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.

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.

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.

Uncertainty Analysis for Ship Powering Performance Prediction Based on Model Tests

2015 ◽  
Author(s):  
Baoshan Wu ◽  
Shaopeng Ji ◽  
Wentao Wang
Keyword(s):  
Uncertainty Analysis ◽  
Performance Prediction ◽  
Open Water ◽  
Model Tests ◽  
International Standards ◽  
Design Phase ◽  
Rotating Speed ◽  
Calm Water ◽  
Energy Efficiency Design Index ◽  
Resistance Tests

International standards of energy efficiency design index (EEDI) for new ships from 2013 to 2025 have been in effect and it is very importance to make preliminary verification of EEDI of a ship at its design phase. Generally, a set of ship model tests in towing tank, including resistance tests, propeller open water tests and propulsion tests, are performed. However, it is a challenge yet to analyze the uncertainty in ship performance prediction based on these model tests. In this paper, a real example of bulk carrier is presented to demonstrate implementation of the ISO GUM into uncertainty analysis for prediction such powering performance in calm water, illustrating the detailed procedure for performance of model tests and uncertainty analysis in prediction. It is shown in this example the ship speed and the propeller rotating speed at 85% MCR are predicted at the level of confidence 95% as (13.65±0.19) knots and (132.9±1.6) rpm, respectively and additionally, the significant sources of uncertainty come from the measurement of drag in resistance tests and the towing forces in propulsion tests. That means higher precision or more repeat model tests would be required to obtain higher accuracy in prediction of a ship powering performance and less uncertainty in preliminary verification of EEDI at its design phase.

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.

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.

scholarly journals Computational and Experimental Study on Pressure Drop in a Fluidised Bed with Different Air Distributor Designs

2020 ◽  
Vol 17 (2) ◽  
pp. 8043-8051
Author(s):  
A. S. M. Yudin ◽  
A. N. Oumer ◽  
N. F. M. Roslan ◽  
M. A. Zulkarnain
Keyword(s):  
Pressure Drop ◽  
Perforated Plate ◽  
Area Ratio ◽  
Maximum Pressure ◽  
Fluidised Bed ◽  
Key Factor ◽  
Minimum Number ◽  
Maximum Pressure Drop ◽  
Free Area ◽  
Distributor Plate

Fluidised bed combustion (FBC) has been recognised as a suitable technology for converting a wide variety of fuels into energy. In a fluidised bed, the air is passed through a bed of granular solids resting on a distributor plate. Distributor plate plays an essential role as it determines the gas-solid movement and mixing pattern in a fluidised bed. It is believed that the effect of distributor configurations such as variation of free area ratio and air inclination angle through the distributor will affect the operational pressure drop of the fluidised bed. This paper presents an investigation on pressure drop in fluidised bed without the presence of inert materials using different air distributor designs; conventional perforated plate, multi-nozzles, and two newly proposed slotted distributors (45° and 90° inclined slotted distributors). A 3-dimensional Computational Fluid Dynamics (CFD) model is developed and compared with the experimental results. The flow model is based on the incompressible isothermal RNG k-epsilon turbulent model. In the present study, systematic grid-refinement is conducted to make sure that the simulation results are independent of the computational grid size. The non-dimensional wall distance,  is examined as a key factor to verify the grid independence by comparing results obtained at different grid resolutions. The multi-nozzles distributor yields higher distributor pressure drop with the averaged maximum value of 749 Pa followed by perforated, 45° and 90° inclined distributors where the maximum pressure drop recorded to be about one-fourth of the value of the multi-nozzles pressure drop. The maximum pressure drop was associated with the higher kinetic head of the inlet air due to the restricted and minimum number of distributor openings and low free area ratio. The results suggested that low-pressure drop operation in a fluidised bed can be achieved with the increase of open area ratio of the distributor.

SHAFT LOADS ON AZIMUTH PROPULSORS IN OBLIQUE FLOW AND WAVES

2021 ◽  
Vol 153 (A1) ◽  
Author(s):  
H Amini ◽  
S Steen
Keyword(s):  
Mechanical Design ◽  
Bending Moment ◽  
Ship Hull ◽  
Propeller Shaft ◽  
Towing Tank ◽  
Oblique Flow ◽  
Straight Line ◽  
Calm Water ◽  
Bending Loads ◽  
Marine Technology

A range of model experiments have been carried out in calm water and waves for an oil spill vessel model with twin tractor azimuth thrusters at different heading angles and advance coefficients in the large towing tank at the Marine Technology Centre in Trondheim, Norway. Propeller shaft bending loads have been measured using a shaft dynamometer capable of measuring all shaft side force and bending moment components as well as propeller torque and thrust. The results include the loads on the propeller shaft with and without the presence of a ship hull model at the same heading angles and advance velocities in order to study the wake influence from the ship hull on the hydrodynamic loads. Results show that the ship hull wake has a much stronger effect on the propeller loads when the propeller is azimuthed outward from the ship hull centreline than inward. Measurements from the experiments in waves are also presented for the same thruster model in a straight-line course for both the head and following sea states under different wave conditions. Larger bending loads are found in head sea conditions compared with the following sea conditions. Generally it is found that the shaft bending loads and lateral forces are quite large, which is important to consider in the mechanical design layout and for dimensioning of components.

Development of a Mathematical Model for Performance Prediction of Planing Catamaran in Calm Water

2019 ◽  
Vol 161 (A2) ◽  
Keyword(s):  
Experimental Data ◽  
Mathematical Model ◽  
Performance Prediction ◽  
Data Evaluation ◽  
Empirical Equations ◽  
Calm Water ◽  
Semi Empirical ◽  
The Mathematical Model ◽  
Comparison With Experimental Data

In this paper, an attempt has been made to predict the performance of a planing catamaran using a mathematical model. Catamarans subjected to a common hydrodynamic lift, have an extra lift between the two asymmetric half bodies. In order to develop a mathematical model for performance prediction of planing catamarans, existing formulas for hydrodynamic lift calculation must be modified. Existing empirical and semi-empirical equations in the literature have been implemented and compared against available experimental data. Evaluation of lift in comparison with experimental data has been documented. Parameters influencing the interaction between demi-hulls and separation effects have been analyzed. The mathematical model for planing catamarans has been developed based on Savitsky’s method and results have been compared against experimental data. Finally, the effects of variation in hull geometry such as deadrise angle and distance between two half bodies on equilibrium trim angle, resistance and wetted surface have been examined.

Dynamic Instability of a High-Speed Planing Boat Model

2000 ◽  
Vol 37 (03) ◽  
pp. 146-152
Author(s):  
Eric Thornhill ◽  
Brian Veitch ◽  
Neil Bose
Keyword(s):  
Dynamic Stability ◽  
High Speed ◽  
Research Council ◽  
Dynamic Instability ◽  
National Research Council ◽  
Scale Model ◽  
Clear Water ◽  
Towing Tank ◽  
Stability Limits ◽  
Resistance Tests

A series of bare-hull resistance and self-propulsion tests were carried out on a 1/8 scale model of a 11.8 m long, waterjet-propelled planing hull in the clear water towing tank at the National Research Council of Canada's Institute for Marine Dynamics. The bare-hull resistance tests, performed with the waterjet inlets closed, spanned a range of eight model velocities and nine ballast conditions consisting of three displacements each with three positions of the longitudinal center of gravity. The hull was then fitted with two model waterjet thrusters and tested over the same speeds and ballast conditions. Dynamic instability, or porpoising, was seen during certain high-speed tests. A discussion of this behavior and its relation to published dynamic stability limits is given.

Numerical Modelling of a Planing Craft with a V-Shaped Spray Interceptor Arrangement in Calm Water

2020 ◽  
Author(s):  
Mikloš Lakatoš ◽  
Kristjan Tabri ◽  
Abbas Dashtimanesh ◽  
Henrik Andreasson
Keyword(s):  
Reaction Force ◽  
The Other ◽  
Numerical Comparison ◽  
Total Resistance ◽  
Stagnation Line ◽  
Planing Craft ◽  
Water Conditions ◽  
Calm Water ◽  
Wetted Surface Area ◽  
Novel Concept

V-shaped spray interceptors are a novel concept of spray deflection on planing craft. Conventional spray rails are positioned longitudinally on the bottom of the hull and detach the spray from hull deflecting it towards the sides or slightly down and aftward. The V-shaped spray interceptors, on the other hand, are located in the spray area forward of the stagnation line such that they would deflect the oncoming spray down and aftward, thereby producing a reaction force that reduces the total resistance. An experimental study reported that the V-shaped spray interceptors to reduce the total resistance at low planing speed by up to 4%. This paper features a numerical comparison of two planing craft, one equipped with a conventional setup of longitudinal spray rails and the other with a V-shaped spray interceptor. Both configurations were simulated in calm water conditions and were free to pitch and heave in a speed range of Fr∇ = 1.776 to 3.108. The numerical model was analyzed for grid sensitivity and numerical results were compared with experimental results. The two concepts were compared in terms of total resistance, lift, running position and wetted surface area. Conventional spray rails were shown to account for up to 5.6% of total lift and up to 6.5% of total resistance. The V-shaped spray interceptor was shown to reduce the total resistance by up to 8%. Since the V-shaped spray interceptor was located in the spray area forward of the stagnation line, it deflected the oncoming spray thereby producing a horizontal reaction force (-1.5% of RTM) in the direction of the craft’s motion. The rest of differences in the total resistance of the hulls equipped with the conventional spray rails and the V-shaped spray rails was due to absence of the resistance of the absent spray rails.

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