Subjects: Agriculture, Forestry,Livestock & Aquatic Products Science >> Soil Science submitted time 2024-08-14 Cooperative journals: 《干旱区科学》
Abstract： 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.
Subjects: Biology >> Ecology submitted time 2024-08-14 Cooperative journals: 《干旱区科学》
Abstract： 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.
Subjects: Biology >> Ecology submitted time 2024-08-14 Cooperative journals: 《干旱区科学》
Abstract： 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.
Subjects: Geosciences >> Atmospheric Sciences submitted time 2024-08-14 Cooperative journals: 《干旱区科学》
Abstract： 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.
Subjects: Biology >> Ecology submitted time 2024-08-14 Cooperative journals: 《干旱区科学》
Abstract： 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.
Subjects: Biology >> Ecology submitted time 2024-08-14 Cooperative journals: 《干旱区科学》
Abstract： 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.
Subjects: Biology >> Ecology submitted time 2024-08-14 Cooperative journals: 《干旱区科学》
Abstract： 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.
Subjects: Geosciences >> Hydrology submitted time 2024-08-14 Cooperative journals: 《干旱区科学》
Abstract： 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.
Subjects: Geosciences >> Other Disciplines of Geosciences submitted time 2024-08-13
Abstract： The traditional uniformity coefficient Cu cannot reflect the uniformity of gap-graded granular mixtures. This paper proposes a new index Cmu 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 Cmu values are calculated from the obtained G0 values and can be expressed as a function of FC and PSR. The rationality of the proposed Cmu is verified. The Cmu 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 Cmu are given.
Peer Review Status:
Awaiting Review
Subjects: Mechanics >> Biomechanics submitted time 2024-08-13 Cooperative journals: 《应用力学学报》
Abstract：
Objective This study aimed to analyze and compare the athlete's center of mass(COM)velocity,COM height,ground reaction force(GRF),and lower limb joint moment of different levels of athletes during pole vault run-up and takeoff,so as to explore the technical characteristics of the transition between run-up and takeoff,which provides reference and help for the training and competition of pole vault.Methods A large-scale three-dimensional(3D)motion capture system(200 Hz)and three force platforms(2 000 Hz)were used to collect the kinematics and ground reaction force data of male elite pole vaulters,and five first-class athletes,four master athletes and three international master athletes were analyzed.Mann-Whitney U test was utilized for biomechanical parameters between every two groups within international master athletes,master athletes,and first-class athletes.Wilcoxon signed ranks test was used between every two corresponding biomechanical parameters of the second-to-last step,the last step,and takeoff.Results The athletes' COM velocity,COM height,GRF,and lower limb joint moment showed significant differences between the different level groups of pole vaulters,and the biomechanical parameters of the second-to-last step,the last step,and the takeoff also displayed significant differences.Conclusion Based on the data of this study,the male pole vaulters showed biomechanical characteristics that varied with their levels.The COM velocity and GRF of the international master athletes indicate their higher sports competence.The differences between the biomechanical parameters of the second-to-last step,the last step,and takeoff,including COM velocity,COM height and GRF,might display the technical characteristics of pole vault movement transition,which indicate the kinematic and kinetic transition characteristics of pole vault from run-up to takeoff.
Subjects: Mechanics >> Biomechanics submitted time 2024-08-13 Cooperative journals: 《应用力学学报》
Abstract：
It is necessary to accurately identify the mechanical properties of skin tissue for diagnosis,evaluation and treatment of skin tissue diseases by means of mechanical modeling.Therefore,this paper proposes a skin tissue constitutive parameter identification method using adaptive simulated annealing optimization algorithm combined with approximation model technology.First,the finite element method was used to simulate the skin uniaxial tensile test,and the numerical mechanical response data of skin tissue were obtained under different parameter combinations.In order to improve the computational efficiency of parameter identification,response surface model,Kriging model,and ellipsoidal neural network were constructed to replace the repeated simulation calculation process,and the fitting accuracy of the three approximation models was verified by the determination coefficient R2.Finally,an adaptive simulated annealing optimization algorithm was used to identify the constitutive parameters that best matched the uniaxial tensile test results of skin tissue of common pig belly through inversion with the objective of minimizing the root mean square error of the test curve and the numerical calculation curve: C10=0.140 1 MPa,k1=24.51 MPa,k2=0.496 1,κ=0.317 1,and φ=13.86°.The results show that the ellipsoidal neural network model is more suitable for fitting the nonlinear relationship between skin constitutive model parameters and stress-strain response.The comparison between the identified numerical and experimental curves shows that the adaptive simulated annealing algorithm combined with the approximation model is a fast and reliable method to identify the anisotropic hyperelastic constitutive parameters of skin tissue.
Subjects: Mechanics >> Hydromechanics submitted time 2024-08-13 Cooperative journals: 《应用力学学报》
Abstract： During the thermal exploitation of enhanced geothermal system(EGS),reservoir permeability varies dynamically under the influence of stress.In order to reveal the coupling mechanism between the permeability of fractured rock matrix and stress field and its influence on the performance of heat mining,a thermo-hydro-mechanical(THM)coupling model of dual mediums including matrix and fracture was established based on the THM coupling theory,and the THM field of the reservoir is analyzed when the matrix and fracture permeability change with the stress.The results show that under the combined action of thermal stress and water pressure,the matrix permeability decreases gradually,and the fracture permeability increases exponentially.Hence,the rate of recovery heat is mainly determined by the dynamic changes of the fracture permeability.However,the predicted fracture permeability is 41.8% higher than the actual permeability if the dynamic changes of the matrix permeability is ignored during the simulation.As a result,the predicted heat breakthrough time is advanced,which would underestimate the system running life of nearly two years.Therefore,it is significant to evaluate the service life of EGS system to consider the coupling effect of fracture and matrix permeability and stress simultaneously.
Subjects: Mechanics >> Hydromechanics submitted time 2024-08-13 Cooperative journals: 《应用力学学报》
Abstract：
Based on the SST k-ω turbulence model,the surface wind pressure of nine high-rise buildings,such as balconies,different concave and convex shapes and different grid types,is analyzed in detail.The wind pressure distribution characteristics of the building surface under different facade forms are clarified,and the mechanism of the facade form's influence on the surface wind pressure of the high-rise buildings is revealed in combination with the flow field information around the high-rise buildings.The results show that the maximum value of windward wind pressure coefficient increases and the maximum value of negative value of leeward wind pressure coefficient decreases with the addition of balcony on the facade.And balcony density has some influence to these.At the same time,the balcony will cause the flow to separate at the top of the balcony on the top floor of the building and form a local negative pressure on the top of the windward surface of the high-rise building.Compared with the smooth facade,the concave and convex facades will lead to an increase in the wind pressure difference between the windward surface and the leeward surface of the high-rise building.The phenomenon of pressure mutation will occur in the area near the top of the building,and a large negative value will appear at the corner of the wall.The addition of vertical grilles will also increase the pressure difference between the windward and leeward surfaces of high-rise buildings,while the lateral and rectangular grilles have a relatively small impact on structural wind loads.
Subjects: Mechanics >> Hydromechanics submitted time 2024-08-13 Cooperative journals: 《应用力学学报》
Abstract：
In order to explore the breakage mechanism and crack expansion pattern of concrete under jet impact,a numerical model of abrasive water jet impacting concrete was constructed based on smooth particle hydrodynamics(SPH)method.The relationship of stress propagation and breakage mode inside concrete,abrasive volume fraction and porosity of concrete with crack length,failure particle number,pit depth and pit diameter was investigated.It is indicated that cracks have strong hindering effect on stresses,and the superposition of reflections with boundary stress waves cause stress concentration in some regional,forming the central microcracks and internal broken blocks.The crack length increased by nearly 2.30 times,the number of failed particles by 3.38 times,and the pit depth value by 4.00 times,with abrasive volume fraction of 20% compared to 0%,indicating that the addition of abrasives to the jet substantially increased the breakage effect.The greater porosity of concrete is,the more diffuse cracks distribute,the larger of damage area,the greater of damage degree,and the greater fractal dimension are,indicating that porosity reduces the concrete compressive strength and that materials with large porosity are more prone to breakage.
Subjects: Mechanics >> Other Disciplines of Mechanics submitted time 2024-08-13 Cooperative journals: 《应用力学学报》
Abstract：
In order to study the influence of soil parameters and soil interface on soil vibration response when the hollow trench is on the layered foundation,a two-dimensional finite element analysis model was established by using the Comsol simulation physical field.In the study,the difference in soil vibration response performance of layered foundations with different soil parameters was analyzed,and the results showed that when the depth of the hollow trench reaches near the soil interface of the layered foundation,the vibration intensification phenomenon occurs,and this phenomenon is divided.The influence of the Poisson's ratio and density of the layered soil as well as the modulus of elasticity.Changes in soil parameters will also lead to changes in the vibration response of the soil.Specifically,the greater the density,the greater the vibration response of the soil; while the elastic modulus and Poisson's ratio need to be considered for delamination.The greater the elastic modulus of the lower layer,the greater the vibration response of the soil,and the opposite is the case for the upper layer; the lower the Poisson's ratio of the lower layer,the greater the vibration response of the soil,while the upper layer exhibits Poisson's ratio when the trench depth is less than 0.5 m.The smaller the soil mass,the greater the vibration response,but when the depth is greater than 0.5 m,the resulting acceleration curve shows a staggered state.
Subjects: Mechanics >> Other Disciplines of Mechanics submitted time 2024-08-13 Cooperative journals: 《应用力学学报》
Abstract：
Based on the fast boundary element method and three-dimensional kinematic finite fault model,the ground motion of a complex site under the action of dip-slip fault is solved.Taking a three-dimensional near fault sedimentary basin as an example,the dynamic Green's function in the frequency domain is used to calculate the ground motion of the disbanded radiation field,and the phase change of the seismic wave in the frequency domain reflects the dynamic fracture process of the seism genic fault in the time domain,which breaks through the bottleneck that deterministic sources are challenging to simulate high-frequency seismic wave scattering.The seismic response in the time domain is obtained by designing the frequency domain and the adaptive inverse transform program of the fast boundary element method.The fast boundary element method simulation of ground motion based on a deterministic kinematic finite source model is realized in both the frequency domain and time domain.The amplification effect of near field sedimentary basin ground motion under the dynamic fracture of dip-slip fault is analyzed quantitatively,and the coupling mechanism of near-fault effect and basin effect of an earthquake is revealed.The results show that there is an apparent coupling between the near-fault effect and basin focusing effect,which significantly affects the spatial distribution of ground motion in the basin area.The ground motion at the center of the basin is 3.97 times larger than the input ground motion near the fault.The permanent displacement decreases with the increase of fault distance. In the area of sedimentary basin,the duration of seismic motion is significantly prolonged,and the soft soil deposit amplifies the external input velocity pulse,resulting in large amplitude long-period velocity pulse; Sedimentary basins will dramatically increase the distribution range of near-fault strong earthquakes.This paper develops an efficient and accurate ground motion simulation method for near near-fault complex sites.The research conclusions are of great significance for seismic zoning near-fault sedimentary basins and seismic design of engineering structures.
Subjects: Mechanics >> Other Disciplines of Mechanics submitted time 2024-08-13 Cooperative journals: 《应用力学学报》
Abstract： The conventional meshless method uses the moving least squares(MLS)as an approximate function,but since MLS does not have the property of Kronecker delta,it is difficult to exert the essential boundary condition.LRPIM is a meshless method using radial interpolation approximate function.The essential boundary condition can be directly put without special treatment,which can improve the computational efficiency while maintaining high accuracy.In this paper,LRPIM linear programming method is applied to the contact problem of mechanical joint surface.LRPIM meshless method was used to calculate the global stiffness and global force; according to the displacement condition,the contact linear complementarity equation is derived; a calculation model based on LRPIM is established.Several typical contact problems are calculated by using linear complementary algorithm and numerical integration.The pressure distribution and contact deformation of the contact surface are obtained.The influence of shape parameter of interpolation function and integral domain size on the calculation results is analyzed.The results show that the influence of the shape parameter αc of the interpolation function on the contact force is small,and the shape parameter q takes -0.5～1.2,which has a good convergence effect.When the dimensionless size of the integral domain aqx and aqy is greater than 1.5,the calculation results begin to converge,and divergence occurs when aqx and aqy is greater than 2.5.The convergence effect is the best when they are equal to 2.1.The calculation results are compared with the existing results,indicating that the method in this paper has high computed accuracy.
Subjects: Mechanics >> Other Disciplines of Mechanics submitted time 2024-08-13 Cooperative journals: 《应用力学学报》
Abstract：
To discuss the behavior of ultra-high performance concrete(UHPC)under a low-speed compressive impact,the parameters of continuous surface cap(CSC)model in the LS-DYNA are calibrated,based on the material characteristics of UHPC.The low-speed impact analysis model of UHPC using SHPB technology is established and verified with experimental results.On this basis,the effect on the dynamic increase factor(DIF)varying in the uniaxial compressive strength and strain rate of UHPC specimen under the low-speed impact is discussed.A regression formula to calculate DIF for UHPC is established.The results are as follows:Based on appropriate parameter values,the established analysis model using the calibrated CSC model for UHPC has an accepted accuracy.The variation trend of the stress ratio between the front-end and rear-end of UHPC specimen under different uniaxial compressive strengths is generally similar,but the simulation effect demonstrates a downtrend with the increase of strain rate for the calibrated CSC model.The DIF value of UHPC increases with the increase of strain rate,but decreases with the increase of uniaxial compressive strength,indicating the clear strain rate and strength effects.The formula to calculate DIF for UHPC coupling with strain rate and uniaxial compressive strength can well agree with the analysis results and avoid overestimating the DIF values of UHPC to a certain extent,indicating certain applicability for estimating the dynamic behavior of UHPC under a low-speed impact.
Subjects: Mechanics >> Other Disciplines of Mechanics submitted time 2024-08-13 Cooperative journals: 《应用力学学报》
Abstract：
The changing process of internal defects of steel fiber reinforced concrete,such as initiation and expansion,needs to be studied from a mesoscopic perspective.In order to establish a more realistic mesoscopic random distribution model of steel fiber reinforced concrete,an efficient and reliable mesoscopic modeling method of steel fiber reinforced concrete is proposed.The secondary development of the ABAQUS program is carried out in Python language,which avoids the tedious problem of the information transfer process between different software in modeling.A new interference judgment method for polygon aggregate and steel fiber is proposed—point line method,and the equation of taking points on the boundary of arbitrary elliptical aggregate is derived,which improves the efficiency of aggregate delivery.Based on the above method,the failure process of steel fiber concrete specimen under uniaxial compression is simulated and compared with the test results.The results show that the delivery ratio of second graded polygon aggregate is 70%,the delivery ratio of second graded elliptical aggregate is 69% in 2D mesoscopic model and the intersection of steel fiber in modeling process is eliminated.The failure patterns and stress-strain curves obtained by numerical simulation are in good agreement with the experimental results.The feasibility of the proposed method is further verified.
Subjects: Mechanics >> Other Disciplines of Mechanics submitted time 2024-08-13 Cooperative journals: 《应用力学学报》
Abstract：
In order to obtain the mode Ⅰ stress intensity factor with high accuracy,a method for determining mode Ⅰ stress intensity factor based on symplectic geometry method is proposed.By constructing a fan-shaped region at the crack tip,separating the full state vector of the crack tip under the symplectic geometry method,combined with the displacement field at the crack tip,the stress intensity factor is calculated.Based on the theoretical solution of the displacement field around the mode I crack tip,the effects of the number of characteristic points,the size of center angle and radius length on the accuracy of stress intensity factor are studied.The results show that the number of characteristic points has a great influence on the accuracy of solving mode I stress intensity factor by this method.As the number of characteristic points is greater than 37,the relative error tends to 0 stably; the sector center angle has little effect on the accuracy of stress intensity factor,but under the same accuracy requirements,different sector center angles need different number of feature points; as the sector radius is too small,the solution of stress intensity factor is unstable and the relative error is large due to the influence of the plastic region at the crack tip in the fracture process.By comparing the relative errors,it can be found that the accuracy of the mode I stress intensity factor calculated by the proposed method is high,and the stress intensity factor can be accurately obtained only by obtaining the displacement field around the crack tip.It solves the problem that the previous solution system has complex steps in the case of complex stress,resulting in the inability to accurately obtain the mode I stress intensity factor.
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