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Cable Analysis on a Draped Feature

Updated August 14, 2020

This article applies to:
  • Terrain Forestry
  • RoadEng Forestry

Once the desired equipment and logging system parameters have been entered (see article here) you may start analyzing various cable roads for deflection, clearance, load, and tensions.  In the following example you will analyze the deflection of a predefined cable road using the previously defined equipment and logging system. 

Files for this tutorial section on cable analysis can be downloaded here: Cable

  • File | Open <Terrain>\Cable\CableAnalysis-1.terx.
  • Select the feature named Deflection1-0 by clicking with the selection cursor or by using the Select - By name function found in the Home ribbon.

The Profile window has been set up to display this draped feature (see the Properties Panel); the ground profile is defined by the surface model.

  • Select the Cable-Analysis tab in the ribbon bar, then click on the New buttonThe D-line System dialogue box shown below will appear.

Cable 13-7.png

Note: The cable 13-icon2.png New, cable 13-icon4.png Edit and cable 13-icon3.png Delete buttons in the Cable-Analysis ribbon operate on the selected features.

  • Press the Calculation Parameters button to open the D-Line Calculation Options dialogue box.
  • Change the parameters to match those shown in figure below (Simple third point, 8% Deflection) then press OK to return to the previous dialogue box.

Cable 13-8.png

  • In the D-line System dialogue box, change the parameters to those shown in Figure below:
    • Select the correct Logging System.
    • Set Head Spar to use Start of feature.
    • Set Haulback Block to use End.
    • Set Haulback Block Height to 4.0
    • Press OK.

Cable 13-9.png ​​​​

Note:  In the D-Line System dialogue box, the location and height of the Head Spar, Haulback Block, and, if applicable, Skyline Tail Spar can be customized.

With the Start box checked in the Head Spar (Landing) section, the yarder will be placed at the start of the selected feature (usually station 0).  Uncheck the Start box to specify the station explicitly.  The Cut Depth value can be used to account for earthworks at the landing; use a negative value when fill has raised the landing elevation above the profile.

With the End box checked in the Haulback Block section, the block will be placed at the end of the selected feature.  Uncheck the End box to specify the station explicitly.  Alternatively, you can press the Auto-calc Tail Station button and the haulback block Station will be set to the furthest position where the deflection line clears the ground (clearance can be set by pushing the associated  button).  The haulback block Height can also be specified.

The Skyline Tail Spar parameters are configured in the same manner as the Haulback Block parameters.

In both the plan and profile view, a D-line is shown that does not clear the reference surface as it first contacts the ground near station 0+065.  This ground interference is shown as intersecting lines in the profile view and by the change from a green to red in the plan view as shown in Figure below.

Cable 13-10.png

  • To modify the displayed D-Line configuration press cable 13-icon4.pngEdit in the Cable-Analysis ribbon. 
  • In the D-Line System dialogue box, press Auto-calc Tail Station to set the haulback block at the furthest station where the deflection line clears the ground.  Then press OK

The resulting view in the main screen should be similar to the image in figure below.

Cable 13-11.png

It is possible to move or duplicate the feature in the Plan window to examine the deflection at other locations.

  • Optional: Move the end points of the Deflection1-0 feature and notice how the Profile updates to show the new ground profile.

    • Press cable 13-icon4.png Edit in the Cable-Analysis ribbon.
    • Press Auto-calc Tail Station.
    • Press OK to see the new tail position. ​​

Note:  The example above uses simple third point deflection to approximate cable deflection, but 3 other analysis methods are available for cable analysis in the software.  The functionality of the four methods is summarized below:

Maximum Flying Load Given Clearance

You define the carriage clearance from ground (which defines the deflection at each calculation point) and the computer calculates the maximum load that can be lifted at each point. The load is limited by the working tensions in the cables.

This analysis shows the largest payload that can be lifted to a given height above ground. Although a large load may be lifted near the tail hold, it may not be possible to transport it back to the landing.

Note that no load can be lifted above the tight skyline position (chord) so some points may be impossible to calculate and will be left out of the results.

Minimum Deflection Given Load

You define the load and the computer finds the minimum deflection possible to lift the load without exceeding the working tensions of the cables.

This analysis is used to simulate the transport of the load to the landing when the skyline or haulback is dynamically adjusted; appropriate for a running skyline. The carriage location shows the maximum possible clearance.

Deflection for Fixed Skyline Given Load

You specify the midspan deflection and load, the computer calculates the cable tensions and actual deflection for all the calculation points. Cables are allowed to exceed their working tensions.

This analysis is used to simulate the transport of the load to the landing when the skyline is fixed. The carriage location information shown in the Profile window is similar to the results of a chain and board analysis.

Simple Third Point Deflection

A specified deflection is applied at the two third points on the proposed D-Line to produce a simple geometric representation of the system.  There is no calculation of tensions or loads.

  • Optional: Experiment with some of the other calculation types:
    • Press cable 13-icon4.png Edit in the Cable-Analysis ribbon.
    • Press the Calculation Parameters button.
    • Set a Type of analysis and modify parameters of interest.
    • Press OK to see the new calculation.
  • Choose File | New, do not save changes.