Solid Stress Research Articles

Numerical investigation of Bi-model slurry transportation in a straight pipe

Slurry transportation through a pipeline system is a conventional mode of conveying solid material, which several industries have adopted across the globe. However, this mode of transportation is a complex phenomenon that requires high suspension stability of the particulates and high-energy requirements to deliver the solid materials continuously. Further, the researchers have adopted various techniques to make the continuous flow of solid materials through pipeline systems, such as additive addition and increasing the percentage of fine particles in the mixture. However, the accurate bi-model for the transportation of solid materials is not yet established. Therefore, in the present work, different mixture ratios (65:35, 75:25, 85:15 and 95:05) of silica sand and fly ash are considered to investigate the slurry flow characteristics. A numerical investigation is carried out for a bi-model slurry flow of silica sand (2650 kg/m3) and fly ash (2100 kg/m3) particulates having a mean diameter of 450 and 75 μm through a horizontal pipeline of 0.0549 m diameter. The accuracy of the numerical model and the procedure adopted for the current simulation is also validated by the available results in the literature. The work's outcomes reveal a significant drop in pressure with the increase in the percentage of fly ash in silica sand slurry. Further, the contours of the solid concentration, velocity distribution, granular pressure, granular temperature and wall shear stress are also envisaged and discussed in detail to analyze the effects of fly ash in silica sand slurry. Furthermore, Specific energy consumption is also calculated from the empirical relation for the different silica sand and fly ash ratios. The calculations show that the slurry mixture of 35% of fly ash in 65% of silica sand requires the least energy for transportation.

A Review of the Continuum Theory-Based Stress and Drag Models in Gas-Solid Flows

The continuum theory-based models, which include solid stress models and gas-solid drag models, are required for the modeling of gas-solid flows in the framework of the Eulerian–Eulerian method. The interactions among particles are characterized by their diverse behaviors at different flow regimes, including kinetic motion, particle–particle collision and enduring friction. It is difficult to describe the particle behaviors at various regimes by mathematical methods accurately. Therefore, it is very important to develop proper solid stress models that can capture the inherent characteristics of the flow behaviors. In addition, the gas-solid fluidization system is a typical heterogeneous system, which exhibits locally inhomogeneous structures such as bubbles or particle clusters with different shapes and sizes. Due to these inhomogeneous characteristics, the gas-solid drag model has become one of the key challenges in the simulation of gas-solid flows. Various forms of constitutive relations for solid stress models and gas-solid drag models have been reported in the literature. In this paper, we reviewed the solid stress models crossing various flow regimes and drag models in both micro- and mesoscales, which provide a useful reference for model selection in simulating gas-solid flows.

Acoustic speech features in social comparison: how stress impacts the way you sound

The use of speech as a digital biomarker to detect stress levels is increasingly gaining attention. Yet, heterogeneous effects of stress on specific acoustic speech features have been observed, possibly due to previous studies’ use of different stress labels/categories and the lack of solid stress induction paradigms or validation of experienced stress. Here, we deployed a controlled, within-subject psychosocial stress induction experiment in which participants received both neutral (control condition) and negative (negative condition) comparative feedback after solving a challenging cognitive task. This study is the first to use a (non-actor) within-participant design that verifies a successful stress induction using both self-report (i.e., decreased reported valence) and physiological measures (i.e., increased heart rate acceleration using event-related cardiac responses during feedback exposure). Analyses of acoustic speech features showed a significant increase in Fundamental Frequency (F0) and Harmonics-to-Noise Ratio (HNR), and a significant decrease in shimmer during the negative feedback condition. Our results using read-out-loud speech comply with earlier research, yet we are the first to validate these results in a well-controlled but ecologically-valid setting to guarantee the generalization of our findings to real-life settings. Further research should aim to replicate these results in a free speech setting to test the robustness of our findings for real-world settings and should include semantics to also take into account what you say and not only how you say it.

Effect of mesoscale structures on solid phase stress in gas–solid flows

Solid phase stress plays an important role in hydrodynamic modeling and simulations of gas–solid flows. However, heterogeneous gas–solid flows are typically regarded as homogeneous systems. Their solid phase stresses are usually calculated by the classical kinetic theory of granular flow (KTGF) without considering mesoscale structures, which is a major source of inaccuracies. This work investigates the effect of mesoscale structures in gas–solid flows via a dilute-dense two-phase partition, and proposes a phase-specific model to predict solid phase stress. Subsequently, the sensitive of threshold for phase partition is discussed, and a specific threshold is utilized in the proposed model to investigate the effect of mesoscale structures on solid phase stress with large-scale particle-resolved direct numerical simulation (PR-DNS) data. Numerical results show that classical KTGF underestimates the solid phase stress due to the ignorance of these structures.

A unified numerical model for two-phase porous, mush and suspension flow dynamics in magmatic systems

SUMMARYMagmatic systems in the Earth’s mantle and crust contain multiple phases including solid crystals, liquid melt and low viscosity fluids. Depending on depth, tectonic setting and chemical composition, magmatic systems can range from partially molten rock at low melt fraction to magma mushes at intermediate melt fraction to magmatic suspensions at high melt fraction. However, the theories underpinning most process-based models of magmatic systems describe magma as a single-phase fluid, or as a two-phase mixture either in the porous flow regime at low melt fractions or in the suspension flow regime at high melt fractions. Connections between the two-phase end-member theories are poorly established and hinder investigations into the dynamics of mush flows at intermediate phase fractions, leaving a significant gap in bridging trans-crustal magma processing from source to surface. To address this knowledge gap and unify two-phase magma flow models, we develop a 2-D system-scale numerical model of the fluid mechanics of an n-phase system at all phase proportions, based on a recent theoretical model for multiphase flows in igneous systems. We apply the model to two-phase, solid-liquid mixtures by calibrating transport coefficients to theory and experiments on mixtures with olivine-rich rock and basaltic melt using a Bayesian parameter estimation approach. We verify the model using the method of manufactured solutions and test the scalability for high resolution modelling. We then demonstrate 1-D and 2-D numerical experiments across the porous, mush and suspension flow regimes. The experiments replicate known phenomena from end-member regimes, including rank-ordered porosity wave trains in 1-D and porosity wave breakup in 2-D in the porous flow regime, as well as particle concentration waves in 1-D and mixture convection in 2-D in the suspension flow regime. By extending self-consistently into the mush regime, the numerical experiments show that the weakening solid matrix facilitates liquid localization into liquid-rich shear bands with their orientation controlled by the solid stress distribution. Although the present model can already be used to investigate three-phase mixtures using conceptually derived transport coefficients, more rigorous calibration to experiments and end-member theories is needed to ensure accurate timescales and mechanics. With a self-consistent way to examine multiphase mixtures at any phase proportion, this new model transcends theoretical limitations of existing multiphase numerical models to enable new investigations into two-phase or higher magma mush dynamics.

Microdevice-based mechanical compression on living cells.

Compressive stress enables the investigation of a range of cellular processes in which forces play an important role, such as cell growth, differentiation, migration, and invasion. Such solid stress can be introduced externally to study cell response and to mechanically induce changes in cell morphology and behavior by static or dynamic compression. Microfluidics is a useful tool for this, allowing one to mimic invivo microenvironments in on-chip culture systems where force application can be controlled spatially and temporally. Here, we review the mechanical compression applications on cells with a broad focus on studies using microtechnologies and microdevices to apply cell compression, in comparison to off-chip bulk systems. Due to their unique features, microfluidic systems developed to apply compressive forces on single cells, in 2D and 3D culture models, and compression in cancer microenvironments are emphasized. Research efforts in this field can help the development of mechanoceuticals in the future.

Do Tumor Mechanical Stresses Promote Cancer Immune Escape?

Immune evasion-a well-established cancer hallmark-is a major barrier to immunotherapy efficacy. While the molecular mechanisms and biological consequences underpinning immune evasion are largely known, the role of tissue mechanical stresses in these processes warrants further investigation. The tumor microenvironment (TME) features physical abnormalities (notably, increased fluid and solid pressures applied both inside and outside the TME) that drive cancer mechanopathologies. Strikingly, in response to these mechanical stresses, cancer cells upregulate canonical immune evasion mechanisms, including epithelial-mesenchymal transition (EMT) and autophagy. Consideration and characterization of the origins and consequences of tumor mechanical stresses in the TME may yield novel strategies to combat immunotherapy resistance. In this Perspective, we posit that tumor mechanical stresses-namely fluid shear and solid stresses-induce immune evasion by upregulating EMT and autophagy. In addition to exploring the basis for our hypothesis, we also identify explicit gaps in the field that need to be addressed in order to directly demonstrate the existence and importance of this biophysical relationship. Finally, we propose that reducing or neutralizing fluid shear stress and solid stress-induced cancer immune escape may improve immunotherapy outcomes.

Comprehensive study on degradation profile of firocoxib and structural elucidation of its key degradation products

Firocoxib is widely used in veterinary medicine as a non-steroidal analgesic and anti-inflammatory drug substance. Herein, a comprehensive study on the degradation profile of firocoxib was performed through force degradation studies to understand its degradation profile and characterize its major degradation products (DPs). Firocoxib drug substance was subjected to acidic, alkaline, oxidation (H2O2, KMnO4, and K2Cr2O7), thermal (solid and solution state), and photolytic (solid and solution state) stress degradation, as recommended in the ICH guidelines. Firocoxib and its major DPs were adequately separated by investigational HPLC method, which utilized a HALO C18 (100 × 2.1 mm, 2.0 µm) column. Mobile phase-A for the HPLC method is composed of 0.1% formic acid in water and mobile phase-B acetonitrile. A total of six major DPs were observed for firocoxib drug substance under these stress degradation conditions. Structural elucidation of the DPs performed using liquid chromatography-high resolution mass spectrometry and comparison of their fragmentation profile with that of the parent compound. For further structural confirmation of two major DPs, DP-2 and DP-6 were isolated and purified from the stressed samples using a preparative HPLC and analyzed by comprehensive nuclear magnetic resonance (NMR) spectroscopy studies. Most probable mechanistic pathways for the formation of DPs of firocoxib under various stress degradation conditions were postulated to understand its degradation profile. Based on the results from forced degradation, firocoxib was found to be quite stable under basic and thermal conditions, and somewhat unstable under acidic, oxidative, and photolytic conditions. The results of this study should facilitate quality monitoring and establish a stability profile of firocoxib drug substance and drug products. These results may also assist in the design and development of new formulations made with firocoxib drug substance with desired shelf life.

NIMG-108. PHYSICAL STRESSES IN BRAIN TUMORS

Abstract Solid stress, distinct from fluid pressure, is a physical force contained in and transmitted by solid components of the brain tumor, including cells and the matrix they produce. Solid stress has been shown to promote tumor progression, and decrease anticancer therapy efficacy. This is especially relevant in brain tumors, as the rigid skull results in these trapped forces, increasing intracranial pressure, and potentially leading to other complications, including neuronal cell death. Here we present a novel method of quantifying these physical stresses in situ in both mice (glioblastoma [U87], brain metastasis [BT474], and ependymoma models) and patients. Briefly, following a craniotomy, mechanical forces that include solid stress are released, which causes the tissue to deform in peaks (areas under compression) and valleys (areas originally under tension). This tissue deformation is imaged via high-resolution ultrasound and analysed via custom MATLAB code to produce an accurate 3D model of the entire mouse brain, including the tumour region. For human samples, a pre-operative MRI is used to generate a detailed 3D model of the human brain. During surgery, the trapped physical stresses results in a bulge of the dura post craniotomy. We use BrainLab to measure the craniotomy induced brain deformation, which is then registered to the pre-operation MRI before being analysed in an identical fashion to the murine models using SolidWorks and Abaqus. We further show that in the brain metastases model, chemotherapy reduces compression stresses by 51%. Further, our technique results in fast processing time (~ 15 minutes), and has the potential to prevent the need for intraoperative MRI based on position simulations. As such, solid stress measurements provide a new class of mechanical biomarkers that can be correlated to clinical outcomes for predictive and prognostic value.

Targeting Tumor Physical Microenvironment for Improved Radiotherapy (Small Methods 11/2022)

Inside Back Cover In article number 2200570, Ma, Xu, and co-workers highlight the biophysical cue, a new hallmark of cancer, serving as a significant factor in tumor microenvironment forming a physical microenvironment, including extracellular matrix microarchitecture, stiffness, interstitial fluid pressure, and solid stress. It plays an essential role in affecting radiotherapy efficacy. Meanwhile, radiotherapy also affects tumor physical microenvironment, leading to different cancer cell behaviors. Targeting tumor physical microenvironment may greatly improve radiosensitivity.

Fluid-structure interaction analysis of eccentricity and leaflet rigidity on thrombosis biomarkers in bioprosthetic aortic valve replacements.

This work intends to study the effect of aortic annulus eccentricity and leaflet rigidity on the performance, thrombogenic risk and calcification risk in bioprosthetic aortic valve replacements (BAVRs). To address these questions, a two-way immersed fluid-structure interaction (FSI) computational model was implemented in a high-performance computing (HPC) multi-physics simulation software, and validated against a well-known FSI benchmark. The aortic valve bioprosthesis model is qualitatively contrasted against experimental data, showing good agreement in closed and open states. Regarding the performance of BAVRs, the model predicts that increasing eccentricities yield lower geometric orifice areas (GOAs) and higher normalized transvalvular pressure gradients (TPGs) for healthy cardiac outputs during systole, agreeing with in vitro experiments. Regions with peak values of residence time are observed to grow with eccentricity in the sinus of Valsalva, indicating an elevated risk of thrombus formation for eccentric configurations. In addition, the computational model is used to analyze the effect of varying leaflet rigidity on both performance, thrombogenic and calcification risks with applications to tissue-engineered prostheses. For more rigid leaflets it predicts an increase in systolic and diastolic TPGs, and decrease in systolic GOA, which translates to decreased valve performance. The peak shear rate and residence time regions increase with leaflet rigidity, but their volume-averaged values were not significantly affected. Peak solid stresses are also analyzed, and observed to increase with rigidity, elevating risk of valve calcification and structural failure. To the authors' knowledge this is the first computational FSI model to study the effect of eccentricity or leaflet rigidity on thrombogenic biomarkers, providing a novel tool to aid device manufacturers and clinical practitioners.

Homogenization of discrete mesoscale model of concrete for coupled mass transport and mechanics by asymptotic expansion

Mass transport phenomenon in concrete structures is strongly coupled with their mechanical behavior. The first coupling fabric is the Biot's theory according to which fluid pressure interacts with solid stress state and volumetric deformation rate of the solid induces changes in fluid pressure. Another coupling mechanism emerges with cracks which serve as channels for the fluid to flow through them and provide volume for fluid storage. Especially the second coupling mechanism presents a challenge for numerical modeling as it requires detailed knowledge about cracking process. Discrete mesoscale mechanical models coupled with mass transport offer simple and robust way to solve the problem. On the other hand, however, they are computationally demanding. In order to reduce this computational burden, the present paper applies the asymptotic expansion homogenization technique to the coupled problem to deliver (i) continuous and homogeneous description of the macroscopic problem which can be easily solved by the finite element method, (ii) discrete and heterogeneous mesoscale problem in the periodic setup attached to each integration point of the macroscale along with (iii) equations providing communication between these two scales. The transient terms appear at the macroscale only, as well as the Biot's coupling terms. The coupling through cracking is treated at the mesoscale by changing conductivity of the conduit elements according to the mechanical solution, otherwise the two mesoscale steady state problems are decoupled and can be therefore solved in a sequence. This paper presents verification studies showing performance of the homogenized solution.

Microarchitectural mimicking of stroma-induced vasculature compression in pancreatic tumors using a 3D engineered model.

Fibrotic tumors, such as pancreatic ductal adenocarcinoma (PDAC), are characterized for high desmoplastic reaction, which results in high intra-tumoral solid stress leading to the compression of blood vessels. These microarchitectural alterations cause loss of blood flow and poor intra-tumoral delivery of therapeutics. Currently, there is a lack of relevant in vitro models capable of replicating these mechanical characteristics and to test anti-desmoplastic compounds. Here, a multi-layered vascularized 3D PDAC model consisting of primary human pancreatic stellate cells (PSCs) embedded in collagen/fibrinogen (Col/Fib), mimicking tumor tissue within adjunct healthy tissue, is presented to study the fibrosis-induced compression of vasculature in PDAC. It is demonstrated how the mechanical and biological stimulation induce PSC activation, extracellular matrix production and eventually vessel compression. The clinical relevance is confirmed by correlating with patient transcriptomic data. Furthermore, the effects of gradual vessel compression on the fluid dynamics occurring within the channel is evaluated in silico. Finally, it is demonstrated how cancer-associated fibroblast (CAF)-modulatory therapeutics can inhibit the cell-mediated compression of blood vessels in PDAC in vitro, in silico and in vivo. It is envisioned that this 3D model is used to improve the understanding of mechanical characteristics in tumors and for evaluating novel anti-desmoplastic therapeutics.

An inertial number regulated stress model for gas-particle flows with particle friction and volume fraction gradient

In this study, a solid stress model that can be used in both dilute and dense regimes for simulation of gas-particle flows with comprehensive considerations of friction and the effect of local solid volume fraction gradient is proposed. In the dilute regime, solid stress is closed by a modified kinetic theory that accounts for the effect of particle friction and volume fraction gradient. In the dense regime, solid stress is closed by the inertial number model. The transition from dilute to dense regimes is realized by using a dimensionless parameter χ , which is a function of the inertial number I s . This new model is validated with experimental data and discrete particle simulation from spout-fluid bed and bubbling fluidized bed. When compared with the traditional kinetic-frictional stress model, this new model improves the transition from dilute to dense regimes and the particle velocity predictions in both beds. • A solid stress model is proposed in both dilute and dense regimes for gas-solid flow. • The model comprehensively considers the effect of friction and volume fraction gradient. • The expression of excluded volume is derived from the generalized van der Waals theory. • The model gives a better prediction of spout-fluid bed and bubbling fluidized bed.

Assessment of kinetic theory for gas–solid flows using discrete particle method

Kinetic theory is a common choice for closing the solid phase stress in the continuum theory for dilute and moderate dense gas–solid flows. In this article, methods are proposed for postprocessing the data obtained from discrete particle simulations, and the results are then used to critically assess the fundamental assumptions of kinetic theory. It is shown that (i) the fundamental assumptions and predictions of kinetic theory are, respectively, valid and accurate in homogeneous granular flows, as expected. Those results prove that the methods for data postprocessing are effective; (ii) in the case of nonequilibrium and heterogeneous gas–solid flows, nearly all fundamental assumptions get challenged, and the predictions of kinetic theory, in terms of collision frequency and particle pressure, deviate significantly from the statistical results of discrete particle simulation. Therefore, the standard kinetic theory is insufficient to provide the constitutive laws for continuum modeling of heterogeneous gas–solid flows.

Magnetic resonance elastography of malignant tumors

Cancer biomechanical properties, including high stiffness, solid stress, and interstitial pressure, as well as altered micro-architecture, are drivers of tumorigenesis, invasiveness and resistance to treatment. Magnetic resonance elastography is an emergent non-invasive imaging method to assess the tumor mechanical properties in a spatially resolved fashion. Several MRE acquisition and reconstruction methods have been developed to assess tumors and surrounding tissues. It is increasingly recognized that the visco-elastic properties assessed with MRE are useful for characterizing malignant tumors and evaluating treatment response in various organs. Generally, malignant tumors, except brain tumors, have high stiffness and high visco-elastic ratio or fluidity. MRE transducers, acquisition sequences and reconstruction algorithms are continuously improved to increase depth penetration and spatial resolution, and limit artifacts at spatial discontinuities. Moreover, assessment of compression stiffening might provide new biomarkers of the altered physical traits of cancer. Increasing research and clinical validation will improve the efficacy of MRE for cancer characterization.

Applying the new experimental midpoint concept on strain energy density for fracture assessment of composite materials

A mixed-mode I/II fracture criterion for predicting the fracture response of composite materials is proposed. This criterion is derived based on a comprehensive study and the consideration of the physics of fracture onset. The fracture phenomenon that causes the various damage mechanisms at the vicinity of the crack tip is examined. It is elucidated that the stress distribution at the crack tip ought to be defined using the reinforcement isotropic solid (RIS) stress state. This new criterion, which is called Improved Strain Energy Density with Mid-point (ISEDM), includes the effect of the fracture process zone (FPZ) and T-stress, which remarkably affect the mixed-mode fracture process, particularly, when mode II is dominant. Substituting the strain energy density in a pure mode I with the strain energy density in the midpoint of mixed-mode I/II is the creative idea employed in proposing this criterion. Because in pure mode I the effects of FPZ are minimal, change of fitting point on fracture limit curve (FLC) from KIc to midpoint critical stress intensity factors (CSIF’s) makes it possible to consider the effects of FPZ more accurately. In the ISEDM criterion, fracture behavior depends on mechanical properties and CSIF’s of the midpoint. Crack initiation angle is considered along minimum strain energy density and this angle is derived in the midpoint of mixed-mode I/II. RIS theory is used as an applicable theory for modeling orthotropic materials in this paper and causes valid and reliable fracture behavior to be extracted. In addition, changing fracture point from pure mode I to the mid-point of experimental data causes the effects of FPZ to be considered without estimating the toughening mechanisms in this zone, and the fracture behavior is extracted with higher accuracy. FLC’s in comparison with available experimental data prove that the ISEDM criterion anticipates the fracture behavior of orthotropic materials well. Finding KIIc based on the analytical method is a valuable achievement. In this article, KIIc can be predicted with appropriate accuracy, only by CSIF’s of mid-point and using ISEDM criterion.

Coupling solid and fluid stresses with brain tumour growth and white matter tract deformations in a neuroimaging-informed model

Brain tumours are among the deadliest types of cancer, since they display a strong ability to invade the surrounding tissues and an extensive resistance to common therapeutic treatments. It is therefore important to reproduce the heterogeneity of brain microstructure through mathematical and computational models, that can provide powerful instruments to investigate cancer progression. However, only a few models include a proper mechanical and constitutive description of brain tissue, which instead may be relevant to predict the progression of the pathology and to analyse the reorganization of healthy tissues occurring during tumour growth and, possibly, after surgical resection. Motivated by the need to enrich the description of brain cancer growth through mechanics, in this paper we present a mathematical multiphase model that explicitly includes brain hyperelasticity. We find that our mechanical description allows to evaluate the impact of the growing tumour mass on the surrounding healthy tissue, quantifying the displacements, deformations, and stresses induced by its proliferation. At the same time, the knowledge of the mechanical variables may be used to model the stress-induced inhibition of growth, as well as to properly modify the preferential directions of white matter tracts as a consequence of deformations caused by the tumour. Finally, the simulations of our model are implemented in a personalized framework, which allows to incorporate the realistic brain geometry, the patient-specific diffusion and permeability tensors reconstructed from imaging data and to modify them as a consequence of the mechanical deformation due to cancer growth.

Elastic–plastic analysis of the plane strain under combined thermal and pressure loads with a new technique in the finite element method

Abstract This research aims to find a new way to address thermal loads within the framework of the elastic–plastic relationship, especially when the loads, such as thermal and pressure ones, are combined. While the residual force method was employed to attempt to find the convergence of a nonlinear solution, it was unable to do so. For this purpose, a mathematical relationship was derived to address thermal loads and add them to the hierarchy of the specified elements method as a subroutine. The findings of the developed program were verified by comparing the numerical results with those of the analytical solution of a thick-walled cylinder loaded with heat load and internal pressure; the results proved the correctness and accuracy of the method used. The method offers a way to redevelop old programs that are unable to effectively address the thermal load in elastic–plastic relations without changing said programs significantly but only by adding the subroutine and some very simple modifications. The solution technique provided in this article can be utilized in many related cases, such as plane stress, axisymmetric solid, and three-dimensional stress analyses.

Hydrodynamic Predictions of the Ultralight Particle Dispersions in a Bubbling Fluidized Bed

Particle and gas flow characteristics are numerically simulated by means of a proposed gas–particle second-order moment two-fluid model with particle kinetic–friction stress model in a bubbling fluidized bed. Anisotropic behaviors of gas–solid two-phase stresses and their interactions are fully considered by the two-phase Reynolds stress model and their closure correlations. The dispersion behaviors of the non-spherical expand graphite and spherical heavy particles are predicted by using the parameters of distributions of particle velocity, porosity, granular temperature, and dominant frequency. Compared to particles density 2700 kg/m3, ultralight particles exhibit the higher voidages with big bubbles and larger axial-averaged velocity of particles and stronger dispersion behaviors. Maximum granular temperature is approximately 3.0 times greater than that one, and dominant frequency for axial porosity fluctuations is 1.5 Hz that is 1/3 time as larger as that heavy particle.