Inertial Mechanisms Research Articles

Flow instabilities driven by Prandtl number effect and rotation-depth coupling effect in the cylinder with a top disk

We employed linear stability analysis to investigate the Prandtl number (Pr) effect and rotation-depth coupling effect on the complex flow instability in a cylinder with a top disk. The dependence of the critical Rayleigh number on the Pr number, as well as the relationship between the critical disk rotation rate and the aspect ratio at Pr = 6.7, were obtained. Results reveal that the flow stability increases with increasing Pr number, and the convection instability stems from the inertial mechanism for 0.011 ≤ Pr ≤ 0.0258 and thermal buoyancy mechanism for 1.4 ≤ Pr ≤ 28.01. Regarding the rotation-depth coupling effect for the melt with Pr = 6.7, a decreasing melt level leads to a general increase in the critical disk rotation rate. Furthermore, within the interval of aspect ratio (ratio of depth to cylinder radius) 0.7 ≤ Γ ≤ 1.62, multiple transitions of the flow state from stable to unstable and then back to stable were observed with increasing disk rotation rate before finally becoming unstable. Energy analysis reveals that multiple transitions in the flow state are attributed to the competition between thermal buoyancy and inertial mechanisms.

Rate sensitive plasticity-based damage model for concrete under dynamic loading

In this manuscript, a rate-sensitive plasticity-based damage model for concrete subjected to dynamic loads is presented. The developed rate-sensitive damage model incorporates the key experimental evidence related to strain rate and damage rate. With increasing strain rates, the model is able to predict a decrease in the rate of damage evolution due to artificial stiffening effects together with a final higher level of damage. The major contribution of the work is to include the effect of damage rate, strain rate and also to consider all the physical mechanisms of damage. This is achieved by using a power law model to relate the rate of damage to the equivalent plastic strain rate. The damage parameter considers hydrostatic, tension and compression damage. Such a damage definition helps in the prediction of pulverized damage due to a loss in cohesive strength at increased hydrostatic stress, shear-induced compressive damage and tensile microcracking. Strong volumetric deformation of the material that includes hydrostatic and compaction damage is also considered in the model. Because hydrostatic damage accounts for the reduction in stiffness and compaction damage accounts for the increase in stiffness under pure compressive loading. A strain rate-dependent failure surface is considered and with increasing strain rate there is an increase in the size of the failure surface which is capped at an upper limiting value. The incremental effective stress-strain relationship is defined in terms of rate of damage, accumulated damage and viscosity parameters reflecting the inherent inertial, thermal and viscous mechanisms respectively. The stress-strain relationship in the model also accounts for stress reversals that occur due to interference of an incident and reflected wave, by including a Heaviside function. The developed model is implemented in LS-DYNA using vectorized UMAT. Verification, validation and parameterization of the developed model have been made through several numerical analyses.

Tricritical state and quasi-periodicity triggered by the non-linear elasticity in an Upper Convected Maxwell fluid confined between two co-oscillating cylinders about zero-mean

The effects of harmonically co-oscillating the inner and outer cylinders about zero mean rotation in a Taylor–Couette flow are examined numerically using Floquet theory, for the case where the fluid confined between the cylinders obeys the upper convected Maxwell model. Although stability diagrams and mode competition involved in the system were clearly elucidated recently by Hayani Choujaa et al. (2021) in weakly elastic fluids, attention is focused, in this paper, on the dynamic of the system at higher elasticity with emphasis on the nature of the primary bifurcation. In this framework, we are dealing with pure inertio-elastic parametric resonant instabilities where the elastic and inertial mechanisms are considered of the same order of magnitude. It turns out, on the one hand, that the fluid elasticity gives rise, at the onset of instability, to the appearance of a family of new harmonic modes having different axial wavelengths and breaking the spatio-temporal symmetry of the base flow: invariance in the axial direction generating the O(2) symmetry group and a half-period-reflection symmetry in the azimuthal direction generating a spatio-temporal Z2 symmetry group. On the other hand, new quasi-periodic flow emerging in the high frequency limit and other interesting bifurcation phenomena including bi and tricritical states are also among the features induced by the fluid elasticity. Lastly, and in comparison with the Newtonian configuration of this system, the fluid elasticity leads to a total suppression of the non-reversing flow besides emergence of instabilities with lower wavelengths. Such a comparison provides insights into the dynamics of elastic hoop stresses in altering the flow reversal in modulated Taylor–Couette flow.

Retinal hemorrhage variation in inertial versus contact head injuries

BackgroundAbusive head trauma (AHT) is frequently accompanied by dense/extensive retinal hemorrhages to the periphery with or without retinoschisis (complex retinal hemorrhages, cRH). cRH are uncommon without AHT or major trauma. ObjectiveThe study objectives were to determine whether cRH are associated with inertial vs. contact mechanisms and are primary vs. secondary injuries. Participants and settingThis retrospective study utilized a de-identified PediBIRN database of 701 children <3-years-old presenting to intensive care for head trauma. Children with motor vehicle related trauma and preexisting brain abnormalities were excluded. All had imaging showing head injury and a dedicated ophthalmology examination. MethodsContact injuries included craniofacial soft tissue injuries, skull fractures and epidural hematoma. Inertial injuries included acute impairment or loss of consciousness and/or bilateral and/or interhemispheric subdural hemorrhage. Abuse was defined in two ways, by 1) predetermined criteria and 2) caretaking physicians/multidisciplinary team's diagnostic consensus. ResultsPediBIRN subjects with cRH frequently experienced inertial injury (99.4 % (308/310, OR = 53.74 (16.91–170.77)) but infrequently isolated contact trauma (0.6 % (2/310), OR = 0.02 (0.0004–0.06)). Inertial injuries predominated over contact trauma among children with cRH sorted AHT by predetermined criteria (99.1 % (237/239), OR = 20.20 (6.09—67.01) vs 0.5 % (2/339), OR = 0.04 (0.01–0.17)).Fifty-nine percent of patients with cRH, <24 h altered consciousness, and inertial injuries lacked imaging evidence of brain hypoxia, ischemia, or swelling. ConclusionscRH are significantly associated with inertial angular acceleration forces. They can occur without brain hypoxia, ischemia or swelling suggesting they are not secondary injuries.

Longitudinal wave attenuation and bandgap analysis of a novel type hybrid tunable resonator metamaterial

Achieving vibration suppression or wave attenuation of tunable local resonance metamaterials without physical modification of the resonator has received a lot of attention recently. In this paper, a hybrid tunable metamaterial with a resonator containing a lever mechanism, an electromagnetic device, and a feedback system is proposed to achieve tunable bandgap and longitudinal wave attenuation. Unlike ordinary metamaterials, inertial amplification mechanisms and negative stiffness elements are involved in our proposed metamaterials. The function of the electromagnetic device and the feedback control are considered to theoretically derive the dispersion relation. The effective mass, the effective stiffness, the displacement transmission rate, and the band structure of the proposed metamaterial are analyzed, and the contributions of some key parameters on the bandgap are investigated. The accuracy of the analytical band structure is verified by the wave transmittance curves obtained by numerical simulation and the transient displacement response of a single oscillator. The results show that the proposed metamaterial yields broadband tunable bandgap in the low-frequency range, which enables the isolation of low-frequency longitudinal vibrations. This study provides a novel option for constructing integrated metamaterials to achieve vibration suppression and wave attenuation.

Analytical modeling and 3D printing of locally resonant composite sandwich metamaterials with inertial amplification mechanisms

In this paper, a locally resonant sandwich metamaterial beam with inertial amplification mechanisms is presented for flexural vibration attenuation. This sandwich metamaterial is proposed as a lightweight structure with a low-frequency stopband. An analytical model was developed to derive the equations of motion for the resonator core and skin plate using Hamilton’s principle. Analytical solutions for the stopband boundary frequencies were derived from the equations of motion. The analytical solutions demonstrated that inertial amplification resonators can exhibit lower resonance frequencies than linear spring-mass resonators with the same weight and spring constant. It was also shown that the proposed sandwich beam exhibited a lower frequency stopband in exchange for the stopband width. Finite element method analyses and experiments were performed to investigate the frequency response of the sandwich beam. The flexural vibration of the sandwich beam was significantly attenuated within a certain frequency range. The frequency range with low transmissibility agreed well with the stopband predicted by the analytical solutions.

Design and additive manufacturing of elastic metamaterials with 3D lever-type inertial amplification mechanisms for mitigation of low-frequency vibration

This paper proposes a three-dimensional lever-type inertial amplification metamaterial for the mitigation of low-frequency vibration. This metamaterial was developed as a small, stiff, and single-phase structure that can inhibit the transmission of vibration in a certain frequency range below 100 Hz. An analytical model was developed to derive analytical solutions for the resonance and anti-resonance frequencies of the metamaterial unit cell. A dispersion equation was also derived to investigate the vibration transmissibility of the periodic structure. Finite element analysis was performed to obtain the frequency response of the unit cell and periodic structures. The analytical solutions were then verified through comparisons with the results of the finite element analysis. The proposed metamaterial was fabricated via selective laser sintering of a thermoplastic resin, and experiments were performed to measure the vibration transmissibility of the unit cell loaded with a mass and that of the periodic structures. A unit cell with a diameter of 100 mm and height of 65.8 mm showed low transmissibility in a wide frequency range around the anti-resonance frequency at 80 Hz while supporting up to 9.45 kg mass.

Three-dimensional ultra-wide elastic metamaterial with inertial amplification mechanisms having optimized flexure hinges

The aim of this paper is to obtain an ultra-wide low-frequency stop band in three dimensions by using inertial amplification mechanisms. A two-stage remote center flexure mechanism design is introduced that allows 3D assembly of inertial amplification mechanisms while enabling ends of the inertial amplification mechanisms to bend in two orthogonal axes so that broadband excitations coming from all directions can be impeded. Cross flexure and split flat flexure hinges that restrain undesired torsional, in-plane and out-of-plane bending modes of the inertial amplification mechanisms are utilized for the first time in order to maximize the stop band frequency range. An octahedron and 3D arrays of octahedrons are generated with the use of these mechanisms. By making design improvements and topological changes on the mechanisms forming the octahedron, the stop band of the octahedron is widened. Finally, the bandwidth is maximized by optimizing the thicknesses of the flexures in the inertial amplification mechanisms. Eventually, a 3D elastic metamaterial with an ultra-wide band gap between 33.7 Hz and 457.5 Hz is obtained, yielding arithmetic mean normalized bandwidth of 172.6%.

Beam-type metastructure with X-shape inertial amplification mechanisms for vibration suppression

A new type of beam-type metastructure periodically attaching single- or multi-stage X-shape inertial amplification (XIA) mechanisms is designed to realize efficient elastic wave attenuation and wide bandgaps benefiting the vibration suppression. Band structures of the unit cell and vibration response of the finite beam are validated numerically and experimentally. Numerical results show that compared with the triangular inertial amplification beams with the same added masses, XIA mechanisms generate wider bandgaps with higher attenuation constants at the same frequency band, for the same inertia amplification (IA) angle or same installation space. Parametric studies reveal that XIA mechanisms lead to the coupling effect of transverse wave and longitudinal wave, and induce a newly emerging bandgap. Moreover, the variations of IA angle, amplification ratio and number of stages apply basically similar effects on band structures, except the IA span. Finally, in order to explore practical applications on vibration suppression of XIA mechanisms, two schemes of multiple mechanisms in a unit cell and the hybrid unit cell are investigated. The proposed designs of XIA mechanisms have the potential to improve the capability of vibration suppression of the structures in engineering practices.

Stability and receptivity analyses of mixed convection in unstably stratified horizontal boundary layers

A linear stability analysis is employed to investigate thermal effects in shear flows. The cases analysed consist of unstably stratified horizontal boundary layers under a mixed convection regime, where forced and free convection mechanisms compete. Governing equations are given by the incompressible Navier–Stokes equations with the Oberbeck–Boussinesq approximation, where the base flow comes from their boundary layer approximation. Modal and non-modal analyses are used to investigate the behaviour of small-amplitude disturbances superposed to this base flow. An evaluation of the inertial, shearing and buoyancy mechanisms in the mixed convection boundary layer stability is performed through variations in the Reynolds, Prandtl and Richardson numbers. On the one hand, the spectra lead to the parametric conditions for the time-asymptotic onset of instability, which is still caused by Tollmien–Schlichting (TS) waves as in the traditional Blasius case. However, thermal effects have a destabilizing effect on them, more so for liquids than gases. On the other hand, the pseudospectra obtained from a resolvent analysis indicate the existence of transient growth at this same onset. However, contrary to the traditional Blasius case, thermal effects cause it to be dominated by the continuous frequency spectrum instead of the discrete TS modes. In order to elucidate this qualitative change, a componentwise input–output analysis is employed to quantify the receptivity to specific external disturbances. It shows that thermal effects directly impact the conversion of thermal to kinetic linear disturbance energy, causing a strong amplification of the flow response due to the non-normality of the linear operator. Results reveal that heating from below causes the forcing and response modes of the input–output analysis to have a free-stream spatial support due to non-modal excitation of the continuous spectrum. Such a behaviour suggests that the unstably stratified boundary layer is susceptible to free-stream thermal disturbances, which can potentially impact bypass transition.

Seismic metamaterials based on coupling mechanism of inertial amplification and local resonance

Inertial amplification mechanisms could be used to control the propagation of elastic waves in beams and slabs, but it was a difficult problem to apply inertial amplification mechanisms to seismic metamaterials to design low-frequency broadband. This paper presents a inertially amplified locally resonant seismic metamaterial (IALR-SM) using the coupling mechanism of inertial amplification and local resonance. In contrast to the locally resonant seismic metamaterial (LRSM), the large-mass columns as local resonators of IALR-SM are attached to the connector and small-mass columns to form the inertia amplification structures. The finite element method calculates the eigenmodes’ band structure and displacement vector field. Numerical results indicated that the bandwidth of the IALR-SM increases by 194% compared to LRSM for seismic surface waves below 20 Hz. The formation mechanism of the yield in large band gaps is attributed to the coupling mechanism of local resonance and inertial amplification. In addition, the numerical effects of geometric parameters on the band gaps are investigated. The findings showed that the side length of the small-mass columns plays a vital role in determining which coupling mechanism is dominant. Finally, field experiments demonstrated that the IALR-SM generates low-frequency broadband.

Numerical Simulation of Particle Filtration by Rectangular Fibres within a Parallel and Staggered Array

In this research, two-dimensional numerical simulation is used to examine the filtration performance of rectangular fiber filters. Ansys Fluent is employed to obtain the stable flow field distribution and the DPM model is used to calculate the particle trajectories in the flow field. The effect of pertinent factors such as fiber arrangement, particle-to-fiber diameter ratio, and Stokes number on the performance of rectangular fiber filters are analyzed. The simulation results indicate that both the parallel and staggered arrays of rectangular fibers have a significant influence on the capture efficiency and pressure drop. At the same flow velocity, the pressure drop of the fibers with a parallel array is lower than that of the staggered array fiber model. The capture efficiency of the staggered array model and the parallel array model increases with the increase of the ratio of particle to fiber diameter and the Stokes number. When the interception and inertial impaction mechanisms domiant, the filter with a staggered fiber array structure performs batter than the parallel array in terms of capture efficiency. The research results can provide a theoretical basis for the structure optimization and design of the air filter with multi-layer fiber.

Overview of Common Thermophysical Property Modelling Approaches for Cryogenic Fluid Simulations at Supercritical Conditions

Computational Fluid Dynamics (CFD) frameworks of supercritical cryogenic fluids need to employ Real Fluid models such as cubic Equations of State (EoS) to account for thermal and inertial driven mechanisms of fluid evolution and disintegration. Accurate estimation of the non-linear variation in density, thermodynamic and transport properties is required to computationally replicate the relevant thermo and fluid dynamics involved. This article reviews the availability, performance and the implementation of common Real Fluid EoS and data-based models in CFD studies of supercritical cryogenic fluids. A systematic analysis of supercritical cryogenic fluid (N2, O2 and CH4) thermophysical property predictions by cubic (PR and SRK) and non-cubic (SBWR) Real Fluid EoS, along with Chung’s model, reveal that: (a) SRK EoS is much more accurate than PR at low temperatures of liquid phase, whereas PR is more accurate at the pseudoboiling region and (b) SBWR EoS is more accurate than PR and SRK despite requiring the same input parameters; however, it is limited by the complexity in thermodynamic property estimation. Alternative data-based models, such as tabulation and polynomial methods, have also been shown to be reliably employed in CFD. At the end, a brief discussion on the thermophysical modelling of cryogenic fluids affected by quantum effects is included, in which the unsuitability of the common real fluid EoS models for the liquid phase of such fluids is presented.

Development of new pole-changing winding for lifting and transport mechanisms

In many industries, lifting and transport machines are used, particularly cranes, conveyors, and hoists. Taking into account their wide prevalence and large installed capacity, as well as the complexity of the operating mode, special attention is paid to the creation of new energy- and resource-saving electric drives that facilitate the start-up process and ensure accurate stopping of highly inertial lifting and transport mechanisms. In this direction, one of the priority tasks is the development of two-speed pole-changing motors that meet the requirements of the electric drive of lifting and transport mechanisms. Based on the method of "Discretely-given spatial functions", a pole-changing winding was obtained for a ratio of 1/5 poles at 30 slots of the stator. Analysis of the electromagnetic properties of the developed pole-changing winding showed that, compared with a close analog, the differential scattering coefficient on the p=1 side of the pole decreases from 1.7% to 1.3%, and on the p=5 side of the pole decreases from 15.9% to 9.7%, and also in the picture of the magnetomotive force, the presence of higher harmonic ones on the side of the first velocity decreases up to 6%, and from the second speed up to 20%.

Pool scrubbing in unit 1 of fukushima daiichi

Under the frame of OECD/BSAF and ARC-F projects, CIEMAT estimated that around 40% of the Cesium initial inventory in the reactor core and nearly 60% of the Iodine one of the Unit 1 of Fukushima Daiichi, got absorbed in the suppression pool. CIEMAT has critically reviewed the bases of the MELCOR pool scrubbing module, including the major assumptions and approximations underneath, under the prevailing conditions in Unit 1 of Fukushima Daiichi during fission product scrubbing. The results have shown that most fission product mass is retained in the water nearby the injection point as a consequence of diffusiophoresis and inertial mechanisms. However, some of the approximations underneath the corresponding models have been found to be questionable and some new formulations have been considered and implemented within the stand-alone SPARC-90 code, which is the basis of the MELCOR models for pool scrubbing. In particular, a model capable of describing the scrubbing effect of jet injection has been implemented. This work presents better-fitted models for the scenario and, after implementing them into the SPARC-90 code, the resulting moderate quantitative impact on the accident scenario of Unit1 in Fukushima Daiichi, has been discussed to be well within the uncertainty range associated to the original code estimates. However, updating of MELCOR concerned models for fission products trapping in pools is highly recommended for physical consistency.

A Polar Robust Kalman Filter Algorithm for DVL-Aided SINSs Based on the Ellipsoidal Earth Model.

Autonomous underwater vehicles (AUVs) play an increasingly essential role in the field of polar ocean exploration, and the Doppler velocity log (DVL)-aided strapdown inertial navigation system (SINS) is widely used for it. Due to the rapid convergence of the meridians, traditional inertial navigation mechanisms fail in the polar region. To tackle this problem, a transverse inertial navigation mechanism based on the earth ellipsoidal model is designed in this paper. Influenced by the harsh environment of the polar regions, unknown and time-varying outlier noise appears in the output of DVL, which makes the performance of the standard Kalman filter degrade. To address this issue, a robust Kalman filter algorithm based on Mahalanobis distance is used to adaptively estimate measurement noise covariance; thus, the Kalman filter gain can be modified to weight the measurement. A trial ship experiment and semi-physical simulation experiment were carried out to verify the effectiveness of the proposed algorithm. The results demonstrate that the proposed algorithm can effectively resist the influence of DVL outliers and improve positioning accuracy.

Theoretical analysis of 2D meta-structure with inertia amplification

This study proposed a square-grid structure (SGS) attached with inertial amplification mechanisms (IAMs) to obtain a better vibration isolation effect with low frequency and wide band gaps. According to the different stiffness assumptions of the IAM connecting rods, the proposed meta-structure is defined as two different types, 10° of freedom (DOF) elastic system (E-IAM) and 2-DOF rigid system (R-IAM). The motion equations of the two systems are given based on Newton's motion theorem and Lagrange's theorem, respectively. Dispersion relations and motion modes of the infinite system are discussed to obtain lower and wider band gaps. Vibration transmission characteristics of 20 × 20 meta-structures are also conducted. For the E-IAM system, ultra-low frequency vibration isolation can be achieved when the stiffness ratio of the connecting rod is the same in both vertical and horizontal directions and less than the main spring. The approximate analytical expression of the dispersion curve of the R-IAM system is given. Because the denominator is always greater than 1, it is proved that the cut-off frequency of the R-IAM system is always lower than that of the SGS. For finite R-IAM structures, when the longitudinal stiffness is asymmetric in both directions, multiple local resonant band gaps can be obtained in the passband, which is very beneficial to vibration reduction.

Cloud Droplet Nucleation Simulation and Parameterization

Abstract Cloud droplet nucleation is classically defined as a droplet growing to a size such that its ambient supersaturation exceeds its surface equilibrium water vapor pressure. Unactivated particles are always in equilibrium with the ambient vapor pressure. Further studies showed that such an equilibrium assumption leads to many more cloud droplets being nucleated due to neglecting kinetic growth limitations, including the inertial mechanism, evaporation mechanism, and deactivation mechanism. Moreover, the inertial mechanism results in great discrepancy between the actual size and the critical size of nucleation for large aerosol particles. These issues complicate cloud droplet nucleation parameterization for applications in cloud modeling. To establish a physically based nucleation scheme, we established a highly size-resolved Lagrangian parcel model. Vapor diffusion and heat conduction were calculated according to Maxwell theory, and the surface vapor density and temperature were explicitly simulated. The surface temperature variation of a droplet with its size was considered. The surface supersaturation of a droplet, taking into account the surface temperature variation, is different from its equilibrium supersaturation at its large sizes. The nucleation simulation showed that the inertial and deactivation mechanisms can impact droplet nucleation. Moreover, very large nuclei can trigger rain embryo formation in a short time period. Even though there are kinetic limitations, the classical equilibrium assumption can be applied to determine the primary nucleation number of cloud droplets. Meanwhile, a regression formula for the size of a nucleated droplet and its dry aerosol size was established.

Inertially amplified seismic metamaterial with an ultra-low-frequency bandgap

In last two decades, it has been theoretically and experimentally demonstrated that seismic metamaterials are capable of isolating seismic surface waves. Inertial amplification mechanisms with small mass have been proposed to design metamaterials to isolate elastic waves in rods, beams, and plates at low frequencies. In this Letter, we propose an alternative type of seismic metamaterial providing an ultra-low-frequency bandgap induced by inertial amplification. A unique kind of inertially amplified metamaterial is first conceived and designed. Its bandgap characteristics for flexural waves are then numerically and experimentally demonstrated. Finally, the embedded inertial amplification mechanism is introduced on a soil substrate to design a seismic metamaterial capable of strongly attenuating seismic surface waves around a frequency of 4 Hz. This work provides a promising alternative way to conceive seismic metamaterials to steer and control surface waves.

Influence of Jet on Aerosol Retention by Pool Scrubbing Under Multihole Injector

In severe nuclear power plant accidents, when the containment is in a serious challenging state, the gas mixture in the containment can be injected into the spent fuel pool through the multihole injector by the containment depressurization measure, to reduce the risk of containment overpressure failure and the release of radioactivity to the environment. The pool scrubbing efficiency of aerosol under the jet regime is studied on the small-scale aerosol pool scrubbing facility, focusing on the influence of mass flux, steam fraction, submergence, particle diameter, and pool initial temperature on the aerosol decontamination factor (DF). The results show that under the jet regime, the DF value is significantly greater than that in the bubble regime and the effect of jet flow on the mechanism of steam condensation and aerosol removal of the rising zone is weak under the conditions explored. DF increases with the increase of mass flux owing to the droplet interception and inertial collision aerosol removal mechanisms. Because the high pool temperature weakens the aerosol removal by steam condensation, DF decreases with the increase of initial pool temperature under the conditions explored. Based on the experimental data and the analysis of the removal mechanism under the jet regime, an empirical model of aerosol DF considering mass flux, steam fraction, pool temperature, submergence, and particle size is established and verified by the international experiments. The proposed model can be used to calculate DF in the process of containment overpressure discharge.