Viscous Pressure Resistance Research Articles

Effects of Homogeneous and Inhomogeneous Roughness on the Ship Resistance

Ship hull roughness can significantly increase the ship resistance. The roughness caused by biofouling attached to the ship hull is not uniform but has a random distribution. The purpose of this study is to investigate how the inhomogeneous surface roughness distribution affects the ship resistance and the various resistance components. The KRISO container ship (KCS) is considered as a case study. To model the inhomogeneous surface roughness, the ship hull is divided into three segments with equal wetted surface area. Combinations of three roughness heights, denoted as P, Q, and R with ks values of 125 μm, 269 μm, and 425 μm, respectively, are considered to obtain homogeneous and inhomogeneous roughness arrangements (PPP, QQQ, RRR, PQR, PRQ, QPR, QRP, RPQ, and RQP). CFD method is utilized in this study, utilizing RANS equations and k-ω SST turbulence model. A VoF method is used to model the free surface. CFD simulation results show that for the homogeneous roughness, the total resistance coefficient CT increases with increasing ks (PPP < QQQ < RRR), as expected. For the inhomogeneous roughness, the friction resistance coefficient CF increases in the order PQR < PRQ < QPR < QRP < RPQ < RQP, consistent with results from earlier studies. In all the cases, the friction resistance (CF) is the dominant component of the total resistance. As Re increases from 2.2 x 109 to 2.7 x 109, the percentage of the friction resistance decreases, while the percentage of the wave resistance increases. The viscous-pressure resistance decreases slightly as Re increases from 2.2 x 109 to 2.7 x 109.

Investigation on Calm Water Resistance of Wind Turbine Installation Vessels with a Type of T-BOW

Given the typical characteristics of self-propulsion and jack-up wind turbine installation vessels (WTIVs), including their full and blunt hull form and complex appendages, this paper combines the model test method with the RANS-based CFD numerical prediction method to experimentally and numerically study the resistance of the optimized hull at different spudcan retraction positions. The calm water resistance components and their mechanisms of WTIVs based on T-BOW were obtained. Furthermore, using the multivariate nonlinear least squares method, an empirical formula for rapid resistance estimation based on the Holtrop method was derived, and its prediction accuracy and applicability were validated with a full-scale ship case. This study indicates that the primary resistance components of such low-speed vessels are viscous pressure resistance, followed by frictional resistance and wave-making resistance. Notably, the spudcan retraction well area, as a unique appendage of WTIVs, exhibits a significant “moonpool additional resistance” effect. Different spudcan retraction positions affect the total calm water resistance by approximately 20% to 30%. Therefore, in the resistance optimization design of WTIVs, special attention should be paid to the matching design of the spudcan structure and the hull shell plate lines in the spudcan retraction well area.

Numerical Analysis of the Drag Reduction Performance of a Double M-Ship Boat With Stepped Planning-Air Coupling

Abstract In this paper, analyze the influence of the stepped planning structure on the drag performance by observing waveform diagrams at the stern of the double M-ship and water–air and pressure distribution diagrams at the bottom of the ship. This study uses the combined stepped planning-air drag reduction technology to improve the sailing characteristics of the double M-ship. Research findings: The stepped planning contributes to a reduction in bottom pressure, enhances water–air distribution, and augments the amplitude of hull movement. Within the design speed range, the maximum drag reduction rate achieved by the stepped planning is 7.574%. However, this enhancement comes at the expense of increased viscous pressure resistance, which becomes the predominant resistance when sailing at full speed; Injecting air at the stepped planning can effectively reduce the viscous pressure resistance increased by the stepped planning. The combined drag reduction technology of stepped planning and air successfully realizes the total drag reduction at the double-M ship's high speed. The total resistance experienced when air is injected at the stepped planning is reduced by up to 20.981% compared to the original hull.

Numerical Study on the Influence of Water Depth on Air Layer Drag Reduction

Over the years, air lubrication technology has been widely applied to maritime vessels, demonstrating its significant energy-saving and emission-reducing effects. However, the application of this technology in inland waterway transportation faces unique challenges due to the shallower water depths, particularly during low water periods. Under such conditions, the formation of the air layer and its associated drag-reduction effects may undergo alterations. Conducting research on air lubrication technology in shallow water conditions holds great practical significance for promoting its application in inland waterway vessels. Therefore, a numerical study is undertaken to examine the impact of water depth on Air layer Drag Reduction (ALDR) to promote the use of ALDR technology on inland canal boats with shallow water depths. The object was a specific river-sea direct ship model, and a groove was created at the bottom of the model with air injection. At two distinct speeds, numerical simulations were run for four different depths: deep water, moderate water, shallow water, and ultra-shallow water. A comparative examination of the air layer morphology on the ship bottom and drag reduction was conducted to investigate the impact of water depth on ALDR and confirm the viability of using ALDR technology on shallow-water navigation boats. The results indicate that due to the change in the velocity and pressure fields at the bottom of the ship, the efficiency of drag reduction and the form of the air layer on the ship’s bottom are significantly impacted by variations in water depth in restricted waters. However, the total resistance can still be significantly reduced by setting grooves on the hull with air injected in shallow waterways. Reduced frictional resistance no longer predominates the overall resistance reduction in shallow water; the proportion of the decrease in viscous pressure resistance rises and can reach up to 4.8 times the decrease in frictional resistance. The research confirms the application prospects of this technology on inland waterway transport ships.

Investigation of An Inverted Bow on Frigate Hull Resistance

This study discusses the inverted bow design on the combatant hull form. Changes in the shape of the stem angle and flare bow are used as analytical parameters to investigate the ship's performance. Ship resistance and motion will be predicted using the Computational Fluid Dynamics (CFD) approach using the Reynolds Averaged Navier Stokes (RANS) equation and the k-ε turbulence model. The volume of fluid (VOF) method is applied to simulate the change in the free surface between water and air using an overset mesh technique. The ship's movement is limited to sinkage and trim motions, so the movement's accuracy can be predicted. The results revealed that the inverted bow reduced the total resistance by 6.30%, whereas the trim and sinkage showed no significant changes. The breakdown of the reduction ratio showed that friction resistance components were reduced by 10.62%, wave resistance by 44.05%, and viscous-pressure resistance by 45.33%. This highlights the effectiveness of an inverted bow in optimizing wave and viscous pressure, enhancing overall ship performance.

Review on the ship drag reduction technology

The development of the theory of turbulence has made a breakthrough in the application of drag reduction technology on ships, which contributes to energy saving and environmental protection. When a ship is sailing, it has to overcome resistance. Total resistance includes frictional resistance, wave-making resistance, and viscous pressure resistance, in which frictional resistance acts as the main resistance for low-speed ships, and for high-speed ships, the main resistance is wave-making resistance. This paper reviews the ship drag reduction technology by giving a brief introduction to drag reduction methods using grooves, bulbous bows, bubbles, hydrofoils, wall vibration, and high-polymer additive respectively, as well as their principles.

Development of a small-sized tanker with reduced greenhouse gas emission under in-service condition based on CFD simulation

In the present study, the hull form and appendage of a 6.5 k DWT tanker was improved to reduce greenhouse gas emissions in the in-service navigation condition. The conventional hull form of the 6.5 k DWT tanker has been designed in terms of performance in the ideal condition of a calm-sea. On the contrary, the performance of a ship in the in-service condition should take the added resistance due to wind and waves in the real sea into consideration. In order to reduce the added resistance due to waves, the bow hull form was modified to have a sharper entrance with increased length between perpendiculars. This was intended to ensure that the waves follow the curved bow surface more smoothly, thereby reducing the added resistance due to waves. The stern hull form was also modified to have V-shaped section shapes to reduce viscous pressure resistance. In addition, the flow control fins were optimized in terms of position and angle of attack. The added resistance of the resulting hull form was then analyzed numerically in regular wave with a varying wavelength ratio λ/Lpp=0.5∼2.0. The added resistance in regular waves was subsequently integrated with respect to the wavelength to obtain the added resistance in irregular waves. Finally, by combining it with the sea state occurrence probability, the daily fuel oil consumption (DFOC) was able to be calculated for the actual in-service routes for the tanker. The entire process of hull form modification and evaluation was conducted with free-surface CFD simulation in the presence of regular waves. A series of model tests was undertaken to confirm the improvements of the optimal hull form over the original in terms of performance in waves as well as calm-sea performance. The resulting DFOC and daily CO2 emissions for the optimal hull form in the in-service conditions was found to be reduced by 14.8%. Furthermore, the calm-sea DFOC and CO2 emissions were also improved by 15.6%.

Mechanism analysis and prediction of longitudinal cut wave pattern resistance based on CFD simulation

Inspired by ITTC 2021 (International Towing Tank Conference), this paper implements the Longitudinal Cut Method (LCM), a methodology to predict wave pattern resistance (Rwp), within Computational Fluid Dynamics (CFD) simulation to explore its mechanism and feasibility in predicting wave resistance (Rw). To accurately predict the free surface, a validation study, including the grid convergence index (GCI), wave profile, and wave pattern, is conducted for a Series 60 ship model. Next, Rwp is appropriately evaluated and compared with the experiment. The influence of the transverse wave component on the LCM analysis is also discussed. Furthermore, a comparison between the EFD (Experimental Fluid Dynamics) and CFD-based LCM is made through the analysis of the Wigley Catamaran, highlighting the advantages of the present approach. Finally, the limitations of the LCM theory are systematically discussed with the nonlinear bow wave analysis of a wall-sided ship model by introducing the local adaptive mesh refinement (LAMR) approach. For the fine hull form, LCM has been validated as a suitable methodology for directly predicting Rw and consequently the other primary resistance components (frictional resistance Rf and viscous pressure resistance Rpv) by one simulation. In contrast, due to energy dissipation of the non-negligible nonlinear local field wave component in the downstream wake region, Rw could be underestimated for the full hull form.

INVESTIGATING THE COMPARISON OF SHIP RESISTANCE COMPONENTS BETWEEN U AND V-SHAPED HULLS

The selection of a hull design with minimal drag is an important effort to reduce emission levels on ships. Two different hull shapes, U and V hulls, have unique properties that affect their drag production, which has been studied extensively in the past. This study aims to re-examine the differences between the two hull types by conducting a simple analysis of drag prediction results using empirical and numerical slender body methods. Both hull models in this study have the same size and volume. The results indicate that the U hull has a higher frictional resistance ( ) than the V hull due to its wider wetted surface area ( ). Additionally, the viscous pressure resistance ( ) and form factor coefficient ( ) of the U hull are also higher than those of the V hull. However, for Froude numbers (Fr) above 0.245, the U hull has lower wave resistance ( ) than the V hull, whereas for Fr below 0.245, the U hull has higher . Overall, the U hull produces a higher total resistance ( ) than the V hull at low speeds, but a lower at high speeds. Therefore, the choice of hull shape for minimizing a ship's resistance is influenced by the desired speed of service. If Fr is low, below 0.24, a V-shaped hull is more suitable. However, if Fr is higher than 0.24, a U-shaped hull is more appropriate.

Numerical Evaluation of the Wave-Making Resistance of a Zero-Emission Fast Passenger Ferry Operating in Shallow Water by Using the Double-Body Approach

The consideration of shallow water effects has gained in importance regarding inland operations. The interaction between the keel and the riverbed affects the hydrodynamic characteristics of marine vessels. The highly complex nature of the interference phenomenon in catamarans makes the shallow water problem more complicated as compared to monohulls. Hence, catamarans are very sensitive to speed changes, as well as to other parameters, such as the shallow water effects. This makes the design of catamarans more challenging than their monohull equivalents. At lower Froude numbers, the higher importance of the frictional resistance makes the greater wetted surface of the catamaran a disadvantage. However, at higher speeds, there is the potential to turn their twin hulls into an advantage. This study aims to investigate the wave-making resistance of a zero-carbon fast passenger ferry operating in shallow water. The URANS (unsteady Reynolds-averaged Navier–Stokes) method was employed for resistance simulations. Then, the double-body approach was followed to decompose the residual resistance into viscous pressure and wave-making resistance with the help of the form factors of the vessel calculated at each speed. The characteristics of the separated wave-making resistance components were obtained, covering low, medium, and high speeds. Significant findings have been reported that contribute to the field by providing insight into the resistance components of a fast catamaran operating in shallow waters.

STUDY OF FROUDE AND HUGHES METHODS BY NUMERICAL TOWING TANK

The resistance of a cargo ship is calculated by numerical towing tank. RANSE multi-phase parallel solver with K-Z SSTturbulent model and VOF formulation is applied. Computational results from double model (without free surface) areused to obtain 1+k in Hughes’ method and those with free surface are analyzed by both Froude and Hughes’ approachesto investigate model and full scale correlation. ITTC recommended uncertainty study is carried out to evaluate numericalerror due to grid density. The computed wave elevation, wake distribution and resistance components by fine, mediumand coarse meshes are cross-compared and validated against experiment data where applicable. It is found that gridresolution has most effect on wave pattern. The predicted friction and viscous-pressure resistance coefficients arerelatively grid independent from present numerical simulation.

Numerical investigation into the resistance performance for the damaged DTMB 5415 ship in calm water and regular head waves

ABSTRACT This paper demonstrates the feasibility of Computational Fluid Dynamics (CFD) to predict the motion responses of the damaged ship and the total resistance in calm water and regular head waves. The head waves are described with a fifth-order Stokes scheme. Two benchmarking studies are done to respectively validate the accuracy of the applied numerical approach in predicting the total resistance and ship's motions. By comparing the total resistance of the intact ship with motions and the damaged ship, it can be obtained that the increased total resistance due to the flooding flow almost comes from the viscous pressure resistance. Moreover, added resistance generated by head waves is a considerable factor affecting the resistance performance of the ship. The increased value can be several times even more than ten times that of the upright-floating intact ship in calm water.

Numerical study on the mechanism of drag reduction for interceptors on planing boats

The drag reduction effect of interceptors on planing boats has been widely proven, but the mechanism of the effect has been rarely studied in terms of drag components, especially for spray resistance. The resistance was caused by the high gauge pressure under the boats transformed from the dynamic pressure, and it is the largest drag component in the high-speed planing mode. In this study, numerical simulations of viscous flow fields around a planing boat with and without interceptors were conducted. A two degrees of freedom motion model was employed to simulate the trim and sinkage. The numerical results were validated against the experimental data. The flow details with and without the interceptor were visualized and compared to reveal the underlying physics. A thinner and longer waterline could be achieved by the interceptor, which made the boat push the water away more gradually, and hence, the wave-making resistance could be decreased. The improved waterline also reduced the component of the freestream normal to the hull surface and led to the less transformed dynamic pressure, resulting in the lowAer spray resistance. Furthermore, the suppression of the flow separation could also be benefited from the interceptor; the viscous pressure resistance was therefore decreased.

Numerical Study on the Hydrodynamic Performance of Antifouling Paints

This study presents a simple numerical method that can be used to evaluate the hydrodynamic performances of antifouling paints. Steady Reynolds-averaged Navier-Stokes equations were solved through a finite volume technique, whereas roughness was modeled with experimentally determined roughness functions. First, the methodology was validated with previous experimental studies with a flat plate. Second, flow around the Kriso Container Ship was examined. Lastly, full-scale results were predicted using Granville’s similarity law. Results indicated that roughness has a similar effect on the viscous pressure resistance and frictional resistance around a Reynolds number of 107. Moreover, the increase in frictional resistance due to roughness was calculated to be approximately 3%–5% at the ship scale depending on the paint.

Wing body junctions in ship hydrodynamics

Starting with the 1st of January 2013, all ships greater than 400 gross tons have to comply with design or operational energy efficiency index, in order to reduce the greenhouse emissions. From the naval architect’s point of view, the emission reduction measures can be hydrodynamic, structural, technological and operational. The hydrodynamic measures, which are the first that can be taken into consideration in order to reduce the EEDI, are materialized through the optimization of the hull. The Naval Architect may interfere on the bulbous bow, hydrodynamic shoulders, bulb stern, transom or appendages, the drag being then modified by reducing the wave, viscous pressure or frictional resistance components. Another way to improve the hydrodynamics of a ship is the use of Energy Saving Devices (ESD). These are appendages, mounted on the ship hull, developed to improve the flow near the propeller, which operate in the non-uniform wake field of the ship. The flow mechanism around ESDs comes down to wing-body juncture flow problems and, due to their application to the ship appendage flow, they have recently received much attention in ship hydrodynamics. Despite its simple geometric configuration, the wing-body junction flow is a very complicate flow due to the so-called horseshoe vortex system determined by the adverse pressure gradient induced by the presence of the obstacle and the three-dimensional boundary layer separations around the junction. The horseshoe vortex flow affects the drag, lift and causes a persistent lack of uniformity in the wake and is also considered as one source of the noises, vibration and unsteady inflow for the propeller.

On the viscous resistance of ships sailing in shallow water

Accurate resistance prediction for ships sailing in vertically restricted waterways is highly required to improve the design and operation for large ships entering harbors and for vessels navigating in inland waters. The methods derived from deep water may lead to large errors, and studies considering shallow water effects are needed. As most ships sailing in shallow water operate at a low Froude number, the viscous resistance dominates the total resistance and becomes the main concern. In this study, a Wigley hull and the KCS (KRISO Container Ship), which have available benchmark data, are applied. A typical 86 m long inland ship is then chosen to further investigate the influence of a different hull form. Results show that the friction and the viscous pressure resistance depend on ship types, speeds, and water depths. A formula to predict a ship's friction in shallow water is given with some constants determined based on ship's characteristics. A form factor defined based on computed ship's friction is suggested, and an empirical expression is provided for each ship applied. With the investigations for three ship forms, this study is expected to provide inspirations to further improve the prediction of ship's viscous resistance in shallow water.

A physics-based simulation for AUV underwater docking using the MHDG method and a discretized propeller

Abstract A physics-based simulation for AUV docking with a stationary dock was performed with the multi-block hybrid dynamic grids method (MHDG) and a discretized propeller. URANS equations were coupled to 6DOF equations via UDF to predict the instantaneous velocity and position. The MHDG method uses a multi-block mesh topology, moving mesh, and dynamic-layer method to grid the domain, move the rigid body and its sub domain, and re-mesh the skewed mesh respectively, which can improve computation accuracy and speed. The numerical methods were validated by a comparison with open water curves and the velocity history in AUV free running between simulation and tests. Two docking modes were validated: constant RPM docking and brake docking. In constant RPM docking, the AUV velocity increased gradually, by approximately 11.5% in 6.0 s. The dock had less effect on AUV resistance except that the resistance increased and then declined as the AUV passed through the neck point of the dock. The tip vortex pairs extended and damped downstream of the rotating propeller. In brake docking, the propeller acted as a resistance part and led to a decrement of 46.2% in the velocity in nearly 9 s. The viscous pressure resistance occurred after the braking propeller.

Mechanics Analysis of Drag Reduction in Hull Motion under Wind and Waves

ABSTRACT Lu, J. and Zhang, H., 2018. Mechanics analysis of drag reduction in hull motion under wind and waves. In: Liu, Z.L. and Mi, C. (eds.), Advances in Sustainable Port and Ocean Engineering. Journal of Coastal Research, Special Issue No. 83, pp. 970–975. Coconut Creek (Florida), ISSN 0749-0208. Taking a large-scale container hull as a numerical simulation object, the computational fluid dynamics (CFD) theory is combined with the super-vacuolar drag reduction technique to reduce the hull boom resistance and total resistance. The hull type line is optimized, the joint drag reduction is carried out to improve the stability of the supercavity, and the SHIPFLOW software is used to simulate the hull resistance. The results show that after the optimization of ship types, because the wave peak change of shipboard is more gentle, viscous resistance is also reduced. Compared with the amplitude of the wave resistance, the change range of the viscous pressure resistance is smaller. The application of supercavita...

An investigation into the effect of biofouling on the ship hydrodynamic characteristics using CFD

To reduce the fuel consumption and green-house gas emissions of ships, it is necessary to understand the ship resistance. In this context, understanding the effect of surface roughness on the frictional resistance is of particular importance since the skin friction, which often takes a large portion in ship drag, increases with surface roughness. Although a large number of studies have been carried out since the age of William Froude, understanding the roughness effect is yet challenging due to its unique feature in scaling. In this study, a Computational Fluid Dynamics (CFD) based unsteady Reynolds Averaged Navier-Stokes (RANS) resistance simulation model was developed to predict the effect of barnacle fouling mainly on the resistance and hull wake characteristics of the full-scale KRISO container ship (KCS) hull. Initially, a roughness function model was employed in the wall-function of the CFD software to represent the surface conditions of barnacle fouling. A validation study was carried out involving the model-scale flat plate simulation, and then the same approach was applied in full-scale flat plate simulation and full-scale 3D KCS hull simulation for predicting the effect of barnacle fouling. The increase in frictional resistance due to the different fouling conditions were predicted and compared with the results obtained using the boundary layer similarity law analysis of Granville. Also, a further investigation of the roughness effect on the residuary resistance, viscous pressure resistance and wave making resistance was carried out. Finally, the roughness effect on the wave profile, pressure distribution along the hull, velocity distribution around the hull and wake flows were examined.

The effect of appendages on the hydrodynamic characteristics of an underwater vehicle near the free surface

An underwater vehicle typically has various appendages such as sail, rudders and hydroplanes. These appendages affect the hull hydrodynamic characteristics, including the resistance components and the form of the generated wave due to the motion of the vehicle near the free surface. The effect of the appendages on the hydrodynamic characteristics of an underwater vehicle near the free surface is studied. Initially the DARPPA SUBOFF submarine without the appendages is selected and hydrodynamic characteristics, including the friction resistance, viscous pressure resistance, wave resistance and shape of the created wave on the free surface are calculated for Froude numbers in the range of 0.128–0.84 and non-dimensional submergence depths 1.3, 2.2, 3.3 & 4.4. Then, by adding the appendages and comparing these two conditions, the effect of appendages is obtained. The results of computations indicate that the appendages cause a mean increase of about 16% in the total resistance. This increment is due to viscosity of fluid and also the interaction of the main hull with the appendages. There are no significant changes in the wave pattern and wave making resistance due to the presence of appendages.