Assessment and development of a ROM for linearized aeroelastic analyses of aerospace vehicles (original) (raw)
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Recent Advances in Reduced-Order Modeling and Application to Nonlinear Computational Aeroelasticity
& Proceedings 저널· 프로시딩즈| 기술보고서| 해외 …, 2008
Reduced-order models (ROMs) are usually thought of as computationally inexpensive mathematical representations that offer the potential for near real-time analysis. Indeed, most ROMs can operate in near real-time. However, their construction can be computationally intensive as it requires accumulating a large number of system responses to input excitations. Furthermore, ROMs usually lack robustness with respect to parameter changes and therefore must often be rebuilt for each parameter variation. Together, these two issues underline the need for a fast and robust method for adapting pre-computed ROMs to new sets of physical or modeling parameters. To this effect, this paper reports on recent advances in this topic. In particular, it describes a recently developed interpolation method based on the Grassmann manifold and its tangent space at a point that is applicable to structural, aerodynamic, aeroelastic and many other ROMs based on projection schemes. This method is illustrated here with the adaptation of CFD-based aeroelastic ROMs of complete fighter configurations to new values of the free-stream Mach number. Good correlations with results obtained from direct ROM reconstruction and high-fidelity linear and nonlinear simulations are reported, thereby highlighting the potential of the described ROM adaptation method for near real-time aeroelastic predictions using pre-computed ROM databases. example, in the transonic regime. This cost is such that CFD-based nonlinear aeroelastic codes are applied nowadays to the analysis of a few, carefully chosen configurations, rather than routine analysis.
Adaptation of Aeroelastic Reduced-Order Models and Application to an F-16 Configuration
AIAA Journal, 2007
The proper orthogonal decomposition method has been shown to produce accurate reduced-order models for the aeroelastic analysis of complete aircraft configurations at fixed flight conditions. However, changes in the Mach number or angle of attack often necessitate the reconstruction of the reduced-order model to maintain accuracy, which destroys the sought-after computational efficiency. Straightforward approaches for reduced-order model adaptation—such as the global proper orthogonal decomposition method and the direct interpolation of the proper orthogonal decomposition basis vectors—that have been attempted in the past have been shown to lead to inaccurate proper orthogonal decomposition bases in the transonic flight regime. Alternatively, a new reduced-order model adaptation scheme is described in this paper and evaluated for changes in the freestream Mach number and angle of attack. This scheme interpolates the subspace angles between two proper orthogonal decomposition subspaces, then generates a new proper orthogonal decomposition basis through an orthogonal transformation based on the interpolated subspace angles. The resulting computational methodology is applied to a complete F-16 configuration in various airstreams. The predicted aeroelastic frequencies and damping coefficients are compared with counterparts obtained from full-order nonlinear aeroelastic simulations and flight test data. Good correlations are observed, including in the transonic regime. The obtained computational results reveal a significant potential of the adapted reduced-order model computational technology for accurate, near-real-time, aeroelastic predictions.
Hybrid Finite-Volume Reduced-Order Model Method for Nonlinear Aeroelastic Modeling.
A fully coupled partitioned fluid–structure interaction technology is developed for transonic aeroelastic structures undergoing nonlinear displacements. The Euler equations, written in an arbitrary Lagrangian–Eulerian coordinate frame, describe the fluid domain, whereas the structure is represented by a quadratic modal reduced-order model. A Runge–Kutta dual time-stepping method is employed for the fluid solver, where three upwind schemes are considered, viz., Advection Upwind Splitting Method plus-up, Harten-Lax-van Leer with Contact, and Roe schemes. The Harten-Lax-van Leer with Contact implementation is found to offer a superior balance between efficiency and robustness. The developed fluid–structure interaction technology is applied to modeling transonic flutter, and the quadratic reduced-order model is demonstrated to offer dramatic improvements in accuracy over the more conventional linear method.
CEAS Aeronautical Journal, 2015
We implement reduced order modelling techniques for aeroelastic predictions of the HIRENASD and S 4 T wings in order to represent CFD based high-fidelity solutions efficiently. Model reduction techniques such as non-intrusive Polynomial Chaos Expansion and Proper Orthogonal Decomposition are applied to both static and dynamic aeroelastic cases. The high-fidelity solutions are obtained by fluid structure interaction analysis using a 3D Euler unsteady aerodynamic solver and structural modal solution from a finite element solver. The model order reduction strategy is based on a multidisciplinary approach since both structural and aerodynamic input parameters are employed. The model order reduction is performed not only to represent the high-fidelity computational analyses when small variations of input parameters are considered but also to characterize the flutter responses of the S 4 T wing in a broad range of input values over the entire flight regime for Mach numbers between 0.60 and 1.20. The efficient aeroelastic analyses performed using the developed reduced order models agreed well with the high-fidelity computational analyses.
Reduced-order modeling for linearized aeroelasticity of fixed wings in transonic flight
Journal of Fluids and Structures, 2005
This paper presents a methodology for the identification of a reduced-order model (ROM) for the perturbation aeroelastic analysis of fixed wings in transonic flight. It is based on a linearized, frequency-domain, boundary-field integral equation for the solution of the unsteady perturbation potential flow about steady-state reference wing configurations. The resulting transfer functions between structural Lagrangean variables and generalized aerodynamic forces are approximated by means of rational expressions, and the aeroelastic ROM is identified by coupling them with the structural operator. With the aeroelastic operator recast in a reduced-order form, transonic flutter boundaries are detected through a classical eigenvalue analysis and the time-domain state-space aeroelastic model is also obtained. Applications of the methodology presented to a widely known aeroelastic test case reveal a remarkable agreement with the measured speed and frequency of flutter. r
Reduced-order fluid/structure modeling of a complete aircraft configuration
Computer Methods in Applied Mechanics and Engineering, 2006
... the exclusive use of linear aerodynamic theories for predicting the unsteady aerodynamic forces. ... Because of this computational cost, the potential of CFD-based nonlinear aeroelastic codes ... possible however to address this limitation with the use of reduced-order models (ROMs ...
2014
In the past much effort has been made to utilize advanced computational fluid dynamic (CFD) programs for aeroelastic simulations and analyses of military and civil aircraft. Although the use of CFD has become broad for static aerodynamic calculations nowadays, it is limited in the field of unsteady aeroelasticity due to enormous size of computer memory and unreasonably long CPU time associated with the large number of mode shapes in the structural model. While a military airplane model may need 20-50 modes, commercial aircraft models typically require as many as 200 modes to describe the motion of the structure with sufficient accuracy. Thus, both aeroelastic and CFD researchers have explored and developed various ways to reduce the size of the unsteady aerodynamic system and minimize the memory and CPU time. Unfortunately, although these reduced-order models (ROM) retain much of the characteristics of the original full-order models and reproduce the full responses quickly and faith...
Static/Dynamic Correction Approach for Reduced-Order Modeling of Unsteady Aerodynamics
Journal of Aircraft, 2006
Presented is a newly devised static/dynamic correction approach for eigenvector expansion based reduced-order modeling (ROM). When compared to the fundamental Ritz ROM formulation, along with the static and multiple static correction ROM approaches, the technique is demonstrated to have much better performance in modeling unsteady linearized frequency-domain aerodynamics in regions of the complex frequency plane near the imaginary axis, and up to a prescribed frequency of interest. As with the static and multiple static correction approaches, the method requires a directly computed solution at zero frequency. The method then requires one additional direct solution to be computed at some nonzero frequency, which typically is the maximum frequency of interest. When compared to the multiple static corrections method, the method circumvents the necessity of having to determine each of the multiple static corrections, which require a solution to an alternate set of equations that must be formulated and which can be costly to solve for large systems. We also consider the feasibility of using a proper orthogonal decomposition (POD) to determine approximations for the least damped fluid-dynamic eigenvectors. We demonstrate that in certain situations these approximate eigenvectors can be used in conjunction with the static/dynamic correction ROM approach to achieve an improvement in performance over the recently devised POD/ROM method where the POD shapes alone are used as ROM shape vectors. Finally, we illustrate how the method can be coupled with a structural model to compute the Mach-number flutter speed trend for a large computational-fluid-dynamics model of a three-dimensional transonic wing configuration.
Journal of Fluids and Structures, 2004
A reduced-order model (ROM) is developed for aeroelasfiic analysis using the CFL3D version 6.0 computational fluid dynamics (CFD) code, recently developed at the NASA Langley Research Center. This latest version of the flow solver includes a deforming mesh capability, a modal structural definition for nonlinear aeroelastic analyses, and a parallelization capability that provides a significant increase in computational efficiency. excellent agreement with the aeroelastic analyses computed using the CFL3Dv6.0 code directly.
Computational aeroelastic modelling of airframes and turbomachinery: progress and challenges
Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 2007
Computational analyses such as computational fluid dynamics and computational structural dynamics have made major advances towards maturity as engineering tools. Computational aeroelasticity (CAE) is the integration of these disciplines. As CAE matures, it also finds an increasing role in the design and analysis of aerospace vehicles. This paper presents a survey of the current state of CAE with a discussion of recent research, success and continuing challenges in its progressive integration into multidisciplinary aerospace design. It approaches CAE from the perspective of the two main areas of application: airframe and turbomachinery design. An overview will be presented of the different prediction methods used for each field of application. Differing levels of nonlinear modelling will be discussed with insight into accuracy versus complexity and computational requirements. Subjects will include current advanced methods (linear and nonlinear), nonlinear flow models, use of order reduction techniques and future trends in incorporating structural nonlinearity. Examples in which CAE is currently being integrated into the design of airframes and turbomachinery will be presented.