scholarly journals Near-Field Measurements of Water-Entry Sound of Low-Speed Metal Balls in a Non-Anechoic Tank

2021 ◽  
Vol 2021 ◽  
pp. 1-11
Author(s):  
Qi Li ◽  
Yihan Yang ◽  
Dajing Shang ◽  
Rui Tang ◽  
Fangzhou Deng
Keyword(s):  
Kinetic Energy ◽  
Time Domain ◽  
Power Level ◽  
Near Field ◽  
Average Power ◽  
Water Entry ◽  
Transient Signal ◽  
Water Tank ◽  
Ball Size ◽  
The Impact

As one of the target characteristics, water-entry sound characteristics are of great significance to study, and its research has certain reference value for the detection of sea target. The water-entry sound of an underwater target is a transient sound signal, and it is mainly measured in open water such as the sea and lakes. However, due to the short duration of the acoustic signal and the modulation effect of the measuring environment, it is difficult to measure water-entry sound. To deal with this problem, in this work, the water-entry sound of a metal ball was measured in a water tank in a laboratory. The measurements were made in the direct acoustic control area 0.45 m away from the drop point of the ball to eliminate the influence of reflection. Through a time-domain integration, the power of the transient signal of the water-entry sound of the metal ball was obtained. The energy of the initial impact sound and the pulsating-bubble sound was investigated, as was the impact of ball size, entry velocity, and other factors on the characteristics of the water-entry sound. The results show that by combining the virtual-source method with the time-domain integral in the near field, the energy of the incoming sound can be obtained accurately. The results are consistent with closed-space measurements. The water-entry sound includes the initial impact sound and the pulsating-bubble sound. The energy of the pulsating-bubble sound is 3–5 orders of magnitude larger than that of the initial impact sound. The average power level of the water-entry sound is proportional to the ball size and the 2/3 power of the slamming velocity. The relation between the average power level and the 1/3 power of the kinetic energy is an exponential function with base 10. Based on the kinetic energy variety of metal balls entering the water, an acoustic model of this system is established. The results can be used for reference to other transient sound measurements.

Analysis of the Dielectric Loss in the Transmission Line Based on Time Domain BLT Equation

2013 ◽  
Vol 756-759 ◽  
pp. 4287-4291 ◽  
Author(s):  
Wan Jin Wang ◽  
Zhi Wu Xuan
Keyword(s):  
Dielectric Loss ◽  
Transmission Line ◽  
Time Domain ◽  
Transient Signal ◽  
Signal Source ◽  
Response Voltage ◽  
Calculation Results ◽  
The Time Domain ◽  
The Impact ◽  
Dielectric Insulation

Dielectric loss is caused due to imperfect dielectric insulation, in order to study the impact of the dielectric loss consider a uniform loss transmission line with leak conductance. The BLT equation from the frequency domain to time domain is derived to improve the time domain BLT equation, and the aim of using the time domain BLT equation to calculate load voltage of the transmission line with transient signal source, through the calculation results to analyze the impact of the dielectric loss. The results showed that the attenuation of the terminal load transient response voltage occurred when the dielectric loss exists, and this effect is nonlinear.

scholarly journals Characteristics of Slamming Pressure and Force for Trimaran Hull

2021 ◽  
Vol 9 (6) ◽  
pp. 564
Author(s):  
Zhe Sun ◽  
Xupeng Sui ◽  
Yanzeng Deng ◽  
Li Zou ◽  
A. Korobkin ◽  
...  
Keyword(s):  
Fluid Dynamics ◽  
Time Domain ◽  
Water Entry ◽  
Impact Pressure ◽  
Analytical Models ◽  
Quadratic Relation ◽  
Pressure Force ◽  
Computational Fluid Dynamics Cfd ◽  
The Time Domain ◽  
The Impact

In this paper, the characteristics of the impact pressure and force of a trimaran section was studied by Computational Fluid Dynamics (CFD). The time domain features of the slamming pressure or force showed a strong correlation with the penetration depth regardless of the specific ways of water entry. The effects of velocity and acceleration on the impact pressure and force were analyzed. It was found that the initial impact of the main hull and the wet-deck slamming were predominantly affected by the entry velocities, whilst the acceleration had almost no effect for initial impact. The impact velocity presented a quadratic relation with slamming pressure/forces, and the relation between acceleration and wet-deck slamming pressure/force was linear. These were consistent with the patterns implied by analytical models such as the Wagner or MLM (Modified Logvinovich model) theories.

scholarly journals A New Method to Determine the Impact of Individual Field Quantities on Cycle-to-Cycle Variations in a Spark-Ignited Gas Engine

Energies ◽  
2021 ◽  
Vol 14 (14) ◽  
pp. 4136
Author(s):  
Clemens Gößnitzer ◽  
Shawn Givler
Keyword(s):  
Kinetic Energy ◽  
Flow Field ◽  
Turbulent Kinetic Energy ◽  
Negative Impact ◽  
Operating Conditions ◽  
Engine Operation ◽  
Gas Engine ◽  
Cycle Simulation ◽  
Simulation Results ◽  
The Impact

Cycle-to-cycle variations (CCV) in spark-ignited (SI) engines impose performance limitations and in the extreme limit can lead to very strong, potentially damaging cycles. Thus, CCV force sub-optimal engine operating conditions. A deeper understanding of CCV is key to enabling control strategies, improving engine design and reducing the negative impact of CCV on engine operation. This paper presents a new simulation strategy which allows investigation of the impact of individual physical quantities (e.g., flow field or turbulence quantities) on CCV separately. As a first step, multi-cycle unsteady Reynolds-averaged Navier–Stokes (uRANS) computational fluid dynamics (CFD) simulations of a spark-ignited natural gas engine are performed. For each cycle, simulation results just prior to each spark timing are taken. Next, simulation results from different cycles are combined: one quantity, e.g., the flow field, is extracted from a snapshot of one given cycle, and all other quantities are taken from a snapshot from a different cycle. Such a combination yields a new snapshot. With the combined snapshot, the simulation is continued until the end of combustion. The results obtained with combined snapshots show that the velocity field seems to have the highest impact on CCV. Turbulence intensity, quantified by the turbulent kinetic energy and turbulent kinetic energy dissipation rate, has a similar value for all snapshots. Thus, their impact on CCV is small compared to the flow field. This novel methodology is very flexible and allows investigation of the sources of CCV which have been difficult to investigate in the past.

scholarly journals Double-Deck Metal Solenoids 3D Integrated in Silicon Wafer for Kinetic Energy Harvester

Micromachines ◽  
2021 ◽  
Vol 12 (1) ◽  
pp. 74
Author(s):  
Nianying Wang ◽  
Ruofeng Han ◽  
Changnan Chen ◽  
Jiebin Gu ◽  
Xinxin Li
Keyword(s):  
Kinetic Energy ◽  
Power Density ◽  
Energy Harvester ◽  
High Efficiency ◽  
Vibrational Energy ◽  
Average Power ◽  
Wafer Level ◽  
Peak Voltage ◽  
Silicon Mold ◽  
Casting Technique

A silicon-chip based double-deck three-dimensional (3D) solenoidal electromagnetic (EM) kinetic energy harvester is developed to convert low-frequency (<100 Hz) vibrational energy into electricity with high efficiency. With wafer-level micro electro mechanical systems (MEMS) fabrication to form a metal casting mold and the following casting technique to rapidly (within minutes) fill molten ZnAl alloy into the pre-micromachined silicon mold, the 300-turn solenoid coils (150 turns for either inner solenoid or outer solenoid) are fabricated in silicon wafers for saw dicing into chips. A cylindrical permanent magnet is inserted into a pre-etched channel for sliding upon external vibration, which is surrounded by the solenoids. The size of the harvester chip is as small as 10.58 mm × 2.06 mm × 2.55 mm. The internal resistance of the solenoids is about 17.9 Ω. The maximum peak-to-peak voltage and average power output are measured as 120.4 mV and 43.7 μW. The EM energy harvester shows great improvement in power density, which is 786 μW/cm3 and the normalized power density is 98.3 μW/cm3/g. The EM energy harvester is verified by experiment to be able to generate electricity through various human body movements of walking, running and jumping. The wafer-level fabricated chip-style solenoidal EM harvesters are advantageous in uniform performance, small size and volume applications.

scholarly journals Classification of standing and sitting phases based on in-socket piezoelectric sensors in a transfemoral amputee

2020 ◽  
Vol 0 (0) ◽  
Author(s):  
Tawfik Yahya ◽  
Nur Azah Hamzaid ◽  
Sadeeq Ali ◽  
Farahiyah Jasni ◽  
Hanie Nadia Shasmin
Keyword(s):  
Time Domain ◽  
Classification Accuracy ◽  
Sensory System ◽  
Metabolic Energy ◽  
Support Vector ◽  
Data Set ◽  
Transfemoral Amputee ◽  
Sit To Stand ◽  
Optimal Classifier ◽  
The Impact

AbstractA transfemoral prosthesis is required to assist amputees to perform the activity of daily living (ADL). The passive prosthesis has some drawbacks such as utilization of high metabolic energy. In contrast, the active prosthesis consumes less metabolic energy and offers better performance. However, the recent active prosthesis uses surface electromyography as its sensory system which has weak signals with microvolt-level intensity and requires a lot of computation to extract features. This paper focuses on recognizing different phases of sitting and standing of a transfemoral amputee using in-socket piezoelectric-based sensors. 15 piezoelectric film sensors were embedded in the inner socket wall adjacent to the most active regions of the agonist and antagonist knee extensor and flexor muscles, i. e. region with the highest level of muscle contractions of the quadriceps and hamstring. A male transfemoral amputee wore the instrumented socket and was instructed to perform several sitting and standing phases using an armless chair. Data was collected from the 15 embedded sensors and went through signal conditioning circuits. The overlapping analysis window technique was used to segment the data using different window lengths. Fifteen time-domain and frequency-domain features were extracted and new feature sets were obtained based on the feature performance. Eight of the common pattern recognition multiclass classifiers were evaluated and compared. Regression analysis was used to investigate the impact of the number of features and the window lengths on the classifiers’ accuracies, and Analysis of Variance (ANOVA) was used to test significant differences in the classifiers’ performances. The classification accuracy was calculated using k-fold cross-validation method, and 20% of the data set was held out for testing the optimal classifier. The results showed that the feature set (FS-5) consisting of the root mean square (RMS) and the number of peaks (NP) achieved the highest classification accuracy in five classifiers. Support vector machine (SVM) with cubic kernel proved to be the optimal classifier, and it achieved a classification accuracy of 98.33 % using the test data set. Obtaining high classification accuracy using only two time-domain features would significantly reduce the processing time of controlling a prosthesis and eliminate substantial delay. The proposed in-socket sensors used to detect sit-to-stand and stand-to-sit movements could be further integrated with an active knee joint actuation system to produce powered assistance during energy-demanding activities such as sit-to-stand and stair climbing. In future, the system could also be used to accurately predict the intended movement based on their residual limb’s muscle and mechanical behaviour as detected by the in-socket sensory system.

scholarly journals RF Small and large signal characterization of a 3D integrated GaN/RF-SOI SPST switch

2021 ◽  
pp. 1-6
Author(s):  
Frédéric Drillet ◽  
Jérôme Loraine ◽  
Hassan Saleh ◽  
Imene Lahbib ◽  
Brice Grandchamp ◽  
...  
Keyword(s):  
Power Level ◽  
Coplanar Waveguide ◽  
Average Power ◽  
Input Power ◽  
Capacitive Coupling ◽  
Rf Switch ◽  
Large Signal ◽  
Waveguide Transmission ◽  
Signal Characterization

Abstract This paper presents the radio frequency (RF) measurements of an SPST switch realized in gallium nitride (GaN)/RF-SOI technology compared to its GaN/silicon (Si) equivalent. The samples are built with an innovative 3D heterogeneous integration technique. The RF switch transistors are GaN-based and the substrate is RF-SOI. The insertion loss obtained is below 0.4 dB up to 30 GHz while being 1 dB lower than its GaN/Si equivalent. This difference comes from the vertical capacitive coupling reduction of the transistor to the substrate. This reduction is estimated to 59% based on a RC network model fitted to S-parameters measurements. In large signal, the linearity study of the substrate through coplanar waveguide transmission line characterization shows the reduction of the average power level of H2 and H3 of 30 dB up to 38 dBm of input power. The large signal characterization of the SPST shows no compression up to 38 dBm and the H2 and H3 rejection levels at 38 dBm are respectively, 68 and 75 dBc.

Time Domain Models for Damping-Controlled Fluidelastic Instability Forces in Tubes With Loose Supports

2010 ◽  
Vol 132 (4) ◽  
Author(s):  
Marwan Hassan ◽  
Achraf Hossen
Keyword(s):  
Time Domain ◽  
Cross Flow ◽  
Work Rate ◽  
Interaction Parameters ◽  
Similar Response ◽  
Fluid Force ◽  
Support Interaction ◽  
Fluidelastic Instability ◽  
The Impact ◽  
Normal Work

This paper presents simulations of a loosely supported cantilever tube subjected to turbulence and fluidelastic instability forces. Several time domain fluid force models are presented to simulate the damping-controlled fluidelastic instability mechanism in tube arrays. These models include a negative damping model based on the Connors equation, fluid force coefficient-based models (Chen, 1983, “Instability Mechanisms and Stability Criteria of a Group of Cylinders Subjected to Cross-Flow. Part 1: Theory,” Trans. ASME, J. Vib., Acoust., Stress, Reliab. Des., 105, pp. 51–58; Tanaka and Takahara, 1981, “Fluid Elastic Vibration of Tube Array in Cross Flow,” J. Sound Vib., 77, pp. 19–37), and two semi-analytical models (Price and Païdoussis, 1984, “An Improved Mathematical Model for the Stability of Cylinder Rows Subjected to Cross-Flow,” J. Sound Vib., 97(4), pp. 615–640; Lever and Weaver, 1982, “A Theoretical Model for the Fluidelastic Instability in Heat Exchanger Tube Bundles,” ASME J. Pressure Vessel Technol., 104, pp. 104–147). Time domain modeling and implementation challenges for each of these theories were discussed. For each model, the flow velocity and the support clearance were varied. Special attention was paid to the tube/support interaction parameters that affect wear, such as impact forces and normal work rate. As the prediction of the linear threshold varies depending on the model utilized, the nonlinear response also differs. The investigated models exhibit similar response characteristics for the lift response. The greatest differences were seen in the prediction of the drag response, the impact force level, and the normal work rate. Simulation results show that the Connors-based model consistently underestimates the response and the tube/support interaction parameters for the loose support case.

Selection of random vibration theory procedures for the NGA-East project and ground-motion modeling

2021 ◽  
Vol 37 (1_suppl) ◽  
pp. 1420-1439
Author(s):  
Albert R Kottke ◽  
Norman A Abrahamson ◽  
David M Boore ◽  
Yousef Bozorgnia ◽  
Christine A Goulet ◽  
...  
Keyword(s):  
Ground Motion ◽  
Time Domain ◽  
Random Vibration ◽  
Amplitude Spectrum ◽  
Motion Modeling ◽  
Peak Response ◽  
Vibration Theory ◽  
Random Vibration Theory ◽  
The Time Domain ◽  
The Impact

Traditional ground-motion models (GMMs) are used to compute pseudo-spectral acceleration (PSA) from future earthquakes and are generally developed by regression of PSA using a physics-based functional form. PSA is a relatively simple metric that correlates well with the response of several engineering systems and is a metric commonly used in engineering evaluations; however, characteristics of the PSA calculation make application of scaling factors dependent on the frequency content of the input motion, complicating the development and adaptability of GMMs. By comparison, Fourier amplitude spectrum (FAS) represents ground-motion amplitudes that are completely independent from the amplitudes at other frequencies, making them an attractive alternative for GMM development. Random vibration theory (RVT) predicts the peak response of motion in the time domain based on the FAS and a duration, and thus can be used to relate FAS to PSA. Using RVT to compute the expected peak response in the time domain for given FAS therefore presents a significant advantage that is gaining traction in the GMM field. This article provides recommended RVT procedures relevant to GMM development, which were developed for the Next Generation Attenuation (NGA)-East project. In addition, an orientation-independent FAS metric—called the effective amplitude spectrum (EAS)—is developed for use in conjunction with RVT to preserve the mean power of the corresponding two horizontal components considered in traditional PSA-based modeling (i.e., RotD50). The EAS uses a standardized smoothing approach to provide a practical representation of the FAS for ground-motion modeling, while minimizing the impact on the four RVT properties ( zeroth moment, [Formula: see text]; bandwidth parameter, [Formula: see text]; frequency of zero crossings, [Formula: see text]; and frequency of extrema, [Formula: see text]). Although the recommendations were originally developed for NGA-East, they and the methodology they are based on can be adapted to become portable to other GMM and engineering problems requiring the computation of PSA from FAS.

Sign in / Sign up

Export Citation Format

Share Document