Numerical Simulation of Regular Wave in a Tank

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Numerical Simulation of Regular Wave in a Tank Authors: Monica Campos Silva, Dr. student PENO/UFRJ email: mcsilva@peno.coppe.ufrj.br Waldir Terra Pinto, Dr.

1 Numerical Simulation of Regular Wave in a Tank Authors: Monica Campos Silva, Dr. student PENO/UFRJ mcsilva@peno.coppe.ufrj.br Waldir Terra Pinto, Dr. FURG w_pinto@dmc.furg.br Marcelo de A. Vitola, Dr. LabOceano/COPPE/UFRJ vitola@peno.coppe.ufrj.br Carlos Antonio Levi, Dr. LabOceano/COPPE/UFRJ levi@peno.coppe.ufrj.br

2 Summary Introduction; Numerical Wave Tank Set up of the Numerical Model Grid generation Parametric Study NWT Conclusions Next steps Acknowledgement

3 Introduction Offshore structures submitted to wave loads Molikpaq platform

4 Introduction Model Testing measuring structural loads and response FPSO model LabOceno/COPPE/UFRJ Wavemaker LabOceno/COPPE/UFRJ

5 Introduction Numerical Modeling supply information to help the planning of experimental tests supply field information difficulty obtained in experimental tests.

6 NWT without structures Set up of the numerical model, CFX (i) Computational Domain (2D) Flap-type wavemaker; Beach slope: 1:3;

7 Numerical Model: Set up of the numerical model, CFX (ii) Boundaries Conditions: (iv) Numerical Model: Wavemaker Bottom Beach Endwall Top Wall Wall Wall Wall Opening Parameter Setting Model Laminar Multiphase model Homogeneous model Analysis Type Transient Convergence criteria RMS < 1E-7 Run Mode Serial (iii) Initial Condition: Zero-velocity field Hydrostatic pressure distribution

8 Numerical Model: Grid Generation ICEM-CFX

9 Parametric Study: Parameters: 1. Geometry of the domain: Top boundary location Length of domain 2. Grid refinement 3. Time step 4. Spatial discretization scheme 5. Time discretization scheme 6. Body force averaging type 7. Interface Compression Level

10 Parametric study Initial Setup Parameter Numerical settings 1. Geometry of the domain: h fs-top = 1.0 m 2. Grid refinement: Test 01: n. hexa = 5,289 z min = m x = m Aspect ratio = Time step t = 0.02 s 4. Spatial discretization scheme High order 5. Time discretization scheme 2 nd order backward Euler 6. Body force averaging type Volume-Weighted 7. Interface Compression Level 0

11 Parametric study: Influence of VOF value in the free surface location Water.VOF = 0.5

12 Parametric study: Influence of variable on horizontal velocity profile Test 32 WSV = Water Superficial Velocity X (m/s) WV = Water Velocity u (m/s) Water Velocity u

13 Parametric study (Conclusions) Geometry of domain: top boundary: Distance from mean free surface to top boundary showed small influence on free surface results. length (simple x double): Grid refinement: The length of the domain had not significantly influence on free surface and velocity field results. in the region around the free surface: Both direction x and z has influence on free surface results in the region under wave: Small influence of mesh refinement of both direction were observed on velocity field.

14 Parametric study (Conclusions) Time step: t T p /100 to avoid free surface damping Spatial and time discretization schemes: Better agreement: spatial scheme: 2 nd (UDS) or High Order and time discretization: 2 nd order (BE) Body force averaging type and Interface Compression Level Both parameters did not show great influence on numerical results

15 Parametric study: Final Setup Parameter Numerical settings 1. Geometry of the domain: h fs-top = 1.0 m 2. Grid refinement: Test 10: n. hexa = 36,352 z min = m x = m Aspect ratio = Time step t T p / Spatial discretization scheme 2 nd order upwind differencing scheme 5. Time discretization scheme 2 nd order backward Euler 6. Body force averaging type Volume-Weighted 7. Interface Compression Level 0 Details in Silva et al. SOBENA 2010

16 Numerical Wave Tank (NWT) T p (s) θ max ( o ) S (m) (H/L) theory h w = 1.5 m;

17 Test 032: T p = 2 s; θ max = 5.81º; t = 0.02 s

19 NWT numerical results x 1 st order wavemaker theory

20 NWT Wave height Wave length

21 NWT

22 NWT Field velocity: Issues Test 032: t = 19.4s Test 032: T p = 2 s; θ max = 5.81º; t = 0.02 s

23 NWT Field velocity: Issues

24 NWT Field velocity: Issues Test 032 t = 19.4s

25 NWT Field velocity: Issues Test 032 t = 19.4s

26 NWT Field velocity: Issues Test 032 t = 19.4s

27 NWT Field velocity: Issues Test 032 t = 19.4s

28 Conclusions Numerical model seems to be a useful tool for estimate the free surface behaviour in monochromatic wave generated in laboratory. Further investigations are necessary to verify the preliminary numerical results observed for velocity field under wave.

29 Next steps Checking the numerical results from CFX with the ones from Fluent;

30 Acknowledgement

31 Thanks for your attention!

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