Abstract:The majority of problems in aircraft production and operation require decisions made in the presence of uncertainty. For this reason aerodynamic designs obtained with traditional deterministic optimization techniques seeking only optimality in a specific set of conditions may have very poor off-design performances or may even be unreliable. In this work, we present a novel approach for robust and reliability-based design optimization of aerodynamic shapes based on the combination of single and multi-objective … Show more
“…For small errors in the sample estimate of and (exact values indicated by ×) are acceptable but optimal variance reduction cannot be achieved 1 . Pisaroni 27 suggests a least-square fitting procedure to obtain the model constants but uses the cost model of Giles 18 . For the multilevel variance estimate we used the approach of Geraci 28 where the number of pilot samples chosen across levels equals the samples chosen across model fidelities.…”
Section: Insights On Model Correlation and Optimal Samplingmentioning
confidence: 99%
“…Where is an estimate of the approximation‐model mean . Pisaroni 32 uses a weighted formulation of bias and statistical error in a multilevel control variate formulation called the continuation MLMC. In this work we consider the analysis error ε to be negligibly small (similar to the work of Ng 16 and Geraci 1 ).…”
In this work we propose, analyse, and demonstrate a new adjoint-based multilevel multifidelity Monte Carlo framework called FastUQ. The framework unifies the multifidelity analysis of Ng 1 , multilevel multifidelity analysis of Geraci 2 and an adjoint error correction surrogate model due to Ghate 3. The optimal mean squared error estimator shows that introducing multilevel in a multifidelity framework guarantees reduction in computational cost. Moreover, unlike the surrogate model of Ghate 3 , the method does not suffer from the curse of dimensionality. FastUQ is demonstrated here to quantify uncertainties in aerodynamic parameters due to surface variations caused by the manufacturing processes for a highly loaded turbine cascade. A stochastic model for surface variations on the cascade is proposed and optimal dimensionality reduction of model parameters is realised using goal-based principal component analysis considering the adjoint sensitivities of multiple quantities of interest (QoI). The proposed method achieves a reduction of 70% in computational cost in predicting the mean quantities like total-pressure loss and mass flow rate compared to state-of-art MLMC method. The robustness of the method is shown in application to the highly non-linear case of a heavily loaded turbine cascade operating at off-design conditions.
“…For small errors in the sample estimate of and (exact values indicated by ×) are acceptable but optimal variance reduction cannot be achieved 1 . Pisaroni 27 suggests a least-square fitting procedure to obtain the model constants but uses the cost model of Giles 18 . For the multilevel variance estimate we used the approach of Geraci 28 where the number of pilot samples chosen across levels equals the samples chosen across model fidelities.…”
Section: Insights On Model Correlation and Optimal Samplingmentioning
confidence: 99%
“…Where is an estimate of the approximation‐model mean . Pisaroni 32 uses a weighted formulation of bias and statistical error in a multilevel control variate formulation called the continuation MLMC. In this work we consider the analysis error ε to be negligibly small (similar to the work of Ng 16 and Geraci 1 ).…”
In this work we propose, analyse, and demonstrate a new adjoint-based multilevel multifidelity Monte Carlo framework called FastUQ. The framework unifies the multifidelity analysis of Ng 1 , multilevel multifidelity analysis of Geraci 2 and an adjoint error correction surrogate model due to Ghate 3. The optimal mean squared error estimator shows that introducing multilevel in a multifidelity framework guarantees reduction in computational cost. Moreover, unlike the surrogate model of Ghate 3 , the method does not suffer from the curse of dimensionality. FastUQ is demonstrated here to quantify uncertainties in aerodynamic parameters due to surface variations caused by the manufacturing processes for a highly loaded turbine cascade. A stochastic model for surface variations on the cascade is proposed and optimal dimensionality reduction of model parameters is realised using goal-based principal component analysis considering the adjoint sensitivities of multiple quantities of interest (QoI). The proposed method achieves a reduction of 70% in computational cost in predicting the mean quantities like total-pressure loss and mass flow rate compared to state-of-art MLMC method. The robustness of the method is shown in application to the highly non-linear case of a heavily loaded turbine cascade operating at off-design conditions.
“…Moving away from the multi-level/multi-index paradigm, multi-fidelity methods that are based on different physical models rather than multiple discretizations have been proposed, e.g., in [25][26][27][28][29].…”
This paper presents a comparison of two multi-fidelity methods for the forward uncertainty quantification of a naval engineering problem. Specifically, we consider the problem of quantifying the uncertainty of the hydrodynamic resistance of a roll-on/roll-off passenger ferry advancing in calm water and subject to two operational uncertainties (ship speed and payload). The first four statistical moments (mean, variance, skewness, and kurtosis), and the probability density function for such quantity of interest (QoI) are computed with two multi-fidelity methods, i.e., the Multi-Index Stochastic Collocation (MISC) and an adaptive multi-fidelity Stochastic Radial Basis Functions (SRBF). The QoI is evaluated via computational fluid dynamics simulations, which are performed with the in-house unsteady Reynolds-Averaged Navier–Stokes (RANS) multi-grid solver $$\chi$$
χ
navis. The different fidelities employed by both methods are obtained by stopping the RANS solver at different grid levels of the multi-grid cycle. The performance of both methods are presented and discussed: in a nutshell, the findings suggest that, at least for the current implementation of both methods, MISC could be preferred whenever a limited computational budget is available, whereas for a larger computational budget SRBF seems to be preferable, thanks to its robustness to the numerical noise in the evaluations of the QoI.
“…Another possibility when dealing with uncertainty quantification is the use of variable fidelity methods in combination with Multi Level Monte Carlo approaches [24,25]. However, several levels of fidelity for a given black box problem are not always available, and the number of samples required to accurately compute statistics for large scale industrial problems is still very large.…”
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