Weak discontinuities in one-dimensional compressible nonideal gas dynamics

This article concerns the study of various parameter effects on the propagation of weak discontinuities by using the method of characteristics. Analytical solutions of the quasi-linear system of hyperbolic partial differential equations (PDEs) are obtained and examined the evolutionary behavior of shock in the characteristic plane. The general behavior of solutions to the Bernoulli equation, which determines the evolution of weak discontinuity in a nonlinear system, is studied in detail. Also, we discuss the formation and distortion of compressive and expansive discontinuities under the van der Waals parameter effect and small particles for planar and cylindrical symmetric flow. The comparison between planar flow and cylindrical symmetric flow is studied under the influence of nonidealness and mass fraction of dust particles. It is found that the compressive waves become shock after a certain lapse of time. The medium considered here is the mixture of van der Waals gas with small dust particles.

A METHOD FOR MONITORING BULGE OF ANCIENT CITY WALL AFTER REPAIR

The ancient city wall is affected by factors such as environment and man-made factors, and the formed bulging disease is particularly prominent, and even caused irreversible damage to the ancient city wall. Therefore, the bulging monitoring after the repair of the city wall should be the top priority of the deformation monitoring of the city wall. This paper proposes a new plan for monitoring the bulge after the repair of the city wall. According to the point cloud data before the repair, the characteristic plane is fitted to determine the bulge range of the city wall, and then observation signs are placed on the surface of the repaired city wall at the corresponding location where the bulging deformation is severe. By using a total station to monitor the space coordinates of the observation signs, the deformations perpendicular to the wall can be obtained through coordinate conversion, and then the bulging of the repaired city wall can be determined. The actual application results show that this method can effectively monitor the swelling of the ancient city wall after the repair.

Experimental and computational modeling of bulk residual stress for aeronautical components with distinct geometries

To predict and minimize machining distortion in the manufacturing process, bulk residual stresses in aeronautical components with distinct geometries were investigated via experimental mechanics and numerical simulation. The residual stress state was appropriately simplified according to geometric/processing feathers and deformation patterns of the investigated parts. In each case study, an optimal experimental method was selected to reconstruct the concerned stress tensor. Thereafter, qualitative comparison and validation were performed using cross-method verification and/or numerical simulation. Additionally, the spatial resolution and distribution characteristics of the residual stress were analyzed and discussed in detail. The results revealed that thermal and mechanical nonuniformity caused by material processing is the main source of bulk residual stress in the investigated components. Furthermore, the effectiveness of the contour method on the measurement of different geometric components was verified by numerical simulation. Combining the accurate measurement of the characteristic plane and the appropriate numerical simulation of the global stress field, an engineering-oriented approach for full-field stress evaluation was proposed. This research can provide valuable engineering guidance and suggestions for stress evaluation and distortion analysis prior to manufacturing of integral structures.

Structural, Morphological and Elemental Analysis of Selectively Etched and Exfoliated Ti3AlC2 MAX Phase

In the present research major focus is on the synthesis of materials that can be easily used in small portable devices and as energy storage devices. Here we focused on a new family of 2D materials Ti3C2 (MXenes). Ti3AlC2 (MAX phase) was intercalated using selective etching of Aluminium present in the MAX phase. The etching was done using HF in combination with HCl followed by delaminated in DMSO medium using ultrasonication. The synthesized samples were physically characterized via XRD, SEM and EDX. The XRD spectra confirms the formation of MXene through its characteristic plane (002) arising at 2θ~9°. The morphological study revealed the stacked layered sheet like structure obtained through SEM. The elemental confirmation of removal of Al was done using EDX spectroscopy.

Position-singularity analysis of a special class of the Stewart parallel mechanisms with two dissimilar semi-symmetrical hexagons

SUMMARYIn this paper, for a special class of the Stewart parallel mechanism, whose moving platform and base one are two dissimilar semi-symmetrical hexagons, the position-singularity of the mechanism for a constant-orientation is analyzed systematically. The force Jacobian matrix [J]T is constructed based on the principle of static equilibrium and the screw theory. After expanding the determinant of the simplified matrix [D], whose rank is the same as the rank of the matrix [J]T, a cubic symbolic expression that represents the 3D position-singularity locus of the mechanism for a constant-orientation is derived and graphically represented. Further research shows that the 3D position-singularity surface is extremely complicated, and the geometric characteristics of the position-singularity locus lying in a general oblique plane are very difficult to be identified. However, the position-singularity locus lying in the series of characteristic planes, where the moving platform coincides, are all quadratic curves compromised of infinite many sets of hyperbolas, four pairs of intersecting lines and a parabola. For some special orientations, the quadratic curve can degenerate into two lines or even one line, all of which are parallel to the ridgeline. Two theorems are presented and proved for the first time when the geometric characteristics of the position-singularity curves in the characteristic plane are analyzed. Moreover, the kinematic property of the position-singularity curves is obtained using the Grassmann line geometry and the screw theory. The theoretical results are demonstrated with several numeric examples.

A note on the correspondence between the x, t-plane and the characteristic plane in a problem of interaction of plane waves of finite amplitude

The head-on interaction, in the one-dimensional, unsteady isentropic flow of a perfect gas, of a simple compression wave and a simple expansion wave is studied by considering typical examples. The physical aspect of the problem is discussed in (1); in this note the possibility of shock formation is ignored, and the correspondence defined by the complete mathematical solution of the equations of isentropic flow between the x, t-plane and the plane of the characteristic variables is elucidated.The solution is distinguished by the appearance of two limit lines and a second-order limit point where they meet. It is found that the image of the characteristic plane in the x, t-plane is four-sheeted; all sheets overlap each other, but each covers only part of the plane, and the only point common to all sheets is the second-order limit point, where both limit lines are cusped (§ 3·1).The solution also contains an edge of regression, and a discussion of the properties of this type of singularity will be found in §§ 2 and 2·1.