Properties Of Elastic Waves Research Articles

Research on damage identification of wind power tower structure based on deformation and vibration dual parameter analysis

Abstract During the operation of the wind turbine, the force on the wind turbine tower is mainly caused by the vibration source at the top. As a high-rise structure with a large span, traditional vibration mechanics is used to analyze the overall force on the tower body, but the analysis of vibration modes or modes is slightly insufficient. This article adopts the analysis method of elastic wave dynamics to identify damage to the structure of wind power towers based on deformation and vibration dual parameter analysis. This article analyzes the propagation characteristics of elastic waves in tower structures, concrete bases, and foundation parts when damaged. This article develops a remote online monitoring and early warning platform for wind power tower bodies based on the attenuation properties of elastic waves. This article monitors the vibration and inclination of the tower drums of 5 wind turbines (# 13, # 31, # 34, # 49, and # 52). The tower drums have not undergone irreversible tilting or torsional deformation. However, through vibration analysis, it is suggested to check whether there is crushing between the tower drums and the concrete base, as well as whether there are local cracks on the surface of the concrete base. There may be local damage to the foundation ring of tower #31. It is recommended to check for local cracks in the foundation ring. This ensures the safe operation of wind power towers and has certain practical application value.

Mechanics of Materials: Multiscale Design of Advanced Materials and Structures

Materials can now be designed and architectured like structural components for targeted mechanical and physical properties. Structures and microstructures should not be studied independently and their design will benefit from a multiscale approach combining nonlinear continuum mechanics approaches and physical descriptions of elasticity, viscoplasticity, phase transformations and damage of microstructures, at various scales. The aim of the workshop was to gather outstanding junior and senior researchers in the various branches of mathematics, physics and engineering sciences suited to address the question of design of materials and structures by means of multiscale discrete and continuum approaches to their constitutive behavior. Examples include atomic or macroscopic lattices, random or periodic cellular materials, smart materials like shape memory alloys, 3D woven composites, acoustic and electromagnetic metamaterials, etc. Modern continuum mechanics relies on sophisticated constitutive laws for anisotropic materials exhibiting elastoviscoplastic behavior, still a field of intense research with new mathematical concepts. In particular size-dependent properties are addressed by resorting to generalized continua such as gradient or micromorphic and phase field models. The latter are attractive for the simulation of microstructure evolution coupled with mechanics, due to thermodynamic and metallurgical processes and damage. Scale transition and homogenization methods for continuous and discrete systems are required for the determination of effective material and structural behavior. Metamaterials are architectured materials specifically designed to achieve certain propagation and dispersion properties of elastic and plastic waves. Optimization strategies for the design of optimal architectures are involved in the design process. Target functions for optimization are now based on multicriteria (stiffness, strength, thermal expansion, transport properties, anisotropy etc.).

Research on the Attenuation Characteristics of Frequency Domain Parameters in Different Rock Medium

Abstract This study examines the frequency attenuation characteristics of elastic waves in marble, granite, and red sandstone through laboratory tests and numerical simulations based on ABAQUS software on eight rock samples. The correlation between the distance of the decay of the peak frequency and the petrophysical and mechanical parameters is also analyzed. The results show that elastic waves undergo stepwise attenuation of their peak frequency during laboratory attenuation tests. This finding was confirmed by numerical simulations. As elastic waves propagate through a rock medium, the amplitude of the high-frequency peak area near the excitation frequency decreases rapidly, while the proportion of low-frequency signals increases. As the propagation continues, the signal spectrum is dominated by low-frequency components, resulting in a stepwise attenuation of the peak frequency. It has been observed that the step decay distance of the peak frequency of elastic waves varies with the degree of particle bonding, which can be used to characterize the attenuation properties of elastic waves in a medium.

Dual-functional pentamode metamaterial with water-like and topological transmission properties

In this paper, a water-like pentamode metamaterial (PM) with a single metallic material is designed and the topological edge-state transmission properties of elastic waves in the PM are thoroughly investigated. Numerical results indicate that by introducing structural perturbation into PM, the Dirac point degeneracy at K-point can be opened and topological band inversion can be generated. Topological edge states are also obtained by organizing PM structural units, which are robust to defects such as bending and cavities. In addition, it also has the mimics water in acoustic properties over a wide frequency range, i.e. it exhibits transparency when surrounded by water. Therefore, it will have both good transmission efficiency and acoustic stealth performance when used as an underwater waveguide. The dual-functional PM proposed in this study provides theoretical guidance for designing underwater stealth acoustic waveguides.

Elasticity meets topology.

Harnessing the unique vectorial properties of elastic waves, Wu et al. find new degrees of freedom for realizing novel topological phases.

Propagation of solitary waves in origami-inspired metamaterials

We propose a design strategy for creating origami-like mechanical metamaterials with diverse non-linear mechanical properties and capable of remote actuation. The proposed triangulated cylindrical origami (TCO)-inspired metamaterials enable the highly desirable strain-softening/hardening and snap-through behaviors via a multi-material and highly deformable hinge design. Moreover, we couple these novel non-linear mechanical properties of the TCO origami-inspired metamaterials with the transformative ability of hard-magnetic active materials, allowing for untethered shape- and property-actuation in the developed metamaterials. We develop a mathematical modeling framework for the proposed TCO origami-inspired metamaterials, building on approximating the highly deformable hinges as a combination of longitudinal and rotational springs. We validate the accuracy of the developed mathematical modeling approach by comparing the analytically predicted compressive response of a unit cell structure with the corresponding numerical and experimental results. Using the developed mathematical modeling framework, we investigate the magnetic field-induced large deformation and superimposed solitary wave propagation in the TCO origami-inspired metamaterial system. We show that the proposed metamaterial allows us to tune the key characteristics of the enabled non-linear solitary waves, including their characteristic width and amplitude. The proposed design strategy for readily manufacturable origami-inspired metamaterial systems paves a novel path for practical engineering applications. Our studies also underscore the potential of magneto-mechanical interaction in the design of reconfigurable metamaterial systems with superior non-linear mechanical and elastic wave properties.

Elastodynamic property closures of elastic waves in polycrystalline materials

In polycrystalline materials like many metals, grainy microstructures significantly influence elastodynamics. Bulk waves scattering at grain boundaries cause attenuation and speed variation in waves. This depends on grain characteristics, including local elasticity and spatial properties. These are modeled statistically to homogenize the microstructure or elastodynamic fields, within bounds. For example, the elasticity of a homogenized medium can't exceed that of individual grains. 'Property closure' is the range within which microstructures yield specific properties like Young's modulus. This presentation introduces property closures for modeling elastic wave properties, specifically attenuation and velocity, in metal alloys. The focus is on the modeling framework and integrating microstructure statistics. An excting prospect of this work is in linking measurable wave properties with other physical quantities dependent on microstructure.

Constrained nonlinear amplitude-variation-with-offset inversion for reservoir dynamic changes estimation from time-lapse seismic data

We develop a novel elastic amplitude-variation-with-offset (AVO) inversion process to estimate the fluid saturation and effective pressure or variations in these properties from time-lapse seismic data sets. These changes occur in oil and gas reservoirs caused by fluid injection or hydrocarbon production that leads to changes in the elastic wave properties, reflectivity, and seismic response. Our method is based on a seismic forward model that consists of a linearized AVO equation and a rock-physics model. The AVO equation links the elastic wave properties to seismic reflection amplitudes, whereas the rock-physics model maps the saturation and pressure into seismic velocities and density. The inversion approach relies on the gradient descent technique to estimate the unknown variables by searching for the minimum of the least-squares misfit between the observed and modeled data. The first-order gradient equations of the least-squares data misfit function with respect to effective pressure and water saturation are derived by using the adjoint-state method and the chain rule. The optimization method used to minimize the misfit function and obtain the best optimal solution is a limited-memory quasi-Newton algorithm. This inversion process allows us to incorporate prior constraints by using the logistic function to map the model variables to a bounded range. To achieve a stable solution to ill-posed inversion problems, optimal regularization weights are applied. The application of the developed workflow on 1D synthetic and real well-log data from the Edvard Grieg oil field simulating various saturation-pressure conditions during production demonstrates the validity of the approach with different noise levels. The inversion is then applied to a 2D synthetic data set modeled from the reservoir model of the Smeaheia field, a potential site for a large-scale offshore CO2 storage field located in the North Sea. Our results illustrate that our inversion method efficiently and accurately estimates reservoir saturation and pressure variations.

Elastic waves in fluid-saturated porous materials with a couple-stress solid phase

Fluid-saturated porous materials have attracted extensive attention in micro/nanoscale applications owing to their excellent mechanical properties. Couple-stress theory can be used to depict the size effect of micro/nanoelastic materials, which cannot be ignored when the internal characteristic length of materials is comparable with the material size or wavelength. However, it has not been extended to porous materials. In this paper, we investigate the size effect of elastic-wave propagation in micro/nano fluid-saturated porous materials by combining couple-stress theory with Biot theory and introducing the higher order micro-inertia effect, establish the motion equations for elastic waves in fluid-saturated porous materials containing a couple-stress solid phase. The reflection and transmission properties of elastic waves at the interface between an elastic solid and a couple-stress fluid-saturated porous material are numerically analyzed. The results suggest that an increase in characteristic length can lead to an increase in the phase velocity of shear wave and further influence the reflection and transmission of elastic waves. A comparison among the proposed theory, Biot theory and experimental data indicates that the introduction of couple-stress and higher order micro-inertia effects allows for a more accurate calculation of the propagation properties of elastic waves in fluid-saturated porous materials, and it can provide a theoretical basis for applications of elastic waves in micro/nano porous materials, such as nondestructive testing.

Elastic wave properties in ultra-high strength steel (HV670) exposed to various corrosive solutions

Elastic wave properties in ultra-high strength steel (HV670) exposed to various corrosive solutions

Using a Synthetic Borehole Model to Determine the Pore Aspect Ratio Dependence of Velocities from Acoustic Well-Logging Data

Revealing the elastic wave properties of carbonate rocks with complex pore structures and improving the reliability of carbonate reservoir descriptions have always been a global challenge in the field of carbonate geophysical exploration. In this study, we established a synthetic borehole model by selecting different particle sizes of cement, carbonate cuttings, and micro-silicon as the matrix, and silicon disks as the pores in carbonate rocks. We conducted four sets of low-porosity (0-3%) borehole models with different pore aspect ratios (ARs) and measured the P- and S-wave velocities ( V P and V S ) at the well-logging scale obtained from an acoustic logging system with one source and two receivers. The results indicate that the relationship between velocities and porosities in these borehole models follows a linear relation, with the pore AR significantly influencing the velocities at any given porosity. The velocity variation caused by pore AR reaches 560 m/s and 410 m/s at 3% porosity for the P-wave and S-wave within the AR range of 0.017-0.13. The theoretical DEM models provide a high and broad estimation of V P and V S at the well-logging scale in our measurement. They could perform better in fractured formation than in dissolved porous formation in carbonate reservoirs. The linear relation of V P and V S is independent of the pore AR and is effective for both fractured and dissolved porous formations. The change of V P / V S in different pore AR is more responsive to porosity and nonlinear dependent on the pore AR. The relationship between the defined normalized V P and V S indicates the pore AR has a more significant effect on V S than V P in our model. The constructed borehole models provide a unique opportunity for evaluating the availability of rock physics models at an acoustic logging scale. The study’s findings have significant implications for improving the reliability of carbonate reservoir descriptions and enhancing the accuracy of geophysical exploration in carbonate rocks with complex pore structures.

Shale distribution effects on the joint elastic–electrical properties in reservoir sandstone

AbstractWe investigated the effect of shale distribution on the joint elastic wave and electrical properties of shaly reservoir sandstones using a dataset of laboratory measurements on 75 brine‐saturated (35 g/L salinity) rock samples (63 samples from the literature, 12 newly measured samples). All the data were collected using the ultrasonic (700 kHz) pulse‐echo measurement technique for P‐ and S‐wave velocities (Vp, Vs), attenuations (Qp−1, Qs−1), and a four‐electrode method for resistivity under elevated hydrostatic confining pressures between 10 and 50 MPa (pore fluid pressure 5 MPa). The distribution of volumetric shale content was classified by comparing the calculated dry P‐wave modulus to the modified Upper Hashin–Shtrikman bound for quartz and air mixtures, assuming pore‐filling shale. This scheme in particular allowed us to distinguish between pore‐filling and load‐bearing shale distributions according to idealized definitions, which provides new insight into the joint ultrasonic properties and resistivity behaviour for shaly sandstones. In resistivity–velocity space, the resistivity of load‐bearing shale increases with increasing velocity which form a more distinct trend with steeper gradient compared to those for partial pore‐filling shale and clean sandstones. Moreover, the pore‐filling shale trend straddles the clean sandstone trend and meets the load‐bearing shale trend between 100 and 150 apparent formation factors. In resistivity–attenuation space, the highest attenuations exist when the volumetric shale content is close to the frame porosity (for Qp−1 in particular), at the transition between pore‐filling and load‐bearing shales. The results will inform the development of improved rock physics models to aid reservoir characterization from geophysical remote sensing, particularly for joint seismic and controlled source electromagnetic surveys.

A computational framework for uncertain locally resonant metamaterial structures

Locally resonant metamaterial structures, i.e., structures artificially engineered with periodic arrays of small resonators, are attracting a growing interest among scientists. The main reason lies in their remarkable attenuation properties of elastic waves over finite frequency ranges, named band gaps, resulting from periodicity and local resonance. Yet, very little attention has been paid to investigate whether and to which extent the behavior of these structures may be affected by uncertainties. This is indeed the purpose of our study, which proposes a comprehensive computational framework to calculate the frequency response of uncertain locally resonant structures, assuming an interval model for all the relevant parameters of the resonators: mass, stiffness and damping.The computational framework is conceived for finite-element models of the locally resonant structure and standard mass-spring-dashpot models of the resonators. The key steps are an exact dynamic condensation of the degrees of freedom within the resonators, the derivation of an exact and elegant expression for the transfer matrix of the locally resonant structure via the Sherman-Morrison-Woodbury formula, the calculation of the interval frequency response via either a sensitivity-based method or a global optimization method, the choice being driven by a preliminary monotonicity test. Considering two typical locally resonant structures, a beam and a plate, the computational framework proves easy to implement, accurate and robust as compared with the standard Monte Carlo method.

Revealing topological attributes of stiff plates by Dirac factorization of their 2D elastic wave equation

Dirac factorization of the elastic wave equation of two-dimension stiff plates coupled to a rigid substrate reveals the possible topological properties of elastic waves in this system. These waves may possess spin-like degrees of freedom associated with a gapped band structure reminiscent of the spin Hall effect. In semi-infinite plates or strips with zero displacement edges, the Dirac-factored elastic wave equation shows the possibility of edge modes moving in opposite directions. The finite size of strips leads to overlap between edge modes consequently opening a gap in their spectrum eliminating the spin Hall-like effects. This Dirac factorization tells us what solutions of the elastic wave equation would be if we could break some symmetry. Dirac factorization does not break symmetry but simply exposes what topological properties of elastic waves may result from symmetry breaking structural or external perturbations.

A Double-Rail Phononic Crystal Model for the Ballasted Track

To investigate the properties of elastic waves propagating in the periodic ballasted track, a double-rail phononic crystal (DRPC) model which consists of two parallel rails fastened on equally spaced sleepers supported by ballast is proposed in this study. The presented numerical results show that there are twelve characteristic waves occurring in the DRPC. These waves can be divided into three kinds. Within the calculated frequency range, the first kind of characteristic wave always propagates except an initial lower frequency range. The second kind of characteristic wave has alternative pass bands and stop bands, showing obvious phononic property of the DRPC. The wavenumbers of the third kind of characteristic wave have larger imaginary parts, implying that this kind of wave is evanescent wave and can only propagate a few spans of the track away from the source. The numerical results show more advantages of the DRPC for explaining the elastic wave propagation mechanism in the ballasted track than the single-rail phononic crystal (SRPC) model.

Vibrational Dynamics of Pd-Ni-P Bulk Metallic Glasses: a Local Pseudopotential Study

In the present paper, Phonon modes and elastic constant of three different concentrations of PdxNi1-xP (Pd64Ni16P20, Pd40Ni40P20 and Pd16Ni64P20) bulk metallic glass are calculated using (1) Hubbard-Beeby (HB) and (2) Takeno-Goda (TG) approach along with our well established local model potential. The Hartree (H), Farid et al (F) and Sarkar et al (S) local field correlation functions (LFCF) are employed to examine the effect of the screening function on the collective dynamics of Pd-Ni-P bulk metallic glasses. Results are also reported for phonon dispersion curve, propagation elastic wave and elastic properties viz: bulk modulus BT, modulus of rigidity G, Poisson’s ratio ξ, Young’s modulus Y, Debye temperature ƟD. However, the calculated elastic constants results agree well with other theoretical and available experimental data.

Shear elastic surface waves and system symmetry

The effect of the anisotropy of an elastic medium and a crystal on the properties of surface waves is considered. It leads to symmetry breaking of a semi-bounded space with respect to reflection. This fact affects the possibility of the existence and properties of surface elastic shear waves. It is shown that, while maintaining the crystallographic symmetry in crystals with the surface orientation (110), the anisotropy breaks the indicated symmetry, but retains the possibility of propagation of surface waves with their strong modification. In the case of an anisotropic half-space with a thin film coating, which allows the propagation of the Love waves in an isotropic medium, anisotropy leads to the absence of such stationary waves.

Dispersion relations of anti-plane elastic waves in micro-scale one dimensional piezoelectric semiconductor phononic crystals with the consideration of interface effect

In this paper, the propagation properties of anti-plane elastic waves in a piezoelectric semiconductor (PS) layered periodic composites are theoretically investigated. The periodic layered composites consist of periodically repeated two micro-scale geometrical thickness PS slabs with different elasticity, piezoelectricity and charge carriers. Following consideration of the coupling mechanical anti-plane displacement, electric potential and perturbation of charge carriers, the influences of interface effects resulted from homo- and hetero-junctions on the dispersion relations of anti-plane elastic waves are systematically discussed. It is found that homo- and hetero-junctions can be approximately treated as rigid imperfect interfaces, which can enhance the width of band-gaps of anti-plane elastic waves, especially for high-frequency short-wavelength anti-plane elastic waves. The establishment of mathematical models and the revelation of physical mechanisms are all fundamental to the analysis and optimization of micro-scale energy harvesters based on the propagation of anti-plane elastic waves.

Estimation of directional crack density and fluid properties from well logs in vertical wells

The study of elastic properties of fractured/cracked rocks has been an important subject of interest in seismology and geophysical exploration. Downhole logging provides a direct measurement of fractured rock properties in terms of elastic wave velocities and anisotropy. Most existing studies only provide qualitative descriptions of fracture properties as evidenced from the acquired measurements. To better use downhole measurements, we have derived a comprehensive theoretical analysis and developed an inversion technique to characterize fracture properties. Theoretical results for cracked rocks show that crack density, crack alignment direction, and crack filling materials are the three main fracture parameters that strongly affect the elastic wave properties of fractured rocks. Furthermore, a detailed analysis of the crack effects on elastic properties shows that the measured elastic moduli can be used to evaluate the crack parameters of cracked rocks. We assume that cracks with any orientational distribution can be divided into two parts: horizontal and vertical. Based on the theoretical analysis, we develop an inversion method to estimate fracture parameters from well logs acquired in a vertical borehole. We assume a rock-physics model for rocks that adds effective horizontal and vertical cracks that are filled with liquid in an isotropic background, the elastic and fluid properties of which are inverted from the measured logs. The inversion method enables the quantification of the directional crack density and crack-filling material when applied to field logging measurements acquired in fractured formations. Theoretically predicted fracture properties are validated with formation microresistivity scan logging data and are consistent with the interpretation results.

Machine-learning based design of digital materials for elastic wave control

Materials for wave control need to be both anisotropic and spatially distributed. Traditional method is to first design a microstructure with anisotropic property, and then change geometric parameters of the microstructure according to analytical theory or numerical calculation. Unlike the traditional method, mechanical properties of digital materials can be easily tuned by changing the 0/1 ordering without changing the geometry of digital materials. However, determining suitable orderings of digital materials according to target properties remains a key challenge. In this paper, we establish a digital structural genome to solve this problem. By combining the developed machine learning method with finite element method, we can quickly calculate elastic wave properties of digital materials with all orderings and finally establish a digital structural genome quickly and accurately. The complete digital structural genome provides us with a fast approach to design anisotropy and spatial distribution of materials. Our research unequivocally shows that the establishment of a complete structural genome database of digital materials is of great significance for inverse design multifunctional structures, and can opens an avenue to achieve wave control on demand, such as corner cloak and acoustic carpet cloak.