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.

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.

Numerical Analysis of Planing Boats in Regular and Irregular Head Waves Using a 2D+t Method

2015 ◽  
Author(s):  
Hendrik Haase ◽  
Jan P. Soproni ◽  
Moustafa Abdel-Maksoud
Keyword(s):  
Numerical Analysis ◽  
High Speed ◽  
The State ◽  
Operating Conditions ◽  
Head Waves ◽  
Calm Water ◽  
Rough Water ◽  
Small Craft ◽  
Vertical Accelerations ◽  
Hydrodynamic Evaluation

A large number of small craft with a demand of high speed are planing vessels (Faltinsen, 2005). Their hulls are designed to plane, a condition, in which the boat's weight is carried mainly by hydrodynamic rather than hydrostatic forces. In order to reach the state of stable planing, planing hulls usually have hard chines, a transom stern and a certain deadrise angle, which is often constant in the aft and becomes larger towards the bow. Smaller deadrise angles are associated with a higher dynamic lift, which is often beneficial for the calm water performance. However, smaller deadrise angles also lead to higher vertical accelerations the crew is exposed to when the boat travels in rough water. To ensure good performance in all operating conditions, a hydrodynamic evaluation of the boat's behaviour both in calm water and in waves is important.

scholarly journals Tank Tests with a Scaled Model of a BOC-50 Sailing Yacht Model in Calm Water and in Regular and Random Head Waves

2015 ◽  
Vol 5 (6) ◽  
Author(s):  
Dimitrios Liarokapis ◽  
Konstantina Sfakianaki ◽  
Giannis Papantonatos ◽  
Gregory Grigoropoulos
Keyword(s):  
Scaled Model ◽  
Head Waves ◽  
Calm Water ◽  
Sailing Yacht

Experiments and Computations for KCS Added Resistance for Variable Heading

2015 ◽  
Author(s):  
Hamid Sadat-Hosseini ◽  
Serge Toxopeus ◽  
Dong Hwan Kim ◽  
Teresa Castiglione ◽  
Yugo Sanada ◽  
...  
Keyword(s):  
Surface Profile ◽  
Engine Performance ◽  
Head Wave ◽  
Added Resistance ◽  
Local Flow ◽  
Wake Field ◽  
Head Waves ◽  
Calm Water ◽  
Free Surface Profile ◽  
Peak Location

Experiments, CFD and PF studies are performed for the KCS containership advancing at Froude number 0.26 in calm water and regular waves. The validation studies are conducted for variable wavelength and wave headings with wave slope of H/λ=1/60. CFD computations are conducted using two solvers CFDShip-Iowa and STAR-CCM+. PF studies are conducted using FATIMA. For CFD computations, calm water and head wave simulations are performed by towing the ship fixed in surge, sway, roll and yaw, but free to heave and pitch. For variable wave heading simulations, the roll motion is also free. For PF, the ship model moves at a given speed and the oscillations around 6DOF motions are computed for variable wave heading while the surge motion for head waves is restrained by adding a very large surge damping. For calm water, computations showed E&lt;4%D for the resistance,&lt;8%D for the sinkage, and &lt;40%D for the trim. In head waves with variable wavelength, the errors for first harmonic variables for CFD and PF computations were small, &lt;5%DR for amplitudes and &lt;4%2π for phases. The errors for zeroth harmonics of motions and added resistance were large. For the added resistance, the largest error was for the peak location at λ/L=1.15 where the data also show large scatter. For variable wave heading at λ/L=1.0, the errors for first harmonic amplitudes were &lt;17%DR for CFD and &lt;26%DR for PF. The comparison errors for first harmonic phases were E&lt;24%2π. The errors for the zeroth harmonic of motions and added resistance were again large. PF studies for variable wave headings were also conducted for more wavelength condition, showing good predictions for the heave and pitch motions for all cases while the surge and roll motions and added resistance were often not well predicted. Local flow studies were conducted for λ/L=1.37 to investigate the free surface profile and wake field predicted by CFD. The results showed a significant fluctuation in the wake field which can affect the propeller/engine performance. Additionally it was found that the average propeller inflow to the propeller is significantly higher in waves.

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.

Pilot and Observer Performance in Simulated Low Altitude High Speed Flight

1965 ◽  
Vol 7 (3) ◽  
pp. 257-265 ◽  
Author(s):  
Ben Schohan ◽  
Harve E. Rawson ◽  
Stanley M. Soliday
Keyword(s):  
Atmospheric Turbulence ◽  
High Speed ◽  
Target Identification ◽  
Observer Performance ◽  
Acceleration Time ◽  
Acceleration Time Histories ◽  
Time Histories ◽  
Low Altitude ◽  
Vertical Accelerations

Responses of experienced pilots and aerial observers were studied in simulated low-altitude, high-speed (LAHS) flight. The pilots “flew” three-hour surveillance missions at airspeeds of .4M and .9M in different degrees of simulated atmospheric turbulence. Flying ability decreased from .4 to .9M; however, intensity of vertical accelerations did not seem to affect flying ability except at the most severe levels. Target identification was unimpaired by either turbulence or airspeed. The observers also flew three-hour missions while experiencing acceleration time histories recorded from the pilot's flights. Target identification deteriorated as airspeed increased from 0.4 to 0.9 Mach. Gust intensity did not affect performance of any of their tasks. Performance efficiency on all tasks did not deteriorate from beginning to end of the missions of both pilots and observers.

A study on vertical motions of high-speed planing boats with automatically controlled stern interceptors in calm water and head waves

2014 ◽  
Vol 10 (3) ◽  
pp. 335-348 ◽  
Author(s):  
Mohammad Hossein Karimi ◽  
Mohammad Saeed Seif ◽  
Majid Abbaspoor
Keyword(s):  
High Speed ◽  
Head Waves ◽  
Calm Water

Assessment of URANS surface effect ship models for calm water and head waves

2017 ◽  
Vol 67 ◽  
pp. 248-262 ◽  
Author(s):  
Shanti Bhushan ◽  
Maysam Mousaviraad ◽  
Frederick Stern
Keyword(s):  
Surface Effect ◽  
Head Waves ◽  
Calm Water ◽  
Surface Effect Ship

Unsteady Numerical Simulation of the Behavior of a Ship Moving in Head Sea

2019 ◽  
Author(s):  
Adrian Lungu
Keyword(s):  
Free Surface Flow ◽  
Surface Flow ◽  
Incoming Wave ◽  
Grid Convergence ◽  
Head Waves ◽  
Calm Water ◽  
Unsteady Numerical Simulation ◽  
Resistance Coefficients ◽  
Regular Head Waves ◽  
Numerical Approaches

Abstract The paper follows a previous work of the author that dealt with ship resistance and self-propulsion numerical investigations, proposing a series of numerical simulations performed to assess the seakeeping performances of the KCS model which moves in regular head waves. Various simulations of the free-surface flow around the hull equipped with rudder moving either in calm water or in heading waves are proposed. For the calm water case, in which a series of six Fr numbers is considered, verification and validation based on the grid convergence tests are performed. Then, a series of five different simulations for various incoming wave characteristics are presented and discussed in every detail. Comparisons with the experimental data [1], [2] are provided aimed at validating the numerical approaches in terms of the total resistance coefficients as well as the heave and pitch motions characteristics. Several remarks will conclude the findings of the present work.

scholarly journals Full-Scale CFD Analysis of Double-M Craft Seakeeping Performance in Regular Head Waves

2021 ◽  
Vol 9 (5) ◽  
pp. 504
Author(s):  
Deniz Ozturk ◽  
Cihad Delen ◽  
Simone Mancini ◽  
Mehmet Ozan Serifoglu ◽  
Turgay Hizarci
Keyword(s):  
Full Scale ◽  
Stokes Wave ◽  
Added Resistance ◽  
Motion Responses ◽  
Seakeeping Performance ◽  
Head Waves ◽  
Calm Water ◽  
Maximum Improvement ◽  
Fifth Order ◽  
Regular Head Waves

This study presents the full-scale resistance and seakeeping performance of an awarded Double-M craft designed as a 15 m next-generation Emergency Response and Rescue Vessel (ERRV). For this purpose, the Double-M craft is designed by comprising the benchmark Delft 372 catamaran with an additional center and two side hulls. First, the resistance and seakeeping analyses of Delft 372 catamaran are simulated on the model scale to verify and compare the numerical setup for Fr = 0.7. Second, the seakeeping performance of the full-scale Double-M craft is examined at Fr = 0.7 in regular head waves (λ/L = 1 to 2.5) for added resistance and 2-DOF motion responses. The turbulent flow is simulated by the unsteady RANS method with the Realizable Two-Layer k-ε scheme. The calm water is represented by the flat VOF (Volume of Fluid) wave, while the incident long waves are represented by the fifth-order Stokes wave. The residual resistance of the Double-M craft is improved by 2.45% compared to that of the Delft 372 catamaran. In the case of maximum improvement (at λ/L = 1.50), the relative added resistance of the Double-M craft is 10.34% lower than the Delft 372 catamaran; moreover, the heave and pitch motion responses were 72.5% and 35.5% less, respectively.

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