scholarly journals CALCULATION OF DAMPERS OF LOW-FREQUENCY ACOUSTIC FILTERS TYPE

2021 ◽  
Vol 6 (4) ◽  
pp. 11-17
Author(s):  
A. N. Golovin
Keyword(s):  
Dynamic Characteristics ◽  
Pressure Pulsation ◽  
Fluid Pressure ◽  
Low Frequency ◽  
Hydraulic Losses ◽  
Acoustic Filters ◽  
The Given

The article provides analytical dependencies that allowing harmonization the required dynamic characteristics of fluid pressure pulsation dampers with the parameters of their main elements at the given level of hydraulic losses on the devices.

scholarly journals Hearing at threshold intensities: by slow mechanical traveling waves or by fast cochlear fluid pressure waves

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Haim Sohmer
Keyword(s):  
Soft Tissue ◽  
Hair Cells ◽  
Traveling Wave ◽  
Basilar Membrane ◽  
Fluid Pressure ◽  
Low Frequency ◽  
Frequency Discrimination ◽  
Outer Hair Cells ◽  
Common Mechanism ◽  
Frequency Stimulation

The three modes of auditory stimulation (air, bone and soft tissue conduction) at threshold intensities are thought to share a common excitation mechanism: the stimuli induce passive displacements of the basilar membrane propagating from the base to the apex (slow mechanical traveling wave), which activate the outer hair cells, producing active displacements, which sum with the passive displacements. However, theoretical analyses and modeling of cochlear mechanics provide indications that the slow mechanical basilar membrane traveling wave may not be able to excite the cochlea at threshold intensities with the frequency discrimination observed. These analyses are complemented by several independent lines of research results supporting the notion that cochlear excitation at threshold may not involve a passive traveling wave, and the fast cochlear fluid pressures may directly activate the outer hair cells: opening of the sealed inner ear in patients undergoing cochlear implantation is not accompanied by threshold elevations to low frequency stimulation which would be expected to result from opening the cochlea, reducing cochlear impedance, altering hydrodynamics. The magnitude of the passive displacements at threshold is negligible. Isolated outer hair cells in fluid display tuned mechanical motility to fluid pressures which likely act on stretch sensitive ion channels in the walls of the cells. Vibrations delivered to soft tissue body sites elicit hearing. Thus, based on theoretical and experimental evidence, the common mechanism eliciting hearing during threshold stimulation by air, bone and soft tissue conduction may involve the fast-cochlear fluid pressures which directly activate the outer hair cells.

Study of Temperature Effect on Servovalve-Controlled Fuel Metering Unit

2015 ◽  
Vol 137 (6) ◽  
Author(s):  
Bin Wang ◽  
Haocen Zhao ◽  
Ling Yu ◽  
Zhifeng Ye
Keyword(s):  
Steady State ◽  
Temperature Variation ◽  
Dynamic Characteristics ◽  
Numerical Study ◽  
Step Response ◽  
Fuel Temperature ◽  
Wide Range ◽  
Fuel Rate ◽  
Testing Condition ◽  
The Given

It is usual that fuel system of an aero-engine operates within a wide range of temperatures. As a result, this can have effect on both the characteristics and precision of fuel metering unit (FMU), even on the performance and safety of the whole engine. This paper provides theoretical analysis of the effect that fluctuation of fuel temperature has on the controllability of FMU and clarifies the drawbacks of the pure mathematical models considering fuel temperature variation for FMU. Taking the electrohydraulic servovalve-controlled FMU as the numerical study, simulation in AMESim is carried out by thermal hydraulic model under the temperatures ranged from −10 to 60 °C to confirm the effectiveness and precision of the model on the basis of steady-state and dynamic characteristics of FMU. Meanwhile, the FMU testing workbench with temperature adjustment device employing the fuel cooler and heater is established to conduct an experiment of the fuel temperature characteristics. Results show that the experiment matches well with the simulation with a relative error no more than 5% and that 0–50 °C fuel temperature variation produces up to 5.2% decrease in fuel rate. In addition, step response increases with the fuel temperature. Fuel temperature has no virtual impact on the steady-state and dynamic characteristics of FMU under the testing condition in this paper, implying that FMU can operate normally in the given temperature range.

scholarly journals Hysteresis Characteristic in Hump Region of a Pump-Turbine Model

2016 ◽  
Author(s):  
Deyou Li ◽  
Hongjie Wang ◽  
Jinxia Chen ◽  
Torbjørn K. Nielsen ◽  
Daqing Qin ◽  
...  
Keyword(s):  
Guide Vane ◽  
Pressure Sensors ◽  
Low Frequency ◽  
Rotational Frequency ◽  
Hysteresis Phenomenon ◽  
Pump Turbine ◽  
Hysteresis Characteristic ◽  
Hydraulic Losses ◽  
Measurement Direction ◽  
Turbine Model

The hump characteristic is one of the major instabilities in pump-turbines. When pump-turbines operate in the hump region, strong noise and serious fluctuations could be observed, which are harmful to the safe and stable operations and even destroy the whole unit as well as water conveyance system. In this paper, a low specific speed (nq = 36.1 min−1) pump-turbine model was experimentally investigated. Firstly, the hump characteristic was obtained under 19 mm guide vane opening. More interestingly, when the hump characteristic was measured in two directions (increasing and decreasing the discharge), the hysteresis characteristic was found during the hump region. The analysis of performance characteristics reveals that the hump instability is resultant of Euler momentum and hydraulic losses, and different Euler momentum and hydraulic losses in the two development processes lead to hysteresis phenomenon. Then, 12 pressure sensors were mounted in the different parts of the pump-turbine model to obtain the time and frequency characteristics. The analysis of fast Fourier transform confirms that the hump characteristic is related to the low-frequency (0.04–0.15 times rotational frequency) vortices. The occurrence and cease of vortices depend on the operating condition and measurement direction, which contribute to the hysteresis characteristic. Finally, the type of the low-frequency vortices was analyzed through the cross power spectrum.

scholarly journals Analysis and Experimental Investigation of Vibration Characteristics of Rotary Platform of Hydraulic Excavator under Complex Working Conditions

2021 ◽  
Vol 2021 ◽  
pp. 1-10
Author(s):  
Tinghao Li ◽  
Fuxiu Liu ◽  
Zhaojun Li ◽  
Mingjin Lu ◽  
Qiulu He
Keyword(s):  
Working Conditions ◽  
Dynamic Characteristics ◽  
Pressure Pulsation ◽  
Vibration Characteristics ◽  
Hydraulic Excavator ◽  
Rotary Platform ◽  
Road Excitation ◽  
Engine Excitation ◽  
Internal Relationships ◽  
Excitation Pressure

The rotary platform is the load-bearing substrate of a hydraulic excavator. The dynamic characteristics of the rotary platform directly affect the reliability and safety of the whole machine of a hydraulic excavator. In this work, the characteristics of the main external excitations acting on the hydraulic excavator such as the engine excitation, pressure pulsation excitation of the piston pump, inertial excitation of the working device, and road excitation are analyzed. The vibration transmission paths under the action of external excitations are ascertained. A vibration test method for the rotary platform of the hydraulic excavator is proposed. The vibration characteristics of the rotary platform under complex working conditions are researched, and the internal relationships between the vibration characteristics of the rotary platform and the engine excitation, pressure pulsation excitation of the piston pump, and road excitation are analyzed experimentally. The results show that the rotary platform is subjected to different excitations when it is under different working conditions. Moreover, the internal relationships between the dynamic characteristics of the rotary platform and the external excitation characteristics can be discovered by analyzing the vibration signals of the rotary platform, and the dynamic characteristics of the whole machine of the hydraulic excavator can be deeply studied based on the vibration characteristics of the rotary platform.

scholarly journals Fluid–structure interaction analysis of fluid pressure pulsation and structural vibration features in a vertical axial pump

2019 ◽  
Vol 11 (3) ◽  
pp. 168781401982858
Author(s):  
Liaojun Zhang ◽  
Shuo Wang ◽  
Guojiang Yin ◽  
Chaonian Guan
Keyword(s):  
Pressure Pulsation ◽  
Interaction Analysis ◽  
Equivalent Stress ◽  
Fluid Structure Interaction ◽  
Fluid Pressure ◽  
Structural Vibration ◽  
Interaction Method ◽  
Fluid Structure ◽  
Structure Interaction ◽  
Axial Pump

Current studies on the operation of the axial pump mainly focus on hydraulic performances, while the coupled interaction between the fluid and structure attracts little attention. This study aims to provide numerical investigation into the vibration features in a vertical axial pump based on two-way iterative fluid–structure interaction method. Three-dimensional coupling model was established with high-quality structured grids of ADINA software. Turbulent flow features were studied under design condition, using shear–stress transport k-ω turbulence model and sliding mesh approach. Typical measure points along and perpendicular to flow direction in fluid domain were selected to analyze pressure pulsation features of the impeller and fixed guide vane. By contrast, vibration features of equivalent stress in corresponding structural positions were investigated and compared based on fluid–structure interaction method. In order to explore fluid–structure interaction vibration mechanism, distribution of main frequencies and amplitudes of the measure points was presented based on the Fast Fourier Transformation method. The results reveal the time and frequency law of fluid pressure pulsation and structural vibration at the same position in the vertical axial pump while additionally provide important theoretical guidance for optimization design and safe operation of the vertical axial pump.

Role of fascia in maintenance of muscle tension and pressure

1981 ◽  
Vol 51 (2) ◽  
pp. 317-320 ◽  
Author(s):  
S. R. Garfin ◽  
C. M. Tipton ◽  
S. J. Mubarak ◽  
S. L. Woo ◽  
A. R. Hargens ◽  
...  
Keyword(s):  
High Frequency ◽  
Muscle Tension ◽  
Fluid Pressure ◽  
Low Frequency ◽  
Testing Procedure ◽  
Force Transducer ◽  
High Frequency Stimulation ◽  
Low Frequency Stimulation ◽  
Frequency Stimulation

The effect of fasciotomy on muscle tension (measured by a force transducer attached to the tendon) and interstitial fluid pressure (measured by Wick catheters in the muscle belly) was studied in the anterolateral compartments of 13 dog hindlimbs. Muscle tension and pressure were monitored in the tibialis cranialis muscle after low- and high-frequency stimulation of the peroneal nerve to produce twitch- and tetanic-type contractions. Fasciotomy decreased muscle force during the low-frequency stimulation by 16% (35.3 +/- 4.9 to 28.4 +/- 3.9 N) and during the high-frequency stimulation by 10% (60.8 %/- 4.9 to 54.8 +/- 3.9 N). Muscle pressure decreased 50% after fasciotomy under both conditions, 15 +/- 2 to 6 +/- 1 mmHg and 84 +/- 17 to 41 +/- 8 mmHg), respectively. Repeated functional evaluations during the testing procedure indicated that muscle fatigue was not a major factor in these results. It was concluded that fascia is important in the development of muscle tension and changes in interstitial pressure. Furthermore, the results raised questions concerning the merits of performing a fasciotomy for athletes with a compartment syndrome.

scholarly journals Testing donation menus: on charitable giving for cancer research – evidence from a natural field experiment

2019 ◽  
pp. 1-22
Author(s):  
MARIANNA BAGGIO ◽  
MATTEO MOTTERLINI
Keyword(s):  
Cancer Research ◽  
Field Experiment ◽  
Charitable Giving ◽  
Research Evidence ◽  
Low Frequency ◽  
Behavioral Responses ◽  
Average Amount ◽  
Charitable Behavior ◽  
Natural Field Experiment ◽  
The Given

AbstractBehavioral economics research has helped with understanding charitable behavior and has shown that charities can encourage donations by carefully designing their pledges. However, there is still scope to extend current research on who gives, what drives the decision to donate and at what levels, especially when behavioral insights are applied in context. In cooperation with a major Italian charity for cancer research, this study implements a natural direct mail field experiment, with over 150,000 letters sent to donors. By exploring the behavioral responses to different donation anchors, evidence was found that, within the given framework, including donation menus significantly increased the average amount donated without affecting the likelihood of donation. Furthermore, introducing additional explanations of how to make a payment significantly increased overall returns. Lastly, individual heterogeneity (high- and low-frequency donors, as well as senior and junior donors) had a direct effect on donations.

An Efficient Technique for Design of Hydraulic Engine Mount via Design Variable-Embedded Damping Modeling

2005 ◽  
Vol 127 (1) ◽  
pp. 93-99 ◽  
Author(s):  
Jun-Hwa Lee ◽  
Kwang-Joon Kim
Keyword(s):  
Dynamic Characteristics ◽  
Low Frequency ◽  
High Amplitude ◽  
Nonlinear Damping ◽  
Efficient Design ◽  
Equivalent Viscous Damping ◽  
Damping Characteristics ◽  
Design Variables ◽  
Engine Mount ◽  
Stiffness And Damping

For an efficient design of hydraulic mounts, it is most important to have a good mathematical model available, which must be simple yet capable of representing dynamic characteristics of the hydraulic mounts accurately. Under high amplitude excitations in the low-frequency range, the hydraulic mounts show strongly frequency-dependent stiffness and damping characteristics, which are related with so-called inertia track dynamics. Since nonlinear damping models based on fluid mechanics are typically used to predict the dynamic characteristics of the hydraulic mounts, relations between various design variables, such as geometry of the inertia track, and resultant stiffness and damping characteristics are understood only by tedious numerical computations. In this paper, the use of an equivalent viscous damping model—derived from a nonlinear model and represented in terms of design variables in an explicit manner—is proposed and, based on the equivalent linear model, are presented simple as well as very useful formulas for an efficient design of the hydraulic mounts.

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