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Wave Conditions (wave + condition)

Distribution by Scientific Domains

Earth and Environmental Science	50%

Selected Abstracts

Dynamics of multiple intertidal bars over semi-diurnal and lunar tidal cycles, North Lincolnshire, England

EARTH SURFACE PROCESSES AND LANDFORMS, Issue 10 2008
Selma van Houwelingen
Abstract Multiple intertidal bars are common features of wave-dominated sandy beaches, yet their short-term (<1 month) and small-scale (<1 km) morphology and dynamics remain poorly understood. This study describes the morphodynamics of multiple intertidal bars in North Lincolnshire, England, during single and lunar tidal cycles under two contrasting conditions , first when significant wave height was <0·5 m and second when significant wave height frequently exceeded 1 m. The relative importance of swash, surf and shoaling processes in determining morphological change was examined using detailed field observations and a numerical model. The beach featured four intertidal bars and both cross-shore and longshore bar morphology evolved during the field investigation, particularly under medium to high wave-energy conditions. Numerical modelling suggests shoaling processes are most common on the seaward two bars under calm wave conditions (Hs < 0·5 m) and that surf zone processes become more common during neap tides and under more energetic (Hs < 0·5 m) conditions. Surf processes dominate the inner two bars, though swash influence increases in a landward direction. The numerical modelling results combined with low tide survey data and high-resolution morphological measurements strongly suggest changes in the intertidal bar morphology are accomplished by surf zone processes rather than by shoaling wave or swash processes. This is because shoaling waves do not induce significant sediment transport to have any morphological effect, whereas swash action generally does not have enough scope to act as the swash zone is much narrower than the surf zone. It was found, however, that the absolute rate of morphological change under swash action and surfzone processes are of similar magnitudes and that swash action may induce a significant amount of local morphological change when the high tide mark is located on the upper bar, making this process important for bar morphodynamics. Copyright © 2007 John Wiley & Sons, Ltd. [source]

Wave and sediment dynamics along a shallow subtidal sandy beach inhabited by modern stromatolites

GEOBIOLOGY, Issue 1 2008
J. E. ECKMAN
ABSTRACT To help define the habitat of modern marine stromatolites, wave-dominated flow and sediment transport were studied in the shallow subtidal region (1,2 m depth) along the slightly concave, windward face of Highborne Cay, Exuma, Bahamas , the only face of the cay that includes a population of stromatolites concentrated near the region of highest curvature of the beach. Wave energy impacting this island's most exposed beach was driven by local wind forcing which increases largely in response to the passage of atmospheric disturbances that typically affect the region for periods of a few days. Although some wave energy is almost always noted (maximum horizontal orbital speeds at the bottom are rarely <10 cm s,1), wave conditions remain comparatively calm until local winds increase above speeds of ,3,4 m s,1 at which point maximum wave speeds rapidly increase to 50,80 cm s,1. Stromatolites, which are largely restricted to the shoreward side of a shallow platform reef, are sheltered by the reef beyond which wave speeds are one to four times higher (depending on tidal stage). Moreover, stromatolite populations are predominantly found along a region of this wave-exposed beach that experiences comparatively reduced wave energy because of the curved morphology of the island's face. Maximum wave speeds are 1.4 to 2 times higher along more northern sections of the beach just beyond the locus of stromatolite populations. A quantitative model of sediment transport was developed that accurately predicted accumulation of suspended sediment in sediment traps deployed in the shallow subtidal zone along this beach. This model, coupled with in situ wave records, indicates that gross rates of suspended sediment deposition should be two to three times higher northward of the main stromatolite populations. Regions of the beach containing stromatolites nevertheless should experience significant rates of gross suspended sediment deposition averaging 7,10 g cm,2 day,1 (,4,6 cm day,1). Results suggest that one axis of the habitat of modern marine stromatolites may be defined by a comparatively narrow range of flow energy and sediment transport conditions. [source]

Experimental and modeling study of the autoignition of cyclopentene

INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 1 2008
M. Yahyaoui
Ignition delay times of cyclopentene,oxygen,argon mixtures were measured behind reflected shock waves. Mixtures contained 0.5% or 1% of hydrocarbons for equivalence ratios ranging from 0.5 to 1.5. Reflected shock wave conditions were as follows: temperatures from 1300 to 1700 K and pressures from 7 to 9 atm. When compared with the previous results obtained under similar conditions, it can be observed that the reactivity of cyclopentene is much lower than that of cyclohexene, but very close to that of cyclopentane. A kinetic mechanism recently proposed for the combustion of cyclopentene in a flame has been used to model these results, and a satisfactory agreement is obtained. The main reaction pathways have been derived from the flow rate, simulated temporal profiles of products, and sensitivity analyses. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 40: 25,33, 2008 [source]

Statistical investigation of the nonlinear dynamical behavior of offshore structures

PROCEEDINGS IN APPLIED MATHEMATICS & MECHANICS, Issue 1 2008
Jürgen Reimers
The increasing amount of reports concerning damages of ships, structures and loss of cargo due to wave structure interaction demand the development of systems to predict critical situations in the offshore environment. Within the last years, research has been done to predict encounter with critical wave or wave groups such as "rogue waves" or the so,called "three sisters". The aim of such research is to develop programs that predict dangerous incidents and possibly alert the crew in time. The dangers of such extreme wave situations are severe, but occurrence of them is rather rare. Additionally and more often, structures are endangered because of fluid,structure,interaction leading to critical dynamical system behaviour in a wave environment that shows no extreme wave heights. The severeness of these incidents then depends on the experience and correctness of decision concerning the evasive actions of the master and his crew. Taking nonlinear effects into account, the statistical investigation of structures in waves shows critical behaviour of ships and structures without the absolute necessity of heavy sea conditions or the occurrence of dangerous sea phenomena. This paper describes the development of a program that uses a Monte,Carlo,Simulation technique based on a common panel,method for the creation of added masses and added dampings to predict the behaviour of the structure in several wave conditions. It shows possible ways to prevent the occurrence using similar early warning systems to those in development for critical wavegroups. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]