Towards an understanding of form drag at Three Tree Point

Sally Warner, Parker MacCreadyUniversity of Washington

Jim Moum, Jonathan Nash, Uwe StöberOregon State University

September 22, 2010 IMSPO, Seattle, WA

Form drag and mixing

U0

Form dragpressure

large form drag

small form drag

blunt body

streamlined body

Form drag and mixing

U0

Form dragpressure

Tidalenergyconversion

Form drag causes:

- internal wave generation

- eddy generation

- local mixing and dissipation

Motivation for this study

Seattle

Tacoma

Edwards et al., 2004

Puget Sound, WA

PointThree Tree

Previous work

McCabe et al., 2006

> Measured the internal form drag

> Measured the external form drag

Our goal> Measure the total form drag with bottom pressure sensors

Cruise at TTP in Dec. 2009

Seattle

Tacoma

Puget Sound, WA

PointThree Tree

Pressure sensors (PPODs) at Three Tree Point (TTP)

PPODs

-200 -100 0 100 [m]

-122.41 -122.39 -122.37 -122.35

47.48

47.47

47.46

47.45

47.44

47.43

47.42

PPOD pressure signalsRaw PPOD data [psi]

12/03 12/04 12/05 12/06 12/07 12/08 12/09 12/1050

100

150

200

250

300

350

GMT 2009

psi

TTP01TTPANTTP02TTP03TTP04TTP05TTP06TTP07TTP08TTPASTTP09TTPHS

-200 -100 0 100 [m]

-122.41 -122.39 -122.37 -122.35

47.48

47.47

47.46

47.45

47.44

47.43

47.42

350

300

250

200

150

100

12/03 12/05 12/07 12/09

12/03 12/04 12/05 12/06 12/07 12/08 12/09 12/10−0.05

−0.04

−0.03

−0.02

−0.01

0

0.01

0.02

0.03

0.04

0.05

GMT 2009

m

Residual pressure signalOffset plot of pressure [m of SSH]

-200 -100 0 100 [m]

-122.41 -122.39 -122.37 -122.35

47.48

47.47

47.46

47.45

47.44

47.43

47.42

12/03 12/05 12/07 12/09

0.05

0.04

0.03

0.02

0.01

0

-0.01

-0.02

-0.03

-0.04

-0.05

−2

−1

0

1

2

N/m

12/05 12/06 12/07 12/08 12/09 12/10−500

0500

100015002000

GMT 2009

W/m

Residual dragResidual pressures

Residual form drag and wave drag

}

W/m

N/m

x 104

}

}1 cmof SSH

N

S

Tidal conversion rate per unit width

−250

−200

−150

−100

−50

m

−3000 −2000 −1000 0 1000 2000 3000−0.4

−0.2

0

0.2

0.4

m/m

meters from tip of TTP

topographicheight

topographicslope

N

N

S

S

}}

}

Running mean: ~300 W/m times width: ~0.7 MW

ROMS model of TTP

http://faculty.washington.edu/dsuth/MoSSea/

Modeling the Salish SeaDavid Sutherland

Domain for TTP model

ROMS model of TTPsurface vorticity [1/s]

TTP

Bottom pressure sensors can be used to measure form drag on topography in the ocean.

A numerical model will help to quantify the total form drag and understand the physical processes that play a role in energy conversion at Three Tree Point.

Conclusions / future work>

>

Thank you