No 1/1996

        The paper presents a numerical method for analysis of flow inside waterjets. The method is based on modelling the waterjet intake, channel and outlet by a discrete distribution of sources and modelling the impeller, guide vanes and other lifting elements by a lifting surface comprising discrete distribution of vortices and sources/sinks. The method is intended to predict flow streamlines and velocity distribution, pressure distribution, hydrodynamic forces and presence of cavitation on elements of a waterjet of a given geometry and prescribed operational parameters. Numerical results are compared with the data acquired during a specially arranged series of experiments with a waterjet model installed on top of a cavitation tunnel.
(POLISH MARITIME RESEARCH, No 1/1996)

        The paper discusses problems related to design of highly skewed propellers. These propellers require application of special methods both in hydrodynamics and in strength analysis. Their blades are influenced by the phenomenon known as hydroelasticity. Namely, the geometry of the blades may change considerably under loading, leading to meaningful changes in hydrodynamic characteristics. This phenomenon should be taken into account in the design procedures of highly skewed propellers.
(POLISH MARITIME RESEARCH, No 1/1996)

        The paper presents shortly characteristics of a hyperbaric environment, which saturated divers stay in, and of thermal-flow phenomena occuring in it. Such an environment is distinctly different from the earth atmosphere. Thermophysical properties of compressed breathing mixtures can disturb, apart from their physiological impact on the human organism, its regular functioning, as well as facilities and systems which have to assure divers' comfort and safety. The theoretical and experimental research works, performed by the Chair of Thermal Engineering, Technical University in Szczecin and reviewed in this paper, make it possible to highlight some poorly recognized thermodynamic processes which occur in compressed breathing atmospheres. Application of the results can be helpful in carring out further research and designing new saturated diving systems.
(POLISH MARITIME RESEARCH, No 1/1996)

        A mathematical description of the energy conversion and transmission occuring in the marine electric generating set, comprised of gas turbine engine, synchronous generator and its control systems, is presented. The set structure is decomposed and its variables systematized. Power processes in the set are considered as macro-dynamic phenomena and engine-to-consumer energy flow is assumed continuous. A model structure is made suitable for its verification on the basis of measurements during full scale experiments. A purpose and applicability of the model is highlighted.
(POLISH MARITIME RESEARCH, No 1/1996)

        This paper presents a method of reducing electric energy consumption in ships which consists in application of the variable frequency in ship's electric installation, dependent on main engine loading.
(POLISH MARITIME RESEARCH, No 1/1996)

        The paper describes a method for calculation of the variable forces acting on the screw propeller. A general approach to the problem and a mathematical model are presented. The method is based on the unsteady lifting surface method. To obtain the results the potential flow theory is used. The geometry of the screw propeller and the velocity field before it can be arbitrary. In the calculations the change of the wake vortex sheet geometry is taken into account. The method can be used to calculate the thrust force in the condition of ship's motion in waves.
(POLISH MARITIME RESEARCH, No 2/1996)

        During positioning of a floating craft by means of a mooring system different kinds of displacement of the vessel are generated due to the sea exciting forces: quasistatic displacement, first order motions (of high frequency) and second order motions (of low frequency). The corresponding loads in the lines of the anchor mooring system of the vessel are generated following the displacement of the vessel. The motion equations of the ship equipped with the anchor mooring system are presented in the paper. Their solution is presented with regard to non-linear terms of the equations and the random exciting forces, in the form of numeric simulation in the time domain. The sample calculations were performed for a geological vessel fitted with the 4-line positioning system.
(POLISH MARITIME RESEARCH, No 2/1996)

        An advanced computational method was applied to calculate forces and moments developed on marine rudder located in propeller slipstream. The common vortex lattice model was applied for screw propeller to determine velocity distribution in propeller slipstream. Surface vorticity distribution was used to calculate pressure distribution on rudder surface. A series of calculations was performed to validate the method and the prepared computer program. Obtained results, compared with the available experimental data, confirmed the reliability of the presented method.
(POLISH MARITIME RESEARCH, No 2/1996)

        Dynamic characteristics of a modernized low pressure casing of the 13K215 turbine and a foundation frame of the large gabarite stand for testing multi-span rotor systems as well as the bending stiffness of a flexible coupling which connects rotors of the 13K215 turbine set were investigated with the use of mode analysis approach. The ABAQUS FEM analysis computer software system was used. The presented examples of the mode analysis application refer to the real objects. In all the cases interesting information was gathered and utilized to modify dynamic characteristics of the investigated structures. It speaks for practical applicability of the analysis method particularly while connected with FEM application.
(POLISH MARITIME RESEARCH, No 2/1996)

        Different importance measures applicable to ship power plant system components are presented. Birnbaum's and Lambert's importance measures were applied to choose the most important components of one of the power plant systems onboard the KOPALNIA KLEOFAS.
(POLISH MARITIME RESEARCH, No 2/1996)

        The paper contains results of pilot calculations of the plates exposed to pressure or wheel loading, which are compared with the data found in literature sources. The permanent set of the typical deck plates, generated during the entire loading cycle, was also calculated. The investigation was aimed at the determination of a practically useful relationship between concentrated load and permanent set of plate. This is a partial result of the research carried out by the CTO, Gdańsk, on request of the Polish Register of Shipping (PRS).
(POLISH MARITIME RESEARCH, No 3/1996)

        The paper contains the analysis and conclusions arising from practical application of the BOS-L computer system to the ship flow investigation. A short description of the computer system and example of calculation are included. The results from the basis for the analysis of possible applications of the BOS-L system as a tool for ship hull design. The conclusions of the paper arise from the comparison of the experimental data and calculation results.
(POLISH MARITIME RESEARCH, No 3/1996)

        A method of safety analysis of submersible's hoisting cables is sketched in the paper. The problems of description of loads applied to the cables and their influence on system's service reliability is also discussed.
(POLISH MARITIME RESEARCH, No 3/1996)

        The paper deals with the fatigue life prediction of beams under variable periodic stress due to combined bending moment, torsional moment and axial force. It is assumed that the envisaged service life can be considered as a set of states and that the stress components in each state are given in the form of Fourier series. The equivalent state of stress with in-phase constant-amplitude components are determined on the basis of Cempel's theory of energy transforming systems. It enables to estimate the time to fatigue failure without application of any cycle counting method and hypothesis of fatigue damage cumulation.
(POLISH MARITIME RESEARCH, No 3/1996)

        A computerized calculation method of the axial vibrations of a ship power transmission system is presented. The vibrations may cause increasing failure frequency of the engine crankshaft and be a source of dangerous ship hull and superstructure forced vibrations. The shaftline axial vibrations are coupled with the torsional-bending vibrations through the engine cranshaft and are forced by the propeller induced hydrodynamic forces (if torsional - axial coupling is taken into account). Several computer algorithms for analyzing the problem have been elaborated by the author. Nonlinear algorithms for determining the dynamic characteristics of thrust bearing, engine main bearing and axial detuner are also presented. A crankshaft deformation analysis was carried out to determine coupling coefficients of the torsional, bending and axial vibrations. Sample calculations of ship axial vibrations were performed and compared with experimental results. (POLISH MARITIME RESEARCH , No 3/1996)

        Ship speed and fuel consumption calculations were performed based on foreign ship operation investigations and on the use of two ship speed distribution optimization methods. One of them was elaborated by Technical University in Berlin by means of the calculus of variations, the other by Maritime Institute in Gdańsk using the differential calculus. A comparison of the calculation results indicated that both methods are equivalent and revealed differences less than 0.2%; moreover the latter method is far simpler. Fuel consumption savings which can be achieved in relation to a ship operated in the traditional way were also confirmed.
(POLISH MARITIME RESEARCH, No 3/1996)

        Simple formulae for calculating stress ranges in longitudinal ship hull members, exceeded with an assumed probability, are proposed. The stress ranges can be applied to fatigue life assessment. The assessment is based on approximation of long term stress range distribution by the Weibull's distribution and S-N curves application. The total stress range is calculated in the form of sum of global and local components, multiplied by partial stress range coefficients. The global stresses are caused by general bending in vertical and horizontal planes. The local stresses result from bending of stiffeners or plating. Approximate values of the partial stress coefficients were found on the basis of long term stress distribution direct calculations, performed for 6 ships. Approximate values of dynamic stress cycle numbers that occur during ship lifetime and coefficients defining the Weibull's distributions were also found.
(POLISH MARITIME RESEARCH, No 4/1996)

        In the paper a method is presented of bifurcation load determination by analyzing imperfect structural systems with no limit points. Results of the calculations carried out by applying the method to square plates with different boundary conditions at midsurface edges and different initial deflection values are presented and discussed.
(POLISH MARITIME RESEARCH, No 4/1996)

        Laboratory investigations of the influence of bearing sleeve transverse stiffness on operation effectiveness of the sliding radial seals applicable to ship CP (controllable pitch) propellers, are presented. The tests were carried out on the full-scale seal which cooperated at first with the typical, i.e. thick-walled, bearing sleeve and then the thin-walled one. Their results confirmed that development of a new generation of such seals, but lighter and more effective, is possible.
(POLISH MARITIME RESEARCH, No 4/1996)

        The paper contains identification results of linear, nonlinear and neural models of ship dynamics. Simple SISO and MIMO models were evaluated in their traditional and neural versions. The identification algorithms were effected off-line. The MATLAB numerical software was employed to execute the identification computations. Results of the research completed by using the VLCC tanker model are presented.
(POLISH MARITIME RESEARCH, No 4/1996)

        The determination of mutual relations between ship, water region, hydrometeorological conditions and position finding system depends on kinds of waterway and manoeuvre being made, for which different methods of defining safe manoeuvring water region are used. The paper presents some methods of defining a safe manoeuvring water region, applied in navigation practice and designing waterways. Some contemporary simulation and optimization methods are also discussed which make it possible to define safe manoeuvring water region for ships in terms of shipping safety criteria. Such elements of waterways as the fairway, port entrance, anchorage, turning area and port basin are considered.
(POLISH MARITIME RESEARCH, No 4/1996)

        Ship safe sailing consists in continuous observation of the situation at sea, determination the anticollision manoeuvre, if necessary, the realization of it and safe voyage to a point of destination. So it is necessary to determine ship safe trajectory as a sequence of ship course changing manoeuvres. Each manoeuvre is undertaken on the basis of information obtained from the anticollision system. In this paper safe ship control in a collision situation is presented with taking into account passing many moving objects, considered as multistage decision-making process in a fuzzy environment. A branch-and-bound method is used to determine optimum safe trajectory of the ship according to the International Rules of the Road at Sea.
(POLISH MARITIME RESEARCH, No 4/1996)