Structural Dynamic Effects Research Articles

Aerostructural Analysis of a Deployable Aeroshell in Transonic Flow

The deployable aeroshell, a contemporary reentry system, utilizes a thin flexible membrane surface sustained by pressurized gas to efficiently decelerate a reentry vehicle at high altitudes while enabling low-ballistic-coefficient flight. When an in-flight aerodynamic force is applied, the membrane structure undergoes large deformation that may affect its performance. Hence, a coupled analysis that considers the feedback effect of structural deformation is essential for accurately predicting the behavior of such reentry vehicles. In this study, a numerical framework for coupled aeroelastic analysis was constructed in a partitioned manner using open-source software to elucidate the combined effect of structural deformation and compressible flow dynamics and characterize the aerodynamic performance of reentry vehicles with inflatable structures. The results revealed that the membrane surface was deformed elastically by the aerodynamic force owing to the large difference in pressure distribution between the front and back of the aeroshell. Fluctuating behavior was observed in the aerodynamic coefficients owing to the small-amplitude oscillation of the capsule. This oscillation was induced by the large wake behind the vehicle. Several wrinkles and concave-shaped depressions formed on the membrane surface, which exhibited a circumferential movement tendency with time.

Quantum delocalization, structural order, and density response of the strongly coupled electron liquid

We investigate the impact of electronic correlations and quantum delocalization onto the static structure factor and static density response function of the strongly coupled electron liquid. In contrast to a classical system, the density response of the electron liquid vanishes on small length scales due to quantum delocalization effects, which we rigorously quantify in terms of imaginary-time correlation functions and dynamic Matsubara response functions. This allows us to analyze the interplay of structural order and dynamic quantum effects as it manifests itself in the dynamic Matsubara local field correction. Finally, we identify an effective electronic attraction in the spin-offdiagonal static density response when the wavelength of the perturbation is commensurate with the average interparticle distance.

Generic fully coupled framework for reliability assessment of offshore wind turbines under typical limit states

Offshore wind turbines (OWTs) generally experience harsh marine environments with uncertainties in marine loads, soil properties, and material properties; therefore, the structural integrity assessment of OWTs is a challenging task. Most of the previously proposed methods for reliability assessment are time-consuming and neglect the coupling effects of aerodynamics, hydrodynamics, and OWT structural dynamics under complex environmental loads. In this study, a fully coupled framework for the reliability assessment of OWTs is proposed, in which a dynamic simulation tool in the time domain is combined with surrogate models. The established Kriging, multivariate regression, and support vector regression surrogate models are compared to determine the most feasible model. Furthermore, the influence of different solving methods, such as first-order reliability method (FORM), importance sampling (IS), and subset simulation (SS), on the estimation of structural reliability indexes are discussed. The superiority of the estimated reliability indexes in the safety assessment of OWTs is proved using the SS method based on the Kriging surrogate model. Subsequently, the potential failure modes of an OWT under different operational states are revealed, indicating that excessive tower vibrations must be eliminated for stable power production from OWTs. Furthermore, the SS method is found to be feasible as it ensures the estimation accuracy of the reliability indexes of the parked OWT based on Kriging and the other surrogate models. Finally, the significance of soil–structure interactions in the reliability index estimation is investigated, and the equivalent coupled spring boundary is proposed from the perspectives of structural safety and simulation accuracy.

Diffusive dynamics of a model protein chain in solution.

A Markov state model is a powerful tool that can be used to track the evolution of populations of configurations in an atomistic representation of a protein. For a coarse-grained linear chain model with discontinuous interactions, the transition rates among states that appear in the Markov model when the monomer dynamics is diffusive can be determined by computing the relative entropy of states and their mean first passage times, quantities that are unchanged by the specification of the energies of the relevant states. In this paper, we verify the folding dynamics described by a diffusive linear chain model of the crambin protein in three distinct solvent systems, each differing in complexity: a hard-sphere solvent, a solvent undergoing multi-particle collision dynamics, and an implicit solvent model. The predicted transition rates among configurations agree quantitatively with those observed in explicit molecular dynamics simulations for all three solvent models. These results suggest that the local monomer-monomer interactions provide sufficient friction for the monomer dynamics to be diffusive on timescales relevant to changes in conformation. Factors such as structural ordering and dynamic hydrodynamic effects appear to have minimal influence on transition rates within the studied solvent densities.

The Effects of Flexible Cylinder Structural Dynamics to the near Wake Turbulence

The utilization of a rigid and projecting surface, coupled with an agitator and vortex generator, frequently results in the dissipation of more energy than the production of turbulence that meets the required criteria. By contrast, a passively oscillating flexible protruding surface can generate a greater turbulence level. In the current study, a circular finite cylinder (cantilever) was used as the geometry of the rigid and protruding surface. Both the material and the aspect ratio were varied. Also, a local Reynolds number within the subcritical flow range (102 < ReD < 105) was considered. The results from the rigid protruding surface (finite cylinder) serve as a validation of the published results and a benchmark for the improvement of the turbulence generated by the flexible protruding surface. The results obtained via an ultrasonic velocity profiler have further demonstrated that the flexible cylinder is capable of generating greater turbulence by examining the turbulence intensity, the turbulence production term and the Reynolds stress. All the flexible cylinders that oscillate show an increase in turbulence production but at different percentages. The cylinders studied in this work ranged from the least structural stiffness (EVA) to moderate (aluminum) and the highest structural stiffness (carbon steel). Through studying the normalized amplitude responses graph for the flexible cylinders, it is found that the oscillating motion does indeed contribute to the increment. A further examination of the results shows that the increase is due to the structural velocity instead of just the oscillating motion.

Experimental Validation of a Structure-Borne Sound Model of a Direct Drive Wind Turbine Generator

In this paper the methodology and results of the validation of a multi-physical system model of a direct drive wind turbine are presented. The analyzed model serves the purpose of examining the structure borne sound resulting from electromagnetic excitations inside the turbine’s generator. To study the accuracy of this model and to increase the confidence in the simulation results, an experimental validation is performed in the course of this work. Hereby, the simulation results are compared with data from a measurement campaign in which the real generator was tested on a full-scale system test bench. The validation takes the structure-borne sound transfer, modal behavior of the generator and effects of structural dynamics into account.

Dynamic catalysis of sub-nanometer metal clusters in oxygen dissociation

When the catalyst size decreases down to the nanometer or even sub-nanometer scale, their geometric and electronic structures are very different from the bulk materials. Especially, their structural dynamics can greatly affect catalytic performances. Herein, we report a theoretical study on oxygen dissociation on Ag19 cluster, a critical step of ethylene epoxidation, to investigate the effect of structural dynamics on the catalytic activity. Combining ab initio molecular dynamics (AIMD) and free energy calculation, we obtain the free energy profiles under different temperatures and find sudden drops in the reaction free energy and barrier at certain temperature ranges. The reaction entropy change shows a positive peak because of the different melting temperatures between initial and final states. Additionally, we further investigate the oxygen diffusion process on the Ag cluster and compare it with the Au and Cu clusters. We find that weak adsorption of oxygen on the silver cluster leads to its facile diffusion and thus reduces the melting temperature of the cluster, therefore facilitating partial oxidation under mild conditions.

Numerical analysis of the primary and secondary structural dynamic interaction effects on elastic floor response spectra

In modern seismic design, the assessment of seismic behavior in secondary structures relies on the evaluation of the primary structure's acceleration at the support of the secondary structure. To enable effective secondary structure design, a thorough understanding of the interaction between the primary and secondary structures is essential. This article conducts an analysis based on parametric data, delving into the dynamic interaction between these structures. In this study, both the elastic primary and secondary structures are represented as single-degree-of-freedom systems. The governing equations of motion for both the coupled and uncoupled systems are derived and solved using the numerical method. Subsequently, the floor response spectrum (FRS) is computed for both coupled and uncoupled configurations. This investigation focuses on the impact of three crucial parameters: the tuning ratio (T_r), the mass ratio (μ), and the damping ratio (ξ_s) on the FRS. The analytical findings reveal that dynamic interaction does not significantly affect the FRS when the mass ratio is very low, at 0.1%. However, for a range of 0.8 ≤ T_r ≤ 1.2, dynamic interaction has a substantial influence on the FRS. Additionally, this study underscores that lower damping ratios in the secondary structure result in a more pronounced coupling effect on the FRS.

Labor productivity in the agriculture, structural shifts and economic growth in the Central and Eastern European countries

Purpose. In our article, we assess the scope and directions of changes in agricultural labor productivity compared to other sectors of the economy.
 Methodology / approach. For our survey we choose 15 countries: (і) EU countries – Bulgaria, Czech Republic, Estonia, Hungary, Latvia, Lithuania, Poland, Romania, Slovakia and Slovenia, as well (іі) post-Soviet European countries – Ukraine, Moldova, Belarus, russia and also (ііі) Albania for period 1996–2019. We use an empirical methodology designed to analyze structural decomposition of labor productivity into the growth effect within the sector and structural dynamic and static effects, often called ‘shift-share analysis’. We analyze process of convergence of sectoral labor productivity and its impact on economic growth.
 Results. Labor productivity grows in the agricultural sector of the economy at the fastest rate, on average by almost 12 % per year. The growth effects within the industry takes a dominant position in all sectors of the economy in the countries of Central and Eastern Europe and its share is on average 88.5 %, and the structural effects are as follows: the dynamic effect is almost 1%, the static effect is 10.4 %. We have confirmed that the agricultural sector is gaining weight in the economic growth of the countries of Central and Eastern Europe, the influence of the service sector is increasing, although together they do not exceed the influence of the growth of value added in industry.
 Originality / scientific novelty. For the first time we have used the methodology of decomposition of labor productivity growth into three effects: growth, dynamic and static ones for the period before the financial crisis 2008 and after the crisis for 15 countries of Central and Eastern Europe. Using panel GLS estimator with fixed effects we estimate the impact of labor productivity on economic growth in different sectors for 1991–2020 period. 
 Practical value / implications. The main results of the study can be used for elaboration of effective economic policy in agriculture development in Central and Eastern European countries; for identification of structural shifts in labor productivity in different sectors of the economy before and after the financial crisis; for estimation of the level of convergence between different sectors of the economy; determining main factors of increasing value added in agriculture in Ukraine and other Central and Eastern European countries; implementation structural changes in economy in the period of crisis.

A Dynamic Model Updating Method with Thermal Effects Based on Improved Support Vector Regression

The dynamic modeling of structures in a thermal environment has become a new research topic in structural dynamics. The amount of calculation caused by the complexity of the structure and the size of the FEM, which increase the difficulty in modeling the structural dynamic thermal effects are considered. In this study, model updating in thermal temperature environment is proposed based on the hierarchical method and improved SVR, and an iterative procedure is presented. First, the dynamic problem of structure under a thermal environment is classified into a thermal model and a structural dynamic model, and they are both constructed with the FE method. As a result, the model updating process is conducted for both the thermal model and structural dynamic model. Different from the variables in other model updating methods, the updating variables, which are composed of the mechanical characteristics and thermal parameters, in the proposed method are dominated by the temperature distribution of the structure. A surrogate model based on improved SVR is adopted in the hierarchical model updating approach to make the updating process more efficient. Finally, the improved SVR method is validated on a typical nonlinear function, and the proposed method is validated by updating the model of an elastic thin plate and a wing structure in a thermal environment.

Structural and photosynthetic dynamics mediate the response of SIF to water stress in a potato crop

Solar-induced Fluorescence (SIF) has an advantage over greenness-based Vegetation Indices in detecting drought. This advantage is the mechanistic coupling between SIF and Gross Primary Productivity (GPP). Under water stress, SIF tends to decrease with photosynthesis, due to an increase in non-photochemical quenching (NPQ), resulting in rapid and/or sustained reductions in the fluorescence quantum efficiency (ΦF). Water stress also affects vegetation structure via highly dynamic changes in leaf angular distributions (LAD) or slower changes in leaf area index (LAI). Critically, these responses are entangled in space and time and their relative contribution to SIF, or to the coupling between SIF and GPP, is unclear. In this study, we quantify the relative effect of structural and photosynthetic dynamics on the diurnal and spatial variation of canopy SIF in a potato crop in response to a replicated paired-plot water stress experiment. We measured SIF using two platforms: a hydraulic lift and an Unmanned Aerial Vehicle (UAV) to capture temporal and spatial variation, respectively. LAD parameters were estimated from point clouds and photographic data and used to assess structural dynamics. Leaf ΦF estimated from PAM fluorescence measurements were used to represent variations in photosynthetic regulation. We also measured foliar pigments, operating quantum yield of photosystem II (PSII), photosynthetic gas exchange, stomatal conductance and LAI. We used a radiative transfer model (SCOPE) to provide a means of decoupling structural and photosynthetic factors across the diurnal and spatial domains. The results demonstrate that diurnal variation in SIF is driven by photosynthetic and structural dynamics. The influence of ΦF was prominent in the diurnal SIF response to water stress, with reduced fluorescence efficiencies in stressed plants. Structural factors dominated the spatial response of SIF to water stress over and above ΦF. The results showed that the relationship between SIF and GPP is maintained in response to water stress where adjustments in NPQ and leaf angle co-operate to enhance the correlation between SIF and GPP. This study points to the complexity of interpreting and modelling the spatiotemporal connection between SIF and GPP which requires simultaneous knowledge of vegetation structural and photosynthetic dynamics.

Effects of Structural Dynamics on Charge Carrier Transfer in B-DNA: A Combined MD and RT-TDDFT Study.

Hole transfer along the axis of duplex DNA has been the focus of physical chemistry research for decades, with implications in diverse fields, from nanotechnology to cell oxidative damage. Computational approaches are particularly amenable for this problem, to complement experimental data for interpretation of transfer mechanisms. To be predictive, computational results need to account for the inherent mobility of biological molecules during the time frame of experimental measurements. Here, we address the structural variability of B-DNA and its effects on hole transfer in a combined molecular dynamics (MD) and real-time time-dependent density functional theory (RT-TDDFT) study. Our results show that quantities that characterize the charge transfer process, such as the time-dependent dipole moment and hole population at a specific site, are sensitive to structural changes that occur on the nanosecond time scale. We extend the range of physical properties for which such a correlation has been observed, further establishing the fact that quantitative computational data on charge transfer properties should include statistical averages. Furthermore, we use the RT-TDDFT results to assess an efficient tight-binding method suitable for high-throughput predictions. We demonstrate that charge transfer, although affected by structural variability, on average, remains strong in AA and GG dimers.

Size-Sensitive Dynamic Catalysis of Subnanometer Cu Clusters in CO2 Dissociation

Small cluster catalysts are highly size-dependent and exhibit complex structural dynamic effects during catalytic reactions. Understanding their structural dynamics is of great importance in tuning the catalytic performances of small clusters that widely exist in supported catalysts. However, very little is known about the size dependence of the dynamic effect of small clusters. In this work, we systematically study the free energies and barriers of catalytic dissociation of CO2 at different temperatures on dynamical Cu clusters with different sizes by ab initio molecular dynamics. The reaction shows an abnormal entropic effect on Cu clusters, and more interestingly, it shows size sensitivity. On the Cu7 cluster, the entropy curve shows a reverse peak shape with increasing temperature, and it is surprising to find that it has a complex pulse shape on the Cu19 cluster. The detailed analysis shows that such temperature dependences can be attributable to the nontrivial behaviors of adsorption-induced phase transitions of the subnanometer Cu clusters during the dissociation of CO2. Our work not only demonstrates the complexity of the temperature dependence of the surface reaction on cluster sizes but also provides useful insight into the phase transition catalysis of dynamic clusters.

Postflutter Analysis of Bridge Decks Using Aerodynamic-Describing Functions

An aerodynamic describing function (ADF)-based model for simulating the nonlinear self-excited forces on bridge decks is developed, where the ADFs can be conveniently identified using the experimentally or numerically obtained free or forced vibration data. An efficient calculation procedure based on the ADFs is accordingly established to predict the nonlinear flutter state and/or postflutter limit cycle oscillations (LCOs). Two numerical examples are utilized to demonstrate the simulation accuracy and efficiency of nonlinear bridge flutter with the proposed ADF-based model. The capabilities of the ADF-based model in capturing typical features of nonlinear postflutter vibration such as LCO and a hysteresis phenomenon are demonstrated. A nondimensional postflutter index is designed to quantitatively assess the postflutter performance of bridge decks. Finally, the effects of structural dynamics and aerodynamic properties (e.g., structural damping ratios, natural frequencies, and aerodynamic derivatives) on the postflutter behavior of a bridge deck are examined in terms of the wind speed extension after the critical state with acceptable postcritical vibrations and the proposed postflutter index.

Structural dynamics effects on the electronic predissociation of alkyl iodides

The correlation between chemical structure and predissociation dynamics has been evaluated for a series of linear and branched alkyl iodides with increasing structural complexity by means of femtosecond time-resolved velocity map imaging experiments following excitation on the second absorption band (B-band) at around 201 nm. The time-resolved images for the iodine fragment are reported and analyzed in order to extract electronic predissociation lifetimes and the temporal evolution of the anisotropy while the experimental results are supported by ab initio calculations of the potential energy curves as a function of the C-I distance. Remarkable similarities are observed for all molecules consistent with a major predissociation of the initially populated bound Rydberg states 6A″ and 7A′ through a crossing with the purely repulsive states 7A″, 8A′ and 8A″ leading to a major R + I*(2P1/2) (R = CH3, C2H5, n-C3H7, n-C4H9, i-C3H7 and t-C4H9) dissociation channel. The reported electronic predissociation lifetimes are found to decrease for an increasing size of the linear radical, reflecting the shifts observed in the position of the crossings in the potential energy curves, and very likely a greater non-adiabatic coupling between the initially populated Rydberg states and the repulsive states leading to dissociation induced by other coordinates associated to key vibrational normal modes. The loss of anisotropy is fully accounted for by the parent molecular rotation during predissociation and the rotational temperature of the parent molecule in the molecular beam is reasonably derived.

Wilson disease missense mutations in ATP7B affect metal-binding domain structural dynamics

Wilson disease (WD) is caused by mutations in the gene for ATP7B, a copper transport protein that regulates copper levels in cells. A large number of missense mutations have been reported to cause WD but genotype–phenotype correlations are not yet established. Since genetic screening for WD may become reality in the future, it is important to know how individual mutations affect ATP7B function, with the ultimate goal to predict pathophysiology of the disease. To begin to assess mechanisms of dysfunction, we investigated four proposed WD-causing missense mutations in metal-binding domains 5 and 6 of ATP7B. Three of the four variants showed reduced ATP7B copper transport ability in a traditional yeast assay. To probe mutation-induced structural dynamic effects at the atomic level, molecular dynamics simulations (1.5 μs simulation time for each variant) were employed. Upon comparing individual metal-binding domains with and without mutations, we identified distinct differences in structural dynamics via root-mean square fluctuation and secondary structure content analyses. Most mutations introduced distant effects resulting in increased dynamics in the copper-binding loop. Taken together, mutation-induced long-range alterations in structural dynamics provide a rationale for reduced copper transport ability.

Analyzing the background and resonant effects of wind-induced responses on large-span roofs

Estimating the wind-induced responses is a crucial task in the wind-resistant design for large-span roofs. Due to the complexity of the aerodynamic and structural dynamic properties, the background and resonant effects on large-span roof structures are difficult to be estimated and understood by civil engineers. This paper defines the basic response as the quasi-static response subjected to completely coherence wind load. On this basis, conceptual analyses on the background and resonant effects are carried out. Through 18336 samples of wind tunnel data on typical flat, cantilevered, cylindrical, spherical, and saddle large-span roofs, 23940 cases of parametric wind-induced response analyses are conducted. The parametric analysis results turned out to be supportive and complementary to the conceptual analysis results. Finally, the principles and empirical formula of the background and resonant factors are summarized, which leads to better understanding of the wind-induced effects on large-span roof structures for engineers. The approach can also be used for quick estimating the equivalent static wind loads in engineering practices, especially in the preliminary design stages.

Vibrational spectroscopy of hydroxylated α-Al2O3(0001) surfaces with and without water: An ab initio molecular dynamics study.

Using gradient- and dispersion-corrected density functional theory in connection with ab initio molecular dynamics and efficient, parametrized Velocity-Velocity Autocorrelation Function (VVAF) methodology, we study the vibrational spectra (Vibrational Sum Frequency, VSF, and infrared, IR) of hydroxylated α-Al2O3(0001) surfaces with and without additional water. Specifically, by considering a naked hydroxylated surface and the same surface with a particularly stable, "ice-like" hexagonal water later allows us to identify and disentangle main spectroscopic bands of OH bonds, their orientation and dynamics, and the role of water adsorption. In particular, we assign spectroscopic signals around 3700 cm-1 as being dominated by perpendicularly oriented non-hydrogen bonded aluminol groups, with and without additional water. Furthermore, the thin water layer gives spectroscopic signals which are already comparable to previous theoretical and experimental findings for the solid/(bulk) liquid interface, showing that water molecules closest to the surface play a decisive role in the vibrational response of these systems. From a methodological point of view, the effects of temperature, anharmonicity, hydrogen-bonding, and structural dynamics are taken into account and analyzed, allowing us to compare the calculated IR and VSF spectra with the ones based on normal mode analysis and vibrational density of states. The VVAF approach employed in this work appears to be a computationally accurate yet feasible method to address the vibrational fingerprints and dynamical properties of water/metal oxide interfaces.

Evolutionary conservation of the allosteric activation of factor VIIa by tissue factor in lamprey

Background Previous studies have provided insight into the molecular basis of human tissue factor (TF) activation of activated factor VII (FVIIa). TF-induced allosteric networks of FVIIa activation have been rationalized through analysis of the dynamic changes and residue connectivities in the human soluble TF (sTF)/FVIIa complex structure during molecular dynamics (MD) simulation. Evolutionary conservation of the molecular mechanisms for TF-induced allosteric FVIIa activation between humans and extant vertebrate jawless fish (lampreys), where blood coagulation emerged more than 500 million years ago, is unknown and of considerable interest. Objective To model the sTf/FVIIa complex from cloned Petromyzon marinus lamprey sequences, and with comparisons to human sTF/FVlla investigate conservation of allosteric mechanisms of FVIIa activity enhancement by soluble TF using MD simulations. Methods Full-length cDNAs of lamprey tf and f7 were cloned and characterized. Comparative models of lamprey sTf/FVIIa complex and free FVIIa were determined based on constructed human sTF/FVIIa complex and free FVIIa models, used in full-atomic MD simulations, and characterized using dynamic network analysis approaches. Results Allosteric paths of correlated motion from Tf contact points in lamprey sTf/FVIIa to the FVIIa active site were determined and quantified, and were found to encompass residue-residue interactions along significantly similar paths compared with human. Conclusions Despite low conservation of residues between lamprey and human proteins, 30% TF and 39% FVII, the structural and protein dynamic effects of TF activation of FVIIa appear conserved and, moreover, present in extant vertebrate proteins from 500 million years ago when TF/FVIIa-initiated extrinsic pathway blood coagulation emerged.

Ultimate and fatigue load mitigation by an inertial-driven passive flap, using a geometrically exact multibody formulation

The paper characterizes the performance of a passive flap concept when applied to a modern very large conceptual wind turbine. The passive flap responds automatically to blade and/or tower vibrations, inducing a change of camber that opposes dynamic loads on the wind turbine. This is obtained in a purely passive manner, without the need for actuators or sensors.The present study is based on a detailed, geometrically exact multibody formulation of the device, which is able to capture all kinematic and structural dynamic effects of this inertia-driven device. The present modeling of the passive device improves on previous studies conducted with simplified models.Results show a significant ability in the reduction of both fatigue and ultimate loads, including the case of flap-specific fault scenarios. Solutions for limiting losses in energy yield caused by non-null average flap rotations in the partial load region are also investigated. The present analysis motivates further studies aimed at reaping the benefits of load alleviation enabled by the passive flap, for example by designing a new enlarged rotor at similar key loads on the rest of the machine.