Development of concentration-gradient FACE experimental facilitics.

自由空气CO2浓缩(Face)实验作为一种研究植被对大气中CO2浓度升高的反应的方法，一直受到人们的关注。本研究旨在开发一种新的人脸识别系统。面环内的二氧化碳浓度不会像现有的或计划的面环实验那样保持在统一的水平，但会产生一个恒定的浓度梯度，以便在一个面环内调查植被对不同二氧化碳浓度的反应。主要研究结果如下：1.模拟研究表明，即使风从相反的方向吹来，也可以通过调整二氧化碳释放的位置和强度来产生类似的浓度梯度。2.风洞实验表明，在现有的结构中，来自二氧化碳释放设施的鼓风机、管道和射流(机器效应)的影响会很大，如果使用纯CO2气体和灌溉管来释放二氧化碳，效果会更小，使用许多细长的垂直管子时更是如此。3.利用灌溉管道和纯CO2气体，开发了一个浓度梯度面系统的原型。戒指的形状是一个又长又窄的六边形。二氧化碳排放基于风速和风向进行前馈控制。在大多数情况下，可以产生浓度梯度，但不是恒定的。较难产生梯度的情况是低风速(小于0.5m/S)和风从高浓度区吹向低浓度区的情况。然而，控制方法仍有很大的改进空间。

Free Air CO2 Enrichment (FACE) experiments have been attracting much attention as a research method on vegetation reaction to the elevated CO2 concentration in the atmosphere. This study aims at developing a new FACE system. The CO2 concentration within the FACE ring would not be kept at a uniform level, as existing or planned FACE experiments, but a constant gradient of the concentration would be created, so that vegetation reactions to different CO2 concentrations would be investigated within one FACE ring. Main results are as follows :l.A simulation study revealed that even if the wind blows from the opposite direction, a similar concentration gradient could be created by adjusting the CO2 release positions and strength.2.Wind tunnel experiments showed that effects of blowers, pipes, and jets from the CO2 release facilities (machine effects) would be large in the existing configurations, much less if we use pure CO2 gas and irrigation tubes for CO2 release, and even much less with the use of many thin vertical tubes.3.Using irrigation tubes and pure CO2 gas, a prototype concentration-gradient FACE system was developed. The shape of the ring was a long and narrow hexagon. CO2 release was feedforward-controlled based on the wind speed and direction. In most cases, a concentration gradient could be created, though not constant. Difficult cases to create a gradient were that of the low wind speed (less than 0.5m/s) and that in which the wind blew from the high concentration area to the low one.As a conclusion, a prototype of a concentration-gradient FACE system was successfully developed. However, there remained much room for improvement of the control method.