Creating and attaching Mid-cable Objects to spans
Learn how to attach mid-cable objects to your spans
Table of Contents
Mid-cable objects are additional objects that can be placed along a cable span to simulate real-world scenarios. In this article, you will learn to create, attach and adjust the properties of mid-cable objects.
Neara supports the modelling of 4 different types of mid-cable objects that attach to a single cable of a span:
- Marker balls,
- Rota markers,
- Vibration dampers, and
- Tiger tails.
You can visualise and perform various dynamic analyses such as Finite Element Analysis (FEA) on constructions with these mid-cable objects attached.
Neara also supports the visualisation of spreaders:
If you are only interested in spreaders, jump to Attaching a mid-cable object below.
Creating a mid-cable object type
To model one of the 4 single cable mid-cable objects, you must first add a new object type entry and specify it's properties.
Click the Library menu from the menubar and select Mid-Cable Objects.
This will open up the Mid-Cable Object Library. You may find it useful to move or dock the panel at the bottom of your workspace.
Create a new entry and in the Type column, choose between marker ball, rota marker, vibration damper and tiger tail. Please see images below for their respective visual representations.
For each mid-cable object type, you can also specify the Key, Length, Mass, Wind Area and Drag Coefficient. The Key is a user-defined name to help you easily identify the each entry you have created, by default it will be called MidCableObjectType1 however, this can be changed by clicking on the cell and updating the name. The Length, Mass, Wind Area and Drag Coefficient are all physical parameters that are taken into account when FEA is performed on constructions with these mid-cable object types attached.
Attaching a mid-cable object
Once you have created a mid-cable object type entry (with the exemption of spreaders, which don't require one), you can place a new mid-cable object of that type onto your desired span. See: Using the Conductor tool to place & configure conductor spans
Ensure you have the Select tool active and click on your span. This will automatically open the Properties panel. You may find it useful to move or dock the panel onto one side of your workspace.
In the Properties panel, navigate to the Spans tab. You will see a section called Mid-cable objects for span. If your span contains multiple sections, you will need to specify the section of the span (i.e. between which two poles) you want to place the mid-cable object using the dropdown menu.
Single cable objects
At the top of the Mid-cable objects for span table, click Add new entry and assign it the type you just created.
You will see the object appear in the middle of the chosen span section on the first cable in the Perspective view. Here you can change the Cable Index to change the cable that it lies on. You can also adjust its position by changing the Position Reference and Position Offset.
Single cable mid-cable objects are accounted for when analysing conductor behaviour including cable sag and blowout, and pole loading using FEA. See: How to set up FEA simulations.
Ensure you select a type when adding a new entry.
Spreaders
At the top of the Spreaders table, click Add new entry.
You will see the spreader appear in the middle of the chosen span section in the Perspective view.
You can adjust its position by changing the Position Reference and Position Offset. Spreaders do not have any physical properties and thus, are not accounted for when FEA is performed.
Analysis methodology
FEA
The mass
, wind area
and drag coefficients
of mid cable objects are combined with those of the cable before analysis in the FEA engine, to determine cable sag and point tip load calculations.
The exception to this are spreaders, which are assumed to have negligible mass
Static analysis
In static analysis, the load of the objects is spread out over the cable as follows:
- The cable mass increases by a uniform mass from all the objects attached to it, and
- The wind area of the objects is incorporated as an increase in the diameter for wind load of the cable.
Example
If we place five 7kg marker balls on a single cable:
The cable mass will increase by 5 ✕ 7kg = 35kg
The wind area will increase as follows:
- Sum of the wind area of all objects, scaling the result by the ratio of the
object type drag coefficient
tocable type drag coefficient
- For example, if the
object drag coefficient
is double that of the cable, then Neara will double the sum of the wind area of all objects
- For example, if the
- Add the scaled value to the
wind area
of the cable
The object drag coefficient
is therefore accounted for in the new wind area, and the drag coefficient
for the cable will remain unchanged.