Pressure-dependent Model Research Articles

A robust simulator of pressure-dependent consumption in Python

Abstract Modeling of pressure-dependent users’ consumption is mandatory to simulate accurately the hydraulics of water distribution networks (WDNs). Several software solutions already exist for this purpose, but none of them actually permits the easy integration and testing of new physical processes. In this paper, we propose a new Python simulator that implements a state-of-the-art pressure-dependent model (PDM) of users’ consumptions based on the Wagner’s pressure–outflow relationship (POR). We tested our simulator on eight large and complex WDNs, for different levels of users’ demands. The results show similar precision and efficiency to the ones obtained by the authors of the original model with their MATLAB implementation. Moreover, in case of fully satisfied users’ demands, our simulator provides the same results as EPANET 2.0 in comparable computational times. Finally, our simulator is integrated into the open-source, collaborative, multi-platform, and Git versioned Python framework OOPNET (Object-Oriented Python framework for water distribution NETworks analyses); thus, it can be easily reused and/or extended by a large community of WDN modelers. All this work represents a preliminary step before the incorporation of new processes such as valves, pumps, and pressure-dependent background leakage outflows.

Optimal design and cost analysis of water distribution networks based on pressure-dependent leakage using NSGA-II

Leakage from water distribution networks (WDNs) is inevitable. Therefore, during design a WDN, engineers add a percentage of each nodal water demand as leakage discharge to total node demand. The amount of leakage depends on the pressure, which is not known at the design stage. Considering a constant percentage of node demand in lieu of its leakage makes the problem worse. In this study, the effect of leakage on the optimal WDN design was investigated by developing the matrix form of the gradient algorithm while accounting for leakage using the pressure-dependent model. Non-dominated genetic algorithm version II (NSGA-II) was used as the optimization engine with two objectives which includes minimizing the network construction cost and minimizing the total network pressure deficiency. Two well-known two- and three-loop WDNs in literature were studied. The results indicated that the pressure-dependent leakage varies between 12.9 and 29.44% of the node demand while the network construction cost stays the same if compared with the fixed percentage leakage model, and the construction cost would increase by 17–31%, if leakage is not accounted for. This is expected the optimized diameters and hydraulic characteristics of the networks being affected by the leakage calculation method.

Influence of enhanced Coulomb’s model on the draw-in of the hood inner panel

A constant coefficient of friction (Coulomb) is commonly used as the current industry standard to describe friction on the sheet metal forming simulation software. The use of constant Coulomb’s friction may reduce precision and so the effectiveness of the simulation to represent real-world processes. This paper presents an approach using a physical measurement of friction combined with pressure dependent friction model as an input for the metal forming simulation of a hood inner part on AutoForm. The input variable parameters are the constant Coulomb and the enhanced pressure-dependent model. For the output this study analyses the Forming Limit Diagram (FLD) and blank’s draw-in in a real problem provided by a car manufacturer.

Influence of the contact with friction on the deformation behavior of advanced high strength steels in the Nakajima test

This work presents a new understanding on the deformation mechanics involved in the Nakajima test, which is commonly used to determine the forming limit curve of sheet metals, and is focused on the interaction between the friction conditions and the deformation behaviour of a dual phase steel. The methodology is based on the finite element analysis of the Nakajima test, considering different values of the classic Coulomb friction coefficient, including a pressure-dependent model. The validity of the finite element model is examined through a comparison with experimental data. The results show that friction affects the location and strain path of the necking point by changing the strain rate distribution in the specimen. The strain localization alters the contact status from slip to stick at a portion of the contact area from the pole to the necking zone. This leads to the sharp increase of the strain rate at the necking point, as the punch rises further. The influence of the pressure-dependent friction coefficient on the deformation behaviour is very small, due to the uniform distribution of the contact pressure in the Nakajima test. Moreover, the low contact pressure range attained cannot properly replicate real contact condition in sheet metal forming processes of advanced high strength steels.

Heterogeneous Catalysis Models of High-Temperature Materials in High-Enthalpy Flows

This work investigates atomic recombination of gas species impinging on high-temperature materials used for thermal protection system of spacecraft entering Earth’s atmosphere. Heterogeneous catalysis models of pre-oxidized PM1000, an oxide dispersion-strengthened Ni-Cr superalloy, and silicon-carbide-coated (SiC-coated) carbon-fiber-reinforced SiC used on the European eXPErimental Re-entry Testbed (EXPERT) are fitted making use of recombination coefficients obtained experimentally from exposing these materials to highly dissociated nitrogen and oxygen flows in a plasma wind tunnel. These models are finite-rate catalytic models that consider associative adsorption, thermal desorption, and Langmuir–Hinshellwood and Eley–Rideal reactions. Recombination coefficients from different techniques are included to increase the variation of surface temperature and partial pressure of the sampling, which also increased the level of verification of the methods applied here. A pressure-dependent model for copper oxide at 320 K is also fitted, which is of special interest for investigations in ground facilities because it is commonly used as highly catalytic reference surface on plasma diagnostic probes. The materials investigated here present full surface coverage up to 1500 K at reentry relevant pressures, and the Langmuir–Hinshellwood mechanism is the dominant mechanism for a wide pressure and temperature range.

Assessing mechanical response of CO2 storage into a depleted carbonate reef using a site-scale geomechanical model calibrated with field tests and InSAR monitoring data

Geomechanical risks of injection have raised concerns regarding secure CO2 storage. In this work, a combined monitoring and modeling approach is used to assess the stress changes and surface uplift associated with CO2 injection into a depleted carbonate reef of the Michigan basin. A site-scale geomechanical model is built by assigning mechanical properties of formations using well-log and experimental data. Gravity load is applied to the model to estimate the vertical component of stress as well as different lateral boundary displacement scenarios to estimate horizontal stresses. We used a poroelastic pressure-dependent model (instead of a linear elastic mechanical earth model) to calibrate initial stresses using hydraulic fracture test data measured at depleted reservoir status. Multi-phase fluid flow-geomechanical simulations are performed to estimate the poroelastic response during (1) primary depletion (2) field-scale CO2 injection phase (3) a hypothetical forecast scenario in which well bottom hole pressure (BHP) reach 45000 KPa. The predicted surface uplift is less than 1 mm at the end of the field-scale CO2 injection phase which is in good agreement with Interferometric Synthetic Aperture Radar (InSAR) uplift measurement. Although the InSAR data shows an insignificant uplift, hydromechanical modeling of injection shows that CO2 injection still causes reservoir deformation emphasizing the role of carbonate overburden and reservoir formation mechanical properties and limited size of reef on diminishing the surface deformation. Modeling indicates poroelastic response of caprock matters to estimate uplift. The lower permeability of the top two layers provides additional barrier to large uplift. Also, history of subsidence due to production should be accounted to predict uplift due to a follow up injection correctly. This study shows the significance of combining a calibrated geomechanical model with field measured stresses and monitoring data to be used as a tool to ensure the safety of CO2 storage.

Variational multiscale method for fully coupled thermomechanical interface contact and debonding problems

In this study, a computational framework is proposed for thermomechanical contact and debonding problems with proper thermal resistance at the interface. Using the Variational Multiscale (VMS) framework, we present a fully coupled thermomechanical formulation with an explicit expression of the pressure at the contact interface. The formulation considers the quasi-static balance of the momentum and the transient heat transfer problem in a fully coupled fashion. At the interface, two different contact constitutive models are utilized for tension and compression. For tensile problems, in the mechanical phase, a tensile debonding model is employed, whereas in the thermal phase, the displacement-dependent model is employed. For compressive problems, in the mechanical phase, a Coulomb frictional model is employed while in the thermal phase, a pressure-dependent model is embedded. Because of the naturally derived interface stability terms that possess area- and stress-weighting, the proposed VMS formulation accommodates contact/debonding and contact/frictional sliding at the interface due to both thermal and mechanical loading without losing numerical stability. The proposed method is applied to a class of numerical test problems with discontinuity at the interfaces, and good agreement with analytical and numerical data is achieved.

Pressure-Dependent Models in Ship Piping Systems

This paper aims to evaluate the feasibility of pressure-dependent models in the design of ship piping systems. For this purpose, a complex ship piping system is designed to operate in firefighting and bilge services through jet pumps. The system is solved as pressure-dependent model by the piping system analysis software EPANET and by a mathematical approach involving a piping network model. This results in a functional system that guarantees the recommendable ranges of hydraulic state variables (flow and pressure) and compliance with the rules of ship classification societies. Through this research, the suitability and viability of pressure-dependent models in the simulation of a ship piping system are proven.

Direct Kinetics and Product Measurement of Phenyl Radical + Ethylene.

The phenyl + ethylene (C6H5 + C2H4) reaction network was explored experimentally and theoretically to understand the temperature dependence of the reaction kinetics and product distribution under various temperature and pressure conditions. The flash photolysis apparatus combining laser absorbance spectroscopy (LAS) and time-resolved molecular beam mass spectrometry (MBMS) was used to study reactions on the C8H9 potential energy surface (PES). In LAS experiments, 505.3 nm laser light selectively probed C6H5 decay, and we measured the total C6H5 consumption rate coefficients in the intermediate temperature region (400–800 K), which connects previous experiments performed in high-temperature (pyrolysis) and low-temperature (cavity-ring-down methods) regions. From the quantum chemistry calculations by Tokmakov and Lin using the G2M(RCC5)//B3LYP method, we constructed a kinetic model and estimated phenomenological pressure-dependent rate coefficients, k(T, P), with the Arkane package in the reaction mechanism generator. The MBMS experiments, performed at 600–800 K and 10–50 Torr, revealed three major product peaks: m/z = 105 (adducts, mostly 2-phenylethyl radical, but also 1-phenylethyl radical, ortho-ethyl phenyl radical, and a spiro-fused ring radical), 104 (styrene, co-product with a H atom), and 78 (benzene, co-product with C2H3 radical). Product branching ratios were predicted by the model and validated by experiments for the first time. At 600 K and 10 Torr, the yield ratio of the H-abstraction reaction (forming benzene + C2H3) is measured to be 1.1% and the H-loss channel (styrene + H) has a 2.5% yield ratio. The model predicts 1.0% for H-abstraction and 2.3% for H-loss, which is within the experimental error bars. The branching ratio and formation of styrene increase at high temperature due to the favored formally direct channel (1.0% at 600 K and 10 Torr, 5.8% at 800 K and 10 Torr in the model prediction) and the faster β-scission reactions of C8H9 isomers. The importance of pressure dependence in kinetics is verified by the increase in the yield of the stabilized adduct from radical addition from 80.2% (800 K, 10 Torr) to 88.9% (800 K, 50 Torr), at the expense of styrene + H. The pressure-dependent model developed in this work is well validated by the LAS and MBMS measurements and gives a complete picture of the C6H5 + C2H4 reaction.

A Content-Based Active-Set Method for Pressure-Dependent Models of Water Distribution Systems with Flow Controls

AbstractIn this paper a new method is proposed that solves for the steady state of pressure-dependent models (PDMs) with flow control valves. Rather than model flow devices individually, the method...

Inducible rodent models of glaucoma.

Glaucoma is one of the leading causes of vision impairment worldwide. In order to further understand the molecular pathobiology of this disease and to develop better therapies, clinically relevant animal models are necessary. In recent years, both the rat and mouse have become popular models in glaucoma research. Key reasons are: many important biological similarities shared among rodent eyes and the human eye; development of improved methods to induce glaucoma and to evaluate glaucomatous damage; availability of genetic tools in the mouse; as well as the relatively low cost of rodent studies. Commonly studied rat and mouse glaucoma models include intraocular pressure (IOP)-dependent and pressure-independent models. The pressure-dependent models address the most important risk factor of elevated IOP, whereas the pressure-independent models assess "normal tension" glaucoma and other "non-IOP" related factors associated with glaucomatous damage. The current article provides descriptions of these models, their characterizations, specific techniques to induce glaucoma, mechanisms of injury, advantages, and limitations.

TSPICA: Temperature- and Pressure-Dependent Coarse-Grained Force Field for Organic Molecules.

Coarse-grained (CG) force fields optimized for a thermodynamic state typically lack transferability to different thermodynamic conditions. This work aims to improve the SPICA (formerly SDK) force field's transferability at higher temperatures and pressures via a relatively simple scaling of the CG parameters while remaining consistent with SPICA at ambient conditions. The temperature- and pressure-dependent model, termed tSPICA, agrees better with experimental data over a wider range of temperature and pressure than the standard SPICA model for molecular assembly thermodynamic properties. tSPICA shows an improvement in response to increasing temperature for the test case of a C12E6 aqueous solution showing behavior nearer to that experimentally determined.

Numerical simulation of impinging spray characteristics under high ambient pressures with an improved droplet collision model

Impinging spray characteristics under high ambient pressures (10–60 atm) were investigated experimentally and numerically. A recently proposed pressure-dependent droplet collision model was adopted to determine the collision outcomes. The results being compared to the predictions of Estrade et al. and O’Rourke’s droplet collision models. The comparison shows that the present pressure-dependent model accounts for the previous experimental observation and theory that increasing of ambient pressure promotes droplet bouncing, which was absent in the predictions of Estrade et al. and O’Rourke’s droplet collision model. Moreover, Estrade et al. and O’Rourke’s model tend to over-predict droplet size under high ambient pressures, results in the multi-tips in the spray shape, which however was seldom seen in the experimental shadowgraphs and predictions of the present model. Additionally, predictions of present model also account for the previous experiment that increasing of ambient pressure suppresses droplet breakup. Droplet velocity characteristics of impinging sprays under different ambient pressures were further investigated. The results show that, increasing of ambient pressure plays more aerodynamic resistance on the droplet together with the droplet bouncing-induced kinetic energy dissipation result in the reduced droplet velocity, and long-time droplet velocities tend to “converge”.

From benzene to naphthalene: direct measurement of reactions and intermediates of phenyl radicals and acetylene.

Hydrogen-abstraction-C2H2-addition (HACA) is one of the most important pathways leading to the formation of naphthalene, the simplest two-ring polycyclic aromatic hydrocarbon (PAH). The major reaction channels for naphthalene formation have previously been calculated by Mebel et al., but few experiments exist to validate the theoretical predictions. In this work, time-resolved molecular beam mass spectrometry (MBMS) was used to investigate the time-dependent product formation in the reaction of a phenyl radical with C2H2 for the first time, at temperatures of 600 and 700 K and pressures of 10 and 50 Torr. A pressure-dependent model was developed with rate parameters derived from Mebel et al.'s calculations and from newly calculated pathways on the C8H7 PES at the G3(MP2,CC)//B3LYP/6-311G** level of theory. The model prediction is consistent with the MBMS product profiles at a mass-to-charge ratio (m/z) of 102 (corresponding to the H-loss product from C8H7, phenylacetylene), 103 (the initial C8H7 adduct and its isomers plus the 13C isotopologue of phenylacetylene), 128 (naphthalene), and 129 (C10H9 isomers plus the 13C isotopologue of naphthalene). An additional C8H7 isomer, bicyclo[4.2.0]octa-1,3,5-trien-7-yl, not considered by Mebel et al.'s calculations, contributes significantly to the signal at m/z 103 due to its stable energy and low reactivity. At high C2H2 concentrations, bimolecular reactions dominated the observed chemistry, and the m/z 128 and m/z 102 MBMS signal ratio was measured to directly determine the product branching ratio. At 600 K and 10 Torr, branching to the H-loss product (phenylacetylene) on the C8H7 PES accounted for 7.9% of phenyl radical consumption, increasing to 15.9% at 700 K and 10 Torr. At 50 Torr, the branching was measured to be 2.8% at 600 K and 6.2% at 700 K. Adduct stabilization is favored at higher pressure and lower temperature, which hinders the formation of the H-loss product. The pressure-dependent model predicted the observed branching ratios within the experimental uncertainty, indicating that the rate parameters reported here can be used in combustion mechanisms to provide insights into phenyl HACA reactions and PAH formation.

Cross-impingement and combustion of sprays in high-pressure chamber and opposed-piston compression ignition engine

Spray cross-impingement in a high-pressure chamber (10–30 atm) was studied experimentally, the results being compared to the spray opposed-impingement. The comparison was subsequently extended to the spray combustion in a model opposed-piston compression ignition engine. To account for the ambient pressure effects in collision outcomes, a recently proposed pressure-dependent droplet collision model was implemented in the KIVA-3V computer program for simulating the experiments. Compared with the widely used Estrade et al.’s and O’Rourke’s models, the pressure-dependent model produces satisfactory predictions to spray characteristics. The uncertainty of the kinetic energy recovery coefficient, which affects the post-collision characteristics of bouncing droplets, was found to cause insignificant difference in model predictions. In the high-pressure chamber, droplet collisions in cross-impingement occur earlier than those in the opposed-impingement and result in more coalescence, consequently producing larger droplet sizes. With increasing the ambient pressure, the increasing tendency of droplet bouncing diminishes the difference of these two spray impingements. In the model OPCI, the presence of strong swirling flow deflects sprays from impingement and therefore the opposed-impingement shows slightly better combustion performance by producing more spatially uniform droplet distribution. However, the spray cross-impingement enhances droplet collision hence promotes atomization in the absence of swirling flow.

A Realistic Transport Model with Pressure-Dependent Parameters for Gas Flow in Tight Porous Media with Application to Determining Shale Rock Properties

A nonlinear transport model for single-phase gas flow in tight porous media is developed. The model incorporates many important physical processes that occur in such porous systems: continuous flow, transition flow, slip flow, Knudsen diffusion, adsorption and desorption into and out of the rock material, and a correction for high flow rates. This produces a nonlinear advection–diffusion type of partial differential equation with pressure-dependent model parameters and associated compressibility coefficients, and highly nonlinear apparent convective flux (velocity) and apparent diffusivity. A key finding is that all model parameters should be kept pressure dependent for the best results. An application is to the determination of rock properties, such as porosity and permeability, by history matching of the simulation results to data from pressure-pulse decay tests in a rock core sample (Pong et al. in ASME Fluids Eng Div 197:51–56, 1994).

Prediction of ionic liquids viscosity at variable temperatures and pressures

The viscosity of ionic liquids (ILs) plays an important role in the chemical industry, material science and environmental science. This work presents a temperature- and pressure-dependent (η-T-P) model based on the norm indices for describing the viscosity of ILs. While the parameters for the temperature and pressure dependence of the viscosity have been generally set as constants in previous work, they are adjusted based on the molecular structures in the η-T-P model. Because ILs consist of only cations and anions, the norm indices are derived from cations and anions, respectively. However, the close connection between the interaction of the cations and anions and IL viscosity cannot be neglected; therefore, another set of norms is further deduced to represent the cation–anion interaction. The η-T-P model is developed using 349 ILs (3228 data points) in the temperature range of 253.15–573.00 K and the pressure range of 0.06–300.00 MPa. Consequently, a η-T-P model is derived with convincing results, as evaluated by the following statistical parameters: the squared correlation coefficient (R2), Fisher significance (F) and the overall average absolute relative deviation (AARD), which are 0.964, 1809 and 4.62%, respectively.

Spray Impingement and Combustion in a Model Opposed-Piston Compression Ignition Engine

ABSTRACTSpray impingement and combustion in a model opposed-piston compression ignition engine was investigated experimentally and computationally. A recently proposed pressure-dependent droplet collision model was implemented in the KIVA-3V computer program for the Reynolds Average Navier–Stokes calculation, which was validated against the time-averaged experimental data for the cylinder pressure. Compared with the widely-used O’Rourke model, the present model produces physically appraised predictions by accounting for the propensity of droplet bouncing upon collision at high engine pressures—a physical phenomenon overlooked in the previous models. The results show that droplet collisions can be promoted either by the impingement of the sprays from the oppositely placed three-nozzle fuel injectors under the condition of low engine speed and high load, or by the interaction of the sprays from each fuel injector in the presence of in-cylinder swirling flow. Motivated by fully utilizing the space of the combustion chamber, a new spray layout possessing the S2 symmetry was proposed and computationally investigated in the study. Compared with Hofbauer’s spray layout of the C2 symmetry, the present layout tends to produce more distributed premixed fuel mass and hence results in a longer ignition delay time but a higher peak heat release rate.

Simulation research on the anisotropic cutting mechanism of KDP crystal using a new constitutive model

ABSTRACTPotassium dihydrogen phosphate (KDP) exhibits anisotropic and hydrostatic pressure-dependent mechanical characteristics during processing. However, none of the existed material models is capable of describing the mechanical properties of the crystal. Thus, a new constitutive model, which combines the anisotropic elastic and pressure-dependent plastic model has been proposed in this paper. In addition, the tensile stress failure criterion is adopted as the fracture criterion of KDP crystal. Subroutine of the new material model is programmed and integrated into the commercial finite element software LS-DYNA. On the basis of that, the unknown material parameters of KDP are successfully identified with the aid of the nanoindentation/scratch technique and finite-element simulation. Finally, 2-D and 3-D cutting simulations applying the new model are performed to investigate the influence of cutting parameters on the brittle ductile transition depth and cutting force. The simulation results show good agreement with the KDP cutting experiment results, which confirm the validity and capability of the proposed constitutive model.

Rate- and pressure-dependent friction model for rubber material based on the elastoplastic formulation

Rate- and pressure-dependent friction model for rubber material based on the elastoplastic formulation