Nonlinear Response of C/C Composite Laminated Panels with Temperature Gradients under Guassian Pressure Waves

2013 ◽  
Vol 470 ◽  
pp. 1062-1068 ◽  
Author(s):  
Yun Dong Sha ◽  
Xiao Bo Jie ◽  
Lin Zhu
Keyword(s):  
Thermal Protection ◽  
Element Model ◽  
Carbon Composite ◽  
Temperature Gradients ◽  
System Response ◽  
Equivalent Linearization ◽  
Total System ◽  
Thin Walled Structures ◽  
Thin Walled ◽  
High Level

Carbon-Carbon composite material is widely used as the thermal protection systems (TPS) of hypersonic vehicles for its special mechanical and heat-proof capabilities. The thin-walled structures with this kind of materials would exhibit large displacement response under high-level acoustic loads. Usually, the external heating is non-uniform. In the paper, a finite element model for analyzing nonlinear random dynamic behaviors of Carbon-Carbon composite panels with temperature gradients under Guassian sound excitation is founded. The total system response is decomposed into the time-independent component and the time-dependent component, using the equivalent linearization technique. Numerical results include root mean square (RMS) values of maximum deflections, time histories and power spectrum densities (PSD) of the deflection response. The results obtained in this paper can contribute to the thorough understanding of thermo-acoustic response of composite thin-walled structures.

scholarly journals Dynamic Analysis of Tapered Thin-Walled Beams Using Spectral Finite Element Method

2019 ◽  
Vol 2019 ◽  
pp. 1-13 ◽  
Author(s):  
Yiping Shen ◽  
Zhijun Zhu ◽  
Songlai Wang ◽  
Gang Wang
Keyword(s):  
Finite Element ◽  
Finite Element Model ◽  
Wind Turbine ◽  
Element Model ◽  
Rotor Blades ◽  
Mode Shapes ◽  
Modal Frequency ◽  
Thin Walled Structures ◽  
Thin Walled ◽  
Spectral Finite Element

Tapered thin-walled structures have been widely used in wind turbine and rotor blade. In this paper, a spectral finite element model is developed to investigate tapered thin-walled beam structures, in which torsion related warping effect is included. First, a set of fully coupled governing equations are derived using Hamilton’s principle to account for axial, bending, and torsion motion. Then, the differential transform method (DTM) is applied to obtain the semianalytical solutions in order to formulate the spectral finite element. Finally, numerical simulations are conducted for tapered thin-walled wind turbine rotor blades and validated by the ANSYS. Modal frequency results agree well with the ANSYS predictions, in which approximate 30,000 shell elements were used. In the SFEM, one single spectral finite element is needed to perform such calculations because the interpolation functions are deduced from the exact semianalytical solutions. Coupled axial-bending-torsion mode shapes are obtained as well. In summary, the proposed spectral finite element model is able to accurately and efficiently to perform the modal analysis for tapered thin-walled rotor blades. These modal frequency and mode shape results are important to carry out design and performance evaluation of the tapered thin-walled structures.

Influences of Thermal Loads on Nonlinear Response of Thin-Walled Structures in Thermo-Acoustic Environment

2011 ◽  
Vol 105-107 ◽  
pp. 220-226 ◽  
Author(s):  
Yun Dong Sha ◽  
Zhi Jun Gao ◽  
Fei Xu
Keyword(s):  
High Speed ◽  
Nonlinear Response ◽  
Large Deflection ◽  
Thermal Protection ◽  
Thermal Loads ◽  
Acoustic Response ◽  
Restoring Force ◽  
Acoustic Environment ◽  
Thin Walled Structures ◽  
Thin Walled

Thin-walled structures of future hypersonic flight vehicles will encounter complex loadings and exhibit obvious nonlinear responses. The thermal loads from high speed flow or engine jet flow can cause thermal buckling of thin-walled structures, such as Thermal Protection System (TPS). If the structures are loaded with intense acoustic loads simultaneously, large deflection nonlinear response, including snap-through, can be induced. Snap-through will give rise to large amplitude stress cycles and non-zero mean stress, which can lessen the fatigue life markedly. Starting from Hooker’s Law with thermal components, the large deflection governing equations of motion for simply-supported plate under thermo-acoustic loadings are derived. The partial differential equation (PDE) of motion which is difficult to solve is then transformed with Galerkin’s method to the system of ordinary differential equations (ODE) under modal coordinates. The displacement responses under different combinations of temperature increments and sound pressure levels are calculated by employing Runge-Kutta method. Typical thermo-acoustic responses are predicted: 1) random vibration around pre-buckled equilibrium position, 2) persistent snap-through between post-buckled positions, 3) intermittent snap-through, 4) vibration around one of the two post-buckled positions. By dividing the restoring force term in the equation into linear term and nonlinear one, the evolutions of each term are obtained to illustrate the mechanism of thermo-acoustic response and the contributions of each force, including shear force, thermal force and membrane force. Thus a further insight into thermo-acoustic response has been achieved.

Modeling the Varying Dynamics of Thin-Walled Aerospace Structures for Fixture Design Using Genetic Algorithms

2011 ◽  
Vol 223 ◽  
pp. 652-661
Author(s):  
Mouhab Meshreki ◽  
Helmi Attia ◽  
József Kövecses
Keyword(s):  
Numerical Models ◽  
Research Work ◽  
Computational Effort ◽  
Computational Time ◽  
Fixture Design ◽  
Structural Elements ◽  
Thin Walled Structures ◽  
Thin Walled ◽  
High Flexibility ◽  
High Level

Fixture design for milling of aerospace thin-walled structures is a challenging process due to the high flexibility of the structure and the nonlinear interaction between the forces and the system dynamics. At the same time, the industry is aiming at achieving tight tolerances while maintaining a high level of productivity. Numerical models based on FEM have been developed to simulate the dynamics of thin-walled structures and the effect of the fixture layout. These models require an extensive computational effort, which makes their use for optimization very unpractical. In this research work, a new concept is introduced by using a multi-span plate with torsional and translational springs to simulate the varying dynamics of thin-walled structure during machining. A formulation, based on holonomic constraints, was developed and implemented to take into account the effect of rigid fixture supports. The developed model, which reduces the computational time by one to two orders of magnitude as compared to FE models, is used to predict the dynamic response of complex aerospace structural elements including pockets and ribs while taking into account different fixture layouts. The model predictions are validated numerically. The developed model meets the conflicting requirements of prediction accuracy and computational efficiency.

scholarly journals Numerical Models of the Connection of Thin-Walled Z-Profile Roof Purlins

Materials ◽  
2021 ◽  
Vol 14 (21) ◽  
pp. 6573
Author(s):  
Přemysl Pařenica ◽  
Petr Lehner ◽  
Jiří Brožovský ◽  
Martin Krejsa
Keyword(s):  
Cross Section ◽  
Numerical Models ◽  
Element Model ◽  
Cross Sectional ◽  
Physical Test ◽  
Thin Walled Structures ◽  
Practical Design ◽  
Thin Walled ◽  
Bolt Connection ◽  
Experimental Preparation

High thin-walled purlins of Z cross-section are important elements in steel wide-span structures. Their behaviour is influenced by many variables that need to be examined for every specific case. Their practical design thus requires extended knowledge of their behaviour for the possible configurations and dimensions. Numerical analysis verified by experimental investigation can thus enrich such knowledge. Numerical models have the advantage of repeatability and the ability to offer parametric changes. The parametric study presented shows a detailed description of a finite element model of thin-walled cross-sectional roof purlins connected to other roof elements. Models include various approaches to modelling bolt connection. Two schemes of purlins, with and without cleats, are presented. The results of different approaches in numerical modelling are compared with the results of a physical test on a real structure. The article shows a significant agreement in the case of specific approaches and points out the differences with others. The results can be helpful in terms of how to approach the modelling of thin-walled structures and the effective approach to experimental preparation.

Influence of the Subtended Angle on the Behavior of Folded Tape Springs

2018 ◽  
Author(s):  
Marinus G. de Jong ◽  
Werner W. P. J. van de Sande ◽  
Just L. Herder
Keyword(s):  
Finite Element ◽  
Cross Section ◽  
Strain Energy ◽  
Element Model ◽  
Constant Cross Section ◽  
Curvature Analysis ◽  
Thin Walled Structures ◽  
Constant Radius ◽  
Thin Walled ◽  
Force Generator

Tape springs are thin-walled structures with zero longitudinal and constant transverse curvature. Folding them twice and connecting both ends creates a tape loop which acts as a linear guide. When using a tape spring with a non-constant cross-section, a force generator can be created. At this time there is insufficient understanding of the influence of the tape spring’s cross-section on its behavior. This study investigates the influence of the subtended angle on the tape spring’s behavior, especially the energy distribution and the fold radius. A tape spring is once folded in a finite element model. By performing a curvature analysis of this folded geometry, the different regions within a tape spring are identified. This information is used to identify the amount of strain energy of each region. Finally, the fold radius and fold angle are determined by analyzing the geometry of the bent region. The analysis showed that the energy within the transition regions cannot be neglected. The energy within these regions as ratio of the total energy and the length of the transition regions both increase with the subtended angle. It is also shown that the fold radius is not constant when the subtended angle is small. Therefore, when designing a force generator using tape loops, the energy within the transition regions should be taken into account. The subtended angle should not be small to ensure a constant radius.

scholarly journals On the Directivity of Acoustic Waves Generated by the Angle Beam Wedge Actuator in Thin-Walled Structures

Actuators ◽  
2019 ◽  
Vol 8 (3) ◽  
pp. 64 ◽  
Author(s):  
Sergey Shevtsov ◽  
Valery Chebanenko ◽  
Maria Shevtsova ◽  
Evgenia Kirillova ◽  
Evgeny Rozhkov
Keyword(s):  
Experimental Study ◽  
Acoustic Waves ◽  
Lamb Waves ◽  
Oscillation Amplitude ◽  
Element Model ◽  
Propagation Length ◽  
Thin Walled Structures ◽  
Plastic Panel ◽  
Thin Walled ◽  
The Waves

The paper aims to develop improved acoustic-based structural health monitoring (SHM) and nondestructive evaluation (NDE) techniques, which provide the waves directivity emitted by the angle beam wedge actuators in thin-walled structures made of plastic materials and polymeric composites. Our investigation includes the dispersive analysis of the waves that can be excited in the studied plastic panel. Its results allowed to find two kinds of generated acoustic waves—anti-symmetric Lamb waves (A0) and shear horizontally polarized SH waves (SS0). The bounds of the chosen frequency range for the experimental and numerical studies were accepted as a compromise between the desire to obtain a high defect resolution by generating short waves, their adjustable directivity, and maximum propagation length. The finite element model for the transducer was built by using the results of an actuator structure experimental study. The frequency response functions for the actuator current and oscillation amplitude of the footprint surface demonstrated good agreement. The found eigenfrequencies of the actuator’s structure were used for the numerical and experimental study of the Lamb and SH wave generation and propagation in a thin-walled plastic panel. Our results convincingly demonstrated the satisfactory directivity of the actuated waves at their excitation on the frequencies that corresponded to the natural modes of the actuator oscillation. The authors assume that an efficient use of the proposed technique for other analyzed quasi-isotropic materials and applied actuators can be provided by preliminary research using a similar approach and methods presented in this article.

Nonlinear Response of Carbon-Carbon Laminated Panels to Random Acoustic Excitation under a Gradient Temperature Field

2014 ◽  
Vol 696 ◽  
pp. 23-29 ◽  
Author(s):  
Yun Dong Sha ◽  
Hao Yuan Wang ◽  
Huan Yu
Keyword(s):  
Finite Element ◽  
Structural Integrity ◽  
Dynamic Strength ◽  
Element Model ◽  
Carbon Composite ◽  
Distribution Functions ◽  
Numerical Results ◽  
Equivalent Linearization ◽  
Element Formulation ◽  
Random Response

Future missions for aircraft will expose structures to severe thermal and acoustic loads. Efficient analysis methods for predicting nonlinear random response and fatigue life are urgently important. This paper presents a finite element model for analyzing nonlinear random dynamic behaviors of Carbon-Carbon composite panels under temperature gradients and Guassian excitations. The temperature distribution over the plate follows double sine curve. A finite element formulation combined with the equivalent linearization approach and normal mode method is established. The global system of equations is reduced to a set of nonlinear, coupled modal equations. Examples are given for an orthotropic C/C composite laminated panel at various combinations of temperatures gradients and sound pressure levels. Numerical results include RMS values of maximum deflection, time histories of deflection response and stress response, power spectrum densities, probability distribution functions and higher statistical moments. Numerical results verified all three types of panel motions for a simply supported orthotropic laminated plate: small-deflection random vibration about the initial equilibrium positions, snap-through motions between the two buckled positions, and nonlinear random response about new equilibrium positions after post-buckling. Numerical results will provide the important reference basis to aero engine structural integrity design and improving the structure dynamic strength and working life.

Nonlinear Response of Carbon-Carbon Composite Panels Subjected to Thermal-Acoustic Loadings

2011 ◽  
Vol 117-119 ◽  
pp. 876-881 ◽  
Author(s):  
Yun Dong Sha ◽  
Fei Xu ◽  
Zhi Jun Gao
Keyword(s):  
High Speed ◽  
Random Vibration ◽  
Nonlinear Response ◽  
Elevated Temperatures ◽  
Thermal Protection ◽  
Random Noise ◽  
Carbon Composite ◽  
Dynamic Responses ◽  
Composite Panels ◽  
Thin Walled

Carbon-Carbon composite materials are widely used as the surface thermal protection systems (TPS) of advanced high-speed air-craft and spacecraft. The thin-walled structures with this kind of materials would exhibit large displacement response under high-level acoustic loads and possibly display buckling at elevated temperatures. Reliable experimental data are difficult to acquire because of the high costs and difficulties with instrumentation at high acoustic intensity and elevated temperatures. Thus, in the design process greater emphasis will likely be placed on improved mathematical and computational prediction methods. Among these researches, the simulation methods for nonlinear response of thin-walled composite panels under thermo-acoustic loadings are being developed emphatically .This paper presents a nonlinear finite element model for analyzing nonlinear random dynamic behaviors of Carbon-Carbon composite panels under the combined effects of thermal and random acoustic loads. The acoustic excitation is assumed to be a band-limited Gaussian random noise and uniformly distributed over the structural surface and the thermal load is assumed to be a steady-state with different predefined temperature distribution. Three types of motion: 1) linear random vibration about one of the two buckled positions, 2) snap-through motion between the two buckled positions, and 3) nonlinear random vibration over the two thermally buckled positions can be predicted. And the dynamic response behaviors of the structures are discussed. Based on this, the influences of sound pressure level (SPL) and elevated temperatures on the dynamic responses are analyzed emphatically.

Dynamic Response of Pre/Post Buckled Thin-Walled Structure under Thermo-Acoustic Loading

2011 ◽  
Vol 80-81 ◽  
pp. 536-541 ◽  
Author(s):  
Yun Dong Sha ◽  
Ji Yong Li ◽  
Zhi Jun Gao
Keyword(s):  
Dynamic Response ◽  
Dynamic Responses ◽  
Transverse Displacement ◽  
Response Characteristics ◽  
Thin Walled Structures ◽  
Fem Method ◽  
Operating Environments ◽  
Thin Walled ◽  
Frequency Changes ◽  
High Level

Advanced aircraft and spacecraft structures are exposed to increasingly severe operating environments, including a combination of mechanical, aerodynamic, acoustic and thermal loads. Such loading conditions can cause thin-walled structures to respond in a nonlinear fashion and exhibit complex response characteristics. This paper investigates the dynamic response of pre/post buckled thin-walled structure under high level random acoustic loading. Firstly, different orders of critical buckling temperatures and modal frequencies under alternative temperatures are obtained using Finite Element Method (FEM), and the modal frequency changes in a disorder fashion are discussed in detail. Then with coupled BEM/FEM method, the dynamic responses including transverse displacement, strain and stress of a stiffened rectangular plate under thermo-acoustic loading are simulated. By comparing the response characteristics of the plate in pre/post buckled conditions, some valuable conclusions are derived, which can be used to explain the response behaviours of thin-walled structures.

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