Simple Simulation Model Research Articles

Regularization of the Logarithmic Mean for Robust Numerical Simulation

To calculate the driving temperature difference between the hot and the cold side of a heat exchanger, the use of the logarithmic mean temperature difference is common practice. To provide high robustness in complex dynamic system models, a robust formulation of the logarithmic mean (logmean) function becomes vital. As the analytic definition of the logmean function naturally comes along with singularities and limitations for specific input conditions, it is essential to extend and modify it for heat exchanger modeling. This paper proposes how the logmean function can be extended to be valid in all four quadrants of the Cartesian coordinate system and how to bridge the resulting definition gaps. Special focus lies on the robust formulation in such a way that it can be easily handled by numerical solvers. This includes the numerical approximation of the logmean by use of its integral form by implicit ODE solvers with variable step width. Furthermore a way is presented to flatten the naturally steep gradients in the vicinity of the x- and y-axes without manipulating the function in the uncritical regions. All the modifications on the logmean are finally applied in a simple simulation model written in the object-oriented programming language Modelica to examine the robustness of the approach.

Simplified test program for hydrodynamic CFD simulations of wind-powered cargo ships

Four practical simplifications for modeling the hydrodynamic properties of a wind-powered cargo ship with CFD and a route simulation model is evaluated. We first test how much the drift-induced hull forces are dependent on Froude number, model scale, and heel angle. Then, we test the mathematical assumptions in the MMG maneuvering model, with particular focus on the rudder resistance as a function of drift angle, rudder angle and propeller thrust. The overall goal is to see if the hydrodynamics of the ship can be modeled with both a simplified CFD setup and a simplified route simulation model. For each tested simplification, we find that they can be used under specific conditions, but not always. We give specific recommendations based on our results. To improve the predicted rudder resistance from the MMG model, we suggest a slightly modified model based on classical lifting line theory. All the numerical experiments are performed using the open source CFD library OpenFOAM. The simulation setup is described, including details of the mesh design. The numerical uncertainty is quantified, and the simulations are compared against benchmark experiments.

Study of ion cyclotron range of frequencies heating characteristics in deuterium plasma in the Large Helical Device

The characteristics of ion cyclotron range of frequencies (ICRF) minority ion heating with a hydrogen minority and deuterium majority plasma were studied by ICRF modulation injection experiments in the Large Helical Device (LHD). In recent experiments with deuterium plasma, no significant increase in the neutron emission rate due to ICRF second harmonic deuteron heating was observed. Therefore, in this study, the neutron emission rate was used to refer to the information regarding the thermal ion component. Like the results of the observations of the heating efficiencies at various minority proton ratios, the experimental results showed good agreement with the simple model simulation of ICRF wave absorption. During these experiments, the accelerated minority hydrogen ions were observed by neutral particle analyzers. The counting rates of the energetic particles were higher in the lines of sight passing through the helical ripple than across the magnetic axis, and the counting rate decreased as the minority hydrogen ion ratio increased. The dependence of the minority hydrogen ion ratio on the density of the energetic ions was consistent with the experimentally observed heating efficiencies and simulations. The heating efficiency of ICRF minority ion heating could be well explained by simple model simulation in the LHD deuterium experiment.

Evaluation of the effect of radioactivity to the environment in wooden houses within the evacuation area at Fukushima

The accident at Fukushima Daiichi Nuclear Power Plant caused radioactive materials to spread outside the plant. To limit exposure in the area, air dose rates have been measured. When the dose rate exceeded the acceptable upper bound, the area was decontaminated by stripping the soil and washing roads. Immediately after the accident, it was not clear how much of an effect outdoor contamination had on dose rates inside houses. This paper discusses the effect of outdoor contamination on indoor air dose rates and factors influencing those dose rates based upon actual measurements taken of a wooden house standing on flat land in the area around the power plant. In addition, the effects of indoor horizontal distribution, height distribution, and decontamination are discussed using simple model simulations. As a result, the following was found, although within the range of air dose rates and location conditions measured in this study. Horizontal variation in indoor air dose rates decreases monotonically toward the centre of the house. Once decontamination has been performed, the overall dose rate decreases and variation becomes smaller. This trend is thought to be mainly due to expansion of a low-dose area. Vertical changes in indoor air dose rates are not straightforward. It is estimated that the dose rate decreases near the ground surface, then tends to increase going higher and finally decreases even higher up. This change in dose rates is thought to be due to the effect of radioactive materials permeating the soil. Recognition of the effects of these factors is important when estimating indoor air dose rates because indoor air dose rates are affected by the degree of decontamination, house size, and degree of penetration of radionuclides into the soil.

A new structure optimization method for forced air-cooling system based on the simplified multi-physics model

Energy storage systems equipped with lithium-ion batteries are susceptible to fire and explosion hazards, especially when such batteries are used to power electric vehicles. One of the most important reasons for these undesirable consequences is the lack of an effective battery thermal management system. In this regard, an optimization method for the forced air-cooling system is introduced based on a simplified multi-physics simulation model. The simplified multi-physics model consists an electro-thermal coupling model and a flow resistance network model. The accuracy of the simplified multi-physics model is verified by comparison with experimental results. Subsequently, the deflector angle and cell space in the forced air-cooling system are optimized, respectively, based on the simplified multi-physics model, via an exhaustive search method and a genetic algorithm. Finally, the verification platform for the forced air-cooling system is built. After the optimization of deflector angle and cell space, the maximum temperature and temperature difference are limited to 38℃ and 2℃, with a reduction of about 30% and 80%, with respect to the unoptimized version. The consistency between the simulated and measured maximum temperature further confirms the effectiveness of the structure optimization method. In that, the method proposed in this paper is of great significance to shorten the time of structural optimization for forced air-cooling systems.

Development of a Modelica-based simplified building model for district energy simulations

Urban Building Energy Simulation (UBES) is an efficient tool to investigate and subsequently reduce energy demand of urban areas. Nevertheless, UBES has always been a challenging task due the trade-off between accuracy, computational speed and parametrization. In order to reduce these computation and parameterization requirements, model reduction and simplification methods aim at representing building behaviour with an acceptable accuracy, but using less equations and input parameters. This paper presents the development and validation results of a simplified urban simulation model based on the ISO 13790 Standard and written in the Modelica language. The model describes the thermo-physical behaviour of buildings by means of an equivalent electric network consisting of five resistances and one capacitance. The validation of the model was carried out using four cases of the ANSI/ASHRAE Standard 140. In general, the model shows good accuracy and the validation provided values within the acceptable ranges.

Construction and application of a high precision 3D simulation model for geomechanics of the complex coal seam

The high-precision 3D simulation model for geomechanics of a complex coal seam is the necessary premise for the research on intelligent shearer and unmanned mining. However, at present, a simulation model for geomechanics of a complex coal seam generally has the problems of simplifying complex geological structures and low accuracy for structures. In order to meet the needs of a coal seam simulation model in the mining process of an intelligent shearer, it is necessary to optimize the simplified model of a coal seam. Therefore, based on a 3D simplified simulation model constructed with discrete element technology, the complex coal seam application plug-in was compiled with the help of an Application Program Interface. Moreover, according to the geological characteristics, new attributes were added to the structures to complete the construction of the model of a complex coal seam. Finally, the model was verified with laboratory experiments. The results showed that the high-precision 3D simulation model for geomechanics of a complex coal seam effectively improved the accuracy of the modeling. The real-time transmission and the real-time sharing of multi-source data were realized by considering the 3D simulation model for geomechanics of a complex coal seam as the core. Additionally, the purpose of the real-time sensing of the coal cutting state was achieved in order to lay the foundation for the realization of unmanned mining.

Investigation of Rotating Eddy Current Testing Simulation Using Simplified Model

To reduce the time of simulation for rotating Eddy current testing (RECT) technique, a simplified model without modeling probe was proposed previously. However, the applicability of the simplified simulation model was unknown. In this paper, the applicability of the simplified model for the RECT technique was investigated. The application condition of the simplified model was provided by comparing it with the results of the traditional simulation model. The simplified model was suitable for the study of cracks shorter than 70% size of the uniform Eddy current induced by the probe in a traditional model or experiment. The experiment was conducted to validate the simplified model. Moreover, using the simplified model, the effects of crack depth, orientation, and exciting frequency were studied. The deeper the crack depth was, the greater peak value of [Formula: see text] signal was. The crack angle was linear with the phase of signal. The exciting frequency affected the amplitude and phase of the signal at the same time.

A simplified model to assess the thermal performance of pavement solar collectors

The assessment of thermal performance and efficiency of the Pavement Solar Collector (PSC) systems is essential in designing such systems. In this paper, a simplified simulation model is developed to predict PSC's performance at the design stage. Due to its simplicity, accuracy, and extremely quick simulation run-time, the model output can be linked with other thermal models and renewable heat sources to apply real-time changes in the PSC systems and used in the automation of a PID-controller. The output results show good compatibility between the predicted and simulated data, where the relative error values for model parametrization and validation are less than 0.21% and 0.5%. In terms of computational cost, a yearly long-term performance run time of the present model was simply 3 s (without parametrization), 300,000 times faster than a FEM model for only one month. A systematic sensitivity analysis on different design parameters shows that the efficiency index increases with an increase in pipe spacing, pipe embedment depth, and flow rate, while it decreases with an increase in the asphalt thermal conductivity in the wintertime. Also, the variation of the heat transfer coefficient UA* and correlation parameter k in different PSC configurations was established.

Measurements and simulations of sung multiphonics on a trombone played by an artificial mouth

Playing a sung multiphonic on a brass instrument is a specialised technique in which the performer sounds one pitch through lip vibration while simultaneously singing a different pitch. The result is typically a complex sound in which several different pitches are audible. A full acoustical description of the sound generation process would include the mutual interactions of the two nonlinear flow valves (vocal folds and lips), the player’s windway resonances, and the resonances of the instrument. Velut et al. (JASA 2016) reported measurements of mouth pressure, pressure inside the mouthpiece, and radiated sound while a trombone player performed various sung multiphonics. A simplified time domain simulation model replacing vocal folds and windway by a sinusoidal source was partially validated. In the present work the human player has been replaced by an artificial mouth, allowing the “sung” mouth pressure to be provided either by a sinusoidally excited loudspeaker or a human singer. Results are broadly in agreement with those of Velut et al., and with time domain simulations using sinusoidal forcing in the mouth cavity.

Control of a service satellite during its mission on space debris removal from orbits with high inclination by implementation of an ion beam method

The largest population of space debris is observed in the low-Earth-orbit region with altitudes of 600–1000 km and inclinations of 80–100°. As follows from the predictive calculations, space debris removal from this region exactly is of the first priority. For this reason, our article discusses the problems of controlling the motion of service spacecraft – space debris object cluster when the space debris object is removed from a low orbit with high inclination. In the conceptual design of the spacecraft presented hereinafter, the electric propulsion system contains two electric propulsion thrusters of stationary plasma thruster type, each of which is mounted with the possibility of independent rotation respect to two mutually perpendicular directions. An ion beam injector forms an ion beam with 65 mN of thrust. Spacecraft motion control, including the thrust vector control, is provided by coordinated rotation of thrusters. For such concept, a strategy and an algorithm for controlling the motion of the spacecraft center of mass are proposed, which are based on the control of the spacecraft lateral and longitudinal motion that is understood as the control of the relative distance between the spacecraft and the space debris object. The strategy of spacecraft lateral motion control assumes that due to the thrusters' rotation the spacecraft should be displaced in such a way that the vector of the relative range between the spacecraft and the space debris object coincides with the direction of the transversal of the orbital coordinate system. For the practical implementation of the control, an algorithm has been developed for controlling the thrusters' rotation to create the required values of the spacecraft acceleration projections. The mathematical model includes the equations of motion of the spacecraft center of mass taking into account the aerodynamic deceleration. The solar panels' orientation to the Sun is provided by the spacecraft roll rotation relative to its longitudinal axis and turning the solar panels relative to their axis of rotation. The change in the ion beam momentum transfer is considered using a simple simulation model. Mathematical modeling was performed for the following parameters of the initial orbit: altitude: 800 km; eccentricity: 0.0005; and inclination: 900. For the proposed control algorithm, a range of possible thrust of a single thruster was 51–60 mN. The simulation results show that the proposed control can be used to remove space debris object from low orbits with high inclination, taking into account the roll spacecraft rotation to keep the solar panels’ orientation to the Sun.

SAFETY OF TRANSPORT OPERATIONS PERFORMED USING PALLET LOAD UNITS

During transport operations, even under normal operating conditions, the loading unit is subject to inertial forces, which may cause deformation of the unit, and in extreme cases, its disintegration. Stretch film wrapping is the most commonly used method of securing a load unit. This paper presents a new simplified simulation model of a class A load unit, with a layered structure, secured with stretch film. Between the layers of packaging, stick-slip friction was applied. A method of estimating the containment force was also proposed. This model can be used to pre-determine the number of film layers necessary to ensure load stability. Simulations can reduce the amount of film used and the number of stability tests performed experimentally.

Preparation and properties of a magnetorheological material used for pipeline and pressure vessel damage repair

Rapid repair of damaged pressure vessels and pipelines has always been a key technology in the study of safe storage and transportation. In this study, a magnetorheological material with curing and bonding abilities which can be combined with strong magnet as a rapid repair technology, was prepared by using surface modified carbonyl iron powder and epoxy resin. The reaction process and structure of the material were studied by infrared spectroscopy analysis, X-ray diffraction analysis, X-ray photoelectron spectroscopy and scanning electron microscopy. The optimum ratio was determined by orthogonal experiment, and mechanical experiments was designed to explore various mechanical properties of the material. The repair effect of the material was tested by a simplified simulation model, and the mechanism was also explained by numerical simulation.

Parametric optimisation of resistance temperature detector design using validated virtual prototyping approach

The study presents a successful approach used in development of new design of thermal product. The high uncertainty of dynamic thermofluid process analysis and the need of fast exploration of large dataset of design parameters require elaboration of this new approach. It combines detailed thermoCFD simulation models that are validated with physical experiments, with simplified thermostructural simulation models. The need for such an approach is predetermined by the request for fast processing of big data with certain level of accuracy and detail. The approach is demonstrated by a case study of resistance temperature detector design development.

Modelling the hydrological responses of green roofs under different substrate designs and rainfall characteristics using a simple water balance model

In spite of many well-known benefits of green roofs, their widespread adoption as source control measures in urban stormwater management requires the use of adequate modelling tools. The purpose of this study was to develop a simple water balance model for green roof runoff simulation based on conceptual hydrological processes and integrated into green roof designs. The model was calibrated and validated with a pilot experimental dataset that included various green roof configurations. The validated model was applied to simulate the hydrological responses of green roofs under different substrate designs and rainfall characteristics. Results showed that the model Nash-Suttcliffe efficiency (NSE) values under calibration and validation period ranged from 0.933 to 0.982, and the volume errors of relative percentage difference (RPD) varied from −1.45% to 5.35%, which indicated the simulated runoff processes of green roofs were satisfactorily accurate. The sensitivity analysis of parameters (e.g., increased parameters by 50%) showed the most sensitive parameter for simulating green roof runoff was the initial substrate water content, which changed by −74.5% for runoff volume and 58.5% for time to runoff. For a 50% increase in the saturated substrate hydraulic conductivity, it increased runoff volume by 60.2%; as well as the substrate depth increased runoff volume by 56.5% and changed time to runoff by −46.3%. The simulated hydrograph indicated that decreasing the saturated substrate hydraulic conductivity distinctly delayed time to runoff and increased runoff retention. Similarly, the runoff rate declined and runoff generation time was delayed with an increase in the substrate depths. Runoff retention percentages of the green roofs declined as rainfall depths increased. With rainfall intensity decreasing, mean time to runoff of the green roofs significantly increased from 30.0 min to 113.3 min. Runoff detention effects of green roofs were distinctly enhanced with the peak rainfall intensity delayed. This study provided a simple modelling tool for simulating hydrological responses of green roofs under a wide set of substrate characteristics and rainfall conditions in order to guide green roof design.

JUE Insight: The effect of new market-rate housing construction on the low-income housing market

I illustrate how new market-rate construction loosens the market for lower-quality housing through a series of moves. First, I use address history data to identify 52,000 residents of new multifamily buildings in large cities, their previous address, the current residents of those addresses, and so on for six rounds. The sequence quickly reaches units in below-median income neighborhoods, which account for nearly 40 percent of the sixth round, and similar patterns appear for neighborhoods in the bottom quintile of income or percent white. Next, I use a simple simulation model to roughly quantify these migratory connections under a range of assumptions. Constructing a new market-rate building that houses 100 people ultimately leads 45 to 70 people to move out of below-median income neighborhoods, with most of the effect occurring within three years. These results suggest that the migration ripple effects of new housing will affect a wide spectrum of neighborhoods and loosen the low-income housing market.

Performance evaluation of off-grid solar chemical heat pump for cooling/heating

Facing the current energy situation, the world’s energy supply and consumption is developing in diversification, cleanliness, and efficiency. Chemical heat pump (CHP) systems using calcium sulfate have been well studied in recent decades. However, systematic research based on simulations and experiments of coupling the off-grid CHP system and solar thermal system for cooling and heating (Solar Chemical Heat Pump: SCHP) is still insufficient. In this study, a simplified simulation model has been built for heat/mass transfer analysis of the SCHP heat storing step using the finite difference method (FDM) in order to make SCHP design easily. Simulated results were compared with previous experimental data to ensure feasibility. The effects of heat-transfer fluid type, heat exchanger structure, solar irradiance, and ambient air temperature on the chemical heat storage performance of the SCHP system were examined by the simulation. This study quantified reactant temperature, dehydration conversion, and COPs. Using the low-viscosity heat-transfer fluid, increasing the exchanger heat and the solar collector area can obtain a higher COP even under low solar irradiance and low ambient air temperature conditions.

Uncertainty Reduction for Model Error Detection in Multiphase Shock Tube Simulation

Abstract Uncertainty quantification (UQ) is an important step in the verification and validation of scientific computing. Validation can be inconclusive when uncertainties are larger than acceptable ranges for both simulation and experiment. Therefore, uncertainty reduction (UR) is important to achieve meaningful validation. A unique approach in this paper is to separate model error from uncertainty such that UR can reveal the model error. This paper aims to share lessons learned from UQ and UR of a horizontal shock tube simulation, whose goal is to validate the particle drag force model for the compressible multiphase flow. First, simulation UQ revealed the inconsistency in simulation predictions due to the numerical flux scheme, which was clearly shown using the parametric design of experiments. By improving the numerical flux scheme, the uncertainty due to inconsistency was removed, while increasing the overall prediction error. Second, the mismatch between the geometry of the experiments and the simplified 1D simulation model was identified as a lack of knowledge. After modifying simulation conditions and experiments, it turned out that the error due to the mismatch was small, which was unexpected based on expert opinions. Last, the uncertainty in the initial volume fraction of particles was reduced based on rigorous UQ. All these UR measures worked together to reveal the hidden modeling error in the simulation predictions, which can lead to a model improvement in the future. We summarized the lessons learned from this exercise in terms of empty success, useful failure, and deceptive success.

Heat transfer and viscous polymer melting capacity correlation in self-controlled torsion induced extrusion

A novel design concept of torsion screw configuration has been proposed to improve polymer melting ability. The heat transfer and melt flow behavior of a two-phase viscous polymer, induced by torsion elements in a screw compression section, were analyzed with the computational fluid dynamics simulation. It has been found that screws with added torsion elements have larger Nusselt number and liquid mass fraction, and shorter melting zone compared to that of a conventional screw. The heat transfer and melting capacity improve with the increasing number of torsion elements and their preferred arrangement in the screw. A simplified simulation model of torsion and standard elements has been developed to predict the heat transfer and melt flow mechanism, and the simulation results are in consistent with the field synergy theory. The existence of torsional flow in the region of torsion channels increases the perturbation of the fluid, improves interaction between temperature gradient and velocity vectors, resulting in improved mass and heat transfer and rapid melting of polymers. Furthermore, the paper proposed a qualitative melt flow model of polymers in the channel of torsion element.

A Simplified ALE model for finite element simulation of ballistic impacts with bullet splash – development and experimental validation

An original simplified finite element model is proposed to simulate the effects of non-penetrating ballistic impacts causing the so-called bullet splash phenomenon (complete bullet fragmentation), while no fragmentation is caused to the target. The model is based on the Arbitrary Lagrangian Eulerian formulation (ALE) and it simulates the impact as a fluid-structure interaction. The bullet splash phenomenon has been tested by experimental analyses of AISI 304L plates impacted by 9x21 FMJ (full metal jacket) bullets. The model has been developed with the aim of creating a simplified approach to be used in the industry and forensic sciences to simulate the non-penetrating interaction of soft impactors with hard targets. Comparisons between evidence and simulation results lead to the conclusion that the proposed approach can be used in a conservative way to estimate both local and global effects of bullet-splash phenomena.