Thesis (MBA)--Stellenbosch University, 2001. / ENGLISH ABSTRACT: The replacement of earthmoving machines forms a significant portion of the annual capital expenditure on South African mines. The decision on the timing of the replacement varies substantially between different operations, but frequently it is not based on any scientific study or analysis. The reason for this is that most textbooks propose complex calculations for the determination of an optimal replacement point, and subsequently the mathematical effort serves as a deterrent to those who are tasked with replacement evaluation. This study proposed a simple graphic method which is suitable for everyday use, and which can quickly be adapted when conditions change. The model furthermore makes provision for the analysis of the replacement of both the current machines (the so-called defenders) as well as an evaluation of potential replacement machines (the so-called challengers). In addition, the model also makes provision for the incorporation of non-cash factors, such as productivity and reliability. / AFRIKAANSE OPSOMMING: Die jaarlikse vervanging van grondversuiwing masjienerie maak 'n groot deel uit van die kapitaalplan van die meeste Suid-Afrikaanse myne. Die metode van besluitneming oor die presiese tydsberekening van die vervanging verskil ook tussen die verskillende organisasies, maar dit is selde gebaseer op 'n wetenskaplike analiese. Die rede hiervoor is dat die meeste handboeke komplekse wiskunde modelle voorstel vir die berekening van 'n optimate masjien vervangingspunt. The kompleksiteit gee daartoe aan dat baie nie kans sien om dit te probeer doen nie, en gevolging wegskram van enige analise. Hierdie studie projek stel 'n eenvoudige grafiese model voor vir allerdaagse gebruik, wat ook vinning gewysig kan word as toestande verander. The model maak ook voorsiening vir die analise van beide die huidige masjien (die sogenaamde verdediger) se optimale vervangingspunt, sowel as die evaluasie van potentiele nuwe masjiene (die sogenaamde aanvallers.) Die model maak verder ook voorsiening vir faktore wat nie normaalweg in geldwaarde beskryf word nie soos byvoorbeeld produktiwiteit en betroubaarheid.

Indiana University-Purdue University Indianapolis (IUPUI) / In this thesis, a high- fidelity multibody dynamics model of a backhoe for simulating the digging operation is developed using the DIS (Dynamic Interactions Simulator)multibody dynamics software. Sand is used as a sample digging material to illustrate the model. The backhoe components (such as frame, manipulators links,track segments, wheels and sprockets) are modeled as rigid bodies. The geometry of the major moving components of the backhoe is created using the Pro/E solid modeling software. The components of the backhoe are imported to DIS and connected using joints (revolute, cylindrical and prismatic joints). Rotary and linear actuators along with PD (Proportional-Derivative) controllers are used to move and steer the backhoe and to move the backhoes manipulator in the desired trajectory. Sand is modeled using cubic shaped particles that can come into contact with each other, the backhoes bucket and ground. A cubical sand particle contact surface is modeled using eight spheres that are rigidly glued to each other to form a cubical shaped particle, The backhoe and ground surfaces are modeled as polygonal surfaces. A penalty technique is used to impose both joint and normal contact constraints (including track-wheels, track-terrain, bucket-particles and particles-particles contact). An asperity-based friction model is used to model joint and contact friction. A Cartesian Eulerian grid contact search algorithm is used to allow fast contact detection between particles. A recursive bounding box contact search algorithm is used to allow fast contact detection for polygonal contact surfaces and is used to detect contact between: track and ground; track and wheels; bucket and particles; and ground and particles. The governing equations of motion are solved along with joint/constraint equations using a time-accurate explicit solution procedure. The sand model is validated using a conical hopper sand flow experiment in which the sand flow rate during discharge and the angle of repose of the resulting sand pile are experimentally measured. The results of the conical hopper simulation are compared with previously published experimental results. Parameter studies are performed using the sand model to study the e ffects of the particle size and the orifi ces diameter of the hopper on the sand pile angle of repose and sand flow rate. The sand model is integrated with the backhoe model to simulate a typical digging operation. The model is used to predict the manipulators actuator forces needed to dig through a pile of sand. Integrating the sand model and backhoe model can help improving the performance of construction equipment by predicting, for various vehicle design alternatives: the actuator and joint forces, and the vehicle stability during digging.

Indiana University-Purdue University Indianapolis (IUPUI) / In this thesis, an explicit time integration code which integrates multibody dynamics and the discrete element method is used for modelling the excavation and moving operation of cohesive soft soil (such as mud and snow) by bulldozers. A soft cohesive soil material model (that includes normal and tangential inter-particle force models) is used that can account for soil compressibility, plasticity, fracture, friction, viscosity and gain in cohesive strength due to compression. In addition, a time relaxation sub-model for the soil plastic deformation and cohesive strength is added in order to account for loss in soil cohesive strength and reduced bulk density due to tension or removal of the compression. This is essential in earth moving applications since the soil that is dug typically becomes loose soil that has lower shear strength and lower bulk density (larger volume) than compacted soil. If the model does not account for loss of soil shear strength then the dug soil pile in front of the blade of a bulldozer will have an artificially high shear strength. A penalty technique is used to impose joint and normal contact constraints. An asperity-based friction model is used to model contact and joint friction. A Cartesian Eulerian grid contact search algorithm is used to allow fast contact detection between particles. A recursive bounding box contact search algorithm is used to allow fast contact detection between the particles and polygonal contact surfaces. A multibody dynamics bulldozer model is created which includes the chassis/body, C-frame, blade, wheels and hydraulic actuators. The components are modelled as rigid bodies and are connected using revolute and prismatic joints. Rotary actuators along with PD (Proportional-Derivative) controllers are used to drive the wheels. Linear actuators along with PD controllers are used to drive the hydraulic actuators. Polygonal contact surfaces are defined for the tires and blade to model the interaction between the soil and the bulldozer. Simulations of a bulldozer performing typical shallow digging operations in a cohesive soil are presented. The simulation of a rear wheel drive bulldozer shows that, it has a limited digging capacity compared to the 4-wheel drive bulldozer. The effect of the relaxation parameter can be easily observed from the variation in the Bulldozer's velocity. The higher the relaxation parameter, the higher is the bulldozer's velocity while it is crossing over the soil patch. For the low penetration depth run the bulldozer takes less time compared to high penetration depth. Also higher magnitudes of torques at front and rear wheels can be observed in case of high penetration depth. The model is used to predict the wheel torque, wheel speed, vehicle speed and actuator forces during shallow digging operations on three types of soils and at two blade penetration depths. The model presented can be used to predict the motion, loads and required actuators forces and to improve the design of the various bulldozer components such as the blade, tires, engine and hydraulic actuators.