Fast UAV path planning in urban environments based on three-step experience buffer sampling DDPG

The path planning of Unmanned Aerial Vehicle(UAV)is a critical issue in emergency communication and rescue operations,especially in adversarial urban environments.Due to the continuity of the flying space,complex building obstacles,and the aircraft's high dynamics,traditional algorithms cannot find the optimal collision-free flying path between the UAV station and the destination.Accordingly,in this paper,we study the fast UAV path planning problem in a 3D urban environment from a source point to a target point and propose a Three-Step Experience Buffer Deep Deterministic Policy Gradient(TSEB-DDPG)algorithm.We first build the 3D model of a complex urban environment with buildings and project the 3D building surface into many 2D geometric shapes.After transformation,we propose the Hierarchical Learning Particle Swarm Optimization(HL-PSO)to obtain the empirical path.Then,to ensure the accuracy of the obtained paths,the empirical path,the collision information and fast transition information are stored in the three experience buffers of the TSEB-DDPG algorithm as dynamic guidance information.The sampling ratio of each buffer is dynamically adapted to the training stages.Moreover,we designed a reward mechanism to improve the convergence speed of the DDPG algorithm for UAV path planning.The proposed TSEB-DDPG algorithm has also been compared to three widely used competitors experimentally,and the results show that the TSEB-DDPG algorithm can archive the fastest convergence speed and the highest accuracy.We also conduct experiments in real scenarios and compare the real path planning obtained by the HL-PSO algorithm,DDPG algorithm,and TSEB-DDPG algorithm.The results show that the TSEBDDPG algorithm can archive almost the best in terms of accuracy,the average time of actual path planning,and the success rate.

Enhancing corrosion resistance of 7150 Al alloy using novel three-step aging process

The effects of a novel three-step aging process （T76＋T6） on the electrochemical corrosion behavior of 7150 extruded aluminum alloy were evaluated and compared with those of the conventional retrogression and re-aging process （T77）. The open circuit potential （OCP）, cyclic polarization and electrochemical impedance spectra （EIS） of the A1 alloys were measured after treatment in three solutions （3.5% NaCl （mass fraction）; 10 mmol/L NaCl ＋ 0.1 mol/L Na2SO4; 4 mol/L NaCl ＋ 0.5 mol/L KNO3 ＋ 0.1 mol/L HNO3）. The parameters including the corrosion potential, pitting potential, pit transition potential and steepness, and potential differences were extensively discussed to evaluate the corrosion behavior of the Al alloys. The electrochemical and scanning electron microscopy （SEM） data show that compared with the 7150-T77 Al alloy, the T76 ＋ T6 aged 7150 A1 alloy exhibits better resistance to pitting corrosion, inter-granular corrosion （IGC） and exfoliation corrosion, which is attributed to further coarsening and inter-spacing of the grain boundary particles （GBPs） as revealed by transmission electron microscopy. Furthermore, the hardness tests indicate that an attractive combination of strength and corrosion resistance was obtained for the 7150 Al alloy with T76 ＋ T6 treatment.

Effect of three-step homogenization on microstructure and properties of 7N01 aluminum alloys

The effect of different homogenization treatments on the microstructure and properties of the 7N01 aluminum alloy was investigated using hardness measurements, electrical conductivity measurements, tensile and slow strain rate tests, electron probe microanalysis, optical microscopy, scanning electron microscopy, and transmission electron microscopy. The results revealed that three-step homogenization improved the uniformity of Zr distribution by eliminating segregation of the main alloying elements. During the second homogenization step at 350 °C for 10 h, coarse and strip-like equilibrium η phases formed which assisted the nucleation of Al3Zr dispersoids and reduced the width of the precipitate-free zone of A13Zr dispersoids. As a result, coarse recrystallization was greatly reduced after homogenization at 200 °C, 2 h ＋ 350 °C, 10 h ＋ 470 °C, 12 h, which contributed to improving the overall properties of the 7N01 aluminum alloys.

Effect of a novel three-step aging on strength, stress corrosion cracking and microstructure of AA7085

The influence of a novel three-step aging on strength, stress corrosion cracking(SCC) and microstructure of AA7085 was investigated by tensile testing and slow strain rate testing combined with transmission electron microscopy(TEM). The results indicate that with the increase of second-step aging time of two-step aging, the mechanical properties increase first and then decrease, while the SCC resistance increases. Compared with two-step aging, three-step aging treatment improves SCC resistance and the strength increases by about 5%. The effects of novel three-step aging on strength and SCC resistance are explained by the role of matrix precipitates and grain boundary precipitates, respectively.

Short-term efficacy of robotic and laparoscopic spleen-preserving splenic hilar lymphadenectomy via Huang’s three-step maneuver for advanced upper gastric cancer: Results from a propensity scorematched study

BACKGROUND Robotic surgery has been considered to be significantly better than laparoscopic surgery for complicated procedures.AIM To explore the short-term effect of robotic and laparoscopic spleen-preserving splenic hilar lymphadenectomy(SPSHL)for advanced gastric cancer(GC)by Huang’s three-step maneuver.METHODS A total of 643 patients who underwent SPSHL were recruited from April 2012 to July 2017,including 35 patients who underwent robotic SPSHL(RSPSHL)and 608 who underwent laparoscopic SPSHL(LSPSHL).One-to-four propensity score matching was used to analyze the differences in clinical data between patients who underwent robotic SPSHL and those who underwent laparoscopic SPSHL.RESULTS In all,175 patients were matched,including 35 patients who underwent RSPSHL and 140 who underwent LSPSHL.After matching,there were no significant differences detected in the baseline characteristics between the two groups.Significant differences in total operative time,estimated blood loss(EBL),splenic hilar blood loss(SHBL),splenic hilar dissection time(SHDT),and splenic trunk dissection time were evident between these groups(P<0.05).Furthermore,no significant differences were observed between the two groups in the overall noncompliance rate of lymph node(LN)dissection(62.9%vs 60%,P=0.757),number of retrieved No.10 LNs(3.1±1.4 vs 3.3±2.5,P=0.650),total number of examined LNs(37.8±13.1 vs 40.6±13.6,P=0.274),and postoperative complications(14.3%vs 17.9%,P=0.616).A stratified analysis that divided the patients receiving RSPSHL into an early group(EG)and a late group(LG)revealed that the LG experienced obvious improvements in SHDT and length of stay compared with the EG(P<0.05).Logistic regression showed that robotic surgery was a significantly protective factor against both SHBL and SHDT(P<0.05).CONCLUSION RSPSHL is safe and feasible,especially after overcoming the early learning curve,as this procedure results in a radical curative effect equivalent to that of LSPSHL.

Auxiliary principle and three-step iterative algorithms for generalized set-valued strongly nonlinear mixed variational-like inequalities

An auxiliary principle technique to study a class of generalized set-valued strongly nonlinear mixed variational-like inequalities is extended. The existence and uniqueness of the solution of the auxiliary problem for the generalized set-valued strongly nonlinear mixed variational-like inequalities are proved, a novel and innovative three-step iterative algorithm to compute approximate solution is constructed, and the existence of the solution of the generalized set-valued strongly nonlinear mixed variational-like inequality is shown using the auxiliary principle iterative sequences generated by the algorithm technique. The convergence of three-step is also proved.

ZnO micro-nano composite hydrophobic film prepared by the three-step method

The hydrophobicity of the lotus leaf is mainly due to its surface micro-nano composite structure. In order to mimic the lotus structure, ZnO micro-nano composite hydrophobic films were prepared via the three-step method. On thin buffer films of SiO2, which were first fabricated on glass substrates by the so,gel dip-coating method, a ZnO seed layer was deposited via RF magnetron sputtering. Then two different ZnO films, micro-nano and micro-only flowerlike structures, were grown by the hydrothermal method. The prepared films have different hydrophobic properties after surface modification. The structures of the obtained ZnO films were characterized using x-ray diffraction and field-emission scanning electron microscopy. A conclusion that a micro-nano composite structure is more beneficial to hydrophobicity than a micro-only structure was obtained through research into the effect of structure on hydrophobic properties.

Three-step acupuncture and cupping therapy:an effective approach to treat cervicogenic headache

As early as 1983,Sjaastad proposed the concept of cervicogenic headache(CH)in the World Headache Conference,that is,the pain from upper cervical joints and muscles can be referred to the head.CH is a group of syndromes mainly caused by dysfunction of the upper cervical spine and its component muscles,ligaments,bony,vertebral arteries and/or soft tissue elements,usually not accompanied by neck pain.Therefore,the treatment strategy of CH focuses on pain relief and repair cervical lesions.Patients with painful disorders of upper cervical zygapophysial joints showed significant headache relief after directly treated at disordered cervical joints[1].

Three-Step Difference Scheme for Solving Nonlinear Time-Evolution Partial Differential Equations

In this paper, a special three-step difference scheme is applied to the solution of nonlinear time-evolution equations, whose coefficients are determined according to accuracy constraints, necessary conditions of square conservation, and historical observation information under the linear supposition. As in the linear case, the schemes also have obvious superiority in overall performance in the nonlinear case compared with traditional finite difference schemes, e.g., the leapfrog(LF) scheme and the complete square conservation difference(CSCD) scheme that do not use historical observations in determining their coefficients, and the retrospective time integration(RTI) scheme that does not consider compatibility and square conservation. Ideal numerical experiments using the one-dimensional nonlinear advection equation with an exact solution show that this three-step scheme minimizes its root mean square error(RMSE) during the first 2500 integration steps when no shock waves occur in the exact solution, while the RTI scheme outperforms the LF scheme and CSCD scheme only in the first 1000 steps and then becomes the worst in terms of RMSE up to the 2500th step. It is concluded that reasonable consideration of accuracy, square conservation, and historical observations is also critical for good performance of a finite difference scheme for solving nonlinear equations.

JOINT RANDOM OPTIMIZED THREE-STEP SEARCH ALGORITHM BASED-ON GRAY AND CHROMATIC INFORMATION

In this letter, an improved three-step search algorithm is presented, which uses both gray and chromatic information to boost the performance with random optimization and converge the motion vectors to global optima. Experimental results show that this algorithm can efficiently improve the PSNR after motion compensation.

General Convergence Analysis for Three-step Projection Methods and Applications to Variational Problems

First a general model for a three-step projection method is introduced, and second it has been applied to the approximation solvability of a system of nonlinear variational inequality problems in a Hilbert space setting. Let H be a real Hilbert space and K be a nonempty closed convex subset of H. For arbitrarily chosen initial points x0, y0, z0 ∈ K, compute sequences xn, yn, zn such thatT ： K→ H is a nonlinear mapping onto K. At last three-step models are applied to some variational inequality problems.

A new three-step procedure for pancreatic head carcinoma with invasion of superior mesenteric artery

Pancreatic head carcinoma is characterized by high malignancy and a low survival rate and its mortality ranks fourth for malignant tumors with a 5-year survival rate of only 5%[1].Treatment of this cancer relies on surgical resection.However,the resection rate is only about 20%,because majority of the patients are classified as unresectable when diagnosed due to distant metastasis or

编织碳纤维复合材料加强铝合金帽型薄壁梁动态弯曲特性研究

金属/复合材料混合薄壁结构可同时满足汽车车身抗撞性和轻量化的要求。旨在对比研究不同纤维铺层方式铝/碳纤维复合材料(Aluminum/Carbon Fibre Reinforced Plastic,Al/CFRP)混合帽型薄壁梁的动态弯曲特性。通过三点弯曲试验比较分析各试件的弯曲失效行为与耐撞性能,结合试验结果建立有限元模型且验证其准确性,并进一步分析压头尺寸、压头形状和冲击位置对混合梁弯曲性能的影响。结果表明,铺层角度较铺层顺序对试件弯曲性能影响更大,压头尺寸越大、压头形状越相对扁平或冲击位置越远离中间时可获得较好的耐撞特性。研究所用方法与所得结论可为类似抗弯结构耐撞性设计提供参考。

变厚度铺层Nomex蜂窝夹层件固化变形的数值模拟

为准确预测变厚度铺层夹层结构的固化变形,基于热-化学-结构多物理场耦合方法对AS4/8551碳纤维/环氧树脂复合材料-Nomex蜂窝夹层结构的固化过程进行数值模拟。考虑材料时变特性的影响,结合复合材料瞬时线弹性本构模型、细观力学理论和改进的Gibson等效理论建立起夹层结构三维有限元仿真模型,研究了结构在整个固化周期中的固化度场、温度场和应力-应变场的分布关系,并同已有的实验结果进行对比验证,最后通过解析模型分析预固化工艺对结构回弹变形的影响规律。结果表明:建立的有限元模型能够比较准确地反映结构固化过程,固化变形的平均预测误差为4.8%,最大预测误差不超过6.0%;变厚度铺层设计对较薄区域面板的固化应力影响较大,表现为沿厚度方向的向上剪切应力,在冷却阶段集中于结构端部并转化为结构翘曲;面板预固化处理削弱了固化放热和材料各向异性对夹层结构固化变形的影响,0.25预固化程度下结构最大变形的降低幅度达到14.78%。研究结果为复杂设计蜂窝夹层件制造精度的提升和工艺优化提供了重要参考。

碳/玻混杂纤维复合材料自行车前叉的铺层设计及耐疲劳验证

与传统金属材料相比,混杂纤维复合材料具有轻质高强、耐疲劳和抗冲击韧性好等优点。为了得到既满足力学要求又节约成本的较优性能的前叉,通过有限元分析对碳纤维/玻璃纤维混杂复合材料的自行车前叉进行铺层优化设计。自行车前叉分为叉身和立管,在不改变材料铺层角度和厚度的前提下,分别改变叉身和立管的层间混杂比和铺层材料(碳纤维预浸布/玻璃纤维预浸布)顺序,计算前叉在服役状态下的力学性能。通过对比材料最大应力值以及材料成本,获得该条件下最优的前叉设计。结果表明:混杂复合材料叉身的最内层材料应该用玻璃纤维铺设。当自行车前叉叉身混杂比为1∶2,铺层顺序为[G_(3)CGC];自行车前叉立管混杂比为3∶13,铺层顺序为[GCG12C2]时,所得碳/玻混杂复合材料前叉方案为最优铺层设计。5万次加速疲劳测试实验表明:采用优化后的铺层方案制备复合材料自行车前叉,可以满足前叉的耐疲劳性要求。

复合材料层压板结构铺层设计的三级优化方法

针对复合材料层压板结构的铺层设计,提出了一种三级优化方法。第一级,进行结构区域划分并建立初始层压板,通过刚度简化消除初始铺层顺序对优化设计的影响,以强度、刚度、稳定性等约束下重量最小为目标,优化各区域的铺层厚度。第二级,为满足相邻区域铺层连续的工艺要求,采用共享铺层组进行铺层整合,并优化各铺层组内的铺层顺序,进一步增大结构刚度。第三级,优化确定所有共享铺层组中每个单一铺层的保留或去除,在强度、刚度、稳定性等约束下,得到结构最优重量。算例表明,本文所提铺层设计的三级优化方法具有一定的有效性,且对复合材料机翼这样的复杂结构具有良好的适用性。

碳纤维复合材料层压成型工艺优化及验证

碳纤维产品在汽车改装个性化定制领域的需求迅速增长,但其对手工层压技术的研究相对缺乏。研究提出了一种汽车饰件手工碳纤维层压成型的方法,给出了碳纤维饰件优化后参数工艺表和外观质量的评价维度。对底胶粘度与时间的关系、面胶气泡的形成、不均匀压力分布以及避免材料浪费的问题提出了解决办法,并进行实验验证。结果表明,底胶与碳布粘贴的最佳静置时间60 s、面胶固化温度60℃且保温时间10 min为最佳;饰件特征面处面胶涂抹量是平面处的2倍,用薄膜缠绕方法能确保压力均匀,碳布边长大于饰件2 cm为最佳裁剪尺寸,面漆烘干温度为60℃且保温时间20 min为最佳。研究为汽车定制行业改进手工碳纤维层压技术提供了贡献,其应用潜力可扩展至其他需要高性能复合材料解决方案的领域。

层合复合材料壁板的热颤振特性分析

采用壁板颤振分析的有限元方法,从壁板的正则化弯曲刚度、屈曲临界温升、颤振临界速压和极限环颤振幅值等参数的角度,分析了不同铺层方向和不同铺层顺序对层合复合材料壁板的颤振特性的影响,并给出了几种常见铺层方式层合复合材料壁板的颤振特性。结果表明,在设计复合材料壁板的铺层方向和铺层顺序时,一般可以通过壁板正则化弯曲刚度的大小来对颤振速压进行比较。但是在某些特殊的铺层情况下,随着温度升高,发生频率重合型颤振的耦合模态会发生演变,这时正则化弯曲刚度较大的壁板也有可能在较低的速压下发生颤振。

引发方式、铺层对纤维增强复合材料圆柱壳吸能特性影响的冲击试验研究

对作为吸能元件的纤维增强复合材料圆柱壳的吸能特性进行了试验研究。制备了不同铺层角度和不同引发方式的玻璃纤维/聚酯树脂基圆柱壳,通过对该圆柱壳进行动态试验,探求铺层方式和引发方式对该吸能元件吸能效果的影响,以及该复合材料层合壳体压溃过程的破坏机理。

基于铺层参数的复合材料耐压壳协同优化设计

在给定的材料性能条件下,以耐压壳纤维体积分数和层合板厚度为设计变量,以结构质量最小为优化目标进行复合材料耐压壳的布局优化;以铺层参数作为优化变量,综合考虑结构的稳定性及其材料强度,实现了结构铺层方式的优化设计;通过协调各子系统优化结果,实现了适用于潜水器复合材料耐压壳结构/材料一体化的协同优化设计.结果表明:耐压壳结构质量较优化前的降幅为20.57%,临界失稳压力为30.78MPa,失效指数为0.675,优化结果达到预期效果.所提出的基于铺层参数的协同优化方法能够对复合材料耐压壳进行优化设计,解决了直接以铺层角作为设计变量的优化效率低的问题.