modellingof_oceancirculation Flashcards
why should we modell currents?
1.)because cage culture is directly exposed to dynamics of the ocean
- )ocean dynamics also determine production environment :
- temp
- currents, tides
- salinity
- nutrients - ) to find suitable sites
- )to find out water interactions betw. locations (sea lice)
5) part of the traffic light management
why are local currents important for aquaculture farms?
affects:
- feeding dynamcis
- cage deformation
- water exchange
- the layout of the farm (dimesion of moorings etc)
- sedimentation below fish cages
very sensitive to currents are de lousing, cage net cleaning, wellboat operations
what are the two main ways for measuring currents?
point measurement
profile measurement
how do you do point measurements?
what 2 instruments do you use?
sensor placed in the water column,– measuring the current
- propeller based senor (=mechanical sensor)
- accoustic sensor
how do you do profile measuremnets?
what is the instruments you use when doing a profile measurement?
accoustic sensor
–> placed in the water, measuring horizontal/vertical currents up to hundreds of meters away from the sensor
what are sources of error of measuring currents?
- mechanical sensors need minim speed
- sensors depend on maintenance
- accoustic sensors can be configured for better accuracy (–> battery life shorter)
…..
–> quality insurance important
what are drifters? what do they do?
how are they build up?
for measuring currents
- they follow the current, track the pathway
build:
surface buoy and drogue placed at specific depth
may include:
GPS
Sensor
satellite communication
what is the difference between measurements and models ?
measurement give point values or vertical profile
models give values over spatial ares, showing complete pictures
both tools have inaccuracies and errores
how can we get the best result in modelling ocean currents?
by using models whic are corrected by measurments
what equation describes the dynamics of fluid?
navier stokes equation
what is the effect of the coriolis force?
what is the reason for coriolis force?
defection of water/wind movements to the right on the norther and to the left on the souther hemishphere
earth rotataion
is the corriolis force stronger the futher you move to the poles orr the furthere you move to the equator?
…to the pole
what are the two challenges of current modelling?
- setting up equation with the correct values an initial forces
- solving the equation
what is diskretizierung? (discretiziation)
gewinnung einer diskreten teilmenege aus einer kontiniuerelichen daten/informationsmenge
what are the two ways of discretization?
horizontal
vertical
what is horizontal disecretization based on?
based on squares/ grids
how should the resolution be when modelling a large area and how when modellig a small area
modelling large area: low resolution
modelling small area you can increase the resolution
what is resolution in hortizontal disctretization?
resolution=how big each cell is
high resolution =small boxes/cells
on what can vertical disretiziation be based on?
what are the layers called that are created in the vertical discretization ?
based on depth alone = z layer
or
based on bottom terrain = sigma layers
what additional input data do we need for realistic current modelling?
- bottom topography
- weather
- rivers
- tides (tidal cuurents)
- initial values
- forcing at the outer boundaries of the measurement area
what are applications for current models?
3
a lot in AQC:
- currents at aquaculture locations (looking for potentail locations)
- to calculate infection risks between locations
- to estimate sedimentation (where and how much sediments)
how can high accuracy be assesd through?
4
- qualtitative evaluation of current patteren
- comparison with drifter data +point/profile measurements
- comparison with temp and sailinity profiles
- studying tidal dynamics
explain how the size of model cells is a trade off between running time and accuracy?
smaller cells require shorter time step and cover less area per cell –> need a lot of time
larger cells give less accurate bathymetry and coast line + small dynamics are not represenetd
what are souces of error?
-all datat input (bathymtry, river run off, weather, boundary values)
- limited resolution and detail
-hydrostatic assumption
numerical calculation schemes
ture or falls:
although there are so many source of error models can still give good represantation of tidal current, episodal changes, statistical properties of current speed and direcetions.
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