University of Macau / Faculty of Science and Technology / Department of Civil and Environmental Engineering

This thesis explores three consolidation problems derived from the daily operations of major international airfreight forwarders. First, we study the freight forwarder's unsplittable shipment planning problem in an airfreight forwarding network where a set of cargo shipments have to be transported to given destinations. We provide mixed integer programming formulations that use piecewise-linear cargo rates and account for volume and weight constraints, flight departure/arrival times, as well as shipment-ready times. After exploring the solution of such models using CPLEX, we devise two solution methodologies to handle large problem sizes. The first is based on Lagrangian relaxation, where the problems decompose into a set of knapsack problems and a set of network flow problems. The second is a local branching heuristic that combines branching ideas and local search. The two approaches show promising results in providing good quality heuristic solutions within reasonable computational times, for difficult and large shipment consolidation problems. Second, we further explore the freight forwarder's shipment planning problem with a different type of discount structure - the system-wide discount. The forwarder's cost associated with one flight depends not only on the quantity of freight assigned to that flight, but also on the total freight assigned to other flights operated by the same carrier. We propose a multi-commodity flow formulation that takes shipment volume and over-declaration into account, and solve it through a Lagrangian relaxation approach. We also model the "double-discount" scheme that incorporates both the common flight-leg discount (the one used in the unsplittable shipment problem) and the system-wide discount offered by cargo airlines. Finally, we focus on palletized loading using unit loading devices (ULDs) with pivots, which is different from what we assumed in the previous two research problems. In the international air cargo business, shipments are usually consolidated into containers; those are the ULDs. A ULD is charged depending on whether the total weight exceeds a certain threshold, called the pivot weight. Shipments are charged the under-pivot rate up to the pivot weight. Additional weight is charged at the over-pivot rate. This scheme is adopted for safety reasons to avoid the ULD overloading. We propose three solution methodologies for the air-cargo consolidation problem under the pivot-weight (ACPW), namely: an exact solution approach based on branch-and-price, a best fit decreasing loading heuristic, and an extended local branching. We found superior computational performance with a combination of the multi-level variables and a relaxation-induced neighborhood search for local branching.

Shipment consolidation is a logistics strategy whereby many small shipments are combined into a few larger loads. The economies of scale achieved by shipment consolidation help in reducing the transportation costs and improving the utilization of logistics resources. The fundamental questions about shipment consolidation are i) to how large a size should the consolidated loads be allowed to accumulate? And ii) when is the best time to dispatch such loads? The answers to these questions lie in the set of decision rules known as shipment consolidation policies. A number of studies have been done in an attempt to find the optimal consolidation policy. However, these studies are restricted to only a few types of consolidation policies and are constrained by the input parameters, mainly the order arrival process and the order weight distribution. Some results on the optimal policy parameters have been obtained, but they are limited to a couple of specific types of policies. No comprehensive method has yet been developed which allows the evaluation of different types of consolidation policies in general, and permits a comparison of their performance levels. Our goal in this thesis is to develop such a method and use it to evaluate a variety of instances of shipment consolidation problem and policies. In order to achieve that goal, we will venture to use matrix-analytic methods to model and solve the shipment consolidation problem. The main advantage of applying such methods is that they can help us create a more versatile and accurate model while keeping the difficulties of computational procedures in check. More specifically, we employ a discrete batch Markovian arrival process (BMAP) to model the weight-arrival process, and for some special cases, we use phase-type (PH) distributions to represent order weights. Then we model a dispatch policy by a discrete monotonic function, and construct a discrete time Markov chain for the shipment consolidation process. Borrowing an idea from matrix-analytic methods, we develop an efficient algorithm for computing the steady state distribution of the Markov chain and various performance measures such as i) the mean accumulated weight per load, ii) the average dispatch interval and iii) the average delay per order. Lastly, after specifying the cost structures, we will compute the expected long-run cost per unit time for both the private carriage and common carriage cases.

This research study was a qualitative study involving eight current or former school board members of a recently annexed, rural, impoverished, Latino school district in South Texas. The purpose of this intrinsic case study was to highlight the plight of rural education, specifically the plight of a poor school district by examining the perceptions of the school board members. This study was organized around the following sensitizing concerns (Blumer, 1969; Patton, 2002; Schwandt, 2001): What were the school board members’ perceptions about the school district prior to the annexation? What were the school board members’ perceptions of the factors that contributed to the annexation? What were the school board members’ perceptions of the effect of the annexation on the community? The method of inquiry was conversational information interviews (Patton, 2002), two unstructured interviews with each school board member, going where the interviews took me (Fontana & Frey, 2005). The themes revealed in the research included (1) power dynamics, with three sub-themes, (a) trusting those in power, (b) deferring to those in power, and (c) becoming those in power; (2) denial of the obvious, and (3) unspoken paternalism—the Anglo patron system. This study offers implications for policy, practice, and additional research in the areas of rural communities and rural school districts, but most importantly, it provides evidence that rural colonias located along the U.S.-Mexico border have unique educational needs. Rural school districts located along this border need strong school leaders with “a critical leadership of place that support community as a context for learning, understand that schools and their local communities are inextricably linked and that the ability of each to thrive is dependent upon the other” (Budge, 2006, p.8).

Granular aggregates of quartz subjected to triaxial compression under constant effective pressures (Pe) undergo macroscopic failure at critical stress states that depend on the effective mean stress. Although the mode of failure and mechanical response vary systematically with mean stress at failure, prefailure loading at subcritical stress states may induce yielding, and subcritical load paths may influence behavior at failure. Here, I investigate how the failure of quartz aggregates at conditions favoring compaction depends on consolidation history and load path in the transitional and ductile deformation regimes in terms of strain localization and microfracture fabric. Three distinct non-standard triaxial compression load paths were employed; the paths involve different preconsolidation of the aggregates at subcritical isotropic stress followed by differential loading with increasing or decreasing confining pressure. Deformed aggregates were injected with epoxy and studied using optical microscopy techniques to determine microscopic damage evolution for the different load paths. Microfracture data show that preconsolidation at subcritical isotropic loads facilitates formation of campaction bands during subsequent triaxial compression in the transitional regime. The preferred orientation of intragranular cracks evolves from near random fabrics for isotropic loading to strongly preferred orientations parallel to the maximum principal compression direction for differential loading, with the strongest preferred orientation within the compaction bands. Aside from the preconsolidation, different load paths have only a minor effect on the mechanical response during macroscopic failure.

The production of sand can be a major issue in many young, unconsolidated sandstone formations where there is little to no cement holding the individual sand grains together. When such reservoirs are produced, quite often operators face problems with reduced well productivity and equipment failure. Because of these issues, the industry has developed numerous techniques in its effort to control formation sand production. Sand consolidation is one technology that has been studied and used since the 1940s. The theory behind sand consolidation technology is to place a liquid material which will create a grain to grain contact that will bind individual sand grains together. Most consolidation treatments contain a preflush to clean and wet the surface, the consolidating system to bind the sand grains and give residual strength, and, finally, an overflush to ensure the formation is still able to produce fluids. With the successful placement of this fluid, the sand grains will be locked in placed so that they will not be produced. The technology has gone through many phases of conception since the 1940s; however, most consolidation material that is pumped in the past has been based upon an epoxy or furan backbone. While there are many technologies available, for the purpose of my research, the epoxy technology was experimentally investigated. The testing of the fluid involved investigating numerous additives to obtain the correct residual strength of the sample, as well as the necessary retained permeability. For the epoxy fluid, the optimal preflush, epoxy system and overflush formulations were determined after 250 checkout tests. Based upon these tests, the fluid was optimized to its working time and UCS results. The optimal system included the addition of PA2 to the preflush, along with PA1 and an aromatic amine curing agent to the epoxy system. PA1 and PA2 are adhesion promoter additives which were deemed necessary as a result of the testing. This system was then tested further in a HP/HT cell. While there is still room for improvement with respect to retained permeability, the system still performs very well in terms of UCS.

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An experimental study was conducted to verify experimentally whether sand consolidation by high-temperature alkaline treatment was possible in the heavy oil Bachaquero-01 reservoir. The experiments were conducted using sand samples from a core taken from well LL-231 from Bachaquero-01 reservoir. The sample was placed in a vertical 18 in. long aluminum cylindrical cell with an ID of 1.5 in. The top half of the cell was thermally insulated and the bottom half was cooled. The alkaline treatment (pH 11 -12) at 230ºC - 250ºC and 900 – 1000 psig was injected at 20 ml/min for 3 to 6 hours at the top of the cell and liquid produced at the bottom of the cell. After each experiment, the cell contents were removed and analyzed to determine if consolidation occurred. An electron microprobe was used to analyze both loose and polished epoxy-mounted sand grains to determine any change in texture and composition of the sand pack and precipitation and growth of secondary phases. Results showed that under the experimental conditions reached in the laboratory; the consolidation of Bachaquero-01 sand did not occur. However some secondary materials were produced in the runs where sand samples were cleaned of oil. It was noticed that the amount of these secondary phases was not sufficient to bridge the sand grains. These results indicate that further research is needed to better understand and optimize the parameters affecting the consolidation of Bachaquero-01 sands.

This dissertation focuses on the recent supply chain initiatives, such as Vendor Managed Inventory (VMI) and Third-Party Logistics (3PL), enabling the coordination of supply chain entities; e.g., suppliers, buyers, and transporters. With these initiatives, substantial savings are realizable by carefully coordinating inventory, transportation, and pricing decisions. The impact is particularly tangible when the transporter's role and the transportation costs are explicitly incorporated into decision mechanisms that aim to coordinate the supply channel. Furthermore, expanding the perspective of channel coordination by introducing the transporter as an individual party in the channel provides tangible benefits for each member of the channel. Recognizing the need for further analytical research in the field of multi-echelon inventory and channel coordination, we developed and solved a class of integrated inventory and transportation models with explicit shipment consolidation considerations. Moreover, we examined transporter-buyer and supplier-transporter-buyer channels and solved centralized and decentralized models for these channels with the aim of investigating the impact of transporters on channel performance. In this dissertation, we also developed efficient coordination mechanisms between the transporter and the other parties in the channel.

This research study was a qualitative study involving eight current or former school board members of a recently annexed, rural, impoverished, Latino school district in South Texas. The purpose of this intrinsic case study was to highlight the plight of rural education, specifically the plight of a poor school district by examining the perceptions of the school board members. This study was organized around the following sensitizing concerns (Blumer, 1969; Patton, 2002; Schwandt, 2001): What were the school board members' perceptions about the school district prior to the annexation? What were the school board members' perceptions of the factors that contributed to the annexation? What were the school board members' perceptions of the effect of the annexation on the community? The method of inquiry was conversational information interviews (Patton, 2002), two unstructured interviews with each school board member, going where the interviews took me (Fontana & Frey, 2005). The themes revealed in the research included (1) power dynamics, with three sub-themes, (a) trusting those in power, (b) deferring to those in power, and (c) becoming those in power; (2) denial of the obvious, and (3) unspoken paternalism-the Anglo patron system. This study offers implications for policy, practice, and additional research in the areas of rural communities and rural school districts, but most importantly, it provides evidence that rural colonias located along the U.S.-Mexico border have unique educational needs. Rural school districts located along this border need strong school leaders with "a critical leadership of place that support community as a context for learning, understand that schools and their local communities are inextricably linked and that the ability of each to thrive is dependent upon the other" (Budge, 2006, p.8).