Computational Dynamics Method Research Articles

Comprehensive effects of aerodynamic performance and dynamic strength of aircraft wings after bird strike in numerical simulation

ABSTRCT To enhance the bird strike resistance of fixed-wing aircraft wings, a combined computational approach integrating nonlinear solid mechanics and fluid dynamics was employed to analyze the bird strike characteristics of both traditional aluminum alloy skins and novel composite materials skins. Additionally, a standardized procedure was established to simulate aircraft structural damage more comprehensively, swiftly, and accurately during bird strikes, along with diagnostic analysis of flow field changes near the wing post-impact. This method not only quantifies wing strength damage but also establishes corresponding relationships between damage severity and aerodynamic performance degradation. The research findings indicate that the deformation of composite material skin wings is only a quarter of that of aluminum alloy skin wings. Composite material skins absorb less harmful energy compared to aluminum alloy skins, with consistently lower stiffness reduction rates at various bird strike velocities. Velocity distribution on deformed wings with composite material skins exhibits minimal deviation compared to normal wings, thereby preventing airflow separation. The research results provide more comprehensive guidance for the selection of materials for bird strike resistance of aircraft wings and the airworthiness evaluation after bird strikes. Highlights This paper establishes a standardized procedure that enables a more comprehensive, faster, and higher-precision simulation of structural damage to the aircraft during a bird strike on the wing and allows for the diagnostic analysis of the flow field changes near the wing after bird strike. By coupling nonlinear solid mechanics and fluid dynamics computational methods, the aerodynamic performance of the wings at different angles of attack post-deformation is investigated. This approach not only quantifies the strength damage to the wings but also establishes corresponding relationships between the degree of damage and the deterioration in aerodynamic performance. The research yields insights into the aerodynamic performance degradation patterns with varying angles of attack for both composite material skin and aluminum alloy skin deformed wings. These findings can serve as valuable references for pilots in emergency situations, aiding in their decision-making regarding aircraft control.

Quasi-direct Quantum Molecular Dynamics: The Time-Dependent Adaptive Density-Guided Approach for Potential Energy Surface Construction.

We present a new quasi-direct quantum molecular dynamics computational method which offers a compromise between quantum dynamics using a precomputed potential energy surface (PES) and fully direct quantum dynamics. This method is termed the time-dependent adaptive density-guided approach (TD-ADGA) and is a method for constructing a PES on the fly during a dynamics simulation. This is achieved by acquisition of new single-point (SP) calculations and refitting of the PES, depending on the need of the dynamics. The TD-ADGA is a further development of the adaptive density-guided approach (ADGA) for PES construction where the placement of SPs is guided by the density of the nuclear wave function. In TD-ADGA, the ADGA framework has been integrated into the time propagation of the time-dependent nuclear wave function and we use the reduced one-mode density of this wave function to guide when and where new SPs are placed. The PES is thus extended or updated if the wave function moves into new areas or if a certain area becomes more important. Here, we derive equations for the reduced one-mode density for the time-dependent Hartree (TDH) method and for multiconfiguration time-dependent Hartree (MCTDH) methods, but the TD-ADGA can be used with any time-dependent wave function method as long as a density is available. The TD-ADGA method has been investigated on molecular systems containing single- and double-minimum potentials and on single-mode and multi-mode systems. We explore different approaches to handle the fact that the TD-ADGA involves a PES that changes during the computation and show how results can be obtained that are in very good agreement with results obtained by using an accurate reference PES. Dynamics with TD-ADGA is essentially a black box procedure, where only the initialization of the system and how to compute SPs must be provided. The TD-ADGA thus makes it easier to carry out quantum molecular dynamics and the quasi-direct framework opens up the possibility to compute quantum dynamics accurately for larger molecular systems.

Thermal Conductivity of Liquid Lead for the Fast Nuclear Reactor Coolant, Calculated by the Green-Kubo Method Using Molecular Dynamics Simulation

Comprehensive information about nuclear reactor coolant materials for application in heat-transfer systems is very important. One important physical property that needs to be known is the thermal conductivity. The goal of this work is to predict the thermal conductivity value of the liquid lead, which is one of the important candidates for cooling materials for Gen-IV fast nuclear reactor designs. The thermal conductivity of liquid lead in this study was predicted using the Green-Kubo scheme and the molecular dynamics (MD) computational method to collect the simulation data. The MD simulation was done in the NVT ensemble, using the Lennard-Jones interaction potential. We observe the thermal conductivity of the liquid lead can be studied based on the diffusion physical process. The thermal conductivity of the liquid lead obtained from this research is λ = 0.0113T + 8.8539 [W/mK]. As a conclusion, this result is very suitable, compared with the available experimental data, then the Green-Kubo method can be used to calculate the thermal conductivity of liquid metal as lead.

Fluid-induced vibration analysis of centrifugal pump including rotor system based on Computational Fluid Dynamics and Computational Structural Dynamics coupling approach

The flow-induced vibration of centrifugal pump under the effect of stator-rotor interaction are studied by Computational Fluid Dynamics method and Computational Structural Dynamics method based on the principle of one-way decomposition fluid-structure interaction. Firstly, the unsteady flow characteristics in centrifugal pump are studied by adopting the Computational Fluid Dynamics method, the numerical model of the whole flow field of the centrifugal pump is established, and the pulsating pressure characteristics of volute and impeller in the centrifugal pump are analyzed. The accuracy of the flow field modeling method and calculation method in this paper is verified by external characteristic test. Secondly, the vibration characteristic test of centrifugal pump is carried out, and the structural dynamic model and boundary conditions of centrifugal pump are verified and corrected in the modal test. Finally, the flow-induced excitation calculated by the flow field is simultaneously applied to the structural dynamics model of the centrifugal pump according to different transmission ways, and the flow-induced vibration of the whole centrifugal pump including the rotor system is calculated and analyzed by the Computational Structural Dynamics method in conjunction with rotor dynamics. Compared with the vibration test results, the validity of the flow-induced vibration calculation method of centrifugal pump in this paper is verified. The results show that under the influence of stator-rotor interaction effect, the blade passing frequency and shaft frequency are the main characteristic frequencies of pressure pulsation and dynamic response in the centrifugal pump.

Minimum-Lap-Time Planning of Multibody Vehicle Models via the Articulated-Body Algorithm

Minimum lap-time planning (MLTP) is a well-established problem in the race car industry to provide guidelines for drivers and optimize the vehicle’s setup. In this paper, we tackle the 3D nature of the problem in its full extension, making no simplifying assumptions on the mechanics of the system. We propose a multibody vehicle model, described by rigorous dynamical equations. To effectively handle the resulting complexity, we devised an efficient direct dynamics computational method based on Featherstone’s articulated-body algorithm (ABA). To solve the MLTP, we employed a direct-collocation technique, discretizing the problem so that all information of the 3D track is pre-processed and directly embedded into the discrete problem. This discretization approach turns out to be perfectly compatible with our vehicle model, leading to a solution in accessible computational time frames. The high level of detail of the model makes the proposed approach most useful for in-depth vehicle dynamics analyses on complex tracks. To substantiate the analysis, we provide a comparison with the results obtained by a double-track model on the Nürburgring Nordschleife circuit. Consistently with the average trend defined by the double track, the proposed model features a more dynamically rich behavior, realistically capturing the higher-order effects elicited by the sharp corners and the highly variable slope of the track.

Introducing NMR strategies to define water molecules that drive metal binding in a transcriptional regulator

Staphylococcus aureus CzrA is a paradigmatic member of the ArsR family of transcriptional metalloregulators, which are critical for the bacterial response to stress. Zinc binding to CzrA, which induces DNA derepression, is entropically driven, as shown by calorimetry. A detailed equilibrium dynamics study of different allosteric states of CzrA revealed that zinc induces an entropy redistribution that controls for DNA binding regulation; however, this change in conformational entropy only accounts for a small net contribution to the total entropy. This difference between the change in conformational entropy vs. total entropy of zinc binding implies a significant contribution of solvent molecule rearrangements to this equilibrium. However, the absence of major structural changes suggests that solvent rearrangements occur mainly on the protein surface and/or from zinc desolvation, concomitant with a dynamical redistribution of conformational entropy. Previous results also suggest that zinc binding not only leads to a redistribution of protein internal dynamics, but also release of water molecules from the protein surface. In turn, these water molecules may make a significant contribution to the allosteric response that results in dissociation from the DNA.Quantifying the differential hydration of two conformational states that share very similar crystal structures and then correlating this with the protein's solvent entropy change constitutes an unresolved problem, even when thermodynamics suggest a significant contribution of solvent entropy. Here, we present different avenues to dissect hydration dynamics in a metal-binding transcriptional regulator that provide different insights into this complex problem. We explore primary solution NMR tools for probing protein–water interactions: the laboratory frame nuclear Overhauser effect (NOE) and its rotating frame counterpart (ROE) between long-lived water molecules and the protein residues. The wNOE/wROE ratio is a promising tool for the detection of hydration dynamics near the surface of a protein in a site-specific manner, minimizing contamination from bulk solvent. Molecular dynamics simulations and computational methods designed to provide a spatially resolved picture of solvent thermodynamics were also employed to provide a more complete panorama of solvent redistribution.

A new approach to analyzing wellbore pressure dynamically in well-killing

Casing pressure during well-killing is both an unknown variable that must be addressed and a time-dependent function. Therefore, the calculation of the dynamic reaction of wellbore pressure during well-killing is a dynamic indeterminate boundary problem. Due to the intricacy of the analytical solution technique, finding an analytical solution for the dynamic issue of uncertain boundaries is nearly impossible. Current numerical simulation software is only capable of resolving problems with defined bounds (such as flow or pressure) and is incapable of continuously calculating the wellbore pressure, which varies dynamically with well-killing time. Developing a dynamic reaction computation method for wellbore pressure during well-killing can solve this issue. Based on the mathematical model and definite solution conditions of the wellbore pressure dynamic response under well-killing conditions, this paper applies the finite difference principle and constructs the calculation method of choke and kill wellbore pressure dynamic response through reasonable mesh division of wellbore and gradual iteration of the calculation process. The resultsdemonstrate that the maximum wellhead casing pressure value and the time node of peak value are both highly congruent with the measured data, indicating the method’s high reliability and highlighting its significance for the progress of oil and gas well control safety.

A novel strong ground motion duration to reduce computation time of structural time history analysis

As a widely used dynamic computation method for seismic response analysis of structures, time history analysis (THA) can be a time-consuming procedure in some situations. In order to reduce the calculation time, this study proposed a novel strong ground motion duration which can truncate the head and tail weak signals of records before THA. The initial point of proposed duration refers to the concept of bracketed duration, while the termination point is determined by the maximum displacement responses of equivalent single-degree-of-freedom (SDOF) systems of the structure. The relationship between the fundamental period and period-lengthening level of structure is counted from previous research and fitted with a formula which is used to compute the period range of equivalent SDOF systems. After comparing the structural responses and time-saved percentage of truncated records by proposed duration with those by other definition of durations, results prove that the proposed duration has significant time-saving procedure and reliable computation results on THA.

An Efficient Modeling Method for the Simulation of Ball Bearing Dynamics

Abstract Efficiency and accuracy play an important role in numerical simulation for ball bearings dynamics. In this work, three kinds of contact models are developed in vector form to represent the interactions in ball/raceway, ball/cage, and cage/raceway. Considering the fluctuation induced by friction and divergence by damping force in ball bearings, the dynamic computational methods based on the modifications in the formulation of friction and acceleration are proposed. Then the simplified ball bearing system is simulated by fixed and variable step integration methods. The comparison of results from both solutions and applied step size has indicated the validity and higher efficiency of the proposed methods. Furthermore, a full dynamics simulation of a 100 angular-contact ball bearing is conducted. Results show that the proposed models and methods have satisfactory stability and accuracy under a considerably long simulation time step.

Dynamic Characteristics Analysis of 3D Blade Tip Clearance for Turbine Blades with Typical Cracks

As well known, the crack is a typical fault of turbine blades, which is difficult to detect due to the weak fault features contained in the rotor vibration. Although some fault diagnosis methods based on blade tip timing (BTT) are proposed to detect blade cracks, the limited fault features can be extracted because the BTT signals contain only one-dimensional fault information. Based on the dynamic analysis, the cracked blade undergoes three-dimensional (3D) deformation so that it would be reflected in the changes of the three-dimensional blade tip clearance (3D-BTC). Therefore, the dynamic characteristics of the 3D-BTC of turbine blades with typical cracks should be investigated to obtain its change rule and achieve a more comprehensive diagnosis of blade cracks. In this paper, the 3D finite element model of the turbine blisk is established, and the fluid-thermal-solid coupling analysis is implemented to calculate the blade deformation. Then, a novel dynamic computation method is proposed to calculate the 3D-BTC based on the blade deformation. The typical blade cracks are taken into consideration, and the dynamic characteristics of the 3D-BTC regarding the typical cracks are analyzed to obtain its change rule. The results show that abundant crack fault information can be obtained based on the 3D-BTC, which can facilitate the comprehensive diagnosis of turbine blade cracks.

Synthesis and conformational studies of 5-bromo-1-[(N-substituted-carbamoyl)methyl]-7-azabenzimidazoles

The Cs2CO3-catalysed condensation of 5-bromo-7-azabenzimidazole with a series of bromomethyl ketones has afforded a small library of ten, novel 5-bromo-1-[(N-substututed-carbamoyl)methyl]-7-azabenzimidazoles. Rotamerism in the products, as evidenced by the splitting of 1H- and 13C-NMR signals, is attributed to hindered internal rotation about the amide N-C(=O) bond, and has been explored using dynamic NMR (DNMR) analysis and computational methods at the GIAO B3LYP/6-311+G(2d,p) level of theory. Coalescence temperatures have been obtained for representative examples and rotational barriers determined experimentally and theoretically. A detailed theoretical analysis has been undertaken to explore conformations which may contribute to the relative populations of the s-cis and s-trans rotamers. The products have also been screened for cytotoxicity and activity against two parasitic protozoan strains (Plasmodium falciparum and Trypanosoma brucei).

Dynamic data‐driven computation method for the number of waiting passengers and waiting time in the urban rail transit network

Excess passengers gathering on the urban rail transit platform in a short time brings huge security risks to passengers and the daily operation of urban rail transit. However, the real-time monitoring method of passenger flows, which relies on manual methods, cannot satisfy the requirement of daily operations at the network level anymore. This study proposes a dynamic data-driven computation and monitoring method for the number of waiting passengers on platforms to recognize the operational risk in real-time. For waiting passengers on platforms, the waiting time duration before boarding is also calculated based on a first-come-first-service basis. It can be used to provide real-time information services to passengers and evaluate service quality. Moreover, the proposed methodology relies solely on the AFC data and the train timetable, which makes it easy to implement in the daily operation of any urban rail transit system. Finally, taking the Beijing rail transit network as a case study, the real-time number of waiting passengers on each platform, and the time duration passengers should wait before boarding are calculated dynamically. Meanwhile, the spatio-temporal distribution of passengers’ waiting time and waiting passengers are detailly analyzed based on the method of cluster analysis and the complex network theory.

Electrostatic Map of the SARS-CoV-2 Virion Specifies Binding Sites of the Antiviral Cationic Photosensitizer.

Electrostatics is an important part of virus life. Understanding the detailed distribution of charges over the surface of a virus is important to predict its interactions with host cells, antibodies, drugs, and different materials. Using a coarse-grained model of the entire viral envelope developed by D. Korkin and S.-J. Marrink’s scientific groups, we created an electrostatic map of the external surface of SARS-CoV-2 and found a highly heterogeneous distribution of the electrostatic potential field of the viral envelope. Numerous negative patches originate mainly from negatively charged lipid domains in the viral membrane and negatively charged areas on the “stalks” of the spike (S) proteins. Membrane (M) and envelope (E) proteins with the total positive charge tend to colocalize with the negatively charged lipids. In the E protein pentamer exposed to the outer surface, negatively charged glutamate residues and surrounding lipids form a negative electrostatic potential ring around the channel entrance. We simulated the interaction of the antiviral octacationic photosensitizer octakis(cholinyl)zinc phthalocyanine with the surface structures of the entire model virion using the Brownian dynamics computational method implemented in ProKSim software (version r661). All mentioned negatively charged envelope components attracted the photosensitizer molecules and are thus potential targets for reactive oxygen generated in photosensitized reactions.

Numerical studies on displacement-imbibition process of pore-network extracted from the microfluidic chip

The flow law of two-phase flow under complex capillary structure can be applied to explain the variability of development efficiency during the displacement, imbibition, and huff-and-puff process with different construction parameters. Microfluidic chips have attracted considerable attention as an effective laboratory research method on the displacement and imbibition processes in the complex pore-network. While, laboratory methods provide only an extremely limited amount of information, numerical simulation can reveal more detailed flow field information of two-phase flow in complex pore-network. In particular, computational dynamics methods can simulate the fluid flow process in the complex capillary structure. To this end, our study aimed to analyze the influence of different parameters on the oil recovery and swept area by relying on numerical simulations, dynamic analysis, and previous studies. Furthermore, by using distribution maps with flow filed and phase filed, we uniquely focused on the flow field information and dynamic process analysis during the displacement-imbibition process to elucidate the mechanism of remaining oil, trapped and displaced. Moreover, we examined the sensitivity characteristics of cumulative oil recovery during the displacement-imbibition process within a reasonably narrow parameter variation range. Lastly, some follow-up improvement suggestions were provided to facilitate the oil recovery under displacement-imbibition process.

A Self-Adaptive-Coefficient-Double-Power Sliding Mode Control Method for Lower Limb Rehabilitation Exoskeleton Robot

Lower limb rehabilitation exoskeleton robots have the characteristics of nonlinearity and strong coupling, and they are easily disturbed during operation by environmental factors. Thus, an accurate dynamic model of the robot is difficult to obtain, and achieving trajectory tracking control of the robot is also difficult. In this article, a self-adaptive-coefficient double-power sliding mode control method is proposed to overcome the difficulty of tracking the robot trajectory. The method combines an estimated dynamic model with sliding mode control. A nonlinear control law was designed based on the robot dynamics model and computational torque method, and a compensation term of control law based on double-power reaching law was introduced to reduce the disturbance from model error and environmental factors. The self-adaptive coefficient of the compensation term of the control law was designed to adaptively adjust the compensation term to improve the anti-interference ability of the robot. The simulation and experiment results show that the proposed method effectively improves the trajectory tracking accuracy and anti-interference ability of the robot. Compared with the traditional computed torque method, the proposed method decreases the tracking error by more than 71.77%. The maximum absolute error of the hip joint and knee joint remained below 0.55° and 1.65°, respectively, in the wearable experiment of the robot.

Local stereo matching algorithm using modified dynamic cost computation

Stereo matching is an essential subject in stereo vision architecture. Traditional framework composition consists of several constraints in stereo correspondences such as illumination variations in images and inadequate or non-uniform light due to uncontrollable environments. This work improves the local method stereo matching algorithm based on the dynamic cost computation method for depth measurement. This approach utilised modified dynamic cost computation in the matching cost. A modified census transform with dynamic histogram is used to provide the cost in the cost computation. The algorithm applied the fixed-window strategy with bilateral filtering to retain image depth information and edge in the cost aggregation stage. A winner takes all (WTA) optimisation and left-right check with adaptive bilateral median filtering are employed for disparity refinement. Based on the Middlebury benchmark dataset, the algorithm developed in this work has better accuracy and outperformed several other state-of-the-art algorithms.

Contribution of the Na+/K+ Pump to Rhythmic Bursting, Explored with Modeling and Dynamic Clamp Analyses.

The Na+/K+ pump, often thought of as a background function in neuronal activity, contributes an outward current (Ipump) that responds to the internal concentration of Na+ ([Na+]i). In bursting neurons, such as those found in central pattern generator (CPG) neuronal networks that produce rhythmic movements, the [Na+]i and therefore the Ipump, can be expected to vary throughout the burst cycle. This responsiveness to electrical activity, combined with independence from membrane potential, endow Ipump with dynamical properties not common to channel-based currents (e.g., voltage- or transmitter-gated or leak channels). Moreover, in many neurons, the pump's activity is modulated by a variety of modulators, further expanding the potential role of Ipump in rhythmic bursting activity. This paper shows how to use a combination of modeling and dynamic clamp methods to determine how Ipump and its interaction with persistent Na+ current influence rhythmic activity in a CPG. Specifically, this paper will focus on a dynamic clamp protocol and computational modeling methods in heart interneurons of medicinal leeches.

Conformational study of a strained DNA/RNA by dynamic 1H NMR biospectroscopy and computational methods for molecular modelling, simulation and biopectroscopic studies of DNA/RNA of gum cancer cells

Conformational study of a strained DNA/RNA by dynamic 1H NMR biospectroscopy and computational methods for molecular modelling, simulation and biopectroscopic studies of DNA/RNA of gum cancer cells

Rank-Pooling-Based Features on Localized Regions for Automatic Micro-Expression Recognition

Facial micro-expression is a subtle and involuntary facial expression that exhibits short duration and low intensity where hidden feelings can be disclosed. The field of micro-expression analysis has been receiving substantial awareness due to its potential values in a wide variety of practical applications. A number of studies have proposed sophisticated hand-crafted feature representations in order to leverage the task of automatic micro-expression recognition. This paper employs a dynamic image computation method for feature extraction so that features can be learned on certain localized facial regions along with deep convolutional networks to identify micro-expressions presented in the extracted dynamic images. The proposed framework is simple as opposed to other existing frameworks which used complex hand-crafted feature descriptors. For performance evaluation, the framework is tested on three publicly available databases, as well as on the integrated database in which individual databases are merged into a data pool. Impressive results from the series of experimental work show that the technique is promising in recognizing micro-expressions.

Modeling the snow load distribution by methods of computational fluid dynamics

Метод вычислительной гидродинамики для анализа распределения снега и образования сугробов начал применяться в 1990-х годах. Однако трудоемкость данного метода за последние 30 лет позволила выработать и верифицировать модели только для конкретных явлений и ситуаций. В данной статье рассмотрены наиболее значимые результаты в области применения методов вычислительной гидродинамики, проанализированы недостатки и ограничения.