Transient Pressure Research Articles

Investigations on CO2 migration and flow characteristics in sandstone during geological storage based on laboratory injection experiment and CFD simulation

CO2 geological storage in tight sandstone reservoirs is an effective method of CO2 capture, utilization, and storage (CCUS). CO2 migration and flow characteristics in sandstone during geological storage affect the physical and mechanical properties of rocks significantly. In this study, laboratory injection experiments combined with X-ray computed tomography (CT) scanning and scanning electron microscopy (SEM) tests, and computational fluid dynamics (CFD) numerical simulation have been conducted to investigate the effect of geological and engineering parameters on CO2 migration and flow characteristics. The results show that: (1) The injection rate and injection pressure affect the Sc-CO2 migration path. Moreover, the fluid velocity and fluid pressure affect the pressure distribution in pores significantly. Limiting the injection rate and pressure during the CO2 geological storage is beneficial for the stability of the storage. (2) The pressure distribution of the fluid changes with orders of magnitude depending on the injection pressure. However, the overall transient relative pressure is almost consistent and the fluid pressure in the bending section of the bending pores exhibits a linearly decreasing trend. (3) SEM tests provide a connection between laboratory experiments and CFD simulation on microscopic scale. The injection pressure and the acoustic emission (AE) energy have a positive correlation to a certain extent. The Sc-CO2 migration path could be forecasted preliminarily through the fluctuation of the injection pressure-time curves and AE response. The results enrich the theory of CO2 migration and flow characteristics during CO2 geological storage.

Cavitation evolution and flow field characteristics of transient flows with multi-point water-column separations in undulating pipeline

Transient flows with water-flow-induced multi-point cavitation inside an undulating pipeline are investigated experimentally under conditions of fast valve closure for three typical test cases by using high-precision pressure transducers, high-speed photography and particle image velocimetry (PIV) techniques. For low initial velocity condition, the transient pressure at the monitoring point (PT1) downstream the valve quickly decreases to the cavitation pressure and fluctuates near it. The leading-edge velocity of the dispersed bubble-like cavitation group first increases with its occurrence and then accelerates and reaches an extreme value before decreasing to zero due to the viscous force and the decrease of water flow inertia, and finally the water flows upstream in reverse, i.e. the leading-edge accelerates and collapses behind the valve. At the same time, the transient pressure rises sharply to maximum 81.86 m due to the return of the compression wave and then decreases sharply to cavitation again because of the switch of the pressure waves. Then, the second cavitation intensity is weak and the corresponding pattern is fog-like, and finally decreases gradually with a cyclic period of about 0.38 s. The transient pressure at the monitoring point (PT2) at the peak of the undulating pipeline also maintains at the cavitation pressure corresponding to the big bubble occurrence moment in addition to its fluctuation near the cavitation pressure including first and second cavitation. Its maximum pressure is 72.16 m and the corresponding cavitation pattern is small and bigger bubbles at different cavitation stages. For middle initial velocity, the typical pattern of the corresponding cavitation is the large cavity with free surface at PT2, the corresponding higher maximum pressures are 102.36 m at PT1 and 84.81 m at PT2. The evolution process of the cavity including bubble mergence, morphological deformation, motion and collapse is analysed based on the broken wave and hydraulic dynamic theories. For high initial velocity, larger cavities occur both downstream the valve and at the peak point of undulating pipeline, and thus the corresponding higher maximum pressures due to larger cavity collapse are 140.56 m at PT1 and 127.98 m at PT2. In particular, complete water column separation with transparent large cavity occur downstream the valve.

Investigation of energy storage applications on nickel fluoride nanomaterials under shock wave flow environments

In this research article, we have conducted the comparative studies on ambient and 200 shock loaded NiF2 sample using a table top pressure-driven shock tube (Reddy Tube) for supercapacitor application. The stability of structural, morphological and electrochemical properties of the shock loaded and unloaded were tested and analysed. The shock wave of 2.2 Mach number with transient pressure of 2.0 MPa with 864 K temperature was made to strike on two test samples (ambient and 200). The molecular and crystallite structure stabilities of the test samples were examined by XRD and FTIR. The surface morphology was investigated by FESEM and electrochemical measurements such as Cyclic Voltammetry (CV), Galvanostatic Charge-Discharge (GCD) techniques were performed to investigate the super capacitive behaviour of NiF2 sample for loaded and unloaded conditions. The obtained results revealed changes in crystallite size and particle size and it still maintains its phase stability of rutile NiF2 after 200 shocked conditions. Further, the electrochemical measurements exhibit higher capacitance of 1770.5 F/g for 200 shock loaded condition which is very high range when compared with ambient condition. Furthermore, it measured high energy density (88.52 Wh/kg) and power density (1499.8 W/kg) at 2 A/g current density which is very higher compared to others. Hence under high shocked conditions, the electrochemical properties were enhanced due to shock wave impacts on the NiF2 material.

Large-scale survey of excitatory synapses reveals sublamina-specific and asymmetric synapse disassembly in a neurodegenerative circuit

In the nervous system, parallel circuits are organized in part by the lamina-specific compartmentalization of synaptic connections. In sensory systems such as mammalian retina, degenerating third-order neurons remodel their local presynaptic connectivity with second-order neurons. To determine whether there are sublamina-specific perturbations after injury of adult retinal ganglion cells, we comprehensively analyzed excitatory synapses across the inner plexiform layer (IPL) where bipolar cells connect to ganglion cells. Here, we show that pre- and postsynaptic component loss occurs throughout the IPL in a sublamina-dependent fashion after transient intraocular pressure elevation. Partnered synaptic components are lost as neurodegeneration progresses, while unpartnered synaptic components remain stable. Furthermore, presynaptic components are either lost first or simultaneously with the postsynaptic component. Our results demonstrate that this degenerating neural circuit exhibits differential vulnerability of excitatory synapses depending on IPL depth, highlighting the ordered disassembly of synapses that is specific to laminar compartments of the retina.

Intake pressure control based on improved super-twisting for altitude ground test facilities

This paper focuses on the problem of rapid tracking of engine transient pressure, an improved super twisting algorithm (STA) is adopted to control the intake pressure of the engine. The high altitude platform is analyzed systematically, the mathematical model is derived, and the system and control object model are established. It is improved on the basis of classical STA method and has better control effect than PID control methods and LADRC. Transient state tests of the engine under three different working conditions(acceleration/deceleration state of pushing/pulling accelerator lever, engine intake pressure changing from 50kPa to 60kPa, and engine intake pressure changing from 60kPa to 70kPa) are simulated and verified. The simulation results show that, compared with the traditional PID and active disturbance rejection control(LADRC)strategies, the method proposed in this paper can track the inlet pressure of the engine in transition state quickly, and can reach and stabilize the given set value accurately and quickly.

Experimental study on ventilation shaft locations for alleviating transient pressure induced by high-speed trains passing through underground station

Experimental study on ventilation shaft locations for alleviating transient pressure induced by high-speed trains passing through underground station

Experimental and simulation study of a hydraulic piezoelectric energy harvester under different connection modes

Pressure pulsation from water hydraulic system exhibits great potential in vibration energy harvesting. Herein a novel hydraulic piezoelectric energy harvester is proposed, which exhibits excellent insulation and sealing performance. The effect of connection modes such as single output, series and parallel connection, on the energy harvesting performance is investigated at different parameters by the experiment. The theoretical analysis and simulation study are employed to explain the energy harvesting process. The results show that the transient voltage exhibits alternating characteristics, and it has the same period with the transient pressure. The piezoelectric disk closer to the liquid inlet has greater energy harvesting ability. The voltage increases as the static pressure rises and the main influence factor is pulsation amplitude rather than static pressure. Moreover, the root mean square voltage of series connection is highest, and it increases with the increasing resistance, but the average power first increases and then decreases. The parallel connection mode has higher average power and lower optimal resistance. The average power and power density can respectively reach 394 μW and 1.34 mW/cm3 under 3 MPa and 20 KΩ. This paper can provide methods for the sustainable power supply of sensors in water hydraulic system.

Experimental study on sub-regimes of air-water slug flow in a rectangular micro-channel

In mini/micro-channel two-phase flow, slug flow occurs easily because of the significant influence of surface tension and the low gravitational effect on the flow. Although an irregularity of slug flow has been reported, previous studies on mini/micro-channel slug flow have mainly concerned the slug flow with the alternate of film and liquid slug zones regularly. Therefore, the present study investigates sub-regimes of micro-channel slug flow with regular or irregular alternating film and liquid slug zones to understand their principal characteristics. Experiments are performed to visualize and simultaneously measure the transient local pressure of the air-water mixture flow in a horizontal rectangular channel with a 2 mm height and 1 mm width. Superficial Reynolds numbers for liquid and gas phases range from 56 to 1116 and 5.75 to 245, respectively. With the aid of visualization data, slug flow is categorized into two types of stable slug flow and four types of unstable slug flow. Present slug flow data is compared with previous correlations for predicting the regime of bubble formation mechanism, flow regime boundaries, and frictional pressure gradient. Measured temporal pressure records are analyzed using a fast Fourier transform and digital Butterworth filter, while a dominant frequency is identified from the normalized average power spectrum. Then, the local pressure fluctuation at the dominant frequency is examined for different types of slug flow using the visualization results. A morphological repetition is confirmed to be associated with the pressure fluctuation: the repeated film and liquid slug zones in both types of stable slug flow, the alternative between liquid-only flow and a group of gas bubbles and liquid slugs in type 3 unstable slug flow, and the periodic variation of bubble length in type 4 unstable slug flow. However, no correlation between morphological characteristics and pressure fluctuation is found in type 1 and 2 unstable slug flows.

Experimental Study on Motion Characteristics of Cavity Attached to the Tail of Underwater Vehicle

The formation and development of an attached cavity at the tail of an underwater moving vehicle involves a complex multiphase flow, which determines the load characteristics and motion stability of the vehicle. In this study, an experimental method was used to explore the formation process and motion characteristics of the cavity at the tail of the vehicle, and a pressure sensor installed at the tail of the model was used to establish the relationship between the evolution of the tail attachment cavity and transient pressure. The study found that the process of pulling and breaking the attached cavity was accompanied by the generation of bidirectional jets, and reducing the cavitation number could weaken the occurrence of jet impact. When the ventilation flow reaches the critical value Q¯in = 1.28, the cavity pulsates. In addition, increasing the ventilation flow does not increase the size of the tail cavity, and the length of the cavity at the closure increases with the decrease of the cavitation number.

New Green’s Function Method for Solving Underground Oil Seepage Problems

Abstract Compared with the variables separation method and integral-transform method, Green’s function method is much more applicable and thus of great practical significance. Based on the general steps of Green’s function method, a new method is originally raised to get Green’s function in oil and gas flow problems through underground formations. After that, the transient pressure solution is get for flow in a spherical reservoir by using this method. This case enlarged the application of Greenʼs method function, and this work can also be a good foundation for the solution of more and more complicated flow problems in oil and gas reservoirs.

Diagnosing Hydro-Mechanical Effects in Subsurface Fluid Flow Through Fractures

Hydro-mechanically induced transient changes in fracture volume elude an analysis of pressure and flow rate transients by conventional diffusion-based models. We used a previously developed fully coupled, inherently non-linear numerical simulation model to demonstrate that harmonic hydraulic excitation of fractures leads to systematic overtones in the response spectrum that can thus be used as a diagnostic criterion for hydro-mechanical interaction. The examination of response spectra, obtained from harmonic testing at four different field sites, for the occurrence of overtones confirmed their potential for the hydro-mechanical characterization of tested reservoirs. A non-dimensional analysis identified relative aperture change as the critical system parameter.

Physical model of non-adiabatic blowdown of cryo-compressed hydrogen storage tanks

This paper describes a model of hydrogen blowdown dynamics for storage tanks needed for hydrogen safety engineering to accurately represent incident scenarios. Heat transfer through a tank and pipe walls affects the temperature and pressure transients inside the storage vessel and at the nozzle exit, and thus the characteristics of the resulting hydrogen jet in the case of loss of containment. Current non-adiabatic blowdown models are validated against experiments performed with hydrogen storage tanks at only ambient temperature. The effect of heat transfer for cryo-compressed hydrogen is more significant due to a larger difference of temperature between the stored hydrogen and the surrounding atmosphere, especially in case of equipment insulation failure during an incident. Our previous work demonstrated that the heat transfer through a discharge pipe wall can significantly affect the mass flow rate of cryogenic hydrogen releases. Thoroughly validated models of non-adiabatic blowdown dynamics for cryo-compressed hydrogen are missing at the moment. This work develops further the non-adiabatic blowdown model at ambient temperature using the under-expanded jet theory developed at Ulster University, to expand it to cryo-compressed hydrogen storage tanks. The non-ideal behaviour of cryo-compressed hydrogen due to low temperatures is taken into account through the high-accuracy Helmholtz energy formulations. The developed model includes effect of heat transfer at both the tank and the discharge pipe walls. The model is thoroughly validated against sixteen tests on blowdown of hydrogen storage tanks with initial pressure 0.6–20 MPa ab and temperature 80–310 K, through release nozzle of diameter in the range 0.5–4.0 mm, performed within the PRESLHY project. The model well reproduces the experimental pressure and temperature recordings in the storage tank during the entire blowdown duration for the whole set of sixteen tests. In conjunction with the volumetric source model, explained in detail, the physical model allows to perform CFD simulations accurately reproducing the temperature distribution in time and space for the cryogenic hydrogen jet experiment.

The LIFUS5 separate effect test facility experimental programme

The LIFUS5 facility is a separate effect test facility aimed at investigating the heavy liquid metal-water interaction. It has been designed and constructed to withstand high pressure and temperature (i.e. up to 200 bar and up to 500 °C) and to record the fast pressure transients in heavy liquid metal melt. This type of transient is typical of a Steam Generator Tube Rupture event in a pool type Gen IV Heavy Liquid Metal cooled Fast Reactor system, and should be investigated from the safety point of view because it could potentially induce, beyond the damaging of the internal structures (HX tube bundle, above core structures, Fuel Assembly, Control Rods, etc.) several negative effects on the operation of the reactor. These include an insertion of positive reactivity into the system or reduced cooling efficiency due to steam dragging into the core. It will also have an effect on the chemistry control of the cooling. All these effects compromise the safety and the reliability of the system. The twenty years experimental programme and the different LIFUS5 configurations are presented in the paper, as well as the experimental campaigns and test matrix characterizing the heavy liquid metal-water interaction phenomena and data for codes validation.

Estimation of heterogeneous permeability using pressure derivative data through an inversion neural network inspired by the Fast Marching Method

Reservoir heterogeneity significantly impacts the fluid flow behavior in porous media. In subsurface communities including hydrocarbon or geothermal recovery, geological storage of CO2 or H2, and hydrology, transient pressure data are often used to infer the subsurface rock properties (e.g., permeability field) due to its ready availability and quick response. The accurate estimation of such properties is critical to accurately predict fluid flow in porous media.In this work, we propose a deep learning (DL) approach inspired by the Fast Marching Method (FMM), namely the Inversion Neural Network (INN), to inversely infer heterogeneous reservoir model parameters using transient pressure data. The forward model used to generate training data for the INN is established based on a semi-analytic asymptotic solution to the diffusivity equation using the diffusive time of flight (DTOF). The FMM solves the Eikonal equation for the DTOF and provides the partial derivative of pressure drop to the natural logarithm of time (hereafter pressure derivative). The pressure derivative data are then used to predict reservoir model parameters by the INN. In the homogeneous scenario, the INN architecture is a relatively simple fully connected neural network as a proof-of-concept to validate the feasibility, and it directly correlates the permeability value with the pressure derivative. In the heterogeneous scenario, as the heterogeneous permeability field is estimated based on sparse observational data of pressure derivatives, we adopt the convolutional neural network (CNN) to flexibly deal with the image-based properties, and leverage transfer learning to efficiently train a robust INN in the heterogeneous scenario.We first validated that INN can infer the homogeneous permeability fields through numerical experiments by testing root-mean-square-error (RMSE) around 1.086 md. Inspired by that, observational data with different sparsity are used to train convolutional INN and predict heterogeneous permeability fields. As the number of observational locations (nobs) increases from 3 × 3 to 48 × 48, the testing RMSE in heterogeneous scenarios decreases from 187.510 md to 18.080 md. Besides, we found that transfer learning significantly improves the predictive accuracy at low nobs, with relative error decreased by 17.25%. Finally, noisy pressure derivative data under different nobs are used to history match the heterogeneous reservoir model, and INN can infer the permeability field with a low error of 9.6% at nobs=7×7. Without an iterative procedure for parameter estimation, the INN demonstrates to perform permeability inversion with CPU time in the magnitude of 9.2×10−4 s on a single GPU (NVIDIA Quadro P2200). The FMM-inspired INN sets up the basis for the accurate characterization of reservoir model heterogeneity by inverting pressure derivative data with both decent predictive accuracy and computational efficiency.

Optimal pump-valve coupling operation strategy of complex long-distance water-conveyance systems based on MOC

Transient simulation is crucial for protecting complex pump-valve water conveyance pipeline systems from extreme pressure and water level oscillations. In order to numerically simulate the transient response in a complex pump-valve water conveyance system, a transient flow calculation model was established adopting the method of characteristics (MOC). Based on the proposed model, the transient pressure and the water level fluctuation process were numerically predicted under steady-state operation state, and then the results were compared to the actual measured data. Due to the good agreement between the simulation results and the actual measured data, the model established based on MOC is effective and practical. 41 operational scenario switching schemes were designed according to the uniform experimental design, to study the operation sequence and time differences of pumps and valves during operational scenario switching state. The results show that the operational time interval has a major impact on the transient process under the operational scenario switching state in complex pump-valve systems, and also indicate that delayed pump startup can alleviate the pressure extremum of pipeline systems and effectively control water level fluctuation of such systems. In addition, this study points out the optimal operational sequence and the maximum and minimum allowable time intervals between the pump and the valve under operational scenario switching state in such systems. Finally, an optimized joint operation scheme for pumps and valves with simple operation and small water-level oscillation were proposed under operational scenario switching state.

Numerical studies on a new strategy to mitigate pressure waves by accelerating trains through a long tunnel

The present work focused on exploring a strategy for mitigating the aerodynamic effects by accelerating through the tunnel. A three-dimensional, unsteady, compressible, and RNG k-ε turbulence model is adopted to simulate the pressure waves generated by high-speed trains passing through the tunnel at different speed modes. The findings demonstrated that trains cruising inside tunnels in an acceleration mode could effectively reduce the transient pressure on trains and tunnels while maintaining the efficiency of the passage. The acceleration method could alter the time at which the pressure maximum appeared at the head train surface, resulting in hysteresis that could effectively reduce the unexpected increase in the transient pressure due to the high-speed approach of the train into the tunnel. Throughout the pressure variation process, the acceleration mode could effectively improve the pressure variation at the train nose-point region compared to the uniform-speed mode. The acceleration modes with a lower acceleration (V325-375) and a higher acceleration (V300-400) reduced the pressure peaks by 15.37% and 5.63%, respectively. In addition, for most of the tunnel, the two acceleration modes could reduce various key pressure indicators on the tunnel walls as well. These results indicate that an accelerating train could be an alternative for higher-speed passing through tunnels to balance the passage efficiency and passenger safety and comfort.

An experimental and numerical study to evaluate performance parameters of GIS circuit breaker during low current interruption

Abstract The basic philosophy of two-stage blast interrupter is combination of self-blast and puffer-interrupter principles. Gas circuit breaker (GCB) with two-stage blast interrupter has two gas chambers. High gas pressure in one chamber generates by using arc energy and in other chamber, by mechanical compression. In such type of breakers, interruption becomes quite difficult at low currents and hence optimization of gas chambers design is essential. In view of above, a numerical program has been developed to calculate SF6 gas pressure-rise in various interrupter volumes and gas flow rates across different passages of interrupter w.r.t. time. To validate model developed in the study, an experimental set-up is established and measured transient gas pressure-rise generated during 420 kV GCB operation. The effect of speed-time characteristics, stroke length and piston diameter on performance parameters of 420 kV GCB model is analyzed. Further, to understand gas flow pattern across insulated nozzle during GCB operation, authors developed a CFX model. By using this numerical model, effect of nozzle profile, gas flow passage areas and profile of gas discharge vents on transient gas pressure and Mach number distribution across inter-electrode gap and gas flow rates through various outlets has been discussed in detail in the paper.

A review on aerodynamic load and dynamic behavior of railway noise barriers when high-speed trains pass

Noise barriers need to be installed along high-speed railway lines to protect nearby inhabitants from the noise pollution caused by the running of high-speed trains (HSTs). The vertical noise barrier is the main structural type. However, when an HST passes through the noise barriers sited along the track, significant and transient aerodynamic pressure will act on the surface of the noise barriers, resulting in strong dynamic responses and even fatigue damage. Therefore, it is important to determine the train-induced aerodynamic load on the barrier surface and analyze the dynamic behaviors of the noise barriers under such a load for its structural design and to guarantee its safety and durability. This paper is a systematic review of the current literature on the aerodynamic load and dynamic behavior of vertical noise barriers; it includes (1) a summary and analysis of characteristics of such aerodynamic pressure and relevant influencing factors, (2) an introduction to measurement methods of aerodynamic load and relevant pressure models on the surface of noise barriers, and (3) a description of the dynamic response and fatigue analysis of noise barriers under such loads. Finally, potential further studies on this topic are discussed, and conclusions are drawn.

Objective Hemodynamic Cardiovascular Autonomic Abnormalities in Post-Acute Sequelae of COVID-19.

Many COVID-19 patients are left with symptoms several months after resolution of the acute illness; this syndrome is known as post-acute sequalae of COVID-19 (PASC). We aimed to determine the prevalence of objective hemodynamic cardiovascular autonomic abnormalities (CAA), explore sex differences, and assess the prevalence of CAA among hospitalized vs nonhospitalized patients with PASC. Patients with PASC (n= 70; female [F]= 56; 42 years of age; 95% confidence interval [CI], 40-48) completed standard autonomic tests, including an active stand test 399 days (338, 455) after their COVID-19 infection. Clinical autonomic abnormalities were evaluated. Most patients with PASC met the criteria for at least 1 CAA (51; 73%; F= 43). The postural orthostatic tachycardia syndrome hemodynamic (POTSHR) criterion of a heart rate increase of > 30 beats per minute within 5 to 10 minutes of standing was seen in 21 patients (30%; F= 20; P= 0.037 [by sex]). The initial orthostatic hypotension hemodynamic (IOH40) criterion of a transient systolic blood pressure change of > 40 mm Hg in the first 15 seconds of standing was seen in 43 (61%) patients and equally among female and male patients (63% vs 57%; P= 0.7). Only 9 (13%) patients were hospitalized; hospitalized vs nonhospitalized patients had similar frequencies of abnormalities (67% vs 74%; P= 0.7). Patients with PASC have evidence of CAA, most commonly IOH40, which will be missed unless an active stand test is used. Female patients have increased frequency of POTSHR, but IOH40 is equally prevalent between sexes. Finally, even nonhospitalized "mild" infections can result in long-term CAAs.

Numerical Simulation on Transient Pressure Pulsations and Complex Flow Structures of a Ultra-High-Speed Centrifugal Pump at Stalled Condition

A high-speed centrifugal pump is the key facility to deliver oil in an aero-engine. The stable operation is quite important to the safety of the engine. High-speed pump stability is essentially caused by the transient pressure pulsations excited by the complex flow within the pump, which needs to be clarified, especially for the pump under a rotating stall condition. In the current research, unsteady pressure pulsation and the corresponding flow distribution of the high-speed centrifugal pump are analyzed using the delayed detached-eddy simulation (DDES) method. Pressure signals within the pump are extracted by monitoring points. Results show that the dominant components in the pressure spectrum exhibit a significant difference at various flow rates, which locates at the blade passing frequency fBPF under the rated working condition and deviates to five times the shaft frequency (5fn) at the stalled condition. Such phenomenon is not observed in the normal centrifugal pump with low speed when using numerical and experiment methods, and usually the amplitude at fBPF reaches the maximum. Under the stalled condition, the component at 0.2fn is generated and considered as the rotating stall frequency, which is the same at different stalled flow rates. From velocity distribution, it is found that several blade channels are stalled as characterized by the large-scale separation bubbles, which are induced and triggered by the volute tongue.