The Study of Hydroplane for Submarine Hull Form Using Experimental Method and CFD Study
Thu Han Tun
Marine Mechanical Engineering Department, Myanmar Maritime University,Thanlyin, Yangon Region, Myanmar.
SUMMARYIn designing submarines, hull form selection, resistance, and powering are key aspects and alsohydroplanes as horizontal control surfaces are used to control the vertical motions of submarines andother underwater vehicles. The shape, area and location of hydroplanes will depend on the size, speed
and operational requirements of the submarine. Hydroplanes must therefore be able to apply upward or
downward force to submarine and provide a pitching moment. Two pairs of control surfaces arerequired, being normally situated near the fore and aft ends to provide the largest moments. In thisstudy one pair of hydroplane is installed near the aft ends. CFD simulations enable surface condition
analysis using FINEMarine. The results show that the lifting force for the AOA is 25 degrees and 1.4
m/s. Furthermore, in this condition, the pitch motion is close to zero degrees.
NOMENCLATUREAoADHLBLCLCSLOA
LWLRtTVΔ𝛾
1.

Angle of Attack (degree)
Hull Diameter (m)Bow length (m)Cylinder length (m)Conical Stern length (m)Length overall (m)Length waterline (m)Total resistance (N)Draught (m)Speed of vessel (m/s)
Displacement (tonnes)
Conical Stern angle (degree)
INTRODUCTION

Hull form selection, resistance, powering and also hydroplanes are important in designing submarines.
CFD simulation was carried out to control the pitch motion in near-surface conditions. The model hadhydroplanes installed near the aft ends. Hydroplanes are horizontal control surfaces used to control
the vertical motions of submarines and other underwater vehicles.
CFD tools are widely used for the prediction of ship resistance and powering with appendages. Assuch, CFD codes were also used for the pitch motion control. The model experiments were carriedout to measure resistance and downforce in the Ship Model Towing Tank (SMTT) at Marine
Hydrodynamics Centre, Myanmar Maritime University 3. The SMTT is 60m in length, 4m in breadth,and 4m in depth, with a water level of 3m. The maximum carriage speed of the SMTT is 4 m/s.
2.

OBJECTIVE

This paper analyses the performance of hydroplanes for submarine hull form by CFD simulation.

3.

STUDY AREA

Despite being primarily designed for optimal performance when submerged, submarines must also beable to operate well on the water surface. Modern submarine hulls are inefficient when operating on
the surface, resulting in poor resistance performance. Submarines have a low freeboard compared tonormal ship surfaces, meaning the majority of the hull sits below the water surface. As such, whenoperating at relatively high Froude Numbers, wave making resistance becomes dominant.
Hydroplanes are key aspects to control the vertical motions of submarines.
The shape, area and location of hydroplanes will depend on the size, speed and operational
requirements of the submarine. Hydroplanes must therefore be able to apply upward or downward
force to the submarine and provide a pitching moment. Two pairs of control surfaces are required,being normally situated near the fore and aft ends to provide the largest moments. In this study one
pair of hydroplane is installed near the aft ends.
Initially, a 1.5m long wooden model was manufactured and tested in the model basin of the Myanmar
Maritime University for resistance and downward force measurement. A CFD simulation was carriedout to control the vessel's pitch motion.
The CFD solver is capable of calculations with multi-phase flows and moving grids. In the multiphase continuum, considering the incompressible flow of viscous fluid under isothermal conditions,the mass, momentum, and volume fraction conservation equations can be written as (FINE™ / Marine
9.1, Theory Guide) –𝜕⃗ − ⃗⃗⃗⃗𝑈𝑑 )𝑛⃗𝑑𝑆 = 0∫ 𝑝𝑑𝑉 + ∫𝑆 𝑝(𝑈𝜕𝑡 𝑉(1)where V is the domain of interest, or control volume, bounded by the closed surface S, with a unit
⃗ and p represent the velocity and pressure fields, respectively.
normal vector 𝑛⃗ directed outward. 𝑈
When the grid is moving, the so-called “space conservation law” must also be satisfied:𝜕𝑈𝑑 𝑛⃗𝑑𝑆 = 0∫ 𝑑𝑉 = ∫𝑆 ⃗⃗⃗⃗𝜕𝑡 𝑉

4.

STUDY APPROACH

4.1

Determining the main dimensions(2)

The propeller-hull interaction results in the submarine bare hull form being based on the following
five parameters (Burcher & Rydill, 1995):➢➢➢➢➢

The fineness ratio
Prismatic coefficient
Nose radius
Tail angle andThe position of the maximum section.

The dimensions of a submarine model with the parallel middle body form are described in table 1.
L/D relation is 8.3. The vessel design consists of an elliptical main hull, a conical stern andhydroplanes profiled NACA0012 (Figure 1).

Table 1: Main particulars of model at design condition.
Main particulars
Unit
Overall length, LOA (m)1.500
Hull vertical diameter, DVH (m)0.210
Hull horizontal diameter, DHH (m)0.180
Displacement, Δ (tonnes)
0.028
Bow length, LB (m)0.333
Cylinder length, LC (m)0.590
Conical stern length, LCS (m)0.576
Draught, T (m)
0.170
20.20
Conical stern angle, γ (degree)
Hydroplane (NACA0012 profile)
Chord length (m)0.13619
Span length (m)0.055

Figure 1: Model of submarine with hydroplanes.
4.2

Hydrodynamic effect of the model

The model without appendages was tested in the towing tank on the surface condition, with theobservation being made that even keel conditions could not be controlled (Tun & Htun, 2021). The
CFD simulation was also carried out for even keel using FINEMarine. The pressure distribution on
the hull is shown in Figure 2. As a result, the hydroplanes was designed to control the pitching motionof the model (Figure 3). The hydroplanes NACA0012 profile are detailed in Table 2.

Figure 2: Hydrodynamic effect of the model.

Table 2: Coordinates of NACA 0012 airfoil section in mm.
XY0
1.268596
5.02714111.13556
19.36629
29.41263
40.90027
53.40117
66.44957
79.55928
92.24183
104.0247
114.4688
123.185129.8486
134.2113
136.1902.2431314.243122
5.915699
7.167012
7.926912
8.173742
7.941852
7.311578
6.389
5.285656
4.106333
2.946431.894989
1.036515
0.446758
0.171599

Z00000000000000000Figure 3: Hydroplane NACA0012 profile section and 3D model.
4.3

Experimental approach

The towing tests were conducted over a 0.6 to 1.8 m/s speed range (Table 3). The test conditions were:
zero trim, 0.170m of draught, and the towing tank water level was 3m (Tun, Htun and Min, 2021).

4.4

Table 3: Model resistance test.
Total resistance of model
Speed of vessel V (m/s)
Rt(N)
0.6
0.800
0.8
2.187
1.0
4.522
1.2
7.937
1.4
7.457
1.6
12.4971.8
18.015
Numerical approach

Downforce (N)
0.720
2.764
6.129
10.796
10.4468.794
7.363

Numerical methods have strongly advanced in this field, meaning a combined use of both model tests
and CFD codes can be very effective in aiding ship design and for understanding ship hydrodynamics(Watson, 1998). Firstly, CFD simulation was performed to inverstigate the lift force of hydroplane inorder to cover downforce. The flow setting is 1.6 m/s with the AoA 25 degrees.

Figure 5: Generated mesh of the hydroplane(NACA0012).

The CFD simulation tested a speed of 1.6 m/s. A result of hydroplane at 1.6m/s speed and the AoA
25 degrees are shown in Figure 6 (a to c).

(a) Pressure distribution around the hydroplane.

(b) Velocity distribution around the hydroplane.

(c) Streamline around the hydroplane.
Figures 6a-6c: Result of hydroplane at 1.6m/s speed and the AoA 25 degrees.
The average downward and drag forces per hydroplane are 5.8N and 2.3N repectively. Therefore, thetotal downward and drag forces are 11.6N and 4.6N repectively. The designed shape, size and area ofhydroplanes coverd the tested downforce 8.394N from Table 3.
After simulation of downward force, pair of hydroplanes are attached near the aft ends of submarine.
And then, Numerical simulation was carried out for submarine with hydroplanes model to inverstigate
the pitch motion. The initial mesh had an X axis of 30, a Y axis of 10, and a Z axis of 15, with thetotal cells being 1333732 (Figure 7). The minimum mesh width was 0.00135m. The computed firstlayer thickness/the distance of the nearest grid point to the wall (Ywall) was 0.001839m. FINEMarinewith the k-omega turbulence model (SST-menter) was used to perform numerical computations.

Figure 7: Generated mesh of the whole model.
The physical parameters were greater than the mesh parameters in terms of the boundary type of eachsurface. HEXPRESS™ took these conditions into account when computing a mesh in accordancewith the future flow. For instance, a boundary layer mesh was computed to properly capture the flow
next to the wall using a turbulence model. This highlights the importance of defining the boundary
conditions during mesh setup. By default, each physical boundary is defined as a SOLID. Boundary
conditions are listed in Table 4 (FINE™ / Marine 9.1, Theory Guide).
Table 4: Boundary conditions.
Description
Boundary condition typezmin (bottom of domain)
zmax (top of domain)

External Prescribed
External pressurexmin (outlet of domain)

External

xmax (inlet of domain)

Externalymin (- side of domain)

Externalymax (+ side of domain)

External

Model

Solid

Far field

Wall function

The domain size for this application is defined based on the Froude number (Fn) and the bodyreference length (length overall LOA of the model). The default numbers are shown in Figure 8.

Figure 8: Computational domain size.
Wave elevation for submarine without hydroplanes (fixed trim) is shown in Figure 9. Wave elevationof submarine with hydroplane at 1.6m/s speed and the AoA 25 degrees is presented by Figure 10. It
had been observed that hydrodynamic effect on the submarine was reduced due to hydroplanes (Figure11).

Figure 9: Wave elevation of submarine without hydroplanes (fixed trim)

Figure 10: wave elevation of submarine with hydroplanes (free motion)

Figure 11: Hydrodynamic effect of submarine with hydroplanes (free motion and AoA 0 deg)

Figure 12: Hydrodynamic effect of submarine with hydroplanes (free motion and AoA 25 deg)After testing CFD simulation for submarine with hydroplanes, the results are –▪ The total resistance - 14.4N▪ Heave- 0.033m▪ Trim- 0.23 deg by stern

5.

RESULTS DISCUSSION

Resistance increased about 15% from bare hull result at 1.6m/s and the AoA 25 degrees. At thiscondition, the bow wave near the bridge is high due to heave value 0.033m (Figure 10). The results(Figure 11 and 12) show that the hydrodynamic effect on the submarine decreases and the model’strim is nearly zero. Finally the result proved that hydroplanes are very important to ensure the pitch
motion on the near surface or underwater conditions.

6.

REFERENCES

1.

BURCHER, R. and RYDILL, L. (1995) Concepts in Submarine design, Cambridge ocean
technology series.
FINE™/Marine 9.1, Theory Guide.
ITTC 7.5-02-02-01, (2011) Recommended Procedures and Guidelines, Resistance Test,Revision 03.
TUN, T.H. and HTUN, Y.T. (2021) The Experimental Method and CFD Study of the Bare
Hull Form of Underwater Vehicle at Near Surface Condition. ASEAN Engineering Journal,
11(1), pp.24-33.
TUN, T.H, HTUN, Y.T and MIN, A.K, (2021). Comparison of Experimental Towing Test andCFD Analysis of a Bare Hull Model on the Surface. International Journal of Maritime
Engineering, 163(A3).
WATSON D.G.M. (1998) Practical Ship Design, Elsevier Science Ltd, Oxford.

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