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141.
142.
斜度对斜交桥地震作用下的扭转效应影响 总被引:1,自引:0,他引:1
为满足交通工程中线路运行的需要,桥梁斜交有时不可避免.相对于正交桥而言,斜交桥在地震作用下有扭转破坏的趋势.斜度作为斜交桥的主要特征参量,其对斜交桥在地震作用下扭转效应的影响作用,目前研究还存在彼此不同的看法.为此,以一实际工程为原型,建立了不同斜度的桥梁分析模型,利用模态分析和非线性时程分析方法对不同斜度的斜交桥梁在地震作用下的扭转效应展开研究.通过研究发现:斜度增大,斜交桥的扭转周期与平动周期之比线性增加,结构的抗扭刚度减弱,同时桥墩在地震作用下的扭矩作用也将增大.对于上部结构平面内的扭转位移,若梁体端部与桥台之间的伸缩缝宽度足够大,梁体与桥台不发生接触碰撞,增大桥梁的斜度并不能引起上部结构的扭转位移;若梁体与桥台发生接触碰撞,斜度增大,上部结构的扭转位移增大. 相似文献
143.
桃花江旅游景观船闸在布置上因受到枢纽地形与河道防洪的限制,难以满足规范要求.采用几何比尺为1∶25的整体水工模型进行了试验研究,2座枢纽的控制运行条件均为最高通航水位组合,主河道中流速较大,特别是上下游口门处引航道的横向流速较大,不能满足规范要求.修改方案主要通过减小2座船闸上下游引航道与桃花江主河道夹角,并对口门附近地形进行了相应的疏浚.试验结果表明,修改方案有效降低了2座船闸上游口门处横向流速等不利因素. 相似文献
144.
145.
Methods and results are reported from a study of ships companies' exposure to low-frequency motions on three vessels of the Royal Navy. The aim of the study was to investigate relationships between deck accelerations and the incidence of problems such as difficulties with physical tasks, cognitive activities, motion sickness, and work effort. Ship motions were recorded continuously during sea patrols of 10-14 days. The data collected from the three vessels comprised 105 days of ship motions over 12 patrols, with 779 associated daily diaries from 78 participants. Problems most strongly associated with vessel motions were related to the difficulties with physical tasks. Some cognitive aspects of task performance and motion sickness were associated with vertical acceleration magnitudes, but the correlations were less strong than with physical tasks. Practitioner Summary: Little is known about the severity of ship motions that degrade physical and mental performance. The paper offers preliminary estimates of the motion threshold values below which the performance will not be degraded by motion. 相似文献
146.
《Ergonomics》2012,55(9):1426-1440
This study investigated the effects of ship motion on peak spinal loading during lifting. All measurements were done on a ship at sea. In 1-min trials, which were repeated over a wide range of sailing conditions, subjects lifted an 18 kg box five times. Ship motion, whole body kinematics, ground reaction forces and electromyography were measured and the effect of ship motion on peak spinal moments and compression forces was investigated. To investigate whether people time their lifts in order to reduce the effect of ship motion on back loading, trials were performed at a free and at a constrained (lifting every 10s) work pace. With increase of the (local) vertical ship acceleration, increased moments and compression forces were found. Furthermore, lifting at a free work pace did not result in smaller effects of ship motion on spinal moments and compression forces than working at a constrained work pace. 相似文献
147.
以新世纪之交的历史时段作为背景,将中法建筑文化中的两个重要建筑—巴黎卢浮宫金字塔与北京国家大剧院作为对象,试图通过对于这两座地标性建筑的文化特点以及建筑师的文化背景和建筑观念的分析,解读建筑创作的构思方法和表达意象的途径,讨论建筑对于社会产生的共鸣效应、文化认同作用以及建筑师的社会责任. 相似文献
148.
Single-axis rotation technique is often used in the marine laser inertial navigation system so as to modulate the constant biases of non-axial gyroscopes and accelerometers to attain better navigation performance. However, two significant accelerometer nonlinear errors need to be attacked to improve the modulation effect. Firstly, the asymmetry scale factor inaccuracy enlarges the errors of frequent zero-cross oscillating specific force measured by non-axial accelerometers. Secondly, the traditional linear model of accelerometers can hardly measure the continued or intermittent acceleration accurately. These two nonlinear errors degrade the high-precision specific force measurement and the calibration of nonlinear coefficients because triaxial accelerometers is urgent for the marine navigation. Based on the digital signal sampling property, the square coefficients and cross-coupling coefficients of accelerometers are considered. Meanwhile, the asymmetry scale factors are considered in the I-F conversion unit. Thus, a nonlinear model of specific force measurement is established compared to the linear model. Based on the three-axis turntable, the triaxial gyroscopes are utilized to measure the specific force observation for triaxial accelerometers. Considering the nonlinear combination, the standard calibration parameters and asymmetry factors are separately estimated by a two-step iterative identification procedure. Besides, an efficient specific force calculation model is approximately derived to reduce the real-time computation cost. Simulation results illustrate the sufficient estimation accuracy of nonlinear coefficients. The experiments demonstrate that the nonlinear model shows much higher accuracy than the linear model in both the gravimetry and sway navigation validations. 相似文献
149.
为了探求金属蒸气电弧弧前形成机理及宏观参数对微观弧前过程的的影响,基于漂移扩散方程组与泊松方程,对触头分断后的金属蒸气电弧弧前过程进行了数学建模与求解.仿真分析了触头间距离为4 mm,触头间电压为750 V,金属蒸气压强为66.66 Pa,温度为293.15 K条件下金属蒸气电弧的弧前过程.通过仿真结果得到金属蒸气电弧的动态弧前过程形成机理及宏观影响因素,很好地解释了金属蒸气电弧弧前过程中空间电荷时变规律及鞘层的形成机理,并从微观角度解释了开距及二次电子发射系数变化对弧前过程的影响. 相似文献
150.
离子镀膜技术作为一项正在发展的表面镀膜技术,具有良好的耐摩擦、磨损性能。多孤离子镀是最先进的镀膜技术之一,通过阐述分析多弧离子镀的原理、技术优点,研究其应用领域,探求多弧离子镀在海洋船舶材料中的应用,并对该技术进行展望。 相似文献