桑迪亚（Sandia）的爆炸管测试模拟了冲击波条件

You can learn a lot from a blast tube. You can learn more when you couple blast experiments with computer modeling.

桑迪亚国家实验室的研究人员正在使用可配置为120英尺的爆炸管，以证明核武器能够在敌方武器中爆炸的冲击波生存，并帮助验证建模。

桑迪亚（Sandia）最近完成了为期两年的核武器计划测试，并开始对另一项核武器计划进行测试。每个系列都需要仪器，炸药，高速相机和计算机建模。

测试主管内森·格伦（Nathan Glenn）说，测试模拟了部分环境，如果另一个核武器在附近驶下，则重新进入地球大气层的武器将面临。

每个系列均以校准拍摄开始，使团队成员能够验证爆炸波参数，同时验证计算机模型。该团队在直径6英尺的一端悬挂爆炸物，并将压力传感器沿其长度放置。传感器感觉到爆炸压力穿过管的强度 - 更高的压力更接近电荷，从远离电荷。

Modeler Greg Tipton, who helped design the series, said tests validate the computer models of the structural dynamics of the system. “We can then use the models to simulate real environments we can’t actually test to,” he said.

弄清楚如何进行测试

蒂普顿说，这是复杂的，只是分析如何进行测试。压力驱动了需要多大的电荷以及测试文章如何将其定位在管中，这决定了负载或施加到测试单元的力量。反过来，加载决定了测试文章的结构响应。“因此，团队确实进行了端到端的计算，以模拟爆炸，冲击波通过管，对测试单元的冲击传播，然后对冲击波的结构响应。所有数据都用于确定正确的方向，正确的冲击电平，以验证模型。” Tipton说。

一个软件程序模拟了爆炸的爆炸，并通过管道移动。第二个计算在测试单元上移动的冲击。三分之一计算单元对冲击和振动的响应。第四个模拟了该单元从试管中飞行的方式，以便团队可以估算进展的位置，移动的速度以及他们将如何安全地抓住它。Tipton说，每个软件包的双重目的都是计算系统响应以验证模型并帮助设计测试。

软件模拟了explosive going off, for example, helps determine the size of the charge. “They do a number of shots in the tube to calibrate that. You know a charge weight and a pressure at some target location,” he said. “As you up the charge weight, you’re going to up the pressure, and if you do a handful of those tests and a whole bunch of simulations to fill in the blanks, you establish a calibration curve that tells you how much explosive you need to achieve a target pressure.”

帮助分析测试数据的威尔·霍尔茨曼（Wil Holzmann）表示，可能会在压力，应变和加速反应上收集一百多个数据渠道。分析师使用嵌入式信息处理实验数据，并将相同的信号处理方法用于实验和分析数据，并比较响应以评估模型的可信度。

“The objective is to develop validated analytic models for predicting responses to blast loads with a high degree of confidence,” Holzmann said. Researchers can use the validated model to help qualify a weapon to withstand harsh conditions, such as a nuclear blast, that cannot be directly simulated with ground-level blast tube tests.

计划需要比测试时间更长

仪器至关重要。最后一次仅毫秒的测试需要数月的计划。

测量科学与工程学的约翰·格里芬（John Griffin）说：“沟通和技术卓越对成功至关重要”，只有一个机会从爆炸的极端环境中获取数据。“设计，硬件的保护，关键要素的冗余以及对连接的彻底验证是确保我们获得该机会的数据的关键。”

桑迪亚国家实验室研究人员正在使用爆炸管来帮助验证计算机建模并证明冲击波对核武器的影响。（照片由桑迪亚国家实验室提供）

Over the past three years, Sandia developed a new mobile instrumentation unit, a large-data acquisition system designed to self-check the accuracy and “health” of connections before and after testing.

A hardened trailer encloses the system so it can be placed near a blast test. The system can store up to 16 million samples per channel and record about 1 gigabyte per second at the maximum sample rate, Griffin said. For comparison, he said, this equates to more than 70 hours of digital music or about 1,100 songs.

Glenn said it’s more of an art than a science to measure pressure pulses. “If you don’t have it set up right and mounted right, the data is worthless,” he said. “There are racks and racks of instrumentation with wires coming at you. It makes your head dizzy just looking at it.”

Specialty high-speed imaging employed

High-speed imaging that measures pressure changes also helps assess a shock wave’s impact. In the past, researchers used streak cameras that viewed images through a quarter-inch by 6-inch slit. Streak cameras are similar to document scanners, imaging a column of pixels and generating an image by the object moving rapidly past the scan.

Sandia National Laboratories researchers use wavefront imaging taken at 35,000 frames per second to analyze blast wave dynamics invisible to the eye and determine how well nuclear weapons could survive a shock wave. (Photo courtesy of Sandia National Laboratories)

现在，一种名为Synthetic Schlieren的摄影技术，由光学工程师Anthony Tanbakuchi为恶劣的环境实施，可实现更大的视野。合成Schlieren检测到压力，温度和密度变化引起的光学指数的变化。Schlieren效果与在道路上看到的涟漪相当。Tanbakuchi说，常规的Schlieren（在单数中表示条纹的德语单词）技术需要大型光学，特殊照明和其他复杂，敏感的光学配置，对于大规模测试而言是不切实际的。Synthetic Schlieren除可选的背景外不需要任何特殊设置，并且没有尺寸限制，因为它在背景中寻找子像素移动以检测光学索引变化。

The team combines synthetic imaging algorithms with image stabilization codes Tanbakuchi developed to image a blast wave front. Sandia’s 50-year history of extreme testing means it has a huge code base to solve these problems.

合成的Schlieren可用于从压力到温度成像的所有物品。Tanbakuchi说：“但是，当我们还将其与我们开发的数据融合技术相结合时，最有价值的是您可以看到带有仪器数据和模型数据的压力波阵线。”“那是全图真正出现的时候。”