Axial Ends Research Articles

Double cylinder implosion experiments at the National Ignition Facility

Cylindrical implosion experiments are used to directly measure instability growth in a convergent geometry, providing a wealth of data for model validation. Double cylinders are a natural extension of the platform and enable measurements at a classically unstable interface, the outer surface of the inner cylinder, which experiences no ablative stabilization from the laser drive. However, the utility of this platform relies upon maintaining adequate axial uniformity of the inner cylinder during the implosion. Although previous smaller-scale double cylinder experiments exhibited acceptable levels of axial uniformity, radiation-hydrodynamics simulations of larger-scale double cylinders predict more axial non-uniformity induced by the impedance mismatch as the shock wraps around the axial ends of the inner cylinder. A mechanism to reduce axial non-uniformity in these larger double cylinder implosions is presented, and preliminary experimental data confirms the efficacy of the selected mitigation approach.

A numerical survey of parameters to reach ignition condition for axial compression of a large-sized field reversed configuration

Field reversed configuration (FRC) is widely considered as an ideal target plasma for magneto-inertial fusion. However, its confinement and stability, both proportional to the radius, will deteriorate inevitably during radial compression. Hence, we propose a new fusion approach based on axial compression of a large-sized FRC. The axial compression can be made by plasma jets or plasmoids converging onto the axial ends of the FRC. The parameter space that can reach the ignition condition while preserving the FRC’s overall quality is studied using a numerical model based on different FRC confinement scalings. It is found that ignition is possible for a large FRC that can be achieved with the current FRC formation techniques if compression ratio is greater than 50. A more realistic compression is to combine axial with moderate radial compression, which is also presented and calculated in this work.

Thermal characterization of an interior permanent magnet electric motor

An engineering approach for thermal characterization of an interior permanent magnet electric motor (EM) with a specific aim to identify the interdependency between its mean coil temperature and the maximum component temperatures at the conditions with constant and variable loads/speeds is proposed. For specifying the convective thermal boundary condition between stator and rotor that spins at variable speeds/directions, an experimental study aimed at devising the empirical heat transfer correlation for the Taylor-Couette airflow with varying rotating speed/direction is performed. It is firstly revealed that the responsive air-gap heat convection to angular acceleration follows the characteristic of a single-degree-of-freedom (SDOF) dynamic system. Along with the heat transfer correlation for the unsteady Taylor-Couette airflow, the nonhomogeneous thermal conductivity model that considers the orthogonality effect of the bent coiled winding at its two axial ends is integrated with an iteration scheme for calculating the air bulk temperature in an entrapped air chamber. The favorable experimental validation with the maximum discrepancies between predicted and measured component temperatures less than 7 % in steady and unsteady running conditions affirms the accuracy of the proposed simulation model. At a rotating speed of 4800 rev/min and power output of 1688 W, the maximum-to-mean temperature differences of stator winding, magnetic stripe, and steel sheet of stator reach respectively 6.75 °C, 3.21 °C, and 6.94 °C. Particularly, all the maximum component temperatures are well correlative with the mean temperature of the stator winding at the various steady/unsteady operating conditions. This finding extends the application of lumped thermal network analysis that predicts the averaged components’ temperatures; and enables the on-line monitoring for the maximum component temperatures using a mean stator-winding temperature as the controlling factor.

Compressive anisotropy effects and crack evolution mechanisms of 3D5d braided composites induced by thermo-oxidative ageing

Ageing cracks and loading directions will affect mechanical behaviors of thermo-oxidative aged 3D braided composites. Here we report ageing crack propagations, compressive responses, in-situ strain evolutions, full-field damage distributions and crack evolution mechanisms of aged three-dimensional five-directional (3D5d) braided composites along out-of-plane (OP) and in-plane (IP) loading based on X-ray micro-computed tomography and digital image correlation technique. Ageing cracks are distributed at both axial ends that corresponding to the yarn arrangement and extend to the interior with the increase in ageing time. Compressive modulus, strength, retention rate and damage mode show ageing weakening behaviors and anisotropy effects. Strain distributions exhibit structure correlation. Ageing cracks affect the surface strain and damage distributions but not internal shear modes during OP loading. Yarn arrangement affects damage evolution and accumulation. Ageing cracks change the damage evolution path in both directions. The synergistic effect of ageing crack with IP loading is greater than that with OP loading. It is expected that this work can provide a clear guideline for the structural optimization and durability design of 3D braided composites.

Micromagnetic Study of the Dependence of Output Voltages and Magnetization Behaviors on Damping Constant, Frequency, and Wire Length for a Gigahertz Spin Rotation Sensor.

In this report, we studied the dependence of output voltage on the damping constant, the frequency of the pulse current, and the wire length of zero-magnetostriction CoFeBSi wires using multiphysics simulation considering eddy currents in micromagnetic simulations. The magnetization reversal mechanism in the wires was also investigated. As a result, we found that a high output voltage can be achieved with a damping constant of ≥0.03. We also found that the output voltage increases up to a pulse current of 3 GHz. The longer the wire length, the lower the external magnetic field at which the output voltage peaks. This is because the demagnetization field from the axial ends of the wire is weaker as the wire length is longer.

Computational analysis of effects of clot length on Acute ischemic stroke recanalization under different cyclic aspiration loading conditions.

Acute ischemic stroke, the second leading cause of death worldwide, results from occlusion of a cerebral artery by a blood clot. Application of cyclic aspiration using an aspiration catheter is a current therapy for the removal of lodged clots. In this study, we perform finite element simulations to analyze deformation of long clots, having length to radius ratio of 2-10, which corresponds to clot-length of 2.85-14.25 mm, under peak-to-peak cyclic aspiration pressures of 10-50 mmHg, and frequencies of 0.5, 1, and 2 Hz. Our computational system comprises of a nonlinear viscoelastic solid clot, a hyperelastic artery, and a nonlinear viscoelastic cohesive zone, the latter modeling the clot-artery interface. We observe that clots having length-to-radius ratio approximately greater than two separate from the inner arterial surface somewhere between the axial and distal ends, irrespective of the cyclic aspiration loading conditions. The stress distribution within the clot shows large tensile stresses in the clot interior, indicating the possibility of simultaneous fragmentation of the clot. Thus, this study shows us the various failure mechanisms simultaneously present in the clot during cyclic aspiration. Similarly, the stress distribution within the artery implies a possibility of endothelial damage to the arterial wall near the end where the aspiration pressure is applied. This framework provides a foundation for further investigation to clot fracture and adhesion characterization.

A Model and Experimental Validation for a Piston Rings—Squeeze Film Damper: A Step Toward Quantifying Air Ingestion

Abstract Rotor-bearing systems often rely on squeeze film dampers (SFDs) to increase the dynamic stability and reduce rotor motion amplitudes while traversing critical speeds. In aircraft engines, to increase the damping capacity within a limited physical space, piston rings (PRs) seal the axial ends of a squeeze film land. However, lubricant still leaks through the slit in the PR abutted ends, and air enters into the film to make a bubbly oil mixture with a much reduced damping capability. This paper presents a volume of fluid (VOF) model for a PR sealed ends SFD facing ambient air (not submerged in lubricant and prone to air entrainment) and delivers predictions benchmarked against experimental results obtained in a dedicated test rig. A lubricant feeds pressure and flows large enough to prevent air ingestion vary with the damper geometry, the lubricant inlet and outlet conditions, and the kinematics of the journal. A parametric study for a typical SFD shows the period-averaged gas volume fraction (GVF) increases as the journal squeeze film velocity (vs) increases and as the film clearance decreases. Most importantly, the location of the PR slit relative to the feedhole affects the amount of air drawn into the film. When the PR slit faces a feedhole, the film land is mostly filled with a pure lubricant. The GVF increases as the arc distance from the PR slit to the feedhole increases. The physical model, anchored by the test data, effectively addresses a fundamental challenge in SFD design and operation; namely, quantifying the amount of air ingested and its effect on the damper forced performance.

Experimental study on the evolution of mechanical properties of hot dry rocks under alternating temperature loads

Inspired by the physical process of thermal expansion and cold shrinkage, this study proposes a new idea to improve the capacity to form complex fractures (i.e., fracability) in hot dry rock (HDR) under alternating temperature loads. However, the evolution of the HDR mechanical properties under alternating temperature loads is rarely reported. This study analyzed the evolution mechanism of the HDR rock mechanics properties under alternating temperature loads by using the high-temperature high-pressure rock mechanics triaxial test system. The results show that mechanical parameters such as compressive strength, dilatancy stress, and elastic modulus are significantly reduced after alternating temperature loading, compared with those after simple heat treatment. After alternating temperature loading, compared with the case of simple heat treatment, the HDR rock samples reach the dilatancy stress earlier; its stress-strain curve features a visible concave arc at the micro-fracture closure segment; the axial loading ends up with the shear failure and enhanced complexity. The microstructural analysis shows that cyclic thermal stress occurs inside the HDR as the temperature increases and extensive mineral metasomatism is triggered, which is dominated by quartz penetrating plagioclase via metasomatism. Therefore, the decrease of quartz content and the HDR mineral metasomatism under alternating temperature loads are the fundamental causes for the great changes in the HDR mechanical properties.

Bearing Fault Diagnosis of Hot-Rolling Mill Utilizing Intelligent Optimized Self-Adaptive Deep Belief Network with Limited Samples.

Given the complexity of the operating conditions of rolling bearings in the actual rolling process of a hot mill and the difficulty in collecting data pertinent to fault bearings comprehensively, this paper proposes an approach that diagnoses the faults of a rolling mill bearing by employing the improved sparrow search algorithm deep belief network (ISAA-DBN) with limited data samples. First, the fast spectral kurtosis approach is adopted to convert the non-stationary original vibration signals collected by the acceleration sensors installed at the axial and radial ends of the rolling mill bearings into two-dimensional (2D) spectral kurtosis time–frequency images with higher feature recognition, and the principal component analysis (PCA) technique is used to decrease the dimension of the data in order to achieve a high diagnosis rate with a limited number of samples. Subsequently, the sparrow search algorithm (SSA) is used to realize the intelligent optimized self-adaptive function of a deep belief network (DBN). Furthermore, the firefly disturbance algorithm is employed to improve the spatial search capability and robustness of SSA-DBN in order to achieve better performance of the ISSA-DBN method. Finally, the proposed approach is experimentally compared to other approaches used for diagnosis. The results show that the proposed approach not only retains the useful features of the data through dimension reduction but also improves the efficiency of the diagnosis and achieves the highest diagnosis accuracy with limited data samples. In addition, the optimal position of the sensor for diagnosing rolling mill roll faults is identified.

Simulation of an industrial scale scCO2 beam dyeing process

An industrial dyeing process in supercritical carbon dioxide has been modelled with computational fluid dynamics using Ansys Fluent software. In order to investigate the distribution of the dye carrier fluid, the flow resistance of the fabric has been accurately characterised. For this purpose, in the first part of the work a plain-woven fabric geometry was created in the open software Tex-Gen and modelled in Ansys Fluent to predict the permeation of fluid through the pores of the fabric material and to estimate the relationship between local fluid velocity and pressure drop. The second part of the study focused on evaluating the influence of beam structure, inlet flow rate, fabric height on the fluid flow through the fabric, which must be uniform to achieve a homogeneous level of dyeing. From the simulations the main obstacle to achieving a uniform flow velocity in the fabric is the pressure rise that occurs in the beam and creates a slight difference in permeation velocity between the two axial ends of the fabric; other disturbances, such as the effect of the perforated structure of the beam, are usually minor. Due to the low viscosity of supercritical carbon dioxide, inertial losses predominate over viscous losses in the porous medium. This means that approaches based only on the permeability of the fabric and the application of Darcy's law are inadequate to correctly predict the response of a dyeing unit when using carbon dioxide.

Analysis of Deflection in Visco-Thermoelastic Beam Resonators Subjected to Harmonic Loading

This paper analyses the transverse deflection in a homogeneous, isotropic, visco-thermoelastic beam when subjected to harmonic load. The ends of the beam are considered at different boundary conditions (both axial ends clamped, both axial ends simply supported and left end clamped and right end free). The deflection has been studied by using the Laplace transform. Numerical computation of analytical expression of deflection obtained after Inverse Laplace transform has been done using MATLAB software. The graphical observations have been discussed under various boundary conditions for different values of time and length. The above work has applications in design of resonators.

Thermal performance of a cylindrical shell-like thin networked pulsating heat pipe

The cylindrical vapor chamber with its interior vapor–liquid circulation facilitated by the pulsating heat pipe network at the 50% filling ratio of distilled water was proposed. The total heating area of the two annular evaporators at both axial ends is identical with the middle condenser cooling area. With the equal heat flux emitted from each evaporator, the measurements of the overall thermal resistance, the Nusselt numbers of evaporator and condenser, the temporal pressure variation and the skin temperature uniformity over the condenser were carried out with the total heating power in the range of 30–90 W at the inclination angles of 0 (horizontal), π/6, π/3, π/2 (vertical) and six cooling airflow rates for each heating power tested. The thermal resistances of the two evaporators were both decreased as the heater power increased but their difference was systematically enlarged by tilting the vapor chamber from horizontal to vertical orientations. The power spectrum of the time-domain pressure signal revealed two dominant frequencies in association with the vapor bubble agitations in the pulsating heat pipe network at all the test conditions. These frequencies and the heating power dominated the thermal performances of the vapor chamber after demonstrating that the responses of the dominant frequencies to the changes in heating and cooling conditions correlated well with the corresponding variations in the overall thermal resistance and the temperature uniformity of the condenser. Referring to the results measured from the planar vapor chambers in the literature, the comparative thermal performances of the cylindrical thin vapor chamber were disclosed. A set of empirical correlation was developed to permit the evaluation of the overall thermal resistances of the two evaporators for relevant applications.

A half-salamo-based pyridine-containing ligand and its novel NiII complexes including different auxiliary ligands: syntheses, structures, fluorescence properties, DFT calculations and Hirshfeld surface analysis

Three novel multinuclear NiII complexes, namely, bis{μ-2-methoxy-6-[8-(pyridin-2-yl)-3,6-dioxa-2,7-diazaocta-1,7-dien-1-yl]phenolato}bis[thiocyanatonickel(II)], [Ni2(L)2(NCS)2], 1, bis{μ-2-methoxy-6-[8-(pyridin-2-yl)-3,6-dioxa-2,7-diazaocta-1,7-dien-1-yl]phenolato}bis[azidonickel(II)], [Ni2(L)2(N3)2], 2, and catena-poly[[{2-methoxy-6-[8-(pyridin-2-yl)-3,6-dioxa-2,7-diazaocta-1,7-dien-1-yl]phenolato}nickel(II)]-μ-dicyanamidato], [Ni(L)(dca)] n , 3 {dca is dicyanamide, C2N3, and HL is 2-methoxy-6-[8-(pyridin-2-yl)-3,6-dioxa-2,7-diazaocta-1,7-dien-1-yl]phenol, C16H17N3O4}, with a half-salamo-based pyridine-containing HL ligand have been synthesized and characterized by FT–IR, UV–Vis absorption spectroscopy, X-ray crystallography, Hirshfeld surface analysis and density functional theory (DFT) calculations. The central NiII ions in complexes 1–3 are hosted in the half-salamo-based N3O-donor cavity of the organic ligand. Complex 1 is a centrosymmetric dimer and two [Ni(L)(NCS)] units form a centrosymmetric dimeric structure, which is bridged by two phenolate O atoms. The two N atoms at the axial ends are provided by two NCS− ligands. In complex 1, each NiII ion has a six-coordinated octahedral geometry. Complex 2 is similar to 1, but they differ in that the auxiliary NCS− ligand is replaced by N3 −. However, complex 3 is a one-dimensional coordination polymer constructed from [Ni(L)(dca)] units, which are connected by the auxiliary bidentate dca ligand via N-donor atoms. As with complexes 1 and 2, the NiII ion in 3 has a six-coordinated octahedral geometry.

On the Effect of the Gap of End Seals on Force Coefficients of a Test Integral Squeeze Film Damper: Experiments and Predictions

Abstract An integral squeeze film damper (ISFD) offers the advantages of a lower number of parts, a shorter axial span, a lighter weight, a split manufacturing, and high precision on its film clearance construction. An ISFD does not only add damping to reduce shaft vibration amplitudes and to enhance the stability of a rotor-bearing system but also can be used to tune a rotor-bearing system natural frequency, and thus increasing the operational safety margin between the running shaft speed and the system critical speed. In spite of the numerous commercial applications, the archival literature is scant as per the experimental quantification of force coefficients for ISFDs. This paper details the results of an experimental and analytical endeavor to quantify and to predict the dynamic force coefficients of an ISFD, hence bridging the gap between theory and practice. With an axial length of 76 mm, the test damper element has four arcuate film lands, 73 deg in arc extent at a diameter of 157 mm, and each with a clearance (c) equaling to 0.353 mm. As is customary, the damper has its axial ends sealed with end plates produced by a set of installed shims giving an axial gap (d) equal to 1.5c, 1.21c, and 0.8c. A baseline configuration, namely, open ends, is also tested without the end seals in place. In the test rig, the ISFD and its housing are flexibly mounted while the rotor is rigid and stationary (no spinning). The lubricant is an ISO VG46 oil supplied at a low pressure, 1 to 2 bar(g) and ∼47 °C inlet temperature, typical of compressor applications. The test procedure applies static loads on the ISFD and records the bearing static offset or eccentricity to verify the structure stiffness, and meanwhile, individual hydraulic shakers deliver dynamic loads along two orthogonal directions to produce motions over a set frequency range, 10 Hz to 160 Hz. The ISFD produces direct damping and inertia that increase with the journal static eccentricity albeit at a lower rate than predictions from a computational squeeze film flow model that includes lubricant compressibility. The end seals are effective in significantly raising the damping coefficient while reducing the oil through flow rate. The damper with the tightest sealed ends (d = 0.8c) shows nearly 20 times more damping that the open ends ISFD albeit also revealing a significant stiffness hardening (negative virtual mass) as the excitation frequency increases. On the contrary, the open ends ISFD and the sealed-ends configurations with gaps d = 1.21c and 1.5c produce a (positive) virtual mass that exceeds the test element physical mass and thus softens the test element direct dynamic stiffness. For the configurations with loose end seals (d = 1.21c or larger to open ends), the model predicts well the damping coefficients but under predicts the added masses by 50% or more. Note this virtual mass coefficient, largely ignored in practice, can make the test element either extremely stiff as with the sealed damper configuration with the smallest gap d = 0.8c, or very soft as with the ISFD with end seals gap = 1.21c or 1.5c. Hence, designers are cautioned not to pursue overly tight end sealed dampers as the mineral lubricant, nearly incompressible though always having a small amount of entrapped gas, may behave distinctly when confined to a squeezed film volume and having no adequate routes to escape or flow through.

Saint-Venant End Effects in the Plane Problem for Linearly Elastic Functionally Graded Materials

An isotropic elastic strip, with a continuous inhomogeneity profile for Young’s modulus is considered, subject to a self-equilibrated load on one of its axial ends and free of traction on the remainder of its surface boundaries. By taking advantage of the analytical flexibility of an exponential inhomogeneity profile, the full equations of linear theory of elasticity are employed to find the two-dimensional Saint-Venant decay rate in terms of an inhomogeneity parameter that measures gradation steepness in a Functionally Graded Material (FGM). The results show that softening axial inhomogeneity may be introduced to engineered FGM strips and beams to accelerate the decay of stresses. For a hardening axial inhomogeneity on the other hand, the end effects extend beyond a one-width-size distance from the loaded end. The plane problem end effects are shown to decay faster compared to the anti-plane shear counterparts, consistent with what is observed in homogeneous media. For inhomogeneity in the lateral direction from the core toward the outer edges, the qualitative behaviour changes with the degree of inhomogeneity. Whether the core is softer or harder relative to the outer edges, a steep lateral gradation of elastic modulus can significantly increase the decay length of end effects.

Experimental studies into the performance of the lead coolant axial pump wet ends to justify main circulation pumps for the HMLC reactor plant circuits

The paper presents the results of the studies to justify the design solutions for the main circulation pumps of the heavy liquid-metal cooled reactor plant circuits. A substantial difference has been shown in the performance of pumps for the heavy liquid-metal coolant transfer. The studies have confirmed the qualitative difference in the cavitation performance of coolants, the state of the gases and vapors they contain, the influence of supply and discharge devices, and the effects of the impeller blade section performance and geometry and the hub-tip ratio on the pump performance. The studies were performed based on NNSTU’s lead-cooled test facilities with the coolant temperature in a range of 440 to 550 °C and the coolant flow rate of up to 2000 t/h. The outer diameter of the impellers and the straightening devices was about 200 mm, and the thickness of the flat 08Kh18N10T-steel blades was 4.0 mm and that of the airfoil blades was up to 6.0 mm. The pump shaft speed changed in a stepped manner from 600 rpm to 1100 rpm after each 100 rpm. The studies were conducted to justify the engineering and design solutions for pumps as applied to conditions of small and medium plants with fast neutron lead cooled reactors currently under investigation at NNSTU (BRS-GPG). The experimental results can be recommended for use to design other HLMC transfer pumps.

Экспериментальные исследования характеристик проточных частей осевых насосов для свинцового теплоносителя в обоснование главных циркуляционных насосов контуров РУ с ТЖМТ

Экспериментальные исследования характеристик проточных частей осевых насосов для свинцового теплоносителя в обоснование главных циркуляционных насосов контуров РУ с ТЖМТ

Memory response in the vibration of a micro-scale beam due to time-dependent thermal loading

This study proposes a computationally efficient approach about the dynamic response of a homogeneous, transversely isotropic, thermoelastic micro-beam resonator subjected to time-dependent thermal loading. Due to the shortcomings of power law distributions in fractional derivatives, the usage of some other forms of derivatives with few other kernel functions are proposed. With this motivation, the heat transport equation is defined in an integral form of a common derivative on a slipping interval by incorporating the three-phase-lag memory-dependent heat transfer which is modeled based on Euler-Bernoulli beam theory. The beam is assumed to be clamped-clamped conditions on its axial ends. Employing the Laplace transform technique, the analytical solutions have been obtained. Further, incorporating residual calculus, the inversion of the transformed solutions are performed. The analytical expressions for the deflection has been computed numerically for a Silicon micro-beam using Maple software. The new approach is able to portray material heterogeneities and the non-locality of the new kernel allows the full describing of the memory within structure and media with different scales, which cannot be described by classical fractional derivative and also that of the memory-dependent derivative.

Improvement of lubrication performance of water lubricated polymer bearing via enlarged axial end bearing diameter

Purpose The purpose of this paper is to improve the lubrication performance of a water-lubricated polymer bearing with axial grooves, especially enlarge the minimum film thickness. Design/methodology/approach The bearing diameter is enlarged near the axial ends of the journal, with axial openings of a trumpet shape. A numerical model is developed which considers the proposed trumpet-shaped openings, bush deformation and grooves. The generatrix of the trumpet-shaped opening is assumed to be a paraboloid. Three different variations are covered, and the influences of the trumpet-shaped openings’ parameters on the bearing performance are analyzed. Findings The appropriate trumpet-shaped openings at the axial ends effectively increase the minimum film thickness, and the impact of trumpet-shaped openings on load carrying capacity is very small or even negligible. For the water-lubricated polymer bearing with axial grooves analyzed in this paper, the appropriate trumpet-shaped openings increase the minimum film thickness from 0.53 to 11.14 µm and decrease the load carrying capacity by 2.48 per cent. Practical implications The results of this study can be applied to marine propeller shaft systems and other systems with polymer bearings. Originality/value This paper has presented an approach for significantly increasing the minimum film thickness of a water-lubricated polymer bearing. A study on the performance improvement of water-lubricated polymer bearings with axial grooves is of significant interest to the research community.

One-Dimensional Models for Time-Dependent Transport in Solid Cylinders

We present a set of 1-D transport models for solid cylinders of material irradiated with particles on the axial ends. The models are based on 1-D models originally developed for evacuated ducts with reflecting walls. The goal of this work is to show that 1-D models can be used for time-dependent transport in solid cylinders. A future use of this approach will apply these models to the high-energy density physics problem of a Marshak wave propagating down a cylindrical foam or other experiments. The models we present use a Galerkin procedure to project the radial dependence of the 3-D transport equation onto an expansion in terms of polynomials. Results demonstrate that for steady state problems with low scattering ratios, a three-basis function expansion can adequately capture the 3-D solution as computed via Monte Carlo. Smaller number of basis functions did not result in adequate solutions. As the radius of the cylinder increases, the 1-D model is more effective. Results from time dependent problems indicate that the 1-D models move particles too fast down the cylinder at early times, but are accurate on the order of 10 or more mean-free times. Our results indicate that 1-D models may be effective in modeling 2-D Marshak waves, but further work is necessary to answer this question.