Actual Physical Process Research Articles

Toward Sustainable Development: Exploring the Value and Benefits of Digital Twins

The complexity and number of data streams generated by internal processes exceed the capabilities of most current simulation environments. Consequently, there is a need for the development of more advanced solutions that can handle any number of simultaneous simulations. One of the most promising ideas to address these and other challenges is the concept of a Digital Twin (DT), which refers to a digital representation or a virtual model designed to accurately reflect an intended or actual physical product, system, or process (i.e., a physical twin). As a Digital Twin spans the life-cycle of its physical twin, its development and application can bring considerable benefits to organizations seeking to improve existing processes as well as implement new ones. However, few studies have comprehensively examined the value and benefits of Digital Twins. To fill this gap, this study aims to provide a better understanding of this technology by reviewing the contemporary literature, with a particular focus on the documented case studies, as well as reported business and industrial deployments. The results obtained show that Digital Twins have proven beneficial for maintenance, cost reduction, optimization, simulation performance, monitoring, product life-cycle understanding, assessment validation, performance evaluation, product design, and safety and risk mitigation. In addition, when considering the human factor, DTs can facilitate education and training, team collaboration, and decision making. Undeniably, Digital Twins are a game changer for safer, faster, and more sustainable development.

Theoretical and simulation analysis for R290 leakage from split-type air conditioners

Propane (R290) is a promising refrigerant for split-type household air conditioners with the advantages of energy saving, environmentally friendliness and low charge. Nevertheless, the large scale use of R290 has been hindered by its high flammability. The potential fire hazards can be relieved by reducing R290 releasable charge, and numerous methods have been put forward. In the authors’ previous papers, the method of refrigerant pump-down was proposed and a mathematical model of critical releasable charge (CRC, ignition threshold of leakage) was developed by dimensional analysis, but it is difficult to reflect the actual physical process of R290 dispersion. To reveal the leakage and dispersion mechanism of R290, a new numerical model of CRC is developed based on mechanism analysis in this work, in which the turbulent jet model, Coanda effect and dimensional analysis are involved. The predicted CRCs agree well with experimental and simulated data. Besides, the influence of indoor air speed with its direction parallel to the IDU panel on R290 concentration field is investigated by computational fluid dynamics (CFD) under different releasable charges. It is found that there is a transition value of air speed, below which the fire hazards decrease greatly with the increase of air speed, on the contrary, when the air speed is above the transition value, raising air speed has little impact on fire hazards.

A novel temperature calculation method of canned permanent magnet synchronous motor for vacuum pump

Accurate temperature prediction is vital for the canned permanent magnet synchronous motor (CPMSM) used in the vacuum pump, as it experiences severe heating. In this paper, a novel motor temperature calculation method is proposed, which takes into account the temperature impact on the heat transfer capacity. In contrast to existing electromagnetic-thermal coupled calculation methods, which solely address the temperature effect on the motor electromagnetic field, the proposed method comprehensively considers its impact on motor losses, permanent magnet magnetic properties, thermal conductivity, and heat dissipation ability of motor components, resulting in a motor temperature simulation that closely resembles the actual physical process. To verify the reliability of the proposed temperature calculation method, a 1.5 kW CPMSM was chosen as the research subject. The method was used to analyze the temperature distribution characteristics of the motor and assess the impact of ambient temperature on motor temperature rise. Furthermore, a prototype was fabricated, and an experimental platform was established to test the motor temperature. The results demonstrate good agreement between the calculated results obtained using the proposed method and the experimental data. This research not only provides a theoretical foundation for optimizing the design of the CPMSM but also provides valuable insights into its operational safety and reliability.

IoT and Digital Twin: a new perspective for Cultural Heritage predictive maintenance

In the construction sector, the maintenance and monitoring of buildings are of fundamental importance, both in civil and cultural heritage buildings, ensuring their preservation, safety, and proper functioning over time. The preservation of the built heritage is one of the main objectives that a nation must pursue, and thanks to the ever-increasing spread of new technologies, it is possible to apply innovative approaches capable of monitoring in real-time the progressive damage of structures or intercepting sudden situations capable of causing extensive damage. Traditional monitoring methodologies, employed so far, are based on direct inspections and manual data collection, and are often expensive and only sometimes effective. In this scenario, a significant contribution has been made by the Internet of Things (IoT) paradigm, which has made it possible to collect real-time data from sensors placed on the structures to be monitored, thus enabling the implementation of predictive maintenance methodologies. A further contribution to the development of these methodologies has come from the emergence of the concept of the Digital Twin (DT), a digital model of an intended or actual real-world product, system or physical process that serves as an effectively indistinguishable digital counterpart of it for practical purposes such as simulation, integration, testing, monitoring and maintenance. In order to make the DT even more effective, it is possible to link it to the real structure through BIM, i.e. a process applied to existing buildings or monuments that aims not only at the mere restitution of the three-dimensional model but above all at the creation of so-called ‘intelligent models’. The latter is rich in geometric information, including the state of conservation of materials, in which all components are parametric objects with well-defined semantics and can contain all the historical information derived from an adequate documentary analysis. Starting from the above, this paper aims to present a methodology for monitoring an existing building, exploiting innovative technologies based on DT and IoT concepts. The case study analyzed is the Scientific Library of the University of Salerno, and the first results of the experiment are more than satisfactory.

An image reconstruction algorithm for spectral exterior CT problem based on edge-preserving diffusion and edge-preserving smoothing

The exterior CT problem is a special x-ray CT imaging problem, which is often used for nondestructive inspections of large tubular samples. It can image a pipeline wall with a relatively small detector. However, exterior imaging is challenging owing to the incomplete data obtained. In this paper, we propose a regularization model for the exterior CT problem, in which an edge-preserving diffusion and edge-preserving smoothing regularizer is employed. In addition, the polychromatic characteristic of the emitted x-rays is also considered so that the model is closer to the actual physical process. Using the linearization strategy, a corresponding solution algorithm is derived. The proposed model and the algorithm are verified with both simulated data and real data. It is shown that the two type of artifacts, exterior problem artifacts and beam-hardening artifacts, can be effectively suppressed.

Towards a holistic digital twin solution for real-time monitoring of aquaculture net cage systems

Digital twins and relevant concepts are being applied in a wide variety of ways, and they are of most use when an actual real-world physical system or process (a physical twin) is changing over time and when measurement data correlated with this change can be captured. In this work, a digital twin model was implemented for real-time monitoring of aquaculture net cage systems, which is notoriously challenging because of several difficult-to-measure properties, such as forces on and deformation of the flexible netting structures, waves and flow field alterations around the cage and complex stiffness behaviour of the mooring elements made by fibre ropes. These properties were set to be adaptable according to the resultant outputs, such as cage responses and mooring loads that were continuously compared with the measurement data obtained from remote monitoring sensors. In this way, real-time sensor data were assimilated into the numerical simulation model for representing the actual net cage system. No dedicated sensors were used for fish monitoring, but the fish behavioural responses to current, wave and cage deformation were modelled according to relevant field observational data. A wireless sensor network has also been tested for the digital twin implementation, which was found to be suitable for practical uses in fish farms.

Study on the slip characteristics of rock inhomogeneous friction interface

Theory assumes that the friction along the discontinuous interface is uniform, and the selection of uniform distribution of friction resistance along the interface is a simplification of the actual physical process. This assumption leads to unsafe design. Therefore, the numerical simulation and experimental methods are used to study the slip of the discontinuous interface with non-uniform friction. This study used a numerical model comprised of two blocks with completely matching contact interfaces. The friction coefficient of one part of the contact surface differed from that of the other, resulting in a non-uniform friction interface. The model was simulated under biaxial compression. First, a normal load of 3 MPa was applied, followed by a shear load until the contact interface slipped. The initiation and propagation of slippage at the contact interface and the changes in the stress field at the slippage contact interface were monitored. The slip started from the area with low frictional strength and gradually expanded to the area with high frictional strength with increasing shear load. The transfer of the slip from an interface with a small friction coefficient to a high friction strength resulted in stress concentration at the interface of the non-uniform friction interface. Engraving using an engraving machine produces a discontinuous interface in which one part of the interface has high friction strength, whereas the other part has low friction strength. The shear load is applied using a shear instrument to cause the discontinuous interface to slip. At the same time, DIC monitored the displacement of the discontinuous interface. The comparison found that the rule of the experimental results is the same as that of the numerical simulation. Reinforcement measures (enhanced friction strength) for areas with low friction strength can effectively prevent slip damage. Based on the distribution of shear stiffness of the rock discontinuous interface, the friction properties of the entire fracture interface can be obtained to accurately identify areas with low frictional strength, and targeted reinforcement measures should be carried out to prevent slip damage.

Shielding Capability Research on Composite Base Materials in Hybrid Neutron-Gamma Mixed Radiation Fields

The 16N monitoring system operates in a mixed neutron-gamma radiation field and is subject to high background radiation, thus triggering instability in the 16N monitoring system measurement data. Due to its property of actual physical process simulation, the Monte Carlo method was adopted to establish the model of the 16N monitoring system and design a structure-functionally integrated shield to realize neutron-gamma mixed radiation shielding. First, the optimal shielding layer with a thickness of 4 cm was determined in this working environment, which had a significant shielding effect on the background radiation and improved the measurement of the characteristic energy spectrum and the shielding effect on neutrons was better than gamma shielding with the increase in the shield thickness. Then, functional fillers such as B, Gd, W, and Pb were added to the matrix to compare the shielding rates of three matrix materials of polyethylene, epoxy resin, and 6061 aluminum alloy at 1 MeV neutron and gamma energy. The shielding performance of epoxy resin as the matrix material was better than that of the aluminum alloy and polyethylene, and the shielding rate of boron-containing epoxy resin was 44.8%. The γ-ray mass attenuation coefficients of lead and tungsten in the three matrix materials were simulated to determine the best material for the gamma shielding performance. Finally, the optimal materials for neutron shielding and gamma shielding were combined, and the shielding performance of single-layer shielding and double-layer shielding in mixed radiation field was compared. The optimal shielding material-boron-containing epoxy resin was determined as the shielding layer of the 16N monitoring system to realize the integration of structure and function, which provides a theoretical basis for the selection of shielding materials in a special working environment.

Mathematical Model for Oil Recovery Prediction of Polymer Microsphere Conformance Control Based on the Stream Tube Method

Oil recovery is an essential parameter for reservoir development performance evaluation, but there is no specific research on the theoretical oil recovery prediction model of polymer microspheres (PMs)' conformance control. This research aims to establish an oil recovery prediction model that depends on the definition of oil recovery based on stream tube theory. PMs' enhanced oil recovery mechanism is to plug the pore throat to expand the swept area. The assumption that the stream tube between injection and production wells is trapezoidal is proposed. Based on this premise, the area sweep efficiency equation suitable for the rhombus inverse nine-spot well pattern is established based on the stream tube theory. The vertical sweep efficiency equation is optimized by introducing the equivalent mobility ratio. Additionally, the model's adaptability and validity are studied. The analysis results show that oil recovery decreases with increasing injection rate, injection concentration, and PMs size but increases with the increasing injection period. The theoretical oil recovery is 1.37%, and the actual oil recovery of the field application is 1.22%, with an error of 0.15%. This model has good consistency with the actual physical process of the field application. The oil recovery prediction model can provide oil recovery and optimize PMs' conformance control injection scheme. This study fills the gap in the mathematical model for oil recovery prediction of PMs' conformance control.

Unbinned likelihood analysis for X-ray polarization

ABSTRACT We present a systematic study of the unbinned, photon-by-photon likelihood technique which can be used as an alternative method to analyse phase-dependent, X-ray spectro-polarimetric observations obtained with IXPE and other photoelectric polarimeters. We apply the unbinned technique to models of the luminous X-ray pulsar Hercules X-1, for which we produce simulated observations using the ixpeobssim package. We consider minimal knowledge about the actual physical process responsible for the polarized emission from the accreting pulsar and assume that the observed phase-dependent polarization angle can be described by the rotating vector model. Using the unbinned technique, the detector’s modulation factor, and the polarization information alone, we found that both the rotating vector model and the underlying spectro-polarimetry model can reconstruct equally well the geometric configuration angles of the accreting pulsar. However, the measured polarization fraction becomes biased with respect to the underlying model unless the energy dispersion and effective area of the detector are also taken into account. To this end, we present an energy-dispersed likelihood estimator that is proved to be unbiased. For different analyses, we obtain posterior distributions from multiple ixpeobssim realizations and show that the unbinned technique yields $\sim 10{{\ \rm per\ cent}}$ smaller error bars than the binned technique. We also discuss alternative sources, such as magnetars, in which the unbinned technique and the rotating vector model might be applied.

Approximate properties of stochastic functional differential equations with singular perturbations

This work focuses on stochastic functional differential equations (SFDEs) with wide-band noise perturbation, which is a class of actual physical process and has wide application in the modeling of communication and signal system. Using functional derivatives together with martingale methods and weak convergence techniques, this paper examines the asymptotic properties of the underlying systems as the small parameter tends to zero. Based on the techniques, this paper also establishes the average principle for a class of SFDEs with two-time scales. As a special case, this paper also considers a class of integro-differential equations with wide-band noise perturbation and examines its approximate properties. As an example, a scalar stochastic Lotka–Volterra integro-differential system with wide-band noise perturbation is investigated.

Remote Sensing of Surface Melt on Antarctica: Opportunities and Challenges

Surface melt is an important driver of ice shelf disintegration and its consequent mass loss over the Antarctic Ice Sheet. Monitoring surface melt using satellite remote sensing can enhance our understanding of ice shelf stability. However, the sensors do not measure the actual physical process of surface melt, but rather observe the presence of liquid water. Moreover, the sensor observations are influenced by the sensor characteristics and surface properties. Therefore, large inconsistencies can exist in the derived melt estimates from different sensors. In this study, we apply state-of-the-art melt detection algorithms to four frequently used remote sensing sensors: two active microwave sensors, ASCAT (Advanced Scatterometer) and Sentinel-1, a passive microwave sensor SSMIS (Special Sensor Microwave Imager/Sounder), and an optical sensor MODIS (Moderate Resolution Imaging Spectroradiometer). We intercompare the melt detection results over the entire Antarctic Ice Sheet and four selected study regions for the melt seasons 2015-2020. Our results show large spatiotemporal differences in detected melt between the sensors, with particular disagreement in blue ice areas, in aquifer regions, and during wintertime surface melt. We discuss that discrepancies between sensors are mainly due to (1) cloud obstruction and polar darkness, (2) frequency-dependent penetration of satellite signals, (3) temporal resolution, and (4) spatial resolution, as well as (5) the applied melt detection methods. Nevertheless, we argue that different sensors can complement each other, enabling improved detection of surface melt over the Antarctic Ice Sheet.

A frost model based on the frost layer's supporting function

The existence of frost has adverse effects the normal operation of air source heat pumps. Therefore, establishing an accurate frost model is of great significance to suppressing the formation of frost layers on cold surfaces. Since the frost layer grows gradually and cumulatively layer by layer in the actual physical frosting process, it is important to consider the supporting function of the lower frost layer in the process. This study proposes the use of the ice volume fraction threshold of the frost layer to determine whether the supporting condition is satisfied, in addition to using the threshold to determine the occurrence of frosting. A new frost model is developed with the given volume fraction threshold fitting formula. In order to verify the accuracy of the proposed model, the simulation results were compared with 17 groups of experimental results from four representative experiments. It was found that the simulation results of this model were in good agreement with the experimental data, and the average error of thickness did not exceed 4.9%, while the average error of density was less than 5.5%.

Mechanism of flash boiling bubble breakup based on rim-like structure

Flash boiling is an important phenomenon in internal multiphase flow and could lead to unique spray structures. Many researchers have investigated this phenomenon using optical diagnostic methods, and progress has been made in spray morphology studies as well as bubble dynamics inside the nozzle. However, the detailed transition mechanism from in-nozzle bubble to out-nozzle spray droplets has not been experimentally observed, and present theories could not elaborate the morphology change in the micro-scale droplets with high velocities. To illustrate the transition procedure from bubble to droplets of flash boiling bubbles, high-speed imaging technique is adopted on a specially designed optical nozzle with a two-dimensional ambient cavity to investigate the transition from in-nozzle flash boiling bubbles to out-nozzle spray droplets. A unique rim-like structure has been observed, and quantitative and qualitative analyses are made to figure out the nature of this rim. Based on the study, the driving force, as well as the transition process of flash boiling bubbles, has been demonstrated in detail, it is found that under high superheated degrees, the bubble burst process is governed by joint effort of thermal phase change and mechanical deformation. Based on the observed phenomena and theoretical analysis, a new flash boiling spray breakup theory that coincides with the actual physical process has been established.

New practical discrete non-spherical N-body method: Validation with the Brazil nut effect

This paper presents an implementation of the contact dynamics method for discrete non-spherical particles. The algorithm can handle particles with a wide range of geometries as long as they are described in triangular surface meshes. The contact detection between particles is organized into two phases: coarse-grained and fine-grained contact detection. Specifically, different hierarchies of grids are utilized to perform fast contact detection: (a) A spatial sorting method is utilized for coarse-grained contact detection, where each non-spherical particle is represented with a corresponding bounding-sphere (b) The Polygonal Contact Method is introduced into the fine-grained contact detection phase to accurately determine the active contact areas between the interacting particles. These techniques solve the difficulties of determining the action point(s) of contact force and torque between non-spherical particles. The smooth (force-based) method is employed to calculate the contact force and torque, which is generally regarded as conforming to the actual physical process. Particularly, the non-linear Hertz and Mindlin-Deresiewicz theories are adopted to calculate the normal and tangential forces. The non-spherical Brazil nut effect under the shear vibration mode is simulated as validation by comparing with the existing experimental results. The simulation results confirmed that the convection and percolation mechanism mutually affect the nut heap's behavior and finally drive the rise of the Brazil nut from the bottom to the top layer.

Local well-posedness of strong solution to a climate dynamic model with phase transformation of water vapor

The primitive three-dimensional viscous equations for atmospheric dynamics with the phase transformation of water vapor are studied. According to the actual physical process, we give the heating rate, mass of water, and precipitation rate, which are related to temperature and pressure. In fact, this system strictly obeys the conservation of energy and is used to make better climate predictions. Providing H2 initial data and boundary conditions with physical significance, we prove the local well-posedness of a unique strong solution to the moist atmospheric equations by the contractive mapping principle and the energy method in the H2 framework.

Numerical study of unmanned aerial vehicle (UAV) in dry microburst environment using large eddy simulation (LES) model

PurposeIn a microburst wind, the profiles and characteristics are significantly different from those of normal boundary layer winds. The objective of this work is to study the microburst effect on the performance of aircraft for providing guidelines to frame escape strategies.Design/methodology/approachLarge eddy simulation model is used to study the effect of microburst by simulating the actual physical process of microburst-generated downdraft environment over the unmanned aerial vehicle. In this work, an attempt has been made to simulate the dry microburst (microburst not accompanied by rain) numerically using the impinging jet model to explore the effect of microburst at 12° angle of attack for flight take-off condition with a Mach number 0.04.FindingsThe numerical results revealed the aerodynamic performance loss of an aircraft in the microburst-generated downdraft during take-off condition quantitatively. This could be a more valuable information to the aviation industry. The authors believe that the results shown in this paper will be useful for the designers of aircraft. This will also help train the pilots to control the airplanes in a microburst environment.Practical implicationsSevere thunderstorms are significant weather phenomena that have a significant impact on various facets of national activity, including civil and defence operations, specifically aviation, space vehicle launch and agriculture, in addition to their potential to cause damage to life and property.Originality/valueThe maximum percentage of pressure increases on the upper surface of the aircraft between 2 and 7 s is 99.86% under the microburst-generated downdraft condition. The flight escape maneuver could be initiated, before increasing the pressure on the upper surface of the aircraft. The aircraft flies with high airspeed through the microburst environment, where the microburst-generated downdraft is most severe.

Dual-task convolutional neural network based on the combination of the U-Net and a diffraction propagation model for phase hologram design with suppressed speckle noise.

In this paper, a dual-task convolutional neural network based on the combination of the U-Net and a diffraction propagation model is proposed for the design of phase holograms to suppress speckle noise of the reconstructed images. By introducing a Fresnel transmission layer, based on angular spectrum diffraction theory, as the diffraction propagation model and incorporating it into U-Net as the output layer, the proposed neural network model can describe the actual physical process of holographic imaging, and the distributions of both the light amplitude and phase can be generated. Afterwards, by respectively using the Pearson correlation coefficient (PCC) as the loss function to modulate the distribution of the amplitude, and a proposed target-weighted standard deviation (TWSD) as the loss function to limit the randomness and arbitrariness of the reconstructed phase distribution, the dual tasks of the amplitude reconstruction and phase smoothing are jointly solved, and thus the phase hologram that can produce high quality image without speckle is obtained. Both simulations and optical experiments are carried out to confirm the feasibility and effectiveness of the proposed method. Furthermore, the depth of field (DOF) of the image using the proposed method is much larger than that of using the traditional Gerchberg-Saxton (GS) algorithm due to the smoothness of the reconstructed phase distribution, which is also verified in the experiments. This study provides a new phase hologram design approach and shows the potential of neural networks in the field of the holographic imaging and more.

Y-Mat: an improved hybrid finite-discrete element code for addressing geotechnical and geological engineering problems

PurposeContinua and discontinua coexist in natural rock materials. This paper aims to present an improved approach for addressing the mechanical response of rock masses based on the combined finite-discrete element method (FDEM) proposed by Munjiza.Design/methodology/approachSeveral algorithms have been programmed in the new approach. The algorithms include (1) a simpler and more efficient algorithm to calculate the contact force; (2) An algorithm for tangential contact force closer to the actual physical process; (3) a plastic yielding criterion (e.g. Mohr-Coulomb) to modify the elastic stress for fitting the mechanical behavior of elastoplastic materials; and (4) a complete code for the mechanical calculation to be implemented in Matrix Laboratory (MATLAB).FindingsThree case studies, including two standard laboratory experiments (uniaxial compression and Brazilian split test) and one engineering-scale anti-dip slop model, are presented to illustrate the feasibility of the Y-Mat code and its ability to deal with multi-scale rock mechanics problems. The results, including the progressive failure process, failure mode and trajectory of each case, are acceptable compared to other corresponding studies. It is shown that, the code is capable of modeling geotechnical and geological engineering problems.Originality/valueThis article gives an improved FDEM-based numerical calculation code. And, feasibility of the code is verified through three cases. It can effectively solve the geotechnical and geological engineering problems.

Investigation of Fracture Width Change under Closure Pressure in Unconventional Reservoir Based on the Hertz Contact Theory

To describe the fracture width is crucial for the flow conductivity evaluation, which influences the exploitation efficiency of unconventional oil and gas resources. Commonly, as the proppants fill in the fracture, the deformation will happen under the closure pressure to resist the fracture width change. Therefore, it is significant to develop the theoretical model to predict the variation. In this work, the mathematical model for the propping behavior of proppants in the fracture under closure pressure is established based on the Hertz contact theory. Compared with the existing models, the developed model considers both the proppant insertion and the elastic compression among the proppants, which is closer to the actual physical process. Furthermore, the experimental cases with different proppant sizes are taken to verify the model, and the good conformity presents its rationality. The parameter sensitivity analysis of this model shows that the fracture width change increases with the increase of the average diameters of proppants ( D ) and it declines with the improving of proppant elasticity modulus ( E 1 ) and Poisson’s ratio ( v 1 ).