One-dimensional Numerical Model Research Articles

Dynamic heat transfer characteristics of ice storage in smooth-tube and corrugated-tube heat exchangers

The ice storage system is one of the most promising techniques for flexibility enhancement of building cooling load. In this paper, the performances of smooth-tube and corrugated-tube heat exchangers for ice storage are compared by experiments and numerical simulation. The heat transfer process of the ice storage and melting within the heat exchangers is numerically analyzed used Python. The fast one-dimensional numerical model is verified by the experimental results. The temperature variation of the heat transfer fluid (HTF) in the corrugated tube is analyzed and compared with that in the smooth tube. The results show that under the same conditions, the ice storage duration of the corrugated tube is shortened by 25% and the melting duration is shortened by 16% compared with those of the smooth tube. During the ice storage process, the temperature difference between the inlet and outlet of the heat transfer fluid in the corrugated tube is 0.4 °C less than that of the smooth tube on average. The temperature change rate is 30% faster than that of the smooth tube. During the melting process, the temperature difference between the inlet and outlet of the heat transfer fluid in the corrugated tube is 0.1 °C higher than that of the smooth tube on average, and the temperature change rate of corrugated-tube heat exchanger is 2.5 times and 9 times faster than that of the smooth tube during the ice-storage and melting process. The corrugated-tube heat exchanger has superior performances in ice storage system in the comparison with the smooth-tube heat exchanger.

A novel downstream Flood Hazard Grade Index incorporating upstream Hydrograph Characteristics to predict Debris Flow Runoff

The July 2020 debris flow in Japan caused enormous damage, and briefing sessions on disaster prevention have prompted demands for detailed explanations and predictions of such phenomena in high-risk areas. It is necessary to obtain four-dimensional risk information, which considers temporal changes in disaster risk, rather than limiting the analysis to conventionally static information. In this study, we developed a method for setting the boundary conditions necessary for debris flow prediction via a four-dimensional hazard map using various types of digital information. To understand the effects of hydrograph characteristics from the upstream, flow discharge was analysed under different flow conditions, such as topography-driven riverbed shear stress, using a one-dimensional numerical model that considers water and sediment flow. Our results suggested that characteristics of the upstream inflow hydrograph affect flood runoff processes downstream; therefore, we developed a separate downstream flood hazard grade index that uses characteristics of the upstream inflow hydrograph as input.

Numerical modelling of porosity with combined gas and shrinkage effects in HPDC

High-pressure die casting is a manufacturing process in which near-net-shape components are produced rapidly under a pressurized environment. However, due to the relatively higher cooling rate prevailing during the process, isolated liquid pockets form at certain locations, leading to increased porosity formation. A one-dimensional deformable grid numerical model has been developed for predicting the evolution of a single pore in an elementary volume, which combines the diffusion model with the shrinkage affected growth. The model accounts for the change in pore size due to shrinkage and inter-granular growth. This model can provide predictions in representative volumes and be used for component level predictions by combining with a macroscopic model.

PROGRESSIVE DAMAGE ANALYSIS OF STEEL-REINFORCED CONCRETE BEAMS USING HIGHER-ORDER 1D FINITE ELEMENTS

The present work investigates progressive damage in steel-reinforced concrete structures. An elastic-perfectly plastic material response is considered for the reinforcing steel constituent, while the smeared-crack approach is applied to model the nonlinear behavior of concrete. The analysis employs one-dimensional numerical models based on higher-order finite elements derived using the Carrera unified formulation (CUF). A set of numerical assessments is presented to study the mechanical response of a steel-reinforced notched concrete beam loaded in tension. The predictions are found to be in very good agreement with reference experimental observations, thereby validating the numerical approach. It is shown that CUF allows for the explicit representation of the constituents within the composite beam, resulting in accurate solutions in a computationally efficient manner.

Land subsidence caused by seasonal groundwater level fluctuations in Kawajima (Japan) and one-dimensional numerical modeling with an evolutionary algorithm

The causes of land subsidence in Kawajima, Japan, have been investigated through data compilation and numerical modeling. Land subsidence has progressed despite a gradual increase in the hydraulic head in the long term. Taking into account the temporal changes and depth distribution of groundwater abstractions, the contraction of formations, and the complexity of the hydrogeological structures, it is proposed that agricultural groundwater use is one of the main triggers for land subsidence. A one-dimensional numerical simulator for coupled groundwater flow and soil deformation was developed with an evolutionary algorithm for model calibration. The calculated spatiotemporal changes in the past-maximum effective stress showed that plastic consolidation in the clayey layers progressed part by part every summer season resulting in long-term and gradual land subsidence under the same range of groundwater level fluctuations. The results also showed that the plastic deformation occurred in both the Holocene and Pleistocene sediments in the drought years, leading to significant subsidence. The model’s predictive performance showed good potential except for a structural prediction error after the Tohoku Earthquake in 2011. The scenario analysis indicated that management of the groundwater level in summer is one of the effective countermeasures in suppressing land subsidence caused by seasonal groundwater level fluctuations. These methodologies and findings can be used for groundwater management in similar cases around the world. Additional investigation is necessary on the influence of large earthquakes in deformation conditions in order to further improve the developed model.

One-Dimensional Unsteady Numerical Model of Gas Suspension Flow Caused by Gravitational Sedimentation of Particles with a Constant Velocity

One-Dimensional Unsteady Numerical Model of Gas Suspension Flow Caused by Gravitational Sedimentation of Particles with a Constant Velocity

One-dimensional numerical model for unsteady solute transport in open channels under multi-point loading

A numerical method for solving the unsteady-one-dimensional advection-dispersion equation for solute transport in streams and channels imposed with multiple point-loading is presented. The numerical technique proposes to solve the equation, which also includes a first-order decay term and a loading term, using techniques similar to those employed by the finite volume method (FVM). The channel length is segmented into cells and the solution aims at evaluating the concentrations at the cell interfaces or the internal nodes, at prescribed time steps for the steady condition of the flow. The results are computed commencing from a specified time level with known spatial concentration within the domain. It is assumed that the boundary nodes at the two ends of the channel, one each at the upstream and the downstream, are specified with solute concentration values or its spatial gradient at all times. Unlike the standard within-the-cell spatial approximations of a variable assumed in the finite volume or finite element schemes, the proposed method models the spatial variation of the solute concentration within a cell by an analytical expression in terms of the concentrations at the two boundary nodes of the cell and the influx rate of point-loading, if any, located within the cell. Using such a closed-form function based upon the true nature of the problem not only helps in capturing the spatial variation of concentration within a cell more precisely but also allows a better approximation of its spatial gradients at the cell interfaces, thus helping to achieve a more accurate computation of the inter-cell dispersive fluxes. The performance of the proposed algorithm is evaluated against analytical benchmarks, a standard finite difference scheme, and one public-domain computational package. Data sets reported from field tests are used for demonstrating the potential of the technique in simulating real situations.

Insight into [formula omitted] based perovskite solar cell performance using SCAPS Simulator

The organic/inorganic Perovskite Solar Cells (PSC) are considered promising devices thanks to their higher efficiency, which made them a broad field of several studies, especially methylammonium lead iodide solar cells, However, the presence of lead, high toxicity, and low stability are the main obstacles in front of the commercialization of these devices. Herein, the one-dimensional SCAPS-1D numerical simulator model has been used to investigate the performance of PSC, using the Europium (Eu) instead of some Pb atoms to reduce undesirable effects, which give (MAPb1−xEuxI3) as absorber layer. Therefore, to enhance the performance parameters of the device and to achieve a higher power conversion efficiency (PCE) value compared to those existing in the literature, the study of the thickness effect and the active layer defects, using different Hole Transport Layer (HTL): NiOx,PEDOT:PSS,Spiro−OMeTAD,Cu2O was performed. In addition, the optimization of HTL parameters by varying the thickness and the concentration of the shallow acceptor was carried out. This Results show that the Cu2O as HTL with a thickness of 10 nm and concentration of the shallow acceptor of 1016 cm−3, combined with MAPb1−xEuxI3 active layers with a thickness of 289.5 nm and defect concentration of 1014 cm−3 gives the best PCE with a value of 21.72%.

Packed bed combustion of binary mixtures of wood particles of different shapes and sizes

• Combustion of binary mixtures of particles of different sizes and shapes. • Experiments compared with numerical model. • Mean particle size and sphericity make model agree well with experiment. • Model must include particle overlap and wood grain orientation. This paper presents the results of experiments and numerical modelling on the quasi-steady overfeed combustion and gasification of binary mixtures of fuel particles of different sizes and shapes in a fixed bed. The particles used comprised six different parallelepipedal shapes cut from wood, which were combined to give various binary mixtures. Physically appropriate definitions of average quantities for a packed bed are the volume surface or Sauter mean diameter and a related average sphericity, and the main objective of the work was to determine whether these could be used to model bed combustion of a particle mixture. Measured gas concentration and temperature profiles in the burning bed are compared with a one-dimensional numerical model, which is shown to give good predictions using these mean quantity definitions. Samples of bed solids taken after the conclusion of each experiment give insight into the variation of particle mass, size and sphericity during combustion, and the averages of these also agreed with model predictions, with the caveat that the model can only calculate the average particle size, and is not able to reproduce the individual burning histories of different sizes of particles. The effects of different orientations of the wood fibres in the particles are evident from the experimental data. The results show the importance of including these effects as well as the reduction in bed specific surface area due to particle overlap in calculations.

Numerical analysis on the flow instability of a 700 °C ultra-supercritical tower boiler

The boiler equipment should be able to adapt to the load requirements and overcome the interference of various external conditions. By establishing a one-dimensional single-channel general numerical calculation model suitable for flow instability analysis of ultra-supercritical boilers at 700 °C, the rules of flow in the tubes are calculated. The 7th loop and the 22nd loop of the boiler water wall are selected as typical loops, and the dynamic characteristics of the two loops are calculated. The results show that after applying different multiples of heat flux disturbance, regardless of whether metal heat storage is considered, the inlet and outlet mass flow rates of the two circuits show inverse dynamic responses and eventually return to a steady state. When considering heat storage, it takes about 63 s for the 7th loop to return to stability. The recovery and stabilization time of the 22nd loop is about 60 s. Metal thermal storage has a positive effect on the settling time of the pipe section after heat flux disturbance. And when the maximum heat flux disturbance is applied, the maximum wall temperatures of the two loops are 443.9 °C and 446.5 °C, and the boiler can operate safely and stably.

Mathematical Modeling of Gas Hydrates Dissociation in Porous Media with Water-Ice Phase Transformations Using Differential Constrains

2D numerical modeling algorithms of multi-component, multi-phase filtration processes of mass transfer in frost-susceptible rocks using nonlinear partial differential equations are a valuable tool for problems of subsurface hydrodynamics considering the presence of free gas, free water, gas hydrates, ice formation and phase transitions. In this work, a previously developed one-dimensional numerical modeling approach is modified and 2D algorithms are formulated through means of the support-operators method (SOM) and presented for the entire area of the process extension. The SOM is used to generalize the method of finite difference for spatially irregular grids case. The approach is useful for objects where a lithological heterogeneity of rocks has a big influence on formation and accumulation of gas hydrates and therefore it allows to achieve a sufficiently good spatial approximation for numerical modeling of objects related to gas hydrates dissociation in porous media. The modeling approach presented here consistently applies the method of physical process splitting which allows to split the system into dissipative equation and hyperbolic unit. The governing variables were determined in flow areas of the hydrate equilibrium zone by applying the Gibbs phase rule. The problem of interaction of a vertical fault and horizontal formation containing gas hydrates was investigated and test calculations were done for understanding of influence of thermal effect of the fault on the formation fluid dynamic.

Research on Sediment Laden Flow Characteristics in Water Conveyance System

In the long-distance water conveyance channels or pipelines of sediment laden flow, due to the change of the flow discharge, there may be different levels of siltation condition, and regular dredging work needs to be carried out. If the water conveyance channels are an open system, it is easier to dredge, but if it is a pressurized pipeline system, dredging is more difficult. Some water delivery irrigation projects of sediment laden flow could not be promoted due to the unresolved problem of siltation. This paper takes a long-distance gravity flow pipeline system as the research object. The distribution branch pipe on the main pipeline is connected to the downstream reservoir for field irrigation. According to the pipe data, the one-dimensional full pipeline numerical model and the three-dimensional pipe calculation model were established respectively. The flow velocity calculation of main pipeline under the condition of simultaneous irrigation of different numbers of distribution branch pipes, and the distribution of different velocities in the pipe was obtained. At the same time, the three-dimensional unsteady flow analysis was carried out to analyse the flow characteristics and siltation patterns in the main pipeline under different flow discharge. It is helpful to predict the silt phenomenon that may exist in the water pipeline in advance by calculation, and give technical suggestions for the pipeline design.

Effect of ambient temperature, metabolic heat and clothing insulation on the required external active heating for the survival of humans exposed to sub-zero temperatures

Active heating in extremely cold weather clothing would be useful to save the life of an injured or sick person due to low metabolic rate. A fully dressed thermal manikin is useful in evaluating the performance of the active heating ensemble. The thermal manikin tests are time-consuming and could be done only after making the complete ensemble. An experiment that is designed to evaluate the performance of an active heating fabric fixed to a set of layers of extreme cold climate clothing using a guarded hot plate instrument would save a lot of time as it skips the processes of garmenting and subsequent evaluation on the thermal manikin. In this work, a guarded hot plate placed inside a cold chamber is used to investigate the external heating required for the prolonged comfort of the wearer at various sub-zero ambient temperatures, clothing insulation and metabolic heat. A plain woven active heating fabric sandwiched between a knitted fabric and nonwoven of different insulation/thickness is used to perform experiments. The external heat required to keep the test plate (representing the human skin) at 307 ± 1 K (34 ± 1 °C) is measured at different experimental conditions. Further, a one-dimensional numerical model based on coupled conduction–radiation heat transfer with heat generation was developed and validated with experimental results. The experimental temperature profiles match well with the numerical temperature profiles at different locations, justifying the numerical methodology adopted in this work. This suggests that the developed numerical model would also be useful to estimate the required active heating as per the wearer’s requirement and an available power source. Both the experimental and numerical results suggest that the external active heating required to maintain test plate (skin) temperatures within the human skin comfortable range is a function of ambient temperature, metabolic heat and clothing (nonwoven) insulation.

An efficient model for simulation of temperature field of steel-concrete composite beam bridges

Thermal performance between steel and concrete differs significantly and leads to the complexity of the temperature field and effect of steel–concrete composite bridges. Refined numerical models and accurately calibrated thermal parameters can solve the transient analysis of complex temperature fields. However, the method is inefficient and difficult to apply to analyzing massive historical data in calculating design temperature loads. In this paper, a vertical discrete and dimensionality-reduced model of the steel–concrete composite bridge is deduced and established for rapid temperature load calculation. A MATLAB-based state equation solving method is proposed to implement the one-dimensional efficient numerical model. Besides, an outdoor sunshine experiment is conducted to study the temperature field. The outdoor sunshine experiment measurements and refined model simulations verify the efficient numerical model. The computational efficiency of the efficient model is nearly 1000 times higher than that of the refined model, achieving rapid calculation of the composite bridge temperature field. The efficient thermal model proposed in this paper provides a powerful tool for analyzing the temperature field and effect and calculating the design temperature load of the composite bridge.

Fully Implicit Form of Differential Quadrature Method for Multi-Species Solute Transport in Porous Media

Solute transport problems, including sequential multi-species transport phenomena, frequently occur in soil systems. The goal of this paper is to present a novel one-dimensional numerical model with a fully implicit form of differential quadrature method for solving multi-species solute transport equations. The analytical results of three multi-species solute dispersion problems with three- and four-chain members are used to analyse the developed model. Simultaneously, the outcomes of the developed model are compared with the performance of the fully implicit fourth-order finite difference method. Finally, the accuracy of the established model is discussed and evaluated. According to the numerical experiments, the derived model is very useful and widely applicable.

Validation of an Empirical Model with Risk Assessment Functionalities to Simulate and Evaluate the Tailings Dam Failure in Brumadinho

The failure of tailings dams causes ecological damage and economic loss and can cause casualties. The simulation of the tailings’ spill path in the event of tailings dam failures (TDFs) can mitigate the risk by the provision of spatial information for disaster prevention and preparedness. In order to close the gap between basic one-dimensional spill-path routing models and complex numerical models, this paper examines an empirical model based on the freely available Laharz model. The model incorporates a tailings-specific planimetric area regression from the literature to describe the spatial extent of tailings flows based on the released volume. By providing information about affected residents and infrastructure, such a model can be used for preliminary risk evaluation. The model was validated against the TDF in Brumadinho (2019) and reached hit rates of over 80%, critical success indices of approximately 60% and false alarm ratios of roughly 30%. The latter is particularly evident in the overestimation of the lower part of the tailings flow. The risk assessment identified 120 affected residents, 117 destroyed buildings (109 reported) and several kilometres of affected roads (1.9 km) and railway (2.75 km). However, the OpenStreetMap-based part of the risk assessment inherits some uncertainties to be investigated in the future.

A novel mechanism for thermal management at the cold side of a pulsed two-stage thermoelectric micro-cooler with different PCM heat sink shapes

A new mechanism for thermal management at the cold side of a pulsed two-stage thermoelectric micro-cooler (Two-stage μTEC) is presented. The Two-stage μTEC operates under different electric current values at each stage and uses a phase change material (PCM) in different heat sink shapes for temperature control in the cold junction. A geometric factor γ is defined for designing an optimal heat sink based on reducing the cross-sectional area of the second stage thermoelements. The aim is to save the amount of PCM used and keep the cold side temperature (Tc) constant for as long as possible. This thermoelectric device is proposed to treat skin diseases and is suitable for use in cryomassage. A one-dimensional numerical model is considered in the system’s heat transfer, and cooling by natural convection on the hot side is considered. PCM is used as a cooling substance because it can absorb large amounts of latent heat at a nearly constant temperature. The influence of the electric current pulse and the γ geometric relationship on the micro-cooler are analyzed to determine the optimum operating values that allow a constant temperature of 243 K to be reached in the cold junction. The temperature of the cold side is kept constant by using different electric currents in each stage for the geometric factor γ=4 during Δtpulse=95.7s. On the other hand, the optimization of the heat sink, the geometric factor

The role of creep in geopressure development

This study developed a one-dimensional numerical model of sedimentation and compaction based on the equivalent isochrone framework to investigate the impact of creep on geopressure during burial. In this framework, the void ratio is a function of effective stress and strain rate; the change in void ratio is the same with each order of magnitude decrease in strain rate at a constant effective stress. We simulated lower void ratio and higher overpressure when creep was included compared to cases where no creep was present and void ratio is only a function of effective stress. Creep causes apparent overconsolidation. The apparent overconsolidation ratio is used to quantify the magnitude of creep; this is the vertical distance from the normal compression curve in a void ratio v. effective stress plot. The magnitude of creep depends on the loading rate, and increases with depth at sites with low sedimentation rates. These findings bridge the gap between laboratory and field observations on rock compression behaviours. For example, it provides one explanation why laboratory-derived compression curves have a higher void ratio at a given effective stress. In addition, it suggests under what conditions the rock will behave elastically. Thematic collection: This article is part of the Geopressure collection available at: https://www.lyellcollection.org/cc/geopressure

Factors affecting the cathode/electrolyte interfacial pH change during water reduction: A simulation study

Water reduction reaction to produce hydrogen has been extensively studied in electrochemical and photoelectrochemical water splitting. The cathode/electrolyte interfacial pH change (ΔpH) during water reduction has a non-negligible impact on the activity and stability. However, there are difficulties in experimentally detecting pH change of the localized solution close to the electrode. Herein, a one-dimensional finite element numerical computational model is proposed to simulate the water reduction process. Potential, bulk pH, temperature, and buffer species are considered as variable factors to investigate their effects on interfacial pH change. The interfacial ΔpH could decrease to a large extent as the bulk pH increases. The ΔpH in the whole diffusion layer would decrease when buffer species is introduced. Whereas, the impact of temperature is less significant. According to the simulation results, raising the bulk pH and introducing buffer species can keep the interfacial pH change within 1 unit, which is an efficient route to stabilize water electrolysis.

A one-dimensional modelling methodology of printed circuit heat exchangers for steady, off-design and transient feasibility in a supercritical CO[formula omitted] power block

As the most widely-used heaters and recuperators in supercritical CO2 (sCO2) power cycles, the Printed Circuit Heat Exchangers (PCHEs) have received considerable interest to investigate their steady, off-design and transient behaviour mainly by simulations, which remains a challenging task accounting for various application scenarios. After an introduction and comparison about the state-of-art PCHEs numerical approaches, this paper presents a generic one-dimensional (1D) numerical PCHE modelling methodology featured by (1) ability fulfilling the steady, off-design and transient simulation; (2) precise capture of the non-linear local variations in the thermo-physical properties of sCO2; (3) feasibility for a wide range of flow patterns, working fluids, and operation conditions. The off-design prediction via the proposed 1D PCHE modelling methodology is justified by validating its Modelica implementation against previous literature. Later, one optimal Nusselt correlation out of five candidates is identified to reproduce two typical transient power cycle operations, i.e., ‘shutdown and startup’ and ‘ramp-up’ scenario. These scenarios are validated by experiments at the Pinjarra Hills High Pressure Loop (PHPL) of the University of Queensland. The proposed 1D PCHE model successfully follows the changing rules of the time-varying temperature of both hot- and cold-side working fluids, though a slight time lag is observed between the simulation and experiment, which is caused by the modelling assumptions. In general, the presented 1D PCHE modelling methodology is credited for the steady, part-load and transient performance evaluation of sCO2 power blocks and the corresponding control strategy development. Several crucial future work is summarized for guidance.