Theory and Measurements of the Propeller-Induced Vibratory Pressure Field

1972 ◽  
Vol 16 (02) ◽  
pp. 124-139
Author(s):  
W. R. Jacobs ◽  
J. Mercier ◽  
S. Tsakonas
Keyword(s):  
High Speed ◽  
Pressure Field ◽  
Processing Technique ◽  
Experimental Program ◽  
Signal Processing Technique ◽  
Experimental Procedure ◽  
Surface Theory ◽  
Blade Frequency ◽  
Development Center ◽  
Theoretical Results

A theory has been developed, based on lifting surface theory, for evaluation of the pressure field generated by an operating propeller in a nonuniform inflow field. In addition, an experimental procedure and a signal processing technique for measuring small pressure levels accurately have been established and utilized in an extensive experimental program. Theoretical results obtained by means of a computer program developed for the CDC 6600 high-speed digital computer agree well with those of experiments conducted at Davidson Laboratory and at the Naval Ship Research and Development Center. The difficulty of accurately establishing by measurements the decay of small pressures at points farther than one radius from the propeller precludes the possibility of determining the blade-frequency force exerted on a flat boundary by integrating the measured signatures. In contrast, integration of double the theoretical free-space pressure over the flat boundary appears to be a feasible and meaningful approach.

Propeller Loading-Induced Velocity Field by Means of Unsteady Lifting Surface Theory

1973 ◽  
Vol 17 (03) ◽  
pp. 129-139
Author(s):  
W. R. Jacobs ◽  
S. Tsakonas
Keyword(s):  
Velocity Field ◽  
High Speed ◽  
Pressure Field ◽  
Numerical Procedure ◽  
Nonuniform Flow ◽  
Surface Theory ◽  
Loading Function ◽  
Lifting Surface ◽  
Space Function ◽  
Induced Velocity

An analysis based on the lifting surface theory has been developed for evaluation of the vibratory velocity field induced by the loading of an operating propeller in both uniform and nonuniform inflow fields. The analysis demonstrates that in the case of nonuniform flow the velocity at any field point is made up of a large number of combinations of the frequency constituents of the loading function with those of the space function (propagation or influence function). A numerical procedure has been developed adaptable to a high-speed digital computer (CDC 6600), and the existing program, which evaluates the steady and unsteady propeller loadings, the resulting hydrodynamic forces and moments, and the pressure field, has been extended to include evaluation of the velocity field as well. This program should thus become a highly versatile and useful tool for the ship researcher or designer.

A Comparison of Contrarotating Propellers with Other Propulsion Systems: Results of Model Experiments

1972 ◽  
Vol 9 (01) ◽  
pp. 99-120
Author(s):  
J. Strom-Tejsen
Keyword(s):  
High Speed ◽  
High Performance ◽  
Experimental Program ◽  
Propulsion Systems ◽  
Single Screw ◽  
Propulsion Performance ◽  
American Export ◽  
General Investigation ◽  
Twin Screw ◽  
Development Center

An experimental program was carried out at the Naval Ship Research and Development Center to determine the propulsion performance of a high-speed containership with twin-screw, contrarotating, and overlapping-propeller arrangements. The afterbody lines for the contrarotating arrangements were developed as a modification to a 25.5-knot, twin-screw containership design being considered for construction by the American Export Isbrandtsen Lines. Results for the contrarotating version include effect of off-design shaft speed and torque ratios as well as application of single and twin rudders. Results are also given for the design using a single screw in case it should be necessary at a later date to replace the contrarotating with a single-screw unit. Experiments on the overlapping-propeller arrangement were carried out to make the comparison between the contrarotating and twin-screw designs a part of a general investigation of propulsion arrangements for high-performance merchant ships. Conclusions and recommendations for some further investigations are given.

scholarly journals A Remote Sensor System Based on TDLAS Technique for Ammonia Leakage Monitoring

Sensors ◽  
2021 ◽  
Vol 21 (7) ◽  
pp. 2448
Author(s):  
Hongbin Lu ◽  
Chuantao Zheng ◽  
Lei Zhang ◽  
Zhiwei Liu ◽  
Fang Song ◽  
...  
Keyword(s):  
Signal Processing ◽  
Limit Of Detection ◽  
Processing Technique ◽  
Tunable Diode Laser ◽  
Sensor System ◽  
Signal Processing Technique ◽  
Suppression Effect ◽  
Output Wavelength ◽  
Deviation Analysis ◽  
Remote Sensor

The development of an efficient, portable, real-time, and high-precision ammonia (NH3) remote sensor system is of great significance for environmental protection and citizens’ health. We developed a NH3 remote sensor system based on tunable diode laser absorption spectroscopy (TDLAS) technique to measure the NH3 leakage. In order to eliminate the interference of water vapor on NH3 detection, the wavelength-locked wavelength modulation spectroscopy technique was adopted to stabilize the output wavelength of the laser at 6612.7 cm−1, which significantly increased the sampling frequency of the sensor system. To solve the problem in that the light intensity received by the detector keeps changing, the 2f/1f signal processing technique was adopted. The practical application results proved that the 2f/1f signal processing technique had a satisfactory suppression effect on the signal fluctuation caused by distance changing. Using Allan deviation analysis, we determined the stability and limit of detection (LoD). The system could reach a LoD of 16.6 ppm·m at an average time of 2.8 s, and a LoD of 0.5 ppm·m at an optimum averaging time of 778.4 s. Finally, the measurement result of simulated ammonia leakage verified that the ammonia remote sensor system could meet the need for ammonia leakage detection in the industrial production process.

scholarly journals Application of UAV in Search and Rescue Actions in Underground Mine—A Specific Sound Detection in Noisy Acoustic Signal

Energies ◽  
2021 ◽  
Vol 14 (13) ◽  
pp. 3725
Author(s):  
Paweł Zimroz ◽  
Paweł Trybała ◽  
Adam Wróblewski ◽  
Mateusz Góralczyk ◽  
Jarosław Szrek ◽  
...  
Keyword(s):  
Signal Processing ◽  
Acoustic Signal ◽  
Processing Technique ◽  
Underground Mine ◽  
Search And Rescue ◽  
Reference Spectrum ◽  
Signal Processing Technique ◽  
Time Frequency ◽  
Communication Device ◽  
Frequency Representation

The possibility of the application of an unmanned aerial vehicle (UAV) in search and rescue activities in a deep underground mine has been investigated. In the presented case study, a UAV is searching for a lost or injured human who is able to call for help but is not able to move or use any communication device. A UAV capturing acoustic data while flying through underground corridors is used. The acoustic signal is very noisy since during the flight the UAV contributes high-energetic emission. The main goal of the paper is to present an automatic signal processing procedure for detection of a specific sound (supposed to contain voice activity) in presence of heavy, time-varying noise from UAV. The proposed acoustic signal processing technique is based on time-frequency representation and Euclidean distance measurement between reference spectrum (UAV noise only) and captured data. As both the UAV and “injured” person were equipped with synchronized microphones during the experiment, validation has been performed. Two experiments carried out in lab conditions, as well as one in an underground mine, provided very satisfactory results.

Study of the Effect of Hole Clearance and Thread Fit on the Self-Loosening of Threaded Fasteners

2006 ◽  
Vol 129 (6) ◽  
pp. 586-594 ◽  
Author(s):  
Sayed A. Nassar ◽  
Basil A. Housari
Keyword(s):  
Analytical Investigation ◽  
The Self ◽  
Time Data ◽  
Experimental Procedure ◽  
Test Setup ◽  
Threaded Fasteners ◽  
Service Load ◽  
Real Time Data ◽  
Theoretical Results ◽  
Simplified Mathematical Model

This study provides an experimental and theoretical investigation of the effect of hole clearance and thread fit on the self-loosening of tightened threaded fasteners that are subjected to a cyclic transverse service load. An experimental procedure and test setup are developed in order to collect real-time data on the rate of clamp load loss per cycle as well as the loosening rotation of the bolt head. Three levels of hole clearance are investigated; namely, 3%, 6%, and 10% of the bolt nominal diameter. For the commonly used 2A thread fit for a selected bolt size, three classes of the nut thread fit are considered; namely, 1B, 2B, and 3B. A simplified mathematical model is used for the analytical investigation of the effect of the hole clearance and thread fit on threaded fasteners self-loosening. The experimental and theoretical results are presented and discussed.

EXPRESS: The effect of low frequency equalisation on preference and sensorimotor synchronisation in music

2021 ◽  
pp. 174702182110371
Author(s):  
Scott Beveridge ◽  
Estefanía Cano ◽  
Steffen A. Herff
Keyword(s):  
Body Movement ◽  
Low Frequency ◽  
Empirical Support ◽  
Processing Technique ◽  
Original Version ◽  
Upper Body ◽  
Signal Processing Technique ◽  
Band Energy ◽  
Sensorimotor Synchronisation ◽  
Specific Frequency

Equalisation, a signal processing technique commonly used to shape the sound of music, is defined as the adjustment of the energy in specific frequency components of a signal. In this work we investigate the effects of equalisation on preference and sensorimotor synchronisation in music. Twenty-one participants engaged in a goal-directed upper body movement in synchrony with stimuli equalised in three low-frequency sub-bands (0 - 50 Hz, 50 - 100 Hz, 100 - 200 Hz). To quantify the effect of equalisation, music features including spectral flux, pulse clarity, and beat confidence were extracted from seven differently equalised versions of music tracks - one original and six manipulated versions for each music track. These music tracks were then used in a movement synchronisation task. Bayesian mixed effects models revealed different synchronisation behaviours in response to the three sub-bands considered. Boosting energy in the 100 - 200 Hz sub-band reduced synchronisation performance irrespective of the sub-band energy of the original version. An energy boost in the 0 - 50 Hz band resulted in increased synchronisation performance only when the sub-band energy of the original version was high. An energy boost in the 50 - 100 Hz band increased synchronisation performance only when the sub-band energy of the original version was low. Boosting the energy in any of the three subbands increased preference regardless of the energy of the original version. Our results provide empirical support for the importance of low-frequency information for sensorimotor synchronisation and suggest that the effect of equalisation on preference and synchronisation are largely independent of one another.

Application Of Elastic Layers To Register Pressure Field On The Model Surface In Supersonic Flow

2016 ◽  
Vol 11 (1) ◽  
pp. 23-33
Author(s):  
Maxim Golubev ◽  
Andrey Shmakov
Keyword(s):  
Surface Waves ◽  
High Frequency ◽  
High Speed ◽  
Pressure Pulsation ◽  
Pressure Field ◽  
Leading Edge ◽  
Supersonic Wind Tunnel ◽  
Register Pressure ◽  
Elastic Layers ◽  
Sharp Leading Edge

The work presents the results of application of panoramic interferential technique which is based on elastic layers (sensors) usage to obtain pressure distribution on the flat plate having sharp leading edge. Experiments were done in supersonic wind tunnel at Mach number M = 4. Sensitivity and response time are shown to be enough to register pressure pulsation against standing and traveling sensor surface waves. Applying high-frequency image acquiring is demonstrated to make possible to distinguish at visualization images high-speed disturbances propagating in the boundary layer from low-speed surface waves

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