State and Force Estimation on a Rotating Helicopter Blade through a Kalman-Based Approach
Abstract
:1. Introduction
2. Methodologies: Theoretical Background
2.1. Multibody Structural Model
2.1.1. Finite Segment Beam Formulation
2.2. Aerodynamic Model
2.2.1. Aerodynamic Loads
- is the air density.
- is the velocity vector evaluated at the stage . Considering the blade modeled as a rigid body, is expressed as:
- and are the aerodynamic coefficients; in general, they are tabular values for a given airfoil. Important for the evaluation of the total thrust produced by the rotating blades is the expression of the lift coefficient . This contribution focuses on small angles of attack and low values of the Mach number, such that a linear relation is guaranteed, with a representing the lift slope of the section, and (Figure 2). and are respectively the pitch and inflow angles of the section. More details about the derivation of are given in Section 2.2.2.
- c indicates the chord of the blade at stage r.
2.2.2. Uniform Inflow Model
2.3. Kalman Filter for Implicit Scheme
- Correction—updating of the solution of the previous step with the available observations :
3. Workflow for Estimation of States and Loads on a Rotor Blade
- Writing the vector in Equation (19) as a function of and , i.e., the orientation and velocity of a given point;
- Modeling the aerodynamic forces as external loads without explicit dependence on the states.
- Definition of the set of loads. This decision should be made in conjunction with the previous step. For multiple distributed loads, the definition of a subset of loads could be useful to reduce the number of observations needed. For the case in Figure 5, the full input vector is ; a good choice could be the selection of loads close to the tip , because their contributions to the dynamics of the blade are higher.
- Extrapolation of along the blade span. The components of the velocity vector along the blade can be approximated as a linear function of the position r:
- Evaluation of the lift distribution along the blade span. Recalling Equation (5), and given a certain flight condition with known pitch angle , the only unknown in the elemental lift will be the inflow angle :The iterative process in Section 2.2 can thus be applied to find the exact value of at each time-step.
4. Numerical Validation on a 2-Blade Rotor Model
- Noisy reference observation data generated in Python code by simulating the coupled structural-aerodynamic model. Estimation of a subset of lumped loads on the same structural model without aerodynamic and subsequent distributed load evaluations.
- Reference observation data generated in MBDyn on a similar, but independently-formulated structural-aerodynamic model. Estimation of a subset of lumped loads on the structural Python model and subsequent evaluation of distributed loads.
4.1. Kalman-Based Estimation
- The aerodynamic loads give higher contribution in the proximity of the blade tip;
- The in-plane loads are much smaller than the out-of-plane ones, namely, ,
4.1.1. Reference Noisy Data
- The sensor layout does not include in-plane quantities, e.g., position sensors in direction.
- Only out-of-plane loads are considered in the estimation, even if the reference sensors come from a coupled multibody-aerodynamic simulation which includes lift and drag forces. The choice to not estimate the drag forces was because the resulting magnitude would be comparatively small with respect to the computed lift.
4.1.2. Reference Data from Mbdyn
- Finite segment: ;
- Finite volume: .
5. Conclusions
Author Contributions
Funding
Conflicts of Interest
References
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Blade Structural Properties | Blade Elastic Properties | ||||
---|---|---|---|---|---|
Total mass | 82.76 | kg | 5.69E8 | N | |
Chord | 0.537 | m | 4.00E5 | Nm | |
Total Length | 6.988 | m | 4.00E5 | Nm | |
Radius | 7.420 | m | 8.40E5 | Nm/rad | |
Root Hinges—Distance From Hub | Root Hinges—Elastic Properties | ||||
Flap offset | 0.289 | m | Flap damping characteristic | 7.50E3 | Nms/rad |
Lag offset | 0.269 | m | Lag damping characteristic | 7.00E3 | Nms/rad |
Pitch offset | 0.432 | m |
Position Sensors | Velocity Sensors | ||
---|---|---|---|
elem3 | z | elem3 | z |
elem4 | z | elem4 | z |
Position Sensors | Velocity Sensors | ||
---|---|---|---|
elem3 | z | elem3 | z |
elem4 | z | elem4 | z |
elem4 | y |
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Cumbo, R.; Tamarozzi, T.; Jiranek, P.; Desmet, W.; Masarati, P. State and Force Estimation on a Rotating Helicopter Blade through a Kalman-Based Approach. Sensors 2020, 20, 4196. https://doi.org/10.3390/s20154196
Cumbo R, Tamarozzi T, Jiranek P, Desmet W, Masarati P. State and Force Estimation on a Rotating Helicopter Blade through a Kalman-Based Approach. Sensors. 2020; 20(15):4196. https://doi.org/10.3390/s20154196
Chicago/Turabian StyleCumbo, Roberta, Tommaso Tamarozzi, Pavel Jiranek, Wim Desmet, and Pierangelo Masarati. 2020. "State and Force Estimation on a Rotating Helicopter Blade through a Kalman-Based Approach" Sensors 20, no. 15: 4196. https://doi.org/10.3390/s20154196