scholarly journals Dynamic Analysis of Shells

1995 ◽  
Vol 2 (5) ◽  
pp. 413-426 ◽  
Author(s):  
Charles R. Steele ◽  
Jason A. Tolomeo ◽  
Deborah E. Zetes
Keyword(s):  
Excitation Frequency ◽  
Computer Code ◽  
Material Behavior ◽  
Shell Structures ◽  
Acoustic Excitation ◽  
Rigid Surface ◽  
Implicit Methods ◽  
Shell Surface ◽  
Fine Mesh ◽  
Broad Overview

Shell structures are indispensable in virtually every industry. However, in the design, analysis, fabrication, and maintenance of such structures, there are many pitfalls leading to various forms of disaster. The experience gained by engineers over some 200 years of disasters and brushes with disaster is expressed in the extensive archival literature, national codes, and procedural documentation found in larger companies. However, the advantage of the richness in the behavior of shells is that the way is always open for innovation. In this survey, we present a broad overview of the dynamic response of shell structures. The intention is to provide an understanding of the basic themes behind the detailed codes and stimulate, not restrict, positive innovation. Such understanding is also crucial for the correct computation of shell structures by any computer code. The physics dictates that the thin shell structure offers a challenge for analysis and computation. Shell response can be generally categorized by states of extension, inextensional bending, edge bending, and edge transverse shear. Simple estimates for the magnitudes of stress, deformation, and resonance in the extensional and inextensional states are provided by ring response. Several shell examples demonstrate the different states and combinations. For excitation frequency above the extensional resonance, such as in impact and acoustic excitation, a fine mesh is needed over the entire shell surface. For this range, modal and implicit methods are of limited value. The example of a sphere impacting a rigid surface shows that plastic unloading occurs continuously. Thus, there are no short cuts; the complete material behavior must be included.

Static and Dynamic Burst Analysis of Cylindrical Shells

2006 ◽  
Author(s):  
Liping Xue ◽  
Cunjiang Cheng ◽  
G. E. O. Widera ◽  
Zhifu Sang
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Cylindrical Shell ◽  
Three Dimensional ◽  
Element Model ◽  
Computer Code ◽  
Material Behavior ◽  
Burst Pressure ◽  
Implicit Methods ◽  
Element Method

The purpose of this paper is to determine whether the finite element method can be employed to accurately predict the burst pressure of a specific cylindrical shell subjected to internal pressure. Both static and dynamic analyses were carried out. The computer code ANSYS is employed to perform a static, nonlinear analysis (both geometry of deformation and material behavior) using three-dimensional 20 node structural solid elements. The “Newton-Raphson Method” (N-R method) and the “Arc-Length Method”, are both employed to solve the nonlinear equations. The finite element code LS-DYNA is used to generate a three-dimensional finite element model by use of eight-node brick elements for the dynamic analysis. Both explicit and implicit methods are used to simulate the dynamic response of cylinders. A comparison with various empirical equations shows that both static and dynamic finite element method simulations can be employed with sufficient accuracy to predict the burst pressure of a specific cylindrical shell.

Effects of Acoustic Excitation on a Swirling Diffusion Flame

2010 ◽  
Vol 132 (12) ◽  
Author(s):  
Michael E. Loretero ◽  
Rong F. Huang
Keyword(s):  
Flow Field ◽  
Bluff Body ◽  
Excitation Frequency ◽  
Excitation Amplitude ◽  
Mie Scattering ◽  
Flame Length ◽  
Laser Doppler Velocimeter ◽  
Scattering Method ◽  
Acoustic Excitation ◽  
Characteristic Modes

A swirling double concentric jet is commonly used for nonpremixed gas burner application for safety reasons and to improve the combustion performance. Fuel is generally spurted at the central jet while the annular coflowing air is swirled. They are normally separated by a blockage disk where the bluff-body effects further enhance the recirculation of hot gas at the reaction zone. This paper aims to experimentally investigate the behavior of flame and flow in a double concentric jet combustor when the fuel supply is acoustically driven. Laser-light sheet assisted Mie scattering method has been used to visualize the flow, while the flame lengths were measured by a conventional photography technique. The fluctuating velocity at the jet exit was measured by a two-component laser Doppler velocimeter. Flammability and stability at first fuel tube resonant frequency are reported and discussed. The evolution of flame profile with excitation level is presented and discussed, together with the reduction in flame length. The flame in the unforced reacting axisymmetric wake is classified into three characteristic modes, which are weak swirling flame, lifted flame, and transitional reattached flame. These terms reflect their primary features of flame appearances, and when the acoustic excitation is applied, the flame behaviors change with the excitation frequency and amplitude. Four additional characteristic modes are identified; e.g., at low excitation amplitudes, wrinkling flame with a blue annular film is observed because the excitation induces vortices in the central fuel jet and hence gives rise to the wrinkling of flame. The central jet vortices become larger with the increase in excitation amplitude and thus lead to a wider and shorter flame. If the excitation amplitude is increased above a certain value, the central jet vortices change the rotation direction and pacing with the annular jet vortices. These changes in the flow field induce large turbulent intensity and mixing and therefore make the flame looks blue and short. Further increase in the excitation amplitude would lift the flame because the flow field would be dramatically modified.

The local extinction and the nonlinear behaviors of a premixed methane/air flame under low-frequency acoustic excitation

2020 ◽  
Vol 34 (13) ◽  
pp. 2050138 ◽  
Author(s):  
Yongchao Sun ◽  
Mingbo Sun ◽  
Jiajian Zhu ◽  
Yang Xie ◽  
Hongbo Wang ◽  
...  
Keyword(s):  
High Speed ◽  
Excitation Frequency ◽  
Dominant Frequency ◽  
Local Extinction ◽  
Acoustic Excitation ◽  
Flame Extinction ◽  
Buoyant Force ◽  
Hot Gas ◽  
Nature Frequency ◽  
Production Zone

The local extinction and the nonlinear behavior of a premixed methane/air flame under acoustic excitation are investigated experimentally. High-speed photography and high-speed schlieren imaging are used to investigate the oscillation characteristics of the premixed methane/air flame. The flame structure shows a periodic fluctuation when the acoustic excitation is performed to the flame. The local flame extinction can be observed during the flame evolution process. During the local flame extinction process, the flame is found to be cut into two components, then the downstream one extinguishes shortly. The Particle Image Velocimetry (PIV) results suggest that the lower velocity at the separation point is one of the reasons for the flame local extinction. The flame without the acoustic excitation oscillates with a dominant frequency of 18 Hz, which is shown by the schlieren images to be related to the evolution of the hot gas around the flame driven by the buoyant force. When the acoustic excitation frequency is 100 Hz, the structure of the hot gas is destroyed, meanwhile the amplitude of the nature frequency decreases significantly. The hot gas structure appears regularly with the increasing excitation frequency. As a result, the amplitude of the nature frequency also increases gradually. Proper Orthogonal Decomposition (POD) analysis shows that the dominant frequency of the flame without the acoustic excitation is mainly caused by the evolution of the production zone of the flame and the fluctuation of the flame tip. The evolution of the production zone is driven by the buoyant force, which indicates that the result from POD method is consistent with the conclusion obtained from the high-speed schlieren images. Two dominant modes are obtained when the excitation frequencies are 100 and 200 Hz. The two modes are mainly caused by the process of the local flame extinction and the increasing flame length.

Flow Field and Vibration Behavior of Straight Transonic Compressor Cascade due to External Acoustic Excitation

2013 ◽  
Author(s):  
Manlu Li ◽  
Anping Hou ◽  
Xiaodong Yang ◽  
Mingming Zhang ◽  
Peng Wang
Keyword(s):  
Flow Field ◽  
Excitation Frequency ◽  
Experimental Studies ◽  
Attack Angle ◽  
Mode Shapes ◽  
Acoustic Excitation ◽  
Fe Model ◽  
Compressor Cascade ◽  
Time Step ◽  
Vibration Behavior

A fluid-structure coupled approach is utilized to study the influence of external acoustic excitation on straight compressor cascade flow field and blade vibration behavior. Interaction between fluid and structure are dealt with in a coupled manner, based on the interface exchange of information between the aerodynamic and structural model. The computation fluid mesh is updated at every time step with an improved algebraic method. The flow field of cascade with/without external acoustic excitation is carried out using a 3D unsteady CFD model based on moving boundary way, as well as some experimental studies based on transonic wind tunnel. Then coupled with blade FE model, mode shapes, frequencies, vibration stress and the structural deformations of blade are identified. The performance of the cascade is obtained by computational and experimental ways, consistency of numerical and test results shows that the numerical model is suitable. The numerical results show that acoustic excitation has a greater impact on negative and designed attack angle in contrast to high positive attack angle. The cascade wake and blade surface pressure frequency characteristic are changed and the main frequency is almost the same as the acoustic excitation frequency. Compared results with no excitation, the vibration characteristics of the blade is changed, also the vibration behavior is sensitive to the excitation amplitude and frequency.

Coupling Continuum and Discrete Models of Materials with Microstructure: A Multiscale Algorithm

2010 ◽  
Vol 638-642 ◽  
pp. 2755-2760 ◽  
Author(s):  
Vittorio Sansalone ◽  
Patrizia Trovalusci
Keyword(s):  
Computer Code ◽  
Material Behavior ◽  
Discrete Models ◽  
Specific Class ◽  
Homogenization Procedure ◽  
Nonlinear Fem ◽  
Macroscopic Scale ◽  
Macroscopic Models ◽  
Multiscale Algorithm ◽  
Gauss Points

The importance of a multiscale modeling to describe the behavior of materials with microstructure is commonly recognized. In general, at the different scales the material may be described by means of different models. In this paper we focus on a specific class of materials for which it is possible to identify (at the least) two relevant scales: a macroscopic scale, where continuum mechanics applies; and a microscale, where a discrete model is adopted. The conceptual framework and the theoretical model were discussed in previous work. This approach is well suited to study multifield and multiphysics problems. We present here the multiscale algorithm and the computer code that we developed to implement this strategy. The solution of the problem is searched for at the macroscale using nonlinear FEM. During the construction of the FE solution, the material behavior needs to be described at Gauss points. This step is performed numerically, formulating an equivalent problem at the microscale where the inner structure of the material is described through a lattice-like model. The two scales are conceptually independent and bridged together by means of a suitable localization-homogenization procedure. We show how different macroscopic models (e.g. Cauchy vs. Cosserat continuum) can be easily recovered starting from the same discrete system but using different bridges. The interest of this approach is shown discussing its application to few examples of engineering interest (composite materials, masonry structures, bone tissue).

The Effect of Acoustic Excitation on Boundary Layer Separation of a Highly Loaded LPT Blade

2012 ◽  
Author(s):  
Chiara Bernardini ◽  
Stuart Benton ◽  
Jeffrey P. Bons
Keyword(s):  
Boundary Layer ◽  
Shear Layer ◽  
Separation Bubble ◽  
Active Flow Control ◽  
Excitation Frequency ◽  
Acoustic Excitation ◽  
Intensity Level ◽  
Inlet Section ◽  
Suction Surface ◽  
Highly Loaded

An experimental investigation of the effect of acoustic excitation on the boundary layer development of a highly loaded low-pressure turbine blade at low-Reynolds number is investigated. The aim of this work is to study the effect of excitation at select frequencies on separation which could give indications about active flow control exploitation. The front-loaded L2F blade is tested in a low-speed linear cascade. The uncontrolled flow presents a separation bubble on the suction surface at Reynolds numbers below 40,000. For these conditions, the instability of the shear layer is documented using hot-wire anemometry. A loudspeaker upstream of the cascade is directed towards the passage inlet section. A parametric study on the effect of amplitude and frequency is carried out. The effect of the excitation frequency is observed to delay separation for a range of frequencies. However, the control authority of sound is found to be most effective at the fundamental frequency of the shear layer. The amplitude of perturbation is significant in the outcome of control until a threshold value is reached. PIV measurements allow a deeper understanding of the mechanisms leading to the reduction of separation. Data has been acquired with a low inlet turbulence level (<1%) in order to provide a cleaner environment which magnifies the effects of the excitation frequency, and with an increased turbulence intensity level of 3% which is representative of more typical engine values. Integrated wake loss values are also presented to evaluate the effect on blade performance.

scholarly journals HITCAN for Actively Cooled Hot-Composite Thermostructural Analysis

1992 ◽  
Vol 114 (2) ◽  
pp. 315-320
Author(s):  
C. C. Chamis ◽  
P. L. N. Murthy ◽  
S. N. Singhal ◽  
J. J. Lackney
Keyword(s):  
Material Properties ◽  
Metal Matrix ◽  
Composite Structures ◽  
Local Stress ◽  
Computational Procedure ◽  
Computer Code ◽  
Thermomechanical Properties ◽  
General Purpose ◽  
Material Behavior ◽  
Process Effects

A computer code, HITCAN (High Temperature Composite Analyzer) has been developed to analyze/design hot metal matrix composite structures. HITCAN is a general purpose code for predicting the global structural and local stress-strain response of multilayered (arbitrarily oriented) metal matrix structures both at the constituent (fiber, matrix, and interphase) and the structure level and including the fabrication process effects. The thermomechanical properties of the constituents are considered to be nonlinearly dependent on several parameters, including temperature, stress, and stress rate. The computational procedure employs an incremental iterative nonlinear approach utilizing a multifactor-interaction material behavior model, i.e., the material properties are expressed in terms of a product of several factors that affect the properties. HITCAN structural analysis capabilities (static, load stepping—a multistep static analysis with material properties updated at each step, modal, and buckling) for cooled hot structures are demonstrated through a specific example problem.

The Effect of Acoustic Excitation on Boundary Layer Separation of a Highly Loaded LPT Blade

2013 ◽  
Vol 135 (5) ◽  
Author(s):  
Chiara Bernardini ◽  
Stuart I. Benton ◽  
Jeffrey P. Bons
Keyword(s):  
Boundary Layer ◽  
Shear Layer ◽  
Separation Bubble ◽  
Active Flow Control ◽  
Excitation Frequency ◽  
Acoustic Excitation ◽  
Intensity Level ◽  
Inlet Section ◽  
Suction Surface ◽  
Highly Loaded

An experimental investigation of the effect of acoustic excitation on the boundary layer development of a highly loaded low-pressure turbine blade at low-Reynolds number is investigated. The aim of this work is to study the effect of excitation at select frequencies on separation which could give indications about active flow control exploitation. The front-loaded L2F blade is tested in a low-speed linear cascade. The uncontrolled flow presents a separation bubble on the suction surface at Reynolds numbers below 40,000. For these conditions, the instability of the shear layer is documented using hot-wire anemometry. A loudspeaker upstream of the cascade is directed towards the passage inlet section. A parametric study on the effect of amplitude and frequency is carried out. The effect of the excitation frequency is observed to delay separation for a range of frequencies. However, the control authority of sound is found to be most effective at the fundamental frequency of the shear layer. The amplitude of perturbation is significant in the outcome of control until a threshold value is reached. PIV measurements allow a deeper understanding of the mechanisms leading to the reduction of separation. Data has been acquired with a low inlet turbulence level (<1%) in order to provide a cleaner environment which magnifies the effects of the excitation frequency, and with an increased turbulence intensity level of 3% which is representative of more typical engine values. Integrated wake loss values are also presented to evaluate the effect on blade performance.

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