Thermal Damping Research Articles

Imprint of Diabatic Processes in the Waviness of the Jet Stream: An Analysis of Local Wave Activity Budget

Abstract Given the widespread presence of clouds in the midlatitudes, one expects significant effects of condensational and radiative processes on the large-scale circulation of the atmosphere, but these diabatic effects are hard to constrain from observation. The authors propose a simple method to estimate the diabatic effects on the waviness of the jet stream based on the observed column-mean budget of Rossby wave activity. Wave activity in the midlatitudes is maintained by injection due to surface baroclinicity and/or diabatic sources, downstream transport due to advection and wave radiation, and eventual dissipation through mixing and thermal damping. Once the diabatic sources of wave activity are identified from the residual of the budget, one can suppress them and recompute the budget assuming that the transport velocity and damping rate do not change and thereby assess the impact of the diabatic sources. For the Northern Hemisphere, we found significant positive values of the residual in regions coincident with high column cloud water, suggesting that there are diabatic sources of wave activity associated with clouds. In winter, maritime diabatic sources contribute to wave activity over the Atlantic and the Pacific by about 33% and 30%, respectively, while in summer, the numbers are lower. The estimates are based on the assumptions that the perturbed wave sources do not alter the flow and that sources and sinks are geographically separated. For the Southern Hemisphere, this last assumption is questionable, and therefore, the confidence level of the estimates is low.

Stability for the 2D magnetic Bénard system with partial dissipation and thermal damping near an equilibrium

In this paper, we focus on the Boussinesq equations with magnetohydrodynamics convection, in which the temperature obeys degenerate damped wave equations. Under the influence of an equilibrium, we prove that the 2D magnetic Bénard system remains stable in the whole space . In particular, we obtain the decay rate and large‐time behavior. Without the coupling, the 2D MHD system with only vertical dissipation is not known to be stable. It is revealed that both the thermal damping and the horizontal background magnetic field are indispensable.

Advanced Peak Phase of ENSO under Global Warming

Abstract El Niño–Southern Oscillation (ENSO) is the leading mode of interannual ocean–atmosphere coupling in the tropical Pacific, greatly influencing the global climate system. Seasonal phase locking, which means that ENSO events usually peak in boreal winter, is a distinctive feature of ENSO. In model future projections, the ENSO sea surface temperature (SST) amplitude in winter shows no significant change with a large intermodel spread. However, whether and how ENSO phase locking will respond to global warming are not fully understood. In this study, using Community Earth System Model Large Ensemble (CESM-LE) projections, we found that the seasonality of ENSO events, especially its peak phase, has advanced under global warming. This phenomenon corresponds to the seasonal difference in the changes in the ENSO SST amplitude with an enhanced (weakened) amplitude from boreal summer to autumn (winter). Mixed layer ocean heat budget analysis revealed that the advanced ENSO seasonality is due to intensified positive meridional advective and thermocline feedback during the ENSO developing phase and intensified negative thermal damping during the ENSO peak phase. Furthermore, the seasonal variation in the mean El Niño–like SST warming in the tropical Pacific favors a weakened zonal advective feedback in boreal autumn–winter and earlier decay of ENSO. The advance of the ENSO peak phase is also found in most CMIP5/6 models that simulate the seasonal phase locking of ENSO well in the present climate. Thus, even though the amplitude response in the winter shows no model consensus, ENSO also significantly changes during different stages under global warming.

A simple model linking radiative–convective instability, convective aggregation and large-scale dynamics

Abstract. A simple model is presented which is designed to analyse the relation between the phenomenon of convective aggregation at small scales and larger-scale variability that results from coupling between dynamics and moisture in the tropical atmosphere. The model is based on single-layer dynamical equations coupled to a moisture equation to represent the dynamical effects of latent heating and radiative heating. The moisture variable q evolves through the effect of horizontal convergence, nonlinear horizontal advection and diffusion. Following previous work, the coupling between moisture and dynamics is included in such a way that a horizontally homogeneous state may be unstable to inhomogeneous disturbances, and, as a result, localised regions evolve towards either dry or moist states, with divergence or convergence respectively in the horizontal flow. The time evolution of the spatial structure of the dry and moist regions is investigated using a combination of theory and numerical simulation. One aspect of the evolution is a spatial coarsening that, if moist regions and dry regions are interpreted as convecting and non-convecting respectively, represents a form of convective aggregation. When the weak temperature gradient (WTG) approximation (i.e. a local balance between heating and convergence) applies, and horizontal advection is neglected, the system reduces to a nonlinear reaction–diffusion equation for q, and the coarsening is a well-known aspect of such systems. When nonlinear advection of moisture is included, the large-scale flow that arises from the spatial pattern of divergence and convergence leads to a distinctly different coarsening process. When thermal and frictional damping and f-plane rotation are included in the dynamics, there is a dynamical length scale Ldyn that sets an upper limit for the spatial coarsening of the moist and dry regions. The f-plane results provide a basis for interpreting the behaviour of the system on an equatorial β plane, where the dynamics implies a displacement in the zonal direction of the divergence relative to q and hence to coherent equatorially confined zonally propagating disturbances, comprising separate moist and dry regions. In many cases the propagation speed and direction depend on the equatorial wave response to the moist heating, with the relative strength of the Rossby wave response to the Kelvin wave response determining whether the propagation is eastward or westward. Within this model, the key overall properties of the propagating disturbances, the spatial scale and the phase speed, depend on nonlinearity in the coupling between moisture and dynamics, and any linear theory for such disturbances therefore has limited usefulness. The model described here, in which the moisture and dynamical fields vary in two spatial dimensions and important aspects of nonlinearity are captured, provides an intermediate model between theoretical models based on linearisation and one spatial dimension and general circulation models (GCMs) or convection-resolving models.

Practical Exploration of the 'Open or Close' Concept: Evaluation of the Hygrothermal Performance of a Bioclimatic Innovation for Onion Bulb Preservation

Substantial losses occur during the storage of onion bulbs due to the inadequacy of available preservation technologies. In an endeavor to contribute to a solution, we evaluate the thermal efficacy of a bioclimatic innovation known as the "solar cell" for onion bulb preservation. This assessment involves recording temperature data from both external and internal walls, as well as indoor and outdoor air temperatures, solar irradiation, and relative humidity levels indoors. These measurements offer insights into crucial performance parameters such as thermal phase shift, thermal inertia, thermal decoupling between internal and external environments, relative humidity, damping factor, and thermal amplitude. Furthermore, we examine the impact of external factors, including external temperature and solar radiation. Across different facades, the thermal phase shift of the chamber's structure averages between 5.5 and 10.87 hours. Notably, the maximum thermal phase shift is observed to be 11.67 hours on the Eastern wall. The lowest recorded thermal damping factor is 0.081 on the Western wall, while the highest is 0.337 on the Northern wall. The study of thermal decoupling between the internal and external environments reveals a potential temperature differential of 13.7°C and 9.5°C during the day, and-6°C at night, contingent on the time of year. Consequently, the "close or open" operational mode proves to be of significant interest. Exposed to solar radiation peaking at 1041 W/m2, the temperatures of the external facades of the walls experience a substantial increase, reaching up to 52.3°C. Meanwhile, the internal environment maintains a thermal range of 24.21°C to 31.68°C under a maximum airflow of 0.18 m/s. The average relative humidity within the storage chamber fluctuates between 42.65% and 87%. Hence, the solar cell demonstrates its capacity to create optimal conditions of 25°C-30°C and 0.062 m/s for onion bulb conservation. Nevertheless, further enhancements are warranted for effective humidity control.

The Potential Role of Seasonal Surface Heating on the Chaotic Origins of the El Niño/Southern Oscillation Spring Predictability Barrier

AbstractThe Spring Predictability Barrier (SPB) phenomenon is characterized by the reduced accuracy of El Niño/Southern Oscillation (ENSO) forecasts during the spring, which substantially limits our ability to predict ENSO events. By investigating the nonlinear dynamic characteristics of ENSO systems simulated by a box model, we found that the strong surface heating process in spring may contribute to the SPB by regulating the different coupling processes between the ocean and atmosphere. Specifically, the intensified springtime surface heating increases the Sea Surface Temperature (SST), further amplifying the thermal damping effect of SST anomalies and reducing the dynamic connection between zonal SST gradient and upwelling process, and finally increasing the chaotic degree of ENSO systems simulated by the box model. The enhanced chaotic degree of ENSO systems leads to a more rapid growth of initial errors in the forecast model in spring, potentially leading to the SPB phenomenon.

Interplay of Landau Quantization and Interminivalley Scatterings in a Weakly Coupled Moiré Superlattice.

Double-layer quantum systems are promising platforms for realizing novel quantum phases. Here, we report a study of quantum oscillations (QOs) in a weakly coupled double-layer system composed of a large-angle twisted-double-bilayer graphene (TDBG). We quantify the interlayer coupling strength by measuring the interlayer capacitance from the QOs pattern at low temperatures, revealing electron-hole asymmetry. At high temperatures when SdHOs are thermally smeared, we observe resistance peaks when Landau levels (LLs) from two moiré minivalleys are aligned, regardless of carrier density; eventually, it results in a 2-fold increase of oscillating frequency in D, serving as compelling evidence of the magneto-intersub-band oscillations (MISOs) in double-layer systems. The temperature dependence of MISOs suggests that electron-electron interactions play a crucial role and the scattering times obtained from MISO thermal damping are correlated with the interlayer coupling strength. Our study reveals intriguing interplays among Landau quantization, moiré band structure, and scatterings.

Radiative loss and ion-neutral collisional effects in astrophysical plasmas.

In this paper, we study the role of radiative cooling (RC) in a two-fluid model consisting of coupled neutrals and charged particles. We first analyse the linearized two-fluid equations where we include radiative losses in the energy equation for the charged particles. In a one-dimensional geometry for parallel propagation and in the limiting cases of weak and strong coupling, it can be shown analytically that the instability conditions for the thermal mode and the sound waves, the isobaric and isentropic criteria, respectively, remain unchanged with respect to one-fluid radiative plasmas. For the parameters considered in this paper, representative for the solar corona, the RC produces growth of the thermal mode and damping of the sound waves. In the weak coupling limit, the growth of the thermal instability and the damping of the sound waves is as derived in Field (Field 1965 Astrophys. J. 142, 531(doi:10.1086/148317)) using the charged fluid properties. When neutrals are included and are sufficiently coupled to the charges, the thermal mode growth rate and the wave damping both reduce by the same factor, which depends on the ionization fraction only. For a heating function that is constant in time, we find that the growth of the thermal mode and the damping of the sound waves are slightly larger. The numerical calculation of the eigenvalues of the general system of equations in a three-dimensional geometry confirm the analytic results. We then run two-dimensional fully nonlinear simulations that give consistent results: a higher ionization fraction or lower coupling will increase the growth rate. The magnetic field contribution is negligible in the linear phase. Ionization-recombination effects might play an important role because the RC produces a large range of temperatures in the system. In the numerical simulation, after the first condensation phase, when the minimum temperature is reached, the fraction of neutrals increases four orders of magnitude because of the recombination. This article is part of the theme issue 'Partially ionized plasma of the solar atmosphere: recent advances and future pathways'.

Vibrational anharmonicity of A-band related optical center and its temperature dependence studied by femtosecond laser excitation in bulk natural diamond

Unusual A-band spectra with well-resolved quasi-periodical phonon progressions of multiple peaks (N\(\sim \)9) were excited in a natural diamond by 515-nm, 300-fs laser pulses at variable pre-heating temperatures of 24-200oC. The non-radiative multi-phonon part of the relaxation path was comparable with the total relaxation energy (zero-phonon line energy), pointing out some extended defects (e.g., dislocations) as the recombination center of the A-band emission. The derived temperature dependences of the peak intensities, separations and half-widths of the separate spectral peaks in the A-band phonon progressions indicate the different trends for vibration-free zero-phonon transition and vibration-related lower-energy transitions to high vibrational levels of the bottom state – lower thermal damping and more softened phonon for the zero-phonon transition, also implying the extended defect origin of the A-band photoluminescence.

Thermal damping of the motion of a piston: Any irreversibility implies dissipation

We consider the motion of a frictionless piston that separates the surrounding atmosphere from an ideal gas enclosed within a cylinder, with no friction or viscous dissipation arising within the gas or surrounding atmosphere. Although no mechanically based dissipative mechanisms act, the motion of the piston is still damped if heat transfer between the gas and the piston occurs at a finite rate. Hence, as long as some kind of irreversibility develops within the system, such as irreversible heat transfer, the piston will not oscillate back-and-forth indefinitely and must eventually come to rest. We provide detailed thermodynamic and numerical analyses of this thermal damping, various aspects of which should prove useful to both students and instructors when discussing the first and second laws of thermodynamics.

Acoustical, vibrational, and thermal investigations of pyrolytic carbon black reinforced natural rubber composites

The present study aims to utilize the carbonaceous filler (pyrolytic carbon black (PCB)) obtained from tire waste to fabricate composites for thermal, vibrational, and acoustical applications. Four composites were fabricated by increasing the PCB content (0, 10, 20, and 30 parts per hundred rubber (phr)) in the natural rubber (NR) matrix following ASTM D3182-21a standard. The optimum curing time was determined using a Moving Die Rheometer based on the ASTM D2084-19 standard. The physical, functional, microstructural, wettability, thermal, and mechanical properties of fabricated NR/PCB composites were comprehensively examined. Further, from an application standpoint, the study influence of increasing PCB content in a polymer matrix on thermal conductivity (TC), vibration damping, and sound transmission loss (STL) of the fabricated NR/PCB composites was investigated following ASTM E1530-19, ASTM E756-05, and ASTM E2611-17 standards, respectively. The study results indicate significant enhancement in the properties of the composites with increased PCB content. Specifically, the reinforcement of 30 phr of PCB in the polymer matrix led to a notable increase in TC (at 40 °C) by approximately 21.16% compared to NR/PCB0 composite. Also, the configuration mild steel (MS) + NR/PCB30 achieved the highest damping ratio, measuring 6.56 at the third vibration mode. Moreover, the average STL value of the NR/PCB30 composite showed a notable improvement of approximately 17.19% when compared to the NR/PCB0 composite, underscoring the effectiveness of PCB in enhancing the desired properties of the NR-based composites.

Mechanisms of model bias impacting responses of the Atlantic cold tongue to greenhouse warming

The Atlantic cold tongue, which typically peaks in boreal summer, exerts a pronounced regional and global impact on the climate and socio-economy. Projected future changes in the Atlantic cold tongue are full of uncertainty, mainly arising from a model bias in simulating its mean state, with less biased models projecting a stronger weakening in amplitude. However, the underlying mechanisms remain unknown. Here, we find that model bias exerts its influence through modulating atmospheric thermal damping and upwelling of subsurface anomalous warming induced by the weakened Atlantic meridional overturning circulation (AMOC). In less biased models, the Atlantic cold tongue, compared to the western equatorial Atlantic, features a cooler mean climate sea surface temperature (SST), and is subjected to smaller thermal damping induced by mean climate evaporation and consequently, faster SST warming. Moreover, equatorial subsurface warming associated with a reduced AMOC is advected to the surface via mean climate upwelling, enhancing faster SST warming in the east, a feedback stronger in less biased models that produce greater climatological upwelling. The above asymmetric SST warming would be amplified by the Bjerknes feedback, leading to a weakened Atlantic cold tongue. These findings may help to predict future changes in the Atlantic cold tongue and its influences.

On the uniform stability of a thermoelastic Timoshenko system with infinite memory

<abstract><p>The present research is aim at investigating a thermoelastic Timoshenko system with an infinite memory term on the shear force while the bending moment is under the influence of a thermoelastic dissipation governed by Fourier's law. We prove that the system's stability holds for a broader class of relaxation functions. Under this class of relaxation functions $ h $ at infinity, we establish a relation between the decay rate of the solution and the growth of $ h $ at infinity. Moreover, we drop the boundedness assumptions on the history data. We employ Neumann-Dirichlet-Neumann boundary conditions for our result. In comparison to the bulk of results in the literature, which frequently enforce the "equal-wave-speed" constraint, the present result shows that the infinite memory of the beam and the thermal damping are strong enough to guarantee stability without any conditions on the parameters.</p></abstract>

Global solution of 3D MHD-Boussinesq system with mixed partial dissipation and thermal damping

Global solution of 3D MHD-Boussinesq system with mixed partial dissipation and thermal damping

Stability results of a laminated beam with Cattaneo's thermal law and structural damping

Stability results of a laminated beam with Cattaneo's thermal law and structural damping

Energy Performance of Vernacular Architecture in Various Desert Climates

Summer 2022 is officially the 2nd hottest summer in France since 1900. It resulted in three episodes of heat waves over a total of thirty-three days. Heat waves are characterized by very high temperatures (exceeding seasonal averages) during the day and night for at least three consecutive days. According to initial estimates, it caused a surplus of more than 11,000 deaths in 2022 in France. In France, despite new thermal standards, the thermal comfort of new housing in hot weather remains very inadequate. Thanks to these empirical developments vernacular architecture has demonstrated its adaptation in particularly harsh climates. The objective of this research is to understand the design strategies of four vernacular houses located in four deserts (Algerian Sahara, Arizona, Libyan desert, and Yemen) to ensure summer comfort in hot environments. The thermal behavior of these four vernacular houses has been studied through dynamic thermal simulations performed with the software ‘ArchiWIZARD’, using the same climate conditions. The results are interpreted in terms of operative temperature and related to building compacity. They show how vernacular architecture, located in desert climates, considered summer thermal comfort with design strategies. The thermal inertia of the four case studies is characterized by the daily thermal damping. The results also show the contribution of natural night ventilation on the energy performance of these four vernacular architectures in hot and arid climates.

Elastomer Composites with High Damping and Low Thermal Resistance via Hierarchical Interactions and Regulating Filler.

Modern microelectronics and emerging technologies such as wearable electronics and soft robotics require elastomers to integrate high damping with low thermal resistance to avoid damage caused by vibrations and heat accumulation. However, the strong coupling between storage modulus and loss factor makes it generally challenging to simultaneously increase both thermal conductance and damping. Here, a strategy of introducing hierarchical interaction and regulating fillers in polybutadiene/spherical aluminum elastomer composites is reported to simultaneously achieve extraordinary damping ability of tan δ>1.0 and low thermal resistance of 0.15cm2 KW-1 , which surpasses state-of-the-art elastomers and their composites. The enhanced damping is attributed to increased energy dissipation via introducing the hierarchical hydrogen bond interactions in polybutadiene networks and the addition of spherical aluminum, which also functions as a thermally conductive filler to achieve low thermal resistance. As a proof of concept, the polybutadiene/spherical aluminum elastomer composites are used as thermal interface materials, showing effective heat dissipation for electronic devices in vibration scenarios. The combination of outstanding damping performance and extraordinary heat dissipation ability of the elastomer composites may create new opportunities for their applications in electronics.

Modelling of energetic particle drive and damping effects on TAEs in AUG experiment with ECCD

The impact of electron cyclotron current drive (ECCD)-driven current on toroidicity-induced Alfvén eigenmodes (TAEs) in experiments on the AUG tokamak is investigated numerically. The dynamical evolution of the plasma profiles and equilibria are modelled with European transport solver, while ion cyclotron resonance heating-accelerated H-minority ions exciting TAEs are assessed with the PION code. TAEs, their drive and damping are computed with the codes CASTOR and CASTOR-K. In the set of discharges analysed, two groups of TAEs are observed, differing in frequency and radial location. Experimental observations show that when counter-ECCD is applied the higher frequency group of approximately 150 kHz is suppressed, while the lower frequency modes of 125 kHz are amplified. When co-ECCD is applied, depending on the location of the ECCD current deposition layer, both groups of TAE can be suppressed. Numerical calculations of energetic particle drive and thermal plasma damping show that neither one effect could explain the variety of the experimental observations. The fine balance between the drive, sensitive to the TAE position, and the radiative and continuum damping effects could only explain the experiment if the effects are considered all together.

Thermal Buckling, Vibration and Damping Behavior of Viscoelastic-FGM Sandwich Doubly Curved Panels

Thermal Buckling, Vibration and Damping Behavior of Viscoelastic-FGM Sandwich Doubly Curved Panels

Rattling-like behavior and band convergence induced ultra-low lattice thermal conductivity in MgAl2Te4 monolayer

Inspired by the excellent stability exhibited by experimentally synthesized two-dimensional (2D) MoSi2N4 layered material, the thermal and electronic transport, and thermoelectric (TE) properties of MgAl2Te4 monolayer are systematically investigated using the First-principles calculations and Boltzmann transport theory. The mechanical stability, dynamic stability, and thermal stability (900 K) of the MgAl2Te4 monolayer are demonstrated, respectively. The MgAl2Te4 monolayer exhibits a bandgap of 1.35 eV using the HSE06 functional in combination with spin-orbit coupling (SOC) effect. Band convergence in the valence band is favorable to improve the thermoelectric properties. The rattling thermal damping effect caused by the weak bonding of MgTe bonds in MgAl2Te4 monolayer leads to ultra-low lattice thermal conductivity (0.95/0.38 W/(m·K)@300 K along the x-/y-direction), which is further demonstrated by the phonon group velocities, phonon relaxation time, Grüneisen parameters, and scattering mechanisms. The optimal zT of 3.28 at 900 K is achieved for the p-type MgAl2Te4 monolayer, showing the great promising prospect for the excellent p-type thermoelectric material. Our current work not only reveals the underlying mechanisms responsible for the excellent TE properties, but also elaborates on the promising thermoelectric application of MgAl2Te4 monolayer material at high temperature.