Using a Low-Fidelity Potential Flow Model as a Surrogate for a High-Fidelity Viscous Flow Model

2018 ◽  
Author(s):  
Jack S. Rossetti ◽  
John Dannenhoffer
Keyword(s):  
Viscous Flow ◽  
Potential Flow ◽  
Flow Model ◽  
High Fidelity ◽  
Potential Flow Model

scholarly journals High-Fidelity Representation of Three-Hour Offshore Short-Crested Wave Field in the Fully Nonlinear Potential Flow Model REEF3D::FNPF

2020 ◽  
Author(s):  
Weizhi Wang ◽  
Csaba Pakozdi ◽  
Arun Kamath ◽  
Hans Bihs
Keyword(s):  
Wave Field ◽  
Potential Flow ◽  
Flow Model ◽  
Offshore Structures ◽  
High Fidelity ◽  
Fully Nonlinear ◽  
Space And Time ◽  
Nonlinear Potential ◽  
Potential Flow Model ◽  
Wave Properties

Abstract Stochastic wave properties are crucial for the design of offshore structures. Short-crested seas are commonly seen at the sites of offshore structures, especially during storm events. A long time duration is required in order to obtain the statistical properties, which is challenging for numerical simulations because of the high demand of computational resources. In this scenario, a potential flow solver is ideal due to its computational efficiency. A procedure of producing accurate representation of short-crested sea states using the open-source fully nonlinear potential flow model REEF3D::FNPF is presented in the paper. The procedure examines the sensitivity of the resolutions in space and time as well as the arrangements of wave gauge arrays. A narrow band power spectrum and a mildly spreading directional spreading function are simulated, and an equal energy method is used to generate input waves to avoid phase-locking. REEF3D::FNPF solves the Laplace equation together with the boundary conditions using a finite difference method. A sigma grid is used in the vertical direction and the vertical grid clustering follows the principle of constant truncation error. High-order discretisation methods are implemented in space and time. Message passing interface is used for high performance computation using multiple processors. Three-hour simulations are performed in full-scale at a hypothetic offshore site with constant water depth. The significant wave height, peak period, kurtosis, skewness and ergodicity are examined in the numerically generated wave field. The stochastic wave properties in the numerical wave tank (NWT) using REEF3D::FNPF match the input wave conditions with high fidelity.

Performance of a Propeller in a Wake and the Interaction of Propeller and Hull

1965 ◽  
Vol 9 (02) ◽  
pp. 1-36
Author(s):  
Quentin Wald
Keyword(s):  
Potential Flow ◽  
Flow Model ◽  
Practical Case ◽  
Viscous Effects ◽  
Actuator Disk ◽  
Potential Flow Model

Relations are developed which describe the propeller-hull interaction and the efficiency of the wake-operating propeller in the practical case where both potential and viscous effects are important. Momentum equations and the actuator disk representation of the propeller are used. Thrust deduction and efficiency are found to be functions of both the local and the ultimate wake velocity which are, in turn, expressible as functions of the static and total pressures in the propeller plane. The two velocity ratios have opposite effects on the thrust deduction, hence a potential-flow model simulating the velocity at the propeller plane and ignoring the ultimate wake-velocity deficiency arising from viscosity is inadequate.

A Two-Dimensional Potential Flow Model of the Wave Field Generated by a Semisubmerged Body in Heaving Motion

1988 ◽  
Vol 32 (02) ◽  
pp. 83-91
Author(s):  
X. M. Wang ◽  
M. L. Spaulding
Keyword(s):  
Free Surface ◽  
Boundary Conditions ◽  
Potential Flow ◽  
Flow Model ◽  
Second Order ◽  
Two Dimensional ◽  
Third Order ◽  
The Third ◽  
Potential Flow Model ◽  
Good Agreement

A two-dimensional potential flow model is formulated to predict the wave field and forces generated by a sere!submerged body in forced heaving motion. The potential flow problem is solved on a boundary fitted coordinate system that deforms in response to the motion of the free surface and the heaving body. The full nonlinear kinematic and dynamic boundary conditions are used at the free surface. The governing equations and associated boundary conditions are solved by a second-order finite-difference technique based on the modified Euler method for the time domain and a successive overrelaxation (SOR) procedure for the spatial domain. A series of sensitivity studies of grid size and resolution, time step, free surface and body grid redistribution schemes, convergence criteria, and free surface body boundary condition specification was performed to investigate the computational characteristics of the model. The model was applied to predict the forces generated by the forced oscillation of a U-shaped cylinder. Numerical model predictions are generally in good agreement with the available second-order theories for the first-order pressure and force coefficients, but clearly show that the third-order terms are larger than the second-order terms when nonlinearity becomes important in the dimensionless frequency range 1≤ Fr≤ 2. The model results are in good agreement with the available experimental data and confirm the importance of the third order terms.

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