Flexcom > Data Inputs > $LOAD CASE

Purpose

To specify Dean’s Stream regular wave loading.

Theory

Refer to Deans Stream Wave for further information on this feature.

Keyword Format

Blocks of lines which define the wave loading parameters.

Block defining a Dean’s Stream Function wave:

[OPTION=SUPERPOSE]

Wave Height, Wave Period [, Direction] [, Eulerian Current Velocity] [, Order of Expansion] [, Max Iterations] [,

Number of Ramp Steps] [, Equivalent Airy Wave Amplitude] [, Equivalent Airy Wave Period]

A non-zero Equivalent Airy Wave Period with no Equivalent Airy Wave Amplitude (or an amplitude of 0) is invalid. Order of Expansion, Max Iterations and Number of Ramp Steps default to 15, 100 and 5, respectively.

Table Input

Dean's Stream - Multiple Order

Input:	Description
Wave Height:	The Dean’s Stream wave height (crest to trough).
Wave Period:	The Dean’s Stream wave period.
Direction:	The wave direction, measured anti-clockwise from the global-Y direction. All waves in Flexcom emanate from the origin. The default direction is 0°.
Eulerian Current Velocity:	The velocity of the underlying current. This value defaults to 0. See Note (b).
Order of Expansion:	The order of expansion of the Dean’s Stream Function equations which defines the wave. This value defaults to 15. See Note (c).
Max Iterations:	The maximum number of iterations to be used in solving the Dean’s Stream function equations. This value defaults to 100.
Number of Ramp Steps:	The number of ramp steps over which the wave height is applied. This value defaults to 5. See Note (d).

Dean's Stream - Equivalent Airy

Input:	Description
Wave Height:	The Dean’s Stream wave height (crest to trough).
Wave Period:	The Dean’s Stream wave period.
Direction:	The wave direction, measured anti-clockwise from the global-Y direction. All waves in Flexcom emanate from the origin. The default direction is 0°.
Eulerian Current Velocity:	The velocity of the underlying current. This value defaults to 0. See Note (b).
Order of Expansion:	The order of expansion of the Dean’s Stream Function equations which defines the wave. This value defaults to 15. See Note (c).
Max Iterations:	The maximum number of iterations to be used in solving the Dean’s Stream function equations. This value defaults to 100.
Number of Ramp Steps:	The number of ramp steps over which the wave height is applied. This value defaults to 5. See Note (d).
Equivalent Airy Wave Amplitude:	The amplitude of an Airy wave used to determine vessel response to the Dean’s Stream wave. The default value is 0. See Note (e).
Equivalent Airy Wave Period:	The period of the Airy wave used to determine vessel response to the Dean’s Stream wave, if this feature is used. The default is the Dean’s Stream wave period. See Note (e).

Dean's Stream - Superposition of Harmonics

Input:	Description
Wave Height:	The Dean’s Stream wave height (crest to trough).
Wave Period:	The Dean’s Stream wave period.
Direction:	The wave direction, measured anti-clockwise from the global-Y direction. All waves in Flexcom emanate from the origin. The default direction is 0°.
Eulerian Current Velocity:	The velocity of the underlying current. This value defaults to 0. See Note (b).
Order of Expansion:	The order of expansion of the Dean’s Stream Function equations which defines the wave. This value defaults to 15. See Note (c).
Max Iterations:	The maximum number of iterations to be used in solving the Dean’s Stream function equations. This value defaults to 100.
Number of Ramp Steps:	The number of ramp steps over which the wave height is applied. This value defaults to 5. See Note (d).

Notes

(a)If your analysis includes vessel response to a Dean’s Stream wave:

•Using the Multiple Order option means that the order of the response will be the same as the order of expansion of the Dean’s Stream Function.

•Using the Equivalent Airy option means that the response will be first order (sinusoidal).

•Using the Superposition of Harmonics option means that that response will be calculated as a superposition of N individual components, where N is the order of expansion of the Dean’s Stream function.

(b)The Eulerian current velocity corresponds to the current recorded by a stationary meter. The principal consequence of an underlying current is a Doppler shift of the apparent wave period.

(c)The order of expansion of the Dean’s stream function is essentially a measure of how non-linear a wave is. In deep water the order can be relatively low (between 3 and 5), while in shallow water the order can be as high as 30.

(d)The Fourier theory formulations used by Flexcom to solve the Dean’s Stream function equation can occasionally lead to multicrested solutions, particularly in shallow water. In order to eliminate this, the wave height is gradually increased to the required height in the number of ramp steps specified.

(e)You can specify an equivalent Airy wave amplitude without inputting a corresponding period, in which case the Dean’s Stream wave period is used by default. Specification of an Airy wave period without a corresponding wave amplitude is invalid. Of course, if an analysis does not include vessel response to waves, equivalent Airy wave parameters are immaterial and unused.