How-to Rock Dumping

This How-to describes how to set up Qinsy for rock dumping operations.
Some settings like the definition of the dump bays and the dump shapes are defined in Database Setup.
Other parameters can be entered online in the Session Setup Dredging pages.

On this page:

Database Setup

Prior to defining a Dredging System the observations that support the dredging system should be defined (usually part of a Dredging Sensor system type).
For example the dredging status (e.g. dumping/dredging/sailing loaded), current measurement, open/close bay door observation, etc.
Note that this is optional, all the values can also be entered/overruled online.

Add a new Dredging Sensor system for status and/or open/close sensors:

The current measurement can be defined with a miscellaneous system. If this is not set up, you can enter a manual value Online in the Session Setup.
Add an observation for velocity and one for direction:

Define a new Dredger System. Set Type to “Rock Dumper”.
If you have interfaced to a dredging computer then select the specific "Status" observation.
If you operate only manually then select “Not Used”:

On the next page the optional current observations and the bays are defined:

The Current observations can be used to calculate the settling location of the dumped material.
The observations can be left at “Not Used” when only manual input of the current is required.

Define the number of bays.
Every bay is represented by a node position, width and height.
Select the respective node offset. This node represents the center of the bay.
The height of the node is also important: it is used for the fall height calculation.

Optionally a closed/open sensor can be defined.
Note that online one can manually enter/overwrite the state of the bay doors.

The dump shape represents how the dumped material will be visualized on the seafloor.
Three options are available:

• Rectangular - The volume will be divided equally over the bay area.
• Heap - The volume is divided in a spherical shape. Cells in the center get the most volume and at the edge the least.
• Triangular - The volume is divided over the bay in a triangular shape.

Save the Template and start the Controller.

Online - Controller

The dredging setup can be found in the Session Setup - Dredging pages.

For rock dumping the pages Design, Production and Dumping are relevant.

Design

The design height is relevant to calculate the dynamic settling location. Select your reference here, this reference will be used to calculate the dynamic settling location.

In the above example, the Grid file is selected. However, there are other options:

• Manual height
• Design File - *.qgfdesign
• Terramodel File - old *.pro format

Production

Enter the Water density. This is used to determine the relative material density.

For dumping, the trip volumes should be defined. A trip volume is the volume of the material currently in the bay.
Different trip volume mode options exist:

• Manual - total Value - One value is entered that will be spread equally among the bays.
• Manual - per bay - Specify the volume per bay.
• Automatic - Only relevant when TDS sensor or production sensors are defined. Volume is taken from the sensor.

Dumping

Material

Select the properties of the material that will be dumped:

Drag Along and Drag Across coefficients are used in determining the dynamic settling location of the dump.
Set to 1 if unknown. The user can empirically determine these coefficients by comparing the actual (surveyed) dump position versus the theoretical position.

The densities should be absolute. The relative density is derived by subtracting the water density.

In Situ Density - Density of the material once suspended in water. This occurs when the material is dumped.

Solid Density - Density of the dry material.

By default keep values equal. If In Situ Density is smaller than Solid Density then the volume used to update the sounding grid will be larger than the entered trip volume.

Dumping

Load Discharge setup:

• By Time - The current bay volume will be dumped in a fixed number of seconds despite the current trip volume.
• By Rate - The current bay volume will be dumped with a user defined volume per second. The time it takes to discharge a bay depends on the bay volume.

Bay Opened/Closed:

The user can disable bays here. Bays that are disabled will not take part in the dumping process.
The user can define if the bay door is opened or closed.
If a bay door sensor is interfaced then only Automatic or Disabled can be selected.

Current measurement

If a sensor is interfaced you can select it here or you can select Manual Input and enter the figures.
Note the current direction that is expected is the true direction.
Velocity in survey units/sec.

Current Reference

• Relative - When the sensor is mounted on the vessel. The COG and SOG are incorporated in the velocity measurement so ignored in the calculation.
• Absolute - When an external current measurement is used, for instance a sensor on a buoy or a radar. In that case the own vessel COG and SOG are taken into account.

For an explanation of all the available Dredging options and settings, use the F1 inline Help.

Navigation display

The Navigation Display can show the actual bay location on the dredger and whether it is opened or closed.
For an opened bay a cross is drawn through it:

In order to activate the dredge bay and settling location open the View Properties dialog Objects:

Note: only enabled bays are drawn. Every bay can be switched on and off in the Controller's Session Setup.

Dumping action in sounding grid

The Controller must be recording to be able to activate this option.

The grid must be filled. If no pre-survey was carried out the grid cells can be set to zero with the Sounding Grid Utility.

Dumping is carried out when…

A)    A dredging status observation was selected and the state changes to dumping and the doors are open.

B)    The doors are opened during the dumping state.

C)    No status observation is defined and a bay door is opened.

The trip volume is transferred to the Grid. The volume is expanded with the factor Density Solid/ Density In-Situ.

The grid is updated with the dumped material at the bay settling location.

Calculating the dynamic settling location

Currently, to determine the fall height the bay center position is used to look up a DTM height or manual height.
Together with the center bay node height this determines the fall height. The formula is used to obtain displacements.
By adding the displacements in across and along position to the bay center position one can calculate the settling location. 

Offset - fall height * (coefficient of resistance * current speed) / sqrt (relative density * gravity * char diameter)

The formula uses relative density. This is obtained by subtracting the water density from the solid density. The water density can be entered in the product page.