Dissipation Mechanism Research Articles

Experimental Investigation of Embedment Depth Effects on the Rocking Behavior of Foundations

Shallow foundations supporting high-rise structures are often subjected to extreme lateral loading from wind and seismic activities. Nonlinear soil–foundation system behaviors, such as foundation uplift or bearing capacity mobilization (i.e., rocking behavior), can act as energy dissipation mechanisms, potentially reducing structural demands. However, such merits may be achieved at the expense of large residual deformations and settlements, which are influenced by various factors. One key factor which is highly influential on soil deformation mechanisms during rocking is the foundation embedment depth. This aspect of rocking foundations is investigated in this study under varying subgrade densities and initial vertical factors of safety (FSv), using the PIV technique and appropriate instrumentation. A series of reduced-scale slow cyclic tests were performed using a single-degree-of-freedom (SDOF) structure model. This study first examines the deformation mechanisms of strip foundations with depth-to-width (D/B) ratios of 0, 0.25, and 1, and then explores the effects of embedment depth on the performance of square foundations, evaluating moment capacity, settlement, recentering capability, rotational stiffness, and damping characteristics. The results demonstrate that the predominant deformation mechanism of the soil mass transitions from a wedge mechanism in surface foundations to a scoop mechanism in embedded foundations. Increasing the embedment depth enhances recentering capabilities, reduces damping, decreases settlement, increases rotational stiffness, and improves the moment capacity of the foundations. This comprehensive exploration of foundation performance and soil deformation mechanisms, considering varying embedment depths, FSv values, and soil relative densities, offers insights for optimizing the performance of rocking foundations under lateral loading conditions.

Synthesis and properties of 12442-family superconductor

We report a synthesis of two members of recently discovered high-temperature superconductors of 12442 family, with formula MCa2Fe4As4F2 (M=Rb,K) and transition temperatures of 32.7 and 34.6K, respectively. Quality of the samples was assessed using X-ray powder diffraction, superconducting transitions were identified through transport and magnetic experiments. The temperature dependence of the upper critical field and vortex activation energy was investigated under magnetic fields up to 19T. Two distinct thermally activated flux flow regimes were observed in both systems. Field dependences of activation energy U0(H) indicate a change in the properties of vortex matter in these regimes and distinctly different dissipation mechanisms, reminiscent of cuprate HTSC.

Time-Dependent Nuclear Energy-Density Functional Theory Toolkit for Neutron Star Crust: Dynamics of a Nucleus in a Neutron Superfluid

We present a new numerical tool designed to probe the dense layers of neutron star crusts. It is based on the time-dependent Hartree-Fock-Bogoliubov theory with generalized Skyrme nuclear energy-density functionals of the Brussels-Montreal family. We use it to study the time evolution of a nucleus accelerating through superfluid neutron medium in the inner crust of a neutron star. We extract an effective mass in the low velocity limit. We observe a threshold velocity and specify mechanisms of dissipation: phonon emission, Cooper pairs breaking, and vortex rings creation. These microscopic effects are of key importance for understanding various neutron star phenomena. Moreover, the mechanisms we describe are general and apply also to other fermionic superfluids interacting with obstacles like liquid helium or ultracold gases. Published by the American Physical Society 2024

The Viscosity of Liquids in the Dual Model

In this paper, a reliable model of the viscosity in liquids in the dual model of liquids (DML) framework is developed. The analytical expression arrived at exhibits the correct T–dependence Arrhenius-like exponential decreasing trend, which is typical of Newtonian simple fluids. The model is supported by the successful comparison with both the experimental values of the viscosity of water, and with those related to the mechano-thermal effect in liquids under low-frequency shear, discovered a few years ago, for which the first-ever theoretical interpretation is given by the DML. Moreover, the approach is even supported by the results of numerical models recently developed, that have shown that dual liquid models, such as the DML, provides very good agreement with experimental data. The expression of viscosity contains terms belonging to both the subsystems constituting the liquid, and shows an explicit dependence upon the sound velocity and the collective vibratory degrees of freedom (DoF) excited at a given temperature. At the same time, the terms involved depend upon the Boltzmann and Planck constants. Finally, the physical model is coherent with the Onsager postulate of microscopic time reversibility as well as with time’s arrow for macroscopic dissipative mechanisms.

Numerical assessment of hydrodynamic behavior and energy dissipation during high-head Francis turbine shutdown

This paper examines the instability and energy dissipation of a high-head Francis turbine during shutdown using improved delayed detached eddy simulation, which involves linearly reducing the guide vane opening from 9.84° (best efficiency point) to 0.8° [Spin-No-Load (SNL)]. The results demonstrate a linear increase in water head, with hydraulic efficiency dropping from 93% to 30%. Pressure fluctuations in the vaneless space are mainly due to blade passing frequency and low-frequency components at SNL. High-amplitude pressure fluctuations occur below 37.4% opening in the draft tube, with the dominant frequency under 0.32 times the blade passing frequency. Three vortex structures are identified within the draft tube, a columnar vortex rope in the first stage, multiple helical vortex ropes in the second stage, and discrete vortex structures in the third stage. The most significant axial and radial velocity fluctuations are evident during the second and third stages. Turbulent kinetic energy generation and work done by Reynolds stress are the main sources of power loss. Energy dissipation primarily occurs at the outlet of the runner blades, while it corresponds to the positions of the vortex structures in the draft tube, suggesting that vortex flow structures are the primary mechanism of energy dissipation in the turbine. This study introduces a numerical shutdown model using the dynamic mesh technique, clarifies the relationship between guide vane opening and performance parameters, and identifies the three-stage vortex evolution and energy dissipation mechanisms, offering novel insights into transient instabilities in high-head Francis turbines.

An energy-based criterion for defining slope failure considering the coupling effect of groundwater table and impact loading

Slope instability poses significant risks in tunnel construction, particularly under the influence of impact loading and fluctuations in groundwater table. This study addresses the complexity of energy transformation and distribution in slopes affected by these factors. The research aims to analyze the local dynamic Factor of Safety (FOS) from the perspective of energy-based criterion, considering groundwater table, impact loading, and load position. Key findings indicate that the groundwater table is the most influential factor on slope stability, followed by load position and impact loading. The overall dynamic FOS was observed to peak at 0.35 s and trough appears at 1.0 s during impact loading, stabilizing after 2 s. The evolution of the overall dynamic FOS is explained from the energy dissipation and transformation mechanisms. These insights provide a critical basis for risk assessment and prevention in complex slope scenarios, contributing to sustainable infrastructure development in line with UN SDG 11 (Sustainable Cities and Communities).

Mechanical Failure Characteristics and Energy Dissipation Laws of the Coal–Concrete Combination under Impact Rates

Mechanical Failure Characteristics and Energy Dissipation Laws of the Coal–Concrete Combination under Impact Rates

A 62Hz high-Q 4-spiral mechanical resonator fabricated of a silicon wafer.

High purity silicon is considered as the test mass material for future cryogenic gravitational-wave detectors, in particular Einstein Telescope-low frequency and LIGO Voyager [(LIGO) Laser Interferometer Gravitational-Wave Observatory]. To reduce the thermal noise of the test masses, it is necessary to study the sources of corresponding losses. Mechanical resonators with frequencies 300 Hz-6kHz are successfully used for studying, for example, losses in optical coatings of the test mass. However, the frequency range of the interferometric gravitational-wave detectors starts at 10Hz, and the investigation of different dissipation mechanisms for the test masses in the low-frequency region is relevant. We developed a design of a four-spiral mechanical resonator for studying dissipation and noise in the low frequency range. The resonator was fabricated of a 3-in. silicon wafer using an anisotropic wet etching technique. It consists of four spiral cantilevers on a common base, linked together with additional coupling beams for increasing the frequency difference between the resonator normal modes corresponding to the fundamental flexural off-plane mode of a single spiral cantilever. The measured Q-factor of the 62Hz out-of-phase mode of the four-spiral silicon resonator at room temperature is limited mainly by the thermoelastic loss. At 123K, the measured Q = (1.5 ± 0.3) × 107. The main contribution to the total loss comes from clamping and surface losses.

Multi-scale study on the crack resistance and energy dissipation mechanism of modified rubberized concrete

This study investigates the impact of rubber aggregates with different particle sizes, volume proportions, and pretreatment methods on the crack resistance and energy dissipation properties of rubberized concrete (RuC). The mechanisms of crack resistance and energy consumption are analyzed from macroscopic, mesoscopic, and microscopic perspectives using static and dynamic performance tests, digital image correlation (DIC), and scanning electron microscopy (SEM). These techniques reveal changes in crack patterns, interface transition zones, and pore characteristics. The findings demonstrate that rubber aggregates significantly slow crack propagation and enhance damping energy dissipation, with the volume content of rubber being the most critical factor. The inclusion of rubber aggregates introduces "cavity defects" into the concrete structure, which accounts for RuC's reduced strength compared to standard concrete while highlighting its advantages in vibration reduction and energy absorption. These insights are essential for advancing research on material modifications and microscopic numerical simulations, contributing to reduced carbon emissions.

Full-field investigation of dissipative mechanisms and thermoelastic inversion effects within glass-fiber reinforced polyamides subjected to low-cycle fatigue

A comprehensive thermomechanical investigation has been conducted to study the local kinematic and calorimetric responses of wet glass-fiber reinforced polyamide 6.6 subjected to tensile-tensile low-cycle fatigue tests. Digital image correlation (DIC) and quantitative infrared thermography (QIRT) were combined simultaneously to monitor the onset and development of spatial heterogeneities. Fields of strain, strain rates, intrinsic dissipation and resulting thermoelastic sources were successively observed and thoroughly analyzed with regards to the main fiber orientation and water content. Areas of precocious heterogeneities were detected from the very beginning of the loading, roughly propagating along the main fiber orientation. A ratcheting effect induced by the positive mean stress was observed and accompanied by a slight cyclic creep of the specimens. At high water content, the thermoelastic inversion phenomenon appeared and progressively spread along the gage part of the specimen, highlighting both glassy and rubbery behavior of the samples investigated.

Dragonfly wings-inspired, anti-freezing, ultra-stretchable, and transparent nano-structure sodium alginate-based hydrogel for non-delayed wearable sensing at low-temperatures.

Conductive hydrogels are regarded as an optimal flexible electronic material. Nevertheless, simultaneously achieving excellent mechanical and conductive properties in hydrogels necessitates attention. The high mechanical properties of hydrogels were achieved by employing a strategy that involves constructing a nano-structure network inspired by the highly ordered structure of dragonfly wings. The conductivity and anti-freezing of the hydrogel were enhanced through the construction of a conductive mechanism, achieved by combining ions with nano-particles. The hydrogel exhibits outstanding properties, including anti-freezing, ultra-stretchable (6000%), impressive conductivity (16.2Sm-1), a transparency level of up to 91.2%, and excellent sensitivity in strain sensors. Regulation of the hydrogel matrix's topology and the formation of bionic nano-structures synergistically establish the hydrogel's ultra-stretching and energy dissipation mechanism. The high conductivity of the hydrogel is achieved by constructing a synergistic conduction pathway, which incorporates nano-particles and ions. Under the stretching-induced effect of hydrogel, it facilitates a more efficient path for conduction, thereby enhancing its conductivity and sensing sensitivity under significant strains. Subsequently, this hydrogel was successfully applied to wearable sensor technology, demonstrating surprisingly remarkably prompt non-delayed sensing performance even at low-temperatures. It presents abundant opportunities for expanding the application of hydrogels in flexible electronics.

Study on dynamic mechanical properties and damage characteristics of wollastonite fiber reinforced oil well cement paste

In cement engineering, the cement sheath is not only influenced by elevated temperatures, increased pressure, and the static load confining pressure within the formation but also encounters external impact loads. These loads can rupture the cement paste, compromising the cement sheath’s interlayer sealing capability. Consequently, this can give rise to an annular flow of oil, gas, and water. Hence, this study introduces wollastonite fiber (WF) into the cement slurry to modify the cement paste. The investigation explores the mechanical properties, energy evolution, and damage characteristics of the cement paste with WF under dynamic impact loads. This is achieved by simulating the dynamic impact loads experienced downhole using the separated Hopkinson pressure bar (SHPB) technique. A straightforward SHPB model is constructed using ABAQUS finite element simulation software, and its accuracy is confirmed through experimental validation. The impact test outcomes revealed a notable enhancement in the dynamic load peak strength of the cement paste cured for 14 days. Specifically, there was an increase of 136.75%, 202.10%, and 320.55% compared to the control group at impact speeds of 6 m/s, 8 m/s, and 10 m/s, respectively. The absorption energy increased remarkably, showing 356.03%, 388.61%, and 142.14%, respectively. The simulation findings confirm that the devised simple SHPB model effectively replicates electrical signals aligned with the observed experimental results. The dispersed fibers create a three-dimensional network within the cement paste. This network enhances the impact resistance of the cement paste by leveraging the mechanisms of crack deflection, fiber fracture, and energy dissipation through fiber pull-out.

Rate-dependent FDEM numerical simulation of dynamic tensile fracture and failure behavior in frozen soil

Considering that the dynamic fracture and failure behaviors of frozen soil play a crucial role in the safety and stability of engineering foundations in cold regions, this study aimed to reveal the dynamic tensile mechanical properties and damage failure mechanisms of frozen soil under impact loading. Dynamic Brazilian disk (BD) tests were conducted on frozen soil at different temperatures and loading velocities using a split Hopkinson pressure bar (SHPB) apparatus, followed by numerical simulations using the finite discrete element method (FDEM), focusing on the dynamic tensile deformation characteristics, failure patterns, tensile strength, and energy dissipation mechanisms of the frozen soil. The experimental results indicated that the dynamic tensile mechanical properties of frozen soil were influenced by both temperature and loading velocity. As the temperature decreased and loading velocity increased, the tensile strength of frozen soil significantly increased and showed a linear correlation with the loading velocity. At lower loading velocities, the cracks tended to propagate along the paths of least resistance, forming fewer but longer macrocracks. With increasing loading velocities, the number of cracks markedly increased, and their distribution became more diffuse, leading to a greater extent of failure in the frozen soil. An exponential damage cohesive interface model that considers rate effects was proposed to describe the dynamic tensile fracture mechanical behavior of frozen soil accurately. This model addresses the rate sensitivity of frozen soil and effectively accounts for the temperature effect by considering the volume of ice content and cryogenic suction. A comparison of the FDEM numerical simulation results with the experimental data indicated a good consistency in the overall trends, thus validating the effectiveness and applicability of the FDEM in simulating the dynamic tensile mechanical behavior of frozen soil.

Research on comprehensive heat dissipation characteristics of AlSi7Mg TPMS heat sinks manufactured by laser powder bed fusion

The comprehensive heat transfer characteristics of triply periodic minimal surface heat sinks were investigated in this research, and triply periodic minimal surface structures were manufactured by laser powder bed fusion with AlSi7Mg powder. The average surface temperature, thermal resistance, heat transfer coefficient, and specific heat transfer coefficient of heat sinks were tested, and the heat dissipation mechanism was analyzed by finite element thermal flow analysis. The results of thehomogeneous triply periodic minimal surface show that Primitive has the best comprehensive heat transfer performance under forced convection, and Gyroid is the best without forced convection. Compared with homogeneous and gradient triply periodic minimal surfaces, the P-Quadratic ΙΙ structure has the best comprehensive heat transfer performance under forced convection and natural thermal conductivity. Compared with homogeneous Primitive, the average convection heat transfer coefficient of P-Quadratic ΙΙ is increased by 13.44 % ∼ 19.78 %. The finite element thermal flow analysis shows that the narrow tube effect of Bernoulli’s principle and eddy current enhanced the heat transfer performance of Primitive and gradient Primitive.

Hierarchical Modeling of the Thermal Insulation Performance of Novel Plasters with Aerogel Inclusions

Silica aerogel possesses a significantly lower thermal conductivity compared to still air at room temperature, thanks to its high porosity and advanced thermal and physical properties. It is extensively investigated for its potential use as an insulation material, usually being incorporated into other matrix materials, such as cement plasters, to enhance the overall thermal performance with minimal weight load. The development of lightweight thermal insulation materials is a key step in reducing energy consumption in hot and cold environments during construction and in thermal equipment. The superior insulation capabilities of aerogels stem from their nanostructured SiO2 framework, which induces nanoscale rarefaction effects on the enclosed air near the SiO2 structure. This study reconstructed the nanostructured SiO2 network of modern aerogels using microscopy imaging and the literature data and integrated it into sophisticated heat transfer simulations at a microscopic level to predict its thermal performance. The simulation assumed conduction as the primary energy dissipation mechanism, incorporating local rarefaction effects based on kinetic theory approaches. SiO2 aggregates were modeled as interconnected strings of spherical beads, with variations in the aggregate size explored in a parametric study. Nanoscale rarefaction phenomena, such as slip wall and Knudsen diffusion, prevalent at these grain sizes and structures, were incorporated to refine the modeling approach. The degree of the aerogel content relative to the effective properties of the multiphasic material was then investigated systematically along the multilayered mortar thickness and on a representative multiphasic layer at the mesoscopic level. The results quantify the significant decrease in the thermal conductivity of the heterogeneous material as the porosity of the aerogel increased. The insulation performance of this aerogel incorporated into cement plasters was assessed with this hierarchical approach and validated against experimental data, providing insights for the optimization of the fabrication process and potential applications in construction.

Evolution of Dissipative Regimes in Atomically Thin Bi2Sr2CaCu2O8 + x Superconductor

AbstractThermoelectric transport is widely used to study Abrikosov vortex dynamics in unconventional superconductors. However, only a few thermoelectric studies have been conducted near the dimensional crossover that occurs when the vortex‐vortex interaction length scale becomes comparable to the sample size. Here, the effects of finite size on the dissipation mechanisms of the Nernst effect in the optimally doped Bi2Sr2CaCu2O8 + x high‐temperature superconductor are reported, down to the atomic length limit. To access this regime, a new generation of thermoelectric chips based on silicon nitride microprinted circuit boards is developed. These chips ensure optimized signals while preventing sample deterioration. The results demonstrate that lateral confinement at the nanoscale can effectively reduce vortex dissipation. Investigating vortex dissipation at the micro‐ and nano‐scale is essential for creating stable, miniaturized superconducting circuits.

Structural design of “straw and clay” based on cellulose nanofiber/polydopamine and its interfacial stress dissipation mechanisms

Cellulose nanofiber (CNF) is often incorporated as reinforcements into various matrices to optimize the mechanical properties of composites. However, the role of CNF in structural design interface components has been mostly neglected. Inspired by the architectural structure of “straw and clay”, CNF and polydopamine (PDA) were used as the “straw phase” and “clay phase”, respectively, to construct PDA/CNF self-assembled coatings on the carbon fiber (CF) surface via covalent bonding and non-covalent self-assembly. The organic coatings endowed the CF with high specific surface area, roughness and polarity, as well as a broad and gentle interfacial layer of the CF/epoxy resin composites. After self-assembly, the monofilament tensile strength (TS) of the fiber and the interlaminar shear strength (ILSS) of the CF/epoxy resin composites were increased by 13.44 % and 31.88 %, respectively. This investigation furnishes ideas for improving the mechanical performances of composites from the viewpoint of surface structure design and interface modulation.

Improved sound absorption by size gradient granular materials due to Brazil-nut effect

Granular material is attracting increasing research momentum due to its prevalence and rich unique properties. Nevertheless, compared with its numerous functions in other areas, the application of granular material in acoustic waves has received less attention. In this paper, we propose that by exploiting Brazil-nut effect induced particle size segregation in granular material, a significant improvement in the sound absorption can be achieved. Firstly, sound absorptions by particles with step-increasing sizes have been analyzed. It is found that size-dependent mechanisms of sound energy dissipation may occur. Secondly, sound absorptions by size-mixed particles with vibration treatment have been studied. As a result of the Brazil-nut effect induced size segregation, the size-mixed particles with initially limited sound absorptivity exhibited remarkably improved sound absorbing capability, with both broadened absorbing band and raised low-frequency absorption. This work demonstrates that simple processing of the granular material may become a promising way to create premium sound absorbers.

Experimental study of magnetorheological fluids under large periodic deformations

Abstract Magnetorheological (MR) fluids are smart materials whose properties can be controlled by a magnetic field. They are used in a variety of applications with tailored operating parameters, facilitating broad and relatively straightforward implementation and control of the functional properties of these systems.

The aim of the study was to determine the variation in shear stress of MR fluids under varying shear deformation directions and different magnetic field induction levels. The experiments were carried out with the use of three commercially available fluids: MRF-122EG, MRF-132DG, and MRF-140CG, which primarily differ in the volumetric fraction of ferromagnetic particles. These fluids are designed for use in mechanical energy dissipation devices clutches, and brakes are characterized by high stability and a broad controllability range.

The experiments were performed using a rotational rheometer with a parallel plate measuring system to examine shear stress variability during both the deformation and rest phases. The study applied relatively large deformations, exceeding the linear viscoelastic range and the deformation corresponding to the yield point.

The test results revealed variations in the shear stress values across successive loading cycles, as well as fluctuations during the rest phase. It was also found that, depending on magnetic field induction level (i.e., the level of fluid magnetization), the rest period could result in either a decrease (relaxation) or an increase (hardening) in shear stress values. These findings have practical significance, particularly for MR fluid devices operating in shear mode.

A weight-based efficiency measure for energy dissipating devices for flexible rockfall barriers

Flexible barriers are essential passive measures which are able to protect human life, structures and infrastructures from rockfall hazards. When a barrier is impacted, a significant portion of energy dissipation is concentrated in targeted components, named brakes, which can be replaced after the rockfall event. Several technologies exist, differing in both constitutive elements and energy dissipation mechanisms, but experimental data are generally restricted by producers. The present paper compares the various technologies thanks a new efficiency index, that is the ratio between the component potentially dissipated energy and its weight. To analyse the effects of the design parameters, four of the most common brakes are analytically modelled. It is shown that the performance of the devices is variable and depends on the working mechanism and the adopted material. In particular, plastic deformation energy dissipation induced by buckling is generally more efficient than the one caused by bending. Finally, a discussion on the force that activates the brake is proposed. The proposed analyses are of paramount importance for the conceptual design of new energy dissipation devices in rockfall risk mitigation structures.