Wave Induced Deformation and Stress Responses in HDPE Circular Net Cage: A Numerical Approach

2012 ◽  
Vol 217-219 ◽  
pp. 2299-2303
Author(s):  
Jian Hang Du ◽  
Zhen He ◽  
Feng Lin Yan ◽  
Guo Yan Yu

A 3D numerical model was developed to analyze the deformation and stress characteristics of HDPE material circular net cage exposed to waves, using the finite element method (FEM). The total wave forces acting on the structure were evaluated with method combining analytical and numerical, and served as boundary conditions during the simulation. Testing cases were performed eventually based on the actual conditions in Zhanjiang bay. The results show that wave height is an important factor that affects the dynamics response characteristics of net cages as well as the working conditions of the cages in sea environment, and the peak stress of the flotation structure always occurs at the mooring points. We also suggest that the net cages that constructed inside Zhanjiang Bay may not fail even during the storm process when in normal working condition.

2021 ◽  
Vol 9 (12) ◽  
pp. 1445
Author(s):  
Mingyuan Ma ◽  
Hong Zhang ◽  
Dong-Sheng Jeng ◽  
Chien Ming Wang

In the present study, a semi-analytical model based on the small-amplitude wave theory is developed to describe the wave fields around a single gravity-type cylindrical open fish net cage. The cage may be submerged to different depths below the free-water surface. The fish cage net is modelled as a flexible porous membrane, and the deflection of the net chamber is expressed by the transverse vibration equation of strings. The velocity potential is expanded in the form of the Fourier–Bessel series and the unknown coefficients in these series are determined from matching the boundary conditions and the least squares method. The number of terms for the series solution to be used is determined from convergence studies. The model results exhibit significant hydroelastic characteristics of the net cages, including the distribution properties of wave surface, pressure drop at the net interface, structural deflection, and wave loading along the cage height. In addition, the relationships between wave forces on the net cage with hydrodynamic and structural parameters are also revealed. The findings presented herein should be useful to engineers who are designing fish cage systems.


Author(s):  
Kyujin Shim ◽  
Pascal Klebert ◽  
Arne Fredheim

Structure and design of fish cages can be improved by the knowledge of the flow pattern around and inside the net cages. To address this problem, commercially available computational fluid dynamics (CFD) software is used to analyze this problem by calculating the drag and the flow velocity distribution around cylinders with different porosities. The results of these simulations are compared with the data from experiments which have been previously published. Aquaculture cages are very large structures that consist mainly of netting, which can be approximated by small cylinders connected at knots. But due to the large number of these cylinders (millions for a single salmon farming cage), it is computationally expensive to model the exact geometry. Bio fouling is another factor which is of particular interest as fouled nets (lower porosity) can significantly reduce flow of well-oxygenated water reaching the fish during normal rearing conditions. Therefore the numerical approach used to simulate the flow through and around the net cage is to consider it as a circular cylinder with a porous jump boundary. Drag coefficient and flow pattern are compared with available experimental data. Vertical cylinders are used for this study. Different porosities have been used for the simulations as for the experiments (0%, 75%, 82% and 90% open area) in order to simulate the impact of the fouling on the load of the net structures and the flushing of the cage. The results show that a porous jump with a pressure drop proportional to velocity squared has the best agreement with measured data.


2021 ◽  
Vol 2021 ◽  
pp. 1-9
Author(s):  
Fenghui Li ◽  
Yunhai Cheng ◽  
Fei Wu ◽  
Chang Su ◽  
Gangwei Li

Shotcrete is often subject to poor ductility and cracking problems, particularly under high stresses. In order to deal with these issues, the feasibility of adding polypropylene macrofibers to shotcrete was verified. To ascertain the supporting effect, dry shotcrete, wet shotcrete, and wet polypropylene macrofiber-reinforced shotcrete (WPMS) were used as samples. Furthermore, the mechanical response characteristics thereof in uniaxial compression tests were compared and analyzed by acoustic emission (AE) monitoring. The results showed that the three materials were brittle, but the ductility, residual strength, and bearing capacity of polypropylene macrofiber-reinforced shotcrete were significantly enhanced. The energy absorption value of plain shotcrete was higher in the cracking stage, while that of polypropylene macrofiber-reinforced shotcrete was greater in the postpeak stage, which showed that the polypropylene macrofiber-reinforced shotcrete had the characteristics of a high crack-initiation strength and toughness. Besides, the energy release from fiber shotcrete occurred after the peak stress rather than near the peak stress. The average energy absorbed by polypropylene macrofiber-reinforced shotcrete was significantly higher than that in dry shotcrete and wet shotcrete, which implied that polypropylene macrofiber-reinforced shotcrete could mitigate the brittle instability of a shotcrete layer. A constitutive model of damage statistics was established based on the test data. The comparison between the experimental data and the fitting results can reflect the characteristics of the total stress-strain curve of such shotcrete. The results provide a basis for the optimization of polypropylene macrofiber-reinforced shotcrete layers.


1999 ◽  
Vol 43 (04) ◽  
pp. 229-240
Author(s):  
H. R. Riggs ◽  
R. C. Ertekin

One design for a mobile offshore base is to link serially as many as five large semisubmersibles to form a platform long enough to support large aircraft. This paper investigates the linear, wave-induced response characteristics of serially-connected semisubmersibles. A major motivation of this study is to understand more completely the forces required to link semisubmersible modules. The impact of connector strategy and damping on the response, especially the connector forces, is investigated, and the response "modes" which contribute to the connector forces are evaluated in detail. It is shown that the response characteristics can be impacted significantly by the connection strategy, and that connector damping can be a significant source of energy loss when compared to radiation damping. The wet natural frequencies and normal modes are also determined and used to explain the response characteristics of different connection strategies. Although the analyses are based on a specific semisubmersible design, the results provide insight on how other systems of connected semisubmersibles would likely behave.


2017 ◽  
Vol 2017 ◽  
pp. 1-11 ◽  
Author(s):  
Tingye Qi ◽  
Guorui Feng

To understand the characteristics of the acoustic emission (AE) and electrical resistivity of cemented coal gangue backfill (CGB) under uniaxial compression, the variations in these characteristics at 1 day, 3 days, and 7 days are analyzed by means of a stress-strain-resistivity-AE test, and the microperformances are investigated. The research results indicate that the AE can reflect the initiation and propagation of cracks and later explain the variation of the resistivity of the specimens under the uniaxial loading. The cumulative energy curve of AE is approximately two straight lines corresponding to the peak stress, and the difference in the linear slope gradually decreased with the increasing curing time due to the lower pore solution content and the compact pore structure. The relationships between the stress and resistivity and the loading condition before and after the peak stress at different curing times were established. Therefore, it is of great significance to predict the stability of the filling body by monitoring the AE and resistivity variations of the filling body. In addition, it is possible to calculate the roof stress using the relation equation between the resistivity and stress.


Author(s):  
Longfei Xiao ◽  
Jianmin Yang ◽  
Zhiqiang Hu

The low frequency (LF) response of a soft yoke moored 160kDWT FPSO in shallow water is investigated by conducting frequency domain computations and wave basin model tests. An incident wave with Hs = 4.1m and Tp = 8.9s is applied. An obvious LF part appears in the measured wave spectrum at water depth of 16.7m. As a result, the 1st order LF wave force exists and is much larger than the 2nd one. The difference of the spectrums is about one hundred times. The LF wave drift force increases enormously. Consequently, much larger resonant surge response is induced. The LF surge amplitude at h = 16.7m is about 7 times the one at h = 29.0m and 9 times the one in deep water, although the 2nd order response changes a little. Therefore, in very shallow water, LF part of incident waves should be taken into account carefully and LF wave forces and wave induced motions will be very serious.


1982 ◽  
Vol 1 (18) ◽  
pp. 108
Author(s):  
Bernard LeMehaute ◽  
James Walker ◽  
John Headland ◽  
John Wang

A method of calculating nonlinear wave induced forces and moments on piles of variable diameter is presented. The method is based on the Morrison equation and the linear wave theory with correction parameters to account for convective inertial effects in the wave field. These corrections are based on the stream function wave theory by Dean (1974). The method permits one to take into account the added wave force due to marine growth in the intertidal zone or due to a protective jacket, and can also be used to calculate forces on braces and an array of piles.


2020 ◽  
Vol 2 (1) ◽  
pp. 51-62
Author(s):  
Budiman Budiman ◽  
Daharmi Astuti

Purpose: This study aims to determine the contract system used and the profit-sharing system of floating net cages in Merangin Village, Kuok District, Kampar Regency. Method: field research using a descriptive qualitative analysis approach. Data collected through interviews and direct observation. Finding: the results of the study revealed that in the practice of floating net cage fish cages between cage owners and employees namely Syirkah Mudharabah, in terms of the legal aspects of the Mudharabah Syirkah, the Rukun Syirkah Mudharabah, Terms, Principles, Contracts and Profit Sharing (profits and losses) that contained in the study of Muamalah Jurisprudence. Implication: socialization about business cooperation needs to be carried out in the perspective of the Shari'ah by relevant parties, to increase the understanding of the local community about the concept of business cooperation following Islamic Shari'ah


2019 ◽  
Vol 7 (3) ◽  
pp. 256
Author(s):  
Carolus P Paruntu ◽  
Suria Darwisito ◽  
Antonius P Rumengan ◽  
Hengky J Sinjal ◽  
Billy Wagey ◽  
...  

The purpose of the community partnership program is to increase the capacity of independent and sustainable marine fish farmers groups.  Specific targets are 1) Increasing the quantity and quality of fish products from marine aquaculture in floating net cages, and 2) Enhancing partners' understanding and skills in terms of effective and efficient marine fish aquaculture technology in floating net cages. The main problems recorded, namely: 1) lack of knowledge of marine fish aquaculture technology in floating net cage; 2) fish harvest time that requires a long time, and 3) poor financial management.  To overcome these problems, an approach is carried out through direct education and training, mentoring, and management of fisheries business management in the field to partners.  After that, each trainee in the partner group is given the opportunity until they can do it themselves.  The target that will be achieved at the end of this education and training is that all group members and their families have knowledge of: 1) superior marine fish polyculture technology in floating net cage and 2) good financial management. Keywords: Fish cultivator group, floating net cage, South Motandoi village, financial management, marine fish polyculture technologyAbstrakTujuan program kemitraan masyarakat (PKM) adalah meningkatkan kapasitas kelompok pembudidaya ikan laut yang mandiri dan berkelanjutan. Target khusus adalah 1) peningkatan kuantitas dan kualitas produk ikan hasil budidaya laut dalam karamba jaring apung, dan 2) peningkatan pemahaman dan ketrampilan mitra dalam hal teknologi budidaya ikan laut dalam karamba jaring apung yang efektif dan efisien. Permasalahan utama yang terekam, yaitu: 1) kurang pengetahuan tentang teknologi budidaya ikan laut dalam karamba jaring apung (KJA); 2) waktu panen ikan yang membutuhkan waktu yang lama, serta 3) pengelolaan keuangan yang kurang baik. Untuk mengatasi masalah tersebut dilakukan pendekatan melalui penyuluhan dan pelatihan, pendampingan, dan pendidikan manajemen usaha perikanan secara langsung di lapangan kepada mitra. Setelah itu, setiap peserta pelatihan dalam kelompok mitra tersebut diberikan kesempatan sampai mereka bisa melakukannya sendiri.  Target akhir yang dicapai dalam PKM ini adalah semua anggota kelompok maupun keluarganya mempunyai pengetahuan tentang: 1) teknologi polikultur budidaya ikan laut dalam karamba jaring apung yang unggul, dan 2) manajemen keuangan yang baik.  Kata-kata kunci: Kelompok pembudidaya ikan, karamba jaring apung, Desa Motandoi Selatan, manajemen keuangan, teknologi polikultur ikan laut


2018 ◽  
Vol 8 (9) ◽  
pp. 1517 ◽  
Author(s):  
Chungkuk Jin ◽  
Junho Choi ◽  
Moo-Hyun Kim

This paper investigates the response characteristics of a stow net under wave and current excitations, as well as the feasibility of its monitoring system to check net functionality and prevent loss of fishing gears. The stow-net model is based on one of existing types used in southwest coast of South Korea. The measured wave and current data there are acquired and inputted as environmental loads for numerical simulations. The Morison equation for a moving object with equivalent net model is utilized as the external-force estimator, which has been validated by many researchers regarding fish-cage studies. Since the modelling of all the net elements is inefficient in terms of computational time in time-domain simulations, cruder equivalent-drag net elements are devised with equivalent wet mass, projected area, and axial stiffness. The performance of stow net is highly influenced by current velocity. Stow nets submerge more in stronger currents, which results in less wave forces. The proposed monitoring system can provide useful information, such as net functionality and loss of stow net, using the minimum number of monitoring sensors.


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