Akarsu Havzası Sistemlerinin Planlanması İçin Genel Maksatlı Bir Simulasyon Modeli

Abstract

Bu çalışmada, akarsu havzalarının planlanmasında kullanılmak üze re, çeşitli fiziksel sistem konfigûrasyonlarmın benzeştirilmesine imkan verebilen, genel maksatlı bir simülasyon modelinin geliştirilmesi amaç lanmıştır. Bu amaçla geliştirilen ve çalışma içerisinde "SIMULAX" adıyla referans verilecek olan modelde, sulama, içme-kullanma, hidro-elektrik enerji ve düşük akımların kontrolü gibi maksatlar ele alınmıştır. Modelin tasarımında düğüm noktalan yöntemi kullanılmıştır. Düğüm noktalan, akarsu havzası sistemlerini oluşturan çeşitli fiziksel bileşenleri temsil et mektedir. Sistem konflgürasyonu, bağlantı elemanlarıyla birbirine bağlı düğümlerden oluşan bir şebeke şeklinde şematize edilmekte ve fiziksel yapı bu temsili bileşenler yardımıyla tanımlanarak modele aktarılmakta dır. Modelde, çeşitli maksatlar için tasarlanmış 22 adet düğüm tipi yer almaktadır. Bu düğümler, teorik ve pratik karakteristikleri itibariyle, sis tem konfigûrasyonlarmın çok sayıda kombinezonunu üretebilecek özel liklere sahiptirler. Modelin en önemli özelliği modüler bir yapıda düzen lenmiş olmasıdır. Modüler yapı, uygulamada belirli bir esneklik sağlamakta ve modelin değişik sistemlere adapte edilebilmesini kolaylaş tırmaktadır. Biriktirme haznelerini temsil eden düğümler oldukça detaylı olarak ele alınmıştır. Modelde, bu düğümlerin işletilmesi için hazırlanmış çeşitli alternatif politikalar mevcuttur. Bunlar arasında, koruma (hedging) stratejilerinin uygulandığı politikalar da yer almaktadır. Öte yandan modele, gerekli olduğu takdirde yeni politikaların ilave edilmesi de mümkün olabilmektedir. Model, sistemlerin fiziksel performanslarının ölçülmesinde kullanılan çeşitli istatistikleri ve durum değişkenlerinin fre kans dağılımlarını hesaplamaktadır. Modelin diğer bir yapısal özelliği de, "SIMULAX 1" ve "SIMULAX 2" olarak adlandırılmış olan iki alt modelin kombinasyonu şeklinde organize edilmiş olmasıdır. "SIMULAX 1" simü lasyon modeli, "SIMULAX 2" ise "SIMULAX l"in ürettiği sonuçların tablo lar ve grafikler halinde ekrandan izlenmesini ve gerektiğinde yazıcıdan alınmasını sağlayan bir izleme modelidir. "SIMULAX"ı oluşturan bilgisayar programlan, BASIC dilinde kodlan mış olup, "Micro-Soft" Disk İşletim Sistemi (MS-DOS) kullanılarak, IBM uyuşumlu tüm mikrobilgisayarlarda çalıştırılabilir. Uygulamalar sırasın da karşılaşılabilecek bellek sorunlanyla İlgili olarak "SIMULAX"a bir bel lek kontrol programı yerleştirilmiştir. Bu program, gözönüne alınan sis tem için, "SIMULAX'in gereksinim duyacağı bellek büyüklüğünü önceden bildirmeyi amaçlayan bir uyan programıdır. "SIMULAX", Ankara Su Temini Projesi Hazneler Sistemine uygulana rak test edilmiştir. Bu proje için daha önce yapılmış olan bir çalışmanın sonuçları, "SIMULAX'in ürettiği sonuçlarla karşılaştırılmış ve aralarında belirli bir uyumun mevcut olduğu görülmüştür.

Recently, the increase of the importance of water resources, which constitute a wide potential among natural resources, has caused the evaluation of these resources under a wider perspective, and brought into actuality the multi-purpose and multi-objective planning of development projects. However, the enlargement of project scales has made these projects more complex and also more difficult to be analysed by present classical methods. Therefore systems analysis approach is being used, and new and modern solution techniques brought by this approach are being tried to be adapted to the problems in this field. Simulation models which are one of the most powerful and basic means of systems analysis approach, are widely used in the planning, design and operation studies of the river basin systems. Many of the modelling techniques require the idealization of the real system at a certain level, whereas in simulation models there is no obligation for a great deal of simplification. Thus, it becomes possible that the prototype is represented more realistically and more information is acquired about its behaviour. Since simulation models contain no algorithm for optimization, the optimal solution can not be obtained automatically and directly. Principally, there is need in simulation studies both for the development of a model, and for numerous trials made on the system in hand by the help of the model. While analysing river basin systems by simulation models, numerous physical system configurations and numerous alternatives for each of the configurations (which are formed with various project sizes) should be considered. On the other hand for each one of these alternatives a large number of design with various targets must be produced and different operation policies should be applied. Many simulation models related to the planning and operation of river basins have been developed. Many of these are prepared by taking a certain physical system configuration as a basis and are used to determine the optimal dimensions of the projects constituting the system or to investigate the optimal operation policies of pre-designed projects of which the dimensions are determined beforehand. The field of application of such models which are prepared according to specific properties of a certain physical system, is quite limited. In many of these models changing of the operation rules is very difficult. Thus, the development of XXI general models which make the simulation of numerous physical system configurations (made by combination of various projects) possible and which include different variations of operation rules or which can permit an easy adaptation of new policies suitable to the specific properties of the system under analysis becomes very important. In this study, it is tried to develop a general simulation model, which will contain the above-cited properties as much as possible, for use in the analysis of multi-reservoir and multi-purpose river basin systems. Purposes such as irrigation, water supply, hydro-electric energy and low flov control have been considered in this model referred as "SIMULAX" in the study. In the design of SIMULAX, the method of nodes has been used. The nodes designed to represent various physical components (reservoirs, diversions, hydro-electric plants, irrigation networks, etc.) which constitute river basin systems are defined in a mathematical and logical structure so as to be able to simulate various activities. The nodes are formed to set up the required relations with each other. System configurations are schematized by a network with nodes attached to each other with directional lines or in some cases in the form of a tree. The correspondence between the nodes in the system is formed by the help of connection elements defined to characterize natural river channels or artificial transmission lines. The physical structure and the characteristic properties of the system are defined by the aid of these schemes and are adapted to SIMULAX. A great number of combinations of system configurations can be generated by the help of the nodes and connection elements which the model contains. The number of combinations depend upon the number of node types which are present in the model and the theoretical and practical characteristics of the nodes; it represents a measure of the power of the model in representing real systems and in a way it is a measure of the model's generality. While the increase of node number and characteristic properties of nodes increases the model's elasticity and its possibility of adaptation to different systems, but, it also increases its size and complexity. It is obvious that alternative plans that can be designed for river basins and the system configurations that have to be taken into account during the formation of these plans may exhibit quite different properties and complex relations. For this reason, in the choice of node types included in SIMULAX, the representation of the components that can be met widely in real systems and of typical connections have been given priority. The model has 22 types of nodes. For each type, a symbol and a type number is prescribed. Furthermore each node has been shown by a simple symbolic figure to be used in the system scheme. The nodes have been classified into 3 categories. In the first category, there are nodes which do not have any intra-node activity and which function only for input-output and continuity (inflow nodes, terminal nodes, regulated flow control nodes, loss control nodes, confluence nodes and low flow xxu nodes). In the second category, there are nodes which are defined to represent the projects by which the water is supplied (5 types of diversion nodes for various purposes and 8 types of reservoir nodes). In the third category, nodes characterizing the projects by which water is used for certain purposes (irrigation nodes, water supply nodes and hydro-electric plant nodes) take place. A general expression which represents the system configuration is obtained in the model by making a symbolic derivation and with the aid of this expression the physical system is defined. In this derivation, two sets are defined, one being the set of nodes, the other being the set of connection elements. The set of nodes is the union of 22 sub-sets which characterize node types included in SIMULAX. These sub-sets are named by type numbers of the nodes to which they correspond. Each one of the nodes on the system configuration is an element of one of these sub-sets by its type. The elements of the sub-sets are expressed with double indices. The first index shows the type number of the node the element represents, the second index shows the order number. The set of connection elements is made up of connection vectors expressed with one index. To each one of the nodes on the scheme which shows the system configuration, regardless of their types, an order number is given from upstream to downstream (according to the route the flow follows). These numbers define both the positions of the nodes on the scheme and the order of simulation. The connection elements which link the nodes on the system configuration to one another are also numbered. These numbers are at the same time the order numbers belonging to the vectors in the set of connections elements. Each one of these vectors correspond to a connection position vector defined to show the positions of the connections on the scheme. The first and second indices of these double-indexed vectors show the order numbers of nodes at upstream and downsteam ends of connections, respectively. The adaptation of the system scheme to SIMULAX is very easy and practical. In order to do this, it is sufficient to enter the numbers showing type numbers of nodes (according to the order on the scheme) and the positions of connections (according to order of connection) after the system is schematized and required definitions on the scheme are made. SIMULAX, by the aid of the system setting up program, evaluating these informations forms the system configuration and makes the necessary transformations in order to be adapted to the system. In the model, monthly time period is used. Each month flows at various nodes on the scheme are simulated in order following the numbers determining the positions of nodes. When simulations of all of the nodes on the scheme is completed for a month, returning to the beginning the same procedure is repeated for the next month. This routine continues similarly till the end of the simulation period. During execution the procedure followed at any one of the nodes has three stages; input operations related to determination of follows coming to the XX1U node from upstream node or nodes, intra-node operations, output operations related to flows leaving the node which will be transmitted to downstream node or nodes. A matrix called transmission matrix is used in order to symbolize the transmission of flows from one node to another. The elements of this matrix are fictitious variables defined to transmit flows at the connections at any time step. After the outflows are calculated, they are assigned to these variables and transmitted to node or nodes downstream. Intra-node operations are algebraic and logic operations which simulate the activities at the components which the nodes represent. These operations are quite simple for nodes which are in the first and third categories and they do not include any rules. But at nodes belonging to the second category controlling the flows, these operations are more complex and include certain rules. Nodes defined to represent storage reservoirs have a strong influence on the system's behaviour. For this reason, decision mechanisms to be formed to control the activities at these nodes carry great importance. Under different conditions, many different decisions may arise with respect to keeping the water in the reservoir or releasing the water from the reservoir for various purposes. The number of these decisions increases rapidly as the number of purposes increases. On one hand contradictions appear between storage and outflow related to certain purposes, on the other hand certain priorities or necessities may arise between various outflows. In the model logical procedures have been used which take the standard policy as basis and which make possible the evaluation of various variations that include the formation of conditions as different as possible and the decisions to be taken depending on these conditions. In the critical months, modification of the standard policy is made by applying hedging strategies. Hedging is releasing of water with a certain restriction instead of releasing the total amount of water required to meet the demand in order not to cause greater deficiencies in following months. Thus, it is possible to see how decisions, which can range from keeping the water in reservoirs to releasing it, effect the behaviour of reservoirs, and therefore that of the system. In the single-purpose reservoirs, the problem of priority between releases from the lake and flows to be left downstream has been tried to be solved by the help of a priority coefficient. In multi-purpose reservoirs, it is important how flows to be drawn from the lake for different purposes and outflow to be released downstream will be determined in cases of deficiency. For these cases, coefficients that determine how the allocations will be made, have been inserted in the operation policies. Sometimes, in order to meet a mandatory demand, a certain amount of water should be released downstream, and afterwards if the withdrawal of water from the lake meets the demands completely, an additional amount of water may be released downstream related to storage conditions. These types of decisions can be made with the operation policies SIMULAX includes. XXIV At each diversion node, a rule curve has been developed to determine flows that will be released downstream and that will be diverted. SIMULAX contains a quite detailed procedure to make faster and more correct decisions about the system's power and behaviour, to compare alternatives and to calculate physical performance indices which carry great importance for gaining more information about the system. Furthermore, the frequency distributions of the values the state variables take during the operation of the system are calculated. On the basis of these distributions and performance indices, the values that will be assigned to the decision variables for the next trial can be chosen more correctly and thus it becomes possible to decrease the number of trials. Another property of SIMULAX is that it is a combination of two sub-models. "SIMULAX 1" is the simulation model, "SIMULAX 2" is a monitoring model which makes it possible to follow on the monitor the results "SIMULAX1" generates in tables and graphics and to take printouts when necessary. SIMULAX 1 is made up of 3 units named , and . is the program unit, is the input data unit and is the output data unit of SIMULAX 1. SIMULAX 2 consists of a single program unit called . Since the outputs of SIMULAX 1 are inputs to SIMULAX 2, is the input data unit for SIMULAX 2. SIMULAX has a modular structure. Subroutines and data files have been grouped in packages according to the types of nodes they belong and each one of these packages has been named as a "module". All execution activity belonging to any node, following the organization of SIMULAX, is realized in the module belonging to this node. The modules, at the same time, are also theoretically parts of SIMULAX. One of the most important reasons why SIMULAX is planned in a modular form is to have the possibility of expanding the model. In some systems, components may be found which have not been defined in SIMULAX or whose representation may be difficult. In this situation new node types must be added to the model, to simulate these components. It should be pointed out that such an enlargement is not difficult and would not cause any problem related with the model's structure and organization. Adding a new nodes type to SIMULAX means to prepare a new module in which subroutine and data files related to this node will be found. The computer programs of SIMULAX have been coded using the programming language known as BASICA or GW-BASIC; they can be run in all IBM compatible microcomputers using Micro Soft Disk Operating System (MS-DOS). A memory control program has been included in SIMULAX, related with memory problems that can arise during applications. This program, for the system considered, is a warning program which aims to indicate the memory capacity required by XXV SIMULAX. The system must be divided into suitable sub-systems for analysis when any capacity problem is met related with the system's size. If output flows of an upstream sub-system are kept in a data file belonging to a terminal node, these outputs will function as inputs of an inflow node belonging to an other downstream sub-system. SIMULAX records the results it generates during execution in files it creates automatically in peripheral memories. Thus, input and output data for each alternative may be kept in directories opened under various names in peripheral memories (harddisk or diskettes). It is preferred to do the monitoring directly from the screen. Since the study is based on trials and the generated results come in large numbers, loss of time, by sending many unnecessary outputs to the printer, is thus prevented. Getting a printout of only the necessary outputs, under the control of the user, is preferred (any output, if wanted can be directly sent to the printer during the monitoring of the results on the screen). SIMULAX has been applied numerous times on various hypothetical examples in order to verify the model; software problems, appearing due to the reason that SIMULAX consists of many subroutines a great number of which are quite detailed, have been solved by a great effort. Later on, SIMULAX has been applied to the Reservoirs System of Ankara Water Supply Project. The results of an earlier study made for this project have been compared with the results generated by SIMULAX and it has been observed that a certain accordance exists between them.