Field Verification of Linear and Nonlinear Hybrid Wave Models for Offshore Tower Response Prediction

1997 ◽  
Vol 119 (3) ◽  
pp. 158-165 ◽  
Author(s):  
A. T. Couch ◽  
J. P. Conte
Keyword(s):  
Velocity Field ◽  
Response Time ◽  
Wave Model ◽  
Linear Wave ◽  
Surface Boundary ◽  
Wave Steepness ◽  
Hybrid Wave ◽  
Time Histories ◽  
Wave Models ◽  
Measured Response

Accuracy of the prediction of the dynamic response of deepwater fixed offshore platforms to irregular sea waves depends very much on the theory used to determine wave kinematics. A common industry practice consists of using linear wave theory, which assumes infinitesimal wave steepness, in conjunction with empirical wave stretching techniques to provide a more realistic representation of near-surface water kinematics. The current velocity field is then added to the wave-induced fluid velocity field and the wave-and-current forces acting on the structure are computed via Morison’s equation. The first objective of this study is to compare the predicted responses of Cognac, a deepwater fixed platform, obtained from several popular empirical wave models with the response Cognac predicted based on the hybrid wave model. The latter is a recently developed higher-order, and therefore more accurate, wave model which satisfies, up to the second-order in wave steepness, the local mass conservation and the linear free surface boundary conditions at the instantaneous wave surface. The second objective of this study is to correlate the various analytical response predictions with the measured response of Cognac. Availability of a set of oceanographic and structural vibration data for Cognac provides a unique opportunity to evaluate the prediction ability of traditional analytical models used in designing such structures. The results of this study indicate that (i) the use of the hybrid wave model provides predicted platform response time histories which overall are in better agreement with the measured response than the predictions based on the various stretched linear wave models; and (ii) the Wheeler stretching technique produces platform response time histories which overall are more accurate than those obtained by using the other stretching schemes considered here.

scholarly journals Far-Field Characteristics of Linear Water Waves Generated by a Submerged Landslide over a Flat Seabed

2020 ◽  
Vol 8 (3) ◽  
pp. 196
Author(s):  
Haixiao Jing ◽  
Yanyan Gao ◽  
Changgen Liu ◽  
Jingming Hou
Keyword(s):  
Shallow Water ◽  
Water Depth ◽  
Water Waves ◽  
Wave Model ◽  
Linear Wave ◽  
Far Field ◽  
Constant Depth ◽  
Low Froude Number ◽  
Dispersive Model ◽  
Wave Models

Understanding the propagation of landslide-generated water waves is of great help against tsunami hazards. In order to investigate the effects of landslide shapes on the far-field leading wave generated by a submerged landslide at a constant depth, three linear wave models with different degrees of dispersive properties are employed in this study. The linear fully dispersive model is then validated by comparing the results against the experimental data available for landslides with a low Froude number. Three simplified shapes of landslides with the same volume, which are unnatural for a body of incoherent material, are used to investigate the effects of landslide shapes on the far-field properties of the generated leading wave over a flat seabed. The results show that the far-field leading crest over a constant depth is independent of the exact landslide shape and is invalid at a shallow water depth. Therefore, the most popular non-dispersive model (also called the shallow water wave model) cannot be used to reproduce the phenomenon. The weakly dispersive wave model can predict this phenomenon well. If only the leading wave is considered, this model is accurate up to at least μ = h0/Lc = 0.6, where h0 is the water depth and Lc denotes the characteristic length of the landslide.

scholarly journals Horizontal circulation and jumps in Hamiltonian wave models

2013 ◽  
Vol 20 (4) ◽  
pp. 483-500 ◽  
Author(s):  
E. Gagarina ◽  
J. van der Vegt ◽  
O. Bokhove
Keyword(s):  
Velocity Field ◽  
Water Wave ◽  
Hamiltonian Dynamics ◽  
Hamiltonian Formulation ◽  
Three Dimensional ◽  
Wave Model ◽  
Wave Dispersion ◽  
Flow Profile ◽  
New Model ◽  
Wave Models

Abstract. We are interested in the modelling of wave-current interactions around surf zones at beaches. Any model that aims to predict the onset of wave breaking at the breaker line needs to capture both the nonlinearity of the wave and its dispersion. We have therefore formulated the Hamiltonian dynamics of a new water wave model, incorporating both the shallow water and pure potential flow water wave models as limiting systems. It is based on a Hamiltonian reformulation of the variational principle derived by Cotter and Bokhove (2010) by using more convenient variables. Our new model has a three-dimensional velocity field consisting of the full three-dimensional potential velocity field plus extra horizontal velocity components. This implies that only the vertical vorticity component is nonzero. Variational Boussinesq models and Green–Naghdi equations, and extensions thereof, follow directly from the new Hamiltonian formulation after using simplifications of the vertical flow profile. Since the full water wave dispersion is retained in the new model, waves can break. We therefore explore a variational approach to derive jump conditions for the new model and its Boussinesq simplifications.

Ocean Surface Modeling in Vary Wind Field

2011 ◽  
Vol 480-481 ◽  
pp. 1452-1456
Author(s):  
Li Bo ◽  
Zhong Yi Li ◽  
Yue Jin Zhang
Keyword(s):  
Wind Field ◽  
Wave Spectrum ◽  
Wave Model ◽  
Ocean Surface ◽  
Ocean Waves ◽  
Surface Modeling ◽  
Ocean Wave ◽  
Statistical Characteristics ◽  
Linear Wave ◽  
Wave Models

In ocean surface modeling a popular method of wave modeling is making use of ocean wave spectrum, which is a physical wave model and based on linear wave theories. The ocean waves produced in this way can reflect the statistical characteristics of the real ocean well. However, few investigations of ocean simulation have been focused on turbulent fluid under vary wind field in this way, while all ocean wave models are built with the same wind parameters. In order to resolve the problem of traditional method, we proposed a new method of dividing the ocean surface into regular grids and generating wave models with different parameters of wind in different location of view scope. The method not only preserves the fidelity of statistical characteristics, but also can be accelerated with the processing of GPU and widely used in VR applications.

scholarly journals Hurricane Gustav (2008) Waves and Storm Surge: Hindcast, Synoptic Analysis, and Validation in Southern Louisiana

2011 ◽  
Vol 139 (8) ◽  
pp. 2488-2522 ◽  
Author(s):  
J. C. Dietrich ◽  
J. J. Westerink ◽  
A. B. Kennedy ◽  
J. M. Smith ◽  
R. E. Jensen ◽  
...  
Keyword(s):  
Gulf Of Mexico ◽  
Hurricane Katrina ◽  
Storm Surge ◽  
Unstructured Mesh ◽  
Wind Waves ◽  
Wave Model ◽  
Small Scale ◽  
Research Division ◽  
Time Histories ◽  
Southern Louisiana

AbstractHurricane Gustav (2008) made landfall in southern Louisiana on 1 September 2008 with its eye never closer than 75 km to New Orleans, but its waves and storm surge threatened to flood the city. Easterly tropical-storm-strength winds impacted the region east of the Mississippi River for 12–15 h, allowing for early surge to develop up to 3.5 m there and enter the river and the city’s navigation canals. During landfall, winds shifted from easterly to southerly, resulting in late surge development and propagation over more than 70 km of marshes on the river’s west bank, over more than 40 km of Caernarvon marsh on the east bank, and into Lake Pontchartrain to the north. Wind waves with estimated significant heights of 15 m developed in the deep Gulf of Mexico but were reduced in size once they reached the continental shelf. The barrier islands further dissipated the waves, and locally generated seas existed behind these effective breaking zones.The hardening and innovative deployment of gauges since Hurricane Katrina (2005) resulted in a wealth of measured data for Gustav. A total of 39 wind wave time histories, 362 water level time histories, and 82 high water marks were available to describe the event. Computational models—including a structured-mesh deepwater wave model (WAM) and a nearshore steady-state wave (STWAVE) model, as well as an unstructured-mesh “simulating waves nearshore” (SWAN) wave model and an advanced circulation (ADCIRC) model—resolve the region with unprecedented levels of detail, with an unstructured mesh spacing of 100–200 m in the wave-breaking zones and 20–50 m in the small-scale channels. Data-assimilated winds were applied using NOAA’s Hurricane Research Division Wind Analysis System (H*Wind) and Interactive Objective Kinematic Analysis (IOKA) procedures. Wave and surge computations from these models are validated comprehensively at the measurement locations ranging from the deep Gulf of Mexico and along the coast to the rivers and floodplains of southern Louisiana and are described and quantified within the context of the evolution of the storm.

scholarly journals Non-linear wave data assimilation with an ANN-type wind-wave model and Ensemble Kalman Filter (EnKF)

2010 ◽  
Vol 34 (8) ◽  
pp. 1984-1999 ◽  
Author(s):  
Ahmadreza Zamani ◽  
Ahmadreza Azimian ◽  
Arnold Heemink ◽  
Dimitri Solomatine
Keyword(s):  
Kalman Filter ◽  
Data Assimilation ◽  
Ensemble Kalman Filter ◽  
Wind Wave ◽  
Wave Model ◽  
Linear Wave ◽  
Wave Data ◽  
Non Linear

scholarly journals Spatially Tracking Wave Events in Partitioned Numerical Wave Model Outputs

2019 ◽  
Vol 36 (10) ◽  
pp. 1933-1944 ◽  
Author(s):  
Haoyu Jiang
Keyword(s):  
Grid Point ◽  
Wave Model ◽  
Ocean Waves ◽  
Model Verification ◽  
Analysis Model ◽  
Wave Parameters ◽  
Numerical Wave ◽  
Wave Models ◽  
Spectral Partitioning ◽  
The Impact

AbstractNumerical wave models can output partitioned wave parameters at each grid point using a spectral partitioning technique. Because these wave partitions are usually organized according to the magnitude of their wave energy without considering the coherence of wave parameters in space, it can be difficult to observe the spatial distributions of wave field features from these outputs. In this study, an approach for spatially tracking coherent wave events (which means a cluster of partitions originating from the same meteorological event) from partitioned numerical wave model outputs is presented to solve this problem. First, an efficient traverse algorithm applicable for different types of grids, termed breadth-first search, is employed to track wave events using the continuity of wave parameters. Second, to reduce the impact of the garden sprinkler effect on tracking, tracked wave events are merged if their boundary outlines and wave parameters on these boundaries are both in good agreement. Partitioned wave information from the Integrated Ocean Waves for Geophysical and other Applications dataset is used to test the performance of this spatial tracking approach. The test results indicate that this approach is able to capture the primary features of partitioned wave fields, demonstrating its potential for wave data analysis, model verification, and data assimilation.

scholarly journals Non-Synchronous Response Of Rabots Glaciar and Storglaciaren To Recent Climatic Change

1990 ◽  
Vol 14 ◽  
pp. 331-332
Author(s):  
Keith A. Brugger
Keyword(s):  
Steady State ◽  
Response Time ◽  
Mass Balance ◽  
Climatic Change ◽  
Regional Climate ◽  
Wave Model ◽  
Equilibrium Line Altitude ◽  
Local Climate ◽  
Climatic Oscillations ◽  
Basin Topography

Rabots glaciär and Storglaciären are small valley glaciers located in the Kebnekaise massif of northern Sweden. Rabots glaciär flows west from the summit of Kebnekaise (2114 m) and Storglaciären flows east; thus regional climate affecting the glaciers is the same. The glaciers are of comparable size and geometry, although differences exist in the variation of ice thickness and the subglacial bedrock topography within the respective basins. The thickness of Rabots glaciär appears to be relatively uniform over much of its length and its bed smooth. The bed over which Storglaciären flows is characterized by a “riegel and basin” topography and ice thicknesses vary accordingly. Advance and retreat of the glaciers during the last 100 years has been documented by historical records and photographs, measurements of ice retreats, and detailed glacial and geological studies. Both advanced to their maximum 20th century extents around 1916. In their subsequent retreat, Rabots glaciär has lagged behind Storglaciären by 10 years. Mass-balance studies for the years 1981–87 suggest that while the “local” climate for each glacier is slightly different (in terms of the magnitude of acumulation and ablation), variations in local climate are synchronous. Non-synchronous response of the glaciers is therefore attributed to differences in glacier dynamics, which are quite apparent when velocity profiles are compared. Ice velocities on Rabots glaciär vary little from an average of −7.5 m/yr, resulting in a longitudinal strain rate, r, of about 6 × 10−3yr −1. In contrast, values for r on Storglaciären are as high as 2.5 × 10−2 yr−1 owing to greater ice velocities and variation in ice velocity. Since the response time of a glacier is proportional to 1/r, the lower strain rates found on Rabots glaciär probably account for its more sluggish retreat. A simple, non-diffusive, kinematic wave model is used to analyze the response of the glaciers to a step-like perturbation in mass balance. This model predicts that the response time of Storglaciären is on the order of 30 years and that a new steady-state profile would be attained in about 50 years. The predicted response time of Rabots glaciär is about 75 years, its new steady-state profile being reached after more than 100 years. More accurate analyses of each glacier's response to climatic change use a time-dependent numerical model which includes the effects of diffusion. The climatic forcing in these modelling efforts is represented by the changes in mass balance resulting from changes in the equilibrium line altitude (ELA). ELAs can be correlated to regional meteorological variables which in turn are used to create a “synthetic” record of ELA variations where necessary. Therefore climatic oscillations since the turn of the century can be simulated by the appropriate changes in ELA. Using synchronous variations of ELAs and their 1916 profiles as datum states, the modeled behavior of Rabots glaciär and Storglaciären shows that: (a) the rates of ice retreat for each glacier are in reasonable agreement with those observed; and (b) Rabots glaciär took slightly longer than Storglaciären to react to the slight warming that occurred shortly after their 1916 advance.

Fatigue Analysis of a Jacket Structure to Linear and Weakly Nonlinear Random Waves

2019 ◽  
Vol 141 (6) ◽  
Author(s):  
Naser Shabakhty ◽  
Arash Khansari
Keyword(s):  
Dynamic Response ◽  
Engineering Practice ◽  
Linear Wave ◽  
Fe Model ◽  
Random Waves ◽  
Weakly Nonlinear ◽  
Analysis And Design ◽  
Jacket Structures ◽  
Wave Models ◽  
Nonlinear Random Waves

Jacket structures have been widely used in oil and gas industry and are increasingly becoming competitive as a support structure of wind turbines at different water depths. These types of structures usually fix in transition or shallow waters where numerous field observations and experiments have shown that water particles tend to exhibit non-Gaussian characteristics. However, current engineering practice ignores the wave nonlinearity for the analysis and design of these structures. The application of linear irregular models might result in considerable uncertainties in the obtained wave loads and consequently the dynamic response and thus it is highly questionable. Therefore, it is crucial to calculate the dynamic response of jacket structures under both linear and nonlinear wave models to investigate the validity of linear wave models in different sea states. In this paper, the finite element (FE) model of a jacket structure located in Persian Gulf (SP17 jacket) is setup and applied to perform a comparative study of the dynamic response to both linear and weakly nonlinear random waves. The fatigue life of the jacket structure is then calculated under both wave models. This paper will substantially improve the understanding of the dynamic response of jacket structures under fatigue damage.

scholarly journals Wave Modeling—Missing the Peaks

2009 ◽  
Vol 39 (11) ◽  
pp. 2757-2778 ◽  
Author(s):  
Luigi Cavaleri
Keyword(s):  
Wave Model ◽  
Sensitivity Study ◽  
New Physics ◽  
Lower Atmosphere ◽  
Physical Interaction ◽  
Extreme Conditions ◽  
Wind Variability ◽  
Nonlinear Energy Transfer ◽  
The Difference ◽  
Wave Models

Abstract The paper analyzes the capability of the present wave models of properly reproducing the conditions during and at the peak of severe and extreme storms. After providing evidence that this is often not the case, the reasons for it are explored. First, the physics of waves considered in wave models is analyzed. Although much improved with respect to the past, the wind accuracy is still a relevant factor at the peak of the storms. Other factors such as wind variability and air density are considered. The classical theory of wave generation by J. W. Miles’s mechanism, with subsequent modifications, is deemed not sufficiently representative of extreme conditions. The presently used formulations for nonlinear energy transfer are found to lead to too wide distributions in frequency and direction, hence reducing the input by wind. Notwithstanding some recent improvements, the white-capping formulation still depends on parameters fitted to the bulk of the data. Hence, it is not obvious how they will perform in extreme conditions when the physics is likely to be different. Albeit at different levels in different models, the advection still implies the spreading of energy, hence a spatial smoothing of the peaks. The lack of proper knowledge of the ocean currents is found to substantially affect the identification of how much energy can—in some cases—be concentrated at a given time and location. The implementation of the available theories and know-how in the present wave models are often found inconsistent from model to model. It follows that in this case, it is not possible to exchange corresponding pieces of software between two models without substantially affecting the quality of the results. After analyzing various aspects of a wave model, the paper makes some general considerations. Because wave growth is the difference between processes (input and output) involving large amounts of energy, it is very sensitive to small modifications of one or more processes. Together with the strong, but effective, tuning present in a wave model, this makes the introduction of new physics more complicated. It is suggested that for long-term improvements, operational and experimental applications need to proceed along parallel routes, with the latter looking more to the physics without the necessity of an immediately improved overall performance. In view of the forthcoming increase of computer power, a sensitivity study is suggested to identify the most critical areas in a wave model to determine where to invest for further improvements. The limits on the description of the physics of the processes when using the spectral approach, particularly in extreme conditions, are considered. For further insights and as a way to validate the present theories in these conditions, the use is suggested of numerical experiments simulating in great detail the physical interaction between the lower atmosphere and the single waves.

scholarly journals Slope distribution in front-back asymmetric stochastic Lagrange time waves

2010 ◽  
Vol 42 (02) ◽  
pp. 489-508 ◽  
Author(s):  
G. Lindgren
Keyword(s):  
Particle Velocity ◽  
Random Fields ◽  
Wave Model ◽  
Linear Wave ◽  
Multivariate Normal ◽  
Ocean Engineering ◽  
Expected Number ◽  
Measuring Station ◽  
Predetermined Level ◽  
The Waves

The stochastic Lagrange wave model is a realistic alternative to the Gaussian linear wave model, which has been successfully used in ocean engineering for more than half a century. In this paper we present the slope distributions and other characteristic distributions at level crossings for asymmetric Lagrange time waves, i.e. what can be observed at a fixed measuring station, thereby extending results previously given for space waves. The distributions are given as expectations in a multivariate normal distribution, and they have to be evaluated by simulation or numerical integration. Interesting characteristic variables are the slope in time, the slope in space, and the vertical particle velocity when the waves are observed close to instances when the water level crosses a predetermined level. The theory has been made possible by recent generalizations of Rice's formula for the expected number of marked crossings in random fields.

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