International Journal of Current Engineering and Technology

ISSN 2277 - 4106

© 2014 INPRESSCO. All Rights Reserved.
Available at http://inpressco.com/category/ijcet

Research Article
CFD Simulation and Analysis for Free Surface Computations around Fixed
‘DTMB 5415’ Model
Suyog S. KadamȦ*, Shivprakash B. BarveȦ, Harshada A. Gurav Ḃ, Vilas S KanthaleȦ
Ȧ
Department of Mechanical Engineering, MAEER’s MIT College of Engineering, Pune, India
b
Department of Mechanical, Abhinav Education Society’s College of Engineering, Pune, India

Accepted 12 March 2014, Available online 01 April 2014, Special Issue-3, (April 2014)

Abstract

One important issue in the CFD application is the prediction of the power demand of a new ship. For this purpose the
interaction between the hull, rudder and the propeller must be correctly accounted for. This project presents results of
the computations performed in the ETSIN for different ships with the RANSE free surface commercial solver CFX. Some
of the computational results are validated against experimental data in terms of various global and local quantities. The
CFX code is based on a finite volume Discretization. The turbulence model used in the calculations was the SST (Shear
Stress Transport) model, and the volume of fluid method is used to model the free-surface flow. The incompressible
turbulent free surface flow around the complex hull form of the DTMB 5415 model at two different speeds has been
numerically simulated using the RANSE code CFX. The Volume of Fluid method (VOF) has been used with CFX for
capturing the free surface flow around the ship model at the two speeds. The simulation conditions are the ones for which
experimental and numerical results exist. The standard k– e turbulence model has been used in CFX code. The grid
generator ICEM CFD has been used for building the hybrid grid for the RANSE code solver. The results compare well
with the available experimental and numerical data.

Keywords: RANSE, Nodes &boundary conditions, Drag Force & drag Coefficient

1. Introduction presents results of the computations performed in the

ETSIN for US navy combatant DTMB 5415 ship with the
1
Fluid dynamics is the science of fluid motion. RANSE free surface commercial solver CFX. Some of the
Computational fluid dynamics (CFD) is the science of computational results are validated against experimental
predicting fluid flow, heat transfer, mass transfer, data in terms of various global and local quantities. The
chemical reactions, and related phenomena by solving the CFX code is based on a finite volume Discretization. The
mathematical equations which govern these processes turbulence model used in the calculations was the SST
using a numerical process. Computational Fluid Dynamics (Shear Stress Transport) model, and the volume of fluid
is ―a wind tunnel in the computer.‖ It is a method by method is used to model the free-surface flow. The
which one uses certain algorithms or other numerical numerical schemes use higher order cells to satisfy the
formulas to analyze the fluids' flow. It is one of the most momentum, pressure and turbulence quantities where each
important high tech tools for measuring the performance hexahedral cell is further subdivided into eight sub-
of model. Computational fluid dynamics (CFD) has volumes. A control volume is formed from the sub-
progressed rapidly in the past 50 years. It has been used in volumes surrounding a grid node and a first order finite
many industrial fields and plays an irreplaceable role in element basis function is used for each sub volume. The
engineering design and scientific research. CFD is the art momentum and pressure are simultaneously satisfied using
of replacing the differential equation governing the Fluid a coupled solution system. All the numerical equations are
Flow, with a set of algebraic equations (the process is solved using algebraic multi-grid acceleration with
called Discretization), which in turn can be solved with the implicit smoothing. Parallel computation on a 2 processors
aid of a digital computer to get an approximate solution. PC was adopted to reduce the required computational
One important issue in the CFD application is the time.
prediction of the power demand of a new ship. For this
purpose the interaction between the hull, rudder and the Table 1 Terms & Nomenclature
propeller must be correctly accounted for. This paper
Term Meaning
Aft stern or rear side
*Corresponding author: Suyog S. Kadam

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ANSYS The software used for CFD analysis. complicated to create; they give much better results
especially at the ship wake. Comparisons between
Ratio of longest edge length to shortest experimental and computed values show a relatively good
Aspect Ratio edge length. ( Measure of quality of agreement between them using structured meshes. The
mesh) structured mesh is based on a O-grid block distribution.
BEM Boundary Element Method. The O-grid creation capability is simply the modification
Computation Fluid Dynamics. of a single block or blocks to a 5 sub block topology (7
Calculation method or software which sub-blocks in 3D) as shown in figure for a simple 2D case.
CFD
enables hydrodynamic optimization of  The mesh quality can also be determined in ICEM. It
hull form. should be positive. The quality is given in determinant
Depth of water to which a ship sinks form as follows
according to its load. Vertical distance  Here, the number of cells are shown on Y axis while
Draft mesh quality is shown on X axis.
between ship’s waterline and lowest
point of its keel.  A Determinant value of 1 would indicate a perfectly
It is the resistance of the fluid to the regular mesh element, 0 would indicate an element
Drag degenerate in one or more edges, and negative values
moving body In longitudinal direction.
would indicate inverted elements. [1]
DTMB David Taylor Model Basin.
FEM Finite Element Method.
[2] Structure of CFD Code
FDM Finite Difference Method
Forward front of ship Tao Xing and Fred Stern, IIHR— Hydro science &
Froude number describes the vessel’s Engineering, C. Maxwell Stanley Hydraulics Laboratory,
relative speed, which depends on vessel The University of Iowa.
length
2.1 Pre Processing

Froude number One limiting factor of the practical application of RANSE

(Fn) solvers lies in the model preparation (grid), which - is
Where, usually very time-consuming, thus using highly qualified
v = vessel speed in [m/s] (1 manpower for low added value work, - and can hardly be
knot = 0.5 m/s) automated for shape variations involved in an optimal
g = 9.81 m/s2 design process. This explains the hard work performed by
L = vessel’s waterline length grid generation specialists to provide tools that reduce
FVM Finite Volume Method these issues. Such a software package is used in the
computer program which calculate the present work which collects the advantages of being
ETSIN CFD steady inviscid flow around a ship hull, independent from solvers, including many user requested
wave pattern and resistance capabilities and having automation and scripting
Hull outer body of ship capabilities that make it directly incorporable into an
Reynolds Averaged Navier Strokes optimal design procedure.
RANSE
Equation
Vessels resistance against moving eg.
2.2 Solver
Resistance
Wind resistance, friction resistance etc.
The offer in term of flow calculation tools is very large.
SST Shear stress transport
However, when looking at ship specific issues, i.e. those
VOF Volume of fluid involving a free surface, mainly two types of approaches
are considered. The potential flow approaches based on
2. Literature Review boundary elements methods have now proven to be
efficient for a number of basic problems like steady flow
[1] RANSE with free surface computations around assessment (wave resistance problem) and response in
fixed DTMB 5415 model waves (sea keeping problems). Many teams, from both
commercial solver providers and maritime scientific
Martín Priego Wood1, Leo M. González1, Jorge community, are investigating the use of RANSE solvers
Izquierdo1, Adrián Sarasquete2 and for ship design problems. This is continuously leading to
Luis Pérez Rojas1(1 School of Naval Architecture, improvement in accuracy and extension of the range of
Polytechnic University of Madrid (Spain),2Baliño S.A.) application of these methods. However, only a small
number of them can nowadays be practically involved in
Different calculations have been done with unstructured ship design, and they still require high level skills that
and structured meshes obtaining qualitative and prevent them to be currently used by most design offices.
quantitative better results with the structured ones. This The Reynolds Averaged Navier-Stokes Equations
points out that although structured meshes are much more discredited by finite differences, by taking into account the

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complete nonlinear free surface conditions. Solver is 3.2 Meshing

dedicated to flow analysis around bodies piercing the free
It is also called as Discretization. Domain is discredited
surface or close to it, and gives accurate prediction of all
into a finite set of control volumes or cells. The discredited
the components of ship resistance.
domain is called the ―grid‖ or the ―mesh.‖ General
conservation (transport) equations for mass, momentum,
2.3 Post Processing
energy, etc., are discredited into algebraic equations. All
Another limiting factor to the use of RANSE methods in equations are solved to render flow field.
design procedure and especially in optimal design is
related with the complexity of phenomena to be looked at,
and with the difficulty to extract relevant figures of merit
from the large amount of information provided by these
solvers. Again, this aspect is worked on by many teams’
specialists in this area. Several software packages are now
commercially available for this purpose, among which the
one used in the present work, ANSYS CFX. It gathers a
large number of user required capabilities which enable a
full exploitation of CFD results, and also has high Fig. 3 Final meshed model of US navy Combatant DTMB
automation and scripting capabilities which make it a good 5415
component of any optimal design approach. [11]
The meshed model of ship shown above has following
[3] Applied Computational Fluid Dynamics specifications.
Methodology by André Bakker.
Methodology includes- Table 2 Mesh Details of Elemental Parts
 Modeling
 Meshing Element parts No. of elements/cells
 Defining boundary conditions AIR 1055208
 Computational method GEOM 20892
 Post processing INLET 3610
OPENING 44460
3. Procedure OUTLET 3610
SHIP BOTTOM 4832
SHIP TOP 3487
3.1 Modeling
SHIP TOP1 1680
SYMMETRY 44868
As we know, this analysis contains two typeso fluids.
WATER 1116430
Therefore ―Multiphase modeling‖ is done. The modeling
WATER AIR INTERFACE 19212
is done in ANSYS ICEM. This process involves step by
WATER BOTTOM 17784
step creation of geometry. First points are created and then
they are joined by curves. Then surfaces are created and
blocking is done. The detailed procedure is shown below Total elements: 2020907; Total nodes: 1929333
3.3 Boundary Conditions
For the simplification of the problem, the reference states
are selected while introducing the boundary conditions.
Here these references are-
For ideal fluids
Reference temperature- 25˚C
Reference pressure – 1 atm.
Fig.1 Blocking of Model
Reference index for radiation properties- 1

3.4 Post-Processing

In the post processing the results are reviewed in one of

the two ways. Either graphically or alpha numerically.
Graphically it shows contours, vector plots, charts, iso-
surfaces, flow lines and animation. Numerically it gives
Integral values, Drag, lift, and torque calculations,
Averages, standard deviations, Minima, maxima,
Fig.2 Actual Ship model in Ansys ICEM
Comparison with experimental data.

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For given test conditions, we are getting the results of

following.

Graphical results

 Mesh quality checks

 Y plus plot
 Y plot
 Water & air velocity streamline Fig. 6 Minimum angle check
 Aspect ratio at interference
 Vector plots

Analytical results

 Drag force
 Drag coefficient

Table 3 Comparison between Experimental &

Computational Values

Parameter Experimental data Computational

data Fig.7 Y plus plot
Length (m) 5.72 5.72
Beam (m) 0.76 0.7242
Draft (m) 0.248 0.248
Wetted surface 4.486 4.861
area (m2)
Density (kg/m3) 999 997

4. Results and Validation

4.1 Analytical results
Table 4 Analytical Results

Drag force 46.6928 Fig. 8 Y plot

Drag Coefficient 4.368

4.2 Graphical results

Fig. 9 Aspect ratio at interference

Fig. 4 Aspect Ratio Check

Fig. 5 Determinant check Fig.10 Water and air velocity streamlines

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create; they give much better results especially at the ship

hull. Comparisons between experimental & computed
values shows relatively good agreement between them
using structured meshes.

Future Scope

This analysiswasonly about ―Drag‖ & ―Mesh quality‖ but

further using this technique we can also obtain following
results,
 Fuel Economy
Fig.11 Water velocity vector plot at the interference  Wake Coefficients
 Actual Velocity profiles & isolines
 Wave elevations
 Wave profile at required section
 Balancing, Stability & effect of waves on ship &
stock on the ship
 Heating & cooling of engine
 Also results for other ship parts like Propeller
Further by changing the type of mesh, diffrent results of
different accurecy can be obtained.

References
Fig. 12 Vector plot of air a 25 wall shear
Martín Priego Wood1, Leo M. González1, Jorge Izquierdo1, Adrián
Sarasquete2 and Luis Pérez Rojas (2007), RANSE with free surface
4.3 Validation
computations around fixed DTMB 5415 model and other
Baliño’s fishing vessels. 9th International Conference on Numerical
Table 5 Comparison between Experimental and Ship Hydrodynamics Michigan, USA.
Computational Results Tao Xing and Fred Stern, IIHR— Hydro science & Engineering, C.
Maxwell Stanley Hydraulics Laboratory, The University of Iowa.
André Bakker. Applied Computational Fluid Dynamics
Experimental Computational Metin Ozen, Ph.D., CFD Research Corporation Ashok Das, Ph.D.,
Drag force 45.21 N 46.6928 N Applied Materials Kim Parnell, Ph.D., Parnell Engineering and
Drag Consulting. CFD Fundamentals and Applications.
4.23 4.368 Introduction to Computational Fluid Dynamics (CFD)
coefficient
Wenbin Song, Andy Keane, Hakki Eres, Graeme Pound, and Simon Cox.
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% Error = (Computational value – Experimental value) / Computing Environment.
Experimental Value Leo Lazauskas, Cyberiad, First Draft: 16 Dec. 2009, Resistance and
Squat of Surface Combatant DTMB Model 5415: Experiments and
Predictions
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New York, USA)
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like the Combatant DTMB 5415 modelhas been B. Godderidge1 A.B. Phillips, S. Lewis, S.R. Turnock, D.A. Hudson, and
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