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EN
In the classic water hammer (WH) theory, 1D liquid flow in a quasi-rigid pipe is assumed. When the pipe is flexible or is fixed to the foundation with elastic supports, the dynamic fluid structure interaction (FSI) should be taken into account for more accurate modelling of the system behaviour. The standard model of WH-FSI for a straight pipe reach is governed by fourteen hyperbolic partial differential equations of the first order, two for 1D liquid flow and twelve for 3D motion of the pipe. This model is presented in the paper and an algorithm for its numerical solution based of the method of characteristics is proposed. Basic boundary conditions (BC) are shortly discussed. The important condition at the junction of two subpipes fixed to the foundation with a viscoelastic support is presented in details and a general method of its solution is proposed.
EN
Transient flows in closed conduits are of interest from over a century, but the dynamic interaction between the fluid and the pipe is taken into consideration more thoroughly just from a few decades. A standard model of the phenomenon consists of fourteen first order partial differential equations (PDE), two for a one-dimensional (1D) liquid flow and twelve for 3D pipe motion. In many practical cases however, a simpler four equations (4E) model can be used, where 1D longitudinal pipe movement is assumed. A short description of waterhammer event with fluidstructure interaction taken into account is presented in the article. The 4E mathematical model is presented in detail with the assumptions and main algorithms of computer program that has been developed. Two phase flow is assumed not to take place, but the friction between the liquid and the pipe wall are taken into consideration. A method of characteristics (MOC) with time marching procedure is employed for finding the solutions, but instead of direct solving the resulting finite difference equations (FDE) the “wave method” is proposed. Some other important elements of the algorithm are presented and selected results of numerical computations as well.
EN
Precise source localization in passive sonar with linear, horizontal passive array and matched beam processing algorithms requires, among others, accurate determination of the fixed array position and orientation. Geographical coordinates of the array can be evaluated quite simple with precise GPS receiver. Especially important problem is then the accurate determination of the array orientation. It is not a trivial problem and simple compass measurements may produce precision troubles. At the paper a method that compares the known trajectory of a moving acoustic source and its bearings computed with the array system software is developed. The method is based on minimizing the function of square error between the true and candidate-estimated target positions. Another interesting feature of proposed algorithm is the possibility of optimizing the error function with respect to parameters that model in an assumed way signal prapagation characteristics.
EN
The main problem addressed in the paper is an idea of modification and generalization of Root-MUSIC method. The algorithm is commonly used for uniform linear arrays. A concept how to generalize this method for non-uniform arrays is presented. An additional parametric test is also proposed for the selection of signal roots. Selected results of shallow water acoustic targets location (in bearing), with passive, linear array of hydrophones is also presented. The data used were acquired with an array situated in littoral waters, made and tested at Marine Technology Centre. A short background of array processing methods, especially subspace-based algorithms is included as well. Some important practical problems are also shortly discussed.
EN
The review of parametric methods of multiple underwater sources direction of arrival (DOA) estimation by a passive array of sensors is presented in this paper. The most common in literature model of far, narrow-band sources is assumed. Deterministic and stochastic maximum likelihood methods and their advantages and disadvantages are described. The subspace fitting approach is presented as well. A good performance of parametric methods is payed with high computational cost of searching the optimal parameters set. The reparameterisation method, lowering the computational cost of optimisation, is described in the last section of this paper.
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