International Journal of Coastal, Offshore and Environmental Engineering
Volume:8 Issue: 2, Spring 2023

The structural integrity of fixed platform may be affected from excessive load on structure and insufficient strength of the structure. Another factor which affects the structural integrity is seabed subsidence. Seabed subsidence occurs due to vertical movement of soil layers and soil consolidation. The impact of seabed subsidence will lead to decreased of air gap and cause wave hits the deck. The aim of the study is to determine the effect of wave load in deck by pushover and reliability analysis. The pushover analysis is performed first by considering 100-year environmental load to obtain RSR. The wave height at the collapse is calculated based on RSR. The wave load in deck calculation is according to American Petroleum Institute (API). The pushover with inclusion wave load in deck is necessary to be carried out to gain the updated RSR. The reliability analysis is computed by involving base shear at the collapse from pushover analysis with wave load in deck. Monte Carlo simulation technique method is adopted in the analysis which generating one million data of wave height and wave period as random variables. This study is also to perform the probability of failure and reliability index due to wave load in deck. As expected, the updated RSR with wave load in deck is lower than the RSR without wave load in deck. Then, the probability of failure increases with the increase of the depth of subsidence. Therefore, the reliability index decreases with the increase of the depth of subsidence.

One of the important parameters that should be considered in designation of weak clay and peats treatment systems is the influence zone wherever there are infrastructures or sensitive buildings in the vicinity of the treatment area. Since large vertical and horizontal displacements occur in these treatment systems, the soil around the project undergoes large strains that should be accounted for in project planning prior to finalization of the treatment system. The treatment systems for weak clays and peats are often a combination of prefabricated vertical drains plus vacuum and/or surcharge preloading. For investigation of the impact of preloading agents, and FEM simulation of two case histories were performed. One the project incorporates the combination of surcharge and vacuum preloading while the other one consisted of only vacuum preloading without surcharge embankment. Based on the verified models, different scenarios were introduced for comparison of impact of the vacuum and preloading agents on the magnitude of the influence zone. Regarding the impact of surcharge embankment, it was shown that reducing the height of surcharge can drastically reduce the influence zone in both numerical simulations. The application of vacuum preloading as the only preloading agent has decreased the influence zone drastically and for urban areas or places that sensitive infrastructures exist might be an ideal option for similar cases. Regarding the impact of magnitude of vacuum pressure on the influence zone it was shown that application of a stable high vacuum pressure can significantly reduce the diameter of the influence zone.

We can divide atmosphere into two mediums, barotropic and baroclinic. Due to horizontal gradient of density, baroclinic medium causes to produce various horizontal gradient of pressure with respect to height and implies various horizontal velocities at different layers of the atmosphere. Therefore; geostrophic wind varies with respect to height in this medium. The horizontal gradient of density not only would produce by horizontal gradient of temperature, but also by horizontal gradient of humidity or combination of both. If horizontal gradient of density would be by both horizontal gradient of temperature and horizontal gradient of humidity – as they are existing in natural air – in the case; vectorial difference of geostrophic wind with respect to height is; dense wind. If horizontal gradient of density is related to gradient of temperature solely; vectorial difference between geostrophic wind from top level and bottom level of the layer is; thermal wind. And if horizontal gradient of density is solely related to gradient of specific humidity; vectorial difference between geostrophic wind from top level and bottom level of the layer is; moist wind. The purpose of this paper is confirmation of three versions of dense wind, introduction five particular types of thermal wind and present two prominent types of moist wind in natural medium of air. Formulae related to each type are derived and every one of them, represents effects of one type of variation of geostrophic wind with respect to height.

The open waters of the north Indian Ocean (NIO), which itself includes the Persian Gulf (PG), the Gulf of Oman (GO), and the Arabian Sea (AS), are subject to different meteorological forcing that can affect surface fluxes of these environments. In this study, latent heat flux (QLH), sensible heat flux (QSH), and surface wind stress (τ) between these regions are investigated. The reanalysis data from the data sets of the National Centers for Environmental Prediction (NCEP) and the European Center for Medium-Range Weather Forecasts (ECMWF) for these three regions for 14 years (2013-2000) are used. The results are compared with the measured data in the GO that show ECMWF reanalysis data are more consistent with the measured data in this period. We compare the average monthly, seasonal and annual values of QLH, QSH and τ of the PG, GO, and AS. The annual averages of QLH for the PG, the GO, and the AS are -128.63, -118.76, and -118.03 (Wm-2) and the annual averages of QSH are -1.28, -3.88, and -5.67 (Wm-2) respectively. The annual averages of τ are 0.074, 0.075, 0.036 (Pa) for these areas respectively. Also the annual average SST is 27, 26.56, and 27.14 (⁰C) respectively for these areas. Based on the results, different regimes of the PG wind with dust storms, and the limited and semi-closed space of the PG with its shallow depth, leads to different behaviors of QLH and QSH in PG area, in comparison with the other two environments (namely GO and AS).

Coastal displacement due to hydrodynamic factors and changes in sea level has serious impacts on adjacent ecosystems, economic infrastructure, and human communities. Rapid fluctuations in the Caspian Sea level have created unstable conditions for coastal environments since the twentieth century. This study aims to evaluate the amount of shoreline displacement and Morphological changes in the shoreline at the location of the Gomishan wetland between 1995 and 2019 and its impact on this international wetland. To this end, by processing Landsat satellite images in the mentioned years using the Normalized Difference Water Index (NDWI), the water body was separated from non-water to extract the shoreline. The results show a significant displacement of the shoreline ranging from -136 to -1072 meters downstream of the Gorganrud River estuary in the southern region and a forward displacement of the shoreline inside the sea from 135 to 7781 meters, with most of the displacement occurring in the northern section. The studied area was classified into three groups based on the shoreline displacement (high, medium, and low). The results show that the northern part of the Gomishan wetland experienced the highest amount of shoreline displacement, and the amount of shoreline displacement gradually decreased in the central and southern regions. Additionally, the results show a significant relation with the period of decreasing the Caspian Sea level during the study period.

Estuaries are transition zones between the sea and land, and are constantly affected by tides. These areas are biologically important and sensitive. Tiab estuary, 7 km from away from the coast of Strait of Hormuz, is covered with mangroves and is also used for navigation by small commercial boats. This estuary is facing sedimentation issues nowadays which troubled navigation of vessels. Since the local wind conditions of the area is different seasonally, the influence of this difference on the transformation of the shoreline is considered for the years 2019 and 2020. The wind direction in the area is mainly SSW during summer, while is totally diverse during winter. Sentinel-2 satellite images have been used with similar water-level conditions. Normalized Difference Water Index and K-means algorithm are used for shoreline detection. The results show that the area of the estuary is more than 10 hectares smaller in summertime than in wintertime. The correlation coefficient of the seasonal transformation of the shoreline in 2019 and 2020 is 0.84, which shows that the seasonal transformation was similar in the two years. Shoreline transformation was at most along the curvatures of the river, whether in upstream or downstream. It was however varied between 45 and 200m. Some dissimilarity in shoreline transformation was detected between the two years of study, specifically in upstream of the river, which is suggested to be due to human activities. It is believed that those parts of the estuary with high transformation are subject to permanent transformation in long term.