Robustness Of Theory Research Articles

Novel airfoil for improved supersonic aerodynamic performance

PurposeThis study aims to validate the linear flow theory with computational fluid dynamics (CFD) simulations and to propose a novel shape for the airfoil that will improve supersonic aerodynamic performance compared to the National Advisory Committee for Aeronautics (NACA) 64a210 airfoil.Design/methodology/approachTo design the new airfoil shape, this study uses a convex optimization approach to obtain a global optimal shape for an airfoil. First, modeling is conducted using linear flow theory, and then numerical verification is done by CFD simulations using ANSYS Fluent. The optimization process ensures that the new airfoil maintains the same cross-sectional area and thickness as the NACA 64a210 airfoil. This study found that an efficient way to obtain the ideal airfoil shape is by using linear flow theory, and the numerical simulations supported the assumptions inherent in the linear flow theory.FindingsThis study’s findings show notable improvements (from 4% to 200%) in the aerodynamic performance of the airfoil, especially in the supersonic range, which points to the suggested airfoil as a potential option for several fighter aircraft. Under various supersonic conditions, the optimized airfoil exhibits improved lift-over-drag ratios, leading to improved flight performance and lower fuel consumption.Research limitations/implicationsThis study was conducted mainly for supersonic flow, whereas the subsonic flow is tested for a Mach number of 0.7. This study would be extended for both subsonic and supersonic flights.Practical implicationsConvex optimization and linear flow theory are combined in this work to create an airfoil that performs better in supersonic conditions than the NACA 64a210. By closely matching the CFD results, the linear flow theory's robustness is confirmed. This means that the initial design phase no longer requires extensive CFD simulations, and the linear flow theory can be used quickly and efficiently to obtain optimal airfoil shapes.Social implicationsThe proposed airfoil can be used in different fighter aircraft to enhance performance and reduce fuel consumption. Thus, lower carbon emission is expected.Originality/valueThe unique aspect of this work is how convex optimization and linear flow theory were combined to create an airfoil that performs better in supersonic conditions than the NACA 64a210. Comprehensive CFD simulations were used for validation, highlighting the optimization approach's strength and usefulness in aerospace engineering.

Finite volume based asymptotic homogenization of viscoelastic unidirectional composites

The previously developed finite volume based asymptotic homogenization theory designed for unidirectional composites with finite-sized microstructures is further extended to non-ageing linear viscoelastic region via correspondence principle. The theory is a unified framework able to accommodate general loadings, both out-of-plane and in-plane. It first transforms the problems in time domain to Laplace domain via elastic–viscoelastic correspondence principle, solves the problems in transformed region, and transforms the solutions back to time domain through numerical inversion technique. In Laplace domain, the microscale problems are solved up to the third term of expansion, and the homogenized stiffness tensors of all orders are passed to the macroscale, leading to the solutions of macroscale displacements. The method’s capability is assessed through comparison with direct numerical solution, showing increasing accuracy with increasing truncation order and decreasing scale ratio, and further enhancement by reconstructing boundary layer. The robustness of theory is verified through parametric studies. The possibility of reducing the highest order of spatial derivative of homogenized displacement is also investigated. The finite volume based methodology marks the theory’s uniqueness among the existing higher order asymptotic homogenization methods, providing an efficient alternative to solve the viscoelastic composite structural problems.

On Performance of Sparse Fast Fourier Transform Algorithms Using the Flat Window Filter

The problem of computing the Sparse Fast Fourier Transform(sFFT) of a $K$ -sparse signal of size $N$ has received significant attention for a long time. The first stage of sFFT is hashing the frequency coefficients into $B(\approx {K})$ buckets named frequency bucketization. The process of frequency bucketization is achieved through the use of filters: Dirichlet kernel filter, aliasing filter, flat filter, etc. The frequency bucketization through these filters can decrease runtime and sampling complexity in low dimensions. It is a hot topic about sFFT algorithms using the flat filter because of its convenience and efficiency since its emergence and wide application. The next stage of sFFT is the spectrum reconstruction by identifying frequencies that are isolated in their buckets. Up to now, there are more than thirty different sFFT algorithms using the sFFT idea as mentioned above by their unique methods. An important question now is how to analyze and evaluate the performance of these sFFT algorithms in theory and practice. In this paper, it is mainly discussed about sFFT algorithms using the flat filter. In the first part, the paper introduces the techniques in detail, including two types of frameworks, five different methods to reconstruct spectrum and corresponding algorithms. We get the conclusion of the performance of these five algorithms, including runtime complexity, sampling complexity and robustness in theory. In the second part, we make three categories of experiments for computing the signals of different SNR, different $N$ , and different $K$ by a standard testing platform and record the run time, percentage of the signal sampled, and $L_{0},L_{1},L_{2}$ error both in the exactly sparse case and general sparse case. The result of experiments is consistent with the inferences obtained in theory. It can help us to optimize these algorithms and use them correctly in the right areas.

Is Development Uniquely Modern? Athens on the Doorstep

North/Wallis/Weingast (2009) define the problem of development as the transition from natural state to open access order and propose a theory of the natural state as a stable system. A small number of natural states develop by moving to doorstep and then into the transition proper that led to open access orders in a few modern states. NWW’s focus on early modern Europe gives the impression that the transition happened only once in human history and leaves the theory vulnerable to confounding variables of modernity, such as the industrial revolution, technological change, or colonialism. If the conditions predicted by the theory produced a similar result prior to modernity, the theory's robustness is supported. We consider ancient Athens as an out-of-sample test, showing that conditions similar to those NWW assert for early modern Europe held in Athens, and tests that support our claim. Changes in Athenian policy in the direction of open access are predicted and explained by reference to changing Athenian revenue demands, sources of revenue, and capacity for coercion.

Independence Under Fire: Extra-legal Pressures and Coalition Building in WTO Dispute Settlement

This study uses detailed quantitative analyses of the complete history of rulings made by the Panels and the Appellate Body of the WTO Dispute Settlement Mechanism during its first ten years of operation, to assess the robustness of theories regarding the decision-making of these institutions. Regression analyses are used to test for correlation between the success of Complainants in dispute settlement and a variety of factors, representing the hypothesized capacity of states to influence Panels and the Appellate Body through dimensions of political and economic power, the impact of the relative practical capacities of states in dispute settlement proceedings, and the formation of coalitions of states in support of a particular Complainant or Respondent. The results of the regression analyses - that few significant correlations exist between the independent variables and the dispute outcomes - provide evidence that the judicial institutions of the Dispute Settlement Mechanism are independent from Member State influence. The one reliable correlation found in these analyses demonstrates that a Complainant state does have substantial advantage in Panel proceedings if it has previously participated in more disputes than the Respondent.

Is the Government Failure Theory Still Relevant? A panel analysis using US state level data

Abstract The purpose of this paper is to empirically examine the robustness of the government failure theory. A core feature of the government failure theory is demand heterogeneity. Previous studies have brought into question the robustness of the government failure theory, due to inconsistent results concerning the explanatory power of demand heterogeneity. Therefore, in this paper we revisit this important research agenda using US state level panel data. We find the two‐way fixed effects model a suitable model for testing the government failure theory's robustness and present findings which indicate that observable demand heterogeneity has a positive effect on the size of the nonprofit sector. This paper also empirically examines the relevance of the complementary financing hypothesis in terms of the cooperative nature of the governmental and nonprofit sector relationship; that is where governments delegate the production of quasi‐public goods to the nonprofit sector.