Flex Joint

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Flex Joint

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Flex Joint components are typically used to specify the properties of flexible or articulated joints connecting pipe sections, cables, or stinger sections. A Flex Joint component is either referenced by a Line component or an Articulated Stinger component.


A flex joint is characterised by wet and dry weights, and must also have an associated rotational stiffness. The stiffness specification can be either linear or non-linear – a Type drop-down list on the Flex Joint component allows you to choose which, with Linear the default.



The Linear Properties – Define dialog for specifying linear Flex Joint properties is illustrated in the figure below. Note that the specification of an actual Rotational Stiffness value for linear flex joints is mandatory.


Linear Flex Joint Properties

Linear Flex Joint Properties




A similar Properties dialog is presented for a non-linear flex joint, except that the Rotational Stiffness slot is now absent. Instead a Curve drop-down list is enabled allowing you to define a non-linear stiffness relationship either using a Manual or Automatic definition. The Manual option allows you to specify the non-linear curve in terms of moment-angle data pairs using the Moment Angles Curves dialog button. The Automatic option allows you to define positive and negative free rotation angle limits using the Rotation Angles dialog button. These limits are then combined with a Boltzmann function to automatically generate a corresponding non-linear moment-angle curve. When you define a non-linear relationship, it is automatically graphed on the right-hand side of the component view, as shown in the example specification of the first figure above. For both linear and non-linear flex joints, the Weight in Air and Weight in Water inputs are mandatory.

Additional articles provide information on the Flex Joint Data Inputs and Flex Joint Best Practice.