Name: measurements of waves in a wind-wave tank under steady and time-varying wind forcing
Uploaded: 2018-02-13T13:00:00.000+00:00
Duration: 8 min 54 s
Description: Watch this Scientific Journal Video about Measurements of Waves in a Wind-wave Tank Under Steady and Time-varying Wind Forcing at JoVE.com

这项工作得到了以色列科学基金会306/15 号赠款的支持。

1. 系统准备
<ol><li>用自来水将水箱装满20厘米深, 以满足深水条件;清洗任何可能影响表面张力的污染物的水面。</li>
	<li>在所需的提取处放置仪表托架。<ol>
<li>装入托管管并将其放置在测试部分气流部分的中心。</li>
		<li>在计算机控制的垂直舞台上安装波形测量仪, 以实现其静态校准。</li>
	</ol>
</li>
	<li>将汉莎组件放置在所需的提取位置, 并在7厘米的横向距离上从波形表中定位, 以消除波规组件与光路的干扰。 注: 建议使用不透明窗帘, 以防止 PSD 暴露于周围光线, 以及保护环境不受激光束的虚假反射。<ol>
<li>将激光定位在水箱下方, 使光束垂直定向, 并聚焦光束。</li>
		<li>将菲涅耳透镜放置在试验区内尽可能高的水面上, 以尽量减少透镜对气流的扰动。</li>
		<li>确保偏转激光束击中透镜在其中心部分的极端风条件下计划在实验阶段。</li>
		<li>将扩散屏幕完全安装在透镜的焦点平面上, 然后检查透镜和屏幕的水平和垂直对准。</li>
		<li>确保当水面静止时, 任何两个平行的垂直激光光束在中心上完全击中扩散屏。 注意: 这可以用两个相同的激光器进行测试, 它们位于一定距离。</li>
		<li>定位 PSD, 确保扩散屏的整个区域位于探测器的有效区域内。通过将透镜设置调整为透镜与屏幕之间的实际距离来执行 PSD 透镜的聚焦。</li>
	</ol>
</li>
</ol>2. 传感器的校准和操作
<ol><li>
测波仪的标定
	<ol>
<li>对每个测量位置和实验运行中预期的最大风速进行波形校准。<ol>
<li>设置传感器的垂直位置, 使平均水位近似于传感线长度的中间。</li>
			<li>将风机速度设置为所需值, 并允许风平稳地吹过足够长的时间 (2-3 分钟)。</li>
			<li>使用示波器, 手动调整波形测量器的灵敏度、增益和偏移量, 使用调理单元, 以确保在波形场中, 与最高波峰和最低槽相对应的电压值在 a/d 范围内。转换器 (+/-10 V)。</li>
			<li>关闭鼓风机几分钟, 直到水的表面变得完全不受干扰。</li>
			<li>通过垂直移动波形表 , 验证浸没长度是否在预期的最峰和槽值内。</li>
			<li>使用自定义的常规在静止水中自动校准波形测量仪在一定深度下淹没测量器, 并在5秒内记录每深度的平均电压输出。</li>
			<li>将二次校准多项式与记录的数据相匹配, 以获得依赖h (V), 其中h是沉没深度 (对应于瞬时表面高程), 作为测量输出电压V的函数。</li>
			<li>直观地验证安装的校准多项式的质量 (图 3)。</li>
		</ol>
</li>
	</ol>
</li>
</ol><img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/56480/56480fig3.jpg"> 图3。测波仪的标定曲线。<a href="http://cloudflare.jove.com/files/ftp_upload/56480/56480fig3large.jpg" target="_blank">请单击此处查看此图的较大版本.</a>
<ol start="2"><li>
汉莎的标定与调整
	<ol>
<li>验证传感器组件每次位移后汉莎的性能。<ol>
<li>使用在水平玻璃板上放置的光学楔形棱镜, 将激光光束与模拟已知水面坡度的光轴偏移。</li>
			<li>使用示波器或自定义的数据采集程序, 在扩散屏幕上采样偏激光光斑的 PSD 输出。</li>
			<li>从实测坐标激光光斑坐标计算光束偏转角和斜率;将结果与已知的楔形角进行比较。</li>
			<li>使用一个或多个棱镜对多个偏转角重复该过程。 注: 采用从2.5°到17.5°的偏转角楔形棱镜;如果由于 psd 与扩散屏的不协调性而导致测试失败, 请手动调整 psd, 以纠正不对齐。此过程使用2D 水平平移阶段和级别手动执行, 非常耗时。</li>
		</ol>
</li>
		<li>
PSD 线性度校验与标定程序
		<ol>
<li>将已打印在扩散屏幕上的透明工作表上的相同间距的网格放在一起, 使其坐标轴、 x和y分别与向下和交叉风向对齐 (图 4)。 注: 网格方便准确地将激光光束定向到扩散屏幕上所需的位置, 或者使用一组棱镜或沿风向和风向方向将激光移动到扩散屏下。</li>
			<li>使用棱镜集, 偏转垂直激光束, 在扩散屏上获得激光光斑的多个径向位置, 同时保持恒定的方位角。 注: 分辨率为1厘米, 最大半径为7厘米, 用于9个方位角。</li>
			<li>将激光光斑移动到x方向中的多个位置, 同时保持y坐标常量, 然后将移动的方向更改为y, 并保持x常量。 注意: 所用的范围和分辨率与上一节中的相同。</li>
			<li>每次校准时, 在网格上收集大约50点。 注: 激光光斑坐标由 psd 获取, 并使用连接到 psd 的标准双通道示波器进行评估。<ol>
<li>对于每个方向, 使用数据的线性拟合来产生校准系数, 将 PSD 传感器上的激光束的坐标转换为扩散屏幕上相应的坐标。 注意: 在图5中绘制了 PSD 校准的一个示例, 其中列出了沿测试部分中线所采取的一组点。当扩散屏和传感器的轴线正确对准时, 传感器的响应和校准系数在各个方向上几乎是相同的。网格方便了校准程序, 允许在扩散屏幕上轻松地确定激光斜率坐标。</li>
			</ol>
</li>
		</ol>
</li>
	</ol>
</li>
</ol><img alt="Figure 4" class="xfigimg" src="/files/ftp_upload/56480/56480fig4.jpg"> 图4。扩散屏幕网格.网格方便准确地将激光光束定向到扩散屏幕上所需的位置, 无论是使用一组棱镜, 还是沿风向和风向方向将激光移动到扩散屏下方<a href="http://cloudflare.jove.com/files/ftp_upload/56480/56480fig4large.jpg" target="_blank">请单击此处以查看此图的较大版本.</a>
<img alt="Figure 5" class="xfigimg" src="/files/ftp_upload/56480/56480fig5.jpg"> 图5。PSD 校准曲线.该图表明, 将 PSD 输出电压转换为坐标将产生足够的结果。<a href="http://cloudflare.jove.com/files/ftp_upload/56480/56480fig5large.jpg" target="_blank">请单击此处查看此图的较大版本.</a>
3. 实验程序和数据采集
注意: 有关以下步骤中使用的用户界面, 请参见辅助图 1 。
<ol><li>使用自定义生成的程序用户界面设置鼓风机频率。 注: 在最初未受干扰的水面上, 几乎逐步增加风速, 其次是在规定的持续时间 (120s) 内稳定的气流速率, 以及风机的近脉冲关闭。</li>
	<li>确定不同的稳定风速和所需风机设置的数量。</li>
	<li>调整压力传感器设置, 以预期的范围内的动态压力变化检测到的皮托管。</li>
	<li>确保在每一个实现的开始, 没有风和水面不受干扰 (镜面平滑)。与鼓风机的操作同步启动数据采集。</li>
	<li>记录瞬时表面高程、沿横风向方向的表面斜率分量、托管管输出监测平均风速U和按规定采样速率从鼓风机控制器发出的电压变化 (300 Hz 或渠道使用了)。 注: 由程序获取的波形测量器的电压自动转换为表面高程, 使用图 3中显示的校准系数。</li>
	<li>继续取样, 以便在鼓风机关闭后记录衰减波场的足够时间。</li>
	<li>取样完成后, 确保自动实验程序允许有足够的时间 (取决于系统) 在启动下一次运行之前使水表面处于未受干扰的状态。</li>
	<li>保存所有记录的数据以供后续处理。</li>
	<li>执行规定的认识的数字 (通常100独立奔跑被发现足够)。</li>
	<li>计算记录数据的集合平均参数, 作为鼓风机启动后所经过的时间的函数。</li>
	<li>对测试部分中对应于选定目标风速的鼓风机下一设置重复整个过程。</li>
</ol>

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作者没有什么可透露的。

本实验协议的目的是在不稳定的风强迫下, 在时间和空间上演化的波场进行定量表征。由于风浪本质上是随机的和三维的, 因此在时间和空间上变化很快, 在时间依赖的风力强迫下, 一个不断增长的风浪场个体认识的记录只能提供对治理的定性估计。波形参数。为了实现该协议的目标, 获得统计上可靠的时间和提取相关波特性, 需要应用具有相同风变化模式的大量实验运行的时间分辨集合平均。由于?...

自古以来, 众所周知, 水面上的波浪被风所激发。目前对控制这一进程的物理机制的理解远非令人满意。许多试图描述风力发电的理论在过去几年中提出了1,2,3,4, 但他们的可靠的实验验证还没有可用。在海洋中随机风浪的测量是极具挑战性的, 因为不可预知的风可能会在方向上和震级上变化得很快。实验室实验的优点是可控制的条件, 使长期和可重复的测量。
在实验室环境的恒定风强迫下, 风浪在空间中演化。几十年前在稳态强迫下进行的波浪的早期实验室实验仅限于瞬时表面高程测量5,6,7,8。最近的研究还使用各种光学技术来测量瞬时水表面倾角, 如汉莎9,10。这些测量允许得到一些有限的质量信息的三维结构的风波场。当风强迫是不稳定的, 因为它是在野外试验中, 引入额外的复杂性, 以风的激励问题, 因为产生的波场的统计参数不仅在空间, 但时间也不一样。到目前为止的尝试, 以定性和定量地描述波浪演变模式在时间依赖强迫下仅部份地成功了11,12,13,14,15,16. 不同似然的物理机制的相对贡献可能导致激发和波浪的增长由于风作用仍然是未知数。
我们的实验设施的目的是为了能够积累准确和多样的统计信息的变化的风波场特征在稳定或不稳定的风强迫。两个主要因素有助于进行这些详细的研究。首先, 该设施的适度规模导致了相对较短的特征演化尺度的时间和空间。第二, 整个实验由计算机完全控制, 从而使实验运行在不同实验条件下的性能能够自动、实际地实现, 无需人工干预。这些特性的实验设置是非常重要的, 在进行实验的波浪兴奋从休息的冲动风。
本文研究了风波在稳定强迫下的空间生长, 为风速17。根据植物19所提出的里程18理论, 将结果与增长率估计进行了比较。对比表明, 实验结果与理论预测有显著差异。在17中还获得了其他重要参数, 例如测试部分中的平均压降, 以及特征静压波动的绝对值和相位。在空气-水界面上的剪切应力对于描述风与波浪之间的动量和能量传递是必不可少的17,19。因此, 在大量的提取和风速下, 进行了对数边界层的详细测量, 并对水波上的湍流波动进行了分析, 结果为20。本文所确定的空气-水界面的摩擦速度u*的值用于获取在我们的设施21中测量到的风浪的无量纲统计参数。将这些值与大型实验装置和野外试验中获得的相应无量纲参数进行了比较。以前的21表明, 在适当的尺度下, 小规模设施所获得的风波场的重要特征与较大实验室积累的相应数据没有显著差异。安装和露天测量。这些参数包括具有代表性的波浪高度和波长的空间增长, 表面高程的频谱的形状, 以及较高统计矩的值。
随后在我们的设施中进行的研究22,23表明, 风波本质上是随机的和三维的。为了更好地了解风波的3D 结构, 我们尝试使用立体视频成像22对扩展区域的水面高程进行定量的时间依赖性测量。由于现有的计算机电源不足, 而且处理算法还不够有效, 这些尝试被证明只是部分成功。结果表明, 采用传统的电容式波规和汉莎, 可为风浪的空间结构提供有价值的信息。同时应用这两种仪器, 可以独立测量瞬时表面高程和瞬时表面斜率的两个分量的高时间分辨率23。这些测量允许估计波浪的主导频率和主要波浪长度, 并且提供对波浪结构的洞察在正常风向的方向。一种可由计算机控制的马达垂直移动的托管管, 它补充了传感器的集合, 用于测量风速。
所有这些研究表明, 随机和三维的风波导致测量参数的显著变化, 即使在稳定的风强迫和单一测量位置。因此, 需要长时间的测量与实测波场的特征时间尺度相称, 以积累足够的信息来提取可靠的统计量。为了获得有价值的物理洞察力的机制, 控制波场的空间变化, 必须在许多地点进行测量, 并尽可能多的价值的风速尽可能在测试部分。为了实现这一目标, 最好采用自动化的实验程序。
非恒定风强迫下的波浪实验引入了一个额外的复杂程度。在这类研究中, 必须将瞬时测量参数与风速的瞬时水平联系起来。考虑以近脉冲风强迫作为一个重要例子, 从静止的波浪中激发的实验。在这种情况下, 需要许多独立的测量, 在风的作用下演变的风波场, 在不同的时间根据相同的规定模式24。有意义的统计参数, 表示为自空气流动开始以来所经过的时间函数, 然后通过平均从独立认识积累的集合中提取的数据来计算。这项工作可能涉及连续抽样的十个和上百个小时。完成这样一项雄心勃勃的任务所需的实验课程总持续时间, 除非实验完全自动化, 否则整个方法是行不通的。直到最近, 在风浪设施中没有这样的完全计算机化的实验程序。这是在非恒定强迫下缺乏可靠的风浪统计数据的主要原因之一。
由于该实验所用的设施不是从商用的现成硬件构造的, 所以这里提供了其主要部件的简要描述。
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/56480/56480fig1.jpg"> 图1。示意图 (不缩放) 实验设施的视图.1-鼓风机;2流入沉降室;3-流出沉降室;4-消音器盒;5试验段;6滩;7-换热器;8蜂窝;9喷嘴;10-板式;11瓣;12-仪器运输;13波计由步进电机驱动;14-由步进电机驱动的托管管。<a href="http://cloudflare.jove.com/files/ftp_upload/56480/56480fig1large.jpg" target="_blank">请单击此处查看此图的较大版本.</a>
实验设施包括一个封闭环风洞安装在一个波坦克 (示意图视图显示在图 1)。测试部分为5米长, 0.4 米宽, 0.5 米深。壁和地板由6毫米厚的玻璃板组成, 并被封闭在一个由铝型材制成的框架内。一个40厘米长的襟翼提供平滑的扩展气流剖面从喷嘴到水面。波浪能吸收的海滩由多孔的包装材料制成位于坦克的末端。计算机控制的鼓风机允许在测试区段达到平均气流速度在15米/秒。
该定制电容式100毫米长波测量仪由阳极氧化钽制成。0.3 毫米线安装在一个垂直的阶段, 由 PC 控制的步进电机驱动, 为波规校准设计。一个直径为3毫米的托管管, 用于测量测试部分中央气流部分的动态压力。
测量瞬时2D 水表面斜率的汉莎安装在与测试部分分离的框架上, 可以定位在罐体上的任意位置 (图 2)。汉莎由四主要部分组成: 激光二极管、菲涅尔透镜、扩散屏和位置传感探测器 (PSD) 组件。激光二极管产生 650 nm (红色), 200 兆瓦可获得焦点激光束直径约0.5 毫米。26.4 厘米直径的菲涅尔透镜, 焦距为22.86 厘米, 将传入的激光光束定向到位于透镜后焦平面上的 25 x 25 厘米2扩散屏幕。
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/56480/56480fig2.jpg"> 图2。激光斜率计 (汉莎) 的示意图.1-激光二极管;2-菲涅尔透镜;3-扩散屏幕;4位传感器检测器 (PSD)。<a href="http://cloudflare.jove.com/files/ftp_upload/56480/56480fig2large.jpg" target="_blank">请单击此处查看此图的较大版本.</a>
该协议描述了允许执行实验的过程, 在这种情况下, 在时间依赖的风力强迫下, 测量非恒定波的许多参数。考虑到实验设施的技术局限性, 可以根据所需风速的时间来调整程序。本议定书具体描述了在每一个实现中, 风开始几乎在最初平静的水的冲动的实验。稳定的风强迫, 然后持续足够长的风波场在测试段各处达到准稳态状态。风最后被关闭, 再几乎冲动。在各个阶段, 记录了多个波形参数。该程序允许计算出许多统计代表性的集合-平均数量表征瞬时局部风波场是新颖的, 并在最近在我们的设施进行的实验过程中发展22,23,24。

<table><tbody><tr><td>PSD</td><td>THORLABS</td><td>PDP90A</td><td></td></tr><tr><td>Laser Diode</td><td></td><td></td><td>any laser pointer &amp;le; 200 mW</td></tr><tr><td>Aspheric Fresnel Lens</td><td>EDMUND OPTICS</td><td>#46-390</td><td>Diameter 10.4&#039;&#039;, Focal length 9&#039;&#039;</td></tr><tr><td>Wave-gauge</td><td></td><td></td><td>custom made</td></tr><tr><td>Pressure Transducer</td><td>MAMAC SYSTEMS</td><td>PR-274-R2-VDC</td><td></td></tr><tr><td>Signal Conditioner</td><td></td><td></td><td>custom made</td></tr><tr><td>Diffusive screen</td><td>EDMUND OPTICS</td><td>#02-147</td><td></td></tr><tr><td>Water tank</td><td></td><td></td><td>custome made</td></tr><tr><td>A/D card PCI-6221</td><td>National Instruments</td><td>779066-01</td><td></td></tr><tr><td>Pitot tube</td><td>KIMO Instruments</td><td>12971</td><td></td></tr><tr><td>15&amp;deg; Nom. VIS-NIR Coated, Wedge Prism</td><td>EDMUND OPTICS</td><td>#47-624</td><td></td></tr><tr><td>10&amp;deg; Nom. VIS 0&amp;deg; Coated, Wedge Prism</td><td>EDMUND OPTICS</td><td>#49-444</td><td></td></tr><tr><td>2.5&amp;deg; Nom. Fused Silica Wedge Prism Uncoated</td><td>EDMUND OPTICS</td><td>#84-863</td><td></td></tr><tr><td>4&amp;deg; Nom. Uncoated, Wedge Prism</td><td>EDMUND OPTICS</td><td>#43-650</td><td></td></tr><tr><td>5.0&amp;deg; Nom. Fused Silica Wedge Prism Uncoated</td><td>EDMUND OPTICS</td><td>#84-865</td><td></td></tr><tr><td>LabView Full Development System</td><td>National Instruments</td><td>776670-35</td><td></td></tr></tbody></table>

measurements of waves in a wind-wave tank under steady and time-varying wind forcing

这篇手稿描述了一个实验程序, 它允许获得不同的定量信息的时间和空间演化的水波兴奋的时候依赖和稳定的风强迫。利用电容式波浪测量仪和激光斜率计 (汉莎) 测量了风波装置试验段沿线多个位置的瞬时水面高程和瞬时面斜率的两个分量。计算机控制的鼓风机在水箱的水中提供气流, 其速率可能会随时间而变化。在目前的实验中, 测试部分的风速最初从静止到设定值快速增加。它然后保持恒定为规定的期间;最后, 气流被关闭。在每次实验运行的开始, 水面是平静的, 没有风。鼓风机的操作是同时启动的, 并获得由计算机提供的所有传感器的数据;数据采集一直持续到坦克中的波浪完全衰减。在相同的强迫条件下进行的多个独立运行允许确定统计可靠的集合平均特征参数, 以定量地描述在初始开发阶段的风浪变化时间, 作为提取功能。该程序还允许描述在稳定的风力强迫下的波浪场的空间演化, 以及当风被关闭后, 随着海浪的衰减, 作为提取的函数。

在图 6、图 7和图 8中绘制了代表性的集合平均结果。瞬时曲面高程的 RMS 值的变化 <η2>1/2的特征是随机风波振幅的特点, 如图 6所示, 作为时间流逝的函数, 因为鼓风机的启动。显示的结果与板式、 x和三目标风速 ( U. ) 的距离为3。</...

Watch this Scientific Journal Video about Measurements of Waves in a Wind-wave Tank Under Steady and Time-varying Wind Forcing at JoVE.com

Measurements of Waves in a Wind-wave Tank Under Steady and Time-varying Wind Forcing

这篇手稿描述了一个完全计算机控制的程序, 允许获得可靠的统计参数, 从实验的水波的稳定和不稳定的风强迫在一个小规模的设施。

稳定时变风强迫下风浪罐中波浪的测量

This manuscript describes an experimental procedure that allows obtaining diverse quantitative information on temporal and spatial evolution of water ...

measurements-waves-wind-wave-tank-under-steady-time-varying-wind

Universidad de Cartagena UDEC

Research

Education

JoVE Journal

JoVE Core

Engineering

Physics

Electrical Engineering

Unit 1

First and Second-Order Circuits

Waves

SCIENTISTS IN ACTION

8.6K 次观看.  Tel-Aviv University. 这篇手稿描述了一个完全计算机控制的程序, 允许获得可靠的统计参数, 从实验的水波的稳定和不稳定的风强迫在一个小规模的设施。

视频: Measurements of Waves in a Wind-wave Tank Under Steady and Time-varying Wind Forcing

Exploring the Effects of Atmospheric Forcings on Evaporation: Experimental Integration of the Atmospheric Boundary Layer and Shallow Subsurface

Evaporation is directly influenced by the interactions between the atmosphere, land surface and soil subsurface. This work aims to experimentally study evaporation under various surface boundary conditions to improve our current understanding and characterization of this multiphase phenomenon as well as to validate numerical heat and mass transfer theories that couple Navier-Stokes flow in the atmosphere and Darcian flow in the porous media. Experimental data were collected using a unique soil tank apparatus interfaced with a small climate controlled wind tunnel. The experimental apparatus was instrumented with a suite of state of the art sensor technologies for the continuous and autonomous collection of soil moisture, soil thermal properties, soil and air temperature, relative humidity, and wind speed. This experimental apparatus can be used to generate data under well controlled boundary conditions, allowing for better control and gathering of accurate data at scales of interest not feasible in the field. Induced airflow at several distinct wind speeds over the soil surface resulted in unique behavior of heat and mass transfer during the different evaporative stages.

A protocol for the design and construction of a soil tank interfaced to a small climate controlled wind tunnel to study the effects of atmospheric forcings on evaporation is presented. Both the soil tank and wind tunnel are instrumented with sensor technologies for the continuous in situ measurement of environmental conditions.

在探索大气蒸发强迫的影响:大气边界层和浅地层的实验整合

Evaporation is directly influenced by the interactions between the atmosphere, land surface and soil subsurface. This work aims to experimentally study ...

科研

环境科学

Visually Based Characterization of the Incipient Particle Motion in Regular Substrates: From Laminar to Turbulent Conditions

Two different experimental methods for determining the threshold of particle motion as a function of geometrical properties of the bed from laminar to turbulent flow conditions are presented. For that purpose, the incipient motion of a single bead is studied on regular substrates that consist of a monolayer of fixed spheres of uniform size that are regularly arranged in triangular and quadratic symmetries. The threshold is characterized by the critical Shields number. The criterion for the onset of motion is defined as the displacement from the original equilibrium position to the neighboring one. The displacement and the mode of motion are identified with an imaging system. The laminar flow is induced using a rotational rheometer with a parallel disk configuration. The shear Reynolds number remains below 1. The turbulent flow is induced in a low-speed wind tunnel with open jet test section. The air velocity is regulated with a frequency converter on the blower fan. The velocity profile is measured with a hot wire probe connected to a hot film anemometer. The shear Reynolds number ranges between 40 and 150. The logarithmic velocity law and the modified wall law presented by Rotta are used to infer the shear velocity from the experimental data. The latter is of special interest when the mobile bead is partially exposed to the turbulent flow in the so-called hydraulically transitional flow regime. The shear stress is estimated at onset of motion. Some illustrative results showing the strong impact of the angle of repose, and the exposure of the bead to shear flow are represented in both regimes.

Two different methods for characterizing the incipient particle motion of a single bead as a function of the sediment bed geometry from laminar to turbulent flow are presented.

从层流到湍流条件下的规则基底表面初始粒子运动的可视化表征

Two different experimental methods for determining the threshold of particle motion as a function of geometrical properties of the bed from laminar to ...

工程学

Simultaneous Measurement of Turbulence and Particle Kinematics Using Flow Imaging Techniques

Numerous problems in scientific and engineering fields involve understanding the kinematics of particles in turbulent flows, such as contaminants, marine micro-organisms, and/or sediments in the ocean, or fluidized bed reactors and combustion processes in engineered systems. In order to study the effect of turbulence on the kinematics of particles in such flows, simultaneous measurements of both the flow and particle kinematics are required. Non-intrusive, optical flow measurement techniques for measuring turbulence, or for tracking particles, exist but measuring both simultaneously can be challenging due to interference between the techniques. The method presented herein provides a low cost and relatively simple method to make simultaneous measurements of the flow and particle kinematics. A cross section of the flow is measured using a particle image velocimetry (PIV) technique, which provides two components of velocity in the measurement plane. This technique utilizes a pulsed-laser for illumination of the seeded flow field that is imaged by a digital camera. The particle kinematics are simultaneously imaged using a light emitting diode (LED) line light that illuminates a planar cross section of the flow that overlaps with the PIV field-of-view (FOV). The line light is of low enough power that it does not affect the PIV measurements, but powerful enough to illuminate the larger particles of interest imaged using the high-speed camera. High-speed images that contain the laser pulses from the PIV technique are easily filtered by examining the summed intensity level of each high-speed image. By making the frame rate of the high-speed camera incommensurate with that of the PIV camera frame rate, the number of contaminated frames in the high-speed time series can be minimized. The technique is suitable for mean flows that are predominantly two-dimensional, contain particles that are at least 5 times the mean diameter of the PIV seeding tracers, and are low in concentration.

The technique described herein offers a low cost and relatively simple method to simultaneously measure particle kinematics and turbulence in flows with low particle concentrations. The turbulence is measured using particle image velocimetry (PIV), and particle kinematics are calculated from images obtained with a high-speed camera in an overlapping field-of-view.

流成像技术同时测量湍流和粒子运动学

Numerous problems in scientific and engineering fields involve understanding the kinematics of particles in turbulent flows, such as contaminants, marine ...

Power Input Measurements in Stirred Bioreactors at Laboratory Scale

The power input in stirred bioreactors is an important scaling-up parameter and can be measured through the torque that acts on the impeller shaft during rotation. However, the experimental determination of the power input in small-scale vessels is still challenging due to relatively high friction losses inside typically used bushings, bearings and/or shaft seals and the accuracy of commercially available torque meters. Thus, only limited data for small-scale bioreactors, in particular single-use systems, is available in the literature, making comparisons among different single-use systems and their conventional counterparts difficult.
This manuscript provides a protocol on how to measure power inputs in benchtop scale bioreactors over a wide range of turbulence conditions, which can be described by the dimensionless Reynolds number (Re). The aforementioned friction losses are effectively reduced by the use of an air bearing. The procedure on how to set up, conduct and evaluate a torque-based power input measurement, with special focus on cell culture typical agitation conditions with low to moderate turbulence (100 &#60; Re &#60; 2&#183;104), is described in detail. The power input of several multi-use and single-use bioreactors is provided by the dimensionless power number (also called Newton number, P0), which is determined to be in the range of P0 &#8776; 0.3 and P0 &#8776; 4.5 for the maximum Reynolds numbers in the different bioreactors.

The power input in stirred bioreactors can be measured through the torque that acts on the impeller shaft during rotation. This manuscript describes how an air bearing can be used to effectively reduce friction losses observed in mechanical seals and improve the accuracy of power input measurements in small-scale vessels.

实验室规模搅拌生物反应器的功率输入测量

The power input in stirred bioreactors is an important scaling-up parameter and can be measured through the torque that acts on the impeller shaft during ...

生物工程

制造稳定的、具有生物相关性的体模材料

A Stable Phantom Material for Optical and Acoustic Imaging

Establishing tissue-mimicking biophotonic phantom materials that provide long-term stability are imperative to enable the comparison of biomedical imaging devices across vendors and institutions, support the development of internationally recognized standards, and assist the clinical translation of novel technologies. Here, a manufacturing process is presented that results in a stable, low-cost, tissue-mimicking copolymer-in-oil material for use in photoacoustic, optical, and ultrasound standardization efforts.
The base material consists of mineral oil and a copolymer with defined Chemical Abstract Service (CAS) numbers. The protocol presented here yields a representative material with a speed of sound c(f) = 1,481 &#177; 0.4 m&#183;s-1 at 5 MHz (corresponds to the speed of sound of water at 20 &#176;C), acoustic attenuation &#945;(f) = 6.1 &#177; 0.06 dB&#183;cm-1 at 5 MHz, optical absorption &#181;a(&#955;) = 0.05 &#177; 0.005 mm-1 at 800 nm, and optical scattering &#181;s&#39;(&#955;) = 1 &#177; 0.1 mm-1 at 800 nm. The material allows independent tuning of the acoustic and optical properties by respectively varying the polymer concentration or light scattering (titanium dioxide) and absorbing agents (oil-soluble dye). The fabrication of different phantom designs is displayed and the homogeneity of the resulting test objects is confirmed using photoacoustic imaging.
Due to its facile, repeatable fabrication process and durability, as well as its biologically relevant properties, the material recipe has high promise in multimodal acoustic-optical standardization initiatives.

作者聚焦:用于光学和声学成像的稳定 Phantom 材料  

This protocol describes the fabrication of a stable, biologically relevant phantom material for optical and acoustic biomedical imaging applications, featuring independently tunable acoustic and optical properties.

用于光学和声学成像的稳定幻影材料

Establishing tissue-mimicking biophotonic phantom materials that provide long-term stability are imperative to enable the comparison of biomedical imaging ...

医学

Stability of Floating Vessels

Source: Alexander S Rattner and Kevin Rao Li Department of Mechanical and Nuclear Engineering, The Pennsylvania State University, University Park, PA
 The objective of this experiment is to demonstrate the phenomenon of stability of floating vessels - the ability to self-right when rolled over to the side by some external force. Careful design of hull shapes and internal mass distribution enables seagoing vessels to be stable with low drafts (submerged depth of hull), improving vessel maneuverability and reducing drag. 
In this experiment, a model boat will first be modified to enable adjustment of its center of mass (representing different cargo loadings) and automated tracking of its roll angle. The boat will be placed in a container of water, and tipped to different angles with varying heights of its center of mass. Once released, the capsizing (tipping over) or oscillating motion of the boat will be tracked with a digital camera and video analysis software. Results for the maximum stable roll angle and frequency of oscillation will be compared with theoretical values. Stability calculations will be performed using geometric and structural properties of the boat determined in a computer aided design environment.

The Buoyant Force and Stability of Floating Vessels

浮动容器的稳定性

Source: Alexander S Rattner and Kevin Rao Li Department of Mechanical and Nuclear Engineering, The Pennsylvania State University, University Park, PA
 The ...

教育

JoVE Science Education

机械工程

Turbulence Sphere Method: Evaluating Wind Tunnel Flow Quality

Source: Jose Roberto Moreto and Xiaofeng Liu, Department of Aerospace Engineering, San Diego State University, San Diego, CA
Wind tunnel tests are useful in the design of vehicles and structures that are subjected to airflow during their use. Wind tunnel data are generated by applying a controlled air flow to a model of the object being studied. The test model usually has a similar geometry but is a smaller scale compared to the full-sized object. To ensure accurate and useful data is collected during low speed wind tunnel tests, there must be a dynamic similarity of the Reynolds number between the tunnel flow field over the testing model and the actual flow field over the full-sized object.
In this demonstration, wind tunnel flow over a smooth sphere with well-defined flow characteristics will be analyzed. Because the sphere has well-defined flow characteristics, the turbulence factor for the wind tunnel, which correlates the effective Reynolds number to the test Reynolds number, can be determined, as well as the free-stream turbulence intensity of the wind tunnel.

Turbulence Measurements at Varying Air Speeds

湍流球法:评估风洞流量质量

Source: Jose Roberto Moreto and Xiaofeng Liu, Department of Aerospace Engineering, San Diego State University, San Diego, CA
Wind tunnel tests are useful ...

航空工程

Measuring Turbulent Flows

Source: Ricardo Mejia-Alvarez and Hussam Hikmat Jabbar, Department of Mechanical Engineering, Michigan State University, East Lansing, MI
Turbulent flows exhibit very high frequency fluctuations that require instruments with high time-resolution for their appropriate characterization. Hot-wire anemometers have a short enough time-response to fulfill this requirement. The purpose of this experiment is to demonstrate the use of hot-wire anemometry to characterize a turbulent jet.
In this experiment, a previously calibrated hot-wire probe will be used to obtain velocity measurements at different positions within the jet. Finally, we will demonstrate a basic statistical analysis of the data to characterize the turbulent field.

Measuring Turbulent Flows Using Hot-Wire Anemometers

测量紊流

Source: Ricardo Mejia-Alvarez and Hussam Hikmat Jabbar, Department of Mechanical Engineering, Michigan State University, East Lansing, MI
Turbulent flows ...

稳定时变风强迫下风浪罐中波浪的测量

摘要

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流成像技术同时测量湍流和粒子运动学

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用于光学和声学成像的稳定幻影材料

用于光学和声学成像的稳定幻影材料

用于光学和声学成像的稳定幻影材料

浮动容器的稳定性

湍流球法:评估风洞流量质量

测量紊流