Dipartimento di Elettronica e Informazione MATEOANTASME Project meeting

Dipartimento di Elettronica e Informazione MATEO-ANTASME Project meeting Milano, May 21, 2007

Outline 2 1. The research unit 2. Expected contributions to ANTASME 3. Deliverables 4. WP 6: Object-oriented modelling of mechatronic electrohydraulic systems 5. WP 7: Object-oriented modelling of spacecraft dynamics

The DEI research unit Prof. Paolo Rocco (person in charge) Prof. Gian. Antonio Magnani Tiziano Pulecchi (Ph. D candidate) Luca Viganò (Ph. D candidate) 3

Expected contributions to ANTASME 4 § DEI will develop multi-domain modelling and simulation environments for aerospace systems, with specific attention to mechatronic electrohydraulic systems and to spacecraft attitude and orbit dynamics. § The environments will offer hierarchical modular modelling capabilities, to ensure models reuse, and a “natural” (i. e. not requiring a specific modelling knowledge) approach to complex model definition. § A library of basic models of the physical components for aerospace systems shall be developed.

Tools: the modelling language Modelica Main features: § Object-oriented language: class = model § Modelica is based on equation, not on assignments: • Acausal approach. • Reuse of classes. § Multidomain approach: • Electrical • Mechanical • Hydraulic • … Website: www. modelica. org 5

Tools: the simulation environment Dymola A commercial package for multi-domain simulation based on Modelica. It is used both in the academy and in industry: • Daimler Chrysler • BMW • Audi, • Volkswagen • Toyota • … Website: www. dymola. com 6

7 Completed deliverables WP 6 WP 7

8 WP 6: OO modelling of mechatronic electrohydraulic systems Objectives: § § Models of DDV (Direct Drive Valve) electrohydraulic actuators; Integration of the model within a realistic helycopter system model. Deliverables: § § 6. 1 (completed): “Design description of the object-oriented library for mechatronic electrohydraulic systems” 6. 2 (after 12 months): “Assessment of the performance of the mechatronic electrohydraulic library in a case study” Presented by Luca Viganò

Helicopter flight mechanics model 9 Flight mechanics model Fully parametrized Some features: - Level 1 simulation compliant (Padfield, ’ 96) MBC rotor model (flapping states), Pitt-Peters/Keller dynamic wake Engine RPM dynamics Aerodynamics of lifting surfaces and fuselage (look-up-table based) - Atmospheric gust - 3 D virtual environment

Flight Control Model Helicopter Control Geometry in a FBW configuration: - 4 main stationary servoactuators (left, aft, right, tail) - Collective/cyclic blade pitch commands (C, P, R, Y) to L, A, R, T servos displacements: interlink+primary mixer reproduced by FCS software. - Mechanical swashplate Main/tail rotor servoactuators modules: - Geometric transformations - 1 dof (or >complex if needed) mechanical impedance - Easy parametrization by means of records. 10

Servoactuator Model 11 3 Level of details possible for each servoactuator: - 2 nd order plus saturation and rate limiter (classical flight sim. model) - Simplex hydraulic system (no electrical dynamics) - Complex DDV model (electrical and hydraulic redundancies)

Servoactuator Model Medium and high-detail servoactuator model assembled with the mechatronic electrohydraulic library (deliverable 6. 1) : ü Duplex hydraulic system ü Quadruplex electrical system ü Nonlinear friction ü Elastic support ü Detailed valve/cylinder model ü … DDV, closed-loop, redundant model tested for nominal and faulty conditions (jammed valve or one hydraulic line operative) 12

13 Case Study Helicopter digital AFCS provided by a standard inner-outer loops strategy: Inner loop: ACAH (Attitude Command Attitude Hold): • Scheduled LQ explicit model following (Lewis & Stevens, ’ 92) • Bandwidths compliant with ADS 33 (Level 1, 2) Ø Outer loop: • Hold modes (IAS hold, ALT hold, HDG hold, …) • Turn coordination Ø Turbulence on (severe) Empirical external load on servos: Justified by difficult airload predictability and good disturbance rejection at all frequencies. DC load + vibratory load Nb/rev (actuator performance specification) Load case 1: 98% peak-to-peak stall load (62% DC + 36% vib. ) Load case 2: 50 % Load case 1

Case Study: Test 1: hover, vertical climb (1575 ft/min), yaw rate pulse, long. acceleration 14

Case Study: Test 1 – Aft Servo Valve jam (t=50 sec. ) 15

Case Study: Test 2 16 Test 2: accel. from hover to 100 kts IAS, roll/pitch/heave periodic commands

17 Case Study: Test 2 – Aft Servo Valve jam (t=200 sec. )

Conclusions 18 A Modelica library for mechatronic electrohydraulic systems has been developed and used for the assessment of performance of a detailed DDV actuator, in nominal or faulty conditions. The isolated servo model has been integrated with an existing Modelica helicopter flight mechanics simulator, in such a way as to preserve modularity of both models. Avionic integration of DDV-FBW servoactuators has been tested in simulation using a standard AFCS structure: Physical redundancies work fine, concealing faults at flight mechanics level Servo tracking performances and robustness can be evaluated in a sufficiently realistic framework Availability of numerically affordable but realistic external load model could improve model accuracy and help to reduce conservatism in control design.

WP 7: OO modelling of spacecraft dynamics 19 Objectives: § § Development of a library for simulation of spacecraft attitude and orbit dynamics Verification in a case study Deliverables: § § 7. 1 (completed): “Design description of the modelling library for spacecraft dynamics” 7. 2 (after 12 months): “Assessment of the performance of the spacecraft dynamics library in a realistic case study” Presented by Tiziano Pulecchi

20 What can a Modelica Space Flight Dynamics Library do? • The SFDL provides the user with a very intuitive and ready for use modelling and simulation tool, specially suitable for rapid design and multi-architecture assessment of a generic space vehicle. • Lists of models for the most commonly used AOCS sensors, actuators and controls are available, as basic model components from whose interconnection the complete spacecraft can be quickly obtained. • Multiple architectural configurations can be quickly evaluated leading to the system final definition. • The SFDL capabilities will be proved in a case study consisting in the ACS design for a fine attitude pointing GEO spacecraft endowed with a single solar array rotating in the orbital plane (maximum energy adsorption).

The spacecraft model • 21 The object-oriented framework allows the user to build a complex system from elementary models. The complete spacecraft can be obtained as the interconnection of the following main systems: § § § Dynamics: includes the modeling of the spacecraft as the interconnection (through a revolute joint) of two rigid bodies, the main body and the solar array, and the definition of the spacecraft initial conditions (i. e. , orbit, attitude); Sensors: defines the actual spacecraft on board sensors; The availability of a star sensor for precise attitude reference, a GPS receiver, gyroscopes and a three axes magnetometer will be assumed; Controls: describes the AOCS, including algorithms for control strategies, attitude determination, data fusion, etc. ; § Actuators: defines the actuators set equipping the considered spacecraft.

Dynamics 22 Dynamics: • solar_array model: based on standard Modelica Multi. Body library components. Ref. epoch (sun at Ares point) angle formed in the ecliptic plane between the vernal equinox and the sun position vectors • spacecraft main_body: Spacecraft. Dynamics model § Initial conditions defined by selecting the desired orbit, simulation initial time and initial spacecraft misalignment; § Alternative choice: standard Modelica Multi. Body initialization option; § Spacecraft inertial properties, geometry definition retrieved from ad hoc records.

23 Sensors: § Broad choice of models available for the most commonly used aerospace sensors, including star trackers, gyroscopes, GPS receivers, magnetometers, sun sensors and horizon sensors. § The sensor suite can be easily obtained by suitably connecting this standard models.

24 Control: § § High precision attitude control for large, asymmetric spacecraft can be suitably achieved via a set of RWs; Albeit the RWs provide full three axes controllability of the spacecraft, angular momentum will build up in the RWs eventually reaching saturation and thus leading to loss of control authority; The removal of the excess momentum is achieved by means of external torques provided by magnetotorquers (inexpensive); The control architecture comprises algorithms devoted to: • computation of the torque required to meet the specified control • • § requirements; control allocation between the two actuator sets; computation of RWs angular momentum variation and magnetotorquers magnetic dipole To this end, SFDL control components can be exploited.

25 Control • Required control torque: Spacecraft angular rate • RW angular momentum Magnetic field vector RWs angular momentum dynamics (fine attitude pointing): Coils magnetic dipole • Magnetotorquers exponentially stabilizing feedback control law:

26 Actuators: § Broad choice of models available for the most commonly used aerospace actuators, including several architecture for reaction wheels, control moment gyroscopes, impulsive thrusters and magneto torquers. § The sensor suite can be quickly obtained by suitably connecting standard SFDL models.

Simulation • • 27 Magnetic field and solar radiation pressure data used for simulation can be downloaded from the National Geophysical Data Center website (http: //www. ngdc. noaa. gov/stp/GOES/goes. html); Data recorded by GOES-7 geostationary satellite from 4 till 8 January 1996, representative of in orbit environmental conditions. Magnetic field b 2 component Solar radiation pressure

28 Simulation RWs angular momentum Coils magnetic dipoles