Evolution of Subduction Cusps From the Perspective of Trench Migration and Slab Morphology

The geometries of trenches vary worldwide due to continuous plate boundary reorganization. When two trenches intersect to generate a corner, a subduction cusp is formed. Although subduction cusps are frequently observed throughout historical plate movement reconstructions, few studies have been conducted to explore the controlling factors of trench migration and slab morphology along subduction cusps. Here, we use a 3-D dynamic subduction model to explore the influence of the overriding plate strength, initial slab-pull force, and initial cusp angle on the evolution of subduction cusps. Our numerical model results suggest the following: 1) subduction cusps have a tendency to become smooth and disappear during the subduction process; 2) the slab dip angle is smallest in the diagonal direction of the subduction cusp, and a larger cuspate corner angle leads to a larger slab dip angle; 3) the asymmetric distribution of the overriding plate strength and initial slab-pull force determine the asymmetric evolutionary pathway of subduction cusps. Our results provide new insights for reconstructing the evolution of subduction cusps from seismological and geological observations.

Trajectory Design for the ESA LISA Mission

The three Laser Interferometer Space Antenna (LISA) spacecraft are going to be placed in a triangular formation in an Earth-trailing or Earth-leading orbit. They will be launched together on a single rocket and transferred to that science orbit using Solar Electric Propulsion. Since the transfer Δv depends on the chosen science orbit, both transfer and science orbit have been optimised together. For a thrust level of 90 mN, an allocation of 1092 m/s per spacecraft is sufficient for an all-year launch in 2034. For every launch month a dedicated science orbit is designed with a corner angle variation of 60° ± 1.0° and an arm length rate of maximum 10 m/s. Moreover, a detailed navigation analysis of the science orbit insertion and the impact on insertion errors on the constellation stability has been conducted. The analysis shows that Range/Doppler measurements together with a series of correction manoeuvres at the beginning of the science orbit phase can reduce insertion dispersions to a level where corner angle variations remain at about 60° ± 1.1° at 99% C.L. However, the situation can become significantly worse if the self-gravity accelerations acting during the science orbit phase are not sufficiently characterised prior to science orbit insertion.

Study on Film Cooling Performance of Round Hole Embedded in Different Shaped Craters and Trenches

Film cooling effectiveness can be improved significantly by embedding a round hole in trenches or craters. In this study, film cooling performances of a transverse trench, W-shaped trench and elliptic trench were compared and analyzed in detail. The CFD models for trench film cooling were established and validated via the experimental results. Inside the transverse trench, a pair of recirculating vortices is formed, which promotes the coolant spreading in a lateral direction. The decrease of trench width and increase of trench depth both improve the film cooling effectiveness of the transverse trench. For the W-shaped trench, the guide effect of the corner angle further improves the lateral spreading capability of coolant and generates higher cooling effectiveness than a transverse trench with the same depth and width. The flow characteristics of the elliptic trench are similar to that of the round hole, and the kidney vortex pair takes a dominant role in the flow fields downstream of the coolant exit. Accordingly, the elliptic trench generates the worst cooling performance in these shaped trenches. The increase of trench depth and decrease of trench width both result in an increase of the discharge coefficient for trench film cooling. For the W-shaped trench, the increase of the corner angle causes a decrease of the discharge coefficient. For the elliptic trench, the discharge coefficient increases with the decrease of the elliptic aspect ratio (major axis/minor axis).

FE Simulation Investigation of Magnesium Alloy by Equal Channel Angular Processing

Magnesium alloy is one of the structure metals of great potential. The hcp structure makes its plasticity is poor at room temperature, which severely limits the development of magnesium alloy. Magnesium alloy plastic problem can be resolved through grain refinement method, and equal channel angular processing is one of the more effective methods of grain refinement. In this paper, two-dimensional dynamic simulation of equal channel angular processing for magnesium alloy were done with the finite element software. The deformation of magnesium alloy was analyzed when die angle and die corner angle were different. The results show that: in the main deformation zone, when die angles were different, the sample deformation in the horizontal direction is very uniform. But in the sample longitudinally direction, the greater the die angle, the more uniform the sample deformation. Die corner angle has no significant effect on the uniformity of the longitudinally deformation of the sample, but its affects the size of the dead zone and sample warpage.

Amplification and structure of streamwise-velocity fluctuations in compression-corner shock-wave/turbulent boundary-layer interactions

In this work, we study the effect of the compression-corner angle on the streamwise turbulent kinetic energy (sTKE) and structure in Mach 2.8 flow. Krypton tagging velocimetry (KTV) is used to investigate the incoming turbulent boundary layer and flow over$8^{\circ }$,$16^{\circ }$,$24^{\circ }$and$32^{\circ }$compression corners. The experiments were performed in a 99 %$\text{N}_{2}$and 1 % Kr gas mixture in the Arnold Engineering Development Complex (AEDC) Mach 3 Calibration Tunnel (M3CT) at$Re_{\unicode[STIX]{x1D6E9}}=1750$. A figure of merit is defined as the wall-normal integrated sTKE ($\overline{\text{sTKE}}$), which is designed to identify turbulence amplification by accounting for the root-mean-squared (r.m.s.) velocity fluctuations and shear-layer width for the different geometries. We observe that the$\overline{\text{sTKE}}$increases as an exponential with the compression-corner angle near the root when normalized by the boundary-layer value. Additionally, snapshot proper orthogonal decomposition (POD) is applied to the KTV results to investigate the structure of the flow. From the POD results, we extract the dominant flow structures and compare each case by presenting mean-velocity maps that correspond to the largest positive and negative POD mode coefficients. Finally, the POD spectrum reveals an inertial range common to the boundary-layer and each compression-corner flow that is present after the first${\approx}10$dominant POD modes.

Differential photothermal and photodynamic performance behaviors of gold nanorods, nanoshells and nanocages under identical energy conditions

The corner angle structure of Au nanostructures could more efficiently convert the photon energy into the photodynamic performance.

Computational Fluid Dynamics Simulations in Flow Past Arrays of Finite Plate: Marine Current Energy Harvesting Applications

Computational fluid dynamics simulations have been conducted for flows past two finite tandem plates at Reynolds number of 50,000. Large Eddy Simulations (LES) were employed in two and three-dimensional geometries to study the interference between tandem plate pair. In order to study the effects of plate corner angle on the flow field and drag forces, two different plate end corners, 90° and a sharp 45° corner angle, were also investigated. The switching from 90° to 45° corners complicate the flow pattern, increase the mean value of drag force and the fluctuations of the drag on the plate. As vortices shed from the upstream plate and reached close proximity to the face of the downstream plate, the vortex cores deformed highly. This behavior reduces the drag coefficient in the downstream plate. Drag coefficient was higher in the 45° case, for both the up and downstream plates by 5% and 10% respectively. Drag coefficient of downstream is recovered almost fully in the 45° case with just 3% difference from the upstream compared to 7% difference in 90° case. Lagrangian Coherent structures were identified and presented in a two-dimensional geometry. This gave a better understanding of the wake flow structure and their influence on the hydrodynamic loading on plates. Contours of vorticity fields and iso-surfaces of Q-criterion, and pressure distribution around the plates were also presented and discussed.