Inertial Effects Research Articles

Evaluation of the Inertial and Kinematic Interactions Effects on the Seismic Behavior of Single Piles Embedded in Sand Using Different Theoretical Approaches

Evaluation of the Inertial and Kinematic Interactions Effects on the Seismic Behavior of Single Piles Embedded in Sand Using Different Theoretical Approaches

Inertial and turbulent flow in hydro‐mechanically coupled KGD‐like fractures

AbstractFluid flow in deformable fractures is important to many applications including hydraulic stimulation. Fracture flow simulations typically rely on the Poiseuille flow model which presumes laminar quasi‐steady‐state flow conditions with negligible inertia. The high flow rates involved in industrial applications bring these assumptions into question. The GG22 flow model is a new method to capture inertial effects and turbulent flow phenomena with a moderate increase in computational complexity. Here we develop and verify the first hydro‐mechanically coupled finite element – finite volume model for fracture flow which uses the GG22 model. We use the model to examine fracture flow between oscillating elastic plates and show that inertia may elicit phase‐shifts in the fluid response, larger fluid pressures and rock mass stresses, and induce wave‐like behaviour even in a quasi‐static rock mass. We then apply the model to hydraulic stimulation of a cemented fracture in both the viscous and toughness dominant propagation regimes and examine the influence of inertia and turbulence compared to Poiseuille flow. We demonstrate that inertial effects due to the variation of aperture are negligible in two‐dimensional KGD‐like fractures with constant injection rates. If the flow rates are large enough to invoke turbulent flow behaviour, then significantly different fracture propagation behaviour is observed. The modelling established in this article will serve as the basis to examine the role of inertia and turbulence in axisymmetrical radial fractures and dynamic stimulation with pressure pulsing where we expect the role of inertia to be more significant.

In vitro acne disease model from inertial focusing effect for studying the interactions between sebocyte glands and macrophages.

Acne is one of the most widespread skin diseases. The acne mechanism is intricate, involving interactions between different types of cells (i.e., sebocytes and macrophages). One of the challenges in studying the mechanism of acne is that current in vitro culture methods cannot reflect the 3D cellular environment in the tissue, including inflammatory stimuli and cellular interactions especially the interactions between sebocytes and immune cells. To solve this issue, we generated an in vitro acne disease model consisting of 3D artificial sebocyte glands and macrophages through the inertial focusing effect method. Using this model, we produced a controllable inflammatory environment similar to the acne pathogenetic process in the skin. The 3D artificial sebocyte glands and macrophages can be separated for analyzing each cell type, assisting the in-depth understanding of the acne mechanism. This study indicates that proinflammatory macrophages promote lipid accumulation and induce oxidative stress in sebocyte glands. Additionally, in an inflammatory environment, sebocyte glands induce macrophage polarization into the M1 phenotype. Employing this model for drug screening, we also demonstrated that, cannabidiol (CBD), a clinically investigated drug, is effective in restoring lipid accumulation, oxidative stress, inflammatory cytokines and macrophage polarization in the acne disease.

Evaluation of the flow state and static performance of smooth annular liquid seals

The static fluid-induced force and stiffness coefficient of the smooth annular seal directly affect the rotor system stability. In this paper, a computational fluid dynamics method is applied to investigate the flow characteristics of a smooth annular seal for various eccentricities, discharge/supply pressures and rotational speeds under different flow conditions (laminar, transition, and turbulent flow). The influence factors and formation mechanism of the static instability in the smooth annular liquid seal are analyzed. Results show that laminar flow dominates the flow state at a rotational speed of ω= 2000 rpm. As the rotational speeds increase, the transition flow (2000-7000 rpm) gradually transits to the turbulent regime (ω> 7000 rpm). The direct static stiffness decreases first and then increases from laminar to transition flow state, and the viscosity effect is the dominant factor. For transition and turbulent flow with high eccentricities (ε= 80 %), the dominant viscous effect and inertial effect lead to the negative radial force and negative direct static stiffness coefficients. The smooth annular liquid seal shows best performance in the laminar flow and worst performance in the turbulent flow.

Simulation and Validation of Fluid Inertia Effects in External Gear Machines Using Lumped Parameter Modeling

Abstract Lumped parameter modeling is a consolidated technique for analyzing the fluid dynamic behavior of positive displacement machines, owing to their computational swiftness and the ease of integrating other physical domains affecting the operation of the machine. With some very limited exceptions, this modeling technique typically neglects fluid inertia and momentum effects. This paper proposes an approach to study the effects of fluid inertia affecting the pressurization and depressurization of the tooth space volumes of an external gear pump. The approach is based on considering the fluid inertia in the pressurization grooves and inside the control volumes with a peculiar subdivision. Further, frequency-dependent friction is also modeled to provide realistic damping of the fluid inside these channels. Validation of the model has been performed by comparing the lumped parameter model with a full three-dimensional Navier–Stokes solver. The quantities compared, such as tooth space volume pressures and outlet volumetric flow rate, show a good match between the two approaches for varying operating speeds. A comparison with the experiments supports the modeling approach as well. The paper finally, also discusses which operating conditions and geometries play a significant role that governs the necessity to model such fluid inertia effects in the first place.

SIMULATION OF FLOW AND HEAT EXCHANGE IN A HEAT ACCUMULATOR TANK

The article deals with the research of thermal energy storage tanks. It is proposed to use a «thermal core» to minimize the effects of thermal stratification and high thermal inertia. The thermal core consists of a binary tube placed along the central axis of the tank, filled with a paraffin mixture with a melting point of 45 to 65oC and a density of 0,880 to 0,915g/cm3 at 15oC. In the study the Fluent software package was used to model the temperature distribution in the tank under free convection conditions, the data was then converted to the Transient Thermal module of the ANSYS software package for further calculations of the unsteady temperature distribution in the thermal core. The study showed that a 1400-liter thermal energy storage device, heated for 1 hour by a heat-transfer fluid at 115oC, cools down to 50oC in 4 hours. The research also revealed the need to improve the tank design based on the analysis of the hydrodynamic structure of the flow in the tank, as evidenced by the trajectory distribution of free convective flows. The authors concluded that the use of a heat core, regardless of the type of paraffin used to form it, helps to reduce temperature stratification by height in the tank and that the type of paraffin used has no significant effect on the overall cooling of the tank. However, using ceresin as a core filler results in a slightly higher average tank temperature. Based on the results of the study, the time of complete cooling of the tank was determined by the non-uniform temperature field of all elements of the tank.

Engineering an extremely high flow rate micropump and integrating with an inertial microfluidics for rapid and efficient blood plasma extraction from fingertip blood with lancets

Extracting blood plasma is a necessary step for many medical diagnostics, and inertial microfluidics has attracted significant attention in separating plasma and blood cells from blood. However, external pump was mandatorily needed to generate sufficient flow rate and inertial effect to achieve the separation performance, which led to requirement of blood in mL scale due to the connectors and tubings from the external pump to the microfluidics. An integrated microfluidics was developed herein to rapidly extract blood plasma from only 4 μL whole blood drawn from fingertip with lancet, which included a highly efficient pneumatic peristaltic micropump (PPM) and a spiral inertial microfluidics with trapezoidal cross-sectional areas. Experiment results clearly demonstrated: (1) blood plasma can be rapidly extracted within 3 minutes with efficiency up to 97% from 45X diluted blood, (2) an extremely high flow rate of 3,500 μL/min was recorded with our triple PPM under applied pressure of 300 kPa and operation frequency of 10 Hz, which is competitive to the current commercial external syringe pump, (3) sufficient applied pressure is critical to the performance of PPM, because it can maintain the efficient stroke volume while minimizing the dead volume during iterative pumping process.

Particle dynamics in compressible turbulent vertical channel flows

In this work, we carry out direct numerical simulations of particle suspensions in the compressible turbulent vertical channel (TVC) flows with Mach number Ma = 1.5 and particle Stokes number St = 1–100. The compressibility effect is considered in the particle dynamic model for the first time in the study of compressible particle-laden wall turbulence. We find that in both incompressible and compressible flow, gravity weakens the wall-normal and spanwise fluctuations of particle velocities as the Stokes number increases. However, compared to the incompressible flow case, the compressible effect amplifies the mean velocity, fluctuations of velocity, and slip velocity of particle in the streamwise direction. The wall-normal and spanwise fluctuations of particle velocities are augmented by the compressible effect in the channel core region. Moreover, in the core region, the effect of fluid compressibility on the wall-normal and spanwise fluctuations of particle velocities attenuates as the Stokes number increases, indicating a competition between the compressible effect and the particle inertia effect. We, furthermore, conduct the quadrant analysis of the local fluctuation velocities of fluid at particle positions and observe preferential distributions in the second and the fourth quadrants at y+ = 12.5–13.5. For compressible TVC flows, the pattern of probability distributions is more elongated, and the percentage is slightly higher in the second and fourth quadrants than that of incompressible flows. This observation implies that more particles locate in the ejection and sweep events in compressible flows than that in incompressible flows, which is anticipated to influence the particle wall-normal transport.

An accurate solution method for the dynamic characteristics of three-layered partial-interaction composite beams

In the dynamic analysis of three-layered partial interaction composite beams (PICBs), it is not clear whether the effects of shear deformation and rotary inertia all need to be considered, and the shear-locking problems often occurs in existing finite element methods. To improve computational efficiency, accuracy and stability, an analytical method is proposed by considering the shear slips at the interface and the independent rotary angles among the sub-elements. In the proposed method, a matrix containing the natural frequencies of the three-layered PICB is appropriately established by using the solutions to differential equations of motion rather than the shape function in finite element methods. The main improvement of the proposed method is the analyticity of solutions, which can effectively avoid shear-locking problems often mentioned in finite element methods and obtain accurate solutions due to no introduction of approximate shape functions. The present results agree well with the analytical and numerical results in the literature, which validates the accuracy of the proposed method. The effects of shear deformation and rotary inertia on the dynamic behaviors of three-layered PICBs are discussed. It reveals that the shear deformation can not be ignored but rotary inertia can be ignored in the dynamic analysis of three-layered PICBs, which can effectively reduce the computation complexity. In general, the proposed method has practical value in natural frequency analysis of the three-layered PICB with high computational efficiency, accuracy and stability.

Topology optimization for infinite fatigue life of cyclic symmetric structures subjected to non-proportional loading

This paper presents a density based topology optimization method for infinite fatigue life constraints of non-proportional load cases, with a specific focus on parts with cyclic symmetry. Considering non-proportional loads in topology optimization significantly broadens the types of design problems that can be handled. The method estimates the local variation in Signed von Mises stress using a smooth min/max function and constrains the resulting stress amplitude using established stress based topology optimization methods. Accounting for non-proportionality of loading significantly increases the computation cost with respect to existing proportional methods, as the time-varying stress field needs to be computed. Inertia effects are neglected in the structural analysis. Therefore, a quasi-static analysis is used to obtain the stress history. To reduce the computational cost, advantage is taken of cyclic symmetric properties to reduce the number of necessary time steps to evaluate. This reduces the computational cost roughly proportional to the number of unique load time steps present in the repeated segments as opposed to a standard implementation. The method is tested on numerical examples in 2D and 3D for both proportional and non-proportional loads and was found to be locally accurate up to the accuracy of the constraint aggregation.

Reduced Order Modeling of Dynamic Mechanical Metamaterials for Analysis of Infinite and Finite Systems

Abstract Dynamic mechanical metamaterials (MMs) are artificial media composed of periodic micro-structures, designed to manipulate wave propagation. Modeling and designing MMs can be computationally demanding due to the broad design space spanned by the geometric and material parameters. This work aims to develop a generalized reduced order modeling approach for determining MM dynamics in low frequency ranges with accuracy and speed, using a limited number of parameters and small matrices. The MM unit cells are treated as assemblies of structural elements with discrete degrees-of-freedom, whose effective stiffness and inertia are determined by optimizing energy criteria based on continuum results derived from a small number of eigen-study simulations. This proposed approach offers a parameterized and discretized representation of MM systems, which leads to fast and accurate computation of eigen-study results for periodic arrays, as well as dynamic responses in time domain for finite-sized arrays. The high computational efficiency and physical accuracy of this method will help streamline the modeling process and aid in design discovery and optimization, especially in combination with machine learning and data-driven techniques.

Virtual Synchronous Generator (VSG) Control Strategy Based on Improved Damping and Angular Frequency Deviation Feedforward

The output active power of a grid-connected inverter controlled by a traditional virtual synchronous generator (VSG) has the problems of oscillation and steady-state errors. A VSG control strategy based on improved damping and angular frequency deviation feedforward is proposed. This strategy reduces the steady-state error of active power by adding a transient damping link to a traditional VSG damping feedback channel. At the same time, the angular frequency deviation feedforward compensation is used to improve the response speed of the VSG to the active power instruction and reduce the active power overshoot in the dynamic process. First, the VSG active power closed-loop small-signal model is established. The effects of inertia and damping on the dynamic and steady-state performance of the VSG are analyzed by the root locus method. The effect of the proposed control strategy on the system is analyzed by using a closed-loop zero-pole diagram. This strategy improves the precision of active power control the dynamic performance of the system effectively. Finally, the effectiveness and superiority of the proposed control strategy are verified by Matlab/Simulink simulation and semi-physical simulation platform RT-LAB.

Effects of Kerr-type viscoelastic coupling layer with different stiffnesses on stochastic stability of Rayleigh double beams

This paper discusses the stochastic stability of a double Rayleigh beam system connected by a Kerr-type three-parameter elastic layer with two different stiffnesses, under compressive axial loads. The beams are modeled using the Rayleigh beam theory, and the axial forces consist of a constant component and a time-dependent stochastic function. The study investigates the almost-sure and moment stability of the double beam system subjected to stochastic compressive axial loading, utilizing the Lyapunov exponent and moment Lyapunov exponents. In the case of weak noise excitations, a singular perturbation method is employed to derive second-order expansions of the moment Lyapunov exponent and the Lyapunov exponent. Monte Carlo simulation is included to validate the obtained results. A numerical study is conducted for selected parameters, and the almost-sure and moment stability in the first and second perturbation are graphically presented. The results provide insights into the influences of different stiffnesses, damping, and the shear parameter of the Kerr-type layer on the stochastic stability of the coupled Rayleigh beam mechanical system, considering the effects of rotational inertia. It is quantitatively and qualitatively determined that reducing the stiffness of one part of the Kerr-type layer leads to a decrease in the stable region of stochastic stability, while reducing the shear parameter results in an increase in the stable region of stochastic stability. Furthermore, a quantitative relationship between different dampings of the Kerr-type viscoelastic layer is determined, where increasing either of the two damping parameters leads to an expansion of the stable region of stochastic stability. The inclusion of rotational inertia effects through the Rayleigh beam theory contributes to more accurate approximations of the obtained solutions.

Investigation of the rate-mediated form-function relationship in biological puncture

Puncture is a vital mechanism for survival in a wide range of organisms across phyla, serving biological functions such as prey capture, defense, and reproduction. Understanding how the shape of the puncture tool affects its functional performance is crucial to uncovering the mechanics underlying the diversity and evolution of puncture-based systems. However, such form-function relationships are often complicated by the dynamic nature of living systems. Puncture systems in particular operate over a wide range of speeds to penetrate biological tissues. Current studies on puncture biomechanics lack systematic characterization of the complex, rate-mediated, interaction between tool and material across this dynamic range. To fill this knowledge gap, we establish a highly controlled experimental framework for dynamic puncture to investigate the relationship between the puncture performance (characterized by the depth of puncture) and the tool sharpness (characterized by the cusp angle) across a wide range of bio-relevant puncture speeds (from quasi-static to sim 50 m/s). Our results show that the sensitivity of puncture performance to variations in tool sharpness reduces at higher puncture speeds. This trend is likely due to rate-based viscoelastic and inertial effects arising from how materials respond to dynamic loads. The rate-dependent form-function relationship has important biological implications: While passive/low-speed puncture organisms likely rely heavily on sharp puncture tools to successfully penetrate and maintain functionalities, higher-speed puncture systems may allow for greater variability in puncture tool shape due to the relatively geometric-insensitive puncture performance, allowing for higher adaptability during the evolutionary process to other mechanical factors.

Computational investigation on the non-isothermal phase change during cavitation bubble pulsations

During cavitation bubble pulsations, a phase change intensively occurs near the collapsing moment due to high pressure and temperature inside bubbles, accompanying distinctive flow features: the rate of evaporation and condensation significantly changes according to the phase change regime. To account for this non-isothermal effect, the high-fidelity computational framework incorporating the physics-based cavitation model and a new fluid property model based on artificial neural network is proposed. The key finding of this study is the interplay between the thermal and inertial effects during multiple pulsations. At the early stages of bubble contraction, the phase change is primarily driven by fluid inertia. However, as the bubble continues to compress, the thermal effect becomes dominant and controls the entire phase change region at each moment of collapse. It is observed that the isothermal model relying on the inertial bubble growth rate only, does not capture this transition of dominance and eventually fails to predict multiple pulsations. The physics-based cavitation model successfully captures the bubble pulsation beyond the second collapse. These findings highlight that explicit consideration of the non-isothermal effect is essential for problems with varying phase change regimes, and a phase change model reflecting this effect is vital for accurate computations.

Quasilinear theory of Brillouin resonances in rotating magnetized plasmas

Both spin and orbital angular momentum can be exchanged between a rotating wave and a rotating magnetized plasma. Through resonances the spin and orbital angular momentum of the wave can be coupled to both the cyclotron rotation and the drift rotation of the particles. It is, however, shown that the Landau and cyclotron resonance conditions which classically describe resonant energy–momentum exchange between waves and particles are no longer valid in a rotating magnetized plasma column. In this case a new resonance condition which involves a resonant matching between the wave frequency, the cyclotron frequency modified by inertial effects and the harmonics of the guiding centre rotation is identified. A new quasilinear equation describing orbital and spin angular momentum exchanges through these new Brillouin resonances is then derived, and used to expose the wave-driven radial current responsible for angular momentum absorption.

Heat Transfer and Performance Enhancement of Porous Split Elliptical Fins

To augment the heat transfer phenomenon, the infusion of various fin geometry over the heated plate is being investigated by various researchers. Solid fins of the porous medium can enhance the convective heat transfer, providing a higher surface area-to-volume ratio for heat transfer. In this work, the fluid flow pattern and thermodynamic analysis of porous-based split elliptical fins mounted staggered over a heated base plate is numerically studied with the Reynolds numbers in the range of 783 to 1839, which is dependent on the fin dimension. The variable parameters were dimensionless transverse offset ( TO ∗ = transverse offset / diameter ), which varied from 0 to 0.5; dimensionless longitudinal offset ( L O ∗ = longitudinal offset / diameter ), which varied from 0 to 0.25; porosity (ɸ), which varies from 0.8 to 0.92; pores per inch (PPI), which was 10; permeability ( P n ); and inertial parameter ( F ). To count the viscous and inertial effect inside the porous zone, the Forchheimer–Brinkman extended Darcy model was adopted. The associated parameters, the Nusselt number (Nu), frictional coefficient ( C f ), and performance evaluation criteria (PEC), are thoroughly analyzed over the TO ∗ and LO ∗ combination. The results of the investigation revealed that the highest value of Nu and PEC was obtained by TO ∗ = 0.5 and L O ∗ = 0 at ɸ = 0.92 , which were approximately 54% and 79% higher than the solid circular fin at Re = 1839 . Additionally, a response function based on Nu was obtained using the response surface method, and cuckoo optimization was assessed to identify the optimal Nu. The optimal Nu is established at TO ∗ = 0.4141 and L O ∗ = 0 ( ɸ = 0.92 and Re = 1839 ) and was validated with the present investigation with an accuracy of 1.20%.

Nonlinear dynamics of an artificial muscle with elastomer–electrode inertia: Modelling and analysis

Artificial muscles are dielectric elastomeric system that mimic the response of the natural muscle and are helpful in many bio-mimicking applications. The existing literature is based on the assumption that electrodes are compliant and are focused on materials with greater extensibility than biological matter. The present work deals with the modelling and nonlinear dynamic analysis of dielectric elastomers considering the elastomer–electrode inertia and damping effect for bio-mimicking. The distinguishing point of the proposed work is the appearance of terms related to the elastomer–electrode inertia effect in the governing equation. Further, the biological muscle’s nonlinear elastic behaviour is incorporated using the Fung material model. Equilibrium stretch variation with parameter exhibits cusp catastrophe. The effect of electrode inertia on the equilibria is examined. Single-well and double-well potential energy characteristics are obtained for constant voltage. The basin of attraction illustrates the sensitiveness of system dynamics on the initial state and damping. The system response, when subjected to time-varying voltage, is explored. Multi-frequency response exists due to harmonic, sub-harmonic, and super-harmonic resonance condition. The resonant frequency variation with geometry and inertia is presented. Time-varying voltage may lead to chaotic behaviour illustrated through the bifurcation diagram. The presence of a strange attractor and positive Lyapunov exponent in the chaotic region further justify the existence of chaos. Additionally, chaotic behaviour is obtained in the case of single-well and double-well potential. Also, the existence of similar attractors with same fractal dimension is shown. The inertia effect significantly changes the dynamic characteristic from chaotic to non-chaotic or vice-versa. The mechanical and electrical load may lead to chaotic or non-chaotic behaviour depending on the geometry of the elastomer. The chaotic region’s dependence on the damping value is also obtained. Our results show that electrode inertia significantly impacts the elastomer under quasi-static and dynamic conditions. The proposed work gives a foundation for precisely designing artificial muscle for practical applications like soft robotics, artificial arms, and different prosthetic implants.

Rapid Screening of Urinary Tract Infection Using Microfluidic Inertial-Impedance Cytometry.

Urinary tract infection (UTI) diagnosis based on urine culture for bacteriuria analysis is time-consuming and often leads to wastage of hospital resources due to false-positive UTI cases. Direct cellular phenotyping (e.g., RBCs, neutrophils, epithelial cells) of urine samples remains a technical challenge as low cell concentrations, and urine characteristics (conductivities, pH, microbes) can affect the accuracy of cell measurements. In this work, we report a microfluidic inertial-impedance cytometry technique for label-free rapid (<5 min) neutrophil sorting and impedance profiling from urine directly. Based on size-based inertial focusing effects, neutrophils are isolated, concentrated, and resuspended in saline (buffer exchange) to improve consistency in impedance-based single-cell analysis. We first observed that both urine pH and the presence of bacteria can affect neutrophil high-frequency impedance measurements possibly due to changes in nucleus morphology as neutrophils undergo NETosis and phagocytosis, respectively. As a proof-of-concept for clinical testing, we report for the first time, rapid UTI testing based on multiparametric impedance profiling of putative neutrophils (electrical size, membrane properties, and distribution) in urine samples from non-UTI (n = 20) and UTI patients (n = 20). A significant increase in cell count was observed in UTI samples, and biophysical parameters were used to develop a UTI classifier with an area under the receiver operating characteristic curve of 0.84. Overall, the developed platform facilitates rapid culture-free urine screening which can be further developed to assess disease severity in UTI and other urologic diseases based on neutrophil electrical signatures.

Role of Droplet Dynamics on Contact Line Depinning in Shearing Gas Flow.

Sessile droplets exposed to shearing gas flows resist depinning owing to surface tension and contact angle hysteresis. It is known that contact line depinning occurs when the shearing gas flow is large enough to deform the droplet beyond its contact angle hysteresis. This work explores the contact line depinning process by visualizing growing droplets on a porous layer in laminar shear gas flows. High-speed imaging of droplets revealed an oscillatory motion in droplets, which is speculated to originate from an interaction between the drag force and surface tension effects. This oscillatory motion creates an inertial force within the droplet which combines with the drag force when droplet acceleration is in the stream-wise direction. The combined effect competes against the droplet adhesion force, setting the depinning criteria. Analyzing droplet images revealed that droplet local velocity and acceleration (i.e., sessile droplet dynamics prior to detachment from the substrate) increase with the superficial gas velocity. At the same time, the contact line depinning occurs at a smaller droplet size for higher superficial gas velocities. This results in a "hill-like" variation of the inertial force as a function of the convective Weber number, Weconv, causing a local maximum in the inertial force data (Weconv scales the inertia effects of the shear flow to surface tension effects). For the experimental condition tested in the current study, the inertial force created in the droplet could reach up to half of the adhesion force, making the drag force only responsible for the other half to depin the droplet contact line. Even at low superficial gas velocities, which featured lower droplet oscillations, the inertial force created in the droplet was considerable with respect to the adhesion force, reaching around one-third of the adhesion force.