Radial Heterogeneity Research Articles

Torsional dynamic response of a large-diameter pipe pile in transversely isotropic unsaturated soils considering construction disturbance

Large-diameter pipe piles are widely applied in various civil engineering fields due to their outstanding load-bearing capability. The unsaturated characteristics, anisotropy, and heterogeneity of the soil jointly affect the dynamic response of the pipe pile. However, most previous studies were limited to single-phase or two-phase soil. This paper develops an analytical model for the torsional vibration of a pipe pile in transversely isotropic unsaturated soils considering construction disturbance. Based on transversely isotropic unsaturated soil theory, a pipe pile-soil interaction model has been developed, while the effect of construction disturbance is simulated by the radial heterogeneity of the soil. The general solution for the unsaturated soil is obtained using the separation of variables method with the boundary conditions. Then, the solution for the whole pipe pile-soil system is derived by considering the pile-soil interface conditions. The accuracy of the proposed solution is verified through comparisons with previous research results. The results show that unsaturated characteristics, construction disturbance, and transverse isotropy of the soil have significant effects on the impedance of large-diameter pipe piles. Specifically, with a low degree of saturation, there will be significant prediction errors when using previous works based on single-phase or two-phase soil theory to predict the dynamic response of large-diameter pipe piles.

Enhanced graphitization and reduced radial heterogeneity of carbon fibers inheriting from irradiated/thermo-chemically stabilized PAN-fibers

The cross-section of carbon fibers (CFs) possessed radial heterostructure, which restricted its mechanical properties. In this paper, heating and γ-irradiation were integrated during PAN fibers stabilization process to improve the radial structure of CFs. The synergy between irradiation and heating during stabilization caused the decrease of ID/IG, increase of crystal size, and reduction of pore fractal dimension in whole CFs. Through Raman spectra along fibers cross-section, a radial heterogeneity was found during the whole carbonization process. The combination of γ-irradiation and heating reduced the ID/IG of core part more significantly compared to the skin part of CFs, which weakened radial heterogeneity of CFs. At the same time, it significantly enhanced the tensile strength of CFs. Subsequently, a hierarchy model with three zones containing outer-surface, sub-surface and core parts was presented to explain the evolution of tensile strength for CFs. The γ-irradiation during stabilization enhanced the structure of each part in CFs by generating more cross-linked structures.

Preparation and characterization of stationary phase gradients on C8 liquid chromatography columns

Continuous C8 stationary phase gradients are created on commercial Waters Symmetry Shield RP8 columns by strategically cleaving the C8 moieties in a time-dependent fashion. The method relies on the controlled infusion of a trifluoroacetic acid/water/acetonitrile solution through the column to cleave the organic functionality (e.g., C8) from the siloxane framework. The bond cleavage solution is reactive enough to cleave the functional groups, even with polar groups embedded within the stationary phase to protect the silica. Both the longitudinal and radial heterogeneity were evaluated by extruding the silica powder into polyethylene tubing and evaluating the percent carbon content in the different sections using thermogravimetric analysis (TGA). TGA analysis shows the presence of a stationary phase gradient in the longitudinal direction but not in the radial direction. Two different gradient profiles were formed with good reproducibility by modifying the infusion method: one exhibited an ‘S’-shaped gradient while the other exhibited a steep exponential-like gradient. The gradients were characterized chromatographically using test mixtures, and the results showed varied retention characteristics and an enhanced ability to resolve nicotine analytes.

FO-SPR Model for Full-Spectrum Signal Analysis of Back-reflecting FO-SPR Sensors to Monitor MOF Deposition.

In this study, we explore the full-spectrum capabilities of fiber-optic surface plasmon resonance (FO-SPR) for analyzing heterogeneous samples with increased comprehensiveness. Our approach involves refining a literature-derived FO-SPR model to more precisely reflect experimental data obtained using a back-reflecting sensor configuration. Key enhancements in our model include adjustments to the thickness and permittivity of the gold SPR-active layer on the FO-SPR sensor as well as improvements to the angular distribution of light within the system. We apply this optimized model to the investigation of the deposition process of a metal-organic framework (MOF), specifically ZIF-8, using FO-SPR. By closely examining the temporal variations in the FO-SPR signal during MOF layer formation, we simultaneously determine the evolving thickness and refractive index (RI) of the MOF layer, offering a dual-parameter analysis. Our results demonstrate that a full-spectrum analysis of the FO-SPR signal can extract critical information from samples exhibiting radial heterogeneity. This advancement significantly enhances the quantitative assessment of various phenomena that alter the refractive index in the sensor's domain, such as adsorption and binding processes. This work thus represents a significant step forward in the field of FO-SPR sensor technology, promising broad applications in areas requiring the precise detection and analysis of complex samples.

Microtissue Culture Provides Clarity on the Relative Chondrogenic and Hypertrophic Response of Bone-Marrow-Derived Stromal Cells to TGF-β1, BMP-2, and GDF-5.

Chondrogenic induction of bone-marrow-derived stromal cells (BMSCs) is typically accomplished with medium supplemented with growth factors (GF) from the transforming growth factor-beta (TGF-β)/bone morphogenetic factor (BMP) superfamily. In a previous study, we demonstrated that brief (1-3 days) stimulation with TGF-β1 was sufficient to drive chondrogenesis and hypertrophy using small-diameter microtissues generated from 5000 BMSC each. This biology is obfuscated in typical large-diameter pellet cultures, which suffer radial heterogeneity. Here, we investigated if brief stimulation (2 days) of BMSC microtissues with BMP-2 (100 ng/mL) or growth/differentiation factor (GDF-5, 100 ng/mL) was also sufficient to induce chondrogenic differentiation, in a manner comparable to TGF-β1 (10 ng/mL). Like TGF-β1, BMP-2 and GDF-5 are reported to stimulate chondrogenic differentiation of BMSCs, but the effects of transient or brief use in culture have not been explored. Hypertrophy is an unwanted outcome in BMSC chondrogenic differentiation that renders engineered tissues unsuitable for use in clinical cartilage repair. Using three BMSC donors, we observed that all GFs facilitated chondrogenesis, although the efficiency and the necessary duration of stimulation differed. Microtissues treated with 2 days or 14 days of TGF-β1 were both superior at producing extracellular matrix and expression of chondrogenic gene markers compared to BMP-2 and GDF-5 with the same exposure times. Hypertrophic markers increased proportionally with chondrogenic differentiation, suggesting that these processes are intertwined for all three GFs. The rapid action, or "temporal potency", of these GFs to induce BMSC chondrogenesis was found to be as follows: TGF-β1 > BMP-2 > GDF-5. Whether briefly or continuously supplied in culture, TGF-β1 was the most potent GF for inducing chondrogenesis in BMSCs.

Insighting Evolution of Radial Heterogeneity in Photochemically and Thermochemically Stabilized PAN Fibers from Nanomechanics and Microscopic Imaging

Insighting Evolution of Radial Heterogeneity in Photochemically and Thermochemically Stabilized PAN Fibers from Nanomechanics and Microscopic Imaging

Analytical solution for dynamic responses of offshore wind turbines supported by pipe pile in radially heterogeneous soil

Offshore wind turbines (OWTs) are subject to the combined action of dynamic environmental loads including wind, waves, and earthquake loads. This paper proposes an analytical solution for the dynamic response of OWTs supported by pipe pile in heterogeneous viscoelastic soil. The analytical model accounts for various interactions that affect OWTs dynamic response. The pipe pile-internal soil is calculated by utilizing the Helmholtz method, the pipe pile-external soil is calculated by utilizing the transfer matrix method, the pipe pile-wave is evaluated by utilizing the diffraction wave theory, and the tower drum-wind is calculated by utilizing the Bernoulli method. The dynamic responses of the pipe pile and tower are established by enforcing the boundary conditions of the displacement continuity and stress equilibrium. The developed analytical solution is degenerated into simplified analytical solutions under various conditions, which was validated by comparing its predictions with the results of available numerical and analytical solutions. The validated simplified solution is then utilized investigate the effects of some critical parameters on OWTs response. The results show that the OWTs response under the combined action of earthquake, wave and wind loads is strongly affected by the presence of water and soil inside the pipe pile, soil radial heterogeneity.

A close-formed solution for the horizontal vibration of a pipe pile in saturated soils considering the radial heterogeneity effect

Based on the theory of Biot’s two-phase medium and Novak’s thin layer, a coupled mechanical model of pipe pile and radially inhomogeneous saturated soil is established by comprehensively taking into account the saturated surrounding soil’s construction disturbance effect and the influence of the pipe pile’s saturated inner soil. First, the displacements and horizontal impedances of the surrounding and inner soil are derived using the potential function, Laplace transformation and variable separation methods. Second, the analytical solution for the horizontal impedance of pile head is obtained by combining the conditions of the displacement continuity and stress equilibrium on the soil-pile interface. Finally, the obtained solution for the pile head’s horizontal impedance is reduced to validate the rationality of the proposed solution by making comparisons with existing solutions. On this basis, a detailed parametric analysis is given to explore the influence of the pile parameters and construction disturbance effect on the horizontal vibration characteristics of pipe pile.

Processing-controlled radial heterogeneous structure of carbon fibers and primary factors determining their mechanical properties

Commercial polyacrylonitrile (PAN)-based carbon fibers, T800S and T700S, were gradually etched from the surface to the inside by thermal oxidation at 600 °C up to 10 h for investigating microstructure and resulting mechanical properties depending on the position in the radial direction. While T800S showed a gradual decrease in mechanical properties with respect to the oxidation time, those of T700S showed an unusual behavior due to the existence of a transition zone between the skin and the core, where the structural development was shown to be as high as the surface. This transition zone is presumed to be due to the collisions (shear stress-induced alignment) between the skin and core as the difference in their degree of structural development is large. In addition, as a result of analyzing various microstructures over a wide range from macroscopic to atomic/bond scale, it was confirmed that microvoid diameter and crystalline orientation were dominant structural factors in determining the mechanical properties of carbon fibers. However, the graphitic crystal size and ID/IG ratio (the amounts of defects) showed little variation along the radial direction. Based on those overall analyses, more detailed structural sketches of two different types of CFs from the skin to cores are suggested. We believe that the integrated studies on radial heterogeneity and structure-property relationships of carbon fibers provide essential information for manufacturing high-performance carbon fibers.

Analytical solution for horizontal vibration of end-bearing single pile in radially heterogeneous saturated soil

Employing Biot's dynamic equations and Novak's thin-layer theory, an analytical model for the horizontal vibration of a single pile embedded in the radially heterogeneous saturated soil is established. Firstly, the frequency-domain response of surrounding soil is derived by means of the potential function, Laplace transformation and variable separation methods. Secondly, the analytical solution for the horizontal impedance of pile head is deduced by combining the conditions of the displacement continuity and stress equilibrium on the soil-pile interface. Finally, the obtained solution is degenerated to validate its accuracy via independent comparisons with different existing solutions. On this basis, the effect of soil radial heterogeneity on the horizontal vibration of an end bearing pile is further discussed by conducting an extensive parametric analysis.

Radial microstructure development of polyacrylonitrile (PAN)-based carbon fibers

The radial microstructure development of polyacrylonitrile-based carbon fibers is traced during continuous carbonization from 400 to 1400 °C. Based on the changes in the microstructure and mechanical properties of the fibers, it is confirmed that they undergo four distinctive stages depending on the temperature: (1) further cyclization in a remained unstabilized structure (400–600 °C), (2) crosslinking by dehydrogenation (600–800 °C), (3) crosslinking by denitrogenation (1000–1200 °C), and (4) development of turbostratic structure (1200–1400 °C). A structural analysis of the surface, skin, and core regions reveals that the innermost structure (core) originates from a high degree of structural relaxation. In contrast, densification is dominated in the outermost structure (surface). Such a radial heterogeneity is attributed to gas evolution along the radial direction of the fibers during the high-temperature carbonization and fiber shrinkage. The tensile strength exhibits a strong relationship with the crystal sizes as compared to the degree of disorder and amorphous structures, indicating that the crystal growth by densification has a greater influence on the tensile properties than the structure relaxation.

Fractured formation evaluation by seismic attenuation derived from array acoustic log waves based on modified spectral ratio method and an extended Biot's poroelastic model

A comprehensive application of the seismic attenuation deduced from the array acoustic log waves by using modified spectral ratio method together with an extended Biot's poroelastic model has been developed for detection and evaluation of fractures in carbonate and sandstone formations. First, profile of amplitude ratio based on deconvolution interferometry (DCI) and modified spectral ratio method (MSRM) are introduced and applied on array acoustic waveforms to derive the seismic attenuation factors. Second, an extended Biot's poroelastic model with consideration of fracture parameters is described and derived for its expression of attenuation. Both the computational method and the theoretical model are tested on simulated sonic data and meaningful results are obtained which are connected with analysis of application on field data in final section. Finally, the MSRM and extended Biot's poroelastic model are applied to field waveforms acquired from carbonate and sandstone formation in oilfields of Petro China. In the present study, we mainly focused on the subject of fracture identification and evaluation in both carbonate and sandstone formation. Field application results show that within frequency range of 1–40 kHz, attenuation derived from sonic log waves by using MSRM has close relationship with fracture development. Meanwhile, the simulation responses based on the extended Biot's poroelastic model verify the fact that the attenuation magnitude is mainly sensitive to fracture porosity. Our results also suggest that profile of amplitude ratio can be a potentially useful indicator of fracture identification and evaluation, and, maybe also an interpreting toll of radial heterogeneity.

A NUMERICAL APPROACH FOR PERMEABILITY ESTIMATION IN RADIALLY HETEROGENEOUS RESERVOIRS

Analytical solutions are used extensively for pressure transient analysis in radially heterogeneous reservoirs. They are generally used for evaluating variation of reservoir properties along the reservoir radius. However, the available analytical solutions are not sufficiently accurate to determine boundaries of zones. As a result, the interior boundaries of heterogeneous zones are often estimated as a function of the average permeability of zones, which sometimes is a cause of nonunique solutions. As a matter of fact, the skin factor does not provide accurate information about the radius and permeability of an altered zone separately. A new numerical well test procedure is presented in this paper based on the finite element method and a special zonal discretization that utilizes nonlinear regression, which is able to detect the interior boundaries of heterogeneous zones. The results demonstrate that this numerical approach is able to capture the spatial variation of permeability in the radially heterogeneous reservoirs under various boundary conditions. A key advantage of this numerical procedure is quantifying heterogeneity in terms of the radius and permeability of the dissimilar zones, whereas analytical methods generally provide a combination of these parameters.

New Analytical Solution to Predict the Vertical Impedance of a Large-Diameter Pipe Pile in Soil Considering Wave Propagation in Visco-Elastic Continuum

According to the theories of wave propagation in visco-elastic continuum and Rayleigh-Love rod, a simplified model in axisymmetric conditions for the longitudinal vibration of large-diameter pipe pile (LDPP) in radially heterogeneous surrounding soil with viscous damping is presented. The relevant analytical solution for dynamic impedance at pile head is derived by using complex stiffness transfer method, which is also validated via independent comparisons with previous solutions. Besides, parametric analyses are carried out to reveal both the radial heterogeneity of surrounding soil and the lateral inertia effect of pile shaft on the dynamic impedance of LDPP. The obtained analytical solutions are suitable for the longitudinal vibration issues of floating LDPP in visco-elastic surrounding soil with radial heterogeneity, which can be conveniently degenerated to describe the longitudinal vibration of a floating solid pile in soil with radial heterogeneity as well as a floating LDPP or solid pile in radially homogenous soil.

Optimization of Thick-Walled Viscoelastic Hollow Polymer Cylinders by Artificial Heterogeneity Creation: Theoretical Aspects.

A theoretical solution of the problem of thick-walled shell optimization by varying the mechanical characteristics of the material over the thickness of the structure is proposed, taking into account its rheological properties. The optimization technique is considered by the example of a cylindrical shell made of high-density polyethylene with hydroxyapatite subjected to internal pressure. Radial heterogeneity can be created by centrifugation during the curing of the polymer mixed with the additive. The nonlinear Maxwell–Gurevich equation is used as the law describing polymer creep. The relationship of the change in the additive content along with the radius r, at which the structure is equally stressed following the four classical criteria of fracture, is determined in an elastic formulation. Moreover, it is shown that a cylinder with equal stress at the beginning of the creep process ceases to be equally stressed during creep. Finally, an algorithm for defining the relationship of the additive mass content on coordinate r, at which the structure is equally stressed at the end of the creep process, is proposed. The developed algorithm, implemented in the MATLAB software, allows modeling both equally stressed and equally strength structures.

Dopant Redistribution, Phase Propagation, and Electrochemical Properties of Co-Free Layered Cathodes

With the increasing demand for higher energy density in Li-ion battery applications, the development of Ni-based layered oxide cathodes has been focused on increasing the Ni content. However, higher Ni content gives rise to structural and thermal instability of the cathodes and potential safety concerns in applications. The battery community has made great efforts to achieve better battery performance, with manipulating the doping chemistry and engineering the microstructure being two of the most popular yet not well-understood methods.[1–6] Recent studies suggest that manipulating the dopant distribution is effective to improve cathode stability and battery performance.[1,7] However, the prediction of dopant distribution patterns primarily relies on thermodynamics-based theoretical calculations. Therefore, there is strong research need to understand the kinetic factors by experimentally investigating the dopant distribution, local chemical and structural changes and their interplay in the practical synthesis. In this presentation, we will first discuss our recent progress in probing dopant redistribution, phase propagation, and local chemical changes in the synthesis of layered oxide battery cathodes. Then we will show that these multiscale doping strategies enhance the electrochemical performance of Co-free layered cathodes by improving the cycling stability, rate capability, thermal stability, and self-discharge resistance.We investigated the dopant distribution, phase propagation and local chemical changes in the synthesis of layered oxide cathodes at multiple length scales using multielement-doped LiNiO2 as a platform. We observed that dopants Mg and Ti diffuse dynamically from the surface to the bulk of cathode particles below 300 °C long before the formation of layered phase. After calcination, Ti is still enriched at the cathode particle surface while Mg has a relatively uniform distribution throughout cathode particles. We also observed that Ni oxidation completes earlier at the particle surface than in the bulk. Ni oxidation and phase propagation are heterogeneous at the mesoscale and exhibit in two forms- radial heterogeneity and mosaic-like heterogeneity, which vary with calcination conditions. Globally, phase transformation takes place from the initial mixed hydroxide phase to the layered phase through a metal oxide-liked intermediate phase. We probed the layered cathode synthesis at multiple length scales in single particle, as well as at ensemble-averaged electrode scale, which connects the local materials properties with the global electrochemical behavior. These findings enrich the understanding of multiscale layered cathode formation and can potentially inform the cathode design, such as dopant distribution and 3D chemical homogeneity.Ultimately, the resulting materials deliver a material-level specific energy of ∼780 W h/kg at C/10 with 96% retention after 50 cycles, and ~680 Wh/kg with 77% retention after 300 cycles. The dopants reduce the Li/vacancy ordering and mitigate the irreversible phase transformations. Ni dissolution is suppressed due to enhanced interfacial stability. The multielement-doped LiNiO2 also shows higher thermal stability, increased self-discharge resistance, and enhanced Li+ kinetics. Our promising battery performance suggests that there is a large space to manipulate the three-dimensional distribution of dopants to improve the stability of LiNiO2.

Temporal and spatial evolution of biochar chemical structure during biomass pellet pyrolysis from the insights of micro-Raman spectroscopy

Biomass pellet is a popular fuel, and pyrolytic char can be a promised carbon material, further understanding char structural evolution can promote its utilization. To deeply investigate the evolution of char chemical structure and its heterogeneity during biomass pellet pyrolysis process, a new method was developed to fragment the char in space, and the chemical structures of the fragmented sections were analyzed by a micro-Raman spectroscopy (equipped with a 532 nm laser). The first-order Raman spectra (800–1800 cm−1) of varied positions of sawdust pellet pyrolytic char were curve-fitted with 10 Gaussian bands to reveal the temporal and spatial evolutions. The results indicate that pyrolysis of sawdust pellet can be divided into two stages: i) the decomposition of raw biomass (temperature heterogeneity in pellet remains); ii) the condensation reactions of aromatic ring systems (temperature in pellet becomes uniform). The axial and radial heterogeneity of char chemical structure is mainly caused by heat transfer when the whole pellet temperature is uniform during heating. While mass transfer, in accordance with volatile diffusion, can eliminate the heterogeneity of char chemical structure by volatile-char interaction. The combined effects of heat and mass transfer lead to a heterogeneity in pellet char chemical structure.

RESULTS OF VERA APPLICATION TO THE AP1000® PWR STARTUP

This paper describes the application of the Virtual Environment for Reactor Applications, VERA, under development by the Consortium for Advanced Simulation of LWRs (CASL) to the core physics analysis of the AP1000 PWR. The AP1000 PWR features an advanced first core with radial and axial heterogeneities which provides significant enhancements compared to traditional first cores, allowing best fuel usage and short transition to the equilibrium cycle with subsequent fuel reloads. These core advanced features can pose some challenges to the core physics tools making application of VERA to the AP1000 PWR first core especially relevant to qualify VERA performance. This paper focuses on the qualification efforts at hot zero power conditions, where Monte-Carlo reference solutions have also been established. In particular, the paper focuses on the comparison of the predictions obtained with VERA for the four AP1000 units that recently started up with the measured values. It is shown that there is excellent agreement between VERA and the key reactor physics parameters measured during the AP1000 startup.

New Analytical Solutions for Longitudinal Vibration of a Floating Pile in Layered Soils with Radial Heterogeneity

Based on the theory of wave propagation in three-dimensional (3D) continuum, a new analytical approach for the longitudinal vibration characteristics of a floating pile in layered soils with radial heterogeneity is developed by employing a viscous-type damping model. Firstly, an analytical solution for the longitudinal complex impedance at the pile head is deduced by employing the Laplace transform and complex stiffness technique with the compatibility conditions of the pile and radially inhomogeneous surrounding soil. Secondly, a semi-analytical solution in the time domain is further acquired by using the inverse Fourier transform method. Furthermore, the corresponding analytical solutions are validated through contrasts with previous solutions. Finally, parametric analyses are underway to investigate the effect of radial heterogeneity of surrounding soils on longitudinal vibration characteristics of floating piles. It is indicated that the proposed approach and corresponding solutions can provide a more wide-ranging application than the simple harmonic vibration for longitudinal vibration analysis of a floating pile in soils.

Quantitative multi-scale characterization of single basalt fibres: Insights into strength loss mechanisms after thermal conditioning

This article presents an experimental investigation to quantify the effects of high temperature exposure (400–600 °C) on the mechanical properties of single basalt fibres. To this purpose, a combination of single edge notch tension and nanoindentation micro-pillar splitting methods was used to provide an assessment of the fracture toughness of as-received and thermally treated basalt fibres. Similar values were obtained by the two different methods, and interestingly both highlighted an increase in KIc after heat treatment, up to 22% after exposure at 600 °C for 1h (1.59±0.06MPam). The increase in KIc suggests that microstructural changes occur in the fibres, as confirmed by high-speed nanoindentation mapping. Local radial heterogeneity in the fibre structure and elastic modulus and, possibly, the loss of defect orientation originally induced during the fibre drawing process are envisaged to control the decay of basalt fibres tensile strength during high temperature exposure, mimicking a thermal recycling process for composites.