Resistance measurement and cfd test on darpa subboff model

this ppt is about DARPA submarine resistance measurement , i cinduct a cfd test on star ccm and open foam also

1. NAME – ARIJIT BISWAS ROLL NO- 24NA91R01 PhD 1 st Year Research Scholar SUB – Self Study Course Supervised by Prof Swapnadip De Chowdhury (NA) Joint supervised by Prof Nilanjan Das Chakladar (ME) Resistance of Under Water Vehicle

2. CONTENTS OF SLIDES INTRODUCTION PHYSICS BEHIND RESISTANCE RESISITANCE MEASURMENT ITTC FORMULA LITERATURE REVIEW MODELLING SIMULATIONS MESHING VALIDATION RESULTS ( star CCM+) OPEN FOAM SETUP CONCLUSION GOAL

3. INTRODUCTION Underwater vehicles are specialized systems designed to operate beneath the surface of water for various purposes such as exploration, surveillance, data collection, defense, and resource extraction. These vehicles can be broadly categorized into manned and unmanned types, with unmanned vehicles further divided into Remotely Operated Vehicles (ROVs) and Autonomous Underwater Vehicles (AUVs) . One of the key performance parameters of underwater vehicles is hydrodynamic resistance , which directly affects propulsion efficiency and energy consumption. Computational Fluid Dynamics (CFD) plays a vital role in analyzing and optimizing the flow behavior around these vehicles to minimize drag and enhance performance.

4. PHYSICS BEHIND RESISTANCE What is resistance? What Stops Things from Moving Freely? -The word “resistance” comes from the root word “resist” , which means to oppose or stand against something . So, in the context of motion — Resistance is the force that tries to stop an object from moving forward. Where Does Resistance Come From? Resistance comes from the interaction between a moving object and the surrounding fluid (like water or air) . When an object moves through a fluid, the fluid does not simply move aside — it pushes back . That push-back is resistance , and it comes from two main sources: Friction (Viscous Effect) Pressure Difference (Shape Effect) Wave-Making (at Free Surface) Fluid Dynamics Around a Submerged Body Water flow divides around the hull — creates boundary layer Stagnation point at the nose, flow separation may occur at aft Pressure is high at front , low at rear → causes drag Viscous shear stress acts along hull → friction drag Near surface? → Wave-making resistance appears

5. RESISTANCE MEASURMENT Towing Tank A towing tank is a long and narrow water channel designed for hydrodynamic testing of marine models. Dimensions typically range from 50 to 400 meters in length , 3–6 meters in width, and 1.5–4 meters in depth. Walls are lined with damping materials to absorb wave reflections and minimize interference. Water is usually calm and temperature-controlled to ensure consistent fluid properties (e.g., density, viscosity). Submarine Model A precisely scaled-down replica of the actual submarine, e.g., the DARPA SUBOFF, typically made at a 1:10 or 1:20 scale. Constructed using materials like fiberglass, resin, or CNC-machined metal/plastic for rigidity and a smooth surface finish. Includes guide rails or support arms to maintain fixed orientation and depth during towing. Some models are modular to allow variation in appendages (e.g., with or without sail, fins, or propulsors). Towing Carriage A motorized gantry system that runs on rails along the towing tank. It tows the model at precise, constant velocities ranging from 0.1 to 5 m/s , depending on the scale. Equipped with: Servo-motors for speed control Data acquisition systems Force sensors (load cells) mounted between the model and the carriage

6. RESISTANCE MEASURMENT Force Measurement System (Load Cells / Force Transducers) High-precision strain gauge-based sensors that record the force required to tow the model. Installed between the model mount and towing carriage to measure: Axial force → total resistance Optionally, vertical force → lift or buoyant imbalance Calibrated before every test run to ensure zero-offset and accuracy Outputs : Resistance vs. time Average steady-state drag Possibly side forces or moments if multi-axis sensors are used

7. Fundamentals of Resistance in Underwater Vehicles Reynolds number and Froude number ITTC formula

8. LITERATURE REVIEW Title : Fabrication of Durable Superhydrophobic Surfaces with a Mesh Structure and Drag Reduction by Chemical Etching Technology Authors : Fan, J.; Zhang, M.; Li, H. Method : Mesh-structured stainless steel was chemically etched and fluorinated to create a robust superhydrophobic surface. Test : Drag was measured in a recirculating water tunnel at various Reynolds numbers. Result : Drag was reduced by 18.6% under turbulent flow. remained effective after 10 abrasion cycles and 30-day immersion. Insight : Realistic durability makes this suitable for operational subs, not just lab models. Surface roughness alone wasn’t sufficient — chemical hydrophobization was critical. Title : Synergistic Drag Reduction by Microgroove Surfaces and Mucus Simulation Authors : Zhang, K.; Li, J.; Zhang, C.; Liu, X.; Wang, Y. Method : CFD was used to simulate fluid flow over artificial mucus layers with microgrooved textures. Result : Drag was reduced up to 21.3% , especially at Re > 10⁵.Mucus-like viscoelastic response delayed boundary layer transition , reducing turbulence. Insight : Combining physical and rheological mechanisms gives an adaptive drag response across multiple flow regimes — ideal for maneuvering AUVs Surface Engineering – Superhydrophobic and Microstructured Coatings Surface Modifications – Riblets and Grooves Title : Drag Reduction on AUV Grooved Surfaces: Experimental and Numerical Study Authors : Zhang, S.; Wu, X.; Ma, S.; Li, L.; Chen, H. Method : AUV models with and without longitudinal grooves tested in a controlled tank with LDV flow tracking. Result :Grooved designs showed 17% reduction in total resistance at high Reynolds numbers.Grooves helped sustain laminar flow up to higher velocities. Insight : Grooves passively manipulate boundary layer transition and are manufacturing-friendly alternatives to coatings.

9. Title : Experimental and numerical analysis on suitability of S-Glass–Carbon fiber reinforced polymer composites for submarine hull Authors : Natarajan, E. et al. (2023) Study Method - Investigated hydrostatic pressure resistance and hydrodynamic drag of hybrid S-glass/carbon fiber composite cylinders. Conducted both Finite Element Analysis (FEA) and pressure chamber experiments to simulate submerged conditions. Compared against traditional mild steel and aluminum alloys. Results Drag Force : Composite hulls had 12–18% lower drag compared to steel due to smoother surface finish and lower weight-induced deformation. Weight Reduction : 45% lighter than equivalent steel hull, directly reducing displacement drag. Deformation : Reduced radial strain under pressure, meaning hull maintains shape better under load, helping streamline flow. Fatigue : Carbon fibers resisted delamination better than pure S-glass alone. Insight The hybrid composite reduces drag through lower hydrodynamic footprint , enhanced surface smoothness , and stiffness-to-weight superiority . It's well-suited for next-gen submersibles with reduced energy budgets. Title : Design and testing of a composite pressure hull for deep autonomous underwater vehicles Authors : Elkolali , M. & Alcocer , A. (2022) Study Method Designed a deep-sea AUV hull using carbon fiber-reinforced epoxy laminate. Analyzed its compressibility, internal volume, drag, and buoyancy-to-weight ratio. Built a prototype and tested in controlled underwater deployment trials. Results Drag Coefficient : Reduced by ~15% compared to a steel-hull baseline due to more uniform curvature under load. Stiffness vs. Flow : Less deflection in turbulent flow means shape consistency and reduced form drag. Surface Finish : Molded CF surface had low boundary-layer disruption, verified using CFD. Mass-to-Volume Ratio : Enabled better hydrodynamic shape without exceeding density limits for neutral buoyancy. Insight The study confirms that carbon composites enable advanced hull shaping and improve hydrodynamic efficiency, not just strength. Especially effective for deep-sea, long-endurance AUVs where drag and structural integrity are both critical. LITERATURE REVIEW Carbon Reinforced composites

10. CFD EXPERIMENTS OF DARPA SUBOFF MODEL Geometry Preparation Domain Creation Boundary Conditions MESHING Physics Setup Solver Setup Post-Processing Validation CFD EXPERIMENT

11. MODELLING OF AUV Geometry – DARPA SUBOFF ( without appendages) L/D = 8.575 SECTION LENGTH CURVE USED RADIUS BOW PART LENGTH 1.016 m 5 th Degree Polynomial 0 - 0.254 m PARALLEL MIDDLE PART LENGTH 2.229 m Constant Cylinder 0.254 m STERN LENGTH 1.111 m 5 th Degree Polynomial (Reversed) 0.254 – 0 m CAD Model of DARPA SUBOFF TOTAL LENGTH = 4.356 m MAXIMUM DIAMETER = 0.508 m

12. MODELLING OF AUV Aft body Forebody Curve Equation Aft body Curve Equation Parallel Middle Body Equation Aft Body Cap Equation Fore body

13. COMPUTATIONAL DOMAIN Velocity Inlet condition top and bottom Boundary 1. Eliminates the fluid reflection 2.Facilitates the modeling of an open sea Applying the dispersion relation of linear surface waves to the stationary waves generated by the SUBOFF geometry

14. COMPUTATIONAL DOMAIN Damping function in STAR CCM+ Source Term (damping function) Linear function Quadratic function = damping constant for the linear part = damping constant for the quadratic part     Peric & Maksud 2016

15. Prism Layer Mesh Generation Thickness of the Prism Layer Surface Preparation – Surface Remesher Is used to enhance the quality of surface Prism Layer Mesh Generation Volume Mesh Generation White (2006) Boundary layer thickness for a turbulent flow over a flat plate Wall MESHING

16. MESHING White (2006) Thickness of the prism Layer Prism layer stretching factor It is recommended to use a value from 1.05 to 1.2 Number of layers L = 4.356 m U = 3.02 m/s v = 0.00000089088 Re L = 14766433.19 Thickness of the prism layer Prism layer stretching (r) Number of layers (y + =100 ) 0.066 1.1 23 = 23

17. MESHING

18. MESH QUALITY

19. SIMULATION SETUP VOF Method uses First-order upwind scheme Local Courant number > High-Resolution Interface Capturing (HRIC) scheme Local Courant number < A combination of both these schemes ≤ Local Courant Number ≤ Time Step Formula = 0.016 s Physics Models

20. RESULT The Total resistance Value = 107.73526874076619 N I select the Half part of that model because of symmetry and less of computational time so the total resistance of full body DARPA SUBOFF is = (107.73526874076619 *2) N = 215.470537482 N Froude Number = 0.462 Velocity of Wave = 3.01 m /s

21. VALIDATION Variable CFD Value Measurements (Edward Dawson) Relative Difference Resistance Force (N) 215.470 231.109 6.77 % Froude Number = 0.462 Velocity of Wave = 3.01 m /s TITLE - An investigation into the effects of submergence depth, speed and hull length-to-diameter ratio on the near surface operation of conventional submarines Author - Dawson, E (2014). University of Tasmania

22. RESULTS V= 1.34 m/s V= 1.53 m/s V= 1.65 m/s V= 1.78 m/s V= 1.98 m/s V= 2.12 m/s V= 2.32 m/s V= 2.58 m/s V= 2.45 m/s

23. RESULTS 2.76 m/s 2.89 m/s 3.02 m/s 3.18 m/s 3.23 m/s 3.27 m/s 3.34 m/s 3.57 m/s 3.84 m/s

24. RESULTS

25. RESULTS CFD Value Cd vs Fr Experimental Value Combine CFD & Experimental CFD Value Resistance vs Froude Number

26. OPEN FOAM CAD File blockMeshDict surfaceFeaturesDict decomposeParDict snappyHexMesh Making Background Mesh Making finer surface Mesh of . stl running parallel run For . stl file Snappy Mesh Boundary Condition blockMesh File Environment Mesh Domain decomposeParDict

27. OPEN FOAM MESH

28. CONCLUSION Geometry Reconstruction : The DARPA SUBOFF submarine geometry was accurately recreated using the published mathematical equations for the bow, mid-body, afterbody, and afterbody cap sections. CFD Validation in STAR-CCM+ : The model was initially validated using STAR-CCM+ CFD simulations. Hydrodynamic performance, including resistance and flow behavior, matched expected results, confirming geometric and setup accuracy. Transition to OpenFOAM : Following STAR-CCM+ validation, the focus shifted to OpenFOAM to replicate and extend the simulations using open- source tools. Mesh Generation in OpenFOAM : A detailed mesh was created using snappyHexMesh , including: Proper surface refinement for hull resolution. Prism layers for boundary layer capture (wall-resolved turbulence modeling). Volume mesh tailored for free-surface and wave-resistance simulations.

29. GOAL Promote Open-Source CFD Usage : Demonstrate that OpenFOAM can reliably replicate industry-standard CFD simulations. Develop a validated workflow for submarine resistance analysis using free, open-source tools. Long-Term Goal : Establish a cost-effective, open-source pipeline for academic and research-based naval hydrodynamic simulations.

30. REFERENCE Fan, J., Zhang, M. and Li, H., 2025. Fabrication of Durable Superhydrophobic Surfaces with a Mesh Structure and Drag Reduction by Chemical Etching Technology.  Coatings ,  15 (4), p.402. Zhang, K., Li, J., Zhang, K. and Zhang, J., 2025. Optimization of surface microgrooves and their performance and mechanism of synergistic drag reduction with bionic mucus.  Ocean Engineering ,  317 , p.120029. Zhang, K., Li, J., Zhang, C., Zhang, J. and Zhang, B., 2025. Simulation and mechanism of the synergistic drag reduction performance of two types of microgroove surfaces and mucus.  International Journal of Heat and Fluid Flow ,  115 , p.109837. Zhang, S., Wu, X., Ma, S., Wang, Z., Sun, Z. and Hu, M., 2024. Experimental and numerical simulation study of drag reduction on AUV grooved surfaces.  Ocean Engineering ,  314 , p.119610. Natarajan, E., Freitas, L.I., Santhosh, M.S., Markandan , K., Al-Talib, A.A.M. and Hassan, C.S., 2023. Experimental and numerical analysis on suitability of S-Glass-Carbon fiber reinforced polymer composites for submarine hull.  Defence Technology ,  19 , pp.1-11. Elkolali , M. and Alcocer , A., 2022. Design and testing of a composite pressure hull for deep autonomous underwater vehicles.  IEEE Access ,  10 , pp.85831-85842. Amiri, M.M., Esperança , P.T., Vitola , M.A. and Sphaier , S.H., 2018. How does the free surface affect the hydrodynamics of a shallowly submerged submarine?.  Applied ocean research ,  76 , pp.34-50. Takahashi, K. and Sahoo, P.K., 2019, June. Fundamental CFD study on the hydrodynamic performance of the DARPA SUBOFF submarine. In  International Conference on Offshore Mechanics and Arctic Engineering  (Vol. 58776, p. V002T08A052). American Society of Mechanical Engineers.