Comprehensive Simulation Model Research Articles

Concentrating photovoltaic/thermal collectors coupled with an anaerobic digestion process: Dynamic simulation and energy and economic analysis

This work presents a dynamic analysis of an anaerobic digestion plant, in which concentrating photovoltaic/thermal collectors are used to match a part of both heating and power demand of the process. The system is supplied by the organic fraction of municipal solid waste. The system also includes a thermal storage tank and an auxiliary heating system. An up-grade section is also included, to produce biomethane, suitable for injection into the natural gas pipeline network.For such hybrid solar-biomass system, a comprehensive simulation model was developed in MATLAB®, calculating the time-dependent production of biomethane as a function of the operating temperature within the digester. The model, based on differential equations and thermal balances, accounts for both thermal and biological phenomena occurring within the process, taking into consideration the geometrical and structural characteristics of the system. The consistent Anaerobic Digestion Model 1 is used to model the biological process, evaluating the biogas production as a function of a series of operating variables: the digester operating temperature, mass flowrate and temperature of the hot water entering the digester, ambient temperature, mass flowrate and composition of the organic waste in input. The model also calculates the electric consumption of the upgrading process, used to convert the biogas into biomethane. Such model was integrated into the simulation platform of the overall plant, developed in TRNSYS, evaluating the energy, environmental and economic performance of the entire system. A case study is presented, showing the dynamic performance of the system under evaluation: for such case, a primary energy saving of 24% was found, with respect to a conventional digester; around 20% of the overall thermal energy demand is met by solar energy; finally, a promising payback time of about 3 years was estimated.

Bike-Repositioning Using Volunteers: Crowd Sourcing with Choice Restriction

Motivated by the Bike Angels Program in New York's Citi Bike and Boston's Blue Bikes, we study the use of (registered) volunteers to re-position empty bikes for riders in a bike sharing system. We propose a method that can be used to deploy the volunteers in the system, based on the real time distribution of the bikes in different stations. To account for (random) route demand in the network, we solve a related transshipment network design model and construct a sparse structure to restrict the re-balancing activities of the volunteers (concentrating re-balancing activities on essential routes). We also develop a comprehensive simulation model using a threshold-based policy to deploy the volunteers in real time, to test the effect of choice restriction on volunteers (suitably deployed) to re-position bikes. We use the Hubway system in Boston (with 60 stations) to demonstrate that using a sparse structure to concentrate the re-balancing activities of the volunteers, instead of allowing all admissible flows in the system (as in current practice), can reduce the number of re-balancing moves by a huge amount, losing only a small proportion of demand satisfied.

A Digital Displacement Hydrostatic Wind-turbine Transmission

In 1984 a hydrostatic wind-turbine transmission with ‘secondary control’ was proposed by Stephen Salter using the, then only conceptual, Digital Displacement® (DD) principle for controlling the flow of the primary, rotor-driven, ring-cam pump. This transmission ‘could achieve the correct ratio of tip-speed to wind-speed in conjunction with true synchronous generation’.
 In the following years DD machines were progressively developed. To start with they were relatively small in capacity but the power ratings were systematically increased, until it seemed that a high-power hydrostatic wind-turbine transmission might indeed be feasible. In 2006, Artemis Intelligent Power (Artemis), a company that had been formed from Salter's original university team, began working on a megawatt-scale, hydrostatic, wind-turbine transmission based on new pump and motor designs. In 2011 Artemis completed a 1.5 MW transmission and dynamometer test-rig. This was one of the largest hydraulic transmissions ever made and, with a shaft-to-shaft efficiency of 93%, one of the most efficient. Using secondary control to respond rapidly to gusting wind and to instantaneous grid faults, it was also the most controllable. This paper discusses the design of the transmission and test-rig and presents the results of steady-state efficiency tests. Subsequent papers will describe systematic experimental work to account for the various energy losses and to develop a comprehensive simulation model of the DD wind-transmission.

A research on regenerative braking energy recovery: A case of Addis Ababa light rail transit

In Ethiopia, strong dependency on hydropower presents risks to energy security issues due to the vulnerability of the country to recurrent and prolonged droughts. The problem is also linked to trade-off in drinking, industrial and agricultural water needs; the impact of silt and sedimentation on lakes and reservoirs; and disputes over water resources. The Ethiopian railway industry is at the core of all these energy issues, for example the new preference for the supply of energy for traction purposes has been given to hydropower. However, power cuts continue, leading to uncertainty. In addition, separate railway repair units are also starving for their energy demands. This clearly has negative effect on the overall performance of the railway industry. Furthermore, as energy requirements rise, railways will have to fight for the scarce energy with other priority sectors. Therefore, energy is the last big issue to be overcome by industry in the coming decades. In this regard, regenerative energy could be one of the promising energy source to maximize energy efficiency of the railway. Consequently, this paper has assessed and examined the main factors that influence regenerative braking energy recovery as well as evaluated regenerative energy potential of Addis Ababa light rail transit. To this end, a mathematical model, consisting of a series of empirical formulas have been developed and detail analysis has been performed. To verify the empirical formulas and mathematical models a comprehensive simulation model of Addis Ababa light rail transit system using Mathlab/Simulink has been developed. Consequently, the simulation results confirmed the consistency of the proposed mathematical model. Finally, based on different scenarios; this paper concluded that, it is possible to save up to 32% of the electrical energy for the light rail transit network in Addis Ababa (AALRT).

Modelling of polymer optical fiber-based solar concentrators

A comprehensive model for the theoretical simulation of luminescent solar concentrators (LSCs) has been developed and examined. It can simulate the interdependent effects of multiple dopants having two main electronic energy states, which are incorporated simultaneously into the fiber core, as well as the effect of the cladding. The available experimental results appear to confirm the accuracy of the model, which is a valuable tool for gaining insight into the behavior of LSC prototypes, since it may guide the designers at the early stages of optimization processes.

Hydrogen-rich syngas production via integrated configuration of pyrolysis and air gasification processes of various algal biomass: Process simulation and evaluation using Aspen Plus software

In the present study, hydrogen-rich syngas production via integrated configuration of pyrolysis and air gasification processes of different algal biomass is investigated at relevant industrial condition. A comprehensive steady state equilibrium simulation model is developed using Aspen Plus software, to investigate and evaluate the performance of pyrolysis and air gasification processes of different algal biomass (Algal waste, Chlorella vulgaris, Rhizoclonium sp and Spirogyra). The model can be used as a predictive tool for optimization of the gasifier performance. The developed process consists of three general stages including biomass drying, pyrolysis and gasification. The model validation using reported experimental results for pyrolysis of algal biomass indicated that the predicted results are in good agreement with experimental data. The effect of various operational parameters, such as gasifier temperature, gasifier pressure and air flow rate on the gas product composition and H2/CO was investigated by sensitivity analysis of parameters. The achieved optimal operating condition to maximize the hydrogen and carbon monoxide production as the desirable products were as follows: gasifier temperature of 600 °C, gasifier pressure of 1 atm and air flow rate of 0.01 m3/h.

Simulation of an Industrial-Scale Reactive Liquid–Liquid Extraction Tower Using Polar PC-SAFT Toward Understanding and Improving the Hydrolysis of Triglycerides

A comprehensive model for simulation and optimization of industrial-scale splitting towers that is able to predict the yield for the hydrolysis of bio-based triglyceride feedstocks is presented in this work. This model includes a variable glycerol equilibrium ratio, which is a function of the composition and temperature and is calculated using the polar version of the perturbed chain statistical association fluid theory (PC-SAFT), the autocatalytic effect of fatty acids in hydrolysis, and isomerization of poly-unsaturated fatty acids. Model validation is performed using process data from three real-life splitting towers covering four feedstock types, i.e., tallow, rapeseed oil, palm oil, and palm fatty acid distillate. Due to the composition gradients of the organic phase throughout the tower, it is crucial to properly account for the changes in the glycerol equilibrium ratio. The importance of feedstock flow rate, water/oil ratio, and temperature profile throughout the tower is analyzed and confirmed by sensitivity analysis. Our results show that modifying the temperature profile may shift the reaction equilibrium toward the fatty acid product. This knowledge is crucial for improving the energy and resource efficiency of fatty acid production, thereby improving its economic and environmental sustainability.

Modeling and Simulation of PGSPAD-Based Silicon Photomultipliers

This article presents and develops a novel comprehensive simulation model for perimeter gated single-photon avalanche diode-based silicon photomultipliers (PGSPAD SiPMs). A PGSPAD is a modification of single-photon avalanche diodes (SPADs) that contains a third terminal to mitigate perimeter edge breakdown. It does this without excessively enlarging the device area. The applied gate voltage modulates the dynamic range, breakdown voltage, and dark current characteristics. The proposed PGSPAD SiPM model correctly mimics the current–voltage transfer function and the avalanche-quench process of the SiPM detector and is verified by the experimental measurements of a PGSPAD SiPM fabricated in a commercial 0.5- $\mu \text{m}$ CMOS process. The model includes the dark current of the PGSPAD device. This was not included in previous SiPM models. The effect of the number of triggered microcells versus the total number of microcells and the impact of different parameters on the PGSPAD SiPM performance with added gate terminal are evaluated. The photon–electron spectrum with the effect of an extra gate terminal has been studied. Simulation results show very good agreement with experimental measurements.

A strategy for advanced biofuel production and emission utilization from macroalgal biorefinery using superstructure optimization

The rapid increase in the emission of greenhouse gases over the years signifies the urgent need to explore fuels that emit less CO2, such as biofuels. CO2 emission can be reduced further by productively utilizing the CO2 generated during industrial processes. In this study, we have proposed a strategy to produce advanced biofuel from macroalgal biorefinery and to utilize all waste streams from processing into value-added products. To achieve this aim, we developed a novel superstructure for biorefinery process synthesis based on Saccharina japonica (macroalgae) to determine an optimal design of the biorefinery. Process integration was performed to utilize direct greenhouse gas emissions from the biorefinery and to reduce pollutant emissions and freshwater consumption. A techno-economic and environmental mixed-integer non-linear model was formulated based on this superstructure. To achieve the economic and environmental goals, two objective functions were studied: maximization of the net present value and minimization of CO2 emissions. A comprehensive sensitivity and Monte Carlo simulation model was formulated to evaluate the effects of variation in key model parameters on the overall economics and to perform the risk assessment, respectively. The minimum ethanol selling price range for the integrated design was found to be USD 0.36–0.56/L. The optimal design achieved a 90% reduction in CO2 emissions, from 4.86 kg/s to 0.42 kg/s, as well as a 38.6% reduction in freshwater consumption. The risk of the optimal design was found to be 20–44% on the basis of the minimum selling price of ethanol. Therefore, this design can be implemented as an economically and environmentally feasible approach to biofuel production.

A new Simulation-Based Approach in the Design of Manufacturing Systems and Real-Time Decision Making

Abstract The principles and tools made available by the Industry 4.0, smart factories, or the Internet of Things (IoT), along with the adoption of more comprehensive simulation models, can significantly help the industry to face the current, huge external and internal challenges. This paper presents a new simulation-based approach to support decision making in the design and operational management of manufacturing systems. This approach is used to evaluate different layouts and resources allocation, and help managing operations, by integrating a simulation software with real-time data collected from the production assets through an IoT platform. The developed methodology uses a digital representation of the real production system (that may be viewed as a form of a digital twin) to assess different production scenarios. A set of key performance indicators (e.g. productivity) provided by the simulation can be used by the Manufacturing Execution System (MES) to generate production schedules. The developed approach was implemented and assessed in a real case study, showing its robustness and application potential. Its extension to other industrial contexts and sectors seems, therefore, quite promising.

Heating Simulation of a Li-Ion Battery Cylindrical Cell and Module with Consideration of Gas Ejection

We have developed a comprehensive 3D heating test simulation model of a Li-ion battery cylindrical cell and module, taking gas flow and combustion into account. The model is based on the equivalent circuit model and includes not only the heating of a cell (joule heating and thermal decomposition) but also gas ejection flow from the cell and combustion. First, the validation of the cell model for surface temperature and voltage profiles was conducted for a commercial 18650-type cell with an actual heating experiment. Subsequently, a simulation model of the battery module, composed of total 98 cells heated by a burner, was developed, and the behavior of thermal runaway was evaluated. This model makes it possible to evaluate the events that occur from the start of heating the battery module to gas ejection, including housing melting, separator shutdown, and the propagation of thermal decomposition reactions between the cells, and might be a helpful tool for designing battery cells and modules.

Electrical and optical analysis of organic light-emitting diode through simulation study with an EQE over 34%

The comprehensive simulation model has been demonstrated to study the electrical and optical properties of dual active layer organic light-emitting diode (OLED), and the device structure we used is as follows: ITO/PEDOT/TAPC/MADN/BEPP/TPBi/Al. The device current density obtained of 25 mA/cm2 and the maximum power density with a peak value of 125 mW/cm2 is measured at the knee voltage of 5 V. In the best device performance for an OLED with an external quantum efficiency (EQE) of 34%, a maximum brightness of up to 105cd/m2, current density has a maximum value of 47.5 cd/A and CIE coordinates of (0.47, 0.51). The results obtained from the modeling maximum light outcoupled efficiency (OCE) about 26.47% in the isotropic optical channel. Besides, luminance and current efficiency characteristics are measured with respect to current density. Therefore, it is believed that the use of a double emission layer for an OLED has excellent potential for the development of a high-performance device.

Load carrying capacity of a novel magnetic-liquid double suspension fixed pad thrust bearing

Purpose Proposing a new type of water-lubricated thrust bearing meets the load-bearing requirements of high-power shaft-less rim driven thrusters. Design/methodology/approach The designs were tested by establishing a bearing thermal-fluid-magnetic comprehensive simulation model and developing bearing fluid film force and magnetic simulation. Lubrication performance tests were carried out on the bearing test rig. Findings The Halbach array of magnet blocks is able to reach the maximum magnetic force. The material of sheath can help increase the magnetism. The magnetism is able to reduce wear during low-speed and the start-stop phase, while the eddy current loss at high speeds will lead to a decrease in magnetic force. The experiment found that the bearing was more stable at low speeds and would not demagnetize due to the temperature rise, but it is necessary to pay attention to the running stability at high speeds to prevent rubbing and impact. Originality/value An innovative combination of hydrodynamic pressure and permanent magnetic repulsion was observed to form a magnetic-liquid double suspension bearing with large bearing capacity. Peer review The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-08-2020-0295

A comprehensive study on thermal modeling of SLM process under conduction mode using FEM

Selective laser melting (SLM) has emerged as one of the leading additive manufacturing (AM) processes for the fabrication of complex metallic components, due to its capability to achieve high quality at acceptable times. However, due to the complexity of physical phenomena occurring during SLM, such as heat transfer and phase transformations, laser absorption, molten metal flow, and moving interfaces, it is still necessary to conduct research in order to achieve a deeper understanding of the process and improve it. In the present work, a comprehensive simulation model for the study of conduction mode single-track SLM process of 316L stainless steel is presented. This model incorporates temperature and phase-dependent material properties for both powder bed and substrate, detailed calculation of the absorption coefficient, and temperature-dependent boundary conditions. The simulation results are in excellent agreement with experimental findings, regarding the morphology and dimensions of melt pool under various process conditions. Moreover, with the proposed model, analysis of power losses as well as cooling and heating rates is conducted, identifying the characteristics of SLM process and providing valuable insights for its optimization.

LBfoam: An open-source software package for the simulation of foaming using the Lattice Boltzmann Method

This paper presents a 2D/3D Free Surface Lattice Boltzmann Method simulation package called LBfoam for the simulation of foaming processes. The model incorporates the essential physics of foaming phenomena: gas diffusion into nucleated bubbles, bubble dynamics and coalescence, surface tension, the stabilizing disjoining pressure between bubbles, and Newtonian and non-Newtonian rheological models. The software can simulate the growth and interaction of bubbles, and predict final foam structures. The implementation is based on the Palabos library (in C++), which enables large-scale parallel simulations. The software is freely available under the GNU Affero General Public License version 3. Program summaryProgram title:LBfoamCPC Library link to program files:https://doi.org/10.17632/zgxfx6xk4t.1Developer’s repository link:https://github.com/mehdiataei/LBfoamCode Ocean capsule:https://codeocean.com/capsule/8471850Licensing provisions: Affero General Public License (AGPL) v3Programming language: C++Nature of problem: Foaming is a process by which nucleated gas bubbles expand in liquid media such as a molten polymer or a liquid metal to create a cellular structure, which has many applications in industries such as automotive, aerospace, furniture and packaging. This comprehensive simulation model for foaming allows industry to determine optimum foaming conditions more quickly and more accurately, while providing a platform for researchers to study phenomena observed in foaming.Solution method: LBfoam implements a 2D/3D Free Surface Lattice Boltzmann Method (FSLBM) solver that can simulate various foaming phenomena. The model couples the Navier–Stokes and the advection–diffusion equations, and incorporates all essential aspects of foaming such as the growth and interaction of bubbles. All routines are written in C++ and are parallelized using the Message Passing Interface (MPI) library.

State transients in storage systems for energy fluids

As the world adopts cleaner and/or renewable energy sources, energy fluids (e.g. hydrogen, ammonia, liquefied natural gas, liquid air, etc.), their transport, and their storage are becoming increasingly important. Feed/product flows, flashing recirculation flows, evaporation, condensation, heat leak, and boil-off gas removal lead to state transients in their storage systems with significant mechanical, safety, environmental, and efficiency implications. This study presents a comprehensive simulation model based on a novel stretchable and spatially moving grid for predicting spatiotemporal transients in a cylindrical storage tank. The model is fully validated under limiting scenarios and then applied to several industrial storage terminals involving liquid hydrogen, liquid air, and liquefied natural gas. In addition to its novel grid formulation, the model offers significant advances over simpler lumped-parameter and complex fluid dynamics models in the literature and commercial process simulators. It gives useful practical insights into boil-off gas removal, pressure management, evaporation/condensation, and compressor sizing/operation.

Experimental and Numerical Study of Wax Deposition in a Laboratory-Scale Pipe Section under Well-Controlled Conditions

Detailed local and averaged measurements of wax deposition in an annular pipe section were conducted and combined with a comprehensive simulation model. The objective of the study was to contribute...

Mathematical Modelling of Gimballed Tilt-Rotors for Real-Time Flight Simulation

This paper introduces a novel gimballed rotor mathematical model for real-time flight simulation of tilt-rotor aircraft and other vertical take-off and landing (VTOL) concepts, which improves the previous version of a multi-purpose rotor mathematical model developed by ZHAW and Politecnico di Torino as part of a comprehensive flight simulation model of a tilt-rotor aircraft currently implemented in the Research and Didactics Simulator of ZHAW and used for research activities such as handling qualities studies and flight control systems development. In the novel model, a new formulation of the flapping dynamics is indroduced to account for the gimballed rotor and better suit current tilt-rotor designs (XV-15, V-22, AW-609). This paper describes the mathematical model and provides a generic formulation as well as a specific one for 3-blades proprotors. The method expresses the gimbal attitude but also considers the variation of each blade’s flapping due to the elasticity of the blades, so that the rotor coning angle can be represented. A validation of the mathematical model is performed against the available literature on the XV-15 Tilt-rotor aircraft and a comparison between the previous model is provided to show the improvements achieved. The results show a good correlation between the model and the reference data and the registered performance allow real-time flight simulation with pilot and hardware in the loop.

Optimization method of switch jumper setting based on strategies for reducing conductive interference in railway

Traction current can to impose conductive interference on the railway signalling system, which is also known as unbalanced traction current interference. In the station turnout section, the traction current may cause obvious interference on both receiving apparatus of track circuit and cab signalling apparatus due to the installation of multi-jumpers, wing rails, and insulated joints inside the turnout. This paper analyzes the above structural characteristics of turnouts in depth. By establishing a comprehensive simulation model of one-transmitter and two-receiver track circuit in turnout section and simulating the complete return current path along with traction network–locomotive–rails, the mechanism of traction current conductive interference in the turnout section is then illustrated, using Multisim and MATLAB/Simulink simulation platform. Finally, based on the Analytic Hierarchy Process (AHP), an optimization method of switch jumper setting is studied. The simulation results show that the conductive interference in the turnout section mainly involves two factors: The inherent turnout structure definitely results in different impedance of two rails, and the inductive cab signal is partly bypassed in the turnout center (nose rail). Especially, conductive interference magnitude depends on the jumper location. Therefore, in engineering practice, it is feasible to reduce the interference to a certain degree by reasonable settings of the switch jumper.

Multiscale computational fluid dynamics modeling and reactor design of plasma-enhanced atomic layer deposition

Plasma-enhanced atomic layer deposition (PEALD) is one of the most widely adopted deposition methods in the semiconductor industry. It is chosen largely due to its superior ability to deliver ultra-conformal dielectric thin-films with high aspect-ratio surface structures, which are encountered more and more often in the novel design of metal-oxide-semiconductor field-effect transistors (MOSFETs) in the NAND (Not-And)-type flash memory devices. Compared with the traditional thermal ALD method, PEALD allows for lower operating temperature and speeds up the deposition process with the involvement of plasma species. Despite its popularity, the development of PEALD operation policies remains a complicated and expensive task, which motivates the construction of an accurate and comprehensive simulation model. While existing models have described the individual or partially coupled domains, none of these models has captured all three domains in the PEALD process: surface reaction, macroscopic gas transport, and plasma generation. In this work, a comprehensive multiscale computational fluid dynamics (CFD) model is developed for a remote PEALD reactor used in the deposition of HfO2 thin-films. First, a previously developed kinetic Monte-Carlo (kMC) model is adapted for the multiscale simulation to describe the surface reactions. Then, two macroscopic models, specifically tailored for the remote plasma reactor, are formulated to describe the dynamic behaviors of the plasma generation and bulk species transport domains, respectively. Additionally, an integrated message passing interface (MPI) scheme is built to couple and resolve the communication between different scales in the model. The model results are then validated with experimental data and an automated workflow is established for model calculations without human intervention. Finally, a set of baseline operating conditions derived from the model simulation results is proposed to guarantee the production of high-quality thin-films.