Pressure Oscillations Research Articles

Fuel-Cell Performance and Stability during Liquid-Water Removal Cycles

Water management is crucial for achieving high-performance proton-exchange-membrane fuel cells (PEMFCs), as it helps keep the electrolyte hydrated while avoiding performance degradation and cell shutdown due to liquid-water accumulation. According to ex-situ measurements [1-3], accumulation of liquid water in gas-diffusion layers (GDLs) of PEMFCs is a transient process that can be accompanied with oscillations in capillary pressure and saturation. To understand how liquid-water accumulation and drainage impact PEMFC performance hysteresis and stability, a transient cell-level model that accounts for electrode structure and composition and is computationally efficient is needed. A number of volume-averaged models that describe the electrode structure through pore-size distribution have been developed in the past [4-7], but they are steady-state and thus cannot predict dynamic PEMFC performance. Existing transient models have also not been used to analyze cyclic liquid-water accumulation [8-10].In this work, a transient two-phase 2D PEMFC model is developed in the open-source fuel-cell modeling software OpenFCST [11] and applied to analyze PEMFC performance hysteresis and stability during liquid-water accumulation and drainage cycles. The model accounts for the electrode structure through a mixed-wettability pore-size-distribution framework and incorporates a novel dynamic boundary condition to describe the experimentally observed cyclic liquid-water accumulation. Results of the numerical simulations are compared to transient current-density and resistance data at two polarization scan rates and during voltage steps measured with an in-house single-channel cell at multiple operating conditions. This work demonstrates how high breakthrough pressure and rapid liquid-water removal from GDLs may cause highly unstable fuel-cell operation with strong hysteresis and oscillations in the polarization curve (such as those in the figure below) that closely resemble experimental reports [12]. Numerical simulations also reveal the existence of a scan rate that maximizes polarization hysteresis due to a match between the time scale of GDL flooding and of a complete voltage sweep. Fast-scan polarization sweeps are shown most suitable for detecting catalyst-layer flooding that depends on its wettability and occurs within single seconds in contrast to GDL flooding that takes hundreds of seconds. Overall, this work brings more attention to the transient analysis of fuel-cell performance under wet conditions.Figure: Polarization-curve oscillations caused by cyclic liquid-water removal from the cathode GDL. Similar fluctuations have been experimentally observed in [12]. Transient graphs show the dynamics of current density and cathode GDL saturation. Operating conditions are 60 °C, 90% RH, 1.5 atm; scan rate is 0.5 mV/s. References J. T. Gostick et al., J. Electrochem. Soc. 157.4 (2010) C. Quesnel et al., J. Phys. Chem. C 119.40 (2015) D. Ziegler, B.Sc. thesis, Hochschule Mannheim / University of Alberta (2020) A. Z. Weber et al., J. Electrochem. Soc. 151.10 (2004) M. Eikerling, J. Electrochem. Soc. 153.3 (2006) V. Mulone and K. Karan, Int. J. Hydrog. Energy 38.1 (2013) Zhou et al., J. Electrochem. Soc. 164.6 (2017) R. J. Balliet and J. Newman, J. Electrochem. Soc. 158.8 (2011) I. V. Zenyuk et al., J. Electrochem. Soc. 163.7 (2016) A. Goshtasbi et al., J. Electrochem. Soc. 166.7 (2019) M. Secanell et al. ECS Transactions 64.3 (2014) C. Ziegler and D. Gerteisen, J. Power Sources 188.1 (2009) Figure 1

Numerical study on dominant oscillation frequency of unstable steam jet under heaving condition

With its advanced efficiency in heat transfer, the steam direct contact condensation method is now extensively employed in many areas. The pressure oscillation characteristics of unstable steam jets under heaving conditions were investigated numerically in this study. The dominant oscillation frequency gradually rose with the decrease of the heaving period and the increase of the heaving amplitude. The dominant oscillation frequency under the heaving condition was higher than that under the static condition, with a maximum increase of 27.4%. The inertia and condensation dominated the evolution of steam bubbles at the necking stage under heaving conditions. With the decrease of the heaving period and the increase of heaving amplitude, the additional force induced by heaving movement increased, contributing to the condensation heat transfer enhancement. A dimensionless correlation predicting the dominant oscillation frequency at a low flow rate under heaving conditions was fitted, and the maximum error was within ±6.2%.

Effect of sinusoidal pressure gradient on MHD flow of viscoelastic fluid in a channel

Unsteady Hydro Magnetic oscillatory flow of incompressible viscoelastic fluid in a channel packed with porous material is investigated under the influence of oscillatory pressure gradient. Moreover, the applied magnetic field of moderate strength interacts with electrically conducting fluid, to generate a resistive volumetric body force. In addition to it, viscoelastic fluidity, characterizing the non-Newtonian behavior in conjunction with permeability of the medium as well as sinusoidal sheared flow due to imposed favorable pressure gradient, contribute to the novelty of the study. The previous work was confined to constant motion of the lower plate but the present work includes the sinusoidal motion of the lower plate in addition to the constant motion. The importance lies with the fact that the coupling effect of sinusoidal fluctuation and viscoelastic fluidity go hard in industrial applications, particularly in process industry. The governing equations characterizing the flow are solved analytically. The striking results of this study are: the formation of inverted boundary layer in case of oscillatory lower plate with moderately escalated time span but such instability leading to flow reversal, does not appear in case of constant motion of the lower plate. Hence, it is recommended that for stability of flow and to avoid flow reversal, higher frequency of oscillation as well as larger time span is not desirable. The elastico-viscosity property reduces the volume flow rate which may be useful to control the efflux and differentiates the state of motion (resulting low skin friction) and state of rest (resulting high skin friction) in respect shearing effects at the bounding surfaces.

Confined deflagration of propanal/air in the presence of intrinsic instability at elevated pressures

The partial oxidation process is a chemical technique with a high risk of deflagration, which involves directly mixing of fuels with oxidizers at elevated conditions. Under non-standard conditions, the deflagration behaviors of fuels are often unavailable to the general public, which hampers progress in further basic research. In this study, the deflagration behaviors of propanal-air mixtures at 75 °C and 0.1–1.0 MPa were investigated, and the effect of initial pressure (P0) and equivalence ratio (φ) on the deflagration characteristics of propanal was discussed. To explain the similarities and differences in the deflagration characteristics under various conditions, the buoyancy instability, hydrodynamic instability and thermal-diffusion instability suffered by the flames were also analyzed. Results show that the pressure generated by the burned mixture is a cubic function of time, and the state of flame propagation can be determined by the monotonicity of the second-order derivative of pressure. Moreover, the peak deflagration pressure (Pm) is more sensitive to changes in φ on the fuel-lean side, but Pm/P0 at the fuel-rich condition is markedly higher than Pm/P0 at the fuel-lean condition. At all φ, an increase in P0 effectively shortens the ignition time and reduces the minimum ignition energy. Nevertheless, there are discernible differences in the variation patterns of the deflagration time (θm) with P0 at various φ. Specifically, θm gradually prolongs with increasing P0 at fuel-lean conditions, whereas it tends to be the same at different P0 and φ = 1. Furthermore, under fuel-rich conditions, θm progressively shortens as P0 increases. The decrease in θm is attributed to the increasing flame speeds in the presence of intrinsic instability, and the self-accelerating flame yields pressure waves, which travel faster than the flame. Then a series of reflected pressure waves are formed after the pressure waves strike the vessel wall, interacting with the flame front and resulting in the pressure oscillation. Moreover, increasing P0 advances the pressure oscillation and augments the intensity of pressure oscillation.

Mode identification and decomposition analysis of self-excited thermodynamic oscillations in hypersonic inlet/isolator of a scramjet

The self-excited pressure and velocity oscillations caused by the downstream back pressure in a hypersonic inlet/isolator directly affect the operational stability of a scramjet. In this work, we conduct the two-dimensional unsteady RANS (Reynolds averaged Navier–Stokes) simulation to predict the flow field in the Mach 7 inlet/isolator with 147 times the freestream static pressure. With the model validated, the time evolution process of the instantaneous flow fields in the isolator is analyzed first. It is shown that the structure of the shock train exhibits an up-down asymmetry. The flow oscillations as observed near the upper wall are more complex than those near the lower wall. Furthermore, the dominant frequency of the wall pressure oscillations is approximately 520 Hz. However, the self-excited oscillations in the isolator flow are dominated with approximately 510 Hz mode but coupled with multiple harmonic higher frequencies. To identify and decompose the modes of these oscillations in the unsteady flow of the isolator, different mode decomposition technologies are applied to further examine the mechanism of such oscillations. By conducting Proper Orthogonal Decomposition (POD) analysis on the x-axis velocity and Mach number fields, it is shown that the first two modes consist of more than 77% of the total oscillations’ kinetic energy. Additionally, the oscillations of the quadrilateral separation zone and low-speed zone near the upper wall largely determine the dominant frequency of the overall unsteady flow field. As Dynamic Mode Decomposition (DMD) investigation is conducted on the x-axis velocity and Mach number fields, it is found that the identified first mode is almost the same as that identified by using POD. It is also found that both DMD and POD can well predict the viscous flows such as the separation zone, shear layer, and low-speed zone. Finally, the dominant frequencies predicted by the POD and DMD are revealed to be very close to the dominant frequency of the wall static pressure oscillations. The movements of multiple shock waves near the upper wall are the major incentive for the complicated change in the entropy generation rate. In general, the self-excited thermodynamic oscillations phenomenon as observed in the hypersonic inlet/isolator in a scramjet could be well analyzed by decomposing and identifying the dominant modes, which contribute mostly to the total energy of such oscillations.

CBN‐reinforced Al2O3–Ti(C,N) composites with high toughness sintered under oscillatory pressure

AbstractHigh‐toughness Al2O3–Ti(C,N) composites reinforced by cBN particles were prepared by the new oscillating pressure sintering technique. The density, phase, and microstructure evolution of the Al2O3–Ti(C,N)‐cBN composites sintered at different temperatures were studied, and their effects on the mechanical properties were investigated. The results show that when the sintering temperature increases from 1300 to 1500°C, the heat preservation time shortens, whereas the density and interface bonding strength of the composites increase. In addition, cBN particles can play the role of crack bridging and be pulled out when the composites fracture, improving the toughness of the Al2O3–Ti(C,N)–cBN composites. However, when the sintering temperature further rises to 1600°C, a new phase of TiB2 forms, and the solid solubility of C and N in Ti(C,N) increases, leading to a decrease in density and mechanical properties. As a result, when the Al2O3–Ti(C,N)–cBN composite is sintered at 1500°C, its mechanical properties reach the maximum values of 21.5 GPa, 5.7 MPa m1/2, and 731 MPa for hardness, fracture toughness, and flexural strength, respectively.

Analysis of Gas Turbine Combustor Exhaust Emissions: Effects of Transient Inlet Air Pressure

Gas turbine combustors are often subjected to combustion instabilities because of variability of operating conditions, affecting components, and altering exhaust emissions. Herein, the analysis focuses on simulating numerically the non‐premixed combustion as unsteady flamelet combustion and detailed kinetic mechanism. The goal is analyzing exhaust gases under unsteady inlet airflow conditions to define operation guidelines. The numerical approach is validated using data from the literature for nonperturbed cases. Three periodical perturbations of different amplitude show differences with the nonperturbed case. Besides emission of exhaust gases, the temperature field is sensitive to airflow inlet conditions. According to the simulation results, a strong dependence of temperature and pressure in primary and dilution zones of combustor exists on the inlet air pressure condition. Emissions of flue gases like CO and NOx respond to combustor thermal behavior showing high sensitivity to inlet air pressure as well. Results indicate that moderate pressure oscillations may derive into flashback effects.

Influence of dwell time on the hydraulic behaviour utilizing multiple injection strategies and a piezoelectric diesel injector

The electric dwell time is defined as the duration between two electric pulse signals. It is a crucial parameter when multiple injection strategies are employed. The influence of electric dwell time on the hydraulic behaviour utilizing pilot injection strategy, split injection strategy, post injection strategy and a commercial piezoelectric diesel injector has been analysed experimentally. To do so, a sweep of electric dwell time from 1.15 ms up to 3 ms in all multiple injection strategies using rail pressures of 80, 100 and 120 MPa, and a back pressure of 5 MPa was performed. A fuel mass of 110 mg was injected in all cases analysed employing operating conditions defined from the characteristics curves of injected mass. The hydraulic behaviour was characterized through to measure the first and second hydraulic delay at opening and closing injector, the pressure oscillations generated during the first injection event, and injected fuel mass during second injection event in an injection discharge curve indicator, which is based on the Bosch tube method. In summary, the paper concludes that the hydraulic dwell time depends on the injected mass during the first injection event, and the dynamic response of injector. Moreover, a short electric dwell time causes an increase of injected fuel mass during second injection event, which can be attributed to combine two effects provoked by overlapping the first and second mass flow rate signals, namely, a reduction in the hydraulic delay at opening injector, and an increase in the hydraulic delay at closing injector. Finally, the present research provides information which can be employed to optimization the modulation of injection rate in a diesel engine.

Unstable combustion behavior of syngas/air mixture with different components in a narrow gap disk reactor

In this paper, the combustion behavior of the syngas/air mixture in a narrow gap disk reactor were explored. Besides, the influence of the hydrogen volume fraction and the mixture equivalence ratio in syngas on the property of propagating flames were investigated in the narrow gap disk reactor under the gap thicknesses of 8 mm, 6 mm, 4 mm, 3 mm, and 2 mm, respectively. The focus was placed on the behavior of the flame propagation under the gap thickness of 2 mm. The research results demonstrated that the increase of the hydrogen volume fraction from 5 % to 30 % exerted a significant impact on the flame propagation velocity (FPV) and the pressure in the tube. Moreover, the equivalence ratio of this mixture could markedly affect both the propagation characteristics and morphology of flames. Strong flame instabilities accompanied by pressure oscillations were observed in the reactor at a 2 mm gap thickness during the later stages of flame propagation. Notably, there were significant differences in unstable combustion behavior between different syngas components. Moreover, the combined action of heat losses and compression waves leads to significant flame instability. The insights gained from this study have practical implications in various production applications. For example, optimizing hydrogen volume fraction and mixture equivalence ratios can enhance combustion efficiency and reduce pressure fluctuations in industrial reactors, leading to improved energy utilization and reduced environmental emissions.

The use of oscillatory positive expiratory pressure devices for voice therapy

Over the last three years, a variety of oscillatory positive expiratory pressure (OPEP) devices have been commonly used by voice therapist and trainers (e.g. Acapella Choice, Shaker Deluxe, Shaker Medic Plus, New Shaker), even if they were not originally created for voice-treatment purposes. OPEP are intended to be used by physiotherapists to mobilize secretions from the lower airway when treating excessive sputum or secretion retention. The mechanism of oscillatory OPEP is based on a continuous and rapid shuttering of airflow, which in turn produces modulation of the oral and tracheal air pressure as patients blows into them. People diagnosed with cystic fibrosis and neurogenic diseases are usually recommended using OPEP devices [1, 2]. OPEP devices are different from expiratory/inspiratory muscle strength training devices, which have no oscillatory mechanisms inside.

Efficient two-dimensional simulation of primary reference fuel ignition under engine-relevant thermal stratification

Despite vast research on engine knock, there remains a limited understanding of the interaction between reaction front propagation, pressure oscillations, and fuel chemistry. To explore this through computational fluid dynamics, the adoption of advanced numerical methods is necessary. In this context, the current study introduces ARCFoam, a computational framework that combines dynamic mesh balancing, chemistry balancing, and adaptive mesh refinement with an explicit, density-based solver designed for simulating high-speed flows in OpenFOAM. First, the validity and performance of the solver are assessed by simulating directly initiated detonation in a hydrogen/air mixture. Second, the study explores the one/two-dimensional (1D/2D) hotspot ignition for the primary reference fuel and illuminates the impact of transitioning to 2D simulations on the predicted combustion modes. The 2D hotspot simulations reveal a variety of 2D physical phenomena, including the appearance of converging shock/detonation fronts as a result of negative temperature coefficient (NTC) behavior and shock wave reflection-induced detonation. The main results of the paper are as follows: (1) NTC chemistry is capable of drastically changing the anticipated reaction front propagation mode by manipulating the local/global reactivity distribution inside and outside the hotspot, (2) subsonic hotspot ignition can induce detonation (superknock) through the generation of shock waves and subsequent wall reflections, and (3) while the 1D framework predicts the initial combustion mode within the hotspot, significant differences between 1D and 2D results may emerge in scenarios involving ignition-to-detonation transitions and curvature effect on shock/detonation front propagation.

Performance Analysis of Electro‐Hydraulic Actuation System Using Multi‐Domain Physics‐Based Modeling

AbstractMulti‐domain physics‐based modeling is a versatile technique in the discipline of numerical modeling to solve engineering problems and it is an essential tool for predicting and simulating the multi‐domain physics behavior of interacting complex engineering systems [1]. But most of the modern‐day engineering systems are quite complex and developing physics‐based models of these systems needs critical domain expertise from various fields of physics and engineering. The complex nature of these systems makes it challenging and time‐consuming to develop high‐fidelity physics‐based models. Hence the data‐driven or hybrid approaches are still being extensively used in many industries despite their limited usability and scalability, unlike the physics‐based models. Though the COTS tools like SIMSCAPE, DYMOLA, etc. are providing readily available foundational blocks for physics‐based modeling they are not always sufficient to represent the custom component designs that made up these complex systems. Hence this paper recommends the development of physics‐based component models that can be re‐used. These component models when developed like modular blocks can improve the re‐usability during system model development. This can reduce the dependency on the critical domain expertise of the engineers. While emphasizing the importance of physics‐based modeling techniques this paper presents how this approach can enable the fault injection into system models and help identification of reasons for faults like pressure oscillations on an Electro‐Hydraulic Actuation System.

Analysis of the Vibrational Behavior of dual-fuel RCCI combustion in a Heavy-Duty Compression Ignited Engine fueled with Diesel-NG at Low Load

In the field of internal combustion engines, the Low Temperature Combustions (LTC) appear to have the potential to reduce the formation of both soot and nitrogen oxides. One of the most promising LTC is Reactivity Controlled Compression Ignition (RCCI) which is based on the combustion of a lean low reactivity fuel-air mixture generated in the intake manifold and autoignited by small injections of high reactivity fuel introduced at high pressure in the combustion chamber. By the combination of net-zero natural gas and biodiesel, such LTC methodology might represent a suitable solution moving toward zero-emissions in transportation sector.Despite the potential to reduce pollutant emissions, Low Temperature Combustion strategies face a challenge in controlling the angular position where the combustion takes place which can be overcome by a proper management of the high-pressure injections.One potentially interesting application is related to trucks, mainly because they have long periods of idling, since emissions can be drastically reduced by means LTC. A single cylinder research engine for heavy duty application is operated under steady state conditions at low load and speed to analyze the possibility of controlling the engine behavior in dual fuel RCCI mode. The results indicate that the combustion mode switches from the dual-stage to gaussian within a narrow angular range. A further advance of the start of injection can generate misfires and significant variations in typical combustion indexes, while a delayed start of injection can cause impulsive combustion that rises the cylinder temperature and results in high-frequency pressure oscillations inside the combustion chamber. These oscillations are related to the combustion chamber typical resonance frequency, and if relevant in amplitude and persist for a long time, they might generate a potential source of failures.

Microstructure and mechanical properties of SiC-GNPS-SiCW ceramics by oscillatory pressure sintering

The preparation of SiC-based ceramics with high densification, high strength and exceptional toughness is still a severe challenge. In the present work, an advanced sintering technique namely oscillatory pressure sintering (OPS) was applied to prepare SiC ceramics with one-dimensional silicon carbide whiskers (SiCw) and two-dimensional graphene nanoplatelets (GNPs) as reinforcing phases, and the microstructure and mechanical properties were comprehensively investigated. When the contents of GNPs and SiCw were 1 wt% and 5 wt% respectively, the relative density of SiC-based ceramics reached 99.86%, while the Vickers hardness, flexure strength and fracture toughness were 31.55 GPa, 742 MPa and 7.32 MPa m1/2, respectively. The interface was strengthened, meanwhile the grain size was decreased, both of which enhanced the flexural strength of the composites. Results also proved that crack deflection and bridging as well as the bridging of GNPs and SiCw toughened SiC-based ceramics. Furthermore, the coherent interfaces of SiC/GNPS and SiC/SiCw with good match were observed, leading to an enhancement of mechanical properties of such ceramics.

Study on reduction of pressure oscillation in low-velocity steam jet condensation

To mitigate the high-amplitude pressure oscillations generated during the steam low-speed jet condensation process and reduce the risk of dynamic load damage to the suppression pool and its adjacent facilities, this study designed a temperature-rising cylinder scheme based on the characteristics of low-speed steam jet condensation pressure oscillation and studied the mitigation effect of this scheme through experiments. The experimental results showed that this scheme could effectively reduce the time of low-velocity steam jet condensation in the high-amplitude pressure oscillation region. For instance, at a steam mass flow rate of 30 kg/m2s, the time was reduced from 6300 s to 700 s, which significantly improves the safety of the pool and nearby facilities. Moreover, the scheme does not affect the suppression ability of the pool and can ensure the long-term effective operation of the suppression system.

Experimental Investigation of Column Separation Using Rapid Closure of an Upstream Valve

In this study, the phenomenon of column separation that occurs in the downstream pipeline of a rapid closure valve is experimentally investigated. Special attention is paid to the dynamic behavior of the formation, growth, and collapse processes of cavities, which are observed using a high-speed camera. Synchronized images of cavity patterns and measured pressure histories are analyzed to elucidate the process of water column separation, the mechanism of column separation events, and the influence of parameters on the transient flow. Experimental results indicate that during the collapse process of vapor cavities, a superposition phenomenon involving a positive pressure wave and collapse wave occurs, resulting in a nearly three times rise of Joukowsky pressure. In all test cases, the maximum pressure of the pipeline exceeded 150 times the reservoir static pressure. A new classification for a water hammer combined with cavitation (four types of pressure oscillation patterns) is proposed based on whether the duration of column separation decreases sequentially and the maximum pipeline pressure follows the first collapse of cavities at the valve. As the initial flow velocity increases, there is generally an increase in maximum pressure; however, this trend may be scattered under certain operation conditions.

The influence of spinal venous blood pressure on cerebrospinal fluid pressure

In Alligator mississippiensis the spinal dura is surrounded by a venous sinus; pressure waves can propagate in the spinal venous blood, and these spinal venous pressures can be transmitted to the spinal cerebrospinal fluid (CSF). This study was designed to explore pressure transfer between the spinal venous blood and the spinal CSF. At rest the cardiac-related CSF pulsations are attenuated and delayed, while the ventilatory-related pulsations are amplified as they move from the spinal venous blood to the spinal CSF. Orthostatic gradients resulted in significant alterations of both cardiac- and ventilatory-related CSF pulsations. Manual lateral oscillations of the alligator’s tail created pressure waves in the spinal CSF that propagated, with slight attenuation but no delay, to the cranial CSF. Oscillatory pressure pulsations in the spinal CSF and venous blood had little influence on the underlying ventilatory pulsations, though the same oscillatory pulsations reduced the ventilatory- and increased the cardiac-related pulsations in the cranial CSF. In Alligator the spinal venous anatomy creates a more complex pressure relationship between the venous and CSF systems than has been described in humans.

Structural response for vented hydrogen‐air deflagrations: Effects of volumetric blockage ratio

AbstractThe explosion venting experiments of hydrogen‐air premixed gas were carried out in a 1‐m3 cuboid container. The effects of the obstacles parallel to the vent on the structural response of the container during the explosion venting were investigated. The internal overpressure and acceleration of the vessel wall were captured by acceleration and pressure sensors, respectively. The time–frequency distributions of pressure and acceleration were obtained by a Short‐Time Fast Fourier Transform. The effects of obstacles on the dynamic structure response were studied by analyzing the internal overpressure, vibration acceleration, and high‐speed videos. With the increase of obstacles, the maximum overpressure and vessel vibration increased, and the maximum overpressure and maximum vibration acceleration appeared earlier. The vibration signals had two dominant frequencies, 300‐600 Hz and 900‐1200 Hz. The low‐frequency vibration (300–600 Hz) was induced by acoustic oscillation of the internal pressure. The high‐frequency vibration (900–1200 Hz) was a container resonance triggered by the coupling of the flame and the acoustic wave. As VBR increased, the duration of high‐frequency oscillations decreased gradually; the increase of obstacles would weaken the high‐frequency structural response of the container. The results can guide the design of hydrogen explosion protection and mitigation measures.

Stabilized mixed material point method for incompressible fluid flow analysis

This paper proposes novel and robust stabilization strategies for accurately modeling incompressible fluid flow problems in the material point method (MPM). To address the modeling of Newtonian fluids with incompressibility constraints, a new mixed implicit MPM formulation is proposed. Here, instead of solving the velocity and pressure fields as the unknown variables like the typical Eulerian computational fluid dynamics (CFD) solver, the proposed approach adopts a monolithic displacement–pressure formulation inspired by the mixed-form updated-Lagrangian Finite Element Method (FEM). To satisfy the inf–sup stability condition, two stabilization strategies are integrated into the formulation: the variational multiscale method (VMS) and the pressure-stabilization Petrov–Galerkin method (PSPG). By concurrently solving the displacement and pressure fields, the developed monolithic solver obviates the need for free-surface detection as well as Dirichlet and Neumann pressure imposition, in contrast to the fractional-step method. This attribute mitigates spurious pressure and velocity oscillations in simulating dynamic and transient flow problems. This study also addresses other prevalent challenges in MPM simulations, such as the pressure oscillations triggered by cell-crossing errors, particle-distribution-induced quadrature errors, and particle-grid information transfer. To resolve these issues, the quadratic B-Spline basis function, the delta-correction method, and the Taylor particle-in-cell method are incorporated into the proposed mixed MPM formulation, thereby enhancing numerical stability. The efficacy of the proposed stabilized incompressible MPM framework is validated through several benchmark cases, comparing the obtained results with other numerical methods and analytical solutions. Furthermore, the method’s capability in simulating real-world problems involving violent free-surface fluid motion is demonstrated through comparisons with experimental results of water sloshing and dam break scenarios.

Design an Optimum Air Duct for Oscillating Water Column Wave Energy Device

Oscillating Water Column (OWC) is a technology that harvests wave energy to generate electricity. It works by harnessing the wave-induced pressure oscillation in the opening mouth of OWC. The oscillation of the pressurised air is extracted using a turbine placed at the top of the OWC structure. Although OWC has been studied for many years, designing an optimum air duct for such devices is still an open research area. The air duct plays a crucial role in the energy conversion process, as it is responsible for directing the airflow towards the turbine, and its design can greatly affect the performance and efficiency of the system. The article aims to study how the air duct design impacts the power output form. Moreover, the result will be compared with the conventional air duct design. The OWC performance is analysed using Computational Fluid Dynamic (CFD) software to identify which shape of the air duct has high efficiency. Autodesk Inventor is used to design the OWC devices modified from the basis design. Then these designs are imported into CFD software to simulate and obtain the energy extraction result. The CFD software is chosen to simulate the hydrodynamics problem. In this study, the oval design shows significant improvement in the energy extraction performance compared to the basis design. The oval design managed to produce 9.81, 10.02, and 11.66 J/kg of mechanical energy compared to 9.81, 9.82, and 10.04J/kg as prompted by the basis air duct design at the wave height of 0.2505, 0.75, and 2.25m, respectively. The result shows that the non-edge produces higher air pressure than the sharp edge of the air duct shape. Thus, the oval air duct design is more efficient, and it may increase the performance of the OWC wave energy converter device at a low wave height of 0.75 m.