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1
Content available Residual Ultimate Strength of Box Girders with Variable Cracks
Ao L., Wang D.
TransNav : International Journal on Marine Navigation and Safety of Sea Transportation
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2015
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Vol. 9, no. 2
193--198
EN
The aim of the present study is to investigate the residual ultimate strength characteristics of box girders with variable cracks under torsional loading. A series of finite element models are established by changing the crack length and crack angle using a commercial FEA program, ABAQUS. The cracks are located at the center and torques are applied on both ends of the box beam. Different aspect ratios are considered to evaluate the effects of cracks on box beams for various widths and lengths of panels in the middle yielding region. The accuracy of the nonlinear FEA results is veri?ed by a comparison with previous predicted formulas. Based on the FEA results, the relationship between the residual ultimate strength and crack parameters can be indicated in a function with period of in the form of Fourier series.
2
Content available Experimental Study of Forces Exerted on Ships Due to the Vertical Walls of Navigation Channels
Fathi-Kazerooni M., Seif M. S.
TransNav : International Journal on Marine Navigation and Safety of Sea Transportation
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2015
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Vol. 9, no. 2
199--203
EN
Ship maneuvering in restricted waters of harbor basins and navigation channels had been the main concern in recent years due to sudden increase of ship’s size. When the ship enters a navigation channel the lateral boundary of the channel exerts a transverse force and turning moment on the ship hull. These forces are so important in the analysis of safety of ship navigation in the channels. Ship model test in the towing tank is a reliable method to evaluate these forces. Therefore systematic model tests are held for modeling of the forces exerted on the tanker ship and dhow model traveling alongside a vertical wall. A database of the interaction forces is developed and the specific hydrodynamic effects related to the phenomena are discussed. The results can be used for simulation of ship maneuvering and assessment of safety limits for navigation of ships alongside the quay walls and breakwaters.
3
Content available An Integrated Model of Motion, Steering, Positioning and Stabilization of an Unmanned Autonomous Maritime Vehicle
Gerigk M. K., Wójtowicz S.
TransNav : International Journal on Marine Navigation and Safety of Sea Transportation
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2015
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Vol. 9, no. 4
591--596
EN
In the paper the aim of an interdisciplinary research is presented. The research method is introduced. An object the unmanned autonomous maritime vehicle is briefly described. The key research problem concerns a combined model of the vehicle motion including the loads of lift and hydrodynamic nature. The model takes into account the gravity and displacement forces, resistance and thrust forces, lift and other hydrodynamic forces. One of the major research tasks is to precisely predict the position of the vehicle. To do that an integrated model of acquiring, analyzing and processing the signals is necessary. The processed signals may then be used for the precise steering of the vehicle. The vehicle should be equipped with a stabilization system. Some information on an integrated steering, positioning and stabilization system of the vehicle is briefly presented in the paper. Such the system enables to obtain a fully autonomous vehicle. Some information on the propulsion and underwater energy supply systems are presented in the paper, too.
4
Content available The Analysis of Motion Dynamics and Resistance of the Multipurpose Boat Operating in Shallow Water
Kulczyk T., Górnicz T.
TransNav : International Journal on Marine Navigation and Safety of Sea Transportation
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2014
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Vol. 8, no. 3
359--363
EN
Polish market of small boats has been developed very dynamically in recent years. Market competition forces the shipyards to build new more efficient hull forms and to cut the cost of production as well. This is why modern computer simulation programs are used more often by naval architects. Another trend is to design more universal ships that may be used by larger number of diversified customers. This paper presents project proposal of multipurpose boat hull form. The boat was design to fulfil the requirements imposed by public services like water police, fire brigades, and border guards. It is supposed to be operated on unexplored floodplains and other type shallow waters. The analysis of boat’s motion was based on computer simulations. The resistance curve was evaluated with two methods: comparison study of model test results of similar ships and CFD methods. The results obtained from Ansys Fluent and FINE/Marine systems were compared in this paper. It was shown that taking into consideration dynamic trim and sinkage has a significant impact on free surface capture and resistance values.
5
Content available Steady-state Manoeuvring of a Generic ASD Tug in Escort Pull and Bow-rope Aided Push Operation
Artyszuk J.
TransNav : International Journal on Marine Navigation and Safety of Sea Transportation
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2014
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Vol. 8, no. 3
449--457
EN
This paper is devoted to expand the very promising research undertaken in the author's previous work, basically done on simplified modelling the escort push operation. Now, the other two modes of a tug's employment, as stated in the title, are covered. The special focus is again set on the indirect towing in that the towline force is much higher than the thruster force. The ratio of these two forces, referred to as the relative towing force (or amplification ratio) is evaluated together with the hull drift angle and the thruster(-s) angle for a given escort speed. This mutual relationship is known as the tug performance diagram. Although rather generic (container-type) formulas are derived, they are supplied for exemplification purposes with simple, analytically given hull hydrodynamic forces. The aim is also here to provide a basis for further sensitivity analysis of the model and possible improvement/optimisation to the tug design. The obtained charts also could serve as rough and clear guidance for towmasters while escorting.
6
Content available Optimizing the Seakeeping Performance of Ship Hull Forms Using Genetic Algorithm
Bagheri L., Ghassemi H., Dehghanian A.
TransNav : International Journal on Marine Navigation and Safety of Sea Transportation
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2014
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Vol. 8, no. 1
49--57
EN
Hull form optimization from a hydrodynamic performance point of view is an important aspect of ship design. This study presents a computational method to estimate the ship seakeeping in regular head wave. In the optimization process the Genetic Algorithm (GA) is linked to the computational method to obtain an optimum hull form by taking into account the displacement as design constraint. New hull forms are obtained from the well-known S60 hull and the classical Wigley hull taken as initial hulls in the optimization process at two Froude numbers (Fn=0.2 and Fn=0.3). The optimization variables are a combination of ship hull offsets and main dimensions. The objective function of the optimization procedure is the peak values for vertical absolute motion at a point 0.15LBP behind the forward perpendicular, in regular head waves.
7
Content available Drag and Torque on Locked Screw Propeller
Tabaczek T., Bugalski T.
TransNav : International Journal on Marine Navigation and Safety of Sea Transportation
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2014
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Vol. 8, no. 3
441--447
EN
Few data on drag and torque on locked propeller towed in water are available in literature. Those data refer to propellers of specific geometry (number of blades, blade area, pitch and skew of blades). The estimation of drag and torque of an arbitrary propeller considered in analysis of ship resistance or propulsion is laborious. The authors collected and reviewed test data available in the literature. Based on collected data there were developed the empirical formulae for estimation of hydrodynamic drag and torque acting on locked screw propeller. Supplementary CFD computations were carried out in order to prove the applicability of the formulae to modern moderately skewed screw propellers.
8
Content available Coefficients of Propeller-hull Interaction in Propulsion System of Inland Waterway Vessels with Stern Tunnels
Kulczyk J., Tabaczek T.
TransNav : International Journal on Marine Navigation and Safety of Sea Transportation
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2014
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Vol. 8, no. 3
377--384
EN
Propeller-hull interaction coefficients - the wake fraction and the thrust deduction factor - play significant role in design of propulsion system of a ship. In the case of inland waterway vessels the reliable method of predicting these coefficients in early design stage is missing. Based on the outcomes from model tests and from numerical computations the present authors show that it is difficult to determine uniquely the trends in change of wake fraction and thrust deduction factor resulting from the changes of hull form or operating conditions. Nowadays the resistance and propulsion model tests of inland waterway vessels are carried out rarely because of relatively high costs. On the other hand, the degree of development of computational methods enables’ to estimate the reliable values o interaction coefficients. The computations referred to in the present paper were carried out using the authors’ own software HPSDKS and the commercial software Ansys Fluent.
9
Content available Challenges to Ship Hydrodynamics in the XXI Century
Kobyliński L.
TransNav : International Journal on Marine Navigation and Safety of Sea Transportation
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2014
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Vol. 8, no. 3
353--358
EN
The beginning of twenty-first century is characterized with important changes in world shipping and exploitation of ocean resources. Three important trends are clearly visible: environment protection, safety and economy. They materialize in important changes in the structure of world fleet where some existing ship types are going to disappear and new ship types emerge. Increasing the size of some ship types is another visible tendency. Stress on environment protection has serious impact on the hydrodynamic characteristics of ships whether with regard to safety zero accident rate is the goal. Important challenges to ship hydrodynamics caused by those tendencies are discussed in the paper.
10
Content available Approximate Method of Calculating Forces on Rudder During Ship Sailing on a Shipping Route
Żelazny K.
TransNav : International Journal on Marine Navigation and Safety of Sea Transportation
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2014
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Vol. 8, no. 3
459--464
EN
Service speed of a ship in real weather conditions is a basic design parameter. Forecasting of this speed at preliminary design stage is made difficult by the lack of simple but at the same accurate models of forces acting upon a ship sailing on a preset shipping route. The article presents a model for calculating forces and moment on plane rudder, useful for forecasting of ship service speed at preliminary stages of ship design.
11
Content available The Impact of Sloshing Liquids on Ship Stability for Various Dimensions of Partly Filled Tanks
Krata P.
TransNav : International Journal on Marine Navigation and Safety of Sea Transportation
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2013
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Vol. 7, no. 4
481--489
EN
Liquid sloshing phenomenon taking place in partly filled ships’ tanks directly affects the stability of a vessel. However, only static calculations are carried out onboard ships nowadays and static transfer of liquid weight is taken into account in the course of routine stability calculation. The paper is focused on a dynamic heeling moment due to liquid sloshing in tanks onboard ships. A number of numerical simulations of liquid sloshing taking place in a moving tank is carried out. The wide range of ship’s tanks is taken into account. The conducted CFD simulations are experimentally verified. Finally, the method of an assessment of the liquid sloshing impact on ship transverse stability is worked out. The key point of the method is a dynamic coefficient describing relation of the researched dynamic heeling moment and the quasi-static one in terms of dynamic stability of a vessel which is related to the weather criterion of ship stability assessment.
12
Content available Determination of Inertia Forces Acting on Break Bulk Cargo en Route
Chepok A. O.
TransNav : International Journal on Marine Navigation and Safety of Sea Transportation
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2013
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Vol. 7, no. 4
477--479
EN
The paper presents the analytical method of defining inertia forces that act on break bulk cargo as a result of the oscillatory motion of the vessel exposed to the effect of ambient forces. Considering that the linear models of roll, pitch and heave applicable in this case, the problem is solved by expressing the angle of heel, the angle of pitch, and the amplitude of heave. The obtained functions are differentiated and the inertia forces are determined by means of applying the Newton's second law.
13
Content available remote Double-Mode Classical Cepheid Models - Revisited
Smolec R., Moskalik P.
Acta Astronomica
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2008
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Vol. 58, No. 3
233--261
EN
For many years modeling of double-mode pulsation of classical pulsators was a challenging problem. Inclusion of turbulent convection into pulsation hydrocodes finally led to stable double-mode models. However, it was never analyzed, which factor of turbulent convection is crucial. We show that the double-mode behavior displayed in the computed models results from incorrect assumptions adopted in some of the pulsation hydrocodes, namely from the neglect of buoyant forces in convectively stable layers. This leads to significant turbulent energies and consequently to strong eddy-viscous damping in deep, convectively stable layers of the model. Resulting differential reduction of fundamental and first overtone amplitudes favors the occurrence of double-mode pulsation. Once buoyant forces in convectively stable regions are taken into account (as they should), no stable double-mode behavior is found. The problem of modeling double-mode behavior of classical pulsators remains open.
14
Content available remote Convective Hydrocodes for Radial Stellar Pulsation. Physical and Numerical Formulation
Smolec R., Moskalik P.
Acta Astronomica
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2008
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Vol. 58, No. 3
193--232
EN
In this paper we describe our convective hydrocodes for radial stellar pulsation. We adopt the Kuhfuß (1986) model of convection, reformulated for the use in stellar pulsation hydrocodes. Physical as well as numerical assumptions of the code are described in detail. Described tests show, that our models are numerically robust and reproduce basic observational constraints. We discuss the effects of different treatment of some quantities in other pulsation hydrocodes. Our most important finding concerns the treatment of the turbulent source function in convectively stable regions. In our code we allow for negative values of source function in convectively stable zones, which reflects negative buoyancy. However, some authors restrict the source term to non-negative values. We show that this assumption leads to very high turbulent energies in convectively stable regions. The effect looks like overshooting, but it is not, because turbulence is generated by pulsations. Also, turbulent elements do not carry kinetic nor thermal energy into convectively stable layers. The range of this artificial overshooting (as we shall call it) is as large as six local pressure scale heights, leading to unphysical internal damping through the eddy-viscous forces, in deep, convectively stable parts of the star.
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