modellingof_oceancirculation

Question 1

why should we modell currents?

Answer 1

1.)because cage culture is directly exposed to dynamics of the ocean

2. )ocean dynamics also determine production environment :
   - temp
   - currents, tides
   - salinity
   - nutrients
3. ) to find suitable sites
4. )to find out water interactions betw. locations (sea lice)
   5) part of the traffic light management

Question 2

why are local currents important for aquaculture farms?

Answer 2

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

Question 3

what are the two main ways for measuring currents?

Answer 3

point measurement

profile measurement

Question 4

how do you do point measurements?

what 2 instruments do you use?

Answer 4

sensor placed in the water column,– measuring the current

• propeller based senor (=mechanical sensor)
• accoustic sensor

Question 5

how do you do profile measuremnets?

what is the instruments you use when doing a profile measurement?

Answer 5

accoustic sensor

–> placed in the water, measuring horizontal/vertical currents up to hundreds of meters away from the sensor

Question 6

what are sources of error of measuring currents?

Answer 6

• mechanical sensors need minim speed
• sensors depend on maintenance
• accoustic sensors can be configured for better accuracy (–> battery life shorter)
  …..
  –> quality insurance important

Question 7

what are drifters? what do they do?

how are they build up?

Answer 7

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

Question 8

what is the difference between measurements and models ?

Answer 8

measurement give point values or vertical profile

models give values over spatial ares, showing complete pictures

both tools have inaccuracies and errores

Question 9

how can we get the best result in modelling ocean currents?

Answer 9

by using models whic are corrected by measurments

Question 10

what equation describes the dynamics of fluid?

Answer 10

navier stokes equation

Question 11

what is the effect of the coriolis force?

what is the reason for coriolis force?

Answer 11

defection of water/wind movements to the right on the norther and to the left on the souther hemishphere

earth rotataion

Question 12

is the corriolis force stronger the futher you move to the poles orr the furthere you move to the equator?

Answer 12

…to the pole

Question 13

what are the two challenges of current modelling?

Answer 13

1. setting up equation with the correct values an initial forces
2. solving the equation

Question 14

what is diskretizierung? (discretiziation)

Answer 14

gewinnung einer diskreten teilmenege aus einer kontiniuerelichen daten/informationsmenge

Question 15

what are the two ways of discretization?

Answer 15

horizontal

vertical

Question 16

what is horizontal disecretization based on?

Answer 16

based on squares/ grids

Question 17

how should the resolution be when modelling a large area and how when modellig a small area

Answer 17

modelling large area: low resolution

modelling small area you can increase the resolution

Question 18

what is resolution in hortizontal disctretization?

Answer 18

resolution=how big each cell is

high resolution =small boxes/cells

Question 19

on what can vertical disretiziation be based on?

what are the layers called that are created in the vertical discretization ?

Answer 19

based on depth alone = z layer

or

based on bottom terrain = sigma layers

Question 20

what additional input data do we need for realistic current modelling?

Answer 20

• bottom topography
• weather
• rivers
• tides (tidal cuurents)
• initial values
• forcing at the outer boundaries of the measurement area

Question 21

what are applications for current models?

3

Answer 21

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)

Question 22

how can high accuracy be assesd through?

4

Answer 22

• qualtitative evaluation of current patteren
• comparison with drifter data +point/profile measurements
• comparison with temp and sailinity profiles
• studying tidal dynamics

Question 23

explain how the size of model cells is a trade off between running time and accuracy?

Answer 23

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

Question 24

what are souces of error?

Answer 24

-all datat input (bathymtry, river run off, weather, boundary values)
- limited resolution and detail
-hydrostatic assumption
numerical calculation schemes

Question 25

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.

Answer 25

true