The paper is devoted to the development of a methodical approach to risk assessment in the construction and subsequent operation of the offshore part of pipelines associated with the manifestation of natural and other factors. The research methodology includes analysis of data on the environment and climate of the regions of the construction of the offshore part of known pipelines, taking into account the technology of their construction and the influence of natural factors on the possibility of occurrence of trouble situations. The influence of unfavorable events on the construction process is described in terms of the average annual probability of hazardous phenomena and the delay in the process of pipe laying using the critical limitations of the operation of pipelaying vessels of various classes. Situations that lead to downtime construction with an inaccurate forecast of storm conditions are considered. Based on the developed approach, a calculation of the probabilities for estimating the factors during the laying of pipelines along the proposed routes in the Black Sea and possible losses of time from changes in weather conditions was performed.

]]>Verbal behavior of beluga whale Delphinapterus leucas acoustic ally stimulated by noise-like signal during demonstration of video images was studied. Video images were shown by an underwater monitor and acoustic stimuli were transmitted by a speaker in the frequency range up to 18 kHz. Characteristics of acoustic stimuli are presented. Demonstration of acoustic ally accompanied video images to the animal was shown to stimulate acoustic response of with a latent period of 0.5 to 1.2 seconds. Detailed acoustic response reaction of 16 s duration, consisting of 14 packages of high-frequency impulses is presented. Also presented are packages with a stable temporal structure: one package of the first type with a modulation coefficient of 0.175 ± 0.025; one package of second type with a modulation coefficient of 0.91 ± 0.03 and mixed packages consisting of two packages of the first type and other two of the first and second type packages. The conducted series of experiments clearly indicate that the acoustic reaction of the Dolphin can be interpreted as a verbal response to the video and acoustic impact.

]]>With application to the task of remote measurement of the Arctic Sea ice cover thickness from under water, the effect of vertical heterogeneity of acoustic properties of sea ice of various type and age categories caused by their layered structure on phase of reflection coefficient of acoustic low-frequency harmonic plane wave at its normal incidence on sea water-ice interface is investigated by a method of model experiment. Two acoustic models of the real sea ice cover are considered: one with constants, another with continuously changing with cover thickness acoustic parameters — elastic medium density, velocity and attenuation coefficient of longitudinal acoustic waves in the medium. Graphic curves of thickness of the sounded ice cover as function of reflection coefficient phase calculated for each of two considered acoustic models of arctic sea ice are presented. It is shown that in order to increase reliability of ice thickness data it is reasonable to use typified acoustic models of sea ice cover which parameters are adequate to its certain type, age category and period of annual cycle within limits of which the measurements are conducted.

]]>The flooding mechanism in the Kuban River Delta, caused by the rise of the level of the Sea of Azov due to atmospheric impact, was investigated with the use of the tightly-coupling numerical model ADCIRC+SWAN. The aforesaid model is implemented on an unstructured mesh with high spatial resolution, including the Kuban Delta, the Sea of Azov, and the Kerch Strait. As an atmospheric forcing, the following items were used – wind of different gradations of speed and direction, uniform in space; a single cyclone moving along a zonal trajectory through the center of the Azov Sea at different speeds. It is established that the flooding of the Kuban Delta has two characteristic features: the north-west wind is the most dangerous one for flooding the delta; the intensive delta flooding occurs only at a wind speed exceeding 20 m/s. The cyclone translation speed has a significant impact on the flooding area of the Kuban Delta. The slower cyclones cause more significant water level rise at the delta sea boundary, which leads to its more intensive flooding. At cyclone translation speeds of 7 m/s and less, more than a third of the delta area is flooded. It is shown that the floods in the Kuban Delta shall be caused by a stronger wind in comparison with the Don Delta.

]]>Zoning of the Baltic Sea was carried out according to the type of density stratification. Areas are marked out where the profile of the sea water density is well approximated by a two- or three-layer model. The values of the parameters of layered models, such as the depth of pycnoclines and the amplitude of the density jumps at the interfaces of the layers as a percentage of the total density change are determined. Such a zoning makes it possible to simplify the preliminary investigation of internal gravity waves in the considered region, effectively reducing it to the use of known analytical results for interfacial waves in layered fluid. It is also easy to carry out preliminary estimates of their kinematic and nonlinear characteristics. Variabilitу of these zones from winter to summer is discussed. Hydrological data for calculating the density field are taken from the database of the generalized numerical model of the environment (Generalized Digital Environmental Model Database, GDEM). In addition, calculated temperature and salinity data were used within the framework of the ocean model of the Rossby Center (RCO) for the Baltic Sea. For most points with close coordinates in RCO and GDEM, the type of density stratification is the same.

]]>To study the geostrophic flow instability with a linear vertical velocity shear in a vertically bounded layer the eigenvalue problem solution is considered. The vertical buoyancy diffusion effect on stable and unstable flow perturbations dynamics is taken into account in the model equation. The problem is reduced to a numerical solution of a non-self-adjoint third order differential equation with a small parameter at the highest derivative under the boundary conditions typical for the ocean. The solutions are sought as the power expansions at zero. The eigenvalues calculation leads to the search for the roots of a high-degree polynomial. The eigenvalue spectra are presented for various values of the problem dimensionless parameter. The results of the eigenvalues calculation are compared with the results obtained by an alternative method for solving an equivalent problem. It is noteworthy that the flow instability examined is an oscillatory instability, which is fundamentally different from the typical monotonous instability of fronts on the scales of the intrusion formation everywhere except for the equatorial zone. The results obtained are significant for analyzing the mechanisms of intrusive layers formation, which occur in the Arctic basin under conditions of absolutely stable stratification (decrease of the mean temperature with depth is accompanied by increase of the mean salinity).

]]>The effect of subinertial sea level atmospheric pressure fluctuations on the inflow intensity of the surface Atlantic waters through the Strait of Gibraltar and its impacts on the dynamics of the Alboran Sea is studied. The results confirm that the exchange flows in the Strait is affected by atmospheric processes of much larger spatial scale than the Strait of Gibraltar itself. The Ligurian Sea is the region where atmospheric pressure fluctuations correlate better with Atlantic inflow anomalies through the Strait of Gibraltar. Correlation between in situ measurements of the surface flow velocity in the Strait of Gibraltar and NCEP-CFSR reanalysis data of the atmospheric pressure for the whole Mediterranean basin shows that a decrease of atmospheric pressure in the Ligurian Sea leads to an intensification of the Atlantic water inflow, and conversely, an increase of atmospheric pressure to a decrease. The hypothesis about the remote effect of atmospheric pressure fluctuations in the Atlantic water inflow through the Strait of Gibraltar is confirmed by the results of a simulation based on a one-dimensional hydrodynamic model. The subinertial variability of the Atlantic inflow induced by atmospheric pressure fluctuations has an impact on the formation of the mesoscale dynamics of the Alboran Sea. This is confirmed by an analysis of the HF-radar surface current measurements in the Alboran Sea and satellite observations of chlorophyll-a concentration.

]]>Institute of Marine Geology and Geophysics FEB RAS performs regular registration of sea waves in the coastal zone of Sakhalin Island and Kuril Islands for the purpose of investigating infragravity (IG) waves and dangerous marine phenomena using autonomous bottom wave loggers (sea level fluctuations). The one-second discreteness is used in devices and allows recording not only IG waves, but else swell and wind waves without distortion. As a result of longterm observations of sea level, it was possible to detect the phenomenon of IG waves modulation by the tides on the shelf of Sakhalin Island. Analysis from field data and numerical models of marine surface gravity waves showed that in the coastal zone the energy was transferred from the low-frequency waves to higher-frequency motions in the result of nonlinear wave-wave interaction. This explains the tidal modulation of the energy of the short infragravity waves, that was observed in the records of the bottom pressure on the southern shelf of the Sakhalin Island. The obtained results confirm the possibility of using the Longuet-Higgins and Stewart models for determining the coefficients for increasing the amplitude and the period of the IG waves both in the surf zone and outside it. Similar changes in tidal beaches are common throughout the world and thus, tidal modulation of IG energy in the surf zone can be an effect of coastal processes and regional seismic activity in many coastal areas. The study of the processes considered here is important, since IG waves contribute to the formation of the shoreline.

]]>Results devoted to different aspects of oceanographic models for non-hydrostatic dynamics reported during two-three last decades are discussed in this review. Achievement in this field was obtained mainly due to the progress in computational hydrodynamics which marked a qualitatively new current level of World ocean dynamics and its regions modelling. Wide thematic of non-hydrostatic modelling includes consideration of the processes and phenomena with pronounced vertical movements. For their description, taking into account the dynamic component of pressure is desirable and in some cases essential. Statement of particular boundary value problems for non-hydrostatic dynamics equations subsystems, methods of their realization and, finally, evaluation and analysis of non-hydrostatic effects are the objectives of the present review. The basis of oceanographic non-hydrostatic models consists in formulation and methods of resolving of boundary problems for the Navier—Stokes equations of viscous incompressible fluid dynamics. A necessary consideration of such works is a section of this review. The presentation focuses at works which use the most common projections method of oceanographic models realization by different types of domain discretization: finite-difference grid, finite-volume, finiteelement and different forms of solution presentation: in boundary conformal coordinates, series, spectral decomposition etc. These approximations are tested and used for separate mesoscale processes and non-hydrostatic dynamics of subdomain of the region in the frame of a large-scale model. The structure of the projection method determines the splitting operator of the task and computation of the velocity fields approach at stages of time step. The hydrostatic problem solution can serve as such an approach. Such a suitable approach links hydrostatic approach with a non-hydrostatic module for the Navier—Stokes equations. That is emphasized in this review.

This review is brief. We tried not to overload it either with formulas, where it was possible, or bibliography because each cited reference in general contains its own wide bibliography. Its goal is presentation in a simple and general view of the status of matured non-hydrostatic modelling which elements will in the near future make it possible to resolve boundary problems of non-hydrostatic dynamics of wide regions and longest section of World ocean shelf on the basis of parallel computing.

]]>Dynamical loads are estimated on underwater vertical cylindrical parts of offshore platforms from the forcing of fully nonlinear internal wave motions generated by multicomponent barotropic tidal flow over topography along a vertical section for the conditions of the Sea of Okhotsk (Aniva Bay, near the south-eastern part of the Sakhalin Island shelf). The evolution of this process is analysed using numerical model of Euler equations for incompressible density-stratified fluid in a vertical plane. The intensity of pressure on lateral underwater surface and the rate inertia moment are expressed according to Morison’s formula for a cylindrical pile of 2.5 m diameter and 42 m height and computed as functions of time. They can reach values of 2.3∙10^{5} N and 4.8∙10^{6} N∙m, respectively, during the tidal cycle. The frequency of the appearance of large peak values in the internal wave velocity field and the probabilities of the corresponding high loads are also calculated.