Non-uniform Conditions Research Articles

Investigation of the Initiation of Composite Mode I/II Crack in Gas‐Bearing Rock Caused by Nonuniformly Distributed Heat Flux

ABSTRACTTo investigate the patterns of rock crack initiation caused by the nonuniformly distributed heat flux resulting from fracture air‐vapor pressure, the fracture air‐vapor pressure control equation was deduced, and five spatial distribution forms of heat flux were established. The crack initiation criterion considering nonuniform heat flux conditions was proposed based on the modified maximum tangential stress criterion, the theory was validated using FEM and FE‐FEM numerical methods. The results show that the peak value of nonuniform heat flux determines the maximum value of the crack surface temperature, and the distribution form determines the range of high‐temperature and low‐temperature regions on the crack surface. Axisymmetric heat flux induces centrosymmetric cracking, and nonaxisymmetric heat flux induces noncentrosymmetric cracking. It was observed that when qmax = 5000 mW/m2, there is a mutation line in the critical crack initiation angle, which mutates from −90° to 90°. The position of the mutation line decreases with increasing heat flux.

Recovering the properties of the interstellar medium through integrated spectroscopy: Application to the z∼0 ECO volume-limited star-forming galaxy sample

Deriving physical parameters from integrated galaxy spectra is paramount to interpret the cosmic evolution of the star formation, chemical enrichment, and energetic processes at play. Previous studies have highlighted the power of interstellar medium tracers but also the associated complexities that can be captured only through sophisticated modeling approaches. We developed modeling techniques to characterize the ionized gas properties in the subset of $2052$ star-forming galaxies from the volume-limited, dwarf-dominated, z∼0 ECO catalog (stellar mass range M_*∼10^8-11,M_⊙). Our study sheds light on the internal distribution and average values of parameters such as the metallicity, ionization parameter, and electron density within galaxies. We used the MULTIGRIS statistical framework to evaluate the performance of various models using strong lines as constraints. The reference model involves physical parameters distributed as power laws with free parameter boundaries. Specifically, we used combinations of 1D photoionization models (i.e., considering the propagation of radiation toward a single cloud) to match optical H2 region lines, in order to provide probability density functions of the inferred parameters. The inference predicts nonuniform physical conditions within galaxies. The integrated spectra of most galaxies are dominated by relatively low-excitation gas with a metallicity around $0.3$,Z_⊙. Using the average metallicity in galaxies, we provide a new fit to the mass-metallicity relationship which is in line with direct abundance method determinations from the low-metallicity calibrated range up to high-metallicity stacks. The average metallicity shows a weakly bimodal distribution which may be due to external (e.g., refueling of non-cluster early-type galaxies) or internal processes (higher star-formation efficiency in metal-rich regions). The specific line set used for inference affects the results and we identify potential issues with the use of the S2 line doublet. Complex modeling approaches may capture diverse physical conditions within galaxies but require robust statistical frameworks. Such approaches are limited by the inherent 1D model database as well as caveats regarding the gas geometry. Our results highlight, however, the possibility to extract useful and significant information from integrated spectra.

Tip-clearance pressure fluctuations between conventional pump-jet propulsor and pump-jet propulsor with rotor blade crown in non-uniform inflow

The suppression of the pressure fluctuations in the tip clearance of the pump-jet propulsor is of great significance in improving its noise radiation level. This study considers adding rotor blade crown structure to propose a new type of pump-jet propulsor. The hydrodynamic performance of conventional pump-jet propulsor and pump-jet propulsor with rotor blade crown was analyzed in non-uniform inflow conditions by conducting experimental tests and numerical simulation. The results show that after the introduction of the rotor blade crown, the open water coefficients of the two types of pump-jet propulsors show similar trends. However, the thrust and torque coefficients and the rotor blade propulsion efficiency of pump-jet propulsor with rotor blade crown are slightly smaller than those of the conventional pump-jet propulsor. Furthermore, the temporal and spatial distribution of the pulsating fluctuations of the blade tip clearance in the flow direction is changed, and the pressure fluctuations inside and near the clearance are suppressed. The line spectra characteristic of the pressure fluctuations of the blade tip clearance is all at the rotor blade passing frequency and its harmonics, and line spectra are all reduced to varying degrees. Theoretically, the range of rotor blade passing frequency line spectrum magnitude reduction is 2.78–24.07 dB, while the range of magnitude reduction obtained in the experimental test is 0.66–19.42 dB. This study provides an important theoretical basis and engineering reference for improving the noise radiation level of the pump-jet propulsors.

Diffeomorphism Invariant Minimization of Functionals with Nonuniform Coercivity

We consider the minimization of a functional of the calculus of variations, under assumptions that are diffeomorphism invariant. In particular, a nonuniform coercivity condition needs to be considered. We show that the direct methods of the calculus of variations can be applied in a generalized Sobolev space, which is in turn diffeomorphism invariant. Under a suitable (invariant) assumption, the minima in this larger space belong to a usual Sobolev space and are bounded.

Effect of Nonuniform Foundation Support on Concrete Slab Responses

The ability to spatially map the stiffness of the foundation layers under concrete pavements with intelligent compaction has created a need to define limits on the allowable stiffness variations in a given construction area as well as the maximum size of a non-complaint area which does not require remedial action. In order to work towards this goal, a two-dimensional finite element analysis was completed to determine the effects of four nonuniform subgrade support conditions (relative to uniform support) on the tensile stresses in a concrete slab under tandem axle loading and temperature curling. The slab responses showed that certain nonuniform subgrade support conditions have a greater impact on the slab tensile stresses relative to the uniform support irrespective if the slab is experiencing curling. A soft support along the longitudinal slab edge and a subgrade with randomly assigned 9 ft2 (0.84 m2) soft and stiff areas were found to decrease the slab performance relative to a uniform subgrade assumption. In the most extreme case, the nonuniform support with soft longitudinal edges had a maximum stress that was 63 percent greater than the uniform soft support. In this analysis, subgrade nonuniformities produced the potential for bottom-up or top-down fatigue cracking depending on the interaction of the axle location, temperature differential, and local support condition.

Thermo-elastic analysis for clamped laminated arches subjected to non-uniform temperature boundary conditions

This paper delves into the thermo-mechanical behavior of clamped composite laminated arches exposed to non-uniform thermal environments. Exact solutions for temperature, displacements, and stresses in laminated arches with arbitrary thickness and number of layers are derived based on the theory of thermoelasticity. Given the complexity of the inhomogeneous temperature conditions at the edges, a specialized temperature function is constructed to accurately satisfy the non-homogeneous thermal boundary conditions. On the basis of Fourier’s law of heat conduction and the principle of superposition, the analytical temperature solution is obtained with the transfer matrix method. Clamped support conditions are addressed by incorporating unit pulse functions and Dirac delta functions into the analysis. The state equation is established with displacements and stresses serving as the state variables. According to the continuity conditions at the interfaces and the mechanical conditions on the surfaces of the laminated arch, the exact solutions for displacements and stresses are uniquely determined. The convergence and comparison studies confirm the efficacy and accuracy of the proposed method. Furthermore, three detailed numerical examples are presented to explore the effects of surface temperature, thickness-to-radius ratios, material properties, and layer numbers on the distributions of temperature, displacements, and stresses within the laminated arches.

Secondary flow characteristics and their relationship with thermal performance inside the absorber under non-uniform heat flux

Under the focusing characteristics of parabolic trough solar collectors, enhancing secondary flow intensity and shifting the secondary flow vortex center towards the bottom of the absorber can extend the lifespan of the absorber and improve thermal performance. This study combines the Monte Carlo Ray Tracing method (MCRT) and the Finite Volume Method (FVM) to investigate the fluid flow and heat transfer characteristics inside the absorber under non-uniform thermal boundary conditions. The effects of inlet flow rate (Vin), inlet temperature (Tin), and protrusion structures on the secondary flow vortex position are examined. Through numerical analysis, secondary flow intensity (Se), heat transfer coefficient (h), Nusselt number (Nu), and friction factor (f) are calculated. The results show that increasing the Tin significantly enhances secondary flow intensity, thereby improving heat transfer within the absorber. Specifically, when Tin increases from 400.15 to 600.15 K, Se increases by a factor of 7.87, while h increases by 98.96%. Increasing the Vin shifts the secondary flow vortex downward, enhancing heat transfer at the bottom of the absorber. For example, when Vin increases from 100 to 200 L min−1, Se remains largely unchanged, while h increases by 44.68%. Compared to semi-cylindrical protrusions, tetrahedral protrusions are more effective at suppressing the upward shift of the secondary flow vortex, reducing velocity losses caused by fluid-wall interaction, and achieving better heat transfer enhancement. Under conditions of Tin = 500.15 K and Vin = 100 L min−1, the Nu increases by 14.6% for tetrahedral protrusions and 7.3% for semi-cylindrical protrusions, while the f increases by 12.3% and 10.9%, respectively, compared to the smooth absorber.

Impact and analysis of corrosion on elastic stress in a composite disk under parabolic temperature distribution using the Rayleigh-Ritz method with trigonometric Ritz functions

This study conducts an in-depth impact and analysis of corrosion on the elastic stresses within a composite disk exposed to a parabolic temperature distribution. The disk, reinforced with steel fibers, is modeled as a thermo-elastic composite material to evaluate its performance under thermal and corrosive conditions. The Rayleigh-Ritz method, a widely recognized numerical approach for solving boundary value problems, is utilized to derive analytical solutions for both radial and tangential stresses. This method applies the principle of minimum potential energy to approximate displacement fields through Trigonometric Ritz Functions, which are subsequently employed to calculate stress components. The parabolic temperature distribution imposes a non-uniform thermal load across the disk, significantly altering the stress distribution. The study explores how the inherent thermal properties of the composite material interact with temperature variations, resulting in intricate stress patterns. By systematically varying temperature parameters, the analysis uncovers the sensitivity of stress components to thermal gradients. Comparative evaluations are performed for different temperature profiles, identifying critical regions of stress concentration. The findings offer essential insights into the behavior of thermo-elastic composites under non-uniform thermal and corrosive conditions, establishing a robust analytical framework for future research and practical engineering applications. This research emphasizes the necessity of integrating both thermal effects and Trigonometric Ritz Functions in the design and analysis of composite structures exposed to varying temperature loads and corrosion.

Analysis of elastic stresses and thermal creep effect for a composite disk under the parabolic distribution of temperature using the Rayleigh-Ritz method with trigonometric Ritz functions

This research provides a detailed examination of the thermal creep effect on elastic stresses in a composite disk exposed to a parabolic temperature distribution. The disk, reinforced with steel fibers, is treated as a thermo-elastic composite material. The Rayleigh-Ritz method, a widely recognized numerical approach for solving boundary value problems, is utilized to derive analytical solutions for the radial and tangential stresses. This method employs the principle of minimum potential energy to approximate displacement fields using Trigonometric Ritz Functions, which are subsequently applied to calculate the stress components. The parabolic temperature distribution imparts a non-uniform thermal load across the disk, significantly affecting the stress distribution. The study explores how the thermal creep effect, intrinsic to the composite material, interacts with thermal variations, resulting in intricate stress patterns. By adjusting temperature parameters, the analysis demonstrates the sensitivity of stress components to thermal gradients. Comparative assessments are performed for various temperature profiles, identifying critical areas of stress concentration. The findings offer significant insights into the behavior of thermo-elastic composites under non-uniform thermal conditions, providing a robust analytical foundation for future research and engineering applications. This research emphasizes the necessity of considering both thermal creep effects and Trigonometric Ritz Functions in the design and analysis of composite structures subjected to varying temperature loads.

Prediction of critical heat flux in a rod bundle channel with spacer grids based on the Eulerian two-fluid model

The critical heat flux (CHF) is a vital parameter influencing the safety and efficiency of reactor cores. In this study, the Eulerian two-fluid model coupled with the extended wall boiling model in STAR-CCM+ was employed to simulate the departure from nucleate boiling (DNB) phenomenon in a 5 × 5 pressurized water reactor (PWR) fuel rod bundle channel with spacer grids under non-uniform heating conditions. The transition in boiling curves was used as the criterion of DNB occurrence, while the temperature distribution of rod surfaces was utilized for CHF location predictions. The predicted CHF value and CHF location exhibited good agreement with the experimental data. The deviation between calculated and experimental CHF values was within 15% and the deviation between predicted and experimental CHF locations was within one grid-to-grid span length. The results of this study suggested good prospects for the application of two-phase CFD model in predicting CHF in fuel assemblies with spacer grids.

DESIGN CRITERIA FOR CONTINUOUSLY REINFORCED CONCRETE OVERLAY BASED ON PERFORMANCE

This scientific article by Karl H. Renner discusses the design criteria for continuously reinforced concrete pavement (CRCP) overlays, focusing on performance-based improvements for deteriorating sections of the U.S. Interstate Highway system. The paper highlights the challenges posed by existing pavements, including their inadequate design to handle unanticipated heavy traffic loads and environmental stressors. The author evaluates the effectiveness of CRCP overlays in extending the lifespan and durability of these pavements by conducting a comprehensive survey of 23 highway projects across 13 states. Renner elaborates on the advantages of CRCP overlays, such as improved structural integrity, reduced maintenance costs, and better load transfer without the need for frequent joint repairs, which conventional pavements require. The article also covers the technical aspects of overlay design, including the importance of uniform overlay thickness, the role of steel reinforcement, and the introduction of leveling courses to mitigate issues arising from non-uniform base conditions. The study concludes that CRCP overlays, while initially more expensive, offer long-term economic benefits and superior performance compared to other resurfacing methods. The findings advocate for their use in rehabilitating existing pavements to meet current and future traffic demands effectively. This comprehensive approach not only enhances pavement durability but also contributes to a better understanding of overlay design practices, paving the way for further research and development in pavement engineering. (Abstract generated by AI tool ChatGPT 4)

An experiment-modeling integrated approach to characterize friction between composites prepregs during preforming

An experiment-modeling integrated approach to characterize friction between composites prepregs during preforming

Radially-azimuthally discretized blade-element momentum theory for skewed coaxial turbines

Radially-azimuthally discretized blade-element momentum theory for skewed coaxial turbines

Corrigendum to ‘Numerical study on fluid flow and heat transfer characteristics of supercritical CO2 in horizontal tube under various non-uniform heating conditions’ [Int. J. Heat Mass Transf. 236 (2025) 126399

Corrigendum to ‘Numerical study on fluid flow and heat transfer characteristics of supercritical CO2 in horizontal tube under various non-uniform heating conditions’ [Int. J. Heat Mass Transf. 236 (2025) 126399

Arithmetic optimization based MPPT for photovoltaic systems operating under nonuniform situations.

Photovoltaic (PV) modules may encounter nonuniform situations that reduce their useable power volume, causing ineffective maximum power point tracking (MPPT). Moreover, due to the incorporation of bypass diodes, power-voltage (P-V) graph has multi-peaks when each component of the module receives different solar irradiation. This paper proposes a solution to this problem using an arithmetic optimization algorithm (AOA) for MPPT in PV systems operating in nonuniform situations. The non-operational regions associated with the voltage are excluded using a single-ended primary inductance converter (SEPIC) with voltage step-up and step-down capability. The AOA-MPPT algorithm gets current and voltage as inputs from the PV modules. It computes the converter's duty cycle and regulates the operational point to keep MPP under all working conditions. The proposed AOA-MPPT's efficacy under different insolation patterns has been validated using three nonuniform conditions in terms of convergence, tracking speed, steady state oscillations, and tracking efficiency. In simulations, the proposed AOA-MPPT method and SEPIC converter demonstrated quick response and excellent steady-state performance. The tracking efficiency of the AOA-MPPT is above 99% and settling time is 200 to 300ms for all three non-uniform conditions.

Equivalent contact temperature (ECT) for personal comfort assessment – definition of comfort limits for winter conditions

This article revisits the Equivalent Contact Temperature (ECT) model by incorporating winter scenarios with seat heating, which were unaddressed in previous studies. The research focuses on enhancing the model’s accuracy in evaluating thermal comfort for seated individuals under non-uniform conditions, particularly for the buttocks and back. These contact areas are crucial for both local and overall comfort, especially with Personalised Environmental Control Systems (PECS), like seat heating and ventilation, which operate close to the body. PECS are more energy efficient than traditional HVAC systems, offering customisation to individual comfort preferences while enhancing individual thermal comfort and energy efficiency in buildings and vehicles. A participant study at air temperatures of 17 °C and 18 °C validated the ECT approach, confirming the effectiveness of seat heating and revealing key correlations between ECT values and thermal comfort ratings. Additionally, an equivalent skin temperature and a comfort evaluation scheme for winter conditions were introduced.

Analysis of elastic stresses for a composite disk under the parabolic distribution of temperature using the rayleigh-ritz method with trigonometric ritz functions

This study presents a comprehensive analysis of the elastic stresses in a composite disk subjected to a parabolic temperature distribution. The disk, reinforced with steel fibers, is modeled as a thermo-elastic composite material. The Rayleigh-Ritz method, a well-established numerical technique for solving boundary value problems, is employed to derive analytical solutions for the radial and tangential stresses. The method leverages the principle of minimum potential energy to approximate the displacement fields using Trigonometric Ritz Functions, which are then used to compute the stress components. The parabolic temperature distribution introduces a non-uniform thermal load across the disk, significantly influencing the stress distribution. The study investigates how the temperature effect, inherent in the composite material, interacts with the thermal variations, leading to complex stress patterns. By varying the temperature parameters, the analysis reveals the sensitivity of the stress components to thermal gradients. Comparative analyses are conducted for different temperature profiles, highlighting the critical regions of stress concentration. The results provide valuable insights into the behavior of thermo-elastic composites under non-uniform thermal conditions, offering a robust analytical framework for future research and practical applications in engineering design. This study underscores the importance of considering both thermal and Trigonometric Ritz Functions in the design and analysis of composite structures subjected to varying temperature loads.

Supercritical n-decane heat transfer in a vertical tube subjected to high-temperature crossflow air

Supercritical n-decane heat transfer in a vertical tube subjected to high-temperature crossflow air

Stability Study of Single‐Layer Spherical Shell Roof Under Nonuniformly Distributed Snow Load

ABSTRACTAfter snowfall, the snow load distribution on building roofs is generally nonuniform, and most cases of large‐span structural collapse are related to nonuniform load. The existing regulations provide limited snow distribution coefficients for different roofs, and with the diversification of building forms, they can no longer meet the current calculation requirements for roof snow loads. This article conducts numerical simulations of wind‐induced snow drift on a spherical shell roof, which rise‐span ratio is 1/5. It is found that the friction velocity of the roof is distributed in a band shape and is higher in the windward direction, whereas the friction velocity on the leeward side is lower, which increases the possibility of snow accumulation. Based on this, a simplified snow load distribution model is proposed to improve the economic efficiency of the project. Based on the above research, the stability analysis of K6 single‐layer Kevitt mesh shell was carried out using ABAQUS finite element software. The results show that under uniformly distributed load conditions, the buckling modes of the structure are symmetrical, whereas under nonuniform snow load conditions, the first mode deforms more on the side with higher load, and the position of structural deformation is closer to the edge; when the snow cover range is the same, the larger the extreme snow load, the more unfavorable it is for structural stability; when the extreme snow load is the same, the smaller the snow coverage, the more unfavorable the initial defect is for structural stability.

Spatially-Resolved Characterisation of Large-Format PEMFC Electrodes: Electrochemical Impedance, ECSA and O2 Concentration

Fuel cell stacks are growing: both in numbers deployed in the field but also in terms of active electrode areas. The pursuit of higher-power applications and power densities means that cell active areas upwards of 400cm² are now commonplace. With larger electrodes comes an increased risk of non-uniform distributions of current density, temperature and reactant concentrations, which may lead in turn to locally-accelerated degradation and premature failure. Whilst detailed CFD/FEA modelling and simulation can help to refine designs, direct observations via in-situ and in-operando measurements are vital to verify model outputs and identify complex phenomena that models can fail to capture.Our group has developed three spatially-resolved diagnostic techniques along with instrumentation, measurement systems and software tools designed to make their application as straightforward as possible for the characterisation of large-format PEMFC MEAs.Spatially-resolved electrochemical impedance spectroscopy (SR-EIS) has been demonstrated using a commercially-available, segmented current sensor plate. A new software tool integrates a multiplexer for automated SR-EIS measurements, along with automatic equivalent circuit fitting and visualisation of spatially-resolved Ohmic, charge transfer and mass transport-related losses.A novel technique has been developed for the measurement of distributed electrochemical surface area (dECSA), allowing localised changes in ECSA resulting from non-uniform ageing to be determined for the first time.Finally, a chronoamperometric sensor array is demonstrated for the spatially-resolved measurement of in-plane oxygen concentration at the PEMFC cathode.In combination, these characterisation techniques offer a significant advance in PEMFC diagnostics, providing a deeper insight into non-uniform conditions and degradation in large-format PEMFCs.