Breaking waves

Storyboard

The air currents over the ocean drive the movement of the water, generating waves that behave differently under fluctuations depending on the depth. This phenomenon is known as wave breaking. Wave breaking occurs because the propagation speed of a wave is greater in areas of deeper water. Thus, as waves approach the shore, those from deeper areas tend to overtake those from shallower areas, resulting in the characteristic breaking of the wave.

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Mechanisms

Iframe

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Code
Concept
Angular frequency
Break of the wave on the beach
Wave description
Wave group velocity
Wave phase velocity
Wave speeds
Wave vector

Mechanisms

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Break of the wave on the beach

Description

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When a wave reaches the shore, it starts to climb up the beach slope, becoming progressively shallower and slower. A following wave tends to rise over the preceding wave. As the water becomes deeper in this situation, it becomes faster and tends to overtake the previously arrived water. This interaction ultimately leads to the wave breaking, creating the phenomenon known as surf.

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Angular frequency

Concept

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Recalling that angular velocity represents the angle traversed per unit of time, it can be observed that the expression

$\displaystyle\frac{2\pi}{T}$



corresponds to a complete revolution ($2\pi$) divided by the time the period ($T$), which is required for one cycle. Therefore, the angular frequency ($\omega$) is defined as

$ \omega = \displaystyle\frac{2 \pi }{ T }$

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Wave vector

Concept

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The wave vector ($k$) is the factor that multiplies the position and corresponds to the value for which, if the wave moves along a wave length ($\lambda$), it assumes the same shape it initially had. For this to occur, the following condition must be met:

$kx = k\lambda = 2\pi$



Therefore, with the wave length ($\lambda$), we establish that:

$ k =\displaystyle\frac{2 \pi }{ \lambda }$

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Wave phase velocity

Concept

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The speed of waves depends on the water depth and the factor the wave vector ($k$), which is calculated using the wave length ($\lambda$) as follows:

$ k =\displaystyle\frac{2 \pi }{ \lambda }$



Regarding the phase speed ($c_p$), which corresponds to the speed at which each wave crest moves, this can be determined using the ocean depth ($h$) and the gravitational Acceleration ($g$). The phase speed ($c_p$) is calculated as:

$ c_p =\sqrt{\displaystyle\frac{ g }{ k } \tanh( k h )}$

The phase velocity refers to the speed at which a specific oscillation or wave moves.

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Wave group velocity

Concept

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Waves have a speed that depends on the water depth and the factor the wave vector ($k$), calculated using the wave length ($\lambda$) as follows:

$ k =\displaystyle\frac{2 \pi }{ \lambda }$



For the group speed ($c_g$), which represents the speed at which the entire wave train moves, not each individual wave, it can be calculated using the phase speed ($c_p$). This is determined with the ocean depth ($h$) and the gravitational Acceleration ($g$), in the following way:

$ c_p =\sqrt{\displaystyle\frac{ g }{ k } \tanh( k h )}$



Finally, using this information, the group speed ($c_g$) can be calculated through the following expression:

$ c_g =\displaystyle\frac{ c_p }{2}\left(1 + \displaystyle\frac{2 k h }{\sinh(2 k h )}\right)$

The group velocity is the speed at which the train or group of waves moves through the water medium.

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Wave speeds

Image

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There are two characteristic speeds in wave mechanics. On one hand, there is the speed at which a specific wave travels, which can vary based on frequency, thus differing from one wave to another.

The second type of speed observed is that of a wave packet, that is, a group of waves of different frequencies and phases which, when superimposed, form a group that moves as a unit. This speed is known as the group velocity.

Both can be observed in this animation:

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Wave description

Concept

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A wave can be approximately described as a sinusoidal function depending on the variables the position ($x$) and the time ($t$).

The function incorporates the values of the wave height ($z$) at each point, as well as the maximum wave height ($z_0$), the wave vector ($k$), and the frecuencia angular ($\omega$):

$ z ( x , t ) = z_0 sin( k x - \omega t )$

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Model

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Calculations

Variables

Symbol
Text
Variable
Value
Units
Calculate
MKS Value
MKS Units
$\omega$
omega
Angular frequency
rad/s
$\omega$
omega
Frecuencia angular
rad/s
$h$
h
Ocean depth
m
$T$
T
Period
s
$x$
x
Position
m
$t$
t
Time
s
$z$
z
Wave height
m
$k$
k
Wave vector
1/m

Parameters

Symbol
Text
Variable
Value
Units
Calculate
MKS Value
MKS Units
$g$
g
Gravitational Acceleration
m/s^2
$c_g$
c_g
Group speed
m/s
$z_0$
z_0
Maximum wave height
m
$c_p$
c_p
Phase speed
m/s
$\pi$
pi
Pi
rad
$\lambda$
lambda
Wave length
m


First, select the equation: to , then, select the variable: to

Calculations

Symbol
Equation
Solved
Translated

Calculations

Symbol
Equation
Solved
Translated

Variable Given Calculate Target : Equation To be used


Equation

#
Equation

$ c_g =\displaystyle\frac{ c_p }{2}\left(1 + \displaystyle\frac{2 k h }{\sinh(2 k h )}\right)$

c_g = c_p*(1 + 2* k * h / sinh( 2 * k * h ))/2


$ c_p =\sqrt{\displaystyle\frac{ g }{ k } \tanh( k h )}$

c_p =sqrt( g * tanh( k * h ) / k )


$ k =\displaystyle\frac{2 \pi }{ \lambda }$

k = 2* pi / lambda


$ \omega = \displaystyle\frac{2 \pi }{ T }$

omega = 2* pi / T


$ z ( x , t ) = z_0 sin( k x - \omega t )$

z_xt = z_0 *sin( k * x - omega * t )

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Wave description

Equation

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A wave can be approximately described as a sinusoidal function depending on the variables the position ($x$) and the time ($t$).

The function incorporates the values of the wave height ($z$) at each point, as well as the maximum wave height ($z_0$), the wave vector ($k$), and the frecuencia angular ($\omega$):

$ z ( x , t ) = z_0 sin( k x - \omega t )$

$\omega$
Frecuencia angular
$rad/s$
9454
$z_0$
Maximum wave height
$m$
9462
$x$
Position
$m$
9451
$t$
Time
$s$
9450
$z$
Wave height
$m$
9452
$k$
Wave vector
$1/m$
9453

ID:(12307, 0)



Wave vector

Equation

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The wave vector ($k$) is with the wave length ($\lambda$) equal to:

$ k =\displaystyle\frac{2 \pi }{ \lambda }$

$\pi$
Pi
3.1415927
$rad$
5057
$\lambda$
Wave length
$m$
9455
$k$
Wave vector
$1/m$
9453

ID:(12309, 0)



Angular frequency

Equation

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The angular frequency ($\omega$) is with the period ($T$) equal to

$ \omega = \displaystyle\frac{2 \pi }{ T }$

$\omega$
Angular frequency
$rad/s$
9010
$T$
Period
$s$
5078
$\pi$
Pi
3.1415927
$rad$
5057

ID:(12335, 0)



Wave phase velocity

Equation

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The phase speed ($c_p$) corresponds to the speed at which each wave crest moves, which can be determined using the values the ocean depth ($h$), the wave length ($\lambda$), and the gravitational Acceleration ($g$). The speed the phase speed ($c_p$) is calculated as follows:

$ c_p =\sqrt{\displaystyle\frac{ g }{ k } \tanh( k h )}$

$g$
Gravitational Acceleration
9.8
$m/s^2$
5310
$h$
Ocean depth
$m$
9459
$c_p$
Phase speed
$m/s$
9460
$k$
Wave vector
$1/m$
9453

ID:(12305, 0)



Wave group velocity

Equation

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The group speed ($c_g$) is calculated using the values of the wave vector ($k$), the ocean depth ($h$), and the gravitational Acceleration ($g$) as follows:

$ c_g =\displaystyle\frac{ c_p }{2}\left(1 + \displaystyle\frac{2 k h }{\sinh(2 k h )}\right)$

$c_g$
Group speed
$m/s$
9461
$h$
Ocean depth
$m$
9459
$c_p$
Phase speed
$m/s$
9460
$k$
Wave vector
$1/m$
9453

ID:(12304, 0)