scholarly journals Spatial Fluctuating Pressure Calculation of Underwater Counter Rotating Propellers under Noncavitating Condition

2018 ◽  
Vol 2018 ◽  
pp. 1-12
Author(s):  
L. X. Hou ◽  
A. K. Hu
Keyword(s):  
Fourier Transform ◽  
Hydrodynamic Interaction ◽  
Pressure Field ◽  
Spherical Surface ◽  
Hydrodynamic Performance ◽  
Fluctuating Pressure ◽  
Pressure Distributions ◽  
Pressure Calculation ◽  
Calculation Results ◽  
The Given

The spatial fluctuating pressure field (FPF) of counter rotating propeller (CRP) under noncavitating condition is investigated. The hydrodynamic performance and pressure distributions on the blade surfaces are obtained through low-order potential-based panel method, which is also used to analyze the hydrodynamic interaction between the front and rear propellers of CRP as well as the hydrodynamic interference between any solid surface and propeller. The interaction between the given solid spherical surface and propeller is used to simulate the spatial FPF of propeller, and the fluctuating pressure induced by a propeller over one revolution is analyzed in frequency domain through fast Fourier transform. The method proposed is validated through two given propellers by comparing the calculation results with test data. The FPFs of the front and rear propellers are calculated and compared with that of the corresponding single propeller. The result shows that the CRP produces weaker FPF compared with the single propeller.

Experimental Study and Numerical Analysis of Sihui Metro Depot and the Superstructure

2012 ◽  
Vol 226-228 ◽  
pp. 176-180
Author(s):  
Jing Zhang ◽  
Bin Zhang ◽  
Ying Hua Liu ◽  
Long Qi Wang ◽  
Yu Bin Wu
Keyword(s):  
Time History ◽  
Field Tests ◽  
Element Model ◽  
Test Analysis ◽  
3 Dimensional ◽  
Dimensional Finite Element ◽  
Calculation Results ◽  
History Of ◽  
The Given ◽  
The Waves

Field tests were carried out on Sihui metro depot of Beijing metro line 1 and its superstructure. The acceleration time history of sleepers and floors of the building was obtained, and the waves-propagation laws of building were studied through the tests. Test analysis shows that the structure vibrations show zigzag tendencies ascends with the height of the building. Based on current situation of Sihui metro depot, a metro-soil-building 3-dimensional finite element model is established on ANSYS. By using actual acceleration of sleepers as inputs, the dynamic responds rule of the superstructure is obtained. Compared calculation results with the experimental results, the given numerical model can predict the vibrations of the building induced by moving trains quite well. This method can provide guidance and technical support for future development of superstructure.

A Calculation Method to Investigate the Effects of Geometric Parameters and Operational Conditions on the Static Characteristics of Aerostatic Spherical Bearings

2018 ◽  
Vol 141 (2) ◽  
Author(s):  
Hailong Cui ◽  
Huan Xia ◽  
Dajiang Lei ◽  
Xinjiang Zhang ◽  
Zhengyi Jiang
Keyword(s):  
Experimental Data ◽  
Calculation Method ◽  
Reynolds Equation ◽  
Geometric Parameters ◽  
Static Characteristics ◽  
Optimal Parameters ◽  
Film Pressure ◽  
Operational Conditions ◽  
Pressure Distributions ◽  
Calculation Results

In this paper, a calculation method based on matlab partial differential equations (PDE) tool is proposed to investigate the static characteristics of aerostatic spherical bearings. The Reynolds equation of aerostatic spherical bearings is transformed into a standard elliptic equation. The effects of geometric parameters and operational conditions on the film pressure, bearing film force, and stiffness are studied. The axial and radial eccentricities result in different film pressure distributions; the bearing film force and stiffness are significantly influenced by geometric parameters and operational conditions. The relative optimal parameters are confirmed based on the calculation results. A comparison between the numerical and experimental results is also presented. The highest relative error between the numerical results and the experimental data is 11.3%; the calculation results show good agreements with the experimental data, thus verifying the accuracy of the calculation method used in this paper.

APPLICATION OF ELASTIC DEFORMATIONS TO PARABOLOIDAL SURFACE MAKING

2020 ◽  
Vol 3 ◽  
pp. 11-19
Author(s):  
A.V. NEMENKO ◽  
M.M. NIKITIN
Keyword(s):  
Control System ◽  
Active Control ◽  
Material Removal ◽  
Spherical Surface ◽  
Parabolic Mirror ◽  
Concave Mirror ◽  
Elastic Deformations ◽  
Elastic Bending ◽  
Active Control System ◽  
The Given

The transformation of a spherical concave mirror into a parabolic one with the help of elastic bending deformations is considered. The magnitude and direction of the load, which creates the necessary bend for transforming the mirror with the given parameters, are determined. Uneven material removal during machining is replaced by the bend of an optically accurate spherical surface already obtained. The application of the results to the creation of an active control system for the shaping of the surface of a paraboloid of rotation is considered. The proposed finishing technology is aimed at solving the problem of guaranteed obtaining optically accurate surface of a parabolic mirror.

The Pressure Field Near a Ship Propeller

1958 ◽  
Vol 2 (01) ◽  
pp. 57-66
Author(s):  
John P. Breslin
Keyword(s):  
Sound Pressure ◽  
Pressure Field ◽  
Subsequent Paper ◽  
Naval Architecture ◽  
Fluctuating Pressure ◽  
Comparison With Experiment ◽  
Lifting Line ◽  
Ship Propeller

A brief summary is given of efforts in the field of naval architecture on the problem of determining the vibratory forces and moments produced by a ship propeller, and an account of the principal contributions made by aeronautical researchers on the problem of computing the fluctuating pressure field near a propeller. This pressure is derived from a lifting-line representation and the expressions are then interpreted in terms of the fields of two doublet distributions. It is shown that this result can be verified by specializing the expressions for the sound-pressure field of a propeller. Some characteristics of the pressure field are discussed briefly. Detailed evaluations and comparison with experiment will be presented in a subsequent paper.

Flow field behind a complex total pressure distortion screen

2019 ◽  
Vol 233 (14) ◽  
pp. 5075-5092
Author(s):  
M Sivapragasam
Keyword(s):  
Flow Field ◽  
Total Pressure ◽  
Design Methodology ◽  
Pressure Field ◽  
Alternative Interpretation ◽  
Interface Plane ◽  
Screen Design ◽  
Pressure Distributions ◽  
Water Jet Cutting ◽  
Distortion Index

The flow field behind a complex total pressure distortion screen is investigated experimentally and numerically. The distortion screen is designed using an established design methodology and fabricated by water-jet cutting technique. The distorted total pressure field behind the screen is quantified by a distortion index parameter, which is evaluated from computations and experiments for several values of inlet Mach number. The root-mean-square error between the target total pressure values and that achieved by the screen design at the aerodynamic interface plane is 4.75%. The evolution of the distorted total pressure field downstream of the screen is presented in detail in terms of radial and circumferential total pressure distributions and their gradients. An alternative interpretation of the distorted total pressure field is made by means of defining a total pressure flux existing behind the screen and expanding it using derivative-moment transformation technique. It is seen that the circumferential vorticity is a major contributing factor to the total pressure flux.

Marine Ducted Propeller Blade Fracture Fault Diagnosis Technology Based on CFD

2014 ◽  
Vol 488-489 ◽  
pp. 1219-1223
Author(s):  
Li Jian Ou ◽  
Feng Hong Wang ◽  
Wei Zhang
Keyword(s):  
Fault Diagnosis ◽  
Numerical Model ◽  
Flow Field ◽  
Unsteady Flow ◽  
Hydrodynamic Performance ◽  
Analysis Method ◽  
Fluctuating Pressure ◽  
Ducted Propeller ◽  
Pressure Time ◽  
Ducted Propellers

The numerical model of the unsteady flow field of ducted propellers is based on CFD (computational fluid dynamics). By applying the numerical model, the unsteady flow field of the ducted propeller with the fracture in different positions of a certain blade is simulated and its unsteady hydrodynamic performance is numerically analyzed. By extracting the fluctuating pressure data of the duct inner wall monitoring points,the fluctuating pressure-time oscillogram of ducted propellers is obtained, and then the spectrum is obtained by FFT transformation of the oscillogram. A blade fracture fault diagnosis technology of ducted propellers, which combines oscillogram analysis method with spectrum analysis method, is put forward by analyzing and studying the oscillogram and the spectrum.

scholarly journals Numerical Analysis of Influence of the Hull Couple Motion on the Propeller Exciting Force Characteristics

2019 ◽  
Vol 7 (10) ◽  
pp. 330 ◽  
Author(s):  
Li ◽  
Zhou ◽  
Liu ◽  
Wang
Keyword(s):  
Exciting Force ◽  
Hydrodynamic Performance ◽  
Navier Stokes ◽  
Fluctuating Pressure ◽  
Frequency Peak ◽  
Couple Motion ◽  
Disk Plane ◽  
Bearing Force ◽  
Force Characteristics ◽  
Motion Amplitude

The numerical calculation was performed for the KRISO Container Ship (KCS) hull-propeller-rudder system with different freedom hull motion by employing the Reynolds-Averaged Navier-Stokes (RANS) method and adopting the overset grid. Firstly, the numerical simulation of hydrodynamics for a bare hull with the heave and pitch motion is carried out. The results show that the space non-uniformity of a nominal wake in the disk plane with motion is comparable to the case without motion. However, the time non-uniformity increases sharply and it has a significant positive relationship with the motion amplitude. Then, the propeller exciting force is calculated in the case including single heave, single pitch and their couple motion. It was found that both the ship and propeller hydrodynamic performance deteriorated dramatically due to the hull motion. Furthermore, the spectrum peak at the motion frequency is dominant in all the peak values and the larger the amplitude is, the higher the motion frequency peak is expected to be. For the propeller bearing force, the effect of the different hull motions appears as linear superimposition. However, the superimposition of different hull motions enlarges the propeller-induced fluctuating pressure in a single motion.

An algorithm for Morlet wavelet transform based on generalized discrete Fourier transform

2019 ◽  
Vol 17 (05) ◽  
pp. 1950030
Author(s):  
Hua Yi ◽  
Peichang Ouyang ◽  
Tao Yu ◽  
Tao Zhang
Keyword(s):  
Fourier Transform ◽  
Wavelet Transform ◽  
Discrete Fourier Transform ◽  
Time Domain ◽  
Morlet Wavelet ◽  
Wavelet Function ◽  
Linear Convolution ◽  
Calculation Results ◽  
Morlet Wavelet Transform ◽  
The Time Domain

Continuous wavelet transform (CWT) is a linear convolution of signal and wavelet function for a fixed scale. This paper studies the algorithm of CWT with Morlet wavelet as mother wavelet by using nonzero-padded linear convolution. The time domain filter, which is a non-causal filter, is the sample of wavelet function. By making generalized discrete Fourier transform (GDFT) and inverse transform for this filter, we can get a geometrically weighted periodic extension of the filter when evaluated outside its original support. From this extension of the time domain filter, we can get a causal filter. In this paper, GDFT-based algorithm for CWT, which has a more concise form than that of linear convolution proposed by Jorge Martinez, is constructed by using this causal filter. The analytic expression of the GDFT of this filter, which is essential for GDFT-based algorithm for CWT, is deduced in this paper. The numerical experiments show that the calculation results of GDFT-based algorithm are stable and reliable; the running speed of GDFT-based algorithm is faster than that of the other two algorithms studied in our previous work.

New discrete reactive power factor definition of the two-terminal network

2017 ◽  
Vol 65 (3) ◽  
pp. 369-373
Author(s):  
M. Siwczyński ◽  
M. Jaraczewski
Keyword(s):  
Fourier Transform ◽  
Power Factor ◽  
Reactive Power ◽  
New Method ◽  
Unitary Operators ◽  
Calculation Results ◽  
The Fourier Transform ◽  
Definition Of ◽  
Operator Decomposition

Abstract This paper describes a new method of determining the reactive power factor. The reactive power factor herein is calculated on the basis of time samples and not] with the Fourier transform of signals, like it was done previously. The new reactive power factor calculation results from the receiver admittance-operator decomposition into the product of self-adjoint and unitary operators. This is an alternative decomposition to another one, namely into a sum of the Hermitian and skew-Hemiitian operators.

scholarly journals A Hydrodynamic Methodology And CFD Analysis For Performance Prediction Of Stepped Planing Hulls

2015 ◽  
Vol 22 (2) ◽  
pp. 23-31 ◽  
Author(s):  
Hassan Ghassemi ◽  
Mojtaba Kamarlouei ◽  
Sajad Taj Golah Veysi
Keyword(s):  
High Speed ◽  
Hydrodynamic Performance ◽  
Hydrodynamic Characteristics ◽  
Geometrical Parameters ◽  
Cfd Analysis ◽  
Analysis Model ◽  
Marine Coatings ◽  
Resistance Reduction ◽  
Calculation Results ◽  
Fruitful Research

AbstractNowadays all efforts in planing hull research are focused on resistance reduction for achieving the highest speed in fast planing crafts. Furthermore, many fruitful research projects have been carried out on marine coatings, planing equipment, and optimization of propeller and hull form, which revolutionized industry of high - speed crafts and made them an efficient survival vehicle in coastal areas and rivers. In this paper the hydrodynamic performance of planing hulls are investigated by means of a modified Savitsky model for both non-stepped and stepped bodies. Meanwhile, in order to meet this goal reasonably, effective geometrical parameters of planing hull are investigated and then operational hydrodynamic characteristics of the craft are predicted by using a computational program. Finally, the calculation results are verified by means of a CFD-analysis model.

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