The wave-induced forces on a submarine pipeline near the ocean floor consist of several components, inertial forces, drag forces, lift forces, and under some conditions, eddy-induced forces. The measurements of forces on horizontal cylinders near the bottom and loaded by regular and stochastic waves show very complex functions. For the analysis of the results it is desirable to decompose the measurements into components with dominant frequencies corresponding to the peak frequencies in the spectral density. For the linear case the KALMAN filter is a suitable tool of data analysis when appropriate models are chosen. In the present case this method has been used to decompose the measurements of the water surface elevation, the horizontal and the vertical force component, therefore a new mathematical model and a new observation model are introduced.

1 Introduction

The behavior of submerged horizontal pipeline elements placed on or very closed to the sea bed cannot theoretically be described in a convincing manner. Especially the problems with respect to the flow field in the proximity of pipelines have not exactly been solved in the past. Thus the acting forces are functions of many different parameters which creates a number of complex phenomena. To get an insight into the hydrodynamic effects of pipeline loads, this paper is to understand as a first step to analytical treatment of large-scale experiments. A new mathematical model and a new observations model are therefore introduced. These models are discussed and applied in the present case to the analysis of the measurements of waves and loads of a horizontal cylinder. In the present paper the discussion of the influence of inertia forces and damping forces in the dynamical equation is given. The starting point are mathematical models in continuum which correspond to the Ito stochastic differential equations.

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