Flexible Flow Line Research Articles

A taxonomy of flexible flow line scheduling procedures

We present a taxonomy for flexible flow line scheduling procedures. Flexible flow lines are flow lines with parallel machines on some or all production stages. The taxonomy groups procedures according to their general solution approach. It distinguishes optimal and heuristic procedures. Heuristic procedures are split into holistic and decomposition approaches. While holistic approaches consider the complete scheduling problem in an integrated way, decomposition approaches divide the problem with respect to the production stages, the individual jobs, or the sub-problems to be solved (batching, loading, and sequencing). We explicitly mention the inclusion of setups in a study and list the respective objective criteria.

Subsea Development of Okwori and Nda Oil Fields, Niger Delta

Summary Addax Petroleum's operated Okwori oil field, offshore Nigeria, illustrated the benefits of reviving shelved projects, because of an insufficient return on investment using more traditional approaches, by applying more recent technical and contractual solutions. The Okwori project demonstrated the feasibility of developing small and geologically complex offshore oil fields in medium water depth of 440 ft with subsea technologies traditionally used for large fields. In the subsurface, the Okwori wells combined multiple selective completions hydraulically controlled from the surface with expandable sand screens as the downhole sand exclusion solution. This combination of equipment in subsea wells used to fully develop a small offshore oil field marked another technological first in Nigeria. Far away from pre-existing facilities and with less than 50 million bbl of median technical reserves at the time of project sanction, the Okwori oilfield development went a step further than the more usual subsea tieback to a pre-existing offshore production facility. The Okwori development plan was based on horizontal subsea trees flowing to a leased spread-moored floating production storage and offloading (FPSO) vessel by means of (6-in.) flexible subsea flowlines and risers. The Okwori leased production facilities had a built-in capability for additional tiebacks such as the Nda oil field, whose development was completed in October 2006, or for later redeployment in other parts of the acreage depending on further exploration and appraisal drilling. A review of the field operations to date highlighted a steep learning curve in the formulation of completion design, completion fluids, stimulation, downhole sand exclusion systems, and bean-up/bean-down procedures.

Two hybrid meta-heuristics for the finite horizon ELSP in flexible flow lines with unrelated parallel machines

This article addresses the economic lot sizing and scheduling problem in flexible flow lines with unrelated parallel machines over a finite planning horizon. The objective is determination of a cyclic schedule that minimizes the sum of setup and inventory holding costs per unit time without any stock-out. A new mixed zero–one nonlinear mathematical programming has been developed for the problem. Due to difficulty of obtaining the optimal solution especially for medium and large-sized problems, we have also proposed two algorithms: a hybrid genetic algorithm (HGA) and a simulated annealing (SA). Two efficient constructive heuristic algorithms have been also proposed that provide some initial solutions for the algorithms. Moreover, a new local search approach has been proposed to improve solution quality of algorithms. The two proposed solution methods are compared on 180 randomly generated problems. Computational results indicate the superiority of the proposed HGA in compare to the SA with respect to the solution quality, but the proposed SA outperforms the proposed HGA with respect to the required computations time.

A hybrid genetic algorithm for the finite horizon economic lot and delivery scheduling in supply chains

In this paper, we investigate the lot and delivery scheduling problem in a simple supply chain where a single supplier produces multiple components on a flexible flow line (FFL) and delivers them directly to an assembly facility (AF). It is assumed that all of parameters such as demand rates for the components are deterministic and constant over a finite planning horizon. The main objective is to find a lot and delivery schedule that would minimize the average of holding, setup, and transportation costs per unit time for the supply chain. We develop a new mixed integer nonlinear program (MINLP) and an optimal enumeration method to solve the problem. Due to difficulty of obtaining the optimal solution in medium and large-scaled problems, a hybrid genetic algorithm (HGA) is also developed. The proposed HGA incorporates a neighborhood search (NS) into a basic genetic algorithm that enables the algorithm to perform genetic search over the subspace of local optima. The two proposed solution methods are compared on randomly generated problems, and computational results show that the performance of HGA is very promising because it is able to find an optimal or near-optimal solution for majority of the test problems.

Albacora Leste Field - Subsea Production- System Development

This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper OTC 18044, "Albacora Leste Field - Subsea Production System Development," by C.E.C.V. Longo, S.J.A. Neto, and M.T.R. de Paula, Petrobras; F.M. Lopes Jr., Technip; and C.A.F. Godinho, SPE, Prysmian, prepared for the 2006 Offshore Technology Conference, Houston, 1–4 May. The Albacora Leste field-development plan comprises 30 horizontal wells tied back to a floating production, storage, and offloading (FPSO) platform moored by use of an innovative spread mooring system (SMS). All risers are flexible and installed in a free-hanging configuration. Environmental conditions and FPSO motion were factors in flexible-riser design. All flexible lines were anchored by means of torpedo piles. The full-length paper describes field development, including planning, design, qualification, manufacturing, and installation activities. Introduction The Albacora Leste field is in the deep north area of the Campos basin approximately 120 km off the coast of Brazil. Water depths in this field range from 800 to 2000 m, and oil densities range from 17 to 21°API. The field development comprises 30 horizontal wells (16 production wells and 14 injection wells, three of which are in a piggyback configuration) tied back to a host FPSO, P-50 by flexible risers and flowlines. Bending-stiffener and top riser accessories development and qualification represented an important and challenging success factor for the project. Three test benches were designed and assembled to perform the long-term fatigue tests for the gas-export flexible riser and to validate the new concept of the stiffener hanging systems. The FPSO will be moored in 1230 m of water by use of an innovative differential-compliance anchoring system. The oil, after treatment and storage on the FPSO, is pumped to a shuttle tanker. The produced gas then is cleaned and compressed, and a fraction of the total volume is used for power generation, gas lift, and internal consumption; the remaining volume is exported to shore by way of Platform PGP-1 in the Garoupa field, Campos basin. During the design phase, continuous gas lift and electrical-submersible-pump (ESP) artificial-lift methods were selected as potential candidates for the wells. However, at the time of the design phase, an ESP that could handle the high oil flow rates expected was not available, so the decision was made to use continuous gas lift as the artificial-lift method for the production wells. The approved gas lift design strategy eliminated pressure-operated valves and adopted a very simple and reliable well completion that included a single gas lift orifice valve. A high-discharge-pressure gas compressor was installed topside to guarantee continuous gas injection through the orifice valve at normal well-operation conditions and kickoff.

SCHEDULING OF FLEXIBLE FLOW LINES WITH BLOCKING BY MEMETIC ALGORITHMS

This paper presents an efficient memetic algorithm (MA) for scheduling a flexible flow line problem by assuming processor blocking (FFLPB). The proposed MA is used to solve a mixed-integer model of the FFLPB developed in the literature. The flexible flow line consists of several processing stages in series without intermediate buffers, in which each stage has one or more identical parallel processors. The line produces several different products and each product must be processed by at most one processor in each stage. The mathematical model of the FFLPB is optimally solved and the obtained results are compared with MA runs.

FINITE HORIZON ELSP IN FLEXIBLE FLOW LINES WITH UNRELATED PARALLEL MACHINES

This article addresses the economic lot sizing and scheduling problem in flexible flow lines with unrelated parallel machines over a finite planning horizon. It is assumed that all parameters such as demand rates for the products are deterministic and constant over a finite planning horizon. A new mixed zero-one nonlinear mathematical program for the problem has been developed. Due to the difficulty of obtaining the optimal solution, an efficient constructive heuristic algorithm is also proposed and evaluated. Computational experiments indicate that the proposed heuristic is very hopeful especially for obtaining a near-optimal (or optimal) solution in medium and large-scaled problems.

Batch scheduling of jobs with identical process times on flexible flow lines

We consider a batch scheduling problem for flexible flow lines. A number of jobs have to be scheduled, and each job belongs to a specific product type. Setup costs are incurred when changing a machine from one product type to another. On each stage, all jobs have the same process time. The objective is to minimize setup costs and the mean flow time. We identify an analogy to a pallet-loading problem and present a solution approach that consists of two nested genetic algorithms. The heuristic solves realistic problem sizes in a relatively short amount of time. It can be adjusted by a lookahead-parameter that enables a human planner to effectively manage the trade-off between the two objectives.

Conceptual framework for lot-sizing and scheduling of flexible flow lines

The paper considers the lot-sizing and scheduling problem for flexible flow line production facilities. Flexible flow lines are flow lines with parallel machines on some or all production stages. The objective is to find lot-sizes and a feasible schedule that minimizes set-up, inventory holding and back-order costs. Minimization of mean flow time (measured between entering the first stage and leaving the last) is a secondary objective. An integrative solution approach is presented that can incorporate the interdependencies between lot-sizing and scheduling decisions. Applications of the approach in the semiconductor industry are illustrated.

DEEPWATER GAS FIELD PRODUCTION FROM SUBSEA WELLS INTO COMPRESSED NATURAL GAS CARRIERS THROUGH A HYBRID RISER TOWER

This paper addresses the feasibility of developing an ultra-deepwater gas field by producing directly from subsea wells into Compressed Natural Gas (CNG) Carrier ships. Production interruptions will be avoided as two Gas Production Storage Shuttle (GPSS) vessels storing CNG switch out roles between producing/storing via one of two Submerged Turret Production (STP) buoys and transport CNG to a remote offloading buoy. This paper considers the challenges associated with a CNG solution for an ultra-deepwater field development and the specific issues related to the risers. A Hybrid Riser Tower (HRT) concept design incorporating the lessons learned from the Girassol experience allows minimisation of the vertical load on the STP buoys. The production switchover system from one GPSS to the other is located at the top of the HRT. High-pressure flexible flowlines with buoyancy connect the flow path at the top of HRT to both STP buoys. System fabrication and installation issues, as well as specific met ocean conditions of the GOM, such as eddy currents, have been addressed. The HRT concept can be also used for tiebacks to floating LNG plants.

Scheduling flexible flow lines with sequence-dependent setup times

This paper examines scheduling in flexible flow lines with sequence-dependent setup times to minimize makespan. This type of manufacturing environment is found in industries such as printed circuit board and automobile manufacture. An integer program that incorporates these aspects of the problem is formulated and discussed. Because of the difficulty in solving the IP directly, several heuristics are developed, based on greedy methods, flow line methods, the Insertion Heuristic for the Traveling Salesman Problem and the Random Keys Genetic Algorithm. Problem data is generated in order to evaluate the heuristics. The characteristics are chosen to reflect those used by previous researchers. A lower bound has been created in order to evaluate the heuristics, and is itself evaluated. An application of the Random Keys Genetic Algorithm is found to be very effective for the problems examined. Conclusions are then drawn and areas for future research are identified.

Comparing scheduling rules for flexible flow lines

This paper explores scheduling flexible flow lines with sequence-dependent setup times. Three major types of heuristics are explored. Insertion heuristics (based on insertion heuristics for the traveling salesman problem) attempt to simultaneously equalize workload on all processors at a stage, and minimize total or single-stage flowtimes. Johnson's algorithm for two-stage flow shops and its heuristic extensions to m-machine flow shops are modified for parallel processors and the flexible flow-line environment. A set of naı̈ve greedy heuristics is investigated for comparison purposes. The performance of the heuristics is compared on a set of test problems. Results indicate the range of conditions under which each method performs well.

Configuring flexible flowlines

Flexible machines are machines equipped to respond to a variety of jobs by the selecting appropriate tools, which are available on the machine, to match the tasks required for each incoming job. Computer Numerical Control machines (CNCs) and robots with multiple grippers are examples of such machines. However, the tool holding or tool magazine capacity usually limits the flexibility of these machines. A sequence of such machines, with directed flows, is a flexible flowline, and these are seen as a possible solution for producing large varieties of similar products. In this paper, problems related to configuring flexible flowlines are considered, with the goal of minimizing the line size without requiring any backtracking while processing parts. Several forms of the problem are considered. Scenarios where single part types are produced on identical, tool-magazine capacity limited machines are examined first. These are expanded to include restrictions on processing capabilities as constraints. Multiple-part type scenarios are then modelled, beginning with procedures addressing open magazines, finally followed by restricted machines, with tool magazine size limitations. A mathematical programming formulation for configuring such a line is detailed, and solutions for test cases presented.

An exact approach for batch scheduling in flexible flow lines with limited intermediate buffers

The paper presents a mixed integer programming approach for makespan minimization in flexible flow lines. The line consists of several processing stages in series, separated by finite intermediate buffers, where each stage has one or more parallel identical machines. The problem objective is to determine a minimum length schedule for a mix of part types, where identical parts are scheduled consecutively. The limited intermediate buffers between the stages result in a scheduling problem with machine blocking, where a completed part may remain on a machine and block it until a downstream machine becomes available. Numerical examples modeled after real-world surface mount technology lines for printed wiring board assembly are provided and some computational results are reported to illustrate the approach.

An adaptable problem-space-based search method for flexible flow line scheduling

Leon and Ramamoorthy (1997) developed an adaptable problem-space-based search method. Part of that work included development of a lower bound and comparison of makespans using real-world data. In this note we improve their lower bound and show that the Leon and Ramamoorthy search method found better makespan solutions than their lower bound indicated, including some optimal makespans.

Mixed integer programming for scheduling flexible flow lines with limited intermediate buffers

This paper presents new mixed integer programming formulations for scheduling of a flexible flow line with blocking. The flexible flow line consists of several processing stages in series, separated by finite intermediate buffers, where each stage has one or more identical parallel machines. The line produces several different product types and each product must be processed by, at most, one machine in each stage. A product which has completed processing on a machine may remain there and block the machine until a downstream machine becomes available for processing. The objective is to determine a production schedule for all products so as to complete the products in a minimum time. The basic mixed integer programming formulations have been enhanced to model blocking scheduling with alternative processing routes where for each product a set of routes is available for processing. A reentrant flow line where a product visits a set of stages more than once is also considered. Numerical examples are presented to illustrate applications of the various models proposed.

Scheduling algorithms for computer-aided line balancing in printed circuit board assembly

Generalized flexible flow line (GFFL) is a scheduling environment comprising several machine banks which the products visit in the same order but can skip some machine banks. The type of machines in a bank can differ but they are suitable for performing the same manufacturing tasks. To change one product to another demands a set-up operation of the machine. This paper describes several scheduling algorithms for the GFFL problem. The overall structure of these algorithms is similar, consisting of machine allocation and sequencing phases. The algorithms have been integrated into an interactive production scheduling system for electronics assembly. Sample cases are used to illustrate the operation of the system in practice.

INNOVATIONS IN SUBSEA DEVELOPMENT AND OPERATION

Esso Australia Ltd on behalf of the Esso/BHP joint venture, recently completed Australia's first deep- water oil and gas development, Blackback, in 395 m water depth in eastern Bass Strait. Esso used a phased development approach and an innovative development concept to mitigate the effect of reserves uncertainty. The development consists of three wells in daisy-chain formation tied back to the existing Mackerel platform, 23 km distant. The development also used innovative approaches for installation of flexible flowline and umbilical jumpers from the drilling rig, management of hydrates in the production flowline and control system integration.In the same time frame, Esso repaired the failed electro-hydraulic control systems of two 10-year-old subsea wells. The repair program used an innovative approach to fault diagnosis and field work.

A simulation analysis of sequencing rules in a flexible flowline

The paper concerns a flexible flowline scheduling problem, which arises in the footwear industry. Flexibility of the line allows for manufacturing simultaneously more products in lower quantities, but it also increases the complexity of the task of balancing the line, specially because the mix of products changes everyday. A simulation model to deal with the flexible line is developed and several job sequencing rules and different part input criteria are implemented. The impact of each rule on the quality of the schedules is measured, namely, according to makespan, productivity and average machine utilisation. Computational results concerning a real application are also presented. SIMPLE++ is the simulation language used.

Design of electronic assembly lines: An analytical framework and its application

The design of component assembly lines in Printed Circuit Board (PCB) manufacturing environments is a challenging problem faced by many firms in the electronics industry. The main design approaches to such component assembly lines are the Mini-Line, Flexible Flow Line, and Hybrid Line designs. In this paper, we discuss the operational trade-offs associated with these design alternatives and present a mathematical programming framework that captures relevant system design issues. Each of the design alternatives can be viewed as a special case of the stated mathematical programming model. We develop effective algorithms to solve these mathematical programs. We have used the framework in a specific PCB manufacturing environment to advise managers on the best configuration of their lines. The models were used as sensitivity analysis tools. The results of our computational experiments, combined with qualitative comparisons of different design approaches developed by a crossfunctional team (engineers, manufacturing and product managers), have led to the development of a set of managerial guidelines for the selection of the design plan for component assembly lines in the studied environment.