Hydrodynamic Loads on Net Panels With Different Solidities

2021 ◽  
Vol 143 (5) ◽  
Author(s):  
Heidi Moe Føre ◽  
Per Christian Endresen ◽  
Carina Norvik ◽  
Pål Lader

Abstract Drag forces on nets represent the largest contribution to hydrodynamic loads on traditional fish farms and will have a large impact on total loads on new designs utilizing netting as containment method. Precise methods for estimation of drag loads are needed. This article gives new knowledge on hydrodynamic forces acting on aquaculture nets. It presents results from towing tests, including updated drag and lift coefficients for Raschel-knitted netting materials used in nets for aquaculture, and quantify wake effect. The results include high solidity nets and high towing velocities. It was found that drag loads were close to proportional with the netting solidity for netting solidities ranging from 0.15 to 0.32. The wake effect is quantified through the average velocity reduction factor, which is given as a linear function of solidity. Much of the previously published data are close to the data found through these tests. However, for high solidity nets, the deviation is significant. Therefore, previously published data and models may overestimate drag loads for high solidity nets.

Author(s):  
Heidi Moe Føre ◽  
Per Christian Endresen ◽  
Carina Norvik ◽  
Pål Lader

Abstract Drag forces on nets represent the largest contribution to hydrodynamic loads on traditional fish farms, and will have a large impact on total loads on new designs utilizing netting as containment method. Precise methods for estimation of drag loads are needed. This paper gives new knowledge on hydrodynamic forces acting on aquaculture nets. It presents results from towing tests, including updated drag and lift coefficients for Raschel knitted netting materials used in nets for aquaculture, and quantify wake effect. The results include high solidity nets and high towing velocities. It was found that drag loads were close to proportional with the netting solidity for netting solidities ranging from 0.15 to 0.32. The wake effect is quantified through the average velocity reduction factor, which is given as a linear function of solidity. Much of previously published data are close to the data found through these tests. However, for high solidity nets, the deviation is significant. Therefore, previously published data and models may overestimate drag loads for high solidity nets.


Author(s):  
E. S. Perrot ◽  
N. W. Mureithi ◽  
M. J. Pettigrew ◽  
G. Ricciardi

This paper presents test results of vibration forces in a normal triangular tube bundle subjected to air-water cross-flow. The dynamic lift and drag forces were measured with strain gage instrumented cylinders. The array has a pitch-to-diameter ratio of 1.5, and the tube diameter is 38 mm. A wide range of void fraction and fluid velocities were tested. The experiments revealed significant forces in both the drag and lift directions. Constant frequency and quasi-periodic fluid forces were found in addition to random excitation. These forces were analyzed and characterized to understand their origins. The forces were found to be dependent on the position of the cylinder within the bundle. The results are compared with those obtained with flexible cylinders in the same tube bundle and to those for a rotated triangular tube bundle. These comparisons reveal the influence of quasi-periodic forces on tube motions.


Sarwahita ◽  
2015 ◽  
Vol 12 (1) ◽  
pp. 54-62
Author(s):  
I. Gusti Ayu Ngurah S

ABSTRAK  Pengabdian ini mempunyai tujuan untuk  memberikan pengetahuan dan pengajaran mengenai pembuatan tepung mocaf dan penggunaannya sebagai bahan dasar pengganti tepung terigu dalam pembuatan mie sehingga dapat membantu ibu-ibu di Desa Jaya Sakti dalam memenuhi kebutuhan mereka membuat mie dari tepung mocaf dengan harapan hasil produk dapat dijual sehingga dapat menambah income bagi keluarga mereka. Khalayak sasaran adalah Ibu-ibu PKK dan warga sekitar Desa Jaya Sakti. Pelatihan ini di laksanakan dalam satu kali pertemuan, Pertemuan dilakukan di rumah Kepala Desa Jaya Sakti Muaragembong Bekasi Pertemuan diawali dengan pembukaan kemudian memberikan materi dan praktek pembuatan tepung mocaf, dan pembuatan mie dari tepung mocaf. Untuk bahan dasar mie tepung mocaf digunakan yang telah siap pakai. Tepung  Mocaf  (Modified  Cassava  Flour),  adalah produk tepung  dari ubi kayu/singkong yang diperoses menggunakan prinsip memodifikasi sel ubi kayu dengan cara fermentasi. Mikroba yang tumbuh menyebabkan perubahan karakteristik pada tepung yang dihasilkan, yaitu naiknya viskositas, kemampuan gelasi, daya rehidrasi, dan kemudahan melarutkan. Mikroba   juga   menghasilkan   asam-asam   organic,   terutama   asam   laktat   yang   akan terimbibisi dalam tepung, dan ketika tepung itu diolah akan menghasilkan aroma dan citra rasa khas, yang dapat menutupi aroma dan citra rasa ubi kayu yang cenderung tidak menyenangkan konsumen. Tekstur dan warna tepung mocaf ini lebih halus dan lebih putih dari tepung terigu. Untuk   pengembangan   lebih   lanjut,   maka   tepung   mocaf   diaplikasikan   untuk membuat mie, selain nilai jualnya lebih baik lagi karena menghasilkan produk yang lain dan langsung bisa di konsumsi. Dari hasil kegiatan pengabdian ini terlihat antusias dari para peserta, karena mereka senang mendapatkan pengetahuan baru yang dapat mereka praktekkan di rumah masing- masing.   ABSTRACTThis dedication aims to provide knowledge and teaching about making mocaf flour and its use as a substitute of wheat flour in making noodles so it can help mothers in Jaya Sakti Village in fulfilling their need to make noodles from mocaf flour in the hope that the product can be sold so that can increase income for their families.Target audiences are PKK mothers and residents around Jaya Sakti Village. Trainingthis was held in one meeting, the meeting was held at the Village Head's houseJaya Sakti Muaragembong BekasiThe meeting begins with the opening then gives the material and practice of making mocaf flour, and making noodles from mocaf flour. For basic materials used mocaf flour noodles that have been ready to use.Mocaf Flour (Modified Cassava Flour), is a flour product of cassava / cassava that is processed using the principle of modifying cassava cells by fermentation. Increased microbes cause characteristic changes in the resulting flour, namely increased viscosity, gelability, rehydration, and ease of dissolution. Microbes also produce organic acids, especially lactic acid which will be added to the flour, and when the flour is processed it will produce a distinctive flavor and taste image, which can mask the flavor and taste of cassava that tend to discomfort the consumer. The texture and color of the mocaf flour is finer and whiter than wheat flour.For further development, then the mocaf flour is applied tomaking noodles, in addition to the selling price is better because it produces other products and can directly in consumption.From the results of this devotional activity look enthusiastic from the participants, because they love to get new knowledge that they can practice in their homes.


Author(s):  
Ugur Can ◽  
Sakir Bal

In this study, it was aimed to obtain an accurate extrapolation method to compute lift and drag forces of high-speed vessels at full-scale by using CFD (Computational Fluid Dynamics) based GEOSIM (GEOmetrically SIMilar) method which is valid for both fully planing and semi-planing regimes. Athena R/V 5365 bare hull form with a skeg which is a semi-displacement type of high-speed vessel was selected with a model family for hydrodynamic analyses under captive and free to sinkage/trim conditions. Total drag and lift forces have been computed for a generated GEOSIM family of this form at three different model scales and full-scale for Fr = 0.8 by an unsteady RANS (Reynolds Averaged Navier–Stokes) solver. k–ε turbulence model was used to simulate the turbulent flow around the hulls, and both DFBI (Dynamic Fluid Body Interaction) and overset mesh technique were carried out to model the heave and pitch motions under free to sinkage/trim condition. The computational results of the model family were used to get “drag-lift ratio curve” for Athena hull at a fixed Fr number and so the corresponding results at full scale were predicted by extrapolating those of model scales in the form of a non-dimensional ratios of drag-lift forces. Then the extrapolated full-scale results calculated by modified GEOSIM method were compared with those of full-scale CFD and obtained by Froude extrapolation technique. The modified GEOSIM method has been found to be successful to compute the main forces (lift and drag) acting on high-speed vessels as a single coefficient at full scale. The method also works accurately both under fully and semi-planing conditions.


Author(s):  
Paul E. Thomassen ◽  
Bernt J. Leira

Floating fish cages provide the main production utilities for salmon farming. However, despite their pivotal role in production safety as well as in protection of the environment, there is still much room for improvement in relation to verified structural design procedures and computerized tools for structural analysis. To a large extent they can be regarded as not being in accordance with the state-of-the-art of structural analysis and design for more traditional types of marine structures. In this paper a study of fatigue design for floating fish farms is presented. The study is based on a structure which is being applied by the Norwegian fish farming industry today. The floater is made of steel cylinders which are configured as a square. The formulation for the wave loading is based on a combination of potential theory and horizontal drag forces on the floater. Horizontal and vertical drag forces on the netpen are also accounted for. A fatigue design procedure for floating fish farms in steel is suggested. The procedure is based on a time domain analysis of the structure in irregular waves. For each seastate half an hour (real time) analysis is performed and the stress history for an assumed critical location is computed. Based on the stress histories, the fatigue damage is estimated by application of rain flow counting and a given SN curve. The scatter diagram for the seastates at a given location is generated from the associated wind speed distribution.


1992 ◽  
Vol 114 (2) ◽  
pp. 91-103 ◽  
Author(s):  
A. R. Anaturk ◽  
P. S. Tromans ◽  
H. C. van Hazendonk ◽  
C. M. Sluis ◽  
A. Otter

A new semi-empirical model is derived for calculations of hydrodynamic damping (or drag) forces on smooth or rough cylinders oscillating at small amplitude and high frequency. This model covers the attached flow regime where the conventional Morison’s equation fails to simulate the drag forces acting on circular cylinders. It involves the calculation of the energy dissipated in the boundary layer on the cylinder surface. The empirical input data for the model are amplitude and phase of the wall shear stresses on the cylinder. The model is verified against fluid force measurements from a test tank and published data. These experiments were carried out at small-amplitude / high-frequency with smooth and rough circular cylinders. Data from the literature is also included for verification. Results from the present work can be used to estimate hydrodynamic damping forces for the analysis of jack-up response around resonant frequency. Other applications are dynamic behavior of jackets during installation, SALMs, TLPs and risers.


2021 ◽  
Author(s):  
Heidi Moe Føre ◽  
Per Christian Endresen ◽  
Hans V. Bjelland

Abstract New types of fish farms are often larger and structurally more complex than conventional fish farming structures, and associated challenges concerning safety and costs increase correspondingly. Thus, increased precision in structural design is required, with estimation of hydrodynamic loads on nets as an important topic. Today, both load coefficients for nets and measured netting dimensions are given with relatively high uncertainties. New knowledge for netting materials with high solidities as well as scaled netting commonly applied in model tests are included in the presented study. Results from towing tests and the development of a new mathematical expression for local drag coefficients (for netting twines) indicate that drag coefficients are not only dependent on solidity and Reynolds number, but may also be affected by the velocity reduction and the local velocity at the twines.


2019 ◽  
Vol 141 (5) ◽  
Author(s):  
Nur Alom ◽  
Ujjwal K. Saha

The elliptical-bladed Savonius wind turbine rotor has become a subject of interest because of its better energy capturing capability. Hitherto, the basic parameters of this rotor such as overlap ratio, aspect ratio, and number of blades have been studied and optimized numerically. Most of these studies estimated the torque and power coefficients (CT and CP) at given flow conditions. However, the two important aerodynamic forces, viz., the lift and the drag, acting on the elliptical-bladed rotor have not been studied. This calls for a deeper investigation into the effect of these forces on the rotor performance to arrive at a suitable design configuration. In view of this, at the outset, two-dimensional (2D) unsteady simulations are conducted to find the instantaneous lift and drag forces acting on an elliptical-bladed rotor at a Reynolds number (Re) = 0.892 × 105. The shear stress transport (SST) k–ω turbulence model is used for solving the unsteady Reynolds averaged Navier–Stokes equations. The three-dimensional (3D) unsteady simulations are then performed which are then followed by the wind tunnel experiments. The drag and lift coefficients (CD and CL) are analyzed for 0–360 deg rotation of rotor with an increment of 1 deg. The total pressure, velocity magnitude, and turbulence intensity contours are obtained at various angles of rotor rotation. For the elliptical-bladed rotor, the average CD, CL, and CP, from 3D simulation, are found to be 1.31, 0.48, and 0.26, respectively. The average CP for the 2D elliptical profile is found to be 0.34, whereas the wind tunnel experiments demonstrate CP to be 0.19.


Author(s):  
Rodolfo Marcilli Perissinotto ◽  
William Monte Verde ◽  
Jorge Luiz Biazussi ◽  
Marcelo Souza de Castro ◽  
Antonio Carlos Bannwart

The objective of this research is to investigate the path of oil drops within an Electrical Submersible Pump (ESP) impeller, to evaluate its size and velocity as function of water flow rate and the ESP rotation speed. An experimental study was conducted at University of Campinas - Brazil with an ESP prototype designed to allow flow visualization within the impeller through a transparent shell. A high-speed camera with lighting set captures images of the oil droplets at a rate of 1000 frames per second. The set of data was performed at three rotational speeds — 600 rpm, 900 rpm and 1200 rpm — for three water flow rates — 80%, 100% and 120% of the best efficiency point (BEP). The results reveal that the oil drops become smaller when the rotational speed increases. The same behavior is noticed when the water flow rate increases. Generally, the oil droplets have spherical and elliptical shapes that change as function of their position inside the impeller channel. Furthermore, the drops have random trajectories, but a pattern can be detected in three cases: droplets near the pressure blade, droplets near the suction blade and droplets that move from the suction blade to the pressure blade. The average velocity of the oil droplets that move near the suction blade is significantly higher than the average velocity of the droplets that move near the pressure blade. Velocity changes as function of the impeller radius suggest different accelerations that may be caused by drag forces and pressure forces. The size of the oil drops has no significant influence on their velocities.


2003 ◽  
Vol 125 (1) ◽  
pp. 149-157 ◽  
Author(s):  
Tahsin Engin ◽  
Mesut Gur

In order to optimally design a slurry transportation system, it is necessary to know how the presence of solids will change the performance of the slurry pump to be installed. This paper makes the comparison of some existing correlations available in the literature to predict the head reduction factors of such centrifugal pumps handling slurries. For this purpose, a large number of published data for various centrifugal slurry pump tests in the literature have been used to develop a new correlation and then this correlation and all others have been tested against the data. For the proposed correlation, the mean and average deviations between the calculated and measured head reduction factor is 8.378 and 0.620%, respectively, for all data of mostly handling commercial slurries. It also produces 12.441% mean deviation in the prediction of efficiency ratio for 216 data points. Overall, the new correlation that can be applied to both metal and rubber lined pumps with impeller diameter up to 850 mm, gives remarkably closer fit to the published data of both head and efficiency ratios than all existing correlations.


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