scholarly journals A SOLUTION TO THE OVER-PRODUCTION OF TURBULENCE BENEATH SURFACE WAVES IN RANS MODELS

2018 ◽  
pp. 33
Author(s):  
David R. Fuhrman ◽  
Bjarke Eltard Larsen
Keyword(s):  
Ad Hoc ◽  
Surf Zone ◽  
Breaking Waves ◽  
Wide Spread ◽  
Ocean Engineering ◽  
Cfd Simulations ◽  
The Past ◽  
Rans Models ◽  
Engineering Modeling ◽  
Marked Tendency

CFD simulations of breaking waves with RANS models over the past 20 years have shown a marked tendency to severely over-predict turbulence levels, both outside and within the surf zone. The reason is most likely due to the inherent instability of turbulence closure models, as originally diagnosed by Mayer & Madsen (2000). While they proposed an ad-hoc fix, a fundamentally sound solution to this wide-spread problem has, to date, eluded the coastal and ocean engineering modeling community.

scholarly journals NEW METHODS FOR STABILIZING RANS TURBULENCE MODELS WITH APPLICATION TO LARGE SCALE BREAKING WAVES

2020 ◽  
pp. 19
Author(s):  
Georgios Azorakos ◽  
Bjarke Eltard Larsen ◽  
David R. Fuhrman
Keyword(s):  
Turbulence Model ◽  
Large Scale ◽  
Eddy Viscosity ◽  
Turbulence Models ◽  
Breaking Waves ◽  
Wide Spread ◽  
Cfd Simulations ◽  
New Methods ◽  
Rans Turbulence Models ◽  
Scale Breaking

Recently, Larsen and Fuhrman (2018) have shown that seemingly all commonly used (both k-omega and k-epsilon variants) two-equation RANS turbulence closure models are unconditionally unstable in the potential flow beneath surface waves, helping to explain the wide-spread over-production of turbulent kinetic energy in CFD simulations, relative to measurements. They devised and tested a new formally stabilized formulation of the widely used k-omega turbulence model, making use of a modified eddy viscosity. In the present work, three new formally-stable k-omega turbulence model formulations are derived and tested in CFD simulations involving the flow and dynamics beneath large-scale plunging breaking waves.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/T2fFRgq3I8E

Vom Forst zum Wald. Entwicklungstendenzen im naturnahen Waldbau | From a Production-Oriented Forest to a Multipurpose Forest. New Trends in Near-Natural Silviculture

1999 ◽  
Vol 150 (12) ◽  
pp. 484-488 ◽  
Author(s):  
Wolf Hockenjos
Keyword(s):  
Forest Management ◽  
Timber Harvest ◽  
Timber Harvesting ◽  
Natural Forest ◽  
The Other ◽  
Private Forest ◽  
Wide Spread ◽  
Great Demand ◽  
The Past ◽  
Forest Enterprises

Concepts of near-natural forestry are in great demand these days. Most German forest administrations and private forest enterprises attach great importance to being as «near-natural» as possible. This should allow them to make the most of biological rationalisation. The concept of near-natural forestry is widely accepted, especially by conservationists. However, it is much too early to analyse how successful near-natural forestry has been to date, and therefore to decide whether an era of genuine near-natural forest management has really begun. Despite wide-spread recognition, near-natural forestry is jeopardised by mechanised timber harvesting, and particularly by the large-timber harvester. The risk is that machines, which are currently just one element of the timber harvest will gain in importance and gradually become the decisive element. The forest would then be forced to meet the needs of machinery, not the other way round. Forests would consequently become so inhospitable that they would bear no resemblance to the sylvan image conjured up by potential visitors. This could mean taking a huge step backwards: from a near-natural forest to a forest dominated by machinery. The model of multipurpose forest management would become less viable, and the forest would become divided into areas for production, and separate areas for recreation and ecology. The consequences of technical intervention need to be carefully considered, if near-natural forestry is not to become a thing of the past.

scholarly journals The Accelerations of a Wave Measurement Buoy Impacted by Breaking Waves in the Surf Zone

2021 ◽  
Vol 9 (2) ◽  
pp. 214
Author(s):  
Adam C. Brown ◽  
Robert K. Paasch
Keyword(s):  
Inertial Measurement Unit ◽  
Surf Zone ◽  
Spherical Wave ◽  
Breaking Waves ◽  
Measurement Unit ◽  
High Fidelity ◽  
Wave Measurement ◽  
Near Shore ◽  
Shoaling Waves ◽  
Multiple Deployments

A spherical wave measurement buoy capable of detecting breaking waves has been designed and built. The buoy is 16 inches in diameter and houses a 9 degree of freedom inertial measurement unit (IMU). The orientation and acceleration of the buoy is continuously logged at frequencies up to 200 Hz providing a high fidelity description of the motion of the buoy as it is impacted by breaking waves. The buoy was deployed several times throughout the winter of 2013–2014. Both moored and free-drifting data were acquired in near-shore shoaling waves off the coast of Newport, OR. Almost 200 breaking waves of varying type and intensity were measured over the course of multiple deployments. The characteristic signature of spilling and plunging breakers was identified in the IMU data.

scholarly journals Development and Validation of Quasi-Eulerian Mean Three-Dimensional Equations of Motion Using the Generalized Lagrangian Mean Method

2021 ◽  
Vol 9 (1) ◽  
pp. 76
Author(s):  
Duoc Nguyen ◽  
Niels Jacobsen ◽  
Dano Roelvink
Keyword(s):  
Surface Waves ◽  
Deep Water ◽  
Surf Zone ◽  
Equations Of Motion ◽  
Three Dimensional ◽  
Breaking Waves ◽  
Successful Implementation ◽  
Random Waves ◽  
Mean Motion ◽  
Generalized Lagrangian

This study aims at developing a new set of equations of mean motion in the presence of surface waves, which is practically applicable from deep water to the coastal zone, estuaries, and outflow areas. The generalized Lagrangian mean (GLM) method is employed to derive a set of quasi-Eulerian mean three-dimensional equations of motion, where effects of the waves are included through source terms. The obtained equations are expressed to the second-order of wave amplitude. Whereas the classical Eulerian-mean equations of motion are only applicable below the wave trough, the new equations are valid until the mean water surface even in the presence of finite-amplitude surface waves. A two-dimensional numerical model (2DV model) is developed to validate the new set of equations of motion. The 2DV model passes the test of steady monochromatic waves propagating over a slope without dissipation (adiabatic condition). This is a primary test for equations of mean motion with a known analytical solution. In addition to this, experimental data for the interaction between random waves and a mean current in both non-breaking and breaking waves are employed to validate the 2DV model. As shown by this successful implementation and validation, the implementation of these equations in any 3D model code is straightforward and may be expected to provide consistent results from deep water to the surf zone, under both weak and strong ambient currents.

Distributions of void fraction under breaking waves in the surf zone

2005 ◽  
Vol 32 (14-15) ◽  
pp. 1829-1840 ◽  
Author(s):  
Ashabul Hoque ◽  
Shin-ichi Aoki
Keyword(s):  
Void Fraction ◽  
Surf Zone ◽  
Breaking Waves

scholarly journals SURVEY TECHNIQUES/PROCEDURES AND DATA PROCESSING FOR MONITORING NEARSHORE SEDIMENT TRANSPORT

1982 ◽  
Vol 1 (18) ◽  
pp. 97
Author(s):  
J. Zacks
Keyword(s):  
Sediment Transport ◽  
Surf Zone ◽  
Survey Techniques ◽  
The Past ◽  
Bed Elevation ◽  
Innovative Methods ◽  
Survey Error ◽  
Nearshore Sediment Transport ◽  
The Many ◽  
The Cost

The cost of many coastal projects is often increased by the expensive beach repair and maintenance required to remedy the destabilising effects of structures on the adjoining coastline. Physical and/or mathematical models have been developed for use in planning these projects in order to predict and quantify the effects of marine sediment transport on the coastal topography. Such models need to be calibrated against prototype data and one method of gauging volumetric sediment movement is by successive bathymetric/ topographic profiting surveys which are performed seasonally and annually. Since large quantities of sediment are related to small changes in bed elevation it is clear that this profiling needs to be done with the utmost precision* The areas most affected extend from the beach through the surf zone to water depths of about 25 metres. The surf zone in particular is a dynamic and hostile area which falls outside the traditional activities of both the hydrographic and land surveyors. Consequently innovative methods, deficient in sound survey principle and practice, have often been pursued in this area without any attempt being made to assess the tolerance on the data. This paper attempts to show that it is possible to produce reliable and verifiable results to the required accuracy by using conventional survey equipment and techniques, also by taking the necessary precautions against the many possible sources of survey error. The procedures and techniques described have evolved from NRIO's involvement over the past decade in major projects at Richards Bay, Durban, Koeberg and in False Bay. The results of a recent verification investigation are fully reported in this paper.

scholarly journals LABORATORY EXPERIMENTS ON THE INFLUENCE OF WIND ON NEARSHORE WAVE BREAKING

1988 ◽  
Vol 1 (21) ◽  
pp. 46
Author(s):  
Scott L. Douglass ◽  
J. Richard Weggel
Keyword(s):  
Wind Direction ◽  
Wave Breaking ◽  
Laboratory Experiments ◽  
Surf Zone ◽  
Breaking Waves ◽  
Wave Tank ◽  
Zone Width

The influence of wind on nearshore breaking waves was investigated in a laboratory wave tank. Breaker location, geometry, and type depended upon the wind acting on the wave as it broke. Onshore winds tended to cause waves to break earlier, in deeper water, and to spill: offshore winds tended to cause waves to break later, in shallower water, and to plunge. A change in wind direction from offshore to onshore increased the surf zone width by up to 100%. Wind's effect was greatest for waves which were near the transition between breaker types in the absence of wind. For onshore winds, it was observed that microscale breaking can initiate spilling breaking by providing a perturbation on the crest of the underlying wave as it shoals.

scholarly journals Time Direction of Information Propagation and Cosmology

1972 ◽  
Vol 25 (2) ◽  
pp. 207 ◽  
Author(s):  
DT Pegg
Keyword(s):  
Steady State ◽  
Ad Hoc ◽  
Big Bang ◽  
Information Propagation ◽  
The Past ◽  
The Future ◽  
Consistent Solution ◽  
Electrodynamic Theory ◽  
The Universe ◽  
State Universe

In conventional electrodynamic theory, the advanced potential solution of Maxwell's equations is discarded on the ad hoc basis that information can be received from the past only and not from the future. This difficulty is overcome by the Wheeler?Feynman absorber theory, but unfortunately the existence of a completely retarded solution in this theory requires a steady-state universe. In the present paper conventional electrodynamics is used to obtain a condition which, if satisfied, allows information to be received from the past only, and ensures that the retarded potential is the only consistent solution. The condition is that a function Ua of the future structure of the universe is infinite, while the corresponding function Ur of the past structure is finite. Of the currently acceptable cosmological models, only the steady-state, the open big-bang, and the Eddington-Lema�tre models satisfy this condition. In these models there is no need for an ad hoc reason for the preclusion of advanced potentials.

scholarly journals Prevalence and Characteristics of Back Pain in Children and Adolescents from the Region of Murcia (Spain): ISQUIOS Programme

2022 ◽  
Vol 19 (2) ◽  
pp. 946
Author(s):  
María Teresa Martínez-Romero ◽  
Antonio Cejudo ◽  
Pilar Sainz de Baranda
Keyword(s):  
Back Pain ◽  
Body Mass ◽  
Ad Hoc ◽  
Pubertal Development ◽  
Body Height ◽  
Maturity Stage ◽  
Leg Length ◽  
Anthropometric Measures ◽  
School Aged Children ◽  
The Past

Puberty is a vulnerable period for musculoskeletal disorders due to the existence of a wide inter-individual variation in growth and development. The main objective of the present study was to describe the prevalence of back pain (BP) in the past year and month in school-aged children according to sex, age, maturity status, body mass index (BMI) and pain characteristics. This study involved 513 students aged between 9 and 16 years. Anthropometric measures were recorded to calculate the maturity stage of the students using a regression equation comprising measures for age, body mass, body height, sitting height and leg length. An ad hoc questionnaire composed of eight questions was used to describe BP prevalence in school-aged children. The results showed that the prevalence of BP in school-aged children was observed in 35.1% over the last year (45% boys and 55% girls), and 17.3% (40.4% boys and 59.6% girls, with an association found between female sex and BP) in the last month. The prevalence of back pain in the past year and month was higher the older the students were, or the more pubertal development they had experienced. The prevalence of BP in the last year was also higher in those with overweight or obesity. After adjustment for sex, there was an association between BP and older age and higher BMI in boys and an association between BP and higher pubertal development in girls. In summary, the present study showed that the prevalence of BP was related to the maturity stage and weight of the participants, with different prevalence patterns found according to sex.

scholarly journals Conceptualizing the Parliamentarization and Politicization of European Policies

2019 ◽  
Vol 7 (3) ◽  
pp. 227-236 ◽  
Author(s):  
Niels Gheyle
Keyword(s):  
European Integration ◽  
Ad Hoc ◽  
National Parliaments ◽  
Complete Understanding ◽  
Related Literature ◽  
The Past ◽  
Theoretical Assumptions ◽  
European Policies ◽  
Eu Studies ◽  
The Eu

In the past 20 years, two related literature strands have gradually moved centre stage of the attention of EU Studies scholars. The first is preoccupied with the ‘politicization of European integration’, a multi-faceted concept that aims to tie together a multitude of political and societal manifestations underlying an increasing controversiality of the EU. A second concerns the parliamentarization of the EU, referring to the changing (institutional) role and EU-related activities national parliaments engage in. The key point of this contribution is simple, but often overlooked: We can and should be seeing parliamentarization as a necessary, yet insufficient, component of a wider process of politicization. Doing so goes beyond the often ad hoc or pars pro toto theoretical assumptions in both literature strands, sheds new light on the normative consequences attached to these phenomena, and furthers a more complete understanding of how a ‘comprehensive’ politicization of European policies develops.

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