wave attenuation

PIER 4 CONDOMINUMS PIER 4 CONDOMINUMS Dock and Wave Dock and Wave

Attenuator replacement Attenuator replacement proposalproposal

Presented by Presented by

Bellingham MarineBellingham MarineJune 29June 29thth. 2005. 2005

Existing Conditions at Pier 4 Condominiums:

What’s the COST of a Wave

Attenuator?

Wave Attenuators are the Wave Attenuators are the most site specific most site specific

designed structures in a designed structures in a marina.marina.

Can’t you give me a

SQUARE FOOT NUMBER?

Different shapes and mass;

Different Drafts

Different Widths.

How do I know what size How do I know what size and shape attenuator I and shape attenuator I

need?need?

Determine Design Wave relevant to YOUR site.

Wind Generated Waves

Wake Generated Waves

How does God make waves?How does God make waves?

WIND!WIND!

Wind blows, creating friction Wind blows, creating friction on the surface of a body of on the surface of a body of

water. water.

What Factors Create and Effect Wind Generated

Waves?

Wind Duration

Wind Speed

Fetch

Water Depth

Fetch (n) : a) The distance over which a wind blows. b) The distance traveled by waves with no obstructions

Wind Speed – The average wind velocity over a 3 second gust.

Wind Duration – The length of time the wind blows in minutes or hours.

Water Depth – The depth of the water during the wind event.

How does Man make waves?How does Man make waves?

BOAT WAKES!BOAT WAKES!

Boat Wakes: Under certain conditions the prevailing

cause of waves incident to a facility could be boat wakes. They are more frequent than extreme wave events

and will lead to structural deterioration by cyclic fatigue.

Factors Used to Determine Vessel Wake Size

Boat Length

Boat Displacement

Boat Speed

Boat Hull Shape

Channel Distance to Site

DETERMINE THE DESIGN WAVE

• Once the two different types of waves are evaluated the attenuator Design Wave is determined by identifying the governing load case.

• The Design Wave parameters are identified; which include the wave height, wave length and wave period.

The right size and configuration The right size and configuration of a attenuator will create a calm of a attenuator will create a calm

basin for basin for this specific site.this specific site.

=

=

√≈

.

1.0 .9 .8 .7 .6 .5 .4 .3 .2 .1 0 .1 .2 .3 .4 .5 .6

B/L using a 12’ breakwater

Kt

WAVE TRANSMISSION TABLE GIVEN WAVE PERIOD AND ATTENUATOR WIDTHS PERIOD LENGTH WIDTH 8 9 10 11 12

3.5 63 0.13 0.14 0.16 0.18 0.19 3.25 54 0.15 0.17 0.18 0.20 0.22

3 46 0.17 0.20 0.22 0.24 0.26 2.75 39 0.21 0.23 0.26 0.28 0.31 2.5 32 0.25 0.28 0.31 0.34 0.38

So for Hs = 3.0 as shown in the Wave Tank example; KT will as shown below PERIOD LENGTH WIDTH 8 9 10 11 12

3.5 63 0.55 0.45 0.42 0.40 0.38 3.25 54 0.50 0.41 0.40 0.38 0.34

3 46 0.41 0.38 0.34 0.31 0.30 2.75 39 0.36 0.32 0.30 0.29 0.28 2.5 32 0.31 0.29 0.28 0.27 0.28

So for Hs = 3.0 as shown in Wave Tank example; Hs = 3.0 HT will as shown below PERIOD LENGTH WIDTH 8 9 10 11 12

3.5 63 1.65 1.35 1.26 1.20 1.14 3.25 54 1.50 1.23 1.20 1.14 1.02

3 46 1.23 1.14 1.02 0.93 0.90 2.75 39 1.08 0.96 0.90 0.87 0.84

1.0 .9 .8 .7 .6 .5 .4 .3 .2 .1 0 .1 .2 .3 .4 .5 .6

B/L using a 12’ breakwater

Kt

”

“”