Amplitude Shock Research Articles

Evaluation of an experimental kelp farm’s structural behavior using regression modelling and response amplitude operators derived from in situ measurements

An experimental kelp farming system for exposed ocean conditions was designed, deployed, planted with kelp and instrumented for evaluation of its dynamic response to ocean waves, tides, and currents. The farm featured a novel “lattice” mooring design and anchor lines and cultivation lines (horizontal lines used as kelp growth substrate) made of fiberglass rods. The farm was deployed at a site in Saco Bay, Maine with 13 m (MLLW) water depth. There the farm was exposed to waves with heights up to 5.9 m. Anchor line tension, tide and wave height time series were gathered and processed into response amplitude operators (RAOs) and least squared error linear regression models enabling recognition of meaningful patterns between the forcing factors and the mooring response. Mean mooring line tensions were shown to increase nonlinearly with tide. Anchor line tension response amplitudes were shown to exhibit high sensitivity to both low and high frequency wave forcing. Numerical free-release test simulations suggested natural frequencies in heave of 0.91 Hz, indicating that tension response sensitivities at high frequency could be the result of resonance. Low frequency tension response disproportionate to the low frequency wave forcing could be explained by wave forcing on kelp cultivation arrays modulated by wave group envelopes. Instances of high magnitude, potentially damaging peak tensions, deemed shock loads, were prevalent in most load cases. Anchor line tension dynamics including RAO and shock load magnitudes were shown to be sensitive to mooring stiffness (ratio of tension to resulting elongation) and, in some cases, significant wave amplitude. Patterns of anchor line response indicated that additional mooring elasticity or geometric compliance and use of floatation with less sensitivity to high frequency waves could help avoid the cause of and costly consequences of amplified high frequency loading and high amplitude shock loading. RAOs and regression model results also indicated a subdued response in frequencies associated with ocean swell waves, suggesting desirable performance in waves most dominant in extreme storm events. With the proposed improvements, the farm system design suggests merit as a robust and durable macroalgae biomass production platform.

Improvement of VMD for anomalous collision disturbance based on nonlinear l 1/2 norm

Variational mode decomposition (VMD) is widely used in the fault diagnosis of rotating equipment. The kurtosis index is typically utilized as the objective function to determine the optimal decomposition mode in conventional VMD. However, kurtosis is easily interfered with by abnormal impact signals, seriously affecting the accuracy of VMD in the fault extraction process. Therefore, the instability of the kurtosis index for anomalous disturbances should be addressed. In addition, the number of modal decompositions and the penalty factor are not wisely selected, exerting a significant influence on the decomposition effect of VMD. In this study, we propose an enhanced method for fault diagnosis of rotating machineries under abnormal impact interference, namely the improved nonlinear VMD method based on the l 1/2 norm (INVL). Initially, we employ the whale optimization algorithm to optimize the combination of parameters [] with the aim of achieving the most favorable decomposition outcomes. Subsequently, the decomposed modes undergo preprocessing using the nonlinear tanh function to mitigate the impact of amplitude shocks. Furthermore, we utilize the sparse l 1/2 norm to select fault feature components, thereby evaluating the sparse distribution of modes. The modes exhibiting the lowest l 1/2-norm values are chosen for information reconstruction and envelope analysis. To assess the effectiveness of the proposed method, we conduct simulations and experimental verifications. The results demonstrate that the INVL method effectively suppresses abnormal shocks and successfully extracts bearing fault features in the presence of anomalous collision disturbances.

Single Lead Implantable Cardioverter Defibrillator (ICD) with a Floating Atrial Dipole: A Systematic Review and Non-Comparative Meta-Analysis

Background: A DX implantable cardioverter defibrillator (ICD) system consists of an ICD and a shock lead equipped with two ring electrodes positioned in the atrium, referred to as the DX-lead. This system allows the collection of atrial signals using a single lead. Multiple studies on the device have been conducted over more than a decade. Aims: The aim of this study is to summarise these data in a non-comparative meta-analysis. Methods: A systematic literature review targeting publications on studies including a certain type of ICD, VR-DX ICD, was conducted. Subsequently a meta-analysis of proportions was conducted. Endpoints selected for evaluation included p-wave amplitude (at day 0, <6 months, 6-12 months and >12 months), appropriate and inappropriate shock rates, and all-cause mortality. Results: One randomised controlled trial, 11 prospective cohort studies and registries, and two retrospective studies were selected for analysis. P-wave amplitudes were consistently in a range where they can support clinical decision making across studies and remained stable over a follow-up of up to two years. Pooled shock incidence was consistent with industry standard for appropriate (10.7%) and inappropriate shocks (2.4%) across studies. All-cause mortality was at an average of 5%, increasing, as expected, with duration of study follow-up. Like shock results, mortality was within the expected range. Conclusion: This analysis shows that the VR-DX ICD system works reliably and provides an added benefit compared to single chamber ICD in the form of atrial sensing. Atrial view without requiring a second lead provides clinicians with an attractive, hardware-sparing option for the continuous monitoring of atrial activity.

Numerical validation of homogeneous multi-fluid models

We consider a 1D periodic system containing a large number of layers. Each layer is composed of two sub-layers of compressible fluids having different densities and equations of state. We present a comparison between a detailed numerical solution of the Euler equations that govern the multi-layer system, and two isentropic homogeneous (average) models effectively describing such a complex two-fluid mixture.The first homogeneous model is a 2×2 isentropic one–pressure two-fluid model. The second one is described by a 3×3 system, which additionally takes into account some turbulent effects in terms of the corresponding energy. An effective entropy can be introduced in the second model, which is constant along material lines for smooth solutions. The 2×2 model is recovered from the 3×3 model, in the limit of vanishing turbulent energy.The detailed numerical solution of the multi-layer system is carried out by a suitably designed second order finite-volume shock-capturing scheme in Lagrangian coordinates, which makes use of a new Roe-type numerical flux function.For smooth solutions the two models are both in very good agreement with the detailed numerical solution of multi-layer Euler equations.When a shock develops, the multi-layer solution becomes highly oscillatory and transforms into a dispersive shock for large amplitude shocks. It is found that, in the case of moderate density ratio, the first model shows a better agreement with the corresponding shock velocity. However, for large density ratio, the second model provides a better description of the multi-layer system. The case of moderate (large) density ratio is associated to a monotone (non-monotone) behaviour of the corresponding sound speed in the 2×2 model as a function of the mass fraction of the phases.

Extension of boiling histotripsy lesions by axial focus steering during pulse delivery

Boiling histotripsy (BH) is a pulsed high intensity focused ultrasound (HIFU) method relying on the generation of high amplitude shocks and bubble activity to induce tissues liquefaction. A sequence of pulses, 1–20 ms long, generates boiling bubbles at the focus of the HIFU transducer within each pulse, and the remainder of the pulse then interacts with those bubbles. One effect is the creation of a prefocal bubble cloud due to shock scattering: the shock is inverted when reflected from the bubble wall resulting in sufficient negative pressure to reach intrinsic cavitation threshold immediately proximally to these bubbles. Here, a methodology is proposed to extend the length of this prefocal bubble cloud by steering the focus toward the transducer during the BH pulse and thus accelerate treatment. A BH system comprising a 1.5 MHz 256-element phased array connected to a Verasonics V1 system was used. High-speed imaging in transparent gels was performed to observe the extension of the bubble cloud resulting from shock scattering. Volumetric BH lesions were generated in ex vivo tissue. Results showed a threefold increase of the volumetric ablation rate with focus steering compared to standard BH. [Work supported by NIH R01EB007643, R01GM122859, and R01EB25187.]

A novel rolling bearing fault diagnosis method based on generalized nonlinear spectral sparsity

In the fast kurtogram (FK), kurtosis is used as an indicator to locate the fault frequency band, and is widely aplied to fault diagnosis. However, kurtosis has been proven to favor a single large impulse rather than the required small fault characteristics, especially in the strong interference environment. To eliminate the impact of large-amplitude impact and further improve the accuracy of fault extraction, a method based on generalized nonlinear spectral sparsity (GNSS) is proposed for fault diagnosis of bearings. First, Z-score normalization and generalized nonlinear sigmoid activation function are used for signal preprocessing, and the scale distribution of the signal will be changed to eliminate the effects of large amplitude shocks under noisy environment. Then, to improve the sparsity measure capability, an improved L3/2 norm is used to replace kurtosis as the basis for selecting the best resonance frequency band. Finally, the effectiveness of the GNSS is verified by simulation data and experimental data. Compared with FK method, the performance of fault extraction of the proposed method is significantly improved, especially for the interference of abnormal impact.

Experiments and modeling of the effect of the internal air on the shock response of a porous material

The present experiments consider the shock loading of porous samples under statically evacuated, atmospheric, and pressurized interparticle air conditions. An additively manufactured foam with interconnected pores, made from a titanium alloy, is used as the sample material. Loading by a moderate amplitude shock wave has shown that the effect of the internal air on the mechanical response is noticeable for the sample under pressurized conditions, differing from the responses at atmospheric and evacuated conditions. These observations agree with considerations of the air effect within a two-phase constitutive modeling approach.

The concept of improvement high-strength aluminum alloys FSW joint properties via post-weld explosive treatment

The study describes the theoretical background and technological aspects of the post-weld explosive treatment of high-strength aluminum alloy FSW joints. Although FSW allows to effective join high-strength aluminum alloys, the heat generated during the process causes undesirable changes in the strengthening phase, giving a joint efficiency of about 80%. The load-carrying capabilities of these joints can be increased via post-weld treatment (e.g. shot peening, laser shock peening). The new, potential post-weld treatment that is presented in this paper is based on the affection of the welded joint by a shock wave generated during the detonation of explosive material. Such post-weld explosive treatment would result in the hardening of the low-hardness zone, which often determines the mechanical properties of precipitation-hardened aluminum alloy FSW joints. Studies show that explosive welding of annealed aluminum alloys increases their microhardness by about 25% as the result of a high-velocity collision. If a similar effect can be achieved in explosive hardening, the microhardness of the low-hardness zone will increase entailing an improvement of entire joint mechanical properties. The variety of explosives materials used in metalworking (covering the values of detonation velocity from about 2000 m/s to 8000 m/s) and different systems for shock-wave affection gives many technological possibilities. In this work are discussed two different explosive hardening systems: with direct placement of explosive material on a treated welded plate and with an additional driven plate, which provides a higher pressure impulse. Considering that affecting of high amplitude shock wave introduces defects into the structure and decreases residual stresses in the welded joints, the application of an appropriate technological system creates a potential for improving the load-carrying capacities of discussed joints, especially in a condition of cyclic loading.

Roles of degenerate quantum plasma temperature and stationary heavy nucleus species in nucleus-acoustic shock waves

The warm degenerate plasma model (on the basis of warm degenerate inertialess electron species, warm dissipative inertial light nucleus species, and stationary heavy nucleus species) is considered. The effects of degenerate plasma temperature and stationary heavy nucleus species on the basic features of cylindrical and spherical nucleus-acoustic shock waves propagating in such a warm degenerate plasma system are investigated. The reductive perturbation method (which is valid for small amplitude shock waves) and special stretched co-ordinates (which corresponds to the omission of the dispersion effect, and is appropriate for the monotonic shock waves) are employed. The kinematic viscous force acting in the light nucleus fluid is the only source of dissipation, and is responsible for the formation of monotonic shock waves. It is observed that the basic features of these monotonic shock waves are significantly modified by the effects of degenerate plasma temperature, ultra-relativistically degenerate electron species, and stationary heavy nucleus species. The applications of this new plasma model (defined by generalized Chandrasekhar equation of state which is also valid for finite temperature) in the cold, as well as hot white dwarfs are addressed.

A numerical study of the metal jet induced by a shock wave

In this work, a metal jet induced by a shock wave is studied numerically. Different from the previous works on metal jets, we apply a cut-cell based sharp interface numerical method for the study. The evolution of jets is simulated by the in house code CCGF [X. Bai and X. Deng, Adv. Appl. Math. Mech. 9(5), 1052–1075 (2017)], and the interfacial growth rate is computed and compared with some theoretical models. Various initial conditions, including disturbance amplitude and shock wave strength, are considered here. Based on the model of Karkhanis et al. [J. Appl. Phys. 123, 025902 (2018)], a modified model of the spike velocity is presented to achieve better consistency between the numerical simulation and the model formula under more wide initial conditions (here, the scaled perturbed amplitudes involved are 0.125 and 4, and the incident shock wave Mach number is from 2.5 to 8) in this paper. In order to extend the applicability of the empirical models, an approximate formula for the initial velocity V0 is also obtained; a direct prediction of the spike velocity will become possible when the initial perturbed amplitude and incident shock intensity are known. Relevant figures show that the modified model can estimate a more consistent result with the numerical simulation than the VK or GD model.

Failure evolution in hypervelocity impact of Al spheres onto thin Al plates

Hypervelocity impact (HVI) of Al spheres upon thin Al plates arouses high amplitude shock waves. Along with the wave propagation, the sphere and plate undergo massive failure, breakup and phase changes, and end up with diffusing debris clouds. Combined with the theories of wave interaction and tensile failure, this paper reveals the failure evolution during HVI of Al spheres onto thin Al plates through Smoothed Particle Hydrodynamics (SPH) method. The relation between the failure evolution and the formation process of debris cloud is analyzed. The influence of impact conditions (impact velocity and projectile-diameter-to-plate-thickness ratio) on the failure evolution, the debris cloud formation, and the largest fragment is also discussed. The analysis of the failure evolution and debris cloud formation in this paper can provide new insight for the quantitative study of HVI and space debris protection.

Further developments on observations of the Taylor instability in a dusty plasma

We previously reported the observation of a hydrodynamic-type interchange instability occurring sporadically at the curved interface between two dust clouds of different densities, in a three-dimensional dusty plasma [Pacha et al., Phys. Plasmas 19, 014501 (2012)]. The mechanism for the instability was not conclusively identified. Further analysis of the video images has been performed, showing that the instability is associated with the appearance of large amplitude dust acoustic waves or shocks. Evidence of a dust acoustic shock at the boundary, which could drive a Richtmyer–Meshkov-type instability, will be presented. We also discuss the possibility, suggested by Avinash and Sen [Phys. Plasmas 22, 083707 (2015)], that the observed instability is due to a Rayleigh–Taylor instability driven by a component of the gravitational acceleration, which is perpendicular to the curved boundary.

Shock wave impact on the viability of MDA-MB-231 cells.

Shock waves are gaining interests in biological and medical applications. In this work, we investigated the mechanical characteristics of shock waves that affect cell viability. In vitro testing was conducted using the metastatic breast epithelial cell line MDA-MB-231. Shock waves were generated using a high-power pulse laser. Two different coating materials and different laser energy levels were used to vary the peak pressure, decay time, and the strength of subsequent peaks of the shock waves. Within the testing capability of the current study, it is shown that shock waves with a higher impulse led to lower cell viability, a higher detached cell ratio, and a higher cell death ratio, while shock waves with the same peak pressure could lead to different levels of cell damage. The results also showed that the detached cells had a higher cell death ratio compared to the attached cells. Moreover, a critical shock impulse of 5 Pa·s was found to cause the cell death ratio of the detached cells to exceed 50%. This work has demonstrated that, within the testing range shown here, the impulse, rather than the peak pressure, is the governing shock wave parameter for the damage of MDA-MB-231 breast cancer cells. The result suggests that a lower-pressure shock wave with a longer duration, or multiple sequential low amplitude shock waves can be applied over a duration shorter than the fundamental response period of the cells to achieve the same impact as shock waves with a high peak pressure but a short duration. The finding that cell viability is better correlated with shock impulse rather than peak pressure has potential significant implications on how shock waves should be tailored for cancer treatments, enhanced drug delivery, and diagnostic techniques to maximize efficacy while minimizing potential side effects.

Obliquely propagating ion-acoustic solitary and shock waves in magnetized quantum degenerate multi-ions plasma in the presence of trapped electrons

The properties of obliquely propagating ion-acoustic waves have been investigated in multi-ions magnetized plasma comprising of inertial, positively and negatively charged ion fluids, trapped electrons, and negatively charged stationary heavy ions. The propagation of the waves is oblique to the ambient magnetic field which is along the z-direction. Only fast type of modes exists in the linear regime. The reductive perturbation method was adopted to derive the Korteweg– de Vries (KdV) and Burger equations, as well as the solitary and shock wave solutions of the evolved equations, have been used to analyze the properties of the small but finite amplitude waves. The effects of the constituent plasma parameters, namely, the trapping effect of electrons, the electron degenerate temperature and the viscosity coefficient on the dynamics of the small amplitude solitary and shock waves have been examined. The influence of the magnetic field and the obliquity parameter on the propagation characteristics of ion-acoustic waves are discussed.

Nonlinear Dispersive and Dissipative Electrostatic Structures in Two-Dimensional Electron-Positron-Ion Quantum Plasma

The nonlinear features of two-dimensional ion acoustic (IA) solitary and shock structures in a dissipative electron-positron-ion (EPI) quantum plasma are investigated. The dissipation in the system is taken into account by incorporating the kinematic viscosity of ions in plasmas. A quantum hydrodynamic (QHD) model is used to describe the quantum plasma system. The propagation of small but finite amplitude solitons and shocks is governed by the Kadomtsev-Petviashvili-Burger (KPB) equation. It is observed that depending on the values of plasma parameters (viz. quantum diffraction, positron concentration, viscosity), both compressive and rarefactive solitons and shocks are found to exist. Furthermore, the energy of the soliton is computed and possible solutions of the KPB equation are presented numerically in terms of the monotonic and oscillatory shock profiles

Interface Characterization within a Nuclear Fuel Plate

To predict the performance of nuclear fuels and materials, irradiated fuel plates must be characterized efficiently and accurately in highly radioactive environments. The characterization must take place remotely and work in settings largely inhospitable to modern digital instrumentation. Characterization techniques based on non-contacting laser sensing methods enable remote operation in a robust manner within a hot-cell environment. Laser characterization instrumentation can offer high spatial resolution and remain effective for scanning large areas. A laser shock (LS) system is currently being developed as a post-irradiation examination (PIE) technique in the hot fuel examination facility (HFEF) at the Idaho National Laboratory (INL). The laser shock technique will characterize material properties and failure loads/mechanisms in various composite components and materials such as plate fuel and next-generation fuel forms in high radiation areas. The laser shock-technique induces large amplitude shock waves to mechanically characterize interfaces such as the fuel–clad bond. As part of the laser shock system, a laser-based ultrasonic C-scan system will be used to detect and characterize debonding caused by the application of the laser shock. The laser shock system has been used to characterize the resulting bond strength within plate fuels which have been fabricated using different fabrication processes. The results of this study will be to select the fabrication process that provides the strongest interface.

Modeling of the spherical explosion attenuation process using aqueous foam

The two-phase model of dry aqueous foam dynamic behavior under the strong shock wave influence is presented under assumption that the foam structure under shock loading is destroyed into a suspension of monodispersed microdrops with the formation of a gas-droplet mixture. The system of equations for the model of aqueous foam includes the laws of conservation of mass, momentum and energy for each phase in accordance with the single-pressure, two-speed, two-temperature approximations in a three-dimensional formulation, taking into account the Schiller–Naumann interfacial drag force and the Ranz–Marshall interfacial contact heat transfer. The thermodynamic properties of air and water forming a gas-droplet mixture are described by the Peng–Robinson and Mie–Grueneisen equations of state. The presence of non-uniform process in height of aqueous foam syneresis, which is due to gravitational forces, is taken into account by setting the distribution of the liquid volume fraction in the foam. An additional consideration of the syneresis process during calculating the intensity of interphase drag forces according to the Schiller–Naumann model was controlled by introducing the parameter depending on the spatial distribution of the initial liquid volume fraction of the foam. The spherical explosion is modeled in the form of the shock wave pulse whose energy coincided with the charge energy of the HE used in the experiments. The problem numerical solution is implemented using the OpenFOAM free software package based on the two-step PIMPLE computational algorithm. The numerical solution of the problem, obtained on the basis of the proposed gas-droplet mixture model, is in satisfactory agreement with the experimental data on a spherical explosion in aqueous foam. The analysis of the spherical shock wave dynamics while its propagation through aqueous foam is given. The causes of the significant decrease in the amplitude and velocity shock waves propagation in the medium under study are investigated.

Experimental analysis of transonic buffet on a 3D swept wing using fast-response pressure-sensitive paint

Transonic buffeting phenomena on a three-dimensional swept wing were experimentally analyzed using a fast-response pressure-sensitive paint (PSP). The experiment was conducted using an 80%-scaled NASA Common Research Model in the Japan Aerospace Exploration Agency (JAXA) 2 m × 2 m Transonic Wind Tunnel at a Mach number of 0.85 and a chord Reynolds number of 1.54 × 106. The angle of attack was varied between 2.82° and 6.52°. The calculation of root-mean-square (RMS) pressure fluctuations and spectral analysis were performed on measured unsteady PSP images to analyze the phenomena under off-design buffet conditions. We found that two types of shock behavior exist. The first is a shock oscillation characterized by the presence of “buffet cells” formed at a bump Strouhal number St of 0.3–0.5, which is observed under all off-design conditions. This phenomenon arises at the mid-span wing and is propagated spanwise from inboard to outboard. The other is a large spatial amplitude shock oscillation characterized by low-frequency broadband components at St < 0.1, which appears at higher angles of attack (α ≥ 6.0°) and behaves more like two-dimensional buffet. The transition between these two shock behaviors correlates well with the rapid increase of the wing-root strain fluctuation RMS.

Time-Resolved Vibrational Spectroscopy of Polytetrafluoroethylene Under Laser-Shock Compression.

Shock-wave-induced high pressure and nanosecond time-resolved Raman spectroscopic experiments were performed to examine the dynamic response of polytetrafluoroethylene (PTFE) in confinement geometry targets. Time-resolved Raman spectroscopy was used to observe the pressure-induced molecular and chemical changes on nanosecond time scale. Raman spectra were measured as a function of shock pressure in the 1.2-2.4 GPa range. Furthermore, the symmetric stretching mode at 729 cm-1 of CF2 was compared to corresponding static high-pressure measurements carried out in a diamond anvil cell, to see if any general trend can be established. The symmetric stretching mode of CF2 at 729 cm-1 is the most intense Raman transition in PTFE and is very sensitive to change in pressure. Therefore, it can also be utilized as a pressure gauge for large amplitude shock wave compression experiments. A maximum blueshift of 12 cm-1 for the 729 cm-1 vibrational mode has been observed for the present experimental pressure range. A comparative study on the similarities and differences from the earlier work has been done in detail. One-dimensional radiation hydrodynamic simulations were performed to validate our shock compression results and are in very good agreement.

Influence of Fe 2O 3 nanoparticles on the rhological properties of simulated asthma airway mucus

The properties of mucus in a person with asthma can alter with disease process so that it may lead to the airway embolism. Fe 2O 3 nanoparticles can be used for drug delivery. Up till now, however, little is known about how the Fe 2O 3 nanoparticles influence the properties of airway mucus. In this study, Fe 2O 3 nanoparticles were dispersed with ultrasound, and the morphological properties were measured with scanning electron microscope, atomic force microscope and nanometer laser particle size and zeta potential analyzer. Then the dispersed Fe 2O 3 nanoparticles were added to the simulated asthma airway mucus with different final concentration (0.03, 0.3, and 0.4 mg/mL). The measurements of flow curve, yield stress, large amplitude oscillatory shear (LAOS) and shock scanning were carried out with a rotational rheometer. Experimental results showed that the Fe 2O 3 nanoparticles reduced the zero shear viscosity of simulated asthma airway mucus. With increase of shear rate, the wind speed of mucus was reduced. The yield stress of simulated asthma airway mucus was 19.0 Pa, but the yield stresses of experimental group (0.03, 0.3 and 0.4 mg/mL) were 17.0, 0.99, and 0.7 Pa, respectively. The results showed that the viscoelastic modulus of asthma airway mucus treated with Fe 2O 3 nanoparticles were changed obviously as measured with large amplitude scanning and frequency scanning. By adopting the method of optical phase microscopy, we found that different structures of simulated airway mucus were absorbed. The results showed Fe 2O 3 nanoparticles distroyed mucus structure. The experimental results proved that Fe 2O 3 nanoparticles could change the rheological characteristics of simulated asthma airway mucus. This experimental result would lay a foundation for the further development of airway mucus sticky agent based on the function of Fe 2O 3 nanoparticles.