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891.
A new method that uses time-domain response data under random loading is proposed for detecting damage to the structural elements of offshore platforms. In our study, a time series model with a fitting order was first constructed using the time-domain of noise data. A sensitivity matrix consisting of the first differential of the autoregressive coefficients of the time series models with respect to the stiffness of structural elements was then obtained based on time-domain response data. Locations and severity of damage may then be estimated by solving the damage vector whose components express the degrees of damage to the structural elements. A unique aspect of this detection method is that it requires acceleration history data from only one or a few sensors. This makes it feasible for a limited array of sensors to obtain sufficient data. The efficiency and reliability of the proposed method was demonstrated by applying it to a simplified offshore platform with damage to one element. Numerical simulations show that the use of a few sensors' acceleration history data, when compared with recorded levels of noise, is capable of detecting damage efficiently. An increase in the number of sensors helps improve the diagnosis success rate. 相似文献
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893.
液压传动柔性特征适用于起步工况,机液传动高效无级调速特征适用于作业工况,机械传动高效变速特征适用于转场工况。分析集液压传动、机液传动和机械传动为一体的多模式机液复合传动装置的设计思路在汽车工程上具有理论研究意义和实际应用价值。研究了机液复合传动的功率流传递机理,分析了换挡机构处于功率分流机构、复合传动机构、功率汇流机构和后置换挡机构一处或多处时,分段式机液传动装置各自的性能特征。研究结果表明:功率分流传动方式多适用于中小功率车辆,且马达转矩与传动装置输出转矩比值保持不变;功率汇流传动方式多适用于大功率车辆,使小功率液压件传递大功率成为可能,并能够在输出端起到减速增矩的效果;功率分流和功率汇流互换的传动方式可通过控制行星齿轮双接口及后置换挡机构,保证机液复合传动在不同速度分段中的高效运行;当换挡机构在行星齿轮之间时,可在2个不同区段改变行星齿轮机构的特性参数,使得在整个工作区范围内保持合理的功率配额;当采用多段式行星齿轮功率汇流传动方式时,后置换挡机构扩大了传动装置转速和转矩的覆盖范围。根据上述5类机液传动设计思路,提出对应的多模式机液复合传动装置设计方案。以一款用于扫地车的机液复合传动装置为研究对象,进行运动学和动力学分析,确定相关参数,绘制调速曲线和效率特性曲线,并对其挡位切换优化问题做了简要介绍。该方案充分利用液压传动的无级调速性能和机械传动的高效变速性能,较好地满足了车辆起步、作业和转场工况的要求。 相似文献
894.
Objective To quantitatively analyze the fetal lung echo and right lung volume in the third trimester by real-time three-dimensional ultrasound (3-D US) and evaluate the feasibility of fetal lung maturity. Methods A total of 732 women with normal singleton pregnancies between 28 and 42 weeks of gestation underwent ultrasound examination. The 3-D US equipment with a 3.5-5MHz transabdominal transducer was used for the fetal biometric measurement. The echogenicity ratio between fetal lung and liver was compared. The fetal lung volume was calculated by the rotational multiplanar technique for volume measurement (VOCAL). Results The right fetal lung volume increased with the increase of gestational age with a linear positive correlation (r=0.884, P<0.01). After 34 weeks, the echogenicity ratio of fetal lung to liver was more than 1.1. Conclusion The echogenicity of lung/liver and fetal lung volume could be used as normal fetal predictable indicators for fetal lung maturity. 相似文献
895.
896.
介绍我国铁路建设形势、铁路建设标准化管理的基本框架要求,叙述上海铁路局推行标准化管理的基本特点,重点阐述贯彻标准化管理实践中的突出做法以及对有关问题的思考。 相似文献
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900.
Kinematics analysis and experiment of a cockroach-like robot 总被引:1,自引:0,他引:1
This article describes the structure of the cockroach-like robot. Both kinematics and locomotion control are inspired by biological
observations in cockroaches. Based on cockroach-like robot kinematics analysis, screw theory, and the production-of-exponential
(POE) formula, this paper focuses on the inverse kinematics which uses Paden-Kahan sub-problems to obtain directly the displacement
of joint angles. The forward kinematics derives the relationship between joint angles according to the natural restrictions.
Then, by using the POE formula, it can deduce the body pose and realize online trajectory control and planning. Through simulation
and experimentation, it is proved that the straight-line walking and turning gait algorithms have static stability and the
inverse kinematics analysis of cockroach-like robot is correct. 相似文献