Open Cut » Overburden Removal
The need to maintain and increase dragline productivity is widely recognised as a major priority by Australian dragline operators. Bucket performance is critical to dragline productivity. The design and modification of buckets involves complex and often conflicting performance objectives such as payloads, durability, filltime, required drag force and energy, carry stability, dump times and others.
This project aimed to develop a suite of computer tools to aid in the design and optimisation of bucket systems. Specifically the objectives were to develop and calibrate the following software modules:
- 3d Cad Interface for bucket design
- 2.Bucket and rigging model
- Spoil Particle code and CAD interface
- Cycle controller
- Cycle playback and data display module.
Together these modules allow the simulation and assessment of a complete bucket and rigging system.
All modules, with the exception of module 3 have been fully completed and calibrated. The Cad interface allows the rapid generation of complex bucket shapes for simulation. The bucket and rigging model was calibrated against a scale model dragline (1:25 scale) and gave predicted carry angles that were within about 1 degree of observed over a wide range of carry positions.
Development of the Particle Flow Code (PFC) proved to be the most difficult part of the project. It began with the design and implementation of a simulation and graphics framework within which PFC calculations are carried out. The framework resulting from this effort is flexible and extendable. It is based on principles of object-oriented design and programming and written in the C++ programming language.
PFCs of various levels can be incorporated into this framework, leaving the framework unchanged. Three levels of PFCs can be identified
- A PFC based on mono-sized spherical particles.
- A PFC based on spherical particles with a distribution of sizes.
- A PFC based on non-spherical particles with a distribution of sizes and shapes.
Stage 3 and is expected to be the stage necessary for fully quantitative realistic simulations. The work described in this report is based entirely on a Stage 1 PFC. Although significant theoretical work has been done towards implementing a stage 3 PFC, the development of such a PFC was not completed in this project. The existence of this theoretical base will ease further development of the PFC to Stage 3 and allow optimisation of this PFC for speed of calculation.
Although the PFC is not in its fully featured form, the software has shown the capability to realistically model broad trends in bucket and rigging performance such as:
- Buckets tested took between 2.5 and 4 bucket lengths to fill.
- Drag force VS displacement plots displayed very similar form to observed data
- Short wide buckets fill faster than long narrow ones.
- Hard ground in conjunction with a high drag hitch location leads to a forward flipping motion of the dragline bucket.
We believe that this project has produced good evidence as to the applicability of numerical modelling to dragline bucket filling studies. With full development of the PFC the system should establish itself as a powerful tool for dragline bucket optimisation. In addition with the implementation of a more general ground engaging tool interface it should be applicable to other mining equipment.