scholarly journals Numerical Studies of Propeller Exciting Bearing Forces under Nonuniform Ship’s Nominal Wake and the Influence of Cross Flows

2017 ◽  
Vol 2017 ◽  
pp. 1-15
Author(s):  
Huilan Yao ◽  
Huaixin Zhang
Keyword(s):  
Velocity Field ◽  
Flow Field ◽  
Water Surface ◽  
Free Water ◽  
Measured Data ◽  
Three Dimension ◽  
Numerical Studies ◽  
Exciting Forces ◽  
The Cross ◽  
Commercial Solver

Propeller exciting forces are the main causes of stern vibrations. In this paper, three-dimension exciting bearing forces of one blade and the whole propeller under nonuniform ship’s wake were predicted, and the influence of cross flows on these exciting forces was studied. All simulations were carried out using a commercial solver, STAR-CCM+. To obtain the nominal wake for studying propeller exciting forces, flow field around a bare hull was simulated. Numerical results were widely validated by measured data, especially the velocity field at the propeller plane. Harmonic characteristics of the nonuniform ship’s wake were studied. Then, a propeller under uniform inflow and nonuniform ship’s wake with/without cross flows was simulated. Free-water surface and hull boundary were considered using a specially designed dummy stern. Results show that the influence of cross flows on propeller exciting forces is obvious. As for the exciting forces of one blade, the cross flows have greater influence on the axial force. As for the exciting forces of the whole propeller, the cross flows have greater influence on the transverse and vertical forces, and if the cross flows in ship’s wake are not considered, the amplitudes of the main harmonics of transverse and vertical forces increase obviously.

Effects of vortex-induced velocity on the development of a synthetic jet issuing into a turbulent boundary layer

2019 ◽  
Vol 870 ◽  
pp. 651-679 ◽  
Author(s):  
Tim Berk ◽  
Bharathram Ganapathisubramani
Keyword(s):  
Velocity Field ◽  
Momentum Transfer ◽  
Momentum Flux ◽  
Cross Flow ◽  
Measured Data ◽  
Velocity Fields ◽  
Synthetic Jet ◽  
Vortical Structures ◽  
The Cross ◽  
Induced Velocity

A synthetic jet issuing into a cross-flow influences the local velocity of the cross-flow. At the jet exit the jet is oriented in the wall-normal direction while the cross-flow is oriented in the streamwise direction, leading to a momentum transfer between the jet and the cross-flow. Streamwise momentum transferred from the cross-flow to the jet accelerates the pulses created by the jet. This momentum transfer continuous up to some point downstream where these pulses have the same velocity as the surrounding flow and are no longer blocking the cross-flow. The momentum transfer from the cross-flow to the jet leads to a momentum deficit in the cross-flow far downstream of the viscous near field of the jet. In the literature this momentum-flux deficit is often attributed to viscous blockage or to up-wash of low-momentum fluid. The present paper proposes and quantifies a third source of momentum deficit: a velocity induced opposite to the cross-flow by the vortical structures created by the synthetic jet. These vortical structures are reconstructed from measured data and their induced velocity is calculated using the Biot–Savart law. The three-dimensional three-component induced velocity fields show great similarity to the measured velocity fields, suggesting that this induced velocity is the main contributor to the velocity field around the synthetic jet and viscous effects have only a small influence. The momentum-flux deficit induced by the vortical structures is compared to the measured momentum-flux deficit, showing that the main part of this deficit is caused by the induced velocity. Variations with Strouhal number (frequency of the jet) and velocity ratio (velocity of the jet) are observed and discussed. An inviscid-flow model is developed, which represents the downstream evolution of the jet in cross-flow. Using the measured data as an input, this model is able to predict the deformation, (wall-normal) evolution and qualitative velocity field of the jet. The present study presents evidence that the velocity induced by the vortical structures forming a synthetic jet plays an important role in the development of and the velocity field around the jet.

Application of L-K Optical Flow Algorithm Mixed with Pyramid on Calculating Water Surface Flow Field

2013 ◽  
Vol 333-335 ◽  
pp. 897-903 ◽  
Author(s):  
Zhao Hui Han ◽  
Yan Feng Wang
Keyword(s):  
Velocity Field ◽  
Flow Field ◽  
Optical Flow ◽  
Water Surface ◽  
Image Sequence ◽  
Surface Flow ◽  
Aperture Problem ◽  
Wind Speeds ◽  
Gaussian Pyramid ◽  
Flow Algorithm

A classical Lucas-Kanade optical flow algorithm was used to analysis the IR Image sequence of the wind-driven surface in this paper. Gaussian pyramid representation was introduced to retain both detail components and veracity for velocity field when considering the aperture problem and robustness. Three layers of pyramid for L-K optical flow is the best comparing with other layers (from one to four) in property. L-K optical flow algorithm mixed with pyramid representation shown an qualified power on calculating water surface flow field, demonstrated by optical flow fields on different wind speeds ( from 3m/s to 6m/s).

Velocity Field Measurements in Wake of a Straight-Bladed Vertical Axis Wind Turbine

2011 ◽  
Author(s):  
Yutaka Hara ◽  
Takahiro Suzuki ◽  
Yuki Ochiai ◽  
Tsutomu Hayashi
Keyword(s):  
Velocity Field ◽  
Flow Field ◽  
Wind Turbine ◽  
Blow Up ◽  
Field Measurements ◽  
Vertical Axis ◽  
Three Dimension ◽  
Vertical Axis Wind Turbine ◽  
Thrust Coefficient ◽  
Bem Theory

Small vertical axis wind turbine (VAWT) is promising for the development of wind energy in the built environment due to its insensitivity to yaw. In general, computer codes based on the blade element and momentum (BEM) theory, which have much less calculation time than CFD codes, are used for design and performance prediction of wind turbines. However, the results on small VAWTs obtained by the BEM theory often do not accord with the experimental results due to the low Reynolds number, the dynamic stall effects, and so forth. The three-dimension nature of the flow field around the VAWT rotor may be one of the reasons for the discord. This study aims to elucidate the actual flow field around small VAWT. In this study, velocity field measurements were carried out in the wake of a small straight-bladed VAWT by using an ultrasonic anemometer. The measurements of the V and W velocity components showed the downwash and the blow-up, which proceeded toward the equator level and merged into the horizontal flow. Counter flow of the U component was also observed in the mainstream direction. The wake velocity profile simulated by using the Double-Multiple Streamtube (DMS) model based on the BEM theory showed a similar behavior to that of the measured wake. However, the high thrust coefficient estimated from the measured deficit in the U velocity component almost doubles the estimation by the BEM theory.

A Wave-Free Floating Body in Swaying Oscillation

1988 ◽  
Vol 110 (4) ◽  
pp. 309-314
Author(s):  
S. Yamashita
Keyword(s):  
Water Surface ◽  
Rectangular Cross Section ◽  
Free Water ◽  
Floating Body ◽  
Free Form ◽  
Free Water Surface ◽  
Submerged Body ◽  
Exciting Forces ◽  
Characteristic Features ◽  
The One

This paper deals with the two-dimensional wave-free floating body which generates no radiating waves at a certain frequency when oscillating horizontally on the free water surface. In order to find the characteristic features of the wave-free form, the streamlines are calculated for the wave-free potential. Two kinds of wave-free bodies are given. The one is a floating body, the surface of which is inclined inwardly just below the free water surface, and the other is a fully submerged body. Numerical computations and experimental measurements of the sway exciting forces in waves are carried out for the wave-free bodies and the existence of the wave-free frequency for swaying oscillation is verified experimentally as well as theoretically. Measurements of the motions in waves are also performed on the inwardly inclined floating body that has mainly rectangular cross section. The experimental results are compared with those of the box-shaped floating body.

EFEKTIVITAS TANAMAN GENJER DALAM MENURUNKAN BOD DAN COD LIMBAH CAIR TAHU HASIL PROSES ANAEROB

2016 ◽  
Vol 4 (1) ◽  
Author(s):  
Muhammad Irvan Nurliansyah
Keyword(s):  
Water Surface ◽  
Free Water ◽  
Surface Flow ◽  
Free Water Surface

ABSTRAK Limbah cair tahu merupakan limbah cair yang berasal dari proses pembuatan tahu. Limbah cair tahu mengandung senyawa organik yang tinggi. Pembuangan limbah cair tahu secara langsung ke badan air tanpa dilakukan pengolahan dapat mempengaruhi dan mencemari lingkungan. Suatu cara untuk menanggulangi permasalahan tersebut adalah melakukan pengolahan limbah cair tahu. Salah satu alternatif pengolahan limbah cair tahu yang dapat digunakan adalah fitoremediasi menggunakan tanaman genjer. Penelitian ini bertujuan untuk mengetahui efisiensi pengolahan dan efektivitas waktu tinggal pengolahan limbah cair tahu menggunakan tanaman genjer dalam menurunkan BOD dan COD effluen hasil proses pengolahan anaerob limbah cair tahu. Metode yang digunakan dalam penelitian ini adalah fitoremediasi menggunakan tanaman genjer pada sistem lahan basah buatan Free Water Surface flow dengan waktu tinggal 3 hari, 5 hari dan 7 hari. Hasil penelitian menunjukkan bahwa efisiensi pengolahan secara fitoremediasi pada hari ke 3 untuk BOD dan COD berturut-turut sebesar 21,28% dan 16,13%. Pada hari ke 5 efisiensi pengolahan yang diperoleh untuk BOD dan COD berturut-turut sebesar 52,60% dan 45,93% sedangkan efisiensi pengolahan pada hari ke 7 untuk BOD dan COD berturut-turut sebesar 76,42% dan 70,74%. Waktu tinggal efektif yang diperoleh pada penelitian ini adalah  7 hari dengan nilai BOD dan COD telah berada dibawah baku mutu yaitu berturut-turut sebesar 72,72 mg/l dan 213,33 mg/l.   Kata kunci : limbah cair tahu, fitoremediasi, tanaman genjer, efisiensi pengolahan, waktu tinggal

Remote turbidity measurement with a laser reflectometer

1998 ◽  
Vol 37 (12) ◽  
pp. 255-261 ◽  
Author(s):  
Mark Johnson
Keyword(s):  
Water Surface ◽  
Free Water ◽  
Optical Scattering ◽  
Flowing Water ◽  
Water Stream ◽  
Water Turbidity ◽  
Water Colour ◽  
Contact Measurement ◽  
Optical Instruments ◽  
Better Than

A simple, laser-based reflectometer is described for the measurement of water turbidity via 180° optical scattering. Applications exist both in clean source waters (0-1000NTU) with a minimum detectable turbidity better than 1NTU, and in dense wastewater primary-clarifier sludges. The non-contact measurement is performed from a distance at least up to 10m, substantially avoiding the usual window fouling problems of optical instruments. By measuring directly in the process, through a free water surface or on the side of a flowing water stream, the difficulties of transporting sample to the instrument are also avoided. Extensions to be described allow measurement also of water colour.

Investigations into and optimisation of the performance of sewage detention tanks during storm rainfall events

1999 ◽  
Vol 39 (2) ◽  
pp. 43-52 ◽  
Author(s):  
R. Kowalski ◽  
J. Reuber ◽  
Jürgen Köngeter
Keyword(s):  
Flow Field ◽  
Pollutant Transport ◽  
Cleaning Efficiency ◽  
Rainfall Events ◽  
Transient Phenomena ◽  
Numerical Studies ◽  
Hydraulic Load ◽  
Storm Rainfall ◽  
Different Levels ◽  
Sewage Systems

Combined Sewage Detention Tanks (CSDT) are components of combined sewage systems commonly used in Germany. A lack of knowledge of the processes occurring within these structures causes the engineer to apply conceptual approaches in the simulation of pollutant transport. The investigations presented were implemented in an integrated systematic way. Extensive analytical, experimental and numerical studies of steady and transient phenomena taking place in CSDTs were carried out simulating different levels of hydraulic load. The study of the flow field and the simulation of sedimentation and erosion under realistic conditions resulted in proposals for modification and optimisation of the function of CSDTs. A simple way of predicting the cleaning efficiency is presented.

A Free Water Surface Constructed Wetland in Treating Sugarcane Wastewater

2011 ◽  
Vol 33 (1) ◽  
pp. 71-86
Author(s):  
Doorce S. Batubara ◽  
Donald Dean Adrian
Keyword(s):  
Constructed Wetland ◽  
Water Surface ◽  
Free Water ◽  
Free Water Surface
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