Isotropy Ratio Research Articles

Microstructural evolution and mechanical properties of the in situ La2O3 particle-reinforced titanium alloy prepared by dual-wire-arc directed energy deposition

TA15 titanium alloy components produced via wire-arc direct energy deposition (WA-DED) face challenges related to grain coarsening, suboptimal mechanical properties, and pronounced anisotropy. To address these issues, the current study employed a dual-wire-arc directed energy deposition (DWA-DED) approach to fabricating the alloys by introducing LaF3 quantitatively into the deposition metal using a metal cored wire. The incorporation of LaF3 was predicated on the in situ reaction: 6[O] + 6[H] + 2 LaF3 = La2O3 + 6HF. This reaction effectively removed [H] and [O] from the molten pool, diminishing the presence of the brittle intermetallic compounds and concurrently enhancing toughness. The addition of LaF3 resulted in a notable 56.8% increase in elongation and a 33.1% boost in impact toughness. Moreover, the DWA-DED quantitatively introduced [La], facilitating the precipitation of La2O3 particles. This precipitation reduced the size of primary columnar grains (PCGs) and promoted heterogeneous nucleation of α-laths. As a result, the elongation of the PCGs’ boundaries diversified the α phase transformation, resulting in the reduced multiple of uniform density (MUD) along the building direction. As a result, the isotropy ratio between vertical and horizontal directions also increased, underscoring the efficacy of LaF3 in mitigating anisotropic behaviour in WA-DEDed titanium alloys.

Stress solution of transversely isotropic surrounding rock for shallow buried elliptic tunnels

This paper develops a method to obtain the stress solution of the transversely isotropic surrounding rock for shallow elliptical tunnels. Based on the stress solution of the transversely isotropic surrounding rock for deeply buried elliptical tunnels, the Schwarz alternating method is used to solve the stress of surrounding orthotropic rock with a shallow elliptical tunnel. A MATLAB program is developed to implement the derived theory, and the numerical simulation results are compared with those of existing solution and the finite element software ABAQUS, demonstrating the rationality and correctness of the present theory in this paper. Finally, the influences of factors such as rock and soil transverse isotropy, tunnel depth, and tunnel aspect ratio on the stress distribution around the tunnel are discussed.

Three-dimensional metamaterials exhibiting extreme isotropy and negative Poisson's ratio

This research will develop a new set of mechanical metamaterials with simultaneous ideal elastic isotropy and extreme negative Poisson's ratio through a topology optimization approach. Firstly, we propose a new method to generate a three-dimensional ground structure with geometric cubic symmetry. Secondly, a more efficient topology optimization method is developed by utilizing a small number of both integer and continuous design variables for topological description of the design based on the discrete ground structure. Thirdly, two new geometric constraints are incorporated into the mathematical formulation to ensure creation of designs that are practical. Finally, the genetic algorithm is used to solve this type of mixed-integer programming problems. Several numerical examples have been used to demonstrate the generation of a series of three-dimensional microarchitectures from a single integrated design. The microlattices can also be customized to obtain a broad range of negative Poisson's ratios across different relative densities. The effective material properties and macroscopic deformation behaviors of the designs are numerically validated using commercial software.

How Applicable Are Turbulence Assumptions Used in the Tidal Energy Industry?

As tidal current and marine hydro-kinetic energy converters start to be deployed in pre-commercial arrays, it is critical that the design conditions are properly characterised. Turbulence is known to influence fatigue loads and power production, so developers use turbulence models to generate unsteady flows in order to simulate device performance. Most such models construct a synthetic flow field using a combination of measured parameters and theoretical assumptions. The majority in use today are based on atmospheric flow conditions and may have limited applicability in tidal environments. In the present work, we compare key turbulence model assumptions (which are recommended by the tidal turbine standards and are used in design software) to turbulence measurements from two tidal test sites in Scotland and Canada. Here, we show that the two sites have different levels of conformity to theoretical models, with significant variability within nearby locations at the same site. The agreement with spectral models is shown to be depth-dependent. The vertical component spectrum is better represented by the Kaimal model, while the streamwise spectrum is better represented by the von Kármán model. With the exception of one site, the shear profiles follow a power law, although with a different exponent to that commonly assumed. Both sites show significant deviations from the theoretical length scales and isotropy ratios. Such deviations are likely to misrepresent the loads experienced by a device. These results highlight the turbulence characteristics at real deployment sites, which are not well represented by current models, and, hence, which must be determined using field measurements.

Research Progress on Blue-Phase Liquid Crystals for Pattern Replication Applications.

Blue-Phase Liquid Crystals (BPLCs) are considered to be excellent 3D photonic crystals and have attracted a great deal of attention due to their great potential for advanced applications in a wide range of fields including self-assembling tunable photonic crystals and fast-response displays. BPLCs exhibit promise in patterned applications due to their sub-millisecond response time, three-dimensional cubic structure, macroscopic optical isotropy and high contrast ratio. The diversity of patterned applications developed based on BPLCs has attracted much attention. This paper focuses on the latest advances in blue-phase (BP) materials, including applications in patterned microscopy, electric field driving, handwriting driving, optical writing and inkjet printing. The paper concludes with future challenges and opportunities for BP materials, providing important insights into the subsequent development of BP.

Productivity index of horizontal well in Mishrif formation of Buzurgan oil field – Case study

AbstractHorizontal good technology is one of the recent methods in the drilling and exploitation of geological formations in the best and optimal ways, because of the many and comprehensive advantages that these wells enjoy with the most important measurement and prediction index called productivity index. Which is equivalent to several times higher than the vertical well productivity index, if the field is invested by drilling vertical wells only.The current research focuses on calculating the productivity index by proposing the development point of view of the reservoir formation in the Burgan oil field through the production of oil from the production units approved in the formation (MB21, MC1, MC2) by using of horizontal good technology and comparing it with the value of the productivity index of vertical wells in the same production units.Well-known published methods adopted in the case of steady state and pseudo steady state were used in the calculations of the productivity index, and by comparison with the standard observed results, it was found that the Joshi method was closer than others in the calculations of the productivity index for both steady and pseudo steady state cases. Then the calculations were completed taking into account all conditions and factors that have a significant role in the value of the calculated productivity index.The obtained results revealed that PI increases with [well length, isotropy ratio (Kv/Kh), well thickness vs. well length] increase, while it was decreased with [ drainage area] increase in the case of steady state conditions. Also, the PI increase with length increase in the case of Pseudo steady state condition for all the studied methods, and both of Kuchuck and Economides methods seem to be close in obtained results, but Economides is the closest one to the reality and importance in application with the present case. Completion configuration has an effluence on the PI, and it is increasing with the increase of well opening to the production for such well length.Also, all the results indicated that the use of this type of technology in the field development is good and promising, and gave valuable, excellent, and optimistic results for the future production of the field in a profitable manner.

In-medium effects in central heavy ion collisions at intermediate energies

Energy dissipation and cluster production in central nuclear collisions in the Fermi energy range have been investigated using the large INDRA database. A study of the in-medium nucleon-nucleon cross section, ${\ensuremath{\sigma}}_{NN}^{*}$, has been performed by comparing the results of a model with the measured isotropy ratio of the kinetic energy distributions of the detected protons. This analysis has been done for a large variety of systems at various incident energies from 20 to 100 MeV/nucleon and confirms nicely previous results with enhanced statistics in a full Monte Carlo treatment. Most importantly, it is found that ${\ensuremath{\sigma}}_{NN}^{*}$ is drastically reduced as compared to the vacuum values, due partly to Pauli blocking but also to in-medium effects for which mean values and uncertainties are given. Concerning the cluster production, a coalescence model has been developed to study the parallel and perpendicular velocity distributions of the light clusters ($A\ensuremath{\le}4$). For ${A}_{C}=3$ ($^{3}\mathrm{H}, ^{3}\mathrm{He}$), it is found that the mean internal kinetic energy of the nucleons in the cluster is reduced as compared to the vacuum value. These two results shows that any comparison between experimental and theoretical predictions in heavy-ions induced reactions around and above the Fermi energy must take into account these in-medium effects.

Characterization of Turbulence in an Optically Accessible Fan-Stirred Spherical Combustion Chamber

ABSTRACT Fundamental characteristics of fan-generated turbulence inside a constant-volume combustion chamber (CVCC) with 400 mm inner diameter under high-pressure and high-temperature conditions have been investigated to establish benchmark data for studies of turbulent premixed flame propagation. Here, the CVCC was designed to withstand up to 1.0 MPa initial pressure and 600 K initial temperature and equipped with four fans oriented in a tetrahedron configuration. A time-resolved particle imaging velocimetry (TR-PIV) is employed to characterize the turbulence under various thermodynamic conditions. Additionally, stereoscopic TR-PIV measurements were conducted to characterize the three-dimensional turbulent flow field inside the chamber. The results showed that the chamber could achieve homogenous and isotropic turbulence. A reasonably isotropic stationary turbulence with large turbulence intensities (up to ≈ 4.7 m/s) was achieved in the central region extending to almost 50 mm radius. This has been manifested by near-zero mean velocities and directional invariance of turbulence intensities. Global homogeneity and isotropy ratios in the chamber were close to unity, indicating weak anisotropy. The spectral energy spectra of the generated turbulent flow fields were in satisfactory agreement with the well-known Kolmogorov’s – 5/3 law associated with homogeneous isotropic turbulence irrespective of the intensity of the turbulence. Various spatio-temporal length scales characterizing the turbulent flow field including the integral, Taylor, and Kolmogorov length scales were reported. Turbulence statistics and inherent parameters were investigated at elevated pressure and temperature conditions as well as results from test cases to determine turbulent–flame propagation speeds were reported. Accordingly, the present canonical configuration apparatus can be conveniently adopted for several turbulent combustion studies including mainly the determination of turbulent burning velocity for gaseous and liquid premixed flames in nearly homogeneous isotropic turbulence.

Modulation of turbulent flow field in an oscillating grid system owing to single bubble rise

Modulation of turbulent flow in an oscillating grid system due to controlled release of a bubble train was experimentally investigated using particle image velocimetry (PIV) technique wherein flow field modulation was reported in single bubble resolved manner. The bubble diameter was varied in the range ∼2.70 to 3.52 mm (∼26 to 34 times the single-phase Kolmogorov scale, and ∼1.05 to 1.35 times the single-phase integral length scale). The two-dimensional (2D) instantaneous velocity fields were obtained for both single–phase and bubble train cases at grid Reynolds numbers (Reg) ranging from 1080 to 10,800. The modulation of single-phase turbulence due to bubble was analysed based on the turbulence intensity, isotropy ratio (IR), length scales, specific energy dissipation rates and energy spectra. The single-phase turbulence fluctuating velocity increased ∼5–76% in the inertial subrange region in the presence of bubbles. Presence of bubbles also led to enhancement in the flow field isotropy ratio due to upward acting buoyancy force. It was noted that at high Reg (6480–10800), the IR value of the flow was found to be more dependent on the grid Reynolds number compared with bubble diameter. The integral length scale of the single-phase flow decreased following a power law dependency over the Reg. It was found that the specific energy dissipation rate of single–phase flow increased with an increase in bubble diameter. The energy spectra exhibited a slope less steep than −5/3 which indicates the additional turbulence production by the bubbles in the inertial subrange region. Energy transfer augmentation from large scale to small scale due to bubble was explianed by the dissipative spectrum which showed reduction of the energy in the small scale and an enhancement of the energy in both large scale and inertial subrange.

Scaling the Velocity Gradients in a Vessel Agitated by a Rushton Turbine

AbstractScaling of fluctuation velocity gradients was investigated in a vessel agitated by a Rushton turbine. By using turbulence spectrum analysis, it was derived that, for high Reynolds numbers, the squared dimensionless local fluctuation velocity gradient is proportional to the squared impeller Reynolds number. This theoretical prediction was tested on experimental data in the range Re = 50 000 – 110 556. The calculated isotropy ratios are independent of the impeller Reynolds number, and their inter‐ratios depend on the ratio of the axial and the radial components of the fluctuation velocity. The experiments also support the idea that the isotropy ratios differ from zone to zone in an agitated vessel.

Nuclear Stopping and Pauli Blocking in Heavy-Ion Reactions near Fermi Energy**Supported by the National Natural Science Foundation Of China under Grant Nos 11265013, 11175074, 11264033 and 11464040.

The dissipation phenomenon in the heavy-ion reaction at incident energy near the Fermi energy is studied by simulating the reaction 129Xe+129Sn with the isospin-dependent quantum molecular dynamics model. The calculations involving a proper prescription of implementing the Pauli exclusion principle show that the isotropy ratio measured by free protons emitted in the reaction at energy slightly higher than the Fermi energy is in agreement with the experimental data recently released by the INDRA collaboration. A feasible value of the Pauli-blocking factor is estimated by comparing the theoretical results with the experimental data for the energy range considered here.

Pauli-blocking effect in two-body collisions dominates the in-medium effects in heavy-ion reactions near Fermi energy

The dissipation phenomenon in the heavy-ion reaction at incident energy near Fermi energy is studied by simulating the reactions 129Xe + 129Sn and 58Ni + 58Ni with isospin-dependent quantum molecular dynamics model (IQMD). The isotropy ratio in terms of transverse and longitudinal energies of the free protons emitted in the final states of these reactions is quantitatively analyzed to explore the in-medium correlation of the binary collisions. Comparison of the calculations with the experimental data recently released by INDRA collaboration exhibits that the ratio is very sensitive to the Pauli blocking effect in two-body collisions and Pauli exclusion principle is indispensable in the theoretical simulations for the heavy-ion reactions near the Fermi energy.

Design of a new gravity balanced parallel mechanism with Schönflies motion

In this paper, a new gravity-balanced 3T1R parallel mechanism is addressed. Firstly, structure description, inverse and forward kinematic modeling are performed in detail. Secondly, Jacobian derivation based on screw theory and singularity analysis using Grassmann Line Geometry is performed, and then optimal kinematic design with respect to workspace size, kinematic isotropy and maximum force transmission ratio are conducted. Thirdly, the gravity balancing design using both counterweights and springs is proposed and a prototype of this mechanism is also presented. Results of analysis show that the proposed mechanism has quite a few potential applications.

Experimental investigation on modulation of homogeneous and isotropic turbulence in the presence of single particle using time-resolved PIV

Turbulence modulation of a nearly isotropic flow field due to the presence of single glass particles, with diameters in the range of 1−8mm (~10–77 times the Kolmogorov scale), was studied experimentally in an oscillating grid apparatus. Particle image velocimetry (PIV) was used to obtain the instantaneous, two-dimensional velocity field for grid Reynolds number, Reg, varying from 1080 to 10,800. Fluctuating velocity components, flow field length scales, energy dissipation rates, turbulence intensity modulation and energy spectra were determined. An apparent increase of ~2–25% in the turbulence fluctuating velocity in the inertial subrange was noted compared with the fluid-only system. Presence of the particle led to enhancement in the flow field isotropy ratio and this ratio was found to be more dependent on the particle size compared with grid Reynolds number. The integral length scale for both fluid-only and fluid–particle systems exhibited a decreasing power law dependency on the grid Reynolds number. A critical ratio (0.41) of particle size to integral length scale was obtained which demarcated the regime of attenuation and enhancement of turbulence intensity and found to be valid for general grid turbulence in multiparticle systems as well. Energy dissipation rate was observed to increase with increase in particle size. Both longitudinal and transverse energy spectrum exhibited less steep slope than −5/3 in the presence of particle which was reasoned to the production of turbulence in the inertial subrange region. Energy enhancements from large scale to smaller scale were explained by the dissipative spectrum which showed maximum energy enhancement in the inertial subrange followed by a decaying trend. In general, the role of a particle in modulating turbulence was explained through possible wake oscillation and vortex shedding due to boundary layer separation on the particle surface and interaction with bulk eddies.

Aspects of the momentum dependence of the equation of state and of the residualNNcross section, and their effects on nuclear stopping

With the semiclassical Landau-Vlasov transport model we studied the stopping observable $R_E$, the energy-based isotropy ratio, for the $^{129}$Xe\,+\,$^{120}$Sn reaction at beam energies spanning 12$A$ to 100$A$ MeV. We investigated the impacts of the nonlocality of the nuclear mean field, of the in-medium modified nucleon-nucleon ($NN$) cross section and of the reaction centrality. A fixed set of model parameters yields $R_E$ values that favorably compare with the experimental ones, but only for energies below the Fermi energy $E_F$. Above $E_F$ agreement is readily possible, but by a smooth evolution with energy of the parameter that controls the in-medium modification of $NN$ cross section. By comparing the simulation correction factor ${\cal F}$ applied to the free $NN$ cross section with the one deduced from experimental data [Phys.\ Rev.\ C\,{\bf 90}, 064602 (2014)], we infer that the zero-range mean field almost entirely reproduces it. Also, in accordance with what has been deduced from experimental data, around $E_F$ a strong reduction of the free $NN$ cross section is found. In order to test the impact of sampling central collisions by multiplicity an event generator (HIPSE) was used. We obtain that high multiplicity events are spread over a broad impact parameter range, but it turns out that this has a small effect on the observable $R_E$ and, thus, on ${\cal F}$ as well.

Energetic ions scattered into the loss cone with observations of the Cluster satellite

Abstract. In this paper, we report in situ observations by the Cluster spacecraft of energetic ions scattered into the loss cone during the inbound pass from the plasma sheet into the plasmasphere. During the inbound pass of the plasma sheet, Cluster observed the isotropy ratio of energetic ions to gradually decrease from unity and the isotropic boundary extended to lower L value for higher-energy ions, implying that the field line curvature scattering mechanism is responsible for the scattered ions into the loss cone from the plasma sheet. In the outer boundary of a plasmasphere plume, Cluster 3 observed the increase of the isotropy ratio of energetic ions accompanied by enhancements of Pc2 waves with frequencies between the He+ ion gyrofrequency and O+ ion gyrofrequency estimated in the equatorial plane. Those Pc2 waves were left-hand circularly polarized and identified as electromagnetic ion cyclotron (EMIC) waves. Using the observed parameters, the calculations of the pitch angle diffusion coefficients for ring current protons demonstrate that EMIC waves could be responsible for the ions scattering and loss-cone filling. Our observations provide in situ evidence of energetic ion loss in the plasma sheet and the plasmasphere plume. Our results suggest that energetic ions scattering into the loss cone in the central plasma sheet and the outer boundary of the plasmaspheric plume are attributed to the field line curvature scattering mechanism and EMIC wave scattering mechanism, respectively.

Homogenous and highly isotropic graphite produced from mesocarbon microbeads

Mesocarbon microbeads (MCMBs) are attractive precursors for high-density, high-strength polycrystalline graphite due to their self-sintering capability. They have the shape of a standard sphere and stack in a completely random orientation during compaction, thereby leading to an isotropic texture. In this paper, MCMB-based graphite shows better isotropic property than commercial nuclear graphite, as demonstrated by a coefficient of thermal expansion-based isotropy ratio of 1.00. It was found that variations in apparent density within block are approximately 2–5% in graphitized artifacts. The variation of flexural strength within block is small, revealing excellent homogeneity of MCMB-based graphite. Density distribution measurement indicates that artifacts produced in the same batch also have low variation from block to block. Furthermore, the flexural strength of this material is greatly influenced by heat treatment temperature and mean particle size. The fracture mechanism is also shown by a detail examination of fracture surfaces. These results may help to gain a better understanding of MCMB-based graphite.

Advantages of natural microcrystalline graphite filler over petroleum coke in isotropic graphite preparation

Graphite materials are used in high-temperature gas-cooled reactor (HTR) as moderator and reflector. Nuclear graphite is currently manufactured using coke as the filler; however, improvements in the performance of nuclear graphite are anticipated in order to enhance the safety and lifetime of HTRs. Natural microcrystalline graphite (MG), which is a metamorphic product of coal, is an emerging candidate as filler material. This paper proposes the approach of preparing isotropic graphite using MG fillers. The characterization results of MG ores and purified powder indicate a polycrystalline and near-isotropic structure of MG particles. Thus, near-isotropic graphite with an isotropy ratio of 1.10–1.15 can be easily obtained via cold isostatic pressing. The thermal diffusivity of MG-based green body is much higher than that of coke-based one, therefore facilitates the baking step. The advantages of MG-based graphite also include a high degree of graphitization, and a low coefficient of thermal expansion, both of which are highly beneficial to nuclear applications. As a result, MG exhibits a large potential for the application in isotropic nuclear graphite.

Non-ideal optical isotropy of blue phase liquid crystal

Since 1981, blue phase liquid crystal (BPLC) was regarded as optical isotropy and high contrast ratio (CR) should be achieved easily. However, low CR of BPLC display was reported in all literatures. Here, we show BPLC is non-ideal optical isotropy which leads to poor CR. In our report, BPLC not only revealed primary structure of double-twist cylinder and secondary structure of lattice but also revealed tertiary structure of self-alignment on electrode surface. This finding will be useful to improve CR and inspire researches in display industry and academics.

PIV study of flow through porous structure using refractive index matching

An aqueous solution of sodium iodide and zinc iodide is proposed as a fluid that matches the refractive index of a solid manufactured by rapid prototyping. This enabled optical measurements in single-phase flow through porous structures. Experiments were also done with an organic index-matching fluid (anisole) in porous structures of different dimensions. To compare experiments with different viscosities and dimensions, we employed Reynolds similarity to deduce the scaling laws. One of the target quantities of our investigation was the dissipation rate of turbulent kinetic energy. Different models for the dissipation rate estimation were evaluated by comparing isotropy ratios. As in many other studies also, our experiments were not capable of resolving the velocity field down to the Kolmogorov length scale, and therefore, the dissipation rate has to be considered as underestimated. This is visible in experiments of different relative resolutions. However, being near the Kolmogorov scale allows estimating a reproducible, yet underestimated spatial distribution of dissipation rate inside the porous structure. Based on these results, the $$k-\varepsilon$$ model was used to estimate the turbulent diffusivity. Comparing it to the dispersion coefficient obtained in the same porous structure, we conclude that even at $$Re_p=500$$ the turbulent diffusivity makes up only a small part of mass transfer in axial direction. The main part is therefore attributed to Taylor dispersion.