Abstract Underwater implosion of submerged structures has been studied for more than a century, yet recent high-profile failures have renewed awareness of the remaining risk in modern undersea systems. As pipelines, AUVs, and deep-sea submersibles operate at greater depths and under cyclic loading, exceeding a structure's critical external pressure can trigger a two-stage implosion process: rapid inward wall collapse, followed by abrupt wall arrest that emits damaging pressure pulses. Several notable implosion disasters in the last two decades have prompted increased interest in understanding and preventing catastrophic failure as well as protecting structures and surrounding environments. This review presents the current state-of-the-art of underwater implosion across experimental, numerical, and analytical domains. Emphasis is placed on how shell shape, geometry, and material govern both collapse dynamics and the emitted pressure pulse. Furthermore, UNDEX initiated implosion, sympathetic structures, and partially or fully confined environments are explored. Finally, damage mitigation techniques, including ring stiffeners, foam fillers, and buckle arrestors are discussed. This understanding of a century of work on mechanics, environments, and mitigation strategies provides a framework for treating implosion as a primary design consideration within the undersea engineering ecosystem rather than an unquantified risk.
Abstract This review examines the development of concepts and models describing the spontaneous spatial separation—segregation—of dense flowing granular mixtures. Although particle-scale interactions are largely understood and modern discrete element methods can resolve system dynamics in detail, a central challenge remains: prediction has advanced more rapidly than understanding. Simulation can reveal what happens; it does not, by itself, explain why. We argue that progress requires integrating four complementary approaches: particle-based simulations, continuum descriptions based on continuity, statistical methods extending kinetic theory to dissipative systems, and conceptual models that isolate dominant mechanisms. These are not competing paradigms but distinct lenses on a multi-scale phenomenon. Across them, common mathematical structures recur, including Newtonian dynamics at the particle level and flux--divergence formulations governing transport. A central thesis is that conceptual models remain indispensable. By distilling mechanisms such as kinetic sieving, squeeze expulsion, and force balance, they provide explanatory structure that complements both simulation and formal theory. Recent advances applying particle-level force models of segregation illustrate the value of combining these perspectives. At the same time, each framework encounters limitations. The central challenge is therefore to identify organizing principles that connect mechanisms across scales. Granular segregation serves as a testbed for a broader question: how understanding emerges in systems where the microscopic governing laws are known, yet collective behavior remains difficult to explain.
Abstract The prevalence of gastric diseases is rising worldwide, especially among young adults. Many conditions of the stomach seem to be closely related to its mechanical properties, geometry, and underlying microstructure. Due to the complex coupling between these aspects, effective diagnosis and treatment are often difficult. Predictive material models of the stomach (wall) and simulations based on these could significantly contribute to the overall disease understanding, treatment choice, and surgical planning. However, the development of such material models requires experimental data on the mechanical behavior and structure. For this purpose, this review discusses current experimental approaches for the characterization of the stomach. First, all relevant anatomical, physiological, and mechanical aspects are summarized. Based on its complex organ geometry and regionally varying wall architecture, all experimental studies are grouped in terms of sample scale, differentiating between organ- and tissue-level. Further, the review comprises both mechanical and structural investigations for each sample scale. In particular, each experimental approach is evaluated in terms of working principles and applicability to gastric tissue. Key findings from different studies derived from the same technique are compared and discussed in context with the gastric physiology. Finally, current research gaps are identified, and future directions of gastric research are envisioned with the aim of fully characterizing the mechanical behavior and hierarchical structure of this vital organ. This review offers practical guidance for researchers in defining future experimental designs and a concise summary of existing datasets for constitutive modeling of the stomach
The interaction between wake vortices from an upstream body and a downstream boundary layer is significant for both fundamental and practical aspects of fluid mechanics. An in-depth understanding of the underlying flow physics is crucial for numerous problems in aeronautics, architectonics, and energy related to the complex interferences between different bodies or apparatuses. The incoming wake vortices can generally be divided into streamwise, vertical, and spanwise vortices based on their axial directions relative to the coordinate system of downstream boundary layer. They interact with the downstream boundary layer in different ways. However, the spanwise wake vortex has more profound effects on the downstream boundary layer than the other two, because it simultaneously disturbs the whole span region of boundary layer. Therefore, the vortex dynamics of interaction between spanwise wake vortices and a downstream boundary layer is focused on in this review. The efforts of unveiling the flow physics related to this kind of interaction with different canonical configurations are reviewed as the geometrical complexity increases. The wake-triggered spanwise secondary vortices and the laminar-to-turbulent transition routine caused by their destabilization are highlighted in particular. The transition process characterized by the evolution of secondary vortices is distinct from that of a natural transition or a bypass transition induced by freestream turbulence and is commonly encountered in flows around complex geometries. Finally, areas that deserve more attention in future work are outlined and discussed.
The peripheral tissues consist of skin and subcutaneous tissue. Their multilayered biomechanical properties serve as key health indicators and are crucial for clinical applications. Flexible electronics offer a promising approach for continuous in vivo monitoring of peripheral tissue biomechanics. However, these methods depend on complex dispersion analysis or extensive experimental data fitting, which limits their practicality. This study develops an analytical model based on an eccentric rotating mass (ERM) motor for direct and simultaneous measurement of the elastic moduli and thickness of the top skin layer of bilayer tissue. The analytical model used to evaluate tissue compliance involves three dimensionless parameters: the modulus ratio between the top and bottom layers, the normalized thickness of the top skin layer, and one parameter related to ERM. Both simulations and experiments confirm the model's accuracy, showing average errors of only 10% in the inverse characterization of bilayer moduli and thickness for representative bilayer tissue phantoms, paving the way for the development of flexible devices for in vivo tissue health monitoring.
