Steady-state Case Research Articles

Vehicle roll centre estimation with transient dynamics via roll rate

The roll centre (RC) is a core parameter for vehicle lateral dynamics and control, which can be obtained via suspension geometry configuration or suspension kinematics and compliance (K&C) test. However, these methodologies are used for laboratory tests and are suitable at low lateral acceleration. In other words, the RC is hard to measure directly while the vehicle is running on the road. In this paper, the online RC estimation methodologies including the adaptive sliding mode observer (ASMO) and the extended Kalman filter (EKF) only with roll rate are proposed considering vehicle transient dynamics. The performance of these algorithms is evaluated and compared with the recursive least square with disturbance observer algorithm (RLSDA) via vehicle dynamics study. Simulation results manifest that, compared with the RLSDA with three roll signals, the proposed ASMO and EKF, only with roll rate, can estimate RC successfully for both the transient and steady-state cases and can be applied for online vehicle RC estimation. In detail, the proposed ASMO is recommended for the steady-state case, and the proposed EKF is recommended for the transient case. Furthermore, the static RC is recommended as the estimation initial value to improve estimation.

Temperature dynamics and its effects on gas influx handling during managed pressure drilling operations

With Managed Pressure Drilling (MPD) becoming increasingly important to oil and gas well construction, there has been a growing demand for comprehensive models that can accurately describe the well hydraulic dynamics, especially for complex well geometries, High-Pressure High-Temperature (HPHT) conditions, during well control events, etc. To meet this demand, new multi-phase hydraulic models have been developed. However, despite their improvement over the traditional lumped parameter models, these models typically do not consider detailed temperature effects, which markedly influence well hydraulics and need to be explicitly considered for accurate MPD control.The development of a new integrated multi-phase thermal and hydraulic modeling framework is presented in this paper. This integrated model can estimate the mud temperature in the drillstring and the annulus, as well as the temperature variations of the formation during complex well control situations. The model uses a semi-implicit finite volume approach and solves the mixture energy equation for the wellbore fluids, assuming that all the phases are in thermal equilibrium. Heat transfer between the drillstring and wellbore fluids, and between the wellbore fluids and the formation is calculated using thermal resistance networks.The steady-state and transient temperature behaviors during mud circulation are compared to the steady-state analytical model by Hasan and Kabir and commercial software. These comparisons show good agreement for both steady-state and transient cases. To demonstrate the importance of accurate temperature estimation of the drillstring and annulus fluids in HPHT conditions, offshore kick scenarios for non-aqueous drilling fluids and dynamic kick control methods are simulated. Simulation results indicate that the model enables real-time estimation of crucial parameters during well control, such as the wellbore pressure and temperature profiles, increased outflow and pit gain during kicks, gas thermodynamic behavior including solubility and unloading behavior at low pressure conditions, gas rising velocity, and temperature-dependent formation strength.

Numerical Study of Quenching Distances for Side-Wall Quenching Using Detailed Diffusion and Chemistry

The numerical investigation of quenching distances in laminar flows is mainly concerned with two setups: head-on quenching (HOQ) and side-wall quenching (SWQ). While most of the numerical work has been conducted for HOQ with good agreement between simulation and experiment, far less analysis has been done for SWQ. Most of the SWQ simulations used simplified diffusion models or reduced chemistry and achieved reasonable agreement with experiments. However, it has been found that quenching distances for the SWQ setup differ from experimental results if detailed diffusion models and chemical reaction mechanisms are employed. Side-wall quenching is investigated numerically in this work with steady-state 2D and 3D simulations of an experimental flame setup. The simulations fully resolve the flame and employ detailed reaction mechanisms as well as molecular diffusion models. The goal is to provide data for the sensitivity of numerical quenching distances to different parameters. Quenching distances are determined based on different markers: chemiluminescent species, temperature and OH iso-surface. The quenching distances and heat fluxes at the cold wall from simulations and measurements agree well qualitatively. However, quenching distances from the simulations are lower than those from the experiments by a constant factor, which is the same for both methane and propane flames and also for a wide range of equivalence ratios and different markers. A systematic study of different influencing factors is performed: Changing the reaction mechanism in the simulation has little impact on the quenching distance, which has been tested with over 20 different reaction mechanisms. Detailed diffusion models like the mixture-averaged diffusion model and multi-component diffusion model with and without Soret effect yield the same quenching distances. By assuming a unity Lewis number, however, quenching distances increase significantly and have better agreement with measurements. This was validated by two different numerical codes (OpenFOAM and FASTEST) and also by 1D head-on quenching simulations (HOQ). Superimposing a fluctuation on the inlet velocity in the simulation also increases the quenching distance on average compared to the reference steady-state case. The inlet velocity profile, temperature boundary condition of the rod and radiation have a negligible effect. Finally, three dimensional simulations are necessary in order to obtain the correct velocity field in the SWQ computations. This however has only a negligible effect on quenching distances.

Revealing hidden debottlenecking potential in flare systems on offshore facilities using dynamic simulations – A preliminary investigation

Three flare systems are modeled and total plant depressurization is investigated using dynamic simulations in order to access the debottlenecking potential. Usually, steady-state simulation of the flare network is used for sizing and rating of the flare system. By using dynamic simulations, effects from line packing in the flare system can be studied. The results show that peak flow during a dynamic simulations is significantly lower than the peak flow used in a steady-state case. The three systems investigated span a wide range in flare system size, both in terms of number of process segments disposing into the flare network, in terms of peak design rate, the flare network pipe dimensions and total hold-up volume. Generally, it is observed that the larger the flare system, the larger debottlenecking potential.

Integrative Circuit-Host Modeling of a Genetic Switch in Varying Environments

Synthetic biology is advancing into a new phase where real-world applications are emphasized. There is hence an urgent need for mathematical modeling that can quantitatively describe the behaviors of genetic devices in natural, fluctuating environments. We utilize an integrative circuit-host modeling framework to examine the dynamics of a genetic switch and its host cell in varying environments. For both steady-state and transient cases, we find increasing nutrient reduces the bistability region of the phase space and eventually drives the switch from bistability to monostability. In response, cellular growth and proteome partitioning experience the same transition. Antibiotic perturbations cause the similar circuit and host responses as nutrient variations. However, one difference is the trend of growth rate, which augments with nutrient but declines with antibiotic levels. The framework provides a mechanistic scheme to account for both the dynamic and static characteristics of the circuit-host system upon environmental perturbations, underscoring the intimacy of gene circuits and their hosts and elucidating the complexity of circuit behaviors arising from environmental variations.

An analytical model for thermal convection and convective rolls with a linear eddy viscosity

The aim of this work is to present a theoretical scheme of dry thermal convection and convective rolls in atmospheric boundary layer with a linear eddy viscosity for a steady-state stationary case. For this theoretical study, a few approximations valid for atmospheric boundary layer were used, such as the Boussinesq approximation, and also, the second-order spatial derivative of velocity has been neglected. Analytical models for dry air thermal updraft velocity are presented and wavelength between convective rolls and aspect ratio of rolls have been derived. Using these results, it is shown how the transition between cellular-type convection and roll-type convection depends on thermal stratification of boundary layer, the temperature excess of convective cell at ground level and other meteorological parameters. The analytical results are in agreement with both observational and numerical studies for horizontal convective rolls existent in scientific literature. In addition, it is shown how this presented model can be applied for layers with non-linear eddy viscosity and how it can be used in future studies, and what its limitations are.

SPERT III E-Core critical experiment benchmarks calculation with NECP-X and KENO-VI

The Special Power Excursion Reactor Test (SPERT) III E-Core is a small experimental reactor towards experimental and theoretical investigations of kinetic and safety behavior of nuclear reactors. The SPERT III E-core model was established with a high-fidelity direct whole-core transport code NECP-X and a Monte Carlo code KENO-VI. Most of components of the reactor core were explicitly modeled in these two codes. A series of steady-state cases were calculated, ranging from 2D lattice to 3D whole core, providing the reference solutions for SPERT-III E-Core benchmarks. The complicated geometry of transient rods is modeled by the Constructive Solid Geometry (CSG) method in NECP-X. Numerical results indicate that NECP-X shows the good agreement with KENO-VI for all test cases.

Development of a new nanoparticle sizer equipped with a 12-channel multi-port differential mobility analyzer and multi-condensation particle counters

Abstract. Measuring particle size distributions precisely is an important concern in addressing environmental and human health-related issues. To measure particle size distributions, a scanning mobility particle sizer (SMPS) is often used. However, it is difficult to analyze particle size distributions under fast-changing concentration conditions because the SMPS cannot respond fast enough to reflect current conditions due to the time necessary for voltage scanning. In this research, we developed a new nanoparticle sizer (NPS), which consists of a multi-port differential mobility analyzer (MP-DMA) with 12 sampling ports and multi-condensation particle counters (M-CPCs) that simultaneously measure concentrations of particles classified by the sampling ports. The M-CPC can completely condense particles larger than 10 nm, and the total particle concentrations measured by each CPC in the M-CPCs and an electrometer were in agreement up to 20 000 no.cm-3. We conducted size distribution measurements under steady-state conditions using an aerosol generator and under unsteady conditions by switching the aerosol supply on or off. The data obtained by the NPS corresponded closely to the SMPS measurement data for the steady-state particle concentration case. In addition, the NPS could successfully capture the changes in particle size distribution under fast-changing particle concentration conditions. Finally, we present NPS measurement results of size distributions in a common situation (cooking) as an exemplary real-world application.

High resolution evidence of iron-phosphorus-sulfur mobility at hypoxic sediment water interface: An insight to phosphorus remobilization using DGT-induced fluxes in sediments model

The deterioration of reservoirs in southern China due to the kinetics of Iron (Fe), Phosphorus (P) and sulphide (S) at the sediment-water interface (SWI) is a major problem that needs urgent attention. Studies on the biogeochemistry of Fe, P, and S using high-resolution profile techniques in reservoirs in this region are limited. The diffusive gradient in thin films (DGT) technique, high-resolution dialysis, DGT-computer imaging densitometry (CID), DGT-induced fluxes in sediments (DIFS) and planar optode (PO) device were used to describe the dynamics Fe-P-S in SWI during hypoxia. The results showed the release of Fe-P-S in SWI was due to sulfate reduction and iron reduction influenced greatly by hypoxia. Positive apparent fluxes were recorded indicating that the sediments release Fe-P-S to the overlying water. High positive correlations (r2 > 0.7) for DGT-labile Fe and DGT-labile P in sediments revealed that iron-bound P controlled the release of P at SWI during reductive dissolution. The low correlation between DGT-labile Fe and DGT-labile S (r2 < 0.4) disclosed the combative nature between sulfate reduction and iron reduction process. The low correlation occurred because of the co-precipitation between Fe and S, forming black materials such as monosulfide (FeS) and pyrite (FeS2) in a hypoxic environment. The DIFS model showed the resupply ability (R-values) of P in sediments belonged to the partially sustained case with a steady state case of resupply at TB3 (Tc = 1088s, Kd = 1005.61 cm3/g R = 0.72, K−1 = 0.19 day−1) and TB4 (Tc = 712 s, Kd = 712.53 cm3/g, R = 0.78, K−1 = 0.46 day−1). The resupply rate belonged to the non-steady state case at TB1 (Tc = 10,990 s, Kd = 396.3 cm3/g, R = 0.35, K−1 = 0.07 day−1) and TB2 (Tc = 6097 s, Kd = 578.5 cm3/g, R = 0.45, K−1 = 0.10 day−1). The DGT-CID-PO-DIFS provided a deep insight on the mechanism of Fe-P-S and remobilization of P at SWI leading to Blackwater events and eutrophication.

The benefits of photoacoustics for the monitoring of drug stability and penetration through tissue-mimicking membranes.

The paper demonstrates the potential of photoacoustics for the identification of the mechanisms underlying drug transport through tissue-mimicking systems. Photoacoustic experiments were performed for a model transdermal delivery system, consisting of drug dithranol (in pharmaceutical form) and dodecanol-collodion (DDC) membrane. The spectroscopic data revealed a single-path photodegradation of dithranol in Vaseline (dithranol→danthrone, characterized by the 1st order decay rate of (7.85±0.31)·10-4 s-1), and a multipath degradation in the DDC system, involving danthrone and the unknown compound (characterized by the absorption band at ~400nm) as the final products. The desorption experiments performed enabled the identification of the unknown compound as the photodegradation product of dithranol molecules bound to the membrane matrix. The result led to the incorporation of the adsorption effects and heterogeneous structure of the membrane into the hydrodynamical model of mass transport. The model was tested against the photoacoustic depth-profiling data for dithranol permeation through DDC. The analysis allowed the dispersion and advection coefficients to be determined (D' = (2.05±0.03)⋅10-9 cm2 s-1 and va' = (-5.55±0.05)⋅10-7 cm s-1, respectively). Moreover, it was found, that the dithranol photodegradation rate in the non-steady state system is slower compared to the steady-state case; the effect was attributed to different permeation rates of dithranol and mobile Vaseline particles through the membrane.

Groundwater Evaluation and Management in Ain Sukhna, Egypt

Ain Sukhna has become one of the most important economic areas in Egypt recently. As a result of this economic development, the demand for water has increased, with special emphasis on groundwater. Therefore, in this paper, several scenarios are assessed in order to reach the best scenario for groundwater management giving the opportunity to achieve the development needs of that region.Groundwater Modeling System (GMS) software is used to construct the solid model forsimulating the geometry of the aquifer layers. Then, a conceptual model is developed and calibrated in steady state case. The calibration results are satisfactory showing a good agreement between the calculated and observed heads. Finally, four scenarios are simulated with different pumping possibilities ranging from -25% to + 50% of the current pumping rates. The results show that it will be better if the current pumping rate is reduced by 25% which can make the drawdown values less than the other possibilities. It is also shown that the best recommended places to drill more wells can be in the east and south directions where the least drawdown values are found.

Parasitic Recombination in a Laser with Asymmetric Barrier Layers

In a laser with asymmetric barrier layers (ABLs) two thin barrier layers adjacent to the active region on both sides are intended to prevent bipolar population of the waveguide layers, hence, to suppress parasitic recombination in them. A theoretical model of a laser with ABLs, based on rate equations which acknowledge undesirable carrier leakage inevitable in lasers of this type implemented in practice, is proposed. Solutions to equations are obtained for the steady-state case. By the example of an InGaAs/GaAs quantum-well laser (lasing wavelength λ = 980 nm), the effect of leakages through ABLs on the device characteristics is studied. The parasitic-flux suppression ratios C of ABLs which are required to prevent the adverse effect of waveguide recombination are estimated. In the case at hand, the effect of ABLs becomes appreciable at suppression ratios of C ≥ 102. To suppress 90% of the parasitic current, C should be 2.3 × 104. The effect of ABLs on useful carrier fluxes arriving at the active region is also studied.

A simplified dynamic model of integrated parabolic trough concentrating solar power plants: Modeling and validation

An analytical dynamic model can deepen our understanding of system characteristics. However, no system-scale dynamic model of integrated parabolic trough concentrating solar power (CSP) plants currently exists due to lack of a dynamic model of heat exchanger trains and proper integration of different subsystems. To solve the problems, this work developed a new analytical dynamic model of heat exchanger trains. Furthermore, a simplified analytical model of an integrated parabolic trough CSP consisting of a parabolic trough solar field, thermal energy storage, and power block subsystem is first proposed here. To demonstrate the fidelity of the integrated model, the simulation presented here was compared with the simulation built on a software platform and the corresponding measured data from the Andasol II plant. All the validation results of a steady-state case and two dynamic cases prove that the proposed model can capture the system dominant processes with satisfactory accuracy and computational efficiency. Considering the advantages of reliability, simplicity, and robustness, the integrated model can be applied to design and test system controllers of CSP plants, and various other areas related to the CSP.

Dynamic Equivalent Modeling for Wind Farms With DFIGs Using the Artificial Bee Colony With K-Means Algorithm

With the increasing penetration of wind power, it is recognized that wind power will have a greater and greater impact on the planning and operation of the original power system. And the detailed modeling of wind farm with doubly-fed induction wind generator (DFIG) will require large storage and computation resources, which poses technical challenges for equivalent modeling of wind farm. In this paper, a multi-machine dynamic equivalent modeling method for wind farms with DFIGs is proposed. First, the artificial bee colony with k-means (ABC-KM) algorithm is proposed to improve the effectiveness of wind farm clustering. Second, the operating data composed of wind speed, pitch angle, rotor angular velocity, rotor current, real-time active and reactive power are selected as clustering indicators. A wind farm with DFIGs is divided into several groups and DFIGs in the same group are clustered as one DFIG through equivalent parameter aggregation. The proposed wind farm modeling method consisting of clustering method and clustering indicators is verified by comparing the simulation results of equivalent and detailed models at steady-state and dynamic-state cases.

Analysis of an &lt;i&gt;M&lt;/i&gt;&lt;SUP align="right"&gt;[&lt;i&gt;X&lt;/i&gt;]&lt;/SUP&gt;/&lt;i&gt;G&lt;/i&gt;(&lt;i&gt;a&lt;/i&gt;, &lt;i&gt;b&lt;/i&gt;)/1 queueing model with multiple vacation controllable arrival during multiple vacation and two phases of repair with delay

The objective of this paper is to analyse an M[X]/G(a, b)/1 queueing model with multiple vacation, controllable arrival during multiple vacation and two phases of repair with delay. Whenever the queue size is less than 'a', the server resumes multiple vacation and continues this until at least 'a' customers are waiting in the queue. After finishing a batch of service, if the server is breakdown with probability γ, the server will be sent for repair after a short interval of time called delay time. After this delay, two consecutive phases of repair (first phase repair, second phase repair) are considered. After the second phase of repair or when there is no breakdown with probability 1-γ, the server starts a vacation if the queue length is less than 'a'. Otherwise, the server starts a service under the general bulk service rule. Using supplementary variable technique, the probability generating function of the queue size at an arbitrary time is obtained for the steady-state case. Also some performance measures and cost model are derived. Numerical illustrations are presented to visualise the effect of various system parameters.

High-frequency fluctuations of indoor pressure: A potential driving force for vapor intrusion in urban areas

In this study, we examine the impact of a building's indoor pressure fluctuations in drawing subsurface volatile contaminants into the building, and how the presence of an impervious pavement surrounding the building influences this. Even in the absence of communication between the subsurface soil gas and ambient air fluctuations of building indoor pressure can cause upward advection of contaminated soil gas from the subfoundation zone into a building. For cases with the paved ground surface, the simulated volumetric soil gas entry rates are lower than steady-state cases with constant −5 indoor-outdoor pressure difference, by at least half an order of magnitude. When the indoor pressure fluctuation rate exceeds about 5 Pa/h (which corresponds a sinusoidal fluctuation with a period of 2 h), the predicted indoor air concentration of paved scenarios will be higher than the conventional case. When both the building foundation and surrounding pavement block diffusional escape of the volatile soil gas contaminants to the atmosphere, high subfoundation soil gas contaminant concentrations can exist, and contaminant entry into the building through foundation breaches is enhanced beyond what would be expected from diffusion as the building undergoes normal pressure cycling. Upward advection into the building may be induced even when the indoor pressure appears, based on limited measurements, to be higher than that in the subslab, particularly when the indoor pressure in the building quickly fluctuates. This represents a limitation on VI mitigation approaches that rely on indoor pressurization, if those approaches cannot at the same time control significant fluctuation of indoor pressure.

On the limits of added-mass theory in separated flows and with varying initial conditions

It remains unclear to what extent inviscid added-mass theory accounts for the forces exerted on an accelerating body subjected to separated flow. In this study, reactant forces and velocity-field data are systematically acquired using experimental measurements and simulations of an accelerating circular flat plate. Cases accelerated from rest are compared to cases accelerated from a steady flow state. When the added-mass forces predicted by potential theory and the resistance forces associated with the instantaneous plate velocity are accounted for, the remaining (residual) forces comprise approximately 20% of the peak force, even at high accelerations. In addition, the computed residual forces during accelerations both from rest and steady-state cases yield good collapse with respect to one another, indicating that the total forces are not a strong function of the initial state of the wake. These results suggests that inviscid added-mass theory is inadequate to predict the full reactant force even in the ‘ideal’ condition of impulsive motion from rest.

Three-dimensional thermal Green's functions of quasi-steady-state motion in anisotropic bimaterials and some related problems

Three-dimensional thermal Green's functions of quasi-steady-state motion, as well as that of steady-state conduction in anisotropic bimaterials are derived based on two-dimensional Fourier transform, and are separated as a sum of a full-space Green's function and a complementary part. It is worth mentioning that Green's functions of steady-state case can be obtained directly by replacing the moving source by the static one and be expressed in a more concise form. Although the present paper aims to develop Green's functions in anisotropic bimaterials, the derived solutions can be reduced to simple cases, such as in isotropic or orthotropic materials, in half-space or full-space, and on the interface or surface. Numerical examples are presented to verify the validity of present solutions. Moreover, the comparison between steady-state case and quasi-steady-state cases of two different velocities, indicates high correlation with the properties of material and the distortion of thermal fields induced by inertial effect.

Numerical and experimental campaigns for lead solidification modelling and testing

The Computational Fluid-Dynamics (CFD) modelling of Heavy Liquid Metal (HLM) flows in pool configuration is investigated in the framework of the SESAME project. This paper focuses on the coupling between numerical simulations and experimental activity with the objective to make CFD a valid tool in support to the design of safe and innovative Gen-IV nuclear reactors. The attention is focused on the possible occurrence of lead solidification phenomenon. The aim is to demonstrate that the overall modelling of HLM complex systems can include solidification phenomenology by reproducing small/medium scale experiment, making comparison with experimental results, improving the numerical setting (post-test) and evaluating time scales, limitations and computational costs. A dedicated experimental campaign on the SESAME-Stand facility has been performed by the Research Centre Rez (CVR), relying on the use of CFD support, with the specific objective to build a series of datasets suited also for the CFD modelling validation.The numerical simulations of the SESAME-Stand experimental facility performed in STAR-CCM + are described. The model uses liquid lead as working fluid in the pool and air in the cooling channel. By increasing the mass flow rate in the cooling air channel, the solidification process is initiated and the freezing front propagates in the pool until reaching an internal obstacle. The issues encountered in the pre-test simulations have been fully overcome by means of systematic investigations and all the improvements have been applied in the post-test model. A decisive modelling aspect was the correct implementation of the thermal radiation which plays an important role in the cooling process. The numerical model allowed to reach an increased number of initial steady states and accessible transients, according to the experimental matrix. The comparison with the experimental results shows similar temperature configurations and comparable lead frozen fractions in the steady state cases and good agreement in the fast transient solidification-remelting cases.

Deciphering Residual Emissions: Time-dependent Models for the Nonthermal Interstellar Radiation from the Milky Way.

Cosmic rays (CRs) in the Galaxy are an important dynamical component of the interstellar medium (ISM) that interact with the other major components (interstellar gas and magnetic and radiation fields) to produce broadband interstellar emissions that span the electromagnetic spectrum. The standard modeling of CR propagation and production of the associated emissions is based on a steady-state assumption, where the CR source spatial density is described using a smoothly varying function of position that does not evolve with time. While this is a convenient approximation, reality is otherwise, where primary CRs are produced in and about highly localized regions, e.g., supernova remnants, which have finite lifetimes. In this paper, we use the latest version of the galprop CR propagation code to model time-dependent CR injection and propagation through the ISM from a realistic 3D discretized CR source density distribution, together with full 3D models for the other major ISM components, and make predictions of the associated broadband nonthermal emissions. We compare the predictions for the discretized and equivalent steady-state model, finding that the former predicts novel features in the broadband nonthermal emissions that are absent for the steady-state case. Some of the features predicted by the discretized model may be observable in all-sky observations made by WMAP and Planck, the recently launched eROSITA, the Fermi-LAT, and ground-based observations by HESS, HAWC, and the forthcoming CTA. The nonthermal emissions predicted by the discretized model may also provide explanations of puzzling anomalies in high-energy γ-ray data, such as the Fermi-LAT north/south asymmetry and residuals like the so-called "Fermi bubbles."