Well I am working on a very interesting project concerning a gear system that will rotate a shaft and some gear systems. I am following a tutorial from matlab
User-Added Coordinate Systems
on how to decouple and have two gears rotating.
Well, I need some hold on understanding the following figure, that is the output of the above link.
So what I do next is un-weld the two gears by deleting the conection of F1, and later introducing the common gear constraint by conecting it to the SMLINK port on both gear"_" boxes. I get and unusual message that says:
" * Model not assembled: position violation * Resolve this issue in order to simulate the model."
Can some one explain what is happening?
Also, what is the difference between 1st generation, and multibody Simscape? can I have joint actuators in both cases? and if so how would i be able to implement such in the example given above?
for those who would like to answer, but dont have solid works, the gear block boxes, and figure is the following:
It looks like the right thing to do, but how have you parameterised your gear constraint? Have a look at mech_user_added_css.mdl for the correct way to do it (it's one of the SimMechanics example, but it uses the first generation engine and blocks). Make sure the gear circle radii match what's in the first generation example. It will also help to answer you question about first generation vs. second generation.
SimMechanics was one of the early physical modelling tools produced by MathWorks. A few years later, they produced Simscape and the Simscape engine for modelling multi-domain systems. This was much more powerful than the original SimMechanics, so over the years they migrated SimMechanics functionality over to Simscape, but have kept the original first generation blocks for compatibility issues. Have a look at some of the first generation vs second generation examples and blocks to get an idea.
Related
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.
http://python.dronekit.io/develop/sitl_setup.html
there's a. mentioning that SITL is there for only a few pre-built vehicles. suppose i am designing a completely new model of flying vehicle, can i still simulate that?
Thanks a lot:) My drone design just has another set of mathematical expressions for its roll, pitch and yaw control. So, technically I need changes only in the AP_motors.cpp file (here the commands are converted into motor PWM values) only right? or is it more than that? Please guide me.
You can actually, but at this time there is no detailed documentation to do so. At the moment the best bet is by using RealFlight 8 to design the vehicle (and also to simulate the physics) and then use SITL to control it. You can check how to connect RealFlight to SITL at here http://ardupilot.org/dev/docs/sitl-with-realflight.html. There is also a discussion about building a custom model for RealFlight 8 with SITL at here https://discuss.ardupilot.org/t/building-realflight8-models/23106/34.
I am currently working with multibody mechanical systems using the MultiBody library included in the standard Modelica distribution.
I need to implement a switch between flanges, in order to select position or force control for a given joint.
model FlangeSwitch "Switch between flanges"
Modelica.Mechanics.Translational.Interfaces.Flange_a flange_a_1;
Modelica.Mechanics.Translational.Interfaces.Flange_b flange_b_1;
Modelica.Mechanics.Translational.Interfaces.Flange_a flange_a_2;
Modelica.Mechanics.Translational.Interfaces.Flange_b flange_b_2;
Modelica.Mechanics.Translational.Interfaces.Flange_a flange_a_exit;
Modelica.Mechanics.Translational.Interfaces.Flange_b flange_b_exit;
Modelica.Blocks.Interfaces.BooleanInput u;
equation
if u then
flange_a_exit = flange_a_2;
flange_b_exit = flange_b_2;
else
flange_a_exit = flange_a_1;
flange_b_exit = flange_b_1;
end if;
end FlangeSwitch;
But this approach does not work, the system is not balanced: 10 equations and 12 variables.
Is there any way to do this?
I don't think a Modelica tool will allow this operation (even if you have a balanced model), as it would potentially result in a variable structure system. Which is something Modelica does not support at the moment. See a nice introduction here: https://www.modelica.org/events/modelica2017/proceedings/html/submissions/ecp17132291_Stuber.pdf
Without fully knowing the application you could try two approaches:
Use a model that emulates a rotational clutch, like the Modelica.Mechanics.Translational.Components.Brake with an activated parameter useSupport. This way you can generate a "controllable mechanical connection" for connecting either of the flanges to the support connector. If I read your code correctly you should connect flange_a_2 to the support and the flange_a_exit to either flange_a or flange_b. When activating the brake via the RealInput there will be a mechanical connection.
The second thing you can try is to measure either position or force (which of both you want to apply by a sensor Modelica.Mechanics.Translational.Sensors.PositionSensor and then apply it using the respective source, which in this case would be Modelica.Mechanics.Translational.Sources.Position. Switching between the sources could then be done by switching the Real signals instead of the physical connectors. Mind that is could generate jumps in positions when applying positions directly.
The link you posted is related to non-phyiscal connectors, which are less restrictive compared to the physical connectors. So comparing the two solutions should be done very carefully.
Switching from position as an input to force as an input would require the system of equations to be rebuilt when executing this switch. This will not be possible with current generation Modelica. You will need to find a solution that is based on the same input for the whole simulation.
Would it be enough to initialize position in a way that the system starts the simulation in the point where you want to move it to first (using the Position Source)? What you loose is the movement of the system to this position.
I'm making a simple electric circuit simulator. It will (at least initially) only feature batteries, wires and resistors in series and parallel. However, I'm at a loss how best to simulate said circuit in a good way.
Specifically, I will have batteries and resistors with two contact points each, and wires that go between two contact points. I assume that each component will have a field for its resistance, the current through it and the voltage across it (current and voltage will, of course, be signed). Each component is given a resistance, and the batteries are given a voltage. The goal of the simulation is to assign correct values to all the other fields in real time as the player connects and disconnects components and wires.
These are the requirements:
It must be correct, including Ohm's and Kirchhoff's laws (I'm modeling real world circuits, and there is little point if the model does something completely different)
It must be numerically stable (we can't have uncontrolled oscillations or something just because two neighbouring resistors can't make up their minds together)
It should stabilize relatively quickly for, let's say, fewer than 30 components (having to wait a few seconds before the values are correct doesn't really satisfy "real time", but I really don't plan on using it for more than 10 or maybe 20 components)
The optimal formulation for me (how I envision this in my head) would be if I could assign a script to each component that took care of that component only, possibly by communicating field values with neighbouring components, and each component script works in parallel and adjusts as is needed
I only see problems here and no solutions. The biggest problem, I think, is Kirchhoff's voltage law (going around any sub-circuit, the voltage across all components, including signs, add up to 0), because that's a global law (it says somehting about a whole circuit and not just a single component / connection point). There is a mathematical reformulation saying that there exists a potential function on the points in the circuit (for instance, the voltage measured against the + pole of the battery), which is a bit more local, but I still don't see how to let a component know how much the voltage / potential drops across it.
Kirchhoff's current law (the net current flow into an intersection is 0) might also be trouble. It seems to force me to make intersections into separate objects to enforce it. I originally thought that I could just let each component have two lists (a left list and a right list) containing every other component that is connected to it at that point, but that might not make KCL easily enforcable.
I know there are circuit simulators out there, and they must have solved this exact problem somehow. I just can't find an explanation because if I try googling it, I only find the already made simulators and no explanations anywhere.
I am taking part in a programming competition where the objective is writing a bot that can play a specific game.
The objective of the game is to earn a certain amount of points. You control multiple airships, that you move around, capture islands and navigate drones that carry treasure. You play against one opponent, turns happen simultaneously, and there is a time limit. You can move multiple ships and drones in one turn. You can program your bot in Python, Java or C#.
The exact details don‘t matter, just that each ship has around 15 options each turn (moving and shooting) and overall you have around 10000 different options for each turn (different configurations of airship movements and shooting)
Up until now I approached this competition naively, and haven‘t done anything exceptionally clever (for example, if near enemy, shoot). I have read about minimax algorithms, and I would really like to apply it here (or something similar), you can assume that I can tell the value of a state. My problem is the mass of options for each turn - which create an enourmous branching factor that doesnt let me get very deep.
Question 1: Is there a better, applicable approach to this problem? Perhaps deep-learning or something similar?
Question 2: Is there a way to minimize the branching factor? I`ve read about alpha-beta and similar algorithms, but nothing seems to do the job.
Any help would be much appreciated
The minimax algorithm seems to be natural for these kinds of problems. At first, the game will be modelled in a abstract way and then a solver is used to find the path from current situation to a gamestate which maximize the amount of points. A similar approach to minimax is GOAP, which was implemented in the 1970'er for Shakey the robot under the name STRIPS. But, GOAP and minimax has two problems: first, a abstract model of the game is needed (perhaps in PDDL or in Game Description Language) and second the state-space is to big.
An better alternative to planning is to use a Behavior Tree. Thats a static program which describes the behavior of an agent. No solver is needed and no complete modelling of the game is needed. Instead, a bottom up approach is used with multiple edit-compile-run iterations for finding the optimal behavior tree (Test-driven-development). To implement such programming approach a so called "reactive planner" has to be implemented first which is another word for a realtime scheduler. Thats a module whichs maps a behavior tree onto a gantt-chart for executing an action at a specific moment in time. As introduction, the unity3d Engine is a good starting point, which has a full behaviortree implementation out-of-the-box.