Transient Dynamics Simulations Research Articles

Transient dynamics simulation of helicopter tail transmission shaft damage

Abstract Using the LS-DYNA explicit dynamic analysis software, a finite element model of projectile damage in helicopter tail transmission shaft was established with the Johnson-Cook intensity model. The dynamic response of the tail transmission shaft during bullet penetration was simulated dynamically, revealing that projectile damage is the primary mode of failure. Three typical angles were selected to simulate the penetration process, and results indicate that compared to vertical and 45°bullet penetrations, tail transmission shaft damage is more severe.

Design of a Wave Generation System Using an Oscillating Paddle-Type Device Anchored to Fixed Structures on the Coast

Wave energy, a form of renewable energy, is derived from the movement of sea waves. Wave energy generation devices are technologies designed to harness this resource and convert it into electricity. These devices are classified based on their location, size, wave direction, and operating principle. This work presents the design of an oscillating device for harnessing wave energy. For this purpose, computational fluid dynamics and response surface methodology were employed to evaluate the influence of the percentage of the blade height submerged below the water surface (X1) and the distance from the device to the breakwater in terms of the percentage of the wave length (X2). The response variable studied was the hydrodynamic efficiency (η) of the device. Transient fluid dynamic simulations were carried out using Ansys Fluent software 2023 R1, with input conditions based on a wave spectrum characteristic of the Colombian Pacific Ocean. Analysis of variance determined that both factors and their interaction have significant effects on the response variable. Using the obtained regression model, the optimal point of the system was determined. Numerical results showed that the maximum η of the system was achieved when the device was submerged at 75% of its height and was positioned 10% of the wave length away from the vertical breakwater. Under this configuration, η was 64.8%. Experimental validations of the optimal configuration were conducted in a wave channel, resulting in a η of 45%. The difference in efficiencies can be attributed to mechanical losses in the power take-off system, which were not considered during the numerical simulations.

Design and analysis of a 20-feet modular cold storage system

Cold storage plays an essential role in the cold supply chain, especially for fishery products. Compact cold storage systems that can be easily moved across various locations are attractive for archipelagic regions. This study aims to design and analyze a 20-ft modular cold storage system. The design stages include the development of a geometrical model, calculation of cooling load, and selection of a refrigeration machine. The analysis of the designed cold storage system was performed using transient computational fluid dynamic simulations using Ansys Fluent. The compact 20-ft cold storage design consists of three main rooms: the anteroom, air blast freezer room, and freezer storage room. The calculation results showed a maximum cooling load of about 6.6 kW occurring in the air blast freezer room at noon. According to the temperature distribution from the transient computational fluid dynamic simulation, each room had different cooling characteristics, with the highest cooling rate of 94.59 W/h in the air blast freezer room, achieving a targeted temperature of −40 °C in 5 h.

A three-level regulatory mechanism of the aldo-keto reductase subfamily AKR12D

Modulation of protein function through allosteric regulation is central in biology, but biomacromolecular systems involving multiple subunits and ligands may exhibit complex regulatory mechanisms at different levels, which remain poorly understood. Here, we discover an aldo-keto reductase termed AKRtyl and present its three-level regulatory mechanism. Specifically, by combining steady-state and transient kinetics, X-ray crystallography and molecular dynamics simulation, we demonstrate that AKRtyl exhibits a positive synergy mediated by an unusual Monod-Wyman-Changeux (MWC) paradigm of allosteric regulation at low concentrations of the cofactor NADPH, but an inhibitory effect at high concentrations is observed. While the substrate tylosin binds at a remote allosteric site with positive cooperativity. We further reveal that these regulatory mechanisms are conserved in AKR12D subfamily, and that substrate cooperativity is common in AKRs across three kingdoms of life. This work provides an intriguing example for understanding complex allosteric regulatory networks.

Non-back-drivable clutch based self-locking mechanism of prosthetic joint to improve manipulation stability.

During activities of daily living (ADLs), the wrist is mainly engaged in positioning and directing the hand. Researches have demonstrated that restoring wrist mobility can significantly enhance the manipulation ability, reduce body distortion caused by motion compensation, and improve the quality of life for amputees. However, most daily activities, particularly the delicate ones, place high demands on the ability of wrist to maintain a certain rotation angle, also known as non-back-drivable ability, which poses a challenge to the design of prosthetic wrists. To address this issue, various solutions have been proposed, including motor holding brakes, high reduction ratio reducers, and worm gears. However, the motor holding brake only functions after a power outage and cannot continuously prevent torque from the load end. The latter two solutions may alter the transmission ratio, resulting in reduced movement speed and transmission efficiency. Therefore, how to design a miniaturized non-back-drivable mechanism without changing the transmission ratio so that the forearm rotational freedom can be locked at any position for any duration is a problem to be solved in the research of prosthetic wrist designs. This paper presents a line-contact based non-back-drivable clutch (NBDC) that does not cause changes in the transmission ratio, ensuring the motion performance of the prosthetic limb. At the same time, it does not introduce additional friction in the forward transmission process, guaranteeing the overall efficiency. Most importantly, it only allows the torque transmitting from the motor to the load, prevents the load reversely from driving back even in a power failure condition, significantly improving the stability, safety, and comfort. Detailed kinematic and static analyses of the working process has been conducted, and transient dynamics simulation has been performed to verify its effectiveness. Through experiments, it is demonstrated that the self-locking torque of the output end could reach approximately 600Nmm, and the unlocking torque of the input end is about 80Nmm, which can be effectively integrated in prosthetic wrist rotation joints, contributing to the performance, safety and energy saving of prosthetic joint systems.

Molecular dynamics investigation on the interfacial thermal resistance between annealed pyrolytic graphite and copper.

Modern highly integrated microelectronic products often face the challenge of internal heat dissipation, leading to a significant decrease in their operational efficiency. Annealed Pyrolytic Graphite (APG), due to its superior thermal conductivity, has garnered attention from researchers. The interface thermal resistance between APG and supporting materials like copper significantly affects heat transfer during APG's operation. Existing studies rarely delve into the influence of factors such as the shape of APG material interfaces on thermal resistance from a microscopic perspective. In this paper, utilizing transient thermo-reflectance method and non-equilibrium molecular dynamics simulations, the interface thermal resistance of the APG-Cu structure was investigated under different conditions. The impact of parameters such as copper thickness, interface micro-surface morphology, and APG thickness on the calculated interface thermal resistance was examined. Simulation results revealed that copper thickness had a minor effect on the interface thermal resistance. This is because the phonon participation ratio remains unaffected by changes in the thickness of the copper layer. The interfacial thermal resistance beneath microscopically cylindrical copper surfaces was considerably lower than that of rectangular copper surfaces. This is because beneath the cylindrical surface, the enlarged interface contact area facilitates enhanced thermal transport between the interfaces. The computed results of the radial distribution function in the paper also indirectly validate this viewpoint. The magnitude of interfacial thermal resistance for different APG layers was influenced by the coupling effect of intermolecular forces and the layered stacking structure of APG. The interfacial thermal resistance under the condition of three layers of APG reaches its minimum value, which is 2.2 × 10-9 (K m2 W-1). Furthermore, from the phonon perspective, it is found that the interfacial thermal resistance with different numbers of APG layers is closely related to the localization or delocalization state of phonons. As the number of APG layers increased, the interface thermal resistance showed a trend of initial decrease followed by an increase, this is because the average phonon participation ratio increases and then decreases with the number of APG layers. The average phonon participation ratio reaches its maximum value of 0.45778 under the condition of three layers of APG.

Phonon resonance modulation in weak van der Waals heterostructures: Controlling thermal transport in graphene–silicon nanoparticle systems

The drive for efficient thermal management has intensified with the miniaturization of electronic devices. This study explores the modulation of phonon transport within graphene by introducing silicon nanoparticles influenced by van der Waals forces. Our approach involves the application of non-equilibrium molecular dynamics to assess thermal conductivity while varying the interaction strength, leading to a noteworthy reduction in thermal conductivity. Furthermore, we observe a distinct attenuation in length-dependent behavior within the graphene–nanoparticles system. Our exploration combines wave packet simulations with phonon transmission calculations, aligning with a comprehensive analysis of the phonon transport regime to unveil the underlying physical mechanisms at play. Lastly, we conduct transient molecular dynamics simulations to investigate interfacial thermal conductance between the nanoparticles and the graphene, revealing an enhanced thermal boundary conductance. This research not only contributes to our understanding of phonon transport but also opens a new degree of freedom for utilizing van der Waals nanoparticle-induced resonance, offering promising avenues for the modulation of thermal properties in advanced materials and enhancing their performance in various technological applications.

Numerical and experimental study of two-vehicle overtaking process

The overtaking process between two simplified Ahmed body models is studied using a set of static experiments to provide a comparison basis for the numerical study. Both steady-state (static) and transient (dynamic) simulations are performed. There are notable differences of the drag and side force coefficients between the predicted and experimental results in the wake effects on the overtaking model as well as under a situation when two models are parallel for the static tests. These differences are attributed to the SST [Formula: see text] model, which is a two-equation Reynolds-averaged Navier-Stokes equation (RANS) turbulence model with an assumption of isotropic eddy viscosity, employed in the simulation. A more advanced turbulence model that simulates large-eddy organized motion in a turbulent flow and which uses an anisotropic eddy viscosity formulation in the near-wall flow subregion would increase the prediction accuracy for the overtaking simulation. A comparison of the results for the steady-state and the transient simulations at various relative velocity ratios ([Formula: see text]) shows that the quasi-steady approach is suited to simulate the dynamic two-vehicle overtaking process when the condition [Formula: see text] is met.

Aeroacoustic simulation of transient vortex dynamics inside double-degree-of-freedom orifice-cavity structure subjected to high-intensity acoustic waves

As a noise reduction device commonly used for aero-engines at present, the double-degree-of-freedom acoustic liner has the advantage of broadband noise elimination, which is related to the energy transformation during the process of vortex generation and shedding from its dual orifice-cavity unit when subjected to high-intensity acoustic waves. Based on the compressible linear Navier-Stokes equations with the influence of nonlinear thermo-viscous acoustics, this study simulated the three-dimensional acoustic-vortex coupling field of dual orifice-cavity structures with different orifices' distances under high-intensity acoustic waves with different frequencies. The first and second resonance frequencies of the structures were found by the transmission loss coefficient. Then, through the vortex dynamics analysis, the interference behavior of the vortex shedding with fusion and shifting was observed under the first resonance frequency when the orifices' distance was close. By establishing an energy transfer model, it was found that the energy transfer was concentrated at the upper orifice under the second resonance frequency, and the interference effect increased the vortex kinetic energy and viscous dissipation energy here under the first resonance frequency. The relevant research results provide a theoretical basis for the structural optimization of aerodynamic noise control devices of modern aircraft.

Gas composition tracking feasibility using transient finite difference [formula omitted]-scheme model for binary gas mixtures

Implicit finite difference method is popular numerical method for simulation of transient pipeline dynamics, governed by the system of Euler partial differential equations. If advection equation is included in the mathematical formulation, gas composition tracking is also possible. If implicit scheme is used for gas composition tracking, simulated concentration profiles are distorted due to the occurrence of numerical diffusion, a non-physical phenomenon, caused by the 1st order accurate numerical implicit scheme. Intensity of the numerical diffusion can be decreased by use of θ-scheme with arbitrarily chosen implicitness. In order to evaluate accuracy of such numerical scheme and adequacy for usage in actual application, numerical model must be evaluated on actual gas pipeline system topology with actual measured boundary conditions and compared to actual measured results. Aim of this paper is to assess whether hydrogen concentration tracking is feasible using such approach considering complex grid topologies. Paper highlights the peculiarities of the proposed θ-scheme and finite difference method and its impact on the calculated concentration profile for binary gas mixtures. Non-physical flow reversal issue and its impacts on concentration tracking in looped pipeline system is researched and explained. Simulation results shows high accuracy for simulated values of hydraulic variables compared to the measured values, in some cases fit is perfect. Discrepancy between measured and the simulated values of the pressures at nodes on the main transport route is negligible, while the discrepancy increases with the distance from the main transport routes. The largest discrepancy occurred on the most distant node and was between 1.7006 bar (4.85%) and 1.7119 bar (4.88%), depending on the θ value. On the other hand, simulated concentration profile lacks finer details due to the numerical diffusion effects while the simulated concentration profile lags the measured profile, partly by the impacts of the 1st order accurate scheme and partly by effects of non-physical reversed flows. Discrepancy between simulated and measured amplitude of the tracked concentration profile was negligible, while discrepancy due to the time delay of the simulated and measured profile was more expressed and ranged between 2h to 9h. Largest time delay was caused by the non-physical flow reversal.

Research on High-Speed Vibration and Structure Optimization of Multiwire Sawing Machine

To improve the sawing stability and slicing quality of an existing multi-wire saw under severe vibrations using a high wire speed, its structure is optimized to improve its structural stiffness, so that it can still maintain good operation stability under higher wire speed. First, a finite element simulation model is established based on the shape, structural and material characteristics of the multi-wire saw, and then a transient dynamic simulation calculation is carried out using finite element software to obtain the vibration characteristics of the machine, which is verified with the measured data. The results show that the error between the calculated and the measured value is less than 11.46%, which verifies the accuracy of the simulation. On this basis, a multi-objective optimization design method based on the response surface is used to optimize the structure of the whole machine, and the optimized model is simulated again to evaluate its optimization effect. The results show that the amplitude of the optimized machine at a 2400 m/min wire speed is equivalent to that of the original machine at a 1500 m/min wire speed, and the wire speed is increased by 60% year-on-year with the same operation stability, which can guide research on high-speed multi-wire saws and machine tool vibration control strategies.

Modeling and Analysis of Wave Energy Harvester with Symmetrically Distributed Galfenol Cantilever Beams.

In response to the challenges of difficult energy supply and high costs in ocean wireless sensor networks, as well as the limited working cycle of chemical batteries, a cylindrical wave energy harvester with symmetrically distributed multi-cantilever beams was designed with Galfenol sheet as the core component. The dynamic equation of the device was established, and ANSYS transient dynamic simulations and Jiles-Atherton hysteresis model analysis were conducted to develop a mathematical model of the induced electromotive force of the Galfenol cantilever beam as a function of deformation. Experimental validation demonstrated that the simulated results of the cantilever beam deformation had an average error of less than 7% compared to the experimental results, while the average error between the theoretical and experimental values of the induced electromotive force of the device was around 15%, which preliminarily verifies the validity of the mathematical model of the device, and should be subject to further research and improvement.

Research on the Vibration Reduction Mechanism of a New Tensioning Platform with an Embedded Superstructure

Aiming at the problem of precision driving and vibration suppression for sensitive payloads on-orbit, this paper proposes a new compliant platform based on an embedded superstructure and a smart material actuator. Firstly, the main structure of the platform is designed and optimized to achieve the expected indicators via the response surface method. Then, the vibration reduction mechanism of the platform with the embedded superstructure is studied by establishing an equivalent model. Following that, a four-phase superstructure is matched and designed with a compact space, and the results are verified by finite element modal analysis. Finally, both the tensioning performance and vibration reduction performance under fixed frequency harmonic disturbance are studied via transient dynamic simulation. Based on the obtained results, directions for future improvements are proposed. The relevant conclusions can provide a reference for function integration of precision tensioning and vibration suppression.

Detailed FE aircraft fuselage sections for water impact simulations in the pre-design process chain

The automatic generation of representative fuselage section models with a detailed discretization for the application in computer-aided transient dynamic simulations in the aircraft pre-design process chains is described in this paper. The process consists of Python routines to select and reduce the section from the full fuselage and to refine the mesh and extrude cross-sections in arbitrary zones of the section. By this, different mesh qualities can be integrated in the model according to its individual application. These functionalities were integrated in the structural modelling and sizing framework PANDORA. A simple reinforced panel was used to investigate its structural behaviour with different discretization options under a bending loading condition. Also, a fuselage section model reinforced using either one of the discretization options was subjected to a quasi-static loading. The model was then simulated under crash conditions to investigate its non-linear structural behaviour. The focus of this paper lays on the application and the local structural analysis of the detailed fuselage section in water impact simulations.

Differentiating Thermal Conductances at Semiconductor Nanocrystal/Ligand and Ligand/Solvent Interfaces in Colloidal Suspensions.

Infrared-pump, electronic-probe (IPEP) spectroscopy is used to measure heat flow into and out of CdSe nanocrystals suspended in an organic solvent, where the surface ligands are initially excited with an infrared pump pulse. Subsequently, the heat is transferred from the excited ligands to the nanocrystals and in parallel to the solvent. Parallel heat transfer in opposite directions uniquely enables us to differentiate the thermal conductances at the nanocrystal/ligand and ligand/solvent interfaces. Using a novel solution to the heat diffusion equation, we fit the IPEP data to find that the nanocrystal/ligand conductances range from 88 to 135 MW m-2 K-1 and are approximately 1 order of magnitude higher than the ligand/solvent conductances, which range from 7 to 26 MW m-2 K-1. Transient nonequilibrium molecular dynamics (MD) simulations of nanocrystal suspensions agree with IPEP data and show that ligands bound to the nanocrystal by bidentate bonds have more than twice the per-ligand conductance as those bound by monodentate bonds.

Enhancing Heat Transfer Behaviour of Ethylene Glycol by the Introduction of Silicon Carbide Nanoparticles: An Experimental and Molecular Dynamics Simulation Study.

As the critical component of automotive engine coolant, ethylene glycol (E.G.) significantly matters in heat dissipation. In this study, the key aim is to investigate the heat transfer behaviour of E.G. as nano-additives base fluid. The heat transfer capability of E.G./SiC nanofluid (N.F.) was experimentally and theoretically evaluated via transient hot wire methods and equilibrium molecular dynamics (EMD) simulation, respectively. M.D. simulation exhibited a great ability to accurately forecast the thermal conductivity of N.F. compared with the experiment results. The results confirmed that the thermal stability of N.F. is relatively greater than that of E.G. base fluids. An improvement mechanism of thermal conductivity and thermal stability under an atomic scale via the analysis of mean square displacement (MSD) and radial distribution function (RDF) calculation was elaborately presented. Ultimately, the results indicated that the diffusion effect and the increasing transition rate of liquid atoms are responsible for thermal conductivity enhancement.

Influence of a transient bubble dynamics cavitation model for squeeze film dampers on the run‐up behaviour of a turbocharger rotor

AbstractThe force response of squeeze film dampers and hydrodynamic bearings is significantly influenced by the occurence of cavitation inside the lubricant films. The viscosity of the occuring mixture of oil and air bubbles is vastly different than that of pure lubricant and therefore changes the pressure build‐up and thereby the stiffness and damping properties of the lubrication films. To accurately predict the force response of a squeeze film damper, the cavitation and its effect on the pressure build‐up therefore has to be taken into account. Well known cavitation algorithms for lubrication problems, like the Elrod algorithm or the two‐phase‐model, neglect the transient nature of outgassing and assume instantaneous bubble formation and collapse. In the presented paper, a transient bubble dynamics model based on the Rayleigh‐Plesset‐Scriven equation is utilised instead and its effect on the rotordynamic behaviour of a turbocharger rotor is examined based on fully transient multi body dynamics simulations.

Incorporation of thermal effects into the energy‐momentum consistent elastic model for fiber‐bending stiffness in composites

AbstractOwing to the wide acceptance of fiber reinforced composites in the lightweight structure industry, the need to study its thermo‐elastic behavior in dynamical multi‐body systems still remains an open question. Standard continuum models, by virtue of first‐order gradient of deformation, cannot capture curvature effects and hence appropriate extensions of the standard modeling techniques are indispensable to model the accurate physical stiffness. The fiber‐bending curvature are captured by introducing a higher‐order gradient of the deformation as an independent field in the standard continuum. This work explores in detail, a further extension of this continuum to understand the thermal effects on the bending stiffness of fiber bundle in fiber‐reinforced composites. Our proposed model incorporates the temperature of the composite and its bidirectional dependency with the higher‐order gradients of the deformation into the extended mechanical continuum model. The implementation of the model is pursued in the context of multi‐field mixed finite element method and dynamic variational principle. The principle of virtual power enables our extended non‐isothermal continuum to derive an energy‐momentum scheme of higher order. The resulting time‐integrator exhibits physically consistent locking‐ free numerical behavior in dynamical simulations. Our novel approach is illustrated by simple transient dynamic simulations with a hyperelastic, transversely isotropic, polyconvex material behavior. We investigate the conservation of total energy and total momentum in the framework of thermo‐elasticity and study the spatial and temporal convergence for long‐term dynamic simulations with coarser grids and increased accurate numerical solutions.

TecSB: An Open Web Tool of Energy Efficiency and Solar Energy Integration in Mexican Buildings

There is a need for stakeholders in the construction sector to evaluate energy efficiency and renewable energy generation alternatives appliable to buildings at early design stages. In this regard, public and private organizations have developed tools to compare different options. It was observed that when the objective was to create nearly Zero Energy Buildings (nZEB), the number of tools was still scarce. With this aim, this work presents a new, free digital tool that can predict, among others, energy consumption, energy generation, emissions savings, and payback time. For this purpose, different alternatives applicable to the roof, such as phase change material (PCM), insulation, and reflective paint, as well as to window-to-wall ratios (WWR), with four different glass technologies, can be evaluated. Furthermore, four renewable energy systems were available for comparison: the solar thermal collector (ST), photovoltaic (PV), flat hybrid solar collector (PVT), and low-concentration parabolic solar collector (LCPVT). Our tool was developed based on the results of transient dynamic building simulations of both residential and non-residential building models located in the hot semi-arid conditions of Monterrey, Mexico. Among the results, the small impact of using only reflective paint, the need to combine PCM with insulating material to obtain the best energy savings, and the large impact on emissions savings when using an LCPVT stand out.

Charge Transport Dynamics of Quasi-Type II Perovskite Janus Nanocrystals in High-Performance Photoconductors

CsPbBr3-Pb4S3Br2 Janus nanocrystals (NCs) are the only nanomaterial where the epitaxial structure of perovskite and chalcogenide materials has been realized at the nanoscale, but their exciton dynamics mechanism has not yet been thoroughly investigated or applied in photodetection applications. This work reports an attractive device performance of perovskite photoconductors based on epitaxial CsPbBr3-Pb4S3Br2 Janus NCs, as well as the carrier relaxation and transfer mechanism of the heterojunction. By a combination of transient optical absorption and quantum dynamics simulation, it is demonstrated that the photogenerated holes on CsPbBr3 can be successfully extracted by Pb4S3Br2, while the hole transfer proceeds about three times faster than energy loss and remains "hot" for about 300 fs. This feature has favorable effects on long-range charge separation and transport; therefore, the Janus NCs photoconductors exhibit an exceptional responsivity of 34.0 A W-1 and specific detectivity of 1.26 × 1014 Jones.