Comparison of Two Object-Oriented Modeling Environments for the Dynamic Simulations of a Residential Heat Pump

Object-oriented physical-modelling platforms greatly facilitate the task of the modelling engineer by abstracting away a lot of the complexity associated with sorting the governing equations and also the nuances of the numerical methods used for solving the differential-algebraic equations (DAEs). For this reason, they have been steadily gaining in popularity in the field of thermofluid simulations. In this study, we compare two platforms of this type: Dymola and EcosimPro. Dymola is a physical modelling environment originally developed at Lund University and now being developed by Dassault Systèmes, and is a commercially available implementation of the open-source physical modelling language Modelica. EcosimPro is a proprietary tool developed by Empresarios Agrupados A.I.E originally for the European Space Agency and now sold to the general public. Both platforms utilise object-oriented modelling paradigms such as multiple inheritance, encapsulation (of behaviour within classes), abstraction (hiding model complexity from the user) and acausal equation handling (equations may be written in any order). We use these platforms to conduct a realistic exercise of modelling and simulating a relatively complex residential heat pump system in both heating and cooling modes and comparing the results against measured data. Component libraries have been prepared in both the platforms for modelling system components. Two-phase flow has been accounted for using slip-ratio based void fraction correlations. In general, the component models have been kept as similar as possible between the two platforms. The heat pump under investigation is a residential, 3-ton unit with a scroll compressor. The cooling mode uses a thermostatic expansion valve (TXV) as the expansion device while the heating mode uses a short-tube orifice. A reversing valve controls the flow direction. The heat pump has been tested under both heating and cooling modes as per ASHRAE’s Standard 116-2010 cyclic test conditions. The measured values have been compared against simulations results from both platforms. The refrigerant pressures and temperatures and the heat exchanger air outlet temperatures are compared. The indoor unit air-side capacity and the compressor power consumption integrated over the on-period are also compared. Additionally, the Seasonal Energy Efficiency Ratio (SEER), the Cooling Load Factor (CLF) and the Cyclic Degradation Coefficient (Cd) are compared which help quantify the performance of the heat pump. Finally, qualitative comparisons of the transients associated with the refrigerant charge migration after shutdown have been made, as this migration is responsible for cycling losses associated with dynamic heat pump operation. The two platforms prove to be similarly capable at simulating an advanced cycle. Both platforms can predict the pressure and temperature transients during the on-off cycling of the heat pump, as well as the performance parameters such as accumulated capacities and the SEER rating. Finally, both ­models predict the simulated charge to be within 80% of the actual charge, which enables a more realistic depiction of system transients

Software Tool for Acausal Physical Modelling and Simulation

Modelling and simulation are key tools for analysis and design of systems and processes from almost any scientific or engineering discipline. Models of complex systems are typically built on acausal Differential-Algebraic Equations (DAE) and discrete events using Object-Oriented Modelling (OOM) languages, and some of their key concepts can be explained as symmetries. To obtain a computer executable version from the original model, several algorithms, based on bipartite symmetric graphs, must be applied for automatic equation generation, removing alias equations, computational causality assignment, equation sorting, discrete-event processing or index reduction. In this paper, an open source tool according to OOM paradigm and developed in MATLAB is introduced. It implements such algorithms adding an educational perspective about how they work, since the step by step results obtained after processing the model equations can be shown. The tool also allows to create models using its own OOM language and to simulate the final executable equation set. It was used by students in a modelling and simulation course of the Automatic Control and Industrial Electronics Engineering degree, showing a significant improvement in their understanding and learning of the abovementioned topics after their assessment

Towards automating the sizing process in conceptual (airframe) systems architecting

Presented is a method for automated sizing of airframe systems, ultimately aiming to enable an efficient and interactive systems architecture evaluation process. The method takes as input the logical view of the system architecture. A source-sink approach combined with a Design Structure Matrix (DSM) sequencing algorithm is used to orchestrate the sequence of the sub-system sizing tasks. Bipartite graphs and a maximum matching algorithm are utilized to identify and construct the computational sizing workflows. A recursive algorithm, based on fundamental dimensions of additive physical quantities (e.g., weight, power, etc.) is employed to aggregate variables at the system level. The evaluation, based on representative test cases confirmed the correctness of the proposed method. The results also showed that the proposed approach overcomes certain limitations of existing methods and looks very promising as an initial systems architectural design enabler

EcosimPro Simulation of Transient Flow for Rocket Engine and Test Bench Applications

Storable propellant engine start-up is a complex phase which involves non-stationary hydraulic effects, two-phase flow. Each element of the engine, oxidizer and fuel lines, combustion chamber, has to be verified and qualified. For this purpose test facilities are an indispensable element for development and acceptance for space system, subsystem and components. The partial failure of Ariane 5 flight No 510 on December 7 2001 called for the attention of liquid rocket propulsion engineers on the importance of the simulation of high frequency (HF) instabilities in propellant feed lines. The disturbances observed during the start-up of the flying engine were not triggered in any of the tests performed. As a consequence of the difference in the engine and test bench lines, transient phenomena result not predicable from a test campaign and so highly dangerous for engines performances and operation. The knowledge of the flow characteristics in both the test benches and flying rocket stages is essential for future hardware design. Efforts have to be made for advancing the understanding of the transient flow behaviour in pipes for safe operation of the engine and for reducing the high costs and risks associated with tests. In this context, the development of tools for simulating the behaviour of flight-like feed systems by using non-flight-like test bench equipment are widespread. In the present work a numerical investigation and evaluation of the critical fluid-system parameters is performed by means of the simulation and modeling software EcosimPro 4.4, based on C++ programming language. A hydraulic model of the test bench P2 in Lampoldhausen up to the test facility main valve is built up, as well as a simplified model of the Aestus engine. To validate and qualify the combined test bench-engine model, real on-ground test transients and steady-state results are compared with numerical results. The numerical model has been successfully modified and adjusted and simulation results matched the measured values within acceptable ranges. Good agreement with steady-state-pressure, propellant mass flow rates behaviour and transient start-up in terms of water hammer peaks have been obtained. However, the water hammer frequencies have been not matched accurately due to 1D-restrictions of the code and mainly to different characteristics of the simulated fluids. Future efforts have to be done to improve the implementation of fluid property data bases implementation, especially for NTO (equilibrium condition between NO2 and N2O4 depending on pressure and temperature) and for deeper understanding and investigation of possible influences of the content of pressurization gas content in the liquid fluid on the transient behaviour of the propellant feed system

Golpe de ariete polifásico : modelado, experimentos e simulación

[Abstract] This thesis deals with the experimental and numerical analysis of the water hammer phenomenon generated by the discharge of a pressurized liquid into a pipeline kept under vacuum conditions. This ow configuration induces several multiphase phenomena such as cavitation and gas desorption that cannot be ignored in the water hammer behavior. The motivation of this research work comes from the liquid propulsion systems used in spacecrafts, which can undergo uid hammer effects threatening the system integrity. Fluid hammer can be particularly adverse during the priming phase, which involves the fast opening of an isolation valve to fill the system with liquid propellant. Due to the initial vacuum conditions in the pipeline system, the water hammer taking place during priming may involve multiphase phenomena, such as cavitation and desorption of a non-condensable gas, which may affect the pressure surges produced in the lines. Even though this ow behavior is known, only few studies model the spacecraft hardware configuration, and a proper characterization of the two-phase ow is still missing. The creation of a reliable database and the physical understanding of the water hammer behavior in propulsion systems are mandatory to improve the physical models implemented in the numerical codes used to simulate this ow configuration. For that purpose, an experimental facility modeling a spacecraft propulsion system has been designed, in which the physical phenomena taking place during priming are generated under controlled conditions in the laboratory using inert uids. An extended experimental campaign was performed on the installation, aiming at analyzing the effect of various working parameters on the uid hammer behavior, such as the initial pressure in the line, liquid saturation with the pressurant gas, liquid properties and pipe configuration. The in uence of the desorbed gas during water hammer occurrence is found to have a great importance on the whole process, due to the added compressibility and lower speed of sound by an increasing amount of non-condensable gas in the liquid + gas mixture. This results in lower pressure levels and faster pressure peaks attenuation, compared to uids without desorption. The two-phase ow was characterized by means of ow visualization of the liquid front at the location where the uid hammer is generated. The front arrival was found to be preceded by a foamy mixture of liquid, vapor and non-condensable gas, and the pressure wave re ected at the tank may induce the liquid column separation at the bottom end. While column separation takes place, the successive pressure peaks are generated by the impact of the column back against the bottom end. The resulting experimental database is then confronted to the predictions of the 1D numerical code EcosimPro/ESPSS used to assess the propulsion system designs. Simulations are performed with the ow configuration described before, modeling the experimental facility. The comparison of the numerical results against the experimental data shows that aspects such as speed of sound computation with a dissolved gas and friction modeling need to be improved.[Resumen] Esta tesis presenta un estudio experimental y numérico del fenómeno de golpe de ariete generado por la descarga de un líquido presurizado en una conducción bajo condiciones de vacío. Esta configuración de ujo induce varios fenómenos multifásicos, tales como cavitación y desorción de gases no condensables, que no pueden ser ignorados en el análisis del problema. La motivación de este trabajo de investigación tiene su origen en los sistemas de propulsión con combustibles líquidos utilizados en aplicaciones aeroespaciales, donde el fenómeno de golpe de ariete y el incremento de presión ocasionado puede afectar la integridad del sistema. El golpe de ariete es particularmente adverso durante la fase de cebado, donde la apertura rápida de una válvula de aislamiento permite el llenado de las líneas de combustible, las cuales se encuentran inicialmente al vacío. Debido a esto, junto al fenómeno de golpe de ariete también tiene lugar la cavitación del uido y la desorción de un gas no condensable, los cuales afectan a los incrementos de presión que se producen en las líneas. A pesar de que todos estos fenómenos han sido ampliamente tratados en la literatura científica, existen muy pocos estudios que traten la configuración de ujo descrita y que aborden todos los fenómenos multifásicos ocasionados de forma simultánea. Es por ello que la creación de una extensa base de datos, con las condiciones experimentales bien definidas, es una necesidad para validar y mejorar los modelos físicos implementados en los códigos numéricos, los cuales se utilizan para evaluar el comportamiento de los sistemas de propulsión durante la fase de diseño. Para tal fin, se ha diseñado una instalación experimental que reproduce un sistema de propulsión, de forma que todos los fenómenos físicos que tienen lugar durante el cebado del combustible se generan en el laboratorio bajo condiciones controladas. El estudio experimental llevado a cabo ha permitido analizar el efecto de diversos parámetros de trabajo en el comportamiento del golpe de ariete, tales como la presión inicial de vacío en la línea, saturación del líquido con el gas presurizante, propiedades del líquido y configuración de la conducción. Los resultados muestran como la desorción del gas no condensable afecta de forma significativa el comportamiento del uido durante el golpe de ariete, debido al incremento de compresibilidad y la reducción de la velocidad del frente de onda al aumentar la presencia de gas en la mezcla bifásica. Esto se traduce en menores incrementos de presión y atenuación más rápida de los picos de presión, en comparaci ón con el mismo uido bajo condiciones donde la desorción no tiene lugar. La visualización del ujo allí donde se genera el golpe de ariete ha permitido caracterizar el comportamiento bifásico del uido. El avance del frente líquido en la línea está precedido por una mezcla multifásica de líquido, vapor y gas no condensable, y las ondas de expansión pueden inducir la separación de la columna líquida en el extremo cerrado de la conducción donde impacta el uido. Siempre que la separación de columna tenga lugar, los sucesivos picos de presión se generan por el impacto de la columna líquida contra el extremo cerrado de la línea tras la separación. La base de datos experimental resultante se ha comparado con las predicciones del código numérico 1D EcosimPro/ESPSS simulando la configuración experimental. La comparación de los resultados numéricos con los datos experimentales muestran que es necesario reformular el cálculo de la velocidad del frente de onda cuando existe una fase gaseosa disuelta en el volumen líquido. Además, es preciso incluir en el código un modelo de fricción no estacionario que mejore las predicciones del modelo de fricción quasi-estacionario utilizado actualmente.[Resumo] Esta tese presenta un estudo experimental e numérico do fenómeno de golpe de ariete xerado pola descarga dun líquido presurizado nunha condución baixo condicións de baleiro. Esta configuración de uxo induce varios fenómenos multif ásicos, tales como cavitación e desorción de gases non condensables, que non poden ser ignorados na análise do problema. A motivación deste traballo de investigación ten a súa orixe nos sistemas de propulsión con combustibles líquidos utilizados en aplicacións aeroespaciais, onde o fenómeno de golpe de ariete e o incremento de presión ocasionado pode afectar a integridade do sistema. O golpe de ariete é particularmente adverso durante a fase de cebado, onde a apertura rápida dunha válvula de illamento permite a enchedura das liñas de combustible, as cales se encontran inicialmente ao baleiro. Debido a isto, xunto ao fenómeno de golpe de ariete tamén ten lugar a cavitación do fluído e a desorción dun gas non condensable, os cales afectan aos incrementos de presión que se producen nas liñas. A pesar de que todos estes fenómenos foron amplamente tratados na literatura científica, existen moi poucos estudos que traten a configuración de uxo descrita e que aborden todos os fenómenos multif ásicos ocasionados de forma simultánea. É por iso que a creación dunha extensa base de datos, coas condicións experimentais ben definidas, é unha necesidade para validar e mellorar os modelos físicos implementar nos códigos numéricos, os cales se utilizan para avaliar o comportamento dos sistemas de propulsión durante a fase de deseño. Para tal fin, deseñouse unha instalación experimental que reproduce un sistema de propulsión, de forma que todos os fenómenos físicos que teñen lugar durante o cebado do combustible se xeran no laboratorio baixo condicións controladas. O estudo experimental levado a cabo permitiu analizar o efecto de diversos parámetros de traballo no comportamento do golpe de ariete, tales como a presión inicial de baleiro na liña, saturación do líquido co gas presurizante, propiedades do líquido e configuración da condución. Os resultados mostran como a desorción do gas non condensable afecta de forma significativa o comportamento do fluído durante o golpe de ariete, debido ao incremento de compresibilidade e a redución da velocidade da fronte de onda ao aumentar a presenza de gas na mestura bifásica. Isto tradúcese en menores incrementos de presión e atenuación máis rápida dos picos de presión, en comparación co mesmo fluído baixo condicións onde a desorción non ten lugar. A visualización do uxo alí onde se xera o golpe de ariete permitiu caracteri zar o comportamento bifásico do fluído. O avance da fronte líquida na liña está precedido por unha mestura multifásica de líquido, vapor e gas non condensable, e as ondas de expansión poden inducir a separación da columna líquida no extremo pechado da condución onde impacta o fluído. Sempre que a separación de columna teña lugar, os sucesivos picos de presión xéranse polo impacto da columna líquida contra o extremo pechado da liña tras a separación. A base de datos experimental resultante comparouse coas predicións do código numérico 1D EcosimPro/ESPSS simulando a configuración experimental. A comparaci ón dos resultados numéricos cos datos experimentais mostran que é necesario reformular o cálculo da velocidade da fronte de onda cando existe unha fase gasosa disolta no volume líquido. Ademais, é preciso incluír no código un modelo de fricción non estacionario que mellore as predicións do modelo de fricción quasi-estacionario utilizado actualmente

Ergonomic design applied in a sugar mill interface

In tasks requiring human supervision in an industrial control room there are applied generic disciplines like automatic control and engineering systems. From the point of view of the human computer interaction applied to these disciplines it is necessary to add usability engineering and cognitive ergonomics. This integrated framework is an example of human-centred design on automation systems. The main goal of this work is the application of a cognitive ergonomic guideline for supervisory control in order to improve the efficiency of a sugar mill interface design.Peer ReviewedPostprint (published version

Coordinating industrial production and cogeneration systems to exploit electricity price fluctuations

Las fluctuaciones en el precio de la electricidad, procedentes de la aplicación de programas de respuesta de la demanda, son una oportunidad para que las industrias que cuenten con sistemas de cogeneración puedan reducir sus costes de producción mientras hacen que la red eléctrica sea más estable y segura en su conjunto. Dada la cantidad de factores involucrados y la dificultad que esto supone a la hora de tomar decisiones, en esta tesis se presenta una metodología basada en optimización dinámica que permite la gestión óptima de ambos sistemas y se aplica en simulación al caso de estudio de una industria azucarera. Como principales resultados, se ha obtenido que utilizando la metodología propuesta los costes variables de producción se pueden reducir hasta un 2.55% si se utiliza una tarifa por tramos típica, y en torno a un 5.41% si se utilizan los precios dados por el mercado eléctrico directamente.Departamento de Ingeniería de Sistemas y AutomáticaDoctorado en Ingeniería Industria

A study on modelling, data reconciliation and optimal operation of hydrogen networks in oil refineries

Se ha llevado a cabo un estudio sobre la gestión óptima en tiempo real de redes de hidrógeno en refinerías de petróleo, con referencia a la refinería de Petronor perteneciente al grupo Repsol y situada en Muskiz (Vizcaya). La tesis consiste en la aplicación de técnicas bien conocidas y establecidas como el modelado de procesos y la optimización a un tema interesante en la actualidad: las redes de hidrógeno en refinerías de petróleo. Los resultados obtenidos son coherentes y robustos, y las soluciones alcanzadas pueden ser directamente aplicadas en la práctica industrial. El problema abordado tiene gran relevancia industrial, con el propósito general de mejorar la operación en tiempo real, ahorrar recursos en este caso materiales relativos al hidrógeno, y aumentar el conocimiento del sistema en la medida de lo posible. Asimismo se han desarrollado librerías en el entorno de simulación EcosimPro. Los objetivos de la tesis son: i) la estimación correcta tanto de variables medidas como de variables desconocidas de la red de hidrógeno; ii) la determinación de las condiciones óptimas de operación así como de las producciones óptimas; iii) la exploración de otros enfoques dirigidos a la operación óptima como la técnica de control self-optimizing; iv) la evaluación del interés y potencial aplicabilidad de modelos simplificados de las plantas para la predicción del consumo de hidrógeno en función de la carga de hidrocarburo.Departamento de Ingeniería de Sistemas y Automátic

Creación de una librería de elementos rotacionales mediante EcosimPro

La técnica de la simulación se usa constantemente dentro del ámbito de la ingeniería. Se simulan toda clase de sistemas, ya sean sistemas mecánicos, eléctricos, frigoríficos, de control, etc. El objetivo principal de este proyecto consiste en desarrollar una librería rotacional haciendo uso de una herramienta de modelado y simulación llamada EcosimPro. EcosimPro, es una herramienta de simulación con la que se pueden modelar desde los más simples a los más complejos procesos físicos, en términos de ecuaciones diferenciales algebraicas ó ecuaciones diferenciales ordinarias y eventos discretos. Dentro de los diferentes campos donde se puede aplicar la simulación, en el que se va a centrar el presente proyecto es en el campo de la simulación de sistemas dinámicos, más en concreto en sistemas mecánicos de dinámica rotacional. Una de las características más importantes de las herramientas de simulación es la posibilidad de crear modelos de elementos independientes y poder agrupar varios de estos modelos con propiedades comunes en conjuntos. Esto se conoce como crear una librería. Este será el objetivo principal del proyecto: la creación de una librería de elementos mecánicos rotacionales, a partir de la cual poder implementar distintos sistemas, que posteriormente serán simulados. Además, los modelos que se implementarán mediante EcosimPro serán verificados, ya sea comparando los resultados obtenidos con los obtenidos mediante otras herramientas de simulación, o bien a través de expresiones analíticas equivalentes.Ingeniería Técnica en Mecánic

Heat transfer modelling and analysis of Oxygen/Methane uncooled and film-cooled liquid rocket engines

The high hot gas temperatures and chamber pressures typical of modern liquid rocket engines (LREs) yield high local wall heat fluxes which have to be inevitably managed by the engine active cooling system. Nowadays, regenerative cooling alone might not be enough to counteract such high thermal loads in high-pressure high–performance engines, so cooling capabilities are typically enhanced with the addition of further strategies, such as film cooling or mixture ratio biased peripheral injectors. The prediction of wall heat flux in LREs is of paramount importance during the design phase both for sizing and safety purposes, especially at the nozzle throat where the maximum thermal load occurs. Numerical simulations can help in the prediction, provided that they can be effectively used during the design phase and that suitable modeling is employed. In this framework, this thesis aims at evaluating the suitability of different modeling solutions to predict in affordable times the wall heat flux of LREs employing the oxygen-methane propellant combination, which is nowadays attracting the attention of many developers as a possible cheaper and denser replacement to hydrogen. In particular, the first part of the results presented in this thesis is devoted to the analysis of the throat heat flux, whereas the second part addresses the cylindrical region of the combustion chamber. Computational fluid dynamics (CFD) simplified approaches are presented initially in case of absence of an active cooling system, and validated against experimental data as well as more accurate yet simplified numerical simulations carried out with a higher level of model completeness. Then, the cooling strategy is introduced focusing on gaseous film cooling and mixture ratio bias techniques. Due to the extreme lack of experimental data in the literature regarding the oxygen–methane propellant combination, attention is focused on a second thrust chamber representative of a possible methane–fueled upper stage. The simplified approaches validated for the uncooled case are employed and further improved to perform parametric analyses aimed at investigating how the main design parameters, such as the secondary flow mass flow rate and mixture ratio, affect the throat heat flux and the engine performances. Eventually, the second and final part of the results addresses the low–order modeling of gaseous and liquid film cooling in the cylindrical part of the combustion chamber. An extensive literature review allowed to select the most appropriate formulations to be implemented in the EcosimPro/ESPSS (European Space Propulsion System Simulation) framework, eventually providing a new component to be included in the multi–physics platform. The reliability of the predictions is assessed by analyzing transients and comparing the steady–state results against the selected experimental test cases and CFD numerical simulations performed employing the approaches above