Numerical Investigation Research Articles

Numerical and experimental investigation of film cooling effectiveness distribution predictions that considers the effects of the turbulent Schmidt number

Film cooling is a critical protective cooling technique that is used in gas turbine engines. However, predicting the film cooling effectiveness can be quite challenging due to the complex mixing processes involved. As a result, simulations commonly require experimental validation or modification of their numerical methods. In this study, predictions of film cooling effectiveness distributions were enhanced by an examination of the impact of the turbulent Schmidt number, Sct, on the coolant-covered areas. An existing turbulent viscosity modification method, the MIX model, was utilized to obtain more accurate flow field representations. The definition, physical implications, and role of the turbulent Schmidt number in numerical simulations, along with the principles of the pressure-sensitive paint measurement method, which was used to characterize the film cooling effectiveness, were explored. Both numerical simulations and experimental validation were employed. The study results revealed that small-scale turbulent eddies, which were averaged in the RANS method according to the Sct, critically influenced the mixing between the coolant and the mainstream, thereby impacting the cooling effectiveness. It was also revealed that as Sct decreased, the cooling effectiveness diminished in the streamwise direction but increased in the spanwise and vertical directions, regardless of the momentum ratio value. An Sct value of 0.3 was found to be more suitable than the commonly used value of 0.7, particularly for a low momentum ratio of 0.43. When Sct=0.3, the error in the area-averaged cooling effectiveness was 10 %, while it was 51 % when Sct=0.7. Additionally, an Sct value of 0.3 produced better overall cooling effectiveness distributions. Consequently, an Sct value of 0.3 is recommended for most low-speed and incompressible-flow simulation conditions.

Fire performance of CFRP-strengthened piloti-type columns with fire-resistant materials during standard fire exposure

This paper presents a numerical investigation into the fire endurance of carbon fiber reinforced polymer (CFRP)-strengthened columns, shielded with fire-resistant materials, in piloti-type reinforced concrete buildings. The strengthened column, equipped with a fire protection system, underwent exposure to the ASTM E119 standard time-temperature curve for a duration of 4 h. To comprehensively evaluate the thermal and structural performance of the strengthened column at elevated temperatures and substantiate the effectiveness of the fire protection system, a fully coupled thermal-stress analysis was conducted. The numerical modeling approach employed in this study was rigorously validated through previous experimental studies in conjunction with adherence to the ACI design guideline, specifically ACI 440.2R-17. Using the validated structural fire model, the thermal and structural behaviors of the RC column with an insulated CFRP strengthening system were investigated based on four key performance criteria: glass transition temperature, ignition temperature of polymer matrix, critical temperature of reinforcing bars, and the design axial load capacity at elevated temperatures. Furthermore, a comparative assessment of fire endurance was performed using diverse fire-resistant materials, including Sprayed Fire-Resistive Material (SFRM) and Sikacrete®-213 F, with insulation thicknesses ranging from 10 to 30 mm, during the 4-hour fire exposure period.

Numerical investigation of steering synchronization dynamics of laterally coupled laser array with monolithically-integrated external cold cavity

This study numerically explores the synchronization dynamics of a one-dimension edge-emitting laser array monolithically-integrated with an external cold cavity comprehensively, aiming to achieve an in-phase mode optical field. By employing the optical feedback rate equation, the impact of mutual feedback coefficient and coupling coefficient on the synchronization process are investigated thoroughly. The proposed external cold cavity, designed according to the Talbot effect, could significantly diminish the reflectivity of front facet through separated electrode structure, therefore facilitating the phase-locking process. Consequently, the study uncovers the effective regime for establishing in-phase mode operation. Additionally, the numerical analysis also reveals the vivid synchronization dynamic from a chaotic state to partially-phase-locked, then completely-phase-locked, and ultimately periodic oscillation. Furthermore, the impact of practical fabrication tolerances on the synchronization process are explored as well. Based on the simulation results, our work could offer valuable insights for steering the on-chip optical field and developing novel laser arrays with high beam quality.

Lattice Boltzmann Model for Rarefied Gaseous Mixture Flows in Three-Dimensional Porous Media Including Knudsen Diffusion

Numerical modeling of gas flows in rarefied regimes is crucial in understanding fluid behavior in microscale applications. Rarefied regimes are characterized by a decrease in molecular collisions, and they lead to unusual phenomena such as gas phase separation, which is not acknowledged in hydrodynamic equations. In this work, numerical investigation of miscible gaseous mixtures in the rarefied regime is performed using a modified lattice Boltzmann model. Slip boundary conditions are adapted to arbitrary geometries. A ray-tracing algorithm-based wall function is implemented to model the non-equilibrium effects in the transition flow regime. The molecular free flow defined by the Knudsen diffusion coefficient is integrated through an effective and asymmetrical binary diffusion coefficient. The numerical model is validated with mass flow measurements through microchannels of different cross-section shapes from the near-continuum to the transition regimes, and gas phase separation is studied within a staggered arrangement of spheres. The influence of porosity and mixture composition on the gas separation effect are analyzed. Numerical results highlight the increase in the degree of gas phase separation with the rarefaction rate and the molecular mass ratio. The various simulations also indicate that geometrical features in porous media have a greater impact on gaseous mixtures’ effective permeability at highly rarefied regimes. Finally, a permeability enhancement factor based on the lightest species of the gaseous mixture is derived.

Progress in Seismic Isolation Technology Research in Soft Soil Sites: A Review

Soft soil sites can amplify the peak acceleration by a factor of 1.5 to 3.5 and exhibit the filtering effect on seismic waves. This effect results in the attenuation of high frequencies, amplification of low frequencies, and extension of the predominant period of ground motion. Consequently, soft soil sites have a more pronounced impact on isolation buildings constructed on them. The seismic isolation structure design typically involves assuming rigid foundation for calculations. However, the soil properties can significantly impact the dynamic response of the structure, affecting factors such as input ground motion, changes in vibration characteristics, radiation energy dissipation, and material damping energy dissipation. Therefore, neglecting these influences and relying solely on the rigid foundation assumption for calculations can lead to significant errors in the final seismic response analysis of the structure. Currently, there are numerous LNG storage tanks, museums, and other isolation buildings constructed on soft soil sites. Therefore, research on seismic isolation measures for soft soil sites holds significant practical importance. In light of this, this paper, firstly, provides a systematic summary of seismic isolation strategies and engineering applications for soft soil sites. Secondly, it further discusses advancements in research on the dynamic interactions of soil–isolated structures, covering analytical methods, numerical investigations, and experimental studies on soft soil sites. Lastly, the paper concludes with insights on current research progress and prospects for further studies.

Numerical Investigation on the Hysteretic Performance of Self-Centering Precast Steel–Concrete Hybrid Frame

To improve the construction performance and seismic resilience of precast reinforced-concrete frame structures, an innovative self-centering precast steel–concrete hybrid frame has been proposed and subjected to cyclic loading tests. In this paper, a comprehensive numerical analysis was conducted to further investigate the frame’s hysteretic behavior. Initially, a numerical model was developed using the finite element software OpenSees. Numerical analyses of two frame specimens were conducted, demonstrating good agreement between the numerical and experimental hysteretic characteristics, thus validating the model’s accuracy. Subsequently, based on the numerical simulations, a quantitative comparison of hysteretic performance between a novel frame and a traditional reinforced-concrete frame of the same scale was performed. While the proposed frame exhibited slightly lower initial stiffness and energy dissipation capacity than the traditional frame, it outperformed in terms of load-carrying capacity and self-centering ability. Finally, parametric analyses were carried out to assess the influence of various design parameters on the hysteretic performance, including friction force in the web frictions devices, initial post-tensioned force of the prefabricated steel–concrete hybrid beams, the steel arm length, and the column longitudinal reinforcement ratio. The results showed that increases in these four parameters improved the load-carrying capacity and initial stiffness of the proposed frame. Additionally, an increase in the friction force, steel arm length, or column longitudinal reinforcement ratio enhanced the frame’s energy dissipation capacity, while an increase in the initial post-tensioned force or a decrease in the friction force enhanced the frame’s self-centering capacity.

Numerical Investigation on the Evolution Behavior of Solidification Structure in Titanium Alloy During Vacuum Arc Remelting Process

Numerical Investigation on the Evolution Behavior of Solidification Structure in Titanium Alloy During Vacuum Arc Remelting Process

A Numerical Investigation of the SIR-type Model with a Susceptible R Compartment

A Numerical Investigation of the SIR-type Model with a Susceptible R Compartment

Mathematical Modelling of the Impact of IR Laser Radiation on an Oncoming Flow of Nanoparticles with Methane

Introduction. The study is devoted to the numerical investigation of laser radiation’s effect on an oncoming two-phase flow of nanoparticles and multicomponent hydrocarbon gases. Under such exposure, the hydrogen content in the products increases, and methane is bound into more complex hydrocarbons on the surface of catalytic nanoparticles and in the gas phase. The hot walls of the tube serve as the primary source of heat for the reactive two-phase medium containing catalytic nanoparticles. Materials and Methods. The main method used is mathematical modelling, which includes the numerical solution of a system of equations for a viscous gas-dust two-phase medium, taking into account chemical reactions and laser radiation. The model accounts for the two-phase gas-dust medium’s multicomponent and multi-temperature nature, ordinary differential equations (ODEs) for the temperature of catalytic nanoparticles, ODEs of chemical kinetics, endothermic effects of radical chain reactions, diffusion of light methyl radicals CH3 and hydrogen atoms H, which initiate methaneconversion, as well as absorption of laser radiation by ethylene and particles. Results. The distributions of parameters characterizing laminar subsonic flows of the gas-dust medium in an axisymmetric tube with chemical reactions have been obtained. It is shown that the absorption of laser radiation by ethylene in the oncoming flow leads to a sharp increase in methane conversion and a predominance of aromatic compounds in the product output. Discussion and Conclusion. Numerical modelling of the dynamics of reactive two-phase media is of interest for the development of theoretical foundations for the processing of methane into valuable products. The results obtained confirm the need for joint use of mathematical modelling and laboratory experiments in the development of new resource-saving and economically viable technologies for natural gas processing.

Field and Numerical Investigations on Pumpable Standing Supports Failure Analysis in the Longwall Pre-driven Recovery Room

Field and Numerical Investigations on Pumpable Standing Supports Failure Analysis in the Longwall Pre-driven Recovery Room

Numerical investigation on plastic hinge behavior of hybrid steel-FRP reinforced concrete columns

This paper presents a numerical study on the plastic hinge behavior and rotation capacity of concrete columns reinforced with a combination of steel bars and fiber-reinforced polymer (FRP) bars. A meso-scale numerical model, which considers the internal heterogeneity of concrete and bond behavior between concrete and longitudinal reinforcements, was developed and validated. The failure modes, lateral load-displacement responses, and the physical plastic hinge lengths of hybrid steel-FRP reinforced concrete (SFRC) columns were investigated and compared with those of conventional steel-reinforced concrete columns. The results indicated that the steel yielding zone and curvature localization zone of SFRC columns with FRP longitudinal bars were enlarged, due to the relatively low modulus of FRP bars. After that, a parametric analysis was performed to study the plastic hinge length of SFRC columns with respect to the nominal area ratio of FRP longitudinal bars, shear span-to-depth ratio, axial load ratio, and longitudinal reinforcement ratio. A new empirical model was proposed to predict the equivalent plastic hinge length, which was subsequently integrated into an analytical method for predicting the ultimate rotation. The comparison of predictions with simulation and test results demonstrated the accuracy of both the proposed empirical model and analytical method.

Numerical and Experimental Investigation of Austenite Transformation of Bearing Steel GCr15 in Non-isothermal and Isothermal Processes

Numerical and Experimental Investigation of Austenite Transformation of Bearing Steel GCr15 in Non-isothermal and Isothermal Processes

Damage mechanism of model arch dam subjected to far-field underwater explosion

The dynamic response and damage modes of arch dams subjected to explosions are key topics having been extensively researched in recent years. However, the majority of research employs numerical simulation, and there is a lack of experimental investigations to further support those numerical simulation results. Given this, small-scale model experiments were conducted on the arch dam to investigate its dynamic response to underwater explosions. The findings of these experiments indicated a potential overall damage mode along the crown cantilever profile. A numerical investigation of the experimental arch dam was executed employing the CEL method in combination with the Concrete Damage Plasticity model. The damage development process and cracking mechanism of the arch dam under a far-field underwater explosion were examined. According to the numerical findings, the damage process to the arch dam resulting from a far-field underwater explosion might be divided into two phases: the shock wave action phase and the overall response phase. During the shock wave action phase, slight damage first appeared on the downstream dam face. Later, during the overall response phase, a crack spread from the dam base to dam crest and from the downstream side to the upstream side, eventually penetrating through the crown cantilever profile. The damage mechanism in the shock wave action phase is the reflected rarefaction wave off the downstream dam face causing localized tensile damage to surrounding concrete. While the cracking mechanism in the overall response phase is structural bending-induced tensile damage driven by the overall response.

Numerical Investigation of Wind Turbine Airfoil Icing and Its Influencing Factors under Mixed-Phase Conditions

Icing is a popular research area in wind energy, and the icing problem of the supercooled droplet–ice crystal mixed-phase condition is one of the new challenges. A numerical method for analyzing the icing characteristics of wind turbine airfoil under mixed-phase conditions is presented. The control equations for the dynamics of supercooled droplets and ice crystals are formulated using the Lagrangian method. Equations for the conservation of mass and energy during the icing process involving supercooled droplets and ice crystals are constructed. The impact of erosion phenomena on the mixed-phase icing process is examined, and methodologies for solving the control equations are introduced. The numerical method is utilized for modeling mixed-phase icing under a range of conditions. The results of these simulations are then compared with data obtained from icing wind tunnel tests to assess the validity of the method. The influence of various mixed-phase conditions on ice shapes is studied. It is found that higher icing temperatures correspond to a larger icing range and amount. The increase in supercooled droplet content, ice crystal content, and ice crystal diameter all contribute to enhanced ice accretion. However, the effects of ice crystal content and diameter are relatively minor.

Propulsive Performance of Bionic Underwater Vehicle Based on Four Flexible Oscillating Foils: A Numerical Investigation

Propulsive Performance of Bionic Underwater Vehicle Based on Four Flexible Oscillating Foils: A Numerical Investigation

Influence of relative distance between fault and tunnel on dynamic response of tunnel: An experimental and numerical investigation

The effect of earthquakes on deep tunnels near faults has always been a significant issue in underground engineering research. The presence of fault fracture zones tends to intensify the seismic response of tunnels. On the basis of the Xianglushan tunnel project, the influence of relative distance between fault and tunnel on the dynamic response of tunnel was investigated utilizing laboratory test, shaking table test, and numerical simulation. The results indicated that as the relative distance between the fault and the tunnel increased, the peak acceleration and peak strain of the tunnel first increased and then decreased. The results of numerical simulations and experimental tests demonstrated that changes in relative distance had a significant influence on the dynamic response of the tunnel. Since the Xianglushan tunnel is located near the fault, the superposition of seismic load and the residual tensile and compressive stress led to the appearance of through-type cracks, which eventually resulted in large deformation or even failure. The left arch springing and left spandrel of the tunnel closer to the fault were prone to failure first. This study provides a reference for the seismic dynamic response and failure mechanism of near-fault tunnels.

Numerical investigation of friction-heating-pressurization and its control parameters in the shear band of high-speed landslides

Numerical investigation of friction-heating-pressurization and its control parameters in the shear band of high-speed landslides

From Geometry of Hamiltonian Dynamics to Topology of Phase Transitions: A Review

In this review work, we outline a conceptual path that, starting from the numerical investigation of the transition between weak chaos and strong chaos in Hamiltonian systems with many degrees of freedom, comes to highlight how, at the basis of equilibrium phase transitions, there must be major changes in the topology of submanifolds of the phase space of Hamiltonian systems that describe systems that exhibit phase transitions. In fact, the numerical investigation of Hamiltonian flows of a large number of degrees of freedom that undergo a thermodynamic phase transition has revealed peculiar dynamical signatures detected through the energy dependence of the largest Lyapunov exponent, that is, of the degree of chaoticity of the dynamics at the phase transition point. The geometrization of Hamiltonian flows in terms of geodesic flows on suitably defined Riemannian manifolds, used to explain the origin of deterministic chaos, combined with the investigation of the dynamical counterpart of phase transitions unveils peculiar geometrical changes of the mechanical manifolds in correspondence to the peculiar dynamical changes at the phase transition point. Then, it turns out that these peculiar geometrical changes are the effect of deeper topological changes of the configuration space hypersurfaces ∑v=VN−1(v) as well as of the manifolds {Mv=VN−1((−∞,v])}v∈R bounded by the ∑v. In other words, denoting by vc the critical value of the average potential energy density at which the phase transition takes place, the members of the family {∑v}v<vc are not diffeomorphic to those of the family {∑v}v>vc; additionally, the members of the family {Mv}v>vc are not diffeomorphic to those of {Mv}v>vc. The topological theory of the deep origin of phase transitions allows a unifying framework to tackle phase transitions that may or may not be due to a symmetry-breaking phenomenon (that is, with or without an order parameter) and to finite/small N systems.

A numerical investigation of the polyethylene glycol‐based tetra hybrid nanofluid flow over a stretched porous rotatory disk

AbstractPolyethylene glycol (PEG) is a great heat and mass transmissive fluid that has promising applications in medical, pharmaceutical, and electronic industries. Tetra‐hybrid nanofluids (HNFs) are the most upgraded version of heat and mass transmissive nanofluids that are synthesized by dispersing four distinct nanoparticles in the carrier fluid. The study of the flow of nanofluids and their advanced classes across rotatory disks is receiving remarkable interest in research and innovation due to their considerable applications like gas turbine rotors, aeronautical, medical equipment, rotating machinery, thermal power developing systems, and so forth. Therefore, the present paper aims to inspect the magnetohydrodynamic, steady, three‐dimensional, and incompressible flow of a non‐Newtonian tetra‐HNF over a stretched porous rotating disk. The chosen tetra‐HNF consists of four distinct nanoparticles namely, molybdenum disulfide, copper oxide, magnesium oxide, and zirconium oxide with PEG as the carrier fluid. The flow model is modified with innovative impacts of variable thermal conductivity, thermal radiation, chemical reaction, variable mass diffusivity, and suction/injection to make this research more convenient. The mathematical computation is conducted via the bvp4c numerical method, and the outputs are determined via tables and graphs. Mounting values of the Deborah number amplify the axial velocity while augmentation is noticed in the fluid's radial and azimuthal velocities for rising values of the rotation parameter. Besides, the rotation parameter aids in enhancing both the heat and mass transportation rates while the chemical reaction parameter significantly aids the mass transportation rate. One of the significant results of this inspection is that tetra‐HNF exhibits better heat and mass transportation rates than the ternary‐HNF, and the HNF whereas it has lesser skin friction than the ternary‐HNF, and the HNF.

Seismic Isolation via I-Shaped and T-Shaped Large-Scale Phononic Metamaterials

In this work, the attenuation of surface seismic waves from large-scale phononic metamaterials is numerically studied. The proposed metamaterials consist of rectangular trenches that form either I-shaped or T-shaped cavities embedded at the ground surface. The numerical investigation includes the study of the response of the proposed structures for different values of their geometric parameters. In addition, modifications of the proposed structures where heavy cores coated with a soft material were considered in the cavities were also numerically studied. For a more realistic numerical approach, the transmission spectrum of a selected large-scale phononic metamaterial was also investigated in a suitable half-space numerical scheme. The results of the present research showed that the studied large-scale metastructures could be a very promising potential candidate for seismic shielding applications for the protection of existing urban or countryside structures. The proposed metamaterials are low in cost and easy to construct for the protection of existing buildings, critical infrastructures, or even entire urban areas without need for any kind of intervention at them, therefore providing an effective solution in the field of seismic isolation.