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    • Rahul Ponginan

      Please click here for a short but important announcement   03/26/17

      Dear Users Our Commercial and Academic users around the world can use these same forums here as before i.e. the Altair Support Forum , Commercial users from India with solver queries can go to the Solver Forum for India Commercial Users , Academic Users from India and AOC India Participants are requested to go to the Forum for India Academic Users and AOC India Participants , We will be tending to all queries in all the forums promptly as before, thank you for your understanding. 

Moka89

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  1. Dummy Crash Simulation problems

    Dear Forum, for a project I want to simulate the effect on a person who is driving a car with 13.88 m/s (50 km/h) and crashes into an obstacle with a 90° angle towards the obstacle (straight front crash). The person is represented by a dummy (50% Male), the seat structure was modeled by altair, as well as the dummy. I created two seatbelts with the Hypercrash tool Belt Generator (Hypercrash --> Safety --> Belt Generator) and deformed the seat with the seat deformer (old) (Hypercrash --> Safety --> Seat Deformer --> Geometrical displacement (old)). Due to simplification I removed the complete lower sector of the seat group and replaced it with a rigid body, which is linked to the floor and the seat. I built the model as follows: Loadcases: -Initial velocity: applied to all parts of the model (13.88 m/s) -Imposed velocity: A function, which decreases the speed from 13.88m/s to 0 within 30 ms. Applied to all parts but the dummy itself. -Gravity load: To maintain physical correctness of the dummys motion. -Added Mass: Applied to all nodes of the dummy to be representative for the human weight. Boundary Conditions: -BC for the seat: All degrees of freedom are locked except for the translation in X-axis (which is the direction of motion). This is applied only for the floor and the ground part of the seat. Contact Interfaces: -Interior contact: Contact between the two seat layers (was set by altair when I imported the model, I did not change any values) -Seat to floor: Contact seat to floor (TYPE7) -Feet to floor: Contact feet to floor (TYPE10) -Seatbelt to dummy: Contact upper/lower seatbelt to dummy/seat (TYPE7) -Dummy to seat: Contact Dummy to seat (TYPE7) The problems I am facing now are: -The Runtime for a single simulation is about 9500 seconds. Can this be regarded as normal, considering the model complexicity? -Results of the simulation differ too much from expactations/reality -->Normally I would have expected the backrest to at least do a little motion, but it remains in its position. -Because of the constraints of the seatbelts, the head of the dummy experiences a very high acceleration. -->Is there any chance, that the Belts ease a little bit (in the beginning) and afterwards tension up, just like in reality? -All elements of the part "LINK", ID:6 delete on the beginning of every simulation. I could not figure out the reason for that, neither in the starter file, nor in the engine file. -During the Simulation it reaches one Point, where all the masses go into one single point/node but I can not figure out, why (see attached Video) Please correct me if I am rootedly wrong with my assumptions. Attached you can find my model files. PS: I am aware of the initial penetrations within the seat. Thanks in advance. Greetings. Modell_Dummy_Sitzgruppe_0001.rad Modell_Dummy_Sitzgruppe_0000.rad Modell_Dummy_Sitzgruppe_0000.M00 Simulation_Video.avi
  2. Hello, first of all thank you for your quick answer. Unfortunately the example you sent me does not solve my problem, because the kind of problem I wanted to simulate is a multi chamber simulation of an airbag, whereas you sent me an example of a single chamber airbag. The Image Card I use is AirBagWithCommunication1, the Card Image in the webinar you sent me is another one. From my point of view the problem lies in the communication surfaces, which lie in between two chambers. They need to communicate to each other but the normal tangents exist in outward directions, so that the communication does not work properly, because one of the chambers does not communicate with the neighbouring chambers in both ways, but only in one way. Maybe you can answer me another question: How can I define two normal tangents for one element? Is that even possible? Many thanks and kind regards.
  3. Hello everyone, I am about to simulate an Airbag deploying and I have got following problem: I would like to get this airbag as a system with several chambers by using the Cardimage "Airbagwithcommunication1" the way i can simulate it with Communication surface. The following example shows how it should be built. RBPLI_UP_0000.rad While simulating comes out this error message In general that system has got 4 chambers, for every single chamber appears the same error message. All chambers volume are closed and the mesh elements are normal outward-orientated. By using the Cardimage "Airbag", the simulation runs without any problems. My question is: How can I create the Surface Communication? Knowing that this Surface Communication has been created manual as Shell Elements 3-4 nodes with HyperMesh. Could it be the right element or not? It will be very kind from your side if you tell me what do you mean about the Errors ID 473 and 902. I have attached the Model and OUTPUT-file. Model_1_0000.outModel_1_0001.radModel_1_0000.rad Thank you so much in advance and wish you a wonderful day. Kind regards MisterKarimi
  4. SPH Inlets/Outlets Conditions

    First of all thanks for your tips, gentlemen. Mr. Pagadala could you please specify what you mean by "changing the order of property". Another general question: Is there a way to create SPH elements directly on a surface instead of a volume?
  5. SPH Inlets/Outlets Conditions

    Hello everybody, Is anyone well informed about SPH Inlets/Outlets Conditions? I´m a beginner and have little knowledge, here is my situation: I´m making a simulation of a pipe. The fluid is air. The SPH that are defined at the Inlet should flow through the pipe and be eliminated at the Outlet. First problem is that only a part of the SPH are eliminated at the Outlet. Second problem is that my calculation time is very long even for simple simulations. Some data on the simulation: My units are: kg, mm, ms, kN Formula used to calculate particle mass: c^3x density I selected Simple Cubic for SPH creation, so the Smoothing Length was set automatically. But on the help section of the homepage of Altair there are several formulas for calculating mp and h. Is it correct the way I´ve done it? SPH-Property: qa=1e-20 and qb=1e-20 For the air I chose material law LAW6 and I entered the following values: Air # RHO_I 1.22E-9 0 # Knu .015 # C0 C1 C2 C3 0 0 0 0 # Pmin Psh 0 1.0132E-4 # C4 C5 E0 .4 .4 2.533E-4 I changed the orientation of the surface segments in a way that their normal vectors point towards the interior of the domain. I defined DIST-inlet = 2xh Density function defined: time: 0, 1e30 ; density: 1, 1 For Fscale I entered my actual air density. I defined the velocity function: Time: 0, 500 ; Velosity: 50, 50 DIST-outlet = 2xh Pressure function: Time: 0, 1e30; Pressure: 1, 1 ; For Fscale I entered 0.005. I set for SPH the „SPH Particle Reserve“ Does SPHGLO-control card has an impact on my results and calculation time? i've also attached the files. Thank you. S-pipe_0000.rad S-pipe_0001.rad
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