Showing papers by "Yueming Li published in 2015"

Experimental and numerical investigations on dynamic and acoustic responses of a thermal post-buckled plate

Abstract: Experiments were carried out for a clamped rectangular aluminum plate to study the dynamic and acoustic behaviors in both pre- and post-buckling ranges under thermal loads. Plate temperature was elevated from ambient value to the level above the theoretical critical buckling temperature of the plate. In the whole test temperature range, the measured frequencies decreased to the minimum values in sequence, and then turned to increase as temperature rose. The softening effect of thermal stresses played the leading role in the decreasing stage and the stiffening effect of thermal buckling deflection became the major influence factor in the increasing stage. The later one could drive the temperature equilibrium point of the heated plate to move towards lower temperature range. All the frequencies would not drop to zero due to the inherent initial deflection which provides additional stiffness to the plate. Dynamic responses state two variation trends in different temperature ranges, shifting toward the lower frequency range and closing up in the mid-frequency range. The characters of spectrum responses changed gradually as the temperature was elevated. Numerical simulations gave predictions with same variation trend as the test results.

Vibration and Acoustic Responses of an Orthotropic Composite Conical Shell in a Hygroscopic Environment

Abstract: The vibration and acoustic radiation for an orthotropic composite conical shell in a hygroscopic environment are explored through the wave propagation approach and Galerkin method. Theoretical results of the natural vibration and far field sound pressure are presented with incremental moisture content. The effects of incremental stiffness and different semi-vertex angle on the acoustic radiation characteristics are studied too. It is found that the natural frequencies decrease with incremental moisture content. The wavenumbers associated with the lowest frequency mode reaches the modal indices corresponding to the lowest buckling mode near the critical buckling moisture content. With the increasing moisture content, a shifting of natural frequencies toward lower frequency band could be observed in lower frequency band of the modal density in constant frequency band. The overall sound pressure level (SPL) decreases generally with the moisture content, but shows a marginal increase near the critical buckling moisture content. The modal density and overall SPL decrease with the incremental stiffness generally, which increases with the decrease of the semi-vertex angle.

A return mapping algorithm for unified strength theory model

Abstract: A return mapping algorithm in principal stress space for unified strength theory (UST) model is presented in this paper. In contrast to Mohr–Coulomb and Tresca models, UST model contains two planes and three corners in the sextant of principal stress space, and the apex is formed by the intersection of 12 corners rather than the six corners of Mohr–Coulomb in the whole principal stress space. In order to utilize UST model, the existing return mapping algorithm in principal stress space is modified. The return mapping schemes for one plane, middle corner, and apex of UST model are derived, and corresponding consistent constitutive matrices in principal stress space are constructed. Because of the flexibility of UST, the present model is not only suitable for analysis based on the traditional yield functions, such as Mohr–Coulomb, Tresca, and Mises, but might also be used for analysis based on a series of new failure criteria. The accuracy of the present model is assessed by the iso-error maps. Three numerical examples are also given to demonstrate the capability of the present algorithm. Copyright © 2015 John Wiley & Sons, Ltd.

High-Frequency Dynamic Analysis of Plates in Thermal Environments Based on Energy Finite Element Method

Abstract: The energy density governing equation to analyze the high-frequency dynamic behavior of plates in thermal environments is derived in this paper, in which the thermal effects are considered to change the membrane stress state and temperature dependent material properties of plates. Then the thermal effects on the energy reflection and transmission coefficients are dealt with hereof. Based on the above, an EFEM (energy finite element method) based approximate approach for the energy analysis of coupled plates under nonuniform thermal environments is proposed. The approach could be conducted by three steps: (1) thermal analysis, (2) thermal stress analysis, and (3) forming element matrixes, joint matrixes, and the whole EFEM formulation for the energy analysis. The same mesh model is used for all the three steps. The comparison between EFEM results and classical modal superposition method results of simply supported plates in various uniform thermal environments and coupled plates in nonuniform thermal environments demonstrated that the derived energy governing equation and the proposed approach described well the smooth time- and locally space-averaged energy density. It is found that the distributions and levels of energy density are affected by thermal effects, and the variation trends are related to exciting frequency.

Structural topology optimization on sound radiation at resonance frequencies in thermal environments

Abstract: Thermal and acoustic environments pose severe challenges to the structural design of hypersonic vehicles. One of them is to find optimal design that exhibits ideal acoustic characteristics in a frequency band, which is discussed in this paper through topology optimization aiming at resonance sound radiation in thermal environments. The sound radiation at resonance frequencies is the main component of response, minimization on which is likely to provide a satisfactory design. A bi-material plate subjected to uniform temperature rise and excited by harmonic loading is studied here. Thermal stress is first evaluated and considered as pre stress in the following dynamic analysis; radiated sound power is then calculated through Rayleigh integral. Sensitivity analysis is carried out through adjoint method considering the complicated relationship between stress-induced geometric stiffness and design variables. As the resonance frequency is constantly changing during the optimization, its sensitivity should be considered. It is also noticed that mode switching may occur, so mode tracking technique is employed in this work. Some numerical examples are finally discussed.

Effect of Dead Load on Dynamic Characteristics of Rotating Timoshenko Beams

Abstract: The dynamic characteristics of a rotating cantilever Timoshenko beam under dead load are investigated in this paper. Considering the predeformation caused by dead load and centrifugal force, governing equation of rotating cantilever Timoshenko beam is derived based on Hamilton’s principle, and the influence of the load on natural vibration is revealed. A suit of modal experimental apparatus for cantilever beam is designed and used to test the natural frequencies under the dead load, and the natural frequencies under rotation condition are calculated with a commercial finite element code. Both the experimental result and numerical result are utilized to compare with the present theoretical result, and the results obtained by present modeling method show a good agreement with those obtained from the experiment and finite element method. It is found that the natural frequencies of cantilever beam increase with both the dead load and the rotating speed.

Efficient aero-structural design optimization: Coupling based on reverse iteration of structural model

Abstract: Traditional coupled multi-disciplinary design optimization based on computational fluid dynamics/computational structure dynamics (CFD/CSD) aims to optimize the jig shape of aircraft, and general multi-disciplinary design optimization methodology is adopted. No special consideration is given to the aircraft itself during the optimization. The main drawback of these methodologies is the huge expanse and the low efficiency. To solve this problem, we put forward to optimize the cruise shape directly based on the fact that the cruise shape can be transformed into jig shape, and a methodology named reverse iteration of structural model (RISM) is proposed to get the aero-structural performance of cruise shape. The main advantage of RISM is that the efficiency can be improved by at least four times compared with loosely-coupled aeroelastic analysis and it maintains almost the same fidelity of loosely-coupled aeroelastic analysis. An optimization framework based on RISM is proposed. The aerodynamic and structural performances can be optimized simultaneously in this framework, so it may lead to the true optimal solution. The aerodynamic performance was predicted by N-S solver in this paper. Test shows that RISM predicts the aerodynamic and structural performances very well. A wing-body configuration was optimized by the proposed optimization framework. The drag and weight of the aircraft are decreased after optimization, which shows the effectiveness of the proposed framework.

Theoretical Analyses of Vibration and Sound Radiation Responses of Heated Symmetric Laminated Plates in Pre- and Post-Buckling Ranges

Abstract: This paper presents theoretical investigations of vibration and sound radiation responses of laminated plates in thermal environments. Static thermal stresses are taken into account to describe the stress state of the vibrating plate. First-order shear deformation theory and von Karman nonlinear strain displacement relationship are used to represent the dynamic deformation. And then, governing equations are obtained with Hamilton’s principle. Response characters are studied in both the pre and post-buckling ranges. Results show that the bending stiffness of the heated plate drops in the pre-buckling range and increases after thermal buckling occurs. Thermal environment preforms as two opposite effects before and after buckling. Amplitudes of vibration and radiated sound of the thermal post-buckled plates show opposite variation trends.

Large-scaled simulation on the coherent vortex evolution of a jet in a cross-flow based on lattice boltzmann method

Abstract: Large eddy simulation (LES) is performed on a jet issued normally into a cross-flow using lattice Boltzmann method (LBM) and multiple graphic processing units (multi-GPUs) to study the flow characteristics of jets in cross-flow (JICF). The simulation with 8 1.50´10 grids is fulfilled with 6 K20M GPUs. With large-scaled simulation, the secondary and tertiary vortices are captured. The features of the secondary vortices and the tertiary vortices reveal that they have a great impact on the mixing between jet flow and cross-flow. The qualitative and quantitative results also indicate that the evolution mechanism of vortices is not constant, but varies with different situations. The hairpin vortex under attached jet regime originates from the boundary layer vortex of cross-flow. While, the origin of hairpin vortex in detached jet is the jet shear-layer vortex. The mean velocities imply the good ability of LBM to simulate JICF and the large loss of jet momentum in detached jet caused by the strong penetration. Besides, in our computation, a high computational performance of 1083.5 MLUPS is achieved.

Vibro-acoustic analysis of high-speed trains under aerodynamic pressure

Abstract: The aerodynamic environment is an important factor in the design of high-speed trains, which may lead to structural damage and comfort deterioration. This paper carries out coupled vibro-acoustic analysis based on aerodynamic evaluation to investigate the structural dynamic characteristic in "real" environment. The strategy is implemented using the commercial soft-ware ANSYS. Firstly, CFD aerodynamic analysis is carried out to calculate the dynamic pressures. These aerodynamic loads are then transited to the structural surface through fluid-structure interface using Mechanical ANSYS Parametric Design Language. The full coupled vibro-acoustic system is finally analyzed to evaluate the dynamic response and the inner noise environments. Results show that the aerodynamic pressures are ideally transmitted to structural surface, and the vibro-acoustic response mainly affects the nose cone and the train tail.