Showing papers on "Swell published in 2003"

Investigation of Wave Growth and Decay in the SWAN Model: Three Regional-Scale Applications

Abstract: Wave growth and decay characteristics in a typical wave action model [Simulating Waves Nearshore (SWAN)] are investigated in this paper. This study is motivated by generally poor agreement between model results and measurements for a regional-scale model of a two-day period during the SandyDuck '97 experiment, wherein there is consistent underprediction of lower-frequency (0.05–0.19 Hz) energy. Two separate methods are presented for improving predictions of low-frequency energy: 1) by altering the weighting of the relative wavenumber term that exists in the whitecapping formulation and 2) by disallowing the breaking of swell. The SandyDuck '97 simulation is repeated with the proposed modifications. Using the first modification, a slight improvement is seen, and with the second modification an apparent problem with nonphysical dissipation of swell by the model is corrected. The modifications are then applied to two other test cases, one in Lake Michigan and the other in the Mississippi Bight. Both...

Dynamical coupling of wind and ocean waves through wave-induced air flow

Abstract: Understanding the physical mechanisms behind the generation of ocean waves by wind has been a longstanding challenge1,2. Previous studies3,4,5,6 have assumed that ocean waves induce fluctuations in velocity and pressure of the overlying air that are synchronized with the waves, and numerical models have supported this assumption7. In a complex feedback, these fluctuations provide the energy for wave generation. The spatial and temporal structure of the wave-induced airflow therefore holds the key to the physics of wind–wave coupling, but detailed observations have proved difficult. Here we present an analysis of wind velocities and ocean surface elevations observed over the open ocean. We use a linear filter8 to identify the wave-induced air flow from the measurements and find that its structure is in agreement with ‘critical-layer’ theory3. Considering that the wave-induced momentum flux is then controlled by the wave spectrum and that it varies considerably in vertical direction, a simple parameterization of the total air–sea momentum flux is unlikely to exist.

Swell Transformation across the Continental Shelf. Part I: Attenuation and Directional Broadening

Abstract: Extensive wave measurements were collected on the North Carolina–Virginia continental shelf in the autumn of 1999. Comparisons of observations and spectral refraction computations reveal strong cross-shelf decay of energetic remotely generated swell with, for one particular event, a maximum reduction in wave energy of 93% near the Virginia coastline, where the shelf is widest. These dramatic energy losses were observed in light-wind conditions when dissipation in the surface boundary layer caused by wave breaking (whitecaps) was weak and wave propagation directions were onshore with little directional spreading. These observations suggest that strong dissipation of wave energy takes place in the bottom boundary layer. The inferred dissipation is weaker for smaller-amplitude swells. For the three swell events described here, observations are reproduced well by numerical model hindcasts using a parameterization of wave friction over a movable sandy bed. Directional spectra that are narrow off the s...

Assessment of the reliability of wave observations from voluntary observing ships: Insights from the validation of a global wind wave climatology based on voluntary observing ship data

Abstract: This paper describes development and validation of a global climatology of basic wave parameters based on the voluntary observing ship (VOS) data from the Comprehensive Ocean-Atmosphere Data Set collection. Climatology covers the period 1958–1997 and presents heights and periods for the wind sea, swell, and significant wave height (SWH) over the global ocean on 2° × 2° spatial resolution. Significant wave height has been derived from separate sea and swell estimates by taking square root of the sum of squares for the seas and swells propagating approximately in the same direction and assuming SWH to be equal to the higher of the two components in all other cases. Special algorithms of corrections were applied to minimize some biases, inherent in visual wave data. Particularly, we corrected overestimation of small seas, corrected underestimation of periods, and analyzed separation between sea and swell. Validation included estimation of random observational errors, observation of sampling errors, and comparison with the alternative wave data. Estimates of random observational errors show that for the majority of locations, observational uncertainties are within 20% of mean values, which allows us to discuss quantitatively the produced climatology. Biases associated with inadequate sampling were quantified using the data from high-resolution WAM hindcast for the period 1979–1993. The highest sampling biases are observed in the South Ocean, where wave height may be underestimated by 1–1.5 m because of poor sampling, primarily associated with a fair weather bias of ship routing and observation. Comparison to the other VOS-based products shows in general higher SWH in our climatology, especially in the midlatitudes. However, comparison with the altimeter data shows that even for well-sampled regions, high waves are still underestimated in VOS, suggesting a ubiquitous fair weather bias. Further ways of improving VOS-based wave climatologies and possible applications are discussed.

The Origin of Stationary Planetary Waves in the Upper Mesosphere

Abstract: Satellite observations indicate that quasi-stationary planetary waves often exist to at least 100 km in the winter mesosphere. Waves are also seen in the summer upper mesosphere. A three-dimensional numerical model was used to simulate these waves and to diagnose the physical processes involved. The waves simulated in the model closely resemble observed waves. Several model runs that isolate specific processes are used to determine the relative importance of two forcing mechanisms. In the model, planetary waves that propagate from below are significantly damped at the altitude where gravity wave drag becomes large (about 75 km in the winter midlatitudes) or below if a reversal in the mean wind is encountered. Momentum forcing associated with breaking gravity waves that have been filtered by planetary-scale wind variations below acts to generate planetary waves in the middle and upper mesosphere. The amplitude from in situ forcing by gravity wave breaking exceeds the amplitude from the upward-prop...

Revisiting the Pierson–Moskowitz asymptotic limits for fully developed wind waves

Abstract: The time-honored topic of fully developed wind seas pioneered by Pierson and Moskowitz is revisited to review the asymptotic evolution limits of integral spectral parameters used by the modeling community in the validation of wind-wave models. Discrepancies are investigated between benchmark asymptotic limits obtained by scaling integral spectral parameters using alternative wind speeds. Using state-of-the-art wind and wave modeling technology, uncertainties in the Pierson‐Moskowitz limits due to inhomogeneities in the wind fields and contamination of the original data by crossing seas and swells are also investigated. The resulting reanalyzed database is used to investigate the optimal scaling wind parameter and to refine the levels of the full-development asymptotes of nondimensional integral wave spectral parameters used by the windwave modeling community. The results are also discussed in relation to recent advances in quantifying wavebreaking probability of wind seas. The results show that the parameterization of integral spectral parameters and the scaling of nondimensional asymptotes as a function of U10 yields relations consistent with similarity theory. On the other hand, expressing integral spectral parameters and scaling nondimensional asymptotes as a function of u * or alternative proposed scaling wind speeds yields relations that do not conform to similarity requirements as convincingly. The reanalyzed spectra are used to investigate parameter values and shapes of analytical functions representing fully developed spectra. These results support an analytical form with a spectral tail proportional to f 24.

Wind Stress Vector over Ocean Waves

Abstract: Previous investigations of the wind stress in the marine surface layer have primarily focused on determining the stress magnitude (momentum flux) and other scalar variables (e.g., friction velocity, drag coefficient, roughness length). However, the stress vector is often aligned with a direction different from that of the mean wind flow. In this paper, the focus is on the study of the stress vector direction relative to the mean wind and surface-wave directions. Results based on measurements made during three field campaigns onboard the R/P Floating Instrument Platform (FLIP) in the Pacific are discussed. In general, the wind stress is a vector sum of the 1) pure shear stress (turbulent and viscous) aligned with the mean wind shear, 2) wind-wave-induced stress aligned with the direction of the pure wind-sea waves, and 3) swell-induced stress aligned with the swell direction. The direction of the wind-wave-induced stress and the swell-induced stress components may coincide with, or be opposite to,...

Shrink test--water content method for shrink and swell predictions

Abstract: A new method is proposed to estimate the vertical movement of the ground surface for soil that swells and shrinks due to variations in water content. The water content is used as the main soil parameter and a shrink test is suggested to obtain the relationship between the change in water content and the volumetric strain induced. We propose estimating the change in water content and the depth of seasonal moisture changes from local databases or from existing techniques. The method is evaluated by comparing the predicted movement and the measured movement of four full-scale spread footings over a period of 2 years.

Issues concerning the sea emissivity modeling at L band for retrieving surface salinity

Abstract: [1] In order to prepare the sea surface salinity (SSS) retrieval in the frame of the Soil Moisture and Ocean Salinity (SMOS) mission we conduct sensitivity studies to quantify uncertainties on simulated brightness temperatures (Tb) related to uncertainties on sea surface and scattering modeling. Using a two-scale sea surface emissivity model to simulate Tb at L band (1.4 GHz), we explore the influence on estimated SSS of the parameterization of the seawater permittivity, of the sea wave spectrum, of the choice of the two-scale cutoff wavelength, and of adding swell to the wind sea. Differences between Tb estimated with various existing permittivity models are up to 1.5 K. Therefore a better knowledge of the seawater permittivity at L band is required. The influence of wind speed on Tb simulated with various parameterizations of the sea wave spectrum differs by up to a factor of two; for a wind speed of 7 m s−1 the differences on estimated SSS is several psu depending on the sea wave spectral model taken, so that sea spectrum is a major source of uncertainty in models. We find no noticeable effect on simulated Tb when changing the two-scale cutoff wavelength and when adding swell to the wind sea for low to moderate incidence angles. The dependence of the wind-induced Tb on SST and SSS being weak, we assess the error in SSS estimated assuming that the wind speed influence is independent of SST and SSS. We find errors on estimated SSS up to 0.5 psu for 20°C variation in SST. Therefore this assumption would induce regional biases when applied to global measurements.

Effect of sea state on the momentum exchange over the sea during neutral conditions

Abstract: [1] On the basis of an extensive data set from the air-sea interaction station Ostergarnsholm in the Baltic Sea, the dependence of drag on the ocean of wave state parameters has been studied for near-neutral conditions. For developing sea, the drag depends on wave age, u*/cp (u* friction velocity and cp the phase speed of the dominant waves), in agreement with recent findings over the World Ocean, strongly supporting that the Ostergarnsholm station can be relied upon to give results representative of open ocean conditions. For such conditions, it is demonstrated that the logarithmic wind law is indeed valid. For mixed sea/swell the logarithmic wind law is not valid and the drag coefficient, CD depends on two parameters representing the wave state: u*/cp and E1/E2, where E1 is the energy of the relatively long waves (having a phase velocity larger than the wind speed at 10 m) and E2, the short wave energy. Thus, plotting CD as a function of u*/cp gives a clear ordering of the data in parallel, sloping bands according to the value of E1/E2. Thus, whereas very young and slow waves affect the atmospheric flow similar to rigid roughness elements, with the occurrence of longer waves, an entirely different mechanism gains successively more importance and dynamical coupling with the atmospheric turbulence occurs. It may be speculated that the often observed kink in the wind profile represents the upper bound of a wave-boundary-layer, which is thus an order of magnitude deeper than predicted and observed during growing sea conditions.

Multipeakedness and groupiness of shallow water waves along Indian coast

Abstract: Based on one year wave data collected at 4 locations along the Indian coast, the frequency of occurrence of double-peaked spectra was estimated. It was found that 40% of the data analysed was single-peaked. The double peaked wave spectra were analysed for sea and swell dominated cases and it was found that the observed spectra were mainly swell dominated. Double peaks were observed approximately at 1.7 to 2.4 times the frequency of the main peak. The wave spectrum can be satisfactorily represented by the Scott and Scott-Wiegel spectra with an average correlation coefficient of 0.8. Wave group statistics were estimated and it was found that the mean length of run considering all records for locations 1 to 4 were 1.36, 1.32, 1.28, 1.33 for H > He and 2.21, 2.1, 2.11, 2.16 for H > H mean which were slightly higher than the theoretical values.

On the diffusivity in coastline dynamics

Abstract: [1] The 1D diffusion equation for the dynamics of the coastline is revisited. It is found that the classical evaluation of the diffusivity coefficient over-predicts it by a factor ranging from 1.25 up to infinity since the diffusivity may become zero while the classical prediction is always positive. The over-prediction depends on wave steepness and wave incidence angle. It is larger for swell than for sea waves and it increases with increasing angle. For moderate angles it can easily be about a factor 10. Negative diffusivity occurs in case of large angles, consistent with the large angle morphodynamic instability.

Swell Transformation across the Continental Shelf. Part II: Validation of a Spectral Energy Balance Equation

Abstract: State-of-the-art parameterizations of the interactions of waves with a sandy bottom are evaluated using extensive field observations of swell evolution across the North Carolina continental shelf and hindcasts performed with the spectral wave prediction model CREST. The spectral energy balance equation, including bottom friction and wave–bottom scattering source terms, was integrated numerically for selected time periods with swell-dominated conditions. Incident wave spectra at the model boundary were estimated from buoy measurements near the shelf break, assuming weak spatial variations in the offshore wave field. The observed strong and variable decay of the significant wave height across the shelf is predicted accurately with an overall scatter index of 0.15. Predicted wave directional properties at the peak frequency also agree well with observations, with a 5° root-mean-square error on the mean direction at the peak frequency and a 0.22 scatter index for the directional spread. Slight modifi...

A seismic reflection profile study of lithospheric flexure in the vicinity of the Cape Verde Islands

Abstract: [1] Seismic reflection profile data are used to determine the stratigraphic “architecture” of the flexural moat that flanks the Cape Verde Islands. The moat region is characterized by upward of 1–2 km of poorly to well-stratified material. The two lowermost units thicken from west to east and are attributed to sediment loading and flexure at the nearby West Africa continental margin during Early Cretaceous to early Miocene. The two uppermost units, in contrast, thicken concentrically around the islands and are attributed to the infilling of a flexural moat that formed by volcanic loading since the early Miocene. Flexure modeling shows that the thickness of the moat infill cannot be explained only by surface loading and requires that the downward flexure due to surface loads is opposed by an upward acting subsurface load. The best fit combined surface and buried loading model is for an elastic thickness, Te, of 29 km, a load and infill density of 2700 kg m−3, and a ratio of surface to subsurface loads, f, of 0.2. These results are in accord with spectral studies of free-air gravity anomaly and topography data based on the admittance technique. The subsurface loads are spatially limited to the islands and their submarine flanks. Nevertheless, they are associated with a broad regional uplift of up to ∼400 m. The uplift is large enough to explain why the moat infill is generally tilted away from, rather than toward, the islands. The uplift is too small, however, to account for the height of the swell, upon which the Cape Verde Islands are superimposed. The origin of the Cape Verde swell is not known. However, a normal Te and a modest heat flow anomaly suggest that the swell cannot be fully explained by uplift due to thermal reheating of the lithosphere by an underlying “hot spot” and that other, deep-seated, mantle processes must be involved.

The Influence of Oceanic Swell on Flows Over an Estuarine Intertidal Mudflat in San Francisco Bay

Abstract: In this study, we examine the role that remotely forced ocean waves play in the hydrodynamics of an intertidal, estuarine mudflat. The observations indicate that long-period (10–20 s) ocean waves are a potentially important source of near-bed energy and shear stress in this environment. Over a two-week period in February 2001, we deployed an autonomous SonTek Hydra system on a mudflat in Central San Francisco Bay, and measured velocity and sediment concentration approximately 10 cm from the bed using an acoustic Doppler velocimeter (ADV) and an optical backscatter sensor (OBS). The experiment continued through wet (high tide) and dry (low tide) periods over an entire spring–neap cycle, and thus included the variation of near-bed velocity over a range of timescales. Results show that during large ebb tides, tidally forced flows dominate the near-bed dynamics during calm conditions. Wind waves dominate whenever the wind direction exposes the mudflat to wind coming off the bay (from the south and southwest), as occurs during winter storms. During periods when tidal forcing is limited and wind waves are small, remotely forced ocean swells become an important energy source. These motions appear in the burst samples at frequencies between 0.1 and 0.04 Hz and their energy correlates well ðq > 0:8Þ with ocean swell measured from a buoy offshore of San Francisco. Spectral analysis of data shows that the average energy of ocean waves per tide varied between 2 and 15% of total energy load. Moreover, extreme values in the distribution of ocean waves bring episodic bursts of greater energy onto the estuarine mudflat, which may influence local suspension of sediments. 2003 Elsevier Ltd. All rights reserved.

Bed drag coefficient variability under wind waves in a tidal estuary

Abstract: In this paper we report the results of a study of the variation of shear stress and the bottom drag coefficient CD with sea state and currents at a shallow site in San Francisco Bay. We compare shear stresses calculated from turbulent velocity measurements with the model of Styles and Glenn reported in 2000. Although this model was formulated to predict shear stress under ocean swell on the continental shelf, results from our experiments show that it accurately predicts these bottom stress under wind waves in an estuary. Higher up in the water column, the steady wind-driven boundary layer at the free surface overlaps with the steady bottom boundary layer. By calculating the wind stress at the surface and assuming a linear variation of shear between the bed and surface, however, the model can be extended to predict water column shear stresses that agree well with data. Despite the fidelity of the model, an examination of the observed stresses deduced using different wave-turbulence decomposition schemes suggests that wave-turbulence interactions are im- portant, enhancing turbulent shear stresses at wave frequencies.

Vertical structure in the marine atmospheric boundary layer and its implication for the inertial dissipation method

Abstract: The structure of the marine atmospheric boundarylayer and the validity ofMonin–Obukhov similarity theory over the seahave been investigated using longterm measurements. Three levels of turbulencemeasurements (at 10 m, 18 mand 26 m) at Ostergarnsholm in themiddle of the Baltic Sea have beenanalysed. The results show that turbulentparameters have a strong dependenceon the actual height due to wave influence.The wind profile and thus thenormalised wind gradient are very sensitiveto wave state. The lower part of theboundary layer can be divided into three heightlayers, a wave influenced layerclose to the surface, a transition layer andan undisturbed ‘ordinary’ surfacelayer; the depth of the layers is determinedby the wave state. This heightstructure can, however, not be found for thenormalised dissipation, which is onlya function of the stability, except duringpronounced swell where the actualheight also has to be accounted for. Theresults have implications for the heightvariation of the turbulent kinetic energy(TKE) budget. Thus, the imbalancebetween production and dissipation willalso vary with height according to thevariation of wave state. This, in turn,will of course have strong implicationsfor the inertial dissipation method, inwhich a parameterisation of the TKEbudget is used.

Improvement of Drift Calculation in Mothy Operational Oil Spill Prediction System

Abstract: MOTHY (Modele Oceanique de Transport d'Hydrocarbures) is a pollutant drift model, developed and operated by Meteo-France. MOTHY includes hydrodynamic coastal ocean modelling and real time atmospheric forcing from a global meteorological model. Pollutants can be oil or floating objects. To improve forecasts on the Mediterranean Sea, several methods were tested to inject large scale currents (permanent part) into the MOTHY system. The best results were obtained with monthly means of currents at 5 meters (from Mercator system). The addition of altimetric corrections improved the results. In addition the impact of wave (or swell) current, which is usually neglected in such models, is investigated. The literature has surprisingly little to say on the topic of wave-driven surface oil slicks. Earlier review on oil spill transport modelling includes wave driven transport among potential advection mechanisms. The discussion of wave-induced advection (mass transport) adopts a Lagrangian framework, focusing...

Head protecting body for safety helmet and safety helmet having head protecting body

Abstract: A head protecting body for a safety helmet, in which a first liner member for an impact-on-the-head absorbing liner includes a swell for reinforcing at least one region of a forehead region, a left temple region, a right temple region and an occiput region in an overlapping region with respect to a second liner member having a density lower than that of the first liner member, on an overlapping surface side of the first liner member, and the second liner member includes a hollow having a shape substantially corresponding to the swell. According to this head protecting body, despite that the impact-on-the-head absorbing liner is not broken easily more than necessary near a region reinforced with the reinforcing swell, both the maximum acceleration during impact and an HIC can be decreased effectively.

Surveying the upper Ocean with the Ocean Surveyor - a new Phased Array Doppler Current Profiler

Abstract: A new shipboard current profiler, a 75-kHz ocean surveyor, was operationally used during two research cruises in the tropical Atlantic and the subpolar North Atlantic, respectively. Here, a report is presented on the first experience with this instrument in two very different current regimes, in the Tropics with large vertical shears, and in the subpolar regime with mainly barotropic flow. The ocean surveyor continuously measured currents in the upper ocean from near the surface to about 500–700-m depth. The measurement range showed a dependence on the regional and temporal variations of scattering particles and on the intensity of swell and wind waves. Statistical comparisons are performed with on-station lowered acoustic Doppler current profiler (LADCP) profiles and underway measurements by classic shipboard acoustic Doppler current profiler (ADCP) measurements. Accuracy estimates for hourly averaged ocean surveyor currents result in errors of about 1 cm s–1 for on-station data and of 2–4 cm s–...

Constraining the inertial dissipation method using the vertical velocity variance : Fluxes, surfaces waves, remote sensing, and ocean circulation in the North Mediterranean Sea: results from the FETCH experiment

Abstract: [1] The inertial dissipation method (IDM) is commonly used to measure turbulent fluxes over the ocean. It has the advantage over more direct methods in that it depends on the turbulent fluctuations only in the high frequencies of the so-called inertial subrange. These frequencies are above those of typical ship motions and are considered to be relatively unaffected by flow distortion. However, a drawback in applying the method is that the problem is underdetermined: estimation of the fluxes requires knowledge of the Obukhov length L, which is itself a function of the fluxes. The problem is typically solved by iteration, using an initial L estimated from bulk formulae. This introduces a possible dependency on the initial bulk estimate along with problems of convergence. Recently, several authors have proposed improvements to the basic algorithm. For instance, Dupuis et al. [1997] proposed a parameterization of the imbalance term in the budget of turbulent kinetic energy (TKE). We explore an alternative approach to the problem. In order to constrain the equations resulting from the IDM we use the vertical velocity variance, σ w, measured from the research vessel L'Atalante and an ASIS buoy, both deployed during the 1998 FETCH experiment. These data are compared to several parameterizations of σ w on stability derived in experiments. For unstable cases, the data are found to be well described by the Panofsky and Dutton [1984] parameterization, although the scatter of the data is higher for swell conditions than for pure wind sea, indicating a likely sea state effect. Using measured values of σ w along with this parameterization, the inertial dissipation problem is fully specified. The convergence of the method is satisfactory, and it offers u * estimates independent of bulk formulae.

Constraining the inertial dissipation method using the vertical velocity variance

Abstract: [1] The inertial dissipation method (IDM) is commonly used to measure turbulent fluxes over the ocean. It has the advantage over more direct methods in that it depends on the turbulent fluctuations only in the high frequencies of the so-called inertial subrange. These frequencies are above those of typical ship motions and are considered to be relatively unaffected by flow distortion. However, a drawback in applying the method is that the problem is underdetermined: estimation of the fluxes requires knowledge of the Obukhov length L, which is itself a function of the fluxes. The problem is typically solved by iteration, using an initial L estimated from bulk formulae. This introduces a possible dependency on the initial bulk estimate along with problems of convergence. Recently, several authors have proposed improvements to the basic algorithm. For instance, Dupuis et al. [1997] proposed a parameterization of the “imbalance term” in the budget of turbulent kinetic energy (TKE). We explore an alternative approach to the problem. In order to constrain the equations resulting from the IDM we use the vertical velocity variance, σw, measured from the research vessel L'Atalante and an ASIS buoy, both deployed during the 1998 FETCH experiment. These data are compared to several parameterizations of σw on stability derived in experiments. For unstable cases, the data are found to be well described by the Panofsky and Dutton [1984] parameterization, although the scatter of the data is higher for swell conditions than for pure wind sea, indicating a likely sea state effect. Using measured values of σw along with this parameterization, the inertial dissipation problem is fully specified. The convergence of the method is satisfactory, and it offers u* estimates independent of bulk formulae.

Impact of waves on the sea drag: measurements in the Baltic sea and a model interpretation

Abstract: Measurements from the Baltic Sea and a wind-over-wave coupled model are used to study the wave impact on the sea drag. The study has been carried out for different wave conditions, namely a pure wind-sea, following-swell/ mixed sea and cross-swell/ mixed sea. Measurements reveal the fact that the sea drag is dependent on the sea-state. In stationary conditions and in the absence of severe cross-swell, swell reduces drag compared to wind-sea at the same wind speed. The cross-swell enhances the drag as compared to the following-swell case and the magnitude of the drag coefficient is increased with increasing the angle of swell propagation to the wind. It is shown that the agreement between the model results and measurements is good for pure wind-sea and stationary mixed-sea cases. Discrepancies occur at light winds, where most of the data represent pure swell conditions. During these pure swell conditions the data are characterized by a large variation of the drag coefficient. The variation is caused by mes...

Behavior of a Moored LNG Ship in Swell Waves

Abstract: In the design of oil and gas terminals, six degrees of freedom (SDF) models are often used to calculate the motions of the moored ship and forces in mooring lines and fenders. Although the SDF simulation programs have been used for more than 20 years, there is still little verification of the results with prototype measurements. This paper includes the results of a verification of one of these SDF models using prototype measurements as reference data. The prototype measurements consisted of mooring line loads of liquefied natural gas (LNG) carriers at berth for periods during which environmental conditions were recorded. A study was carried out to simulate these conditions in the model and to compare the model results with the measurements. In addition to mooring line loads, the computed vessel motions have been analyzed. For the studied berth situation, the yaw motion resulting from swell waves is quite dominant and is causing large breast line forces. An empirical expression has been derived to calculate the yaw motions of the moored LNG carrier in swell waves. This expression is a first step in defining a general expression to estimate maximum yaw motions and mooring forces to be used in preliminary harbor design.

An optical technique for determination of layer thickness swell of MDF and OSB

Abstract: A nondestructive optical technique was developed to determine thickness swell of discrete layers within intact samples of wood composites. Layer thickness swell of commercial medium density fiberboard (MDF) and oriented strandboard (OSB) are presented. Layer swell within the sample is important in understanding the swell phenomena of wood composites. Results from standard speci- mens show edge layer thickness swell after 2-, 8-, and 24-hour water soak and include measures of precision and variation for this tech- nique. The relative difference for overall thickness swelling compared between the optical technique and the traditional method de- creased as water exposure time increased and was less than 3.44 percent after 24-hour water exposure. The contributions of high-density surface layers to overall MDF thickness swell were 95.76, 75.50, and 61.77 percent after 2-, 8-, and 24-hour water expo- sure, respectively. The contributions of high density surface layers to overall OSB thickness swell were 74.36, 64.39, and 57.30 per- cent after 2-, 8-, and 24-hour water exposure, respectively. Thickness swell for both products was dominated by the high density sur- face layers throughout the 24-hour soak cycle. However, dense surface layers contributed more to the overall swell measurement during the early period of the soak cycle compared to the swell measurement at the completion of the 24-hour soak cycle. The relative contribution of the core layers to overall thickness swell increased with length of exposure period. This optical technique is recom- mended for the measurement and study of in-situ layer swell properties for all wood composite panel materials.

Analysis of surface wind and roughness length evolution with fetch using a combination of airborne lidar and radar measurements

Abstract: [1] A combination of surface wind speed (SWS) and sea state variables, derived from quasi-simultaneous airborne lidar and radar measurements, made in the framework of the Flux, Etat de mer et Teledetection en Condition de fetcH variable (FETCH) experiment, is used to analyze the evolution of surface roughness length, neutral drag coefficient, and friction velocity coefficient with fetch in the first hundred kilometers offshore over the Gulf of Lion, Western Mediterranean. The study focuses on the Tramontane/Mistral event documented in the afternoon of 24 March 1998. Particular attention is given to SWS derived from nadir lidar measurements. The SWS retrieval methodology developed and validated for open ocean conditions by Flamant et al. [1998] has been modified to account for the specificity of the coastal Mediterranean environment (complex mixture of continental and maritime aerosol; turbid, productive waters). The lidar-derived SWS evolution with fetch observed on 24 March 1998 in the afternoon was validated against in situ and remote sensing measurements made from a buoy, a ship, as well as from the spaceborne altimeter TOPEX. The spatial variability in SWS observed with the airborne lidar was controlled by the structure of the wake regions downstream of the Massif Central and the Maritime Alps, delimiting the longitudinal extension of the Mistral, and was influenced by swell resulting from the action of a steady northeasterly flow coming from the Ligurian Sea in connection with intense Alpine lee cyclogenesis. These findings were supported by the other measurements. It is further shown that, based on a formulation of the dimensionless roughness dependance with wave age, airborne lidar and radar measurements can be combined to provide insight into the evolution with fetch of roughness length, neutral drag coefficient, and friction velocity. Four distinct sea state regimes over a distance of 100 km could be identified from the remotely sensed variables obtained with this novel approach in connection with atmospheric forcing. The dependance of lidar/radar derived drag coefficient with lidar-derived SWS for the four regimes was found to be remarkably consistent with the relationship derived from the buoy measurements. Finally, lidar/radar derived friction velocities were found in good agreement with the buoy and in situ aircraft measurements.

Leakage and Swell in Emulsion Liquid-Membrane Systems: Batch Experiments

Abstract: Emulsion liquid-membrane systems can provide effective systems for removal of impurities in a variety of applications. In these systems, removal efficiency and the ability to concentrate impurities can be impaired because of encapsulated-phase leakage and emulsion swell. This work describes the results of a factorial experimental procedure that measured the effects of several formulation and operating variables on emulsion liquid-membrane leakage and swell. The experimental variables studied were surfactant concentration, osmotic pressure, membrane type, internal-phase volume fraction, and extraction-vessel stir rate. Encapsulated-phase leakage is influenced by all of the variables in a complex fashion. Emulsion swell results are consistent with a simple water-transport mechanism.

Modeling Time Dependent Swell of Clays Using Sequential Artificial Neural Networks

Abstract: This work attempts to implement sequential artificial neural networks (SANN) for modeling time dependent swell of expansive soils. Forty soils with varying properties were selected and tested for expansion under three different initial applied pressures (25, 100, and 200 kPa) to develop the database used for training and testing the neural network. Consequently, a total of 120 swell tests were performed to produce over 1800 data points. The input parameters used in the network included the soil initial dry unit weight and water content, initial applied pressure, percent clay content, plasticity index and the percent swell at time i. The network was programmed to process this information and produce the percent swell at time i + 1. The study demonstrates that there is a possibility to develop a general SANN model that can predict time dependent swell, based on basic soil properties, with relatively high accuracy (correlation r2 = 0.975 between predicted and observed data).