# Sea

The Sea part deals with all environmental conditions associated to the sea. The following parameters can be adjusted.

## Water

### Density scheme

The density scheme enables you to choose how the water density is defined.

Options:

Ref. value (default):

The ASHES reference value for seawater density is used (i.e. seawater at 10C, at the surface, and 3.5 pro salinity, 1026.9 kg/m^3).

User defined:

The density of the water is set by you.

From temperature and salinity:

The value is calculated based a temperature and salinity given by you.

### Seawater density

Density of seawater.

• Default value: 1026.96
• Unit: ${\text{kg}} \over {\text{m}^3}$
• Range: 0 — 10000

### Viscosity scheme

The dynamic viscosity can be found in three different ways. The dynamic viscosity is primarily used to calculate Reynolds number. The kinematic viscosity is the ratio of dynamic viscosity and density.

Options:

Ref. value (default):

The ASHES reference value for dynamic viscosity is used (i.e. seawater at 10C, salinity 3.5%) - 1.386E-3 kg/(s m)

User defined:

You set the value.

From temperature and salinity:

The value is calculated based a temperature and salinity given by you.

### Dynamic viscosity (of seawater)

Dynamic viscosity of seawater.

• Default value: 0.001386
• Unit: ${\text{kg}} \over {\text{m}^3}$
• Range: 0.0001 — 0.01

### Temperature

The temperature of seawater. Temperature is used to calculate density and/or dynamic viscosity if From temperature and salinity is chosen as the repective schemes.

• Default value: 10
• Unit: $°\text{C}$
• Range: -10 — 50

### Salinity

The salinity of seawater. Salinity is used to calculate density and/or dynamic viscosity if From temperature and salinity is chosen as the repective schemes.

Tha average salinity of the worlds oceans is 3.5% = 35g/kg.

• Default value: 3.5
• Unit: $\text{%}$
• Range: -1e+07 — 1e+08

## MSL and Tides

### Mean sea level (MSL)

This value decides how the MSL is relative to the (global) coordinate system origo in ASHES. This value is typically zero. Must be seen in combination with how Seabed: Depth and Sea: Tidal level are set.

One use case for setting MSL different from zero is if you want to use the seabed depth from nautical charts directly. Nautical charts usually DON'T use MSL as the reference point, but rather a lower point such as lower astronomical tide (LAT) (see Tide and Nautical chart).

• Default value: 0
• Unit: $\text{m}$
• Range: -100 — 100

### Tidal level

The sea level relative to MSL. The cause of the difference is typically tides, although the sea level difference from mean sea level can have any origin.

MSL is Mean sea level. The Tidal level is used when finding the Still water level - STL.

Note: The Tidal level does not influencethe level of (marine) growth (see e.g. Monopile).

• Default value: 0
• Unit: $\text{m}$
• Range: -100 — 100

## Waves

### Type

Waves can be modelled in four different ways.

An overview of the different types is given below. For more information about the different types of waves, see the corresponding section of the user manual:

Live

Regular

Irregular-Single spectrum

Irregular-Double spectrum

Options:

Live (default):

The waves are controlled by you and can be changed during the simulation. Only 2D regular waves can be simulated live

Regular:

One regular wave

Irregular - single spectrum:

Wave situation corresponding to a linear combination of regular waves, following the JONSWAP spectrum

Irregular - double spectra:

Combination of 2 JONSWAP spectra. Typically used to model a wave situation that is a combination of wind sea and swell.

Stream function:

Based on stream function theory.

## Wave kinematics

### Kinematic stretching

The Airy theory in its basic form says that the water particle kinematics are applied to the mean water surface not taking wave elevation into account. With this parameter different algorithms to modify kinematics due to wave elevation can be chosen.

Options:

None (default):

Airy theory is applied in its basic form, i.e. no modification due to wave elevation.

Wheeler:

Kinematics are stretched according to Wheeler's algorithm.

### Surface ramp-down

The wave kinematics in the surface zone can be ramped down in order to 1) Improve numerical stability, and/or 2) Better reflect physics/measurments as the max kinematic values typically occur a distance under the surface (and not exactly in the surface as predicted by linear theory).

Options:

None (default):

Linear wave kinematics is applied in its basic form, i.e. no modification.

Linear:

The maximum values of kinematics is found as usual at a given distance below the wave surface. Instead of continued (exponential) increase to the surface, the kinematic (velocity or acceleration) is assumed to decrease linearly to zero at the surface. If this option is chosen, then the distance of max kinematics must be given.

### Surface ramp-down factor

When Surface ramp-down above is set to Linear, then this factor must be set. It is used to calculate the depth below the surface where wave kinematics maximums are assumed to occur. The depth is found as the factor times the amplitude of the wave (component). The minimum value is 0 which implies no ramp-down. The default value is 0.25.

• Default value: 0.25
• Unit:
• Range: 0 — 10

### Depth approximation

Approximate wave kinemetics is applied for deep water if this parameter is set to Deep water. If it is set to None then the full expressions (i.e. for intermediate depths) are always used, even for deep water. Default: Deep water.

Options:

None:

No approximation applied for wave kinematics (even not for deep waters).

Deep water (default):

Approximate wave kinematics are applied for deep waters, i.e. seabed depth greater than half the wave length. For smaller seabed depths, the full formulations (no approximation) are used.

## Currents

### Type

This parameter gives you the option to simulate currents. Currents are water particles moving at a constant velocity (in time). A vertical variation can be applied.

Options:

None (default):

No current.

1 currents:

Currents are simulated with one currents.

2 currents:

Currents are simulated with two independent currents. This can e.g. be wind and tidal currents.

## Current kinematics

### Kinematic stretching

With this parameter different algorithms to modify the kinematics of the currents due to wave elevation can be chosen - as is the case for waves.

Options:

None (default):

No modification due to wave elevation.

Wheeler stretching:

Kinematics are stretched according to Wheeler's algorithm.