Gongcheng Kexue Yu Jishu/Advanced Engineering Science

Generally, the noise transmitted in the optical path mainly includes the influence of optical power, external vibration interference, the intrinsic noise of the optical path, and the influence of thermal motion caused by environmental temperature changes. The optical fiber is extremely sensitive to environmental interference, and any environmental disturbance will bring corresponding phase errors. At the same time, if the signal is preprocessed and filtered, it is easy to cause some small information to be lost and increase reconstruction errors. Aiming at the problem of internal common mode noise affecting measurement accuracy and increasing reconstruction error in micron-level vibration measurement, a differential measurement system based on all-fiber Fabry–Perot (F–P) interference is established. Firstly, according to the phase equation of the F–P interference principle and the 2×2 single-mode fiber coupler during the transmission process, the through arm and the coupling arm have a phase difference of 90°. It is deduced that the signals received by the two output detectors are equal in amplitude and opposite in direct. Then the difference between the two signals can increase the overall signal amplitude, weaken the influence of common mode noise on the signal, and enhance the signal quality. Through the reconstruction displacement analysis of the interference signal, the experimental results show that the reconstruction error of the synthesized signal is reduced by 0.4% in the 2 μm sinusoidal vibration of the mirror. Under 1.4 μm vibration measurement on rough surface, the reconstruction error is reduced by 2.8%. The experimental results also show that the differential structure can reduce the vibration measurement reconstruction error, and the reconstructed waveform is smoother.

A hydrological simulation in the Huaihe River Basin (HRB) was investigated using two different models: a coupled land surface hydrological model (CLHMS), and a large-scale hydrological model (LSX-HMS). The NCEP-NCAR reanalysis dataset and observed precipitation data were used as meteorological inputs. The simulation results from both models were compared in terms of flood processes forecasting during high flow periods in the summers of 2003 and 2007, and partial high flow periods in 2000. The comparison results showed that the simulated streamflow by CLHMS model agreed well with the observations with Nash-Sutcliffe coefficients larger than 0.76, in both periods of 2000 at Lutaizi and Bengbu stations in the HRB, while the skill of the LSX-HMS model was relatively poor. The simulation results for the high flow periods in 2003 and 2007 suggested that the CLHMS model can simulate both the peak time and intensity of the hydrological processes, while the LSX-HMS model provides a delayed flood peak. These results demonstrated the importance of considering the coupling between the land surface and hydrological module in achieving better predictions for hydrological processes, and CLHMS was proven to be a promising model for future applications in flood simulation and forecasting

The main purpose of video background separation is to extract objects of interest from the video, but it is still one of the most challenging tasks in computer vision and other fields due to the influence of noise and lighting changes. The truncated nuclear norm (TNN) algorithm is a classic robust principal component analysis (RPCA) algorithm, which is widely used to separate the background and the front of the video. However, the truncated kernel norm in this algorithm does not have a high degree of approximation to the rank function in the traditional robust principal component analysis, resulting in poor stability and low accuracy in separating the front and background of the video in some complex scenes. To solve this problem, this paper proposes an improved truncated nuclear norm (improved truncated nuclear norm, ITNN) algorithm. The algorithm first replaces the kernel norm in the TNN model with a non-convex γ norm, and analyzes that the non-convex γ norm has a higher degree of approximation to the rank function than the kernel norm . Corresponding model; secondly, in order to solve the proposed model, this paper introduces the generalized alternating direction method of multipliers (GADMM) to solve the model; finally, the proposed ITNN algorithm is applied to multiple public videos In the previous background separation experiment, and by showing the foreground effects of different videos, the effectiveness of the ITNN algorithm was verified from a visual point of view. At the same time, the F-measure value of the video foreground extracted by the proposed algorithm and the comparison algorithm is calculated, which further verifies the effectiveness of the ITNN algorithm from the perspective of quantification. In addition, the experiment also recorded the running time of the video front and background separation of each algorithm, which verified the efficiency of the ITNN algorithm. In a word, this paper verifies the effectiveness and superiority of the proposed ITNN algorithm in the separation of video front and background through experiments.

Rotary vane steering gear has the advantages of compact structure, high mechanical efficiency, and easy installation, and is widely used in ships. The existing rotary vane steering gear is a single-layer hydraulic swing cylinder, and the rotation range of the rudder blade is restricted by the structure of the swing cylinder and has saturated nonlinearity. In addition, the phenomena of rudder impingement, lag and running caused by hydrodynamic interference seriously affect the ship’s course control and rudder anti-roll effect. Aiming at the above problems, a new steering principle of compound structure swing cylinder is proposed based on the mathematical model of direct drive electro-hydraulic servo rotary vane actuator and the analysis of the interference of hydrodynamic force on rudder angle. The double-layer structure is adopted for the compound swing cylinder, the inner layer is rudder driving cylinder, the outer layer is torque decoupling cylinder. The inner and outer rotors rotate in the same direction, which can increase the working range of the rudder blade. Meanwhile, the torque decoupling cylinder rotor outputs boost torque acting on the rudder drive cylinder rotor, which can offset the load torque generated by the hydrodynamic force on the drive cylinder rotor. Improve the rotation accuracy of the rudder blade and solve the problem of force-position coupling in the movement of the rudder. The reverse rotation of the inner and outer rotors can make the steering gear brake and change direction in time, and improve the steering performance. The compound swing cylinder is used for the vane steering gear. The steering gear system has a large stability margin, with amplitude margin of 45.3 dB and phase margin of 99.2°, which meets the design index of servo system. Simulation analysis shows that, compared with the single-layer swing cylinder plus control strategy, the compound swing cylinder has faster response speed and no overshoot, the speed of reaching steady state increased by about 36%, the steady-state error is maintained within ±0.05° under external load interference. When tracking a slope signal with a slope of 0.01°/s, the steering accuracy can be maintained within the ±0.03° position error band, which has high position control accuracy.

Flow separation and vortical dynamics generated by second-order Stokes waves propagating over a submerged rectangular breakwater supported on a rubble mound were investigated using particle image velocimetry (PIV) technology and numerical model based on Reynolds–averaged-Navier–Stokes equations (RANS). Experimental wave surfaces show nonlinear deformation before and after the structure. The asymmetry and skewness of the weatherside wave profile are –0.21 and 0.04, respectively, which indicates a steep front face and gentle rear face. The asymmetry and skewness of the leeside wave profile are –0.39 and 0.99, respectively, which indicates more significant lack of symmetry relative to vertical and horizontal axes. Phase-averaged velocity and vortex fields calculated from PIV data show that clockwise and counterclockwise vortices are generated periodically on the weatherside and leeside of the structure. However, these vortices are not fully developed. The subsequent flow reversal moves the vortices towards the free surface or the structure to make them dissipated. The weatherside vortex pair is confined within a relatively narrow region of about 0.5 times Keulegan–Carpenter number from the weatherside of the structure, which implies smaller wave energy dissipation. Meanwhile, the leeside vortex pair is confined within a relatively wide region of about 1.0 times Keulegan–Carpenter number from the leeside of the structure, which indicates greater dissipation of wave energy. In addition, a small circulation system is found above the upstream shoulder of the rubble mound and its movement is confined within two times the unperturbed wave particle trajectory, which may lead to local scouring. A numerical wave flume was established based on RANS–VOF mode and then verified by experimental results. The applicability of different wave-making methods and the effect of energy dissipation by sponge layer were analyzed. The RANS–VOF model was then used to further study the flow separation of shear boundary layers. Numerical results show that the supply of vorticity mainly comes from the shear boundary layers at the surface of the structure. The adverse vorticity in the shear boundary layers is induced by the adverse pressure gradient imposed by the movement of the vortices previously shed from the structure. The generation, shedding, stretching, advection and dissipation of vortices is expected to significantly change the local flow around submerged structures and hence cause local scour as well as additional loading. Therefore, the effect of the complex flow induced by vortices should be taken into account in engineering design.