A new study published in the journal Results in Engineering by Yu Zhou, Junhui Wang, Yuetang Zhao, and Hui Li argues that the era of pure brute-force resistance may be giving way to something smarter. Instead of building ever-heavier walls, the researchers propose deliberately shaping the geometry of protective obstacles so that the blast wave itself is steered, split, delayed, and partially cancelled. This shift, from what the authors call passive resistance to active regulation, exploits the wave-structure interactions of reflection, diffraction, and interference to redistribute and dissipate explosive energy. It builds on earlier work showing that corrugated blast walls, curtain-type walls of suspended steel plates, and fence-type walls of structural columns can all attenuate shock waves in the open field, often with lighter and cheaper construction than solid barriers. The catch, however, is that in confined spaces many of those measures are aimed at the transmitted wave, while the reflected wave, the true killer indoors, has remained largely unaddressed.

The team’s starting point is a piece of classical shock physics. According to the Rankine-Hugoniot jump conditions, the overpressure of a shock reflected from a rigid wall depends strongly on the strength of the incident wave. When the incident overpressure is small relative to atmospheric pressure, the reflection coefficient approaches two, meaning the reflected wave is roughly twice as strong as the incoming one. But for strong shocks, that coefficient climbs steadily toward eight. A blast wave bouncing repeatedly between rigid boundaries in a confined volume can therefore build up to pressures several times higher than the original front. Any mitigation strategy that works against the transmitted wave alone may do little, or even make things worse, for these amplifying reflections. Understanding and controlling reflection, the researchers conclude, is the critical unresolved problem in confined-space protection.

Using the nonlinear dynamics finite element software LS-DYNA, the team systematically simulated three categories of engineering measures: column-shaped obstacle arrays, slope-shaped obstacles, and a novel forward-positioned variant of the slope design. The blast loading was deliberately severe and conservative: a plane shock wave with a peak overpressure of roughly 1.2 megapascals and a positive-phase duration of about 30 milliseconds, striking a rigid boundary 10 meters away. For comparison, a 1,000-kilogram spherical TNT charge detonated 10 meters from a target produces a positive phase of only around 18 milliseconds, so the simulated loading gives reflected waves ample time to return and superpose on the incident front, creating one of the most unfavorable scenarios possible. The obstacles themselves were treated as rigid bodies, a standard and reasonable assumption for studies focused on wave-structure interaction rather than structural damage.

Before running the parametric studies, the team validated their modeling approach against a real field test, a 3-kilogram TNT explosion conducted near a concrete-filled steel tubular pier. In their simulation of that experiment, the computed peak reflected overpressures at sensors mounted on the pier and in the free field agreed closely with the measured values, with errors ranging from about 2.7 percent to 13.9 percent. The simulations also reproduced the full sequence of wave phenomena, from free propagation in the first fraction of a millisecond to the cylindrical reflection and diffraction that followed as the wave swept past the pier. That agreement gave the researchers confidence that LS-DYNA could faithfully capture the reflection, diffraction, and interference dynamics at the heart of their study.

The column-shaped obstacle arrays produced some of the study’s most surprising results. Drawing on 108 finite element models, the team tested four cross-sectional shapes, semi-circular, triangular, circular, and square, while varying the spacing between columns, the distance to the rigid boundary, and the obstacle radius. The intuitive expectation might be that any obstacle should help, but the opposite was often true. Square columns, with their flat faces inviting normal reflection, were the worst performers on average, and in one configuration they amplified the reflected overpressure by a staggering 116 percent. Triangular and semi-circular columns fared best, because their angled and curved surfaces convert normal reflection into weaker oblique reflection, and their geometry lets more of the blast wave pass through the gaps while making it harder for the reflected wave to travel back. A statistical analysis of the parameter sensitivity showed that the obstacle radius generally had the greatest influence on performance, while the triangular cross-section offered the most balanced and robust behavior. Still, on average, none of the column configurations reduced reflected overpressure overall, underscoring how easily well-intentioned protective geometry can backfire in confined spaces.

The slope-shaped obstacles told a different and more dramatic story. Placed against the rigid boundary, a slope is meant to deflect the incident wave upward and away into the free field. But the simulations revealed a treacherous phenomenon: as the reflected wave from the vertical wall travels down the slope and interacts with the ground, it can catch up with the precursor wave and coalesce into a Mach stem, a localized region of intensified pressure that races ahead of the original reflections. Near the ground, where this Mach stem forms, the free-field peak reflected overpressure reached as high as 1.52 megapascals in some cases. The key insight is that gentle slopes concentrate the reflected wave’s energy and make Mach stem formation more likely, while steep slopes disperse the energy and perform better. Crucially, the inclination angle alone cannot predict performance; at a fixed 45-degree slope, the peak reflected overpressure still varied from 1.19 to 1.52 megapascals depending on the obstacle’s width and height. Dimensions, the authors emphasize, must always be analyzed jointly with angle.

The study’s most promising concept is the forward-positioned slope-shaped obstacle, which moves the slope several meters away from the rigid wall, creating a semi-confined space behind it. In an orthogonal study of 45 configurations, this design achieved reductions in peak reflected overpressure of up to roughly 30 percent. The mechanism is what the authors call graded release: rather than dissipating the blast energy outright, the semi-enclosed space forces the reflected wave to bounce back and forth multiple times, spreading its arrival over a longer interval and weakening the waves that eventually escape. Impulse histories showed that the total impulse at the observation points was nearly unchanged, confirming that the benefit comes from redistributing the reflected energy through repeated interactions rather than absorbing it. The geometry of the gap matters greatly. When the forward distance was 1, 2, or 3 meters, the optimal obstacle height shifted to 4, 3, and 2 meters respectively, meaning that designers who can afford a larger setback can build a shorter, cheaper obstacle with equal or better performance.

The practical implications reach well beyond military engineering. Urban street canyons, tunnels, industrial facilities, and ammunition storage sites all share the confined-space geometry in which reflections amplify blast loads. The findings offer a sobering warning for anyone deploying conventional obstacles indoors: square columns and gently sloped barriers can intensify the very hazard they are meant to reduce, sometimes more than doubling the pressure that occupants experience. At the same time, the results provide a constructive design framework. Triangular or semi-circular columns with carefully chosen radii, steep slopes, or forward-positioned slope obstacles with generous setbacks can genuinely suppress reflected overpressure, and the benefit grows in larger confined spaces. The researchers note that future work will explore combinations of multiple obstacles, and that real-world designs must always be tailored to the specific blast scenario, charge size, and standoff distance. But the central message of the study is already clear: in the fight against confined explosions, the shape of the battlefield matters as much as the strength of the armor, and intelligent geometry can turn a blast wave’s own physics against it.

Subject of Research: Engineering measures to mitigate blast wave reflection intensity in confined spaces

Article Title: Research on engineering measures to mitigate the intensity of blast wave reflection in confined spaces

Article References: Research on engineering measures to mitigate the intensity of blast wave reflection in confined spaces. (n.d.). https://doi.org/10.1016/j.rineng.2026.113354

Image Credits: AI Generated

DOI: Not provided

Keywords: blast waves, confined space explosions, reflected overpressure, LS-DYNA simulation, blast mitigation, protective structures, Mach stem, wave diffraction, shock reflection, slope-shaped obstacles, column-shaped obstacles, protective engineering