In this paper, a 3-D, unsteady vortex lattice model to compute aerodynamic coefficients, using time domain eigenmode analysis, is presented. A computationally efficient technique for constructing a reduced order model of unsteady flow about a low aspect ratio wing, modeled as a cantilever plate of constant thickness, is presented. Analysis demonstrates that limit cycle oscillations of the order of the plate thickness are possible. The eigenmodes of the system, which may be considered as aerodynamic states, are computed and, subsequently, used to construct a computationally efficient, reduced order model of an unsteady flow field. Only a handful of the most dominant eigenmodes are retained in the reduced order model. The effect of the remaining eigenmodes is included approximately, using a static correction technique. An advantage of the present method is that, once the eigenmode information has been computed, the reduced order model can be constructed for any number of arbitrary modes of wing motion very inexpensively. The method is particularly well suited for use in the active control of aeroelastic phenomena, as well as in standard aeroelastic analysis for flutter or gust response. Finally, a numerical example is presented that demonstrates the accuracy and computational efficiency of the present method.

The current empirical study was conducted to investigate the wall neighborhood impact on the twodimensional flow structure and heat transfer enhancement behind a square cylinder. The low-velocity open-circle wind tunnel was used to carry out the study tests considering the cylinder diameter (D)-based Reynolds number (ReD) of 5130. The selected items to compare were different gap height (G/D= 0. 0, 0. 1, 0. 2 and 0. 8). The flow field was measured using particle image velocimetry (PIV) with high image-density camera. The PIV-derived time-averaged quantities, including the streamline pattern, streamwise velocity fluctuation intensity, and reverse-flow intermittency, were examined for the flow past the square cylinder. The measurements of PIV were decomposed with the help of proper orthogonal decomposition (POD) approach that provides a proper view of the POD modes. To obtain the value of the heat transfer enhancement behind the square cylinder, the full-field temperature distributions of flat plate were measured through the temperature-sensitive paint (TSP) technique. Results showed that the maximum heat transfer enhancement was obtained at G/D=0. 2 due to the high unstable flow near the wall.

Mechanical systems with structural symmetries present vibration properties that allow the calculation to be easier and the analysis time to decrease. The paper aims to use the properties involved by the symmetries that exist in mechanical systems for the analysis of the forced response to vibrations. Thus, the study of the properties of systems with symmetries or with identical parts is expanded. Based on a classic model, the characteristic properties that appear in this case are obtained and the advantages of using these properties are revealed. On an example consisting of a truck equipped with two identical engines, the way of applying these properties in the calculation and the resulting advantages is presented.

This comprehensive study investigates the behavior of functionally graded (FG) nanoplates, providing insights into their characteristics and important design considerations. By examining factors such as homogenization models (Voigt Reuss, LRVE, and Tamura), volume fraction laws (power-law model, Viola-Tornabene four-parameter model, trigonometric model), eigenmode, aspect ratios, index material, and small-scale length parameters, the study evaluates their influence on the natural frequency response of simply supported nanoplates. A novel twisting function is introduced and its accuracy in predicting natural frequencies in FG square nanoplates is rigorously validated through numerical comparisons with existing literature. The findings obtained from this research offer valuable guidance for optimizing the design of FG nanoplates and significantly contribute to advancing our understanding of their dynamics and practical applications.

The Jacobian-Free Newton-Krylov (JFNK) method has been widely used in solving nonlinear equations arising in many applications. In this paper, the JFNK solver is examined as an alternative to the traditional power iteration method for calculation of the fundamental eigenmode in reactor analysis based on even-parity neutron transport theory. Since the Jacobian is not formed the only extra storage required is associated with the workspace of the Krylov solver used at every Newton step. A new nonlinear function is developed for the even-parity neutron transport equation utilized to solve the eigenvalue problem using the JFNK. This Newton-based method is compared with the standard iterative power method for a number of multi-groups, one and two dimensional neutron transport benchmarks. The results show that the proposed algorithm generally ends with fewer iterations and shorter run times than those of the traditional power method.

Linear stability analysis of the three dimensional plane wake flow is performed using a mapped finite difference scheme in a domain which is doubly infinite in the cross-stream direction of wake flow. The physical domain in cross-stream direction is mapped to the computational domain using a cotangent mapping of the form y = - βcot (πς). The Squire transformation [2}, proposed by Squire, is also used to relate the three-dimensional disturbances to the equivalent two-dimensional disturbances. The compact finite difference scheme of Lele [3] and the chain rule of differentiation are used to solve the Orr Sommerfeld equation. The result of linear stability analysis indicates that streamwise and the spanwise component of velocity eigenmodes is antisymmetric and the cross stream velocity eigenmode is symmetric. This is consistent with the DNS requirement of plane wake flow pertaining to solvability conditions [5].      

Past studies showed that a micron-sized surface roughness may cause the generation of a significant ‎unstable, stationary wave in a crossflow boundary layer, and consequently promote or delay the laminar-‎turbulent transition. The crossflow boundary layer is usually driven by the favorable pressure gradient ‎which is produced by accelerated inviscid velocity. Hence, for a fixed sweep angle, the magnitude of ‎pressure gradient is the key parameter for the excitation and evolution of the stationary crossflow mode. ‎In order to study the effect of pressure gradient on the excitation and subsequent linear development of ‎stationary mode, a classical Falkner-Skan-Cooke boundary layer is introduced so that the magnitude of ‎pressure gradient can be easily parameterized by an acceleration coefficient. Numerical simulation is ‎performed to induce the stationary perturbation by chordwise-isolated, spanwise-periodic roughness at ‎the lower branch of neutral curve. Then the excited waves develop into Rayleigh modes in the ‎downstream region. The stationary modes with different spanwise wavenumbers in various favorable-‎pressure-gradient boundary layers are simulated and analysed to determine the effect of pressure ‎gradient. And the corresponding coupling coefficients are calculated to connect the initial amplitude and ‎the eigenmode of linear stability theory for implementing the existing prediction method of laminar-‎turbulent transition‎‎.