Research on wind-induced responses of a large-scale membrane structure

The wind-induced responses of a large-scale membrane structure, Expo Boulevard, are evaluated in this study. To obtain the wind pressure distribution on the roof surface, a wind tunnel test is performed. A brief analysis of wind pressure on the membrane roof is conducted first and then an analysis of the wind-induced responses of the structure is carried out using a numerical integral method in the time domain. In the process of calculation, the geometrical nonlinearity is taken into account. Results indicate that mean, RSM and peak values of the structure responses increase nonlinearly while the approaching flow velocity increases. Strong nonlinear characteristics are observed in the displacement responses, whereas the responses of nodal stress and cable axial force show minimal nonlinear properties when the membrane structure is subjected to wind loads. Different values of the damping ratio only have a minimal impact on the RSM response of the structure because the background component is a dominant part of the total dynamic response and the resonant component is too small. As the damping ratio increases from 0.02 to 0.05, the RMS responses of vertical displacement, nodal stress and cable axial force decrease by 8.1%, 6.7% and 17.9%, respectively. Since the mean component plays a significant role in the wind-induced response, the values of the gust response factor are not high for Expo Boulevard.

CHARACTERISTICS AND TRENDS OF CLIMATIC EXTREMES IN CHINA DURING 1959-2014

The spatial and temporal variations of daily maximum temperature(Tmax), daily minimum temperature(Tmin), daily maximum precipitation(Pmax) and daily maximum wind speed(WSmax) were examined in China using Mann-Kendall test and linear regression method. The results indicated that for China as a whole, Tmax, Tmin and Pmax had significant increasing trends at rates of 0.15℃ per decade, 0.45℃ per decade and 0.58 mm per decade,respectively, while WSmax had decreased significantly at 1.18 m·s^(-1) per decade during 1959—2014. In all regions of China, Tmin increased and WSmax decreased significantly. Spatially, Tmax increased significantly at most of the stations in South China(SC), northwestern North China(NC), northeastern Northeast China(NEC), eastern Northwest China(NWC) and eastern Southwest China(SWC), and the increasing trends were significant in NC, SC, NWC and SWC on the regional average. Tmin increased significantly at most of the stations in China, with notable increase in NEC, northern and southeastern NC and northwestern and eastern NWC. Pmax showed no significant trend at most of the stations in China, and on the regional average it decreased significantly in NC but increased in SC, NWC and the mid-lower Yangtze River valley(YR). WSmax decreased significantly at the vast majority of stations in China, with remarkable decrease in northern NC, northern and central YR, central and southern SC and in parts of central NEC and western NWC. With global climate change and rapidly economic development, China has become more vulnerable to climatic extremes and meteorological disasters, so more strategies of mitigation and/or adaptation of climatic extremes,such as environmentally-friendly and low-cost energy production systems and the enhancement of engineering defense measures are necessary for government and social publics.

STUDY ON THE GENESIS OF ASYMMETRICAL DISTRIBUTION CHARACTERISTICS OF PRECIPITATION ASSOCIATED WITH THE TYPHOON HAITANG (2005) FROM THE VIEW OF ATMOSPHERIC FACTOR

The distribution of precipitation field from the typhoon Haitang(2005) during its landing on Fujian province shows obvious asymmetric feature.Based on the NCEP/NCAR FNL(Final Analysis) data,this study reveals the contributions of atmospheric factor to the asymmetrical distribution characteristics of precipitation associated with the typhoon,through the analysis of water vapor condition,vertical ascending motion condition,the calculation of the dry Q vector and its decomposition,and adiabatic heating in the air column of 1000hPa-600hPa(lower atmosphere) and500hPa-100hPa(upper atmosphere).The results are as follows:(1) In the lower atmosphere,the humidity on both sides of typhoon path can be equivalent,while it is more wet on the right side than left in the upper atmosphere,which obviously presents asymmetric distribution characteristics.(2) Both range and intensity of the vertical motion on the right side are wider and stronger than counterparts on the left side no matter in the lower or upper atmosphere.(3) In the upper atmosphere,forcing role of atmosphere in vertical upward motion on the right side of typhoon path is the same as that on the left,while it is significantly different in the lower atmosphere,which is significantly broader in scope and stronger in the intensity,along with obvious asymmetric distribution characteristics.In addition,the further analysis of the Q vector decomposition indicates that the forcing effect of mesoscale weather systems on vertical upward motion is stronger than that of large scale weather systems in the lower atmosphere.(4) The adiabatic heating always exists on both lower and upper atmosphere,and the range and intensity of the adiabatic heating forcing showed asymmetric distribution on both lower and upper atmosphere.(5) In a summary,the upper atmosphere humidity conditions,the forcing role of lower atmosphere in vertical upward motion,especially,to mesoscale weather system,and adiabatic heating in the lower atmosphere,all show similar asymmetric distribution characteristics to that of precipitation field from the typhoon Haitang(2005),that is to say,the atmospheric factors as mentioned above are all contributed to genesis of the asymmetric distribution characteristics of precipitation.

Variations of the thermal growing season during the period 1961–2015 in northern China

Researching into changes in thermal growing season has been one of the most important scientific issues in studies of the impact of global climate change on terrestrial ecosystems. However, few studies investigated the differences under various definitions of thermal growing season and compared the trends of thermal growing season in different parts of China. Based on the daily mean air temperatures collected from 877 meteorological stations over northern China from 1961 to 2015, we investigated the variations of the thermal growing season parameters including the onset, ending and duration of the growing season using the methods of differential analysis, trend analysis, comparative analysis, and Kriging interpolation technique. Results indicate that the differences of the maximum values of those indices for the thermal growing season were significant, while they were insignificant for the mean values. For indices with the same length of the spells exceeding 5°C, frost criterion had a significant effect on the differences of the maximum values. The differences of the mean values between frost and non-frost indices were also slight, even smaller than those from the different lengths of the spells. Temporally, the starting date of the thermal growing season advanced by 10.0–11.0 days, while the ending dates delayed by 5.0–6.0 days during the period 1961–2015. Consequently, the duration of the thermal growing season was prolonged 15.0–16.0 days. Spatially, the advanced onset of the thermal growing season occurred in the southwestern, eastern, and northeastern parts of northern China, whereas the delayed ending of the thermal growing season appeared in the western part, and the length of the thermal growing season was prolonged significantly in the vast majority of northern China. The trend values of the thermal growing season were affected by altitude. The magnitude of the earlier onset of the thermal growing season decreased, and that of the later ending increased rapidly as the altitude increased, causing the magnitude of the prolonged growing season increased correspondingly. Comparing the applicability of selected indices and considering the impacts of frost on the definitions are important and necessary for determining the timing and length of the thermal growing season in northern China.

SATELLITE-BASED ANALYSIS ON THE CONCENTRIC EYEWALL REPLACEMENT CYCLES OF SUPER TYPHOON MUIFA (1109)

Multisatellite data is used to analyze the characteristics of three eyewall replacement cycles(ERCs) during the lifetime of Typhoon Muifa(1109).Spiral rainbands evolutions,concentric eyewall(CE) structure modes,CE durations,and intensity changes are discussed in detail.In addition,an ERC evolution model of Typhoon Muifa is given.There are four main findings.(1) The outer spiral rainband joins end to end to form the outer eyewall after it disconnects from the original(inner) eyewall.The inner eyewall weakens as the outer eyewall becomes axisymmetric and is intensified.The contraction of the outer eyewall causes the inner eyewall to dissipate rapidly.Finally,the ERC ends with an annular eyewall or spiral rainbands.(2) Although the CE duration times of Typhoon Muifa's three ERCs covered a large range,the CE structures were all maintained for approximately 5 h from the formation of the axisymmetric outer eyewall to the end of the cycle.(3) There is no obvious precipitation reflectivity in the eye or moat region for the subsidence flow.The convection within the two eyewalls is organized as a radially outward slope with increasing height.(4) Typhoon intensity estimation results based on ADT may not explain the intensity variations associated with ERC correctly,while the typhoon's warm core data retrieved from AMSU-A works well.

Cloud vertical structures associated with precipitation magnitudes over the Tibetan Plateau and its neighboring regions

本文采用CloudSat/CALIPSO和TRMM卫星资料,对比分析了不同强度降水时青藏高原与其邻近陆地和海洋地区的云宏观和微观垂直结构。结果表明:高原大地形对云层厚度和云顶高度具有压缩效应;与邻近地区相比,高原降水强度较弱,但是季节变化更明显;夏季,无雨时,高原上云冰粒子主要位于较低高度(5-10公里),粒子尺寸和数浓度更丰富;随着降水增强,云冰含量增多,高层冰粒子的聚集度趋于紧密;然而即使是大暴雨,高原地区冰粒子的数浓度也最有可能在100-250 L.1之间,小于其邻近的陆地和热带海洋地区;此外,对于同等级的降水,高原地区冰粒子尺寸的谱分布宽于其它地区。

An FE-Inexact Heterogeneous ADMM for Elliptic Optimal Control Problems with L^1-Control Cost

Elliptic PDE-constrained optimal control problems with L^1-control cost(L^1-EOCP) are considered. To solve L^1-EOCP, the primal-dual active set(PDAS) method, which is a special semismooth Newton(SSN) method, used to be a priority. However, in general solving Newton equations is expensive. Motivated by the success of alternating direction method of multipliers(ADMM), we consider extending the ADMM to L^1-EOCP. To discretize L^1-EOCP, the piecewise linear finite element(FE) is considered. However, different from the finite dimensional L^1-norm, the discretized L^1-norm does not have a decoupled form. To overcome this difficulty, an effective approach is utilizing nodal quadrature formulas to approximately discretize the L^1-norm and L^2-norm. It is proved that these approximation steps will not change the order of error estimates. To solve the discretized problem,an inexact heterogeneous ADMM(ihADMM) is proposed. Different from the classical ADMM, the ihADMM adopts two different weighted inner products to define the augmented Lagrangian function in two subproblems, respectively. Benefiting from such different weighted techniques, two subproblems of ihADMM can be efficiently implemented. Furthermore, theoretical results on the global convergence as well as the iteration complexity results o(1/k) for ihADMM are given. In order to obtain more accurate solution, a two-phase strategy is also presented, in which the primal-dual active set(PDAS)method is used as a postprocessor of the ihADMM. Numerical results not only confirm error estimates,but also show that the ihADMM and the two-phase strategy are highly efficient.