Dynamics Method Research Articles

Unsaturation triggers specific adsorption performance of water films in the clay nanopores

Soil is typically unsaturated, with water films covering the soil particles playing a crucial role in soil mechanics, structure, and element transport. However, the unusual behavior of these water films and the underlying mechanisms are not yet fully understood. This study, which used molecular dynamics methods, sheds light on the distinct interactions between water films and clay surfaces under unsaturation. At the water-mineral interface, water molecules formed a layered structure, while they rearranged as a meniscus as the unsaturation extent increased. On the other hand, unsaturation had a significant impact on the location of water molecules at the water-vapor interface, but only a limited effect at the water-mineral interface. The water’s orientational ordering and hydrogen bonding interactions were significantly affected by changes in relative humidity (RH). Based on the distance-dependent diffusion coefficient, the water molecules within the water film were classified into three types: WT1 (< 5 Å) had faster diffusivity at higher RH, WT2 (5–6 Å) had comparable diffusivity at any RH, and WT3 (> 6 Å) had faster diffusivity at intermediate RH. This classification was supported by the retention dynamics analysis. The specific behaviors mentioned above, which are associated with unsaturation, are closely linked to Na+ hydration. This is because the interaction between water and Na+ is more pronounced than the interaction between water and minerals or Cl−. The results indicate that unsaturation triggers specific adsorption behaviors of water films that cover the clay surfaces. These behaviors should be considered in interfacial processes and environmental engineering.

On the thermodynamics of DNA double strand in the Peyrard-Bishop-Dauxois model

The temperature dependence of energy, partition function, entropy and free energy, describing a first-order-like phase transition of a DNA molecule is calculated based on the direct method of molecular dynamics for the classical Peyrard-Bishop-Dauxois model. It is shown that without taking into account the quantum freezing of the degrees of freedom at low temperatures, the relationship between these quantities is not determined. The latent heat of DNA melting is calculated for homogeneous PolyA/PolyT and PolyG/PolyC DNA chains. It is shown that this melting transition corresponds to a sharp temperature dependence of the heat capacity.

MSD-based transient fluid model of liquid circular angular accelerometer for vibration-induced error analysis

This paper investigates the errors induced by linear vibration in the fluidic system of liquid circular angular accelerometers (LCAAs). A two-dimensional mass-spring-damper model is proposed to analyze the pressure difference between both sides of LCAA transducer subjected to linear vibration in both transient and steady states, where the compressibility of fluid is taken into account. The complex flow patterns of fluid are simplified to the positional changes of fluid particles. Springs and dampers are utilized to simulate the forces inside the fluid and between the fluid and the tube wall. Simulations are carried out based on the linear acceleration step excitation to explore the influence of model parameters, LCAA structure parameters and fluid parameters. The proposed model is validated by comparing the characteristics of the simulated pressure difference with their corresponding theoretical values, and is further verified by the comparison with the results from computational fluid dynamics method. Furthermore, the pressure difference under linear acceleration excitations in various forms is analyzed. The results indicate that the abrupt changes in linear acceleration are the primary cause of pressure difference oscillation, and the compressibility of fluid leads to increased pressure difference.

Molecular dynamics study of the influence of electric fields on water penetration in metal confined nanochannels

Electric field regulation of water penetration in nanochannels is an important method to address membrane fouling issues. Investigating the mechanism of electric field effects on water penetration in metal-confined nanochannels is highly meaningful. This article uses molecular dynamics methods to study the characteristics of water penetration in copper nanochannels. The influence and mechanisms of different types of applied electric fields on the water penetration within the channels were analyzed. The results indicate that applying electric fields in the y and z directions can enhance water penetration efficiency within the channels. Furthermore, a sinusoidal electric field has a greater enhancing effect on water penetration compared to a uniform electric field. Particularly, with a sinusoidal electric field frequency of 50 GHz, favorable water penetration effects were observed, with maximum increases in transport rate and axial diffusion coefficient of 197.5 % and 249.7 % respectively, relative to the absence of an electric field. The sinusoidal electric field exhibited greater capability in accelerating water molecule movement, leading to a rise in system temperature, with a maximum temperature increase of 46.9 %. These findings provide microscopic evidence for the feasibility of electric field regulation of water penetration in nanochannels, offering a theoretical foundation for enhancing nanoconfined water penetration behavior within channels.

Study on Flow Characteristics of Integrated Natural Circulation Reactor Under Inclined Conditions

In order to study the flow characteristics of an integrated natural circulation reactor under inclined conditions, a typical three-dimensional analysis model of natural circulation was established. The natural circulation under inclined conditions was numerically simulated using the computational fluid dynamics method, and the velocity and temperature distribution characteristics of heat exchangers and mixed-flow channels with different inclined angles were analyzed. The results show that as the inclination angle of the heat exchanger flow rate increases, there is a spatial migration phenomenon corresponding to the direction of the average flow rate. A large inclination angle will lead to a serious deterioration of the natural circulation capacity in the lower channel. Under inclined conditions, there is a phenomenon of temperature stratification in the mixed-flow channel.

A study on the effects of long-term radiation exposure on superconducting magnets in MRI-Guided proton therapy

In this publication, we offer the first assessment of the long-term radiation impact on superconducting magnets utilized in MRI-guided proton therapy. We explore both uniform and non-uniform magnetic fields and create three improved therapy plans for shallow (brain), medium (liver), and deep (prostate) targets. The evaluation of radiation damage in superconducting magnets using therapy plans is carried out through the implementation of the Monte Carlo method, molecular dynamics method, and modified NRT model. The results of the three plans show that a large amount of particles do enter the superconducting magnet during the treatment, with a preponderance of photons and neutrons. For superconducting magnets in MRI systems, the closer the coil is to the target area, the greater the radiation damage, and the extent of radiation damage increases with the energy of the incident proton beam. The PKA with high energy can induce temperature fluctuations locally in the superconducting coils, but does not pose a threat to its mechanical properties. Following 20 years of continuous operation, the DPA of the internal coils is about 2.3097E-17, and the maximum dose to insulating layer is about 1.25 Gy. The results of this paper show that MRI-guided proton therapy poses no threat to the long-term operation of superconducting magnets.

Localized Phonon Transport Study of GaN/SiO2 Core/shell Nanowires under Thermal-Stress Coupling.

In order to comprehensively explore the intricate mechanisms of thermo-mechanical interactions, this study employs the molecular dynamics method to investigate the influence of heat flux density, shell thickness and length, as well as stress on the radial interface phonon transport in GaN/SiO2 core/shell nanowire. Additionally, the surface eigenmode decomposition method is employed to analyze the interface phonon dispersion curves. The investigation reveals that with increasing heat flux density, internal thermal stresses intensify, leading to a complex distribution of thermal stresses within the system. Under the influence of thermal stress, the nonlinear acoustic properties interact with phonon scattering, resulting in the pronounced localization of interface phonons. Compressive stress causes an upshift in low-frequency phonons, while tensile stress induces a downward shift in the high-frequency optical branches at the interface. The localized phonon vibrations at the SiO2/GaN interface under nonuniform stress are identified as the primary cause for the abundant presence of nondispersive phonon modes at the radial interface. By elucidating the subtle interplay between lattice vibrations and stress fields, this study offers a novel and profound understanding of thermo-mechanical coupling effects, thereby providing innovative theoretical foundations for the design and performance management of thermoelectric devices.

Fracture behavior of graphene with intrinsic defects and externally introduced defects

Introducing and regulating defects to prepare functional graphene has become a research hotspot. However, most studies focus on the mechanical properties of functional graphene or the influence of a single defect, which cannot reflect the influence of multiple coupled defects on mechanical properties. In this study, molecular dynamics methods were used to investigate the fracture behavior of graphene under the coupled effects of intrinsic defects such as vacancies, cracks, and topological defects, as well as external introduced defects such as epoxy groups and hydroxyl groups. The results showed that the fracture behavior of graphene is strongly related to the defects' type, concentration, and functionality. Under the same conditions, the epoxy group has the strongest leading effect on fracture, followed by cracks, Stone-Wales topological defects, and hydroxyl groups. Based on the tensile simulation of defect-ordered graphene, the critical relative concentrations and functionalities of different defect types leading to fracture were further quantified and validated using an amorphous distribution model. In addition, the fracture mode dominated by epoxy groups is related to its functionality. Excessive or insufficient functionality will exhibit strong brittle fracture characteristics, and when the functionality is at a certain threshold, it will exhibit obvious ductile fracture characteristics; while hydroxyl-dominated fracture presents brittle mode. Finally, the coupled fracture mechanism was analyzed from the aspects of bonding characteristics and system energy. The research results can provide reference and reference for the theoretical research and technological development of graphene.

Effects of Nanowire Doping on Plasmon-Enhanced N2 Dissociation.

Doping a transition metal element into plasmonic systems can tune the optical properties of the system, which will potentially facilitate the plasmon-enhanced catalytic process. In this study, we applied the linear-response time-dependent density functional theory (LR-TDDFT) method with real-time electron dynamics and mean-field Ehrenfest dynamics methods to computationally investigate the effects of doping silver nanowires on plasmon-enhanced N2 dissociation. We calculated the absorption spectra for different doped systems, applied an external electric field to the system, and performed mean-field Ehrenfest dynamics to examine how plasmonic excitation will affect the N2 activation or dissociation. In addition, we also studied how the transition metal dopant affects the system's electronic structure and potential energy surface.

Molecular dynamics simulation study of post‐transition state bifurcation: A case study on the ambimodal transition state of dipolar/Diels–Alder cycloaddition

AbstractThe potential energy surfaces for the reactions of 1,3‐butadiene with 2‐hydroxythioacrolein and 2‐aminoacrolein exhibit ambimodal transition states leading to both dipolar (4 + 3) and Diels–Alder (4 + 2) cycloaddition products, thereby demonstrating a post transition state bifurcation feature. We have investigated the bifurcation dynamics of these reactions using three molecular dynamics (MD) methods: quasi‐classical trajectory, classical MD, and ring‐polymer MD simulations. The trajectory calculations were performed with the semiempirical GFN2‐xTB method with the element‐specific parameters optimized to reproduce the density‐functional theory calculations. The effect of water solvation was examined using an implicit solvation model, revealing significant differences in bifurcation dynamic between gas‐phase and solution‐phase reactions. Nuclear quantum effects were found to play a crucial role in the proton‐transfer process from the (4 + 3) intermediate to the (4 + 3) product in the case of the 2‐aminoacrolein reaction.

Numerically investigating the effect of using nanofluids on the thermal performance and coefficient of performance of a U-tube deep borehole ground source heat pump

In this study, a deep-borehole ground source heat pump was simulated using computational fluid dynamics (CFD) method. The thermal performance and coefficient of performance (COP) of the vertical ground source heat pump simulated with accuracy using CFD for water and 4 different nanofluids as working fluids were investigated. Two nanofluids contained silver and copper metallic nanoparticles and the other two nanofluids contained copper and aluminum oxide nanoparticles. For each of these nanofluids as well as water, the heat exchange rate, total exchanged heat, outlet temperature and COP were calculated and the results were compared together. The results showed that using nanofluids leads to increased exchanged heat. Nanofluids based on aluminum oxide, copper oxide, copper and silver nanoparticles resulted in 4.83, 5.76, 6.9, 7.69 percent increase in total exchanged heat, respectively. In addition to increased exchanged heat, using nanofluids increased the outlet temperature. Also, the results showed that the maximum and minimum increase in COP were 36.5% and 5.2% which were related to using silver and aluminum oxide nanoparticle-based nanofluids, respectively.

Morphological evolution of nano-droplets impinging on cylindrical wall: A molecular dynamics study

The impact of droplets on solid walls is the primary behavior in spray cooling, seawater desalination, self-cleaning, and other technological processes. Based on the molecular dynamics (MD) method, the morphological evolution characteristics of nanodroplets impinging on the copper cylinder wall are studied. The effects of droplet size, initial velocity, impact position, and wall wettability on nanodroplet dynamics are analyzed. The results indicate that a single nanodroplet impacting on a nanocylinder exhibits four distinct impact modes: spread-partially wrapped-deposition (SPD), spread-completely wrapped-deposition (SCD), spread-completely wrapped-splitting-deposition (SCSD), and spreading-partially wrapped-splitting-deposition (SPSD). The trend of the influence of initial velocity and droplet size on the impact mode is similar. As the initial velocity and droplet size increase, the droplet’s kinetic energy and inertia force increase, successively exhibiting the SPD, SCD, and SCSD modes. The trend of the influence of impact position and wall wettability on the droplet impact mode is similar. When the impact eccentricity distance is small, and the wall is highly hydrophilic, it exhibits the SCD mode. With increasing impact eccentricity and enhanced wall hydrophobicity, the adhesion force between the droplet and the cylinder wall decreases, making the droplet less likely to be captured and more prone to splitting, exhibiting the SPSD mode. The change in droplet centroid height and mean square displacement could predict whether the droplet undergoes a splitting mode, and its influence is most significant at the impact position. Constrained by the cylindrical wall, the droplet impacts radially and spreads primarily in that direction. With the enhancement of wall hydrophilicity, the migration region of the three-phase contact line expands, and the droplet spreading transforms into synchronous development along the radial and axial directions. The research results can enrich the dynamic mechanism of micro-nano scale droplet impact and provide potential guidance for optimizing relevant technologies.

On the mechanism of Ca(OH)2 structure modulation by surfactants: Experimental and calculative studies

Surfactants are widely used for structure modulation of calcium-based materials. However, the modification mechanisms underlying the CaO digestion improved by surfactants for Ca(OH)2 production remain unclear. This study employed experiment methods, Density Functional Theory (DFT), and Molecular Dynamics methods (MD) to reveal the mechanism of surfactant modulation at a molecular level. The adsorption energy of Primary Alcohol Ethoxylate (AEO), Sodium Dodecyl Sulfate (SDS), H2O, and Dodecyl Trimethyl Ammonium Bromide (DTAB) on CaO(001) surface were −52.62, −51.98, –23.79, and 3.96 kcal/mol, respectively. The strong chemisorption of AEO and SDS on the surface of CaO improved its structure stability. AEO and SDS weakened the diffusion of H2O to CaO surface, thus causing the reaction between CaO and H2O to be suppressed. After being modulated by SDS and AEO, better crystallinity of Ca(OH)2 and finer crystalline grains were observed with the formation of developed pore structure. AEO has a longer molecular chain, giving better modification performance. On the contrary, DTAB accelerated the diffusion of H2O to CaO surface, leading to more energy released and causing the fast growth of Ca(OH)2 crystals, as evidenced by the much larger particle size compared to that of AEO and SDS. This process led to the creation of a larger pore structure. Desulfurization was used as a performance indicator to evaluate the surfactants modulation efficacy. The sulfur capacity of Ca(OH)2 regulated by 1 % AEO was 100.05 mg/g, being the highest among the used surfactants. For comparison, the sulfur capacity without additives was 49.64 mg/g. This study shows that nonionic surfactants are an ideal choice for regulating the structure of Ca(OH)2, as they can effectively inhibit crystal growth.

Epidemiological model including spatial connection features improves prediction of the spread of pine wilt disease

In recent decades, the tree killing pine wilt disease (PWD) has been spreading globally and has caused substantial damage, particularly in China, resulting in annual losses of nearly $15 billion. This disease is caused by the pine wood nematode (Bursaphelenchus xylophilus) and is transmitted by its vector insect (Monochamus spp.). However, there remains limited understanding of the factors influencing PWD transmission, especially anthropogenic factors. For the first time, we employed a dataset of propagation factors that based on the transportation of pine wood transmission and used an enhanced infectious disease dynamics method to quantitatively predict the likelihood of future PWD infections across the entire distribution range of pine trees in China. The validation results show that the risk of infection in potential areas of PWD will further increase in China, with the average risk surpassing 30% in 2023 and reaching 50% by 2025 in the study areas. Meanwhile, we observe that human factors, such as transportation of timber, are becoming the main cause of the rapid spread of PWD and require extra vigilance. By incorporating spatial connections between samples as features for PWD prediction, the Area Under the Curve (AUC) score of the model reached 0.90. This signifies a highly accurate prediction of the pivotal areas for PWD dissemination, providing valuable guidance for the precise development of prevention and control measures, and presenting innovative approaches for analogous studies.

FSSH-2: Fewest Switches Surface Hopping with Robust Switching Probability.

This study introduces the FSSH-2 scheme, a redefined and numerically stable adiabatic Fewest Switches Surface Hopping (FSSH) method for mixed quantum-classical dynamics. It reformulates the standard FSSH hopping probability without using nonadiabatic coupling vectors and allows for numerical time integration with larger step sizes. The advantages of FSSH-2 are demonstrated by numerical experiments for five different model systems in one and two spatial dimensions with up to three electronic states.

Effect of combined surge and pitch motion on the aerodynamic performance of floating offshore wind turbine

Floating offshore wind turbines (FOWTs) can encounter variations in the phase difference and amplitude of combined surge-pitch platform motion. The phase difference between surge and pitch movement can result in the superposition or cancellation of wind turbine motion, potentially leading to significant changes in its aerodynamic characteristics. Herein, a wind turbine model was developed using the computational fluid dynamics (CFD) method to investigate the aerodynamic performance of the wind turbine. The findings revealed significant variations in the aerodynamics characteristics of the wind turbine when subjected to surge and pitch motions. When the rotor moves forward with a large relative velocity, dynamic stall can be triggered and induce the violent fluctuation of aerodynamic load. Moreover, vortex ring state (VRS) may occur when the wind turbine moves backward, leading to the recirculation of tip and root vortices and possibly causing negative thrust and torque. The trend of the drag force acting on the tower exhibits an almost complete opposition to that of the rotor thrust with the change of phase difference in the combined surge-pitch motion. It is also noted that the tower lift fluctuates asymmetrically, and as the platform motion amplitude increases, the tower lift gradually increases towards one side.

VIRTSI: A novel trust dynamics model enhancing Artificial Intelligence collaboration with human users – Insights from a ChatGPT evaluation study

The rapid integration of intelligent processes and methods into information systems in the Artificial Intelligence (AI) era has led to a substantial shift towards autonomous software decision-making. This evolution necessitates robust human oversight, especially in critical domains like Healthcare, Education, and Energy. Human trust in AI plays a vital role in influencing decision-making processes of users interacting with AI.This paper presents VIRTSI (Variability and Impact of Reciprocal Trust States towards Intelligent systems), a novel rigorous computational model for human-AI Interaction. VIRTSI simulates human trust states, spanning from overtrust to distrust, through user modelling. It comprises: 1. A trust dynamics representational model based on Deterministic Finite State Automata (DFAs), illustrating transitions among cognitive trust states in response to AI-generated replies. 2. A trust evaluation model based on Confusion Matrices, originating from machine learning and Accuracy Metrics, providing a quantitative framework for analysing human trust dynamics. As a result, this is the first time that trust dynamics have been thoroughly traced in a representational model and a method has been developed to assess the impact of possibly harmful states like overtrust and distrust.An empirical study on the recently launched Large Language Model of generative AI, ChatGPT (version 3.5), provides a radical underexplored AI-generated platform for evaluating the human-AI interaction through VIRTSI. The study involved 1200 interactions of real users as well as AI experts together with experts in two very different domains of evaluation, namely software engineering and poetry. This study traces trust dynamics and the emerging human-AI interaction, in concrete examples of real user synergies with generative AI. The research reveals the vital role of maintaining normal trust states for optimal human-AI interaction and that both AI and human users need further steps towards this goal. The real-world implications of this research can guide the creation and evaluation of user interfaces with AI and the incorporation of functionalities in the development of generative AI chatbots in terms of trust by providing a new rigorous DFA representational method of trust dynamics and a corresponding new perspective of confusion matrix evaluation method of the dynamics’ impact in the efficiency of human-AI dialogues.

A comprehensive study on passive cooling of a PV device using PCM and various fin configurations: Pin, spring, and Y-shaped fins

This study addresses the need for effective passive cooling strategies in compact photovoltaic (PV) modules by exploring three distinct fin shapes—pin fin, Y-shaped fin, and spring fin—utilizing both numerical simulations and experiments. The objective is to enhance heat transfer rates in PV devices through extended surfaces and phase-change material (PCM). Departing from conventional approaches like metal foams and plate fins that contribute to increased weight and system complexity, the research employs the finite volume method in computational fluid dynamics for numerical simulations, validated with experimental data. Comparative scenarios include fins with the same cross-sectional area and the same volume, revealing that the pin fin configuration outperforms others significantly. An experimental focus on pin fin numbers and lengths demonstrates a remarkable 9 °C temperature reduction with fully saturated pin fins, translating to a 4 % increase in efficiency and a noteworthy 0.8 V enhancement in open-circuit voltage. The findings underscore the potential of this proposed PV-PCM passive cooling approach for achieving performance enhancements while being easily constructed at a lower cost, providing a cost-efficient solution with clear quantitative results indicating temperature reduction, efficiency improvement, and enhanced voltage.

An efficient uncertainty propagation method for nonlinear dynamics with distribution-free P-box processes

The distribution-free P-box process serves as an effective quantification model for time-varying uncertainties in dynamical systems when only imprecise probabilistic information is available. However, its application to nonlinear systems remains limited due to excessive computation. This work develops an efficient method for propagating distribution-free P-box processes in nonlinear dynamics. First, using the Covariance Analysis Describing Equation Technique (CADET), the dynamic problems with P-box processes are transformed into interval Ordinary Differential Equations (ODEs). These equations provide the Mean-and-Covariance (MAC) bounds of the system responses in relation to the MAC bounds of P-box-process excitations. They also separate the previously coupled P-box analysis and nonlinear-dynamic simulations into two sequential steps, including the MAC bound analysis of excitations and the MAC bounds calculation of responses by solving the interval ODEs. Afterward, a Gaussian assumption of the CADET is extended to the P-box form, i.e., the responses are approximate parametric Gaussian P-box processes. As a result, the probability bounds of the responses are approximated by using the solutions of the interval ODEs. Moreover, the Chebyshev method is introduced and modified to efficiently solve the interval ODEs. The proposed method is validated based on test cases, including a duffing oscillator, a vehicle ride, and an engineering black-box problem of launch vehicle trajectory. Compared to the reference solutions based on the Monte Carlo method, with relative errors of less than 3%, the proposed method requires less than 0.2% calculation time. The proposed method also possesses the ability to handle complex black-box problems.

Factor analysis method for delay dynamics in Nigerian Tin Can Island Port for sustainable development

The effect of efficient and effective port system on the economy viability of any nation cannot be over emphasis. This study investigated factors that could be termed as delay causative factors in Nigerian ports industry using TIN CAN Island port complex as a case study. A well-structured questionnaire was developed for this research and 72 respondents, who are port users (custom officers, employees, and customers), were asked to rank the variables perceived to be causing delay at the port according to their respective perception of the effect of each factor on delay factors at the port. The validity of the research instrument was done using Cronbach Alpha. There are several factors that were thought to be working together in reducing efficiency in Nigerian ports and these factors were analyzed using factor analysis method. It was discovered from the analysis that Lack of Government Authority, Ullage Constraint, Inadequate Berthing, Logistics Delay, Financial Constraint and Equipment Breakdown are major factors that cause delay at Tin Can Island Port Lagos. These highlighted factors should be paid special attention in order to reduce delay in Tin Can Island port which will in turns lead to more revenue for the country.