Numerical Investigation Research Articles

Numerical investigation on dynamic flow characteristics of methane condensation in microchannels

Microchannel condensers play an essential role in cryogenic two-phase heat management systems due to their efficient heat transfer characteristics. Thus, it is worth conducting an in-depth study on microscale condensation characteristics of cryogenic fluids. This paper delves into the flow condensation process of methane in microchannels. A two-dimensional transient model with high accuracy for cryogenic fluids has been developed by combining a self-defined program for the source term of the phase transition model. The model fully considers the boundary layer thickness and accurately explores the mesh accuracy. The complete condensation flow patterns are captured for various vapor quality, mass flux, and wall subcooling degrees. The injection flow is a unique flow regime for condensation in microchannels. The decrease in wall subcooling degree and increase in mass flux leads to the separation point at the neck of the injected flow moving towards the exit, while the annular flow region is expanding and the flow pattern transition is lagging. The mass flux improves the heat transfer coefficient more significantly at high vapor quality. During injection and bubble flow, the wall shear stress and local heat transfer coefficient are subject to bouncing and oscillations, which may induce fluctuations in the upstream annular flow. The prediction performance of six classical heat transfer correlations is evaluated. The results indicate that the Nie et al. correlation has the highest comprehensive prediction accuracy with MRD and MARD of -5.00 % and 15.83 %, respectively.

Numerical investigation of impact response of bridge pier subjected to off-center vehicle collision

The increased risk of vehicle collisions on bridge piers causes damage to bridge structures and traffic congestion. In extreme cases, severe collisions caused by trucks lead to bridge collapse and loss of lives. Many studies have been conducted to investigate the dynamic responses of bridge piers subjected to vehicle collisions. Most of them focused on head-on (center-to-center) collisions based on the assumption that they represented the worst scenarios. However, off-center collisions were most often observed in vehicle collision accidents. In this study, bridge piers with different cross-section geometries (i.e., circular, and square) subjected to off-center vehicle collisions are numerically investigated. The results show that off-center vehicle collisions result in more severe spalling damage to the circular piers than head-on collisions. However, the curved surface of the circular piers effectively avoids inducing torsional response under off-center collisions. On the other hand, off-center collisions on square piers induce torsional response, thus more significant deformation, and damage than head-on collisions. Further mechanism analyses are conducted to explain the influence of off-center collisions, focusing on truck type and rectangular cross-section. Furthermore, some meaningful suggestions are put forward to resist off-center vehicle collisions for bridge piers in design process or in service.

Experimental and numerical investigation on seismic performance of SFRC shear walls with CFRP bars

In order to investigate the seismic performance of steel fiber reinforced concrete (SFRC) shear walls with CFRP bars, quasi-static tests were conducted on six full-scale shear walls with a shear span ratio of 2.0, including one steel bars reinforced ordinary concrete (RC) shear wall, one CFRP bars reinforced ordinary concrete (CRC) shear wall and four CFRP bars reinforced SFRC (CSFRC) shear walls. The variables included steel fiber volume fraction (SFVF), axial load ratio and concrete strength grade. The experimental results showed increasing the SFVF could significantly decrease the concrete damage level and improve repairability. Meanwhile, the bearing capacity, ductility, and energy dissipation capacity all improved, and the stiffness degradation slowed. Compared to RC shear wall, the peak load of the CSFRC shear wall with SFVFs of 0 %, 0.75 % and 1.5 % increased by 16.36 %, 30.06 % and 46.01 %, respectively. The residual drift ratio decreased by 54.75 %, 61.61 %, and 52.98 % at 2.2 % drift ratio, respectively. Compared to CRC shear wall, the cumulative energy dissipation of the CSFRC shear wall with SFVFs of 0.75 % and 1.5 % increased by 39.54 % and 94.10 %; and the ductility increased by 5.12 % and 18.06 %, respectively. These improvements indicated that applying SFRC with SFVFs of 0.75 % and 1.5 % to shear walls reinforced with CFRP bars could effectively improve the seismic performance and compensate for the shortcomings of resilient shear walls. In addition, increasing the axial load ratio improved the bearing capacity, but decreased deformation capacity and accelerated stiffness degradation. An increase in concrete strength significantly improved the bearing capacity, stiffness and energy dissipation but reduced ductility. Meanwhile, the stability of lateral loads at large drift ratios weakened. Additionally, a detailed finite element model (FEM) was established using DIANA and the accuracy was verified by comparing the simulation and experimental results. Subsequently, parametric analyses were carried out to study the effects of shear span ratio, CFRP bar ratio, and wall thickness on the seismic behaviour of CSFRC shear walls.

Performance enhancement of solar air heater with two-sided curvilinear transverse rib: Experimental and numerical investigation

Solar energy as prime energy source draws attention of world due to its availability and eco-friendliness. Low performance of solar air heater create curiosity for researchers to increase its performance. To enhance performance of solar air heater active and passive techniques used by researcher. Surface modification is one of the most prominent passive techniques to improve the performance. Present experimental and numerical investigation explore thermal characteristics of two-sided curvilinear rib roughened solar air heater. An indoor experiment was performed on two side curvilinear rib roughened absorber plate having constant heat flux of 1000 W/m2. Parallelly 2-dimensional numerical simulation was also performed to explore flow behavior and to complete investigation within optimum cost. ANSYS Fluent 2021.R was used for performing this simulation with K-ε RNG model with enhanced wall treatment. Velocity inlet and pressure outlet was selected as boundary condition. Main roughness and flow parameters were relative roughness height ( e/ D h = 0.21–0.042), relative roughness pitch ( p/ e = 7.14–35.71), and Reynolds number ( Re = 3800–18,000). Maximum value of Nusselt number improvement ratio and friction factor improvement ratio was 3.17 and 3.26 at roughness and flow parameter of ( e/ D h = 0.042, p/ e = 15, Re = 15,000) and ( e/ D h = 0.042, p/ e = 7.14, Re = 3800) respectively. Thermohydraulic performance parameter achieved its maximum value of 2.77 at e/ D h = 0.042, p/ e = 17.85, and Re = 18,000.

Improving the crashworthiness of bi-tubular architectures with ABS cores under axial loading: Experimental and numerical investigation

In this study, quasi-static axial compression tests were conducted on mild steel bi-tubular architectures with rectangular nested tube (RNT) and square nested tube (SNT) geometries to evaluate their crushing and crashworthiness performance. A multi-criteria decision-making approach was employed to identify the optimal energy-absorbing architecture. The SNT structure, with the smallest gap size between the inner and outer tubes, exhibited the most desirable energy absorption characteristics among the considered cases. Acrylonitrile butadiene styrene (ABS) cores, with either rhombic or square cell configurations, were used to enhance the energy absorption performance of the SNT structure. A finite element model was created to evaluate the responses of the SNT structure filled with ABS cores. The validity of finite element simulations of the ABS cores and optimal architecture under axial compression were confirmed by comparing them with experimental results. The integration of the cores into the nested architecture enhanced crashworthiness performance and contributed to the control of the structure deformation. The SNT structure filled with rhombic ABS core exhibited superior crashworthiness performance compared to the counterpart filled with square core. The energy absorption of nested SNT structures filled with rhombic ABS core can be 116.93% greater than the corresponding non-filled structure. The crashworthiness indices of ABS-filled structures were highly sensitive to the number of cells and wall thickness of the core. A nested architecture with an ABS core could serve as a novel architecture for energy-absorbing devices.

Numerical and experimental verification of column web in transverse compression

This paper focuses on the problem of steel members of open double symmetrical cross-sections in transverse compression. First, the problem is introduced with examples of its application in steel structures of buildings and followed by the overview of selected substantial literature resources and current design codes provisions. The essential part of the paper is a presentation of results of experimental tests and advanced numerical analysis of members subjected to selected cases of transverse compression. Where possible, the results are compared with resistances obtained using provisions in currently valid design codes for steel structures. The influence of selected parameters on the resistance in transverse compression is quantified within the evaluation with specific attention paid to plate buckling of the web. Based on data obtained from the experimental and numerical investigations, the most notable findings are summarized.

Experimental and numerical investigation on axial compression behaviour of prefabricated ECC shell–reinforced concrete column

To improve the mechanical behaviour of traditional reinforcement concrete (RC) column, a novel prefabricated engineered cementitious composite (ECC)–reinforced concrete composite (ECC shell–C) column was proposed in this study. Subsequently, five prefabricated ECC shell–C columns, as well as one cast–in–place (CIP) RC column and one CIP pure ECC column, were designed and manufactured. Then, axial compression tests were carried out to explore their mechanical behaviour with considering the effect of the ECC shell thickness t and stirrup ratio ρv. On this basis, a numerical analysis method for the composite column was developed and verified. And numerical parametric study was carried out to clarify the influence of the design parameters on the axial compression behaviour of the prefabricated ECC shell–RC columns, including the compressive strength of ECC (fc,ecc) and concrete (fc), as well as the longitudinal reinforcement ratio (ρs). The experimental and numerical results demonstrated that the ECC shell can improve cracking resistance, ductility capacity and energy dissipation capacity of the RC column. The accumulated energy dissipation and ductility coefficient of the prefabricated ECC shell–RC columns with different t was 2.13–2.46 times and 1.14–1.35 times greater than those of the RC column, respectively. The ρv had small influence on the bearing capacity of the prefabricated ECC shell–RC columns, which can be appropriately reduced in practical application. The numerical analysis method considering the confinement effect of ECC shell can provide reliable prediction for the axial compression behaviour of prefabricated ECC shell–RC columns. fc,ecc and fc have the positive influence on the bearing capacity of the prefabricated ECC shell–RC columns but have negative influence on the ductility; meanwhile a moderately lower ρs will not significantly reduce the ductility.

Dynamic increase factor of concrete compressive strength in confined split hopkinson pressure bar tests

This study presented a methodology to evaluate the pure strain-rate effect on concrete compressive strength and developed a pure rate dynamic increase factor (DIF) model through numerical and experimental investigations into confined split Hopkinson pressure bar (SHPB) tests. The numerical investigation proposed the methodology to determine the pure rate DIF through confined SHPB tests. Subsequently, the confined SHPB tests were conducted on concrete specimens, and a pure rate DIF model was developed based on this methodology. Additionally, conventional SHPB tests were performed to obtain an apparent DIF, which was then compared to the developed pure rate DIF. The results indicated that the apparent DIF exceeded the pure rate DIF, thus confirming its tendency to overestimate the strain-rate effect on concrete. Therefore, the proposed methodology using confined SHPB tests provides an alternative approach to overcome the limitations of the apparent DIF determined from conventional SHPB tests. Lastly, the developed pure rate DIF model was validated through numerical analyses on conventional SHPB tests and drop-weight impact tests of reinforced concrete beams. This validation demonstrated that the proposed pure rate DIF model effectively considers the strain-rate effect on concrete structures, thereby enabling assessment of the performance of concrete structures under extreme loading conditions.

Experimental and numerical investigation on seismic performance of novel cable-restraining composite rubber bearings for highway bridges

Introducing cable restrainers into isolation bearings is promising to enhance the seismic performance of highway bridges. However, limitations exist in cost, performance, and analysis models of current products typically composed of flat sliding bearings (FBs) and separated cables. Therefore, this study proposes a novel cable-restraining composite rubber bearing (CRCRB) comprising a composite rubber bearing (CRB) as the bearing body and continuous cables. Cyclic tests were conducted on 12 specimens, including cable-restraining FBs and CRCRBs. Then, restoring force models of the bearing bodies were developed via theoretical analysis. Those of the cables were obtained from numerical models based on derived cable profiles. Finally, incremental dynamic analysis (IDA) was performed to evaluate the effects of the CRCRBs and cable models on structural responses. The test results verify the feasibility of the new cable layout and the advantages of the CRBs as the bearing body in restoring force, damping capacity, and residual displacement. As both the radii of the curved segments and the inclination angle of the linear one in the cable profiles decreased, the cable stiffness kept rising during loading. Cable sliding at clamps enlarged the cable-free displacement and residual deformation, and was relieved by adding clamps. The proposed models fit the test data well. The IDA results illustrate the superiority of the CRCRBs in mitigating bridge damage and highlight the importance of using the precise multi-linear cable model instead of the simplified linear one to avoid overestimating responses.

Steel truss reinforced concrete composite walls: Numerical investigation and design consideration

Conventional design practices for reinforced concrete (RC) structural walls in the lower stories of super high-rise buildings involve employing large thickness and dense reinforcement to ensure satisfactory seismic performance. This is necessary to withstand the considerable gravity and seismic forces caused by the superstructure. However, this approach brings a design challenge in engineering practice because excessively thick RC walls not only occupy useable space but also magnify earthquake forces due to the increased self-weight. For this reason, steel truss RC (STRC) composite walls have been developed to address the above-mentioned shortcomings of conventional designs. This paper elucidates the working mechanism of STRC walls under cyclic loading, indicating that these two diagonal embedded steel elements mainly exhibit truss behavior. The working mechanism is further verified through computational models developed in OpenSees with high accuracy and efficiency. Moreover, the design provisions in the current specification are evaluated in terms of the flexural strength and shear strength of STRC walls. Results show that the flexural strength of the design equations for STRC walls in the current specification is underestimated because the contribution of steel trusses is not considered. The findings of this study offer valuable insights into the engineering application of STRC walls.

Effect of particle diameter and void fraction on gas–solid two-phase flow: a numerical investigation using the Eulerian–Eulerian approach

AbstractSudden expansion pipes are crucial in fluid dynamics for studying flow behavior, turbulence, and pressure distribution in various systems. This study focuses on investigating the behavior of a two-phase flow, specifically a gas–solid turbulent flow, in a sudden expansion. The Eulerian–Eulerian approach is employed to model the flow characteristics. The Eulerian–Eulerian approach treats both phases (gas and solid) as separate continua, and their interactions are described using conservation equations for mass, momentum, and energy. The study aims to understand the complex phenomena occurring in the flow, such as particle dispersion, turbulence modulation, and pressure drop. The governing equations are solved using house developed code called FORTRAN, a widely used programming language in scientific and engineering simulations. The results of this study will provide valuable insights into the behavior of gas–solid two-phase flows in sudden expansions, which have important applications in various industries, including chemical engineering, energy systems, and environmental engineering. A parametric study of the impact of particles diameters (20, 120, 220, 500 µm), the solid volume loading ratios $$(0.005, 0.008, 0.01)$$ ( 0.005 , 0.008 , 0.01 ) and area ratios (2.25, 5.76, 9) effect of sudden expansion on the streamlines, local skin friction, pressure, velocity, turbulent kinetic energy, and separation zone.

Numerical Investigation on the Effects of Gap Circulating Flow on Blower Performance under Design and Off-Design Conditions

Blowers are widely used in tasks such as ventilation, exhaust, drying, cooling, heat dissipation, or conveying medium, and they usually consume a lot of energy. There is an inevitable gap between the rotating impeller and static volute casing due to manufacturing tolerance and thermal deformation. The circulating flow in the gap has an important effect on the performance of the blower. In this study, computational fluid dynamics (CFD) was used to investigate the performance of the blower under different flow conditions and gaps, and the accuracy of the numerical simulation was verified by performance experiments. The results show that the flow separation under low flow conditions in the impeller channel can be suppressed by the circulating flow. However, the efficiency of the blower is decreased because a part of the power is used to maintain the circulating flow. Under design conditions, efficiency is reduced by 5.3~8.2%, depending on the gap sizes. Due to the increased flow rate in the impeller channel caused by the gap circulating flow, the net flow rate of the impeller under design conditions is about 12% higher than the inlet flow rate of the blower. Therefore, it leads to an increase of about 12% in impeller efficiency calculated by the net flow rate compared with the inlet flow rate. Finally, the flow field distribution on the impeller channel under different gap conditions was compared, and the effects of the gap on the blower performance were analyzed from the perspective of flow field structure.

Numerical investigations of heat transfer augmentation in a microchannel heat sink with different shaped periodic reentrant cavities on channel sidewalls

Microchannel heat sink is widely applied in high-density heat flux devices for its high efficiency in heat dissipation. However, the most effective geometrical configuration of microchannels for best heat transfer augmentation with least pump power penalty is still unknown. In this research, the heat transfer augmentation in a microchannel heat sink with different shaped periodic reentrant cavities on channel sidewalls are numerically studied. Three different kinds of channel structures are introduced, including convex quarter-circular, concave quarter-circular, and inclined shaped reentrant cavities. The comprehensive performances of the proposed microchannels are compared with that of the smooth straight channel, with respect to the pressure drop, friction coefficient, Nusselt number, and performance factor. The results indicate that the comprehensive performance of the microchannel heat sink with periodic reentrant cavities is superior to the smooth straight channel, because its reentrant cavities can strengthen the mixing of fluids and lower the pressure loss. The proposed microchannels can enhance the heat transfer by 1.7 times, reduce the pressure drop by 3.7%-22.4% at Re 648.2, with the heat transfer entropy production decreased by 15.9%-48.2%. The inclined shaped microchannel has the best overall performance factor among the three proposed channels, which achieves up to 1.59 at Re 648.2.

Numerical investigation of the structure factors of the Read-Rezayi series

Numerical investigation of the structure factors of the Read-Rezayi series

Numerical investigation of wind-induced snowdrift on a long-span saddle-shaped roof based on the k-kl-ω model

Long-span structures are more vulnerable to the imbalanced distribution of snow loads, which is a primary factor contributing to structural failure. The development of snowdrifts is directly related to the shape of buildings, as it significantly affects turbulent characteristics and the process of snow drifting. This study explores the evolution of snowdrifts on a long-span saddle-shaped roof under various wind conditions. The numerical k-kl-ω model is validated against observation data by testing the flow field and snow distribution features of a stepped flat roof and a wind tunnel test. The snowdrift on a long-span saddle-shaped roof is simulated using the proven method, and the snowdrift's properties are studied at different wind speeds, wind angles, and threshold friction speeds. A comparative analysis of wind-induced snowdrift development on open and closed roofs is given, and the snow shape coefficients for each roof partition of the prototype roof are also provided. The findings indicate that the characteristics of snowdrifts on the roof vary with changing wind environmental factors, and the adverse inflow velocity and wind angle are identified. Snow morphology variation is more subject to an influence on changing inflow velocities compared to an alternation in wind-blowing time. The study reveals differences in how wind-driven fresh snow and long-deposited snow distribute themselves, with fresh snow producing more unevenness, potentially affecting roofs' load-bearing capacity.

Numerical Investigation of Rock-Breaking Force Analysis of TBM Disk-Cutters

Numerical Investigation of Rock-Breaking Force Analysis of TBM Disk-Cutters

Investigation of Convective Heat Transfer and Stability on a Rotating Disk: A Novel Experimental Method and Thermal Modeling

Experimental and numerical investigations are conducted on a rotating disk from the perspective of convective heat transfer to understand the effect of heating on the stability of flow. A non-invasive approach with a thermal camera is employed to determine local Nusselt numbers for different rotational rates and perturbation parameters, i.e., the strength of the heat transfer. A novel transient temperature data extraction over the disk radius and an evaluation method are developed and applied for the first time for the air on a rotating disk. The evaluation method utilizes the lumped capacitance approach with a constant heat flux input. Nusselt number distributions from this experimental study show that there is a good agreement with the previous experimental correlations and linear stability analysis on the subject. A significant result of this approach is that by using the experimental setup and developed approach, it is possible to qualitatively show that instability in the flow starts earlier, i.e., an earlier departure from laminar behavior is observed at lower rotational Reynolds numbers with an increasing perturbation parameter, which is due to the strength of heating. Two experimental setups are modeled and simulated using a validated in-house Python code, featuring a three-dimensional thermal model of the disk. The thermal code was developed for the rotating disks and brake disks with a simplified geometry. Experimentally evaluated heat transfer coefficients are implemented and used as convective boundary conditions in the thermal code. Radial temperature distributions are compared with the experimental data, and there is good agreement between the experiment and the model. The model was used to evaluate the effect of radial conduction, which is neglected when using the lumped capacitance approach to determine heat transfer coefficients. It was observed that the radial conduction has a slight effect. The methodology and approach used in this experimental study, combined with the numerical model, can be used for further investigations on the subject.

Numerical Investigation of Hydrogen Role on Detonation of CH4/H2/air Mixtures

ABSTRACT Steady one-dimensional Zeldovich-von Neumann-Dӧring (ZND) calculation and thermo-chemical analysis are performed to investigate the hydrogen role on ZND detonation of CH4/H2/air mixtures. Different hydrogen blend ratios (i.e. Hbr) ranging from 0% to 100% are selected in this paper. The results show that hydrogen blend ratio has a significant impact on the ZND detonation reaction pathway of stoichiometric CH4-air mixtures. When Hbr ≤ 20%, CH4 is converted to CO2 by route 1: CH4 => CH3 => C2H6 => … => CO2 and route 2: CH4 => CH3 => CH3O => CH2O => HCO => CO => CO2. When Hbr ≥ 50%, CH3 in route 2 is directly converted to CH2O through R97 (CH3 + O <=> CH2O + H). This causes different ZND detonation structures. The induction length decreases with hydrogen addition. This is because R0 (H + O2 <=> O + OH) governs the heat release during the induction stage, enhancing the energy absorption in induction stage and the molecular thermal decomposition after leading shock wave. Finally, the effect of hydrogen blend ratio on the detonation cell size is explored, and a prediction model of detonation cell size incorporated with detonation stability parameter and induction length is developed for CH4/H2/air mixtures.

Numerical investigation of a novel flow damping device for mitigating liquid sloshing under bi-directional excitation

Numerical investigation of a novel flow damping device for mitigating liquid sloshing under bi-directional excitation

Numerical Investigation of Thermal Performance for Turbulent Water Flow through Dimpled Pipe

Dimples are tiny indentations on the surfaces of the body that enhance heat transfer and alter fluid flow characteristics on or within the body. Numerical investigations were conducted to analyse the heat transfer and flow characteristics in a cross-combined dimple tube in the range of Reynolds numbers from 6000 to 14000. The finite volume method recognised a novel enhancement model utilising methods for composite-form surfaces. Compared to a smooth tube working similarly, the effects significantly improve the heat transfer index, performance evaluation criteria, and friction factor. A three-dimensional simulation was conducted to clarify the underlying process by which dimples affect thermal performance. The simulation findings suggest that the dimples effectively enhance heat transfer by altering the temperature distribution and increasing the temperature gradient within the central area of the dimple section. A concave surface profile disrupts the flow and prevents the formation of a stable boundary layer, promoting the mixing of hot and cold fluids. Furthermore, the study investigates how geometric characteristics impact thermal and hydraulic efficiencies, emphasising that larger dimples improve overall thermo-hydraulic performance. Specifically, the heat transfer enhancement achieved an average increase of 17.3%, ranging from 18.03% to 38.6%, surpassing that of the traditional smooth tube.