Three-dimensional Evolution Research Articles

Three-dimensional magnetothermal evolution of off-centred dipole magnetic field configurations in neutron stars

ABSTRACT Off-centred dipole configurations have been suggested to explain different phenomena in neutron stars, such as natal kicks, irregularities in polarization of radio pulsars and properties of X-ray emission from millisecond pulsars. Here, for the first time, we model magnetothermal evolution of neutron stars with crust-confined magnetic fields and off-centred dipole moments. We find that the dipole shift decays with time if the initial configuration has no toroidal magnetic field. The decay time-scale is inversely proportional to magnetic field. The octupole moment decreases much faster than the quadrupole. Alternatively, if the initial condition includes strong dipolar toroidal magnetic field, the external poloidal magnetic field evolves from centred dipole to off-centred dipole. The surface thermal maps are very different for configurations with weak B = 1013 G and strong B = 1014 G magnetic fields. In the former case, the magnetic equator is cold while in the latter case, it is hot. We model light curves and spectra of our magnetothermal configurations. We found that in the case of cold equator, the pulsed fraction is small (below a few per cent in most cases) and spectra are well described with a single blackbody. Under the same conditions, models with stronger magnetic fields produce light curves with pulsed fraction of tens of per cent. Their spectra are significantly better described with two blackbodies. Overall, the magnetic field strength has a more significant effect on bulk thermal emission of neutron stars than does the field geometry.

Anisotropic sintering shrinkage behavior of stainless steel fabricated by extrusion-based metal additive manufacturing

Metal additive manufacturing (AM) can be achieved by first extruding polymer-based filaments with densely filled metal particles to create the so-called ‘green’ parts and then experiencing debinding and sintering to produce finished metal components. As a critical step, sintering governs the shape dimension, relative density, and resultant strength of final parts. Thus, there is a growing need for research on understanding and quantifying the sintering-induced anisotropic shrinkage. In this work, the underlying behaviors of anisotropic shrinkage during the entire sintering of extrusion-printed stainless steel 316L parts will be understood and quantified through a combination of theoretical study and experimental investigations including three-directional dilatometry, scanning electron microscopy, and X-ray computed tomography. The three-dimensional size evolution of ‘brown’ parts before sintering will be studied through a macroscopic analysis of shrinkage anisotropy factors and microstructure characterizations. Different filling strategies will be integrated with initial pore distribution characterization for anisotropic dimensional change analysis. The heterogeneous pore distribution will be discussed in conjunction with the anisotropic viscous behavior to eventually unveil the shrinkage performance in the course of sintering. The findings of this work will provide insights into the anisotropic sintering mechanisms and fill the knowledge gap of the relations between extrusion-based metal AM process and sintered structures of metal alloys.

Three-dimensional evolution and interaction of disturbance waves on a gas-sheared liquid film on a horizontal plane near the transition region

Three-dimensional evolution and interaction of disturbance waves on a gas-sheared liquid film on a horizontal plane near the transition region

Simulation of Solid Propellant Regression with Cracks Based on Level-Set Method

Traditional methods are difficult to deal with solid propellant regression in complex geometry, especially for a finocyl grain with cracks. In this work, the Level-Set method is adapted to solid propellant regression. The advantage of this method is the implicit representation of interface and no restriction on geometrical configuration. Therefore, tiny cracks can be easily captured by the Level-Set method without any complex grids. A three-dimensional solid propellant regression evolution process of a finocyl grain is presented. A one-dimensional unsteady internal ballistics numerical method is applied to obtain pressure and thrust time histories, coupled with the three-dimensional grain burnback model. The mass and energy injection in the governing equations can be computed from the Level-Set formulation. And the propellant burning rate can be computed from the local pressure. The results show that a crack increases the head-end pressure and thrust at early stage, because of the increment of the burning surface area. It can be seen from the evolution of propellant regression that the crack gradually expands.

Dynamical Analyses of a Supercell Tornado in Eastern China Based on a Real-Data Simulation

Tornadoes are extremely destructive natural disasters, and East China has become a high-incidence area for tornadoes in China in recent years. On 7 July 2013, an EF2-intensity tornado occurred in Gaoyou County, Jiangsu Province in eastern China, within a supercell storm near a Meiyu frontal system. To investigate the dynamical process of the tornado, a numerical simulation was performed using four one-way nested grids within the Advanced Regional Prediction System (ARPS). Data from a nearby operational S-band Doppler radar are assimilated using a 4D ensemble Kalman filter (4DEnKF) at 5 min intervals. Forecasts are run with a nested 50 m grid, capturing the tornado embedded within the supercell storm with a reasonable agreement with observations. The tornadogenesis processes within the simulation results are analyzed in detail, including the three-dimensional evolution of the tornado vortex. It is found that a cold surge within the rear flank downdraft region plays a key role in instigating tornadogenesis when the leading edge of the cold surge approaches a near-ground convergence center located underneath the main updraft, and the enhancement of the convergence center caused by the descending of the low-level mesocyclone is the direct cause of the rapid increase in tornado vorticity. Backward trajectories are calculated based on model output, and the origins of the parcels feeding the intensifying tornado vortex are identified. It is found that parcels from the mid-level of the rear flank downdraft region follow the cold surge, descending to the ground under the influence of the downdraft in the cold surge, and then entering the convergence center, merging into the core of the tornado and being lifted up. Vertical profiles of the mass and vorticity fluxes into the core of the tornado vortex are examined, and it is found that the near-ground airflow contributes significantly to the growth of the tornado vorticity, with the contribution increasing as it gets closer to the ground.

Structural and electronic phase transition in the van der Waals crystal HfS2 under high pressure

The two-dimensional (2D) to three-dimensional (3D) structural evolution of transition metal dichalcogenides (TMDCs) under high pressure is a significant subject since the change of dimensionality could induce a drastic change in various physical properties. A more compact 3D structure of TMDCs could result in metallization and even superconductivity. In this work, we report an unusual 3D state of an $\mathrm{Hf}{\mathrm{S}}_{2}$ crystal that can still maintain its semiconducting nature over a wide pressure range. X-ray diffraction results show that the layered $\mathrm{Hf}{\mathrm{S}}_{2}$ undergoes a reversible transformation to a 3D $Immm$ structure at $\ensuremath{\sim}12$ GPa, accompanied by a semiconductor-to-semiconductor transition. The Raman and optical absorption measurements show that the phase transition may occur as early as $\ensuremath{\sim}9.2$ GPa. The semiconducting state is stable up to $\ensuremath{\sim}65$ GPa, and the metallization occurs at 68.6 GPa, the maximum pressure in this work. This work not only reports the 2D-to-3D structural phase transition in an $\mathrm{Hf}{\mathrm{S}}_{2}$ crystal driven by pressure, but also gives a clear physical picture that shows the intrinsic electrical transport properties and electronic behavior that enriches our understanding of the electronic behavior of TMDCs and sheds light on the future design of novel optoelectronic devices.

Temperature-Dependent Morphological Evolution during Corrosion of the Ni-20Cr Alloy in Molten Salt Revealed by Multiscale Imaging

Understanding the mechanisms leading to the degradation of alloys in molten salts at elevated temperatures is significant for developing several key energy generation and storage technologies, including concentrated solar and next-generation nuclear power plants. Specifically, the fundamental mechanisms of different types of corrosion leading to various morphological evolution characteristics for changing reaction conditions between the molten salt and alloy remain unclear. In this work, the three-dimensional (3D) morphological evolution of Ni-20Cr in KCl-MgCl2 is studied at 600 °C by combining in situ synchrotron X-ray and electron microscopy techniques. By further comparing different morphology evolution characteristics in the temperature range of 500-800 °C, the relative rates between diffusion and reaction at the salt-metal interface lead to different morphological evolution pathways, including intergranular corrosion and percolation dealloying. In this work, the temperature-dependent mechanisms of the interactions between metals and molten salts are discussed, providing insights for predicting molten salt corrosion in real-world applications.

Revealing the uterine blood vessel network via virtual pathology.

The distribution of the blood vessel network at any point in time in any body tissue, may provide valuable information with regards to the tissue condition and its angiogenesis functionality. The blood vessel three-dimensional network of the endometrium goes through a process of change over a relatively short period of 4 weeks on average. It is well accepted that this angiogenesis is closely related to the success or failure of the implantation of the embryo Objective and rationale: Our study aims to present a method to follow the three-dimensional evolution of the superficial blood vessel distribution in the endometrium throughout the uterine cycle. This method utilizes differences in the observed broadband colors of the blood vessels in order to assess their depth coordinate below the endometrial tissue surface. We implemented the method using microscopic images of fresh, ex-vivo, endometrial samples of different cycle days to obtain the statistical evolution track of the superficial blood vessel population in both human and animal (swine) samples. In human samples we observed a systematic and consistent trend in the BV diameter distribution at different tissue depths. We demonstrate that the magnitude of this trend evolves throughout the course of the female cycle. This method has the potential to further our understanding of the mechanisms of angiogenesis in tissues other than the endometrium. We propose that this method may also contribute to more precise endometrial dating and may assist in more accurate determination of embryo transfer timing within IVF treatments.

Three-dimensional evolution of radiative circumbinary discs: The size and shape of the inner cavity

In this study we present the results of 3D hydrodynamical simulations of circumbinary discs that orbit around analogues of the Kepler-16 and Kepler-34 systems, including the effect of stellar heating and radiative cooling on the thermal disc structure. We find that, compared to their 2D counterparts, the structures of the cavities in 3D circumbinary disc models appear to reach a quasi-stationary state more rapidly, and in a subset of our runs the evidence for this is unambiguous. Furthermore, the sizes and eccentricities of the inner cavity are smaller in 3D compared to 2D. We attribute this difference to enhanced spiral wave dissipation in disc regions above the midplane, where the cooling time is of the order of the dynamical timescale, resulting in smaller inner cavity sizes in 3D disc models. Our results suggest that migrating planets should park closer to the central binary in 3D models of circumbinary discs, and point to the importance of including the 3D structure when simulating circumbinary discs and planets.

Relationship between the heterogeneity of low-permeability reservoirs and the dynamic evolution of fractures under uniaxial compression conditions by CT scanning: A case study in the jiyang depression of Bohai Bay Basin, China

Based on an analysis of core fractures and computed tomography scanning by X-ray under uniaxial compression tests with loading and unloading, this study investigated the three-dimensional evolution of fracture initiation and propagation in different heterogeneity conditions of low-permeability reservoirs. Reservoir heterogeneity affected the 3D dynamic development of fractures. With increasing loading value, fractures with strong heterogeneity in low-permeability reservoirs followed the development sequence from shallow to deep depth in the profile. When the fracture tip reached the incompetent layer, propagation stopped. Subsequently, when the deformation continued to increase, the fracture crossed the incompetent layer and initiated a new fracture at the front end. Therefore, the across-bedding and through-going macro fractures formed in conjugate sets or were Y-shaped, with roughly equal spacing. In the plane, the fractures initiated along the pre-existing bedding parallel fracture and further propagated into large fractures. Consequently, they formed a net-shaped fracture from the edge to the center, with a long development period. These fractures intersected to form a complex, interconnected, and high-fracture-density system in three dimensions. Under the same loading value, owing to uniform lithology, the formation of micro-fractures in the weak heterogeneity of low-permeability reservoirs is difficult. Furthermore, long shear fractures were only produced in a relatively short formation period with a low fracture density. In the plane, the fractures stepped in an en-énchelon and terminated with horse-tailing microfractures. Moreover, the strong heterogeneity of low-permeability reservoirs was more favorable for producing fractures. The fracture volume was 13.17% of the total sample volume compared to 0.67% in the weak-heterogeneity reservoir under the same loading compression. Furthermore, a better fracturing effect was achieved by fracturing along the direction >50° with the natural fracture and under the condition of small differential horizontal stresses.

Perforation induced ligament evolution in low-temperature swirl spray via off-axis holography

Ligaments generated from a perforated sheet are commonly observed in the primary breakup process and have a fundamental influence on spray characteristics. Ignition and combustion instabilities of aeroengines at high altitudes raise the demand for dynamic measurement of ligaments in a low-temperature spray. Picosecond pulsed digital off-axis holography (DOH) system with 65 kHz high-speed and 4.5μm equivalent pixel size high-resolution setups is established. Three-dimensional (3D) evolution of ligaments in a pressure swirl spray under fuel temperature of 245–250 K and fuel pressure of 0.2–0.8 MPa is characterized. The stringy object extraction method optimized by FMCs cross correlation algorithm successfully extracts a 3D arc-shaped ligament in the spray at 0.2 MPa. The transition of ligaments into droplets during two modes of sheet perforation as hole–edge and two-hole interactions at 0.5 MPa is quantified with time resolution up to 15.4μs. Both the nucleation and growth of perforations are found involved with surface waves, and their early diameter growth velocities remain stable in the short term, consistent with Taylor–Culick velocity characteristics. The 3D velocity of a pair of ligaments in the spray at 0.5 MPa is obtained based on the spatial displacement of their daughter droplets within double frames, indicating a downward helical movement trend after separation from the conical swirling sheet. This work demonstrates DOH a powerful tool for 3D morphology extraction and dynamic analysis of ligaments and perforations in the pressure swirl atomization scenario.

The efficient ADI Galerkin finite element methods for the three-dimensional nonlocal evolution problem arising in viscoelastic mechanics

In this article, we investigate and analyze new methods for the numerical solution of the three-dimensional nonlocal evolution problem arising in viscoelastic mechanics. Then these methods combine Galerkin finite element methods (FEMs) for the spatial discretization with corresponding alternating direction implicit (ADI) algorithms, based on the backward Euler (BE) method and Crank-Nicolson (CN) method, respectively, from which, the Riemann-Liouville (R-L) integral term is approximated by relevant convolution quadrature rules. The $ L^2 $-norm stability and convergence of two ADI Galerkin schemes are proved by the energy argument. Numerical results confirm the predicted space-time convergence orders.

New quasiperiodic structures in nematic liquid crystals.

Liquid crystal molecules tend to align with each other, often forming regions of opposite alignment that meet at a boundary-topological defects. These often offer information on configuration of the liquid crystal molecules with competing constraints on their order. Here, we experimentally demonstrate a mechanism to generate topological defects in the form of spatially oscillatory domain walls in nematic liquid crystals. We initially orient the molecules perpendicular to the substrate (i.e. homeotropic alignment) and when a horizontal electric field is applied, domain walls that change their shape with time emerge. These walls form at low frequencies of the applied electric field and remain stable as the frequency increases. If the initial biasing field is at larger frequencies (kHz regime), the domain walls still form, but are not oscillatory. We develop a general theory to predict the three-dimensional liquid crystal director evolution in any two-dimensional varying field. This theory gives the time dependence for the domain walls and confirms that both the oscillatory and straight walls are stable.

Wavelength encoded single-shot high-spatiotemporal resolution all-optical probe

The laser probe is one of the main techniques for capturing ultrafast dynamic processes and has extensive applications in fields such as plasma physics, photochemistry, and biomedical science. In this work, a time-wavelength encoded optical probe generation scheme is proposed, which uses cascaded frequency doubling crystals with different phase-matching angles and independent delay lines to achieve time-wavelength encoding. This method offers single-shot high-spatiotemporal resolution, high frame rate, and a wide range of adjustable time windows. The temporal resolution of the optical probe depends on the pulse width of the second harmonic, which can be adjusted by changing the phase-matching angle of the frequency-doubling crystal. The time window of the optical probe is only related to the change in the delay line, which can be adjusted by changing the length of the delay line. Therefore, the time resolution and time window of the optical probe are independent of each other. An optical probe generation system is constructed with 247 fs temporal resolution, 4 μm spatial resolution, 4.05 THz maximal frame rate, and an adjustable time window from sub-picosecond to 3 ns. The three-dimensional spatiotemporal evolution process of plasma filaments is captured within a single shot by using the optical probe. The experimental results show that the ionization front of the plasma propagates forward at a velocity of <inline-formula><tex-math id="M2">\begin{document}$ {\left(2.963\pm 0.024\right)\times 10}^{8}\;{\rm{m}}/{\rm{s}} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="22-20230727_M2.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="22-20230727_M2.png"/></alternatives></inline-formula>, which is consistent with the theoretical prediction. This demonstrates the feasibility of using the probe for capturing ultrafast events. In the part of discussion, we analyze that the key parameters of the optical probe can reach a maximum frame rate of 35.7 THz, a maximum time resolution of 28 fs, and a time window range that can be adjusted from hundreds of femtoseconds to tens of nanoseconds. Finally, the optimal design parameters of the optical probe are given for different application scenarios. The optical probe generation scheme has good scalability and versatility, and can be combined with any wavelength decoding device, diffraction imaging, holographic imaging, tomography scanning, and other technologies. The high spatiotemporal resolution of the optical probe and the independent adjustability of its parameters provide a feasible solution for single-shot high spatiotemporal resolution captures of ultrafast dynamic processes on a multiple time scale.

Discussion on the wrapping phenomenon of Cu-ZnO system by in-situ investigation during microwave sintering

The microstructure evolution during zinc oxide (ZnO) and metallic copper (Cu) microwave sintering was in situ investigated by using synchrotron radiation computed tomography (SR-CT). Based on the SR-CT experiment, the coupling effect between the materials and the microwave electromagnetic field was discussed. During microwave sintering, special three-dimensional microstructure evolution was directly observed. The copper particles were gradually “wrapped” by surrounding zinc oxide particles. The special phenomenon of "wrapping" may be related to the change in the conductivity of semiconductor ZnO. It was proposed that there might be an "electromagnetic attraction" between particles during the "wrapping" process. The electromagnetic attraction was further discussed by comparing the microstructure evolution in different directions and at different initial distances. The center distance reduction of Cu-ZnO particles in the vertical cross section was more obvious, and the “wrapping” phenomenon was more obvious with a closer initial distance. The electromagnetic attraction proposed in this paper was supported by some experimental phenomena. The research in this article could have implications for revealing the mechanisms of microwave sintering.

On the flow dynamics of wall-mounted low-aspect-ratio rotating cylinders

The flow physics and vortical features attributed to a low-aspect-ratio circular cylinder cantilevered on a laminar boundary layer plate and rotated about its respective axial coordinate were investigated experimentally using Stereo Particle Image Velocimetry. The investigation documents the three-dimensional spatial evolution of on-body dynamics to deep-wake phenomena. In disseminating the more salient global characteristics of the resultant flowfield, the analysis focuses on the particular case of an aspect ratio of 1 driven in continuous rotary motion at a speed ratio of 3. The two key findings are (i) vortex source: a wall-normal swirl develops and reorients into a streamwise vortex at the cylinder's mid-diameter location due to the heavy influence of the incoming boundary layer, local fluid entrainment, and proximity to the wall. (ii) Enhanced downwash: in return, the streamwise vortex primarily drives the production of additional downwash in the wake, which appends to the downwash generated by the cylinder's free end. A two-dimensional planar particle image velocimetry campaign in service of a parametric survey reveals the sensitivity of streamwise vortex production and downwash to rotational rate and cylinder height relative to boundary layer thickness. The streamwise vortex production tends to deteriorate when the cylinder is immersed in the boundary layer due to reduced downwash.

Three-dimensional evolution of the flow unsteadiness in the S-shape of pump-turbines and its correlation with the runner geometry

Pump-turbines (RTP) are the most common mechanical equipment adopted in pumped-hydro power plants and, for grid balancing purposes, are required to sharply switch from pumping to generating mode, and to extend their operative, jeopardizing not only the machine operability but also its life. New design approaches to avoid the onset of unstable behaviours are still far from being defined, and control strategies for accelerating start-up/shut-down procedures are still not effective since these are based on semi-empirical approaches, due to the lack of identification of precursors of the unstable behavior.In this paper, a numerical analysis of the unstable behavior of an RPT during the transition from partial load up to the turbine-brake area was carried out. The fluid-dynamics in different operating points (partial load, run-away condition, turbine brake) was deeply investigated, identifying the rotor-stator mechanisms causing the 3D evolution of the flow field leading to the development of the unstable behavior. Three evolution phases (inception, growth and consolidation) were identified and clearly correlated with the runner geometry and with the S-Shape of the RPT characteristic curve. Customized signal processing strategies were adopted for spectrally characterizing each phase so as to identify potential triggers for new monitoring and control strategies. Moreover, for the first time, a clear fluid-dynamic explanation of the empirical results found in literature on the influence of the runner geometry is provided.

Numerical Investigation of Gas-Liquid Flow in a Multiphase Pump with Special Emphasis on the Effect of Tip Leakage Vortex on the Gas Flow Pattern

In this paper, the gas-liquid flow is comprehensively analyzed under different inlet gas void fractions, and the effect of tip leakage vortex (TLV) on the gas flow pattern in multiphase pumps is revealed. The results show that the gas flow pattern in an impeller is closely related to the centrifugal force, low-pressure region, and vortex motion. Most gas is present near the hub and suction surface of the blade as well as in the TLV. The two- and three-dimensional spatiotemporal evolution of the gas is presented, and the gas motion during the inception, development, and dissipation of TLV is revealed. It is reflected that the gas volume fraction is the highest at the TLV core and gradually weakens along the radial direction with the vortex core at the center. Additionally, the TLV energy dissipation is closely related to the gas and pressure difference, and strong energy dissipation occurs in the jet-wake flow.

Three-dimensional evolution of body and fluid motion near a wall

Evolution of three-dimensional body motion within surrounding three-dimensional fluid motion is addressed, each motion affecting the other significantly in a dynamic fluid–body interaction. This unsteady problem is set near a wall. The spatial three-dimensionality present is a new feature. For inviscid incompressible fluid, a basic nonlinear formulation is described, followed by a linearised form as a first exploration of parameter space and solution responses. The problem reduces to solving Poisson’s equation within the underbody planform, subject to mixed boundary conditions and to coupling with integral equations. Numerical and analytical properties show dependence mainly on the normal and pitch motions, as well as instability or bounded oscillations depending on the position of the centre of mass of the body, and a variety of three-dimensional shapes is examined.

Lateral and vertical growth and linkage of normal faults in Bozhong8-4 structure of Western Bozhong Sag, Bohai Bay Basin, China

Many previous studies have shown that normal faults are formed by growth and linkage of shorter fault segments through time and have suggested various fault growth models. Although these models have yielded useful information on the evolution of normal fault systems in map view, the three-dimensional (3D) evolution of normal faults is poorly understood. Here, we employ an integrated 3D seismic reflection and well dataset to investigate the 3D growth process of fault zone F1 in the Bozhong 8–4 (BZ8-4) structure of the Western Bozhong Sag (WBS). We i) constructed 3D structural models of individual fault surfaces, ii) calculated the dip angles and dip azimuth distributions on fault surfaces, iii) produced D-d profiles and throw contour maps of fault surfaces, and iv) investigated the 2D/3D segmentation characteristics of geometry and displacement distribution. We found that Fault F1 exhibits segmentation characteristics of geometry and displacement distribution both along strike and dip oriented directions. Vertically, fault surfaces can be divided into three areas (lower, middle and upper parts) that correspond to three stages of regional tectonic evolution (intense faulting, relatively quiescent faulting and post-rifting). The coalescence zone of the upper and lower fault surfaces shows as a sub-horizontal anomaly of geometry and displacement distribution that is sub-parallel to the traces of the horizons. The lower and upper parts of fault surfaces also show segmentation characteristics along strike, which are identified by vertically anomalous zones of geometry and displacement distribution. However, the origins of the segmentation in this case are different. The segmentation of the lower part of the fault developed during the rifting stage is caused by the intersection of faults with different strikes, whereas the upper part of the fault is the result of the lateral growth and linkage of overlapping fault segments. Therefore, not all fault segmentation characteristics along strike can be attributed to fault growth and linkage. Based on 3D fault segment identification, we therefore establish a 3D evolution model of fault zone F1. During the deposition of the Shahejie Fm up to the member (Mbr) 3 of the Dongying Fm in the Paleogene, the faults in this area were highly active, with the development of the NE-trending Fault F1, the NEE-trending Fault Fa and the NW-trending Fault F2. The intersection of Faults Fa and F2 with Fault F1 results in Fault F1 exhibiting segmentation in geometry and displacement distribution. From the deposition of the Mbr 2 of the Dongying Fm, these faults ceased to be active. Since the Pliocene (5.2 Ma), under the influence of transtensional stress field, an en-echelon fault zone was developed in the Neogene strata above fault zone F1 active in the rifting stage. While these faults grow and link laterally, their tip-lines propagate along dip-oriented directions and activate the lower faults and link vertically with them to form the present fault zone F1.