• norsk
    • English
  • norsk 
    • norsk
    • English
  • Logg inn
Vis innførsel 
  •   Hjem
  • Fakultet for ingeniørvitenskap (IV)
  • Institutt for bygg- og miljøteknikk
  • Vis innførsel
  •   Hjem
  • Fakultet for ingeniørvitenskap (IV)
  • Institutt for bygg- og miljøteknikk
  • Vis innførsel
JavaScript is disabled for your browser. Some features of this site may not work without it.

Numerical Modelling of the Hydrodynamic Effects of Marine Operations in Broken Ice

Tsarau, Andrei
Doctoral thesis
Åpne
Fulltext not available (Låst)
Permanent lenke
http://hdl.handle.net/11250/2374741
Utgivelsesdato
2015
Metadata
Vis full innførsel
Samlinger
  • Institutt for bygg- og miljøteknikk [2849]
Sammendrag
For sustainable offshore field development and safe navigation in the Arctic seas,

reliable numerical models that are capable of simulating the interactions between

structures, water and sea ice are needed. The Discrete Element Method (DEM) has been

widely used by many researchers worldwide to model the dynamics of broken-ice fields

and the dynamics of structures surrounded by ice. However, despite the large number of

ice-related applications of DEM described in the scientific literature, prior development

of the method has focused mainly on improving the modelling of contact interactions

between ice floes and structures, whereas the effects associated with fluid dynamics

have been largely neglected. This thesis introduces several hydrodynamic models that

can be incorporated into DEM to improve the simulation of marine operations in broken

ice and to enable new applications of the method in ice-related problems.

It was necessary to introduce several hydrodynamic models because the flow regimes

around a structure differ significantly, i.e., the flow regime upstream of the structure is

different from that downstream and from that in the wake of a propeller if the marine

structure is equipped with propellers. Thus, three approaches were considered in this

thesis:

Potential theory was adopted to model the hydrodynamic effect on ice floes

upstream of a structure.

The Vortex Element Method (VEM) was employed to simulate the

hydrodynamics in the downstream wake.

A special technique based on empirical formulas was developed to predict the

dynamics of ice in the propeller wash of a ship.

The novel synthesis of DEM and a potential-flow model presented in this thesis enabled

simulations of the hydrodynamic interactions in multi-body systems, e.g., structures in

broken-ice fields. Unlike standard potential-flow codes, this method can handle the

actual motions of bodies as they arbitrarily move and rearrange themselves in the

system. Specially designed laboratory experiments proved the applicability of this

combined model in predicting the hydrodynamic interaction forces between a structure

and ice floes upstream.

For the first time, the formation of vortices in the flow downstream of an offshore

structure was shown to have an effect on the spreading of broken ice in the wake of the

structure. This effect was efficiently simulated by employing VEM, demonstrating a

new application of the method in ice-related problems.

The propeller-wash effect has been used for decades in Arctic marine operations to

remove ice locally. However, a comprehensive numerical model that can accurately

simulate such operations is presented in this thesis for the first time. A specially

designed full-scale experiment was conducted to calibrate the model, and a set of

independently collected full-scale data was used for a validation study in which the

experimental results were compared with numerical predictions. This study proved the

high accuracy of the model in simulations of an offshore operation in which the

propeller flow of a vessel was employed to clear channels in multi-layered ice rubble.

A number of findings were discovered while validating the developed models and when

performing case studies to demonstrate the capabilities of the models. These findings

are mainly associated with the hydrodynamic effects studied in relation to typical Arctic

offshore operations such as station-keeping in broken ice and ice management and may

therefore be useful to better understand the hydrodynamic processes involved in such

operations. Selected findings that show the importance of hydrodynamics in the

considered marine operations in ice are summarised as follows:

The presence of a bluff structure in a drifting broken-ice field may impose

repulsive hydrodynamic forces on the ice upstream, which may change the freedrift

velocities of the floes by more than 20% in a typical station-keeping

scenario.

The alternating flow due to vortex shedding in the wake of a structure may

contribute to the spreading of broken ice downstream of the structure, which

may eventually lead to full clogging of the wake.

The average hydrodynamic force on an ice piece in a propeller jet was found to

be nearly twice as high as the drag force on an equivalent body in a uniform

flow at the same Reynolds number. It was also found that the jet-induced force

on the ice was proportional to the square of the axial velocity of the propeller jet.
Utgiver
NTNU
Serie
Doctoral thesis at NTNU;2015:281

Kontakt oss | Gi tilbakemelding

Personvernerklæring
DSpace software copyright © 2002-2019  DuraSpace

Levert av  Unit
 

 

Bla i

Hele arkivetDelarkiv og samlingerUtgivelsesdatoForfattereTitlerEmneordDokumenttyperTidsskrifterDenne samlingenUtgivelsesdatoForfattereTitlerEmneordDokumenttyperTidsskrifter

Min side

Logg inn

Statistikk

Besøksstatistikk

Kontakt oss | Gi tilbakemelding

Personvernerklæring
DSpace software copyright © 2002-2019  DuraSpace

Levert av  Unit