Torgeir Vada

• Business Development Manager at DNV GL

This paper presents hull form optimization processes which can be practically applied at hull form design stage. Traditionally hull form development is carried out in calm sea condition to reach target design speed with specified engine power. However, the design condition has been changing since the evolution of EEDI. It is required to satisfy not...

In the present paper, a complete and consistent second-order computation of airgap for a semi-submersible is presented. The second-order sum and difference frequency upwell will be calculated and combined with the linear upwell statistically to find the short-term extremes. The phasing of the low frequency surface elevation with respect to the low...

A time domain coupled analysis and load transfer for floating wind turbine type structures is demonstrated in this paper. Hydrodynamic coefficients are first sent to a time domain solver for coupled analysis including mooring lines and wind turbine. The wave, motions of the structure and auxiliary forces from mooring lines and wind turbine are sent...

In this paper, we will investigate the numerical treatment of irregular frequencies and moonpool resonance by using a Green’s function method. We will look at the interaction of these two resonances and how much the moonpool resonance will influence other results. We will also look at the importance of the meshing including the addition of a mesh i...

The importance of the low frequency motions to air-gap estimation is evaluated on a column-based unit by using a computer program based on the linear and second-order potential theory. First and second order upwells are combined statistically and examined for different short term sea state conditions. To be able to speed up the analysis process, th...

In this paper two methods for modelling the damping in a narrow gap are investigated. The first method is called the Pressure Damping Model. This method has been used in studies of wave energy devices. An attractive feature of this model is that the modified input is directly related to the energy dissipation in the gap, which means that if this di...

The influence from a current on the relative motions and wave drift forces for moored floater can be quite significant. In this paper, a benchmark study is carried out for three programs, MULDIF, WADAM and WASIM, with the focus on their capability on handling the wave-current interaction problem. A semi-submersible model Troll B and a tanker model...

A time domain Rankine source solver is extended to compute the wave added resistance of ships. The proposed approach applies the momentum conservation principle on the near field fluid volume enclosed by the wet surface of a floating body, the free surface and a control surface. The wave added resistance is then calculated by the integration over t...

Present investigation is based on a numerical study using a time-domain Rankine panel method. The effort and novelty is to extend the applicability of the solver to shallower waters and to steeper waves by including additional non-linear effects, but in a way so to limit the increase in computational costs. The challenge is to assess the improvemen...

The linear boundary value problem for the wave dynamics inside a tank is very similar to the solution for the outer hull. Because of this, the boundary value solver for the outer hull can be re-used for the tank. The oscillating hydrostatic pressure in the tank may also be calculated in the same way as for the outer hull. Thereby, the hydrostatic c...

The convergence of drift force computation on a LNGC in shallow water is studied. It is found that the convergence of the result, especially for the pressure integration method, is largely dependent on the mesh quality. Furthermore, the irregular frequencies degenerate the results in the high frequency region. The LNGC analysis has numerical challe...

The Union ironclad warship USS Monitor foundered in heavy seas off Cape Hatteras, North Carolina, on December 31, 1862. This paper focuses on the development and validation of numerical models of a ship foundering using USS Monitor as a test subject. It begins with a brief account of the vessel’s history and the circumstances leading up to the sink...

A numerical method for solving the problem of an arbitrary shear flow around one or more circular cylinders is presented. This extends the applicability of the vortex-in-cell method to compute the viscous flow around a cylinder in the shear layer close to a wall at transcritical Reynolds numbers. The effect of varying the gap between the wall and t...

This paper presents a comparison between a numerical method and experiments for the forces on smooth circular cylinders in planar oscillatory flow of small amplitude. The numerical method is based on the vortex-in-cell method where the vorticity in the flow is represented by a large number of discrete vortices. Calculated time series of both in-lin...

Computational examples showing the dissociation effect by using a finite element method for solving the compressible Euler equations with equilibrium chemistry are presented. The finite element method, that has been used increasingly for solving compressible flow problems due to its flexibility in handling complex geometries and irregular meshes, m...

The first- and second-order wave-diffraction problems are solved for a submerged cylinder of arbitrary shape by the integral-equation method based on Green's theorem. The integral equation is solved by an element method using cubic splines. The first- and second-order force components, transmission and reflection coefficients are presented for two...

The deep draft Spar platform concept is considered a competitive alternative for deep-water field developments. The complete system of Spar floater, mooring lines and risers interacts as an integrated dynamic system subject to the combined excitation of wind, waves and current. This paper will deal only with wave effects. Wave induced loads on the...