Practical Evaluation of Steady Flow Resulting from a Free-Surface Pressure Patch

2009 ◽  
Vol 53 (03) ◽  
pp. 137-150
Author(s):  
Francis Noblesse ◽  
Gérard Delhommeau ◽  
Chi Yang
Keyword(s):  
Free Surface ◽  
Surface Pressure ◽  
High Speed ◽  
Surface Effect ◽  
Practical Method ◽  
Analytical Approximation ◽  
Surface Boundary ◽  
Steady Flows ◽  
Local Flow ◽  
The Green Function

The linearized potential flow resulting from a distribution of pressure that advances at constant speed along a straight path at the free surface of calm water, of effectively infinite depth and lateral extent, is considered. A practical method for evaluating the free-surface elevation caused by the moving free-surface pressure patch—which can be used to model steady flows of air-cushion vehicles, high-speed planing boats, surface-effect ships, and some types of hybrid ships—is given. The key ingredient of this method is a highly simplified analytical approximation to the local-flow component in the expression for the Green function associated with the classic Michell-Kelvin linearized free-surface boundary condition.

An Analysis of Heave Added Mass and Damping of a Surface-Effect Ship

1981 ◽  
Vol 25 (01) ◽  
pp. 44-61
Author(s):  
C. H. Kim ◽  
S. Tsakonas
Keyword(s):  
Free Surface ◽  
High Speed ◽  
Surface Effect ◽  
Practical Method ◽  
Added Mass ◽  
Damping Coefficients ◽  
Calm Water ◽  
Surface Effect Ship ◽  
Long Time ◽  
Computational Procedures

The analysis presents a practical method for evaluating the added-mass and damping coefficients of a heaving surface-effect ship in uniform translation. The theoretical added-mass and damping coefficients and the heave response show fair agreement with the corresponding experimental values. Comparisons of the coupled aero-hydrodynamic and uncoupled analytical results with the experimental data prove that the uncoupled theory, dominant for a long time, that neglects the free-surface effects is an oversimplified procedure. The analysis also provides means of estimating the wave elevation of the free surface, the escape area at the stern and the volume which are induced by a heaving surface-effect ship in uniform translation in otherwise calm water. Computational procedures have been programmed in the FORTRAN IV language and adapted to the PDP-10 high-speed digital computer.

Five Years of Numerical Naval Ship Hydrodynamics at DTNSRDC

1981 ◽  
Vol 25 (04) ◽  
pp. 219-235
Author(s):  
Nils Salvesen
Keyword(s):  
Free Surface ◽  
Numerical Methods ◽  
Initial Period ◽  
Three Dimensional ◽  
Hydrodynamic Performance ◽  
Ship Motions ◽  
Surface Boundary ◽  
Local Flow ◽  
Ship Hydrodynamics ◽  
Naval Ship

In 1974 the Numerical Naval Ship Hydrodynamics Program was established at the David W. Taylor Naval Ship Research and Development Center. The objective of the program is to develop new numerical methods which can be used to evaluate those hydrodynamic performance characteristics which cannot be satisfactorily predicted by traditional methods. In this paper, the accomplishments during the first five-year period (1974–1979) are discussed. During this initial period, the effort was devoted entirely to naval ship free-surface problems. Several successful methods have been developed for solving fully three-dimensional ship-motions, ship-wave-resistance and local-flow problems using linearized free-surface boundary conditions. Numerical methods have also been developed for unsteady and steady two-dimensional problems where the exact free-surface conditions are satisfied. These new numerical methods are more accurate than the conventional computational methods and they can be used to analyze several naval free-surface problems which previously could only be investigated experimentally. It is concluded that the Numerical Naval Ship Hydrodynamics Program should include consideration of all areas in naval ship hydrodynamics where it is believed that the application of advanced numerical techniques and computers can result in better solution techniques.

Zero Speed Rankine-Kelvin Hybrid Method With a Cylinder Control Surface

2015 ◽  
Author(s):  
Hui Li ◽  
Hao Lizhu ◽  
Huilong Ren ◽  
Xiaobo Chen
Keyword(s):  
Free Surface ◽  
Green Function ◽  
Hybrid Method ◽  
Exterior Domain ◽  
Control Surface ◽  
Surface Boundary ◽  
Rankine Source ◽  
Free Surface Boundary Condition ◽  
Interior Domain ◽  
The Green Function

The solution of hydrodynamic problem with forward speed still has some well-known problems such as high oscillation and slow convergence of the wave term when using a moving and oscillating source as the Green function. Recently, Ten and Chen (2010) has come up with a new method to benefit the merits of both the Rankine source and moving and oscillating source by taking a hemisphere as the control surface which separates the fluid region into two domains, but some troubles have been induced in the process of solution. Therefore, in this paper, a cylindrical surface instead of a hemisphere is selected to be the control surface to make the solution easy, and in this method, the control surface isn’t divided into panels. In the interior domain near the ship, the Rankin Green function is used to simplify the calculation. In the exterior domain some distance from the ship, there is no panels representing the free surface by using the Green function which satisfy the free surface boundary condition. The whole fluid region matches by the condition that the velocity potentials and their normal derivatives in the interior domain and exterior domain are equal on the control surface separately. In this paper, we have validated the Rankine-Kelvin hybrid method is applicable by adopting it to solve the zero speed problem in this work.

scholarly journals Numerical Flow Characterization around a Type 209 Submarine Using OpenFOAM

Fluids ◽  
2021 ◽  
Vol 6 (2) ◽  
pp. 66
Author(s):  
Ruben J. Paredes ◽  
Maria T. Quintuña ◽  
Mijail Arias-Hidalgo ◽  
Raju Datla
Keyword(s):  
Free Surface ◽  
Flow Velocity ◽  
Surface Effect ◽  
Surface Condition ◽  
Flow Characteristics ◽  
Scaled Model ◽  
Local Flow ◽  
Near Surface ◽  
Vortical Structures ◽  
Operational Conditions

The safety of underwater operation depends on the accuracy of its speed logs which depends on the location of its probe and the calibration thoroughness. Thus, probes are placed in areas where the flow of water is smooth, continuous, without high velocity gradients, air bubbles, or vortical structures. In the present work, the flow around two different submarines is numerically described in deep-water and near-surface conditions to identify hull zones where probes could be installed. First, the numerical setup of a multiphase solver supplied with OpenFOAM v7 was verified and validated using the DARPA SUBOFF-5470 submarine at scaled model including the hull and sail configuration at H/D=5.4 and Fr=0.466. Later, the grid sensitivity of the resistance was assessed for the full-scale Type 209/1300 submarine at H/D=0.347 and Fr=0.194. Free-surface effect on resistance and flow characteristics was evaluated by comparing different operational conditions. Results shows that the bow and near free-surface regions should be avoided due to high flow velocity gradient, pressure fluctuations, and large turbulent vortical structures. Moreover, free-surface effect is stronger close to the bow nose. In conclusion, the probe could be installed in the acceleration region where the local flow velocity is 15% higher than the navigation speed at surface condition. A 4% correction factor should be applied to the probe readings to compensate free-surface effect.

Disturbance Induced by a Pressure Distribution Moving Over a Free Surface

1970 ◽  
Vol 14 (03) ◽  
pp. 195-203
Author(s):  
T. T. Huang ◽  
K. K. Wong
Keyword(s):  
Free Surface ◽  
Pressure Distribution ◽  
Surface Effect ◽  
Surface Profile ◽  
Wave Theory ◽  
Local Flow ◽  
Closed Form Solutions ◽  
Pressure Trace ◽  
Surface Effect Ship ◽  
Free Surface Profile

This paper uses the linearized water-wave theory to analyze the disturbances induced by a constant pressure distribution with a rectangular planform moving over calm water. The methods developed, however, can be applied to other pressure distributions. Numerical schemes and computation results for typical speeds and beam/length ratios are presented for the pressure trace on the sea floor when the water depth is finite and the local flow pattern when the depth is infinite. For shallow waters, closed-form solutions for both the pressure trace and free-surface profile are obtained. A surface-effect ship acts like a moving pressure distribution as far as the induced disturbances in the water are concerned. Thus, the results of the present study may be useful for the design of surface-effect ships.

scholarly journals Numerical Analysis of Hydrodynamic Loads on Passing and Moored Ships in Shallow Water

Processes ◽  
2021 ◽  
Vol 9 (3) ◽  
pp. 558
Author(s):  
Ji-Yong Park ◽  
Bo Woo Nam ◽  
Yonghwan Kim
Keyword(s):  
Free Surface ◽  
Surface Effect ◽  
Hydrodynamic Pressure ◽  
Simulation Method ◽  
Separation Distance ◽  
Hydrodynamic Forces ◽  
Surface Boundary ◽  
Surface Boundary Conditions ◽  
Surface Models ◽  
Force Time

In this study, hydrodynamic interactions between passing and moored ships were studied by applying a time-domain numerical simulation method. The boundary value problem for a fluid domain was formulated based on a potential flow theory. A numerical method was developed based on a finite element method with an efficient re-mesh algorithm. Regarding the free-surface boundary conditions, both double-body and free-surface models were considered for examining the free-surface effect on the hydrodynamic forces due to the passing ship. First, numerical results were validated by comparison with the model test results of Kriebel et al. (2005), where generic Series 60 hulls were considered as the target model for the passing and moored ships. In addition, hydrodynamic pressure fields and force time-series were investigated to understand the passing ship problem. Second, a series of numerical simulations were performed to study the effects of the passing ship speed, separation distance, water depth, and relative vessel size, which were used to compare the peak values of hydrodynamic forces. The applicability and limitations of the double-body and free-surface models are discussed for predicting passing ship loads.

scholarly journals Multi-fidelity black-box optimization for time-optimal quadrotor maneuvers

2021 ◽  
pp. 027836492110333
Author(s):  
Gilhyun Ryou ◽  
Ezra Tal ◽  
Sertac Karaman
Keyword(s):  
Real World ◽  
High Speed ◽  
Analytical Approximation ◽  
Black Box ◽  
Bayesian Optimization ◽  
Optimization Framework ◽  
Quadrotor Aircraft ◽  
Time Optimal ◽  
Feasibility Constraints ◽  
Generation Problem

We consider the problem of generating a time-optimal quadrotor trajectory for highly maneuverable vehicles, such as quadrotor aircraft. The problem is challenging because the optimal trajectory is located on the boundary of the set of dynamically feasible trajectories. This boundary is hard to model as it involves limitations of the entire system, including complex aerodynamic and electromechanical phenomena, in agile high-speed flight. In this work, we propose a multi-fidelity Bayesian optimization framework that models the feasibility constraints based on analytical approximation, numerical simulation, and real-world flight experiments. By combining evaluations at different fidelities, trajectory time is optimized while the number of costly flight experiments is kept to a minimum. The algorithm is thoroughly evaluated for the trajectory generation problem in two different scenarios: (1) connecting predetermined waypoints; (2) planning in obstacle-rich environments. For each scenario, we conduct both simulation and real-world flight experiments at speeds up to 11 m/s. Resulting trajectories were found to be significantly faster than those obtained through minimum-snap trajectory planning.

Curved surface effect on high-speed droplet impingement

2020 ◽  
Vol 909 ◽  
Author(s):  
Wangxia Wu ◽  
Qingquan Liu ◽  
Bing Wang
Keyword(s):  
High Speed ◽  
Surface Effect ◽  
Curved Surface ◽  
Droplet Impingement

Abstract

Experimental Investigation of Boundary Layer Instabilities on the Free Surface of Non-Turbulent Jet

2012 ◽  
Author(s):  
Matthieu A. Andre ◽  
Philippe M. Bardet
Keyword(s):  
Boundary Layer ◽  
Free Surface ◽  
High Speed ◽  
Particle Tracking Velocimetry ◽  
Capillary Waves ◽  
Wave Growth ◽  
Image Velocimetry ◽  
Planar Laser ◽  
Surface Visualization ◽  
The Waves

Shear instabilities induced by the relaxation of laminar boundary layer at the free surface of a high speed liquid jet are investigated experimentally. Physical insights into these instabilities and the resulting capillary wave growth are gained by performing non-intrusive measurements of flow structure in the direct vicinity of the surface. The experimental results are a combination of surface visualization, planar laser induced fluorescence (PLIF), particle image velocimetry (PIV), and particle tracking velocimetry (PTV). They suggest that 2D spanwise vortices in the shear layer play a major role in these instabilities by triggering 2D waves on the free surface as predicted by linear stability analysis. These vortices, however, are found to travel at a different speed than the capillary waves they initially created resulting in interference with the waves and wave growth. A new experimental facility was built; it consists of a 20.3 × 146.mm rectangular water wall jet with Reynolds number based on channel depth between 3.13 × 104 to 1.65 × 105 and 115. to 264. based on boundary layer momentum thickness.

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