Trailing Suction Hopper Dredger (TSHD) - Object Definitions

This section describes how to define the objects typically used for Trailing Suction Hopper Dredgers (TSHD).
It assumes you have already created a template database and defined the survey geodetics.

On this page:

TSHD Object Definitions

Vessel (dredger) definition

Create a new vessel shape by selecting “Edit” from the menu bar and then “New” and “Object”,

or by right clicking on the tree item 'Object' and selecting 'New Object'.

The following dialog appears:

Select “Vessel” as object type

Enter a name for the vessel shape

Select “Next” twice, the following dialog will appear.

Initially the main window is empty. Click on

to create a new shape definition.

The following dialog pops up:

Use the

button to import an existing vessel shape stored in one of these formats:

Note that 'Shape' file refers to the file that is made in QINSy when a vessel shape is exported.

Clicking on 'Generate' creates a simple vessel shape, not normally suitable for dredging purposes.
Please refer to Database Setup Help pages for assistance in importing existing vessel shapes.

Initially this dialog is empty. Click on

to create a new polygon.

Clicking on

creates a vertex point for the polygon.

Add coordinates for each vertex point created.

A local XYZ coordinate system is used based on the vessel reference point. Define shape, color and fill.
When creating polygons start with one point and then add points in a sequence proceeding around the perimeter in one direction only, i.e. clockwise or anti-clockwise.

Note that a 'Top View' is being created. You can also add profile views from starboard and aft.

Once the initial vessel shape is complete click on

to create additional polygons.

The following dialog shows a complete top view.

If one shape lies inside the perimeter of a second shape, alter the order of the polygons listed on the left. For example, in the picture above, polygon #21 (red fill) lies partially within polygon #20 (white fill). If the order were reversed all of the red filled polygon would not be visible (see below). Polygon #1 is the base; any additional polygons fall on top of polygon #1.
Highlighting a polygon on the left results in its vertices being shown on the right.
The vertex highlighted on the right is colored magenta in the graphic pane.

Switch to Starboard view mode and create a profile view of the dredger.

Switch to

to create a cross profile view of the dredger.

1000 vertices are available, shared between top, starboard and aft views.

Click OK to finish and return to the Object Shape dialog.

It is recommended to export the defined vessel shape.

Click on Finish to exit the Object Shape wizard.

Add variable nodes to this object. Useful nodes are:

the position of each system sensor (e.g. GNSS antennas), position of winches and/or fairleads, and inlets.

To add nodes right click on the tree item 'Variable Node' and select New Node to create another node, e.g.

Enter a node name, the object on which the node is located and the offset values FROM the object reference point TO the new node location.

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Trailing Suction Arm Definition

Upper Pipe

In order to visualize the suction pipes moving relative to the dredger, define a 'pipe' object.

Right click on the tree item 'Object' and select 'New Object'.

This opens the Object Definition wizard again. Since this is a second independent object, the initial dialog is empty.

Select object type 'Vessel' or 'Survey Vessel', either of which can be used for any generic object.

Specify a name for the object.

Select “Next” twice to open the Object Shape dialog.

Follow the directions from Step

through

and define a shape for the starboard upper suction pipe using top, starboard and aft aspects.
Your results should look something like this, or be more elaborate:

At this stage it is useful to add Variable Nodes for the Starboard (SB) Upper Pipe object.

Right click on the tree item 'Variable Node' and select 'New Node'.

Type in a name, select the object on which the node is located and enter the offsets FROM the object reference point TO the new node location.
Add any other variable nodes that are useful. At a minimum add nodes for:

- the center of the pipe elbow where it connects to the inlet.
- The center of the other end of the pipe where it connects to the lower suction pipe.

When there are two trailing arms, export the shape just defined for the starboard side.
Create a new object for the port side and import the starboard shape.
The elbow points in the opposite direction so change the signs for all the X offset values.

Lower Pipe

Repeat the process to define a shape for the starboard and port lower pipes:

Add a variable node at the lower end of the pipe to use as a connection link to the starboard dredge head.

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Dredge Head - Wizard Page 1

Right click on the tree item 'Object' and select 'New Object'. This opens the Object Definition wizard again. Since this is another independent object, the initial dialog is empty.
Unlike the previous objects all defined as 'vessels', a dredge head is of type 'Dredging Tool'.

Select object type 'Dredging Tool'.

Specify a name for the object.

Select “Next”, the following dialog will appear.

Dredge Head - Wizard Page 2

On this page a model of the dredge head can be created. The model is based on a spreadsheet. Overall width and length define the size of the dredgehead, and every cell represents a dredge head height from the base of the head, typically zero.
The number of rows and columns (M, N), cell height and width are user-selectable, M and N must be odd. Cells can also be excluded from the model when footprint is not a square but, for example, oval shaped.

A rectangular grid is defined by:

Entering the overall width and length of the tool, thereby creating a rectangle.

Entering the number of Columns and Rows which divide the rectangle into cells, the length and width of which can be queried by clicking on the 'Info' button.

This results in the creation of an empty spreadsheet. The more columns and rows the more detailed the model will be.

When determining the number of rows and columns of the matrix, take into consideration the required accuracy, sounding grid cell size and available PC power. Every matrix cell will represent a sounding so the more cells, the more CPU load it will take to process the soundings and the higher the accuracy.
However the most important factor is the cell size of the sounding grid you wish to update. If the size is 0.5 by 0.5 units then choose a dredge head model cell size of at least 2 times smaller. This will guarantee that every grid cell is hit by the model’s sounding with every possible dredger heading.

The center cell of the grid becomes the reference point that is linked elsewhere to a defined variable node.

The objective is to enter a height into each cell that represents the distance above (+ve) or below (-ve) the reference point.

Clicking on 'Default' is a shortcut to automatically fill the cells with height values.

The following dialog pops up:

Select the basic shape of the dredge head you need; typically a rectangle for a dredge head.

Enter the maximum Z value. This is the distance from the reference node of the head to the cells representing the suction plane.

Rotate Shape by 90 degrees is only available for the Triangle Wedged shape to let it face the right direction.

After pressing OK the Object-Dredge Head Model dialog is updated:

Cells shown in red are disabled, do not have a height value and are not used in the excavated volume computation.
Cells shown in white are enabled. Each has a height value referenced to the reference node of the cutter head. All enabled cells are actively used in the excavated volume computation.

The cell shown in green represents the center of the model.

The following options are available:

Import - two formats supported as illustrated above.

Info - provides overall information about the model.

Cell - provides some information about the cell which was clicked on and the option to disable the cell by selecting 'Exclude from calculation' under Status.

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Dredge Head - Wizard Page 3

Initially the Object Shape dialog is empty.
Click on

to open the Edit Object Shape dialog.

Follow the same procedure described above to define the dredge head shape in top, starboard and aft views.

Importing Dredge Head Model

From Mapping File

Using the Line Database Manager

create a shape definition as follows:

These numbers create a shape like this:

When defining the Dredging Tool object, import this PRO file as follows:

Enter a description.

Determine the number of cells by entering values for width and length.

Remember the more cells defined the more accurate is the updating of the sounding grid but at the expense of CPU power.

Enter the size of the dredge head in terms of length and width.

These numbers divided by the number of rows and columns determines the cell size.

Click on the Import button and select From Mapping File. This opens the Import dialog:

Use the browse button

to find the correct PRO file to import.

Select the layer on which the design model is stored.

Select the polyline that represents the boundary around the design.

This line can share the same extents as the design model or can be a little larger.

In case the orientation of the model is not reflective of the actual orientation of the dredge head on the ground, it can be rotated: 0, 90, 180 or 270.

A part of the dredge head model can be imported rather than the whole thing.

In our example the height is -4.00m. Setting the Reference Height to -1.00m yields this result for the height at the reference point of the model:

Setting a fill percentage is an alternative way of importing less than the full object.

For example, entering 70% yields the following result for the height at the model reference point:

Switching Exclude Above Reference Height has this effect:

On the left all the values enclosed in the pink area have positive heights and will be used in the computation of volume, which is probably not wanted.
On the right all cells with positive values are disabled.

Click Import. Results depend on settings as illustrated in

,

and

above.

In the Object Shape dialog select From Dredge Head Model from the Import drop down list.

This opens the Import Vessel Shape from Dredge Head Model dialog:

Select the Object to be imported from the drop down list which contains all the defined Dredging Tool objects.

Select the Dredge Head Node from the drop down list which contains all the variable nodes defined on the object. Usually this will be the cutter CoG.

For a cutter head it is usually necessary to apply a 90 degree pitch offset. The effect is this:

Functionality will be explained in the future.

Functionality will be explained in the future.

Import loads the model as an object shape that can be visualized in Online displays.

From Cutter Definition File

The cutter definition file is a text file containing radial distance vs. height.

For example:

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