Structural Dynamic Properties Research Articles

Dynamic compressive behavior of functionally graded triply periodic minimal surface cellular structures

The Triply Periodic Minimal Surface (TPMS) structure is regarded as a porous structure used for impact protection due to its lightweight, high strength, and high specific energy absorption (SEA). This paper investigates the dynamic mechanical properties of the TPMS structure by Split Hopkinson Bar (SHPB) experiments and finite element analysis (FEA). We compare stress peak, SEA, strain rate effect, and deformation pattern for functionally graded Primitive (P), uniform P, and uniform Gyroid (G) structures. It is found that the increasing magnitude of peak stress in the TPMS structures becomes more evident under high-impact loads. As the relative density increases, the strain rate effect becomes more prominent. The uniform G structures exhibit higher plateau stress and SEA than uniform P structures. Besides, graded P structures exhibit a climbing phenomenon compared to uniform P structures in the platform section. The FEA results also demonstrate that higher SEA and plateau stresses are exhibited in the graded P structure. The graded design minimizes the strain rate effect compared to the corresponding uniform structures. It is essential to set a properly graded index to enhance the dynamic energy absorption capacity of the TPMS structure, as more fluctuations occur when the graded index increases.

Finite element model updating and response prediction of a frame structure based on optimal sensor placement

This paper proposes an approach for finite element (FE) model updating and response prediction of frame structures based on optimal sensor placement (OSP), which integrates sensor placement optimization, mode expansion, and model updating techniques. Firstly, sensor optimization layout and modal testing analysis are conducted on a bolted laboratory frame structure. The covariance-driven stochastic subspace identification (SSI-COV) method identifies the real-world structure’s natural frequencies, modal damping, and mode shapes. Secondly, the complete mode shapes are expanded using the measured incomplete modal data from the limited number of sensors. Thirdly, a multi-objective function based on frequency and mode shapes is established to adjust the parameters of the FE model. This ensures that the updated model accurately represents the dynamic properties of the actual structure within a specific frequency range. Finally, the Rayleigh damping of the frame structure is estimated, and the damping matrix is assembled to enhance the accuracy of dynamic response prediction in the updated model. By comparing the response prediction results of the updated FE model with and without considering the updated damping effects to the measurement data of the real-world structure, it is demonstrated that the proposed method considering updated damping effects can more effectively predict the structural response.

An Experimental Study on the Dynamic Properties of 3D-Printed Structures with Different Layer Orientations

An Experimental Study on the Dynamic Properties of 3D-Printed Structures with Different Layer Orientations

Estimation of wind load on supertall buildings using partial output measurements

Supertall buildings possess distinctive characteristics such as high flexibility, low damping, and susceptibility to wind. The impact of the wind load and wind-induced responses plays a critical role in ensuring the safety and functionality of these structures. Consequently, investigating the wind load and wind-induced responses of supertall buildings has immense practical significance and engineering value to guarantee the secure operation of such buildings under strong wind conditions. However, the direct measurement of wind loads and wind-induced responses across all building floors presents substantial challenges, including considerable engineering workload and implementation difficulties. This study proposes a novel approach based on Kalman filtering to estimate wind loads and wind-induced responses in supertall buildings. This approach involves fusing partial acceleration and displacement measurements to estimate wind load and wind-induced response accurately. Additionally, optimized sensor placement was considered based on the iterative process of the effective independence method. Wind-induced responses were obtained through numerical testing and subsequently utilized to estimate the wind loads on a supertall building. Various factors, such as measurement noise, modeling errors of structural dynamic properties, sensor placement, and response synchronization, were thoroughly discussed to assess their impact on the overall analysis.

A consumption-based term structure model of bonds and equity

In this study, I propose a consumption-based asset pricing model to capture the dynamic properties of term structures of bonds and equity. I extend the long-run risks model by introducing a mean-reversion of dividend growth and the external habit formation of a representative agent. The mean-reverting dividend growth generates a negative equity term premium, while the habit formation augments the equity premium and renders an upward-sloping bond yield curve, on average. In addition, fluctuations in the surplus consumption ratio and the conditional variance of consumption growth allow the model to reproduce pro-cyclical variations in bond and equity yield spreads and counter-cyclical variations in bond and equity term premiums, as observed in the U.S. data.

The influence of anions in the ionic liquid-water mixtures on the conformational structures of emeraldine base and emeraldine salt form of polyaniline

The development of antifouling membranes for water filtration applications is challenging. Conducting polymers can show enhanced antifouling characteristics by blending with various polymers, nanomaterials, and Ionic liquids (ILs). In this paper, we perform an all-atom molecular dynamics simulation on a conducting polymer polyaniline (PANI) immersed in IL-water mixtures. Two forms of PANI were considered, namely Emeraldine base (EB) and Emeraldine salt (ES) as well as two different water-mixed ILs are considered namely (a) 1-ethyl-3-methyl imidazolium [EMIM]+ hexafluorophosphate [PF6]- and (b) 1-ethyl-3-methyl imidazolium [EMIM]+ tetra-fluoroborate [BF4]-. We present various intra- and inter-molecular structural properties, solvation thermodynamics, and dynamic properties. We observe that with an increase in IL concentration, the radius of gyration (Rg) value shows a decrease for ES in pure state in both ILs; on the other hand, we see a minimal increase in the Rg values of EB in both ILs. The dihedral angle distribution analysis shows a combination of gauche and trans state for ES, whereas trans state is more pronounced for the case of EB in both water-IL mixtures. The radial distribution function (RDF) analysis between the ortho, meta carbons of the benzene rings, and the amine groups on ES with [BF4]- and [PF6]- show significant structural peaks. On the other hand, EB and ES show lower interaction with the water molecules. The number of hydrogen bonds (h-bonds) between polymer and water is higher for EB than ES in both IL-water mixtures. The hydrogen bond lifetime (τ) values show one-fold higher values for EB than ES. The self-diffusion coefficient (D) values of water show a decrease with an increase in IL concentration. The thermodynamic properties solvation enthalpy (ΔH) and excess molar volume (VmE) for both ES and EB show a more favorable solvation in [EMIM]+[BF4]- when compared to [EMIM]+[PF6]- with an increase in IL concentration. These observations are crucial for selecting ILs and designing sustainable polymers for antifouling membranes.

Exploration and Characterization of Dynamic Properties for Cultural Heritage Conservation: A Case Study for Historical Stone Masonry Buildings in Zanzibar

Ancient civilizations have imprinted their legacy on Zanzibar Stone Town through the construction of revered stone masonry buildings, which are experiencing rapid deterioration due to severe ambient environmental impacts. In response to these challenges, this study presents a comprehensive field exploration through the ambient vibration test (AVT) and numerical prediction of historical stone masonry buildings in Zanzibar Stone Town to analyze the dynamic characteristics. The ambient vibration test (AVT) reveals structural dynamic properties in terms of peak resonance frequencies (fr(avg)), mode shape, and damping ratio, in conjunction with the development of correlation with the geometric parameters of the building. The results reveal fr(avg) ranges between 2.8 and 5.3 Hz for investigated structures, non-uniform deformed mode shapes, and damping ratio ranges between 1.35% and 4.45% at various orientation axes of the understudy buildings. However, the relationship between natural frequencies indicates a higher association with the geometrical parameters of the building, yielding a correlation coefficient (R2) between 0.85 and 0.99. Moreover, the numerical prediction via eigenvalue analysis (EVA) yields a considerable association with the investigated data, quantified by root mean square error (RMSE), mean absolute error (MAE) ranged between 0.29 and 0.3, with Nash–Sutcliffe efficiency (NSE) and R2 between 0.81 and 0.99, respectively. Furthermore, conservation work guidelines were also developed to assist the structural engineer and conservationist in adopting targeted conservation strategies for the efficient preservation of the historical integrity in Stone Town.

Structural, hydrogen storage capacity, electronic and optical properties of Li-N-H hydrogen storage materials from first-principles investigation

Although Li-N-H systems are promising hydrogen storage materials, the structural feature, phonon dynamical, electronic and optical properties of Li-N-H systems are unclear. To solve these problems, we apply the first-principles method to study the structural stability, hydrogen storage capacity, dehydrogenation energy, electronic and optical properties of three Li-N-H systems (Li4NH, Li2NH and LiNH2). The calculated results show that Li4NH and LiNH2 are thermodynamic and dynamical stabilities. Although Li2NH is a dynamical instability, it is a thermodynamic stability at the ground state. Importantly, the calculated gravimetric hydrogen storage capacity is 1.19 wt% for Li4NH, 3.35 wt% for Li2NH and 8.02 wt% for LiNH2, respectively. Essentially, the high hydrogen storage capacity of LiNH2 is related to the formation of [NH2] group due to the strong electronic interaction between N and H. Furthermore, Li2NH shows metallic behavior. However, the calculated band gap is 1.958 eV for Li4NH and 3.016 eV for LiNH2. The change of band gap of Li-N-H hydrides is demonstrated by the dielectric functional. In addition, this LiNH2 with high concentration of hydrogen has better storage optical properties compared to Li4NH and Li2NH.

Evaluation of Material Characteristics and Structural Dynamic Properties of a Historical Church: The Case of 19th Century Bursa Derekoy Church (Ayia Paraskevi)

Derekoy (Ayia Paraskevi) Church, built by the Orthodox Greeks in Bursa, is one of the prominent monuments built in the 19th century. The structure, which lost its community with the population exchange (1923) between Turkey and Greece, has since then been out of service and a rapid deterioration process has begun. Analysis works are frequently implemented for this purpose and become crucial in Turkey, of which a large part is within the earthquake zone. However, the majority of the studies on the preservation of historical buildings are lacking in detailed material analysis and numerical methods. Conducting a series of material tests and numerical analyses for the structure provides more reliable and qualified interventions since they influence the decisions on the reinforcement and protection methods employed for historical buildings. For this purpose, the material characterizations of the mortar, plaster and stones used in the church were carried out by performing physical, chemical, mechanical, petrographic and mineralogical tests on samples taken from the church. Afterwards, mechanical tests of the walls and vibration tests were conducted to determine the dynamic behavior of the building. Based on the results obtained from the analyses, a series of intervention methods were proposed. It is understood that the flat-jack, shear and vibration tests are vital for determining the real structural behavior of the building. Furthermore, it is recommended that vibration tests are carried out on both the overall structure and individual walls to determine the dynamic behavior of similar structures where only outer walls remain standing.

Mechanical and viscoelastic characterization of Al2O3 based polymer nanocomposites: An experimental and molecular dynamics simulation approach

Polymer nanocomposites (PNCs) being revolutionary materials, comprises polymer matrix phase and nanoparticles (NPs) phase. This study focuses on incorporating alumina (Al2O3) into poly-dimethyl siloxane (PDMS) matrix to analyze viscoelastic behavior and damping in response to dynamic mechanical loading. The experiments were performed using nano-DMA for comparing how Al2O3 reinforcement influences structural conformations and dynamic properties of PNCs. At 100 Hz, the storage modulus (E′) increases by 150%, 20%, and 74% for 1.0 wt% NPs with average particle sizes of 25 nm, 80 nm, and 200 nm, respectively. The significant changes in storage modulus and hardness values occur during variable frequencies (10 to 50 Hz) for 1.0 wt%, 9.0 wt%, and 7.0 wt% with reinforcements of 25 nm, 80 nm, and 200 nm, respectively. Adhesion factor and reinforcement efficiency factor highlight complementary effects of reinforcements at different frequencies. Further, an all-atom MD simulation method characterizes static and dynamic properties, predicting comprehensive dynamical and structural–property relationships. This quantifies damping capacity and reveals insights into how Al2O3 alters the material’s behavior. In summary, the study provides a precise comparative analysis of overall PNC performance, emphasizing the intrinsic effect on mechanical properties. It recognizes deformation mechanisms driving energy storage and dissipation for developing PNCs with enhanced mechanical performance.

Dynamic characteristics of stone masonry walls before and after damage: Experimental and numerical investigations

Seismic behavior of masonry walls has been heavily investigated, especially by means of laboratory experiments employing cyclic tests to determine the mechanical parameters and seismic capacity. Nevertheless, the dynamic properties of the tested walls often remain unknown, even though the nature of the seismic response is dynamic and profoundly affected by the structure's dynamic properties. This paper presents an investigation on the dynamic properties of three different masonry wall panels in healthy and damaged states, and examines if damage quantification via tracking the changes in dynamic properties is feasible. Ambient vibration and impact measurements are used for the dynamic identification of wall panels, before and after they are tested in reversed-cyclic in-plane shear-compression tests. The natural frequencies, damping ratios, and mode shapes of the walls are determined and compared to each other. Moreover, the damage progression and its effect on the dynamic features of the URM wall panel is investigated using a discrete element model of the benchmark wall that is validated in terms of the force-displacement response and damage pattern of the wall. The results of the study indicate that changes in natural frequencies and mode shapes are traceable, although it is difficult to infer damage quantification relationships from these changes. The outcomes of this study also highlight that numerical models verified with the nonlinear quasi-static behavior do not necessarily match the wall's dynamic behavior, and that more research is required to update nonlinear numerical models. Overall, the results contribute to the knowledge regarding the dynamic characteristics of masonry walls in healthy and damaged conditions, and to quantify the damage in masonry walls as well as the changes in their dynamic properties.

Evidence of nonlinearity tailoring in static and dynamic responses of honeycomb and auxetic hourglass lattice metastructures

Nature’s morphology and optimal energetic solutions remain the key motivation for designing cellular-based lattice structures. Understanding the nonlinear dynamical behaviors that arise from different lattice topologies of such structures in the metastructure framework is crucial for their successful implementation in various novel designs and technologies related to vibration and shape control. This paper presents a study of the static and dynamic response of auxetic and honeycomb lattices with hourglass or dome-shaped metastructures. The potential tailoring of nonlinearity of such responses through various design parameters that play a vital role in shaping the dynamic properties of such structures is discussed here. The impact of cell design parameters on the resulting macroscopic behavior is assessed using both numerical simulations and experimental studies. The transition from softening to hardening nonlinear dynamic responses is reported with cell topologies ranging from the regular honeycomb to auxetic topologies that are widely used as fundamental cells of cellular materials design. The experimental study is based on the time responses measured to verify the numerical predictions. The experimental system consists of different 3D printed hourglass samples based on the auxetic and honeycomb lattices on which dynamic testing using a laser Doppler vibrometer is performed. The design strategies proposed in this paper can be integrated into a wide range of lattice-based materials for noise and vibration control applications and biomedical devices.

Construction of Reconfigurable and Polymorphic DNA Origami Assemblies with Coiled-Coil Patches and Patterns.

DNA origami nanodevices achieve programmable structure and tunable mechanical and dynamic properties by leveraging the sequence-specific interactions of nucleic acids. Previous advances have also established DNA origami as a useful building block to make well-defined micron-scale structures through hierarchical self-assembly, but these efforts have largely leveraged the structural features of DNA origami. The tunable dynamic and mechanical properties also provide an opportunity to make assemblies with adaptive structures and properties. Here the integration of DNA origami hinge nanodevices and coiled-coil peptides are reported into hybrid reconfigurable assemblies. With the same dynamic device and peptide interaction, it is made multiple higher-order assemblies (i.e., polymorphic assembly) by organizing clusters of peptides into patches or arranging single peptides into patterns on the surfaces of DNA origami to control the relative orientation of devices. The coiled-coil interactions are used to construct circular and linear assemblies whose structure and mechanical properties can be modulated with DNA-based reconfiguration. Reconfiguration of linear assemblies leads to micron scale motions and ≈2.5-10-fold increase in bending stiffness. The results provide a foundation for stimulus-responsive hybrid assemblies that can adapt their structure and properties in response to nucleic acid, peptide, protein, or other triggers.

Numerical Simulation and Influence of Non-Gaussian Vibrations on Flexible Robotic Systems

Random vibration excitation is a standard method for obtaining the dynamic properties of aerospace structures and simulating loading conditions. Shaker-based random excitation and traditional finite element analysis techniques use random vibrations, assuming a Gaussian distribution of excitation impulse magnitudes. While Gaussian signals may sufficiently describe some vibrational environments, many real-world excitations have non-Gaussian distributions. These signals may contain vibrational impulses larger than those observed in a Gaussian signal and could cause damage if not considered. This paper examines the influence of non-Gaussian signals on flexible vs. rigid robotic architectures using NASA JPL’s Pop-Up Flat Folding Explorer Robot (PUFFER) and Cooperative Autonomous Distributed Robotic Explorer (CADRE). The results indicate that flexible systems can be significantly impacted by a non-Gaussian excitation profile and that neither a typical enveloping of a Gaussian excitation nor a superposition of the responses to a worst-case impulse load with the response to a Gaussian signal was sufficient to bound the response due to non-Gaussian excitation. The driving mechanism for increased sensitivity of flexible robotic systems appears to be inertial, and designers may consider shifting the relative flexibility of the system or its constraints to force particular deformation modes or designing hinge mechanisms with increased damping to minimize the influence of non-Gaussian signals on the response of a flexible robotic structure.

A B3LYP-D3 computational study of electronic, structural and torsional dynamic properties of mono-substituted naphthalenes: the effect of the nature and position of substituent.

The effects of selectedsubstituent groups (-CH3, -Br, -CO2CH3, -COOH, and -NH2) and their relative positions on the electronic and structural properties of mono-substituted naphthalenes were investigated theoretically. In order to elucidate the suitability of the studied substituents in different fields including chemistry, spectroscopy, and materials sciences, accurate DFT calculations were performed at the dispersion-corrected B3LYP level of theory (B3LYP-D3/6-311 + + G(d,p)), and the obtained results were then validated by extensive comparisons with available experimental data. Among the studied substituents, the -NH2group causes the maximum reduction of the HOMO-LUMO energy gap. This result revealed clearly the suitability of the -NH2group, compared to other studied substituents, in the chemical synthesis of future organic-semiconductors having small energy gaps. In addition, the level of theory adopted in this study allowed the fine discrimination between the chemical reactivity parameters of the studied congeners, which is very difficult to perform experimentally. On the other hand, the rotational barriers of the studied non-halogen substituent groups were predicted. The greater sensitivity of the rotational barrier heights to the local environments, arising from intra-molecular interactions, was attributed to the -CH3 group. The torsional frequencies, calculated within the harmonic approximation, were also employed to relatively explore the differences between the environments of the same substituent at two different positions. The usefulness of these results can be manifested in the vibrational spectroscopy field, especially, for the IR/ Raman spectral analysis of polycyclic-aromatic congeners. All calculations were conducted within the Density functional theory (DFT) using the so-called dispersion-corrected B3LYP functional (B3LYP-D3) with the carefully selected 6-311 + + G(d,p) basis set. The B3LYP-D3/6-311 + + G(d,p) calculations were performed using the Gaussian 09 program, and the obtained results were visualized by employing the GaussView 6.0.16 program.

A damage-oriented ground motion intensity for degrading super high-rise buildings

To explicitly identify the influence of different seismic damages on the correlation between ground motion intensity measure (IM) and demand measure (DM), with a specific concern of super high-rise buildings, a novel damage-integrated spectral acceleration-based combination-type IM is developed for degrading systems. With the integration of seismic damage measure, inelastic displacement spectrum, and design acceleration spectrum, the prototype of the IM is theoretically derived for single-degree-of-freedom systems with a Q-type hysteretic model. The high-mode effect is reflected by an optimal number of lower modes combined with corresponding modal damage. To estimate the optimal number of modes while maximizing the case-independency of DM predictions, the dynamic properties of concerned damaged and undamaged structures are estimated with the collaboration of the modified flexure-shear model (FSM-MS), and further utilized to establish the regression expression with a large number of near-field and far-field ground motions. The performance of the proposed IM is systematically demonstrated via a case study on two super high-rise buildings, along with other selected IMs.

Geometric effects on impact mitigation in architected auxetic metamaterials

Lightweight materials used for impact mitigation must be able to resist impact and absorb the maximum amount of energy from the impactor. Auxetic materials have the potential to achieve high resistance by drawing material into the impact zone and providing higher indentation and shear resistance. However, these materials must be artificially designed, and the large deformation dynamic effects of the created structures must be taken into consideration when deciding on a protection concept. Despite their promise, little attention has been given to understanding the working mechanisms of high-rate and finite deformation effects of architected auxetic lattice structures. This study compares the static and dynamic elastic properties of different auxetic structures with a honeycomb structure, a typical non-auxetic lattice, at equivalent mass and stiffness levels. In this study, we limit the investigation to elastic material behavior and do not consider contact between the beams of the lattices. It is demonstrated that the equivalent static and dynamic properties of individual lattices at an undeformed state are insufficient to explain the variations observed in impact situations. In particular, the initial Poisson’s ratio does not determine the ability of a structure to resist impact. To gain a thorough comprehension of the overall behavior of these structures during localized, high rate compression, the evolution of the elastic tangent properties under compression and shear deformation was monitored, leading to a more profound understanding. Observations made in one configuration of stiffness and mass are replicated and analyzed in related configurations.

Effect of growth rate on structural, magnetic and spin dynamic properties of Co2FeAl thin films

The growth of high-quality Heusler alloy thin films with low damping is essential for designing low-power spintronic devices. Here, we report a systematic investigation of the structural, magnetic, and spin dynamic properties of Co-based (Cobalt, Iron, Aluminum) Heusler alloy Co2FeAl thin films via growth rate variation in sputtering. We found close stoichiometry comparable with the sputtering target towards higher growth rates. However, the stoichiometry of the films is off from the target at relatively low growth rates. The change in stoichiometry can be understood from the variation in the sputtering yield of each element present in the alloy. Grazing incidence X-ray diffraction patterns show that the films with different compositions have the A2 structure. However, the crystallite size strongly depends on the composition. Magneto-optic Kerr effect hysteresis measurements show low coercivity for all the samples, indicating soft magnetic behavior. Spin dynamics study using ferromagnetic resonance reveals that the film with close stoichiometry with the target exhibits the lowest damping parameter, i.e., 0.00448. Our results demonstrate the importance of sputtering growth rate on the structural, elemental, and magnetic properties of Heusler alloy thin films for spintronic device applications.

Adaptive beam with elastic support based on magnetorheological elastomers for modal modulation and vibration suppression

Owing to the wide modulation capability of their magneto-induced modulus, smart structure-based magnetorheological elastomers (MREs) show great promise for vibration control in numerous engineering applications. In conventional smart structure-based MREs, however, vibration absorption or isolation is mainly used for discrete structural systems, and the requirement for vibration control in continuous structures can limit the application of vibration absorbers and isolators. Therefore, it is necessary to resolve the dynamic properties of the continuous structure to obtain modal information. In this paper, different types of smart beams with adaptive elastic support (AES)-based MREs, containing dual-end elastic support, single-end elastic support, and the combination of a fixed end and an AES at an arbitrary location, are developed to tactically influence the dynamics through magneto-mechanical coupling. A dynamic model of thin-walled beams with AES was established by using the improved Fourier series method (IFSM). The numerical results confirm that the effective suppression bandwidth of the beam with MRE-AES can be shifted as a result of the modal modulation-induced energy transfer from low to high frequencies, which requires a decreasing trend of modal amplitude at the response location as the elastic support stiffness increases. According to the modal analysis, the beams with single-end AES and dual-end AES have a decreasing trend of modal amplitude in the global location as stiffness increases. However, the modal amplitude trend of the beam with a fixed end and an AES is not monotonic at certain locations. The experimental results demonstrate that MRE-AES can effectively attenuate the acceleration responses of the beams with single-end AES and with a fixed end and an AES under harmonic excitation. The resonance peaks in the transmission remarkably shift to higher frequencies with increasing magnetic flux.

Studying structural dynamic properties of KCNE3 in lipid bilayer membrane in the presence of interaction impairing mutations using molecular dynamics simulations

Studying structural dynamic properties of KCNE3 in lipid bilayer membrane in the presence of interaction impairing mutations using molecular dynamics simulations