PERFORMANCE EVALUATION OF THE UT AUTOMATED ROAD MAINTENANCE MACHINE
This final report mainly focuses on evaluating the overall performance of the University of Texas' (UT's) Automated Road Maintenance Machine (ARMM). First, the ARMM's man-machine-balanced control loop was further developed then rigorously tested and evaluated based on (1) accuracy, (2) time, and (3) quality of the resultant seal. For the efficiency evaluation, thirty pavement crack images, which included longitudinal, transverse, and block cracking, were collected from a UT research campus, and field trials were completed at five locations (Austin, San Antonio, Dallas, Corpus Christi, and Travis County) in the state of Texas. Several additional significant improvements were made to the ARMM during the course of this project. Second, the ARMM's productivity was estimated based on (1) the results of the efficiency evaluation of the man-machine control loop, (2) observations made during the series of field trials, and (3) a productivity model. The mathematical model that predicts the productivity of the ARMM under various work conditions was developed as a means for job estimating and for rating the performance of the ARMM. The ARMM's estimated productivity was then compared with the typical productivity rate associated with conventional crack sealing methods. Evaluation results from the field trials and implementation recommendations are also made in this final project report. It was concluded that the introduction of automated methods to the pavement crack-sealing process will improve productivity and quality and can reduce costs and safety risks. The latter is a direct result of reducing normal crew sizes of seven to eight workers to only three to four workers. The reduction in crew size and the increase in productivity of the sealing process translate directly into significant potential cost savings. By automatically recording work completed, the ARMM should help improve project controls; by its ability to work at night, the ARMM should reduce road user costs.
Implementing an Automated Road Maintenance Machine (ARMM): Lessons from the Field
Crack sealing, a routine and necessary part of pavement maintenance , is a dangerous , costly, and labor-intensive operation . Within North America, about $200 million is spent annually on crack sealing, with the Texas Department of Transportation (TxDOT) spending about $7 million annually (labor alone accounts for over 50 percent of these costs). Prompted by concerns of safety and cost, the University of Texas at Austin, in cooperation with TxDOT and the Federal Highway Administration has developed a unique computerguided Automated Road Maintenance Machine for pavement crack sealing. Successful field tests have been undertaken in several TxDOT districts. This paper first describes the ARMM's field implementation and its productivity analysis results. The paper then discusses current research efforts, and improvements and modifications suggested though the technology evaluation during the field trials. The ARMM' s future implementation and work plans are also presented in this paper. 1. Background and Significance of Work Crack sealing , a maintenance operation undertaken by all state departments of transportation , is dangerous , costly, and laborintensive. In pursuing these operations , agencies must contend not only with the substantial personnel turnover and training problems associated with crack sealing , but also with the traffic disruptions that crack sealing operations typically generate. Automating pavement crack sealing can reduce labor and road user costs, improve work quality, and decrease worker exposure to roadway hazards. Approximately $200,000,000 is spent annually on crack sealing in North America. About 25% is privately contracted; labor costs average between 50% and 60% of total crack sealing costs. It is estimated that the ARMM would have a purchase cost of approximately $125,000, a useful life of 5 years, $10,000 annual maintenance costs, and $100,000 in annual cost savings by eliminating three laborers. A very high rate of return (ROR) results. According to the most recent economic analysis [3], if ARMMs were implemented throughout Texas, the direct savings are estimated to be S2.43 million for TxDOT (at 4% MARR) and $2.64 million for the private contractors (at 20% MARR) over a 6 year planning horizon. The user-cost savings are estimated using the widely accepted QUEWZ-E [8, 9] model to be $11.0 million for the 5196 kilometers of the interstate highways in Texas. Total user-cost savings would be much higher since the savings on urban freeways and streets, farm-tomarket roads, and secondary roads are not included in this $11 million estimate . Over a 30 year planning horizon and from a national perspective, the net present worth of automated crack sealing could be in the hundreds of millions of dollars. A man-machine balanced Automated Road Maintenance Machine (ARMM) for automatically sealing pavement cracks has been developed, tested, and successfully demonstrated by the University of Texas at Austin, in cooperation with TxDOT, the FHWA, and Crafco, Inc. (Fig. 1). The previous crack sealing prototype systems (CMU Laboratory Prototype [1], CMU-UT Field Prototype [2], CalDavis Field Prototype [10], UT Field Prototype [3]) were fully autonomous but slow in field operation and impractical [5, 6]. The ARMM uses an xy-manipulator with a rotating turret to blow, seal, and squeegee cracks in one pass , thus greatly improving productivity of the system. While the manipulator is moving within its work area, its frame is stationary. Sealing cracks in one work area and then moving to the next work area is ' Correspond to oungsukr )mail ut xae du or (512 ) 471-0110
Effect of superficial gas velocity on the particle temperature distribution in a fluidized bed with heat production
The heat transfer behavior of particles and gas in an olefin polymerization fluidized bed was numerically analyzed using an in-house developed 3-D computational fluid dynamics discrete element model (CFD-DEM). First the implementation of the model was verified by comparing simulation results with analytical results. A constant volumetric heat production rate was implemented in the particle energy equation to mimic the heat production due to the polymerization reaction. It was found that the probability density function (PDF) of the particle temperature becomes more homogeneous with increasing superficial gas velocity. Furthermore, instantaneous snapshots of the thermal driving force (the difference between the single particle temperature and bed-average gas temperature, Tp− ) for different heat production rates provide detailed insight in the particle temperature distribution inside the fluidized bed. The time- and bed-averaged particle convective heat transfer coefficient, which was calculated by Gunn׳s correlation, was found to be independent of the superficial gas velocity. This is explained by the fact that the relative velocity of gas and particles in the emulsion phase, where most of the particles and gas interact, is hardly influenced when increasing the gas superficial velocity. From the spatial distribution of Nusselt number, it becomes apparent that the high heat transfer regions are found in the wake of rising bubbles, whereas low heat transfer rates are found in the clouds of the bubbles.