Selection Of Mesh Size Research Articles

A Study on the Catch Losses and Mesh Selectivity Related to the Attachment of Marine Mammal Bycatch Reduction Devices on Midwater Trawl Gear

The National Institute of Fisheries Science in Korea is developing marine mammal bycatch reduction devices (BRDs) for high-risk fishing gear, such as trawls. We experimented with two BRD types (guiding nets) attached in front of codend at 30° and 45° angles, and catch losses and mesh size selectivity were investigated. Experimental fishing operations were conducted along the East Coast of South Korea where whales and dolphins are commonly sighted. The catch was classified according to fishing location, BRD type, codend, and covernet, with measurements recorded for body length, maximum girth, and weight. The average selectivity for each haul was analyzed using the ‘selfisher’ package. The catch loss rates with the BRD attached at tilt angles of 30° and 45° were 11% and 29% for common flying squid, 6% and 28% for sailfin sandfish, and 5% and 8% for pearlside. While the mesh selectivity rates for common flying squid and pearlside remained at 0.2–0.5 across all lengths and tilt angles, the mesh selectivity curve for sailfin sandfish was estimated. There were significant differences in catch loss between 30° and 45° angles, with the 30° angle being more effective in catch loss. We observed a masking effect in the codend.

Determination method of mesh size for numerical simulation of blast load in near-ground detonation

In order to improve the overall resilience of the urban infrastructures, it is required to conduct blast resistant design for important building structures in the city. For complex terrain in the city, it is recommended to determine the blast load on the structures via numerical simulation. Since the mesh size of the numerical model highly depends on the explosion scenario, there is no generally applicable approach for the mesh size selection. An efficient method to determine the mesh size of the numerical model of near-ground detonation based on explosion scenarios is proposed in this study. The effect of mesh size on the propagation of blast wave under different explosive weights was studied, and the correlations between the mesh size effect and the charge weight or the scaled distance was described. Based on the principle of the finite element method and Hopkinson-Cranz scaling law, a mesh size measurement unit related to the explosive weight was proposed as the criterion for determining the mesh size in the numerical simulation. Finally, the applicability of the method proposed in this paper was verified by comparing the results from numerical simulation and the explosion tests and was verified in AUTODYN.

A study on the mesh size selectivity by a lternate haul method of trawl using the SELECT model

A study on the mesh size selectivity by a lternate haul method of trawl using the SELECT model

On the Resistance to Buckling Loads of Idealized Hull Structures: FE Analysis on Designed-Stiffened Plates

In this paper, the buckling analysis on simply supported rectangular plates and stiffened panels is carried out. Three different plate thicknesses were proposed (i.e., 3 mm, 4 mm, and 5 mm). The thickness of the longitudinal stringers and sub-stiffeners were also varied. The material that was used was marine grade steel. The load versus the displacement curve and the total energy were measured. The buckling analysis results were examined via finite element (FE) computation. To ensure that the results of the methodology for the finite element were reliable, the benchmark buckling analysis of the experimental test was reconstructed. For the selection of mesh size, the element to thickness ratio method (ELT) was used. The results revealed that the thickness of the plate increases the strength of the stiffened panel. The plate thickness of 5 mm increased by 65.7% and 20.61% compared with the 3 mm and 4 mm plate thicknesses. A change in the thickness of the sub-stiffeners does not significantly change the strength of the stiffened panels. Material S355JR-EN10210 produced a higher ultimate panel collapse load compared with S235JR-EN10025 (A) and S235JR-EN10025 (B).

Isogeometric-analysis-based stiffness spreading method for truss layout optimization

A novel isogeometric analysis-based stiffness spreading method (IGA-based SSM) is proposed for the truss layout optimization design within a continuum, where the topology, geometry, and cross-sectional areas of the truss elements can be simultaneously optimized. The IGA-based SSM based on energy conservation is employed to obtain the spreading stiffness matrices of the truss elements that are embedded in weak IGA background grids. The IGA background grids are constructed using high-order continuous isogeometric elements that can overcome the limitation of discontinuous sensitivity derived by traditional C0 elements. Because the sensitivity required for the optimization can be obtained analytically, gradient-based optimization algorithms can be easily implemented. To verify the effectiveness of the IGA-based SSM for truss layout optimization design, typical illustrative examples are used, considering the compliance minimization optimization problem. The proposed method can provide a continuous and smooth sensitivity field and overcome the numerical inaccuracy caused by interpolation methods, such as the radial basis function. The different background mesh sizes, initial layouts, and orders p of nonuniform rational B-splines basis functions are investigated in truss layout optimization. The results indicate that the selection of the appropriate background mesh size can avoid the problem of discontinuous truss connections, C1-continuous isogeometric elements can provide better optimization designs with a lower computational cost, and the proposed method can provide a clear layout for different initial layouts. Moreover, the spatial truss layout optimization problem and the min–max displacement optimization problem are also studied to further verify the effectiveness of the proposed method. Finally, the proposed method is extended to solve the concentrated force diffusion problem that widely exists in the interstage adapters of launch vehicles by adding the variance constraint of reaction forces. The results indicate that the proposed method can obtain required concentrated force diffusion results with reasonable stiffness distributions.

Phenotypic plasticity in Barilius vagra (Hamilton, 1822) (Teleostei: Danionidae) from two geographically distinct river basins of Indian Himalaya

Truss-based morphometric analysis was used to examine phenotypic plasticity of Barilius vagra (Hamilton, 1822) inhabiting the tributaries of the Alaknanda (Ganga River basin) and Chenab (Indus River basin), two geographically distinct river basins in the Indian Himalaya. Fourteen landmarks were connected to generate a truss network of 90 parameters on the body of fish. Eighty morphometric traits out of ninety morphometric measurements explained statistically significant difference among six sampling locations of Barilius vagra from streams in the Alaknanda and Chenab basins. Discriminant function analysis revealed 82% of Barilius vagra specimens originally classified into their own groups. 95% of the variance was explained by 13 principal components. Morphometric characters (1–6, 1–13, 2–5, 2–6, 2–14, 3–6, 4–6, 4–14, 6–12, 7–8, 7–9, 10–11, and 13–14) contributed greatly in differentiation of B. vagra populations from different river basins. The Alaknanda basin reflected some mixing within populations, which may be due to common environmental conditions and fish migration in these streams. This study will be helpful in framing site-specific conservation and management strategies, such as net mesh size selection, avoiding overexploitation, stock augmentation and food availability for different fish populations.

Mesh Size Selectivity of Tie-Down Gillnets for the Blackfin Flounder (Glyptocephalus stelleri) in Korea

Although gillnet fisheries are increasingly common in Korea, few studies have conducted sea trials using tie-down gillnets. Here, we analyzed the mesh size selectivity using tie-down gillnets with four different mesh sizes (84, 90, 105, and 120 mm) to catch blackfin flounders. A total of 10 sea trials were conducted at depths of 100–140 m in the waters of Yangyang County, Gangwon Province, Korea, and the catching efficiency and mesh size selectivity were comparatively analyzed. The net with a mesh size of 84 mm showed the highest number of catches (373), followed by the 90-mm (363) and 105-mm (307) meshes. The results of the master curve estimation showed that the larger the mesh size, the higher the total length representing the same retention probability. Therefore, the catch rate of small fish decreased with the increasing mesh size. For the 84-mm net, the 50% selection length for small fish (total length ≤ 170 mm) was estimated at 186.9 mm, which was approximately 17 mm larger than the length limit. The results show that when using tie-down gillnets, the size of the fish caught changed according to the changes in the mesh size.

Zooplankton community size-structure change and mesh size selection under the thermal stress caused by a power plant in a semi-enclosed bay

Zooplankton samples were collected using 505, 160 and 77 µm mesh nets around a power plant during four seasons in 2011. We measured total length of zooplankton and divided zooplankton into seven size classes in order to explore how zooplankton community size-structure might be altered by thermal discharge from power plant. The total length of zooplankton varied from 93.7 to 40 074.7 µm. The spatial distribution of mesozooplankton (200 −2 000 µm) populations were rarely affected by thermal discharge, while macro- (2 000 −10 000 µm) and megalo-zooplankton (>10 000 µm) had an obvious tendency to migrate away from the outfall of power plant. Thus, zooplankton community tended to become smaller and biodiversity reduced close to power plant. Moreover, we compared the zooplankton communities in three different mesh size nets. Species richness, abundance, evenness index and Shannon-Wiener diversity index of the 505 µm mesh size were significantly lower than those recorded from the 160 and 77 µm mesh size. Average zooplankton abundance was highest in the 77 µm mesh net ((27 690.0±1 633.7) ind./m3), followed by 160 µm mesh net ((9 531.1±1 079.5) ind./m3), and lowest in 505 µm mesh net ((494.4±104.7) ind./m3). The ANOSIM and SIMPER tests confirmed that these differences were mainly due to small zooplankton and early developmental stages of zooplankton. It is the first time to use the 77 µm mesh net to sample zooplankton in such an environment. The 77 µm mesh net had the overwhelming abundance of the copepod genus Oithona, as an order of magnitude greater than recorded for 160 µm mesh net and 100% loss through the 505 µm mesh net. These results indicate that the use of a small or even multiple sampling net is necessary to accurately quantify entire zooplankton community around coastal power plant.

Protocol for sand control screen design of production wells for clayey silt hydrate reservoirs: A case study

AbstractThe process of extracting natural gas from gas hydrate‐bearing sediments (GHBS) may yield significant sand influx due to the metastable nature of GHBS. Selecting appropriate sand control media is vital to addressing the challenges caused by excessive sand production. This study proposes a protocol called holding coarse expelling fine particles (HCEFP) for sand control design. The protocol aims to provide a new optimization method for screen mesh size selection for clayey silt hydrate reservoirs. Detailed optimizing procedures of proper candidate screen mesh sizes in hydrate exploitation well in clayey silt hydrate reservoirs are depicted based on the HCEFP. Then, the site W18, which is located in the Shenhu area of the northern South China Sea, is taken as an example to illustrate the optimization procedure for screen mesh size selection. The results reveal that complete solid retention via a standalone screen is rarely beneficial as high clay contents can adversely affect wellbore productivity due to excessive plugging. Screen aperture size selection for clayey silt hydrate wells should strike a balance between retaining coarser particles and avoiding screen blockage by the relatively fine particles. Furthermore, longitudinal heterogeneity of the PSDs also increases the difficulties associated with sand control design. Multistage sand control optimization is necessary in hydrate production wells. For Site W18, we recommend that the entire production interval can be divided into two subintervals for multistage sand control operations.

A data-driven framework for error estimation and mesh-model optimization in system-level thermal-hydraulic simulation

Over the past decades, several computer codes have been developed for simulation and analysis of thermal-hydraulics and system response in nuclear reactors under operating, abnormal transient, and accident conditions. However, simulation errors and uncertainties still inevitably exist even while these codes have been extensively assessed and used. In this work, a data-driven framework (Optimal Mesh/Model Information System, OMIS) is formulated and demonstrated to estimate simulation error and suggest optimal selection of computational mesh size (i.e., nodalization) and constitutive correlations (e.g., wall functions and turbulence models) for low-fidelity, coarse-mesh thermal-hydraulic simulation, in order to achieve accuracy comparable to that of high-fidelity simulation. Using results from high-fidelity simulations and experimental data with many fast-running low-fidelity simulations, an error database is built and used to train a machine learning model that can determine the relationship between local simulation error and local physical features. This machine learning model is then used to generate insight and help correct low-fidelity simulations for similar physical conditions. The OMIS framework is designed as a modularized six-step procedure and accomplished with state-of-the-art methods and algorithms. A mixed-convection case study was performed to illustrate the entire framework.

Empirical Solutions and Reliability Assessment of Thermal Induced Creep Failure for Wafer Level Packaging

The accelerated thermal cycling test (ATCT) is a method of testing the electronic packaging reliability characteristic. A component must pass this test before being launched into the market. According to many studies, under thermal loading, the excessive thermal strain and stress occur between the package and substrate because of the coefficient of thermal expansion mismatch, which damages the solder bump of electrical packaging. In the ATCT, −40° C to 125° C is the regular thermal range of packages tested. Furthermore, the homologous temperature exceeds one-third of the melting point (K) of solder, and one should consider the accumulation of creep strain and estimate the creep behavior during the loading procedure; however, the creep strain is very sensitive to mesh size in finite element simulation. Obtaining a stable and reliable creep stain for different packaging structures becomes a must for solder joint reliability assessment. In this paper, we study a feasible and fixed element size, which should be chosen carefully for the same type of electronic packaging structure, for example, wafer level packaging (WLP), as it can affect simulation results and cause the prediction of the packaging life cycle to deviate. In ATCT simulation, there is a big difference in reliability estimation for different element mesh size selection, even if all material properties and structures remain the same. It is essential to find an appropriate and fixed element size for packaging reliability prediction to yield precise and reliable simulation results. This paper aims to find an appropriate element mesh size that can consistently predict the reliability life of various WLPs in an accurate range, and the reliability results of different WLPs under the thermal cycling loading have been validated by experiments. Moreover, the simulation results are summarized by using the Anand and hyperbolic sine creep models with suitable empirical reliability assessment equations, and the results show both creep models can predict the reliability life of WLPs in an accurate range with appropriate mesh control.

Mesh size selectivity of surface and mid-water gillnet for catching freshwater sardines “Sardinella tawilis” (Herre, 1927) in Taal Lake, Philippines

Mesh size selectivity of surface and mid-water gillnet for catching freshwater sardines “Sardinella tawilis” (Herre, 1927) in Taal Lake, Philippines

Differences of alternative methods of measuring abdominal wall hernia defect size: a prospective observational study.

Despite the importance of defect size, there are no standardized recommendations on how to measure ventral hernias. Our aims were to determine (1) if any significant differences existed between various methods of measuring ventral hernias and (2) the effect of these methods of measurement on selection of mesh size. A prospective study of all patients enrolled in a randomized trial assessing laparoscopic ventral hernia repair at a single institution from 3/2015 to 7/2016 was eligible for inclusion. Abdominal wall hernia defect size was determined by multiplying defect length and width obtained separately using each of five methods: radiographic (CT), intraoperative with abdomen desufflated, intraoperative with abdomen insufflated to 15mmHg (intra-abdominal aspect), intraoperative with abdomen insufflated to 15mmHg (extra-abdominal aspect), and clinical. The primary outcome was intraclass correlation between the five different methods of measurement for each patient. Secondary outcome was changes in mesh selection assuming a 5cm overlap in each direction. Fifty patients met inclusion criteria for assessment. The five different measurement methods had an intraclass correlation for each patient of 0.533 (95% CI 0.373-0.697) (weak correlation) for length; 0.737 (95% CI 0.613-0.844) (moderate correlation) for width; and 0.684 (95% CI 0.544-0.810) (moderate correlation) for area. Different types of measurements affected mesh selection in up to 56% of cases. Among five common methods of measuring abdominal wall hernia defect, sizes are only weakly to moderately correlated. Further studies are needed to determine which method results in optimally sized abdominal wall prostheses and superior ventral hernia repair.

Mesh size selectivity of the gillnet in East China Sea

A production test using several gillnets with various mesh sizes was carried out to discover the selectivity of gillnets in the East China Sea. The result showed that the composition of the catch species was synthetically affected by panel height and mesh size. The bycatch species of the 10-m nets were more than those of the 6-m nets. For target species, the effect of panel height on juvenile fish was ambiguous, but the number of juvenile fish declined quickly with the increase in mesh size. According to model deviance (D) and Akaike’s information criterion, the bi-normal model provided the best fit for small yellow croaker (Larimichthy polyactis), and the relative retention was 0.2 and 1, respectively. For Chelidonichthys spinosus, the log-normal was the best model; the right tilt of the selectivity curve was obvious and well coincided with the original data. The contact population of small yellow croaker showed a bi-normal distribution, and body lengths ranged from 95 to 215 mm. The contact population of C. spinosus showed a normal distribution, and the body lengths ranged from 95 to 205 mm. These results can provide references for coastal fishery management.

DETERMINATION OF OPTIMUM MESH SIZE TO MEASURE TOOTH ROOT STRESS OF SPUR GEAR USING FINITE ELEMENT ANALYSIS

Gears are one of the most important power transmission elements. High speed gear and gear which has high loading capacity are necessary for engineering applications. Gears should be analyzed theoretically according to design criteria and tested. Theoretical analysis is generally performed by using finite element methods through simulating gears. In this study, spur gears at definite module and teeth number are modelled by Catia. They are analyzed by using SimXpert and Marc softwares for different loads on pitch circle. Tooth root bending stress values are recorded after analysis. Meshing, mesh size selection and mesh type are one of important steps for FEM. Different meshes (fine and coarse) are used for tooth root and other regions of gear profiles in this study. At tooth root, different mesh sizes are experienced and tooth root stress values are obtained. These values are compared with analytical calculation results to state optimal mesh size.

Design and gillnet selectivity of Pampus argenteus along the Satpati coast, Maharashtra, India

Investigations were carried out for evaluating the design and selectivity of Pampus argenteus gillnets used along the Satpati coast. Satpati, an important marine fish landing centre of Maharashtra, India has the maximum Silver pomfret, P. argenteus landing by mechanized gillnetters. Among the maritime states, maximum landing of pomfret was recorded from Gujarat and Maharashtra in the northwest coast. They are highly relished table fishes in domestic and export markets and command high unit value. In India, the species is available in all the coastal states. Gillnet selectivity plays an important role in fish resource management and helps in maintaining sustainability of the stock. The gillnetters used for pomfret fishing in Satpati carried only one net per vessel and the total fleet length ranged from 10620 m to 11400 m. Gillnets are operated as column and bottom drift and depth of operation ranged from 35 m to 50 m. Gillnets made of Polyamide (PA) monofilament of diameter 0.23 mm to 0.28 mm and mesh size that ranged from 110 mm to 130 mm are commonly used. They are rigged with hanging coefficient between 0.42 and 0.51. Hung length varied from 114 m to 143 m and hung depth from 7.66 m to 9.50 m. The estimated optimum length of small mesh and large mesh was 131.40 mm and 155.29 mm respectively. Findings of the present study indicate a drastic decline in the length at first maturity of Silver pomfret to 199 mm fork length and the optimum mesh size estimated is 166 mm. Selectivity in terms of mesh size selectivity in accordance with the size at first maturity and size at first capture helps to eliminate juveniles from the gear. The knowledge of size selectivity of fishing gear types is crucial to fisheries management in order to achieve sustainable yield.

Mesh size selectivity of Harpodon nehereus gillnet in northern South China Sea

Mesh size selectivity of Harpodon nehereus gillnet in northern South China Sea

Mesh Sensitivity Study of Soil Barrier Subjected to Blast Loading: Numerical Methods Using AUTODYN 3D

The accuracy of numerical result depends on many factors, among which is the selection of appropriate element size. An optimum mesh size is capable in reducing the percentage error and computational time consumption. In this study, a numerical tool i.e AUTODYN 3D is used to determine the optimum element size for the soil barrier subjected to air blast load. The pressure results on barrier surface obtained through one third scale are able to produce results that are in good agreement with published experimental test data as compared to full scale simulation. In this study, the selection of mesh size 20 mm x 20 mm x 20 mm found considerably as the best element size for the case study of a rectangular soil barrier subjected to air blast load by using AUTODYN 3D software.

Comparison of Gill Nets and Fixed‐Frame Trawls for Sampling Threadfin Shad in Tropical Reservoirs

AbstractThreadfin shad Dorosoma petenense populations were sampled quarterly from 2010 to 2011 to determine appropriate sampling techniques for this species in tropical reservoirs of Puerto Rico. Offshore gill netting and night trawling were compared in terms of catch per unit of effort, size distribution, sampling precision, and bycatch. In total, 90 gill net–trawl pairs of catches were compared, which collected more than 80,000 threadfin shad. Gill‐net and trawl catches were not correlated in either number or biomass. Coefficients of variation were greater in gill‐net sampling (0.761 for numbers, 0.747 for biomass) than in trawl sampling (0.433 and 0.465, respectively) and were not dependent on reservoir, sampling season, reservoir section, or any combination of these factors for any gear. There was no correspondence in size distributions between gill‐net and trawl catches. Gill nets collected threadfin shad in the range of 23–169 mm total length (TL) and displayed strong mesh size selectivity, causing distinct unrealistic peaks in size distribution. Gill nets underestimated threadfin shad smaller than 35 mm TL and overestimated shad bigger than 90 mm TL. The size range of threadfin shad collected via trawl was 10–108 mm TL, and trawls did not appear to be as size selective for fish up to 80 mm TL. Trawling was found to be the superior sampling technique for shad populations in pelagic habitats of Puerto Rican reservoirs, which consisted mainly of fish up to 80 mm TL. Trawling provided a more realistic picture of size distributions, collected far less bycatch, was less affected by the schooling of shad, and was less laborious and more cost‐effective than gill nets.

Theoretical model-based quantitative optimisation of numerical modelling for eddy current NDT

Eddy current (EC) nondestructive testing (NDT) is one of the most widely used NDT methods. Numerical modelling of NDT methods has been used as an important investigative approach alongside experimental and theoretical studies. This paper investigates the set-up of numerical modelling using finite-element method in terms of the optimal selection of element mesh size in different regions within the model based on theoretical analysis of EC NDT. The modelling set-up is refined and evaluated through numerical simulation, balancing both computation time and simulation accuracy. A case study in the optimisation of the modelling set-up of the EC NDT system with a cylindrical probe coil is carried out to verify the proposed optimisation approach. Here, the mesh size of the simulation model is set based on the geometries of the coil and the magnetic sensor, as well as on the skin depth in the sample; so the optimised modelling set-up can be useful even when the geometry of EC system, the excitation frequency or the pulsed width is changed in multi-frequency EC, sweep-frequency EC or system and pulsed EC. Furthermore, this optimisation approach can be used to improve the trade-off between accuracy and the computation time in other more complex EC NDT simulations.