Multi-cycle Operations Research Articles

Estimation of lower bounds in scheduling algorithms for high-level synthesis

To produce efficient design, a high-level synthesis system should be able to analyze a variety of cost-performance tradeoffs. The system can use lower-bound performance estimated methods to identify and puune inferior designs without producint complete designs. We present a lower-bound performance estimate method that is not only faster than existing methods, but also produces better lower bounds. In most cases, the lower bound produced by our algorithm is tight.Scheduling algorithms such as branch-and-bound need fast and effective lower-bound estimate methods, often for a large number of partially scheduled dataflow graphs, to reduce the search space. We extend our method to efficiently estimate completion time of partial schedules. This problem is not addressed by existing methods in the literature. Our lower-bound estimate is shown to by very effective in reducing the size of the search space when used in a branch-and-bound scheduling algorithm.Our methods can handle multicycle operations, pipelined functional units, and chaining of operations. We also present an extension to handle conditional branches. A salient feature of the extended method is its applicability to speculative execution as well as C-select implementation of conditional branches.

MPT-based branch-and-bound strategy for scheduling problem in high-level synthesis

A branch-and-bound algorithm based on a maximum possibility table (MPT) is proposed to solve scheduling problems in high-level synthesis. Six efficient priority rules are developed as bounding functions in the algorithm. Extensions for real-world constraints are also considered, including chained operations, multicycle operations, mutually exclusive operations and pipelined data paths. Experimental results indicate that the MPT-based algorithm returns competitive scheduling results at significant savings in execution time as compared with other methods.

A solution methodology for exact design space exploration in a three-dimensional design space

This paper describes an exact solution methodology, implemented in Rensselaer's Voyager design space exploration system, for solving the scheduling problem in a three-dimensional (3-D) design space: the usual two-dimensional (2-D) design space (which trades off area and schedule length), plus a third dimension representing clock length. Unlike design space exploration methodologies which rely on bounds or estimates, this methodology is guaranteed to find the globally optimal solution to a 3-D scheduling problem. Furthermore, this methodology efficiently prunes the search space, eliminating provably inferior design points through the following: 1) a careful selection of candidate clock lengths and 2) tight bounds on the number of functional units or on the schedule length. Both chaining and multicycle operations are supported.

Hot-gas cleanup—sulfur recovery technical, environmental, and economic issues

Abstract Advanced high-efficiency integrated gasification combined cycle (IGCC) power systems employing hot-gas cleanup are being developed to produce electric power from coal. Hot-gas cleanup consists of hot particulate removal and hot-gas desulfurization (HGD) technologies that match or nearly match the temperature and pressure of the gasifier and turbine generator. HGD is carried out using solid regenerable metal oxide sorbents that can remove the sulfur down to low parts per million and can be regenerated with air for multicycle operation. Economic studies have shown that HGD results in lower capital and operating costs than conventional cold gas desulfurization. Development of efficient sorbent desulfurization-regeneration reactor and tailgas treatment subsystems properly integrated with the overall IGCC systems is a key requirement for successful commercialization of HGD.

Lower-bound performance estimation for the high-level synthesis scheduling problem

A given behavioral specification can be implemented on a large number of register-transfer level designs. Instead of producing several designs and selecting the best one, synthesis systems may use estimation to reduce the design space. In this paper, we present a new technique for computing a lower-bound completion time for non-pipelined resource-constrained scheduling problem. Given a data flow graph, a set of resources, resource delays and a clock cycle, we derive a lower-bound on the completion time of a schedule. Our technique can handle chaining, multi-cycle operations and pipelined modules. The technique is very fast and experimental results show that it is also very tight. >

Utilizing Mini-frac Data to Improve Design And Production

Abstract An extension to the current mini-frac procedure is presented to improve the quality of the analysis. The methodology is based on history matching the pressure response during pumping and closure for the mini-frac treatment. This process couples the traditional mini-frac analysis with a three-dimensional hydraulic fracturing simulator. The fracture propagation solution for geometry and extension pressure is coupled with the post injection pressure decline analysis. The coupling process reduces the possible number of parameter uncertainties. The measured fracture extension and decline pressure data is used to establish the appropriate fracture geometry model and to perform parametric studies. Reservoir and fluid parameters are then varied to perform further sensitivity analyses. Repeating the procedure for a multi-cycle mini-frac operation provides the analyst with an opportunity to refine the parametric analyses and select the most probable set of parameters to optimize the treatment. This results in an improved understanding of hydraulic fracture propagation and formation response, which results in a higher probability for further improving production. The fracture-pressure analysis and procedures provided in this paper generally follow the theory of mini-frac analysis originally formulated by Nolte(1,2). An important difference, however, is that the pressure-analysis used here couples a mini-frac simulator with a three-dimensional hydraulic fracture simulator to predict fracture propagation and pressure response. The mini-frac simulator is first used for preliminary analysis and quick estimates of parameters prior to performing more rigorous parametric studies with the 3-D fracturing model. Parametric studies and field case examples are presented to illustrate the improved mini-frac/treatment techniques. Simulated values for permeability and fracture height are then compared to more traditional sources of information from lab analysis and logs. Introduction Hydraulic fracturing continues to be a popular initial completion technique for operators in Western Canada. Whether it is employed to bypass drilling damage or to stimulate tighter zones, well owners have come to rely on hydraulic fracture stimulation to provide greater economic returns. Improved production and economic benefits from hydraulic fracturing have been clearly demonstrated over the years. However, to maximize the economic benefits, the fracture treatment must be optimized to the reservoir. Too often critical parameters in the fracture design are not available prior to initiation of the actual fracture treatment. Time constraints and economics are modern driving forces which expedite the initial completion process. Unfortunately, the result is a lost opportunity to obtain the engineering data required to determine the effectiveness of the completion and capitalize on the ultimate deliverability of the well. Mini-frac pressure decline analysis as presented by Nolte(1,2) first became popular in the 1980's and is used routinely today. An excellent review and detailed description of the theoretical framework and current application of fracture-pressure analysis is given by Nolte in Reference (4). Here Nolte relates the similarity of pressure-transient analysis in reservoirs to fracture-pressure analysis. Nolte, however, places the current state of fracture-pressure analysis in perspective with the statement: "An important difference, however, is that reservoir pressure analysis has developed into a massive discipline during the past 50 years, while fracturing-pressure analysis is in a relative state of infancy. "

FAMOS: an efficient scheduling algorithm for high-level synthesis

FAMOS, an iterative improvement scheduling algorithm for the high-level synthesis of digital systems, is described. The algorithm is based on a move acceptance strategy and various selection functions defined to represent the cost of hardware resources such as functional units and registers. A main feature of the algorithm is that it can escape from local minima. The algorithm can deal with diverse design styles such as multi-cycle operations, chained operations, pipelined datapaths, pipelined functional units and conditional branches. Register costs and maximal time constraints are also considered. To efficiently represent information on the design styles, a graph model called weighted precedence graph is proposed as a general model on which the scheduling algorithm is based. Despite the iterative nature, the proposed algorithm has a polynomial time complexity. Although the optimality of the algorithm is not guaranteed, optimal solutions were obtained for several examples available from the literature.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A formal approach to the scheduling problem in high level synthesis

An integer linear programming (ILP) model for the scheduling problem in high-level synthesis is presented. In addition to time-constrained scheduling and resource-constrained scheduling, a scheduling problem called feasible scheduling, which provides a paradigm for exploring the solution space, is constructed. Extensive consideration is given to the following applications: scheduling with chaining, multicycle operations by nonpipelined function units, and multicycle operations by pipelined function units; functional pipelining; loop folding; mutually exclusive operations; scheduling under bus constraint; and minimizing lifetimes of variables. The complexity of the number of variables in the formulation is O(s*n) where s and n are the number of control steps and operations, respectively. Since the as soon as possible (ASAP), as late as possible (ALAP), and list scheduling techniques are used to reduce the solution space, the formulation becomes very efficient. A solution to a practical problem, such as the fifth-order filter, can be found optimally in a few seconds. >

Applicability of pipelocks as a remedy for intergranular stress corrosion cracking in BWRs

Design, analyses and first application of the Pipelock as a novel long-term multicycle protection for piping systems in Boiling Water Reactor plants damaged by Intergranular Stress Corrosion Cracking in BWRs is described. Confirmatory tests simulating all design and operating conditions including LOCA are also discussed. Pipelocks are mechanical devices which prevent pipe break even if it is assumed that intergranular stress corrosion cracking penetrates through-the-wall and around the entire circumference of the pipe weldment. With a fully cracked weldment, the entrapped wedges lock the pipes together, preventing the ends from separating. In addition to providing defense-in-depth against pipe breaks, pretightening of the Pipelock bolts produces axial and circumferential compressive stresses in the pipe wall at the weldment, thus tending to retard or eliminate crack growth during operation after installing the Pipelock. Pipelocks are designed to meet regulatory requirements 10CFR50—Appendix B and ASME Code Section III requirements for long-term multicycle operation. Installed Pipelocks can be disassembled to permit inservice inspection of the weldment. They therefore can be used through several outages subsequent to the installation, thereby eliminating or postponing the need for pipe changeout. The design of the Pipelock also enables their use on weldments which were previously overlaid.

ENZYME IMMUNOSENSOR USING HAPTEN-BOUND MEMBRANE AND Fab’-β-d-GALACTOSIDASE COMPLEXES

Abstract An enzyme immunosensor using a hapten-bound membrane and Fab’-β-d-galactosidase complexes has been developed to improve the reproducibility and the capability of multi-cyclic operation. The proposed method may be useful for repeated uses of the enzyme immunosensor without exchanging the membranes.

On multicyclic operators

On multicyclic operators

Multicycle adsorption-desorption process for drying xylene cut with CaA zeolites

1. In the drying of a xylene cut in the liquid phase with CaA zeolite, either thermal-vacuum or thermal-gas desorption must be continued for at least 4 h, with a flow rate of desorbing agent amounting to 0.6 liter/(cm2 · min). 2. In multicycle adsorption-desorption drying processes, a drop in the dynamic activity of CaA zeolite with respect to moisture is observed in the first few cycles, after which it remains at 67–87% of the original level. The curves for “coke” content on the CaA zeolite are antibatic to the curves for change in dynamic activity. 3. A test of the applicability of formulas for determining changes in dynamic activity of zeolite with respect to moisture and changes in deposition of “coke” on the zeolite during multicycle operation has demonstrated good agreement between experimental and calculated data.

Drying isopropyl alcohol on NaA zeolite

1. A study of the liquid-phase adsorptive drying of isopropyl alcohol on NaA zeolite has been carried out. 2. It was found that increasing the adsorption temperature to 75‡C has a positive effect, increasing the dynamic activity (the extent of drying remains unchanged at about 0.002 wt. %). 3. It was shown that the stability of zeolite in a multicycle operation is maintained when drying either fresh alcohol or a distillate from reclaimed alcohol.

Calcium removal from sea water by fixed-bed ion exchange

Abstract Calcium removal from sea water prior to evaporation permits increased temperature and concentration during evaporation. The results of laboratory studies on calcium removal by fixed-bed ion exchange are reported. Synthetic regenerants were employed, simulating in composition and total amount the waste brine from the evaporator. In actual practice, use of this brine eliminates the need to purchase regenerant chemicals. Commercial polystyrene sulfonate resins were used at room temperature, employing downflow for the softening step, and upflow for regeneration, without rinse. In multicyclic operation, the effects of particle size, bed depth, flow rate, and regenerant concentration on the degree of calcium removal have been studied. Relations for predicting resin volume and cycle time under given operating conditions are presented as an aid in calculations leading to economic optimization of the process.

The Amex Process for Extracting Thorium Ores with Alkyl Amines

The Amex processes use long-chain alkyl amines for solvent extraction separation of thoriuin and by-products from ore sulfate liquors. Because the extraction power for thorium, uranium, and rare earths depends on ainine class and alkyl structure, appropriate choice of amine allows separate recovery of these metals in multicycle operations. Chloride, nitrate. and carbonate solutions strip extracted metals from the amine. Thorium recovery was>99.8% with four stages of recovery. (auth)