Pressure Fluctuations Research Articles

The manufacturing of a briquette press machine with a pneumatic system

Abstract The use of green energy not only has the potential to preserve fossil fuel reserves but can also have a positive impact on the environment. Briquettes are one of the alternative fuels to reduce the use of fossil fuels. Manual and hydraulic printing of briquettes often experience problems, namely fluctuations in size and pressure in manual printing and leaks in the hydraulic system. Therefore, this research aims to make and test a briquette press machine with a pneumatic system to increase productivity and briquette quality. The results of this study indicate that the effective capacity of the machine is 3,179 kg/hour. The percentage of material left behind is 1.56%. The briquette density value reached 0,58 gr/cm3. The briquette moisture content value is 4.3% and the briquette compressive strength value is 7,22 kg/cm2. The production cost of briquettes is Rp.13,500/kg. BEP is 100 kg/year. R/C ratio is 1,265. NPV of Rp.345,915,642.25. The amount of IRR value obtained in this briquette processing is 45,66% and the PP of this business is 3,6 months. Based on the results of this study, it can be stated that this machine is feasible to use, and the briquette results have met the Indonesian briquette quality.

Comparative Analysis of Hemodynamic Effects of Remimazolam and Propofol Combined with Esketamine in Colonoscopic Procedures in the Elderly.

The debate continues over the differential impact of remimazolam vs propofol on hemodynamic stability. This study aims to elucidate the effects of a combination of remimazolam and esketamine vs propofol and esketamine on hemodynamic parameters in elderly patients undergoing painless colonoscopies. We conducted a randomized controlled trial involving 754 patients, divided equally between two treatment groups. The remimazolam-esketamine group (RE group) received 0.15 mg/kg of remimazolam and 0.3 mg/kg of esketamine. Conversely, the propofol-esketamine group (PE group) was administered 1.5 mg/kg of propofol with 0.3 mg/kg of esketamine. Primary outcomes focused on the incidence of hypotension. Secondary outcomes assessed were other hemodynamic adverse events, intraoperative blood pressure and heart rate fluctuations, usage of vasoactive agents, sedation efficacy, and additional adverse reactions. Hypotension occurred significantly less frequently in the RE group (9.78%, 95% confidence interval[CI]: 6.67-12.87%) compared to the PE group (23.57%, 95% CI: 21.22-30.52%), P<0.001. The RE group also showed lower incidences of sinus tachycardia, sinus bradycardia, and required less support from vasoactive agents (P<0.001). Additionally, the RE group experienced smaller fluctuations in blood pressure and heart rate (P<0.05). Both groups achieved a 100% sedation success rate. Notably, the RE group had a longer induction period but a quicker recovery time (P<0.001), and lower rates of respiratory depression (P=0.006) and injection pain (P<0.001). Remimazolam combined with esketamine offers superior hemodynamic stability and significantly reduces adverse event rates compared to propofol plus esketamine in elderly patients undergoing painless colonoscopies, while maintaining effective sedation.

Investigation on flow–acoustic resonance behaviors inside ducts with tandem cavities using a high-order spectral/hp element method

This study numerically investigates the flow–acoustic resonance behaviors inside ducts with tandem cavities, containing the flow-excited acoustic eigenmodes and elevated flow dynamics under self-sustained acoustic forcing. An advanced high-order spectral/hp element method integrated with implicit large-eddy simulations was utilized to solve the nonlinear compressible Navier–Stokes equations, which effectively identified the fully coupled self-sustained flow–acoustic resonance fields. The benchmark shallow cavity configuration with a length-to-depth (L/D) ratios of 2 was motivated by the experimental findings from Shaaban and Ziada [“Fully developed building unit cavity source for long multiple shallow cavity configurations,” Phys. Fluids 30, 086105 (2018)], in which the intensive flow–acoustic resonance was occurred at a Reynolds number of 1.3×105, and we further investigated three deeper cavity configurations with L/D of 1, 2/3, and 1/2 for numerical validation and further comparison. Subsequently, aeroacoustic characteristics were assessed by analyzing the wall pressure fluctuations, indicating broader resonance regions and augmented pressure pulsation amplitudes extending from main duct to local cavity volumes with larger cavity depths. As feedback, the intensified acoustic forcing can modulate the cavity flow dynamics into stronger fluctuation levels. Furthermore, the spectral proper orthogonal decomposition analysis was conducted on the pressure fields and velocity fields, respectively. The significant fluctuations in acoustic pressure were linked to transitional acoustic modes that were present as global modes in the main duct and local modes in tandem cavities. As for velocity analysis, coherent vortex structures were extracted along the cavity entrances. These vortex structures caused progressively amplified velocity fluctuations and classified the shear layers into two dynamic motions, i.e., a flapping motion in shallow cavities and a rolling-up motion in deep cavities.

On the Generation of Large-Scale Vortical Flow Structures in Pipe Multifurcations

Abstract In many hydraulic power plants, the water supplied through the penstock needs to be distributed to multiple turbines. The application of pipe multifurcations is motivated by economic and efficiency reasoning. However, flow instabilities and large-scale vortical flow structures can occur for some operating conditions, causing high-amplitude pressure and mass flow rate fluctuations. To enhance the understanding of the flow instability inception, we investigate the unsteady flow in a pipe multifurcation with six branches for different operating conditions. The unsteady flow is simulated employing the large eddy simulation approach, where the numerical mesh is constructed such that y + &lt; 1 and a recycling-type boundary condition is utilised to provide the turbulent inflow conditions. While the general flow pattern are described by the time-averaged results, the work focuses on analysing the unsteady physical phenomena occurring in the pipe multifurcation. At part-load operation, the results clearly show the formation of large-scale vortical flow structures stretching into the active branches. The vortices are observed to move around and eventually burst. When one vortex breaks down, the other large-scale vortices reaching into the other active branches are likely to burst and the flow pattern changes. Such events come with decreased turbulence intensity propagating through the branch line, flow separation at the branch line junction, and mass flow rate fluctuations. After a short time, large-scale vortices were established again.

Numerical investigation on effect of non-parallelism on natural transition in boundary layers around underwater axisymmetric bodies

For both fluid mechanics and practical engineering problems, it is important to study the effect of non-parallelism on the natural transition in boundary layers around underwater axisymmetric bodies. This paper develops the method of harmonic linearized Navier–Stokes (HLNS) equations for such boundary layers. The method can be used to study the evolution of small disturbances considering the non-parallelism of the basic flow. Based on the results of the HLNS equations, the transition positions of the boundary layers are predicted by the eN method. Because traditional linear stability theory (LST) neglects non-parallelism, the difference between the results using the HLNS method and those given by LST represents the effects of non-parallelism. Numerical calculations are performed for five classical forebody shapes, and the effect of non-parallelism is identified. (i) At each streamwise location, non-parallelism suppresses low-frequency disturbances while promoting high-frequency ones. The influence on high-frequency disturbances is more obvious. (ii) The effect of non-parallelism on the neutral curve focuses on the region near the critical instability position. Non-parallelism slightly delays the critical instability position for most forebody shapes and pushes the unstable zone toward the high-frequency direction while broadening its frequency bandwidth. (iii) The streamwise range at each growth-rate level is widened, implying that non-parallelism destabilizes the boundary layers. (iv) The transition occurs earlier, indicating that non-parallelism promotes the transition. (v) Non-parallelism shifts the dangerous frequency band toward the high-frequency direction. (vi) Non-parallelism enhances the wall pressure fluctuations (WPF) in the unstable laminar zone.

Turbulent Noise Sources Reduction by Large-Eddy Breakup Devices and Riblets

An experimental study is presented on the application of large-eddy breakup (LEBU) on a flat plate as an outer layer source-targeting device to mitigate the wall pressure fluctuations and lateral coherence length scale of a turbulent boundary-layer developed at zero pressure gradient. Both represent the prominent noise sources for the trailing-edge noise radiation. When a LEBU is placed strategically at the outer part of a turbulent boundary-layer, the wall pressure spectra can establish a self-similar behavior against s′, which is a normalized separation distance between the LEBU’s trailing-edge and the targeted location for noise mitigation. It is found that s′ has to be greater than 3 to achieve an overall reduction in the wall pressure fluctuations. What appears to be the optimal LEBU configuration for the mitigation of wall pressure fluctuations, however, will not be reciprocated in the lateral coherence length. The combined effect would render the LEBU rather ineffective to reduce the frequency-integrated, overall noise radiation. Our previous study has confirmed that riblets, a near-wall source-targeting device, is more effective in the mitigation of the lateral coherence length. Under the principle of non-interference, a combination of riblets and LEBU demonstrates that reduction of the frequency-integrated, overall noise radiation can be achieved, again at s′>3.

CFD Simulation of the turbine start-up of a pump-turbine with investigation of the usage of a porous domain for modelling very small guide vane angles

Abstract With increasing number of transient operations, such as start and stop procedures in pump-turbines, CFD simulations of these sequences have become more important to understand the occurring flow phenomena and evaluate their impact on the pump-turbines lifetime. In the present work, the numerical setup for transient CFD simulations is discussed and a CFD simulation of a turbine start-up using a 29 million node mesh and the SBES turbulence model is carried out. The results demonstrate reasonable accuracy when comparing the overall trends with the available measurement data. However, significant underestimation of torque fluctuations as well as draft tube pressure fluctuations during the initial phase of the start-up is observed. In a subsequent study, the modelling of very small guide vane angles by a porous domain is investigated. An analytical function for the loss coefficient of the porous domain is applied up to different threshold values of the guide vane angle. A guide vane angle of 1° is identified as the best option regarding accuracy and computational effort.

Control of Acoustic Tone Formation using Shape Geometry Modifications and Jet Blowing in a Cavity experiencing Supersonic Flow

Acoustics tones have caused significant damage to sensitive electronic equipment and aircraft respectively. The effects become severe in cavities experiencing turbulent flows and could lead to human fatalities. Studies have compared the effects of cover plate (CP) and jet-blowing (JB) systems in suppressing the propagation of these undesirable effects. The sound pressure levels (SPL) were observed to decrease by 10% and 3% in the former and latter respectively. This study critically examines the combined effect of CP geometry modifications, jet orifice positions as well as integration with other established flow control techniques (FCT) with the possibility of achieving further attenuation in the system. Geometric sizes of the CP are set to 20%, 25% and 30% of the cavity length, with a length-to-depth ratio (l/d) of 5.07 and simulated in a flow field with a Mach number of 1.5. Also, four orifices for jet blowing are varied on the cavity leading and trailing edge wall. The trailing edge modification and trailing edge curvature are also implemented on the cavity. The k-ꙍ turbulence model and second-order discretization method are used to perform the computation. Results show that the trailing edge region produced the largest pressure fluctuations. Also, it was observed that longer cover plates (0.3l) permit the formation of self-oscillating frequencies as the flow field is brought closer to the trailing edge. However, the further inclination of the trailing wall will ensure prompt evacuation and dissipation of the flow turbulence energy. At the trailing edge, the jet-blowing control technique successfully attenuated approximately 10dB in SPL, though a significant amount of turbulence was introduced into the system. Overall, the trailing edge modification, inclined cover plate with a 0.25l and jet blowing on the trailing and leading edges produced an approximate 27.5% reduction in acoustic tone suppression.

The influence of the free runners on the decelerated swirling flow from the draft tube cone of hydraulic turbines.

Abstract Nowadays the renewable energy plays an key role in the development of safe and clean energy. Worldwide and especially in Europe the development of renewable energy is focused on development of new wind and solar power plants. Accordingly, these energy technologies introduce high power fluctuations in the electrical system, which are necessary to compensate by other energy sources. To compensate these power fluctuations, the electrical systems use new technologies as high-capacity electric batteries or classical technologies as hydropower. The new technologies as the batteries are used rarely, while the hydropower remain the only technology to response quickly at the electrical systems requirements. The hydropower with the hydraulic turbines has the capability to adapt faster at the electrical system requirements, but for hydraulic turbines this requirement comes with hydrodynamic consequences. Accordingly, at the outlet of the hydraulic turbines (in the conical diffuser), the hydraulic instabilities are developed (vortex rope occurs) accompanied by high pressure fluctuations. The present paper proposes adding free runner at the inlet of the conical diffuser, which rotates on an axle, with null momentum. For this purpose, have been designed and manufactured a series of four free (additional) runners (with different numbers of blades) to assess the performances of this method. Experimental investigations of unsteady pressure and velocity profiles using LDV system were performed downstream of the free runner. The velocity measurements have been performed on three survey axes, by measuring the meridian and circumferential velocity profiles. The unsteady pressure measurements were achieved at the conical diffuser wall on two levels. To better analyse the relevance of the free runners, the Fourier transform is applied on pressure signals. The results will clarify the functionality and limitations of this method for swirling flow control.

Research on transient flow characterization for gas-containing pipeline filling based on a two-fluid model

For the water-air coupled transient flow phenomenon that occurs when water impacts on trapped air during the start-up filling process of a pressurized pipeline system, this paper utilizes the Euler–Euler two-phase two-fluid model. In this model, both phases are compressible, and they exhibit time- and space-dependent characteristics. The two-phase surge tube example serves as verification that the model can accurately simulate the transient flow of trapped air. The study results indicate that as the gas content in the pipe increases, the pressure attenuation effect becomes more pronounced and there are longer cycles of pressure fluctuation. In the system, gas spreads to both sides of the pipe at different wave crests. When there is no air in the pipeline, meaning the air content is 0, a larger initial boundary value leads to a smaller ratio between its maximum pressure and the initial boundary pressure. The same ratio for a gas content of 7%. However, when trapped air is present, the result is reversed.

Wave mode observation of hydrogen/oxygen driven rotating detonations in the hollow and annular rotating detonation rocket engine

The rotating detonation rocket engine (RDRE) fueled by hydrogen/oxygen propellant represents a promising propulsion technology due to its high thermodynamic efficiency and propellant superior specific impulse. The rotating detonation wave (RDW) must propagate in a specific propagation mode while maintaining the self-sustaining state to ensure stable operation. An experimental system of hydrogen/oxygen fueled RDRE was developed in the present study. The operation of RDRE and propagation mode of RDW were investigated under atmospheric pressure conditions, and both hollow and annular combustors were tested. The high-frequency pressure fluctuations in the RDRE were measured by the dynamic pressure transducer, while a high-speed camera was used to capture images of flame luminescence at the rear end of the RDRE. The experimental results showed that the RDW could be initiated and reached a self-sustaining propagation state with hydrogen/oxygen propellant in the hollow and annular RDRE. A single-wave mode, a two-wave co-rotating mode, and a three-wave co-rotating mode were visualized under different conditions. With the increase in the equivalence ratio, the number of rotating detonation fronts decreased, and the variations in the RDW propagation modes were consistent in the hollow and annular RDRE. However, when the equivalence ratio exceeds 1.2, the propagation velocity decreases sharply in the annular combustor, while in the hollow combustor the RDW propagates stably, revealing a higher upper limit for the equivalence ratio. Also, the dominant frequency distribution was more concentrated in the hollow combustor. The findings provide valuable insight into the variations in detonation modes related to the equivalence ratio and combustor configuration.

Review of Wavenumber-Frequency Spectrum Models of Turbulent Boundary-Layer Wall Pressure Fluctuations

Turbulent boundary layer wall pressure fluctuations are of significant concern in acoustic engineering for both high-speed airborne and underwater vehicles, and the modeling of the associated wavenumber-frequency spectra has been extensively studied. In this paper, a review of 12 models developed between 1964 and 2017 has been conducted, and both the 2D and 1D forms investigated. In this work, fundamental concepts are introduced, followed by a classification of the models into two categories, that is, Corcos-type and non-Corcos-type models. Both the 2D and 1D forms of the 12 models are individually introduced in chronological order. To evaluate these models, comparisons of the 2D and 1D wavenumber-frequency spectra at different speeds and frequencies were conducted. Unlike Corcos-type models, non-Corcos-type models are grounded in a stronger theoretical foundation, with some models accurately reflecting acoustic region characteristics. Corcos-type models exhibit good consistency, however, they require an auto-spectrum as a necessary input, which makes them semiempirical models. In addition, the models within the Corcos-type and the non-Corcos-type were also compared, respectively, and a few important conclusions were accordingly made. The research output from this paper can provide an important practical engineering reference for studies associated with acoustic engineering, such as aircraft cabin noise and submarine hydrodynamic noise.

Optimizing Bionic Blades for Multi-blade Centrifugal Fans: Asymmetric Thickness Inspired by Carangiform Fish

Multi-blade centrifugal fans find wide application across various fields, with their internal airflow exhibiting complex turbulent behavior in three dimensions. Historically, blade optimization relied on constant thickness airfoils, limiting the effectiveness of optimization efforts. However, marine organisms have developed airfoil structures with highly efficient drag reduction, offering a novel approach to optimizing multi-blade centrifugal fans. This study proposes an airfoil optimization design method utilizing variable-thickness airfoils to maintain consistent pressure surface leading-edge parameters. By integrating the Non-dominated Sorting Genetic Algorithm II with biomimetic optimization design, performance improvements are achieved. The study constructs an asymmetric bionic blade using a Bezier curve to fit the mean camber line of the blade. Experimental testing validates the optimized fan's performance, demonstrating the effectiveness of the proposed design approach in reducing the unsteady interaction between the impeller and the volute tongue. This reduction significantly diminishes sound pressure fluctuations on the blade surface. Notably, at the maximum volume flow rate, the optimized fan featuring the asymmetric bionic blade exhibits a remarkable enhancement, with a 10.5% increase in volume flow rate and a notable 1.7 dB reduction in noise compared to the original fan configuration.

Study on the Spatio-temporal Evolutionary Properties of Gas-liquid Two-phase Flow in Centrifugal Pump as Turbine (PAT)

With the increasing complexity of the industrial production process, the transmission medium of the hydraulic turbine is no longer satisfied, and the gas-liquid two-phase mixed medium has to be considered. The presence of gas in the transmission medium will alters the internal flow structure of the hydraulic turbine and affect its operational stability. Therefore, for the purpose of clarifying the influence of inlet gas content on the internal flow of PAT, the unsteady flow of the PAT is simulated in this paper using numerical simulation. Based on the numerical simulation results, the influence of inlet gas content on the internal flow characteristics, characteristics of pressure fluctuation in impeller and volute, and vortex evolution of flow field are analyzed. The accumulation of gas phase leads to the emergence of vortices, and regions with low pressure values appear at the vortex generation. The major factor of the periodic variation of pressure fluctuation between volute and cut-water is the dynamic and static interference of impeller. The increase of gas content causes more flow disorder in the cut-water region and the volute contraction section. Since the gas in the flow channel is predominantly on the suction side of blades, the flow field on the suction side is more complex than that on the pressure side, and the amplitude of pressure fluctuation increases appropriately. The vortex structure is mainly distributed on balance hole, inlet area of impeller and suction side of blade. As the blade rotates, there are new shedding and growth of vortices, and finally attached to the volute wall. Increasing gas content enhances the influence of blade rotation on the vortex evolution characteristics in the volute and impeller.

On the unsteady flow dynamics of a planar-plug nozzle with a semi-extended cowl

Experiments are conducted with a planar-plug nozzle having a 50% cowl extension, operating in over-expanded nozzle pressure ratios ζ=[p0/pa]=2,3, and 4 to study the unsteady flow dynamics on the ramp surface and acoustic features of the flow on the far-field as influenced by the partial cowl extension. Steady pressure measurements and high-speed Schlieren imaging indicated that the flowfield on the ramp surface has shock-boundary layer and shock-shear layer interactions. The three-dimensional flow features on the ramp surface are studied based on oil flow visualization. A proper orthogonal decomposition based modal analysis of the Schlieren images is conducted to identify the dominant spatiotemporal characteristics. Unsteady pressure fluctuations on the ramp surface acquired simultaneously with microphone measurements are analyzed to infer the jet unsteadiness and noise source. Investigations across different ζ reveal the presence of both incipient and complete separation of the jet flow on the ramp. Moreover, the cowl extension delays the ζ at which the dominant screech and jet flapping occur.

A novel reservoir simulation model based on physics informed neural networks

Surrogate models are widely used for reservoir simulations in the petroleum industry to improve computational efficiency. However, the traditional surrogate model mainly relies on the data collected from production wells (e.g., well bottom pressure data and well production data) and ignores the physical mechanism of underground fluid flow; therefore, the surrogate model will be invalid in the case of insufficient data samples. In response to these challenges, a Hard-Soft physics informed neural network (HS-PINN) was proposed to simulate pressure fluctuations around producing wells without relying on any labeled data, where two coupled fully connected neural networks were comprised to control the Hard and Soft constraint conditions. Specifically, in the “Soft Constraint” condition, we employ a modified Lorentz function to incorporate underground flow theory and permeability fields into the loss function. Meanwhile, in the “Hard Constraint” condition, we incorporate an enforcement function in the “output layer” to ensure the network outputs satisfy the boundary and initial conditions. To demonstrate the HS-PINN model's robustness and accuracy abilities, we tested it for single and multi-well production in both noisy low-fidelity and high-fidelity geologic reservoir environments, and the HS-PINN prediction errors were less than 1% in both cases compared to simulation results by the commercial software “COMSOL.” Additionally, we assessed the impacts of varying well interference intensities, adjustments in collocation points counts within the control equations, and diverse geological characteristics on model performance to validate the generalization and stability of HS-PINN. Moreover, the HS-PINN-based surrogate model significantly improves the efficiency of uncertainty quantification tasks compared to simulation-based approaches, requiring only 8% of the computational time. The deep-learning surrogate models developed in this work offer a novel and efficient approach for simulating reservoir development.

Reperfusion injury case following cervical fusion with OPLL: a case report and literature review

IntroductionSpinal cord ischemic reperfusion injury is characterized by an abrupt decline in neurological function and only a few cases have been published in literature. Herein, we present a white cord syndrome following anterior decompression cervical fusion.Case ReportA 54-year-old Jewish male patient was diagnosed with disc herniation among the intervertebral discs at C2, C3, C4, C6, and C7, along with ossification of the posterior longitudinal ligament, pressuring more to the right side of the spinal canal, ruling-out cervical myelopathy. Under general anesthesia and multimodal intraoperative monitoring, he underwent laminectomy surgery from C3 to C6 and cervical fixation from C3 to C7. No blood pressure fluctuations occurred during surgery, and complete pressure release was achieved on the spinal cord and the nerve roots. In addition, neuromonitoring did not indicate any nerve damage during the surgery. A neurologic exam in the post-anesthesia care unit revealed weakness in his right hand and leg. A brain computed tomography scan ruled out cerebrovascular accident, neck computed tomography revealed optimal implant position, and magnetic resonance imaging ruled out spinal cord distress or injury. We treated him with intravenous fluids, steroids, painkillers, and anticoagulants. Following surgery, we involved the occupational therapy department. After a few days, we observed a significant improvement in motor function in the right leg; however, there was no change in the right hand.ConclusionWhite cord syndrome likely arises from reperfusion injury subsequent to surgical decompression of a compressed spinal cord segment. Although infrequent, it is imperative for spine surgeons to recognize this potential complication and apprise patients of it prior to the procedure.

Study on power losses and pressure fluctuations of diffuser mixed flow pump as turbine on different power generation speeds based on energy power models

Variable speed regulation represents an effective means to ensure the efficient operation of the diffuser mixed flow pump as turbine (DMFPAT). This paper employed computational fluid dynamics-based energy power models and high-frequency water pressure fluctuation tests to investigate the power losses and pressure fluctuations of DMFPAT under different power generation speeds. Analysis of power losses reveals that internal power losses in DMFPAT predominantly originate from the turbulent dissipation power (PEPD′) in the entropy production and the turbulent kinetic energy production power (PEBL3) in the energy balance equation, indicating that fully developed turbulence significantly contributes to substantial power losses in DMFPAT. A strong correlation exists between power generation speed and power losses, and decreasing rotational speed results in gradual reduction of power losses in DMFPAT. Additionally, a comprehensive analysis of the pressure fluctuation signals of DMFPAT under variable speed mode was conducted, revealing that the main frequency at each monitoring point is the rotational frequency and its harmonics. As speed decreases, the pressure fluctuation amplitude diminishes. The research presented demonstrates that adjusting the speed not only markedly reduces power losses but also eliminates adverse pressure fluctuations, thereby providing a theoretical basis for the efficient, stable and safe operation of DMFPAT.

Improved severe slugging modeling and mapping

One of the common flow assurance issues in offshore production facilities is riser-based severe slugging. This phenomenon can also occur in horizontal wells, hindering oil and gas production. Severe slugging is a cyclic process that occurs in the late life of reservoirs when there is not enough energy available from the reservoir to push the liquid out of the riser. It is highly undesirable as it results in large fluctuations in pressure, oil, and gas flow rates at the outlet of the riser. To address this challenge, we propose an improved one-dimensional severe slugging modelthat enhances the blowout step of the slugging cycleand Compared to the existing one-dimensional models. For benchmarking, the performance of this proposed model has been compared with experimental data for lab-scale geometry and with the OLGA simulations for field-scale geometry and higher operating pressures. The results demonstrate moderate errors in predicting slug characteristics, affirming the model's reliability and applicability. Additionally, a severe slugging envelope prediction approach has been proposed utilizing the developed model. The proposed severe slugging envelopes modeling approach can demarcate the severe slugging flow region for a given pipeline riser geometry and predict severe slug characteristics, including slug length and slug time within that severe slug flow region. This work significantly contributes to flow assurance strategies in production, optimizing hydrocarbon extraction processes and minimizing operational disruptions.

Seismic Response Characteristics of a Utility Tunnel Crossing a River Considering Hydrodynamic Pressure Effects

As a long lifeline system of buried structures, the utility tunnel (UT) is vulnerable to earthquake invasion. For utility tunnels with inverted siphon arrangements crossing rivers, the seismic response is more complex due to the basin effect of acceleration in the topography and the influence of fluctuating hydrodynamic pressure, but there is currently a gap in targeted seismic response analyses and references. Based on a UT project in Haikou, this paper studied seismic responses of a cast-in-place UT considering the coupled model of water–soil–tunnel structure on ABAQUS software. Herein, the dynamic fluctuation of hydrodynamic pressure is simulated using an acoustic–solid interaction model. A viscoelastic artificial boundary was used to simulate the soil boundary effect, and seismic loads were equivalent to nodal forces. Considering seismic invading direction and varying water elevation, this paper investigates the dynamic response characteristics and damage mechanisms of river-crossing utility tunnels. This study shows that the basin effect causes the soil acceleration around the UT to show variability in different sections, and the amplification factor of the peak acceleration at the central location is almost doubled. The damage and dynamic water pressure of the UT are intensified under bidirectional seismic excitation, and the damage location is concentrated at the junction of the horizontal section and the vertical section. Bending moments and axial forces are the main mechanical behaviors along the axial direction. Changes in river levels have a certain positive effect on the UT peak MISES, DAMAGEC, and SDEG, and it exhibits a certain degree of energy dissipation and seismic damping effect. For the aseismic design of cross-river cast-in-place utility tunnels, bidirectional seismic calculations should be performed, and the influence of river hydrodynamic pressure should not be neglected.