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Re: [Rocketworkbench-devel] Kickoff Elm
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From: Antoine L. <an...@st...> - 2000-02-13 21:51:12
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On Sun, Feb 13, 2000 at 09:42:46AM -0800, Konrad Hambrick wrote: > All -- > > What will be the scope of the Rocket WorkBench ? > > My wish list would be: > > 1. Physical Description > 2. Aerodynamics ( Drag and Stability ) Could you explain those two > 3. Powerplant > 4. Environmental The list was for the moment * propellant combustion simulation/design * Grain Design * Chamber/Injector design * Nozzle Design * Trajectory analysis * Impact Dispersal profiles. * Basic parachute design I'm ready to work on any rocket related project that could help design and understanding of rocket... > > I suppose we might want to begin with a data structure > that describes a rocket. I started working on a similar > project a few years ago but ran out of time between my > real job and my work on the AltAcc. > > Below is my first stab at a data structure describing a > rocket. It is nowhere near complete or even correct as > far as it goes. it is a start. > > Input ? > > Let's get ready to rumble ! > > -- kjh Please take a look to the stock I have put in libsimulation on the cvs or ftp ftp rocketworkbench.sourceforge.net/pub/rocketworkbench I have already do a part of this but not in the same manner. My rocket description file use aerodynamic properties: drag coefficient, lift coefficient, cross-spin coefficient, restoring moment coefficient, damping moment coefficient,... All the aerodynamic parameter to describe the rocket attitude. Of course this method implies that we know those value. If we describe a rocket like you would like to do, it could permit the calculation of aerodynamic properties if we are able to simulate the comportmnent of a body in a compressible fluid. Maybe by finite element analysis if someone know how to do... > > /************************** rocket.h ********************************/ > > struct AtmProf /* optional Atmospheric Info for Sims */ > { > AtmProf * prev; /* linked list ... pointer to prev element */ > AtmProf * next; /* linked list ... pointer to next element */ > double alt; /* altitude of measurement */ > double press; /* measured barometric pressure */ > double temp; /* measured temperature */ > double humidity; /* measured humidity */ > double rho; /* computed air density */ > double viscosity; /* computed air viscosity */ > double dirwind; /* measured wind direction (NSEW) */ > double velwind; /* measured wind velocity */ > }; Humm, interesting. Is it really possible to know those parameter for each point of the atmosphere around the earth... For the moment, I use a simple formula that compute the density of the atmosphere in function of altitude considering a compressible fluid and variable gravitational acceleration. It is easy to demonstrate from a differential equation. density = (Po*M/T)*exp( ((M*G*Mt)/R*T) * (1/(Rt + h) - 1/Rt)) Po: ground pressure M: molar mass of atmosphere T: temperature G: universal gravitational constant Mt: earth mass R: perfect gaz constant Rt: radius of the earth h: altitude It give a fairly good approximation for low altitude. > struct Site /* Launch Site Environmental Data */ > { > double ialt; /* Site Altitude */ > double bpress; /* Site Barometric Pressure */ > double temp; /* Site Temperature */ > double rho0; /* Site Air Density ( computed ) */ Should add site position around a planet, it is important to take care of coriolis acceleration > double rodlen; /* Launch Rod Length */ There is not always rod, especially for big rockets > double theta; /* Launch Angle */ Two angles are needed > double falt; /* Final Altitude for Sim ( crash Alt ;-) */ If the rocket goes in orbit? > atmos * AtmProf; /* [O] pointer to Atmospheric Profile */ > }; We could also add information about plenets, mass, radius... > > struct CD /* optional CD vs Velocity data */ > { > CD * next; /* linked list; pointer to previous */ > CD * prev ; > double mach; /* mach number */ > double rnumber; /* computed Reynolds Number */ > double coff; /* CD at CD.mach */ > }; > > struct Vertex /* Fin Vertices Details */ > { > Vertex * prev; /* linked list */ > Vertex * next; > double z; > double r; > }; > > struct Fins /* Fin Geometry Info */ > { > int numfin; /* number of fins */ > double offset; /* offset from leading tip of stage */ > double thickness; /* max thickness */ > double farea; /* fin surface area */ > int shape; /* enumerated fin shape ( Poly, Para, Ellip */ > int numvert; /* number of vertices */ > Vertex * vertices; /* [O] optional pointer to Vertex.z, .r */ > double fdiam; /* diameter at front of fin can */ > double rdiam; /* diameter at rear of fin can */ > double span; /* fin span */ > double root; /* root chord length */ > double tip; /* tip chord length */ > double midchord; /* mid chord length */ > double sweepback ; /* sweepback distance */ > double parea; /* plan area of fincan */ > double aspectratio; /* aspect ratio */ > }; > > struct Thrust /* Linked List Thrust Curve Tuples */ > { > Thrust * next; > Thrust * prev; > double time; > double thrust; > }; > > struct Motor /* Stolen from RASP ;-) */ > { > char * name; /* engine name */ > char * mfg; /* manufacturer info */ > double diam; /* engine diameter (millimeters) */ > double len; /* engine length (millimeters) */ > double mass; /* initial engine wt. (kilograms) */ > double promass; /* propellant wt. (kilograms) */ > double dtime; /* thrust duration (seconds) */ > Thrust * tcurve; /* thrust curve (Time-sec,Thrust-Newtons) */ > double i_avg; /* average thrust (newtons) */ > double i_tot; /* total impulse (newton-seconds) */ > double i_max; /* peak thrust (newtons) */ > char * delay; /* ejection delays available (sec) */ > Motor * next; /* linked list of motors */ > }; > > struct Stage /* stolen from rasp v4.1 -- needs more ! */ > { > int nose ; /* nose type on stage */ > double length; /* length of stage */ > double diameter; /* max diameter of stage */ > CD * cd; /* kjh added cd per stage */ > double totalw; /* launch wt of stage ( w/ motors(s) ) */ > double dryw; /* dry stage wt ( w/o motor(s) ) */ > double prowt; /* propellant wt of all motors */ > Motor * motors; /* pointer to motor structure */ > double itime; /* Start of motors ( time since LO ) */ > double etime; /* End of engine burn ( absolute time ) */ > double dtime; /* When is the Stage dropped from the rest */ > Thrust * thrust; /* sum of all motors or ->motors.tcurve */ > Fin * fins; /* finfo for stage */ > Stage * next; /* next Stage ( From Bottom, Up ) */ > Stage * prev; /* previous Stage ( just burned out ) */ > }; > > struct Rocket /* What is in a rocket */ > { > char * name; > int nose ; > double diameter; > double length ; > Stage * stages ; > Site * environ ; > }; > > > struct NoseCones { > char * name ; /* Verbose Nose Cone Name */ > int form ; /* M,C&B Formula to Apply */ > } > Noses [ ] = > { > "undefined", 1 , > "ogive", 1 , > "conic", 1 , > "elliptic", 2 , > "parabolic", 2 , > "blunt", 2 > } ; > > struct FinShapes { > char * name ; /* Verbose Fin Shape Name */ > int form ; /* Enum Data */ > } > FinShape [ ] = > { > "undefined", 0 , > "polygonal", 1 , > "elliptical", 2 , > "parabolic", 3 > } ; > > #define NUMFINTYPE ( sizeof FinShapes / sizeof ( struct FinShape )) I will look how those idea could be include in the actual simulator. There is a lot of good idea. If you want to look at that on your own, you can send me patch of the code. Another question, there is somebody who have experiences with finite element analysis and Navier-Stroke equations?? > > > _______________________________________________ > Rocketworkbench-devel mailing list > Roc...@li... > http://lists.sourceforge.net/mailman/listinfo/rocketworkbench-devel -- Antoine Lefebvre ant...@po... |
