Full-automatic high-precision scene 3D reconstruction method with water-area intelligent complementation and mesh optimization for UAV images

ABSTRACTFast and high-precision urban scene 3D modeling is the foundational data infrastructure for the digital earth and smart cities. However, due to challenges such as water-area matching difficulties and issues like data redundancy and insufficient observations, existing full-automatic 3D modeling methods often result in water-area missing and many small holes in the models and insufficient local-model accuracy. To overcome these challenges, full-automatic high-precision scene 3D reconstruction method with water-area intelligent complementation on depth maps and mesh optimization is proposed. Firstly, SfM was used to calculated image poses and PatchMatch was used to generated initial depth maps. Secondly, a simplified GAN extracted water-area masks and ray tracing was used achieve high-precision auto-completed water-area depth values. Thirdly, fully connected CRF optimized water-areas and arounds in depth maps. Fourthly, high-precision 3D point clouds were obtained using depth map fusion based on clustering culling and depth least squares. Then, mesh was generated and optimized using similarity measurement and vertex gradients to obtain refined mesh. Finally, high-precision scene 3D models without water-area missing or holes were generated. The results showed that: to compare with the-state-of-art ContextCapture, the proposed method enhances model completeness by 14.3%, raises average accuracy by 14.5% and improves processing efficiency by 63.6%

Numerical Simulation of Droplet Filling Mode on Molten Pool and Keyhole during Double-Sided Laser Beam Welding of T-Joints

The effects of droplets filling the molten pools during the double-sided laser beam welding (DSLBW) of T-joints was established. The dynamic behavior of the keyhole and the molten pool under different droplet filling modes were analyzed. The results indicated that compared with the contact transition, the stability of metal flow on the keyhole wall was reduced by free transition and slight contact transition. At the later stage of the droplet entering the molten pool via free transition, slight contact transition, and contact transition, the maximum flow velocity of the keyhole wall was 5.33 m/s, 4.57 m/s, and 2.99 m/s, respectively. When the filling mode was free transition or slight contact transition, the keyhole collapsed at the later stage of the droplet entering the molten pool. However, when the filling mode was contact transition, the middle-upper part of the interconnected keyholes became thinner at the later stage of the droplet entering the molten pool. At the later stage of the droplet entering the molten pool via free transition, the flow vortex at the bottom of the keyhole disappeared and the melt at the bottom of the keyhole flowed to the rear of the molten pool, however, the vortex remained during slight contact transition and contact transition

Microstructure and Mechanical Properties of GH4169 Superalloy and Si3N4 Ceramic Joints Brazed with AgCuTi/Cu foam/AgCuTi Composited Filler

GH4169 superalloy and Si3N4 ceramics were vacuum-brazed with AgCuTi+Cu foam composite filler. The effect of brazing temperature on the microstructure and mechanical properties of the GH4169/Si3N4 joint was studied. The results show that the interface microstructure of the GH4169/Si3N4 joint is the GH4169 superalloy/TiCu+Ti2Ni+TiCu2+Ag(s, s)+TiCu4+Cu(s, s)+TiN+Ti5Si3/Si3N4 ceramics. With the increase in brazing temperature, the element diffusion between the base metal and the brazing filler intensifies, and the interfacial reaction layer thickens, which is conducive to the improvement of shear strength. At 850 °C, the maximum shear strength of the joint is 196.85 MPa. After further increases in the brazing temperature, Cu foam dissolves completely, and the Ti-Cu intermetallic compounds increase, which is harmful to the shear strength due to the increases in the brittle phase. However, when the brazing temperature reaches 910 °C, the shear strength of the brazing joint slightly increases under the combined effect of the Ti-Cu intermetallic compounds and the thickness of the reaction layer

Numerical Simulation of Droplet Filling Mode on Molten Pool and Keyhole during Double-Sided Laser Beam Welding of T-Joints

The effects of droplets filling the molten pools during the double-sided laser beam welding (DSLBW) of T-joints was established. The dynamic behavior of the keyhole and the molten pool under different droplet filling modes were analyzed. The results indicated that compared with the contact transition, the stability of metal flow on the keyhole wall was reduced by free transition and slight contact transition. At the later stage of the droplet entering the molten pool via free transition, slight contact transition, and contact transition, the maximum flow velocity of the keyhole wall was 5.33 m/s, 4.57 m/s, and 2.99 m/s, respectively. When the filling mode was free transition or slight contact transition, the keyhole collapsed at the later stage of the droplet entering the molten pool. However, when the filling mode was contact transition, the middle-upper part of the interconnected keyholes became thinner at the later stage of the droplet entering the molten pool. At the later stage of the droplet entering the molten pool via free transition, the flow vortex at the bottom of the keyhole disappeared and the melt at the bottom of the keyhole flowed to the rear of the molten pool, however, the vortex remained during slight contact transition and contact transition

High-Pressure Solidification of Ternary Al-Ni-Sn Alloy

The microstructure, phase composition and mechanical properties of ternary Al-5.4Ni-2Sn (mass fraction) alloy solidified under different high pressures were researched. The results show that the phase composition of the alloy solidified at different pressures is Al, Al3Ni and β-Sn. The thermodynamic phase diagram of the ternary alloy Al-5.4Ni-2Sn was calculated under the equilibrium condition. The results demonstrate that the solidification process is as follows: L→Al3Ni→(α-Al + Al3Ni)eutectic→(α-Al + Al3Ni + β-Sn)eutectic. The hardness values of α-Al phase at ambient pressure, 2 GPa and 4 GPa are 1.5 GPa, 1.62 GPa and 1.99 GPa, respectively. This is an increase of 8% and 32.7%, respectively. The hardness of β-Sn phase decreases by about 31.2% at 4 GPa. When the deformation is 30%, the compressive strength at ambient pressure, 2 GPa and 4 GPa is 538.1 MPa, 1403.2 MPa and 1547.9 MPa, respectively. The compressive strength under high pressure increased by 160.85% and 187.7%, respectively

High-Pressure Solidification of Ternary Al-Ni-Sn Alloy

The microstructure, phase composition and mechanical properties of ternary Al-5.4Ni-2Sn (mass fraction) alloy solidified under different high pressures were researched. The results show that the phase composition of the alloy solidified at different pressures is Al, Al3Ni and β-Sn. The thermodynamic phase diagram of the ternary alloy Al-5.4Ni-2Sn was calculated under the equilibrium condition. The results demonstrate that the solidification process is as follows: L→Al3Ni→(α-Al + Al3Ni)eutectic→(α-Al + Al3Ni + β-Sn)eutectic. The hardness values of α-Al phase at ambient pressure, 2 GPa and 4 GPa are 1.5 GPa, 1.62 GPa and 1.99 GPa, respectively. This is an increase of 8% and 32.7%, respectively. The hardness of β-Sn phase decreases by about 31.2% at 4 GPa. When the deformation is 30%, the compressive strength at ambient pressure, 2 GPa and 4 GPa is 538.1 MPa, 1403.2 MPa and 1547.9 MPa, respectively. The compressive strength under high pressure increased by 160.85% and 187.7%, respectively