A pioneering breakthrough in the modeling of granular materials has been unveiled by researchers at the Hong Kong University of Science and Technology (HKUST). Their newly developed computational framework, the Pore Unit Assembly-Discrete Element Model (PUA-DEM), revolutionizes how we understand the intricate movement and interaction of granular substances such as soils, sands, and powders. These materials, ubiquitous in both natural environments and diverse industrial processes, have long presented formidable challenges to scientists seeking to predict their behaviors accurately, particularly under partially saturated conditions where the interplay between solid particles, air, and water is highly complex.
Traditional computational models attempting to simulate granular flows have largely depended on oversimplified assumptions, treating particles as static or employing one-way coupling mechanisms that insufficiently capture the genuine interactions between fluid phases and particles. This simplification often leads to significant discrepancies when applying these models to real-world scenarios, such as anticipating landslide risks, enhancing irrigation efficiency, or optimizing pharmaceutical powder processing. The paramount complication lies in accurately representing capillary and viscous forces governing multiphase systems where air and water coexist with solid particles, phenomena that are critical yet notoriously difficult to simulate at a pore scale.
The innovative PUA-DEM approach designed by Prof. ZHAO Jidong and his team introduces a rigorous, physics-based representation of the dynamic interactions among particles and fluid phases. Unlike previous models, PUA-DEM achieves a fully coupled multiphase simulation, accounting for the detailed mechanics of particle displacement, fluid flow, and evolving stress and pressure distributions throughout a range of saturation states—from fully saturated to completely dry granular assemblies. This comprehensive modeling capability marks it as the first of its kind to successfully integrate the microscopic processes controlling capillary forces, viscous flow, and particle-fluid coupling into a unified computational platform with remarkably high precision.
The fundamental science driving PUA-DEM hinges upon resolving microscale phenomena such as capillary bridge formation between particles, pressure gradients within pore fluids, and particle swelling due to fluid absorption. By explicitly simulating these physical processes at the grain scale, the model transcends phenomenological approximations and offers unprecedented predictive power. It thereby bridges the gap between laboratory-scale experiments and field-scale behavior, an accomplishment of profound importance for both basic research and applied engineering challenges involving multi-phase granular media.
This development holds transformative potential across numerous sectors. In geotechnical engineering, PUA-DEM’s ability to simulate soil collapse mechanics with precision promises to enhance early warning systems for landslides, mitigating disaster risks and saving lives. Simultaneously, environmental engineers can leverage its multiphase flow predictions to optimize carbon sequestration efforts, modeling how injected fluids interact with subsurface porous formations. The agriculture industry stands to benefit as well, with the model facilitating precision irrigation by simulating water retention and root-soil interactions, thus conserving resources and improving crop yields.
Moreover, the pharmaceutical realm may witness revolutionary advances in powder processing technologies. Drug manufacturing traditionally depends on empirical methods to handle powder flowability and compaction, critical factors affecting dosage consistency and therapeutic efficacy. PUA-DEM offers a scientific basis to optimize these processes through fine-grained simulations of powder behavior during handling and tablet formation. This capability could lead to safer, more effective medications produced with greater efficiency and uniformity, ultimately enhancing patient outcomes worldwide.
The food industry is another prospective beneficiary. Granular food products such as coffee grounds, sugar crystals, and infant formulas present manufacturing and storage challenges related to texture, dissolution rates, and stability. The PUA-DEM model’s precision in capturing fluid-granular interactions could enable manufacturers to design products with optimized sensory and functional properties while minimizing waste and energy consumption during production and storage phases.
In articulating the significance of the model, Prof. Zhao emphasized the paradigm shift represented by PUA-DEM in simulating unsaturated granular systems. He elaborated that by resolving detailed pore-scale fluid-solid interactions, the model not only predicts macroscale behaviors like soil deformation and fluid leakage but also opens pathways for innovative solutions in infrastructure safety, agricultural production, pharmaceutical consistency, and energy resource management. This integration of physics-based multiphase modeling marks a major advancement in computational geomechanics and materials science.
Looking toward the future, Dr. Amiya Prakash DAS, who played a leading role in developing PUA-DEM and recently graduated from HKUST, highlighted plans to further enhance the model’s capabilities. Upcoming research will focus on incorporating irregular particle geometries and wettability effects, thereby refining the fidelity of simulations to reflect natural soil and powder characteristics more accurately. The team also aims to explore hybrid computational techniques to address complex phenomena such as reactive transport and drying-induced cracking, extending the model’s applications to broader scientific and industrial challenges.
The collaboration behind this research includes Dr. Thomas SWEIJEN from Utrecht University, whose expertise augmented the project’s rigorous development and validation phases. Their joint work culminated in the publication titled “Micromechanical Modeling of Triphasic Granular Media” in the prestigious Proceedings of the National Academy of Sciences (PNAS), marking a significant milestone in the scientific understanding of multiphase granular systems.
This study exemplifies the power of interdisciplinary cooperation, merging civil engineering, environmental science, physics, and computational modeling to tackle long-standing challenges in granular material science. The authors hope their work will inspire further research and industrial partnerships, ultimately leading to safer infrastructure, sustainable environmental management, and innovative manufacturing processes rooted in a deeper comprehension of nature’s most ubiquitous particulate materials.
The advent of PUA-DEM epitomizes the stepwise evolution from oversimplified computational paradigms to highly detailed, physically grounded models that reflect the rich complexity of granular materials interacting with fluids. Its implications reverberate across academic disciplines and industry sectors alike, promising a future where predictions of soil stability, fluid migration, and powder behavior are not just approximations but robust, reliable forecasts capable of informing critical decisions on a global scale.
As the model continues to mature, its incorporation into digital twin frameworks, real-time monitoring systems, and advanced process simulations could drive forward the next generation of smart infrastructure and manufacturing methodologies. This transformational shift underscores the vital role of high-fidelity computational mechanics in shaping a safer, more efficient, and sustainable society.
Subject of Research: Not applicable
Article Title: Micromechanical modeling of triphasic granular media
News Publication Date: 2-May-2025
Web References: https://www.pnas.org/doi/10.1073/pnas.2420314122
References: Proceedings of the National Academy of Sciences, DOI: 10.1073/pnas.2420314122
Image Credits: HKUST
Keywords: Earth sciences
