Synergy of Resistance Reduction Effects for a Ship With Bottom Air Cavity

2011 ◽  
Vol 133 (2) ◽  
Author(s):  
E. L. Amromin ◽  
B. Metcalf ◽  
G. Karafiath
Keyword(s):  
Design Method ◽  
Wave Resistance ◽  
Air Cavity ◽  
Towing Tank ◽  
Friction Resistance ◽  
Air Supply ◽  
Resistance Reduction ◽  
Calm Water ◽  
Wetted Surface Area ◽  
Propulsion Power

Friction on a surface covered by an air cavity is much less than friction in water but there is a resistance penalty caused by the cavity tail oscillations. Nevertheless, there is a method for designing the ship bottom form for suppressing these oscillations. This study describes the design method and calm water towing tank tests for a ship with a bottom ventilated air cavity operating at Froude range 0.45<Fr<0.65, where both Fr and cavitation number influence the cavity shape. At this Fr range, wave resistance significantly contributes to the total ship resistance. Model experiments were conducted in the NSWCCD linear tow tank at three diverse drafts. The attained resistance reduction ratio was up to 25%, which is significantly greater than the calculated water friction resistance of the unwetted area of the air cavity. This is a result of the increased ship elevation over the water level due to cavity buoyancy. This contributes to the resistance reduction by decreasing the side wetted surface area and by reducing the submerged volume; thus, there is a synergy of resistance reduction effects. The power spent on air supply is under 2% of the propulsion power.

scholarly journals Analysis of trimaran-pentamaran side hull location based on clearance and staggers with stern form variations

2018 ◽  
Vol 67 ◽  
pp. 04003
Author(s):  
Yanuar ◽  
Wiwin Sulistyawati ◽  
R. Joshua Yones ◽  
Samodero Mahardika
Keyword(s):  
Surface Area ◽  
Optimum Design ◽  
High Speed ◽  
Frictional Resistance ◽  
Experimental Tests ◽  
Hull Form ◽  
Negative Interference ◽  
Friction Resistance ◽  
Resistance Reduction ◽  
Wetted Surface Area

An optimum design of ship is to achieve the required speed with minimum power requirements. On multihull, sidehull position against to mainhull influences the friction resistance and its stability. Frictional resistance of multi-hull increases due to the addition of wetted surface area of hull, but wave making resistance can be lowered by a slender hull form. This research are experimental tests of trimaran with five Wigley hulls on a combination transom and without transom. The test varied on stagger, clearance and trim at several speeds. A ship with formation arrow tri-hull on forward was given to prove the resistance reduction due to cancellation wave which was indicated by negative interference. The influence diverse position of sidehull has shown that model non-transom (NT) stern moreover give beneficial resistance than model with transom (WT) at high speed. Similarly, in the trim conditions that NT more favorable on trim specifically for high speed depending on the position of the sidehull to the mainhull.

scholarly journals Research on Ship Hull Optimisation of High-Speed Ship Based on Viscous Flow/Potential Flow Theory

2020 ◽  
Vol 27 (1) ◽  
pp. 18-28
Author(s):  
Zhang Baoji
Keyword(s):  
High Speed ◽  
Design Method ◽  
Frictional Resistance ◽  
Linear Wave ◽  
Total Resistance ◽  
Friction Resistance ◽  
Resistance Reduction ◽  
Before And After ◽  
Reduction Effect ◽  
Cfd Method

AbstractIn order to quickly obtain practical ship forms with good resistance performance, based on the linear wave-making resistance theory, the optimal design method of ship forms with minimum total resistance is discussed by using the non-linear programming (NLP) method. Taking the total resistance as the objective function (the Michell integral is used to calculate the wave-making resistance and the equivalent plate friction resistance formula is used to calculate the frictional resistance), the hull surface offset as the design variable and appropriate displacement as the basic constraints, and considering the additional constraints, the hull bow shape and the whole ship are optimised, and an improved hull form is obtained. The resistance of the ship before and after optimisation is calculated by the CFD method to further evaluate the resistance reduction effect and performance after optimisation. Finally, an example of optimisation calculation of an actual high-speed ship is given. The obvious resistance reduction results confirm the reliability of the optimisation design method.

Scaling of Resistance From Surface-Effect Ship Model Tests

2013 ◽  
Vol 29 (02) ◽  
pp. 66-75
Author(s):  
Chris B. McKesson ◽  
Lawrence J. Doctors
Keyword(s):  
Surface Effect ◽  
Frictional Resistance ◽  
Wave Resistance ◽  
Complex Case ◽  
Total Resistance ◽  
Towing Tank ◽  
Classic Article ◽  
Calm Water ◽  
Surface Effect Ship ◽  
Friction Line

In the case of conventional (displacement) hulls, model testing is based on the assumption (with or without certain refinements) that the total resistance can be expressed as:RT=RF+RR(1)where Rt is measured in the towing tank, and the frictional resistance, Rf, can be accurately estimated by the application of a friction line and the use of the calm-water wetted surface. It is assumed that the dimensionless residuary resistance RR is the same for the model and the prototype vessel. Our article may be considered to be an extension of the classic article by Wilson, Wells, and Heber (1978) to the more complex case of the surface-effect ship, as follows. Specifically, we opine that:RT=RF+RW+RH+RS+RM+RSPRAY(2)Here, Rw is the wave resistance of the vessel (caused by a combination of the actions of the cushion pressure and the two sidehulls), RH is the transom (hydrostatic) drag, Rs is the seal drag, Rm is the momentum drag, and RspRay is the spray drag. Rt is the only one of these quantities that is measured during the model test. The other components require the use of a variety of estimates. In the article, we present specific examples of our approach as applied to a number of tests on surface-effect ship models that we have studied in recent years.

Effect of Spray-Strake on Patrol Vessel Manoeuvrability

2008 ◽  
Author(s):  
Andi Haris Muhammad ◽  
Adi Maimun ◽  
Omar Yaakob ◽  
Agoes Priyanto
Keyword(s):  
Experimental Data ◽  
Mathematical Model ◽  
Design Method ◽  
Towing Tank ◽  
Water Condition ◽  
Calm Water ◽  
Planing Vessel

This paper describes a design method on the spray-strake parameters of a planing hull (patrol vessel) based on manoeuvring performance in calm water condition. The method set a spray-strake mathematical model which has been developed using experimental data from towing tank. The model selects such a spray-strake parameter which has the effects on manoeuvrability characteristics. In showing these effects, some IMO manoeuvring (for turning circle and zigzag manoeuvre) have been simulated for a planing hull with the designated spray-strake parameter. The results indicate that the spray-strakes attached to the planing vessel have effects on its manoeuvring performance.

Performance Prediction of Planing Hulls With Propeller Tunnels

2006 ◽  
Author(s):  
P. V. V. Subramanyam ◽  
V. Anantha Subramanian
Keyword(s):  
Performance Prediction ◽  
Area Ratio ◽  
Maximum Pressure ◽  
Pressure Measurements ◽  
Forward Region ◽  
Projected Area ◽  
Towing Tank ◽  
Calm Water ◽  
Wetted Surface Area ◽  
Resistance Tests

In order to study the performance of planing hulls with propeller tunnels, the resistance tests have been conducted on two models with and without tunnels in a towing tank for different forward speeds in calm water condition. Two models were provided with tunnels of different tunnel area ratios (The ratio of projected area of tunnels to the projected water-plane area of the model) of 0.07 and 0.12 by keeping the propeller immersion constant. Wetted surface area, trim angle and CG rise were measured at three different drafts as a part of the study. Pressure measurements were also conducted for a chosen case for a design draft. The extrapolation of resistance from model to prototype has been done using modified Froude’s extrapolation method, which takes the average bottom velocity and trim angle into account. The resistance was also calculated using the method given by Savitsky (1964). The results show that the resistance of the model with tunnel is less when compared to that without tunnel for the same model irrespective of the drafts in case of the model with larger tunnel area ratio. Such variation was not exhibited in the case of the model with lesser tunnel area ratio. Hence, it is observed that the model having the larger tunnel area ratio has beneficial effect due to tunnels. The Savitsky method based results have been compared with experimental results. Pressure distribution along the length of the model shows that the maximum pressure peaks occur near the forward region and reduces towards aft with undulations.

Computational Simulations of Wide-Beam Air-Cavity Hull in Waves

2021 ◽  
Author(s):  
Konstantin I. Matveev
Keyword(s):  
Valuable Insight ◽  
Air Cavity ◽  
Wide Beam ◽  
Head Waves ◽  
Calm Water ◽  
Air Lubrication ◽  
Time Histories ◽  
Vertical Accelerations ◽  
Wetted Surface Area ◽  
Solid Hull

An effective method to reduce ship drag is to supply air under specially profiled bottom with the purpose to decrease wetted surface area of the hull and thus its water resistance. Although such systems have been installed on some vessels, the broad implementation of this technique has not yet occurred. A major problem is how to sustain air lubrication in rough water. Modeling of air-ventilated flows is challenging, but modern computational fluid dynamics tools can provide valuable insight. In this study, a wide-beam, shallow-draft hull with a bottom air cavity is considered. This hull imitates a semi-planing boat that can be used for fast transportation of cargo from large marine vessels to shallow shores. To simulate fluid flow around this hull in calm water and head waves, as well as heave and pitch motions of the boat, CFD software Star-CCM+ has been employed. It is found that the air cavity effectiveness decreases in waves; vertical accelerations exhibit high-frequency oscillations; and heave, pitch and vertical accelerations increase, while time-averaged heave, pitch and added drag show non-monotonic behavior with increasing wave amplitude. The air-cavity hull also demonstrates substantially lower vertical accelerations in waves in comparison with a similar solid hull without bottom recess. Time histories of kinematic parameters and distributions of flow field variables presented in this paper can be insightful for developers of air-cavity hulls.

UJI TARIK HIDRODINAMIKMODEL KAPAL BERSAYAP WiSE DENGAN LAMBUNG DASAR BERSTEP

2013 ◽  
Vol 12 (3) ◽  
Author(s):  
Iskendar Iskendar ◽  
Andi Jamaludin ◽  
Paulus Indiyono
Keyword(s):  
Comparative Study ◽  
Model Test ◽  
Hydrodynamic Model ◽  
Surface Effect ◽  
Center Of Gravity ◽  
Test Results ◽  
Flat Bottom ◽  
Towing Tank ◽  
Test Models ◽  
Wetted Surface Area

This paper describes hydrodynamic model tests of Wing in Surface Effect (WiSE) Craft. These craft  was fitted with  stephull  form in different location on longitudinal flat bottom (stepedhull planning craft) to determine the influences of sticking and porpoising motion performances. These motions are usually occured when the craft start to take-off from water surfaces. The test models with scale of 1 : 7 were comprised of 4 (four) stephull models and 1 (one) non-stephull model  as a comparative study. The hydrodynamic  tests were performed with craft speed of 16 – 32 knots (prototype values) in Towing Tank at UPT. Balai Pengkajian dan Penelitian Hidrodinamika (BPPH), BPPT, Surabaya. The resistance (drag) was measured by dynamo meter and the trim of model (draft changing at fore and aft  of model due to model speed) was measured by trim meter. By knowing the value of model trim, the wetted surface area can be determined. Then, the lift forces were calculated based on these measured values. The model test results were presented on tables and curves.  Test results show that models  with step located far away from center of gravity of the WiSE craft tend to porpoising and sticking condition, except if the step location on the below of these center of gravity. While model without step tends to sticking conditions.

scholarly journals Resistance reduction on trimaran ship model by biopolymer of eel slime

2015 ◽  
Vol 12 (2) ◽  
pp. 95-102
Author(s):  
Y. Yanuar ◽  
G. Gunawan ◽  
M. A. Talahatu ◽  
R. T. Indrawati ◽  
A. Jamaluddin
Keyword(s):  
Drag Reduction ◽  
Frictional Resistance ◽  
Skin Surface ◽  
Fish Skin ◽  
Total Drag ◽  
Towing Tank ◽  
Ship Model ◽  
Resistance Reduction ◽  
Towing Tank Test ◽  
Tank Test

Resistance reduction in ship becomes an important issue to be investigated. Energy consumption and its efficiency are related toward drag reduction. Drag reduction in fluid flow can be obtained by providing polymer additives, coating, surfactants, fiber and special roughness on the surface hull. Fish skin surface coated with biopolymers viscous fluid (slime) is one method in frictional resistance reduction. The aim of this is to understanding the effect of drag reduction using eel slime biopolymer in unsymmetrical trimaran ship model. The Investigation was conducted using towing tank test with variation of velocity. The dimension of trimaran model are L = 2 m, B = 0.20 m and T = 0.065 m. The ship model resistance was precisely measured by a load cell transducer. The comparison of resistance on trimaran ship model coated and uncoated by eel slime are shown on the graph as a function of the total drag coefficient and Froude number. It is discovered the trimaran ship model by eel slime has higher drag reduction compared to trimaran with no eel slime at similar displacement. The result shows the drag reduction about 11 % at Fr 0.35.

Resistance of a Ship Undergoing Oscillatory Motion

2010 ◽  
Vol 54 (02) ◽  
pp. 120-132
Author(s):  
Lawrence J. Doctors ◽  
Alexander H. Day ◽  
David Clelland
Keyword(s):  
Finite Depth ◽  
Mean Value ◽  
Wave Resistance ◽  
General Effect ◽  
Towing Tank ◽  
Ship Model ◽  
Average Value ◽  
Unsteady Effects ◽  
Oscillatory Cycle ◽  
Resistance Tests

In this paper, we describe extensions to the research of Doctors et al. (Doctors, L. J., Day, A. H., and Clelland, D., 2008, Unsteady effects during resistance tests on a ship model in a towing tank, Journal of Ship Research, 52, 4, 263–273) and Day et al. (Day, A. H., Clelland, D., and Doctors, L. J., 2009, Unsteady finite-depth effects during resistance tests in a towing tank, Journal of Marine Science and Technology, 14, 3, 387–397) in which the oscillations in the wave resistance during the constant-velocity phase of a towing-tank resistance test on a ship model were measured and predicted, in the cases of relatively deep and relatively shallow water. In the current study, the ship model was towed with a harmonic velocity component superimposed on the usual constant forward velocity. This work constitutes a first step in the understanding of the unsteady hydrodynamics of a racing shell (rowing boat). We show here that the unsteady wave resistance varies considerably from the traditional (steady) average value. Indeed, the wave resistance is frequently negative during part of the oscillatory cycle. However, the general effect is an increase in the temporal mean value of the wave resistance; this suggests that every effort should be made to reduce the unsteadiness of the motion. We also demonstrate that the unsteady wave-resistance theory provides an excellent prediction of the measured effects summarized here. These predictions are often within a few percent of the measured values of the resistance.

An Evaluation of Planing Boat Trim Measurements

2017 ◽  
Author(s):  
Carolyn Judge ◽  
Bill Beaver ◽  
John Zseleczk
Keyword(s):  
Performance Prediction ◽  
Measurement Methods ◽  
The Other ◽  
Test Program ◽  
Towing Tank ◽  
Calm Water

The resistance of a planing hull is known to be highly dependent on trim angle. For several reasons, trim is difficult to measure to the level of accuracy normally attained with other towing tank measurements such as resistance or speed. In a recent study intended to validate CFD methods for planing hulls, 4’ and 8’ long geosim models of the Generic Prismatic Planing Hull (GPPH) were built and tested at USNA. Significant differences were found between the trim of the two models so a separate test program was conducted which focused specifically on the trim measurement of these two models in calm water. Five different trim measurement methods were used simultaneously on one model and then used again on the other model. Trim angles were compared between measurement methods and between models. Trim measurements with the same model agreed well and are the basis for an evaluation of measurement methods. The trim measured on the two different size models did not agree well even though the same instruments were used in most cases. The paper discusses reasons for the confirmed differences in calm water running trim of the two models and suggests ways to take advantage of this knowledge to make the best use of towing tank tests for planing boat performance prediction.

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