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Validation of System Dynamics Models – a Case Study

100%
Lemke J., Łatuszyńska M.
Journal of Entrepreneurship, Management and Innovation
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2013
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vol. 9
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issue 2
45-59
EN
The purpose of this article is the analysis of the system dynamics model validation illustrated by the example of a model of the manufacturing resource allocation. In the first part of the article the authors present an overview of the definitions of validation and verification that can be found in the reference literature. Also, they emphasize the role which validation and verification play in the modeling process. Furthermore, they discuss the techniques of system dynamics model validation with particular focus on tests of the model structure, behavior and policy implications. The second part of the article contains an example of the validation process of a system dynamics model simulating manufacturing resource allocation in an electronic company. The purpose of the model is to assess the long-term effect of assigning workers to individual tasks on such production process parameters as efficiency or effective work time. The authors focus their particular attention on that part of the model which deals with a storehouse, one of the company production units. They conduct tests of its structure and behavior. When validating the structure the authors make use of the information obtained in a series of interviews with the company staff. They also refer to the generally accepted knowledge found in the reference literature. The results generated by the model in the course of the behavior tests are compared with the real data. The authors evaluate both the logic of the system behavior and the level of accuracy of the output data in reference to the real system.
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From Problem Conceptualization to Simulation. the Application of the Systems Dynamics to Water Management Problem

80%
Kazimierz Ś.
Journal of Entrepreneurship, Management and Innovation
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2011
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vol. 7
51-61
EN
The article continues previous text published in "Management Business Innovation" (no. 6, 2010) under the title Stock-And-Flow Thinking In Decision Making. Towards Systemic Procedure of Problem Solving. The methodology presented there is shown in the practical context of water supply management problem in one of the largest cities in Mexico. Basic methodological implications for computer supported problem modeling and simulation are shown, beginning with the Partitioning&Tearing Method, causal diagram of the problem as well as the computer simulation model structure drawn with the VensimTM software.
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Stock-And-Flow Thinking in Decision Making. Toward Systemic Procedure of Problem Solving

80%
Śliwa K.
Management Business Innovation
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2010
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vol. 6
52-61
EN
The article presents fundamental rules of the systemic thinking in decision making and it proposes a unified problem solving procedure. The Partitioning Method is presented and it is shown how that method can be used in discovering system structure or problems. The problem structure is a critical factor in solving them. Special attention is paid to the variables described as Stock-and-Flow which absorbs the problems' dynamics and determine its feedback structure. The analysis is presented as part of the Dynamic Decision Making theory.
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Understanding the Structural Complexity of Induced Travel Demand in Decision-Making: A System Dynamics Approach

80%
Angarita-Zapata J. S., Parra-Valencia J. A., Andrade-Sosa H. H.
Organizacija
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2016
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vol. 49
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issue 3
129-143
EN
Background and purpose: Induced travel demand (ITD) is a phenomenon where road construction increases vehicles’ kilometers traveled. It has been approached with econometric models that use elasticities as measure to estimate how much travel demand can be induced by new roads. However, there is a lack of “white-box” models with causal hypotheses that explain the structural complexity underlying this phenomenon. We propose a system dynamics model based on a feedback mechanism to explain structurally ITD. Methodology: A system dynamics methodology was selected to model and simulate ITD. First, a causal loop diagram is proposed to describe the ITD structure in terms of feedback loops. Then a stock-flows diagram is formulated to allow computer simulation. Finally, simulations are run to show the quantitative temporal evolution of the model built. Results: The simulation results show how new roads in the short term induce more kilometers traveled by vehicles already in use; meanwhile, in the medium-term, new traffic is generated. These new car drivers appear when better flow conditions coming from new roads increase attractiveness of car use. More cars added to vehicles already in use produce new traffic congestion, and high travel speeds provided by roads built are absorbed by ITD effects. Conclusion: We concluded that approaching ITD with a systemic perspective allows for identifying leverage points that contribute to design comprehensive policies aimed to cope with ITD. In this sense, the model supports decision- making processes in urban contexts wherein it is still necessary for road construction to guarantee connectivity, such as the case of developing countries.
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Modeling the Real Estate Prices in Olsztyn under Instability Conditions

80%
Bełej M., Kulesza S.
Folia Oeconomica Stetinensia
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2012
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vol. 11
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issue 1
61-72
EN
The paper deals with the description of the issues related to the dynamics of the real estate market in terms of sharp, unexpected changes in the housing prices which have been observed in the last decade in many European countries due to some macroeconomic circumstances. When such perturbations appear, the real estate market is said to be structurally unstable, since even a small variation in the control parameters might result in a large, structural change in the state of the whole system. The essential problem addressed in the paper is the need to define and discriminate between the intervals of stable and unstable real estate market development with special attention paid to the latter. The research aims at modeling hardly explored field of discontinuous changes in the real estate market in order to reveal the bifurcation edge. Assuming that the periods of sudden price changes reflect an intrinsic property of the real estate market, it is shown that the evolution path draws for most of the time a smooth curve onto the stability area of the equilibrium surface, and only briefly penetrates into the instability area to hop to another equilibrium state.
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The Business Diagnostics Model Addressing its Components Variation Dynamics

80%
Olejniczak J.
Zarządzanie i Finanse
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2013
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vol. 3
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issue 1
103-115
EN
Company diagnostics is a vital element of its safe operation on the competitive market. Among the existing IT solutions, diagnostics is most often used in the Business Intelligence (BI) class systems designed for monitoring company business activities on a current basis (Business Activity Monitoring BAM). But solutions of this type reflect the current situation of the company without addressing the changes in its environment or any feedbacks existing in the company. The approach presented in the paper adopts a diagnostic method based on analysis of the dynamics of changes and interrelations between the relevant elements.
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System dynamics model for policy scenarios of organic farming development

80%
Rozman Č., Pažek K., Prišenk J., Škraba A., Kljajić M.
Organizacija
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2012
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vol. 45
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issue 5
212-218
EN
This paper presents the system dynamics model of organic farming development in order to support decision making. The model seeks answers to strategic questions related to the level of organically utilized area, levels of production and crop selection in a long-term dynamic context. The model will be used for simulation of different policy scenarios for organic farming and their impact on economic and environmental parameters of organic production at an aggregate level. Using the model, several policy scenarios were performed.
8

The Development of Sugar Beet Production and Processing Simulation Model – a System Dynamics Approach to Support Decision-Making Processes

80%
Rozman Č., Škraba A., Pažek K., Kljajić M.
Organizacija
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2014
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vol. 47
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issue 2
99-105
EN
Background: The sugar beet is the main field crop used for sugar production in the temperate climatic zone. The abolishment of the quota system will open new investment opportunities in countries that were forced to abandon sugar industry as the result of the reform in 2006. Present paper describes the modeling of sugar beet production and its processing into sugar for purpose of decision support. Methods: A system dynamics methodology was chosen to model impacts of regional sugar factory investment. We present two basic concepts of system dynamics models at causal loop diagram level. The first holistic model deals with regional planning of new product development and the second one deals with factory model. Results: The holistic model presented main feedback loops and dynamics of main elements in the case of regional investment into sugar industry. The factory model considered the specifics of the beet processing which is a) limited period of beet processing and b) initial adjustment to the production capacity at the start of the production season Conclusions: The model seeks answers to strategic questions related to the whole sugar beet production and processing system and will be used for simulation of different scenarios for sugar production and their impact on economic and environmental parameters at an aggregate level.
9

Sugar Beet Production: A System Dynamics Model and Economic Analysis

80%
Rozman Č., Kljajić M., Pažek K.
Organizacija
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2015
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vol. 48
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issue 3
145-154
EN
Background and Purpose: The sugar beet is the main field crop used for sugar production in the temperate climatic zone. Since investment in sugar beet industry are long term and ireversible the decision support and economic analysis are required in order to maximise investment returns. Methodology: A system dynamics methodology was chosen to model the impacts of regional sugar factory investments. We present the basic concepts of system dynamics (SD) models and their development in the case of sugar beet production and processing systems. Sugar beet economics are also analyzed using the static technological economic simulation model. Results: The simulation provides answers to strategic questions related to the total sugar beet production and processing system and will be used for the simulation of different scenarios for sugar production and their impact on economic and environmental parameters at an aggregate level. Furthermore, the feasibility analysis of sugar beet production revealed that at the current price and intensity levels (yields), we can expect profitable sugar beet production for both white sugar and ethanol. Conclusion: Preliminary results show that under expected production parameters the sugar beet processing and production would be economically feasible.
10
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The Modeling Process of the Materials Management System in a Manufacturing Company Based on the System Dynamics Method

80%
Baran M.
Journal of Entrepreneurship, Management and Innovation
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2013
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vol. 9
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issue 2
79-96
EN
The article presents the steps of modeling of the material management system in a manufacturing company. First, the modeling procedures indicating by Forrester, Łukaszewicz, Souček, Tarajkowski and Sterman were described and the essence of materials management in a manufacturing company was presented. Next, modeling of the materials management system was shown - step by step. Initially, the variables of the mental model connected with materials were defined, then variables in casual loop diagrams were linked. Diagrams were transformed into a simulation model that has been verified. The validation of the simulation model was conducted by using the following methods: assessing the correctness of the boundary of modeling, adequacy of the model structure and adopted values (constants) compared with available knowledge about the modelled system; test of the accuracy and consistency of the units of variables adopted in the model and test of the model behavior in extreme conditions. The study endpoints included the simulation of the model on empirical data, which were collected in the company Alpha and test of the “what ... if ...”. The test showed that the small changes in control norms (constants), which control the system, could have influenced to more rational management of that system.
11

Hybridization of Stochastic Local Search and Genetic Algorithm for Human Resource Planning Management

70%
Škraba A., Stanovov V., Semenkin E., Kofjač D.
Organizacija
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2016
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vol. 49
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issue 1
42-54
EN
Background and Purpose: The restructuring of human resources in an organization is addressed in this paper, because human resource planning is a crucial process in every organization. Here, a strict hierarchical structure of the organization is of concern here, for which a change in a particular class of the structure influences classes that follow it. Furthermore, a quick adaptation of the structure to the desired state is required, where oscillations in transitions between classes are not desired, because they slow down the process of adaptation. Therefore, optimization of such a structure is highly complex, and heuristic methods are needed to approach such problems to address them properly. Design/Methodology/Approach: The hierarchical human resources structure is modeled according to the principles of System Dynamics. Optimization of the structure is performed with an algorithm that combines stochastic local search and genetic algorithms. Results: The developed algorithm was tested on three scenarios; each scenario exhibits a different dynamic in achieving the desired state of the human resource structure. The results show that the developed algorithm has successfully optimized the model parameters to achieve the desired structure of human resources quickly. Conclusion: We have presented the mathematical model and optimization algorithm to tackle the restructuring of human resources for strict hierarchical organizations. With the developed algorithm, we have successfully achieved the desired organizational structure in all three cases, without the undesired oscillations in the transitions between classes and in the shortest possible time.
12

A System Dynamics Model for Improving Primary Education Enrollment in a Developing Country

61%
Pedamallu C., Ozdamar L., Ganesh L., Weber G.-W., Kropat E.
Organizacija
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2010
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vol. 43
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issue 3
90-101
EN
The system dynamics approach is a holistic way of solving problems in real-time scenarios. This is a powerful methodology and computer simulation modeling technique for framing, analyzing, and discussing complex issues and problems. System dynamics modeling is often the background of a systemic thinking approach and has become a management and organizational development paradigm. This paper proposes a system dynamics approach for studying the importance of infrastructure facilities on the quality of primary education system in a developing nation. The model is built using the Cross Impact Analysis (CIA) method of relating entities and attributes relevant to the primary education system in any given community. The CIA model enables us to predict the effects of infrastructural facilities on the community's access of primary education. This may support policy makers to take more effective actions in campaigns that attempt to improve literacy.
13

The Influence Of Financing On The Dynamics Of Housing Prices

61%
Bełej M., Kulesza S.
Folia Oeconomica Stetinensia
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2014
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vol. 14
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issue 2
101-113
EN
Real estate market can be thought of as an open, dynamic system. It means that it is able to exchange stimuli with other open systems, and that its state evolves in a way that might be described mathematically. It turns out that two main processes contribute to the overall evolution of the real estate market: long-term, predictable evolution, interrupted by sharp changes of catastrophic origin. In this picture, national housing funds play an important role in supporting the housing finance: on one hand they could either stimulate or suppress the real estate market influencing the availability of the mortgage credit, but on the other hand, they could also help to stabilize prices. In this study, an attempt was made to determine the degree of relationship between the volume of mortgage financing from national housing funds and the dynamics of real estate prices.
14

Web Application for Hierarchical Organizational Structure Optimization – Human Resource Management Case Study

61%
Kofjač D., Bavec B., Škraba A.
Organizacija
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2015
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vol. 48
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issue 3
177-186
EN
Background and Purpose: In a complex strictly hierarchical organizational structure, undesired oscillations may occur, which have not yet been adequately addressed. Therefore, parameter values, which define fluctuations and transitions from one state to another, need to be optimized to prevent oscillations and to keep parameter values between lower and upper bounds. The objective was to develop a simulation model of hierarchical organizational structure as a web application to help in solving the aforementioned problem. Design/Methodology/Approach: The hierarchical structure was modeled according to the principles of System Dynamics. The problem of the undesired oscillatory behavior was addressed with deterministic finite automata, while the flow parameter values were optimized with genetic algorithms. These principles were implemented as a web application with JavaScript/ECMAScript. Results: Genetic algorithms were tested against well-known instances of problems for which the optimal analytical values were found. Deterministic finite automata was verified and validated via a three-state hierarchical organizational model, successfully preventing the oscillatory behavior of the structure. Conclusion: The results indicate that the hierarchical organizational model, genetic algorithms and deterministic finite automata have been successfully implemented with JavaScript as a web application that can be used on mobile devices. The objective of the paper was to optimize the flow parameter values in the hierarchical organizational model with genetic algorithms and finite automata. The web application was successfully used on a three-state hierarchical organizational structure, where the optimal flow parameter values were determined and undesired oscillatory behavior was prevented. Therefore, we have provided a decision support system for determination of quality restructuring strategies.
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Rola systemu informacyjnego w zarządzaniu organizacją w turbulentnym otoczeniu

51%
Unold J.
Roczniki Naukowe Wyższej Szkoły Bankowej w Toruniu
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2012
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issue 11
285-300
XX
The role of an information system in corporate management in the turbulent environment
16
Content available remote

Simulation of production-sale decision-making with multiobjective optimization by Vensim language

51%
Kasperska E., Kasperski A., Mateja-Losa E.
Organizacja i Zarządzanie : kwartalnik naukowy
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2014
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vol. nr 2
45--65
PL
Celem pracy jest prezentacja pewnych nowych wyników badań przeprowadzonych przez autorów w obszarze analizy wrażliwości i optymalizacji na modelach typu Dynamiki Systemowej. Podstawowe sprzężenia zwrotne w Modelu Produkcja – Sprzedaż zostały przedstawione wraz z wynikami eksperymentów symulacyjnych (obu typów: maksymalizacji zysków ze sprzedaży i minimalizacji kosztów produkcji). Zilustrowano je tak zwanymi zakresami ufności (confidence bounds), używając możliwości wizualizacyjne języka Vensim. Na końcu sformułowano wnioski z pracy.
EN
The aim of our paper is to present some of the latest results of authors' investigations in the area of sensitivity analysis and optimization on a model of the System Dynamics type. The elementary feedbacks in Production-Sale Decision-Making are presented, and results of simulation experiments (both type: maximization of profit from sale and minimization of cost of production) are illustrated in the form of so called confidence bounds. The visual possibilities provided by the simulation language Vensim were used. Conclusions are formulated at the end of this paper.
17
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Zbiory rozmyte w analizie zdolności systemu ekonomicznego do funkcjonowania

51%
Wołoszyn J., Urban W.
Zeszyty Naukowe Małopolskiej Wyższej Szkoły Ekonomicznej w Tarnowie
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2004
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issue 5
173-183
PL
Artykuł omawia możliwości wykorzystania metod teorii zbiorów rozmytych w symulacyjnym badaniu dynamiki systemów ekonomicznych. Rozmyte, z natury rzeczy, rezultaty takich eksperymentów symulacyjnych cechuje wielowymiarowość, dostarczająca szerokiego spektrum informacji o badanym procesie. Klasyczne metody analizy oparte przede wszystkim na przetwarzaniu opisu rzeczywistości w kategoriach systemów probabilistycznych nie są dostosowane do eksploracji potencjalnych możliwości badawczych związanych z wykorzystaniem systemów rozmytych, zwłaszcza w sytuacji gdy badanie dynamiki systemowej jest prowadzone nie tylko w odniesieniu do danego systemu rzeczywistego, ale także w łączności z procesem zmian w warstwie ocen możliwości realnego wystąpienia obrazu tej dynamiki.
EN
The paper presents some ideas, showing that the methods of fuzzy sets may be effective in simulation studies of the economic systems dynamics. Fuzzy, by nature, results of such simulation studies are characterized as multidimensional and providing a wide range of information about the studied process. Classical methods of making analysis, which are mainly based on transforming the description of reality in terms of probabilistic systems, are not adjusted to exploration of potential experimental capacities connected with the use of the fuzzy sets, especially in the situation when the studying of the system dynamics is carried out not only with reference to the real system, but also along with the process of changes brought about in the sphere of a possibilities evaluation of real appearance of a picture of that dynamics. In case of studying the dynamics of economic systems, using the model of a system dynamics along with the fuzzy-collective modification, the concept of verifying feedback may refer to the management process. In the course of that process a loop verifying feedback can be placed. Simulative studying of that loop, from the point of view of the system engineering, should lead to conclusions concerning the quality of the management systems. Stating the relationship between the process of management and the state of the executive system makes it possible to formulate general rules of the theory of the system capacity to function. This theory presents a proposition of a content-related interpretation of the fuzzy results of the simulation studies with the fuzzy-collective modification in the study of the economic systems dynamics.
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