Non-uniform Pressure Distribution Research Articles

Modelling of axial thrust force considering 3D rolling deformation

The axial thrust force in the rolling deformation zone is influenced by interconnected factors, such as the metal transverse flow velocity, rolling pressure distribution, and strip shear deformation, often resulting in roll wear and a lower strip surface quality. Despite its significance in the design and manufacturing of strip mills, the available literature primarily focuses on the single-variable complete difference method as a means of evaluating this force. In this study, a novel approach is proposed for calculating the axial thrust force in the rolling deformation zone, incorporating the coupling variables of the 3D rolling space. The accuracy of the results is confirmed using data obtained from an industrial test rig, indicating that the axial thrust force in the rolling deformation zone can be precisely calculated through the integration of the energy method and the 3D difference method. The results indicate that the axial thrust force decreases with the transverse flow of the metal and the transverse shear deformation of the strip. It increases with a non-uniform distribution of rolling pressure and grows as the crossover angle increases. Conversely, the axial thrust force decreases with an increasing reduction rate of the strip. In general, a non-uniform distribution of rolling pressure enhances the axial thrust force, albeit with a minor effect when the crossover angle exceeds 0.8° Conversely, metal transverse flow significantly reduces the axial thrust force when the crossover angle is small (φ < 0.4°), but only marginally so when the crossover angle falls within the range of 0.4° to 1.0°

Numerical simulation of hydraulic fracture propagation from recompletion in refracturing with dynamic stress modeling

Owing to the rapid decline of oil production from tight oil reservoirs after primary hydraulic fracturing treatment on the horizontal well, a refracturing stimulation is proposed for tight oil recovery. In this study, a fully coupled dynamic stress computational method with a finite-element method is presented, and depletion-induced dynamic stress is simulated by coupled numerical modeling. In addition, the extended finite-element method (XFEM) approach is used to investigate the effect of different parameters on fracture dynamic propagation in recompletion from refracturing. The results highlight the effects of production-induced stress changes following hydraulic fracture propagation. When multiple fractures are stimulated simultaneously from recompletion during refracturing, curved fractures are commonly observed, and the deflected fractures generally divert toward the primary stimulated area with low pore pressure. The results indicate that comprehensive factors can affect the hydraulic fractures propagation from recompletion. The optimal refracturing time window can be determined using the dynamic stress condition and stimulated area. The initial completion spacing, initial fracture length, and recompletion perforation cluster spacing can also affect the fracture geometry from the recompletion. A larger initial fracture length can induce a larger stress change area, whereas a larger distance between the new perforations in recompletion and the old perforations can decrease the depletion-induced stress effect. A high horizontal stress contrast can increase the depletion-induced stress effect because a long fracture extends the area. Owing to the nonuniform pressure and stress distributions, more nonuniform fractures are commonly generated in the refracturing treatment. Thus, temporary plugging injection and proppant inertia must be designed while reducing the number of perforations near the initial perforation positions. This can help decrease the possibility of strong curved fractures and screen out problems.

Generalized model for eigenfrequency analysis of bolted variable-stiffness flanged-cylindrical shells

A general semi-analytical modeling method for the bolted variable stiffness composite cylindrical shell, incorporating precise modeling of the boundary and connecting flanges, is proposed in this paper. The coupling between shells and flanges is achieved through a spring-based penalty function method. A novel bolted joint model for flange connections is introduced, enabling the simulation of non-uniform pressure distributions at the joint interface. The joint model features a stiffness characterization technique that effectively improves adjustability and computational efficiency. The correctness and accuracy of the proposed modeling method are systematically validated through finite element analysis based on the ANSYS commercial software and experimental testing approaches. The series of parameter influence analyses on the bolted variable stiffness composite cylindrical shell with flanges, conducted using the proposed modeling method, accurately demonstrate the influence of geometric dimensions, fiber layup parameters, and bolt parameters on the free vibration behavior of such structures. Furthermore, these analyses aid in a deeper understanding of the dynamic characteristics of such structures, partially highlighting key design considerations and offering valuable guidance for their dynamic optimization design.

An Insight into Perfusion Anisotropy within Solid Murine Lung Cancer Tumors.

Blood vessels are essential for maintaining tumor growth, progression, and metastasis, yet the tumor vasculature is under a constant state of remodeling. Since the tumor vasculature is an attractive therapeutic target, there is a need to predict the dynamic changes in intratumoral fluid pressure and velocity that occur across the tumor microenvironment (TME). The goal of this study was to obtain insight into perfusion anisotropy within lung tumors. To achieve this goal, we used the perfusion marker Hoechst 33342 and vascular endothelial marker CD31 to stain tumor sections from C57BL/6 mice harboring Lewis lung carcinoma tumors on their flank. Vasculature, capillary diameter, and permeability distribution were extracted at different time points along the tumor growth curve. A computational model was generated by applying a unique modeling approach based on the smeared physical fields (Kojic Transport Model, KTM). KTM predicts spatial and temporal changes in intratumoral pressure and fluid velocity within the growing tumor. Anisotropic perfusion occurs within two domains: capillary and extracellular space. Anisotropy in tumor structure causes the nonuniform distribution of pressure and fluid velocity. These results provide insights regarding local vascular distribution for optimal drug dosing and delivery to better predict distribution and duration of retention within the TME.

Numerical simulation of three physical fields in counter‐current ultrasound

AbstractPower ultrasound is a kind of green and environmentally friendly processing technology. Still, because of its uneven distribution of acoustic pressure in the propagation medium, the large‐scale industrial application of ultrasound is limited. In order to make more effective use of ultrasound waves, this paper uses a counter‐current ultrasound‐assisted extraction container as the geometric model of simulation, calculates the distribution of the acoustic pressure field in the container by COMSOL Multiphysics software, and investigates the effect of acoustic pressure on the fluid field, and temperature field. The simulation results showed that the acoustic pressure increased with the increase of ultrasound power and frequency, tended to balance with the rise of propagation distance, and the cavitation effect was more likely to occur. The propagation of ultrasound in the fluid medium increased the velocity and vorticity of the fluid, which was conducive to the generation of mixing effects. Under the ultrasound pulse working mode for 4 min, the fluid temperature on the central axis increased in a stepped order, with a maximum increase of 19.3°C. We can see that the establishment of the simulation model provides some theoretical guidance for the more practical application of ultrasound in the food industry.Practical ApplicationsThe limitation of ultrasound application mainly lies in the nonuniform distribution of acoustic pressure when ultrasound propagates in the fluid medium. Therefore, mastering the distribution of multiple physical fields in the reaction zone through simulation has important technical support and theoretical guiding significance for designing efficient ultrasound‐assisted extraction equipment and large‐scale industrial production of ultrasound.

Influence of Incident Shock on Fuel Mixing in Scramjet

During the operation of hypersonic vehicles, a reciprocal coupling effect is manifested between the inlet and the combustion chamber. This results in an unavoidable non-uniformity of conditions at the combustion chamber’s entrance, which, in turn, influences the fuel mixing within the chamber. The present study employed the Reynolds-averaged Navier–Stokes (RANS) equations to perform a numerical simulation of an X-51-like vehicle, with a focus on examining the impact of isolation section length and multi-injection strategies on the fuel mixing characteristics within the combustion chamber under conditions of non-uniform inflow. The findings indicated that a supersonic non-uniform inlet triggers incident shock waves, leading to a non-uniform pressure distribution across the flow section. Moreover, the position of injection was found to be pivotal in regulating penetration depth and mixing efficiency. The incident shock wave, bow shock, and boundary layer separation shock interacted with each other to increase local pressure. The coupling of high and low pressures generated an adverse pressure gradient that led to boundary layer separation, which further enhanced fuel penetration depth.

Modeling and vibration analysis of bolted composite conical-conical shells with flanges

This paper proposes a general semi-analytical modeling method of bolted composite conical-conical shells with flanges based on the first-order shear deformation theory. The coupling connections between conical shells and flanges are achieved by using the penalty function method. A bolted joint model that considers the non-uniform distribution of interface pressure is proposed, which can efficiently simulate any number of bolt connections between flanges and boundaries and between flanges and flanges. The correctness and effectiveness of the proposed modeling method are confirmed through step-by-step comparisons with finite element analysis and experimental testing. Then, the influence of various parameters on the frequency trajectories and modal shapes of bolted composite conical-conical shells with flanges is analyzed, with a particular focus on frequency veering and modal coupling vibration behaviors in these structures. The analyses indicate that the proposed modeling method can flexibly adjust structural geometric parameters, material parameters, bolt parameters, fiber layer parameters, and so on, which can efficiently guide the dynamic design of bolted composite conical shell structures with flanges.

Numerical simulation for non-uniform PtCo catalyst degradation under different coolant conditions and its effect on PEMFC performance

Long-term non-uniform temperature, pressure and reaction rates distributions in the proton exchange membrane fuel cells (PEMFCs) may result in local catalyst degradation and deteriorate PEMFC performance. However, the problem of non-uniform catalyst degradation in PEMFC stacks is still incompletely understood due to the lacking of advanced experimental methods and three-dimensional (3D) catalyst aging models. In this study, a 3D PtCo alloy catalyst degradation model under voltage cycles is built and a 25 cm2 PEMFC stack containing realistic cathode, anode as well as coolant flow fields is used as the computational domain to analyze in detail the influence of non-uniform catalyst degradation on the performance of the PEMFC during different coolant conditions. The simulation results show that the non-uniform catalyst degradation is strongly dependent on the cathode flow field structure. It can alleviate non-uniform catalyst degradation as well as contribute to improving PEMFC performance when the coolant flow direction is the same as the air, and both coolant flow rate and inlet temperature also are found to significantly affect the local catalyst degradation behavior. Therefore, an optimally designed cathode flow fields structure as well as good water and heat management during operation can help to extend the service life of the PEMFC.

Numerical Investigation of Wind Flow and Speedup Effect at a Towering Peak Extending out of a Steep Mountainside: Implications for Landscape Platforms

Wind flow over complex terrain is strongly influenced by the topographical features of the region, resulting in unpredictable local wind characteristics. This paper employs numerical simulation to study the wind flow at a towering peak extending out of a steep mountainside and the wind-induced effect on onsite landscape platforms. First, the wind flow from seven different directions is explored via 3D numerical simulations, and the wind load distribution on the platforms is highlighted. Second, a 2D numerical simulation is conducted to evaluate the wind speedup effect at the side peak, examining the influence of the side peak height and the mountainside steepness on the wind speedup factor. The numerical simulations presented in this research were validated by replicating a published numerical and experimental study. The results illustrate the amplifying and blocking effects of the surrounding topography, yielding unpredictable and nonuniform wind pressure distribution on the platforms. The presence of the side peak leads to a significant increase in the speedup factor, and the side peak height and the mountainside steepness have a moderate influence on the value of the speedup factor. Additionally, the speedup factor obtained from this study varies significantly, especially near the surface, from the recommendations of several wind load standards. Consequently, the impact of the local terrain and the wind speedup effect must be thoroughly assessed to ensure the structural integrity of structures installed at a similar topography.

Influences of nozzle pressure ratio on flow characteristics of serpentine multi-stream supersonic nozzle

The serpentine multi-stream supersonic nozzle (SMSN) is adopted for the multi-stream exhausted system of the Adaptive Cycle Engine to enhance the stealth performance of next-generation fighter. In this paper, the effects of the nozzle pressure ratio (NPR) on the flow characteristics of the SMSN were studied using the numerical simulation method validated by experimental data. The serpentine configuration leads to the nonuniform pressure distribution. At the mixing position, the expansion and shock waves are generated due to the pressure difference. As the NPR increases, the flow separation and shock wave in the mixing section gradually weaken and disappear. The thrust coefficient rises first and then drops. Due to the flow separation under the design condition, the thrust coefficient is the largest at MPR=6 and TPR=2.272. As the MPR increases at TPR=1.893, the compression effect of the main flow is enhanced on the upper third flow. The thrust coefficient rises first and then drops, and reaches the maximum at MPR=6. As the TPR increases at MPR=5, the compression effect of the main flow is weakened on the upper third flow. The thrust coefficient rises first and then drops, and reaches the maximum at TPR=2.272.

An Air-Bearing Floating-Element Force Balance for Friction Drag Measurement

Abstract It is extremely difficult, if not impossible, for existing force balances to capture very small skin-friction drag (SFD) in a perturbed turbulent boundary layer (TBL), which is characterized by the unpredictable, nonuniform distribution of static surface pressure. A novel force balance is proposed, which combines the level principle, as deployed in Cheng et al.'s (2020, “A High-Resolution Floating-Element Force Balance for Friction Drag Measurement,” Meas. Sci. Technol., 32, p. 035301) force balance, with a single-degree-of-freedom air bearing mechanism. This mechanism acts to eliminate disturbances, such as nonuniform static pressure on the wall associated with high Reynolds number TBL or a TBL under control. As a result, the developed balance may be used to accurately measure SFD in the order of 10−3 N in a TBL with or without control. This balance has been successfully applied to measure the drag reduction (DR) of a TBL manipulated using one array of streamwise microjets, at friction Reynolds number Reτ = 3340 ∼ 5480.

Numerical Study of the Effect of the Ejection Angle on the Cooling Performance of a High-Pressure Gas Turbine

In modern gas turbines, the purge flow plays an important role in improving the performance of the gas turbine, as it is adapted against the problem of the ingestion of hot gases in the inter-disc cavity of the turbine. The performance of this purge flow is necessarily influenced by some geometrical and physical parameters. This paper presents a 3D numerical study on the influence of the ejection angle on the cooling performance in a high pressure transonic gas turbine with the presence of the cavity. Five inclination cavity angles are compared (𝝓 = 30°, 45°,60°,75°and 90°) by using ANSYS Fluent, a steady flow Reynolds average Navier-Stokes equations are solved, and the turbulence model k-ω SST has been chosen based on comparison of the distribution of velocity and heat transfer convective coefficient with experimental results in a previous work. It was seen that that cooling is limited to the suction side because of the non-uniform pressure distribution of the main flow and the high pressure of the stagnation point. The optimal configuration was determined for an ejection angle of 30°.

Study of unsteady flow-induced vibration of centrifugal pump volute casing using fluid-solid coupling

The paper studies the flow-induced vibration of the volute of a centrifugal pump using the coupled approach of computational fluid dynamics (CFD) and finite element method (FEM). In the present paper, a numerical model of the centrifugal pump for fluid-solid coupling solution was established, and the unsteady flow of the centrifugal pump under different working conditions was simulated by unsteady CFD calculations. Then, the fluctuation pressure on the volute inner surface was extracted and used as the fluid load that induces the volute vibration. The volute vibration response including displacement, and acceleration was discussed based on the results of fluid-solid coupling solutions. The results show that the non-uniform distribution of fluctuation pressure along the volute, and the dominant vibration frequencies of the pump volute are blade frequency and its harmonics, and the minimum vibration and stress of the volute appear at the design condition. Overall, this research gives insight into the flow-induced vibration of centrifugal pump volute casing.

A 3D PtCo degradation model for long-term performance prediction of a scaled-up PEMFC under constant voltage operation

The non-uniform distribution of reactants, pressure, temperature and reaction rate in a scaled-up proton exchange membrane fuel cell (PEMFC) can lead to different catalyst degradation rate, impacting the long-term performance of PEMFCs. However, the local catalyst degradation behaviors in a PEMFC stack have not yet been fully understood due to the lack of experimental approaches and catalyst degradation model. In the present study, a numerical model is established for a 200 cm2 commercial-sized PEMFC stack with realistic anode and cathode flow fields. PtCo is employed as the cathode catalyst, and a 3D PtCo catalyst degradation model is developed to analyze the non-uniform evolution of the electrochemical active surface area (ECSA), current density, and Co2+ in the catalyst layers under the constant voltage conditions. The modeling results demonstrated that catalyst degradation is more severe downstream as well as under land of the cathode flow field, and the cathode catalyst layer (CCL) is the area most contaminated by the Co2+. The non-uniform catalyst degradation as well as Co2+ contamination increased the activation losses and local oxygen transport resistance. The catalyst degradation leads to a total power loss of 43.3 % after 80,000 h operation. The aging model provides a better understanding for large scale PEMFC stacks regarding its non-uniform PtCo degradation and can assist the future design of commercial PEMFCs with better lifetime.

Impact of well interference on transient pressure behavior during underground gas storage: A comparative study

Underground natural gas storage (UGS) serves as an environmentally sustainable remedy for mitigating regional and temporal disparities in energy supply and demand. The phenomenon of substantial well interference and non-uniform pressure distributions in UGS, resulting from high injection and withdrawal rates, requires a comprehensive examination. This study presents an analytical model aimed at investigating the ramifications of well interference on transient pressure dynamics during UGS. Employing the Laplace transform method, an analytical framework for diverse wells within UGS is derived, with well interference effects being effectively incorporated through the application of the superposition principle. To validate the proposed analytical solutions under various scenarios, a commercial numerical simulator is employed. The analysis reveals that when an adjacent well is engaged in gas withdrawal, interference induces an initial rise in pressure derivative followed by a subsequent plateau. Conversely, during gas injection into an adjacent well, the pressure derivative curve exhibits a continuous decline, akin to situations characterized by constant pressure boundaries. Notably, the likelihood of interference with a target well is more pronounced when gas injection or production occurs in a vertical well as opposed to a horizontal one. Preliminary data from the Hutubi UGS in China, one of the largest projects of its kind, indicate cumulative gas injection and withdrawal volumes of 155.43 × 108 m3 and 130.81 × 108 m3, respectively, with a maximum storage capacity of 107 × 108 m3. Ultimately, the gas storage volume reaches 93.50% of the UGS's designated capacity. This substantial quantity of stored natural gas equates to the calorific value of 9.88 × 109 kg of crude oil or 1.29 × 1010 kg of coal. In comparison to conventional fossil fuels such as oil and coal, the utilization of natural gas in the Hutubi UGS results in a significant reduction of carbon dioxide emissions, amounting to 1.04 × 1010 kg and 1.38 × 1010 kg, respectively. This contribution advances the field by proposing an analytical model for the systematic analysis of well interference on pressure dynamics within the Hutubi UGS, thereby facilitating the transition from oil and coal to natural gas, a crucial step in the pursuit of cleaner and more sustainable energy production practises.

The Effect of Asynchronous Grouting Pressure Distribution on Ultra-Large-Diameter Shield Tunnel Segmental Response

The complex distribution of synchronous grouting pressure results in excessive tunnel deformation and various structural diseases, especially for ultra-large-diameter shield tunnels. In this study, to reduce the risk of tunnel failure, a three-dimensional refined finite element model was established for the Wuhan Lianghu highway tunnel project, taking into account the non-uniform distribution of synchronous grouting pressure. This study focuses on investigating the development patterns of internal forces, deformations, and damages in segment structures under varying grouting pressure ratios. The results indicate that the primary failure mode of a segment is tensile failure occurring at the outer edge of the arch. Moreover, an increased ratio of grouting pressure between the arch bottom and top leads to a higher positive bending moment value and greater tensile damage at the arch waist. The tunnel ring gradually exhibits distinct “horizontal duck egg” shape deformation. When the grouting pressure ratio is 2.8, there is a risk of tensile cracking at the outer edge of the arch waist. At this time, the segment convergence deformation is 39.71 mm, and the overall floating amount reaches 43.12 mm. This research offers engineering reference for the prediction of internal forces and deformations in ultra-large-diameter shield tunnels during grouting construction, thereby facilitating their application in the development of resilient cities.

3D-Printed Auxetic Skin Scaffold for Decreasing Burn Wound Contractures at Joints.

For patients with severe burns that consist of contractures induced by fibrous scar tissue formation, a graft must adhere completely to the wound bed to enable wound healing and neovascularization. However, currently available grafts are insufficient for scar suppression owing to their nonuniform pressure distribution in the wound area. Therefore, considering the characteristics of human skin, which is omnidirectionally stretched via uniaxial stretching, we proposed an auxetic skin scaffold with a negative Poisson's ratio (NPR) for tight adherence to the skin scaffold on the wound bed site. Briefly, a skin scaffold with the NPR effect was fabricated by creating a fine pattern through 3D printing. Electrospun layers were also added to improve adhesion to the wound bed. Fabricated skin scaffolds displayed NPR characteristics (-0.5 to -0.1) based on pulling simulation and experiment. Finger bending motion tests verified the decreased marginal forces (<50%) and deformation (<60%) of the NPR scaffold. In addition, the filling of human dermal fibroblasts in most areas (>95%) of the scaffold comprising rarely dead cells and their spindle-shaped morphologies revealed the high cytocompatibility of the developed scaffold. Overall, the developed skin scaffold may help reduce wound strictures in the joints of patients with burns as it exerts less pressure on the wound margin.

Numerical analysis on mechanical difference of sandstone under in-situ stress, pore pressure preserved environment at depth

Deep in-situ rock mechanics considers the influence of the in-situ environment on mechanical properties, differentiating it from traditional rock mechanics. To investigate the effect of in-situ stress, pore pressure preserved environment on the mechanical difference of sandstone, four tests are numerically modeled by COMSOL: conventional triaxial test, conventional pore pressure test, in-situ stress restoration and reconstruction test, and in-situ pore pressure-preserved test (not yet realized in the laboratory). The in-situ stress restoration parameter is introduced to characterize the recovery effect of in-situ stress on elastic modulus and heterogeneous distribution of sandstone at different depths. A random function and non-uniform pore pressure coefficient are employed to describe the non-uniform distribution of pore pressure in the in-situ environment. Numerical results are compared with existing experimental data to validate the models and calibrate the numerical parameters. By extracting mechanical parameters from numerical cores, the stress-strain curves of the four tests under different depths, in-situ stress and pore pressure are compared. The influence of non-uniform pore pressure coefficient and depth on the peak strength of sandstone is analyzed. The results show a strong linear relationship between the in-situ stress restoration parameter and depth, effectively characterizing the enhanced effect of stress restoration and reconstruction methods on the elastic modulus of conventional cores at different depths. The in-situ pore pressure-preserved test exhibits lower peak stress and peak strain compared to the other three tests, and sandstone subjected to non-uniform pore pressure is more prone to plastic damage and failure. Moreover, the influence of non-uniform pore pressure on peak strength gradually diminished with increasing depth.

Comparison of wind-resistant capacities of standing seam roof systems under static uniform pressures and dynamic non-uniform wind pressures

Static uniform pressure tests are widely recommended to determine the ultimate capacities of standing seam roof systems in many building standards and guidelines, but such ultimate wind-resistant capacities are usually much different from those under dynamic non-uniform wind pressures. Through the comparison of the ultimate capacities of standing seam roof systems under static uniform pressures and dynamic non-uniform wind pressures by finite element simulations, the definition and calculation steps of influence coefficients of dynamic non-uniform wind pressure distribution (ICDNWPD) are proposed to reflect the effects of actual wind pressure distributions on wind-resistant capacities of the roof cladding systems. The effects of roof zones, support spacings, and terrain categories on the ICDNWPDs of flat roofs are investigated. The results show that the ICDNWPDs of the edge and interior regions are approximately 1.27–1.42 times those of the corner zones, and the ICDNWPDs are more sensitive to the roof zone than the support spacings and terrain categories. The factors of safety of roof systems with larger spans or under smoother terrain or located in the roof corner zone should be greater, which cannot remain constant.

Simulation of a metal pellet spraying generator driven by micro-air pressure

Molten metal droplet techniques are one of the important technologies for printing micro-metal parts. At present, the equipment developed for this technology faces some challenges, such as the requirement for a micro-oxygen environment during operation and a complicated manufacturing process. Consequently, a micro-air-pressure driven metal pellet spraying (MPS) 3D printing generator was designed and manufactured using the drop-on-demand technique, which uses simple and low-cost equipment in an atmospheric environment. A 2D axisymmetric model has been proposed to study the mechanism of droplet generation by using a micro-pneumatic MPS generator. In addition, a proprietary pneumatic MPS generator was also used to conduct droplet generation experiments. The validity of the proposed model was verified through the simulation results of the droplet pattern and droplet diameter, which were in good agreement with the experimental ones. The analysis shows that in the droplet injection forming process, surface tension is dominant for low viscosity liquids at a very small Ohnesorge number (Oh &amp;lt; 0.01). The surface tension was conducive to the maintenance of the molten form of the projectile. During droplet injection, the phenomenon of oblate–prolate oscillation occurs due to the non-uniform distribution of pressure inside the droplet. This phenomenon exerts an influence on the accuracy of the droplet flight trajectory and deposition position. This study serves as a good reference for selecting the suitable settings for producing metal droplets using the MPS generator.