Loss of energy dissipation capacity from the deadzone in linear and nonlinear viscous damping devices

In a viscous damping device under cyclic loading, after the piston reaches a peak stroke, the reserve movement that follows may sometimes experience a short period of delayed or significantly reduced device force output. A similar delay or reduced device force output may also occur at the damper’s initial stroke as it moves away from its neutral position. This phenomenon is referred to as the effect of “deadzone”. The deadzone can cause a loss of energy dissipation capacity and less efficient vibration control. It is prominent in small amplitude vibrations. Although there are many potential causes of deadzone such as environmental factors, construction, material aging, and manufacture quality, in this paper, its general effect in linear and nonlinear viscous damping devices is analyzed. Based on classical dynamics and damping theory, a simple model is developed to capture the effect of deadzone in terms of the loss of energy dissipation capacity. The model provides several methods to estimate the loss of energy dissipation within the deadzone in linear and sublinear viscous fluid dampers. An empirical equation of loss of energy dissipation capacity versus deadzone size is formulated, and the equivalent reduction of effective damping in SDOF systems has been obtained. A laboratory experimental evaluation is carried out to verify the effect of deadzone and its numerical approximation. Based on the analysis, a modification is suggested to the corresponding formulas in FEMA 356 for calculation of equivalent damping if a deadzone is to be considered.     

Estimation of peak relative velocity and peak absolute acceleration of linear SDOF systems

In the seismic analysis and design of structures, the true velocity and absolute acceleration are usually approximated by their corresponding pseudo-values. This approach is simple and works well for structures with small damping (say, less than 15%). When the damping of a structure is enhanced for the purpose of response reduction, it may result in large analysis and design errors. Based on theory of random vibration and the established mechanism of seismic response spectra analysis, a method is developed (1) to predict the relative velocity spectra with any damping ratio level directly from the 5% standard pseudo-acceleration spectrum; and (2) to estimate the peak absolute acceleration. The accuracy of both is validated by using two selected ensembles of ground motion records.     

Static and dynamic inelastic P–Δ effect for seismic design

Seismic influence of P–Δ effect is the subject of this study. First, it is pointed out that the elastic static amplification factor shall be isolated in formulating the dynamic inelastic second order effect. An amplification factor for the static inelastic P–Δ effect is derived. Seismic force reduction factors(SFRF) for given ductility and stability coefficients are computed for one-story, one-span frames. The P–Δ amplification factors for seismic base shears are obtained by dividing SFRFs with and without P–Δ effect. Both P–Δ amplification factors and SFRFs are presented separately with two kinds of period abscissas. The P–Δ amplification factors are dependent on periods with the maximum occurring at about 0.75 s for site type C and approach to the static inelastic counterpart at long periods. Post-yield stiffness cannot fully counteract the adverse impact of the P–Δ effect. Formulas for seismic P–Δ amplification factors are proposed and compared to results of others. Collapse capacity spectra(CCS) are reviewed and their application in codes discussed. Available CCSs are compared with SFRFs with finite ductility computed for two ensembles of seismic records. A comparison reveals that the SFRFs are affected by seismic records, and available CCSs do not always provide upper limits for the SFRFs when stability coefficients are greater than 0.1 for frame models.     

GC-MS法测定地下水中28种半挥发性有机物

本文针对地下水监测网运行维护规范(DZ/T 0307-2017)中的半挥发性有机物,建立了一种液/液萃取-气相色谱质谱联用法,可同时测定28种半挥发性有机物(SVOCs),涵盖规范中除多氯联苯外全部的27个SVOCs.方法 采用二氯甲烷萃取,SIM模式经气相色谱质谱联用仪(GC-MS)对样品进行测定,内标法定量,可实现...     

折射层析成像法测试隧道围岩松动圈

通过应用折射层析成像法在乌鞘岭特长隧道中的测试,说明该方法对于横向速度变化不均一,过渡带速度渐变的地质情况具有分辨率高、图像直观、易于解释,适合对隧道围岩松动圈的测试.     

基于“葵花8号”气象卫星的陇东南地区强对流识别跟踪技术研究

利用常规观测资料、区域自动站资料和“葵花8号”气象卫星资料,对2016年4—9月甘肃省陇东南地区出现的43次强对流天气过程进行分析,确立了强对流云团识别指标、追踪方法及预报指标,并对2018年部分个例进行效果检验。结果表明：（1）利用卫星B13通道（10.4μm）亮温值TBB≤238 K或B08通道（6.2μm）与B13通道亮温差△TBB<0 K双阈值作为强对流云团识别指标,可以准确识别出陇东南地区的强对流天气云团;（2）利用“逆向搜索法”、“面积重叠法”及对云团重心的计算,可以对强对流云团进行准确定位、追踪及移动路径外推预报;（3）建立的强对流天气落区判别指标对该地区短时强降水及冰雹落区具有一定的预报能力。     

动机、成本、风险：家长视角下研学旅游产品价值感知研究

以中小学生自然教育研学旅游作为具体情境,基于539份家长问卷数据阐释研学旅游动机与价值感知之间的关系,并通过成本感知和风险感知探讨其内在机制和边界条件。结果表明,家长感知的研学旅游动机越强烈,越容易感知到研学旅游产品所传递的价值,验证了研学旅游情境下动机对价值感知的积极影响,也形成了对动机与价值之间关系研究的理论补充。并且,这一动机除了直接作用于价值感知外,还会通过成本感知的部分中介作用影响价值感知,揭示了中国家长对于教育价值的重视会削弱其对“利失”的感知。此外,进一步验证了风险感知的积极影响,即家长感知研学旅游的不确定性水平越高,动机对价值感知的积极影响越明显,且会抑制成本感知对价值感知的负向作用,但风险感知水平达到一定高度时,其对成本感知与价值感知间的抑制作用将不显著。因此,面向需求设计打造产品,突出产品价值、加大宣传营销力度、把控活动安全、合理制定价格,获取家长群体的认同接受,将是研学旅游进一步拓展市场的重要考量。     

中国春季气温异常变率的非线性特征

运用一种基于神经网络的非线性主成分分析法(NLPCA)对中国1951-2003年53 a春季气温距平场进行分析,结果表明,春季气温异常变率具有显著的非线性特征,当非线性主元u分别取最大值和最小值时,对应的空间气温异常分布型具有显著的非对称性.     

温度、氮浓度和氮磷比对长心卡帕藻(Kappaphycus alvarezii)吸收氮速率的影响

分别在室内培养箱、海滨室外跑道池和不同自然海区,通过一次性和半连续添加营养、以及检测海区水质和藻体生长的方法,研究了不同氮浓度、温度和氮磷比条件下,长心卡帕藻氮吸收速率的变化和氮吸收速率随时间变化,以及栽培该藻的环境生态贡献。小型实验、中试放大和海区规模栽培结果表明:(1)在10—50μmol/L范围内,该藻吸收氮速率随氮浓度增加而增大;(2)当氮浓度一定时,氮磷比在1—50范围内对该藻吸收氮速率没有产生显著影响(P>0.05);(3)温度对该藻吸收氮速率有显著影响(P<0.05),其中温度在28℃时氮的吸收速率最高;(4)尽管一次性添加营养实验中长心卡帕藻吸收氮速率随时间变化表现出先快后慢的趋势,但是进一步的半连续添加营养实验证实,导致吸收速率下降系底物氮浓度限制,而不是藻本身吸收能力下降,结果还显示卡帕藻具有连续吸收同化无机氮能力;在自然光温度变化和不受底物浓度限制条件下,该藻藻体去除无机氮效率最大维持在0.3μmol/(gFW·h);(5)海南陵水黎安海湾水质数据显示,栽培该藻去除海水富营养化和净化水质作用显著,其去除海水富营养化的年贡献为33t氮素。     

机载三维成像系统

本文简要地阐述了新型机载三维成像系统的产生环境、原理、技术结构、特色及应用领域 ,介绍了飞行检测、应用飞行所取得的成果。为实现高效遥感对地观测体系迈出的第一步。