Search

A numerical investigation was performed to further understand the physical significance of bird striking on a rotary jet-engine fan. A new numerical bird model considering more geometric characteristics than traditional ones was established first, during which the smooth particles hydrodynamic (SPH) method and an equation of state (EOS) were employed. The numerical method and material model were indicated to be reasonable by a validation analysis. Then, a preliminary study of a rigid target struck by a realistic bird from four different orientations including head, tail, bottom and wing sides as well as a traditional hemispherical-ended cylinder model were simulated. It was found that bird geometry and impact orientation had significant effects on impact response and kinetic energy loss of the bird. Furthermore, the same load conditions were conducted on a rotary jet-engine fan and followed by a series of parametric studies, including impact force history, kinetic energy loss of the bird, deformations of the blade tips and von Mises stresses of the blade roots. The results showed that both bird geometry and impact orientation had significant and non-ignorable influence on bird striking on a rotary jet-engine fan and bottom side was the most dangerous case. Considering more geometric characteristics of the bird and impact orientation in studies of bird strike problems was proved to be meaningful and necessary. [ABSTRACT FROM AUTHOR]

Uncertainties to varying degrees often exist in the analysis and design problems of vibro-acoustic systems. This paper investigates the high-frequency vibro-acoustic analysis problem with large levels of fuzzy parameters. By employing the level-cut strategy, the energy balance equations with fuzzy parameters are firstly transformed into the interval forms. Then, by combining the perturbation method, the Sherman-Morrison-Woodbury formula, and the statistical energy analysis, a modified perturbation statistical energy analysis (MPSEA) is proposed to predict the uncertainty propagation of the energy flow in vibro-acoustic systems with fuzzy parameters. Further, the sub-interval technique is introduced in MPSEA to improve its accuracy for the systems with large levels of fuzzy parameters. Numerical simulations of a plate-cavity system and a launcher fairing model with fuzzy parameters are presented to demonstrate the efficiency and accuracy of proposed method. Results indicate that the proposed MPSEA with a suitable number of sub-intervals is capable of predicting the energy flow in vibro-acoustic system with large fuzzy parameter accurately and efficiently. [ABSTRACT FROM AUTHOR]

In the modal test of lightweight structures, the measured data is easily polluted by mass loading effects of transducers. A method is proposed to eliminate the influence of sensors for accurately estimating the frequency response functions (FRFs) of structures. Considering the situation that the multiple accelerometers lead to changes in the dynamic stiffness matrix, the corrected FRFs are derived from the original measured signals based on the Sherman-Morrison-Woodbury formula. The salient feature of the proposed strategy is that the adverse effects of sensors can be eliminated in only one step. Numerical simulations are conducted by employing a six-degrees of freedom spring-mass system, modal frequencies and mode shapes with high accuracy are obtained by measured signals. Experimental investigation is undertaken by using a laboratory solar panel. Results show that the effects of multi-transducers mass can be removed efficiently and the corrected FRFs are in good agreement with the targeted values. The excitation and measurement points are regarded as active coordinates, and the computational efficiency can be significantly improved when the presented method is applied on active coordinates. [ABSTRACT FROM AUTHOR]

An algorithm that integrates Karhunen–Loeve expansion (KLE), finite element method (FEM), and boundary element method (BEM) is proposed to carry out a vibro-acoustic analysis under stationary and non-stationary random excitations which are uncorrelated or correlated. In the KLE, a set of orthogonal basis functions is employed to discretize the auto-covariance function of the excitations and obtain the eigenvalues and eigenfunctions of the auto-covariances. The KLE for correlated random excitation relies on the expansions of correlated random variables. During the response calculation, the FEM and BEM are employed to obtain structural and acoustic responses. A circular piston in an infinite baffle and a stiffened panel excited by stationary or non-stationary random processes are used to illustrate the proposed algorithm's accuracy. Results show that the statistics of vibro-acoustic response are accurately obtained with the proposed method and this method is also applicable for the vibro-acoustic analysis of more complex structures under various types of random excitations. [ABSTRACT FROM AUTHOR]

Wave Based Method (WBM) is an efficient method to analyze mid-frequency dynamic problems. This work extended the WBM to the transverse vibration analysis of a thermal beam with limited uncertain information. Novel wave functions and particular solution function for the thermal beam with deterministic parameters are derived to obtain the dynamic response. Then, by employing the interval perturbation method and sub-interval decomposition technique, the Sub-Interval Perturbation Wave Based Method (SIPWBM) is developed to analyze the uncertain propagation in thermal beams for the first time. Numerical simulations for thermal beams with deterministic parameters and interval parameters are conducted, respectively. The impacts of different thermal effects on deterministic dynamic response are investigated. Simulation results prove that the developed WBM could accurately predict the low- and mid-frequency transverse dynamic response of the thermal beam with deterministic parameters. The thermal stress effect plays a leading role in the low-frequency displacement frequency responses for beams under low-level temperature load. Whereas it is necessary to consider both the temperature-dependent material property effect and thermal stress effect in the mid-frequency transverse vibration analysis of thermal beams. By using the sub-interval decomposition technique and choosing a suitable sub-interval number, the SIPWBM could predict the bounds of the mid-frequency interval dynamic response accurately and efficiently. [ABSTRACT FROM AUTHOR]

The unsteady vortex-lattice method provides a medium-fidelity tool for calculation of low-speed aerodynamic loads based on the potential-flow theory. It has long been favored in research on the aeroelasticity and flight dynamics for flexible aircraft with high aspect ratios. However, the unsteady vortex-lattice method is established in the discrete time domain which brings difficulties to modeling aeroelastic system for stability analysis. An analytical aerodynamic sensitivity calculation scheme is developed in this paper to formulate the aeroelastic equations of motion with UVLM aerodynamics. A free wake model is used to simulate accurate vortex shedding and subsequent wake propagation. Using a small perturbation method, the aerodynamic governing equations are linearized around the equilibrium condition, where the analytical sensitivities can be derived. The surface spline interpolation algorithm is adopted to implement the structure-aerodynamic coupling. Both aerodynamic sensitivities with respect to structural motions and circulation strengths of vortices are obtained. In numerical studies, a time-marching transient response analysis scheme is used to obtain the distributed aerodynamic loads and structural deformations. Analytical sensitivity results are validated by the finite difference method. The proposed analytical sensitivity calculation framework is demonstrated to be applicable to commonly used beam-based flexible wing models, as well as the shell-based finite element models with higher fidelity. The derived sensitivity formulations and related numerical implementations can build the foundation for further studies on aeroelastic optimization and stability analysis. [ABSTRACT FROM AUTHOR]

The nonlinear behavior of the airfoil-store system introduces complexity to its mechanical characteristics, making it essential to identify the system's nonlinear features. This study presents a novel nonlinear subspace identification approach in combination with an aerodynamic force. Based on the dynamic modeling of the airfoil storage system with random force, a linear elastic contribution related to the wind speed is introduced to two sides of motion equations, thereby transforming the original asymmetric linearity into the symmetric stiffness. A nonlinear state-space representation of the airfoil-store system is established, and the nonlinear parameters are identified by the proposed approach. Simulation examples are conducted considering different levels of nonlinearity, measurement noise, and flow speeds. The results demonstrate that the proposed method exhibits strong flexibility and robustness across various wind speeds in the airfoil-store system. It effectively identifies nonlinear stiffness, nonlinear damping, and various types of nonlinearity. [ABSTRACT FROM AUTHOR]

The nonlinear behavior of the airfoil-store system introduces complexity to its mechanical characteristics, making it essential to identify the system's nonlinear features. This study presents a novel nonlinear subspace identification approach in combination with an aerodynamic force. Based on the dynamic modeling of the airfoil storage system with random force, a linear elastic contribution related to the wind speed is introduced to two sides of motion equations, thereby transforming the original asymmetric linearity into the symmetric stiffness. A nonlinear state-space representation of the airfoil-store system is established, and the nonlinear parameters are identified by the proposed approach. Simulation examples are conducted considering different levels of nonlinearity, measurement noise, and flow speeds. The results demonstrate that the proposed method exhibits strong flexibility and robustness across various wind speeds in the airfoil-store system. It effectively identifies nonlinear stiffness, nonlinear damping, and various types of nonlinearity. [ABSTRACT FROM AUTHOR]

Distributed load information is essential for the design and monitoring of aerospace structures. A frequency domain method for the identification of correlated random fluctuating pressure is proposed in which structural responses acquired from limited strain sensors are used. The spatially-correlated power spectral density function of the random fluctuating pressure on the structure is firstly represented by Legendre polynomials w.r.t. the spatial distance multiplying their corresponding frequency-dependent coefficients. Secondly, the transfer matrix is obtained by the stochastic response analysis using distributed load in the form of Legendre polynomials. Then, the coefficients in the power spectral density function model of the pressure are identified by inversion of the transfer matrix together with a modified regularization technique. Finally, the random fluctuating pressure load is reconstructed by the superposition of the identified coefficients multiplying with Legendre polynomials. Numerical simulations on a simply-supported plate subjected to correlated stochastic distributed loads are conducted to verify the proposed method. Factors that may influence the accuracy of identification results are also discussed. To test the performance of the proposed method on complex structures, the gust-induced pressure load on a 3D wing structure is further identified using the proposed method. Results show that the proposed method is capable of identifying the correlated random fluctuating pressure on aircraft structures. [ABSTRACT FROM AUTHOR]