Surfing Samakonishamali jinkanayya fasinolaSamakonishamali jinkanayya fasinolaSamakonishamali jinkanayya fasinolaMina Shina

7/25/2019 Surfing Samakonishamali jinkanayya fasinolaSamakonishamali jinkanayya fasinolaSamakonishamali jinkanayya f

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Physics of SurfingEnergetics of a Surfer

David T. Sandwell(http://topex.ucsd.edu)

Four styles of surfing

Waves Big swell coming? (storms) What makes sets? (dispersion)

Why is Blacks Beach good for surfing?(refraction)

Riding waves catching the wave (speed)

dropping-in (energy conservation)

tube riding (tapping wave energy) need more speed (surfboard drag)

1 2 kg 1 kg

Which ball is going faster when it reaches the bottom?

(a) (b)



Which ball is going faster when it reaches the bottom?

(a) (b) (c)

conservation of energy(assume no friction)

kinetic energy + potential energy = constant

mgH=1

2mv

2m

m

v

H

mv



optimal skateboard ramp(The brachistochrone problem)

What is the best ramp shape for the minimum time down?



60 ft

35 mph

24 ft22 mph15 ft

18 mph4.5 ft10 mph

ocean depth and breaker height - empirical

Hb- height of breaker

db- depth where wave

breaks

db

=1.28Hb



Mavericks video

shallow water waves

cs = gd



breaking waves

db

surfers

empirical relation

Hb- height of breakerdb- depth where wave

breaks

db

=1.28Hb



catching the wave

db

surfers

paddle speed

Hb- height of breakerdb- depth where wave

breaks

cb = 1.28gHb

paddle speed


http:///reader/full/surfing-samakonishamali-jinkanayya-fasinolasamakonishamali-jinkanayya-fasinolasamakonish 10/15

dropping in

Hb

top of wave

bottom of wave

KEbottom= KEtop+ PE

1

2mvd

2=

1

2mcb

2+mgHb

vd2=cb

2+2gHb = 3.28gHb

g - acc. Gravity

cb- wave speedvd- surfer speed after drop

dropping in

59.827.217.023tow-in

35.216.010.08tube

27.912.77.95fun

15.26.94.31.5longboard

vd

(mph)

vd

(m/s)

cb

(m/s)

Hb

(m)

style



correction for surfer height

H' Hb

H'= Hb- 1/2 Hs

effective height = breaker height - 1/2 surfer height

- overhead waves are good- waist high waves are bad- short surfers and heavy boards have an advantage in small waves

Pipeline video

dropping in



dropping in

Hb

top of wave

bottom of wave

KEbottom= KEtop+ PE

1

2mvd

2=

1

2mcb

2+mgHb

vd2=cb

2+2gHb = 3.28gHb

g - acc. Gravity

cb- wave speedvd- surfer speed after drop

dropping in

59.827.217.023tow-in

35.216.010.08tube

27.912.77.95fun

15.26.94.31.5longboard

vd

(mph)

vd

(m/s)

cb

(m/s)

Hb

(m)

style



cutting across

back of wave

front of wave

vd !

cb

cb

2

vd

2=

1.28

3.28=cos

2!

!=~ 50

topview

This angle is independent ofwave height or wave speed!



riding the wave

Suppose the surfer remains on the steepest part of the wave having

a slope s. What is the rate of potential energy increase supplied tothe surfer?

cb s

P E = sgcbside view

v(t)2=vd

2+ sgcb

o

t

! dt

v(t)2=3.28gHb +tsg 1.28gHb

How does speed increase

with time?

speed video



the drag

v(t)2 = 3.28gHb + 1.13g

3 / 2 s Hb

1/ 2 t ! drag

total

velocity

= paddle

drop in+

-

slope of

the curlbreakerheight

duration

of ride

energy

dissipation

Future Research Are the best surf spots in areas of narrow continental margin?

Are sets real? What are the statistical properties of sets? Do setsbecome amplified when they reach shallow water?

How does the shape of the bottom translate into the perfect wave?

What is the terminal velocity for a given breaker height? (Can we establishthe magnitude of the drag term?)

Need to instrument surfers with intertial sensors.

Documents

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