This study proposes two novel star-shaped chiral metamaterial structures, SCM-I and SCM-II, designed for breaking the low-frequency limit and achieving broadband vibration attenuation. SCM-I combines chiral topology with a star-shaped configuration to significantly lower the first band gap frequency (starting at 171.31 Hz), while SCM-II incorporates tooth-shaped ligaments to maximize bandwidth (achieving a coverage ratio of 91.6%). Band structures are calculated using the finite element method, and frequency response analyses verify the attenuation performance. The band gap mechanisms are clarified through vibration mode analysis at band edges. Furthermore, directional wave propagation is systematically investigated via dispersion surfaces, iso-frequency contours, and group/phase velocity maps. Finally, the geometric tunability of the band gaps is demonstrated by analyzing the effects of key geometric parameters. Both SCM-I and SCM-II exhibit excellent wave suppression capabilities, offering new insights for the design of tunable, ultra-low frequency acoustic metamaterials.

Convective thermal cloaks, capable of simultaneously manipulating fluid flow and heat transfer, represent a cutting-edge direction in multi-physics metamaterial research. However, existing studies have been predominantly confined to regular geometric configurations, limiting their applicability in complex engineering environments. To address this, we propose multiphysical coordinate transformation theories for convective thermal cloaks adaptable to arbitrarily-shaped obstacles, facilitating the free manipulation of coupled thermo-hydrodynamic fields. First, based on transformation heat-transfer theory, we derive the analytical transformed dynamic viscosity and thermal conductivity by coupling the parametric equations of the obstacle and cloak geometries. Second, to resolve the physical constraint of negative viscosity components inherent to complex geometric transformations, we introduce an equivalent design scheme based on transformed volumetric forces. This approach effectively converts anisotropic viscosity effects into spatially distributed volumetric forces, thereby circumventing the realizability issues caused by negative viscosity. Numerical simulations demonstrate that our arbitrarily-shaped cloaks effectively manipulate mass, momentum, and energy transport in both uniform and non-uniform thermal convection systems. The designs maintain undisturbed velocity, pressure, and temperature fields external to the cloak, achieving simultaneous hydrodynamic and thermal cloaking. Comparative analysis reveals that the transformed volumetric force approach yields robust cloaking performance comparable to the transformed viscosity approach while offering superior material realizability. This work overcomes the geometric and physical limitations of conventional transformation methods, establishing a foundation for fabricating multi-physics metamaterials with complex geometries.

Hydrodynamic metamaterials provide a transformation-based route for manipulating low-Reynolds-number flows, but many existing designs rely on spatially inhomogeneous and anisotropic material parameters that are difficult to realize and integrate in practical fluidic systems. Here, we propose a body-force-based design strategy for hydrodynamic rot-amplifiers. By mapping coordinate transformations to an equivalent body-force distribution, the proposed method reproduces target transformed flow fields in a homogeneous background fluid without physically constructing complex anisotropic viscosity tensors. Numerical simulations show that the designed rot-amplifiers can simultaneously redirect the central flow direction and enhance the central velocity, leading to Venturi amplification while keeping the external background flow unperturbed. We further reveal that the transformation sequence controls the coupling between rotation and amplification: amplification followed by rotation induces Venturi amplification attenuation and rotational hysteresis, whereas rotation followed by amplification separates the dominant functional regions, eliminating the coupled attenuation and maintaining both target rotation and velocity amplification. The different responses under the two transformation sequences demonstrate transformation-order-induced nonreciprocity and a magnetism-analogous rotational hysteresis response associated with body-force redistribution, pressure-gradient lag, and viscous dissipative driving. Under inhomogeneous incoming flow, body force manipulation locks the central average flow direction to the prescribed direction in the fixed Cartesian frame, with angular deviations below 0.3° for the tested preset angles, whereas viscosity manipulation is passively deflected by the background inflow and shows deviations of approximately 23°. These results establish body-force manipulation and transformation-sequence control as design principles for active multifunctional hydrodynamic metamaterials with Venturi amplification, nonreciprocity, rotational hysteresis, and direction-locking capability.

This study presents three star-shaped chiral structures (SSSR, SDSR, SQSR) with integrated spiral resonators at their ligaments, categorized by resonator count (single, double, quadruple). All configurations generate multiple omnidirectional bandgaps below 1000 Hz. Incorporating a central lead disk enhances bandgap coverage for SSSR (86.13

Two-phase slug flow can cause serious damage to the piping system due to its violent dynamic behavior. Isolated slugs traveling in a void line and impacting on a bend have been studied based on one-dimensional models, which cannot describe reliably the local flow behavior at the bend. In this paper, a two-dimensional model is proposed to better investigate this problem. The Navier-Stokes equations are solved together with a two-equation turbulence model. Moreover, the two-phase volume-of-fluid (VOF) model is employed to capture the moving water-air interfaces. Numerical results are compared with experimental data in the literature and solutions of previous models. To gain more insight, a parameter variation study is carried out. The effects of several factors on the peak pressure and duration of the impact are systematically studied. It is found that the driving air pressure has almost no effect on the peak pressure but it shortens the impact duration. The slug length does not affect the peak pressure, but the impact duration increases with the slug length. With the increasing of the slug density, both the peak pressure and the impact duration increase. With the increasing of the slug velocity, the peak pressure largely increases and the impact duration decreases. Finally, using dimensional analysis, empirical models for impact peak pressure and impact impulse are proposed for practical applications.

Hydrodynamic cloaking offers a transformative approach to drag reduction by manipulating flow without disturbing the surrounding field. However, existing designs for laminar flows require either complex metamaterials with anisotropic properties or multilayer force distributions that are experimentally impractical. This study presents a novel single-layer hydrodynamic cloak for incompressible laminar flows at Re = 100, achieved through a synergistic combination of uniform volume forces and sliding wall boundaries. We employ a machine learning-driven optimization framework using Interior Point Optimizer algorithm to determine optimal control parameters that minimize flow disturbances at the cloak boundary. The objective function, defined as the mean squared error of velocity deviations at monitoring points, quantifies cloaking performance. Comparative simulations demonstrate the superior performance of synergistic control: drag reduction efficiency reaches 99.4%, compared to 89.9% for sliding wall-only and 40.7% for volume force-only control. Flow field analysis confirms the complete elimination of vortex shedding and flow wakes, with all disturbances confined within the cloaking region while maintaining an undisturbed background flow. Additionally, lift fluctuations are entirely suppressed, effectively preventing vortex-induced vibrations. This work establishes the theoretical necessity of dual-mechanism control for achieving zero drag in viscous environments and provides a feasible pathway toward experimental validation, with potential applications in transportation, aerospace, and marine engineering.

Metamaterials provide exceptional control over physical phenomena, enabling many disruptive technologies. However, researches in hydrodynamic meta-devices have mainly used intrusive methods to manipulate material structures, limited by material properties and specific environmental conditions. Each design serves a single function, reducing versatility. This study introduces a meta-hydrodynamics theory using applied force fields to avoid physical contact with the fluid and eliminate the need for inhomogeneous and anisotropic metamaterials, allowing continuous switching between cloaking, shielding, and Venturi amplification. The force field operates independently of the fluid's physical properties, making it adaptable to various fluids and environmental conditions. We derive volumetric force distributions for hydrodynamic devices based on fluid properties and forces equivalence, using the integral median theorem to homogenize these forces for practical applications. The effectiveness of the proposed hydrodynamic devices is validated through numerical simulations and quantitative analyses. By utilizing the electromagnetic forces produced by the interaction between a conducting fluid and an electromagnetic field, we experimentally verified the validity of our theoretical simulations. Our research offers different insights into hydrodynamic meta-devices design, enhancing practical applications and opening avenues for innovative flow manipulation.

A spinel-type Zn0.8Mg0.2(Al1-xGax)(2)O-4 (0 <= x <= 0.5) translucent ceramic was prepared by the hot pressing sintering process. The effect of Ga3+ ions on microstructure, densification, optical, mechanical, and dielectric performance was investigated. The appropriate incorporation of Ga3+ ions reduced the sintering temperature and promoted densification. The translucent ceramic Zn0.8Mg0.2(Al0.8Ga0.2)(2)O-4 with a relative density of 99.6 % exhibited a wide transmission range and excellent mechanical properties. The transmission curve covered a range of 0.23-8.0 mu m. The ceramic Zn0.8Mg0.2(Al0.5Ga0.5)(2)O-4 had a better transmittance, approximately 64.5 % at 2 mu m, and above 55 % in the range of 0.7-6.3 mu m. Its hardness was about 12.01 +/- 0.46 GPa, which is slightly lower than that of MgAl2O4, but higher than that of MgGa2O4, ZnAl2O4, and ZnGa2O4. In addition, the dielectric constant increased with the increase of Ga3+ content and dielectric constant of Zn0.8Mg0.2(Al0.8Ga0.2)(2)O-4 was about 14.08.

The paper designed two novel tooth-shaped metamaterials based on the tooth-shaped characteristics, including the first order tooth-shaped metamaterial (FOTM) and the second order tooth-shaped metamaterial (SOTM). The SOTM produces an ultra-low band gaps (102.6 Hz) compare of the value of the FOTM (184.5 Hz). Among the first 24 order dispersion curves, the band gap coverages of the FOTM and SOTM can reach 68.5% and 74.1%. Even band gap coverages below 500 Hz still reach 34.1% and 44.8%. While the FOTM owns the maximum bandwidths (688.4 Hz). Next, the band gap generation mechanism of tooth-shaped metamaterials is analyzed according vibration modes. The rotational vibrations in its central part and tooth-shaped ligament parts dissipate the elastic wave energy and generate the band gap by analyzing the iso-frequency contour, group velocity and phase velocity. Finally, the influence of the core tooth-shaped ligaments width and length on the band structure of the FOTM and SOTM are studied. For the FOTM and SOTM, increasing the core tooth-shaped ligament height results in a decrease of the band gap. The design exhibits excellent band gap properties and meets the requirements for lightweight design, and it provides a novel solution for multi-low-frequency wide band.

Hydrodynamic cloaks, a type of metamaterials possessing zero-drag properties, show fascinating potential for aerospace, marine engineering, and high-speed transportation. However, achieving zero drag with hydrodynamic cloaks in viscous flows is challenged by the complexity of the Navier–Stokes equations. This study designs spherical hydrodynamic cloaks based on machine learning, which allow objects to move in a viscous fluid without disturbing the flow fields. These cloaks merely require the supply of uniform external forces, unaided by metamaterials, allowing objects wrapped in the cloak to move unimpeded through viscous flow fields. Numerical simulations show that these cloaks provide significant drag reduction efficiency (up to 96.26%) and enhance flow stability by eliminating lift fluctuations. These findings provide new insights into flow control and expand the applicability of hydrodynamic metamaterials to high Reynolds number environments, with promising applications in multiphysics fields such as thermal-hydrodynamic coupling and acoustic-hydrodynamic coupling.

Thermal metamaterials, which are materials with freely regulated thermal flow behaviors, have shown great potential in controlling thermal fields and have received widespread attention. However, traditional thermal metamaterials mainly focus on passive regulation of thermal conductivity or active regulation of heat source alone, neglecting the connection between these two control approaches. Herein, an active coordinate transformation theory is proposed, which can establish a bridge between active and passive manipulation, namely, transforming the manipulation of thermal conductivity into the manipulation of the heat source. This approach can achieve results comparable to those obtained by controlling thermal conductivity to manipulate the thermal field. The feasibility and effectiveness of this control theory can be verified by numerical simulation of the steady state and transient conditions of the thermal cloak. Unlike the anisotropic characteristics of the cloak with transformed thermal conductivity, the proposed cloak does not suffer the anisotropy problem, which reduces the design difficulty of the cloak. Finally, this theory is expected to extend to three dimensions and other fields such as the fluid dynamics, acoustics, and electromagnetics. It broadens the design prospects of thermal metamaterials and opens up novel ideas for the design of thermal metamaterials.

Although significant efforts have been devoted to advancing hydrodynamic cloaks for a single object, limited exploration has focused on cloaking multiple objects. By cloak, we mean a state of hydrodynamic invisibility achieved by eliminating flow disturbances caused by intrusive objects in the surrounding fluids. These gaps in understanding present challenges in developing effective strategies for achieving hydrodynamic stealth for multiple objects in collaborative operations. To address these issues, we propose a multi-object hydrodynamic cloak with isotropic and homogeneous fluid viscosity in viscous potential flows through a combination of neutral inclusion theory and convection-diffusion-balance method. By effectively transforming the intrusive objects into one single object while maintaining the overall invasive volume unchanged—a critical factor in flow disturbances—we successfully derive the analytical solution of fluid viscosity for multi-object hydrodynamic cloaks. Numerical simulations demonstrate the proposed cloaks considerably minimize the hydrodynamic perturbations generated by objects in groups with symmetric or asymmetric distributions, various sizes, and even arbitrary shapes. In addition, we reveal that the antagonism between the defined boundary effect of flow disturbances and vorticity magnitudes primarily determines the effectiveness of the proposed cloaks, laying the foundation for the future development of multi-object hydrodynamic cloaks involving interactions among objects. Hopefully, this research will advance the fields of hydrodynamic metamaterials for multiple objects in collaborative settings and contribute to the broader understanding of complexity science.

Flow control technologies play a crucial role in modern engineering and scientific research. Hydrodynamic metamaterials, as an emerging branch in the field of flow control, have attracted extensive research due to their remarkable potential in flow control, thus leading to the development of hydrodynamic metadevices. Here, we propose a meta-hydrodynamics theory for the active manipulation of fluid flows, which establishes an equivalence relation between volumetric forces and spaces and, consequently, allows for the design of active hydrodynamic metadevices. This equivalence relation can be utilized to accurately tailor the flow fields as long as the manipulation effects of the hydrodynamic metadevices on the flow fields are predetermined. By constructing a mapping relation of coordinate transformation from virtual space to physical space, we can determine the required volumetric force distributions to realize these hydrodynamic metadevices. We exemplify this theory with three different applications: hydrodynamic cloaks, concentrators, and rotators, for which we calculate the corresponding volumetric force distributions. Subsequent numerical simulations reveal the excellent manipulation performances of these hydrodynamic metadevices in both uniform and non-uniform flow fields. Finally, our research is expected to pioneer new perspectives in the development of hydrodynamic metadevices and methodologies for flow control under nonlinear flows with high Reynolds numbers.

Although significant efforts have been directed toward refining active control methods for porous media flows, limited explorations have been devoted to the effects of heterogeneous permeability on fluid flow in such environments. These gaps in understanding pose a challenge in developing effective strategies for regulating flow states in porous media with varying permeability. To address these issues, we propose a hydrodynamic dipole-driven theory, solely leveraging a pair of hydrodynamic point source and sink, to rectify flow in heterogeneous porous media systems, thus enabling precise manipulation of the flow field. By carefully tuning the moment of the hydrodynamic dipole, we demonstrate the complete elimination of flow disturbances arising from permeability heterogeneity, and this restoration of the original uniform flow state effectively homogenizes overall permeability. Furthermore, our theory transcends limitations associated with electroosmotic and magnetic methods that require fluids respond to such physical fields, offering broader applicability and minimizing potential contamination risks. Finally, the inherent relation between potential function and pressure distributions in Dracy's law is established with rigorous theoretical analysis, which lays the foundation for active hydrodynamic metamaterials assisted with hydrodynamic dipole strategy. We anticipate that our findings will significantly advance the field of active flow control, particularly in addressing heterogeneous permeability in complex porous media flows, and provide valuable insights for the development of hydrodynamic metamaterial without reliance on heterogeneous or anisotropic materials.

The possibility of freely manipulating flow in accordance with humans will remain indispensable for breakthroughs in fields such as microfluidics, nanoengineering, and biomedicines, as well as for realizing zero-drag hydrodynamics, which is essential for alleviating the global energy crisis. However, persistent challenges arise from the D’Alembert paradox and the unresolved Navier-Stokes solutions, known as the Millennium Problem. These obstacles also complicate the development of hydrodynamic zero-drag cloaks across diverse Reynolds numbers. Our research introduces a paradigm for such cloaks, relying exclusively on isotropic and homogeneous viscosity. Through experimental and numerical validations, our cloaks exhibit zero-drag properties, effectively resolving the D’Alembert paradox in viscous potential flows. Moreover, they possess the capability to activate or deactivate hydrodynamic concealment at will. Our analysis emphasizes the critical role of vorticity manipulation in realizing cloaking effects and drag-reduction technology. Therefore, controlling vorticity emerges as a pivotal aspect for future active hydrodynamic zero-drag cloak designs. In conclusion, our study challenges the prevailing belief in the impossibility of zero drag, offering valuable insights into invisibility characteristics in fluid mechanics with implications for microfluidics, biofluidics demanding the drug release or biomolecules transportation accurately and timely, and hypervelocity technologies.

In order to reduce vibration and noise with wide frequency, a new extended arrow tetragonal lattice topology is proposed. The band gap characteristics are discussed by combining the finite element method and Bloch's theorem. The generation principle of band gap is explained by vibration mode analysis. By topological optimization of the structure, band gap has obvious optimization effect. The propagation characteristics of elastic waves with a specific frequency in the structure are studied from the point of view of energy. Finally, the band gap frequency range is compared with the transmission function, and the stress cloud diagram is analyzed. The research shows that the structure has good band gaps and can play a good role in vibration and noise reduction. Through the topological design of the structure, the band gap frequency range of the structure is optimized, which provides a new design idea for wide frequency vibration attenuation.

Although thermal metamaterials have garnered considerable attention, the majority of investigations thus far have primarily focused on either steady heat conduction phenomena or steady heat convection systems. However, transient thermally convective flows are prevalent in practical applications. In this study, we employ transformation theory to analytically design convective thermal rot-amplifiers under nonporous-media creeping flows within thermal systems. Through simultaneous manipulation of the effective dynamic viscosity and effective thermal conductivity, we achieve concurrent rotation and amplification of both the dynamic temperature and velocity fields in creeping thermally convective flows. Additionally, convective thermal hysteresis is obtained through dedicated coordinate transformation design, introducing novel thermal regulation mechanisms. Furthermore, the proposed convective thermal rot-amplifiers achieve both hydro-hidden Venturi effect and thermo-hidden Venturi effect, resulting in significantly increased energy harvest efficiencies. We anticipate that the proposed convective thermal rot-amplifiers can be utilized in engineering to vary the orientations of amplified heat fluxes and fluid flows without disturbance, while also shedding light on the hysteresis and nonreciprocity concepts of other meta-devices, and contributing to alleviate the global energy crisis.

The suppression of low-frequency vibration and noise has been the research focus of acoustic metamaterials. Based on the local resonance effect of the subwavelength structure, two new topology optimization methods are proposed in this paper, and two new three-dimensional single-phase material structures are obtained. Based on Bloch theorem and lattice theory, finite element simulations of the single cells with different structures are carried out to analyze and explore the bandgap properties and opening mechanism of the structures. The frequency response spectra are obtained by vibrational transport simulation of the finite-period structures. The results show that both novel metamaterial structures have good bandgap properties, the widest first bandgap width within 2000 Hz reaches 809 Hz, and the total bandgap width percentage reaches 52.7%, and the main vibration forms of opening the bandgap are rotational and offset resonance of the internal structure and torsional resonance of part of the structure.

Static and dynamic metamaterials have been extensively studied for their ability to manipulate different physical fields and directed to broad applications. Because the governing equations of heat transfer consist of nonlinear terms with conservation of mass, momentum and energy, the equations can exhibit elliptical, parabolic, hyperbolic and hybrid configurations under different transfer modes. Such multi-mode transfer characteristics intrinsically make thermal metamaterials distinguish themselves from other metamaterials with unique static and dynamic manipulation mechanisms. Therefore, numerous studies have emerged that use the transformation theory and other methods to control static thermal metamaterials. It leads to the development of thermal cloaks, thermal concentrators, thermal diodes, and so on. Originating from the static style, the manipulation of heat transfer has expanded to dynamic systems in recent years. The introduction of hydrodynamics in metamaterial design leads to numerous novel physics effects, such as dynamic cloaking, zero-drag characteristics, topological heat transfer, nonreciprocal diffusion, and non-Hermitian physics. Moreover, the dynamic thermal metamaterials allow accurate control at both time and space dimensions, leading to exciting applications such as adjustable, reconfigurable, and intelligent thermal meta-devices. However, few studies have systematically analyzed thermal metamaterials from the perspective of static and dynamic manipulation. In this review, we aim at clarifying the connection and distinction of static and dynamic manipulation from the scopes of principle, application, and physical effects. We start with the development of static thermal metamaterials and its application. Subsequently, the development of dynamic thermal metamaterials is presented both in fundamental theory and application. Finally, we summarize the research directions and prospect future research challenges for static and dynamic thermal metamaterials.