scholarly journals Intercomparison of Three Open-Source Numerical Flumes for the Surface Dynamics of Steep Focused Wave Groups

Fluids ◽  
2020 ◽  
Vol 6 (1) ◽  
pp. 9
Author(s):  
Thomas Vyzikas ◽  
Dimitris Stagonas ◽  
Christophe Maisondieu ◽  
Deborah Greaves
Keyword(s):  
Open Source ◽  
Numerical Models ◽  
Computational Cost ◽  
Experimental Results ◽  
Wave Group ◽  
Surface Dynamics ◽  
Wave Interactions ◽  
Sea State ◽  
Wave Groups ◽  
Focused Wave

NewWave-type focused wave groups are commonly used to simulate the design wave for a given sea state. These extreme wave events are challenging to reproduce numerically by the various Numerical Wave Tanks (NWTs), due to the high steepness of the wave group and the occurring wave-wave interactions. For such complex problems, the validation of NWTs against experimental results is vital for confirming the applicability of the models. Intercomparisons among different solvers are also important for selecting the most appropriate model in terms of balancing between accuracy and computational cost. The present study compares three open-source NWTs in OpenFOAM, SWASH and HOS-NWT, with experimental results for limiting breaking focused wave groups. The comparison is performed by analysing the propagation of steep wave groups and their extracted harmonics after employing an accurate focusing methodology. The scope is to investigate the capabilities of the solvers for simulating extreme NewWave-type groups, which can be used as the “design wave” for ocean and coastal engineering applications. The results demonstrate the very good performance of the numerical models and provide valuable insights to the design of the NWTs, while highlighting potential limitations in the reproduction of specific harmonics of the wave group.

The Effect of Directional Spreading on Interaction of Focused Wave Groups With a Cylinder

2004 ◽  
Author(s):  
Eugeny V. Buldakov ◽  
Rodney Eatock Taylor ◽  
Paul H. Taylor
Keyword(s):  
Numerical Solutions ◽  
Amplitude Spectrum ◽  
Wave Group ◽  
Helmholtz Equations ◽  
Incoming Wave ◽  
Wave Groups ◽  
Practical Applications ◽  
Amplitude Spectra ◽  
Focused Wave ◽  
Focused Wave Group

The problem of diffraction of a directionally spread focused wave group by a bottom-seated circular cylinder is considered from the view point of second-order perturbation theory. After applying the time Fourier transform and separation of vertical variable the resulting two-dimensional non-homogeneous Helmholtz equations are solved numerically using finite differences. Numerical solutions of the problem are obtained for JONSWAP amplitude spectra for the incoming wave group with various types of directional spreading. The results are compared with the corresponding results for a unidirectional wave group of the same amplitude spectrum. Finally we discuss the applicability of the averaged spreading angle concept for practical applications.

scholarly journals Creative computing with Landlab: an open-source toolkit for building, coupling, and exploring two-dimensional numerical models of Earth-surface dynamics

2017 ◽  
Vol 5 (1) ◽  
pp. 21-46 ◽  
Author(s):  
Daniel E. J. Hobley ◽  
Jordan M. Adams ◽  
Sai Siddhartha Nudurupati ◽  
Eric W. H. Hutton ◽  
Nicole M. Gasparini ◽  
...  
Keyword(s):  
Open Source ◽  
Numerical Models ◽  
Epistemic Uncertainty ◽  
Process Models ◽  
Third Party ◽  
Sensitivity Analyses ◽  
Surface Dynamics ◽  
New Process ◽  
Creative Computing ◽  
Classroom Use

Abstract. The ability to model surface processes and to couple them to both subsurface and atmospheric regimes has proven invaluable to research in the Earth and planetary sciences. However, creating a new model typically demands a very large investment of time, and modifying an existing model to address a new problem typically means the new work is constrained to its detriment by model adaptations for a different problem. Landlab is an open-source software framework explicitly designed to accelerate the development of new process models by providing (1) a set of tools and existing grid structures – including both regular and irregular grids – to make it faster and easier to develop new process components, or numerical implementations of physical processes; (2) a suite of stable, modular, and interoperable process components that can be combined to create an integrated model; and (3) a set of tools for data input, output, manipulation, and visualization. A set of example models built with these components is also provided. Landlab's structure makes it ideal not only for fully developed modelling applications but also for model prototyping and classroom use. Because of its modular nature, it can also act as a platform for model intercomparison and epistemic uncertainty and sensitivity analyses. Landlab exposes a standardized model interoperability interface, and is able to couple to third-party models and software. Landlab also offers tools to allow the creation of cellular automata, and allows native coupling of such models to more traditional continuous differential equation-based modules. We illustrate the principles of component coupling in Landlab using a model of landform evolution, a cellular ecohydrologic model, and a flood-wave routing model.

scholarly journals Creative computing with Landlab: an open-source toolkit for building, coupling, and exploring two-dimensional numerical models of Earth-surface dynamics

2016 ◽  
Author(s):  
Daniel E. J. Hobley ◽  
Jordan M. Adams ◽  
Sai Siddhartha Nudurupati ◽  
Eric W. H. Hutton ◽  
Nicole M. Gasparini ◽  
...  
Keyword(s):  
Open Source ◽  
Numerical Models ◽  
Epistemic Uncertainty ◽  
Process Models ◽  
Third Party ◽  
Sensitivity Analyses ◽  
Surface Dynamics ◽  
New Process ◽  
Creative Computing ◽  
Classroom Use

Abstract. The ability to model surface processes and to couple them to both subsurface and atmospheric regimes has proven invaluable to research in the Earth and planetary sciences. However, creating a new model typically demands a very large investment of time, and modifying an existing model to address a new problem typically means the new work is constrained to its detriment by model adaptations for a different problem. Landlab is an open-source software framework explicitly designed to accelerate the development of new process models by providing: (1) a set of tools and existing grid structures – including both regular and irregular grids – to make it faster and easier to develop new process components, or numerical implementations of physical processes; (2) a suite of stable, modular, and interoperable process components that can be combined to create an integrated model; and (3) a set of tools for data input, output, manipulation, and visualization. A set of example models built with these components is also provided. Landlab's structure makes it ideal not only for fully developed modelling applications, but also for model prototyping and classroom use. Because of its modular nature, it can also act as a platform for model intercomparison and epistemic uncertainty and sensitivity analyses. Landlab exposes a standardized model interoperability interface, and is able to couple to third party models and software. Landlab also offers tools to allow the creation of cellular automata, and allows native coupling of such models to more traditional continuous differential equation-based modules. We illustrate the principles of component coupling in Landlab using a model of landform evolution, a cellular ecohydrologic model, and a flood-wave routing model.

Accelerated Hydrodynamic Analysis for Spar Buoys With Second-Order Wave Excitation

2020 ◽  
Author(s):  
Antonio Pegalajar-Jurado ◽  
Henrik Bredmose
Keyword(s):  
Early Stage ◽  
Numerical Models ◽  
Computational Cost ◽  
Computational Effort ◽  
Second Order ◽  
Offshore Wind ◽  
Good Prediction ◽  
Linear Wave ◽  
Wave Loads ◽  
Sea State

Abstract The simplified numerical models commonly employed for the pre-design of floaters for offshore wind only include linear wave loads, due to the higher computational effort required by second-order methods. Second-order hydrodynamics, on the other hand, need to be considered from an early stage, since they cause resonance of the moored structure. In the present study, we introduce a new method to include second-order inviscid hydrodynamic loads at a computational cost similar to linear loads. We compare the accelerated method to standard second-order diffraction theory and to second-order Rainey forcing with Sharma & Dean wave kinematics. The comparison, based on the loads and response of a spar floating wind turbine in surge and pitch, is carried out for three different sea states. We find that a good prediction of the second-order resonant response can be obtained with the accelerated method for medium and severe sea states, while the match is not as good for the mild sea state. The accelerated method is between 400 and 850 times faster than commonly used second-order approaches, for an 1-hour realization of a given sea state. This speed up allows the application of the load model in the floater pre-design, where efficient numerical models are the key to achieve optimal designs and the consequent reduction in the cost of the floater.

Average Properties of the Largest Waves in Hurricane Camille

2013 ◽  
Vol 135 (1) ◽  
Author(s):  
H. Santo ◽  
P. H. Taylor ◽  
R. Eatock Taylor ◽  
Y. S. Choo
Keyword(s):  
Wave Breaking ◽  
Ocean Waves ◽  
Wave Group ◽  
Sea State ◽  
Winter Storms ◽  
Order Difference ◽  
Time Histories ◽  
Nonlinear Surface ◽  
Focused Wave ◽  
Focused Wave Group

Ocean waves are known to be both random in time and nonlinear. Surface elevation time histories measured in the Gulf of Mexico during Hurricane Camille in 1969 are re-analyzed. The average shapes of large crests and deep troughs in time are shown to be close to symmetric around the instant when the maximum (or minimum) occurs, with only slight evidence of asymmetry from wave breaking in the time histories. There is considerable vertical asymmetry with higher and sharper crests and smaller and more rounded troughs. Overall, the analysis supports the use of a focused wave group based on the scaled autocorrelation function (NewWave) as proposed by Lindgren and Boccotti, with sum harmonic corrections. There is a very small second order difference setup for both large crests and troughs, consistent with considerable directional spreading in the hurricane sea-state. This spreading is likely to be larger than that usually assumed for nontropical winter storms. The spectral tail is shown to have a decay rate proportional to –4.5 power law midway between the classical JONSWAP (Phillips) –5 form and the –4 slope proposed by Battjes et al. (1987, “A Reanalysis of the Spectra Observed in JONSWAP,” J. Phys. Oceanogr., 17(8), pp. 1288–1295) as a correction to JONSWAP.

Multi-Focused Wave Groups in Wave Flume

2019 ◽  
Author(s):  
Qinghe Fang ◽  
Cunbao Zhao ◽  
Anxin Guo
Keyword(s):  
Irregular Waves ◽  
Frequency Resolution ◽  
Random Wave ◽  
Wave Group ◽  
Wave Groups ◽  
Large Wave ◽  
Wave Flume ◽  
Space And Time ◽  
Focused Wave ◽  
Focused Wave Group

Abstract People can simulate extreme hydrodynamic conditions in a laboratory facility by interfering a numbers of regular waves at a certain point in space and time, which is focused wave. It is obviously higher and steeper than any other wave, e.g. regular or irregular waves, within the propagating wave group. The focused wave occurs at a designed point both in space and time. It represents an event with a large return period which would take a long time to reproduce within a random wave sequence. The focused wave, representing of a large wave occurring in a random sea, is quite frequently used to investigate wave loading on marine or coastal structures. However, most research only employ one single focused wave group. Taking the randomness of the wave-structure interaction, repeated tests would be suggested by some textbooks or codes to eliminate the odd results. However, it would take more time to conduct those tests no matter in the laboratory or in the numerical simulations. In our present work, we use a novel method to experimentally generate several focused wave group with different focus time but same focus point at the same time to obtain multi-focused wave groups. The wave elevation and water particle kinematics are measured. The influence of peak frequency, frequency resolution and period of focused wave group are checked and discussed. The results show that present method can generate stable and repeatable focused wave groups in the wave flume.

scholarly journals Numerical and experimental evaluation of masonry prisms by finite element method

2017 ◽  
Vol 10 (2) ◽  
pp. 477-508 ◽  
Author(s):  
C. F.R. SANTOS ◽  
R. C. S. S. ALVARENGA ◽  
J. C. L. RIBEIRO ◽  
L. O CASTRO ◽  
R. M. SILVA ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Finite Element Method ◽  
High Strength Concrete ◽  
Numerical Models ◽  
High Strength ◽  
Experimental Tests ◽  
Experimental Results ◽  
Concrete Blocks ◽  
Micro Modeling ◽  
Modeling Strategy

Abstract This work developed experimental tests and numerical models able to represent the mechanical behavior of prisms made of ordinary and high strength concrete blocks. Experimental tests of prisms were performed and a detailed micro-modeling strategy was adopted for numerical analysis. In this modeling technique, each material (block and mortar) was represented by its own mechanical properties. The validation of numerical models was based on experimental results. It was found that the obtained numerical values of compressive strength and modulus of elasticity differ by 5% from the experimentally observed values. Moreover, mechanisms responsible for the rupture of the prisms were evaluated and compared to the behaviors observed in the tests and those described in the literature. Through experimental results it is possible to conclude that the numerical models have been able to represent both the mechanical properties and the mechanisms responsible for failure.

scholarly journals A Note on the Numerical Representation of Surface Dynamics in Quasigeostrophic Turbulence: Application to the Nonlinear Eady Model

2009 ◽  
Vol 66 (4) ◽  
pp. 1063-1068 ◽  
Author(s):  
Ross Tulloch ◽  
K. Shafer Smith
Keyword(s):  
Numerical Models ◽  
Buoyancy Frequency ◽  
Complete Suppression ◽  
Numerical Representation ◽  
Vertical Resolution ◽  
Surface Dynamics ◽  
Coriolis Parameter ◽  
Theoretical Predictions ◽  
Vertical Grid ◽  
Similar Restriction

Abstract The quasigeostrophic equations consist of the advection of linearized potential vorticity coupled with advection of temperature at the bounding upper and lower surfaces. Numerical models of quasigeostrophic flow often employ greater (scaled) resolution in the horizontal than in the vertical (the two-layer model is an extreme example). In the interior, this has the effect of suppressing interactions between layers at horizontal scales that are small compared to Nδz/f (where δz is the vertical resolution, N the buoyancy frequency, and f the Coriolis parameter). The nature of the turbulent cascade in the interior is, however, not fundamentally altered because the downscale cascade of potential enstrophy in quasigeostrophic turbulence and the downscale cascade of enstrophy in two-dimensional turbulence (occurring layerwise) both yield energy spectra with slopes of −3. It is shown here that a similar restriction on the vertical resolution applies to the representation of horizontal motions at the surfaces, but the penalty for underresolving in the vertical is complete suppression of the surface temperature cascade at small scales and a corresponding artificial steepening of the surface energy spectrum. This effect is demonstrated in the nonlinear Eady model, using a finite-difference representation in comparison with a model that explicitly advects temperature at the upper and lower surfaces. Theoretical predictions for the spectrum of turbulence in the nonlinear Eady model are reviewed and compared to the simulated flows, showing that the latter model yields an accurate representation of the cascade dynamics. To accurately represent dynamics at horizontal wavenumber K in the vertically finite-differenced model, it is found that the vertical grid spacing must satisfy δz ≲ 0.3f/(NK); at wavenumbers K > 0.3f/(Nδz), the spectrum of temperature variance rolls off rapidly.

Study of the Size Effects and Friction Conditions in Microextrusion—Part II: Size Effect in Dynamic Friction for Brass-Steel Pairs

2007 ◽  
Vol 129 (4) ◽  
pp. 677-689 ◽  
Author(s):  
Lapo F. Mori ◽  
Neil Krishnan ◽  
Jian Cao ◽  
Horacio D. Espinosa
Keyword(s):  
Grain Size ◽  
Friction Coefficient ◽  
Size Effect ◽  
Contact Pressure ◽  
Size Effects ◽  
Numerical Models ◽  
Kolsky Bar ◽  
Experimental Results ◽  
Material Response ◽  
Dynamic Coefficients

In this paper, the results of experiments conducted to investigate the friction coefficient existing at a brass-steel interface are presented. The research discussed here is the second of a two-part study on the size effects in friction conditions that exist during microextrusion. In the regime of dimensions of the order of a few hundred microns, these size effects tend to play a significant role in affecting the characteristics of microforming processes. Experimental results presented in the previous companion paper have already shown that the friction conditions obtained from comparisons of experimental results and numerical models show a size effect related to the overall dimensions of the extruded part, assuming material response is homogeneous. Another interesting observation was made when extrusion experiments were performed to produce submillimeter sized pins. It was noted that pins fabricated from large grain-size material (211μm) showed a tendency to curve, whereas those fabricated from billets having a small grain size (32μm), did not show this tendency. In order to further investigate these phenomena, it was necessary to segregate the individual influences of material response and interfacial behavior on the microextrusion process, and therefore, a series of frictional experiments was conducted using a stored-energy Kolsky bar. The advantage of the Kolsky bar method is that it provides a direct measurement of the existing interfacial conditions and does not depend on material deformation behavior like other methods to measure friction. The method also provides both static and dynamic coefficients of friction, and these values could prove relevant for microextrusion tests performed at high strain rates. Tests were conducted using brass samples of a small grain size (32μm) and a large grain size (211μm) at low contact pressure (22MPa) and high contact pressure (250MPa) to see whether there was any change in the friction conditions due to these parameters. Another parameter that was varied was the area of contact. Static and dynamic coefficients of friction are reported for all the cases. The main conclusion of these experiments was that the friction coefficient did not show any significant dependence on the material grain size, interface pressure, or area of contact.

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