Proportional optimal orthogonalization of measured modes

Baruch, Menahem

doi:10.2514/3.7697

Cited by 25 publications

(4 citation statements)

References 13 publications

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“…The modes are processed by using the author's own procedure described in Chajec and Seibert (2011) and Chajec (2016b). It uses a low number of degrees of freedom (DoFs) mass model (Nowak and Potka nski, 1976), which gives an opportunity to calculate generalized masses as well as complete the measured modes orthogonalization adopted many years ago by author from Baruch (1980). Only the simplified theoretical mass model with up to 250 DoF is used for computation.…”

Section: Work Descriptionmentioning

confidence: 99%

Comparison of flutter calculation methods based on ground vibration test result

Chajec

2019

AEAT

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PurposeA low-cost but credible method of low-subsonic flutter analysis based on ground vibration test (GVT) results is presented. The purpose of this paper is a comparison of two methods of immediate flutter problem solution: JG2 – low cost software based on the strip theory in aerodynamics (STA) and V-g method of the flutter problem solution and ZAERO I commercial software with doublet lattice method (DLM) aerodynamic model and G method of the flutter problem solution. In both cases, the same sets of measured normal modes are used. Design/methodology/approachBefore flutter computation, resonant modes are supplied by some non-measurable but existing modes and processed using the author’s own procedure. For flutter computation, the modes are normalized using the aircraft mass model. The measured mode orthogonalization is possible. The flutter calculation made by means of both methods are performed for the MP-02 Czajka UL aircraft and the Virus SW 121 aircraft of LSA category. FindingsIn most cases, both compared flutter computation results are similar, especially in the case of high aspect wing flutter. The Czajka T-tail flutter analysis using JG2 software is more conservative than the one made by ZAERO, especially in the case of rudder flutter. The differences can be reduced if the proposed rudder effectiveness coefficients are introduced. Practical implicationsThe low-cost methods are attractive for flutter analysis of UL and light aircraft. The paper presents the scope of the low-cost JG2 method and its limitations. Originality/valueIn comparison with other works, the measured generalized masses are not used. Additionally, the rudder effectiveness reduction was implemented into the STA. However, Niedbal (1997) introduced corrections of control surface hinge moments, but the present work contains results in comparison with the outcome obtained by means of the more credible software.

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Section: Work Descriptionmentioning

confidence: 99%

Comparison of flutter calculation methods based on ground vibration test result

Chajec

2019

AEAT

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“…The availability of a mass model makes it possible to calculate the modal generalized masses and to orthogonalize measured modes (the normal modes should be orthogonal). The orthogonalization procedure was adopted from Baruch (1980). It was applied for measured vibration mode shapes improvement with no change of frequencies.…”

Section: Flutter Analysismentioning

confidence: 99%

The effect of wing-tip propulsors on Icaré 2 aeroelasticity

Chajec

Krzymień

Strohmayer

2019

AEAT

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Purpose The separation of energy conversion and propulsor is a promising aspect of hybrid-electric propulsion systems, allowing for increased installation efficiencies and setting the basis for distributed propulsion concepts. University of Stuttgart’s Institute of Aircraft Design has a long experience with electrically powered aircraft, starting with Icaré 2, a solar-powered glider flying, since 1996. Icaré 2 recently has been converted to a three-engine motor glider with two battery-powered wing-tip propellers, in addition to the solar-powered main electric motor. This adds propulsion redundancy and will allow analyzing yaw control concepts with differential thrust and the propeller-vortex interaction at the wing-tip. To ensure airworthiness for this design modification, new ground vibration tests (GVTs) and flutter calculations are required. The purpose of this paper is to lay out the atypical approach to test execution due to peculiarities of the Icaré 2 design such as an asymmetrical aileron control system, the long wing span with low frequencies of the first mode and elevated wing tips bending under gravity and thus affecting the accuracy of the wing torsion frequency measurements. Design/methodology/approach A flutter analysis based on GVT results is performed for the aircraft in basic configuration and with wing tip propulsors in pusher or tractor configuration. Apart from the measured resonant modes, the aircraft rigid body modes and the control surface mechanism modes are taken into consideration. The flutter calculations are made by a high-speed, low-cost software named JG2 based on the strip theory in aerodynamics and the V-g method of flutter problem solution. Findings With the chosen atypical approach to GVT the impact of the suspension on the test results was shown to be minimal. Flutter analysis has proven that the critical flutter speed of Icaré 2 is sufficiently high in all configurations. Practical implications The atypical approach to GVT and subsequent flutter analysis have shown that the effects of wing-tip propulsors on aeroelasticity of the high aspect ratio configuration do not negatively affect flutter characteristics. This analysis can serve as a basis for an application for a permit to fly. Originality/value The presented methodology is valuable for the flutter assessment of aircraft configurations with atypical aeroelastic characteristics.

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“…Reference Basis Algorithm was proposed mainly by Baruch and Berman [1][2][3] in late 70s of 20 th century. This type of algorithm considers structural mass, stiffness and measured modal parameters as three different parameter subsets.…”

Section: Reference Basis Algorithmmentioning

confidence: 99%

Review of the Application of Finite Element Model Updating to Civil Structures

Wang

Tan

Yang

et al. 2013

KEM

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Structural finite element model (FEM) updating in dynamics usually deemed the measured modal parameters as the goal. By modifying the theoretical FEM, the updated modal parameters obtained by the analytical FEM would finally tend to the testing results. But the own complexity of the civil structure leads the optimization problem of FEM updating to be super-size and high non-linear performance. Moreover, the uncertainty and nonuniformity of the structures, material and the environment effect cause the uncertainty of the updating parameters, even the optimization objective function of FEM updating. These features has brought greater difficulty to the model updating in civil engineering structure, especially for the application field. Therefore, in this paper several kinds of methods for FEM updating would be introduced with the comparison of their advantages, disadvantages and the range of application. At the end of this paper, the problems remained to be solved in FEM updating of civil structures are to be presented.

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Proportional optimal orthogonalization of measured modes

Cited by 25 publications

References 13 publications

Comparison of flutter calculation methods based on ground vibration test result

Comparison of flutter calculation methods based on ground vibration test result

The effect of wing-tip propulsors on Icaré 2 aeroelasticity

Review of the Application of Finite Element Model Updating to Civil Structures

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