Estimation of energy expenditure in a work environment: Comparison of accelerometry and oxygen consumption/heart rate regression

The aim of this study was to compare estimation of energy expenditure (EE) in working environments, either from accelerometry or from an individual oxygen consumption/heart rate ([Vdot]O₂/HR) regression curve. The study participants were 46 volunteer workers aged 27±6 years old. A significant correlation between EE predicted by the [Vdot]O₂/HR curve and the accelerometer was observed (r=0.78, p <0.01). However, more disparities were observed between the two methods when the mean job intensity was not within 16% and 23% higher than resting HR. The accelerometer overestimated by a mean of 34.4% the prediction by [Vdot]O₂/HR regression if the intensity of the task was lower than a total of 1000 kcal/shift and underestimated the prediction by a mean of –24.9% if EE estimation of the work shift was higher than a total of 1500 kcal/shift. Despite a high correlation between both methods in the whole group, EE evaluated by accelerometry does not correspond to EE predicted by the [Vdot]O₂/HR regression curves when evaluated individually.     

System reduction using eigen spectrum analysis and Padé approximation technique

A mixed method is proposed for deriving reduced-order models of high-order linear time invariant systems using the combined advantages of eigen spectrum analysis and the Padé approximation technique. The denominator of the reduced-order model is found by eigen spectrum analysis, the dynamics of the numerator are chosen using the Padé approximation technique. This method guarantees stability of the reduced model if the original high-order system is stable. The method is illustrated by three numerical examples.     

某深基坑工程方案设计比选分析

某深基坑工程地下水资源丰富,周边环境非常复杂.针对本工程的现场实际情况,介绍了复杂环境条件下深基坑支护方案设计比选的要点,并结合当地的施工经验来选择支护方案,给类似项目提供了一种方案比选方法,具有一定的实用价值.     

一种基于偏微分方程的蒙面曲面的构造方法

该文以偏微分方程方法构造曲面的理论为基础,研究了基于偏微分方程的蒙面曲面构造,并对3D球蒙面曲面进行优化。首先采用微分方程中的叠加原理,把基于偏微分方程的扫描曲面分为基曲面和形变曲面来构造;其次运用对参数沿其梯度反方向递进迭代的方法使曲面能量函数达极值,同时边界曲线参数区域收敛,从而优化蒙面曲面。     

基于余热与太阳能发电对汽车电源的优化设计

通过采用汽车尾气的余热和太阳能的热量进行发电,将温差发电机、太阳能发电机合成,对汽车的电源进行优化设计,为汽车提供电源,借以减少汽车的油耗和废气的排放．通过与传统汽车油耗对比,确实达到节能减排的目的．     

空气源热泵热水系统的优化设计选择

空气源热泵热水供应是一种高效的建筑节能方式,被广泛地应用于公共建筑卫生热水供应系统。研究了热泵机组的出水规律和用户的用水规律,通过建立全寿命周期成本计算数学模型,对不同名义制热量的热泵机组进行经济效果综合评价,寻找最佳的技术经济点,为设备选型与计算、储热水箱最佳容积的确定,提供参考依据。     

Energy saving effect of building envelope in summer

To explore the energy saving effect of building envelope, the experiments were carried out through a comparison of basic cubicle in summer. Experiments show that if energy efficiency measures are applied only in the external walls and windows, the energy saving cubicles have an average energy efficiency ratio of 27.75% and 27.05% when the air change rates are 1.1 and 1.4 h⁻¹ in summer, with both values being over the standard target value by 25%. And the indoor air temperature of the energy saving cubicle is below that of the basic cubicle. The daily mean temperature difference between the interior surface of insulation wall and no insulation reaches 1.47 °C, and the mean temperature difference is up to 8.52 °C between the interior surface and exterior surface of insulating glass and single glass. The two cubicles were simulated for energy consumption using VisualDOE4.0 software under real weather conditions in summer. The results show that the mean deviation is 10.02% between experimental and simulated energy efficiency ratio. The correctness and validity of simulation results of the VisualDOE4.0 software are proved.     

Optimum cutting speed of block-cutting machines in natural stones for energy saving

Energy consumption of block-cutting machines represents a major cost item in the processing of travertines and other natural stones. Therefore, determining the optimum sawing conditions for a particular stone is of major importance in the natural stone-processing industry. An experimental study was carried out utilizing a fully instrumented block-cutter to investigate the sawing performances of five different types of travertine blocks during cutting with a circular diamond saw. The sawing tests were performed in the down-cutting mode. Performance measurements were determined by measuring the cutting speed and energy consumption. Then, specific energy was determined. The one main cutting parameter, cutting speed, was varied in the investigation of optimum cutting performance. Furthermore, some physico-mechanical properties of the travertine blocks were determined in the laboratory. As a result, it is found that the energy consumption (specific energy) of block cutting machines is highly affected by cutting speed. It is determined that specific energy value usually decreases when cutting speed increases. When the cutting speed is higher than the determined value, the diamond saw can become stuck in the travertine block; this situation can be a problem for the block-cutting machine. As a result, the optimum cutting speed obtained for the travertine mines examined is approximately 1.5–2.0 m/min.     

基于元件活跃性的机电系统动力学相似模拟研究

针对复杂机电系统由于制造条件或成本过高等限制无法建立与原型完全相似的缩尺模型问题,作者以元件活跃性为基础,结合相似理论提出了一种复杂机电系统动力学相似模型的建立方法,该方法通过运用能量法分析系统中各元件的活跃性及其对系统特性的影响程度,元件活跃性越低对系统行为的影响程度越小,改变极低活跃性元件尺度大小不影响系统的响应,因此建立模型时对低活跃性元件可以不按照完全相似比进行缩尺也可以保证模型和原型的动力学相似。实例分析表明该方法可以有效地指导相似模型的建立。