Research on aiming methods for small sample size shooting tests of two-dimensional trajectory correction fuse

The longitudinal dispersion of the projectile in shooting tests of two-dimensional trajectory corrections fused with fixed canards is extremely large that it sometimes exceeds the correction ability of the correction fuse actuator.The impact point easily deviates from the target,and thus the correction result cannot be readily evaluated.However,the cost of shooting tests is considerably high to conduct many tests for data collection.To address this issue,this study proposes an aiming method for shooting tests based on small sample size.The proposed method uses the Bootstrap method to expand the test data;repeatedly iterates and corrects the position of the simulated theoretical impact points through an improved compatibility test method;and dynamically adjusts the weight of the prior distribution of simulation results based on Kullback-Leibler divergence,which to some extent avoids the real data being"submerged"by the simulation data and achieves the fusion Bayesian estimation of the dispersion center.The experimental results show that when the simulation accuracy is sufficiently high,the proposed method yields a smaller mean-square deviation in estimating the dispersion center and higher shooting accuracy than those of the three comparison methods,which is more conducive to reflecting the effect of the control algorithm and facilitating test personnel to iterate their proposed structures and algorithms.;in addition,this study provides a knowledge base for further comprehensive studies in the future.

Melting heat transfer enhancement of a horizontal latent heat storage unit by fern-fractal fins

The latent heat storage(LHS)technique is of crucial importance in chemical energy engineering.Inspired by multi-bifurcated fern leaves,a mimic fern-fractal fin is designed to improve the thermal energy charging efficiency.This paper develops a transient melting model of a rectangular LHS unit using fern-fractal fins,and their melting behaviors are compared with the conventional fins.Besides,a parametric optimization of fernfractal fins is conducted for maximizing the thermal efficiency based on the response surface method(RSM).The results indicate that the temperature uniformity is more superior and the melting duration is shorter for the fern-fractal LHS unit when compared with the conventional one.Interestingly,the fern-fractal LHS device presents a slower heat storage rate during the initial conduction-dominated and early convection-dominated melting stages,while a prominent melting enhancement is achieved during the later melting stage.The shortest melting time is obtained based on the RSM technique when a fern-fractal fin with length ratio α=0.94 and branch angle θ=54.7°is utilized.Compared with a conventional fin,the averaged heat storage rate increases by 88.3%,and the total melting time is declined by 40.3%for an optimized fern-fractal fin.

Cutting performance of micro-textured PCBN tool

To study the efect of micro-texture on the cutting performance of polyrystalline cubic boron nitide(PCBN)tools,five types of micro-textures(circular pits,eliptical grooves,transverse grooves,composite grooves,and wavy grooves)were applied to the rake surface of PCBN tools by an optical fber laser marking machine.Through a combination of three dimensional cutting simulations and experiments,the influences of micro-texture on chip-tool contact area,cutting force,chip morphology,shear angle,and surface roughness during the cuting process were analyzed.The results indicated that the chip--tool contact area and cutting force of both non-textured and micro textured tools increased with increasing cutting speed,while the shear angle decreased with increasing cutting speed.The chip-tool contact area and cutting force of the five types of micro-textured tools were smaller than those of the non textured tool The chip-tool contact area and cutting force obtained by the wavy-groove micro textured tool were the smallest.The chip radius produced by the five types of micro-textured tools was smaller than that produced by the non-textured tool,and the chip morphology was more stable.The transverse-groove micro-textured tool had a better chip breaking efect.The chip rnadius generated by the lliptical groove micro textured tool was 0.96 cm,while that generated by the wavy-groove tool varied from 0.55 cm to 1.26 cm.The presence of a micro-texture reduced the surface roughness of the workpiece by 11.73%-56.7%.Under the same cutting conditions,the five types of micro-textured tools gave a smaller chip--tool contact area,cutting force,chip radius,and surface roughness and a larger shear angle than the non-textured tool.In addition,the elliptical groove and wavy-groove micro-textured tools had better cuting performance.

Design of large-displacement asymmetric piezoelectric microgripper based on flexible mechanisms

The output displacement of the traditional symmetrical microgripper is large,but its micro-components or parts are easily damaged due to the uneven force exerted on the left and right jaws of the gripper.The output force of the traditional asymmetric microgripper is stable.However,its output displacement is small,typically half the output displacement of the symmetric microgripper.To solve these problems,in this study,we designed a large-displacement asymmetric microgripper.First,we calculated the relationship between the theoretical input and output variables based on their geometric relationship.Then,we analyzed the performance of the microgripper using finite element software.Lastly,we used a piezoelectric actuator as the input driver of the microgripper.The errors associated with the theoretical and simulated output displacements were 7.05%and 9.24%,respectively.At 150 V of driving voltage,the maximum output displacement was 224μm,and the actual magnificationwas 11.2 times.Microparts can be gripped in parallel and stably,which confirms the validity of the design.

Design of a flexible piezoelectric microgripper based on combined amplification principles

Aiming to address the problem of the low amplification ratio of traditional microgrippers,a two-stage microgripper based on the principle of combined amplification was designed with a high amplification ratio and large displacement,using a simple and compact structure.The relationship between theoretical input variables and output variables were first calculated by a projection theorem.Secondly,the performance of the microgripper was analyzed by finite element analysis(FEA).Finally,the accuracy of the theoretical calculation and FEA was verified experimentally.The results show that the microgripper has high magnification and can be gripped in parallel,with self-adaptability for many irregular shaped micro objects.The actual magnification was 23.2×,which is greater than similar products.

Absolute pose estimation of UAV based on large-scale satellite image

Obtaining absolute pose based on pre-loaded satellite images is one of the important means of autonomous navigation for small Unmanned Aerial Vehicles(UAVs)in Global Navigation Satellite System(GNSS)denied environments.Most of the previous works have tended to build Convolutional Neural Networks(CNNs)to extract features and then directly regress the pose,which will fail when solving the challenges caused by the huge viewpoint and size differences between“UAV-satellite”image pairs in real-world scenarios.Therefore,this paper proposes a probability distribution/regression integrated deep model with the attention-guided triple fusion mechanism,which estimates discrete distributions in pose space and three-dimensional vectors in translation space.In order to overcome the shortage of the relevant dataset,this paper simulates image datasets captured by UAVs with forward-facing cameras during target searching and autonomous attacking.The effectiveness,superiority,and robustness of the proposed method are verified by simulated datasets and flight tests.

Bubble breakup in a microfluidic T-junction

We conduct a computational fluid dynamics simulation to investigate the behaviors of bubble breakup in a microfluidic T-junction using volume-of-fluid method to represent the interface. The evolution of bubble mor- phology and the distributions of velocity and pressure in flow field are analyzed, and the effect of width ratio between main channel and branch on the bubble mor- phology are evaluated. The results indicate that, the ＂tun- nel＂ breakup, obstructed breakup, combined breakup and non-breakup are observed during the bubble flows through the T-junctions under different condition. The whole bub- ble breakup process undergoes the extension, squeeze and pinch-off stages, while the non-breakup process experi- ences extension and pushing stages. We find that, in the squeeze stage, a local vortex flow forms at the front edge of the bubble for the ＂tunnel＂ breakup while the velocity inside the bubble is of a parabolic distribution for the obstructed breakup. Irrespective of non-breakup regimes, there is a sudden pressure drop occurring at the gas-liquid interface of the bubble in the squeeze stage, and the pres- sure drop at the front interface is far larger than that at the depression region. The transition of the bubble breakup regime through the T-junction occurs with an increase in width ratio of main channel to the branch, which sequen- tially experiences the non-breakup regime, ＂tunnel＂ breakup regime and obstructed breakup regime. The flow regime diagrams are plotted with a power-law correlation to distinguish the bubble/droplet breakup and non-breakup regimes, which also characterize the difference between bubble and droplet breakup through a T-junction.