Cage Deformations Research Articles

Fluid–Structure Interactions of Net Cages—Full-Scale Pushing Tests in the Field

Abstract This paper presents field tests on a full-scale cage, with and without fish, being pushed by a boat in Masfjorden at various speeds. The purpose was to imitate the exposure of net cages to different currents. The tests involved measuring cage deformations, fish behaviors, and the corresponding flow upstream, downstream, and inside the cage. The study found that the experimental setup used can achieve predictable and stable upstream flow for a full-scale net cage. Based on pressure tag data, the volume reductions of the cage, both with and without fish, were estimated at different speeds. Both cases show a similar trend of cage volume reduction with respect to flow speeds as the previous studies. Moreover, the presence of fish had limited the influence on the net volume change. The reduction in speed inside and downstream from the cage was within the range reported in previous literature. Notably, when the cage becomes significantly deformed, it not only reduces flow speed but also alters flow directions, as evidenced by the high variability of flow direction inside the empty cage, particularly at high speeds. The measured flow speed inside the stocked cage also exhibited high variability, but the pattern of variation differed significantly from that of the empty cage, indicating the influence of fish. These findings suggest that traditional flow speed models might oversimplify the flow field in and around fish cages, especially in studies concerning the dispersion of particles, pathogens, and dissolved matter in and out of fish cages.

Comparative study of circular and square gravity-based fish cages with different dimensions under pure current conditions

Two typical gravity-based fish cages with circular and square shapes are modeled in the present study to compare their cage deformations, cultivation volumes and drag forces under different pure current conditions. Two hydrodynamic models, i.e., Morison model and Screen model, are implemented into a general finite element (FE) solver Code_Aster as a new module and employed in the dynamic analyses of the fish cages. Different cage dimensions (i.e., circumferences and design heights) and current velocities are considered in the comparative study. The numerical results indicate that given the same area of netting, the circular cage can gain more cultivation volume than the square cage, especially when the initial cage volume is larger than 100,000 m3. The square cage has a slightly larger drag force per cultivation volume than the circular cage. This study suggests that the circular cage is superior to the square fish cage for large-scale fish farms.

An integrated approach for monitoring structural deformation of aquaculture net cages

The majority of present marine finfish production is conducted in flexible net cages which can deform when they are subjected to water movements generated by currents. The ability to monitor net deformation is important for performing cage operations and evaluation of fish health and welfare under changing environment. This paper presents a new method for real-time monitoring of net cage deformations that is based on an integrated approach where positioning sensor data is incorporated into a numerical model. An underwater positioning system was deployed at a full-scale fish farm site, with three acoustic sensors mounted on a cage measuring positions of the net at different depths. A novel numerical model with an adaptive current field was used to simulate net cage deformations, where the magnitude and direction of the current could be adapted by continuously assessing deviations between the simulated and the measured positions of the net. This method was found to accurately predict the pre-defined current velocity profiles in a set of simulated experiments. In the field experiment, a good agreement was also obtained between the simulated positions of the net and the acoustic sensor data. The integrated approach was shown to be well suited for in-situ real-time monitoring of net cage deformations by using a significantly reduced number of sensors.

Context analysis of Offshore Fish Farming

The in-land and nearshore fish farming is facing capacity limitation and onshore push-out regulations. Huge technological innovations are rapidly evolving toward developing competitive Offshore fish farming. These technological innovations are mainly targeting to innovate new farming concepts that dynamically stable, reliable and compatible with offshore environmental loads and conditions. The dynamic operational behaviour of each farming concept is quite complicated. It is a combination of reinforcing behaviours (Loads, cage deformations, welfare issues, e.g. escaping, stress-related disease) and leveraging behaviours (Biofouling-cleaning, Deterioration-maintenance) and all influenced by fluctuating and harsh environmental loads and conditions. Therefore, the purpose of this paper is to analyse the context of offshore fish farming and explore quantitative descriptions of its reinforcement and leveraging behaviours. The context analysis is a well-known method within systems engineering methodology to illustrate and extract critical interfaces. The context analysis is considered as the first step in building simulation model to quantify the impact of systems interfaces on the entire farming economics, i.e. income and cost.

Effects of the CO₂ Guest Molecule on the sI Clathrate Hydrate Structure.

This paper analyzes the structural, energetic and mechanical properties of carbon dioxide hydrate clathrates calculated using finite cluster and periodic ab initio density-functional theory methodologies. Intermolecular interactions are described by the exchange-hole dipole moment method. The stability, gas saturation energetics, guest–host interactions, cage deformations, vibrational frequencies, and equation of state parameters for the low-pressure sI cubic phase of the CO2@H2O clathrate hydrate are presented. Our results reveal that: (i) the gas saturation process energetically favors complete filling; (ii) carbon dioxide molecules prefer to occupy the larger of the two cages in the sI structure; (iii) blue shifts occur in both the symmetric and antisymmetric stretching frequencies of CO2 upon encapsulation; and (iv) free rotation of guest molecules is restricted to a plane parallel to the hexagonal faces of the large cages. In addition, we calculate the librational frequency of the hindered rotation of the guest molecule in the plane perpendicular to the hexagonal faces. Our calculated spectroscopic data can be used as signatures for the detection of clathrate hydrates in planetary environments.

Structural response of high solidity net cage models in uniform flow

Hydrodynamic loads acting on a fish farm may be affected by the growth of different biofouling organisms, mainly due to increased solidity of the nets. In this paper, the hydrodynamic loads acting on high solidity net cage models subjected to high uniform flow velocities and the corresponding deformation of the net cages are studied. Model tests of net cylinders with various solidities were performed in a flume tank with a simulated current. Standard Morison-type numerical analyses were performed based on the model tests, and their capability of simulating the occurring loads and the observed net cage deformations for different flow velocities was evaluated.Large deformations of the net cage models were observed, and at high velocities the deformations were close to what is physically possible. Net cage deformation appeared to be less dependent on solidity than on flow velocity and weights. Drag forces increased with increasing flow velocity and were dependent on both bottom weights and netting solidity. For the lowest solidity net, drag forces were close to proportional to flow velocity. For the three high solidity nets, the measured drag forces were of similar magnitude, and drag increased less with increasing flow velocity above approximately 0.5m/s than at lower velocities.This study shows that a basic reduced velocity model is not sufficient to model the interaction between the fluid flow and net (hydroelasticity) for high solidity net cages subjected to high flow velocities.The standard numerical analysis was in general able to make good predictions of the net shape, and was capable of making an acceptable estimate of hydrodynamic loads acting on the lowest solidity net model (Sn=0.19). For high solidities and large deformations, numerical tools should account for changes in water flow and the global drag coefficient of the net.

Three-dimensional deformation of a large circular flexible sea cage in high currents: Field experiment and modeling

This paper presents the full-scale measurements of the deformation and current reduction of a large-scale fish sea cage submitted to high currents. Pressure tags were used to measure the cage deformation and the vertical displacement of the bottom ring, while an Acoustic Doppler Current Profiler (ADCP) and Acoustic Doppler Velocimeter (ADV) were used to measure the current reduction. The results show a reduction of 30% of the cage volume for current velocity above 0.6m/s. The measured current reduction in the cage was 21.5%. A simulation model based on super-elements describing the cage shape was applied, and the results show good agreement with the cage deformations. Also the current flow measurements show the interaction between the sea cage and the bathymetry chart.

Selective Degree Elevation for Multi‐Sided Bézier Patches

AbstractThis paper presents a method to selectively elevate the degree of an S‐Patch of arbitrary dimension. We consider not only S‐Patches with 2D domains but 3D and higher‐dimensional domains as well, of which volumetric cage deformations are a subset. We show how to selectively insert control points of a higher degree patch into a lower degree patch while maintaining the polynomial reproduction order of the original patch. This process allows the user to elevate the degree of only one portion of the patch to add new degrees of freedom or maintain continuity with adjacent patches without elevating the degree of the entire patch, which could create far more degrees of freedom than necessary. Finally we show an application to cage‐based deformations where we increase the number of control points by elevating the degree of a subset of cage faces. The result is a cage deformation with higher degree triangular Bézier functions on a subset of cage faces but no interior control points.

Yielding of binary colloidal glasses

The rheological response, in particular the non-linear response, to oscillatory shear is experimentally investigated in colloidal glasses. The glasses are highly concentrated binary hard-sphere mixtures with relatively large size disparities. For a size ratio of 0.2, a strong reduction of the normalized elastic moduli, the yield strain and stress and, for some samples, even melting of the glass to a fluid is observed upon addition of the second species. This is attributed to the more efficient packing, as indicated by the shift of random close packing to larger total volume fractions. This leads to an increase in free volume which favours cage deformations and hence a loosening of the cage. Cage deformations are also favoured by the structural heterogeneity introduced by the second species. For a limited parameter range, we furthermore found indications of two-step yielding, as has been reported previously for attractive glasses. In samples containing spheres with more comparable sizes, namely a size ratio of 0.38, the cage seems less distorted and structural heterogeneities on larger length scales seem to become important. The limited structural changes are reflected in only a small reduction of the moduli, yield strain and stress.

Infrared spectra and structures of diamantyl and triamantyl carbocations

Gas-phase infrared spectra have been recorded for the diamantyl and triamantyl carbocations by infrared multiple photon dissociation (IRMPD) spectroscopy using the free electron laser FELIX. Chemical ionization of the neutral parent diamondoid molecule in an rf ion trap is accompanied by H-atom loss, forming a stable closed-shell carbocation. Comparing the IRMPD spectra with harmonic DFT calculations permits to determine the structures of the species trapped in our set-up. Comparison of experimental and calculated spectra suggests that H-atom abstraction occurs on a tertiary carbon (CH group) rather than on a secondary carbon (CH 2 group), as also indicated by the calculated relative energies of the various isomers. Combining experimental results and DFT calculations, we compare the spectra of neutral and carbocationic forms of adamantane, diamantane and triamantane. Substantial differences are observed between the IR spectra of neutral and ionic species. In the ions, the 3 μ m CH stretching modes become much weaker, while the other mid-IR modes strongly gain in intensity. An intense band centered at 1200 cm −1 due to a CH/CH 2 bending mode appears to be characteristic of the dehydrogenated cationic species. Finally, the intensities of the low frequency modes ( ≤ 900 cm −1) associated with carbon cage deformations appear to be most sensitive to the ionization and dehydrogenation state of the molecules.

Optimal Sensor Positioning to Track Rib Deflections from an Optical System in the Hybrid III Dummy

Objectives: The objective of the study was to determine the optimal use of a new optical device, the RibEye system, intended to obtain internal ribcage deflections from tests using anthropomorphic test dummies. Specifically, the study was designed to determine the most efficacious mounting location of light emitting diodes (LEDs) on the ribs and sternum in the 50th percentile male Hybrid III dummy. Methods: Optical signal drop-out and accuracy assessment tests were conducted. In the former series, symmetric antero-posterior chest compressive loading was accomplished using cylindrical and square indenters, and asymmetrical compressive loading was accomplished using unilateral offset and diagonal belt-type loadings. LEDs were mounted to multiple ribs bilaterally at varying locations on the ribcage. The internal chest potentiometer available in the Hybrid III dummy was used. The latter series, aimed at examining the system accuracy, consisted of tests with LEDs mounted to the 4 corners of the sternum, termed sternum-mounted LED tests; rib-mounted tests wherein LEDs were mounted either to a specific rib or in the intercostal space of two successive ribs; rib-mounted tests with rotated chest simulating oblique loading; and indenter-mounted isolated LED tests. An electro-hydraulic testing device was used to apply compressive loads via an indenter in all tests. Displacement profiles were extracted from the optical system records, drop-out evaluations were conducted, and the system accuracy was evaluated by comparing data from the indenter and/or internal chest potentiometer. Results: In general, results indicated that the RibEye system captures rib cage deformations effectively. Under symmetric loading, LEDs on the sternum responded similar to the internal chest potentiometer. The accuracy of the system depended on the location of position of the LEDs on the rib, magnitude of rib deformation, and potential interference from internal dummy structures such as the presence of the internal chest potentiometer. Optimum locations for LED placement were found to be at a distance of 9 cm, measured along the outer curvilinear path of the rib from the mid-sternum on either side. At this location, the system showed no signal drop-out at deflections representative of the United States current frontal impact Injury Assessment Reference Values. Signal drop-out was also depended on the type of loading: diagonal belt-type loading produced more signal loss. Mounting LEDs away from the center of the rib representing eccentric superior-inferior (z) axis placement also resulted in loss of accuracy. Conclusions: These controlled evaluations provide a fundamental understanding of the performance of the system as installed in the 50th percentile male Hybrid III dummy and its ability to measure both antero-posterior and lateral components of deflections at multiple ribs, including the sternum for frontal impact applications. The system may be optimally used to gather rib deflection data without signal drop-out under symmetrical and asymmetrical loadings when LEDs are mounted on the superior-inferior centerline of the ribs with no eccentricity along the z-axis and at the 9-cm location from the mid-sternum on either side of the ribcage and at any corner on the sternum to obtain sternum deflections.

Electron density topology of cubic structure I Xe clathrate hydrate at high pressure

In this report, we present a detailed powder x-ray diffraction study of the structural properties and charge density topology of structure I Xe clathrate hydrate under high pressure and room temperature. The pressure dependence of the structural parameters was determined by applying a Rietveld analysis to the experimental data. The combined Rietveld/maximum entropy method was used to derive the most probable charge density distribution at each pressure. Our results show that the charge density distribution of the encaged Xe atoms differs depending on the type of host cage at all pressures. Spherical electron density distributions were observed for the Xe atoms in the small cages while the atoms in the large cages showed longitudinal elongated electronic distributions. Along with the observed cage deformations, the change in electronic density distribution represents a clear indication that the guest-host interaction differs significantly between the small and large cages at high pressures. A similar behavior has been previously reported in low-temperature studies of methane clathrate hydrate.

Electronic Spectra of the Crystalline Polymers of C60: Photoluminescence Study at High Pressure

Specific details of the electronic spectra of perfect crystalline polymers of C60 were studied by means of the photoluminescence spectra measurements at normal conditions and at high pressure up to 4 GPa. The structure of the photoluminescence spectra, the intensity distribution between the principal bands and the pressure-induced shift of the bands differ considerably among the pristine C60, linear orthorhombic and planar tetragonal and rhombohedral polymeric phases of C60. Unlike the planar polymers of C60, the linear orthorhombic polymer exhibits irreversible changes in the photoluminescence spectrum under simultaneous application of high pressure and laser irradiation. The changes observed in the photoluminescence spectra of the planar polymeric phases of C60, as compared to the pristine material, are discussed in relation to the corresponding changes in the calculated electronic structure of the pristine C60 and its polymeric phases. The observed photoluminescence spectral structure along with the pressure behavior of the photoluminescence spectra are very sensitive to the structure of the polymers as well as to the C60 cage deformations and can be used to effectively characterize the various polymeric phases of C60.

A model for studies of mechanical interactions between the human spine and rib cage

A three-dimensional mathematical model useful for studies of the mechanics of the human skeletal thorax is described. To construct this model, rib cage elements are incorporated into a previously reported model of the thoracolumbar spine. The vertebrae and bony portions of the ribs and sternum are idealized as rigid bodies. The behavior of the discs, ligaments and costal cartilages are modelled by deformable elements. Appropriate geometric and stiffness property data are assigned to the elements of the model. In constructing the model, it was found that the mechanical response of the costo-vertebral joint is strongly influenced by articulation geometry. Although rigid bodies were used to model calcified portions of the ribs, the model predicted rib cage deformations in close agreement with those measured experimentally. These studies indicate that the rigid body motion of calcified portions of the rib makes a major contribution to the deformation of the rib cage in response to certain types of loadings. Quantitative results are also reported on the roles the rib cage plays in bending responses of the spine, the lateral stability of the spine, and the production and correction of several scoliotic deformities.