Difference between revisions of "Generic EM Drive Information"

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This is a location for assorted information concerning EM Drives. Likely applies to all current experimental efforts.
 
This is a location for assorted information concerning EM Drives. Likely applies to all current experimental efforts.
  
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== Velocity ==
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== Simulating With MEEP ==
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[[MEEP]] is is a free finite-difference time-domain (FDTD) simulation software package developed at MIT to model electromagnetic systems<ref>[http://ab-initio.mit.edu/wiki/index.php/Meep]</ref>.  A number of people, including @aero, have been using it to simulate the evolution of the fields within the EM Drive.
  
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At constant input power, the thrust, and therefore the acceleration, must decrease with time, to ensure that the spacecraft's (change in) velocity never exceeds 2*Power/Thrust.<ref>[http://forum.nasaspaceflight.com/index.php?topic=36313.msg1314503#msg1314503 Rodal's post concerning the energy/thrust constraint.]</ref> Effectively, White proposes that the maximum velocity possibly achievable for these EM Drives is 2*PowerInput/ThrustForce. This energy constraint is known even from Sutton's textbook on Elements of Rocket Propulsion (equation 19-1 Rocket propulsion elements 7th edition- Sutton).
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== Conservation of Energy and Momentum ==
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See [[Energy Conservation]] and [[Momentum Conservation]] for discussions of the implications to these principles.
  
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The higher the ThrustForce/InputPower, the lower the maximum velocity of an EM Drive: MAXIMUM VELOCITY OF EM DRIVE = 2 /(thrustForce/PowerInput)
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== Mode Shape ==
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#(Brady TE mode) ThrustForce/power: 0.00002131 Newton/Watt --> MaximumVelocity = 2/0.00002131 m/s = 93853 m/s = 93.85 km/s
 
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#(Prof. Juan Yang et.al. China)  ThrustForce/power: 0.000290  Newton/Watt --> MaximumVelocity = 2/0.000290 m/s = 6897 m/s = 6.90 km/s
 
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#(Cannae Superconducting)  ThrustForce/power: 0.0009524  Newton/Watt --> MaximumVelocity = 2/0.0009524 m/s = 2100 m/s = 2.10 km/s
 
  
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The maximum velocity of the EM Drive is inversely proportional to Q: <ref>[http://forum.nasaspaceflight.com/index.php?topic=36313.msg1314529#msg1314529 Rodal's post concerning velocity and Q.]</ref> Therefor the higher the Q, the lower the maximum velocity.
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See calculations pertaining to the relationship between thrust and mode shape at [http://forum.nasaspaceflight.com/index.php?topic=36313.msg1317866#msg1317866 Notsosureofit's post] and [http://forum.nasaspaceflight.com/index.php?topic=36313.msg1318217#msg1318217 Rodal's response.]
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#MAXIMUM VELOCITY OF EM DRIVE = 2 /(thrustForce/PowerInput)
 
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#MAXIMUM VELOCITY OF EM DRIVE ~ (2 /(Q*otherParameters))
 
  
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== Kinetic Energy ==
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An EM Drive is a cavity resonator that uses the Quality Factor Q to achieve greater response. There is definitely a peak resonant frequency to achieve the highest Q, though besides Q and frequency, mode shape must also be considered. The shape of the electric and magnetic fields inside the cavity at a given frequency.<ref>[http://forum.nasaspaceflight.com/index.php?topic=36313.msg1319407#msg1319407 Rodal on frequency, Q, and mode shape.]</ref>
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The frame-of-reference kinetic energy issues (for non-relativistic spacecraft speeds) are eliminated by the definition of constant acceleration as acceleration=(delta velocity)/(delta time) so that (delta velocity)=acceleration*(delta time).<ref>[http://forum.nasaspaceflight.com/index.php?topic=36313.msg1315154#msg1315154 Rodal's Post on Changing Kinetic Energy.]</ref> Since from Newton's 2nd law, acceleration=ThrustForce/Mass, the change in velocity is uniquely defined in terms of: ThrustForce, total Mass of the spacecraft and DeltaTime (regardless of velocity-frame-of-reference) directly as (delta velocity)=(ThrustForce/Mass)*(delta time). The intrinsic definition of the change in KineticEnergy of the spacecraft under constant acceleration:
 
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*deltaKineticEnergy = (1/2)*Mass*((delta velocity)^2)
 
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*deltaKineticEnergy = (1/2)*Mass*([(ThrustForce/Mass)*(delta time) ]^2)
 
  
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For the EM Drive to make any sense as a '''closed system''' it implies having memory of its time-history in order to never exceed the critical velocity at which (for constant InputPower throughout the time period (delta time)):
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The natural frequencies (and therefore the mode shapes) of a cavity are sensitive to the [[Experimental Results|dimensions of the cavity]]. <ref>[https://en.wikipedia.org/wiki/Microwave_cavity#Cylindrical_cavity][http://forum.nasaspaceflight.com/index.php?topic=36313.msg1319117#msg1319117 Rodal's post on geometric relations to mode shape.]</ref> A dielectric insert lowers the natural frequency at which a given mode shape takes place.<ref>[http://forum.nasaspaceflight.com/index.php?topic=36313.msg1319655#msg1319655 Rodal on the dielectric's contribution to mode shape.]</ref>
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Here is a plot of what a few mode shapes '''in a cylindrical cavity''' look like when viewed perpendicular to the circular cross section plane.
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*InputPower*(delta time) = (1/2)*Mass*[(ThrustForce/Mass)*(delta time) ]^2 <ref>Consistent with equation 19-1: Rocket Propulsion Elements 7th edition- Sutton</ref>
 
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If the EM drive conserves momentum by interacting with the QuantumVacuum for example, we have an '''open system''' where momentum will be flowing in or out of the cavity, and therefore the open system should be taken into account in the conservation of kinetic energy (which we have not done) in order to arrive at a satisfactory answer.
 
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== Mode Shape ==
 
  
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See calculations pertaining to the relationship between thrust and mode shape at [http://forum.nasaspaceflight.com/index.php?topic=36313.msg1317866#msg1317866 Notsosureofit's post here.]
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<img src="http://forum.nasaspaceflight.com/index.php?action=dlattach;topic=36313.0;attach=632192;image" style="width:15%">
  
 
== References ==
 
== References ==
 
<references />
 
<references />

Latest revision as of 06:34, 13 July 2015

This is a location for assorted information concerning EM Drives. Likely applies to all current experimental efforts.

Simulating With MEEP

MEEP is is a free finite-difference time-domain (FDTD) simulation software package developed at MIT to model electromagnetic systems[1]. A number of people, including @aero, have been using it to simulate the evolution of the fields within the EM Drive.

Conservation of Energy and Momentum

See Energy Conservation and Momentum Conservation for discussions of the implications to these principles.

Mode Shape

See calculations pertaining to the relationship between thrust and mode shape at Notsosureofit's post and Rodal's response.

An EM Drive is a cavity resonator that uses the Quality Factor Q to achieve greater response. There is definitely a peak resonant frequency to achieve the highest Q, though besides Q and frequency, mode shape must also be considered. The shape of the electric and magnetic fields inside the cavity at a given frequency.[2]

The natural frequencies (and therefore the mode shapes) of a cavity are sensitive to the dimensions of the cavity. [3] A dielectric insert lowers the natural frequency at which a given mode shape takes place.[4] Here is a plot of what a few mode shapes in a cylindrical cavity look like when viewed perpendicular to the circular cross section plane.

References

  1. ↑ [1]
  2. ↑ Rodal on frequency, Q, and mode shape.
  3. ↑ [2]Rodal's post on geometric relations to mode shape.
  4. ↑ Rodal on the dielectric's contribution to mode shape.
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