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1.
传统的伪谱(PS)方法,采用傅里叶变换(FT)计算空间导数具有很高的精度,每个波长仅需要两个采样点,而时间导数采用有限差分(FD)近似因而精度较低.当采用大时间步长时,由于时空精度不平衡,PS法存在不稳定性问题.原始的k-space方法可以有效地克服这些问题但是却无法适用于非均匀介质.为了提高原始k-space方法模拟非均匀介质波动方程的精度,我们提出了一种新的k-space算子族.它是用非均匀介质的变速度代替原k-space算子中的常数补偿速度构造得到,引入低秩近似可以高效求解.我们将构造的新的k-space算子应用于耦合的二阶位移波动方程,而不是交错网格一阶速度应力波动方程,使模拟弹性波的计算存储量减少.我们从数学上证明了基于二阶波动方程的k-space方法与基于一阶波动方程的k-space方法是等价的.数值模拟实验表明,与传统的PS、交错网格PS和原始的k-space方法相比,我们的新方法可以在时间和空间步长较大的均匀和非均匀介质中,为弹性波的传播提供更精确的数值解.在保持稳定性和精度的同时,采用较大的时空采样间隔,可以大大降低数值模拟的计算成本. 相似文献
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按照粮食的产销情况,将全国划分为3类粮食功能区域,利用固定效应模型和门槛效应模型分析了农机投入对农业绿色全要素生产率(GTFP)的影响及门槛效应的区域差异。结果表明:农机投入对农业GTFP的影响程度存在区域异质性,农机投入对粮食主销区农业GTFP提升的促进作用最大,粮食产销平衡区次之,粮食主产区最小;农机投入对农业GTFP的影响路径亦存在区域差异,粮食主产区和产销平衡区的农机投入通过促进农业技术效率和农业技术进步进而推动农业GTFP提升,粮食主销区的农机投入通过促进农业技术进步推动农业GTFP提升;农机投入对粮食主产区农业GTFP的影响存在双门槛效应,对粮食主销区和产销平衡区农业GTFP的影响存在单门槛效应。 相似文献
4.
情境教学是培养学生核心素养的重要教学方法,本文提出了情境教学的课堂评价原则:情境具有真实性、情境与教学目标具有关联性、情境应划分水平。同时提出从情境的结构和关系、解决情境中的问题所涉及地理要素的数量及其关联程度两个角度分别对情境水平进行划分,并结合“资源枯竭型城市的发展方向”课例,提出目前情境教学中存在的问题及教学改进建议。 相似文献
5.
在槽式太阳能热发电领域,硝酸镁基熔盐逐渐引起关注。通过六水硝酸镁煅烧法制备无水硝酸镁,采用拉曼、DSC与XRD表征脱水产物,系统研究了环境压力、脱水温度与时间对六水硝酸镁脱水和水解的影响。结果表明,六水硝酸镁在煅烧过程中水解为碱式硝酸镁Mg_3(OH)_4(NO_3)_2,在水溶液中进一步分解为Mg(OH)_2。随着煅烧温度和时间的增加,脱水产物中的含水量逐渐减少,同时水解产物Mg_3(OH)_4(NO_3)_2含量逐渐增加。真空环境下煅烧,可显著降低硝酸镁的水解反应。六水硝酸镁在真空环境下230℃煅烧1.5 h,所制备的无水硝酸镁中水解产物含量为3.63%。制备的硝酸镁可进一步用于硝酸镁基熔盐的研究。 相似文献
6.
The effects of irregularity in elevation of cross-laminated timber buildings have not been fully analysed in literature to provide useful information for the design. In this work, a number of building configurations, regular or irregular in elevation, characterized by a different arrangement per storey of the floor–wall joints have been analysed by means of non-linear dynamic analyses. Comparative results in terms of ratio between the behaviour q-factor of the investigated irregular configurations and that of reference regular ones, show that less dissipative capacity can be expected if the building is irregular due to a disequilibrium among storeys between the actual and the required strength provided by the floor–wall joints. A correlation method to estimate the behaviour q-factor for perfectly regular cross-laminated timber buildings is here presented and extended to in-elevation irregular ones. A new empirical formulation to assess the reliable corrective factor accounting for the irregularity in elevation of cross-laminated timber buildings, according to Eurocode 8 provisions, is also proposed. A final discussion about the implications of in-elevation irregularity on the building design is reported. 相似文献
7.
Abouzar Jafari Mohammad Reza Ghasemi Habib Akbarzadeh Bengar Behrooz Hassani 《Bulletin of Earthquake Engineering》2018,16(2):831-858
Self-centering rocking walls offer the possibility of minimizing repair costs and downtimes, and also nullify the residual drift after seismic events, thanks to their self-centering properties. In this paper, the effect of axial stress ratio on the behavior of monolithic self-centering rocking walls is investigated by utilizing a developed finite element model. To verify the validity of the finite element model, results and observed damage in the model are compared with those of a full-scale wall test. The axial stress ratio is varied from 0.024 to 0.30 while keeping the other structural parameters constant. For qualitative damage evaluation, the observed damage in the model compared with expected damage states of desired performance levels. In order to evaluate the incurred damage quantitatively, the amount of crushing and damage in the wall is calculated by utilizing several ratios (crushing ratio and damage ratio). Furthermore, seismic response factors (i.e., μ, R and Cd) are calculated for different axial stress ratio values. The obtained results showed that, in order to satisfy the requirements of desired performance levels, the maximum axial stress ratio should be approximately within the range of 0.10–0.15. In addition, the maximum overall damage ratio and crushing ratio are suggested to be less than 5%. For axial stress ratio higher than 0.15, the flag-shaped pattern of hysteresis curves completely disappeared and the variation of displacement ductility is less sensitive to axial stress ratio. Considering the maximum axial stress ratio limited to 0.150, values of 4 and 3.5 are conservatively proposed as a period-independent response modification factor and displacement modification factor of the investigated structural wall, respectively. 相似文献
8.
Laurentiu Danciu Karin Şeşetyan Mine Demircioglu Levent Gülen Mehdi Zare Roberto Basili Ata Elias Shota Adamia Nino Tsereteli Hilal Yalçın Murat Utkucu Muhammad Asif Khan Mohammad Sayab Khaled Hessami Andrea N. Rovida Massimiliano Stucchi Jean-Pierre Burg Arkady Karakhanian Hektor Babayan Mher Avanesyan Tahir Mammadli Mahmood Al-Qaryouti Doğan Kalafat Otar Varazanashvili Mustafa Erdik Domenico Giardini 《Bulletin of Earthquake Engineering》2018,16(8):3465-3496
9.
Christophe Martin Gabriele Ameri David Baumont David Carbon Gloria Senfaute Jean-Michel Thiry Ezio Faccioli Jean Savy 《Bulletin of Earthquake Engineering》2018,16(6):2477-2511
The accurate evaluation and appropriate treatment of uncertainties is of primary importance in modern probabilistic seismic hazard assessment (PSHA). One of the objectives of the SIGMA project was to establish a framework to improve knowledge and data on two target regions characterized by low-to-moderate seismic activity. In this paper, for South-Eastern France, we present the final PSHA performed within the SIGMA project. A new earthquake catalogue for France covering instrumental and historical periods was used for the calculation of the magnitude-frequency distributions. The hazard model incorporates area sources, smoothed seismicity and a 3D faults model. A set of recently developed ground motion prediction equations (GMPEs) from global and regional data, evaluated as adequately representing the ground motion characteristics in the region, was used to calculate the hazard. The magnitude-frequency distributions, maximum magnitude, faults slip rate and style-of-faulting are considered as additional source of epistemic uncertainties. The hazard results for generic rock condition (Vs30 = 800 m/s) are displayed for 20 sites in terms of uniform hazard spectra at two return periods (475 years and 10,000 years). The contributions of the epistemic uncertainties in the ground motion characterizations and in the seismic source characterization to the total hazard uncertainties are analyzed. Finally, we compare the results with existing models developed at national scale in the framework of the first generation of models supporting the Eurocode 8 enforcement, (MEDD 2002 and AFPS06) and at the European scale (within the SHARE project), highlighting significant discrepancies at short return periods. 相似文献
10.
Javier Ortega Graça Vasconcelos Hugo Rodrigues Mariana Correia 《Bulletin of Earthquake Engineering》2018,16(9):3871-3904
The awareness and preservation of the vernacular heritage and traditional construction techniques and materials is crucial as a key element of cultural identity. However, vernacular architecture located in earthquake prone areas can show a particularly poor seismic performance because of inadequate construction practices resulting from economic restraints and lack of resources. The horizontal diaphragms are one of the key aspects influencing the seismic behavior of buildings because of their major role transmitting the seismic actions to the vertical resisting elements of the structure. This paper presents a numerical parametric study adopted to understand the seismic behavior and resisting mechanisms of vernacular buildings according to the type of horizontal diaphragm considered. Detailed finite element modeling and nonlinear static (pushover) analyses were used to perform the thorough parametric study aimed at the evaluation and quantification of the influence of the type of diaphragm in the seismic behavior of vernacular buildings. The reference models used for this study simulate representative rammed earth and stone masonry vernacular buildings commonly found in the South of Portugal. Therefore, this paper also contributes for a better insight of the structural behavior of vernacular earthen and stone masonry typologies under seismic loading. 相似文献