Dynamics Simulation Model Research Articles

Molecular dynamics study of carbon dioxide and nitrogen selectivity through poly[bis((methoxyethoxy)ethoxy)phosphazene] (MEEP) membrane

A molecular dynamics simulation model was developed to comprehensively understand carbon dioxide over nitrogen (CO2/N2) selectivity through polyphosphazene-based membrane comprising of poly[bis((methoxyethoxy)ethoxy)phosphazene] (MEEP) selective layer at the molecular level. The effects of temperature, pressure, and initial feed gas composition on the CO2 transport on a polymer membrane were studied. The computed free energy and density profile of the permeating gas mixture exhibited that CO2 molecules express higher interactions with the membrane than N2 molecules, resulting in higher CO2/N2 selectivity. Statistical analysis of gas molecules (CO2, water (H2O), and N2) transportation suggested that hydro- and CO2-philic functional groups in the membrane significantly impact CO2 permeability and CO2/N2 selectivity. This study suggested that Lewis acid–base and hydrogen bonding combinations contribute to CO2 permeation and CO2/N2 selectivity. An equal CO2/N2 selectivity was observed with and without water vapor in the feed gas suggesting that water does not hinder CO2 transport through the membrane.

Comprehensive investigation of corrugated fiberboard boxes with edge vents for ambient loading of chinese cabbage: Part I - Computational fluid dynamics simulation and experimental validation

The ambient (warm) loading of perishable products is widely practiced during their storage and transport. The vent hole design in a corrugated fiberboard box is crucial for providing effective airflow to maintain the freshness of products during ambient loading. In this study, four different corrugated fiberboard boxes with vent hole areas of 0, 2, 3, and 4 % were prepared. The cooling behavior of the Chinese cabbage in the corrugated fiberboard boxes with different air vent holes was verified using a computational fluid dynamics (CFD) simulation model. The results indicated that the cooling rate of the Chinese cabbage in the top and bottom layers of the seven-layer box stacks decreased substantially faster than those in the middle layers of the boxes, regardless of the air vent hole areas. The experimental analysis indicated significant differences in the cooling rates of the Chinese cabbages among the seven-layer box stacks with 0, 2, 3, and 4 % air vent holes; however, the CFD simulation exhibited no significant differences in the cooling rates of the Chinese cabbages among those stacks. The compression strength of the corrugated fiberboard box designed with a 4 % air vent hole area exhibited the lowest value, which was nearly 20 % lower than that of the box with 0 % air vent hole area. Moreover, highly humid conditions were observed in the headspace of boxes, which was a critical factor causing a further decrease in its mechanical property in addition to the inevitable reduction caused by the vent hole design. Thus, the study findings can form the scientific basis for improving the edge-vent corrugated fiberboard box design used for transporting Chinese cabbage by ambient loading.

Computational fluid dynamics simulation analysis of the effect of curved rice leaves on the deposition behaviour of droplets

BackgroundAlthough previous studies on the droplet deposition behaviour of rice leaves have modelled the leaves as flat surface structures, their curved surface structures actually have a significant effect on droplet deposition.ResultsIn this paper, the statistical distribution of the coordinate parameters of rice leaves at the elongation stage was determined, computational fluid dynamics (CFD) simulation models of droplet impact on rice leaves with different curvature radii were built, and the effect of leaf curvature radius on the deposition behaviour and spreading diameter of droplets on rice leaves was studied using validated simulation models. The results showed that the average relative errors of the CFD simulation models were in the range of 2.23–9.63%. When the droplets struck the rice leaves at a speed of 4 m/s, the 50 μm droplets did not bounce within the curvature radii of 25–120 cm, the maximum spreading diameters of 200 and 500 μm droplets that just adhered to the leaves were 287 and 772 μm, respectively. The maximum spreading diameters of 50, 200, and 500 μm droplets that just split were 168, 636, and 1411 μm, respectively. As the curvature radii of the leaves increased, the maximum spreading diameter of the droplets gradually decreased, and droplet bouncing was more likely to occur. However, a special case in which no significant change in the maximum spreading diameter arose when 50 μm droplets hit a leaf with a curvature radius exceeding 50 cm.ConclusionSplitting generally occurred for large droplets with a small curvature radius and small tilt angle; bouncing generally occurred for large droplets with a large curvature radius and large tilt angle. When the droplet was small, the deposition behaviour was mostly adhesion. The change in spreading diameter after stabilisation was similar to the change in maximum spreading diameter, where the spreading diameter after stabilisation greatly increased after droplet splitting. This paper serves as a reference for the study of pesticide droplet deposition and its application in rice-plant protection.

Design and Implementation of Hardware-in-the-Loop Simulation Environment Using System Identification Method for Independent Rear Wheel Steering System

In the automotive field, with the advancement of electronic and signal processing technologies, active control-based chassis systems have been developed to enhance vehicle stability. In this study, a Hardware-in-the-Loop (HiL) simulation environment was developed to effectively improve time and cost during the development process of an independent rear-wheel steering system. The HiL Simulation Environment was developed—a specific test bench capable of simulating driving loads on the prototype. Based on the system identification method, a reaction force modeling technique for the target driving loads was proposed. The full vehicle dynamics simulation model was developed with a lateral maximum error of 4.5% and a correlation coefficient of 0.98, as well as a longitudinal maximum error of 0.1% and a correlation coefficient of 0.99. The reaction force generation system had a maximum error of 2.9%. Using the developed HiL simulation environment, performance verification and analysis of the independent rear-wheel steering system were conducted, showing reductions of 5.1% in lateral acceleration and 5.2% in yaw rate.

A decision support methodology to support military asset and resource planning

ABSTRACT This paper presents a decision-support methodology to support the development and assessment of military asset and resource strategies. The methodology is built around a system dynamics model that allows users to examine the performance of a strategy over time. The novelty of the model lies in its flexibility and ability to address questions about asset planning from both holistic and lifecycle viewpoints. From the user perspective, the decision-support methodology is structured around three phases: (1) Design an asset management strategy, (2) Evaluate strategy using system dynamics simulation model, and (3) Generate performance indicators and analyse results. The methodology is developed and used in a real case study to support the modernisation of the Australian Defence Force. This paper demonstrates that system dynamics offers useful methods to study the dynamics of supply-demand, and support the development of systemic asset and resource management strategies.

Elucidating Interfacial Dynamics of Ti-Al Systems Using Molecular Dynamics Simulation and Markov State Modeling.

Due to their remarkable mechanical and chemical properties, Ti-Al-based materials are attracting considerable interest in numerous fields of engineering, such as automotive, aerospace, and defense. With their low density, high strength, and resistance to corrosion and oxidation, these intermetallic alloys and metal-compound composites have found diverse applications. However, additive manufacturing and heat treatment of Ti-Al alloys frequently lead to brittleness and severe formation of defects. The present study delves into the interfacial dynamics of these Ti-Al systems, particularly focusing on the behavior of Ti and Al atoms in the presence of TiAl3 grain boundaries under experimental heat treatment conditions. Using a combination of molecular dynamics and Markov state modeling, we scrutinize the kinetic processes involved in the formation of TiAl3. The molecular dynamics simulation indicates that at the early stage of heat treatment, the predominating process is the diffusion of Al atoms toward the Ti surface through the TiAl3 grain boundaries. Markov state modeling identifies three distinct dynamic states of Al atoms within the Ti/Al mixture that forms during the process, each exhibiting a unique spatial distribution. Using transition time scales as a qualitative measure of the rapidness of the dynamics, it is observed that the Al dynamics is significantly less rapid near the Ti surface compared to the Al surface. Put together, the results offer a comprehensive understanding of the interfacial dynamics and reveal a three-stage diffusion mechanism. The process initiates with the premelting of Al, proceeds with the prevalent diffusion of Al atoms toward the Ti surface, and eventually ceases as the Ti concentration within the mixture progressively increases. The insights gained from this study could contribute significantly to the control and optimization of manufacturing processes for these high-performing Ti-Al-based materials.

Thermofluid dynamics and droplets transport inside a large university classroom: Effects of occupancy rate and volumetric airflow

The airborne droplets released by humans while speaking or coughing are the main sources of human-to-human contagion for airborne transmissible diseases. Due to the recent SARS-Cov2 pandemic, indoor transmission in classrooms and other environments is an interesting topic investigated by the scientific community. In this work, the thermofluid dynamic conditions and the droplet transport was analysed in a large University Classroom (UC), as a function of the inlet airflow and the occupancy rate. These parameters assume a relevant role in the design stage. However, their effects on droplet transport were not deeply investigated in the literature. Therefore, different conditions were analysed, such as: full occupancy, which represents the design condition where no social distancing is enforced; half occupancy, which is representative of social distancing; and empty UC, to be considered as a term of comparison. The main novelty of this work is related to the analysis of the combined effect of thermal plume and airflow in a large UC. The numerical model for the thermofluid dynamics simulation was validated in a previous work and the droplet emission model was retrieved from the literature. High volumetric airflow is not always beneficial for the reduction of the airborne transmission risk. An important aspect is related to the combined effect of the inlet airflow and the thermal plume, which cannot be ignored if the occupancy rate assumes a significant value. Moreover, the evacuation rate and the age of the droplets are relevant indicators to assess the cleaning time.

Pore-scale investigation on the flow behavior and oil displacement of ultralow IFT surfactant flooding based on CFD simulation

In order to investigate the flow behavior and oil displacement of ultralow interfacial tension (IFT) surfactant flooding, the experimentally validated computational fluid dynamics simulation model is constructed by coupling the Navier-Stokes equations and the Cahn-Hilliard equation. The mixed surfactant solution is prepared using the ionic liquid surfactant and the nonionic surfactant, and the fluid parameters are measured experimentally. Due to the reduced oil-water IFT, the low pressure drop in porous medium and the decreased oil viscosity, ultralow IFT surfactant contributes to increasing the mobility ability of the fluid front in pores, and its optimal injection velocity is 0.01 m/s. In addition, the sweep area of surfactant flooding in oil-wet porous medium is significantly larger than that of brine flooding because of wettability alteration. Finally, for different porosity models, the residual oil content and the pressure drop of surfactant flooding show a 66.7% and 71.4% decrease than those of brine flooding, respectively, proving its better displacement performance.

Effects of government policies reform on environmental sustainability: An integrated approach of PMP and system dynamics simulation model

The government's supportive policies in the agricultural sector may provide some goals intended by policymakers; however, they may have environmental, social, and sometimes economic inefficiencies. Therefore, policy analysis not only needs to examine the effectiveness of these policies from the point of view of economic components but also, in a more comprehensive view, should assess the impact of these policies on other aspects like sustainability. In this study, an integrated Positive Mathematical Programming (PMP) and System Dynamics (SD) model was developed to investigate the effects of the agricultural policy reform on the cultivation pattern and water resources sustainability in the Doroodzan Dam basin in Fars Province, southern Iran, where managing water resources is a seriously challenging due to population growth and periodic drought. The initial investigation involved analyzing how price policies (guaranteed price and world price of crops) and non-price policies (removal of subsidy payments to agricultural inputs and improvement of irrigation efficiency) impacted the cropping pattern. The results of the study showed that the most significant decrease in cropland area occurs due to the removal of agricultural input subsidies. Although this crop pattern can lead to environmental sustainability, it is not considered from the point of view of food self-sufficiency. Based on the results, applying world prices increase cropping area for crops like rice, which is a water-intensive crop. Another point was the high priority of onions, fodder corn, and beans while they are not subjected to governmental pricing intervention. This may indicate the extent of public policies' impact on agriculture. Although under some policy scenarios changes in the gross margin or cropping area do not sound significant, the water-saving nature of these policies is more compelling. Finally, the impact of altering cropping patterns along with climate change and population growth on water indices was assessed using SD modeling. Thus, reforming the government's policies in the agricultural sector may help reduce the water shortage index in the basin. The policy of removing subsidies for the agricultural inputs led to the attainment of the lowest water shortage index.

Investigation of the thermal response characteristics of the loop thermosyphon under convective boundary conditions

The two-phase loop thermosyphon (TPLT) is a highly efficient passive heat transfer device that is widely applied in various fields. This paper experimentally and numerically investigates the thermal response performance of a large-scale TPLT under various convective boundary conditions. Experimental studies have been carried out to explore the effects of different working fluids, filling ratios, cold and heat source temperatures, and mass flow rates on the thermosyphon’s performance. Meanwhile, a two-dimensional Computational Fluid Dynamics (CFD) simulation model of the TPLT is established and validated. The results indicate that the start-up procedure of the TPLT is highly dependent on the heat source temperature and the working fluid. Normally, the TPLT can start when the heat source reaches a certain temperature. In general, using methanol as the working fluid is more favorable to start-up compared to the water and ethanol TPLTs. The experimental results also show that the heat transfer capacity of the TPLT increases with increasing heat source temperature while increasing cooling temperature decreases heat transfer capacity. The best heat transfer performance of a TPLT charging methanol is observed at a filling ratio of 70 % with a heating mass flow rate of 1 L/min. At that point, the convective heat transfer coefficient of outside the evaporator is 1036.7 W/(m2·K). Moreover, the simulation results reveal that the average wall heat flux of the TPLT’s evaporator initially decreases and then gradually stabilizes with time. During stable operation, the wall heat flux density of the evaporator exhibits an initial increase in the pool section followed by a subsequent decrease with increasing wall height. This work provides insight into the heat and fluid flow characteristics of the TPLT under convective boundary conditions.

Hybrid thermo-physical modelling and experimentation of ultrafast laser-based fabrication of polycrystalline core–amorphous shell nitinol nanoparticles

Ultrafast lasers pulses induced ablation of nickel-titanium (NiTi) alloy substrates immersed in deionized water yielded a high-throughput of polycrystalline core - amorphous shell NiTi nanoparticles (NPs) owing to the high pulse energy of femtosecond (fs) lasers. In this study, the alloy NPs were fabricated by varying the laser fluences from 15 to 45 J/cm2. The polycrystalline core - amorphous shell NiTi were confirmed by selected area diffraction patterns via High resolution – Transmission Electron microscopy. Theoretical investigations were carried out via hybrid simulation approach of molecular dynamics simulation and analytical modelling. Molecular dynamics study revealed the spatial and temporal evolution of electron and lattice temperature of NiTi melt pool due to ablation at various laser fluences. The subsequent temporal dynamics of melt-pool temperature along the depth revealed the phase separation via spinodal decomposition process after 40 picoseconds post irradiation of NiTi with ultrafast laser pulse. The analytical modelling incorporating phase explosion theory estimated the thermo-physical expansion of ablated chunks and subsequent fragmentation of NiTi melt pool in liquid–vapor co-existing phase. The parameters of mathematical modelling were evaluated in-conjunction with the experimental results of size distribution of NPs at the laser fluence of 15 J/cm2. Later, the hybrid mathematical model was employed to predict the size of NiTi NPs ablated at higher laser fluences of 30 J/cm2 and 45 J/cm2 and the results were experimentally verified.

Simulation on human respiratory motion dynamics and platform construction

Bronchoscopy has a crucial role in the current treatment of lung diseases, and it is typical of interventional medical instruments led by manual intervention. The scientific study of bronchoscopy is now of primary importance in eliminating problems associated with manual intervention by scientific means. However, for its intervention environment, the trachea is often treated statically, without considering the effect of tracheal deformation on bronchoscopic intervention during respiratory motion. Therefore its findings can deviate from practical application. Thus, studying kinetic problems in respiratory motion is of great importance. This paper developed a mathematical model of mechanical properties of respiratory motion to express respiratory force from the perspective of dynamics of respiratory motion. The dynamical model was solved using MATLAB. Then, a finite element model of respiratory motion was built using Mimics, and the results of respiratory force solution were used as the load of model for dynamics simulation in ABAQUS. Then, a human–computer interaction platform was designed in MATLAB APP Designer to realize parametric calculation and fitting of respiratory force, and a personalized human respiratory motion dynamics simulation was completed in conjunction with ABAQUS. Finally, experimental validation of the interactive platform was performed using pulmonary function test data from three patients. Validation analysis by respiration striving solution, kinetic simulation and experiment found that Dynamical model and simulation results can be better adapted to the individualized study of human respiratory motion dynamics.

Experimental investigation and numerical simulation of transverse heat flux attenuation during fire in utility tunnel

To analyze transverse fire protection, the distribution law and evolution mechanism of transverse heat transfer during fire in utility tunnels is required urgently. In this study, the experiment and numerical simulation were employed to investigate the evolution of transverse heat transfer under the curved ceiling. After validation, the fire dynamics simulation models with unstructured geometry were established to predict the transverse heat flux. Through the experiment and simulation, the fire source and target location under the curved ceiling were considered, and the prediction models of heat flux provided by the flame body before the impingement point and the heat flux provided by the extension flame body and thermal environment were proposed. Based on the proposed models, the shift relationship (competition mechanism) between the components provided by flame body before the impingement point and the extension flame body (including the thermal environment) under the curved ceiling was illustrated. The transverse heat flux attenuation of each component in different fire scenarios with different fire sources and target point locations was compared to reveal the competition mechanism among the components in the heat flux. This work provides a reference for the transverse fire protection design and risk assessment in utility tunnels.

The Impact of Hybrid Energy Storage System on the Battery Cycle Life of Replaceable Battery Electric Vehicle

Compared with batteries, ultracapacitors have higher specific power and longer cycle life. They can act as power buffers to absorb peak power during charging and discharging, playing a role in peak shaving and valley filling, thereby extending the cycle life of the battery. In this article, a replaceable battery electric coupe SUV equipped with a lithium iron phosphate (LiFePO4) power battery is taken as the research object, and a vehicle dynamics simulation model is established on the MATLAB/Simulink platform. Parameter matching and control optimization for a hybrid energy storage system (HESS) are conducted. Through a proven semiempirical cycle model of the LiFePO4 power battery, the operating cycle life model is derived and used to estimate the battery cycle life. World Light Vehicle Test Cycle (WLTC) simulation results show that the HESS with 308 ultracapacitors can extend the cycle life of the LiFePO4 power battery by 34.24%, thus significantly reducing the operation cost of the battery replacement station.

Multi-scale modeling and fast inference for thermal environment analysis of air-cooled data center

Both the thermal environment of a data center room and the internal thermal environment of a server are of great concern, but it is extremely difficult to build and solve full-scale computational fluid dynamics (CFD) simulation models from room scale to chip scale. In this paper, a multi-scale simulation method for data centers is proposed to achieve this aim by coupling room-level, rack-level, and server-level models. Simulations of the designed working conditions were carried out. The results showed that aisle containment systems improve the server's thermal environment, resulting in a drop in the maximum temperature of the server from 87.5 °C to 73.1 °C. A multi-scale model of the data center can be used to optimize system operation parameters conveniently and accurately. In this simulation, air conditioning parameters that contribute to energy savings with higher supply air temperatures and lower supply air volumes while guaranteeing safe server operation were determined. Moreover, fast and accurate prediction of chip temperature by radial basis function (RBF) networks has been proven to be feasible.

Analysis of the vibrational characteristics of diamane nanosheet based on the Kirchhoff plate model and atomistic simulations

Single layer diamond—diamane, has been reported with excellent mechanical properties. In this work, molecular dynamics (MD) simulation and Kirchhoff plate model are utilized to investigate the vibrational characteristics of diamane sheets. The mechanical parameters of diamane sheets, including bending stiffness, Young’s modulus, Poisson’s ratio and coefficient of thermal expansion, are calibrated by using MD simulations. The natural frequencies and corresponding modal shapes of the diamane sheets predicted by the Kirchhoff plate model agree well with that obtained from the MD simulations. It is found that the edges exert marginal effect on the modal shapes when free boundary conditions are applied. Additionally, the Kirchhoff plate model considering the thermal expansion provides reasonable prediction for the natural frequencies of the diamane sheets with all boundary clamped under varying temperatures. This study offers valuable insights into the vibrational properties of diamane sheets, from both a simulation and theoretical standpoint. The findings would be beneficial for the design of nanoscale mechanical resonators utilizing these novel carbon materials.

Dynamic Rupture Modeling and Ground-Motion Simulations of the 2022 Mw 6.6 Luding Earthquake

Abstract The 2022 Mw 6.6 Luding earthquake occurred on the Xianshuihe fault, one of China’s most active faults. Revealing the rupture process of the Luding earthquake and exploring the distribution of high intensities is important for earthquake hazard reduction around the active Xianshuihe fault in the future. Therefore, we modeled the dynamic rupture and ground motions of the Luding earthquake. The dynamic rupture modeling demonstrates that the maximum slip of the fault plane is ∼1.34 m, and the ground-motion simulations show the highest intensity attained is IX. In addition, we conducted a comparative analysis between synthetic data and station observation records, illustrating that our simulation results are compatible with the seismic station observations. We investigated the influence of geometric complexities on the Xianshuihe fault rupture and found that varying the dip angle of the southern segment may lead to premature rupture termination and constrain the rupture propagation. Our study provides insights into the complex geometry’s effect on the physical process of large earthquakes on the Xianshuihe fault.

Down the drain: The dynamic interplay of governance adjustments addressing setbacks in large public–private projects

AbstractLarge government projects involving public–private collaborations inherently suffer from setbacks such as delays, cost overruns, or failure to meet contracted performance. Such setbacks may effectively be addressed through adjustments to contractual and relational governance; yet to date, the dynamics of governance adjustments and their interplay in addressing setbacks is not well understood. This research presents a dynamic theory of how parties can effectively address project setbacks through adjustments to contractual and relational governance. The dynamic theory was generated using longitudinal case data from two large public–private projects in the Netherlands that faced comparable project setbacks but deployed opposing governance adjustments, leading to drastically different project outcomes (i.e., collapse vs. recovery). This theory was then elaborated through two more cases and evidence from the literature. A system dynamics simulation model was then built that reproduces the different governance adjustments and outcomes observed in the four projects and serves to extend theory building. The refined theory not only shows under what conditions adjustments to contractual or relational governance are most effective, but also that governance adjustment interplay may trigger unintended side effects. As such, the theory explains why the careful balancing of governance adjustments is critical to project outcomes.

Understanding Rapid PET Degradation via Reactive Molecular Dynamics Simulation and Kinetic Modeling.

As the demand for PET plastic products continues to grow, developing effective processes to reduce their pollution is of critical importance. Pyrolysis, a promising technology to produce lighter and recyclable components from wasted plastic products, has therefore received considerable attention. In this work, the rapid pyrolysis of PET was studied by using reactive molecular dynamics (MD) simulations. Mechanisms for yielding gas species were unraveled, which involve the generation of ethylene and TPA radicals from ester oxygen-alkyl carbon bond dissociation and condensation reactions to consume TPA radicals with the products of long chains containing a phenyl benzoate structure and CO2. As atomistic simulations are typically conducted at the time scale of a few nanoseconds, a high temperature (i.e., >1000 K) is adopted for accelerated reaction events. To apply the results from MD simulations to practical pyrolysis processes, a kinetic model based on a set of ordinary differential equations was established, which is capable of describing the key products of PET pyrolysis as a function of time and temperature. It was further exploited to determine the optimal reaction conditions for low environmental impact. Overall, this study conducted a detailed mechanism study of PET pyrolysis and established an effective kinetic model for the main species. The approach presented herein to extract kinetic information such as detailed kinetic constants and activation energies from atomistic MD simulations can also be applied to related systems such as the pyrolysis of other polymers.

Study the Effect of Operating Temperature on Performance in Dry Scroll Vacuum Pump

The dry scroll vacuum pump is a kind of variable capacity dry vacuum pump that is applied in chemical, pharmaceutical, semiconductor, and scientific instruments. Analyzing the thermodynamic characteristics of the scroll vacuum pump and studying the impact of operating temperature on its consistent performance are necessary for the design and application of the cooling system of the scroll vacuum pump. Based on the dynamics mesh method, the computational fluid dynamics (CFD) simulation model of a multi-stage dry scroll vacuum pump is established in this study. Under the suction pressure of 1000 Pa, the simulation calculation is carried out at different operating temperatures of fixed scrolls (25 °C, 45 °C, and 65 °C). The results show that the pumping speed, the gas compression power, and the energy efficiency ratio are significantly affected by different temperatures. The operating temperature of the pump has been reduced from 65 °C to 25 °C, the pumping speed is increased by approximately 5.97%, the gas compression power is increased by approximately 4.32%, and the energy efficiency ratio is increased by approximately 1.745%. This research provides a transient simulation method using dynamic mesh technology for the study of the dry scroll vacuum pump, and the results can provide a theoretical basis for the design and application of the cooling system of the dry scroll vacuum pump.