Transient Phenomena Research Articles

The high energy X-ray probe (HEX-P): sensitive broadband X-ray observations of transient phenomena in the 2030s

HEX-P is a probe-class mission concept that will combine high spatial resolution X-ray imaging (<10′′ FWHM) and broad spectral coverage (0.2–80 keV) with an effective area superior to NuSTAR above 10 keV to enable revolutionary new insights into a variety of astrophysical problems, especially those related to compact objects, accretion and outflows. HEX-P will launch at a time when the sky is being routinely scanned for transient gravitational wave, electromagnetic and neutrino phenomena that will require the capabilities of a sensitive, broadband X-ray telescope for follow up studies. These include the merger of compact objects such as neutron stars and black holes, stellar explosions, and the birth of new compact objects. A response time to target of opportunity observation requests of <24 hours and a field of regard of 3π steradians will allow HEX-P to probe the accretion and ejecta from these transient phenomena through the study of relativistic outflows and reprocessed emission, provide unique capabilities for understanding jet physics, and potentially revealing the nature of the central engine.

Transient phenomena and their consideration in load-following control of nuclear power plants

Radical changes have been happening on the source side of the electricity system due to the rolling back of large-sized fossil-fueled power plants and the coming to the front of uncontrollable renewables. As a worldwide consequence, to ensure the permanent balance of the grid, even big-sized units have to be operated in load-following mode, including also nuclear power plants. This mode is conducted by the control system, which must also consider the side effects of this rather dynamic operating mode. In this report, we show up all components of such a control system, including the process model, structural integrity assessment, and control algorithm. All the aforementioned elements are discussed on the basis of a concrete example, and the resulting control behavior of the entire system is also shown. The results demonstrated that a significant reduction in the caused thermal stresses could be achieved while keeping the control quality practically unchanged.

Hybrid-Vlasov simulation of soft X-ray emissions at the Earth’s dayside magnetospheric boundaries

Solar wind charge exchange produces emissions in the soft X-ray energy range which can enable the study of near-Earth space regions such as the magnetopause, the magnetosheath and the polar cusps by remote sensing techniques. The Solar wind–Magnetosphere–Ionosphere Link Explorer (SMILE) and Lunar Environment heliospheric X-ray Imager (LEXI) missions aim to obtain soft X-ray images of near-Earth space thanks to their Soft X-ray Imager (SXI) instruments. While earlier modeling works have already simulated soft X-ray images as might be obtained by SMILE SXI during its mission, the numerical models used so far are all based on the magnetohydrodynamics description of the space plasma.To investigate the possible signatures of ion-kinetic-scale processes in soft X-ray images,we use for the first time a global hybrid-Vlasov simulation of the geospace from the Vlasiator model. The simulation is driven by fast and tenuous solar wind conditions and purely southward interplanetary magnetic field. We first produce global X-ray images of the dayside near-Earth space by placing a virtual imaging satellite at two different locations,providing meridional and equatorial views. We then analyze regional features present in the images and show that they correspond to signatures in soft X-ray emissions of mirror mode wave structures in the magnetosheath and flux transfer events (FTEs) at the magnetopause. Our results suggest that, although the time scales associated with the motion of those transient phenomena will likely be significantly smaller than the integration time of the SMILE and LEXI imagers, mirror-mode structures and FTEs can cumulatively produce detectable signatures in the soft X-ray images. For instance, a local increase by 30% in the proton density at the dayside magnetopause resulting from the transit of multiple FTEs leads to a 12% enhancement in the line-of-sight- and timeintegrated soft X-ray emissivity originating from this region. Likewise, a proton density increase by 14% in the magnetosheath associated with mirror-mode structures can result in an enhancement in the soft X-ray signal by 4%. These are likely conservative estimates, given that the solar wind conditions used in the Vlasiator run can be expected to generate weaker soft X-ray emissions than the more common denser solar wind. These results will contribute to the preparatory work for the SMILE and LEXI missions by providing the community with quantitative estimates of the effects of small-scale, transient phenomena occurring on the dayside.

Relationship between coherent population trapping oscillation and Raman detuning

Coherent population trapping (CPT) oscillation is a transient oscillation phenomenon based on the CPT effect, which is related to the Raman detuning of the coherent bichromatic laser fields from the hyperfine ground-states of three-level Λ system. In this work, sawtooth wave is adopted to modulate the frequency of microwave signal to make Raman detuning change uniformly and stepping. Meanwhile, by building the relationship between the microwave frequency modulation rate and the change rate of Raman detuning, the effects of the change rate and mode of Raman detuning on CPT oscillation are analyzed respectively. The results reveal that when the Raman detuning changes uniformly, the CPT oscillation will occur on condition that the change rate is high enough, and the excited oscillations show non-harmonic oscillation behavior. When the Raman detuning is triggered off by step change, the excited CPT oscillation is a damping oscillation, and the oscillation frequency is equal to the frequency of Raman detuning. The modulation of Raman detuning is realized by using sawtooth wave to modulate the microwave frequency, and then the complete establishment of CPT state and the complete attenuation of CPT oscillation process are achieved. This work presents a new modulation method to realize the CPT oscillation, which shows great application potential in the field of weak magnetic measurements and atomic clocks.

Safety pharmacology of acute psilocybin administration in healthy participants

Psilocybin is being studied for its therapeutic potential in various mental health disorders, such as depression, anxiety, and addiction. Initial studies suggested that psilocybin is generally safe when used under controlled conditions, but more research is needed to better understand its safety profile. We report safety pharmacology data from a pooled analysis of three randomized crossover studies that included 85 healthy participants and 113 single-dose administrations of psilocybin. Single oral doses included 15 mg, 20 mg, 25 mg, and 30 mg psilocybin dihydrate. We investigated subjective effects, blood pressure, heart rate, body temperature, acute and subacute adverse effects, reports of flashbacks, and liver and kidney function before and after the studies. The 20, 25, and 30 mg doses of psilocybin produced stronger effects than the 15 mg dose. Psilocybin at all doses induced higher “good drug effects” than “bad drug effects.” Only the 25 and 30 mg doses increased anxiety. Psilocybin elevated autonomic effects only moderately. Tachycardia (>100 beats/min) was observed with 7% of all psilocybin administrations. Body temperature >38° was reached in 7%, 9%, 17%, and 32% of the participants with the 15, 20, 25, and 30 mg doses, respectively. Kidney and liver function parameters were unaltered at the end of the study. Five participants (6%) reported transient flashback phenomena. No serious adverse reactions occurred. These findings suggest that a single administration of psilocybin is safe with regard to acute psychological and physical harm in healthy participants in a controlled research setting.

Metalens-Based Compressed Ultracompact Femtophotography: Analytical Modeling and Simulations

Single-shot 2-dimensional optical imaging of transient phenomena is indispensable for numerous areas of study. Among existing techniques, compressed ultrafast photography (CUP) using a chirped ultrashort pulse as active illumination can acquire nonrepetitive time-evolving events at hundreds of trillions of frames per second. However, the bulky size and conventional configurations limit its reliability and application scopes. Superdispersive metalenses offer a promising solution for an ultracompact design with a stable performance by integrating the functions of a focusing lens and dispersive optical components into a single device. Nevertheless, existing metalens designs, typically optimized for the full visible spectrum with a relatively low spectral resolution, cannot be readily applied to active-illumination CUP. To address these limitations, here, we propose single-shot compressed ultracompact femtophotography (CUF) that synergically combines the fields of nanophotonics, optical imaging, compressed sensing, and deep learning. We develop the theory of CUF’s data acquisition composed of temporal–spectral mapping, spatial encoding, temporal shearing, and spatiotemporal integration. We also develop CUF’s image reconstruction via deep learning. Moreover, we design and evaluate CUF’s crucial components—a static binary transmissive mask, a superdispersive metalens, and a 2-dimensional sensor. Finally, using numerical simulations, CUF’s feasibility is verified using 2 synthetic scenes: an ultrafast beam sweeping across a surface and the propagation of a terahertz Cherenkov wave.

Melt flow complexity in multi-spot laser welding of asymmetric T-joints

This study investigates melt flow dynamics in asymmetric T-joint laser welding, particularly with sheets inclined up to 45°. This complex scenario requires filler wire, accessible only from the flat sheet side. High-speed imaging at the top and root captures transient phenomena leading to weld imperfections. Research on stainless-steel involved the impact of first-order welding parameters on the weld quality. This included multi-spot laser welding with two beams. The analysis focused on melt pool dynamics under these challenging conditions. The asymmetric root side’s geometry necessitates proper melt flow to form a favorable root topology, avoiding defects like wavy roots and porosity. Key observations included intermittent keyhole openings, transient melt flow effects, and potential spatter ejection at the bottom. The findings offer a comprehensive understanding of 3D asymmetric melt flow, laying the analytical groundwork for enhancing the weld quality.

Tracking plume-regolith interactions in near-vacuum conditions

An experiment to track and measure the transient phenomenon of plume-liberated regolith in near-vacuum conditions was performed in a dedicated plume-regolith facility housed at the University of Glasgow. This facility with a total volume of around 82 m3 can simulate a soft or hard landing event on “extraterrestrial” sub-atmospheric pressures. Particle image velocimetry method was used to estimate the ejection velocity and ejected angle of regolith particles, and its limitations are discussed. Glass microspheres that are matched with the size of the Lunar and Martian moon “Phobos” surface regoliths are used as simulants. With an exit Mach number of 6.6, a heated convergent–divergent nozzle represents the lander nozzle. Preliminary results capture ejecta development up to 30 ms from plume impingement. Flow visualization reveals the initial moments of plume boundary growth and regolith ejection. The vector images indicate a triangular-shaped sheet of particles sweeping from the regolith bed at a positive inclination with a local maximum velocity close to 100 m/s. The low-density “Phobos” simulant advances at a higher speed, reaches higher elevations, and covers a larger spatial area compared to a higher-density “Lunar” simulant. Observation of the crater formation reveals the difference in cohesive forces between the selected simulants. A higher inclination of particle ejection of more than 50° adjacent to the jet indicates particle entrainment originating from the interior of the crater. Stream traces reveal the deflection of ejected particles upon impingement on the lander surface at close proximity.

Occipital Steal Syndrome with Carotid Artery Occlusion–A Physiologic Study with Transcranial Doppler

Occipital or posterior steal syndrome is a constellation of signs and symptoms that arise from abnormal shunting of blood flow from the posterior cerebral circulation into its anterior counterpart leading to transient episodes of neurological deficits due to posterior circulation ischemia. A 45-year-old woman who experienced transient visual phenomena during breath holding was evaluated by transcranial Doppler sonography (TCD) for changes in cerebral blood flow. TCD revealed that the anterior cerebral vascular system was shunting blood away from its posterior counterpart in the setting of hypercapnia, resulting in visual symptoms. Using permissive blood pressure control, the steal phenomenon was resolved.

Transient natural convection flows and heat transfer in a thermally stratified air-filled trapezoidal cavity

This paper focuses on studying the transient behavior of natural convective heat and fluid flow in a two-dimensional trapezoidal cavity subjected to a heated bottom surface, cooling from the top, and thermally stratified inclined surfaces. The Finite Volume (FV) method is employed to numerically simulate the transient flow. The study considers a thermally stratified environment with a Prandtl number of Pr set to 0.71 (for stratified air), an aspect ratio (A) of 0.5, and a large array of Rayleigh numbers (Ra) ranging from 100 to 108. The research examines how the Rayleigh numbers affect the flow structures, transient phenomena, and heat transfer (HT) characteristics within the cavity. The transitional flow reveals several supercritical bifurcations. These include a changeover from symmetric to asymmetric states known as a Pitchfork bifurcation, as well as a shift from a steady-state to a periodic state referred to as a Hopf bifurcation. The Pitchfork bifurcation happens between Ra values of 105 and 2 × 105, while the Hopf bifurcation happens within the range of the Ra values from 4.7 × 105 to 4.8 × 105. Moreover, another bifurcation from a periodic to a chaotic state is observed between Ra of 3 × 107 and 4 × 107. To examine the transient flows during the changeover to chaos, various techniques such as power spectral density (PSD), limit points, limit cycles, trajectory in phase space, and the largest Lyapunov exponent (LLE) are used. Furthermore, convective heat transfer is computed, and its corresponding impact on the Ra values is explained. The flow phenomena within the cavity are measured and verified.

Pinpointing the Blip: Coupled Transient Chemo-Mechanical Properties in Lithium-Metal Batteries

Lithium-metal batteries experience significant mechanical stress as lithium is plated and stripped from the copper current collector during charge and discharge, respectively. Minimizing the negative effects of this stress on cell’s capacity retention over its cycle life is paramount to propel the high-density chemistry to the mainstream. To address this, acoustics have recently emerged as a viable experimental tool to monitor chemo-mechanical properties*.* In this work, we probe the underlying effects of coupled transient phenomena previously reported for Lithium-ion cells. By complimenting physical parameters—Young’s Modulus and damping coefficient, extracted from operando acoustics and pressure measurements—with simulations, we demonstrate that transient chemo-mechanical properties are in part resultant of ionic gradients in the electrolyte. These findings are in agreement with and build upon previous work on the acoustic signals of electrolytes by Wang et al, where acoustics were leveraged to extract mechanical parameters in situ, and of Lithium-ion cells by Hodson et al, where nonlinearities in full-cell Lithium-ion acoustic signals were were hypothesized to be a result of electrolytes. Our results highlight the viability of acoustics as a valuable tool in battery research to non-invasively inspect transient phenomena in batteries.

Understanding Internal Short Circuit Caused Thermal Runaway of Li-Ion Cells through in-Situ Diagnosis

Internal short circuit (ISC) caused thermal runaway of Li-ion batteries has been a challenge for decades due to difficulties in prevention and early detection of ISC. This challenge becomes increasingly urgent in recent years with the rapid growth of electric transportation industries which demand large-format, high-energy-density and fast-charging Li-ion batteries. Various ISC triggering methods have been developed to evaluate failure behaviors and advance safety designs of Li-ion cells and batteries. However, in-situ diagnosis is often overlooked in many ISC triggering methods and tests. Considering that ISC is a highly localized and transient phenomenon, in-situ diagnosis is important in understanding if and how an ISC triggers thermal runaway. In this presentation, our work on triggering ISC while simultaneously monitoring critical ISC parameters, such as ISC current, ISC resistance and ISC temperature, will be discussed to demonstrate the importance of in-situ diagnosis in understanding ISC and thermal runaway of Li-ion cells.

Seasonal Thaws under Mid- to Low-pressure Atmospheres on Early Mars

Abstract Despite decades of scientific research on the subject, the climate of the first 1.5 Gyr of Mars' history has not been fully understood yet. Especially challenging is the need to reconcile the presence of liquid water for extended periods of time on the Martian surface with the comparatively low insolation received by the planet, a problem which is known as the Faint Young Sun paradox. In this paper, we use the Earth-like planet surface-temperature model (or ESTM), a latitudinal energy-balance model with enhanced prescriptions for meridional heat diffusion, and the radiative-transfer code EOS to investigate how seasonal variations of temperature can give rise to local conditions which are conducive to liquid-water runoffs. We include the effects of the Martian dichotomy, a northern ocean with either 150 or 550 m of global equivalent layer, and simplified CO2 or H2O clouds. We find that 1.3–2.0 bar CO2-dominated atmospheres can produce seasonal thaws due to inefficient heat redistribution, provided that the eccentricity and the obliquity of the planet are sufficiently different from zero. We also studied the impact of different values for the argument of perihelion. When local favorable conditions exist, they nearly always persist for >15% of the Martian year. These results are obtained without the need for additional greenhouse gases (e.g., H2, CH4) or transient heat-injecting phenomena (e.g., asteroid impacts, volcanic eruptions). A moderate amount (0.1%–1%) of CH4 significantly widens the parameter space region in which seasonal thaws are possible.

Constraints on Neutron Star Structure from the Clocked X-Ray Burster 1RXS J180408.9−342058

Type I X-ray bursts are rapid-brightening transient phenomena on the surfaces of accreting neutron stars (NSs). Some X-ray bursts, called clocked bursters, exhibit regular behavior with similar light-curve profiles in their burst sequences. The periodic nature of clocked bursters has the advantage of constraining X-ray binary parameters and physics inside the NS. In the present study, we compute numerical models, based on different equations of state and NS masses, which are compared with the observations of a recently identified clocked burster, 1RXS J180408.9−342058. We find that the relation between the accretion rate and the recurrence time is highly sensitive to the NS mass and radius. We determine, in particular, that 1RXS J180408.9−342058 appears to possess a mass less than 1.7M ⊙ and favors a stiffer nuclear equation of state (with an NS radius ≳12.7 km). Consequently, the observations of this new clocked burster may provide additional constraints for probing the structure of NSs.

Biological dispersion in the time domain using finite element method software

Biological tissue exhibits a strong dielectric dispersion from DC to GHz. Implementing biological dispersion in the time domain with commercial finite element method software could help improve engineering analysis of electrical transient phenomena. This article describes the steps required to implement time-domain biological dispersion with commercial finite element method software. The study begins with the presentation of a genetic algorithm to fit the experimental dispersion curve of Solanum tuberosum (potato tuber) to multipoles of first-order Debye dispersion. The results show that it is possible to represent the biological dispersion of S. tuberosum from 40 Hz to 10 MHz in a 4-pole Debye dispersion. Then, a set of auxiliary differential equations is used to transform the multipole Debye dispersion from the frequency domain to the time domain. The equations are implemented in the commercial software COMSOL Multiphysics. A comparison between the frequency and time domain simulations was used to validate the method. An analysis of the electric current with square-wave pulsed voltage was performed. We found that the computer implementation proposed in this work can describe the biological dispersion and predict the electric current.

Testing and modelling of transient adhesion phenomena in rolling-sliding contacts

Transient adhesion effects in rolling–sliding contacts influence all aspects of train–track interaction. This is of high importance specifically when these effects result in critically low adhesion, which poses a risk to traction and braking of railway vehicles. This study presents a model that can replicate the transient changes of the coefficient of adhesion with tested water and solid particle mix. The experimental data for the model are measured using a commercial ball-on-disc tribometer. The experimental results showed a liquid reservoir in front of the contact area that slowly reduces in size. This observation was used in the modelling approach to divide the calculation into two stages where the reservoir is present and when it disappears. The model was able to reproduce the occurrence of low adhesion region seen in experimental results with different particle concentrations.

A Low Cost Real-Time Transient Recorder for High Voltage Systems.

Large-scale incorporation of new energy generation units based on renewable sources, such as wind and photovoltaic power, drastically alters the structure of the power system. Because of the intermittent nature of these sources, switching in grids (connection and disconnection) occurs much more frequently than with conventional sources. As a result, the power system will inevitably experience a large number of transients, which raises questions about the stability of the system and the quality of the electrical energy. Therefore, measuring various types of transients in power system is crucial for stability, power quality, fault analysis, protection design, and insulation design. Transient recorders that are currently used are generally expensive and only suitable for particular locations in power systems. The number of installed transient recorders is insufficient for a comprehensive analysis of problems that may occur. Hence, it is important to have inexpensive and efficient transient recorders that can be installed at multiple points in the power system on various types of objects. It is also essential to have a transient record database with open access, which can be used by researchers to develop new analysis techniques based on artificial intelligence. This paper proposes an inexpensive measurement and acquisition system designed to record transient phenomena on different objects within the power system. The system is designed to use autonomous power, a standardized data acquisition module, a low-budget system for transmitting recorded transient events to the server via mobile network, and a sensor system adapted to the object where transients are recorded. The proposed system is designed to be used for all types of objects in the power system where transients may occur, such as power lines, transmission towers, surge arresters, and transformers. All components of the system are described, and the system is tested under laboratory conditions. The modular nature of the system allows customization to the specifics of the location in power system by choosing appropriate components. The calibration method of the custom designed Rogowski coil is described. The cost analysis of the proposed system and power consumption analysis are performed. The results show that the system's performance meets application requirements at a low cost.

SAINT (Small Aperture Imaging Network Telescope)—A Wide-Field Telescope Complex for Detecting and Studying Optical Transients at Times from Milliseconds to Years

In this paper, we present a project of a multi-channel wide-field optical sky monitoring system with high temporal resolution—Small Aperture Imaging Network Telescope (SAINT)— mostly built from off-the-shelf components and aimed towards searching and studying optical transient phenomena on the shortest time scales. The instrument consists of twelve channels each containing 30 cm (F/1.5) GENON Max objectives mounted on separate ASA DDM100 mounts with pointing speeds up to 50 deg/s. Each channel is equipped with a 4128 × 4104 pixel Andor Balor sCMOS detector and a set of photometric griz filters and linear polarizers. At the heart of every channel is a custom-built reducer-collimator module allowing rapid switching of an effective focal length of the telescope—due to it the system is capable of operating in either wide-field survey or narrow-field follow-up modes. In the first case, the field of view of the instrument is 470 square degrees (39 sq.deg. for a single channel) and the detection limits (5σ level at 5500 Å) are 12.5, 16.5, 19, 21 with exposure times of 20 ms, 1 s, 30 s and 20 min, correspondingly. In the second, follow-up (e.g., upon detection of a transient of interest by either a real-time detection pipeline, or upon receiving an external trigger) regime, all telescopes are oriented towards the single target, and SAINT becomes an equivalent to a monolithic 1-meter telescope, with the field of view reduced to 11′ × 11′, and the exposure times decreased down to 0.6 ms (1684 frames per second). Different channels may then have different filters installed, thus allowing a detailed study—acquiring both color and polarization information—of a target object with the highest possible temporal resolution. The telescopes are located in two pavilions with sliding roofs and are controlled by a cluster of 25 computers that both govern their operation and acquire and store up to 800 terabytes of data every night, also performing its real-time processing using a dedicated fast image subtraction pipeline. Long-term storage of the data will require a petabyte class storage. The operation of SAINT will allow acquiring an unprecedented amount of data on various classes of astrophysical phenomena, from near-Earth to extragalactic ones, while its multi-channel design and the use of commercially available components allows easy expansion of its scale, and thus performance and detection capabilities.

Numerical study of the flow and heat transfer characteristics in a scale model of the vessel cooling system for the HTTR

The reactor cavity cooling system (RCCS) is a passive reactor safety system commonly present in the designs of High-Temperature Gas-cooled Reactors (HTGR) that removes heat from the reactor pressure vessel by means of natural convection and radiation. It is one of the factors responsible for ensuring that the reactor does not melt down under any plausible accident scenario. For the simulation of accident scenarios, which are transient phenomena unfolding over a span of up to several days, intermediate fidelity methods and system codes must be employed to limit the models’ execution time. These models can quantify radiation heat transfer well, but heat transfer caused by natural convection must be quantified with the use of correlations for the heat transfer coefficient. It is difficult to obtain reliable correlations for HTGR RCCS heat transfer coefficients experimentally due to such a system’s size. They could, however, be obtained from high-fidelity steady-state simulations of RCCSs. The Rayleigh number in RCCSs is too high for using a Direct Numerical Simulation (DNS) technique; thus, a Reynolds-Averaged Navier–Stokes (RANS) approach must be employed. There are many RANS models, each performing best under different geometry and fluid flow conditions. To find the most suitable one for simulating an RCCS, the RANS models need to be validated. This work benchmarks various RANS models against three experiments performed on the HTTR RCCS Mockup by the Japanese Atomic Energy Agency (JAEA) in 1993. This facility is a 1/6 scale model of a vessel cooling system (VCS) for the High Temperature Engineering Test Reactor (HTTR), which is operated by JAEA. Multiple RANS models were evaluated on a simplified 2d-axisymmetric geometry. They were found to reproduce the experimental temperature profiles with errors of up to 22% for the lowest temperature benchmark and 15% for the higher temperature benchmarks. The results highlight that the pragmatic turbulence models need to be validated for high Rayleigh natural convection-driven flows and improved accordingly, more publicly available experimental data of RCCS resembling experiments is needed and indicate that a 2d-axisymmetric geometry approximation is likely insufficient to capture all the relevant phenomena in RCCS simulations.

Transient gas-liquid flow phenomena in M-shaped jumper of subsea gas production systems during start-up operation

Removal of the accumulated liquid from jumpers of subsea gas production systems is essential to avoid possible hydrate creation and further damage to the pipeline. However, the displacement of high amounts of accumulated liquid during the production start-up leads to a gas pressure rise. Liquid plugs formed during the liquid displacement impact the structure's elbows. This, in addition to cyclic pressure/forces fluctuations, may lead to harmful flow-induced vibrations (FIV). These flow phenomena that may endanger the jumper structure were explored in air-water experiments performed in a lab-scale jumper. The critical (minimal) gas velocity needed to purge the accumulated liquid was determined and the pressure and force variations during the liquid removal were measured. In addition, the effects of the gas velocity, initial liquid amount, and gas flow ramp-up on the air-water flow phenomena were documented. Results of 3D and 2D numerical simulations (using OpenFOAM) were verified against the experimental data. The effects of employing different RANS turbulence models on the predictions were tested and demonstrated. A simple mechanistic model was established to predict the pressure and force variation during liquid displacement. The model enables inspecting the variation with the operational conditions of each pressure component (i.e., hydrostatic, friction, and acceleration) and examining their significance and contribution to the pressure rise.