Digital in-line holography helping answer questions about burning fuels
Transportation accidents, such as trucks crashing on a highway or rockets failing on a launch pad, can create catastrophic fires. It’s important to know how burning droplets of fuel are generated and behave in those extreme cases, so Sandia researchers have developed 3-D measurement techniques based on digital in-line holography.
Digital in-line holography, known as DIH, is a laser-based technique that has been around since the 1990s. Sandia advanced the technique with new algorithms to mine critical information from recorded holograms and new applications in tough fire environments, says Dan Guildenbecher (1512).
“We live in a 3-D world, and if you think of traditional imaging, it’s 2-D,” he says. “This technique is one of the few that can give you a 3-D measurement of a flow.”
DIH passes a laser through a particle field. The interaction between the laser and the particles creates diffraction patterns, which a camera records. Researchers then use computers to solve diffraction integral equations, allowing them to take light recorded at the camera plane and refocus it back to the original planes of the particle locations. That gives the position of particles as they were in 3-D space.
In a propellant fire, large molten aluminum drops form at the burning surface. They’re lofted into the environment and can severely damage anything they fall on. Researchers study this by passing a laser through fire while high-speed cameras record the diffraction patterns. Refocused digital holograms provide a clear picture of the burning particles. By measuring the size and velocity of thousands of such particles, researchers can better understand how the particles are formed and transported in this flow.
Interested in 3-D particle measurements in complex environments
“Fundamental understanding of particle formation and transport is necessary to develop next-generation [computer] models that predict this scenario,” Dan says. “Due to the corrosive environment, it’s very difficult to measure these phenomena using traditional instruments. You need to have advanced diagnostics and advanced modeling.”
Sandia’s digital in-line holography method uses nanosecond lasers to freeze the motion of particles and kilohertz imaging to track droplets’ size and velocity. Recording and quantifying all droplets in a 3-D volume — the digital hologram — lets researchers quickly measure thousands of individual drops, allowing for accurate quantification of size and velocity. In addition, measuring particle shape enables them to differentiate spherical drops from other particulates in the flow.
Previous work on particle-field DIH largely focused on measuring spherical particles in controlled environments. However, Sandia needed to measure arbitrarily shaped objects in difficult, real-world environments. So Dan and colleagues developed new data processing algorithms that automatically measure complex particle structures in 3-D space, quantifying their accuracy through laboratory experiments. “Validation experiments were instrumental to improving the technique and gave us the confidence to apply the method to a wide range of applications,” he says.
“Sandia has a long history of developing groundbreaking imaging for a wide range of applications. For example, recent rapid advances in high-speed digital imaging have enabled 2-D videography at frame rates from kilohertz to megahertz. This has greatly increased our experimental resolution of many important phenomena,” Dan says. “Digital holography is one of a handful of techniques which allow us to expand these technologies to 3-D.”
DIH is important diagnostic tool in many areas
The researchers also have used DIH to quantify liquid breakup due to strong gas flows and impacts on surfaces. They measured complex, ring-shaped ligaments in 3-D space, which provided new physical insight into how droplets form. “In a transportation accident, the breakup of liquid fuel leads to wide dispersion of droplets and large-scale fire. Liquid breakup must be understood to predict the scale and intensity of such fires,” Dan says.
“By focusing on doing something cutting edge, we discovered applications that no one else had attempted and measured phenomena we never expected,” he says. “I liked that we were able to find so many ways to utilize this exciting technology.”
They also looked at shotgun particles, which Dan says was fun but had a practical purpose. “There’s interest in understanding how particulates behave in explosive environments, and we set up a shotgun as a simulant for this environment.” Results of the successful demonstration were published in a 2013 paper in Optics Letters.
The team published additional papers in such publications as Applied Optics, Optics Express, and Experiments in Fluids, and presented their work at numerous conferences over the past three years. Dan was invited to give talks at the 2015 Gordon Research Conference on Laser Diagnostics in Combustion in Waterville Valley, N.H., and the 2014 Laser Applications to Chemical, Security, and Environmental Analysis conference in Seattle. Dan and Phillip Reu (1512) of Sandia, along with professor Jun Chen and doctoral student Jian Gao of Purdue University, were awarded the 2014 ASME Fluid Engineering Division’s Robert T. Knapp award at the ASME summer meeting. The award recognizes an outstanding original paper resulting directly from analytical or laboratory research.
DIH is a crucial diagnostic tool for a new Laboratory Directed Research and Development (LDRD) project to quantify the breakup of molten components in shock-induced flows. In this environment, changing temperatures and the small size of the particulates distort the hologram image. Dan and colleagues will look at potential improvements to DIH methods that could correct those distortions.
Dan became interested in the field when, as a doctoral student, he ran into limitations in commercial diagnostics for studying multiphase flows. When he joined Sandia in 2011, he teamed with researchers working in digital imaging.
An Early Career LDRD project and the Weapon System Engineering Assessment Technologies (WSEAT) program funded the development work. Team members included Dan and Phillip in collaboration with Chen and Gao.
-- Sue Major Holmes
Explosive Destruction System begins first stockpile project
by Patti Koning
Last month, the Explosive Destruction System (EDS), designed by Sandia for the US Army, began safely destroying stockpile chemical munitions.
The project to destroy 560 chemical munitions at the US Army Pueblo Chemical Depot in Colorado with EDS is a prelude to a much larger operation to destroy the stockpile of 780,000 munitions containing 2,600 tons of mustard agent stored at the Pueblo depot since the 1950s.
The bulk of those munitions will be safely destroyed in the Pueblo Chemical Agent-Destruction Pilot Plant (PCAPP), which will begin operation later this year. The munitions to be destroyed in EDS are considered unsuited for processing by the plant’s automated equipment because they have leaked or have been sampled in the past.
“EDS was originally designed for nonstockpile chemical munitions at recovery sites, many of which are deformed and corroded,” says mechanical engineer Brent Haroldsen (8137), the Sandia project lead. “Stockpile munitions are generally in better shape, but there are always a few that are leaking or damaged. That’s where EDS will come in to keep the plant moving efficiently.”
The Program Executive Office, Assembled Chemical Weapons Alternatives (PEO ACWA) is overseeing the pilot plant as well as the Blue Grass Chemical Agent-Destruction Pilot Plant near Richmond, Kentucky. Once the pilot plant begins operation, the EDS systems will remain at the site to process any additional reject munitions unsuitable for processing in the Pueblo pilot plant.
Latest EDS model destroys munitions twice as fast
The two EDS units that will augment the pilot plant operation work much faster than the original EDS, which took two days to process a single munition.
Sandia designed that system for the Army in the late 1990s to destroy munitions that were discovered unexpectedly.
To safely destroy a few damaged munitions at a time, possibly in populated areas, the original design emphasized transportability, flexibility, redundancy, surety of destruction, and simplicity of manual operation — not rapid processing.
The Army first used EDS in 2001 at the Rocky Mountain Arsenal in Colorado and then at other locations where abandoned munitions were recovered. Sandia then created a larger version, capable of destroying multiple munitions simultaneously and handling munitions with a higher explosive charge. In 2010, Sandia engineers created the Phase 2 Pilot (P2P), which decreased the processing time from two days to one through changes to the heating and cooling system and door clamp design. (See the Sept. 7, 2012, issue of Sandia Lab News.)
Over the years, the basic operation of EDS has remained the same. At its core is a leak-tight vessel in which munitions are placed. An explosive shaped charge opens the metal shell, exposing the chemical agent and burster, a small explosive that disperses the agent. The burster explodes or deflagrates safely inside the vessel. A reagent is then pumped into the chamber to neutralize the chemical agent. The chamber is heated and turned to mix the chemicals and speed the reaction.
Stockpile munitions easier to process
The new EDS, called the Phase Two Retrofit (P2R), incorporates many of the P2P improvements along with a separate boiler/chiller container and larger pipes and pumps to transfer fluids more quickly. Working with stockpile munitions also simplifies the explosion process.
“Nonstockpile munitions are discovered in strange conditions, tangled in tree roots or covered with barnacles. Badly corroded munitions are often stabilized with plaster of Paris and then wrapped in plastic before processing. Consequently, the EDS was designed to be adaptable and flexible,” Brent says.
But stockpile munitions, even problematic ones, are quite uniform. “So we need less flexibility in the design and we can use the shaped-charge explosives more effectively to cut the munitions,” says Brent.
At the pilot plant, EDS will process six munitions a day, starting with 560 reject munitions already set aside. ACWA expects EDS to destroy about 1,300 munitions over the five-year operation, including reject munitions.
Improvements under way to vapor monitoring
In collaboration with Defiant Technologies, the EDS team also is working on an in-situ vapor monitoring system, which is an offshoot of Sandia’s MicroChemLab gas phase system. To ensure the EDS vessel is safe to open following operation, a vapor sample must be collected and analyzed. An in-situ monitoring system would draw a sample from inside the vessel, eliminating the collection step and saving about 45 minutes.
The vapor monitoring system also can monitor for multiple agents simultaneously, so it could be used to monitor the environmental enclosure around EDS or at a munition recovery site. That monitoring is currently being done with specialized gas chromatographs, which are reliable but can only check for one agent at a time.
“The ability to monitor for multiple agents with a single system would further simplify operations,” says Brent.
The two EDS units will spend several years at PCAPP. Meanwhile, the Army continues to use the EDS system to destroy recovered chemical munitions.
-- Patti Koning
Sandia hosts first Nonproliferation Treaty Transparency Visit
Sandia’s success in life extension programs for a variety of nuclear weapons will allow for future reductions in the nuclear weapons stockpile, NNSA Deputy Administrator Don Cook told visitors during Sandia’s first Nonproliferation Treaty Transparency Visit.
Also led by US Ambassador Adam Scheinman, Special Representative of the President for Nuclear Nonproliferation, and attended by other officials from NNSA, Los Alamos National Laboratory, and the Sandia Field Office, the visit was a major US initiative leading up to the Review Conference of the Treaty on the Non-Proliferation of Nuclear Weapons (NPT). The conference occurs every five years and will take place in New York, April 27-May 22.
The recent visit allowed 12 international attendees to observe firsthand Sandia’s multidisciplinary technical work and learn about the technical infrastructure and workforce that support US implementation of the NPT. The group visited the Technology Training and Demonstration Area (TTD) at the Center for Global Security and Cooperation. At the TTD, they learned about Sandia’s contributions to treaty monitoring, arms control, civilian nuclear power, and safeguards support to the International Atomic Energy Agency (IAEA), as well as chemical and biological risk reduction. The group also visited the Z machine, the Integrated Security Facility, and the Thermal Test Complex. On Friday, the same group received similar presentations and tours at LANL.
Paves way for future stockpile reductions
Cook said that increased confidence in the safety, security, and effectiveness of the nation’s deterrent comes from science-based stockpile stewardship and life extension programs, and ultimately paves the way to future reductions in the US nuclear weapons stockpile.
“The reason for that is we’ve got a substantially decreased stockpile from the Cold War and the president has said we can go further,” he said, adding the difficulty is that the stockpile is older than it’s ever been, and old weapons components are subject to degradation as a result of aging.
Cook said he anticipates that stockpile downsizing likely would come from the significant number of weapons the US maintains as a “hedge” against technical failure.
“We extend the life of the weapons, we get more confidence, and we have improved safety and security. Technically, they’ll have the same requirements — no new requirements or capabilities — but because we’ve got greater confidence, then we can begin reducing the hedge weapons,” he said.
The US is pursuing a strategy that will reduce the number of nuclear weapon types from 12 to five, Cook said. The first step in achieving this goal is the current B61-12 Life Extension Program (LEP).
The DOE/NNSA stockpile stewardship activities, Cook said, will result in:
- a reduction of the number of bombs by a factor of two;
- the removal of the last megaton-class weapon, the B83, from the stockpile;
- a reduction of more than 80 percent in the special nuclear materials in the bomb portion of the air leg of the nuclear triad; and
- a commensurate reduction in overall destructive power.
Deputy Laboratories Director and Executive VP for National Security Programs Steve Rottler (0002) said that Sandia’s transition to extending the life of the stockpile began in the 1990s with W87 LEP, the 2000s with the W76 LEP, and continues today with LEPs on the B61 and W80, an alteration on the W88, and a replacement of the arming and fuzing assembly for the Minuteman warheads.
“We’re frankly facing a workload and challenges that this laboratory and the complex have not dealt with in almost 30 years,” he said.
Steve spoke about Sandia’s commitment and general approach to nuclear weapons safety.
“An important philosophy in our approach to underwriting the safety of nuclear weapons is we do not get involved in estimating the probability that a weapon will be exposed to an accident environment. We assume that in the lifetime of every nuclear weapon in our stockpile it will be exposed to a whole set of abnormal environments.” he said.
To withstand any abnormal environments, the weapons are designed so the components providing electrical energy to set off the weapon will fail long before all the barriers in place to prevent that electrical energy from setting off the weapon would fail, he said.
“We do that with very, very high confidence,” Steve added.
The Labs play a “critical role” in “advising the government about the focus necessary to achieve the level of confidence and safety we have in our stockpile today. While we never rest on our laurels, it is a supremely engineered level of confidence,” Sandia President and Labs Director Paul Hommert told the visitors. “It is a legacy, which those of us in this business take deeply seriously, that is embodied in this institution.”
Vice President of Energy, Nonproliferation, and High-Consequence Security Jill Hruby (6000) told the visitors about Sandia’s support for national nuclear security programs, arms control treaties and verification, and international threat reduction.
“We make sure that our weapons are secured in all places and at all times,” she said.
Jill discussed a variety of Sandia programs, including work to ensure the safety of nuclear weapons during ground transportation, security perimeter detection systems for nuclear weapons facilities, the development of tools for arms control treaties with monitoring provisions, and efforts to secure weapons grade materials.
Senior manager Pablo Garcia, who organized Sandia’s portion of the visit, says the visit went “extremely well” and visitors left informed about the interface of US nuclear weapons policy and the technical work.
“All of them told me personally that they were very impressed by the event, the capabilities they saw, and most importantly, the dedication to our mission by everybody they met,” he says.
Sandia “enjoyed hosting our international visitors and showing them how the Labs’ science and engineering expertise is helping strengthen the nation’s commitment to the Nuclear Nonproliferation Treaty. Our work contributes to preventing nuclear weapon proliferation, enabling a safe, secure, and effective stockpile and promoting the peaceful use of nuclear energy,” Paul says. “The open dialogue with our guests, visits to our Z pulsed-power machine, Thermal Test Complex, Integrated Security Facility, and a viewing of nonproliferation technologies showed our guests Sandia’s ongoing commitment to making the world more secure.”
-- Heather Clark