Search Results (219)

Bi-lobed Type C pressure vessels are an attractive cargo-containment option for the marine transport of liquefied carbon dioxide (LCO₂) because they combine the high design pressure of cylindrical Type C tanks with an improved utilization of the prismatic hold volume. Although the structural and sloshing behaviors of such tanks have received considerable attention, their thermal response (heat ingress, boil-off and self-pressurization) has not been thoroughly examined. Furthermore, the influence of tank orientation (vertical versus horizontal) remains unresolved even for conventional cylinders. In this study a bi-lobed Type C tank, derived from a validated single-lobe design through the Senjanović proportioning rule, is analyzed using a two-node lumped-parameter thermal network built in Thermal Desktop 24.2/SINDA/FLUINT, with CO₂ properties supplied by the Span–Wagner equation of state through REFPROP 9.1. The model was verified against the NASA multipurpose hydrogen test bed (MHTB) liquid-hydrogen self-pressurization experiment and against a liquid-CO₂ cargo-tank measurement. Vertical bi-lobed tank (VBT) and horizontal bi-lobed tank (HBT) orientations were then compared at four fill levels ranging from 20% to 90%. The results demonstrate that orientation significantly alters cumulative heat ingress, pressure rise and vapor temperature, with the effect being strongly amplified at low fill levels. The pressure rise is shown to be governed by the onset of boiling, the timing of which is determined by how quickly each orientation warms the liquid to saturation. Full article

The dominance and impact of pronounced thermal buoyancy effects on the thermal and hydrodynamic properties of a horizontally heated cylinder of circular configuration immersed in a vertically ascending laminar flow stream have been numerically investigated. The dynamics are determined by numerically solving the standard energy and two-dimensional laminar Navier–Stokes equations and by incorporating buoyancy through the Boussinesq approximation in the mixed-convection co-flow configuration. The Reynolds number ($Re$) is varied within the range of $80\le Re\le 160$, while the Prandtl number $\left(Pr\right)$ is maintained constant at 0.71. The thermal buoyancy effect of the co-flow configuration is assessed by altering the Richardson number ($0\le Ri\le 1$). The code is validated against and compared against several numerical and experimental results, and its strong prediction capabilities are confirmed. This study examines significantly observed von Kármán vortices and their disappearance at above a threshold Richardson number, which has been identified as the critical Richardson number. This study provides a detailed explanation of a new phenomenon, termed ‘vortex switching’, which arises from the interaction between inertia–buoyancy interactions. The study showcases representative patterns of vorticity, streamlines, and isotherms while also plotting the average Nusselt numbers against the $Ri$ for various $Re$. Furthermore, it offers a correlation for the changes in wake width, recirculation bubble length, and vortex switching length, which are essential for optimizing design and enhancing thermal efficiency. Lastly, the thermal characteristics provide deeper insights into the impact of thermal buoyancy on wake dynamics and heat transfer. Full article

Terrain-induced chassis motion can disturb the soil-entry attitude and soil engagement of seeding components on compact agricultural robots. This study develops an inverted 2RPU–RPS rallel mechanism for a maize seeding robot to regulate the end effector without levelling the entire chassis. The mechanism supports the disc opener and terminal seed tube and provides one vertical translation and two rotations. A nonlinear inverse-kinematic model, a unilateral penetration–downforce model, constrained electric-cylinder dynamics, and a coordinated feedforward–PI controller are established. The roll and pitch loops combine chassis-attitude feedforward compensation with end-effector error feedback, while the vertical loop regulates the opener downforce using a stiffness-based penetration reference and force feedback. MATLAB/Simulink simulations are conducted under isolated attitude disturbances, vertical terrain excitation, and multi-row operation. With maximum chassis roll and pitch disturbances of 4.49° and 3.35°, the end-effector RMSE values are 0.109° and 0.114°, respectively. At a prescribed downforce of 400 N, the downforce RMSE is 11.07 N and the mean disc-opener penetration is 34.99 mm. During the 300 s multi-row simulation, the mean penetration remains 34.96 mm and the downforce RMSE is 12.65 N. The results indicate that the strategy can attenuate chassis-induced disturbances and maintain stable soil engagement under the adopted modelling assumptions. Full article

This study compares the standart (STD) piston with a specially designed MR-1 piston that better meets modern requirements. Firstly, the experimental comparison was conducted at 3000 rpm, with static fuel injection timing advance (ITA) of (30°, 25°, 20°, 17.5°) CA BTDC, and engine load conditions of 100%, 75%, 50%, 25%. Subsequently, the combustion chambers (CCs) were simulated at the same ITA to examine in-cylinder phenomena in more detail. Analysis was performed at full load, where emissions are critical. Reducing the ITA to decrease combustion temperature and NOx emissions resulted in higher soot and UHC emissions, particularly for the STD chamber. However, this trend was not observed with the MR-1 chamber. NOx was reduced further thanks to the lower local peak temperatures, and there was no increase in soot without a significant loss in performance. The increase in UHC was negligible compared to the STD, while CO decreased. The advantages of the MR-1 can be attributed to its ability to increase air movement in the vertical direction, which is better suited for the bowl geometry and spray direction. This results in improved mixture formation in the cylinder by increasing turbulent kinetic energy (TKE) to an optimal level. Additionally, the temperature distribution is more uniform when considering dimensions, heat release duration is shortened and lower pressure and pressure rise rate are achieved. Full article

Pulsar detection holds significant value in spacecraft autonomous navigation, space-based time reference establishment, and space science research. The X-ray telescope is a crucial instrument for pulsar detection, and its focusing mirror—the most critical component—exhibits detection performance directly influenced by the film thickness uniformity. This paper proposes an off-axis biaxial rotation coating method and derives, for the first time, a theoretical model of film thickness distribution on a cylindrical substrate based on classical thin-film deposition theory. Using this model, we systematically analyze the influence of key coating parameters—namely the distances a and b from the evaporation source to the vertical rotation axis and to the horizontal rotation axis, respectively—on thickness uniformity. By optimizing the coating process parameters, the thickness uniformity on the cylindrical substrate is significantly improved. When parameters a and b are within certain ranges and satisfy a specific relationship, a film with thickness uniformity better than 1% can be obtained. Coating experiments are carried out on a mandrel cylinder, and the measured film thickness distribution shows good agreement with theoretical predictions, with a maximum deviation of only 1.2%, thereby validating the accuracy of the proposed model. This work provides a rapid, non-iterative approach for determining coating parameters, significantly improving efficiency and reducing costs. Full article

High-power electric air heaters are key charging components in air thermal energy storage systems, but the dominant heat-loss regions and retrofit basis of existing devices remain unclear. In this study, a three-dimensional conjugate heat-transfer model was developed for an existing 1200 kW vertical electric air heater and validated using three steady-state experimental cases, with a maximum outlet-temperature deviation of 2.17%. Based on the validated model, temperature-field characteristics and segmental heat-loss distributions were analyzed under different mass flow rates. The results show that heat loss was highly non-uniform: Segments 2 and 3 accounted for 37.26% and 54.51% of the total heat loss, respectively, contributing 91.77% in total. A targeted local retrofit scheme was, therefore, proposed by filling the non-flowing inner-cylinder region in Segments 2 and 3 with glass wool and enhancing insulation near local cooling boundaries. After optimization, the average total heat loss decreased from 31.94 kW to 17.69 kW, corresponding to a 44.6% reduction. Under the rated condition, the outlet temperature increased from 1421.6 K to 1482.0 K, providing 584.8 kWh of additional effective thermal storage per cycle and an estimated payback period of 399 d. This study provides a diagnosis-guided retrofit approach for existing high-power electric air heaters. Full article

To investigate the dynamic characteristics of key parameters in a piston gravity energy-storage system, an experimental system for novel piston gravity energy storage is designed and developed. Firstly, the structure and working principle of the piston gravity energy-storage system are analyzed. Adopting a modular modeling approach, the system is divided into four core modules, and the piston motion, vertical cylinder chamber pressure, hydraulic actuator, and turbine power models are established. Subsequently, a case study simulation is conducted on the piston gravity energy-storage system to model its dynamic characteristics during discharge conditions, analyzing the variation patterns of key parameters such as the chamber pressure, flow rate, and output power within the system. Finally, the experimental system integrates a digital controller with proportional–integral power regulation and an automatic mode switching logic to enable the constant power closed-loop control, with real-time acquisition of the chamber height, pressure, flow rate, and electrical parameters. The dynamic responses of various system parameters are analyzed. Experimental results indicate that under constant power charging and discharging conditions, the height of the upper chamber exhibits a linear trend, the pressure in the lower chamber is inversely proportional to the height of the upper chamber, and the flow rate remains stable with charging and discharging power. Neglecting energy losses of the pump and hydraulic turbine and only considering friction and hydraulic losses, the charge–discharge efficiency of the energy-storage experimental system is 65%. Full article

Accurate prediction of hydrodynamic forces on confined oscillating structures is essential in applications related to nuclear engineering, energy systems, offshore devices, and mechanical components subjected to flow-induced vibrations. In this work, two computational fluid dynamics (CFD) methodologies implemented in ANSYS CFX are compared to determine the added-mass coefficients for a square cross-section cylinder confined within a square container: a deforming-mesh method (DMM) and an immersed-boundary method (IBM). Unlike previous studies restricted either to concentric square cylinders or to eccentric configurations treated with potential flow, the present study addresses eccentric confined configurations by solving the incompressible Navier–Stokes equations and focuses primarily on the prediction of added mass under strong confinement. Horizontal, vertical, and combined eccentric displacements are analyzed in detail. Mesh-independence, domain-size sensitivity, and temporal-convergence analyses are performed. Results show that both methods provide closely matching added-mass predictions over a wide range of eccentricities, with relative differences typically below 1% for moderate eccentricities, although discrepancies increase under extreme confinement. Relative to the concentric configuration, the added-mass coefficient increases by about 44% for the most eccentric vertical case and by about 87% for the most eccentric corner-approach case. Force decomposition and pressure-field analysis show that this increase is governed primarily by pressure-induced inertial effects, whereas viscous shear plays a secondary role under the conditions considered. From a practical standpoint, the immersed-boundary method reduced the computational time by approximately 92% in the most demanding case. Full article

Accurate prediction of Rate of Penetration (ROP) in carbonate formations remains constrained by the arbitrary selection of geomechanical input parameters in empirical drilling models. This study presents the first systematic field-based evaluation of sixteen geomechanical properties—grouped into three categories: strength parameters (uniaxial compressive strength (UCS), confined compressive strength (CCS), shear strength, thick-walled cylinder strength (TWC), friction angle, and cohesion), elastic moduli (Young’s modulus, shear modulus, bulk modulus, bulk compressibility, dynamic combined modulus (DCM), Poisson’s ratio, brittleness index), and in situ stress parameters (overburden pressure, minimum, and maximum horizontal stresses)—to identify optimal predictors for ROP modeling across PDC bit sizes of 12.25″ and 8.5″. Continuous wireline log data from two vertical carbonate wells in the Middle East (Well A: 1000–3370 m; Well B: 1945 to 3128 m; total intervals of 2370 m and 1183 m, respectively) penetrating formations comprising limestone, dolomite, sandstone, shale, anhydrite, and marly limestone were used. All sixteen geomechanical properties were computed using Interactive Petrophysics (IP) software with lithology-specific empirical correlations and validated against laboratory core measurements (R² = 0.79–0.95). Pearson and Spearman correlation analyses quantified parameter–ROP relationships, and the Al-Abduljabbar empirical model, recalibrated via multiple nonlinear regression, served as the evaluation framework. DCM consistently exhibited the strongest negative correlation with ROP across both bit sizes and achieved the highest model accuracy (R² = 0.54, AAPE = 25.33%), significantly outperforming the Bourgoyne and Young model (R² = 0.26, AAPE = 36.55%). A statistically validated scale-dependent effect was identified: Fisher’s Z-transformation tests confirmed that the correlation reversal between CCS and UCS across bit sizes is statistically significant (CCS: Z = −16.84, p < 0.001; UCS: Z = −6.75, p < 0.001), establishing CCS as the superior predictor at 12.25″ and UCS as the superior predictor at 8.5″—a finding not previously reported in the ROP literature. This reversal is attributed to the larger contact area of the 12.25″ bit, which promotes confinement-dominated rock failure better described by CCS, whereas the smaller bit produces localized stress concentration better represented by UCS. These results establish that (1) optimal geomechanical input selection is bit-size dependent, (2) nonlinear modeling outperforms linear frameworks for strength–ROP relationships, and (3) parameter relevance outweighs coefficient tuning in model robustness. DCM is recommended as the most operationally practical universal input, requiring only conventional compressional sonic and density logs. This study provides a systematic framework for geomechanical parameter selection with direct implications for drilling optimization in heterogeneous carbonate reservoirs. Full article

Previous studies and current wind-load standards for low-aspect-ratio circular structures primarily consider external pressure and insufficiently address the combined effects of roof openings, internal–external-pressure interaction, and surface roughness. To overcome these limitations, this study investigates the net-pressure characteristics of such structures through wind-tunnel experiments conducted for two aspect ratios and four levels of surface roughness. The vertical variation in net pressure and its implications for wind-load estimation are systematically examined. For smooth surfaces, the net-pressure distribution exhibits pronounced height dependence due to the free-end effect. This dependence diminishes as surface roughness increases, indicating a significant modification of the flow structure around the cylinder. Neglecting this height-dependent behavior leads to substantial inaccuracies in drag-coefficient estimation. Comparisons with existing standards reveal that the drag coefficients specified in AS/NZS 1170.2 and AIJ-RLB overestimate values for smooth surfaces by up to 38.7% and 21.5%, respectively, whereas the AIJ-RLB provisions underestimate values for rough surfaces by approximately 4.7%. To improve predictive accuracy, a simplified model for the circumferential distribution of mean net-pressure coefficients is developed. The proposed model incorporates height-dependent aerodynamic parameters and demonstrates strong agreement with experimental data, with a maximum relative error below 8.6%. This model provides a practical reference for more reliable wind-load estimation in the structural design of low-aspect-ratio circular structures with roof openings. Full article

The conversion of surplus electrical energy into thermal energy represents an effective pathway for increasing the flexibility of renewable-energy systems. This study presents an experimental and numerical assessment of a compact vapor-assisted sensible heat storage unit designed to transform electrical input into stored thermal energy using a controlled evaporation–condensation process inside a vertical steel cylinder. An 800 W immersion heater was employed to generate vapor, while nine temperature sensors monitored the thermal response of the evaporator, enclosure air, and storage medium. Two operating configurations, insulated and non-insulated, were investigated to characterize charging and discharging dynamics. In parallel, CFD simulations performed in ANSYS Fluent were used to analyze coupled heat transfer and phase-change mechanisms. The results demonstrate efficient electrical-to-thermal energy conversion, with rapid temperature rise during charging driven by vapor-assisted convection following the onset of boiling. Experimental data and numerical predictions consistently reveal a transition from conduction-dominated heating to a phase-change-enhanced regime, which accelerates heat distribution and thermal homogenization within the storage unit. Comparative tests further indicate that reduced external losses improve heat retention during discharge. Overall, the combined experimental–numerical approach confirms the capability of the proposed compact system to store electrically generated heat in a stable and repeatable manner, highlighting its potential for daily photovoltaic energy buffering and small-scale renewable-energy applications. Full article

In this study, systematic experiments are conducted on a vertical rigid cylinder with two degrees of freedom in the subcritical Reynolds-number regime. The selected flow conditions cover the excitation stage, the lock-in stage, and the post-lock-in stage of vortex-induced vibration. Structural displacements, hydrodynamic forces, and wake vorticity fields are measured simultaneously using laser displacement sensors, force transducers, and particle image velocimetry. The results show that the cross-flow motion remains dominant throughout the investigated range, while the in-line motion is activated through phase coupling within the lock-in region. A stage-dependent redistribution of hydrodynamic loading is identified. The loading first concentrates in the cross-flow direction during synchronization, then partially shifts toward the in-line direction under coupled motion, and finally becomes spatially dispersed as desynchronization develops. This directional redistribution moderates the peak cross-flow amplitude, broadens the lock-in region, and alters the sequence of force-coefficient peaks. The synchronized wake measurements reveal that the flow evolves from incoherent structures to organized vortex streets and then to fragmented and irregular patterns, directly reflecting the formation and collapse of directional load concentration. These findings establish a consistent linkage between hydrodynamic loading, structural response, and wake evolution, and provide experimental evidence for the coupled dynamics of two-degree-of-freedom vortex-induced vibration, offering physical insight for the design and assessment of realistic marine cylindrical structures. Full article

The complex flow behavior of the metal around the stirring tool during welding directly determines the microstructural evolution, defect formation, and mechanical properties of the welded joint, and thus becomes the core physical process affecting welding quality and process stability. In this study, to characterize the three-dimensional material flow behavior of AZ31 magnesium (Mg) alloy during friction stir welding (FSW), conventional metallographic sectioning was adopted as the primary observation method, and copper foil was used as the marker material. The flow trajectories of the materials after welding were investigated via three configurations of the marker material. The results indicate that three typical characteristic zones exist along the vertical direction, which are the shoulder-affected zone (SAZ), the pin-affected zone (PAZ), and the swirl zone from top to bottom. Specifically, the material in the SAZ is dominated by laminar flow; the PAZ exhibits complex mixed-flow characteristics; while the swirl zone shows an obvious rotational flow pattern. Based on the principles of material mechanics and fluid mechanics, a force-flow coupled “simple flow model around a rotating cylinder” was proposed, which defines three flow modes corresponding to the different characteristic zones within the weld. Full article

Aim: Static guided computer-assisted apicoectomy has been shown to improve the precision of periapical surgery; however, limited data are available regarding its performance and accuracy in hard bone conditions. The primary aim of this study was to collect data on how this technique functions in hard bone and to evaluate the accuracy of different guided approaches under these conditions. Specifically, the accuracy of three surgical instruments—a commercially available bone drill, a bone trephine (partially guided), and an endo-trephine with a stopper (fully guided)—was compared in hard bone. Materials and methods: Sheep mandibles were scanned using cone-beam computed tomography (CBCT) and an intraoral scanner (STL). Digital planning was performed using commercially available dental implant surgical planning software. Guided apicoectomy procedures were carried out with the aid of 3D-printed surgical guides. Following the interventions, matching metal cylinders were inserted into the prepared osteotomies, and post-operative CBCT scans were acquired. Apical deviation from the digitally planned endpoint and angular deviation were analyzed to assess accuracy in hard bone. Results: The drill demonstrated a statistically significantly higher apical deviation compared to the endo-stop trephine (p < 0.001). No statistically significant difference in apical deviation was found between the bone trephine and the endo-stop trephine. Additionally, no significant differences were observed among the three approaches in the mesiodistal (x) and buccolingual (y) directions or in angular deviation; however, a statistically significant difference was detected in the vertical (z) dimension. Conclusions: Within the limitations of this study, static guided apicoectomy proved to be a reliable technique in hard bone conditions. The fully guided trephine approach demonstrated the highest drilling accuracy, while partially guided trephination and drilling showed greater deviations. These findings provide valuable data on the behavior and precision of different endosurgical guided instruments in hard bone and support the use of fully guided systems when high accuracy is required. Full article

An integrated nonlinear dynamic model was developed to investigate resonance in a four-cylinder engine mounted on a viscoelastic foundation. A coupled lumped-parameter formulation captures vertical and torsional responses under unbalanced inertial forces, combustion torque, and stochastic base excitation. Time-domain simulations show that at low rotational speeds the vertical displacement reaches transient amplitudes before converging to periodic oscillations, whereas higher excitation speeds reduce steady-state amplitudes. Torsional motion exhibits initial angles near 0.05 rad that decay below 0.01 rad in steady state, with further reduction at higher speeds. Frequency-domain analysis indicates that vibration energy is concentrated in engine-order harmonics between approximately 8 and 50 Hz, while components above 60 Hz are strongly attenuated, yielding a dynamic range exceeding 50 dB. Finite element modal analysis identifies the first four structural modes between 18 Hz and 666 Hz, revealing an increasingly dominant overall translational mode and a localized directional behavior at higher frequencies. A high-dimensional kernel density spectrogram integrates modal and spectral features to map resonance regions. Results indicate that increasing rotational excitation enhances inertial stiffening, systematically reduces displacement amplitudes, and preserves bounded periodic dynamics without instability. Full article