Multilayer graphene is an exceptional anisotropic material due to its layered structure composed of two-dimensional carbon lattices. Although the intrinsic mechanical properties of graphene have been ...investigated at quasi-static conditions, its behavior under extreme dynamic conditions has not yet been studied. We report the high–strain-rate behavior of multilayer graphene over a range of thicknesses from 10 to 100 nanometers by using miniaturized ballistic tests. Tensile stretching of the membrane into a cone shape is followed by initiation of radial cracks that approximately follow crystallographic directions and extend outward well beyond the impact area. The specific penetration energy for multilayer graphene is ∼10 times more than literature values for macroscopic steel sheets at 600 meters per second.
We present a weakly compressible, thermodynamically consistent, hydrodynamical model for the binary fluid flow in porous media using the one-fluid multiple component formulation, consisting of a ...force balance equation with a weak inertia, weakly perturbed continuity equation, and a volume-preserving, nonlocal Allen–Cahn equation for the phase field variable. This model is called the nonlocal Allen–Cahn-Extended-Darcy (NACED) model. In the incompressible and/or the inertialess limit, it reduces to two limiting models that we focus on in this study: the incompressible, nonlocal Allen–Cahn-Extended-Darcy (NACED) model and nonlocal Allen–Cahn–Darcy (NACD) model, respectively. The weakly compressible model provides a pathway for us to develop thermodynamically consistent numerical algorithms for the incompressible models. Guided by the energy variational formulation of the models, we use the energy quadratization method in time and finite difference method in space on staggered grids to derive second-order, linear, coupled and decoupled, energy dissipation rate preserving schemes for the incompressible models. The decoupled schemes for NACED model are obtained by exploiting the intrinsic relation between the incompressible and weakly compressible model. We then prove that the linear systems resulted from the linear schemes are uniquely solvable. Mesh refinement tests are conducted to confirm the convergence rates and benchmark examples of binary fluid flow motion in porous media with and without gravity are presented to showcase the schemes’ accuracy and usefulness.
•A hierarchy of nonlocal Allen–Cahn and hydrodynamic coupled models for fluid flows in porous media.•Theory-guided thermodynamically consistent approximations for developing numerical schemes.•Second order, linear, energy-dissipation-rate preserving schemes for the NACED and NACD model.•Fully decoupled, unconditionally energy stable numerical schemes and implementations.•Numerical experiments and benchmark examples.
In this study, experiments were performed to investigate the relative energy losses in two models of simple triangular and toothed overflow made of fiberglass in four different landings at three ...depths of 100%, 90%, and 80%. The effective variables in this study were the landing number and the bottom depth at the end of the hydraulic jump. The results of this study showed that at three downstream depths, energy losses decrease with increasing landing number. Also, energy losses in the free projectile mode are higher than in the other two modes due to the full development of the hydraulic jump. In the general comparison mode, the performance of a toothed triangular overflow is better in energy dissipation than in the toothed mode, due to the fracture and compression of the flow lines in contact with the teeth at the end of the overflow projectile. In general, the use of teeth at the end of the overflow projectile causes energy loss in the conditions of 100% of the bottom depth in the toothed triangular overflow compared to the simple triangular overflow by an average of 7%, and in the conditions of 90% and 80% of the bottom depth by about 8% and 10%, respectively.
•Dependence of energy dissipation of turtle carapace on loading rate is revealed.•The role of wavy interface on protection of turtle carapace is unveiled.•The relative contribution of energy ...dissipations at small scale is identified.
The turtle carapace is a biological armor possessing superior damage tolerance. In spite of efforts to characterize the mechanical properties of such biological armor, the protection mechanisms associated with the multilayered structure of turtle carapace are largely unknown. In this study, we carry out the calculations of energy dissipation in dynamic fracture of the turtle carapace. The plastic deformation of keratin-collagen bi-layer, keratin-collagen interfacial debonding, collagen-bone interfacial debonding and crack growth in the boney layer are accounted for in the analyses. It is found that the interfacial debonding and plastic deformation of the keratin-collagen bi-layer contribute equally to toughening of the carapace at low impact velocity, while plastic energy dissipation dominates in the case of high impact velocity. As the impact velocity is increased, energy dissipation in the turtle carapace decreases at first and then increases. We reveal that the low energy dissipation of carapace at intermediate level of impact velocity is attributed to small plastic zones in the keratin-collagen bi-layer. Furthermore, we have identified the role of the waviness of the keratin-collagen and collagen-bone interfaces. The presence of wavy interfaces enhances plastic energy dissipation of the keratin-collagen bi-layer and promotes interfacial debonding, thereby suppressing crack propagation in the boney layer. The findings provide mechanistic explanations for incorporation of wavy interfaces in the multilayered structure of turtle carapace.
Observations reveal massive amounts of O vi around star-forming L* galaxies, with covering fractions of near unity extending to the host halo's virial radius. This O vi absorption is typically ...kinematically centered upon photoionized gas, with line widths that are suprathermal and kinematically offset from the galaxy. We discuss various scenarios and whether they could result in the observed phenomenology (cooling gas flows, boundary layers, shocks, virialized gas). If collisionally ionized, as we argue is most probable, the O vi observations require that the circumgalactic medium (CGM) of L* galaxies holds nearly all of the associated baryons within a virial radius ( ) and hosts massive flows of cooling gas with , which must be largely prevented from accreting onto the host galaxy. Cooling and feedback energetics considerations require cm−3 K for the warm and hot halo gases. We argue that virialized gas, boundary layers, hot winds, and shocks are unlikely to directly account for the bulk of the O vi. Furthermore, we show that there is a robust constraint on the number density of many of the photoionized absorption systems that yields upper bounds in the range cm−3, suggesting that the dominant pressure in some photoionized clouds is nonthermal. This constraint is in accordance with the low densities inferred from more complex photoionization modeling. The large amount of cooling gas that is inferred could re-form these clouds in a fraction of the halo dynamical time, and it requires much of the feedback energy available from supernovae to be dissipated in the CGM.
Liquid storage tanks are widely used in the industry and can contain not only harmless substances but also various ones that can be explosive and toxic or pollutant, thus implying that both the ...structure and the content must remain safe and operational under different types of loading. The same applies to any tank-connected plant system/item. Yet, past earthquakes repeatedly demonstrated that even if structural damage is prevented in the shell, severe occurrences may still be observed due to sloshing phenomena, which drive the tank-fluid system response with high impacts in case of accidental release of chemicals. Therefore, this paper studies an energy dissipation system consisting of floating roof and external dampers that are utilized to control liquid vibration by augmenting the level of damping. In order to evaluate its effectiveness at the design-level earthquakes, a series of explicit nonlinear dynamic analyses have been performed, and comparisons are provided between floating roofed steel cylindrical tanks equipped with supplemental devices and counterparts without them. Changes in seismic performance because of geometrical variations in the tank (i.e. aspect ratio) and seismic input (i.e. far and near field earthquakes) have been quantified by means of experimentally validated numerical models that account for material and geometrical nonlinearities, as well as for fluid-structure interaction in an explicit manner. Shake-table tests available in the literature have been simulated, and the proposed modelling criteria show a good fit with experimental data on two tank specimens. Analysis data sets involving three tank geometries reveal that even if the dissipation system targets mainly large-capacity tanks, it can be effectively used to enhance the performance of any system, reducing the sloshing wave height which can be excessive especially when the tank is subjected to severe near field ground motions.
•Dynamic response of liquid storage tanks with floating roof is examined numerically.•Tanks with floating roof are analysed with and without dampers used to control liquid vibration.•Experimentally validated numerical models are developed to simulate different tank geometries.•Nonlinear sloshing of the fluid is reproduced by the Arbitrary Lagrangian-Eulerian formulation.•Sloshing wave height peaks can be effectively reduced, thus mitigating damage and related issues.
Abstract
Based on high-resolution turbulence microstructure and near-surface velocity data, frontal instability and its relation to turbulence are investigated inside a transient upwelling filament ...in the Benguela upwelling system (southeast Atlantic). The focus of our study is a sharp submesoscale front located at the edge of the filament, characterized by persistent downfront winds, a strong frontal jet, and vigorous turbulence. Our analysis reveals three distinct frontal stability regimes. (i) On the light side of the front, a 30–40-m-deep turbulent surface layer with low potential vorticity (PV) was identified. This low-PV region exhibited a well-defined two-layer structure with a convective (Ekman-forced) upper layer and a stably stratified lower layer, where turbulence was driven by forced symmetric instability (FSI). Dissipation rates in this region scaled with the Ekman buoyancy flux, in excellent quantitative agreement with recent numerical simulations of FSI. (ii) Inside the cyclonic flank of the frontal jet, near the maximum of the cross-front density gradient, the cyclonic vorticity was sufficiently strong to suppress FSI. Turbulence in this region was driven by marginal shear instability. (iii) Inside the anticyclonic flank of the frontal jet, conditions for mixed inertial/symmetric instability were satisfied. Our data provide direct evidence for the relevance of FSI, inertial instability, and marginal shear instability for overall kinetic energy dissipation in submesoscale fronts and filaments.
Energy dissipation is of fundamental interest and crucial importance in quantum systems. However, whether energy dissipation can emerge without backscattering inside topological systems remains a ...question. As a hallmark, we propose a microscopic picture that illustrates energy dissipation in the quantum Hall (QH) plateau regime of graphene. Despite the quantization of Hall, longitudinal, and two-probe resistances (dubbed as the quantum limit), we find that the energy dissipation emerges in the form of Joule heat. It is demonstrated that the non-equilibrium energy distribution of carriers plays much more essential roles than the resistance on energy dissipation. Eventually, we suggest probing the phenomenon by measuring local temperature increases in experiments and reconsidering the dissipation typically ignored in realistic topological circuits.
Recent progress on highly tough and stretchable polymer networks has highlighted the potential of wearable electronic devices and structural biomaterials such as cartilage. For some given ...applications, a combination of desirable mechanical properties including stiffness, strength, toughness, damping, fatigue resistance, and self‐healing ability is required. However, integrating such a rigorous set of requirements imposes substantial complexity and difficulty in the design and fabrication of these polymer networks, and has rarely been realized. Here, we describe the construction of supramolecular polymer networks through an in situ copolymerization of acrylamide and functional monomers, which are dynamically complexed with the host molecule cucurbit8uril (CB8). High molecular weight, thus sufficient chain entanglement, combined with a small‐amount dynamic CB8‐mediated non‐covalent crosslinking (2.5 mol%), yields extremely stretchable and tough supramolecular polymer networks, exhibiting remarkable self‐healing capability at room temperature. These supramolecular polymer networks can be stretched more than 100× their original length and are able to lift objects 2000× their weight. The reversible association/dissociation of the host–guest complexes bestows the networks with remarkable energy dissipation capability, but also facile complete self‐healing at room temperature. In addition to their outstanding mechanical properties, the networks are ionically conductive and transparent. The CB8‐based supramolecular networks are synthetically accessible in large scale and exhibit outstanding mechanical properties. They could readily lead to the promising use as wearable and self‐healable electronic devices, sensors and structural biomaterials.
Cucurbitnuril‐based supramolecular polymer networks are readily obtained through the in situ polymerization of guest‐functionalized monomers, upon completion with cucurbit8uril as supramolecular crosslinkers. The presence of CB8 host–guest complexes imparts the network with remarkable mechanical performances, including extreme stretchability, high toughness, energy dissipation, and fast room‐temperature self‐healing.
Robots that can move, feel, and respond like organisms will bring revolutionary impact to today's technologies. Soft robots with organism‐like adaptive bodies have shown great potential in vast ...robot–human and robot–environment applications. Developing skin‐like sensory devices allows them to naturally sense and interact with environment. Also, it would be better if the capabilities to feel can be active, like real skin. However, challenges in the complicated structures, incompatible moduli, poor stretchability and sensitivity, large driving voltage, and power dissipation hinder applicability of conventional technologies. Here, various actively perceivable and responsive soft robots are enabled by self‐powered active triboelectric robotic skins (tribo‐skins) that simultaneously possess excellent stretchability and excellent sensitivity in the low‐pressure regime. The tribo‐skins can actively sense proximity, contact, and pressure to external stimuli via self‐generating electricity. The driving energy comes from a natural triboelectrification effect involving the cooperation of contact electrification and electrostatic induction. The perfect integration of the tribo‐skins and soft actuators enables soft robots to perform various actively sensing and interactive tasks including actively perceiving their muscle motions, working states, textile's dampness, and even subtle human physiological signals. Moreover, the self‐generating signals can drive optoelectronic devices for visual communication and be processed for diverse sophisticated uses.
Actively perceiving and responsive soft robots that can use the triboelectric effect and self‐generating electricity to sense and respond to stimuli are demonstrated. They are enabled by self‐powered and highly stretchable triboelectric proximity‐ and pressure‐sensing skins. After homogeneous integration, these soft robots can actively perceive their body‐motions, working states, environment stimuli, baby diaper conditions, and even human pulses by self‐generating electricity.
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