1. Mixed-integer nonlinear programming based optimal time scheduling of construction projects under nonconvex costsRok Cajzek, Uroš Klanšek, 2016, izvirni znanstveni članek Opis: Optimal project scheduling under nonconvex time-cost relations represents a challenging problem in construction management. The nonconvex time-cost relations may appear in a construction project when several different duration options are available for its activities due to alternative technological processes enabled for their realization or wide accessibility of production resources. The source of nonconvexity of the project scheduling optimization problem can also be the project penalty- or bonus-duration relations arranged within the construction contract. The aim of this paper is to present the mixed-integer nonlinear programming (MINLP) based optimal time scheduling of construction projects under nonconvex costs. For this purpose, the MINLP model was developed and applied. A numerical example from literature and an example of construction project time-cost trade-off analysis under practical nonconvex penalty function are given in the paper to demonstrate advantages of MINLP optimization. The example from literature first presented the capability of the MINLP approach to obtain the optimal solution for difficult, highly combinatorial nonconvex discrete project scheduling problem. Thereupon, the following example revealed that the optimal project time-cost curve may take very nonuniform shape on account of discrete nature of activity direct cost options and nonconvex relation between project duration and total cost. In this way, the presented study intends to provide practitioners with new information from the field of optimization techniques for project scheduling as well as an alternative view on performance of total cost when project duration is changed. Ključne besede: extreme environments, construction management, discrete optimization, mixed-integer nonlinear programming, nonconvex costs, time scheduling Objavljeno v DKUM: 12.07.2017; Ogledov: 1577; Prenosov: 411 Celotno besedilo (807,33 KB) Gradivo ima več datotek! Več... |
2. A strategy for MINLP synthesis of flexible and operable processesZorka Novak-Pintarič, Zdravko Kravanja, 2004, izvirni znanstveni članek Opis: Abstract This paper presents a sequential two-stage strategy for the stochastic synthesis of chemical processes in which flexibility and static operability (the ability to adjust manipulated variables) are taken into account. In the first stage, the optimal flexible structure and optimal oversizing of the process units are determined in order to assure feasibility of design for a fixed degree of flexibility. In the second stage, the structural alternatives and additional manipulative variables are included in the mathematical model in order to introduce additional degrees of freedom for efficient control. The expected value of the objective function is approximated in both stages by a novel method, which relies on optimization at the central basic point (CBP). The latter is determined by a simple set-up procedure based on calculations of the objective functionćs conditional expectations for uncertain parameters. The feasibility is assured by simultaneous consideration of critical vertices. The important feature of the proposed stochastic model is that its size depends mainly on the number of design variables and not on the number of uncertain parameters. The strategy is illustrated by two examples for heat exchanger network synthesis. Ključne besede: chemical processing, process synthesis, MINLP, mixed integer nonlinear programming, flexibility, operability, controllability, steady state model Objavljeno v DKUM: 01.06.2012; Ogledov: 2622; Prenosov: 97 Povezava na celotno besedilo |
3. An integrated strategy for the hierarchical multilevel MINLP synthesis of overall process flowsheets using the combined synthesis/analysis approachNataša Iršič Bedenik, Bojan Pahor, Zdravko Kravanja, 2004, izvirni znanstveni članek Opis: This paper describes an integrated strategy for a hierarchical multilevel mixed-integer nonlinear programming (MINLP) synthesis of overall process schemes using a combined synthesis/analysis approach. The synthesis is carried out by multilevel-hierarchical MINLP optimization of the flexible superstructure, whilst the analysis is performed in the economic attainable region (EAR). The role of the MINLP synthesis step is to obtain a feasible and optimal solution of the multi-D process problem, and the role of the subsequent EAR analysis step is to verify the MINLP solution and in the feedback loop to propose any profitable superstructure modifications for the next MINLP. The main objective of the integrated synthesis is to exploit the interactions between the reactor network, separator network and the remaining part of the heat/energy integrated process scheme. Ključne besede: multilevel MINLP, MINLP synthesis, attainable region, economic attainable region, concentration attainable region, continous stirred tank reactor, plug flow reactor, recycle reactor, nonlinear programming, mixed integer nonlinear programme Objavljeno v DKUM: 01.06.2012; Ogledov: 2805; Prenosov: 108 Povezava na celotno besedilo |