyzing speed/power trials have been used by shipyards. With the assistance of the Sea Trial Analysis-Joint Industry Project, ITTC developed guidelines for the execution and analysis of speed/power trials compliant with IMO EEDI. The need to reduce fuel costs and exhaust gas emissions including the upcoming environmental regulations such as EEOI by IMO urge for reliable monitoring of ship performance in service conditions. This requires accurate information of the speed through water. Although the speed log is one of the oldest instruments on board it is not considered the most reliable one. Results of an extensive monitoring campaign on board a 1800 TEU container vessel equipped with six speed logs within SPA-JIP will be presented. The state of art of performance monitoring will be presented.

In the last three years, since the creation of the Marine CFD Group of the Department of Naval Architecture, the developments and studies in the field of numerical hydrodynamic for powering and propulsion of super yacht have been remarkably intensified. The paper intends to give an overview on the most recent applications of the research team through results obtained in recent applications, with the opportunity to introduce the main particulars of the devised CFD methods. Each presented application corresponds to a specific request coming from yacht shipyards, designers or propulsion systems suppliers which initiated and continue to support the Marine CFD Group of the University of Genova over several research projects as a motor of innovation. Presented applications range from resistance prediction of planing hulls in dynamic equilibrium, to a hybrid inviscid-flow/RANSE solver for displacement hulls; from hull CFD based form optimization techniques, to steady and unsteady prediction of cavitating propeller hydrodynamics as well as design and optimization of special propulsion units. The background philosophy used to attack presented problems is coming from a pragmatical naval architect cut: devise new CFD methods that could balance between the results accuracy and the requested time to obtain the solution, in order to be compatible with the time frame of yacht design. J

A unified seakeeping-maneuvering analysis is developed based on the weak-coupling approach
of two-time scale method. At each time step, the second-order horizontal steady forces and
yaw moment are estimated by the far-field method utilizing the Kochin function as a function
of incident-wave frequency and amplitude, relative heading angle between incident wave and
ship, and forward speed, and their magnitudes are added as the wave eect in the maneuvering
motion equations.
The Kochin function representing ship-disturbance waves are evaluated by means of both enhanced
unified theory (EUT) and new strip method (NSM) to see the dierence due to bow wave
diraction, 3D and forward-speed eects in the final results of second-order steady forces and
moment.
Accordingly, the maneuvering-motion simulation provides the instantaneous forward speed of a
ship and the heading angle to the seakeeping analysis. In order to keep the accuracy of the simulation
model, calm water hull derivatives are taken from the captive tests. Then, maneuvering
simulations in waves are carried out by the coupling between slender-ship theory and modular
maneuvering model in the framework of two-time scale method.
Validation of the seakeeping calculation method is made through comparison with the experiment
conducted with bulk-carrier and container ship models advancing in regular oblique waves
and motion-free condition. Good agreement between computed and measured results and also
superiority of EUT to NSM are confirmed for all modes of ship motion and the steady forces
and yaw moment in a wide range of wave frequency.
For the coupled seakeeping-maneuvering model, a comparison of simulated and measured turning
motion in waves indicates the practical reliability of the mathematical model. Improvement
in the estimation of wave-induced steady forces and yaw moment is crucial, particularly in short
waves. Sensitivity study in this wave condition also implies that the steady sway force is the
largest contributor to the phenomenon that the ship drifts to the direction of incident waves.

Every shipping company has a goal to reduce operational costs and increase income. One possible way to achieve that is by optimizing ship's hull in respect to calm water resistance. However, because ships seldom travel at still water conditions, it is important also to introduce the effect of the added resistance in waves.
For large ships, added resistance in waves is mainly the result of wave diffraction around the ship while the added resistance due to motions has a small contribution. The available theoretical methods at the moment find it hard to evaluate accurately the diffraction component of added resistance in short waves. This makes necessary the use of semi-empirical approach or CFD methods.
Added resistance is also important for minimization of the Energy Efficiency Design Index (EEDI). Added resistance affects the selection of suitable Sea Margin and fw correction factor, which accounts for the decrease of speed in representative sea conditions. A reduction  in added resistance will affect positively the EEDI.
The development of computers during last century allowed the use of parametric models created in CAD/CAE systems for representation of hulls forms. New optimization solution techniques such as Sobol functions and genetic algorithms set up the necessary background for effective and quick optimization. All of these are present in CAESES/Friendship-Framework.
In this diploma thesis, the bow of a large tanker (KVLCC2) is optimized in terms of the added resistance in waves using CAESES/Friendship-Framework for creation of parametric model and optimization. Ship's bow is also optimized for total resistance, using Holtrop-Mennen method for estimation of calm water resistance. In the last stage, ship's bow is optimized for EEDI. The resulted maximum continuous rating of ship's main engine is compared with the minimum required power in adverse conditions.

Highlights:  (1)  Effective method for modeling wake in waves has been demonstrated.  (2)  Significant changes in the propulsion performance have been observed in waves.  (3)  Drop in propulsion efficiency due to waves should be taken into account.  (4)  Wave direction is found to have strong influence on the performance drop.