Shock Excitation Research Articles

On the Characteristics of Solitary Waves and Shocks in Nonextensive Plasmas: Collisionality and Kinematic Viscosity Effects

In this article, a comprehensive investigation of the linear and nonlinear waves’ structure in an unmagnetized plasma consisting of nonextensive electrons, considering collisionality and kinematic viscosity effects, is studied. Using a reductive perturbation technique, we have derived a hybrid Korteweg–de Vries–Burgers equation for ion-acoustic (IA) waves. Analytical solutions for solitary waves and shock structures are obtained. We have also solved this equation numerically in order to investigate the basic properties of solitary/shock waves in such a plasma system. The presence of nonextensive electrons with $q$ -distribution influences significantly the solitary and shock wave structures. In other words, the compressive and rarefactive-type solitons or shock waves can also be seen in this plasma model depending on the strength of nonextensivity. On the other hand, the effects of ion-neutral collision and ion kinematic viscosity on the characteristics of IA solitary/shock waves are discussed. It is found that these parameters modify the basic features of the solitonic and shock excitations.

A Reduced-Order Model for Loosening of Bolted Joints Subjected to Axial Shock Excitation

Abstract Maintaining preload in bolted joints is critical for the safe and efficient operation of nearly all built-up structures. Dynamic loss of preload during operation occurs when sufficient shear force is applied to the joint such that slip is induced in at least the threads if not the entire bolt. Such shear forces are often realized when the joint is subjected to sustained vibrations, resulting in loosening over relatively long periods of time, or extreme shock loading where loosening occurs over fractions of a second. Modeling of joint loosening often focuses on complex analytical approaches or high-fidelity simulations using finite element models. While such approaches may succeed for a single bolt, they are unfeasible for use in simulations of entire built-up structures, which may possess dozens to thousands of joints. Thus, there is a need for reduced-order models (ROMs) that capture the dominant governing physics, but at drastically lower computational costs. This research introduces a phenomenological ROM for loosening in bolted joints subjected to axial shock excitation. The model introduces a mathematical relationship between the stiffness of the joint and torque of the fastener and treats the torque as a dynamic internal variable governed by a first-order, ordinary differential equation. The proposed ROM is presented then applied to an experimental study of a split-Hopkinson pressure bar with a threaded joint subjected to extreme shock loading. The results demonstrate that the proposed ROM is able to reproduce the dominant effects of loosening in bolted joints subjected to axial shock excitation.

Non-destructive diagnostic of aircraft engine blades by Fuzzy Decision Tree

A new algorithm for non-destructive diagnosis based on signal classification is proposed. This algorithm permits classifying objects with different properties depending on signals characterizing the objects. In this paper, the algorithm is applied to diagnose blades of aircraft engine gas turbine according to vibration signal after a non-destructive shock excitation and to classify them as defective and faultless. Just like other signal classification algorithms, this algorithm consists of two steps that are signal preliminary transformation and classification. However, these steps are modified in the proposed algorithm. Unlike other algorithms, the fuzzy classifier is used in the classification step. The change of the classifier type causes modification of the preliminary transformation step because the attributes for the classification must be fuzzy. Therefore, fuzzification procedure is added into the step of preliminary transformation. The fuzzy classifier for the problem of aircraft engine blades diagnosis is ordered Fuzzy Decision Tree (oFDT) that is inducted by estimation of Cumulative Mutual Information. This induction has good efficiency for a small set of initial data. The accuracy of the classification of defective and faultless blades for the proposed algorithm is 98.5%, and oFDT for this classification is inducted based on 32 signals only. The comparison with other classification algorithms shows that oFDT based algorithm considered in this paper gives the best result for this problem.

Phase stabilization of a relativistic backward wave oscillator by controlling the cathode characteristics for a slowly rising voltage pulse

We found that the start time in microwave generation of a relativistic backward wave oscillator (RBWO) for a slowly rising voltage pulse demonstrates a large jitter, which can be explained by the spread of explosive electron emission thresholds and plasma formation rates of the explosive emission cathode, and this large jitter is reduced greatly by a weak external RF signal. So, the effects of the emission threshold and plasma formation rate on the oscillation start time of a single RBWO and on the phase synchronization in two parallel RBWOs are investigated using particle-in-cell simulations. The 2D simulations show that a larger emission threshold and a faster plasma formation rate lead to a shorter start time due to the stronger shock excitation provided by the sharper beam current leading edge. For some special emission thresholds, the start time is abnormally long, which is due to the generation of other frequencies because of the shock excitation. The 3D simulations illustrate that with a larger emission threshold and a faster plasma formation rate, phase synchronization can be obtained in two parallel RBWOs even for a large voltage rise time. Therefore, we expect that by choosing the appropriate cathode emission threshold and plasma formation rate, it is possible to realize phase stabilization of an RBWO for a slowly rising voltage pulse even without an external RF signal.

Nonlinear electrostatic effects in MEMS ring-based rate sensors under shock excitation

The vibration response of a capacitive ring-based Coriolis Vibrating Gyroscope (CVG) subjected to in-plane shock is modelled and analysed to quantify the effect of shock on angular velocity measurement. The model developed considers a ring resonator with 8 uniformly spaced support legs and describes the in-plane ring response as the sum of the first 3 modes of a perfect ring and the nonlinear electrostatic force as a Taylor series. When a severe in-plane shock is applied, the rigid body response of the ring reduces the electrode gap significantly and a high order expansion is needed to represent the electrostatic force. These nonlinear forces are shown to cause direct and mixed mode coupling to occur, which can significantly modify the response characteristics. Numerical results are presented and interpreted for a range of shock cases to demonstrate the importance of mode coupling, and estimates are made to quantify the angular rate measurement error caused by shock for devices based on 2θ- and 3θ-modes of operation. To aid the design of devices that are more resilient to shock, a parameter study is performed to identify the modal frequency ratios that minimise this coupling.

Full-Scale Experimental and Numerical Investigations on the Modal Parameters of a Single-Span Steel-Frame Footbridge

In this work, an examination on the modal properties of a single-span steel-frame footbridge is presented. The footbridge is situated in Jawornik (Lesser Poland). The footbridge is symmetrical since its main structure consists of two steel frames of the same shape. The boundary conditions for both frames are the same as well. The study was completed on the basis of numerical as well as experimental investigations. For finite element (FE) analysis, a 3-D model of the single-span steel-frame footbridge was created. For the experimental study, a research scheme for in situ tests was developed. Three kinds of excitation techniques were used during the in situ tests: shock excitation, operational vibration, and slow sine sweep testing. Different functions that estimate natural frequencies, i.e., the power spectral density function (PSD) and the frequency response function (FRF), were applied. The modal assurance criterion (MAC) was used as a mathematical tool for the verification of the mode shapes of natural vibrations obtained in experimental and numerical ways. Good compatibility was recognized between the results obtained for experimental and numerical procedures in terms of both the natural frequency and the mode of vibration. The identified and verified values of the five consecutive natural frequencies of the footbridge were smaller than 5 Hz, but they were recognized as being located outside the frequency range defined as having “maximum risk of resonance”. The numerical and experimental modal analysis revealed that all modes corresponding to the natural frequencies from the 0–5 Hz range have both a symmetrical and an anti-symmetrical nature. In particular, the first vertical mode, which can play a central role from the serviceability of the footbridge point of view has a symmetrical shape. The results of the research might be applicable to the dynamic study of the structure type considered in the analysis, i.e., for the dynamic assessment of a single-span steel-frame footbridge with a relatively large mass as well as stiffness. The investigation proved that ambient vibration modal experiments are enough for the experimental investigation of the modal properties of the structure.

Discovery of a putative supernova remnant around the long-period X-ray pulsar SXP 1323 in the Small Magellanic Cloud

ABSTRACT We report the discovery of a circular shell centred on the Be X-ray binary (BeXB) SXP 1323 in the Small Magellanic Cloud. The shell was detected in an H α image obtained with the Very Large Telescope. Follow-up spectroscopy with the Southern African Large Telescope showed that the shell expands with a velocity of ${\approx }100{\rm \, km\, s^{-1}}$ and that its emission is due to shock excitation. We suggest that this shell is a remnant of the supernova explosion that led to the formation of SXP 1323’s neutron star ${\approx }40\, 000$ yr ago. SXP 1323 represents the second known case of a BeXB associated with a supernova remnant (the first one is SXP 1062). Interestingly, both of these BeXBs harbour long-period pulsars and are located in a low-metallicity galaxy.

Local discontinuous Galerkin method for modeling the nonplanar structures (solitons and shocks) in an electronegative plasma

Using the hydrodynamic equations of cold inertial positive ions with the Maxwellian distribution for light negative ion and electron densities and the Poisson equation, the family of nonplanar (cylindrical and spherical) Korteweg-de Vries (KdV) equations, i.e., the KdV, modified KdV, and extended KdV (EKdV), are obtained for small but finite amplitude ion-acoustic waves. The nonplanar EKdV equation is used to analyze the time-dependent planar and nonplanar soliton and shock structures. It is well-known that the exact solutions of the family of nonplanar KdV equations are not possible. Therefore, a local discontinuous Galerkin (LDG) method is developed for solving the nonplanar EKdV equation numerically. According to this method, the initial and boundary conditions for the solitary and shock waves are accurately identified. The L2 stability of the LDG method is proved for the general nonlinear case. The existence regions for both solitary and shock excitations have been defined precisely depending on the laboratory plasma parameters. Moreover, the effects of the negative-ion temperature ratio and the negative ion concentration on the profiles of the nonlinear structures (solitons and shocks) are examined. The effect of the geometrical divergence on the pulse profile is also reported which indicates that the localized pulses deform as time goes on. Furthermore, it is found that the amplitude of cylindrical structures (solitons and shocks) is larger than that of planar ones but smaller than that of the spherical ones. Moreover, in cylindrical geometry, the nonlinear structures travel slower than in the spherical ones. The implications of our results agree with the experimental observations.

Unveiling the nature of candidate high-mass young stellar objects in the Magellanic Clouds with near-IR spectroscopy

As nearby neighbors to the Milky Way, the Large and Small Magellanic Clouds (LMC and SMC) provide a unique opportunity to study star formation in the context of their galactic ecosystems. Thousands of young stellar objects (YSOs) have been characterized with large-scale Spitzer and Herschel surveys. In this paper, we present new near-IR spectroscopy of five high-mass YSOs in the LMC and one in the SMC. We detect multiple hydrogen recombination lines, as well as He I 2.058 $\mu$m, H$_2$, [Fe II], and [S III] in these highly excited sources. We estimate the internal extinction of each source and find that it is highest for sources with the youngest evolutionary classifications. Using line ratios, we assess the dominant excitation mechanism in the three sources where we detect both H$_2$ 2.12 $\mu$m and [Fe II] 1.64 $\mu$m. In each case, photoexcitation dominates over shock excitation. Finally, we detect CO bandhead absorption in one of our LMC sources. While this feature is often associated with evolved stars, this object is likely young with strong PAH and fine-structure emission lines tracing an H II region detected at longer wavelengths. Compared to high-mass YSOs in the Galaxy, our sources have higher bolometric and line luminosities, consistent with their selection as some of the brightest sources in the LMC and SMC.

Complex for experimental research of elastic wave interactions with ice layer

An adjustable pneumatic generator of acoustic signals with shock excitation was developed. Measuring and computing complex was also created to investigate elastic acoustic wave propagation along ice surface. Experiments on low-frequency acoustic signal propagation from the pneumatic generator were carried out in «water-ice-air» system. The possibility to apply the developed measuring and computing complex for physical modeling of acoustic wave propagation from earthquake sources along ice cover was confirmed.

Nonlinear Model Identification Method for Crane Damage Detection Without Baseline Data

Damage in the structure may lead to significant reduction in local strength. It is of great significance to localize the damage in the early stage for integrity of the structure so as to prevent catastrophic failure. The traditional damage detection techniques is achieved through comparing the current data with the baseline data obtained from the healthy structure. However, the baseline data is not available as the structure is often subjected to operational and environmental variations that may adversely affect the measurement signals. In this paper, model identification method is adopted for crane damage detection. It only requires the data after the structure is damaged. An improved nonlinear model is proposed based on the traditional models. It is denoted as RBF-BL (RBF Network based State Dependent Bilinear) model. Different damage cases are considered in the girder of the crane. The girder is subjected to transient shock excitation. The nonlinear model is constructed based on the vibration response signals and parameter estimation is performed. The anomalous region is initially determined through the model characteristic parameter. Beamforming algorithm is then performed for precise position of the crack. Numerical simulation and experimental validation are implemented to prove the effectiveness of the proposed model for crane damage detection without baseline data.

Structural Design and Isolation Characteristic Analysis of New Quasi-Zero-Stiffness

This project aimed to design a new type of vibration isolation mechanism with quasi-zero-stiffness (QZS) and analyze the QZS systems’ characteristics by computation and numerical simulation. First, the force–displacement and stiffness–displacement relational expressions of the QZS systems were established based on the study of system force and stiffness characteristics. Second, the nonlinear dynamic equations of the system under the excitation of harmonic force and harmonic displacement were established, and the effect of damping ratio, excitation amplitude, and nonlinear term under the transmissibility mechanism system was analyzed by the average method. Finally, the response time and stability of the QZS vibration isolator were analyzed under different circumstances through numerical simulation. The excitation amplitude, damping ratio, and nonlinear term have a great influence on the transmissibility of the system. In addition, under three different working conditions, the mechanism can have good vibration isolation characteristics and can meet the requirement of low-frequency vibration isolation. A novel type of the QZS systems has been investigated, and it is found that the influence of the excitation amplitude and the nonlinear term are just the same on the system transmissibility through the statics and dynamics calculations. Meanwhile, when damping ratio was increased, the transmissibility of the QZS systems could be reduced. The numerical simulations show that the system has faster response and smaller amplitude for sine wave, single shock, and multi-frequency excitations, which is more suitable for low-frequency vibration isolation.

Widespread Shocks in the Nucleus of NGC 404 Revealed by Near-infrared Integral Field Spectroscopy

We present high spatial resolution, integral field spectrograph (IFS) observations of the nearby LINER (low ionization nuclear emission line region) galaxy NGC 404 at 1.25 $\mu$m (J band) and 2.2 $\mu$m (K band) near-infrared wavelengths. Although NGC 404 is thought to host an intermediate mass black hole at its center, it has been unclear whether accretion onto the black hole or another mechanism such as shock excitation drives its LINER emission at optical/near-infrared wavelengths. We use the OSIRIS IFS at Keck Observatory behind laser guide star adaptive optics to map the strength and kinematics of [FeII], H$_2$, and hydrogen recombination lines at spatial resolutions of 1 pc across the central 30 pc of the galaxy. The H$_2$ gas is in a central rotating disk and ratios of multiple H$_2$ lines indicate that the molecular gas is thermally excited, with some contribution from UV fluorescence. The [FeII] emission is more extended and diffuse than the molecular gas and has a different kinematic structure that reaches higher velocities/dispersions. We also map the strength of the CO stellar absorption feature and constrain the dominant age of the nuclear stellar population to $\sim$1 Gyr. Finally, we find regions across the nucleus of NGC 404 with [FeII]/Pa$\beta$ line ratios up to 6.5, $\sim$2.5 times higher than the ratio measured from spatially-integrated spectra. From these high line ratios, we conclude that shocks are the dominate physical mechanism exciting NGC 404's LINER emission and argue that a possible source of this shock excitation is a supernova remnant.

Identification of Concrete Properties in Beam-Type Structures with Defects Based on Dynamic Methods

The problem of concrete properties identification and damage location in model beam type constructions is considered on the basis of application of experimental vibration analysis. As a simple analysis model, beam structures are considered defect-free and with defects. Based on the experimental approach, the model vibrations under shock and vibration excitation are analyzed. On the basis of analytical modeling, the dynamic modulus of elasticity, the velocity of sound in the beam, and the location of the defect are calculated. A technique and an example of the location of a defect in beam type constructions are presented.

The Shocking Power Sources of LINERs∗

Abstract The majority of low-ionization nuclear emission-line regions (LINERs) harbor supermassive black holes with very low accretion rates. However, the accretion flows do not produce enough ionizing photons to power the emission lines emitted on scales of ∼100 pc, and therefore additional sources of power are required. We present and analyze Hubble Space Telescope spectra of three nearby luminous LINERs that are spatially resolved on scales of ≲9 pc. The targets have multiple indicators of an accreting black hole, as well as a deficient ionizing photon budget. We measure diagnostic emission line ratios as a function of distance from the nucleus and compare them to models for different excitation mechanisms: shocks, photoionization by the accreting black hole, and photoionization by young or old hot stars. We also consider the kinematics of the line-emitting gas, as revealed by the widths and shifts of the emission lines. We conclude that, in LINERs with low-luminosity active nuclei, shocks by jets or other outflows are crucial in exciting the gas in and around the nucleus, as suggested by other authors. The physical model that best describes our targets comprises a low-luminosity, accretion-powered active nucleus that photoionizes the gas within ∼20 pc of the galaxy center, and shock excitation of the gas at larger distances.

Powerful mechanical-driven outflows in the central parsecs of the low-luminosity active galactic nucleus ESO 428-G14

ABSTRACT Low-luminosity Active Galactic Nuclei (LLAGNs) are characterized for low-radiative efficiency, much less than one percent of their Eddington limit. Nevertheless, their main energy release may be mechanical, opposite to powerful AGN classes like Seyfert and Quasars. This work reports on the jet-driven mechanical energy and the corresponding mass outflow deposited by the jet in the central 170 parsecs of the nearby LLAGN ESO 428-G14. The jet kinetic output is traced through the coronal line [Si vi] λ19641 Å. It is shown that its radial extension, up to hundreds of parsecs, requires a combination of photoionization by the central source and shock excitation as its origin. From the energetics of the ionized gas it is found that the mass outflow rate of the coronal gas is in the range from 3–8 M⊙ yr−1, comparable to those estimated from H i gas at kiloparsec scales in powerful radio galaxies.

Low-pass-filter-based shock response spectrum and the evaluation method of transmissibility between equipment and sensitive components interfaces

According to the features of the sources of pyroshock and ballistic shock, this study considers the pyroshock and ballistic shock generated by their respective impulsive sources as damped harmonic waves with different frequencies. According to the linear superposition assumption of damped harmonic waves in a linear elastic structure, a shock analysis method based on low-pass-filtered shock signals and their corresponding shock response spectrum (SRS), termed as low-pass-filter-based shock response spectrum (LPSRS), is proposed. LPSRS contains rich information of the frequency distribution of the shock excitation signal. A method to calculate shock transmissibility is proposed based on LPSRS and basic modal information of the equipment structure. LPSRS and SRS curves can be predicted at any given position of the equipment structure. The prediction method is validated by finite element method (FEM) simulation.

Primary shock calibration of accelerometers at Inmetro

This paper presents the primary shock calibration system developed at Inmetro to obtain the shock sensitivity of accelerometers and acceleration measuring chains. The shock exciter employs a pneumatic driver and is based on the mechanical shock between two rigid bodies guided by air bearings. The system follows the ISO standard 16063-13. The shock acceleration is measured by laser interferometry. Details of the calibration system, including the shock machine, data acquisition and signals processing are presented and some measurement results are discussed by the authors.

Detection of Photospheric Features in the Near-infrared Spectrum of a Class 0 Protostar

Abstract We present a near-infrared K-band R ≃ 1500 Keck spectrum of S68N, a Class 0 protostar in the Serpens molecular cloud. The spectrum shows a very red continuum, CO absorption bands, weak or nonexistent atomic metal absorptions, and H2 emission lines. The near-IR H2 emission is consistent with excitation in shocks or by X-rays but not by UV radiation. We model the absorption component as a stellar photosphere plus circumstellar continuum emission with wavelength-dependent extinction. A Markov Chain Monte Carlo analysis shows that the most likely model parameters are consistent with a low-temperature, low-gravity photosphere with significant extinction and no more than modest continuum veiling. Its T eff ≃ 3260 K effective temperature is similar to that of older, more evolved pre-main-sequence stars, but its surface gravity log g ≃ 2.4 cm s−2 is approximately 1 dex lower. This implies that the radius of this protostar is a factor of ∼3 larger than that of 106 year old T Tauri stars. Its low veiling is consistent with a circumstellar disk having intrinsic near-IR emission that is less than or equal to that of more evolved Class I protostars. Along with the high extinction, this suggests that most of the circumstellar material is in a cold envelope, as expected for a Class 0 protostar. This is the first known detection and analysis of a Class 0 protostar absorption spectrum.

Adaptive control of a vehicle-seat-human coupled model using quasi-zero-stiffness vibration isolator as seat suspension

We propose the quasi-zero-stiffness (QZS) vibration isolator as seat suspension to improve vehicle vibration isolation performance. The QZS vibration isolator is composed of vertical spring and two symmetric negative stiffness structures used as stiffness correctors. A vehicle-seat-human coupled model considering the QZS vibration isolator is established as a three degree-of-freedom (DOF) model; it is composed of a quarter car model and a simplified 1 DOF model combined vehicle seat and human body. This model considers the changing mass of the passengers and sets the total mass of the vehicle seat and human body as an uncertain parameter, which investigates the overload and unload conditions in practical engineering. To further improve the vehicle ride comfort, a constrained adaptive backstepping controller law based on the barrier Lyapunov function (BLF) is presented. The dynamic characteristic of the active vehicle-seathuman coupled model under shock excitation was analyzed using numerical method. The results show that the designed controller law can isolate the shock excitation transmitted from the road to the passengers effectively, and both the vehicle and seat suspension strokes remain in the allowed stroke range.