Walter A. Silva

Bio: Walter A. Silva is an academic researcher from Langley Research Center. The author has contributed to research in topics: Aeroelasticity & Flutter. The author has an hindex of 25, co-authored 120 publications receiving 2965 citations.

Reduced-order modeling - New approaches for computational physics

Abstract: 111 this paper, we rcvicw the deve lo l~n~e~~ t of new reducecl-orcler ~ r ~ o t l e l i ~ ~ g tecl~niques ant1 tliscuss their applicalrility to variolts prol)len~s in co~ril)utatior~ul pl~ysics. Eu~pllasis is gi~.cn to r~~ctho(ls basetl 011 j'olterra series re l ) rese~~ta t io~~s and thr proper ortllogo11a1 deco~~~position. Results are reported for cliffcre~~t 11ol11i11ear systct~l~s to 1)rovidc clear cxan~ples of the cor~struc.tio~~ a11t1 usc of recluc~cd-orcler llod(>ls, p;lrtic.ularly ill the 1l11tlti-cliscil)li11:1ry field of c o ~ ~ ~ l ) u t a t i o ~ ~ a l aeroelasticity. U~~s t eady aerodj,nan~ic and aeroelast,ic behaviors of two-di~nrnsional and three-dinle~~sional geo~~~e t r i e s arc. tlcscri1)etl. Large illcreases in co1111)utational efficie~~c,y are ol~t,:ii~lccl thruugl~ the use of rcducetl-order ~r~otlc!ls! thcrebj. justifying the izlitial c.onlputatio11a1 esl)c:~~se of constructing th(:sr r~~oticls and ~ ~ ~ o t i v a t i r ~ g tl~eirusc for ~~~ult i-disc, i[)I i~la~>. design analysis.

Application of nonlinear systems theory to transonic unsteady aerodynamic responses

Abstract: A methodology is presented for using the Volterra-Wiener theory of nonlinear systems in aeroservoelastic (ASE) analyses and design. The theory is applied to the development of nonlinear aerodynamic response models that can be defined in state-space form and are, therefore, appropriate for use in modern control theory. The Volterra-Wiener theory relies on the identification of nonlinear kernels that can be used to predict the response of a nonlinear system due to an arbitrary input. A numerical kernel identification technique, based on unit impulse responses, is presented and applied to a simple bilinear, single-input-single-output (SISO) system. The linear kernel (unit impulse response) and the nonlinear second-order kernel of the system are numerically identified and compared with the exact, analytically defined linear and second-order kernels. This kernel identification technique is then applied to the computational aeroelasticity program-transonic small disturbance (CAP-TSD) code for identification of the linear and second-order kernels of a NACA64A010 rectangular wing undergoing pitch at M = 0.5, M = 0.85 (transonic), and M = 0.93 (transonic). Results presented demonstrate the feasibility of this approach for use with nonlinear, unsteady aerodynamic responses.

Application of nonlinear systems theory to transonic unsteady aerodynamic responses

Abstract: A methodology is presented for using the Volterra-Wiener theory of nonlinear systems in aeroservoelastic (ASE) analyses and design. The theory is applied to the development of nonlinear aerodynamic response models that can be defined in state-space form and are, therefore, appropriate for use in modern control theory. The Volterra-Wiener theory relies on the identification of nonlinear kernels that can be used to predict the response of a nonlinear system due to an arbitrary input. A numerical kernel identification technique, based on unit impulse responses, is presented and applied to a simple bilinear, single-input-single-output (SISO) system. The linear kernel (unit impulse response) and the nonlinear second-order kernel of the system are numerically identified and compared with the exact, analytically defined linear and second-order kernels. This kernel identification technique is then applied to the computational aeroelasticity program-transonic small disturbance (CAP-TSD) code for identification of the linear and second-order kernels of a NACA64A010 rectangular wing undergoing pitch at M = 0.5, M = 0.85 (transonic), and M = 0.93 (transonic). Results presented demonstrate the feasibility of this approach for use with nonlinear, unsteady aerodynamic responses.

Balanced Model Reduction via the Proper Orthogonal Decomposition

Abstract: A new method for performing a balanced reduction of a high-order linear system is presented. The technique combines the proper orthogonal decomposition and concepts from balanced realization theory. The method of snapshotsisused to obtainlow-rank,reduced-rangeapproximationsto thesystemcontrollability and observability grammiansineitherthetimeorfrequencydomain.Theapproximationsarethenusedtoobtainabalancedreducedorder model. The method is particularly effective when a small number of outputs is of interest. It is demonstrated for a linearized high-order system that models unsteady motion of a two-dimensional airfoil. Computation of the exact grammians would be impractical for such a large system. For this problem, very accurate reducedorder models are obtained that capture the required dynamics with just three states. The new models exhibit far superiorperformancethanthosederived using a conventionalproperorthogonal decomposition. Although further development is necessary, the concept also extends to nonlinear systems.

Computation of Unsteady Nonlinear Flows in Cascades Using a Harmonic Balance Technique

Abstract: A harmonic balance technique for modeling unsteady nonlinear e ows in turbomachinery is presented. The analysis exploits the fact that many unsteady e ows of interest in turbomachinery are periodic in time. Thus, the unsteady e ow conservation variables may be represented by a Fourier series in time with spatially varying coefe cients. This assumption leads to a harmonic balance form of the Euler or Navier ‐Stokes equations, which, in turn, can be solved efe ciently as a steady problem using conventional computational e uid dynamic (CFD) methods, including pseudotime time marching with local time stepping and multigrid acceleration. Thus, the method is computationally efe cient, at least one to two orders of magnitude faster than conventional nonlinear time-domain CFD simulations. Computational results for unsteady, transonic, viscous e ow in the front stage rotor of a high-pressure compressor demonstrate that even strongly nonlinear e ows can be modeled to engineering accuracy with a small number of terms retained in the Fourier series representation of the e ow. Furthermore, in some cases, e uid nonlinearities are found to be important for surprisingly small blade vibrations.

Digital Twin: Values, Challenges and Enablers From a Modeling Perspective

Abstract: Digital twin can be defined as a virtual representation of a physical asset enabled through data and simulators for real-time prediction, optimization, monitoring, controlling, and improved decision making. Recent advances in computational pipelines, multiphysics solvers, artificial intelligence, big data cybernetics, data processing and management tools bring the promise of digital twins and their impact on society closer to reality. Digital twinning is now an important and emerging trend in many applications. Also referred to as a computational megamodel, device shadow, mirrored system, avatar or a synchronized virtual prototype, there can be no doubt that a digital twin plays a transformative role not only in how we design and operate cyber-physical intelligent systems, but also in how we advance the modularity of multi-disciplinary systems to tackle fundamental barriers not addressed by the current, evolutionary modeling practices. In this work, we review the recent status of methodologies and techniques related to the construction of digital twins mostly from a modeling perspective. Our aim is to provide a detailed coverage of the current challenges and enabling technologies along with recommendations and reflections for various stakeholders.