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Is it possible, if yes how, to simulate satellite in earth's orbit in MotionView/MotionSolve?

To introduce the problem I want to solve: I want to analyse the deployment of a satellite from a last stage of a rocket.

Is it possible to use something like 'inertia relief' in motionview so I can have the satellite 'floating' in space? I want to avoid fixing the satellite to the ground so I can keep a high level of detail within the simulation.

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HyperMesh

MotionView/MotionSolve

v2020.3

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Praful

Hi Vojtech

What you describe seems feasible with MotionSolve. Depending upon how you want to set up the initial condition you can

model the rocket with its last stage which could include how the satellite is fixed to the rocket and the detaching mechanisms.
Apply initial conditions
Include/exclude gravity conditions.
Simulate the deployment event.

What is the specific part of deployment or conditions of the satellite are you trying to analyze ?

Regards

Praful

VKR

Hello Praful, thank you for your reply.

I talked to my colleagues regarding the problem and in static and dynamic analysis there is setting called 'Inertia relief' which basically allows you to 'hang' things in air (aircraft, satellites). They do this, because there is no rigid body to which you could fix yout object.

And that is exactly what I am solving - how to run a multi-body simulation without having a fixed or grounded component = have everything just hang in the orbit

My goal is to observe how the separation influences the launch vehicle.

Thank you for your time.

Praful

Hello Praful, thank you for your reply.

I talked to my colleagues regarding the problem and in static and dynamic analysis there is setting called 'Inertia relief' which basically allows you to 'hang' things in air (aircraft, satellites). They do this, because there is no rigid body to which you could fix yout object.

And that is exactly what I am solving - how to run a multi-body simulation without having a fixed or grounded component = have everything just hang in the orbit

My goal is to observe how the separation influences the launch vehicle.

Thank you for your time.

Hello Vojtech

The "inertia relief" that you mention is an FE concept to compensate for the lack of constraints.

In multi-body dynamics, constraints are not necessarily required.

In your case, consider a moment at which you wish to begin the simulation. Say 5 or 10 secs prior to the last stage separation.

Model the rocket along with the satellite -
- Provide appropriate mass and inertia values.
- Model how the satellite is constrained to the rocket.
Apply the boundary conditions prevailing at that moment. e.g. Velocity of the rocket (with satellite), thrust forces if any, gravitational force.
Add outputs to measure position, velocity acceleration or force.
First simulate the model and see if it is behaving as expected for the boundary conditions given.
Next, simulate the separation event. This could be a set of commands to the solver with multiple simulate commands that includes
- Initial simulation (5 or 10 secs)
- Removal or constraints or adding of forces that make the satellite separate
- Further simulation for another x seconds.
Post process the results.

A free body diagram might help you to use the right modeling strategy to begin with.

Praful

VKR

Thank you very much, this gave me a very good idea of how to do it.

By giving multiple commands, do you mean the 'sequential simulation' as described in this tutorial?

https://2022.help.altair.com/2022.3/hwsolvers/ms/topics/solvers/ms/ext_retract_analysis_aircraft_intro_r.htm#mv-1011-extension-and-retraction-analysis-of-the-main-landing-gear-of-an-aircraft

https://2022.help.altair.com/2022.3/hwsolvers/ms/topics/solvers/ms/understand_seq_sim_intro_t.htm#mv-1051-understanding-sequential-simulation

GTT Adam

Thank you very much, this gave me a very good idea of how to do it.

By giving multiple commands, do you mean the 'sequential simulation' as described in this tutorial?

https://2022.help.altair.com/2022.3/hwsolvers/ms/topics/solvers/ms/ext_retract_analysis_aircraft_intro_r.htm#mv-1011-extension-and-retraction-analysis-of-the-main-landing-gear-of-an-aircraft

https://2022.help.altair.com/2022.3/hwsolvers/ms/topics/solvers/ms/understand_seq_sim_intro_t.htm#mv-1051-understanding-sequential-simulation

Hi Vojtech,

In terms of deployment, I believe the launch vehicle will only experience the gravitational pull of the planet and any reaction from the satellite leaving the vehicle. Thus, a force can be defined between the launch vehicle and the planet that represents gravity and will act along their line of action like so:

I used an approximate linear force for gravity, but you can use an expression to better represent the force based on the mass of the launch vehicle and the distance from the planet center.

As Praful mentioned, define an initial velocity and direction for the launch vehicle in it's initial conditions. Then watch as the launch vehicle begins its initial trajectory, then falls back to the planet's surface.

The deployment of the satellite can be achieved by using a Template that deactivates a joint at a certain time step. Thus the satellite can be 'released' when intended.

Hope this helps!

Adam Reid

Praful

Thank you very much, this gave me a very good idea of how to do it.

By giving multiple commands, do you mean the 'sequential simulation' as described in this tutorial?

https://2022.help.altair.com/2022.3/hwsolvers/ms/topics/solvers/ms/ext_retract_analysis_aircraft_intro_r.htm#mv-1011-extension-and-retraction-analysis-of-the-main-landing-gear-of-an-aircraft

https://2022.help.altair.com/2022.3/hwsolvers/ms/topics/solvers/ms/understand_seq_sim_intro_t.htm#mv-1051-understanding-sequential-simulation

Hi Vojtech - Yes, I did mean sequential simulation as described in the tutorial.

Chris_Coker

Hello Praful, thank you for your reply.

I talked to my colleagues regarding the problem and in static and dynamic analysis there is setting called 'Inertia relief' which basically allows you to 'hang' things in air (aircraft, satellites). They do this, because there is no rigid body to which you could fix yout object.

And that is exactly what I am solving - how to run a multi-body simulation without having a fixed or grounded component = have everything just hang in the orbit

My goal is to observe how the separation influences the launch vehicle.

Thank you for your time.

Just deactivate gravity. I think you were reading too much into Praful's comments. I think he was giving you detailed modeling steps, not recommending necessarily a sequential simulation. Turning off gravity will allow the model to "float" without being connected to ground.