Flame four-dimensional deflection tomography with compressed-sensing-revision reconstruction

Deflection tomography with limited angle projections was investigated to visualize a premixed flame. A projection sampling system for deflection tomography was used to obtain chronological deflectogram arrays at six view angles with only a pair of gratings. A new iterative reconstruction algorithm with deflection angle compressed-sensing revision was developed to improve reconstruction-distribution quality from incomplete projection data. Numerical simulation and error analysis provided a good indication of algorithm precision and convergence. In the experiment, 150 fringes were processed, and temperature distributions in 20 cross-sections were reconstructed from projection data in four instants. Four-dimensional flame structures and temperature distributions in the flame interior were visualized using the visualization toolkit. The experimental reconstruction was then compared with the result obtained from computational fluid dynamic analysis.     

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导出了用梁端边界条件表示的梁段挠曲线方程,阐述了用此挠曲线方程可十分方便地递 推写出梁各段挠曲线表达式,避免了确定烦琐的积分常数,对于分段较多的连续梁,尤 其方便.     

Shear deformable finite beam elements for composite box beams

The shear deformable thin-walled composite beams with closed cross-sections have been developed for coupled flexural, torsional, and buckling analyses. A theoretical model applicable to the thin-walled laminated composite box beams is presented by taking into account all the structural couplings coming from the material anisotropy and the shear deformation effects. The current composite beam includes the transverse shear and the restrained warping induced shear deformation by using the first-order shear deformation beam theory. Seven governing equations are derived for the coupled axial-flexural-torsional-shearing buckling based on the principle of minimum total potential energy. Based on the present analytical model, three different types of finite composite beam elements, namely, linear, quadratic and cubic elements are developed to analyze the flexural, torsional, and buckling problems. In order to demonstrate the accuracy and superiority of the beam theory and the finite beam elements developed by this study,numerical solutions are presented and compared with the results obtained by other researchers and the detailed threedimensional analysis results using the shell elements of ABAQUS. Especially, the influences of the modulus ratio and the simplified assumptions in stress–strain relations on the deflection, twisting angle, and critical buckling loads of composite box beams are investigated.     

A Green's function approach to the deflection of a FGM plate under transient thermal loading

Summary  Green's function approach is adopted for analyzing the deflection and the transient temperature distribution of a plate made of functionally graded materials (FGMs). The governing equations for the deflection and the transient temperature are formulated into eigenvalue problems by using the eigenfunction expansion theory. Green's functions for solving the deflection and the transient temperature are obtained by using the Galerkin method and the laminate theory, respectively. The eigenfunctions of Green's function for the deflection are approximated in terms of a series of admissible functions that satisfy the homogeneous boundary conditions of the plate. The eigenfunctions of Green's function for the temperature are determined from the continuity conditions of the temperature and the heat flux at interfaces. Received 9 October 2000; accepted for publication 3 April 2001     

Refined Series Methodology for the Fully Coupled Thin-Walled Laminated Beams Considering Foundation Effects

The refined power series solutions are presented for the coupled static analysis of thin-walled laminated beams resting on elastic foundation. For this purpose, the elastic strain energy considering the material and structural coupling effects and the energy including the foundation effects are constructed. The equilibrium equations and the force-displacement relationships are derived from the extended Hamilton's principle, and the explicit expressions for displacement parameters are presented based on power series expansions of displacement components. Finally, the member stiffness matrix is determined by using the force-displacement relationships. For comparison, the finite element model based on the Hermite cubic interpolation polynomial is presented. In order to verify the accuracy and the superiority of the laminated beam element developed by this study, the numerical solutions are presented and compared with results obtained from the regular finite beam elements and the ABAQUS's shell elements. The influences of the fiber angle change and the boundary conditions on the coupled behavior of laminated beams with mono-symmetric I-sections are investigated.     

Multi-beam method to increase the stability of bridge deflection measurement

The main limitation to the accuracy of the detection of a bridge deflection using laser-based optical solutions is atmospheric turbulence because of the laser beam propagation in ground proximity. The multi-beam method is presented to increase the stability of bridge deflection measurement. It is based on the use of a four-beam optical system and a subpixel resolution algorithm for the measurement of the deflection of a laser beam that propagates through the system. To obtain accurate results, different algorithms for measuring the position of the deflected beam in different optical systems are tested and compared. Based on this comparison, the four-beam method based on the macropixels iteration centroid and four-beam optical system is selected, and an accuracy of 0.16 pixels is obtained by the determination of the beam position in our setup. The proposed method is adopted to detect the bridge deflection and an accuracy of 0.01 mm is gained when the scintillation index C_n² is 3×10⁻⁴ m^−2/3.     

棱镜型光热偏振光谱法

提出了一种高灵敏度的棱镜型光热偏转光谱法,给出了系统的理论分析,导出了由泵浦光引起的探测光的偏向角表达式.并与普通型光热偏转技术作了比较,理论分析结果表明,棱镜型光热偏转检测方法比普通型光热偏转技术具有更高的灵敏度.     

Evaluation of micromechanical properties of buckled SiOxNy-loaded membranes by combining the Twyman–Green interferometry with nanoindentation and point-wise deflection technique

In view of applications in MOEMS technology, an interferometric technique has been developed for determination of micromechanical properties of PECVD-deposited SiO_xN_y thin films. By combining the Twyman–Green interferometry with nanoindentation technique, an original “point-wise” deflection method is proposed, particularly appropriated to measure the residual stress in the case of silicon membranes compressively prestressed by SiO_xN_y deposition. For such SiO_xN_y membranes, operating at the first mode of buckling, the nonindentation permits the extraction of Young's modulus and interferometry measures the out-of-plan displacements, respectively. The proposed point-wise deflection technique combines both the interferometric and Young's modulus data, giving the access to the distribution of residual stress versus the optical quality of SiO_xN_y films. The residual stress is monitored as a function of the refractive index of SiO_xN_y, establishing the relationship between the optical and micromechanical properties of deposited thin films. High measuring accuracy and resolution have been demonstrated, allowing measurements to be used to enhance PECVD process control     

Using RGB filters and a circularly polarized system to measure the deflection radius of optically anisotropic-polymeric substrates with a sub-grayscale resolution

Transparent optically anisotropic substrates (TOASs) are a crucial component in flexible electronics. Moreover, knowing the deflection radii of TOASs is essential to estimate the residual stresses of the thin films deposited on them. This paper proposes a novel measurement method to measure the deflection radii of polyimide (PI) substrates. Red, green, and blue filters and a circularly polarized system were used in the proposed method to investigate the influence of measurement precision on the wavelength of light adopted. Moreover, the image averaging technique was adopted to significantly reduce the noise in the fringe. Thus, the proposed method could be performed using only one set of image information and the measurement resolution could be improved to the sub-grayscale order. The experimental results reveal that red light can be adopted to precisely measure the deflection radii of PI substrates (error of 2.90%) However, large errors are caused when green light is used (22.35%). The experimental results reveal that blue light cannot be used to obtain any interferometric fringe patterns to calculate the deflection radius.     

Suppression of Ag deposition by Ar gas in mtorr range and its implication to mitigation of impurity deposition on first mirrors

We observe that Ar gas confined in a tube maintained at a pressure higher than 10 mtorr by a baffled duct is very effective in minimizing the deposition of incoming Ag particles onto the surface of quartz crystal microbalance (QCM) in the tube. Ar gas is introduced into the tube and the gas flow to the main chamber is minimized by a baffled duct. In this way, the tube pressure of 10 mTorr or higher is achieved. The pressure is found to be enough to suppress the deposition of nearly 97% Ag particles onto the QCM in the tube. The suppression of the Ag deposition is successfully explained by reduced mean-free path at the high pressure in the tube. We propose that the present approach can be very promising in the mitigation of impurity particles on first mirrors in thermonuclear reactors.