Simulation of Potential Flow around Surface Ship using SHIPFLOW

Nabila NazLecturerDepartment of Naval Architecture and Marine EngineeringBangladesh University of Engineering and TechnologyDhaka-1000, Bangladesh

Authored by Prof. Md. Mashud Karim and Nabila Naz

Presented by:

Objective

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To analyze the flow around Ship Hull form using a CFD program – SHIPFLOW To determine the potential flow free-surface at different speeds based on a surface singularity panel method To show numerical results of wave pattern, wave elevation and wave making resistance coefficient with varying speeds graphically To compare the computed results with experimental results published by other researchers

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What is Water Waves?

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Waves caused by the movement of ShipWhen ship moves through water creates pressure difference around it causes generation of waves at free surface to maintain constant atmospheric pressure.

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Lord Kelvin (1887) gave a characteristics wave for ship named as Kelvin wave pattern which consists of two types of waves:

Transverse wave Divergent Wave

Ship Wave Pattern

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Determination of Wave Characteristics

Real Wave Pattern

Wave Pattern simulated by CFD

Wave Pattern by EFD at Towing Tank

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What is CFD?• Stands for Computational Fluid Dynamics•virtual towing tank • determines the flow characteristics around ship by mathematical modeling and numerical methods using commercially developed software •possible by the advent of digital computer and advancing with improvements of computer resources

Substantial reduction of lead times and costs of new designs. Ability to study systems where controlled experiments are difficult or impossible to perform (e.g. very large systems). Ability to study systems under hazardous conditions at and beyond their normal performance limits (e.g. safety studies and accident scenarios). Practically unlimited level of detail of results.

Advantages of CFD over EFD

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Where CFD is used?

• Where is CFD used?• Aerospace• Automotive• Biomedical• Chemical

Processing• HVAC• Hydraulics• Marine• Oil & Gas• Power Generation• Sports

Automobile

Aerospace

Biomedical

Sports industry

In swimming

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CFD software- SHIPFLOW developed by FLOWTECH International AB from the long term research done at the Hydrodynamics group of the Naval Architecture Department at Chalmers University of Technology, Gothenburg, Sweden.

Student license is purchased by of Dept. of Naval Architecture and Marine Engineering (NAME), BUET under sub-project CP # 2084 of Higher Education Quality Enhancement Project (HEQEP), UGC, Ministry of Education, Govt. of Bangladesh.

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Simulation of Wave Characteristics by SHIPFLOW

selection of particular ship hull discretize the hull and free surface set up important flow parameters e.g., type of flow, ship speed, solution methods etc. obtain the results validate the results with experimental results

Note: Ship Speed defined by Froude Number (Fn) which eis defined by following:

A mathematical hull with its geometric surface defined as:

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Selection of Hull

Wigley Hull

i) Hull ii) Free Surface

Coarse mesh around hull and free surface

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Discretization of Hull and Free-Surface

i) Hull ii) Free Surface

Fine mesh around hull and free surface

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Discretization of Hull and Free-Surface

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Results

Wave Pattern at different Speed or Froude Number Wave height along the Ship hull Wave making resistance generated by the ship Validation of the results with experimental one

Wave pattern at Fn 0.25

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Shows the characteristics of Kelvin Wave Pattern along color map for Wave height

Wave pattern at Fn 0.267

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Shows the characteristics of Kelvin Wave Pattern along color map for Wave height

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The Wave Elevation/height along ship hull at Fn 0.25

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The Wave Elevation/height along ship hull at Fn 0.267

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Wave Making Resistance as a function varying Fn

Highest peak of resistance is called Hump point Lowest Peak of resistance called Hollow point

A Naval Architect chooses a speed in such a way that the resistance is at hollow or mean level never at Hump point

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Conclusions

(i) The wave pattern around the ship hull consists of transverse and diverging waves at all speeds.(ii) The fine mesh simulation significantly improves the wave profiles particularly at the bow and the first trough but after that the difference between the fine and coarse mesh results becomes insignificant. (iii) The agreement between computation and measurement tends to become worse with the increase in the Froude number.(iv) An increase in the co-efficient of wave making resistance, Cw with Froude number is usually accompanied by a number of humps and hollows in the resistance curve. In sum, based on the CFD simulation, a ship designer can choose optimum speed with minimum power requirement and then proceed to a model test for experimental result.

Future Work

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Flow around Real Ship hull

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Ship Hull-Rudder-Propeller Interaction

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Optimization of Bulbous Bow Shape to minimize resistance

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Acknowledgement

Authors are grateful to Bangladesh University of Engineering and Technology (BUET) and sub-project CP # 2084 of Department of Naval Architecture and Marine Engineering under Higher Education Quality Enhancement Project (HEQEP), UGC, Ministry of Education, Govt. of Bangladesh for providing necessary research facilities during the current research work.

Thank You

• Contact info:Email:nabilanaz@name.buet.ac.bdWebsite: http://teacher.buet.ac.bd/nabilanaz/

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Appendix

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Causes of waves

Disturbances can cause a water wave:pebble striking the surfacedue to wind or movement of a shipmovement of the earth during an earthquakeThe gravitational pull of the sun and moon causes tidal waves.

Waves are deformations of the sea surface.  The deformations propagate with the wave speed, while the water molecules remain at the same positions on average  passing energy through the water.

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Waves caused by Wind

• water surface is initially at rest • when wind blows over water surface causes fluctuation of pressure on the free surface and generate wave