High-speed Vessels Research Articles

Constructive tendencies of speed increase of small and high-speed vessels

Constructive tendencies of speed increase of small and high-speed vessels

Recent advances in vibro-impact dynamics and collision of ocean vessels

The treatment of ship impacts and collisions takes different approaches depending on the emphasis of each discipline. For example, dynamicists, physicist, and mathematicians are dealing with developing analytical models and mappings of vibro-impact systems. On the other hand, naval architects and ship designers are interested in developing design codes and structural assessments due to slamming loads, liquid sloshing impact loads in liquefied natural gas tanks and ship grounding accidents. The purpose of this review is to highlight the main differences of the two disciplines. It begins with a brief account of the theory of vibro-impact dynamics based on modeling and mapping of systems experiencing discontinuous changes in their state of motion due to collision. The main techniques used in modeling include power-law phenomenological modeling, Hertzian modeling, and non-smooth coordinate transformations originally developed by Zhuravlev and Ivanov. In view of their effectiveness, both Zhuravlev and Ivanov non-smooth coordinate transformations will be described and assessed for the case of ship roll dynamics experiencing impact with rigid barriers. These transformations have the advantage of converting the vibro-impact oscillator into an oscillator without barriers such that the corresponding equation of motion does not contain any impact term. One of the recent results dealing with the coefficient of restitution is that its value monotonically decreases with the impact velocity and not unique but random in nature. Slamming loads and grounding events of ocean waves acting on the bottom of high speed vessels will be assessed with reference to the ship structural damage. It will be noticed that naval architects and marine engineers are treating these problems using different approaches from those used by dynamicists. The problem of sloshing impact in liquefied natural gas cargo and related problems will be assessed based on the numerical and experimental results. It is important for vessel designers to determine the capacity of ships to resist random slamming loads, sloshing loading impact, grounding accidents and ships collisions.

Experimental and numerical modeling of the high speed planing vessel motion

In this paper, the motion of a high speed vessel with planing hull has been investigated using experimental and numerical methods. The aim of this investigation was to compare the results of the model towing test with the numerical results obtained in the Savitsky method.The most important issue in numerical modeling of a planing vessel is to determine its continuous motion conditions, such as trim and draught. Comparing the results, it is concluded that they are in a non-variant range in spite of uncertainties of continuous motion and hence modeling of the positions. Therefore, it could be expected that with more complete modeling, the study of the vessel motion conditions becomes possible, especially for high speed vessels.

Localized Fatigue Failure Analysis of Aluminium Crewboats due to Propeller Pulse Loads: A Case Study

Marine grade alloys are extensively being used in high speed vessels such as patrol crafts, ferries and crew boats, where a reduction of the structural weight is critical to achieve higher speeds [1]. The use of aluminium has forced marine industry engineers to develop methods to design against fatigue failure. This has largely been addressed by the development of design standards, analysis techniques and the improvement of quality control and construction methods [2]. Nevertheless, even with these advancements there is a continued need for the development and improvement of aluminium analysis methods and guidelines [3].

The effect of welding on the strength of aluminium stiffened plates subject to combined uniaxial compression and lateral pressure

Nowadays aluminum stiffened plates are one of the major constituents of the marine structures, especially high-speed vessels. On one hand, these structures are subject to various forms of loading in the harsh sea environment, like hydrostatic lateral pressures and in-plane compression. On the other hand, fusion welding is often used to assemble those panels. The common marine aluminum alloys in the both 5,000 and 6,000 series, however, lose a remarkable portion of their load carrying capacity due to welding. This paper presents the results of sophisticated finite-element investigations considering both geometrical and mechanical imperfections. The tested models were those proposed by the ultimate strength committee of 15 th ISSC. The presented data illuminates the effects of welding on the strength of aluminum plates under above-mentioned load conditions.

HIGH SPEED SHIP TOTAL RESISTANCE CALCULATION (AN EMPIRICAL STUDY)

High speed design studies became very intense studies. One of the subject that can be explore is obtaining total resistace. A high speed ship has four stages of condition when she operates. Starting from low speed condition until developent of dinamics lift force. These four states that happened on high speed ship when she cuise on her operational speed, make a specific consideration on predicting her total resistance. As high speed ship become more widely built and operate in Indonesia, the study of the state of art of high speed vessel especially for obtaining total resistance has became more challenging In this paper is foccused on proposing an applicative methods for high speed resistance calculation based on savitsky method. Result which obtained form empirical study is compared to numerical software. Result of this study shows that there are no significant differences between empirical method and result form software application. Considering of sea margin would be effective to made the empirical method would be applicable. There is a 128,0812 KN of total resistance using empirical method, by considering sea margine factor, and a 128,512 KN of total resistance resulted form software calculation

Numerical analysis of basic base-ventilated supercavitating hydrofoil sections

A numerical analysis of the inviscid flow over base-ventilated intercepted hydrofoils is presented. The low-order, non-linear boundary element formulation used is described along with the significant issues concerning the modelling of supercavities with this method. The use of transom-mounted interceptors is well established for the manoeuvring and trim control of high-speed vessels. The flow field over a forward-facing step at the trailing edge of a blunt-based hydrofoil section, with consequent cavity detachment from the outer edge of the step, is similar to that of the transom-mounted interceptor operating at high speed with free surface detachment from the outer edge. Due to this similarity, the term ‘intercepted’ hydrofoil is used to describe this arrangement. The results presented show that a number of geometric parameters, in particular thickness, leading-edge radius and trailing-edge slope, have a significant effect on the hydrodynamic performance of base-ventilated intercepted hydrofoils.

半滑走型高速船の操縦性能

In this paper, the effects of hull attitude change, ship speed, metacentric height GM and stern appendages such as rudder, shaft bracket, bossing and propeller shaft on maneuverability of a high speed vessel are investigated. Range of Froude number of the studied ship is from 0.6 to 1.0. The hydrodynamic force characteristics are captured by a Circular Motion Test in Hiroshima University Towing Tank. Using the hydrodynamic derivatives, maneuverability indices are calculated. As a result, the following knowledge is obtained through the study: by inclusion of ship attitude change, Y'υ increases, N'r slightly decreases, Y'r -m'x and N'υ significantly increase. The effect of the attitude change is not negligible. Inclusion of the attitude change improves the course stability due to contribution of Y'r and -m'x and N'υ. When ship speed increases and GM decreases, the course stability becomes worse in general although the turning performance is improved. This tendency is the same for displacement typed ships. The bare hull ship becomes unstable for course keeping in any Froude numbers, although the ship with stern appendages is stable. Thus, the effect of stern appendages on the course stability is considerably large. This is mainly due to the increase of absolute values of Y'υ and N'r by the stern appendages.

Roll-Coupling Effect on Ship Maneuverability

Roll-coupling effect on ship maneuvering motions is not negligible for high speed vessels, large container ships, passenger ships etc. To perceive the roll-coupling effect on the ship maneuverability, this paper proposes new simplified formulae for course stability criterion and steady turning index in the framework of the linear motion theory. Then, an approximation is employed where the depth wise acting point of lateral force related to roll moment is constant in any oblique motion mode. The course stability criterion including the roll-coupling effect is written aswhere C′ denotes the usual course stability criterion, and the linear hydrodynamic derivatives and l′ the depth wise acting point of the lateral force. The formula is simple and useful for checking the course stability taking the roll-coupling effect into account. To obtain the hydrodynamic derivatives, oblique towing test and circular motion test with various heel angles were conducted for models of a container ship, a pure car carrier and a ferry. In general, course stability deteriorates with increasing Froude number Fn or decreasing of metacentric height GM′, whereas turning performance improves and the time until response reaches steady turning state increases.

A numerical investigation into the effects of slamming impulsive loads on the elastic–plastic response of imperfect stiffened aluminium plates

Nowadays stiffened aluminium panels have been widely used for marine applications such as building high speed vessels. The panels of high speed vessels are subjected to different in plane and out-of-plane loads. One of the most important out-of-plane loads is the impulse caused by bottom slamming. In the present study, the transient large deflection elastic–plastic responses of a number of stiffened aluminium panels subject to slamming impulsive loads are investigated. The impulsive loads are exerted on the finite element models of aluminium panels proposed by Ultimate Strength Committee of ISSC 2003. Several impact conditions are considered to study the influence of several structural factors such as heat affected zone (HAZ) arrangement, boundary conditions, thickness of plating, number of transverse frames and in-plane fixation. Based on these studies, several design-oriented conclusions are issued. Moreover, this paper outlines the various aspects of the influence of the HAZ presence on the strength of the slam-loaded panels with respect to loading time ratio.

Determining of the hydrodynamic forces on the multi-hull tunnel vessel in steady motion

The research described in this paper was carried out to determine the hydrodynamic forces on the multi-hull tunnel vessel in steady motion. The hull form of vessel is fairly generated by the tunnel hull form generator code using the non-uniform rational B-Spline method. Then, the hydrodynamics simulation is carried out based on finite volume discretization method using volume of fluid model to consider free surface between water and air phases around the vessel. A dynamic mesh restructuring method is applied for grid generation regarding to the heave and pitch motions of vessel in each time step. The calculations of the center of gravity arising, trim angle, pressure, resistance and effective power are studied at various vessel’s speeds. The resistance plot versus velocity has an increasing trend having a hump velocity while the power curve shows a linear-like changes respect to speed increasing. Pressure calculations show that the ratio of hydrostatic pressure to total pressure is decreased at the end point of keel from 100 to 1 % as velocity increases from 5 to 20 m/s. The proposed numerical algorithm is a promising method for hydrodynamic analyses of wide-ranging high speed vessel types, particularly tunnel vessels.

수치계산에 의한 활주선의 항주 자세 및 저항 추정

Prediction of the running posture is important to evaluate the resistance by the numerical calculation for a high speed vessel. Especially for a planing craft having a large variation of running attitude it becomes more essential, but it can not be obtained easily because the running posture and the hydrodynamic forces including the resistance are interacted with each other. So iterative calculation to obtain the dynamic forces according to the changes in attitude is necessary, in this study, considering the calculated hydrodynamic force at the assumed draft as the additional buoyancy the corrected draft is calculated through satisfying the equilibrium between the buoyancy and the hull weight. To verify the derived method three kinds of hull forms were used with the results of model tests, R/V ATHENA and 150 tons class guide vessel for middle-speed semi-planing crafts, 28 feet fast boat for a high-speed planing boat. For all cases with several iterations the converged value of draft can be obtained, lastly the resistance and flow around hull were simulated by using VOF method.

Effect of weld-induced imperfections on the ultimate strength of an aluminium patrol boat determined by the ISFEM rapid assessment method

Marine-grade aluminium alloys are being increasingly used as a hull material of naval vessels, particularly in the case of high-speed patrol vessels for which the requirement for reduced structural weight is critical. Combined with the drive for weight reduction, the demand for operations of aluminium vessels in harsher seaway environments has led to increased interest in the application of limit-state design and analysis procedures, which require evaluation of the ultimate strength of the hull girder. This paper investigates the use of the state-of-the-art rapid assessment procedure ISFEM (intelligent supersize finite element method) to examine the ultimate hull-girder strength under vertical and horizontal bending of a metal inert gas welded aluminium midship section with plate and stiffener scantlings typical of a high-speed patrol vessel. The analysis investigates the effect on ultimate strength of weld-induced imperfections including plate and stiffener distortion, residual stresses and material softening in the weld heat-affected zone.

Design of high-speed planing hulls for the improvement of resistance and seakeeping performance

High-speed vessels require good resistance and seakeeping performance for safe operations in rough seas. The resistance and seakeeping performance of high-speed vessels varies significantly depending on their hull forms. In this study, three planing hulls that have almost the same displacement and principal dimension are designed and the hydrodynamic characteristics of those hulls are estimated by high-speed model tests. All model ships are deep-V type planing hulls. The bows of no.2 and no.3 model ships are designed to be advantageous for wave-piercing in rough water. No.2 and no.3 model ships have concave and straight forebody cross-sections, respectively. And length-to-beam ratios of no.2 and no.3 models are larger than that of no.1 model. In calm water tests, running attitude and resistance of model ships are measured at various speeds. And motion tests in regular waves are performed to measure the heave and pitch motion responses of the model ships. The required power of no.1 (VPS) model is smallest, but its vertical motion amplitudes in waves are the largest. No.2 (VWC) model shows the smallest motion amplitudes in waves, but needs the greatest power at high speed. The resistance and seakeeping performance of no.3 (VWS) model ship are the middle of three model ships, respectively. And in regular waves, no.1 model ship experiences 'fly over' phenomena around its resonant frequency. Vertical accelerations at specific locations such as F.P., center of gravity of model ships are measured at their resonant frequency. It is necessary to measure accelerations by accelerometers or other devices in model tests for the accurate prediction of vertical accelerations in real ships.

Theoretical prediction of running attitude of a semi-displacement round bilge vessel at high speed

Running attitudes of semi-displacement vessels are significantly changed at high speed and thus have an effect on resistance performance and stability of the vessel. There have been many theoretical approaches about the prediction of running attitudes of high-speed vessels in calm water. Most of them proposed theoretical formulations for the prismatic hard-chine planing hull. In this paper, running attitudes of a semi-displacement round bilge vessel are theoretically predicted and verified by high-speed model tests. Previous calculation methods for hard-chine planing vessels are extended to be applied to semi-displacement round bilge vessels. Force and moment components acting on the vessel are estimated in the present iteration program. Hydrodynamic forces are calculated by ‘added mass planing theory’, and near-transom correction function is modified to be suitable to a semi-displacement vessel. Next, ‘plate pressure distribution method’ is proposed as a new hydrodynamic force calculation method. Theoretical pressure model of the 2-dimensional flat plate is distributed on the instantaneous waterplane corresponding to the attitude of the vessel, and hydrodynamic force and moment are estimated by integration of those pressures. Calculations by two methods show good agreements with experimental results.

Design of high-speed planing hulls for the improvement of resistance and seakeeping performance

High-speed vessels require good resistance and seakeeping performance for safe operations in rough seas. The resistance and seakeeping performance of high-speed vessels varies significantly depending on their hull forms. In this study, three planing hulls that have almost the same displacement and principal dimension are designed and the hydrodynamic characteristics of those hulls are estimated by high-speed model tests. All model ships are deep-V type planing hulls. The bows of no.2 and no.3 model ships are designed to be advantageous for wave-piercing in rough water. No. 2 and no. 3 model ships have concave and straight forebody cross-sections, respectively. And length-to-beam ratios of no.2 and no.3 models are larger than that of no.1 model. In calm water tests, running attitude and resistance of model ships are measured at various speeds. And motion tests in regular waves are performed to measure the heave and pitch motion responses of the model ships. The required power of no.1 (VPS) model is smallest, but its vertical motion amplitudes in waves are the largest. No.2 (VWC) model shows the smallest motion amplitudes in waves, but needs the greatest power at high speed. The resistance and seakeeping performance of no.3 (VWS) model ship are the middle of three model ships, respectively. And in regular waves, no.1 model ship experiences ‘fly over’ phenomena around its resonant frequency. Vertical accelerations at specific locations such as F.P., center of gravity of model ships are measured at their resonant frequency. It is necessary to measure accelerations by accelerometers or other devices in model tests for the accurate prediction of vertical accelerations in real ships.

A typical wave wake from high-speed vessels: its group structure and run-up

Abstract. High-amplitude water waves induced by high-speed vessels are regularly observed in Tallinn Bay, the Baltic Sea, causing intense beach erosion and disturbing marine habitants in the coastal zone. Such a strong impact on the coast may be a result of a certain group structure of the wave wake. In order to understand it, here we present an experimental study of the group structure of these wakes at Pikakari beach, Tallinn Bay. The most energetic vessel waves at this location (100 m from the coast at the water depth 2.7 m) have amplitudes of about 1 m and periods of 8–10 s and cause maximum run-up heights on a beach up to 1.4 m. These waves represent frequency modulated packets where the largest and longest waves propagate ahead of other smaller amplitude and period waves. Sometimes the groups of different heights and periods can be separated even within one wave wake event. The wave heights within a wake are well described by the Weibull distribution, which has different parameters for wakes from different vessels. Wave run-up heights can also be described by Weibull distribution and its parameters can be connected to the parameters of the distribution of wave heights 100 m from the coast. Finally, the run-up of individual waves within a packet is studied. It is shown that the specific structure of frequency modulated wave packets, induced by high-speed vessels, leads to a sequence of high wave run-ups at the coast, even when the original wave heights are rather moderate. This feature can be a key to understanding the significant impact on coasts caused by fast vessels.

Comparisons Between Prediction and Experiment for Lift Force and Heel Moment for a Planing Hull

Even in calm water, high-speed vessels can display unstable behaviors such as chine walking, sudden large heel, and porpoising. Large heel results from the loss of transverse stability at high forward speed. When a planing craft begins to plane, the hydrodynamic lift forces raise the hull out of the water. The available righting moment resulting from the hydrostatic buoyancy is, therefore, reduced. As the righting moment resulting from hydrostatic buoyancy is reduced, the righting moment resulting from dynamic effects becomes important. These hydrodynamic righting effects are related to the hydrodynamic lift. This article explores the relationship between the hydrostatic lift and righting moment, the hydrodynamic lift and righting moment, and the total lift and heel-restoring moment of a planing craft operating at planing speeds. A series of tow tests using a prismatic hull with a constant deadrise of 20 measured the lift force and righting moment at various angles of heel and at various model velocities. The model was completely constrained in surge, sway, heave, roll, pitch, and yaw. The underwater volume is determined from the known hull configuration and the underwater photography of the keel and chine wetted lengths. The results presented include the total lift and righting moment with the hydrostatic and hydrodynamic contributions for various model speeds at two model displacements.

Comparisons Between Prediction and Experiment for Lift Force and Heel Moment for a Planing Hull

Even in calm water, high-speed vessels can display unstable behaviors such chine walking, sudden large heel, and porpoising. Large heel results from the loss of transverse stability at high forward speed. When a planing craft begins to plane, the hydrodynamic lift forces raise the hull out of the water. The available righting moment resulting from the hydrostatic buoyancy is, therefore, reduced. As the righting moment resulting from hydrostatic buoyancy is reduced, the righting moment resulting from dynamic effects becomes important. These hydrodynamic righting effects are related to the hydrodynamic lift. This article explores the relationship between the hydrostatic lift and righting moment, the hydrodynamic lift and righting moment, and the total lift and heel-restoring moment of a planing craft operating at planing speeds. A series of tow tests using a prismatic hull with a constant deadrise of 20 measured the lift force and righting moment at various angles of heel and at various model velocities. The model was completely constrained in surge, sway, heave, roll, pitch, and yaw. The underwater volume is determined from the known hull configuration and the underwater photography of the keel and chine wetted lengths. The results presented include the total lift and righting moment with the hydrostatic and hydrodynamic contributions for various model speeds at two model displacements.

Numerical Prediction of Symmetric Water Impact Loads on Wedge Shaped Hull Form Using CFD

Over the past two decades high-speed vessels have extended their service areas from protected waters to the open ocean where frequent and large water impacts can result in structural damage. The accurate prediction of slamming loads, and their consequences on light-weight high-speed vessels, is an essential element of efficient structural design. The aim of this work is to understand and accurately predict the behavior and local slam loads of quasi-2D wedge shaped hull forms impacting water. The computed results, using finite-volume Computational Fluid Dynamics (CFD), are validated against drop test experimental data and compared to a previously published numerical simulation using Smoothed Particle Hydrodynamics (SPH). The CFD results show good agreement with the experimental measurements.