I'm discovering OpenModelica for few days and I would like to study the combination of solar panels and wind turbines to product electricity.
So, i decided to use WindPowerPlants library for the wind part. My start point is from the example WindPowerPlants.Examples.GenericPlantElectricRealData
I would like to have a storage system in load of the system. But I have trouble to understand how to transfer the electrical signal from Quasi-Stationary Multiphase (in output of the wind turbine) to AC multiphase to be able to transfer the power in the load.
Is there a simple solution to just not have QS ? I'm limited by the components of the quasi-stationary library from Modelica.
I'm open to any information, I have certainly missed something or misunderstood.
Thanks !
There is currently no coupling model between quasi static and transient AC systems available in the Modelica Standard Library. The reason for that is, that quasi static models rely on purely sinusoidal voltages and currents but the transient domain wave forms can not be pushed to be sinusoidal. One could only create a coupling model which for example maintains the active and reactive power balance between the quasi static and the transient side.
I recommend to use the components from Modelica.Electrical.QuasiStationary.MultiPhase package and avoid the usage of transient models at all. Even though the quasi static package is limited to linear systems, you should be able to find most of the components you need to perform your investigations. In case you need, for example, a controlled AC power load, the model WindPowerPlants.Sources.IdealRealPowerConductance can be used.
In terms of power flow analysis based on controlled loads and generators I may also draw your attention to the following libraries (see https://modelica.org/libraries):
https://github.com/modelica-3rdparty/PowerSystems (successor of Spot, version 1.0.0 is available)
https://github.com/PowerGrids/PowerGrids (version 1.0.0 was just released a few days ago)
Related
I have been working with Anylogic for about 6 months now and my goal is to model a generic energy supply chain for an energy demand (e.g. storm and heat for a house). As a result I want to evaluate how suitable the components in the energy supply chain are to meet the energy demand.
My idea would be to model the components (Ex. PV->Battery Storage->House) as agents. I would have modeled the energy flow in the agents with SD and individual events of the components (e.g. charging and discharging at the battery) via state diagrams.
Currently I have two problems:
Which possibilities are there to create a variable interconnection of my components (agents). For example, if I do not want to evaluate the scenario PV->Battery Storage->House, but PV->Electrolysis->Tank->Fuel Cell->House. My current approach would be to visually connect the agents with ports and connectors and then pass input and output variables for DS calculation via set and get functions. Are there other possibilities, e.g. to realize such a connection via an input Excel? I have seen a similar solution in the video: "How to Build a True Digital Twin with Self-Configuring Models Using the Material Handling Library" by Benjamin Schumann, but I am not sure if this approach can be applied to SD.
To evaluate the energy supply chain, I would like to add information to the energy flow, for example the type (electricity, heat), generation price (depending on which components the energy flow went through) and others. Is there a way to add this information to a flow in SD? My current approach would be to model the energy flow as an agent population with appropriate parameters and variables. Then agents could die when energy is consumed or converted from electricity to heat type. However, I don't know if this fits with the SD modeling of the energy flow.
Maybe you can help me with my problems? I would basically be interested in the opinion of more experienced Anylogic users if my approaches would be feasible or if there are other or easier approaches. If you know of any tutorial videos or example models that address similar problems, I would also be happy to learn from them.
Best
Christoph
Sounds like what you need is a model that combine agent-based and system dynamics approaches with Agents populating the stocks (in your case energy that then gets converted into heat) depending on their connection. There is an example of AB-SD combination model in 'Example' models and I also found one on cloud.anylogic.com, although it is from a different domain.
Perhaps if you can put together a simple example and share then I'll be able to provide more help.
I'd like to start off by saying that I'm new to StackOverflow and to Modelica.
My goal is to simulate the injector system of a Rotating Detonation Engine. Essentially this is a piping system from a tank to a rocket engine. This system will change depending on the experimental setup, so I chose Modelica (specifically OpenModelica) because of the re-usability of components. The flows encountered will be at high pressures and high flow rates (sustaining a detonation requires this), and choked flow will occur.
My question is this: does the standard "Fluid" library in Modelica allow for choked flow? I understand that a few valves model this, but will the current library be able to capture "choking" in a long rough pipe, or the small end of a converging pipe (basically anywhere choking can happen, despite it not being the design location for a choke)?
If yes, excellent. If not, is there a non-standard library available? Should I be looking at something other than Modelica? I am happy to work on making a new library, but before going through that work I thought I would check to see if anything already existed.
I have read through most of the "Media" and the basics of the "Fluid" libraries and I get the feeling that compressible flow is modeled as a means of increasing accuracy over in-compressible flow, but not to actually handle choked flow.
Thank you for your time. I hope everyone is keeping safe!
The pipe model in the Modelica library does not handle choked flows.
Adding a standard orifice in series with the pipe should help provided the 'zeta' value is adjusted to make the velocity at the orifice match with the speed of sound in the gas. In other words Modelica library does not provide a valid mean of modeling choked flows in pipes.
However, I found a very interesting library called FreeFluids (https://github.com/CarlosTrujilloGonzalez/FreeFluidsModelica) who does have a very good model for choked pipes. An example is provided with the library for a choked air flow in a 10m long diam. 50mm circular pipe. The model returns correct values for air.
In the Thermal Power Library from Modelon, there are two kinds of connectors: flow connector and volume connector.
Based on the tutorial shipped with the library, these two kinds of connectors should NOT be connected with the same kind of connector.
But I checked their code, it seems the codes are the same.
I checked the code in the ThermoSysPro library from EDF and ThermoPower library, too. They also use two kinds of connectors, and the recommendation of connecting principle is also the same.
So I read the code of “MixVolume” and “SteamTurbineStodola”, which include volume connectors and flow connectors respectively, but I am not sure the difference between these two kinds of connectors.
My question is :
Could someone tell me the philosophy of using such two kinds of connectors in thermo-hydraulic systems, and in the code of every component, how should I deal with them so they work like they’re designed for.
Here is a very short and simplified explanation applying to thermo-hydraulic systems.
In flow models (pipes, valves etc.) enthalpy is unchanged and mass flow/pressure drop are related with a static equation.
In volume models pressure and enthalpy are dynamic state variables, that is, mass and energy conservation is "elastic".
As a rule of thumb, you should build thermo-hydraulic system models of alternating flow and volume models (in a staggered grid scheme) to decouple nonlinear systems.
For the dynamic pipe model in the top figure in your post the connectors merely indicate that, internally, the pipe model begins with a volume model and ends with a flow model.
Claytex has a nice blog post on the subject here https://www.claytex.com/blog/how-to-avoid-computationally-expensive-fluid-networks-in-dymola/
Also the authors of the Modelica Buildings Library have done a great effort explaining this in various papers. See e.g. https://buildings.lbl.gov/publications/simulation-speed-analysis-and
These kind of connectors are indeed the same due to modelica language specification. You can only connect two connectors that are interchangeable, that have the exact same amount and type of flow and potential variables. At every node all flows have to sum up to zero and all potentials have to be the same, therefore they have to be type consistent.
The difference is just information wise for the modeler or someone trying to understand the model and all components have been designed with such a thing in mind. It is easiest to understand with electrical components, where you have positive and negative pins which indicate in which direction the current should flow, but this is actually never really forced. Positive and negative pins are, ignoring their name, identical.
Although i don't know the connectors you are talking about i would assume that the VolumePort is a connector of something that has a volume and passes that information, whereas FlowPort passes the information about the mass flow rate. Usually a pipe i guess (?). Broken down to abstract dae theory one could say the names indicate if the potential or the flow variable are considered unknown for the component.
I have to emphasize that these are only indicators and that it is never actually forced by the model or the compiler. It is just how it should logically resolve in the end if you respect these restrictions of only connecting VolumePortto FlowPort connectors.
I'm trying to evaluate an application that runs on a vehicular network using OMNeT++, Veins and SUMO. Because the application relies on realistic traffic behavior, so I decided to use the LuST Scenario, which seems to be the state of the art for such data. However, I'd like to use specific parts of this scenario instead of the entire scenario (e.g., a high and a low traffic load fragment, perhaps others). It'd be nice to keep the bidirectional functionality that VEINS offers, although I'm mostly interested in getting traffic data from SUMO into my simulation.
One obvious way to implement this would be to use a warm-up period. However, I'm wondering if there is a more efficient way -- simulating 8 hours of traffic just to get a several-minute fragment feels inefficient and may be problematic for simulations with sufficient repetitions.
Does VEINS have a built-in mechanism for warm-up periods, primarily one that avoids sending messages (which is by far the most time consuming part in the simulation), or does it have a way to wait for SUMO to advance, e.g., to a specific time stamp (which also avoids creating vehicle objects in OMNeT++ and thus all the initiation code)?
In case it's relevant -- I'm using the latest stable versions of OMNeT++ and SUMO (OMNeT++ 4.6 with SUMO 0.25.0) and my code base is based on VEINS 4a2 (with some changes, notably accepting the TraCI API version 10).
There are two things you can do here for reducing the number of sent messages in Veins:
Use the OMNeT++ Warm-Up Period as described here in the manual. Basically it means to set warmup-period in your .ini file and make sure your code checks this with if (simTime() >= simulation.getWarmupPeriod()). The OMNeT++ signals for result collection are aware of this.
The TraCIScenarioManager offers a variable double firstStepAt #unit("s") which you can use to delay the start of it. Again this can be set in the .ini file.
As the VEINS FAQ states, the TraCIScenarioManagerLaunchd offers two variables to configure the region of interest, based on rectangles or roads (string roiRoads and string roiRects). To reduce the simulated area, you can restrict simulation to a specific rectangle; for example, *.manager.rioRects="1000,1000-3000,3000" simulates a 2x2km area between the two supplied coordinates.
With both solutions (best used in combination) you still have to run SUMO - but Veins barely consums any of the time.
The Modelica Standard Library comes with the Modelica.Media library which makes available thermodynamic properties of fluids.
Quoting from the Modelica.Media documentation:
Media models in Modelica.Media are provided by packages, inheriting
from the partial package Modelica.Media.Interfaces.PartialMedium.
Every package defines:
[...]
A BaseProperties model, to compute the basic thermodynamic properties of the fluid;
setState_XXX functions to compute the thermodynamic state record from different input arguments (such as density, temperature, and composition which would be setState_dTX);
[...]
There are - as stated above - two different basic ways of using the Media library
which will be described in more details in the following section.
One way is to use the model BaseProperties.
[...]
The second way is to use the setState_XXX functions to compute the thermodynamic state record from which all other thermodynamic state variables can be computed [...]
My colleague prefers BaseProperties (he spends most time modeling components),
I prefer the setState_XXX functions (I spend most time writing a property library).
Now we want to develop a simple&small component library together and probably we should agree to use one of the two approaches.
Can you recommend a publication that explains the advantages/disadvantages of the two approaches? Publications that promote the use of the setState_XXX function are preferred of course... ;-)
Are there some simple rules to decide which one of the two approaches to use when modeling a component (e.g. a very simple turbine)?
The components in Modelica.Fluid seem to use both.
The 2 types of patterns for computing properties can both be used for all types of components, but BaseProperties have been designed to make life for the Modeller easy for components with dynamic states, i.e. usually for the storage of mass and energy in volumes. You need to write just the conservation equations, instantiate BaseProperties, equate the relevant variables and you are done. That is often overkill (more equations than minimally needed) for components with a stationary mass and energy balance, like simple valves, pumps and turbines. For that type of components (no dynamic states), the setState_xxx method provide a way to work with the minimally necessary number of equations. I think that is also what you will see in Modelica.Fluid: BaseProperties are used together with dynamic equations for mass- and energy storage, and setState elswhere.
The minimum number of equations is not the whole story w.r.t. computational efficiency, but in geeneral models shoudl not ocmpute more than what is actually needed.