Model systems dynamic models

Homer JB, Hirsch GB (2006) System dynamics modelling for pubhc health background and opportunities, Am J Public Heith 96 452-458... 

In order to gain insight into the consequences of the choice of a certain model and limits, one could perform critical load calculations with different models (complex dynamic models versus simple steady-state models) using various limits and compare the results. In this way, one also gets insight into (i) the differences in vulnerability of the various environmental compartments and related organisms and (ii) the relevance of the different processes in the systems and of the different ways of parameterizing certain processes. 

Angerhofer BJ, Angelides MC (2000) System Dynamics Modelling in Supply Chain Management Research Review, In Joines JA, Barton RR, Kang K, Fishwick PA (eds) Proceedings of the 2000 Winter Simulation Conference, pp 342-351... 

The following three sections present different model applications to analyse the impacts of hydrogen to the economies using the scenarios described in Section 18.3. In Section 18.4 employment effects for ten European countries will be exemplarily analysed with an input-output model. In Section 18.5, GDP effects for different European countries will be analysed with a general equilibrium model. Section 18.6 presents a system dynamic model, which deals with GDP and employment effects. Section 18.7 summarises the different model approaches, presents and discusses the results, and draws overall economic conclusions. 

System-dynamics model ASTRA 18.6.1 General modelling approach... 

Typically, a non-linear system dynamic model is made up of individual lumped models of the components which at a minimum conserve mass and energy across the given component, but may also have a momentum equation if pressure drops must also be analyzed. For most dynamic problems of interest in hybrid studies, however, the momentum equation may be taken as quasi-steady (unless the solver requires the dynamic form to perform the numerical solution). Higher fidelity individual models or reduced order models (ROMs) can also be used, where the connection to the system model would be made at each subcomponent boundary. Since dynamic systems modeling is not as common as steady-state modeling, some discussion of modeling approaches will be given. There are two primary methods used to provide solutions for the pressure-flow dynamics of a system model. 

To give an illustration of our concept, we want to present some rather simple model systems. These models are examples of a typical nonlinear behaviour and they might perhaps serve as an explanation of some specific effects found in experiments (vid. Refs. J, 2, 3). It should be emphasized that the models are rather speculative. However, they are based on both, the physical properties and the relevant physical laws, which determine the dynamics of the system under consideration. 

The four experiments done previously with Rnp (= 0.5, 1, 3, 4) were used to train the neural network and the experiment with / exp = 2 was used to validate the system. Dynamic models of process-model mismatches for three state variables (i.e. X) of the system are considered here. They are the instant distillate composition (xD), accumulated distillate composition (xa) and the amount of distillate (Ha). The inputs and outputs of the network are as in Figure 12.2. A multilayered feed forward network, which is trained with the back propagation method using a momentum term as well as an adaptive learning rate to speed up the rate of convergence, is used in this work. The error between the actual mismatch (obtained from simulation and experiments) and that predicted by the network is used as the error signal to train the network as described earlier. 

In the case of actor-oriented simulation models, system dynamics are produced by actors (persons or organizational units) based on specific activities [261, 426, 599, 604, 771, 813]. 

In process-oriented simulation models, system dynamics are produced by activities through the usage of resources (persons, tools) [571, 596, 597, 691, 925]. 

Kifle D, Sverdrup H, Koca D, Wibetoe G (2013) A simple assessment of the global long term supply of the rare earth elements by using a system dynamics model. Environ Nat Resour Res 3... 

Based on the analysis of coal mine safety production system, this paper will establish the system dynamic model of covering coal mine safety production factors, safety input and safety performance by using the system dynamics principle. The software (Vensim PLE v5. 6a) will be used to dynamically evaluate and quantitatively predict system safety performance. 

THE SYSTEM DYNAMICS MODELING OE COAL MINE SAFETY INPUT AND SAEETY PERFORMANCE... 

In systems engineering perspective, this paper constructs a system dynamics model of safety input and safety performance in coal mine production. It s dynamically simulated the impact of... 

System dynamics modeling was used to show the relationship among the contextual factors and unsafe control actions and the reasons why the safety control structure migrated toward ineffectiveness over time. Most modeling techniques provide... 

First, system dynamics models were created to model the contextual influences on the behavior of each component (patients, pharmaceutical companies, the FDA, and so on) in the pharmaceutical safety control structure. Then the models were combined to assist in understanding the behavior of the system as a whole and the interactions among the components. The complete analysis can be found in [43] and a shorter paper on some of the results [44]. An overview and some examples are provided here. 

Couturier incorporated into the system dynamics models the changes that were proposed by the lOM after the Vioxx events, the changes actually implemented in FDAAA, and the recommendations coming out of the STAMP-based causal analysis. One major difference was that the STAMP-based recommendations had a broader scope. While the lOM and FDAAA changes focused on the FDA, the STAMP analysis considered the contributions of all the components of the pharmaceutical safety control structure to the Vioxx events and the STAMP causal analysis led to recommendations for changes in nearly all of them. 

Appendix D explains how to read system dynamics models, for those unfamiliar with them. 

The three basic components of system dynamics models. 

Fig. 15.11 Example systems dynamics model of software process for a buUd ...

Uniscott Surveys Ltd (1990) [1]. Thames Water Utilities Stored Water Supply System, Dynamic Modelling - Field Test. GPS Level Survey. Report to Thames Water Utilities Ltd. 

Models Considering a Membrane Diffusion Model. Sobotka et al. (1982) claimed that the empirical time delay models previously described do not properly consider the physical nature of the electrode response. Instead, they insisted that models based on Pick s second law are superior and encouraged their use to more accurately model system dynamics. Sobotka et al. (1982), in their review, presented many of the different diffusional models that have been developed and discussed their usefulness. 

LeClaire, R.J. Reilly, G.O. 2005. Leveraging a High Fidelity Switched Network Model to Inform System Dynamics Model of the Telecommunications Infrastructure, System dynamics. 

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