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1
Content available Spectral response of stationary jack-up platforms loaded by sea waves and wind using perturbation method
Rozmarynowski Bogdan, Jesien Wojciech
Polish Maritime Research
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2021
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nr 4
53--62
EN
The paper addresses non-linear vibrations of offshore jack-up drilling platforms loaded by sea waves and wind in their stationary condition using the perturbation method. Non-linearity of dynamic equations of motion for fixed offshore platforms yields from two factors. The first is load excitation generating non-linear velocity coupling in a dynamic system. This coupling is inherent in the modified Morison equation, involving the excitation function in the form of the sum of the inertial and velocity forces of sea waves, taking into account relative wave–structure kinematics. Moreover, the wind acting on the exciting side causes similar effects. The second source is the subsoil‒structure interaction problem, modelled by a system of springs and dashpots that yields stochastic non-linearity of the dynamic system. The matrix equations of structural motion in FEM terms are set up. The perturbation method is adopted to determine the mechanical response of the system, making it possible to determine response spectra of the first and the second approximations for displacements and internal forces of the platform. The paper is the continuation of research detailed in the paper [1]. It is assumed, that the fluctuation parts of the dynamic loading forces are in line with the direction of sea wave propagation. Sea current and lift forces effects are neglected in this study. A numerical example refers to structural data of the Baltic drilling platform in the stationary configuration, i.e. when three legs support the deck above the seawater level.
2
Content available Spectral dynamic analysis of a stationary jack-up platform
Rozmarynowski Bogdan
Polish Maritime Research
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2019
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nr 1
40--48
EN
The paper refers to the dynamic short-term response analysis of the Baltic steel drilling platform (see Fig.2) in a random sea-state represented by one-dimensional wave spectrum proposed by Striekalov and Massel, which is recommended for the Baltic Sea area. The Baltic drilling platform is a jack-up type platform for the exploration and exploitation of oil under the Baltic Sea. The presented analysis deals with the stationary phase of the platform life when its legs are fixed in the sea bottom. The submerged elements of jack-up platforms are relatively slender, thus to assess the in-line wave forces a modified Morison equation is justified. The application of frequency transfer functions to offshore vibration systems leads to structural response spectra whose input is defined by the wave elevation and wind velocity spectra. The analysis can be applied also to support structures for offshore wind turbines.
3
Content available remote Stateczność samopodnoszących pełnomorskich platform wiertniczych w fazie eksploatacji
Rozmarynowski Bogdan
Inżynieria Morska i Geotechnika
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2019
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nr 3
130--136
PL
Współczynnik bezpieczeństwa platformy Petrobaltic na moment obrotowy (stateczność ogólna) oszacowany przy założeniu, że konstrukcja jest traktowana jako układ słupów połączonych sztywnym pokładem, z korekcją efektów drugiego rzędu. Przemieszczenie poziome pokładu platformy wyznaczone za pomocą odpowiedniego modelu MES. Siła krytyczna nogi obliczona przy założeniu jej utwierdzenia w dnie morza. Wpływ odchyłki od idealnej geometrii rur nogi oraz inklinacji nogi na wielkość imperfekcji geometrycznej nóg platformy. Stwierdzenie spełnienia odpowiedniej zależności normowej ze względu na stateczność przez obliczony współczynnik bezpieczeństwa.
EN
The safety factor of a Petrobaltic platform due to rolling moment (global stability) estimated assuming the structure modelled as a system of columns braced by a rigid deck with the second-order effects correction. The horizontal deck deflection computed using a relevant finite element model. The leg buckling load computed assuming its fixation in the seabed. The influence of an imperfection from the ideal geometry, and the leg inclination on the geometric imperfection of the platform legs. Statement of fulfilment of an appropriate standard condition due to stability by the computed safety factor.
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