Distribution of nonlinear wave crests

The distribution of nonlinear wave crests is examined on the basis of a theoretical probability density previously given elsewhere (J. Eng. Mech. 120 (1994) 1009). Certain errors contained in the original theoretical density are corrected, and the corresponding exceedance distribution is derived. The resulting theoretical forms of the probability density and exceedance distribution are then slightly simplified and compared with nonlinear wave data gathered under hurricane conditions. The results indicate that the proposed theoretical forms describe the observed distributions of large wave crests better than the Rayleigh law. However, the quantitative accuracy of the predictions is somewhat poor, as is typical of approximate theories based on Gram–Charlier-type expansions.     

On the calculation of extreme wave heights: A review

Over the past two decades there has been a great deal of interest in calculating design waves for offshore structures. This paper reviews the data limitations, statistical assumptions, distributions, fitting methods, and statistical tests used to determine confidence intervals and goodness of fit. Use is made of an illustrative example from the Grand Banks of Canada to indicate how a design wave could be calculated. It is concluded that no single method will be entirely suitable for all data sets.     

Unevenly compressed flexural-gravitity waves

Free flexural-gravity waves unevenly compressed in an ice-covered basin have been studied using a linear formulation. The conditions were specified allowing determination of the bounds of the angular area of wave disturbances and of the oscillation frequency intervals due to compression. The paper considers the distribution of the wave characteristics over frequency depending on compressive stresses and the direction of wave propagation.Translated by Vladimir A. Puchkin.     

A NEW MODEL FOR PEBBLE BEACH TRACER DISPERSAL

A series of eight tracer experiments were carried out over one year (1983) on a low energy, macro-tidal beach in South Wales, UK. Tracer movement was monitored and 30 pebbles adjacent to coloured tracer pebbles were measured. Measurements were of the A, B, and C axes, roundness, Maximum Projection Sphericity and Oblate-Prolate indices. Analysis shows that through time, the percentage rejection of these properties increased. It is theorised that the surface tracers are 'misfits' or 'rejects' which have not found their equilibrium position in the pebble facies.     

Variability of the O2−H2S zone structure in the Black Sea: ‘Dramatic’ or mesoscale?

This paper discusses the conclusion derived during a joint U.S—Turkey expedition on the R/VKrorr on the dramatic variations of the O₂–H₂S zone in the Black Sea observed over the last 20 years. This conclusion is shown to be invalid since it was based on a comparison of data obtained at two stations only (in 1969 and 1988) that was made in various regions and in different seasons. Examples are provided for the inter-seasonal and mesoscale variations of hydrophysical and hydrochemical characteristics in the O₂–H₂S zone which, as to their scales, are comparable to or even exceed the variations registered during the expedition ofKrorr.Translated by Mikhail M. Trufanov.     

Contaminant concentrations and toxicity of sea-surface microlayer near Los Angeles, California

Sea-surface microlayer samples were collected from six nearshore areas receiving different amounts of anthropogenic inputs. The samples were analyzed for selected trace metals, chlorinated hydrocarbons, and polycyclic aromatic hydrocarbons. The relative toxicities of the samples were determined with fish embryo bioassays.Contaminant concentrations generally increased from offshore to the inshore stations. Contaminant concentrations were several orders of magnitude higher in microlayer samples from the highly industrialized Los Angeles and Long Beach harbors compared to samples from a site 15km offshore. Microlayer samples from the inshore stations were significantly more toxic, and induced significantly more developmental abnormalities and chromosome aberrations, than samples from the offshore stations.     

The effect of copper pollution on mitochondrial degeneration

The authors describe the effect of copper pollution on the mitochondria from various areas of the Torpedo marmorata central nervous system. A high percentage of swollen mitochondria has been observed in neurons from animals experimentally exposed to high level of copper (4 ppm). The correlation with age pigment granules is discussed.