Dipartimento di Elettronica e Informazione

MATEO-ANTASME Project meetingMilano, May 21, 2007

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Outline

1. The research unit

2. Expected contributions to ANTASME

3. Deliverables

4. WP6: Object-oriented modelling of mechatronic electrohydraulic

systems

5. WP7: Object-oriented modelling of spacecraft dynamics

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The DEI research unit

Prof. Paolo Rocco (person in charge)

Prof. GianAntonio Magnani

Tiziano Pulecchi (PhD candidate)

Luca Viganò (PhD candidate)

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Expected contributions to ANTASME

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.

                                                                        

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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

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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• …

Tools: the simulation environment Dymola

Website: www.dymola.com

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Completed deliverables

                                                                        

WP6 WP7

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Objectives:

Models of DDV (Direct Drive Valve) electrohydraulic actuators; Integration of the model within a realistic helycopter system model.

WP6: OO modelling of mechatronic electrohydraulic systems

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

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Helicopter flight mechanics model

Flight mechanics model Fully parametrizedSome 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 3D virtual environment

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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.

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Servoactuator Model

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

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Servoactuator Model

Medium and high-detail servoactuator model assembled with the mechatronic electrohydraulic library (deliverable 6.1) :

Duplex hydraulic system Quadruplex electrical system Nonlinear friction Elastic support Detailed valve/cylinder model …

DDV, closed-loop, redundant model tested for nominal and faulty conditions (jammed valve or one hydraulic line operative)

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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)

Outer loop: • Hold modes (IAS hold, ALT hold,

HDG hold,…)• Turn coordination

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

Turbulence on (severe)

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Case Study: Test 1

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

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Case Study: Test 1 – Aft Servo

Valve jam

(t=50sec.)

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Case Study: Test 2

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

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Case Study: Test 2 – Aft Servo

Valve jam

(t=200sec.)

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Conclusions

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.

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Objectives:

Development of a library for simulation of spacecraft attitude and orbit dynamics

Verification in a case study

WP7: OO modelling of spacecraft dynamics

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

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• 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).

What can a Modelica Space Flight Dynamics Library do?

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• 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.

The spacecraft model

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Dynamics:

• solar_array model: based on standard Modelica MultiBody library components.

• spacecraft main_body: SpacecraftDynamics model

Initial conditions defined by selecting the desired orbit, simulation initial time and

initial spacecraft misalignment;

Alternative choice: standard Modelica MultiBody initialization option;

Spacecraft inertial properties, geometry definition retrieved from ad hoc records.

Dynamics

angle formed in the ecliptic plane between the vernal equinox and the

sun position vectors

Ref. epoch (sun at Ares point)

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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.

Sensors

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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.

Control

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• Required control torque:

• RWs angular momentum dynamics (fine attitude pointing):

• Magnetotorquers exponentially stabilizing feedback control law:

Control

RW angular momentum

Magnetic field vectorSpacecraft angular rate

Coils magnetic dipole

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Actuators

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 can be quickly obtained by suitably connecting standard SFDL models.

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• 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.

Simulation

Solar radiation pressure

Magnetic field b2 component

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Simulation

Coils magnetic dipoles

RWs angular momentum