Applied Mechanics and Materials Vols. 152-154

Abstract: In the conventional seismic data time-frequency analysis, the wavelet transform, wigner ville distribution and so on, cannot meet the high precision time-frequency analysis requirements because of uncertainty principle and cross-term interference. The recently popular Hilbert-Huang transform (HHT) although overcomes these conventional methods’ deficiencies; it still has some unsolved deficiencies due to the theory imperfect. This paper focuses on an improved HHT so as to ameliorate the defect of original HHT. First of all, the wavelet packet transform (WPT) as the preprocessing will be used to the inspected signal, to get some narrow band signals. Then use the empirical mode decomposition (EMD) on the narrow band signals and get the real intrinsic mode function (IMF) by the method of correlation coefficient. From the numerical study and comparison of improved HHT, wavelet transform and HHT, it proves the validity and advantages of this improved method. At last, the improved HHT is applied to marine seismic data by the spectrum decomposition technology, and it well reveals the low frequency shadow phenomenon of the reservoir. The results show that this new method has effectiveness and feasibility in seismic data spectrum decomposition.

Abstract: Gray cast iron specimen was heated to a fixed temperature with high frequency induction heating equipment, then was cooled to room temperature by spraying water to the heated surface. This process was repeated until a crack whose length exceeds 3mm appeared. Transient cyclic heat transfer and stress-strain FEA analysis was conducted to obtain specimen’s stress-strain state, then different LCF life prediction methods based on strain and energy were presented and contrasted, and results showed modified dissipated energy method with maximal hydrostatic pressure was more accurate than other methods. With the help of modified dissipated energy method, the relationship between thermal shock life, highest cooling temperature and cooling speed was studied, and the effect law of highest cooling temperature and cooling heat transfer coefficient on life was obtained.

Abstract: In this paper, the finite element method is employed in conjunction with the abductive network to predict the optimum blank contour of an inner elliptic flange with unevenness in the flanging process. Different flange heights combined with various aspect ratios of the inner elliptic flange are taken into account as the process parameters in this study. A finite element-based code is utilized to investigate the material flow characteristics under different process parameters, and the abductive network is then employed to synthesize the data sets obtained from numerical simulations, thus establishing a predictive model. From this model, an optimal blank contour for producing an elliptic inner flange with unevenness can be found.

Abstract: In order to study the rules of pressure fluctuation and the radial force under different positions in a centrifugal pump with low specific speed, and to find the relationship between each other, the three-dimensional ,unsteady Reynolds-averaged Navier-stokes equations with shear stress transport turbulent models were solved. The pressure fluctuation was obtained. The results showed that the pressure fluctuations were visible. The pressure fluctuations in the volute were relatively low at the design flow rate condition. The blade passing frequency dominates the pressure fluctuations, high frequency contents were found on the outlet of impeller but no high frequency information occured in casing. The radial force on the impeller was unsteady especially at the small flow rate.

Abstract: Comparing with the needles having been studied previously, an articulated needle is more flexible and easier to be steered. In this paper, the sections of an articulated needle are assumed as rigid rods, and an articulated needle is simplified as a spatial linkage mechanism with open link chain. The positions and poses of needle sections are analyzed using the kinematic principle of series robots. The transformation matrixes of positions and pose of needle sections are calculated. A series of coordinate positions of needle sections are got and used to analyze the inserting trajectories of an articulated needle.

Abstract: Needle is a kind of basic medical instruments in minimally invasive surgery. A thin and long needle is inserted into a human body through the skin to perform diagnosis and treatment tasks. In order to improve the steerability of a needle, articulated needle is proposed in this paper. An articulated needle consists of a head with a bevel-tip, several articulations and several sections. Articulations are much easier to be bent, which allows proposed articulated needle to be more easily controlled to achieve a complex curved trajectory. The structure of the articulated needle is investigated for improving its bending performance. The influences of the angle of bevel-tip, the sectional dimension of sections, the number of articulations, the maximum bending angle of articulations, and the distribution of articulations on the bending performance of the needle are studied, which provide the basis for path planning and navigation of an articulated needle.

Abstract: When the magnetic articulated needle is inserting, the magnetic field which can produce the magnetic force of variable direction is required in order to implement the magnetic navigation in three-dimensional space. The paper puts forward a method for generating three-dimensional magnetic field based on the rotaion and translation of multiple permanent magnets. In this method, multiple permanent magnets form a circumference array. Every permanent magnet can rotate around the spin axis of itself in the array plane and move along the direction vertical to the array plane. Thus, in the array center, a magnetic fied which can produce the uniform magnetic flux density is obtained. The direction of magnetic fied is controllable in three-dimensional space and the magnitude of magnetic flux density is variable in a certain range. The simulations by ANSYS verify the feasibility of the proposed method.

Abstract: A simple two-dimensional shear deformable finite beam element is developed in order to examine the effect of the high order interpolation on the modes of deformation of the beam cross section using the ANCF finite element. The new element allows for effect of warping that cannot be captured using previously introduced ANCF beam elements, and relaxes the assumption of planar cross section. The displacement field of the new element is assumed to be cubic in the axial direction and quadratic in the transverse direction. Using this displacement field, new shape functions are formulated and include the quadratic of the transverse direction instead of the linear expression. The displacement gradient and transverse strain component obtained using the new higher order element are introduced. Numerical example is presented in order to compare the results obtained using the new finite element and the results obtained using previously developed ANCF finite element. The results reveal that the cross section remains as a curve surface not a planar one.

Abstract: This particular work consider a pressurized vessel typically made of high strength low alloy steel and containing the geometric misalignment at the cylinder-to-cylinder junction. This misalignment produce in the vessel’s structure is because of girth weld that is evident in most of the fabrication of such type of structures apart from other factors which is beyond the scope of this study. This study evaluates the geometrical effects of mismatch on the structural integrity of the pressure vessel and prediction of stresses at the affected area of the cylinder. Analytical and Finite Element (FE) approaches are employed to analyze the configuration. FE analysis is performed by the use of ANSYS on one quarter of the structure due to symmetry. FE results are also compared with the analytical results of different authors. In addition, maximum allowable mismatch is also determined and is a part of this study.

Abstract: The nonlinear problem of large deflection of an elastically-bossed layered plate under pretension due to lateral load is studied. The approach follows von Karman plate theory for large deflection for a symmetrically layered isotropic case. The thus derived nonlinear governing equations are solved using a numerical finite difference method with the aid of an iteration scheme. For a nearly monolithic plate with a thin boss, the obtained solutions correlate well with those available in literature for a single-layered flat plate, thus validates the presented approach. For three layered symmetric plates made of typical silicon based materials, various initial tension and lateral pressure are implemented. The results indicate that, edge behavior may appear at both the boss edge and the clamped end of the plate, thereby revealing severe variations for the structural responses. Varying the central boss size and relative thickness may have a sensible influence upon the behavior of the bossed layered plate. Furthermore, lateral pressure appears to have a sensible effect upon the nonlinear behavior of the bossed layered plate. For a relatively large initial tension, however, the pretension effect dominates, yielding a total membrane behavior for the bossed plate, regardless of the size of the center boss, except in the vicinity of the clamped edge.