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Spring variable length

Where the properties of the spring element are not static, but vary with time, this tab permits the definition of how the properties change. A typical application of this variation is a winch, and hence it is termed 'simple winch option'. When the tick-box is ticked, the editing options become available.

Simple winch option : ticking this box allows to simulate a simple winch by varying the reference length of the spring as a function of static steps or time.

There are two further options:

• Static: If the tick-box 'Length variation (from static step0) is ticked, the 'edit' button becomes active. Clicking this opens a file open dialogue, which allows you to select a text file, as defined below.

• Dynamic: two options are available in terms of the pay-out speed of the winch - constant speed or time-dependent. These options are selected by radio buttons, as described below.

Variable spring length within static analysis

Change in reference length can be defined as a function of Static analysis steps by activating the checkbox labelled Length variation (from step 0) and pressing the Edit button to point on the text file that contains the relationship between static step number and reference length change.

The file format is illustrated below:

Example 1	0 0.00 1 0.50 2 1.00 10 5.00	The reference length is increased by * +0.50 from step 0 to step 1 * +0.50 from step 1 to step 2 * +4.00 from step 2 to step 10
Example 2	0 0.00 10 -10.00	The reference length is decreased by * -10.00 from step 0 to step 10
Example 3	0 0.00 10 10.00 20 0.00 30 -5.00	The reference length is varied by * +10.00 from step 0 to step 10 * -10.00 from step 10 to step 2 * -5.00 from step 20 to step 30

Variable spring length within dynamic (time-domain) analysis

Change in reference length can be defined as a function of time for time- domain dynamic analysis by selecting either Constant speed or Time-dependent option in the Dynamic frame. You may either specify constant velocity rates (in m/s) or variable velocity rates (in m/s) in a text file. The velocity indicates the pay-out or pull-in rate.

• Constant speed: If this is the preferred option, click the radio button 'on' and enter a value for the 'Length increase or decrease speed' in m/s.

• Time dependent: If this is the chosen option, click the radio button 'on' and click the edit button - this opens a file opening dialogue which allows you to select a text file defining the profile of winch speed against time.

The file format is illustrated below:

Example 1	0.00 0.0 20.00 10.0 40.00 0.0	The reference length is increased by * +10.0m from time 0s to 20s * -10.0m from time 20s to 40s The reference length will remain constant after 40s.
Example 2	0.00 0.00 30.00 -15.00	The reference length is decreased by * -15.0m from time 0s to 30s The reference length will remain constant after 30s.