Engineering process model: Detection of cycles and determination of paths

[摘要] In order to plan the engineering work of large construction projects efficiently, a model of the engineeringprocess is required. An engineering process can be modelled by sets of persons, tasks, datasets and tools,as well as the relationships between the elements of these sets. Tasks are more often than not dependenton other tasks in the engineering process. In large projects these dependencies are not easily recognised,and if tasks are not executed in the correct sequence, costly delays may occur.The homogeneous binary relation 'has to be executed before in the set of tasks can be used todetermine the logical sequence of tasks algebraically. The relation can be described by a directed graphin the set of tasks, and the logical sequence of tasks can be determined by sorting the graph topologically,if the graph is acyclic. However, in an engineering process, this graph is not necessarily acyclic sincecertain tasks have to be executed in parallel, causing cycles in the graph. After generating the graphin the set of tasks, it is important to fuse all the cycles. This is achieved by finding the stronglyconnected components of the graph. The reduced graph, in which each strongly connected componentis represented by a vertex, is a directed acyclic graph. The strongly connected components may bedetermined by different methods, including Kosaraju's, Tarjan's and Gabow's methods.Considering the 'has to be executed before graph in the set of tasks, elementary paths through thegraph, i.e. paths which do not contain any vertex more than once, are useful to investigate the influenceof tasks on other tasks. For example, the longest elementary path of the graph is the logical criticalpath. The solution of such path problems in a network may be reduced to the solution of systems ofequations using path algebras. The solution of the system of equations may be determined directly, i.e.through Gauss elimination, or iteratively, through Jacobi's or Gauss-Seidel's methods or the forwardand back substitution method. The vertex sequence of an acyclic graph can be assigned in such a waythat the coefficient matrix of the system of equations is reduced to staggered form, after which thesolution is found by a simple back substitution. Since an engineering process has a start and an end,it is more acyclic than cyclic. Consequently we can usually reduce a substantial part of the coefficientmatrix to staggered form. Using this technique, modifications of the solution methods mentioned abovewere implemented, and the efficiency of the technique is determined and compared between the variousmethods.

[发布机构] Stellenbosch University