In online structural health monitoring of the fixed offshore jacket platform, the determination of the time-dependent degradation of structures due to damages is the most important step in a maintenance strategy. This paper presents the application of the Hilbert Huang transform method based on the iEEMD (improved ensemble empirical mode decomposition) algorithm to identify the instantaneous natural frequency degradation due to damages of the fixed offshore structure under the random wave excitation. The iEEMD algorithm is proposed to restrain the mode mixing and used to adaptively process the big response data of the offshore structure during the wave loading with a wide frequency range. The vibration response measurement experiment for the offshore structure was conducted in a wave tank in this study. The identified fundamental natural frequencies by the iEEMD-based Hilbert Huang method were evaluated and compared with results of the numerical model of the eigenvalue analysis. The main result demonstrates that the instantaneous frequency degradation and nonlinear time-varying behavior due to the brace damage of the fixed offshore jacket platform can be successfully identified by the iEEMD-based Hilbert Huang transform technique under a wave load.damages, fixed offshore jacket platform, iEEMD-based Hilbert Huang transform, instantaneous natural frequency degradation, wave excitation | INTRODUCTIONThe fixed offshore jacket platforms are usually far away from the mainland and greatly affected by the marine environment. The structural degradation due to damages must to be detected, evaluated in time to ensure the safety of the structure during its service life. Therefore, in recent years, the vibration-based structural health monitoring has been interested in monitoring the damages that caused the frequency degradation to propose the suitable maintenance strategy or repair works in time. [1][2][3][4] The identification of dynamic characteristics including natural frequencies, damping ratios, and the mode shape based on the measured response vibration signals of the displacement and acceleration was

This article is about the calculation of flexible dam structures used for protection of populated areas from flooding, which is actual problem because of the climate changes and inadequate conditions of existing river dykes, which frequently do not satisfy ecological requirements in Russian Federation. Issue of shape calculation of water-filled membranes is considered, depending on internal pressures and external forces. Stability of water-filled membranes under hydrostatic pressure and uplift forces is analyzed. Explanations and requirements for creating new structures of flexible dams are given; they satisfy requirements for ecological infrastructure and provide reliability in terms of construction on biogenic soils and in crowded urban places. Designed structures are biopositive and can be erected without using massive equipment in emergency conditions

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The potential risk of oil spills is constantly increasing, which required special techniques, equipment and effective response plans as well. Oil booms is the most common equipment used for spilled oil clean-up. However, due to different reasons such as extreme hydrological conditions, unreasonable design or poor handling, the failure of booms can happen. The loss rate of boom is acceptable if it is small enough. In the present paper, the behavior of oil with different viscosity around the oil boom is numerically studied using ANSYS FLUENT software. The shape evolution of oil slicks is presented. The loss rates in given conditions are also determined.

Рассмотрены условия применения мобильных дамб из композитных материалов при инженерной защите населенных пунктов и предприятий от затопления. В ходе численного моделирования и экспериментальных исследований физической модели водонаполняемой дамбы определены величины ее относительных деформаций в зависимости от свойств материала оболочки, ее параметров, условий контакта оболочки с основанием и действующих внутренних и внешних нагрузок. Получены эмпирические зависимости, позволяющие определить необходимые параметры водоподпорной оболочки для обеспечения ее устойчивости и надежности функционирования. Ключевые слова: устойчивость дамбы, численная модель, мобильные дамбы, защита от затопления, композитные материалы.