*Flexjoint
To define flex joint elements in the structural discretisation.
Refer to Hinge and Flex Joints for further information on this feature.
A block of lines, the first three of which define (i) the flex joint element or element set, (ii) the weights in air and water of the flex joint, and (iii) the flex joint type. The format of subsequent lines depends on whether the flex joint is linear or non-linear.
Lines defining the flex joint element or element set, the weights in air and water of the flex joint and the flex joint type:
[ELEMENT=Element (Number or Label)] or [SET=Element Set]
Weight in Water, Weight in Air
TYPE=Flex Joint Type
For linear flex joints, the next line simply specifies the rotational stiffness of the flex joint:
Stiffness
For non-linear flex joints, the following lines are used to define a moment-angle curve for the flex joint, with each line defining a single moment-angle data pair:
Moment, Angle
This line may be repeated as often as necessary to fully define the moment-angle curve.
You must specify either one of ELEMENT=Element (Number or Label) or SET=Element Set. The weight in air of the flex joint must be greater than or equal to the weight in water of the flex joint. At least two moment-angle data points must be specified for non-linear flex joints. Flex Joint Type may be either LINEAR or NONLINEAR. If you specify an element label rather than an element number, it must be enclosed in {} brackets.
Input: |
Description |
Element Set/Element: |
The element set or the element (number or label) to which the flex joint properties are being assigned. If you specify an element label rather than an element number, it must be enclosed in {} brackets. |
Weight in Water: |
The total weight in water of the flex joint. This entry is optional, and defaults to 0. |
Weight in Air: |
The total weight in air of the flex joint. This entry is optional, and defaults to 0. |
Rotational Stiffness: |
The rotational stiffness of the flex element or the name of a moment-angle curve which defines the rotational stiffness. |
(a)Flex joints are classified as being linear or non-linear. Linear flex joints are characterised by a (non-zero) rotational stiffness, while the behaviour of non-linear flex joints is defined in terms of a moment-angle curve.
(b)You can assign flex joint properties to a single element or a set of elements defined in the usual way. In the former case you input a number in Column 1, in the latter case you specify the name of the element set.
(c)If a non-linear material curve name is specified for the rotational stiffness, then the non-linear moment-angle curve must be defined in the Moment Angle Curve table.
(d)The units for rotational stiffness are moment/degree.
Input: |
Description |
Curve Name: |
The generic name of the moment-angle curve. |
Moment: |
A moment value for a point on the curve. |
Angle: |
The corresponding angle value (in degrees). |
(a)This table is used to define moment-angle curves that define the behaviour of non-linear flex joints for a particular flex joint element or set of flex joint elements. Moment-angle curves are assigned to flex joint elements using the Define Flex Joints table.
(b)Use as many lines as you need to completely define a particular moment-angle curve. Simply leave Column 1 blank for second and subsequent lines. For subsequent moment-angle curves, put the curve name in Column 1 and specify the moment-angle data in the same way.
(c)The points defining the non-linear moment-angle curve may be specified in any order. Flexcom subsequently sorts the data pairs into ascending order of strain.
(d)If the rotation of the non-linear flex joint element lies between the specified moment-angle data points, Flexcom uses linear interpolation to determine the relevant rotational stiffness of the element.
(e)If the rotation of the non-linear flex joint element lies outside the specified range of the moment-angle curve, then Flexcom simply extrapolates from the first or last section of the curve as appropriate.
(f)If none of the specified angle terms have a negative value, the curve is assumed to be symmetrical about the origin (i.e. the behaviour of the flex joint is the same for both positive and negative strains).