Ship Resistance

Increasing propulsion efficiency, safety, comfort and operability are of the great importance, especially for small ships operating on windy sites like the North Sea and the Baltic Sea. Seakeeping performance of ships and offshore structures can be analysed by different methods and the one that is becoming increasingly important is CFD RANS. The recent development of simulation techniques together with rising HPC accessibility enables performance of advanced seakeeping simulations for ships in a full scale. The paper presents CFD seakeeping analysis for a case study vessel in two variants: V-shaped bulbous bow hull form (as built) and innovative hull form (X-bow type). The study presents the influence of redesigning the ship on selected seakeeping aspects. The advanced CFD model, with the application of overset mesh technique, was described in detail. Selected numerical results were validated on the basis of experimental testing in a towing tank and showed good agreement. The approach demonstrated here of performing the CFD seakeeping simulations for the analysis of ship performance in a full scale and close to real loading conditions has direct application to the design process as well as in determination of optimal operational parameters of any ship.

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.

The importance of a rudder cannot be understated; although relatively small, the hydrodynamic forces and moments developed on it are essential in the assessment of the manoeuvring characteristics of a ship. Additionally, ship rudders are almost always placed downstream of the propeller so they can take advantage of the increased local velocity due to the presence of the propeller. The knowledge of the interaction effects between the rudder and the propeller is a focal aspect for the improvement of ship’s performance. Propeller and rudder are considered as a propulsion unit in which the former is an active device that generates the thrust to keep the ship on move and the latter a control surface that produces the transverse force to keep the ship on course (Kracht 1992). In this paper, a method for rapidly computing the flow field and integrated forces acting on a rudder in a propeller race is presented.

The amounts  of research about catamaran  have generated a practical formula to simplify the calculations of catamaran resistance. Ship designer will calculate the predictions of catamaran resistance rapidly. The aim of this research is focused to search the optimal demihull form where the hull form has the lowest resistance compared to other hull form models with the same displacement. To generate the different hull form, the initial hull form (parent hull) is transformed so that become some models by changing the parameter of coefficient block (Cb) in range ±10% with Lwl, T, H, volume and displacement are constant. The transformed hull form are calculated their total resistance from Froude number (Fr) 0,2 to 0,65 with spacing hull to length ratio (S/L) 0,2 to 0,4. The results of calculation show that the optimal demihull form is Model 4 where the initial hull form Cb +5%. The model has the lowest resistance compared to other models. The comparisons of resistance Model 4 with the configurations of S/L shows that the lowest resistance is S/L 0,4, so that the optimal demihull
form is Model 4 with S/L 0,4.

Ships operate in conditions with wind and waves most of the time and this impact must be taken into account during the ship's design and operation. The added resistance induced by the waves (RAW) can be classified based on the underlying physical phenomena as added resistance due ship's motions RAWM or added resistance due to waves diffraction RAWR. The impact of each component depends on special design characteristics of the ship, and also differentiates with the wave length and sea states. In this work, for operational conditions prevailed in North Atlantic, the correlation between the size of the vessel and the components of RAW was examined as well as the overall impact of the RAW on the performance of the ships, expressed by ratio of RAW over resistance in calm water (CR). For this work, simplified formulas requiring basic particulars of vessels were used. It was demonstrated that the impact of diffraction component RAWR on the RAW increases with increase of vessel size, while the ratio RAW/CR reduces, with the vessel's dimensions increasing. It was also shown, in line with previous works, that the impact of speed is also import for the RAW/CR, with this ratio increasing when the vessel's speed decreases. Last, it was also demonstrated the impact of RAW on different vessels for different sea states

Research, in order to breakdown the resistance components of  trimaran hull form, has been carried out
worldwide. Almost all of the work is focused on the resistance investigation of trimaran configuration in deep sea
condition.  None  of  the  research  has  formulated  the  estimation  of  trimaran  resistance  components  into  certain
equation such as for catamaran. The current work is concentrated on the investigation of the effect of water depth,
namely deep, medium and shallow waters, into the total resistance of the trimaran configuration. Experimental
investigation using ITS model were carried out at a towing tank at various hull separation (S/L = 0.2, 0.3 and 0.4)
and  various  speeds  or  Froude  Numbers.  Special  consideration  is  given  to  medium  and  shallow  water  depth
because  the  Froude  Numbers  are  based  on  water  depth  and  not  based  on  ship  length  such  as  in  deep  water
condition. CFD investigation using a CFD code called Tdyn, is also conducted in order to validate the results of
the experimental investigation. The results of the experimental test and CFD analysis are in good agreement and
comparative studies with other published data strengthen the findings.
Keywords: trimaran, resistance, model test, CFD.