Search Results (5,179)

Business analytics increasingly relies on analytical performance models to support real-time, data-driven decision-making in multi-stage service processes. Discrete-event simulation and process mining offer valuable insights but face scalability and explainability limits when closed-form performance indicators are needed for optimization. This paper develops a systematic procedure for constructing BCMP queueing-network models directly from the structural properties of a business process formalized in BPMN. The framework introduces a six-level state-space hierarchy (V0–V5) that ranges from a full path encoding to a single system-level counter, and three allocation strategies (D1–D3) that govern how the actions of an organizational unit are distributed among its workers. A product-form stationary distribution is derived for the resulting open network with FCFS and infinite-server nodes, yielding closed-form expressions for the mean sojourn time at a node and for the mean process flow time. We validate the framework on the university admissions campaign at RUDN University (2023 cycle, more than 85,000 applications). Numerical experiments show that the baseline mean flow time of about 174 min can be reduced to 111 min—a 33% improvement—by only a 3% increase in total staffing, allocated by greedy coordinate descent. The closed-form model agrees with discrete-event simulation under exponential service times to within 1%, and its analytical tractability enables real-time staffing recommendations that simulation alone cannot deliver. Full article

This study aims to develop polypropylene (PP) as an insulation material by engineering it into a multi-hollow structured board using 3D printing technology. A previous experimental study determined the effective thermal conductivity of the porous PP board using a hot box test, yielding a value of 0.0033 W/mK, which represents a significant improvement over conventional building insulators like rock wool and cellulose. To validate the experimental results, a numerical simulation using COMSOL Multiphysics 6.2 software was conducted to model the heat transfer process within the porous PP board. The simulation employed an appropriate methodology, including parameter definition, geometry creation, material definition, steady-state porous heat transfer module, initial and boundary conditions, meshing, and analysis. The numerical analysis focused on determining the indoor surface temperature, evaluating the total heat flux, and calculating the effective thermal conductivity of the porous PP board. The simulation results revealed an effective thermal conductivity of 0.0036 W/mK, closely matching the experimentally obtained value from the hot box test. The agreement between the experimental and numerical results validates the numerical study and demonstrates the potential of combining 3D printing technology with materials like polypropylene to develop highly efficient insulation solutions for building applications. Full article

The long-term release of heavy metals from inactive tailing ponds poses a persistent threat to groundwater quality, yet the effectiveness of commonly employed risk control measures—such as anti-seepage liners and chemical stabilization—remains insufficiently evaluated under realistic field conditions. This study aims to assess the effectiveness of risk control strategies at a Pb Zn mine tailing pond in Yunnan Province, China. A dynamic 2D numerical pollutant transport model was developed, calibrated, and validated against observed hydraulic heads and metal concentrations from monitoring wells within the study aquifer. The calibrated model showed good agreement with field measurements. Simulation results indicate that anti-seepage liners alone are insufficient to ensure compliance with the Class III standards of the Chinese Groundwater Quality Standards, even under ideal conditions where all leaching from the tailing pond is prevented. In contrast, a combined strategy—chemical stabilization reducing Pb leaching from historically contaminated soils (initial Pb: 183 µg L⁻¹) by at least 70%, together with anti-seepage systems reducing infiltration flux by over 94.4%—would be sufficient to restore groundwater quality to within regulatory limits. Full article

Accurate and rapid prediction of waterflood front propagation and volumetric sweep efficiency remains challenging in ultra-low-permeability reservoirs because of strong heterogeneity, threshold pressure gradients, reservoir anisotropy, complex well-pattern geometry, and layer-dependent flow interference. In this study, an improved 3D streamtube model was developed for waterflood-front tracking and volumetric sweep evaluation in ultra-low-permeability reservoirs. The model incorporates experimentally constrained threshold pressure gradients, anisotropic coordinate transformation, dynamic streamtube flow-rate allocation, Buckley–Leverett-based non-piston displacement, interlayer interference correction, and irregular well-pattern adaptability. A unified calculation framework was established for both injector–producer and injector–fracture streamtube units, enabling 3D integration of layer-specific swept areas into volumetric sweep efficiency. The proposed model was validated against a commercial numerical simulator using a representative well group from Block A of the Changqing Oilfield. The predicted streamtube architecture and sweep-efficiency evolution agree well with numerical simulation results, with an average relative error of approximately 3.1%, while reducing the computational time from 1043 s to 1.42 s for a 30-year simulation. Sensitivity analysis demonstrates that threshold pressure gradient, well spacing, and inter-well connectivity are the dominant controls on sweep efficiency, whereas well-pattern type, interlayer heterogeneity, and reservoir anisotropy exert secondary but non-negligible effects. Field application further reveals a strongly layer-dependent waterflood behavior: the upper sand body preferentially propagates eastward, whereas the lower sand body advances mainly southward, producing a vertically asynchronous and laterally misaligned sweep pattern. These results show that the proposed model provides an efficient and physically interpretable tool for rapid waterflood-front prediction, refined waterflood optimization, and targeted production enhancement in heterogeneous ultra-low-permeability oil reservoirs. Full article

This study presents a transient dynamic analysis of a 3D-printed composite cantilever beam fabricated from short carbon fibre-reinforced polyamide (CF-PA-12). Particular attention is given to acceleration response, vibration damping, and energy dissipation, which govern the transient behaviour and dynamic stability of lightweight composite structures under impulsive loading. The research combines experimental modal analysis (EMA) and transient impact testing with numerical simulations based on classical laminated plate theory (CLPT). A finite element model was developed in Simulia/Abaqus and used within a modal-superposition-based transient framework incorporating experimentally identified damping ratios and measured impact forces. The proposed approach enables realistic prediction of vibration decay and time-dependent acceleration response. Good agreement between experimental and numerical results confirms the capability of the method to reproduce the dynamic behaviour of additively manufactured composite beams subjected to impact excitation. Full article

A mechanically reconfigurable transmitarray (TA) to support point-to-multipoint (PtM) communications via simultaneous dual-beam radiation is presented. The architecture employs two independently rotating flat dielectric TAs whose transmitting element permittivity values are rigorously synthesized to transform the feeder spherical wavefront into concurrent multiple beams, thereby enabling simultaneous dual-beam scanning in both elevation and azimuth. The numerical analysis and full-wave simulations demonstrate that the proposed design strategy can achieve a maximum dual-beam elevation scan of 55° with a 3 dB dual-beam gain bandwidth larger than 18%. A prototype comprising two flat dielectric TAs operating at 35 GHz and producing a mechanically scanned dual-beam has been manufactured using an additive manufacturing process. The measurements are in good agreement with the expected outcomes and confirm the effectiveness of the proposed synthesis strategy. Full article

The factors influencing the cutting efficiency of tunnel boring machine (TBM) cutters in jointed rock masses are very complex. To investigate TBM disc cutter cutting performance under variable cutter spacing and penetration depth, Particle Flow Code (PFC) 2D discrete element numerical simulation is carried out on a granite jointed rock mass. The numerical model adopts a disc cutter tip angle of 20° and tip width of 12 mm, joint spacing of 5 mm, joint inclination angle of 45°, and lateral confining pressure of 2.5 MPa; cutter spacing is set to 60, 80, 100, 120 mm, and penetration depth ranges from 2 mm to 10 mm as research variables. The force chain distribution, jointed rock mass failure modes, penetration load and cutting efficiency of disc cutters under different working conditions are systematically analyzed. An indicator for measuring the cutting efficiency called “crack propagation specific energy” is proposed. Based on the numerical simulation results, a complete quadratic multivariate nonlinear regression model is established to predict cutting efficiency. The results show that the optimal cutting performance occurs at a cutter spacing of 80 mm, where the shear failure proportion of contact bonds and cutting efficiency simultaneously reach the maximum, while incomplete penetration of joint failure surfaces and small cutting areas appear under 60 mm and 120 mm cutter spacing. With the increase in the disc cutter penetration depth, the shear failure proportion of contact bonds rises continuously, and the number of tensile failure microcracks gradually decreases. The research outcomes can provide a theoretical reference for TBM shield tunnel construction parameter optimization. Full article

Fastening screw connections in aluminium alloy photovoltaic (PV) support structures are highly susceptible to premature failure under wind-induced uplift suctions. This paper presents a systematic experimental, numerical, and probabilistic investigation into the tensile pull-out performance and interactive parameters of these joints. Static pull-out tests were performed to classify two typical failure mechanisms: thread stripping combined with base metal tearing (Failure Mode I) and screw shank tensile fracture (Failure Mode II). High-fidelity 3D finite element models incorporating explicit thread geometries were established, matching experimental curves with an error within 5% and accurately replicating micro-stress peeling contours. Furthermore, a multi-stage simulation loop integrating Latin Hypercube Sampling (LHS) and Response Surface Methodology (RSM) was implemented within a large-scale Monte Carlo framework to efficiently quantify parameter sensitivities under the elastic limit state. The global stochastic assessment reveals that the aluminium elastic modulus and RHS wall thickness are the primary positive controlling parameters, exhibiting high sensitivity coefficients of 0.44 and 0.40, respectively. Conversely, the profile width renders a significant negative sensitivity due to local out-of-plane flexing. These quantified indicators provide crucial structural optimisation directives for ensuring the safety of solar tracking and racking systems. Full article

Dissipative structures are open dynamical systems that sustain coherent macroscopic organization by continuously exchanging energy and matter with their environment and generating entropy. A recent thermodynamic analysis of the paradigmatic Malkus–Lorenz waterwheel interpreted the Lorenz system as an engine, deriving an exact formula for its thermodynamic efficiency and showing that efficiency tends to increase as the system is driven far from equilibrium while displaying sharp drops near the Hopf subcritical bifurcation to chaos. Here, we extend that single-engine framework to coupled dissipative structures. We introduce two canonical couplings—master–slave coupling (series) and symmetric diffusive coupling (parallel)—and prove two fundamental association laws allowing us to reduce the composite systems to an equivalent engine with a specified efficiency. We then apply these abstract results to coupled Lorenz waterwheels, deriving efficiency formulas consistent with the underlying power balance. We perform numerical simulations confirming that (a) series coupling induces an increase in thermodynamic efficiency, (b) parallel coupling averages the efficiency of engines and increases total energy flow, (c) synchronization is typically neutral or beneficial for efficiency except in narrow parameter regions, and (d) coupling modifies the curvature of entropy-generation trends. Our theorems suggest a mathematically rigorous and transparent route to define and compute thermodynamic efficiency for generalized flow networks, with potential application to complex systems energetics. Full article

This paper proposes a method for simulating freeze–thaw damage in water-rich sandstone using PFC3D (Particle Flow Code in three dimensions). Water-rich sandstone is idealized as a composite system consisting of rock particles, water particles, and three types of contact surface: rock–rock, rock–water, and water–water. The volume change in water particles is governed by temperature, unfrozen water content, and porosity. During thawing, the volume change in water particles is realized by increasing the porosity after each cycle because the expansion of water particles is reflected by pore enlargement and the accumulation of externally supplied water. The proposed approach is intended for saturated or highly water-rich sandstone under laboratory freeze–thaw conditions with external water replenishment. It represents freeze–thaw damage associated with pore water freezing expansion and porosity-controlled equivalent water replenishment, whereas ice segregation, cryogenic suction, moisture migration, and a moving freezing front are not explicitly considered. A comparison between simulation results and laboratory tests indicates that the proposed method can effectively reproduce the freeze–thaw cycling process in water-rich sandstone. The results show that the mechanical behavior of sandstone after freeze–thaw cycles, including uniaxial compressive strength and elastic modulus, deteriorates significantly. The failure mode changes from shear failure to splitting failure. Freeze–thaw cycling and subsequent uniaxial compression are dominated by tensile damage, with tensile cracks accounting for approximately 90% of the total cracks. The tensile damage rate, Rt, increases exponentially. Crack development induced by freeze–thaw cycling follows an S-shaped trend and can be divided into three stages: slow crack growth from 0 to 10 cycles, rapid crack growth from 10 to 32 cycles, and a reduced growth rate after 32 cycles. The results provide a reference for the freeze–thaw damage analysis of rocks in cold regions and numerical simulations of freeze–thaw cycling processes. Full article

Traditional interferometric optical hydrophones typically employ narrow-linewidth lasers. Although their long coherence length facilitates interference, it also makes the system highly susceptible to spurious interference and phase noise. Low-coherence sources can effectively suppress such parasitic noise; however, their extremely short coherence length imposes stringent stability requirements on the optical path difference (OPD). In underwater environments, ambient disturbances easily cause OPD drift beyond the coherence length, resulting in loss of interference. To address this issue, we propose and experimentally demonstrate a closed-loop hydrophone system that combines low-coherence interferometry with dynamic OPD compensation using a programmable fiber delay line (FDL). Numerical simulations and experiments confirm that the closed-loop compensation algorithm maintains the OPD within the coherence length under environmental perturbations, thereby ensuring long-term stable interference. The prototype achieves a sensitivity of −117.82 dB re rad/µPa at 171 Hz, a noise-equivalent sound pressure spectral density of 8.69 dB re 1 µPa/√Hz, a measured peak phase amplitude of 130 rad, a minimum detectable phase of 14 µrad, and a corresponding logarithmic dynamic range of 139 dB. These results verify the feasibility of integrating low-coherence interferometry with active OPD compensation for low-frequency underwater acoustic detection, under laboratory quasi-static environmental conditions, the proposed closed-loop compensation maintained stable interference throughout a continuous 1.5-h experiment, presenting a differentiated and worthy-of-further-engineering-exploration technical path for high-sensitivity and low-noise optical hydrophones. Full article

This paper presents a recurrent wavelet cerebellar brain controller (RWCBC) for synchronizing uncertain 4-D memristive hyper-chaotic master-slave systems affected by nonlinear uncertainty, memory-dependent dynamics, and bounded external disturbances. The proposed controller combines three elements: a linear stabilizing feedback term, a single-branch recurrent wavelet cerebellar approximator, and a smooth tanh-type robust compensation term. The recurrent association memory is used to exploit temporal information in the synchronization error, whereas the wavelet receptive fields improve local approximation of sharp nonlinear variations in the hyper-chaotic trajectory. The tanh compensation attenuates residual approximation errors and disturbances while avoiding the discontinuity of sign-based switching control. A Lyapunov-based analysis is developed to derive the adaptive learning law and to establish uniform ultimate boundedness (UUB) of the synchronization errors with an explicit ultimate bound. Numerical simulations on a 4-D memristive hyper-chaotic system indicate that the proposed RWCBC provides competitive tracking accuracy and a favorable accuracy-complexity trade-off compared with the considered WCMAC and FBELC baselines under the tested conditions. Full article

Background: Composite attachments play a key role in clear aligner biomechanics; however, their structural stability and wear behavior under repetitive insertion–removal cycles remain poorly understood. Limited evidence exists regarding how composite resins degrade volumetrically and whether such changes influence aligner retention during simulated clinical use. This study evaluated the performance of three commonly used composites for orthodontic attachments. Methods: Digital hemi-arch models were 3D printed and attachments were fabricated using two low-viscosity composites (Transbond™ Supreme LV and Filtek™ Bulk Fill Flow) and one high-viscosity composite (Filtek™ Z250XT). Baseline attachment volumes were assessed using micro-computed tomography (microCT). Nine aligners per model were fabricated to simulate three months of treatment, with each aligner subjected to 30 insertion–removal cycles (270 cycles/model). The maximum tensile force required for aligner detachment was recorded for every cycle. Following mechanical testing, attachments underwent post-test microCT scanning. Intragroup volumetric changes were analyzed using paired t-tests; intergroup differences were assessed with ANOVA, followed by ANCOVA. Tensile-force patterns were evaluated using repeated-measures ANOVA. Results: Significant volumetric loss occurred for Transbond™ Supreme LV and Filtek™ Z250XT, whereas Filtek™ Bulk Fill Flow exhibited minimal wear. Nonetheless, intergroup volumetric differences were not statistically significant. Tensile forces were statistically different between groups for most measurements, yet within each set of 30 cycles, they exhibited a similar pattern of progressively decreasing force. Conclusions: During the simulated three-month period, all three composite resins exhibited some degree of volumetric wear and a progressive decrease in aligner detachment force within each set of cycles. The Filtek™ Bulk Fill Flow exhibited numerically higher and more consistent forces and minimal surface wear; however, no statistically significant differences were observed in total volumetric loss among groups, and the observed variations in tensile forces did not appear to compromise the overall performance of attachments, suggesting that all tested resins maintained clinically relevant retention under the conditions of this study. Full article

This work examines the transient dynamics of synchronous machines under sudden fault conditions, with emphasis on short-circuit events. The study begins with a single-phase synchronous machine operating in open-circuit mode, where short-circuit current expressions are systematically derived and numerically evaluated using advanced integration algorithms. The transient evolution of stator and field currents is analyzed, highlighting their dependency on rotor position, machine parameters, and electromagnetic interactions. A SIMULINK-based model is implemented to simulate the time-domain responses and visualize the effects of parameter variations. The investigation is then extended to a three-phase synchronous machine with damper windings subjected to line-to-line faults. Generalized voltage equations in the d-q reference frame are formulated, leveraging Park’s transformation to enable detailed modeling of transient behavior. Numerical simulations confirm the analytical predictions, revealing the significant influence of rotor angle, leakage inductances, and damper circuits on fault current dynamics. The results provide valuable insights for fault analysis, power system stability assessment, and the design of synchronous machines under transient operating conditions. Full article

The research utilizes Ansys Maxwell 2024 R2, a 3D Finite Element Analysis (FEA) software, to compare the electromagnetic coil parameters, losses, and efficiency of planar spiral circular, square, and round-cornered square (RCS) coils for wireless power transfer (WPT) systems in electric vehicle (EV) applications. This study focuses on key coil parameters such as self-inductance, mutual inductance, and the coupling coefficient, which are crucial for determining power transfer and system efficiency. While analytical calculations for these parameters are straightforward for air-core transformers, they become complex and inaccurate when ferrite cores are incorporated to improve efficiency. Ansys Maxwell overcomes this challenge by employing a numerical method. Simulation results indicate that RCS coils offer uniform magnetic field distribution and reduced losses, similar to circular coils. They also exhibit better coupling and good misalignment tolerance, akin to square coils. These characteristics suggest that RCS coils are a superior choice for WPT applications. Electro-thermal management (ETM) co-simulation of the RCS coil is performed and analyzed using Ansys Icepak 2024 R2. Furthermore, an Ansys Twin Builder 2024 R2 co-simulation of a double-sided LCL-compensated WPT system, incorporating the reduced-order model of the RCS coil, is performed. Under standardized EV conditions, say 85 kHz, 35 mm, and 50 Ω load, the RCS coil achieves an efficiency of 94.81%. The research also includes loss analysis and misalignment tolerance studies, confirming the superiority of RCS coils. Full article