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During the conceptual design of a high speed craft, the most important element of the process is resistance and drag prediction. To increase efficiency in high speed craft design, the prediction of total resistance must be increasingly accurate. To achieve this objective, model towing tank tests were used. Although testing will always be necessary,...
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... half model approach was used to reduce the computational cost, such that a symmetry plane splits the domain down the cen- terline. The computational towing tank domain, with the model hull and the notations of the boundaries is shown in Fig. 5. The domain was taken to extend two model lengths fore of the mo- del, three model lengths aft, two model lengths along the beam considering wave reflection and three model lengths in depth. A wave damping length was selected to avoid interaction be- tween true and reflected waves. For the numerical simulations, the domain was ...
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... numerical simulation visualization of the model hull and free surface elevation at various Froude numbers in the planing regime is shown in Fig. 14. Photos from the experiments at va- rious Froude numbers in the planing regime are given in Fig. 15. Delen and Bal (2015) studied the uncertainty analysis of the resistance tests, which were estimated according to the ITTC (2014) for the same ship model used in the present study. It was reported that the expanded uncertainty value of the resistance test was 0.42% for Fr = 0.90. It was also noted that uncertainty sources in the ...
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Citations
... This effect typically consists in the air volume-fraction being convected in the boundary layer below the water line, causing a reduction of the skin friction. NV is commonly encountered when modelling planing hulls using the VOF method (Gray-Stephens et al., 2021;Avci and Barlas, 2018;Viola et al., 2012), where the hull forms a small acute angle with the free surface. As the latter has the tendency to align with the thin cells close to the hull, air is convected into the water. ...
The presence of mud layers on the bottom of ports and waterways can have negative effects on the hydrodynamic behaviour of marine vessels. This numerical study investigates the effect of muddy seabeds on the full-scale resistance of an oil tanker sailing straight ahead. The objective is to determine the influence of factors such as the densimetric Froude number, UKC and mud rheology at speeds between 3 and 9 knots. The numerical study is conducted using a finite-volume Reynolds-Averaged Navier-Stokes (RANS) flow solver combined with the Volume-Of-Fluid (VOF) method to capture the mud-water interface. At certain critical speeds, the presence of mud increased the ship's total resistance by up to 15 times compared to the case with solid bottoms. The non-Newtonian rheology of mud was found to influence the ship's resistance mainly at low speeds and when sailing through the mud layer. This article also shows that, when sailing through mud, the computed resistance at high speeds may be underestimated because of two effects, namely 'water lubrication' and 'numerical ventilation'.
... In this study, + was used with a value of 50. The + was between 45 -60 to get accurate simulation results [91]. According to ITTC, the calculation of the + value is obtained through Equation (13) [86], where: y is the thickness of the first layer that must be adjusted in making the mesh arrangement, is the length of the hull, Re is the value of the Reynolds number, and is the skin friction coefficient of the object that can use Empirical formula from ITTC'57 [92]. ...
Along with developing high-speed craft technology, the planing hull is growing with modifications for better performance. One such technology is stepped hull, both single and double. Planing hull with steps allows the boat to run at a relatively low drag-lift ratio with lower frictional resistance due to reduced wetted area. In this study, the hull was modified with variations in the position of the double steps, which aimed to determine the effect of the first and second step positions on the total resistance, dynamic trim, and dynamic sinkage generated by computational fluid dynamics (CFD). Based on the analysis results, variations in the position of the stepped can change the hull performance. Shortening the distance between the two steps and moving both rearwards toward the transom can lower the total resistance. The dynamic trim and dynamic sinkage decreased as the position of the two steps was shifted further forward. An equation created in a non-dimensional form relates the positions of two steps to the desired results of total resistance, dynamic trim, and dynamic sinkage, namely: {(x1-x2)/L + (x1x2)/(LB)} × Fr∇, where x1 is distance the first step from transom, x2 is the distance of the second step, L is the length of the boat, B is the beam of the boat, and Fr∇ is the volume Froude number.
... To properly manage the complex mesh generation, a trimmed cell mesher was used. As shown in Fig. 2, the finite volume mesh was constructed utterly in [25] comprising structured hexahedral grids, and the mesh assessment is given in Table 1. Walls with slip boundary conditions were employed in the far field. ...
... It was noted that mesh advancements do not alleviate this problem. In most cases, this issue might result in an unintended drag decrease of up to 30% [25]. In the current study, the phase replacement technique was used to address this problem, as reported by [25]. ...
... In most cases, this issue might result in an unintended drag decrease of up to 30% [25]. In the current study, the phase replacement technique was used to address this problem, as reported by [25]. This approach replaces the water phase with the unwanted air phase in the specified locations. ...
One of the crucial aspects of the conceptual design of a stepped planing hull is the prediction of its performance. To improve performance, the prediction of total resistance must become more accurate. In the field of research, both towing tank experiments and numerical analysis may be used to achieve this goal. In this study, experiments were conducted initially to investigate total resistance of a relatively high-speed craft without a transverse step. Later, numerical computations were carried out to validate the experimental results. After it was determined that the test results and CFD methods were in good agreement, the experimental method continued to investigate the resistance properties of the hull with four different configurations to evaluate the optimal longitudinal position of a single transverse step. The ideal longitudinal position of the single transverse step was evaluated based on a similar relatively high-speed hull with a velocity of up to beam Froude number (FrB) 2.56 in this study, focusing on the FrB range between 2.30 and 2.45.
... The research by Avci et. al. used a y+ value between 45 60 for more accurate results [13], The calculation of the y+ value according to ITTC is stated in the equation below [14] : ...
... The time step used in this study is 0.005 seconds. This refers to ITTC recommendations [13] contained in equation 4. Where L is the length of the ship and U is the speed of the ship. ...
Differences in the depth of the water surface affect the hydrodynamics of the ship so there is a possibility that the ship will behave differently in deep water and shallow water. The surface flow generated by the hull varies radically due to the speed of the ship and the effects of water depth. At a certain speed, the ship experiences a critical speed condition, which will affect the total resistance of the ship. This study examines the Fridsma ship's resistance to differences in water depth at several speeds. Numerical computation is used in this study to simulate the characteristics of a planing hull form. The Finite Volume Method (FMV) is used to observe fluid flow due to differences in water level with the RANS (Reynolds-Averaged Navier - Stokes) equation in predicting ship resistance. K-ε was modeled as a turbulent and volume of fluid (VOF) model to represent the air and water phases. This study uses a morphing grid mesh to analyze the shape of the hull in numerical simulations. The total resistance of Fridsma in shallow waters increased at each speed when compared to the total resistance in deep waters. On average in deep waters, it can reduce the total resistance by around 22.34% compared to shallow waters. This is caused by the squat phenomenon that occurs in the hull.
... Lotfi and Ahmed Gultekin researched to obtain accurate results. Lotfi used the value of y+ [17], and Ahmed Gultekin used a value of y+ 45-60 [18]. Meanwhile, in this research, the results obtained y+ 45-70. ...
CFD is a numerical approach used to solve fluid problems. In the CFD simulation process, the meshing stage is crucial to produce high accuracy. Meshing is a process where the geometric space of an object is broken down into many nodes to translate the physical components that occur while representing the object’s physical shape. The research objective was to analyze the characteristics of the mesh technique in the Finite Volume Method (FVM) using the RANS ( Reynolds - Averaged Navier - Stokes ) equation. The numerical simulation approach used three mesh techniques, namely overset mesh, morphing mesh, and moving mesh. The k-ε turbulent model and VOF ( Volume of Fluid ) were used to model the water and air phases. The mesh technique approach in CFD simulation showed a pattern under experimental testing. This research showed the difference in value to the experimental results, namely by using the moving mesh method, the difference in resistance difference was 8% at high-speed conditions, the difference in trim value at overset mesh was 11%, and the difference in heave value with the moving mesh method was 14% at low speed. The conclusion reported that overset mesh had better than other mesh methods.
... GCI (Grid Convergence Index) has been used for verification study in this study [20]. Only numerical uncertainty arisen from spatial discretization of the computational domain was considered since it has been the predominant component of total uncertainty. ...
In this study, nominal wake field for a geometrically similar model family of a high-speed benchmark vessel (Athena hull) were investigated computationally. Scale effects on nominal wake field of a semi-displacement type vessel were studied in an accurate extrapolation strategy that depends on Re (Reynolds) number. It is known that Re number is the indicator of scale effect at a specific Fr number. In this regard, a model family was generated by two different model scales of Athena hull with a skeg and calm water CFD (Computational Fluid Dynamics) analyses were performed at a constant Fr (Froude) number (Fr=0.8) by an unsteady RANS (Reynolds Averaged Navier-Stokes) solver. The model family was simulated as free to heave and pitch motions and k-e turbulence model was used for modelling the turbulent flow around hull geometries. Nominal wake fractions of Athena hull have been calculated for the model family and GEOSIM-based extrapolation strategy was conducted to reach the full-scale nominal wake fraction. The extrapolated wake fraction was also compared with those of full-scale CFD results, and a good agreement was achieved. It can be noted that the GEOSIM-based extrapolation method can be applied for accurate estimation of the nominal wake fraction of semi-displacement type high-speed vessels.
... The dynamic lift has become obvious at high speeds, but at low speeds the planing hull moves as a displacement vessel. Thus, at high speeds, the hull is subjected to dynamic effects, due to the hull characteristics together with running attitudes (dynamic trim and parallel sinkage or rise) [3]. ...
The design and analysis of high-speed planing hulls have been one of the complicated hydrodynamical issues for naval architects due to the physical complexity of the flow. The focus of this study is the numerical simulation of the flow around a vee-shape hard chine planing hull model (USCG series parent model 5628) using a commercial RANSE code (ANSYS CFX). In order to model the free surface effect, the volume of fluid (VOF) method has been considered. The resistance values were obtained for a range of Froude numbers by implementing Shear Stress Transport (SST) turbulence model. Reasonable agreement of drag results were achieved in comparison with the model experimental data. Additionally, another turbulence model; k-was used for the same investigation to compare the results of the two models and to find the most effective model for planing hulls resistance calculation. The SST model gives more accurate results than k-. Mean errors over most of the Froude number values were less than 10% except at low speeds and at the start of the planing mode where, they were around 12%. Also, the wave pattern for the different speed ranges has been presented in this study to clarify the inverse relationship between the wake angle and speed.
... A numerical ventilation problem becomes a challenge in the study of numerical simulation. Studies on this issue have been conducted to predict the total drag of fast ships [11,12]. The other study, Fridsma hull was used for numerical verification of OpenFOAM code in seaplane simulation during takeoff [13]. ...
... Figure 6 shows that the value of y+ is at a value of 60-70. Meanwhile, Avci et al., in their research used the value of y+ between 45 and 60 to obtain accurate results [12]. According to ITTC, the calculation of the y+ value [26] is as follows: ...
... Figure 6 shows that the value of y+ is at a value of 60-70. Meanwhile, Avci et al., in their research used the value of y+ between 45 and 60 to obtain accurate results [12]. According to ITTC, the calculation of the y+ value [26] is as follows: The wall function (y+) is used to reduce numerical simulation inaccuracies. ...
Spray strips are deflectors added to the hull to reduce the Wetted Surface Area (WSA). The reduced WSA will decrease the total ship drag caused by the deflection of the spray strip installation. The research aimed to predict the function of the spray strip to improve ship performance using Computational Fluid Dynamics (CFD). The numerical approach in this study used the Finite Volume Method (FVM) with the RANS (Reynolds-averaged Navier–Stokes) equation to solve fluid dynamics problems. VOF (Volume of Fluid) was used to model the water and air phases. The results of this study indicated that the number of spray strips would have a significant effect compared to without using a spray strip. Spray strips with three strips could reduce the total resistance by 4.9% at Fr 1.78. Spray strips would increase the total resistance value by 2.1% at low speeds. Spray strips were effective for reducing total resistance at Fr > 1 or the planing mode conditions. The total resistance prediction used three suggestion profiles with the best performance to reduce total resistance by 6.0% at Fr 1.78.
... Moreover, the numerical ventilation problem at hull bottom also attracted attentions. Based on experimental and numerical study, Avci and Barlas (2018) indicated that ventilation problem in numerical simulations of planing crafts may lead to an erroneous resistance reduction of 27%, which referred to the abnormal water-air distribution at the hull bottom. It is also recommended to use the High-Resolution Interface Capturing (HRIC) scheme to solve the VOF transport equation (Ding et al., 2019;Khazaee et al., 2019). ...
It is significant to clarify the tunnel flow mechanism and its effect in a wide speed range for the design of a planing trimaran with large loading capacity and long cruising radius. A numerical investigation of bare hull hydrodynamics of a planing trimaran, designed for waterjet propulsion, is conducted at 0.68 < Fr▽<6.16. The discussion is divided into two conditions of low & hump speed and planing speed, as tunnel effect varies with speed. At Fr▽<1.03, air cushion partly occurs in tunnel, and it is considerable to improve the deceleration and distortion of tunnel flow for resistance reduction. The added wetted area of concave tunnel and the strong wave interaction on tunnel accounts for the earlier hump speed and large hump resistance. Apart from tunnel lift generated by itself, its promotion effect on lift of main hull plays a major role in the rapid hull lifting and moderate resistance growth at 2.74 < Fr▽<5.34. Although the tunnel aerodynamic lift remains small, no more than 3% of total displacement, it helps to decrease resistance by providing bow-lifting moment to keep hull trim unchanged and thus reduce main hull wetted length at 5.34 < Fr▽<6.16.
... Wall function (y+) digunakan untuk mengurangi ketidakuratan perhitungan. Nilai y+ antara 45 -60 untuk mendapatkan hasil yang akurat [13], sedangkan pada penelitian lain menyarankan nilai y+ berada pada rentang 50-150 [14]. Pada penelitian ini digunakan y+ seperti pada Gambar 2. Perhitungan nilai y+ menurut ITTC [15] yang ditunjukkan pada persamaan 4. ...
A high-speed vessel has a range of Froude Number (Fr) > 1. A drag prediction method based on Fr > 1 has high complexity because it is influenced by trim and heave motions. Hence, a specific treatment is necessary to obtain accurate results. This study is using mesh density and mesh shapes to predict the total drag of a planing hull ship. The Computational Fluid Dynamic (CFD) results show good performance in predicting the drag, trim, and heave. Mesh density of 2300K shows the most stabilized result. The trimmed mesh type is more efficient to obtain accurate results because it has a smaller mesh size. The polyhedral mesh type is as good as trimmed mesh but is not as efficient as trimmed mesh and it has largely a time-consuming time.
