AN EXPERIMENTAL STUDY ON THE RELATIVE MOTIONS BETWEEN A FLOATING HARBOUR TRANSHIPPER AND A FEEDER VESSEL IN REGULAR WAVES

The Floating Harbour Transhipper (FHT) is a pioneering logistics solution that was designed to meet the growing demands for coastal transhipment in the mining sector as well as commercial port operations. The primary advantage of the FHT system is that it can reduce transhipment delays caused by inclement weather, by reducing relative motions between the FHT and feeder vessel. The feeder is sheltered when inside the FHT well dock when compared to the more exposed location when a feeder is in a traditional side-by-side mooring arrangement. This paper discusses previously published studies into the relative motions of vessels engaged in side-by-side mooring arrangements and also presents details and results from a series of physical scale model experiments. In these experiments, both side-by-side and aft well dock mooring arrangements are investigated. The results provide strong evidence that the FHT well dock concept can significantly reduce the heave, pitch and roll motions of feeder vessels when transhipping in open seas – this being the cornerstone of any successful open water transhipment operation.

Sloshing Effects on FLNG and LNGC Side-by-Side Offloading

A side-by-side moored offloading configuration has relatively stronger hydrodynamic and mechanical interactions compared to a tandem moored offloading configuration. For instance, due to the narrow gap between FLNG and LNG Carrier, the trapped water resonance induces higher relative motions between the FLNG and LNG Carrier. In addition, due to the partial filling conditions during the offloading operations, the sloshing loads excite ship motions which induce higher loading on the offloading arms. In this research, a time domain sloshing-ship motion coupling analysis module has been developed for analyzing interactions of the side-by-side moored multiple floating platforms. This paper presents the numerical modeling, the validation analysis results, and the sloshing-ship motion coupled effects on the side-by-side offloading analysis.

Effect of a Passive Tuned Mass Damper on Offshore Installation of a Wind Turbine Nacelle

Although the installation of offshore wind turbines takes place in calm seas, successful mating of wind turbine components can be challenging due to the relative motions between the two mating parts. This work investigates the effect of a passive tuned mass damper on the mating processes of a nacelle for a 10-megawatt (MW) offshore wind turbine. A nacelle with lifting wires and a monopile with a mass damper are respectively modelled using the multibody formulation in the HAWC2 program. A single mass damper is tuned to target at the first natural period of the monopile and is coupled to the main program using a dynamic link library. Afterwards, numerical simulations were carried out in turbulent wind conditions and irregular wave conditions typical of offshore installation scenarios. Important response variables including the tower-top motions, nacelle motions, and their relative motions are examined in the analysis. By comparing the time series and response statistics, we found that the tower-top motion is more crucial to the installation process than the lifted nacelle motion. For the relative motions and velocities between the nacelle and the tower top, the tuned mass damper can reduce the short-term maximum values by more than 50% for the examined sea states with spectral period between 4 to 12 seconds. This implies that the weather window for marine operations can be expanded if the tuned mass damper is applied.

TOWARDS STRUCTURELESS BUNDLE ADJUSTMENT WITH TWO- AND THREE-VIEW STRUCTURE APPROXIMATION

The global approaches solve SfM problems by independently inferring relative motions, followed be a sequential estimation of global rotations and translations. It is a fast approach but not optimal because it relies only on pairs and triplets of images and it is not a joint optimisation. In this publication we present a methodology that increases the quality of global solutions without the usual computational burden tied to the bundle adjustment. We propose an efficient structure approximation approach that relies on relative motions known upfront. Using the approximated structure, we are capable of refining the initial poses at very low computational cost. Compared to different benchmark datasets and software solutions, our approach improves the processing times while maintaining good accuracy.

Eccentricity distribution of wide low-mass binaries

ABSTRACT Distribution of eccentricities of very wide (up to 10 kau) low-mass binaries in the solar neighbourhood is studied using the catalogue of El-Badry and Rix (2018) based on Gaia. Direction and speed of relative motions in wide pairs contain statistical information on the eccentricity distribution, otherwise inaccessible owing to very long orbital periods. It is found that the eccentricity distribution is close to the linear (thermal) one f(e) = 2e. However, pairs with projected separations <200 au have less eccentric orbits, while f(e) for wide pairs with s > 1 kau appears to be slightly superthermal, with an excess of very eccentric orbits. Eccentricity of any wide binary can be constrained statistically using direction and speed of its motion. The thermal eccentricity distribution signals an important role of the stellar dynamics in the formation of wide binaries, although disc-assisted capture also can produce such pairs with eccentric orbits.

Effects of Wind-Wave Misalignment on a Wind Turbine Blade Mating Process: Impact Velocities, Blade Root Damages and Structural SafetyAssessment

Most wind turbine blades are assembled piece-by-piece onto the hub of a monopile-type offshore wind turbine using jack-up crane vessels. Despite the stable foundation of the lifting cranes, the mating process exhibits substantial relative responses amidst blade root and hub. These relative motions are combined effects of wave-induced monopile motions and wind-induced blade root motions, which can cause impact loads at the blade root’s guide pin in the course of alignment procedure. Environmental parameters including the wind-wave misalignments play an important role for the safety of the installation tasks and govern the impact scenarios. The present study investigates the effects of wind-wave misalignments on the blade root mating process on a monopile-type offshore wind turbine. The dynamic responses including the impact velocities between root and hub in selected wind-wave misalignment conditions are investigated using multibody simulations. Furthermore, based on a finite element study, different impact-induced failure modes at the blade root for sideways and head-on impact scenarios, developed due to wind-wave misalignment conditions, are investigated. Finally, based on extreme value analyses of critical responses, safe domain for the mating task under different wind-wave misalignments is compared. The results show that although misaligned wind-wave conditions develop substantial relative motions between root and hub, aligned wind-wave conditions induce largest impact velocities and develop critical failure modes at a relatively low threshold velocity of impact.

Influence of floe-floe interactions on wave damping in marginal ice zones

<p>Numerous observations show that in spite of relative motions of floes caused by wave propagation in marginal ice zone (MIZ) direct contacts between them don’t occur. Nevertheless, relative motions of floes may influence formation of oscillating water currents between them which take and dissipate the energy of incoming waves. Full-scale and laboratory experiments were performed to investigate characteristics of water currents between interacting floes. The experiments included the investigation of vertical and horizontal oscillating motions of floes in ice environment. During the experiments we recorded floe accelerations, water pressure and water velocity. Main goal of the experiments was to estimate effective viscosity of water in gapes between interacting floes, describe floe-floe forces caused by the floe accelerations, and estimate the influence of slush formation on the effective viscosity of water. The floe motion was initiated by mechanical pooling, towing with a rope and by original pendulum rig. The experiments were performed in the Van-Mijen Fjord of Spitsbergen in winter seasons of 2018 and 2019, and in the wave flume at UNIS. A lubrication theory was used to describe the dependence of water pressure between interacting floes from their relative speed and the distance between approaching surfaces. Comparison of numerical simulations with experimental records showed that the action of water pressure and the formation of flow jets can prevent direct collision of approaching floes. Obtained analytical formulas are used for the formulation of rheological equations describing the behavior of broken ice in MIZ.                  </p>