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1.
Mega wildfires are one of the environmental disasters worldwide. This study evaluates the pre-fire species diversity and the indirect effects, including habitat loss for one of the largest wildfires in Manavgat (Antalya-Turkey) in 2021, with a two-step methodology. Here, (1) burnt areas in the Manavgat district (2021) were detected with remote sensing data from Sentinel-2A by delta Normalized Burn Ratio calculation for a selected area in Google Earth Engine, and (2) mammals' habitat vector data of International Union for Conservation of Nature (IUCN) Red List were integrated into Habitat and Biodiversity modelling of Terrset to analyze the alpha, beta, gamma diversity and Range Restriction Index for the wildfire region. In the total 4210 km2 study area, 696 km2 of the area was damaged by different fire severity; also, there were 56 mammal species' habitats here. These species include bats (i.e. Nyctalus leisleri), felids (i.e. Felis chaus), rodents (i.e. Rattus norvegicus) and large mammals (i.e. Ursus arctos). 88 % of these species are in IUCN's Least Concern category. The remaining classes are Near Threatened (3.7 %) and Vulnerable (7.4 %). This study also indicated that the burnt area's species richness does not totally consist of endemic species. Therefore, pre-fire species richness analyses of this study can be a base for further studies about the species' post-fire activity and occupancy.Furthermore, the 2021 mega wildfires show us the necessity of wildfire monitoring and risk studies in the entire Mediterranean ecosystem to evaluate the risks to the Sustainable Development Goals. Therefore, post-fire spatial data, fire migration monitorization, and recording of the species' activities should be performed temporally. In this way, the ability of wildlife's recovering, and the direct and indirect effects of the fire will be examined for ecosystems in the long term.  相似文献   
2.
《中国航空学报》2021,34(2):576-585
Creep feed profile grinding of the fir-tree blade root forms of single crystal nickel-based superalloy was conducted using microcrystalline alumina abrasive wheels in the present study. The grinding force and the surface quality in terms of surface topography, subsurface microstructure, microhardness and residual stress obtained under different grinding conditions were evaluated comparatively. Experimental results indicated that the grinding force was influenced significantly by the competing predominance between the grinding parameters and the cross-sectional root workpiece profile. In addition, the root workpiece surface, including the root peak and valley regions, was produced with the large difference in surface quality due to the nonuniform grinding loads along the root workpiece profile in normal section. Detailed results showed that the surface roughness, subsurface plastic deformation and work hardening level of the root valley region were higher by up to 25%, 20% and 7% in average than those obtained in the root peak region, respectively, in the current investigation. Finally, the superior parameters were recommended in the creep feed profile grinding of the fir-tree blade root forms. This study is helpful to provide industry guidance to optimize the machining process for the high-valued parts with complicated profiles.  相似文献   
3.
高志刚  何宇廷  马斌麟  张天宇 《航空学报》2021,42(5):524375-524375
当前航空工业的发展对于超高强铝合金材料的需求十分迫切,实现该材料的国产化并达到良好的质量效果至关重要。为了对中国航空工业中常用的7XXX新型铝合金材料的原始疲劳质量(IFQ)进行评估,选取裂纹萌生时间(TTCI)和当量初始缺陷尺寸(EIFS)作为对比参量,分别对中国飞机机翼用7XXX紧固孔试件和俄系BXXX紧固孔试件开展了低、中、高3种应力水平下的疲劳试验,通过对比分析得到了两种试件在不同应力水平下的TTCI趋于一致,最大仅相差3.71%;得到了每个试件的EIFS,应用疲劳统计学方法验证了两种试件材料各自的EIFS值无显著性差异;提出了一种不同超越概率下的结构细节当量初始缺陷模型,直接有效地对飞机结构细节的质量风险进行了评估;建立并对比分析了两种试件结构细节的通用EIFS分布,结果均小于中国军用手册规定的0.125 mm,且在超越概率为5%时,7XXX材料的通用EIFS值要小于BXXX材料的通用EIFS值。  相似文献   
4.
赵剑  黄悦琛  李海阳  何湘粤 《航空学报》2021,42(11):524829-524829
针对垂直起降运载火箭一子级在返回着陆的过程中存在的参数不确定性,提出了一种基于非侵入式多项式混沌展开的序列优化和可靠度评估的返回轨迹不确定性优化方法。首先,建立了返回多飞行段轨迹在确定性条件下的优化模型。然后,为同时兼顾轨迹的鲁棒性和可靠性,建立了由鲁棒最优目标函数、基于可靠度的路径约束和鲁棒等式约束组成的不确定性返回轨迹优化模型。最后,基于非侵入式多项式混沌展开方法对鲁棒目标函数和等式约束进行量化处理,将原随机鲁棒优化问题转化为高维状态空间中的等价确定性优化问题;为提高路径约束的可靠度评估效率,基于非侵入式多项式混沌展开方法对最可能点法进行改进,进一步发展了序列优化和可靠度评估策略。数值仿真结果表明,所提出的不确定性优化方法具有较好的鲁棒性,可以满足工程可靠性指标要求,同时还具有较高的精度和计算效率。  相似文献   
5.
师彬彬  陈哲涵 《航空学报》2021,42(10):524430-524430
针对单一特征对粉末床缺陷表达不明确导致检测效果不佳的问题,提出了一种基于特征融合的增材制造过程粉末床缺陷视觉检测方法。该算法分别使用SIFT方法、灰度共生矩阵和Hu不变矩提取尺度空间特征、纹理特征和几何特征,借助词袋模型对每张图像构建3组视觉单词直方图,通过串行融合3组视觉单词直方图得到新的特征矩阵,采用特征选择对融合后特征矩阵进行降维,并传入随机森林分类器中进行训练。实验结果表明,不同特征对粉末床不同类型缺陷检测具有不同的贡献,优化特征融合参数后,算法平均准确率达到97.46%,缺陷检测效果明显提升。  相似文献   
6.
随着经济蓬勃发展,水生农作物市场的需求量不断增长,水域水质检测行业显得日益重要,但人工水质水域检测效率低下,为此设计一套可以搭载检测传感器的水质检测蛇形机器人,以提高检测效率、降低检测成本、减轻人工劳动力度。为适应水下环境,该机器人具备小巧、灵活、机动性能好、转弯灵活、对复杂水域适应能力强、可检测不同深度水质的特点,在此针对机器人的移动单元结构设计及强度校核等问题进行分析,可为以后解决此类问题提供一种验证手段。  相似文献   
7.
《中国航空学报》2020,33(10):2794-2806
The unsatisfied surface quality seriously impedes the wide application of incremental sheet forming (ISF) in industrial field. As a novel approach, the interpolator method is a promising strategy to enhance the surface quality in ISF. However, the mechanism for the improvement of surface quality and the influence of interpolator properties on surface roughness are not well understood. In this paper, the influences of process variables (i.e. tool diameter, step size and thickness of interpolators) on the forming process (e.g. surface roughness, forming force and geometric error) are investigated through a systematic experimental approach of central composite design (CCD) in two-point incremental sheet forming (TPIF). It is obtained that the increase in thickness of interpolators decreases the surface roughness in direction vertical to the tool path while increases the surface roughness in direction horizontal to the tool path. Nevertheless, the combined influence between thickness of interpolators and process parameters (tool diameter and step size) is limited. Meanwhile, the placement of interpolator has little influence on the effective forming force of blank. In addition, the geometric error enlarges with the increase of step size and thickness of interpolator while decreases firstly and then increase with an increase in tool diameter. Finally, the influencing mechanism of the interpolator method on surface quality can be attributed to the decrease of the contact pressure due to the increase of contact area with the unchanged contact force. Meanwhile, the interpolator method eliminates the sliding friction on the surface of blank due to the stable relative position between the blank and the interpolator.  相似文献   
8.
《中国航空学报》2020,33(8):2146-2161
Aircraft icing has been proven to be one of the most serious threats to flight safety. During the analysis of flight risk under icing conditions, quantitative assessment and visualization of flight risk are quite essential as they provide safe manipulation strategies in intricate conditions. However, they are rarely studied. Since the icing flight accidents are the result of the coupling of multiple unfavorable factors, in present study, we have proposed a method to quantitatively assess flight risk induced by multi-factor coupling under icing conditions by Monte-Carlo simulation and multivariate extreme value theory. The results demonstrate that the flight risk probability increases with the rise of unfavorable factors. Besides, a flight risk visualization method named flight safety window has been presented to build the flight risk distribution cloud maps in different complex conditions. The cloud maps show that the icing would give rise to atrophy of the safety scope, and the consequence would be even more severe when coupled with other more unfavorable factors. The proposed methods in this study would be useful in flight risk analysis under icing conditions and can enhance the pilot's situational awareness in selecting correct strategies within the safety zone to avoid unsafe manipulation.  相似文献   
9.
胡世威  梁浩  徐兵 《航空学报》2019,40(8):422796-422796
为保障某航天器在服役年限内不发生事故,针对航天器上采用插入焊接技术的精密管道系统进行结构完整性评估。在考虑到系统存在整圈的环形未焊透缺陷基础上,结合工程实践,假设在焊接区域存在更危险的平面缺陷。首先,开展高压气相热充氢试验下的标准拉伸和三点弯试验得到管道系统材料"J-75"在临氢环境下应力应变曲线和断裂韧性。其次,采用有限元程序计算系统在内压、惯性载荷与离面位移作用下的应力分布,考虑到间隙配合中的不确定性,改变模型中的最大间隙多次模拟计算,发现最大应力位置基本不变,以此区域作为假想缺陷的具体萌生区域。最后,采用失效评估图(FAD)方法对存在4种缺陷模式的系统分别进行结构完整性评估。通过引入安全裕度的概念,发现系统在含有初始尺寸(0.15 mm)的4种平面缺陷时,均处于安全状态,并且安全裕度都在2倍以上;通过工程临界分析(ECA)发现随着缺陷尺寸的增大,系统中含有缺陷2(位于管道焊接区域最大应力处的轴对称平面且沿焊深方向扩展的缺陷)时最为危险,且当缺陷深度超过0.61 mm时将断裂失效;考虑到测试数据的弥散性,针对系统最危险的模式,以安全裕度为可靠性指标,将失效评估图方法与可靠性评价相结合,得到系统在含有尺寸为0.15 mm的缺陷2情况下保有足够安全裕度的可靠性下限值超过0.999 5。  相似文献   
10.
    
传统可靠性评估方法只考虑产品处于恒定环境应力下的情况,然而工程实际中产品往往直接暴露于外界的自然环境中,所遭受的工作环境应力或贮存环境应力都是随时间变化的。针对此情况,引入典型地理位置的真实自然环境应力,使用六参数多项式拟合方法得到其环境应力变化趋势,并假定2种时变环境应力模式,在Nelson累积损伤模型的基础上,研究真实时变环境应力下基于加速寿命试验数据的产品可靠性评估方法。结果表明:产品在不同地理位置的可靠寿命差别较大,引入产品所处地理位置的真实环境应力,可更精确地评估产品的可靠性。  相似文献   
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