I have a doubt about the functionment of the Modelica.Fluid.Dissipation.HeatTransfer.HelicalPipe function.
I want to model an helical heat exchanger using the DynamicPipe of the Modelica Standard Library. Does the function allow me to specify such a geometry in order to simulate it with my boundary conditions ? Or does the function just return the heat transfer coefficient with geometry parameters in inputs ? If that's the case is it possible to simulate a flow in a pipe which is helical without using the Bends of the Modelica Standard Library ?
Thanks for your responses and have a good day,
Maxime
Related
I'm trying to get used to the Modelica.Fluid.Dissipation. I want to evaluate the heat transfer coefficient of a straight pipe using the function kc_overall. I tried to followthe UsersGuide example. I'm not sure I understood how to write it and which inputs I have to use. Here's my code:
model Heat_tranfer_calcul
Modelica.SIunits.MassFlowRate M_FLOW=0.3 "input mass flow rate";
Modelica.Fluid.Dissipation.HeatTransfer.StraightPipe.kc_overall_IN_con IN_con(d_hyd=13e-3,L=15);
Modelica.Fluid.Dissipation.HeatTransfer.StraightPipe.kc_overall_IN_var IN_var(cp=4184,eta=8.9e-4,lambda=0.6,rho=1000) ;
equation
Modelica.Fluid.Dissipation.HeatTransfer.StraightPipe.kc_overall(IN_con,IN_var,M_FLOW)
end Heat_tranfer_calcul;
I also tried to get the fluid properties directly from the Modelica.Media.Water.StandardWater.
If someone could help me to uderstand how the function works that would be really helpful.
Maxime
The function kc_overall only takes two arguments — the records IN_con and IN_var. The mass flow rate must be specified through IN_var so your code should be:
model Heat_tranfer_calcul
Modelica.SIunits.MassFlowRate M_FLOW=0.3 "input mass flow rate";
Modelica.Fluid.Dissipation.HeatTransfer.StraightPipe.kc_overall_IN_con IN_con(d_hyd=13e-3,L=15);
Modelica.Fluid.Dissipation.HeatTransfer.StraightPipe.kc_overall_IN_var IN_var(cp=4184,eta=8.9e-4,lambda=0.6,rho=1000, m_flow=M_FLOW);
equation
Modelica.Fluid.Dissipation.HeatTransfer.StraightPipe.kc_overall(IN_con,IN_var);
end Heat_tranfer_calcul;
By the way, it is good Modelica coding practice to use lowercase letters for variable names, that is m_flow instead of M_FLOW.
I am new to modelica, and i don't have this much experience in it, but i got the basics of course. I am trying to model a micrfluidic network. The network consists of two sources of water and oil, controlled by two valves. The flow of the two mediums interact at a Tjunction and then into a tank or chamber. I don't care about the fluid properties of the mixture because its not my purpose. My question is how do redeclare two medium packages (water and oil) in one system component such as the Tjunction or a tank in order to simulate the system. In my real model, the two mediums doesn't meet, becuase every medium passes through the channels at a different time.
I attached the model with this message. Here's the link.
https://www.dropbox.com/s/yq6lg9la8z211uc/twomediumsv2.zip?dl=0
Thanks for the help .
I don't think you can redeclare a medium during simulation. In your case (where you don't need the mixing of the two fluids) you could create a new medium, for instance called OilWaterMixture, extending from Modelica.Media.Interfaces.PartialMedium.
If you look into the code of PartialMedium you'll see that it contains a lot of partial ("empty") functions that you should fill in in your new medium model. For example, in OilWaterMixture you should extend the function specificEnthalpy_pTX to return the specific enthalpy of your water/oil mixture, for a certain water/oil mixture (given by the mass fraction vector X). This could be done by adding the following model to the OilWaterMixture package:
redeclare function extends specificEnthalpy_pTX "Return specific enthalpy"
Oil = Modelica.Media.Incompressible.Examples.Essotherm650;
Water = Modelica.Media.Water.StandardWater;
algorithm
h_oil := Oil.h_pT(p,T);
h_water := Water.specificEnthalpy_pT(p,T);
h := X[0]*h_oil + X[1]*h_water;
end specificEnthalpy_pTX;
The mass fraction vector X is defined in PartialMedium and in OilWaterMixture you must define that it has two elements.
Again, since you are not going to actually use the mixing properties but only mass fraction vectors {0,1} or {1,0} the simple linear mixing equation should be adequate.
When you use OilWaterMixture in the various components, the error log will tell you which medium functions they need. So you probably don't need to extend all the partial functions in PartialMedium.
I am using the Envelope_3 package of CGAL-4.9.1 and I need to compute an upper envelope where the resulting envelope diagram (Envelope_diagram_2<EnvTraits>) could have edges of three different types:
segments
rays
parabolic arcs (conic arcs)
The three provided models of Envelope_Traits_3 are not enough for this.
I therefore need to create my own EnvTraits (which have to be a model of the concept Envelope_Traits_3).
For now, I made a something like the already provided Env_sphere_traits_3<ConicTraits> model, with which I have at my disposal both parabolic arcs and segments (I just use straight arcs).
The problem arises because I also need to be able to use Rays. How could I do this? Is there a Traits class that I can extend (just like I'm doing right now with Arr_conic_traits_2) that provides X_monotone_curve_2s that can be of the three types that I need?
I found the Arr_polycurve_traits_2 class, hoping that it would allow curves of different type to be stored as subcurves, but it actually just allows to store polycurves that are all of the same kind (linear, bezier, conic, circular...).
What you need is a model of the EnvelopeTraits_3 concept and of the ArrangementOpenBoundaryTraits_2 concept. Among all traits classes provided by the "2D Arrangements" package only instances of the templates Arr_linear_traits_2, Arr_rational_function_traits_2, and Arr_algebraic_segment_traits_2 are models of the later concept.
I suggest that you develop something like Env_your_object_traits_3<AlgebraicTraits_2>, where the template parameter AlgebraicTraits_2 can be substituted with an instance of Arr_algebraic_segment_traits_2.
Efi
I've been working on the HM reference software for a while, to improve something in the intra prediction part. Now a new intra prediction algorithm is added to the code and I let the encoder choose between my algorithm and the default algorithm of HM (according to the RDCost of course).
What I need now, is to signal a flag for each PU, so that the decoder will be able to perform the same algorithm as the encoder decides in the rate distortion loop.
I want to know what exactly should I do to properly add this one bit flag to the stream, without breaking anything in the code.
Assuming that I want to use a CABAC context model to keep the track of my flag's statistics, what else should I do:
adding a new context model like ContextModel3DBuffer m_cCUIntraAlgorithmSCModel to the TEncSbac.h file.
properly initializing the model (both at encoder and decoder side) by looking at how the HM initialezes other context models.
calling the function m_pcBinIf->encodeBin(myFlag, cCUIntraAlgorithmSCModel) and m_pcTDecBinIfdecodeBin(myFlag, cCUIntraAlgorithmSCModel) at the encoder side and decoder side, respectively.
I take these three steps but apparently it breaks something.
PS: Even an equiprobable signaling (i.e. without using CABAC contexts) will be useful. I just want to send this flag peacefully!
Thanks in advance.
I could solve this problem finally. It was a bug in the CABAC context initialization.
But I want to share this experience as many people may want to do the same thing.
The three steps that I explained are essentially necessary to add a new syntax element, but one might be very careful with the followings:
In the beginning, you need to decide either you want to use a separate context model for your syntax element? Or you want to use an existing one? In case of CABAC separation, you should define a ContextModel3DBuffer and the best way to do that is: finding a similar syntax element in the code; then duplicating its ``ContextModel3DBuffer'' definition and ALL of its occurences in the code. This way assures that you are considering everything.
Encoding of each syntax elements happens in two different places: first, in the RDO loop to make a "decision", and second, during the actual encoding phase and when the decisions are being encoded (e.g. encodeCtu function).
The order of encoding/decoding syntaxt elements should be the same at the encoder/decoder sides. For example if your new syntax element is encoded after splitFlag and before predMode at the encoder side, you should decode it exactly between splitFlag and predMode at the decoder side.
The context model is implemented as a 3D matrix in order to let track the statistics of syntaxt elements separately for different block sizes, componenets etc. This means that when you want to call the function encodeBin, you may make sure that a correct index is being used. I've made stupid mistakes in this part!
Apart from the above remarks, I found a the function getState very useful for debugging. This function returns the state of your CABAC context model in an arbitrary place of the code when you have access to it. It is very useful to compare the state at the same place of the encoder and the decoder when you have a mismatch. For example, it happens a lot that you encode a 1 but you decode a 0. In this case, you need to check the state of your CABAC context before encoding and decoding. They should be the same. If they are not the same, track back the error to find the first place of mismatch.
I hope it was helpful.
I am trying to find out the parameters for the function below:
$$
\log L(\alpha,\beta,v) = v/\beta(e^{-\beta T} -1) + \alpha/\beta \sum_{i=1}^{n}(e^{-\beta(T-t_i)} -1) + \sum_{i=1}^{N}log(v e^{-\beta t_i} + \alpha \sum_{j=1}^{jmax(t_i)} e^{-\beta(t_i - t_j)}).
$$
However, the conventional methods like fmin, fminsearch are not converging properly. Any suggestions on any other methods or open libraries which I can use?
I was trying CVXPY, but they don't support the division by a variable in the expression.
The problem may not be convex (I have not verified this but it could be why CVXPY refused it). We don't have the data so we cannot try things out, but I can give some general advice:
Provide exact gradients (and 2nd derivatives if needed) or use a modeling system with automatic differentiation. Especially first derivatives should be preferably quite precise. With finite differences you may lose half the precision.
Provide a good starting point. May be using an alternative estimation method.
Some solvers can use bounds on the variables to restrict the feasible region where functions will be evaluated. This can be used to restrict the search to interesting areas only and also to protect operations like division and log functions.