| Equipment and appliances for deep sea mining have risen from a position of virtual non-existence to a major industrial significance. Rare Earth Elements are used in a wide range of modern applications that are highly specific and substitutes are inferior or unknown. In deep sea mining, a track vehicle is preferred to a legged crawler because of the better floatation and the larger traction force requirement for the mining system stability. The miner been in charge of the most complex and dangerous task is the key equipment in deep sea bed mining. The mechanics of tracked vehicles is of continuing interest to organizations and agencies that design and operate tracked vehicles. Deep-ocean mining vehicle system has not only coupled relationship between component systems, but also a variety of design requirements of each system component having specified multi-tasks to accomplish. In order to meet a variety of design multi-objectives tasks of the complex system, multidisciplinary design optimization (MDO) can be done. Since concept design is the most significant influence on the performance of the final product and any modification in the phase of concept design is easier than in detail design, the need to conceptually design a better miner arise. The success or failure in developing the complex miner system is determined by its conceptual design. In order to save time and cost in development of systems, concept design methodologies such as axiomatic design are utilize for development of systems. Choosing a good design amongst several concept designs lowers vulnerability of the result of system design and shortens period of the system development. Deep sea miner designers are presently more concern with the overall optimization of the mining system, but since the crawler (miner) is the most important part its design optimization will be of significant impact to the industry. Deep-sea mining system technology is complex, expensive and difficult to develop due to high cost and risks of physical models constructions making it prohibitive in the early stage of development. Thus, the development of deep-sea mining simulation test system is the early concept of design innovation and it is an effective tool to accelerate the maturity of the technology to ensure stable and reliable performance.An understanding of terrain behavior under vehicular load is of importance to the study of vehicle-terrain interaction. In view of the limitations to the study of vehicle mobility in the field by modeling the terrain as an elastic or rigid, perfectly plastic medium or based on the critical state soil mechanics, the finite element method, or the discrete element method, other practical techniques and approaches were studied. To overcome the limitations of modeling the terrain as an elastic medium or as a rigid, perfectly plastic material, attempts have been made to model the terrain based on the concept of the critical state soil mechanics, as it has the potential capability to predict both the stress and strain in the terrain under vehicular load. With advancements in computer technology and computational techniques in recent years, modeling the terrain using the finite element method (FEM) or using the discrete (distinct) element method (DEM) has emerged. These methods have the potential capability to examine certain aspects of the physical nature of vehicle-terrain interaction in great detail. In many problems in vehicle-terrain interaction, the failure (flow) patterns of soil under the vehicle running gear are very complex and their boundary conditions on the wheel-soil interface vary with design parameters and operating conditions of the wheel, as well as terrain characteristics. This makes it very difficult if not impossible to specify appropriate boundary conditions at the outset. Thus the boundary conditions are primarily based on empirical data and simplifying assumptions.Modeling of the deep sea miner requires a comprehensive understanding of the mechanical behavior of the terrain under loading conditions similar to those imposed by the vehicle. As the performance of the tracked vehicle is primarily dependent upon the normal and shear stress distributions at the track-terrain interface, the basic issue in mathematical modeling of tracked vehicle performance is the development of a suitable relationship between the interacting forces at the track-terrain interface, the vehicle design parameters and the terrain characteristics. In this research, modeling is first done by assuming straight line motion and later steering. The main external forces acting on the miner which are Traction potential, hydrodynamic force, Collecting resistance, Bulldozing resistance, Umbilical forces, and its Weight are considered and the load applied to the soil consists of normal stress and shear stress. Normal stress is caused by vertical pressure from the weight of the vehicle, and can be obtained according to a relationship between sinkage and pressure. Shear stress comes from tractive and braking forces for the vehicle, and can be obtained by using a relationship between shear displacement and shear stress. Using the famous Bekker equation the sinkage can be found and by modification of Muro and O'Brien (2004) work accounting for hydrodynamic and umbilical forces, model equations for miner were developed for static, dynamics and Steering. Compaction resistance is assumed to act on the front contact part of the track belt. For static analysis i.e. the condition when the miner is not moving we have velocity equals zero, slip and slid also equals zero, resultant effective tractive effort on the vehicle and Collecting Resistance equals zero. In Static analysis the required parameters needed to model a miner in order to determine the umbilical force required to keep it stationary was derived. The assumption during dynamic analysis is that the miner is moving along a straight line and equations of its motion expressed in the body fixed frame and maximum traction in dependence of slip were obtained. In Energy analysis, the effective input energy supplied by the driving or braking torque acting on the rear sprocket must equal to the sum of the compaction energy, the slippage energy, the effective driving or braking force energy, the collecting energys and hydrodynamics energy. In Steering forces analysis, hydrodynamics forces are neglected due to low speed of movement during turning and the frictional moment due to skidding of the tracks, angle of lateral inclination of vehicle, longitudinal effective tractive effort, and resultant effective tractive effort were obtained. In order to verify the model equations developed an experimental study became necessary. Bearing in mind that the mass and volume of deep-sea mining systems are very large, an experimental mini-crawler based on similitude theory and dimensional analysis was used with the aim to study the Crawler Traction-slippage during working conditions; the turning radius during steering and to see whether the forces and position obtained correspond to the model equations developed. Relationship between the miner traction and slippage, actual turning radius and that of the model equations verified the study.For the Simulation, basic parameters of a miner and geotechnical parameters of seafloor soil are first used to calculate the miner's contact pressure distributions taken at rest (assuming a rigid track belt). The static amounts of sinkage of front-idler and rear sprocket are calculated using the Bekker equation and the angle of inclination of the miner obtained. For static, dynamics and steering analysis from equations developed the parameters at different eccentricities are determine. MATLAB R2011was used to calculate the forces and the data stored as a MINITAB14data. MINITAB14Software was then used to determine the correlation between the simulated variables data and JMP6SARS software was used to plot the bivariate fit in order to graphically show their relationship. In Statics it was found that there is significance level of accepting the hypothesis that linear relationship exists between the umbilical and slope angles with the simulated variables (Inclination angle, Track thrust, ground reaction and eccentricity). The track thrust and eccentricity will be increasing with increase of the umbilical angle. While the ground reaction and the inclination angle will decrease with increase of the umbilical angle when the umbilical angle is less than zero and increase with increase of the umbilical angle when it is greater than zero. The maximum track thrust and maximum eccentricity will depend on the maximum umbilical angle. While the maximum ground reaction and maximum inclination angle will depend on the maximum absolute value of the umbilical angle. The track thrust, ground reaction and the inclination angle increase with increase of the Slope angle when the slope angle is less than zero and decrease with increase of the slope angle when it is greater than zero. The eccentricity will be increasing with increase of the slope angle. Here the maximum eccentricity will depend on the maximum Slope angle. While the maximum track thrust, maximum ground reaction, and maximum inclination angle will occur when the slope is zero. In dynamics it was found that some variables are related while some are not related to each other. The Umbilical angle and the slope angle are only related to the compaction resistance and of course the effective tractive force. The compaction resistance and the effective tractive force will decrease with increase of the umbilical angle when the umbilical angle is less than zero and increase with increase of the umbilical angle when it is greater than zero. When the slope angle is less than zero they decrease with increase of the slope angle, while when the slope angle is greater than zero the compaction resistance and the effective tractive force will increase with increase of the slope angle. Here the compaction resistance and the effective tractive force will depend on the maximum absolute value of the umbilical angle and will be maxima when the slope angle is zero. The velocity is only related to the hydrodynamic force and of course the effective tractive force. It increases with decrease of the related forces. Here the maximum hydrodynamic force and of course the maximum effective tractive force is when the velocity is minimum. The slip and slid only related to the Slippage energy. The slippage energy increases from0%to around12%and start to decline to around50%slip where it became nearly a constant value. Here the maximum slippage force is when the slip/slid is around12%. In Steering analysis, it was found that some variables are related while some are not related to each other. The Steering ratio is related to Resultant Effective Tractive Effort, Longitudinal Effective Tractive Effort, Ground Reaction, Driving Force, Track Thrust, and Effective Tractive Force. But some variables (such as Longitudinal Effective Tractive Effort, Ground Reaction, Track Thrust, and Effective Tractive Force) have negligible change with respect to the variation of the steering ratio. While Resultant Effective Tractive Effort and Driving Force have a significance linear relationship with steering ratio. Resultant Effective Tractive Effort, Longitudinal Effective Tractive Effort, Effective Tractive Force, Ground Reaction decrease with increase in steering ratio although the Ground Reaction have no significance difference. The Resultant Effective Tractive Effort decreases with increase in steering ratio while the driving forces increase with increase in steering ratio. Umbilical angle is related to all the forces except Hydrodynamics Force and Track Thrust. The Resultant Effective Tractive Effort will increase with increase of the umbilical angle when the umbilical angle is less than zero degree (0°) and decrease with increase of the umbilical angle when it is greater than zero degree (0°). The Longitudinal Effective Tractive Effort, Effective Tractive Force, Ground Reaction, Driving Force, Compaction Resistance, and Weight Component decrease with increase in the umbilical angle without effect of direction, the Resultant Effective Tractive Effort value is maximum when the umbilical angle is at zero degree (0°); while the Longitudinal Effective Tractive Effort, Effective Tractive Force, Ground Reaction, Driving Force, Compaction Resistance, and Weight Component are all maxima at maximum negative umbilical angle. The slope angle is related to all the forces except Hydrodynamics Force and Track Thrust. The Resultant Effective Tractive Effort, Longitudinal Effective Tractive Effort, Effective Tractive Force, ground reactions, Compaction Resistance, and Weight Component increase with increase of the slope angle when the slope angle is less than zero (0°) and decrease with increase of the slope angle when it is greater than zero (0°). The Driving Forces increase with increase in the slope angle without effect of direction. Here the Resultant Effective Tractive Effort, Longitudinal Effective Tractive Effort Effective, Tractive Force, ground reactions, Compaction Resistance, and Weight Component are maxima when the slope angle is zero (0°). While the driving forces are maxima at maximum slope angle. The slip is related to Resultant Effective Tractive Effort, Longitudinal Effective Tractive Effort, Ground Reaction, Driving Force, Track Thrust, and Effective Tractive Force. But only in the driving forces that a linear relationship truly exist. The driving forces decrease with increase in the slip. While the Track Thrust increase from0%to around12%and starts to decline to around50%slip when it became nearly constant. While the Resultant Effective Tractive Effort, Longitudinal Effective Tractive Effort, Ground Reaction and Effective Tractive Forces decrease from0%to around12%and start to increase to around50%slip when it became nearly constant value. Here the maximum forces i.e. the design forces will be taken when the slip is around12%.The design of a deep-sea miner is based on the interactions between the ground and the vehicle taken into account the various surroundings influence and the evaluation of materials, functional principles and the rules for design. The miner will have a partly rigid chassis with two tracks without any sloping inlet of tracks and with slip steering. The main frame of the chassis is completely rigid. The track system is made of the track shoe, sprocket, road wheels, idler, carrier roller and Track body frame. Ambient conditions to be considered for the track system design and optimization are based on the Wenzlawski,(2000) assumptions. The effects of the ambient conditions on materials and functional components are multifarious and not totally explored and therefore complete system of rules for design are not yet in existence. The contact area of the crawler belt on the soil can thus be determined for the total weight of the mining machine in water. Assumption is that the contact pressure of the soil is evenly distributed under the contact area. The relation between contact pressure and shear strength is so small and it was neglected for the limit of trafficability of the soil. The maximum tractive force of the miner will depends only on the soil contact area of the miner, the soil shear strength and the soil deformation and thus the entire concept of the mining system. The driving speed is limited to less than lm/s and each component of the miner track system was analyzed based on the forces/weights acting on it.The optimization algorithm is based on the conventional engineering approach. So based on the known requirements of the track system, the system is optimized, in other words the optimization would start from the known requirement of the track system and subsequently to the unknowns. Dynamic programming which is a technique well suited for the optimization of such multistage decision problems is employed in this work. Track dimensions are optimized to have maximum steering ratio with minimum area of contact; the constraints will be the miner body dimensions. The sprocket is optimized to have minimum power requirement and material volume; with miner crawler chassis dimensions, minimum teeth of the sprocket and strength of the sprocket as constraints. The grouser is optimized to have maximum traction force with minimum material volume; the constraints are allowable soil bearing stress, grouser pitch relationship to the circular pitch of the sprocket, and assumed design relationship between the grouser pitch and grouser height. The track shoe is optimized to have maximum bending moment, and minimum material volume; with centrifugal force less than the chain breaking strength as constraint. The road-wheels are optimized to have minimum rolling resistance and minimum material volume. The constraints are the calculated miner grouser dimensions and length of contact, and the allowable road-wheel spacing to track-pitch ratio. The Idler-wheel is optimized to have minimum material volume; with calculated miner track dimensions (sprocket and road-wheel) and the idler wheel support load as constraints. The carrier roller is optimized to have minimum material volume. The constraints will be the calculated miner road-wheel dimensions, minimum allowable radii of the carrier roller and the carrier roller ability to support the load. The track body is optimized to have maximum allowable stress with minimum material volume with miner crawler chassis dimensions and the track body support the load as constraints will be. The optimization was done using codes written in MATLAB R2011.RecurDyn Software has a fully integrated linear and non-linear FEA capability allowing the creation of detailed realistic models for design studies and product's performance improvement making it possible to simulate overall motion as well as local deformations and stresses. RecurDyn solver is powerful and it is2-20times faster than other dynamic solutions because of its advanced fully recursive algorithm. RecurDyn is also highly robust and stable thus models require much less parameters tuning to produce results. The optimized designed miner was simulated for both linear motion and also Steering motion. The bushing forces acting on the track are studied in order to know the nature of the track loading and it was found that during driving both the right and left tracks have the same pattern of force distribution with the right track having a higher value than the left track. The difference between the track forces is more during driving in the normal plane and decay occurs after the first second. It was found during steering condition that the right track which is the outer track and the left track which is the inner track are not having the same force distribution pattern. They are interwoven and decaying with the decay earlier in the outer track. |
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