Short Duration Impulses Research Articles

Understanding pickleball noise at the source: The vibroacoustics of the pickleball paddle and ball

Pickleball continues to be America's fastest-growing sport, growing by roughly 150% every year with 48.3 million US adults (19% of the adult population) having played at least one game in 2023. This immense popularity and growth is accompanied by a similar increase in the number and voracity of complaints from the residential communities surrounding pickleball courts. This paper aims to explain the source of the pickleball noise—a short duration impulse with a strong tonal component near 1250 Hz—due to the impact of the pickleball ball and paddle, with a specific focus on the vibrational modes of the paddle that contribute most strongly to the tonal nature of the sound. Experimental modal analysis was performed on several paddles (wood, aluminum, composite, and carbon fiber) as well as the first paddle to meet the new USA Pickleball Quiet Category requirements. Spectral analysis of the impact identifies the offending tonal component near 1250 Hz to be a strongly radiating “membrane-type” mode of the paddle surface. Paddles for which this mode shape has a significantly higher or lower in frequency and amplitude result in a much less annoying impact sound. The role of vibrational modes in the ball will also be considered.

Morphology and properties of CL-20/MTNP cocrystal prepared via facile spray drying

Cocrystal of 2,4,6,8,10,12-hexaazaisowurtzitane/1-methyl-3,4,5-trinitropyrazole (CL-20/MTNP) in a 1:1 molar ratio is a promising energetic material, since it combines the superior detonation performance of CL-20 and good mechanical sensitivity of MTNP. In order to promote its progress to practical use, a rapid, facile and candidate large-scale manufacture method-spray drying was used to prepare the CL-20/MTNP cocrystal in this study. The morphology, crystal structure and thermodynamic behavior of the resulted CL-20/MTNP-SD cocrystal, raw materials and the cocrystal prepared via solvent evaporation method (CL-20/MTNP-E) were systematically studied by scanning electron microscopy (SEM), X-ray diffraction spectroscopy (XRD) and differential scanning calorimetry (DSC), respectively. The resulted CL-20/MTNP-SD cocrystal shows a regular spherical shape with diameter narrowly distributed from 0.2 µm to 2 µm. This morphology is different from the rod-like shape of CL-20/MTNP-E cocrystal. The crystal structure and thermal behavior CL-20/MTNP-SD is similar to the CL-20/MTNP-E cocrystal, and totally different to the raw materials. Additionally, the initiation temperature and activation energy for thermal decomposition of the CL-20/MTNP-SD cocrystal are slightly lower than the CL-20/MTNP-E cocrystal. The short pulse slapper sensitivity of cocrystals have been investigated. The spray drying method endows CL-20/MTNP cocrystal with the ability of being initiated by short-duration impulse. And the slapper impact initiating threshold of CL-20/MTNP-SD cocrystal is even lower than the commonly used initiating explosive 2,2′,4,4′,6,6′-hexanitrostilbene (HNS). This result evokes a prospective application of CL-20/MTNP-SD cocrystal as an initiating explosive for short impulse shockwave.

Survivability of embedded microelectronics in precision guided projectiles: Modeling and characterization

Precision guided projectiles (PGPs) experience severe shock loads during launch emanating from the propellant gasses and the surrounding air. Our most recent multiphysics effort showed that the complex flow environment during launch would result in the development of severe shock loads in the confined barrel space and at muzzle exit. The focus of the current effort is the survivability of the embedded integrated circuit chips and printed circuit boards (PCB). Four aspects of the work were accordingly examined. The first is concerned with the development of a new polymeric encapsulation technique to protect the embedded microelectronic systems (EMES). The second with testing the effectiveness and endurance of the newly proposed encapsulation techniques using instrumented pneumatic drop weight impact test facility. The third with constructing bottom-up multi-level micromechanics based homogenization schemes, accounting for complex constitutive material models of a multilayer circuit board, to determine the effective elastic properties of the PCB for the numerical FE simulations. The fourth with conducting three-dimensional high-resolution dynamic FE simulations to evaluate the structural integrity of the potted PCB assembly in response to the short duration impulse and to elucidate the experimental findings. The results of our experimental and numerical efforts reveal that the newly devised encapsulation technique is highly effective in protecting EMES and can be used to audit the survivability of the microelectronics that are embedded in PGPs.

Pulse Buckling of a Thin Walled CFRP Cylindrical Shell – A Numerical Approach

The present study investigates the behaviour of a CFRP cylindrical shell under compressive pulse loading. The in-pulse analyses are performed numerically, using the finite element code ABAQUS. The dynamic buckling load is determined using the Budiansky & Hutchinson criterion. Parameters like the shape of pulse loading and pulse duration were varied, and their influence on the Dynamic Load Factor (DLF) was investigated. The investigation shows that DLF tends to increase well above unity for short duration impulses, while for the larger duration the value is decreasing towards unity. The shape of the pulse also has a significant influence on the DLF value. DLF<1 was found only for a trapezoidal pulse. For sinusoidal pulse shape, the static buckling load of the CFRP shell was consistently below the dynamic one.

Soil Fatigue from Induced Seismicity

Induced seismicity and the effects on civil engineering systems are not completely understood and infrequently studied. One specific area that is not well known is soil fatigue which includes factors such as understanding the natural conditions of the subsurface as well as operational parameters under short duration impulse loads. With the increase of geoinduced seismic activity, soil fatigue becomes of greater concern to structures in the vicinity of this seismic load. The foundations of these structures can be affected by impulse loads which can ultimately cause failure. The lack of quantitative data puts the reliability of these civil engineering systems at risk as they are not fully evaluated to determine if they are functioning as they are intended in the environments they are designed to support.

A comparison of accelerometer and piezofilm-based force balances for hypersonic shock tunnels

A blunt double-cone model, equipped with a three-component accelerometer or piezofilm-based force balance system, is tested in the IITB-Shock Tunnel at 0 º and 10 º angle of inclinations during force measurement experiments. Conventional accelerometer force balance theory and soft computing-based adaptive neuro fuzzy inference system have been adopted to recover the axial and normal forces. In order to arrive at the time varying forces, these balances are calibrated using impulse hammer tests at single or multiple points. Necessity of multipoint calibration has also been demonstrated during recovery of forces for both the balances. Genetic algorithm in conjunction with adaptive neuro fuzzy inference system has been implemented herein to train the system for force prediction. Encouraging agreement has been noted between the predictions made using accelerometer force balance theory and adaptive neuro fuzzy inference system-based recovery of forces from accelerometer and piezofilm balances. Thus, present studies not only provide the methodology for calibration and implementation of piezofilm based force measurement, but also recommend its usage in short duration impulse facilities.

Application of neural-networks and neuro-fuzzy systems for the prediction of short-duration forces acting on the blunt bodies

Present studies deal with application of finite element method and intelligent soft computing techniques viz. neural network (NN) and adaptive neuro-fuzzy inference system (ANFIS) for the prediction of short duration impulse, ramp and hat forces. Two blunt bodies viz. a hemisphere and a blunt cone with cylindrical aft body have been considered in these investigations. Training of the NN and ANFIS has been carried out using one axial acceleration and two normal accelerations obtained from known input forces and a moment. It is shown here that the NN is unable to recover the unknown forces and moment. However, ANFIS-based strategy is found better for prediction of the same forces and moment. Thus, novelty of these studies exists in the assessment and successful implementation of the soft computing techniques like NN and ANFIS for prediction of the unknown short-duration force and moment time histories. These predictions are also cross-checked for the error, and it has been observed that the ANFIS can be used for short-duration force prediction in high-speed aerospace applications.

DIAGNOSTICS OF ROLLING BEARINGS FOR AUXILIARY ELECTROMOTORS OF ELECTRIC LOCOMOTIVE USING PARAMETRIC MODEL AND ENVELOPE SPECTRUM

Goal : increase of efficiency for diagnostics of rolling bearing faults using an autoregressive model to calculate AR coefficients and further application of pre-whitening AR filter and envelope spectra to extract weak faults signs. Method of doing research: diagnostics of rolling bearing faults involves signal acquisition technique and application of the AR model for better analysis of short duration signal properties and impulses. The Akaike information criterion is used to ensure optimum adaptation of AR coefficients to a fault bearing. The AR coefficients are defined with Yule-Walker equitation. The advantages of pre-whitening AR filter are presented due to the low efficiency regarding the power spectral density of the parametric model. The experimental study of vibration characteristics of the auxiliary electromotor body of electric locomotive defines the frequency band 5,5 — 7 kHz with the rolling bearing vibration, and this frequency band can be used for further extraction the envelope spectra. Value: the research shows a capability of the pre-whitening AR model to store valuable information not only about different faults concerning outer, inner race, rollers of bearings but also about the technical condition of the cage, the signs of which are displayed on the envelope spectra directly after the AR filter.

Fore-body and base heat flux measurements on a typical crew module in short duration impulse facilities

Experiments are carried out to measure forebody and base heat flux on a typical Crew Module at Mach numbers 5.8 and 8 over the enthalpy range of 1.5–3.73MJ/kg. Towards this, two scaled down models namely 1:55 and 1:40 are tested in 0.15m pressure and in 1m combustion driven shock tunnels. Forebody and stagnation point heat flux are measured through E-type co-axial thermocouples whereas, platinum thin film gauges are used to measure base heat flux. Forebody heat flux for the range of α (0–20deg) shows that the stagnation point heat flux move towards the bottom surface and the top surface experiences low heat flux as the angle of attack increases. At the base, the level of heat flux is found to be low and the maximum value is 3% of the stagnation point heat flux. The minimum heat flux is observed to be at the center of the base and increases radially outwards. The measured stagnation point heat flux is found to be ∼50% higher than the Fay–Riddell correlation for dissociated air, using Newtonian velocity gradient. On the other hand, if the Fay–Riddell correlation is modified by incorporating experimentally generated velocity gradient, the difference reduces to 14.25%. Finally, once the real gas effect is added to the Fay–Riddell correlation along with experimentally generated velocity gradient, the difference further reduces to 9.4%. Thus, the correct choice of transport properties and velocity gradient plays a crucial role to accurately predict the stagnation point heat flux.

Complex Exponential Pseudomodes of LTI Operators Over Finite Intervals

In applications including radar and ultrasonic inspection, an observed signal can often be modeled as the output over a finite interval of a linear, time-invariant (LTI) operator having a short-duration impulse response. For processing such as filtering and compression it would be useful to have approximations to eigenfunctions of the operator. It has been shown that discrete-time complex exponentials are asymptotic pseudomodes (i.e., approximate eigenvectors) of sequences of Toeplitz matrices. In this letter we show that complex exponentials over the observation interval are pseudomodes of LTI operators, corresponding to pseudoeigenvalues that are samples from the operator’s frequency response, and how the level of approximation depends on the ratio of the impulse response duration to observation interval length. This implies that the Fourier Series basis for the observation interval can be used as an orthonormal set of approximate eigenfunctions.

Localizing energy in granular materials

A device for absorbing and storing short duration impulses in an initially uncompressed one-dimensional granular chain is presented. Simply stated, short regions of sufficiently soft grains are embedded in a hard granular chain. These grains exhibit long-lived standing waves of predictable frequencies regardless of the timing of the arrival of solitary waves from the larger matrix. We explore the origins, symmetry, and energy content of the soft region and its vibrational modes.

Fast response co-axial thermocouple for short duration impulse facilities

A fast response Chromel–Alumel (K-type) co-axial thermocouple is designed, fabricated, calibrated and tested in a shock tunnel. The freestream Mach number of 5.75 and the total enthalpy of 0.92 MJ/kg are simulated to study the stagnation point heat flux of a hemi-spherical model through transient temperature trace. The realized K-type co-axial thermocouple of 3 mm in length and 1.6 mm in diameter is flush mounted at the stagnation point of a 7.5 mm radius hemi-spherical model. The achieved response time of the realized K-type co-axial thermocouple is ~3 µs, which is sufficient enough to capture the transient temperature signal. A steady tunnel flow time of 1.8 milliseconds is used to get the average stagnation point heat flux. The measured stagnation point heat flux is 22.96 W/cm2, which is well matched with the Fay–Riddell value within 5.5%. The realized K-type co-axial thermocouple is robust, responds fast, and can be contoured to any type of model surface.

On an asymptotic analysis problem related to the construction of an attainability domain

Problems of constructing and analyzing the properties of attainability domains play an important role in control theory and its applications. In particular, this applies to control under impulse constraints that reflect the energetics of a process. The situation is complicated by the possible instability of the process under variation (in particular, under relaxation) of constraints related to boundary and intermediate conditions. Stability of the problem is also missing, in general, under relaxation of state constraints. In these cases, it is natural to focus on the asymptotic variant of the statement; this is especially expedient when one has to deal with initially asymptotic requirements. In all these cases, it seems expedient to use analogs of J. Warga’s approximate solutions. At the same time, to seek necessary approximate (and, in fact, asymptotic) solutions, it is natural to use generalized modes. For problems with impulse constraints and discontinuity in the coefficients of control actions, such modes lead to phenomena described by products of discontinuous functions and generalized functions even in the class of linear systems. In a large series of his studies, to overcome the arising difficulties, one of the authors used constructions of extension in the class of finitely additive measures. The present paper follows this approach and is ideologically relevant to the engineering problem of controlling the thrust of an engine under conditions of a given program of variation of its orientation; it is postulated that energy resources are completely consumed in a natural (for a number of impulse control problems) mode of short-duration impulses: the set of time instants at which the instantaneous control is different from zero can be embedded in an interval of vanishingly small length. Within these short periods of time, the engine should consume all energy resources while obeying some other constraints (making the sense of moment constraints) to a high degree of accuracy. In addition, one should take into account the possible discontinuity of the functions defining the coefficients of control actions. As a natural analog of the attainability domain, we use an attraction set, whose construction, together with the subsequent study of its main properties, constitutes the goal of the present study.

Research Papers. An Approach to Design Broadband Air Backed Piezoelectric Sensor

Abstract In this work, an approach to the design of broadband thickness-mode piezoelectric transducer is pre- sented. In this approach, simulation of discrete time model of the impulse response of matched and backed piezoelectric transducer is used to design high sensitivity, broad bandwidth, and short-duration impulse response transducers. The effect of matching the performance of transmitting and receiving air backed PZT-5A transducer working into water load is studied. The optimum acoustical characteristics of the quarter wavelength matching layers are determined by a compromise between sensitivity and pulse duration. The thickness of bonding layers is smaller than that of the quarter wavelength matching layers so that they do not change the resonance peak significantly. Our calculations show that the −3 dB air backed transducer bandwidth can be improved considerably by using quarter wavelength matching layers. The computer model developed in this work to predict the behavior of multilayer structures driven by a transient waveform agrees well with measured results. Furthermore, the advantage of this this model over other approaches is that the time signal for optimum set of matching layers can be predicted rapidly

Characterization of wave propagation in elastic and elastoplastic granular chains

For short duration impulse loadings, elastic granular chains are known to support solitary waves, while elastoplastic chains have recently been shown to exhibit two force decay regimes [ Pal, Awasthi and Geubelle Granular Matter 15 747 (2013)]. In this work, the dynamics of monodisperse elastic and elastoplastic granular chains under a wide range of loading conditions is studied, and two distinct response regimes are identified in each of them. In elastic chains, a short loading duration leads to a single solitary wave propagating down the chain, while a long loading duration leads to the formation of a train of solitary waves. A simple model is developed to predict the peak force and wave velocity for any loading duration and amplitude. In elastoplastic chains, wave trains form even for short loading times due to a mechanism distinct from that in elastic chains. A model based on energy balance predicts the decay rate and transition point between the two decay regimes. For long loading durations, loading and unloading waves propagate along the chain, and a model is developed to predict the contact force and particle velocity.

Vaporizing Foil Actuator: A Versatile Tool for High Energy-rate Metal Working

High energy-rate metalworking has significant advantages, in that short time scales change the fundamental nature of the forming process and short duration impulses can be used with much lighter and more agile equipment because large static forces do not need to be resisted. Here, we propose the use of thin aluminum foils that are intentionally vaporized by a pulsed electric current, in order to create an intense mechanical impulse. The driving pressures can be a few GPa's, and have been used to launch sheet metal workpieces to velocities in excess of 1km/s. Applications including impact welding, forming, embossing, shearing, and powder compaction have been demonstrated and will be presented in this paper.

Electrically driven plasma via vaporization of metallic conductors: A tool for impulse metal working

Forming, cutting and welding of metal by impulse has significant advantages, in that short time scales change the fundamental nature of the forming process and short duration impulses can enable much lighter and more agile equipment because large static forces do not need to be resisted. Impulse forming is most commonly executed using electromagnetic forming. However, the application of electromagnetic forming is limited at high energies and large numbers of operations by the availability of long-lived electromagnetic coils (or actuators, as they are sometimes referred to). Low-cost, disposable actuators have been suggested as one method to counteract this issue. Here we propose the use of low-cost foils or wires that are intentionally vaporized by a pulsed electric current, in order to create an intense mechanical impulse. Applications including cutting, forming, and dimensional calibration are demonstrated and discussed. The available literature that could provide design guidance is reviewed. A simple cutting and welding experiment using a vaporizing aluminum foil is demonstrated. Further experiments study the expansion of simple copper tubes using the impulse developed from copper and aluminum wires that are vaporized using capacitor bank discharge with nominal charged voltages between 3.4 and 6.7kV, and peak currents between 60 and 150kA delivered with rise times on the order of 20μs. This gives some guidance on how forming operations may be designed and, opens possible areas for further research.

Measurements of bone-conducted impulse noise from weapons using a head simulator

High-intensity impulse sounds are generally considered to be more damaging than continuous sounds, so understanding the attenuation performance of hearing protection devices against impulse noise is key to providing adequate protection for exposed persons. The maximum attenuation of hearing protection devices is limited by bone-conducted sound. Weapon fire noise in the form of short duration impulses can reach peak levels of 170 dB SPL at the shooter’s ear, a sound level for which maximum hearing protection is recommended and for which bone-conducted sound will be a significant factor. However, current acoustic test fixtures do not capture the bone-conducted sound paths. In this study, an anatomically correct head simulator built specifically to measure bone-conducted sound was used to evaluate the effects of impulse noise generated by hand guns and rifles at several peak sound pressure levels ranging between 120 dB SPL and 170 dB SPL. Time histories of the acceleration of the temporal bones and the sound pressure transmitted into the cranial cavity were recorded. Results investigating the linearity of the bone-conducted response to impulse noise at high peak levels and the effects of hearing protection on the sound level and vibrations inside the head are presented.

Using impulsive peak insertion loss of hearing protectors with impulsive damage risk criteria

Impulsive noise presents special challenges for hearing conservation. The scientific community continues to search for an impulsive noise exposure criterion which accurately assesses the hearing damage risk for both short and long duration impulses. Other factors, such as the use of hearing protectors, earmuffs and earplugs, also affect the hearing damage risk but the current criteria do not address methods for using the attenuation of hearing protectors in impulsive noise. The relatively new ANSIS12.42-2010 “Methods for the Measurement of Insertion Loss of Hearing Protection Devices in Continuous or Impulsive Noise using Microphone-in-Real-Ear or Acoustic Test Fixture Procedures” describes methods for measuring the peak insertion loss of a hearing protector in impulsive noise. This paper will describe a method to apply the peak insertion loss data to impulsive noise damage risk criteria for an estimate of allowable impulsive noise exposure when using hearing protection.

The effect of reverberation on the performance of cepstral mean subtraction in speaker verification

Speaker verification (SVR) performance is degraded under reverberation conditions. Cepstral mean subtraction (CMS) is often applied to the feature vectors in order to compensate for convolutive effects of transmission channels, which are considered to have a short-duration impulse response. The effect of reverberation on the performance of CMS applied to the feature vectors in SVR is investigated. Although CMS was found effective in reducing the effect of reverberation for short reverberation time (RT), in cases of long RT, it is shown that CMS may degrade SVR performance rather than improve it. Hence, CMS should not to be used in these cases. In addition, the effect of the room volume was tested and found less critical than the effect of long RT.