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Xu, Qian. "Damage Index Analysis of Retaining Wall Structures Based on the Impulse Response Function and Virtual Impulse Response Function." Shock and Vibration 2021 (October 18, 2021): 1–21. http://dx.doi.org/10.1155/2021/9741732.
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To identify the damage within retaining wall structures, the Hilbert–Huang Transforms of the impulse response function and virtual impulse response function were performed. The Hilbert marginal energy ratio spectrums of the impulse response function and virtual impulse response function were acquired. To reflect damage information effectively, those bands with stronger damage sensitivity were extracted via the threshold value ε0. Then, the Hilbert feature bands, which were more sensitive to damage within retaining walls, were selected by considering the contribution of the residual band to the damage identification. Based on the feature bands, the Hilbert damage feature vector, which reflects the variations of Hilbert marginal energy ratio caused by damage, was created. Based on the damage feature vector, two damage identification indexes (the energy ration standard deviation and Energy Ration Standard Deviation), which were based on the impulse response function and virtual impulse response function, respectively, were proposed to identify damage within retaining walls. To investigate the validity of the damage indexes, vibration tests on a pile plate retaining wall were done. The test results show that the damage feature vector is a zero vector or the value of damage index is zero when the wall is undamaged. The damage feature vector is a nonzero vector or the value of the damage index is more than zero when the wall is damaged. Thus, the damage state of the wall can be detected sensitively via the damage feature vector or damage indexes. Partial damage causes greater fluctuation of trend surface of the damage index. The location of partial damage can be diagnosed validly via the coordinate of peak value in the trend surface. The quantitative relationship formula between the damage index and damage intensity is established. The damage intensity of the wall can be calculated reversely, when the damage index is available. Either the energy ration standard deviation or Energy Ration Standard Deviation can be used to detect the damage state, diagnose the damage location, and identify the damage intensity. In comparison with the energy ration standard deviation, the stability and damage sensitivity of the Energy Ration Standard Deviation is much better.
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Vadarevu, Sabarish B., Sean Symon, Simon J. Illingworth, and Ivan Marusic. "Coherent structures in the linearized impulse response of turbulent channel flow." Journal of Fluid Mechanics 863 (January 30, 2019): 1190–203. http://dx.doi.org/10.1017/jfm.2019.15.
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We study the evolution of velocity fluctuations due to an isolated spatio-temporal impulse using the linearized Navier–Stokes equations. The impulse is introduced as an external body force in incompressible channel flow at $Re_{\unicode[STIX]{x1D70F}}=10\,000$. Velocity fluctuations are defined about the turbulent mean velocity profile. A turbulent eddy viscosity is added to the equations to fix the mean velocity as an exact solution, which also serves to model the dissipative effects of the background turbulence on large-scale fluctuations. An impulsive body force produces flow fields that evolve into coherent structures containing long streamwise velocity streaks that are flanked by quasi-streamwise vortices; some of these impulses produce hairpin vortices. As these vortex–streak structures evolve, they grow in size to be nominally self-similar geometrically with an aspect ratio (streamwise to wall-normal) of approximately 10, while their kinetic energy density decays monotonically. The topology of the vortex–streak structures is not sensitive to the location of the impulse, but is dependent on the direction of the impulsive body force. All of these vortex–streak structures are attached to the wall, and their Reynolds stresses collapse when scaled by distance from the wall, consistent with Townsend’s attached-eddy hypothesis.
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Au, Eu Ving, Gregory MacRae, Didier Pettinga, Bruce Deam, Vinod Sadashiva, and Hossein Soleimankhani. "Seismic response of torsionally irregular single story structures." Bulletin of the New Zealand Society for Earthquake Engineering 52, no. 1 (2019): 44–53. http://dx.doi.org/10.5459/bnzsee.52.1.44-53.
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Impulse ground motions are applied to single story structures with different in-plane wall strength and stiffness, rotational inertia, and out-of-plane wall stiffness to obtain the dynamic response considering torsion. A simple hand method to evaluate the impulse response is developed. It is shown that the median increase in response of the critical component considering torsion from many earthquake records is similar to that from impulse records. Using this information, a simple design methodology is proposed which enables the likely earthquake response of critical elements considering torsion to be obtained from building analyses not considering torsion. A design example is also provided.
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Wei, Xue Ying, Tuo Huang, and Nan Li. "Numerical Derivation of Pressure-Impulse Diagrams for Unreinforced Brick Masonry Walls." Advanced Materials Research 368-373 (October 2011): 1435–39. http://dx.doi.org/10.4028/www.scientific.net/amr.368-373.1435.
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Pressure-impulse diagrams have been extensively used for damage assessments of structural components subject to a specified blast loading. In this paper, a numerical method is used to generate pressure-impulse diagrams for unreinforced masonry walls subjected to blast loading. A previously developed plastic damage material model accounting for strain rate effects is used for brick and mortar. Three levels of damage criteria are defined based on maximum deflection of the wall and rotation of the supports. The obtained blast response for unreinforced masonry walls are validated against field test data. It is shown that the obtained pressure-impulse diagrams have an improved ability to evaluate the damage level of masonry walls.
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Jia, Zhenzhen, Qing Ye, and He Li. "Damage Assessment of Roadway Wall Caused by Dynamic and Static Load Action of Gas Explosion." Processes 11, no. 2 (2023): 580. http://dx.doi.org/10.3390/pr11020580.
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In order to obtain the damage characteristics of a roadway wall caused by a gas explosion, the damage evaluation theory of a roadway wall under the dynamic and static loads of a gas explosion is analyzed in this paper. Meanwhile, an evaluation method (overpressure–impulse criterion) is selected to evaluate the damage of the roadway wall under the impact load of the gas explosion. A mathematical model and a physical analysis model of the roadway wall damage are established by LS-DYNA software. The dynamic response of the roadway wall caused by the dynamic and static loads of the gas explosion is numerically simulated. The overpressure and impulse of gas explosion propagation are measured, while the damage data of the roadway wall under different overpressure and impulse loads are obtained. The P-I curves of the roadway wall under different dynamic and static loads of gas explosion are drawn. The fitting formula of P-I curves of the roadway wall is obtained. The influence of different geostress loads (0–20 MPa) on the P-I curve is analyzed. The shape of the P-I curve is similar under different geostress conditions. The difference is mainly shown in different sizes of P0 and I0. The numerical simulation results show that the P-I curve and the effect of geostress on roadway wall damage could reflect the dynamic response of the roadway wall. The damage degree and damage range of the roadway wall increase with the increase in explosion load energy. Under the action of different geostresses, the overpressure asymptote P0 and the impulse asymptote I0 show linear changes. The above research results could provide a theoretical basis and data support for the evaluation of roadway wall damage caused by gas explosions.
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Xu, Qian. "Damage Identification Investigation of Retaining Wall Structures Based on a Virtual Impulse Response Function." Shock and Vibration 2016 (2016): 1–13. http://dx.doi.org/10.1155/2016/1346939.
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To eliminate the influence of excitation on the wavelet packet frequency band energy spectrum (ES), ES is acquired via wavelet packet decomposition of a virtual impulse response function. Based on ES, a character frequency band vector spectrum and damage eigenvector spectrum (DES) are created. Additionally, two damage identification indexes, the energy ratio standard deviation and energy ratio variation coefficient, are proposed. Based on the damage index, an updated damage identification method for retaining wall structures is advanced. The damage state of a retaining wall can be diagnosed through DES, the damage location can be detected through the damage index trend surface, and the damage intensity can be identified by establishing a quantitative relationship between the damage intensity and damage index. To verify the feasibility and validity of this damage identification method, a vibration test on a pile plate retaining wall is performed. Test results demonstrate that it can distinguish whether the retaining wall is damaged, and the location of partial damage within the retaining wall can be easily detected; in addition, the damage intensity of the wall can also be identified validly. Consequently, this damage identification theory and method may be used to identify damage within retaining wall structures.
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Wu, Di, Fangshuo Mo, and Jianmin Ge. "Effects of coupling between loudspeaker and wall on impulse response measurement." Journal of the Acoustical Society of America 131, no. 4 (2012): 3284. http://dx.doi.org/10.1121/1.4708279.
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Li, Wen Sheng, Hui Yang, and Bo Zhang. "Dynamic Analysis on Explosion Resistance Performance of Reinforced Concrete Wall." Advanced Materials Research 1078 (December 2014): 162–65. http://dx.doi.org/10.4028/www.scientific.net/amr.1078.162.
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Based on the finite element software ABAQUS, this paper deals with numerical simulation to dynamic response of reinforced concrete wall under blast loading. Study shows that the explosion resistance performance of the wall with four edges fixed or with two opposite edges fixed are better than that of the wall one edge fixed and another opposite edge simply supported. The greater the explosion impulse, the bigger the maximum displacement of the wall. When reinforcement ratio of the wall increases, the explosion resistance performance of the wall will be improved. At the same time, reasonable reinforcement and external conditions should be made sure. Keywords: Blast Loading, Numerical Simulation, Shear Wall, Dynamic Response
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Gaiser, James E., Terrance J. Fulp, Steve G. Petermann, and Gary M. Karner. "Vertical seismic profile sonde coupling." GEOPHYSICS 53, no. 2 (1988): 206–14. http://dx.doi.org/10.1190/1.1442456.
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P-wave and S-wave displacements occur at high angles of incidence in vertical seismic profiles (VSPs). Therefore, the coupling of a geophone sonde to the borehole wall must be rigid in all directions. A sonde that is well coupled should have no resonant frequency within the seismic band and should provide geophone outputs that accurately represent the earth’s ground motion. An in‐situ coupling response experiment conducted under normal VSP field conditions provides a measure of the sonde‐to‐borehole wall coupling. The sonde is locked in the borehole and a surface source is excited at different offsets and azimuths. An analysis of the P-wave direct arrivals enhances damped oscillations that represent an estimate of the coupling impulse response. This response is characterized by the viscoelastic behavior of a Kelvin model related to the complex compliance [Formula: see text], where κ is the elastic spring constant, η is the damping constant, and ω is the angular frequency. The complex modulus κ−iωη is proportional to the contact width of the sonde with the borehole wall. Increasing the width by a factor of 4.5 causes a similar increase in κ−iωη where the resonant frequency and initial amplitude of the coupling impulse response increase by a factor of two. Also, the initial amplitude of the coupling impulse response appears to be inversely proportional to the locking force of the sonde. For a constant contact width, increasing the locking force by a factor of 1.37 decreases the amplitude of the response by 3.5 dB.
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Pastor, J., B. Soria, and C. Belmonte. "Properties of the nociceptive neurons of the leech segmental ganglion." Journal of Neurophysiology 75, no. 6 (1996): 2268–79. http://dx.doi.org/10.1152/jn.1996.75.6.2268.
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1. The electrical responses of nociceptive (N) lateral and N medial neurons of the leech segmental ganglion to mechanical, chemical, and thermal stimulation of the skin were studied in a superfused ganglion-body wall preparation. 2. Mechanical indentation of the skin > 10 mN evoked in both types of cells a sustained discharge of impulses; afterdischarge was often observed with suprathreshold stimulations. 3. Application to the cutaneous receptive area of 10-100 mM acetic acid or of NaCI crystals and solutions also elicited a firing response in N medial and N lateral cells. In contrast, capsaicin applied to the skin (3.3 x 10(-5) to 3.3 x 10(-2) M) excited N lateral but not N medial neurons. Likewise, impulse discharges were obtained when capsaicin was applied to the cell bodies of N lateral but not of N medial neurons. 4. In both types of N neurons, heating of the skin above 39 degrees C evoked a discharge of impulses whose frequency was roughly proportional to temperature values. 5. Application of repeated suprathreshold heating cycles at 10-min intervals enhanced the impulse frequency of the response (sensitization). Shorter time intervals between heating cycles depressed the response to heat. Sensitization could not be obtained by equivalent soma depolarizations obtained by intracellular current injection. 6. Impulse discharges evoked by irritant agents were also augmented by previous application of noxious heat. 7. N lateral neurons fired in response to low-pH solutions and capsaicin directly applied onto the ganglion. N medial neurons responded inconsistently to acid and were insensitive to capsaicin. Action potentials evoked in N lateral cells by capsaicin had a slow rise, a prominent hump, and a prolonged afterhyperpolarization. 8. It is concluded that N neurons of the leech segmental ganglion respond to different modalities of noxious stimuli applied to their peripheral receptive fields and develop sensitization after repeated noxious stimulation. These properties are typical of mammalian polymodal nociceptors; thus N neurons may be a simple model for analysis of membrane mechanisms associated with polymodality of nociceptive neurons.
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Shi, Cheng, Zhi-Kang Ni, Jun Pan, Zhijie Zheng, Shengbo Ye, and Guangyou Fang. "A Method for Reducing Timing Jitter’s Impact in Through-Wall Human Detection by Ultra-Wideband Impulse Radar." Remote Sensing 13, no. 18 (2021): 3577. http://dx.doi.org/10.3390/rs13183577.
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Ultra-wideband (UWB) impulse radar is widely used for through-wall human respiration detection due to its high range resolution and high penetration capability. UWB impulse radar emits very narrow time pulses, which can directly obtain the impulse response of the target. However, the time interval between successive pulses emitted is not ideally fixed because of timing jitter. This results in the impulse response position of the same target not being fixed, but it is related to slow-time. The clutter scattered by the stationary target becomes non-stationary clutter, which affects the accurate extraction of the human respiration signal. In this paper, we propose a method for reducing timing jitter’s impact in through-wall human detection by UWB impulse radar. After the received signal is processed by the Fast Fourier transform (FFT) in slow-time, we model the range-frequency matrix in the frequency domain as a superposition of the low-rank representation of jitter-induced clutter data and the sparse representation of human respiratory data. By only extracting the sparse component, the impact of timing jitter in human respiration detection can be reduced. Both numerical simulated data and experimental data demonstrate that our proposed method can effectively remove non-stationary clutter induced by timing jitter and improve the accuracy of the human target signal extraction.
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Xu, Qian. "Investigation of Stability Alarming for Retaining Wall Structures with Damage." Shock and Vibration 2017 (2017): 1–12. http://dx.doi.org/10.1155/2017/4691947.
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To warn of the stability of retaining wall structures with damage, a simplified mechanical model and a finite element model of this retaining wall-soil coupling system are established. Via finite element model updating, a baseline finite element model of the wall-soil system is acquired. A damage alarming index ERSD (Energy Ratio Standard Deviation) is proposed via the wavelet packet analysis of a virtual impulse response function of dynamic responses to this baseline finite element model. The internal relationships among the alarming index, earth pressure, and damage stability of the wall are analyzed. Then, a damage stability alarming method for the retaining walls is advanced. To verify the feasibility and validity of this alarming method, vibration tests on the baseline finite element model of a pile plate retaining wall are performed. The ERSD is used as an alarm for the damage stability of the wall. Analysis results show that, with an increase in the ERSD, the stability of the wall changes from a stable state to an unstable one. The wall reaches a critical stable state when the alarming index reaches its threshold value. Thus, the damage stability of this pile plate retaining wall can be alarmed via ERSD.
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Miller, A. Jared, Scott D. Sommerfeldt, Jonathan D. Blotter, and David C. Copley. "A hybrid method for creating auralizations of vibroacoustic systems." Noise Control Engineering Journal 70, no. 6 (2022): 552–61. http://dx.doi.org/10.3397/1/377048.
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A hybrid method for creating a unified broadband acoustic response from separate low-frequency and high-frequency simulation responses is proposed. This hybrid method is ideal for creating simple auralizable approximations of complex acoustic systems. The process consists of four steps: 1) creating separate low- frequency and high-frequency responses of the system of interest, 2) interpolating between the two responses to get a single broadband magnitude response, 3) introducing amplitude modulation to the high-frequency portion of the response, and 4) calculating approximate phase information. Once the appropriate frequency response is obtained, an inverse fast Fourier transform is applied to obtain an impulse response. An experimental setup of an acoustic cavity with one flexible wall is used to validate the hybrid method. The simulated and measured impulse responses are both convolved with various excitation signals, so the validity of the approach could be assessed by listening. Listening tests confirm that the method is able to produce realistic auralizations. The degree of realism is subject to a few limitations, such as pitch differences and dependence on the presence of transients in the excitation signal, but these limitations are incidental and only indirectly related to the proposed method.
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Chrz, D., N. Maness, D. Chen, and M. Stone. "MECHANICAL IMPULSE RESPONSE AS A MEASURE OF TOMATO FRUIT MATURITY." HortScience 29, no. 7 (1994): 739g—739. http://dx.doi.org/10.21273/hortsci.29.7.739g.
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A mechanical impulse system for determining tomato fruit maturity and size was tested, for development of a rapid, nondestructive fruit testing instrument. Fruit were grouped into various maturity categories, ranging from immature green to red, and impulse spectra were obtained at a site over the locule at marked locations. Resistance to puncture was measured on the locular side of the pericarp wall at the same locations. A sonic resonant frequency band was weakly correlated with fruit maturity category. Stronger correlations existed with pericarp puncture resistance and fruit weight. A description of essential components and utilization of the instrument for fruit firmness determination will be presented. Supported by OCAST (Oklahoma Center for the Advancement of Science and Technology) grant AR2-069, USDA grant 92-34150-7190 and the Oklahoma Agricultural Experiment Station.
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Zhou, Zou, Guoli Zhang, Fei Zheng, Tuyang Wang, Longjie Chen, and Nan Duan. "A Graph Optimization-Based Acoustic SLAM Edge Computing System Offering Centimeter-Level Mapping Services with Reflector Recognition Capability." Security and Communication Networks 2021 (December 3, 2021): 1–17. http://dx.doi.org/10.1155/2021/9126833.
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Robots can use echo signals for simultaneous localization and mapping (SLAM) services in unknown environments where its own camera is not available. In current acoustic SLAM solutions, the time of arrival (TOA) in the room impulse response (RIR) needs to be associated with the corresponding reflected wall, which leads to an echo labelling problem (ELP). The position of the wall can be derived from the TOA associated with the wall, but most of the current solutions ignore the effect of the cumulative error in the robot’s moving state measurement on the wall position estimation. In addition, the estimated room map contains only the shape information of the room and lacks position information such as the positions of doors and windows. To address the above problems, this paper proposes a graph optimization-based acoustic SLAM edge computing system offering centimeter-level mapping services with reflector recognition capability. In this paper, a robot equipped with a sound source and a four-channel microphone array travels around the room, and it can collect the room impulse response at different positions of the room and extract the RIR cepstrum feature from the room impulse response. The ELP is solved by using the RIR cepstrum to identify reflectors with different absorption coefficients. Then, the similarity of the RIR cepstrum vectors is used for closed-loop detection. Finally, this paper proposes a method to eliminate the cumulative error of robot movement by fusing IMU data and acoustic echo data using graph-optimized edge computation. The experiments show that the acoustic SLAM system in this paper can accurately estimate the trajectory of the robot and the position of doors, windows, and so on in the room map. The average self-localization error of the robot is 2.84 cm, and the mapping error is 4.86 cm, which meet the requirement of centimeter-level map service.
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Parlin, Nicholas J., William G. Davids, Edwin Nagy, and Toney Cummins. "Dynamic response of lightweight wood-based flexible wall panels to blast and impulse loading." Construction and Building Materials 50 (January 2014): 237–45. http://dx.doi.org/10.1016/j.conbuildmat.2013.09.046.
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Dai, H. L., and X. Wang. "Non-Linear Dynamic Response of a Single Wall Carbon Nanotube Subjected to Radial Impulse." Archive of Applied Mechanics 76, no. 3-4 (2006): 145–58. http://dx.doi.org/10.1007/s00419-006-0011-2.
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Xu, Qian. "Investigation of Damage Diagnosis of Retaining Wall Structures Based on the Hilbert Damage Feature Vector Spectrum." Shock and Vibration 2019 (October 7, 2019): 1–22. http://dx.doi.org/10.1155/2019/3509470.
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To diagnose damages within the retaining wall structure, the Hilbert marginal energy spectrum was acquired via the Hilbert–Huang transformation of virtual impulse response functions of responses to the retaining wall under ambient excitations. Based on the Hilbert marginal energy spectrum, the Hilbert damage feature vector spectrum was created. On the basis of the damage feature vector spectrum, a damage identification index was proposed. Based on the damage feature vector spectrum and damage index, the damage state of the retaining wall was detected by the damage feature vector spectrum, damage locations of the wall were diagnosed by the damage index trend surface, and the damage intensity of the wall was identified by the quantitative relationship between the damage index and damage intensity. Based on this, a damage diagnosis method for retaining wall structures was proposed. To verify the feasibility and validity of the damage diagnosis method, both model tests and field tests on a pile plate retaining wall are performed under ambient excitations. Test results show that the damage state of the wall can be detected sensitively, damage locations can be diagnosed validly, and damage intensity can be identified quantitatively via this damage diagnosis method.
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ZENIT, R., and M. L. HUNT. "The impulsive motion of a liquid resulting from a particle collision." Journal of Fluid Mechanics 375 (November 25, 1998): 345–61. http://dx.doi.org/10.1017/s0022112098002596.
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When two particles collide in a liquid, the impulsive acceleration due to the rebound produces a pressure pulse that is transmitted through the fluid. Detailed measurements were made of the pressure pulse and the motion of the particles by generating controlled collisions with an immersed dual pendulum. The experiments were performed for a range of impact velocities, angles of incidence, and distances between the wall and the pairs of particles. The radiated fluid pressure was measured using a high-frequency-response pressure transducer, and the motion of the particles was recorded using a high-speed digital camera. The magnitude of the impulse pressure was found to scale with the particle velocity, the particle diameter and the density of the fluid. Additionally, a model is proposed to predict the impulse field in the fluid based on the impulse pressure theory. The model agrees well with the experimental measurements.
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Sundaram, Prasannabalaji, Tapan K. Sengupta, and Swagata Bhaumik. "The three-dimensional impulse response of a boundary layer to different types of wall excitation." Physics of Fluids 30, no. 12 (2018): 124103. http://dx.doi.org/10.1063/1.5063700.
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Świerc, Agata, Stanisław Świerc, Henryk Foit, and Piotr Koper. "Applying the Exodus method to calculate the set of impulse response functions of a wall." Energy and Buildings 69 (February 2014): 301–6. http://dx.doi.org/10.1016/j.enbuild.2013.11.019.
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FUKUI, Hirohisa, Hideo FUJITANI, Yoichi MUKAI, Mai ITO, and Gilberto MOSQUEDA. "RESPONSE EVALUATION AND ANALYSIS USING IMPULSE OF BASE-ISOLATED BUILDINGS DURING A COLLISION WITH RETAINING WALL." Journal of Structural and Construction Engineering (Transactions of AIJ) 84, no. 766 (2019): 1533–43. http://dx.doi.org/10.3130/aijs.84.1533.
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Fukui, Hirohisa, Hideo Fujitani, Yoichi Mukai, Mai Ito, and Gilberto Mosqueda. "Response evaluation and analysis using impulse of base‐isolated buildings during a collision with retaining wall." JAPAN ARCHITECTURAL REVIEW 4, no. 1 (2020): 88–104. http://dx.doi.org/10.1002/2475-8876.12205.
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Prodeus, Arkadiy, and Maryna Didkovska. "Assessment of speech intelligibility in university lecture rooms of different sizes using objective and subjective methods." Eastern-European Journal of Enterprise Technologies 3, no. 5 (111) (2021): 47–56. http://dx.doi.org/10.15587/1729-4061.2021.228405.
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The scores of speech intelligibility, obtained using objective and subjective methods for three university lecture rooms of the small, medium, and large sizes with different degrees of filling, were presented. The problem of achieving high speech intelligibility is relevant for both students and university administration, and for architects designing or reconstructing lecture rooms. Speech intelligibility was assessed using binaural room impulse responses which applied an artificial head and non-professional quality audio equipment for measuring. The Speech Transmission Index was an objective measure of speech intelligibility, while the subjective evaluation of speech intelligibility was carried out using the articulation method. Comparative analysis of the effectiveness of parameters of impulse response as a measure of speech intelligibility showed that Early Decay Time exceeded the score of the T30 reverberation time but was ineffective in a small lecture room. The C50 clarity index for all the considered lecture rooms was the most informative. Several patterns determined by the influence of early sound reflections on speech intelligibility were detected. Specifically, it was shown that an increase in the ratio of the energy of early reflections to the energy of direct sound leads to a decrease in speech intelligibility. The exceptions are small, up to 30‒40 cm, distances from the back wall of the room, where speech intelligibility is usually slightly higher than in the middle of the room. At a distance of 0.7–1.7 m from the side walls of the room, speech intelligibility is usually worse for the ear, which is closer to the wall. The usefulness of the obtained results lies in refining the quantitative characteristics of the influence of early reflections of sound on speech intelligibility at different points of lecture rooms.
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Limarchenko, O., O. Nefedov, and O. Sirenko. "VERIFICATION OF THE CONTROL ALGORITHM FOR RESERVOIRS WITH LIQUID BASED ON THE COMPENSATION OF THE FORCE RESPONSE IN DIFFERENT RANGES OF MANIFESTATION OF NONLINEARITIES." Bulletin Taras Shevchenko National University of Kyiv. Mathematics Mechanics, no. 1 (41) (2020): 51–56. http://dx.doi.org/10.17721/1684-1565.2020.01-41.12.51-56.
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Problem about motion of a reservoir with liquid with a free surface is considered based on the compensation of a force response of the liquid on reservoir walls. Such an approach is selected since usual methods of control of mechanical system motion are mostly intended for linear systems of relatively small dimension. However, models of dynamics of the combined motion of reservoirs with liquid are described with relatively high-dimensional nonlinear systems ordinary differential equations. For obtaining the mathematical model of combined motion of a reservoir with liquid with a free surface we use the Hamilton–Ostrogradskiy variational principle, for which it is possible to determine analytically all internal forces of interaction of system component parts. Namely using this algorithm, we determine the main vector of forces of the liquid pressure on reservoir walls (force response of liquid). The algorithm of the motion control of the reservoir with liquid is based on the inclusion of the compensation of the liquid force response to controlling actions, this reduces the motion of the system reservoir–liquid, where the effect of forces from oscillating liquid on the reservoir motion is eliminated. This algorithm was tested for problems of impulse and vibration disturbance of the translational motion of the system in the horizontal plain. We consider the disturbance of the system motion by a force rectangular impulse applied to the reservoir wall, the duration of the impulse is lesser than a quarter of the period of a liquid free oscillations according to the first normal mode. Amplitudes of the impulse were selected with the purpose of analysis of the behavior of the controlled system in different ranges of manifestation of nonlinearities. We state the problem to verify the accuracy of this algorithm for three ranges of manifestation of nonlinear properties in the system, namely, for the linear range (amplitudes of waves on a free surface h do not exceed 0,1 of the radius of a free surface ( <0,1R); for the weakly nonlinear range ( <0,2R) and for the strongly nonlinear range with maximum amplitudes of waves about =0,32R. Numerical modeling enables the determination of errors of developed algorithm, which does not exceed 0,5 %, although they insignificantly increase with the increase of amplitudes of oscillations on a free surface of liquid. At the same time perturbations on a free surface of liquid for the controlled motion are always greater than for the uncontrolled motion.
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Xu, Qian. "Damage Identification of Wind-Break Wall Structures based on the Further Updated Wavelet Packet Frequency Bands Energy Ratio Spectrum." Shock and Vibration 2022 (July 19, 2022): 1–15. http://dx.doi.org/10.1155/2022/8200199.
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Damage will appear in the wind-break wall under the effects of many factors. The wind-break wall may be destroyed when the damage is accumulated to some extent, which may cause accidents. To identify damage within the wind-break wall structure, the Wavelet Packet frequency bands energy ratio spectrum analysis of the virtual impulse response function of responses to the wind-break wall was performed under the effects of excitation. Based on the damage sensitivity analysis of subfrequency bands, a further updated Wavelet Packet frequency bands energy ratio spectrum was proposed. To reflect the damage information sensitively, the feature bands, which were more sensitive to damage, were selected via the threshold value ε0. Then, the Wavelet Packet damage feature vector and damage identification index, which can reflect damage information of the wind-break walls sensitively, were proposed. A damage identification method for wind-break walls was proposed. To verify the validity of this damage identification method, the vibration tests on a pile plate wind-break wall were performed. Damage within the wall was identified via the method. The tests results show that the damage feature vector is a zero vector and the value of damage index is zero, when the wind-break wall is not damaged. The damage feature vector is a nonzero vector and the value of damage index is positive, when the wind-break wall is damaged. Thus, the damage state of the wind-break wall can be detected via the damage feature vector and damage index. With increase of damage accumulated within the wall, the damage intensity and the value of the damage index increase. The quantitative relationship between the damage index and damage intensity is established. The damage intensity can be calculated reversely, when the damage index is available. Thus, the damage intensity of the wind-break wall can be identified via the quantitative relationship between the damage index and damage intensity. In addition, the damage index value of the measuring point, which is much closer to the partial damage, is much larger. The damage index value of the point, which is located at the partial damage, is the largest. Thus, the damage location of the wind-break wall can be diagnosed via the characteristics of damage index for different measurement points. Thus, the damage state, damage location, and damage intensity of the wind-break wall can be identified via this damage identification method.
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Wang, Lei, Xiyue Ma, Rong Li, and Xiangyang Zeng. "Impact of Structural Parameters on the Auditory Perception of Musical Sounds in Closed Spaces: An Experimental Study." Applied Sciences 9, no. 7 (2019): 1416. http://dx.doi.org/10.3390/app9071416.
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This study attempts to investigate the impact of structural parameters (volume, shape, and the wall absorption coefficient) in closed space on the auditory perception of three different musical sound types. With binaural audibility technology and room impulse response measurement (RIR), this paper first verifies the reliability of using ODEON software in simulating simplified closed-space auditory scenes. Then, 96 music binaural signals produced in eight simulated closed spaces with different structural parameters are synthesized. Finally, auditory perception experiment is conducted on the synthesized binaural signals by using pair comparison method, and variance analysis is also made on the experimental results. It is concluded that (1) a hemispherical cabin with a small volume and large wall sound absorption coefficient is most suitable for playing a single instrument, such as the flute or violin, and (2) a cabin with large volume is suitable for playing multiple instruments music such as symphony, but the walls should not be totally reflective. The experimental scheme and results of current study provide guidance for designing the inner structure of the concert hall to achieve preferable auditory perception in practice.
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Suo, Lisheng, and E. B. Wylie. "Complex Wavespeed and Hydraulic Transients in Viscoelastic Pipes." Journal of Fluids Engineering 112, no. 4 (1990): 496–500. http://dx.doi.org/10.1115/1.2909434.
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The classic formula for waterhammer wavespeed is extended to calculate the complex-valued, frequency-dependent wavespeed in a viscoelastic pipe, which takes into account the effect of viscoelasticity of pipe wall material on wave propagation. With the complex wavespeed, the standard impedance or transfer matrix is directly used to analyze resonating conditions in systems including viscoelastic pipes, and the impulse response method presented previously by the authors is applied to compute nonperiodic transients. Numerical results are compared with experimental data and good agreement is observed.
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Li, Xin, Shiqiang Li, Zhihua Wang, Jinglei Yang, and Guiying Wu. "Response of aluminum corrugated sandwich panels under foam projectile impact – Experiment and numerical simulation." Journal of Sandwich Structures & Materials 19, no. 5 (2016): 595–615. http://dx.doi.org/10.1177/1099636216630503.
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The paper studied the dynamic response of square aluminum corrugated sandwich panels under projectile impact. The aluminum foam projectile was utilized to apply the impulse on the sandwich panels. In order to increase the applied impulse under controlled impact velocity ( V < 200 m/s), a cylindrical Nylon mass was adhered to the back of foam projectile. Corrugated sandwich panels with two different configurations were tested and their typical deformation modes were obtained in the experiment. Based on the experiment, corresponding numerical simulations were presented. The energy absorption and deformation mechanism of corrugated sandwich panels were studied through the simulation. The influence of impact velocity, thickness of face sheet and wall thickness of corrugated core were discussed. The results indicated that the corrugated sandwich panels with smaller core height produce larger deformation than the panels with larger core height. The face sheets of corrugated sandwich panel absorbed comparable amount of energy with the corrugated core. The velocity histories show that under the combined action of aluminum foam projectile and nylon back mass, a second peak velocity of front face sheet can be produced during the impact process, which is defined as “accelerating impact stage” in current study. The influence of “accelerating impact stage” to the response of structures is sensitive to the impact velocity.
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Soheyli, Mohamad Reza, A. H. Akhaveissy, and S. M. Mirhosseini. "Large-Scale Experimental and Numerical Study of Blast Acceleration Created by Close-In Buried Explosion on Underground Tunnel Lining." Shock and Vibration 2016 (2016): 1–9. http://dx.doi.org/10.1155/2016/8918050.
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Despite growing demands for structures in water transportation tunnels, underground installations, subsurface dams, and subterranean channels, there is limited field knowledge about the dynamic behavior of these structures in the face of near-fault earthquakes or impulse excitations. This study conducted a large-scale test on underground tunnel excited by two close-in subsurface explosions. The horizontal and vertical acceleration were recorded on the vertical wall of the tunnel and the free field data including the acceleration on the ground surface at 11-meter distance from the tunnel. The frequency domain analysis of recorded results determined the frequency 961 Hz and 968 Hz for 1.69 kg and 2.76 kg equivalent T.N.T., respectively. Then, finite element analysis results were compared with the test data. The comparisons demonstrated a good correlation and satisfied the field data. Finally, based on numerical modeling, a parametric study was applied to determine the effects of shear wave velocity distance of the crater with respect to the tunnel on impulse response of the tunnel.
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Sumala, M., B. Murali Krishna, and T. P. Tezeswi. "Structural Performance of EPS Core Based Cementitious Sandwich Panel under Various Loading Conditions." Journal of Physics: Conference Series 2779, no. 1 (2024): 012073. http://dx.doi.org/10.1088/1742-6596/2779/1/012073.
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Abstract Sandwich panels have gained a lot of popularity in recent years as engineers seek to replace the heavy, rigid constructions with the light weight structures that permit good energy absorption and deformation values. Expanded Polystyrene (EPS) core based cementitious sandwich composite panels are used as load bearing and non-load bearing panels. This EPS panel is a light weight, thermal efficient and reduces the cost of construction. This panel consists of upper and lower face skin and a core layer is sandwiched between the two face layers. In this paper the material for face skin used is structural plaster and for a core layer the material used is EPS. This paper mainly focus on the structural response of EPS core based cementitious sandwich wall panel based on linear quasi-static simulation in ABAQUS using finite element modelling for the axial and flexure loading. Further the performance is assessed under blast load, the pressure impulse (P-I) curves are developed using MATLAB. P-I curve methodology is used to generate the performance of panel. P-I curve implies that there is a significant damage induced on the wall panel. The sandwich wall panel analyzed as an isolated flexural response dominated structural component can safely resist the blast load.
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Zhao, Futian, Jun Liu, Zhimin Xiao, et al. "A Simplified Analytical Solution of Mechanical Responses of Soil Subjected to Repeated Impact Loading." Mathematical Problems in Engineering 2020 (November 4, 2020): 1–10. http://dx.doi.org/10.1155/2020/6920535.
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A simplified dynamic response model is proposed based on the deformation and dynamic stress response characteristics of soil under impact loading. The foundation is divided into two distinct zones: a projection cylinder acting vertically under impact loading and a hollow cylinder outside the projection area. It is assumed that the ramming deformation of the projected cylinder under the vertical impact load is a quasi-static loading process under the maximum contact dynamic stress through the quasi-static method, and the settlement calculation without lateral deformation is given. It is assumed that the inner wall of the hollow cylinder is subjected to horizontal lateral pressure and the analytical solution of the horizontal dynamic stress considering the plastic deformation of soil is given. The simplified dynamic response model can reflect the mechanical response of soil under impulse train load well which can provide reference for similar projects.
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Debski, E. A., and W. O. Friesen. "Role of central interneurons in habituation of swimming activity in the medicinal leech." Journal of Neurophysiology 55, no. 5 (1986): 977–94. http://dx.doi.org/10.1152/jn.1986.55.5.977.
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Swimming activity evoked by light tactile stimulation of a body wall flap in dissected leech preparations undergoes habituation (5). In this study, we examine the activity of several interneurons (cell 204, cell 205, the S cell, and cell 208) during habituation trials to study further the neuronal mechanisms that mediate this decline in responsiveness. Light tactile stimulation of the leech body wall evoked initially a marked excitatory response in cell 204 homologs (segmental swim-initiating neurons) that preceded the initiation of swimming activity. This response decreased over the course of repeated stimulus trials; however, no marked decline in cell 204 activity accompanied the cessation of swim initiation. A similar activity pattern was observed in cell 205. Thus the habituation of swimming activity to stroking of the body wall is not due solely to reduced input to cell 204 and cell 205. The early activity of cell 204 was not correlated to the duration of subsequent swim episodes. However, the impulse frequency of cell 204 during swim episodes was negatively correlated to the period of swim cycles. This correlation between cell 204 activity and cycle period occurred both within individual episodes as well as between trials in a habituation series. Direct stimulation of cell 204 with current pulses evoked swimming activity reliably for an average of 72 trials. Therefore, habituation that results from stroking the body wall (which occurs after approximately 6 trials) is not mediated by plasticity in the connections between cell 204 and the swim oscillator. The S cell fired repeatedly in response to light tactile stimulation. This response declined with repeated trials. Intense intracellular stimulation of the S cell was sufficient to initiate swimming activity in some preparations. The magnitude and duration of the excitation required to initiate swimming by this means were far greater, however, than that which occurred during stroking the body wall. The response of cell 208 (a swim oscillator cell) to body wall stimulation during habituation trials was variable; usually an initial hyperpolarization was followed by some depolarization. No aspect of this response correlated with the onset of habituation. Our results are consistent with the idea that cell 204 and cell 205 are part of the pathway that mediates swimming activity in response to light tactile stimulation of the leech body wall, and that habituation occurs, in part, as the result of reduced sensory input to this cell.(ABSTRACT TRUNCATED AT 400 WORDS)
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Žaliaduonytė-Pekšienė, Diana, Tomas Kazakevičius, Vytautas Zabiela, et al. "Changes of electrophysiological parameters in patients with atrial flutter." Medicina 43, no. 8 (2007): 614. http://dx.doi.org/10.3390/medicina43080078.
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Objectives. The aim of the study was to study some anatomic and electrophysiological features of the right atrium, related to the presence of atrial flutter. Materials and methods. A total 23 patients with type I atrial flutter and 22 patients without atrial flutter were studied. Right atrium size was assessed using echocardiography before intracardiac examination and radiofrequency ablation. Results. Effective refractory periods of coronary sinus, high right atrium, low right atrium were different comparing with the control group (P<0.05). A stimulus–response time between high right atrium and low right atrium positions in anterograde and retrograde ways, an impulse propagation speed along the lateral wall of the right atrium were statistically different comparing both groups (P<0.05). There was a significant correlation among effective refractory periods measured in different sites of the right atrium (r²=0.64, 0.44, 0.44, respectively). All measured effective refractory periods also correlated with stimulus–response time in anterograde way (P<0.05) and impulse propagation speed (P<0.05). Right atrium dimensions were significantly larger in atrial flutter group. There was no correlation between the right atrium dimensions and measured electrophysiological parameters in both groups.Conclusions. The presence of atrial flutter associates with diffuse alterations of the right atrium, but not the focal or single changes of refractoriness.
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van der Harten, Arthur W., and Matthew Azevedo. "Calibrating geometrical acoustics models of non-diffuse rooms." Journal of the Acoustical Society of America 152, no. 4 (2022): A210. http://dx.doi.org/10.1121/10.0016037.
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A case study is presented for the challenging case in which a conference room with a strongly non-diffuse impulse response is measured, and geometrical acoustics models are built and calibrated using two separate software packages simultaneously. Both software packages are able to reproduce the measured flutter echoes, although with surprising input scattering coefficients, particularly for parallel stainless steel wall finishes. Caution is advised concerning common assumptions about scattering coefficients for operable partitions. Furthermore, the authors suggest that benchmarking for acoustics simulation software be performed in strongly non-diffuse rooms, in addition to the existing round robin studies that have traditionally been held using more normal or diffuse rooms.
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Zhang, Peiwen, Xin Li, Tao Jin, Zhihua Wang, and Longmao Zhao. "Dynamic response of circular metallic sandwich panels under projectile impact." Journal of Sandwich Structures & Materials 19, no. 5 (2016): 572–94. http://dx.doi.org/10.1177/1099636215626596.
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The dynamic response of circular sandwich panels with aluminium honeycomb and corrugated cores under projectile impact was investigated experimentally and numerically. Impulse loaded on the panel was controlled by projectile launching velocity and the deformation process of sandwich panels was recorded by a high-speed camera in the experiments. Typical deformation/failure modes of face-sheets and cores were obtained and analysed. The back face-sheet deflections and strain histories of face-sheets were measured and discussed. A parametric study was conducted by LS-DYNA 3D to analyse the effect of geometrical configuration on energy absorption mechanism and back face-sheet permanent deflection of circular sandwich panels. The results indicated that the impact resistance of the structure was sensitive to geometrical configuration. Increasing face-sheet thickness and core relative density significantly improved sandwich structure impact resistance. Increasing foil thickness improved the panel impact resistance more efficiently than decreasing wall side length. The results have important reference value to guide engineering application of the sandwich structure subjected to impact loading.
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Kienzler, R. "Non-linear dynamic response of a single wall carbon nonotube subjected to radial impulse (by H.L. Dai; X. Wang)." Archive of Applied Mechanics 78, no. 5 (2008): 409. http://dx.doi.org/10.1007/s00419-007-0199-9.
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Russo, S., and P. Luchini. "The linear response of turbulent flow to a volume force: comparison between eddy-viscosity model and DNS." Journal of Fluid Mechanics 790 (February 2, 2016): 104–27. http://dx.doi.org/10.1017/jfm.2016.4.
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We identify a benchmark problem simple enough that it can be solved both by an eddy-viscosity model and by direct numerical simulation: this is the linear response of a turbulent flow’s mean-velocity profile to an external volume force. An example of such a force was found in a study of the perturbation induced by bottom topography by Luchini & Charru (J. Fluid Mech., vol. 656, 2010, pp. 337–341). On the other hand, a modification of the method by Quadrio & Luchini (Proceedings of the IX European Turbulence Conference, Southampton, UK, 2002, pp. 715–718) and Luchini et al. (Phys. Fluids, vol. 18, 2006, 121702) to compute the linear impulse response of a wall-bounded turbulent flow allows the response to a volume force to be computed directly. The comparison exhibits significant differences and suggests that there might be fundamental obstacles to designing an eddy-viscosity model that provides the correct result.
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Mander, Thomas J., and Zachery I. Smith. "Composite Steel Stud Blast Panel Design and Experimental Testing." Applied Mechanics and Materials 82 (July 2011): 479–84. http://dx.doi.org/10.4028/www.scientific.net/amm.82.479.
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Based on Federal Aviation Authority (FAA) requirements, project specific blast loads are determined for the design of a new airport traffic control tower. These blast loads must be resisted by exterior wall panels on the control tower, protecting building occupants from intentional explosives attack scenarios. Such blast resistant walls are typically constructed of thick reinforced concrete panels or composite steel plate and rolled sections, as conventional building cladding systems have relatively low blast resistance. While these more robust design approaches are valid, the additional cladding mass they represent will significantly increase the base shear and overturning demand in seismic zones. This paper investigates the use of a light structural system comprised of a steel stud wall assembly partially embedded in a thin layer of concrete to obtain composite action. Fiber reinforced polymer (FRP) composites are also included to increase the blast resistance and aid in keeping the panel weight to a minimum. Two full-scale composite steel stud walls are designed, constructed, and tested dynamically in the BakerRisk shock tube. The stud walls consist of back-to-back 150 mm deep, 14 gauge (1.8 mm thick), cold-formed steel studs spaced at 610 mm on center. Both specimens have a 50 mm thick normal weight concrete layer, reinforced with welded wire mesh that is welded to the stud compression flanges to achieve composite action. Two layers of Tyfo® SEH-51A fiber reinforced composites are used on the tension flange of the steel studs. A single layer of Tyfo® SEH-51A composites is used on the tension face of the concrete layer between the studs for one of the specimens. Web stiffeners are used at the bearing support to prevent premature web crippling shear failure of the specimens. The stud walls are analyzed using single-degree-of-freedom (SDOF) models. A non-linear moment-curvature relationship, accounting for actual material constitutive properties, is used for determining the resistance function of the walls. Blast pressure and impulse data from the shock tube tests is used to compare analytical predictions to the measured displacement-time response. Analytical predictions of panel response for both tests are within ten percent of the observed response based on displacement.
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King, Richard, Wieslaw Woszczyk, and Michail Oikonomidis. "Enhancement of virtual acoustics rendering using boundary mounted dipole loudspeakers." Journal of the Acoustical Society of America 155, no. 3_Supplement (2024): A177. http://dx.doi.org/10.1121/10.0027228.
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The Immersive Media Lab at McGill University hosts a Virtual Acoustics Technology (VAT) system incorporating a suspended array of omnidirectional loudspeakers. Using a convolution reverb engine, acoustic simulations of real spaces can be realized via a catalog of Room Impulse Response measurements. Reflected sound in the room helps to disguise the location of the sound emitters rendering virtual acoustics. One limitation of the system, however, is the interference between the lab’s natural acoustics and the virtual environment generated by the VAT system. The improvement under consideration is to enhance diffusion along the walls of the lab, in order to mask the acoustical characteristics related to the physical dimensions of the room. Dipole loudspeakers are installed on the room boundaries and used to scatter reflections and reverberation along the wall surfaces enlarging the effective radiation surface of the walls. The scattered energy may mask specular reflections and reduce localization of the virtual acoustic sources. Investigations compare the result of scattering reflected sound vertically as opposed to horizontally across the boundaries. Measurements illustrate the effect of the dipole loudspeaker system when used on its own as well as working in conjunction with the existing omnidirectional loudspeaker array.
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Swerdlow, Andy. "A modern metric for acoustic clarity in critical listening environments." Journal of the Acoustical Society of America 152, no. 4 (2022): A104. http://dx.doi.org/10.1121/10.0015690.
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Characteristics of acoustics in small rooms have become less mysterious, more predictable and measurements more common than in past decades. Modern metrics for characterizing the acoustical performance of critical listening environments have not followed the recent predictive improvements. An Acoustic Clarity metric with a variable time window (Rear Reflection Clarity, CRR) is proposed for small (under approximately 200m3) critical listening environments such as recording studio control, mastering, film post, screening, audiophile listening, and similar rooms. The variable time window is defined by the arrival time difference between direct sound and the reflection from the rear wall, which is typically the strongest reflection and is opposite the on-axis response of the loudspeakers. Measured impulse response data collected in situ is presented and analyzed as case studies to characterize CRR. For simplicity, this presentation will focus on only the stereo components of surround-sound environments.
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EDVALDSSON, Garðar, and Achilleas XYDIS. "Latency-free real-time auralisation in hemi-anechoic chambers." INTER-NOISE and NOISE-CON Congress and Conference Proceedings 270, no. 3 (2024): 8120–27. http://dx.doi.org/10.3397/in_2024_4049.
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Real-time auralisation allows users to interact with a simulated acoustical room, providing a more responsive way of evaluating acoustical performance than pre- recorded auralisation. Nevertheless, real-time auralisation is computationally intensive and, therefore, susceptible to latency. This paper presents a novel latency-free real-time auralisation method that enables users to auralise a simulated acoustical event with self-excitation more accurately than current methods. The method uses a loudspeaker system inside a hemi-anechoic chamber. By exploiting the inherent floor reflection of the hemi-anechoic chamber, the impulse response can be trimmed to compensate for the total latency of the loudspeaker system. The method's validity is demonstrated with measurements presenting virtual wall reflections arriving at the correct time at the listening position. The influence of the speaker placement regarding latency is discussed. This method enables users to evaluate a given response more accurately than conventionally possible.
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Kiran, K. K., and JagadishG Kori. "Blast Mitigation of SDOF systems by using M.R.Damper and Base Isolations." Proceedings of the 12th Structural Engineering Convention, SEC 2022: Themes 1-2 1, no. 1 (2022): 1095–100. http://dx.doi.org/10.38208/acp.v1.626.
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Shelter is a basic need for living creatures. The shelter should be safe and secure. The damage of the shelter occurs due to natural hazards and manmade activities. Natural hazards such as earthquake, volcanic eruptions, landslides, flood, etc. Manmade activities may be accidental or intentional. Accidental activities include, internal explosions such as chemical reactions occurring at nuclear power plants, mining, rock cutting etc, gas explosions leakage etc. Hence while designing the structure, additional precautions and considerations should be taken to resist the unpredictable load. Boat load and earthquake load are dynamic, impulse loads. The earthquake load occurs in seconds, In the height of the structures force are distributed and is proportion to mass concentrations, blast load occurs in milli seconds compare to seismic load. In the present study SDOF system exposed to blast load is considered. MATLAB simulation technique is used in the analysis of the SDOF system. The SDOF system consists of Front wall, rear wall and Roof. The load is acting on the structural system are calculated by using analytical method. Base isolations method is one the recent method is used to reduce the response of the structural system under impact load. The semi active control system is used in the analysis. The response is reduced by considerable amount by using Base isolation and MR Damper.
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Jacobi, I., and B. J. McKeon. "Dynamic roughness perturbation of a turbulent boundary layer." Journal of Fluid Mechanics 688 (October 27, 2011): 258–96. http://dx.doi.org/10.1017/jfm.2011.375.
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AbstractThe zero-pressure-gradient turbulent boundary layer over a flat plate was perturbed by a temporally oscillating, spatial impulse of roughness, and the downstream response of the flow field was interrogated by hot-wire anemometry and particle-image velocimetry. The key features common to impulsively perturbed boundary layers, as identified in Jacobi & McKeon (J. Fluid Mech., 2011), were investigated, and the unique contributions of the dynamic perturbation were isolated by contrast with an appropriately matched static impulse of roughness. In addition, the dynamic perturbation was decomposed into separable large-scale and small-scale structural effects, which in turn were associated with the organized wave and roughness impulse aspects of the perturbation. A phase-locked velocity decomposition of the entire downstream flow field revealed strongly coherent modes of fluctuating velocity, with distinct mode shapes for the streamwise and wall-normal velocity components. Following the analysis of McKeon & Sharma (J. Fluid Mech., vol. 658, 2010, pp. 336–382), the roughness perturbation was treated as a forcing of the Navier–Stokes equation and a linearized analysis employing a modified Orr–Sommerfeld operator was performed. The experimentally ascertained wavespeed of the input disturbance was used to solve for the most amplified singular mode of the Orr–Sommerfeld resolvent. These calculated modes were then compared with the streamwise and wall-normal velocity fluctuations. The discrepancies between the calculated Orr–Sommerfeld resolvent modes and those experimentally observed by phase-locked averaging of the velocity field were postulated to result from the violation of the parallel flow assumption of Orr–Sommerfeld analysis, as well as certain non-equilibrium effects of the roughness. Additionally, some difficulties previously observed using a quasi-laminar eigenmode analysis were also observed under the resolvent approach; however, the resolvent analysis was shown to provide reasonably accurate predictions of velocity fluctuations for the forced Orr–Sommerfeld problem over a portion of the boundary layer, with potential applications to designing efficient flow control strategies. The combined experimental and analytical effort provides a new opportunity to examine the non-equilibrium and forcing effects in a dynamically perturbed flow.
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Eissa, Tahra L., Catherine A. Schevon, Ronald G. Emerson, Guy M. Mckhann, Robert R. Goodman, and Wim Van Drongelen. "The Relationship Between Ictal Multi-Unit Activity and the Electrocorticogram." International Journal of Neural Systems 28, no. 10 (2018): 1850027. http://dx.doi.org/10.1142/s0129065718500272.
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During neocortical seizures in patients with epilepsy, microelectrode array recordings from the ictal core show a strong correlation between the fast, cellular spiking activities and the low-frequency component of the potential field, reflected in the electrocorticogram (ECoG). Here, we model the relationship between the cellular spike activity and this low-frequency component as the input and output signals of a linear time invariant system. Our approach is based on the observation that this relationship can be characterized by a so-called sinc function, the unit impulse response of an ideal (brick-wall) filter. Accordingly, using a brick-wall filter, we are able to convert ictal cellular spike inputs into an output that significantly correlates with the observed seizure activity in the ECoG [Formula: see text], while ECoG recordings of subsequent seizures within patients also show significant, but lower, correlations [Formula: see text]. Furthermore, we can produce seizure-like output signals using synthetic spike trains with ictal properties. We propose a possible physiological mechanism to explain the observed properties associated with an ideal filter, and discuss the potential use of our approach for the evaluation of anticonvulsant strategies.
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JACOBI, I., and B. J. McKEON. "New perspectives on the impulsive roughness-perturbation of a turbulent boundary layer." Journal of Fluid Mechanics 677 (April 26, 2011): 179–203. http://dx.doi.org/10.1017/jfm.2011.75.
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The zero-pressure-gradient turbulent boundary layer over a flat plate was perturbed by a short strip of two-dimensional roughness elements, and the downstream response of the flow field was interrogated by hot-wire anemometry and particle image velocimetry. Two internal layers, marking the two transitions between rough and smooth boundary conditions, are shown to represent the edges of a ‘stress bore’ in the flow field. New scalings, based on the mean velocity gradient and the third moment of the streamwise fluctuating velocity component, are used to identify this ‘stress bore’ as the region of influence of the roughness impulse. Spectral composite maps reveal the redistribution of spectral energy by the impulsive perturbation – in particular, the region of the near-wall peak was reached by use of a single hot wire in order to identify the significant changes to the near-wall cycle. In addition, analysis of the distribution of vortex cores shows a distinct structural change in the flow associated with the perturbation. A short spatially impulsive patch of roughness is shown to provide a vehicle for modifying a large portion of the downstream flow field in a controlled and persistent way.
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Huang, Ling, Dong Lei, Bowen Zheng, Guiping Chen, Huifeng An, and Mingxuan Li. "Lightweight Multi-Domain Fusion Model for Through-Wall Human Activity Recognition Using IR-UWB Radar." Applied Sciences 14, no. 20 (2024): 9522. http://dx.doi.org/10.3390/app14209522.
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Impulse radio ultra-wideband (IR-UWB) radar, operating in the low-frequency band, can penetrate walls and utilize its high range resolution to recognize different human activities. Complex deep neural networks have demonstrated significant performance advantages in classifying radar spectrograms of various actions, but at the cost of a substantial computational overhead. In response, this paper proposes a lightweight model named TG2-CAFNet. First, clutter suppression and time–frequency analysis are used to obtain range–time and micro-Doppler feature maps of human activities. Then, leveraging GhostV2 convolution, a lightweight feature extraction module, TG2, suitable for radar spectrograms is constructed. Using a parallel structure, the features of the two spectrograms are extracted separately. Finally, to further explore the correlation between the two spectrograms and enhance the feature representation capabilities, an improved nonlinear fusion method called coordinate attention fusion (CAF) is proposed based on attention feature fusion (AFF). This method extends the adaptive weighting fusion of AFF to a spatial distribution, effectively capturing the subtle spatial relationships between the two radar spectrograms. Experiments showed that the proposed method achieved a high degree of model lightweightness, while also achieving a recognition accuracy of 99.1%.
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Chen, Suwen, Chen-Guang Zhu, Guo-Qiang Li, and Yong Lu. "Blast test and numerical simulation of point-supported glazing." Advances in Structural Engineering 19, no. 12 (2016): 1841–54. http://dx.doi.org/10.1177/1369433216649387.
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The blast resistance of point-supported laminated glass curtain wall has been investigated by means of field blast tests and numerical simulation. Nine site blast tests were carried out, considering two types of glass thickness and six TNT charges ranging from 0.4 to 30 kg. The overpressure and displacement time histories were measured and the failure modes were observed. The overpressure obtained from the measurement panel exhibited a typical pattern of near-field blast with a steep increase followed by a rapid decay within a few milliseconds. The displacement response of the laminated glass panels increased with the increase in the TNT charge almost linearly in the smaller tests (scaled distance ranging 4.5–7 m/kg1/3), which was in line with the increase in the blast impulse in these tests. The failure mode of the point-supported laminated glass panels was featured by tearing off of the polyvinyl butyral layer around the support area, while the glass shards still adhered to the polyvinyl butyral interlayer. Nonlinear dynamic finite element simulation agrees reasonably well with the results from the blast tests. Severe stress concentration has been predicted to occur at the rim of the support holes, leading to initiation of failure at these supports, and this also agrees with the failure mode observed from the blast test. Finally, parametric studies are carried out to investigate the influence of TNT charge weight and the geometric parameters of the panel on the blast response of the glass curtain wall.
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Petojević, Zorana, Radovan Gospavić, and Goran Todorović. "Estimation of thermal impulse response of a multi-layer building wall through in-situ experimental measurements in a dynamic regime with applications." Applied Energy 228 (October 2018): 468–86. http://dx.doi.org/10.1016/j.apenergy.2018.06.083.
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HOWE, M. S. "Edge, cavity and aperture tones at very low Mach numbers." Journal of Fluid Mechanics 330 (January 10, 1997): 61–84. http://dx.doi.org/10.1017/s0022112096003606.
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This paper discusses self-sustaining oscillations of high-Reynolds-number shear layers and jets incident on edges and corners at infinitesimal Mach number. These oscillations are frequently sources of narrow-band sound, and are usually attributed to the formation of discrete vortices whose interactions with the edge or corner produce impulsive pressures that lead to the formation of new vorticity and complete a feedback cycle of operation. Linearized analyses of these interactions are presented in which free shear layers are modelled by vortex sheets. Detailed results are given for shear flows over rectangular wall apertures and shallow cavities, and for the classical jet–edge interaction. The operating stages of self-sustained oscillations are identified with poles in the upper half of the complex frequency plane of a certain impulse response function. It is argued that the real parts of these poles determine the Strouhal numbers of the operating stages observed experimentally for the real, nonlinear system. The response function coincides with the Rayleigh conductivity of the ‘window’ spanned by the shear flow for wall apertures and jet–edge interactions, and to a frequency dependent drag coefficient for shallow wall cavities. When the interaction occurs in the neighbourhood of an acoustic resonator, exemplified by the flue organ pipe, the poles are augmented by a sequence of poles whose real parts are close to the resonance frequencies of the resonator, and the resonator can ‘speak’ at one of these frequencies (by extracting energy from the mean flow) provided the corresponding pole has positive imaginary part.The Strouhal numbers predicted by this theory for a shallow wall cavity agree well with data extrapolated to zero Mach number from measurements in air, and predictions for the jet–edge interaction are in excellent accord with data from various sources in the literature. In the latter case, the linear theory also agrees for all operating stages with an empirical, nonlinear model that takes account of the formation of discrete vortices in the jet.