Samcot_annual_report

Annual Report 2016

SAMCoT

Both the elastic-plastic and the elastic-viscoplastic

models mentioned above are restricted to saturated

frozen soils. However, soils in the Arctic are mostly

unsaturated. Modelling the behaviour of unsaturated

frozen soils is a new field of research and substantial

theoretical development will be required to reach this

goal. To facilitate this research path, Amiri and his

team at NTNU adopted the THM model developed by

Yared Bekele in WP2 and further developed it into an

in-house THM finite-element code similar to PLAXIS.

Bekele defended his PhD thesis, Isogeometric Analysis

of Coupled Problems in Porous Media - Simulation of

Ground Freezing, on 19 May 2016.

During his PhD study, Bekele incorporated a simple non-

linear thermo-elastic material model and successfully

applied it to the simulation of frost heave problems.

After defending his PhD thesis, Bekele worked for 6

months as a researcher trying to incorporate Amiri’s

elastic-plastic model into his THM model. The theore-

tical nature of Amiri’s elastic-plastic model required

significant modifications to the governing equations of

Bekele’s original THM model. The modifications of Beke-

le’s code are now completed and the implementation of

the elastic-plastic model is still progressing.

Rapid coastal erosion threatens Arctic coastal

infrastructure, including communities and industrial

installations. Coastal erosion in the Arctic is a function

of numerous processes, including nearshore hydrodyna-

mics, thermal and mechanical behaviour of frozen and

unfrozen soil, atmospheric forcing, and the presence of

sea ice. In particular, surface waves play an important

role as they force circulation, which can lead to erosion.

The interaction between surface waves and sea ice is

quite complex. On the one hand, sea ice suppresses

waves by scattering and dissipating wave energy, but

on the other hand, the waves can break up the ice. Sea

ice also determines the available fetch and duration for

wave generation and evolution.

As development increases in northern regions, there is

an increased need to understand and predict coastal

erosion in those areas. This means, among other things,

that we need to improve the existing wave models to

take into account the effects of sea ice.

Hongtao Li started as a PhD candidate in September

2016. The main task for Li is to investigate the different

physical processes associated with the interaction bet-

ween waves and sea ice. Li’s study will contribute to the

theoretical development of waves-in-ice models, which

will eventually improve our ability to predict coastal

erosion in the Arctic. In addition to the theoretical work,

Li’s PhD study will put an emphasis on observations and

field data collected using in-situ and remote sensing

measurements. This is very important in order to

understand the governing mechanisms and dominating

physical processes, as well as to validate the theoretical

models under development.

In October 2016, Li participated in experiments on

waves-ice interactions conducted in the ice tank

at Hamburg Ship Model Basin (HSVA) under the EU

Hydralab+ programme. Li gained valuable lab experience

and is currently working with the data, examining

the portion of the wave energy that dissipated due to

colliding floes.

MODELLING THE BEHAVIOUR OF

UNSATURATED FROZEN SOILS

CHARACTERIZATION OF SEA ICE

EFFECTS ON COASTAL WAVES

Long-term settlements due to creep phenomena are of great

importance in cold region engineering. Creep settlements are

highly influenced by the applied stress level and the tempe-

rature. The second simulation shows the effect of changing

applied stress and temperature on the creep settlements of

a foundation over 8 years. As shown in the graph, creep rate

is increasing with increasing stress level and temperature.

As expected, the creep rate of frozen soil in summer time is

more critical than in winter time.

PhD candidate Nadeem Ahmad is working on numerical

modelling of sediment transport in the Arctic environ-

ment. Ahmad uses the open-source Computational

Fluid Dynamics (CFD) code REEF3D for his research, ba-

sed on three-dimensional (3D) Navier-Stokes equations.

The level set method for the free surface along with

the turbulence model is implemented in the code,

which solves complex free surface flows such as wave

breaking, standing waves and flow around hydraulic

structures. In the sediment transport module of the

code, the simulated hydrodynamics is coupled with the

3D morphological model to capture the erosion process.

The model simulates the erosion and deposition,

including the development of bed shear stresses, bed

load and suspended load. In addition, the morphological

calculations are based on sediment properties such

as median sediment size, sediment density, sediment

porosity and the Shields parameter. This makes the

morphological model more robust and efficient when

simulating the erosion process for different morpho-

logies. Ahmad’s contribution to WP6 is appreciable.

Recently, a paper about the numerical modelling of the

Bjørdalen-Isfjorden coastline in Svalbard, where signifi-

cant coastal erosion was observed during a storm event

in September 2015, was submitted to the ISOPE-2017

conference in San-Francisco, USA.

NUMERICAL MODELLING OF

SEDIMENT TRANSPORT -

CFD MODEL REEF3D

Numerical modelling of the Bjørndalen-Isfjorden coastline

at Spitsbergen, where significant coastal erosion was

observed during a storm event in September 2015. The

observations showed that the coastlines with gentle

slopes were severely affected due to the erosion.

U (m/s)

450m 250m 0m

=4.5m

27m

15m

30m 15m 0m

18.5m

17.5m

18.5m

17.5m

18.5m

17.5m

=2.5m

MSL

= 1.8m

= 2.0m

(a) t= 50s

(b) t=76s

(d) t=300s

30m 15m 0m