Serge Sutulo

Mathematical models for ship path prediction in manoeuvring simulation systems

The problem of simulating the ship manoeuvring motion is studied mainly in connection with manoeuvring simulators. Several possible levels of solution to the problem with different degrees of complexity and accuracy are discussed. It is shown that the structure of the generic manoeuvring mathematical model leads naturally to two basic approaches based respectively on dynamic and purely kinematic prediction models. A simplified but fast dynamic manoeuvring model is proposed as well as two new advances in kinematic prediction methods: a prediction based on current values of velocities and accelerations and a method of anticipating the ships trajectory in a course changing manoeuvre.

A Navigation and Control Platform for Real-Time Manoeuvring of Autonomous Ship Models

Abstract The development of a control and navigation platform for an autonomous surface vessel (ASV) being a scaled self-propelled model of a real ship is presented in this paper. The overall system is described under the hardware structure and the software architecture. The system hardware structure is further divided into the command and monitoring unit (CMU) and the communication and control unit (CCU). The ashore based CMU is used to control the ASV through a wireless Ethernet communication; the ASV mainly consists of the on-board CCU. The system software architecture mainly consists of several software loops for collecting the sensor data and controlling the rudder and propeller actuations. Furthermore, a touch panel as the human machine interface (HMI) is used for autonomous and manual control of the ASV has been implemented. Finally, the future experimental implementations of the ASV are discussed in this paper.

Simulation of the Hydrodynamic Interaction Forces in Close-Proximity Manoeuvring

A code for simulating hydrodynamic interaction forces in manoeuvring simulating systems has been created. The algorithm takes into account potential forces only and is based on the Hess and Smith panel method. Own inertial hydrodynamic forces were estimated through pre-calculation of the added masses followed by use of the Thomson–Tait– Kirchhoff equations. Comparative computations of the added masses, surge and sway interaction forces and yaw interaction moments with varying number of surface computational panels showed that on a typical modern PC, an acceptable accuracy in terms of the integrated loads can be reached with a relatively small number of panels permitting real-time simulations with the developed algorithm in the loop. Importance of the account for the local time derivative of the potential has been demonstrated on comparative calculations in simulation of a passing-by manoeuvre. The code can be used for predicting interaction loads with any number of moving objects and fixed obstacles.

Computation of Ship-to-Ship Interaction Forces by a 3D Potential Flow Panel Method in Finite Water Depth

The double-body 3D potential flow code developed earlier for computing hydrodynamic interaction forces and moments acting on the hulls of the ships sailing in close proximity with neighbouring ships or some other obstacles, is extended to the shallow water case. Two methods for accounting for the finite water depth were implemented: use of truncated mirror image series, and distribution of an additional single layer of sources on parts of the seabed beneath the moving hulls. While the first method does only apply to the flat horizontal seabed, the second one can also deal with the arbitrary bathymetry situations. As appropriate choice of the discretization parameters can significantly affect the accuracy and efficiency of the second method, the present contribution focuses on comparative computations aiming at defining reasonable dimensions of the moving panelled area on the sea bottom and maximum admissible size of the bottom panel. As result, conclusions concerning optimal parameters of the additional set of panels are drawn.Copyright

Multi-agent Simulation of Passenger Evacuation from a Damaged Ship under Storm Conditions

Abstract We present a multi-agent model for the simulation of evacuation processes considering ship motions and a method for modeling crowd dynamics. To take into account all aspects of the specifics of evacuation in storm conditions, an information model has been developed. This model is based on three interrelated processes: sea waves dynamics, ship motions under the influence of sea, crowd dynamics affected by ship motions. In our research, we developed a combined method for simulating agents’ movements on the inclined decks of the ship. Our approach combines the well-known implementation of the Social Force model with the possibility of collisions with obstacles. Depending on the specific requirements, it is possible to use various models for ship dynamics in irregular seas. To better support this versatility, a distributed test bench based on the CLAVIRE cloud platform was developed for simulation of passenger evacuation and testing simulations were carried out. The obtained results demonstrate that the developed simulation system could be used for designing contingency plans to assist crew members in the framework of decision support systems (DSS).

A Generalized Strip Theory for Curvilinear Motion in Waves

A simulation-oriented mathematical model for a slender ship manoeuvring in waves was devised as a fusion of two classic linear strip theory implementations used separately in manoeuvring and seakeeping. Two basic requirements were formulated: the generalized model must reduce to the popular Salvesen–Tuck–Faltinsen seakeeping model in the particular case of the rectilinear base motion (constant speed advance) and to the Munk theory in absence of waves and wave-induced motions. It was assumed that the generalized model will then be reasonably consistent in intermediate regimes. The primary problem formulation was performed under the assumption that small-amplitude oscillations with the encounter frequency in regular seas are superimposed with the arbitrary base manoeuvring motion characterized by slowly-varying kinematic parameters. After the velocity potential’s decomposition into the quasi-steady and substantially unsteady parts, application of the Bernoulli equation, and further integration over the wetted surface (which can be taken in its equilibrium or instantaneous position) result in the representation of hydrodynamic forces in the frequency domain through longitudinal distributions of the sectional complex added masses and their longitudinal derivatives. The frequency-dependent coefficients are then approximated with rational fractions and, further, subjected to the Fourier transform. As a result, a set of ordinary differential equations for the time-dependent hydrodynamic forces and auxiliary state variables were obtained. The model was implemented as part of a manoeuvring simulation code and some time histories of various components of the hydrodynamic forces are given as illustrations.Copyright

Computation of Ship-to-Ship Interaction Forces by a Three-Dimensional Potential-Flow Panel Method in Finite Water Depth

A double-body 3D potential-flow code developed earlier for computing hydrodynamic interaction forces and moments acting on the hulls of the ships sailing in close proximity with neighboring ships or some other obstacles, is extended to the shallow water case. Two methods for accounting for the finite water depth were implemented: (1) using truncated mirror image series and (2) distribution of an additional single layer of sources on parts of the seabed beneath the moving hulls. While the first method does only apply to the flat horizontal seabed, the second one can also deal with the arbitrary bathymetry situations. As appropriate choice of the discretization parameters can significantly affect the accuracy and efficiency of the second method, the present contribution focuses on comparative computations aiming at defining reasonable dimensions of the moving paneled area on the sea bottom and maximum admissible size of the bottom panel. As result, conclusions concerning optimal parameters of the additional set of panels are drawn.

A Boundary Integral Equations Method for Computing Inertial and Damping Characteristics of Arbitrary Contours in Deep Fluid

Abstract A modification of Yeung’s boundary-integral method of solving the linear boundary-value problem related to the frequency-domain hydrodynamic characteristics of arbitrary smooth contours intersecting the free surface of the fluid has been further developed. The modification relates to the integral equation’s discretization step and consists in substituting the orthodox one-point collocation with another collocation method satisfying the integral equation in the mean over each rectilinear segment in the polygonal approximation of the contour. Relatively complicated in fluence functions were evaluated analytically. Numerical tests demonstrate that the suggested method shows better accuracy at equal number of panels (segments) and is robust and reliable enough to be recommended for practical calculations.

Hydrodynamic Interaction Forces on Ship Hulls Equipped With Propulsors

Typically, study of hydrodynamic interaction between vessels navigating in close proximity to each other is limited to hydrodynamics of bare hulls. Meanwhile, ship propulsors, especially heavily loaded, which may happen in accelerating motion, can alter substantially the flow and distribution of pressure on the hulls which can be viewed as generalization of the thrust deduction phenomenon. The 3D doubled body potential interaction code based on the source panel method developed earlier by the authors has been enhanced to include the effect of a propeller on each of the interacting ships under the assumption that the propeller jets (slipstreams) are not involved into the interaction. Each propeller is simulated by a disk of sinks further approximated with a polygon composed of identical triangular panels with identical constant sink density linked to the thrust of the propulsor according to the actuator disk theory. Comparative computations were carried out for two identical tanker vessels in the close-proximity overtaking manoeuvre at various values of the loading coefficient of each propeller. The loading coefficient is not supposed to be necessarily defined by the steady propulsion point. Numerical results demonstrate that a heavily loaded propeller substantially modifies the pressure distribution on both hulls resulting in alteration of the hydrodynamic interaction loads, especially of the surge force and yaw moment.

On the Order of Polynomial Regression Models for Manoeuvring Forces

Abstract The paper is investigating certain aspects of polynomial regression models used for representation of hydrodynamic forces acting on a ship performing normal (moderate) manoeuvres. A unique polynomial model of increased order developed by Oltmann, Sharma and Wolf at the end of 70s on the basis of high-precision model tests was taken as a primary one. The model was used to generate sample sets of responses which were further approximated with simpler third-order polynomial models presented here as secondary regressions. The structure of the secondary models was chosen using the stepwise forward regression procedure and the coefficients were further estimated by the least-square algorithm. The resulting model turned out to be much more economical in terms of the number of regressors and estimated parameters and does not include regressors of higher order and acceleration-velocity cross-coupling terms present in the primary model. At the same time, comparisons of the force/moment responses, zigzag manoeuvre time histories and of the spiral curves demonstrated that no tangible loss of accuracy can be traced. The conclusion is made that no terms of the order higher than three should enter polynomial models used in ship manoeuvring. Copyright