分类： 农、林、牧、渔 >> 土壤学 提交时间： 2024-08-14 合作期刊: 《干旱区科学》
摘要： Wind erosion is a geomorphic process in arid and semi-arid areas and has substantial implications for regional climate and desertification. In the Columbia Plateau of northwestern United States, the emissions from fine particles of loessial soils often contribute to the exceedance of inhalable particulate matter (PM) with an aerodynamic diameter of 10 μm or less (PM10) according to the air quality standards. However, little is known about the threshold friction velocity (TFV) for particles of different sizes that comprise these soils. In this study, soil samples of two representative soil types (Warden sandy loam and Ritzville silt loam) collected from the Columbia Plateau were sieved to seven particle size fractions, and an experiment was then conducted to determine the relationship between TFV and particle size fraction. The results revealed that soil particle size significantly affected the initiation of soil movement and TFV; TFV ranged 0.304–0.844 and 0.249–0.739 m/s for different particle size fractions of Ritzville silt loam and Warden sandy loam, respectively. PM10 and total suspended particulates (TSP) emissions from a bed of 63–90 μm soil particles were markedly higher for Warden sandy loam than for Ritzville silt loam. Together with the lower TFV of Warden sandy loam, dust emissions from fine particles (<100 μm in diameter) of Warden sandy loam thus may be a main contributor to dust in the region's atmosphere, since the PM10 emissions from the soil erosion surfaces and its ensuing suspension within the atmosphere constitute an essential process of soil erosion in the Columbia Plateau. Developing and implementing strategic land management practices on sandy loam soils is therefore necessary to control dust emissions in the Columbia Plateau.
分类： 生物学 >> 生态学 提交时间： 2024-08-14 合作期刊: 《干旱区科学》
摘要： Soil erosion caused by unsustainable grazing is a major driver of grassland ecosystem degradation in many semi-arid hilly areas in China. Thus, grazing exclusion is considered as an effective method for solving this issue in such areas. However, some ecological and economic problems, such as slow grassland rejuvenation and limited economic conditions, have become obstacles for the sustainable utilization of grassland ecosystem. Accordingly, we hypothesized that the conflict between grassland use and soil conservation may be balanced by a reasonable grazing intensity. In this study, a two-year grazing fence experiment with five grazing intensity gradients was conducted in a typical grassland of the Loess Plateau in China to evaluate the responses of vegetation characteristics and soil and water losses to grazing intensity. The five grazing intensity gradients were 2.2, 3.0, 4.2, 6.7, and 16.7 goats/hm2, which were represented by G1–G5, respectively, and no grazing was used as control. The results showed that a reasonable grazing intensity was conducive to the sustainable utilization of grassland resources. Vegetation biomass under G1–G4 grazing intensity significantly increased by 51.9%, 42.1%, 36.9%, and 36.7%, respectively, compared with control. In addition, vegetation coverage increased by 19.6% under G1 grazing intensity. Species diversity showed a single peak trend with increasing grazing intensity. The Shannon-Wiener diversity index under G1–G4 grazing intensities significantly increased by 22.8%, 22.5%, 13.3%, and 8.3%, respectively, compared with control. Furthermore, grazing increased the risk of soil erosion. Compared with control, runoff yields under G1–G5 grazing intensities increased by 1.4, 2.6, 2.8, 4.3, and 3.9 times, respectively, and sediment yields under G1–G5 grazing intensities were 3.0, 13.0, 20.8, 34.3, and 37.7 times greater, respectively, than those under control. This result was mainly attributed to a visible decrease in litter biomass after grazing, which decreased by 50.5%, 72.6%, 79.0%, 80.0%, and 76.9%, respectively, under G1–G5 grazing intensities. By weighing the grassland productivity and soil conservation function, we found that both two aims were achieved at a low grazing intensity of less than 3.5 goats/hm2. Therefore, it is recommended that grassland should be moderately utilized with grazing intensity below 3.5 goats/hm2 in semi-arid hilly areas to achieve the dual goals of ecological and economic benefits. The results provide a scientific basis for grassland utilization and health management in semi-arid hilly areas from the perspective of determining reasonable grazing intensity to maintain both grassland production and soil conservation functions.
分类： 生物学 >> 生态学 提交时间： 2024-08-14 合作期刊: 《干旱区科学》
摘要： Atmospheric deposition of nitrogen (N) plays a significant role in shaping the structure and functioning of various terrestrial ecosystems worldwide. However, the magnitude of N deposition on grassland ecosystems in Central Asia still remains highly uncertain. In this study, a multi-data approach was adopted to analyze the distribution and amplitude of N deposition effects in Central Asia from 1979 to 2014 using a process-based denitrification decomposition (DNDC) model. Results showed that total vegetation carbon (C) in Central Asia was 0.35 (±0.09) Pg C/a and the averaged water stress index (WSI) was 0.20 (±0.02) for the whole area. Increasing N deposition led to an increase in the vegetation C of 65.56 (±83.03) Tg C and slightly decreased water stress in Central Asia. Findings of this study will expand both our understanding and predictive capacity of C characteristics under future increases in N deposition, and also serve as a valuable reference for decision-making regarding water resources management and climate change mitigation in arid and semi-arid areas globally.
分类： 地球科学 >> 大气科学 提交时间： 2024-08-14 合作期刊: 《干旱区科学》
摘要： The characteristics of drought in Xinjiang Uygur Autonomous Region (Xinjiang), China have changed due to changes in the spatiotemporal patterns of temperature and precipitation, however, the effects of temperature and precipitation—the two most important factors influencing drought—have not yet been thoroughly explored in this region. In this study, we first calculated the standard precipitation evapotranspiration index (SPEI) in Xinjiang from 1980 to 2020 based on the monthly precipitation and monthly average temperature. Then the spatiotemporal characteristics of temperature, precipitation, and drought in Xinjiang from 1980 to 2020 were analyzed using the Theil–Sen median trend analysis method and Mann–Kendall test. A series of SPEI-based scenario-setting experiments by combining the observed and detrended climatic factors were utilized to quantify the effects of individual climatic factor (i.e., temperature and precipitation). The results revealed that both temperature and precipitation had experienced increasing trends at most meteorological stations in Xinjiang from 1980 to 2020, especially the spring temperature and winter precipitation. Due to the influence of temperature, trends of intensifying drought have been observed at spring, summer, autumn, and annual scales. In addition, the drought trends in southern Xinjiang were more notable than those in northern Xinjiang. From 1980 to 2020, temperature trends exacerbated drought trends, but precipitation trends alleviated drought trends in Xinjiang. Most meteorological stations in Xinjiang exhibited temperature-dominated drought trend except in winter; in winter, most stations exhibited precipitation-dominated wetting trend. The findings of this study highlight the importance of the impact of temperature on drought in Xinjiang and deepen the understanding of the factors influencing drought.
分类： 生物学 >> 生态学 提交时间： 2024-08-14 合作期刊: 《干旱区科学》
摘要： The Three-River Source Region (TRSR) in China holds a vital position and exhibits an irreplaceable strategic importance in ecological preservation at the national level. On the basis of an in-depth study of the vegetation evolution in the TRSR from 2000 to 2022, we conducted a detailed analysis of the feedback mechanism of vegetation growth to climate change and human activity for different vegetation types. During the growing season, the spatiotemporal variations of normalized difference vegetation index (NDVI) for different vegetation types in the TRSR were analyzed using the Moderate Resolution Imaging Spectroradiometer (MODIS)-NDVI data and meteorological data from 2000 to 2022. In addition, the response characteristics of vegetation to temperature, precipitation, and human activity were assessed using trend analysis, partial correlation analysis, and residual analysis. Results indicated that, after in-depth research, from 2000 to 2022, the TRSR's average NDVI during the growing season was 0.3482. The preliminary ranking of the average NDVI for different vegetation types was as follows: shrubland (0.5762)>forest (0.5443)>meadow (0.4219)>highland vegetation (0.2223)>steppe (0.2159). The NDVI during the growing season exhibited a fluctuating growth trend, with an average growth rate of 0.0018/10a (P<0.01). Notably, forests displayed a significant development trend throughout the growing season, possessing the fastest rate of change in NDVI (0.0028/10a). Moreover, the upward trends in NDVI for forests and steppes exhibited extensive spatial distributions, with significant increases accounting for 95.23% and 93.80%, respectively. The sensitivity to precipitation was significantly enhanced in other vegetation types other than highland vegetation. By contrast, steppes, meadows, and highland vegetation demonstrated relatively high vulnerability to temperature fluctuations. A further detailed analysis revealed that climate change had a significant positive impact on the TRSR from 2000 to 2022, particularly in its northwestern areas, accounting for 85.05% of the total area. Meanwhile, human activity played a notable positive role in the southwestern and southeastern areas of the TRSR, covering 62.65% of the total area. Therefore, climate change had a significantly higher impact on NDVI during the growing season in the TRSR than human activity.
分类： 生物学 >> 生态学 提交时间： 2024-08-14 合作期刊: 《干旱区科学》
摘要： The Mongolian Plateau in East Asia is one of the largest contingent arid and semi-arid areas of the world. Under the impacts of climate change and human activities, desertification is becoming increasingly severe on the Mongolian Plateau. Understanding the vegetation dynamics in this region can better characterize its ecological changes. In this study, based on Moderate Resolution Imaging Spectroradiometer (MODIS) images, we calculated the kernel normalized difference vegetation index (kNDVI) on the Mongolian Plateau from 2000 to 2023, and analyzed the changes in kNDVI using the Theil-Sen median trend analysis and Mann-Kendall significance test. We further investigated the impact of climate change on kNDVI change using partial correlation analysis and composite correlation analysis, and quantified the effects of climate change and human activities on kNDVI change by residual analysis. The results showed that kNDVI on the Mongolian Plateau was increasing overall, and the vegetation recovery area in the southern region was significantly larger than that in the northern region. About 50.99% of the plateau showed dominant climate-driven effects of temperature, precipitation, and wind speed on kNDVI change. Residual analysis showed that climate change and human activities together contributed to 94.79% of the areas with vegetation improvement. Appropriate human activities promoted the recovery of local vegetation, and climate change inhibited vegetation growth in the northern part of the Mongolian Plateau. This study provides scientific data for understanding the regional ecological environment status and future changes and developing effective ecological protection measures on the Mongolian Plateau.
分类： 生物学 >> 生态学 提交时间： 2024-08-14 合作期刊: 《干旱区科学》
摘要： Understanding the response of vegetation variation to climate change and human activities is critical for addressing future conflicts between humans and the environment, and maintaining ecosystem stability. Here, we aimed to identify the determining factors of vegetation variation and explore the sensitivity of vegetation to temperature (SVT) and the sensitivity of vegetation to precipitation (SVP) in the Shiyang River Basin (SYRB) of China during 2001–2022. The climate data from climatic research unit (CRU), vegetation index data from Moderate Resolution Imaging Spectroradiometer (MODIS), and land use data from Landsat images were used to analyze the spatial-temporal changes in vegetation indices, climate, and land use in the SYRB and its sub-basins (i.e., upstream, midstream, and downstream basins) during 2001–2022. Linear regression analysis and correlation analysis were used to explore the SVT and SVP, revealing the driving factors of vegetation variation. Significant increasing trends (P<0.05) were detected for the enhanced vegetation index (EVI) and normalized difference vegetation index (NDVI) in the SYRB during 2001–2022, with most regions (84%) experiencing significant variation in vegetation, and land use change was determined as the dominant factor of vegetation variation. Non-significant decreasing trends were detected in the SVT and SVP of the SYRB during 2001–2022. There were spatial differences in vegetation variation, SVT, and SVP. Although NDVI and EVI exhibited increasing trends in the upstream, midstream, and downstream basins, the change slope in the downstream basin was lower than those in the upstream and midstream basins, the SVT in the upstream basin was higher than those in the midstream and downstream basins, and the SVP in the downstream basin was lower than those in the upstream and midstream basins. Temperature and precipitation changes controlled vegetation variation in the upstream and midstream basins while human activities (land use change) dominated vegetation variation in the downstream basin. We concluded that there is a spatial heterogeneity in the response of vegetation variation to climate change and human activities across different sub-basins of the SYRB. These findings can enhance our understanding of the relationship among vegetation variation, climate change, and human activities, and provide a reference for addressing future conflicts between humans and the environment in the arid inland river basins.
分类： 地球科学 >> 水文学 提交时间： 2024-08-14 合作期刊: 《干旱区科学》
摘要： Since the 1950s, numerous soil and water conservation measures have been implemented to control severe soil erosion in the Liuhe River Basin (LRB), China. While these measures have protected the upstream soil and water ecological environment, they have led to a sharp reduction in the downstream flow and the deterioration of the river ecological environment. Therefore, it is important to evaluate the impact of soil and water conservation measures on hydrological processes to assess long-term runoff changes. Using the Soil and Water Assessment Tool (SWAT) models and sensitivity analyses based on the Budyko hypothesis, this study quantitatively evaluated the effects of climate change, direct water withdrawal, and soil and water conservation measures on runoff in the LRB during different periods, including different responses to runoff discharge, hydrological regime, and flood processes. The runoff series were divided into a baseline period (1956–1969) and two altered periods, i.e., period 1 (1970–1999) and period 2 (2000–2020). Human activities were the main cause of the decrease in runoff during the altered periods, contributing 86.03% (–29.61 mm), while the contribution of climate change was only 13.70% (–4.70 mm). The impact of climate change manifests as a decrease in flood volume caused by a reduction in precipitation during the flood season. Analysis of two flood cases indicated a 66.00%–84.00% reduction in basin runoff capacity due to soil and water conservation measures in the upstream area. Soil and water conservation measures reduced the peak flow and total flood volume in the upstream runoff area by 77.98% and 55.16%, respectively, even with nearly double the precipitation. The runoff coefficient in the reservoir area without soil and water conservation measures was 4.0 times that in the conservation area. These results contribute to the re-evaluation of soil and water conservation hydrological effects and provide important guidance for water resource planning and water conservation policy formulation in the LRB.
分类： 地球科学 >> 地球科学其他学科 提交时间： 2024-08-13
摘要： The traditional uniformity coefficient Cu cannot reflect the uniformity of gap-graded granular mixtures. This paper proposes a new index CmuCum to quantify the uniformity of granular mixtures based on the study on their small-strain stiffness G0. The samples of granular mixtures with different fines content (FC) and particle size ratio (PSR) are prepared. The G0 values are determined by quasistatic drained triaxial tests on these samples. The CmuCum values are calculated from the obtained G0 values and can be expressed as a function of FC and PSR. The rationality of the proposed CmuCum is verified. The CmuCum can be used to predict the G0 of granular mixtures when the mechanical coordination number (CNm), shear modulus of particles (Gp), confining stress (σ0) and CmuCum are given.
分类： 力学 >> 生物力学 提交时间： 2024-08-13 合作期刊: 《应用力学学报》
摘要： 目的 对不同等级男子撑竿跳高运动员质心速度、质心高度、地面反作用力和下肢关节力矩等生物力学指标的具体表现进行探讨,试图了解不同等级运动员的整体特征,并发现高水平运动员助跑及起跳过渡衔接的特点。方法 使用大范围的三维动作捕捉系统以及3块测力台对优秀男子撑竿跳高运动员的运动学(200 Hz)和地面反作用力(2 000 Hz)数据进行采集,分析比较了5名一级运动员、4名运动健将和3名国际级运动健将的生物力学指标。对国际级运动健将组、运动健将组和一级运动员组的同一生物力学指标两两之间采用非参数独立样本曼-惠特尼U单侧检验,对所有运动员倒2步、倒1步和起跳相应的生物力学指标两两之间采用非参数配对样本Wilcoxon符号秩单侧检验。结果 不同等级撑竿跳高运动员助跑后两步和起跳的质心速度、质心高度、地面反作用力和下肢关节力矩等生物力学指标有显著性差异; 倒2步、倒1步、起跳相应的生物力学指标之间有显著性差异。结论 基于本研究的数据,男子撑竿跳高运动员表现出随等级而变化的生物力学特点,国际级健将运动员的质心速度、地面反作用力等指标体现了其较高的运动能力。倒2步、倒1步和起跳的质心速度、质心高度和地面反作用力等相应生物力学指标的显著差异反映了撑竿跳高技术动作的衔接特征,体现了撑竿跳高助跑向起跳过渡的运动学和动力学特点。
分类： 力学 >> 生物力学 提交时间： 2024-08-13 合作期刊: 《应用力学学报》
摘要： 通过力学建模方法对病人皮肤组织疾病进行诊断、评估和治疗,需要准确识别皮肤组织的力学性能。为此,提出了一种运用自适应模拟退火优化算法结合代理模型技术的皮肤组织本构参数识别方法。首先,采用有限元方法模拟皮肤单轴拉伸试验,获取不同参数组合下,皮肤组织的数值计算力学响应数据。为提高参数识别的计算效率,分别构建了响应面模型、克里金模型、椭球基神经网络3种代理模型来代替重复的仿真计算过程,并采用决定系数R2对3种代理模型的拟合精度进行校验。最后,利用自适应模拟退火优化算法,以试验曲线与数值计算曲线均方根误差最小为优化目标,通过反演识别出了与普通家猪腹肋部皮肤组织单轴拉伸试验结果最匹配的本构参数:C10=0.140 1 MPa、k1=24.51 MPa、k2=0.496 1、κ=0.317 1、φ=13.86°。结果表明,椭球基神经网络模型更适合拟合皮肤本构模型参数与应力应变响应间的非线性关系。对比识别出的数值计算曲线与试验曲线,表明自适应模拟退火算法结合代理模型技术是识别皮肤组织各向异性超弹性本构参数的快速、可靠方法。
分类： 力学 >> 流体力学 提交时间： 2024-08-13 合作期刊: 《应用力学学报》
摘要： 在增强型地热系统(enhanced geothermal system,EGS)热开采过程中,储层渗透率受应力的影响而动态变化。为揭示裂隙岩体渗透特性和应力之间的耦合作用对系统采热性能的影响,建立双重介质热流固(thermo-hydro-mechanical,THM)耦合模型,分析基质和裂隙渗透率随应力动态变化时储层THM三场变化规律。结果表明:在热应力与水压力共同作用下,基质渗透率逐渐减小,裂隙渗透率呈指数式增加,采热速率主要由裂隙渗透率的动态变化决定,但如果忽略基质渗透率的动态变化,预测的裂隙渗透率比实际提高41.8%,热突破时间提前,会低估近2年的系统运行寿命。因此,同时考虑裂隙和基质渗透率与应力的耦合作用对合理评价EGS系统使用寿命有重要意义。
分类： 力学 >> 流体力学 提交时间： 2024-08-13 合作期刊: 《应用力学学报》
摘要： 针对当前高层建筑典型外立面形式,以长沙市同有大厦为研究对象,基于SSTk-ω湍流模型对增设阳台、不同凹凸外形及不同格栅类型等9种外立面高层建筑表面风压进行了详细分析,明确了不同外立面形式下建筑表面风压分布特性,并结合高层建筑周围流场信息,揭示了外立面形式对其表面风压的影响机理。结果表明:外立面增设阳台会导致迎风面风压系数最大值增加,背风面风压系数负值最大值减小; 同时,阳台会使来流在建筑顶层阳台顶端出现流动分离,在高层建筑迎风面顶部形成局部负压; 相比光滑立面,凹、凸立面会导致高层建筑迎风面和背风面表面风压差增加,建筑物靠近顶部区域会出现压力突变现象,且在墙角处会出现较大负值; 增设竖向格栅同样会增大高层建筑迎风面和背风面压差,而横向和矩形格栅对结构风荷载影响相对较小。
分类： 力学 >> 流体力学 提交时间： 2024-08-13 合作期刊: 《应用力学学报》
摘要： 为研究射流冲击下混凝土的破损机理与裂纹扩展规律,基于光滑粒子流体动力学(smooth particle hydrodynamics,SPH)方法建立了磨料水射流冲击混凝土的数值模型,研究了混凝土内部的应力传播和破损方式,磨料体积分数和混凝土的孔隙率与裂纹长度、失效粒子数、坑深和坑径之间的关系。研究表明:裂纹对应力具有强阻碍作用,与边界应力波的反射叠加会使得应力区域性集中,形成中心微裂纹,以及内部破碎块; 磨料体积分数为20%与0%相比,裂纹长度增加2.30倍,失效粒子数增加3.38倍,坑深值增加4.00倍,证明射流中添加磨料会大幅提高破损效果; 混凝土的孔隙率越大,裂纹分布越发散,损伤区域面积、损伤程度和分形维数越大,证明孔隙会降低混凝土的抗压强度,孔隙率大的材料更易受损。
分类： 力学 >> 力学其他学科 提交时间： 2024-08-13 合作期刊: 《应用力学学报》
摘要： 为研究空沟在层状地基上时,土体参数和土体分界面对土体振动响应的影响,采用Comsol仿真物理场建立了二维有限元分析模型。在研究中,分析了层状地基不同土体参数时的土体振动响应表现差异,结果表明:空沟在深度达到层状地基的土体分界面附近时会出现振动加强现象,该现象受到分层土体的泊松比和密度以及弹性模量的影响。土体参数的变化同样会导致土体振动响应的变化,具体表现为密度越大则土体振动响应就越大; 而弹性模量和泊松比则需考虑分层情况。其中下层弹性模量越大则土体振动响应越大,上层则与之相反; 下层泊松比越小则土体振动响应越大,而上层在空沟深度小于一定范围内时时表现为泊松比越小土体振动响应越大,在当达到一定深度后,上层土体不同泊松比的加速度大小曲线呈现交错状态。
分类： 力学 >> 力学其他学科 提交时间： 2024-08-13 合作期刊: 《应用力学学报》
摘要： 基于快速边界元方法和三维运动学有限断层模型,对倾滑断层作用下复杂场地地震动进行求解。以三维近断层沉积盆地为例,采用频域内动力格林函数求解散射场的地震动,以频域内地震波的相位变化反映发震断层在时域内的动态破裂过程,突破了确定性震源难以模拟高频地震波散射的瓶颈,通过设计快速边界元方法频域-时域自适应逆变换程序得到时域内地震响应,在频域和时域内皆实现了基于确定性运动学有限震源模型的地震动快速边界元法模拟,量化分析了倾滑断层动态破裂下近场沉积盆地地震动的放大效应,揭示了地震的近断层效应与盆地效应的耦合机制。结果表明:近断层效应和盆地聚焦效应存在明显的耦合作用,显著影响了盆地区域地震动的空间分布,盆地中心点的地震动相较于断层附近输入地震动放大了3.97倍; 永久位移随断层距离的增加而衰减; 在沉积盆地区域内,地震动持时显著延长,软土沉积对外部输入的速度脉冲有放大作用,出现幅值较大的长周期速度大脉冲; 沉积盆地会显著增大近断层强震集中性的分布范围。
分类： 力学 >> 力学其他学科 提交时间： 2024-08-13 合作期刊: 《应用力学学报》
摘要： 典型的无网格方法采用移动最小二乘函数(moving least squares,MLS)作为近似函数,但由于MLS不具备Kronecker delta函数性质,本质边界施加困难。LRPIM是采用径向基点插值形函数的无网格方法,本质边界条件无需特殊处理,可以直接施加,在保持高精度的前提下提高计算效率。将LRPIM应用于机械结合面接触问题的计算。根据位移连续条件推导了含接触特性的线性互补方程,建立了基于LRPIM的计算模型,采用线性互补算法利用数值积分计算了几种典型的接触问题,得到了接触面压力分布和接触变形,分析了插值函数形状参数和积分域尺寸对计算结果的影响。研究结果表明,插值函数形状参数αc对接触力的影响较小,而形状参数q取-0.5～1.2时有较好的收敛效果; 积分域无量纲尺寸aqx、aqy大于1.5时计算结果开始收敛,大于2.5时出现发散现象,取值2.1时收敛效果最佳。将计算结果与已有结果进行比较,表明本研究方法有较高的求解精度。
分类： 力学 >> 力学其他学科 提交时间： 2024-08-13 合作期刊: 《应用力学学报》
摘要： 为探讨超高性能混凝土(ultra-high performance concrete,UHPC)材料在低速冲击压缩下的力学性能,应用大型有限元程序LS-DYNA,结合UHPC材料性能,校准了混凝土连续面盖帽(continuous surface cap,CSC)模型中的参数取值,建立了基于SHPB技术的UHPC低速冲击压缩数值模型并与试验验证,在此基础上探讨了低速冲击下试件单轴抗压强度和应变率对UHPC动力增大系数(dynamic increase factor,DIF)的影响,提出了UHPC动力增大系数数值回归公式。结果表明:基于合适的参数选取,应用校准后CSC模型建立的UHPC动态冲击压缩数值仿真模型具有较好的精准性; 在不同的单轴抗压强度下,应用CSC模型得到的UHPC试件前后端面应力比变化趋势大致相同,但随着应变率的提高,CSC模型模拟效果表现出相对下降的趋势; UHPC动力增大系数随着应变率的提高而增大,随着单轴抗压强度的增大而逐渐降低,表现出明显的应变率效应和强度效应; 建立的耦合应变率和单轴抗压强度的UHPC动力增大系数计算公式能较好地吻合数值分析结果,并在一定程度上避免高估UHPC动力增大系数,对低速冲击作用下UHPC动力特性评估具备一定的适用性。
分类： 力学 >> 力学其他学科 提交时间： 2024-08-13 合作期刊: 《应用力学学报》
摘要： 钢纤维混凝土内部缺陷的萌生、扩展等变化过程,需从细观角度出发进行研究。为了建立更加接近实际的钢纤维混凝土细观随机分布模型,提出了一种高效可靠的钢纤维混凝土细观建模方法。采用Python语言对ABAQUS程序进行二次开发,避免了建模中不同软件之间信息传递过程繁琐的问题。提出了一种新的关于多边形骨料和钢纤维的干涉判断方法 ——点线法,推导了在任意椭圆形骨料边界上取点的方程,提高了骨料投放的高效性。基于上述方法,对钢纤维混凝土试件在单轴压缩下的破坏过程进行了模拟并与试验结果进行对比。结果表明:对于二维细观模型中的二级配多边形骨料投放比可以达到70%,椭圆形骨料投放比可以达到69%; 消除了钢纤维在建模过程中相交的现象。数值模拟得到的破坏形态和应力-应变曲线与试验得到的吻合较好,进一步验证了提出的方法可行性。
分类： 力学 >> 力学其他学科 提交时间： 2024-08-13 合作期刊: 《应用力学学报》
摘要： 为得到高精度的Ⅰ型应力强度因子,提出了一种基于辛几何方法测定裂纹尖端Ⅰ型应力强度因子的方法。通过在裂纹尖端构建扇形区域,分离辛几何方法下裂纹尖端的全状态向量,结合裂纹尖端的位移场,计算出裂纹的应力强度因子。利用Ⅰ型裂纹尖端位移场的理论解,研究了扇形区域的特征点个数、圆心角大小以及半径长度对应力强度因子精确度的影响。研究结果表明:特征点个数对该方法求解Ⅰ型应力强度因子的精度的影响较大,特征点个数大于37时,相对误差稳定趋向于0; 扇形圆心角对应力强度因子的精度影响较小,但是相同精度要求下,不同的扇形圆心角需要的特征点个数不同; 扇形半径过小时,由于断裂过程中裂纹尖端塑性区域的影响,应力强度因子的解不稳定且相对误差较大。对比相对误差可以发现该方法计算得到的Ⅰ型应力强度因子的精度较高,且该方法只需得到裂纹尖端的位移场就可以精确得到应力强度因子,解决了以往求解体系在复杂应力等情况下求解步骤复杂,导致无法精确得到Ⅰ型应力强度因子的难题。
点击量
通过
点击量
下载量
评论
待评议
