Dissertationen zum Thema „FlowBox“

The aim of this diploma thesis is to compile a demonstration panel as an example of the functions of intelligent electrical installation KNX. One of the advantages of this system bus is the ability to use devices from multiple manufacturers. A total of 20 devices from 12 different manufacturers are used in this work. The work begins with an explanation of the principle on which the KNX system bus works, followed by a description of the equipment used and the electrical connection of the switchboard according to the wiring diagram. Next, how the whole panel was revived is described. The next chapter contains a detailed description of device programming in ETS, ie setting parameters for individual devices and assigning group addresses. The last chapter deals with visualization and remote control. It explains how a communication channel was created to connect the panel to a server from FlowBox. Using the web interface on this server, a visualization was created, which can be used to remotely control the entire panel from anywhere.

The objective of this project is to develop a boiler modelling methodology, specifically using Flownex, which is capable of running transient simulations for a large variety of coal-fired boiler designs typically used in Eskom. Flownex has been identified as the key software to accomplish the global objective of the Centre for Energy Efficiency under EPPEI at the University of Cape Town, which is to develop a software model of a complete coal-fired power station which includes all the main systems required for independent transient simulation. The boiler model captures the true geometric layout and flow orientation with associated characteristics of a wide variety of boiler designs utilised by Eskom. In order to achieve this, boilers and heat exchangers are grouped according to common physical properties which simplify the modelling process and optimise results. This is preceded by an investigation into the types of boiler designs currently operational in Eskom including available associated geometrical and process characteristics. A study into heat transfer mechanisms applicable to coal-fired boiler heat exchangers was done to ensure fundamental theoretical principles are adhered to during the development of the analytical models, the first step in the modelling process. The Flownex solving methodology is evaluated against the analytical models in a simplified heat exchanger before full detail modelling of heat exchangers are done. The component and method used in Flownex requires convection and radiation heat transfer to be accounted for separately and thus heat exchangers are classified sequentially according to their location in the boiler, this process relies heavily on data obtained in the boiler study. Heat exchangers and auxiliary systems are then integrated into a single system used to obtain steady-state results. The steady-state boiler model is evaluated against actual boiler design data for various loads to prove applicability to various boiler designs and operating conditions.

The study of the steady-state and dynamic behaviour of thermal power plants is of interest and significant benefit in different engineering fields ranging from research and design, to the assistance of operator training, plant optimization, fault finding and failure analysis. In light of the these benefits, and the increasing electrical energy demand in South Africa, the Eskom Power Plant Engineering Institute Centre for Energy Efficiency intends to build a transient simulation model of a coal fired power plant. The software identified for this task is Flownex SE. Flownex is a one-dimensional thermal-hydraulic solver that solves user defined networks by obtaining a numerical solution of the governing equations of fluid dynamics and heat transfer. The software contains a vast library of low level standard industrial components such as valves and pipes that can be linked together to form networks. Due to the overall size and complexity of the intended plant model, it was suggested that individual plant components be modelled separately and then integrated together to form the complete model. The primary objective of this study was to develop one such model, of a deaerator, in Flownex. In addition to being a building block for the complete plant model, the deaerator model will also be used as a standalone model to predict the steady state, transient and non-condensable gas extraction characteristics of the equipment. The first activity performed was to establish the types and operating principles of the deaerators used in industry, particularly in Eskom power stations. This was achieved through a literature survey complemented by six power station visits and a review of some assets owned by Eskom. It was established that the tray and spray type deaerators were the most commonly used deaerator types, and that their operating principle was based on the temperature-solubility relationship of gases in water and Henry's Law. Based on this knowledge, an analytical model of a deaerator was developed. The purpose of this analytical model was to serve as a verification tool for the final Flownex Model. The analytical model was developed by writing a Mathcad algorithm that solved the steady state one-dimensional mass and energy conservation equations around the deaerator boundary together with the oxygen component continuity equation. The model was successfully validated by comparing its predictions to acceptance tests data from an Eskom's Plant 1 power station. The final step was the development, verification and validation of the Flown ex model. The Flownex model was developed and successfully verified by comparing its predictions to that of the analytical model. Three case studies were then performed as a validation exercise in order to demonstrate the integrity of the model in simulating both steady state and transient scenarios. In all three studies the model predicted the unknown values satisfactorily and within acceptable error margins. It was therefore concluded that the primary objective of the study had been met.

Includes bibliographical references.
The Specialization Centre for Energy Efficiency at the University of Cape Town has a goal of building thermo-hydraulic models of an entire power plant. A one-dimensional thermo-hydraulic network solver, Flownex, is the software envisaged to accomplish this goal. The development of appropriate steam turbine models in Flownex supports fulfilment of this goal. Steam turbines of fossil and nuclear power plants make up most of the generating capacity for the majority of industrialised and industrial developing countries, except for those whose power industry depends mainly on hydroelectric power plants [1]. It is therefore a matter of great interest to be ab le to predict the steady state and transient operation of steam turbines. The aim of this dissertation was to use minimal data that was readily available to the end user to develop accurate models. Acceptance test data was used as the primary source because it is more reliable than plant data. Various pressure drop correlations and methods to predict off-design efficiency were investigated. These correlations and methods were solved analytically and implemented in Flownex. Interpretation of the error analysis for the pressure drop correlations established that the general empirical law using inlet conditions and Stodola law in the volume form were the most accurate and consistent in predicting mass flow rate and pressure. The Ray method was shown to be the most accurate to predict off-design efficiency and one of the less complicated to implement. Steady state models were built for four turbine trains using the general empirical and Stodola laws. The results produced by both correlations were similar, showing that for high vacuum conditions either correlation could be used. The general empirical law was the chosen correlation to implement for transient analysis since it was generally more accurate and easier to implement than Stodola. The power predicted by the model was within ±1 % of that of the actual power produced.

The purpose of this thesis was to create a Flowbat program for the calculation of the activity coefficients of species in different electrolyte solutions. In these solutions, electrolytes have dissociated into ions, which greatly increases the non-ideality of the solution even in small concentrations. Modeling of electrolytic solutions becomes essential when bioprocesses are considered, as they typically have several electrolytes present in the considered system. The highly non-ideal behavior must be accounted for accurately when estimating activity coefficients, and consequently the properties of the system at phase and reaction equilibrium. The theory part of this thesis begins by introducing the main principles behind vapor-liquid equilibrium calculations, which are the so-called “phi-phi” and “gamma-phi” approaches, for both electrolyte and non-electrolyte solutions. Next, different alternatives to estimate the fugacity coefficients and activity coefficients in the electrolyte solutions are presented. The fugacity coefficients and activity coefficients are calculated with different equations of state and activity coefficient models, respectively. The selection between the models is not straightforward, but the generally applied approach is to use the activity coefficient models. Because of this, different activity coefficient models, such as eNRTL and LIQUAC, will be mostly examined in this thesis. Some equations of state have also been extended for electrolyte solutions, but they are rarely used due to their inaccuracy in highly non-ideal systems. Inclusion of ionic species also necessitates the use of different thermodynamic standard states for them. Therefore, the general concepts of the generally applied standard state conventions and how they are chosen will be presented as well. The presence of ions in the solution means that the behavior of the solution is dependent on both long- and short-range interactions between species. The short-range interactions can be modeled with typical non-electrolyte activity coefficient models, whereas the modelling of the long-range interactions needs different models. The electrostatic forces induced by the ions are long-range interactions. These phenomena can be modeled through the use of Poisson Boltzmann theory and Born model, and their effect on activity coefficients are accounted mainly with the Debye-Hückel and the mean spherical approximation theories. As most activity coefficient models rely on the Debye-Hückel theory for representing long-range Coulombic interactions, it will be given special attention in the theory part of this thesis. In the applied section of this thesis, symmetric eNRTL activity coefficient model was chosen for a more in-depth analysis, and it was programmed into Flowbat simulation software with the Fortran programming language. The validity of the created Flowbat program was evaluated by comparing its results against the results of the basically identical eNRTL-SR model of Aspen Plus. The tests were performed with the following mixtures: water + 1-propanol + NaCl, water + 1-propanol + NaCl + CaCl₂, water + formic acid, water + ammonia + hydrogen sulfide. Deviations between the activity coefficients of the created Flowbat program and Aspen Plus proved to be negligible. The small deviations are most likely caused by the fundamental differences between the simulation software. Thus, the main goal of the thesis work was reached succesfully. The steps taken during the creation of the Flowbat program and the Aspen Plus simulation have been documented in detail, which can serve as a guideline for the future implementation of the electrolyte models in different process design and analysis studies with electrolyte solutions
Tämän työn tarkoituksena oli luoda Flowbat ohjelma jolla pystytään laskemaan elektrolyyttiliuoksissa olevien komponenttien aktiivisuuskertoimet. Näissä liuoksissa elektrolyytit ovat dissosioituneet ioneiksi, jotka pienissäkin pitoisuuksissa kasvattavat liuoksen epäideaalista käyttäytymistä suuresti. Elektrolyyttiliuosten käyttäytymisen mallintaminen on keskeisessä osassa etenkin erilaisten bioprosessien tarkastelussa, koska näissä prosesseissa on tyypillisesti useita elektrolyyttejä seoksessa. Tämä erittäin epäideaalinen käyttäytyminen täytyy huomioida tarkasti aktiivisuuskertoimia laskettaessa, joka myös vastaavasti vaikuttaa systeemin ominaisuuksiin faasi- ja reaktiotasapainossa. Tämän työn teoriaosa alkaa elektrolyytti- ja ei-elektrolyyttiliuosten kaasu–neste-tasapainolaskentaan käytettävien menetelmien esittelyllä. Näitä menetelmiä kutsutaan ”fii-fii” ja ”gamma-fii” lähestymistavoiksi. Seuraavaksi esitellään eri vaihtoehdot elektrolyyttiliuosten fugasiteettikertoimien ja aktiivisuuskertoimien arviointia varten. Fugasiteettikertoimet voidaan laskea erilaisilla tilanyhtälöillä, kun taas aktiivisuuskertoimet voidaan laskea aktiivisuuskerroin mallien avulla. Valinta näiden mallien välillä ei ole suoraviivaista, mutta yleisimmissä tapauksissa sovelletaan aktiivisuuskerroin malleja. Tästä syystä erinäisiä aktiivisuuskerroin malleja, kuten eNRTL ja LIQUAC, tullaan käsittelemään enimmäkseen tässä työssä. Ionien huomioiminen liuoksessa edellyttää myös eri standarditilojen käyttöä riippuen tarkasteltavasta kohteesta. On siis tarpeellista myös esitellä laajimmin käytetyt standarditilat yleisesti sekä valintaperusteita niiden valinnalle eri seoksilla. Johtuen ionien vaikutuksista, liuoksen käyttäytyminen on riippuvainen eri osaslajien välisistä sekä pitkän kantaman että lyhyen kantaman vuorovaikutuksista. Lyhyen kantaman vuorovaikutuksia voidaan mallintaa perinteisillä ei-elektrolyyteille muodostetuilla aktiivisuuskerroinmalleilla, kun taas pitkän kantaman vuorovaikutuksia täytyy mallintaa eri tyyppisillä malleilla. Ionien aiheuttamat elektrostaattiset voimat ovat pitkän kantaman vuorovaikutuksia. Näitä ilmiöitä pystytään mallintamaan Poisson-Boltzmannin teorian ja Bornin mallin avulla, sekä niiden vaikutus aktiivisuuskertoimiin voidaan huomioida Debye-Hückel ja MSA (mean spherical approximation) teorioiden avulla. Koska suurin osa aktiivisuuskerroinmalleista hyödyntää Debye-Hückel teoriaa pitkän kantaman Coulombisten vuorovaikutusten mallintamiseen, sitä käsitelleään erityisen tarkasti tämän työn teoriaosassa. Työn soveltavassa osuudessa symmetrinen eNRTL aktiivisuuskerroinmalli valittiin perusteellista tarkastelua varten ja tämä malli ohjelmoitiin Flowbat-simulointiohjelmistoon käyttäen Fortran-ohjelmointikieltä. Tämän luodun Flowbat- ohjelman tulosten paikkansapitävyyttä arvioitiin vertaamalla ohjelmalla laskettuja tuloksia Aspen Plus -simulointiohjelmiston käytännössä identtisen ENRTL-SR-mallin laskentatuloksiin. Nämä testit suoritettiin seuraavilla seoksilla: vesi + 1-propanoli + NaCl, vesi + 1-propanoli + NaCl + CaCl₂, vesi + muurahaishappo, vesi + ammoniakki + rikkivety. Erot tässä työssä muodostetun Flowbat-ohjelman ja Aspen Plus -ohjelman laskemissa aktiivisuuskertoimissa osoittautuivat suhteellisen vähäisiksi. Nämä pienet erot johtuvat todennäköisesti käytettyjen ohjelmistojen perustavanlaatuisista eroavaisuuksista. Täten tämän työn varsinainen päämäärä saavutettiin onnistuneesti. Muodostetun Flowbat-ohjelman ja Aspen Plus simulointien luomisen välivaiheet on dokumentoitu työssä yksityiskohtaisesti, joten muodostettua Flowbat-ohjelmaa voidaan tulevaisuudessa käyttää elektrolyyttimallien soveltamiseen erilaisiin prosessisuunnittelu- ja -analyysitarkasteluihin

The High Temperature engineering Test Reactor (HTTR) is an experimental High Temperature Gas-cooled Reactor (HTGR) built by the Japanese Atomic Energy Research Institute (JAERI) to facilitate tests of HTGR technology. One of these test activities involves the validation and verification of thermo-hydraulic codes used in the design of similar HTGR plants. This report details the benchmarking of the Flownex simulation package as used by PBMR (Fly.) Ltd., a South African company developing another type of HTGR known as the Pebble Bed Modular Reactor. The benchmark is of a loss-of-off-site-power event that was tested at the HTTR facility. The event involves a cut of the electric power supply to the circulators, a reactor SCRAM and the activation of the Auxiliary Cooling system to remove decay heat. The need for verification of thermodynamic software is very important in modem nuclear power plant designs, as so much depends on the results produced. Any errors in these results can have serious economic and safety consequences. This report firstly discusses the background of the study, elaborating on the need for the work and the benefit that can be derived from it. Thereafter the process of software verification and validation (V&V) is discussed so that the need for V&V may be clearly understood. Various modelling and simulation methods are then compared, to provide an idea of the work already done in this field. Following this more detail is given on the HTTR test plant and how it is modelled in Flownex. This model is then used for both steady-state and transient simulations, the results of which are then compared with test data. With some exceptions, the study shows that the simulation results are very close to the measured data. Differences are of such a magnitude that they may be attributed to instrumentation inaccuracies. The study contributes to the field in that the methodology of analysing thermo-hydraulic systems is further broadened. The conclusions drawn from this study are aimed at the simulation design engineer, to help him or her understand similar problems and to find solutions faster.
Thesis (M.Ing. (Mechanical Engineering))--North-West University, Potchefstroom Campus, 2005.

Feed-water heaters (FWHs) are an integral part of the power plant with respect to the overall heat recovery, and thus its efficiency. While the main purpose of the FWHs is to heat up the feed-water before being sent to the boiler, there are more added advantages owing to the installation of this equipment to the power plant such as less heat being removed to the atmosphere at the condenser. This report aims at understanding the different types of FWHs in operation and understanding how heat is transferred from the bled steam into the feed-water, and using the understanding to model a transient FWH. The FWH model is a building block towards building a complete transient power plant model. Process operations are all subject to constraints of some sort. The limitations can be in the form of physical geometry, process parameters or lack of correlations that relate known data. The constraints vary in their complexity, and depending on the type of constraints a different mathematical modelling technique can be applied to implement the FWH model. The grey-box modelling technique was chosen to be the appropriate one for analysis as it captures the dynamics that depend on the first principles and correlations whilst still using the global inlet and outlet properties of the FWH. The FWHs have three zones; de-superheating, condensing and sub-cooling zones. The heat transfer characteristics of the three zones are different, and thus their heat duties with the condensing taking a significant amount of the heat duty.

The steam generator plays a primary role in the safety and performance of a pressurized water reactor nuclear power plant. The cost to utilities is in the order of millions of Rands a year as a direct result of damage to steam generators. The damage results in lower efficiency or even plant shutdown. It is necessary for the utility and for academia to have models of nuclear components by which research and analysis may be performed. It must be possible to analyse steam generator performance for both day-to-day operational analysis as well as in the case of extreme accident scenarios. The homogeneous model for two-phase flow is simpler in its implementation than the two-fluid model, and therefore suffers in accuracy. Its advantage lies in its quick turnover time for development of models and subsequent analysis. It is often beneficial for a modeller to be able to quickly set up and analyse a model of a system, and a trade-off between accuracy and time-management is thus required. Searches through available literature failed to provide answers to how the homogeneous model compares with the two-fluid model for operational and safety analysis. It is expected to see variations between the models, from the analysis of the mathematics, but it remains to be shown what these differences are. The purpose of this study was to determine how the homogeneous model for two-phase flow compares with the two-fluid model when applied to a u-tube steam generator of a typical pressurized water reactor. The steam generator was modelled in both RELAP5 and in Flownex. A custom script was written for Flownex in order to implement the Chen correlation for boiling heat transfer. This was significantly less detailed than RELAP5’s solution of a matrix of flow regimes and heat transfer correlations. The geometry of the models were based on technical drawings from Koeberg Nuclear Power Plant, and were simplified to a one-dimensional model. Plant data obtained from Koeberg was used to validate the models at 100%, 80% and 60% power output. It was found that the overall heat transfer rate predicted with the RELAP5 two-fluid model was within 1.5% of the measured data from the Koeberg plant. The results generated by the homogeneous model for the overall heat transfer were within 4.5% of the measured values. However, the differences in the detailed temperature distributions and heat transfer coefficient values were quite significant at the inlet and outlet ends of the tube bundle, at the bottom tube sheet of the steam generator. In this area the water-level was not accurately modelled by the homogeneous model, and therefore there was an under-prediction in heat transfer in that region. Large differences arose between the Flownex and RELAP5 solutions due to difference in the heat transfer correlations used. The Flownex model exclusively implemented the Chen correlation, while RELAP5 implements a flow regime map correlated to a table of heat transfer correlations. It was concluded that the results from the homogeneous model for two-phase flow do not differ significantly when compared with the two-fluid model when applied to the u-tube steam generator at the normal operating conditions. Significant differences do, however, occur in lower regions of the boiler where the quality is lower. We conclude that the homogeneous model offers significant advantage in simplicity over the two-fluid model for normal operational analysis. This may not be the case for detailed accident analysis, which was beyond the scope of this study.
Thesis (MIng (Nuclear Engineering))--North-West University, Potchefstroom Campus, 2013.

The purpose of this study was to serve as a starting point in gaining understanding and experience of simulating a typical Pool Type Research Reactor with the thermal hydraulic software code Flownex®. During the study the following evaluations of Flownex® were done: * Assessment of the simplifying assumptions and possible shortcomings built into the software. * Definition of the applicable modelling methodology and further simplifying assumptions that have to be made by the user. * Evaluation of the accuracy and compatibility with the Pool Type Research Reactor. * Comparing the results of this study with similar studies found in the open literature. For the study the IAEA MTR 10 MW benchmark reactor (IAEA, 1992a) was used. A steady state simulation using Flownex® was done on a single fuel assembly, and this was compared with a model that was developed using the software package EES (Engineering Equation Solver). The results have shown good agreement between the different packages. After this verification, a steady state simulation of the entire core was done to obtain the characteristics of the reactor operating under normal condition. Finally, transient simulations were done on various LOFAs (Loss of Flow Accidents). The results of the various LOFAs were compared with studies that were previously done on the IAEA MTR 10 MW reactor.
Thesis (M.Ing. (Nuclear Engineering))--North-West University, Potchefstroom Campus, 2012.

Large coal-fired power stations are designed to be run predominantly at full load and optimum conditions. The behaviour of plants, operating at low load and varying conditions, is getting more and more attention due to the introduction of variable renewable generation on the grid. Consequently, the need for a fully transient high-fidelity system based model has grown, as this will enable one to study the behaviour of plants under such non-ideal conditions. This report details the development of a feedwater heater, deaerator and turbine component for such a high-fidelity transient system model using the Flownex Simulation Environment, a onedimensional thermohydraulic network solver. The components have been modelled all with the aim of using minimal design input data. The feedwater heater component model includes transient effects and thermodynamic relations to represent aspects such as heater performance, level control and transient inertia. In determining the heat transfer characteristics, the model makes use of plant-performance data and correlates the amount of heat transfer by using the feedwater mass flow as the load indicating parameter. This approach eliminates the need for specific geometrical details to calculate the effective heat transfer area. The level control is modelled by using a level representation built from using heat exchanger design methods. The turbine component is modelled by using Fuls’ Semi-Ellipse law or the pressure drop modelling and Ray’s semi-empirical method for the efficiency modelling. The model also contains transient effects, which include thermal inertia due to the shaft and casing, and rotational inertia due to the shaft. The deaerator component is modelled by adapting the model presented by Banda, and modifying the model to work under various conditions. This involved using curve fit methods in Flownex to use input data to model the pressure drop over the main condensate valve. Each of the mentioned components was validated and verified with plant data and finally packaged into a compound component which is a component consisting of a subnetwork in Flownex. These compound components further contain design inputs which are easily accessible by the user. The component models were integrated into larger networks in which various scenarios can be run. A short transient scenario was run on the low-pressure feedwater train of a specific power station. The scenario involved a turbine trip where the bled steam valves for the heaters were closed suddenly. The speed of the valves closing was however unknown and after closing the valves in approximately 10 seconds, results agreed relatively well with plant data. This illustrated the short transient capabilities of the feedwater heater component model. The three component models (feedwater heater, turbine and deaerator) were finally integrated into a regenerative Rankine cycle and was set up using minimal design data. The boiler, condenser and condensate pump were set as boundary conditions in the network but all extraction points for the network were connected. Steady-state results were obtained for various load cases and the main temperature, flow and pressure results were compared. Results agree well with plant data, even at low load conditions

The world is currently experiencing an energy crisis. To cope with the rising demand in South Africa, nuclear power was identified as a clean, safe and reliable source of electricity. The Pebble Bed Modular Reactor (PBMR) is an inherently safe, next-generation nuclear power plant that uses pebble fuel. In the event of a depressurized loss of coolant (DLOFC) accident, the reactor will passively cool itself, and remain within safe limits. The main purpose of this dissertation was to perform an uncertainty study on the PBMR reactor during a DLOFC accident to demonstrate this safety feature. An extensive literature survey was carried out to research the concept of uncertainty, methods for addressing uncertainty and to gather the required input data to set up a model of the PBMR reactor. The model requirements were established by use of a systematic PIRT process. A detailed model of the reactor was set up in Flownex after making the necessary assumptions and simplifications. A sensitivity and Monte Carlo sampling platform was set up in conjunction with Flownex in order to perform the uncertainty study. During the DLOFC transient, the best-estimate maximum fuel, core-barrel and RPV temperatures reached 1529, 621 and 490’C respectively. Sensitivity studies showed that the parameters that most strongly influence the results are the power profile, decay heat, pebble bed effective conductivity and the properties of the graphite reflector. Variations in fluid properties had a negligible influence on the DLOFC results. Statistical processing of the Monte Carlo simulation results provided uncertainty bands for each output. The conclusion was that with 95% confidence, there is a 5% probability of exceeding maximum fuel, core-barrel and RPV temperatures of 1582, 638 and 503 CC respectively. All three of these temperatures are below the maximum allowable temperature for each respective component. Thus all three components will stay within their code cases during the unlikely event of a DLOFC. The final effort in this study went to verification and validation (V&V) of the results. This process included V&V of the input data, software, the calculation and the model development. These processes included: a detailed internal review; comparison with analytical solutions; comparison with alternative independent calculations; and comparison with experiment. The effective pebble bed thermal conductivity is currently being validated via construction of the Heat Transfer Test Facility (HTTF). The large extent of V&V activities that have been carried out provides a high level of confidence that the results produced in this dissertation are satisfactory, if not slightly conservative.
Thesis (M.Ing. (Mechanical Engineering))--North-West University, Potchefstroom Campus, 2007.

High temperature gas cooled reactors have a special importance in the future of nuclear technology. Due to their high thermal capacity, high burn-up and thermodynamic efficiency, a decrease in the electricity generation cost is expected. New generation high temperature reactors are designed to be inherently safe. The most efficient way of hydrogen production, IS process, requires very high temperatures. Very High Temperature Gas Cooled Reactors (VHTR) of the future are considered as the heat source for hydrogen production. Two fuel types are used in high temperature reactors, namely pebble and prismatic block fuels. The South African Pebble Bed Modular Reactor (PBMR) is a promising design to be built in the near future. A very important aspect of the design of a High Temperature Gas Cooled Reactor (HTR) is to predict the neutronics of the reactor, as this determines the fission heat release. This thesis deals with the development of a model for the prediction of neutronics behaviour of the PBMR core which will be used in conjunction with a thermal hydraulic code for the design of the PBMR.
Thesis (M.Ing. (Mechanical Engineering))--North-West University, Potchefstroom Campus, 2005.

A previously developed turbine modelling methodology, requiring minimal blade passage information, produced a customizable turbine stage component. This stage-by-stage turbine nozzlemodel component was derived from the synthesis of classical turbine theory and classical nozzle theory enabling the component to accurately model a turbine stage. Utilizing Flownex, a thermohydraulic network solver, the turbine stage component can be expanded to accurately model any arrangement and category of turbine. This project focused on incorporating turbine blade passage geometrical information, as it relates to the turbine specific loss coefficients, into the turbine stage component to allow for the development of turbine models capable of predicting turbine performance for various structural changes, anomalies and operating conditions. The development of turbine loss coefficient algorithms as they relate to specific blade geometry data clusters required the investigation of several turbine loss calculation methodologies. A stage-by-stage turbine nozzle-model incorporating turbine loss coefficient algorithms was developed and validated against real turbine test cases obtained from literature. Several turbine models were developed using the loss coefficient governed turbine stage component illustrating its array of capabilities. The incorporation of the turbine loss coefficient algorithms clearly illustrates the correlation between turbine performance deviations and changes in specific blade geometry data clusters.

Boiler feed pump turbines (BFPTs) are in use at a number of Eskom power stations. They utilise bled steam extracted from the main turbine in order to drive multistage centrifugal pumps which supply the boilers with feedwater. With an increase of renewables in the energy mix, the need for Eskom’s coal-fired power stations to run for extended periods at very low loads has arguably never been this great. Various systems affect the ability of these generation units to run economically at low loads. One such system is the boiler feed pump turbine and its associated pumps. A station was selected from Eskom’s fleet based on access to information and the station being a relatively typical plant. The Unit (a boiler and turbogenerator set) selected for study was one with the most thorough instrumentation available for remote monitoring. The BFPT system of this Unit was modelled in Flownex, a one-dimensional thermofluid process modelling package. The model included individual pump stages, steam admission valves and a stage-by-stage turbine model utilising custom stage components. These turbine stage components represent each stage with nozzles and other standard Flownex components. The boundary conditions of the system were set as functions of generator load in order to represent typical values for use in case studies. The relationships between load and boundary conditions were based on large samples of data from the station’s data capture system (DCS). A corresponding standby electric feed pump system was also modelled in Flownex for a comparative case study. After model validation, a number of case studies were performed, demonstrating the functionality of the model and also providing specific results of value to the station in question. These results include the minimum generator load possible with different steam supplies; maximum condenser back pressure before plant availability is affected; the viability of changing the pump leak-off philosophy; and the effect of electric feed pump use on power consumption. The main recommendations from the case studies were as follows: i. to stroke the steam admission valves as per the design charts, ii. to test the operation of the BFPT down to 40 % generator load, iii. to keep the pump leak-off philosophy unchanged, iv. to maintain the cooling water system and condensers sufficiently to avoid poor condenser vacuum, v. to reconsider the decommissioning of the “cold reheat” steam supply, vi. and, to favour use of the BFPT over the electric feed pumps at all generator loads.

It is a great challenge in the design of the PBMR to accurately predict gas flow and heat transfer in the reactor. Understanding the heat transfer at the core-reflector interface in particular is a very important aspect as the reactivity of the control rods housed in the reflectors is highly temperature dependent. It is also very important because the core-reflector interface is on the critical path for heat removal during accident conditions. PBMR has developed an OECD/NEA coupled neutronic/thermal-hydraulic benchmark to aid in the understanding of the different modelling approaches currently employed at PBMR. A comparison of THERMIX-KONVEK and DIREKT results showed large temperature differences at the core-reflector interfaces. Further investigation showed that these differences are as a result of the numerical methods used i.e. Cell-Centred (CC) vs. Vertex-Centered (VC). The present study extended this comparison to Star-CD (CC) and Flownex (VC) which are also used to simulate the reactor at PBMR. An ID MATLAB program that mimics the CC and VC numerical methods was verified against Star-CD and Flownex. This program was then used to model an ID version of the OECD/NEA benchmark. Results were compared with DIREKT and THERMIX-KONVEK. Although the results compared well, there were significant errors at the core-reflector interfaces. The findings of this study were that different numerical methods will predict different temperatures, heat fluxes and (temperature-dependent) sink terms. It was also shown that in addition to the differences resulting from numerical methods, differences were seen between Star-CD and DIREKT and Flownex and THERMIX-KONVEK in the region of the core-reflector boundary. In general, for complicated simulations like that of the pebble bed, the numerical basis of software used to simulate the problem needs to be understood for the problem to be correctly modelled.
Thesis (M.Sc. Engineering Sciences (Nuclear Engineering))--North-West University, Potchefstroom Campus, 2010.

The aim of this Master's thesis is to explore different attitudes and to design various monitoring and detection concepts of volumetric DDoS attacks in core networks. The thesis deals with data flow control protocols with an emphasis on a modern technology of Software Defined Networks. The last part of the thesis describes verification of the theory by setting up a laboratory environment for volumetric DDoS UDP Flood simulation, detection and automated mitigation.

This thesis deals with design and implementation of software architecture for Flexible FlowMon probe, accessories for monitoring high speed computer networks based on IP flows. The probe has been developed in project named Liberouter. There is described flow based monitoring and export formats NetFlow version 5, NetFlow version 9 and IPIFX, which are very widely used. The thesis contains description of hardware part of Flexible FlowMon probe including its requirements for software, which are the base of the whole software architecture. There is detailed description of that part of software architecture which was implemented during the work on this thesis.

Master's thesis analyzes available network device configuration options and describes NETCONF configuration protocol and NETCONF event notifications extension in details. It describes Netopeer, open configuration platform developed on Liberouter project, and its pitote deployment as FlowMon probe remote configuration system. Newly designed Netopeer architecture, which adds support for NETCONF event notifications, was verified by reference implementation. Security of the new design and implementation was analyzed, and recommended system settings were provided. This Master's thesis is based on results of previous bachelor's thesis of author and on existing software tools developed by the Liberouter project.

There are three main results in this dissertation. The first result is the construction of an abstract visual space for rational numbers mod1, based on the visual primitives, colour, and rational radial direction. Mathematics is performed in this visual notation by defining increasingly refined visual objects from these primitives. In particular, the existence of the Farey tree enumeration of rational numbers mod1 is identified in the texture of a two-dimensional animation. ¶ The second result is a new enumeration of the rational numbers mod1, obtained, and expressed, in abstract visual space, as the visual object coset waves of coset fans on the torus. Its geometry is shown to encode a countably infinite tree structure, whose branches are cosets, nZ+m, where n, m (and k) are integers. These cosets are in geometrical 1-1 correspondence with sequences kn+m, (of denominators) of rational numbers, and with visual subobjects of the torus called coset fans. ¶ The third result is an enumeration in time of the visual hierarchy of the discrete buds of the Mandelbrot boundary by coset waves of coset fans. It is constructed by embedding the circular Farey tree geometrically into the empty internal region of the Mandelbrot set. In particular, coset fans attached to points of the (internal) binary tree index countably infinite sequences of buds on the (external) Mandelbrot boundary.

碩士
聖約翰技術學院
自動化及機電整合研究所
93
The integration and control objects of a company should propose then use one effective method with faster process for saving the expense of system development in the current trend which as the professional global division of technology and the system planning etc. The Petri Nets is one kind of Flow Chart tools. It’s not only useful but also with the excellent definition for modeling, testing and analysis of digital logic. The research looking forward, the CPU operation process can be more understandability for the interested user by this mathematic modeling analysis system. After that, the company can be found the analysis ability of Petri Nets and widely implement this method through the research of our paper. The research paper surveyed and reviewed the Petri Nets and the computer structure at first. Afterward, to combine their knowledge for make a static and dynamic model such that the CPU inner structure can be shown as a figural condition. The simulation of paper utilized the Petri Nets which has excellent process ability of disperse dynamic system to build the distributed and dynamic simulation system. The module model don’t change its route rule and without any influence according to the addition module model. Finally, the model is simulation for testing our proposed method using （Petri .NET Simulator 2.0）. The investigation can be applied for control and improve development process of new product, elevate the competitive strength of market and establish the automatic information environment of new product development process.

碩士
中原大學
工業工程研究所
95
The two-machine flowshop problem is considered in which at most one operation in machine 2. Each job must be processed without preemption firstly on machine 1 and then on machine 2. The objective is to minimize the maximum lateness. The problem is NP-hard. Both the heuristic and the branch and bound algorithms are established to solve the problem. The heuristic combined the Johnson’s algorithm (1954) with the EDD rule and sequence jobs from the last position toward the first position. A worst-case analysis is used to analyze the performance of the heuristic.

Very High Temperature Reactors are complex reactors and various system codes have been developed to design different aspects such as neutronics, thermal hydraulics etc. Flownex is one of the system codes and it has been used to model the flow and heat transfer for a pebble fuel element and pebble-bed reactor. Although Flownex has been used to model the High Temperature Test Reactor, the prismatic block was modelled in a simplified manner. The aim of this study was to develop a more integrated model for a single block. A one sixth block was modelled in Flownex and the results were validated by comparing the results with results obtained using the Computational Fluid Dynamics (CFD) code STAR-CCM+. The conduction heat transfer through the prismatic blocks containing the fuel elements in a Very High Temperature Reactor is of crucial importance for the proper operation of the reactor under normal operating conditions and upset conditions. In this study, a model developed in a system code, Flownex is discussed. The model comprised of a collection of 1-D solid conduction heat transfer, convection heat transfer and pipe elements that were arranged in such a manner to represent the heat transfer and fluid flow in the prismatic block using a network approach. The validity of the model was investigated by comparing the heat transfer and temperature distribution in the block for various scenarios with the corresponding values obtained using a detailed CFD model of one twelfth of a prismatic block. Cubical and triangular block verification cases were conducted in Flownex and the results were validated by STAR-CCM+. The results were very comparable; however one issue has to be addressed. The one sixth integrated prismatic block was then modelled for a steady state and the results were also comparable. The outlet helium temperatures predicted by the STAR-CCM+ model was 542.94 C, at the same time the Flownex model predicted 542.98 C. Although the Flownex model did not provide the same detail as the STAR-CCM+ model the agreement between the results obtained with the two codes was satisfactory. Based on these findings it was concluded that Flownex could be used to build a representative integrated network model for a prismatic block reactor.
MIng (Nuclear Engineering), North-West University, Potchefstroom Campus, 2015

Nuclear reactors with improved safety concepts are currently being studied within the nuclear engineering community, with a focus on passive safety features. One of these reactor concepts is the Very High Temperature gas-cooled Reactor (VHTR) of which the Reactor Cavity Cooling Systems (RCCS) is seen as an integral and crucial part of the passive safety concept. Considerable validation and development of the necessary software tools is required to perform analysis and designs of these future reactor concepts. The primary objective of this study is to establish a methodology for the creation of an integrated system level process model of a typical air-cooled RCCS in Flownex®, and to illustrate its applicability by simulating different scenarios that illustrate the operational characteristics of such a system. For this purpose, the existing RCCS conceptual design that is being studied by the KAERI was used as the case study. As a start, selected case studies were performed to verify that the Flownex® models were set up correctly to perform natural circulation flows, both in steady and transient conditions, and with radiation, convection and conduction taking part. These are the major typical physical phenomena in the RCCS. The models were compared with EES (Engineering Equation Solver) models of the same geometries and specifications. There was a good agreement between Flownex® and EES model results. After this verification, a simulation model of the integrated RCCS system was developed. The Flownex® models were applied to model selected possible operational scenarios. The major observations from the results are that: - The RCCS carries with it enough heat to the ambient such that the concrete wall temperature is maintained below the benchmark value of 65°C for the different boundary conditions imposed. - The RCCS maintains its functionality even with three quarters of the risers blocked or in the event that there is a break in one of the chimney pipes.
MIng (Nuclear Engineering), North-West University, Potchefstroom Campus, 2015

The diploma thesis focuses on design of university firewall on Cisco platform. The design deals with important functionalities, which are used in the current solution. These include routing, network address translation, access control lists, VPN. The thesis furher deals with dynamic insertion rules, which are generated based on traffic analysis by Flowmon probe and its ADS module. The new design is implemented in a testing environment and its funcionality is verified. The thesis will serve like feasibility study for final implementation in the production MENDELU network.

This study was based on the uncertainty and sensitivity analysis of a generic 10 MW Materials Test Reactor (MTR). In this study an uncertainty and sensitivity analysis methodology called code scaling applicability and uncertainty (CSAU) was implemented. Although this methodology follows 14 steps, only the following were carried out: scenario specification, nuclear power plant (NPP) selection, phenomena identification and ranking table (PIRT), selection of frozen code, provision of code documentation, determination of code applicability, determination of code and experiment accuracy, NPP sensitivity analysis calculations, combination of biases and uncertainties, and total uncertainty to calculate specific scenario in a specific NPP. The thermal hydraulic code Flownex®1 was used to model only the reactor core to investigate the effects of the input parameters on the selected output parameters of the hot channel in the core. These output parameters were mass flow rate, temperature of the coolant, outlet pressure, centreline temperature of the fuel and surface temperature of the cladding. The PIRT process was used in conjunction with the sensitivity analysis results in order to select the relevant input parameters that significantly influenced the selected output parameters. The input parameters that have the largest effect on the selected output parameters were found to be the coolant flow channel width between the plates in the hot channel, the width of the fuel plates itself in the hot channel, the heat generation in the fuel plate of the hot channel, the global mass flow rate, the global coolant inlet temperature, the coolant flow channel width between the plates in the cold channel, and the width of the fuel plates in the cold channel. The uncertainty of input parameters was then propagated in Flownex using the Monte Carlo based uncertainty analysis function. From these results, the corresponding probability density function (PDF) of each selected output parameter was constructed. These functions were found to follow a normal distribution.
MIng (Nuclear Engineering), North-West University, Potchefstroom Campus, 2014