H∞ Control Design for a Rigid-Flexible Spacecraft under a Fuel Slosh Influence

The spacecraft Attitude Control System (ACS) performance and robustness depend on the interactioneffects between the fuel slosh motion, the panel's flexible motion, and the spacecraft rigid motion, mainly duringtranslational and/or rotational maneuvers. In regards to satellite pointing accuracy flexibility and fuel, slosh is thetwo most important effects that should be considered in the satellite ACS design since their interactions can damage the ACS performance and robustness. Once, the lowest vibration frequencies, normally of the sloshing modeare about six times less than of the ACS bandwidth. Therefore, there is a strong possibility that this mode can destabilize the ACS pointing accuracy. This phenomenon is called spillover because the control effort spills over outside the control bandwidth. As a result, the designer needs to explore the limits between the conflicting requirements of performance, that is, increase of the bandwidth without introduction noise in the ACS keeping the systemrobustness to parameters variation. In this paper, one applies the H infinity control method which can deal withthese two design requirements (performance and robustness) considering the controller error pointing that may belimited by the minimum time necessary to suppress disturbances that affect the satellite attitude acquisition. Theequations of motions are obtained considering the Lagrange method for small flexible deformations and a mechanical model of liquid sloshing which allows modeling and investigating the longitudinal dynamic characteristics of apartially filled liquid tank during a pitch maneuver, satisfying performance and robustness requirements.

H∞ Control Design for a Flexible Spacecraft with Fuel Slosh Dynamics

The spacecraft Attitude Control System (ACS) performance and robustness depend on the interaction effects between the fuel slosh motion, the panel's flexible motion and the spacecraft rigid motion, mainly during translational and/or rotational maneuvers. In regards to satellite pointing accuracy flexibility and fuel slosh are the two most important effects that should be considered in the satellite ACS design since their interactions can damage the ACS performance and robustness. Once, the lowest vibration frequencies, normally of the slosh mode are about six times less than of the ACS bandwidth. Therefore, there is a strong possibility that this mode can destabilize the ACS pointing. This phenomenon is called spillover, because the control effort spills over outside the control bandwidth. As a result, the designer needs to explore the limits between the conflicting requirements of performance, that is, increase of the bandwidth without introduction noise in the ACS keeping the system robustness to parameters variation. In this paper one applies the H infinity control method which is able to deal with these two design requirements (performance and robustness) considering the controller error pointing that may be limited by the minimum time necessary to suppress disturbances that affects the satellite attitude acquisition. The equations of motions are obtained considering Lagrange method for small flexible deformations and a mechanical model of liquid sloshing which allows modeling and investigating the longitudinal dynamic characteristics of partially filled liquid tank during a pitch maneuver. The results of the simulations have shown that the H-infinity controller was able to control the rigid motion and suppress the vibrations

Computational Simulation of Fuel Tank Sloshing for a FSAE car using CFD Techniques

Sloshing refers to the highly random motion of any fluid inside an object where the dynamic forces of the liquid can interact with the object to alter the overall system dynamics. This work summarises the process of designing and simulating the 3-D geometry of a fuel tank using CFD and the volume of fluid (VOF) method considering multi-phase fluid flow predicting fuel slosh movement at a specific capacity within a definite fixed volume.[13-16] As the performance of the engine heavily depends on a constant supply of fuel, the splashing of gasoline inside the partially filled fuel tank can severely affect the performance when subjected to sudden left and right turns during a Slalom in FSAE tracks. This scenario can be modelled, analysed and effectively controlled by reducing pressure intensities inside the tank walls using a set of strategically placed Baffles. Therefore, this study attempts to reduce the sloshing behaviour by considering multiple types of geometries and shows the final geometry chosen using computational simulations inside the fuel tank considering 1.5 litres of fuel and remaining with air inside a 7.3 litres fuel tank, thus predicting the effect of sloshing forces and moments inside the tank structure considering lateral and longitudinal acceleration fields. The model is discussed and results are presented. In addition, this paper can be referred to as a detailed tutorial on how to simulate and take in consideration of all the factors which will be useful in deciding vehicle fuel requirements and optimum design.