Nominal Mesh Research Articles

Mesoscale DVC analyses and parameter calibration for pantographic block in 3-point flexure

In the present work, the mechanical response of a fiber network metamaterial was studied when subjected to 3-point flexure. To account for the initial deformation of the sample due to the fabrication process, backtracking (i.e., the nominal mesh was accurately repositioned in the reference configuration) was implemented in the Digital Volume Correlation (DVC) procedure. Kinematic fields were then measured via DVC at two different scales. Finite element based DVC was validated thanks to a series of initialization steps. The displacement fields were successfully measured and a peculiar deformation mechanism was observed. These measurements were employed to calibrate the constitutive parameters of a second gradient continuum model introduced for modeling this type of metamaterial. Numerical simulations are shown to be in good agreement with experimental measurements at the macroscopic scale.

Estimation of selectivity parameters for target and bycatch fishes of the trammel net fisheries in the northern Aegean Sea (eastern Mediterranean Sea)

The size selectivity of trammel nets was investigated in the northern Aegean Sea using 10 different inner-panel mesh sizes ranging from 16 to 70 mm nominal mesh size (bar length). Selectivity estimates were made for the eight most abundant target and bycatch fish species, namely black scorpionfish, Scorpaena porcus Linnaeus, 1758; annular seabream, Diplodus annularis (Linnaeus, 1758); red mullet, Mullus barbatus Linnaeus, 1758; surmullet, Mullus surmuletus Linnaeus, 1758; round sardinella, Sardinella aurita Valenciennes, 1847; European hake, Merluccius merluccius (Linnaeus, 1758); greater weever, Trachinus draco Linnaeus, 1758; and blotched picarel, Spicara flexuosum Rafinesque, 1810, which accounted for 51.5% by number and 42.7% by weight of the fish caught with trammel nets in the sea trials. The SELECT method was used to estimate the selectivity parameters. Five different selectivity functions (i.e., normal scale, normal location, gamma, log-normal, and bi-normal) were applied with the bi-normal function providing the best fit as it had the lowest deviance value for all species and the lowest values for the dispersion parameter ( D /df). The mesh size of 16 mm in most of the cases retained specimens below the size at first maturity ( L m ). The mesh size of 19 mm seems more appropriate for red mullet, surmullet, and blotched picarel, the mesh size of 22 mm for annular seabream and round sardinella, while for European hake and black scorpionfish, the mesh size larger than 26 mm would be more appropriate.

Catch Comparison of Commercial and Experimental Deep Water Cast Nets with Different Mesh Sizes for Whiting (Merlangius merlangus euxinus) Fishery

In the present study, the commercial (16 mm nominal mesh size) and experimental deep water cast nets with different mesh sizes (20 mm, 24 mm, 28 mm and 32 mm nominal mesh size) were tested to compare the captured fish lengths and catch amounts for whiting (Merlangius merlangus euxinus). Experiments were carried out between July, 11 and August, 29, 2018 in Rize province of the south-eastern Black Sea Region. A commercial fishing boat was chartered for 20-day sea trials and in total, 66 set operations were done for all nets. Generalized Linear Mixed Models (GLMM) was used to compare fish sizes caught with experimental and commercial deep water cast nets. Results showed that more than 70 percent of the individuals caught in cast nets with 16 mm, 20 mm and 24 mm size were below the minimum landing size of whiting (13 cm). Among tested nets, only cast net with 32 mm size caught significantly less individuals under the minimum landing size. Finally, the results obtained from this study are discussed in terms of sustainable fisheries of whiting in the Black Sea.

Estimating selectivity of experimental diamond (T0) and turned mesh (T90) codends in multi-species Mediterranean bottom trawl

The effect of shifting from a diamond mesh codend (T0) to a 90° turned mesh codend (T90) on the size selectivity of seven commercially important species in the Mediterranean bottom trawl fishery was evaluated. During sea trials conducted in the north-western Adriatic, two experimental codends made of 54 mm nominal mesh size netting that differed only in mesh configuration were alternately mounted on the same trawl. Overall, the size selectivity was significantly improved for all the species analysed, shifting from T0 to T90. The difference in the average expected L50values between T90 and T0 was particularly marked in European hake (Merluccius merluccius, 21.26 vs 11.26 cm total length), common squid (Loligo vulgaris, 12.06 vs 7.88 cm mantle length) and mantis shrimp (Squilla mantis, 20.78 vs 13.35 mm carapace length). Both codends had an excessive size selectivity especially for red mullet (Mullus barbatus), Mediterranean horse mackerel (Trachurus mediterraneus) and whiting (Merlangius merlangus), thus involving a commercial loss. These findings demonstrate the efficiency of the T90 codend tested at excluding undersized specimens, especially of hake, whose average L50was above the minimum conservation reference size of 20 cm. The adoption of this practical and inexpensive solution could help improve the management of the demersal resources targeted by the Mediterranean bottom trawl fishery.

The fixtureless inspection of flexible parts based on semi-geodesic distance

Some types of manufactured parts like sheet metals and skins often have a significantly different shape in a free-state position compared to their state-of-use position (as defined by their nominal CAD models) due to a combination of gravity and/or the residual effects of stress. Traditionally known as flexible (nonrigid compliant) parts, these dedicated fixtures are used for inspection operations in order to maintain flexible parts from a free-state position to a state-of-use position. This paper introduces a new automatic defect identification method primarily intended for two less-investigated manufacturing defect types: contour profile errors and hole localization. By combining simple techniques such as mesh boundary detection, fast boundary-based correspondence searches and accurate fast marching on triangulated meshes, the semi-geodesic distances from each boundary vertex on the acquired SCAN mesh to all the other boundary vertices is calculated, stored in a table and then compared to the corresponding values on the part's nominal CAD mesh. The comparisons found in the tables result in an estimation of the location and amplitude of the two aforementioned defect types. Compared to other work in this field, the overall approach does not rely on any mesh registration or finite-element analysis with tedious boundary conditions setup. It is also relatively fast. A fast algorithm/app based on this method was named the AFDA (Automatic Free-state Defect Approximation) and was validated against case studies in the aerospace sector. The results reflect the utility and effectiveness of the proposed approach.

Vibration signature analysis of commodity planetary gearboxes

Abstract Planetary gearboxes excite highly modulated vibration. From the existing literature, contradicting descriptions can be obtained. In order to resolve this situation, six commodity gearboxes are investigated on a test rig. A simple, yet powerful method to extract their vibration signatures is proposed. This novel approach consists of order tracking and singular value decomposition. The experimental data shows only partial agreement with the behavior expected from existing research. The vibration has indeed the structure of a Fourier series with respect to the angle of the planet carrier. However, the predictions concerning the most significant vibration orders made by the literature are not met. From gearboxes applied in conjunction with turbomachinery it is expected that significant vibration order can only occur at integer multiples of the number of planets. This is not met by any of the examined gearboxes. From sequentially phased automotive gearboxes it is expected that the orders below and above the nominal gear mesh order are most significant. The behavior is found in four gearboxes, but they are not sequentially phased. Mathematically it can be shown that the observed behavior is connected to forces with lines of action fixed to the planet carrier.

ОЦЕНКА УРОВНЯ ЭКОНОМИЧЕСКОЙ БЕЗОПАСНОСТИ МИНЕРАЛЬНО-СЫРЬЕВОГО КОМПЛЕКСА БРЯНСКОЙ ОБЛАСТИ

Silicon carbide black grinding powders 54CF180-F36, mass-produced at Volzhsky Abrasive Plant are studied. Powders are screened into fractions according to GOST R 52381. Measurement of a grain width of each fraction was carried out by means of a photome-tric method using specially developed software. For the vast majority of fractions the grain width follows the normal distribution law. The deviation of the grain width from the normal law can be observed at the frac-tions settled on the second sieve and the pallet. With decreasing the nominal mesh size of a pass sieve in each grit size the arithmetic mean of grain width of the main fraction decreases, dispersion reduces from the fraction settling on the second sieve to the fourth and increases at the fraction settling on the pallet. In case of the identical mesh size of a pass sieve the mean and dispersion of grain width fraction increase with grinding powder grit increase. For each grit size the functional dependences of the mean and dispersion of grain width fraction on a mesh size of a pass sieve are established.

ЗАВИСИМОСТЬ СРЕДНЕГО И ДИСПЕРСИИ ШИРИНЫ ЗЕРЕН ШЛИФОВАЛЬНЫХ ПОРОШКОВ КАРБИДА КРЕМНИЯ ЧЕРНОГО ОТ РАЗМЕРА ЯЧЕЙКИ ПРОХОДНОГО СИТА

Silicon carbide black grinding powders 54CF180-F36, mass-produced at Volzhsky Abrasive Plant are studied. Powders are screened into fractions according to GOST R 52381. Measurement of a grain width of each fraction was carried out by means of a photometric method using specially developed soft-ware. For the vast majority of fractions the grain width follows the normal distribution law. The deviation of the grain width from the normal law can be observed at the fractions settled on the second sieve and the pallet. With decreasing the nominal mesh size of a pass sieve in each grit size the arithmetic mean of grain width of the main fraction decreases, dispersion reduces from the fraction settling on the second sieve to the fourth and increases at the fraction settling on the pallet. In case of the identical mesh size of a pass sieve the mean and dispersion of grain width fraction increase with grinding powder grit increase. For each grit size the functional dependences of the mean and dispersion of grain width fraction on a mesh size of a pass sieve are established.

MORPHOMETRIC CHARACTERIZATION OF THE SAND FRACTION IN A SAND GRAIN IMAGE CAPTURE SYSTEM1

ABSTRACT Morphology studies assume significant importance in analysis of phenomena of granular systems packaging, in particular with a view to the use of the technique of soil stabilization named particle size correction in forest roads. In this context, this study aimed to develop and operationalize a Sand Grain Image Capture System and, hereby, determine the morphological indices of the sand fractions of two sandy soils called João Pinheiro (JP) and Cachoeira da Prata (CP). Soil samples, air-dried, were sieved (2.0 mm nominal mesh size) for removal of gravels. The materials that passed through the sieve were subjected to dispersion, washing in 0.053 mm nominal mesh size sieve, removal of organic matter and iron oxides to obtain the clean sand fractions. Subsequently, each soil sample was sieved for separation into twelve classes, between the diameters of 0.149 mm and 1.190 mm, using a Rotap shaker. Next, tests were carried out to characterize the morphometric attributes of the twelve classes of sand fractions of the soils studied. For validation of the performance of the Sand Grain Image Capture System, the results were compared to those obtained using a standard procedure for image analysis. The analysis of the results led to the following conclusions: (i) the sand fraction of the JP soil presented higher values for the morphometric indices roundness, elongation and compactness compared to sand fraction of the CP soil; and (ii) the Sand Grain Image Capture System worked properly, with practicality.

Selectivity and retention of pollock Pollachius virens in a Gulf of Maine trawl fishery

Measuring the size selectivity of pollock, or saithe, Pollachius virens, has been challenging due to the patchy, elusive nature of the species. By using data collected opportunistically during a redfish Sebastes fasciatus selectivity study, selectivity of three sizes of mesh opening (114, 140 and 165mm double 5mm twine diamond) for pollock was determined using a commercial fishing vessel fishing off Provincetown, Massachusetts, USA. Fifty-six tows were completed in March and April 2013; 21 included sufficient catches of pollock to estimate size selectivity. Robust, simple models for the mean L50s (50% selection length) and SR (selection ranges), and confidence intervals, were developed for all three tested codends, incorporating both within and between haul variability. Selection parameters and selection ranges were determined for codends with nominal mesh sizes of 114mm (L50: 34.8cm; SR: 2.4cm), 139mm (L50: 45.6cm; SR: 3.1cm), and 165mm (L50: 52.4cm; SR: 3.6cm). All measures of model validity were positive, indicating robust and reliable findings that can be used to provide guidance to fishery managers, stock assessment scientists, and fishermen on size-dependent retention of pollock by codend mesh size.

Filling holes in digitized point cloud using a morphing-based approach to preserve volume characteristics

Filling holes is a major challenge to reduce digitizing time and makes the digitized model compatible with applications such as finite element (FE) analysis or inertia calculations. Indeed, whatever the sensor used, for accessibility reasons or reflection problems, some parts of the object may be non-measured defining digitizing holes in the digitized point cloud. In this paper, a method based on a mesh deformation is proposed to fill the digitized holes. The proposed method relies on the a priori knowledge of the numerical model as a nominal mesh. After identifying the digitized holes and calculating the differences between the nominal mesh and the point cloud, a deformation of the nominal mesh is performed. This deformation is determined by minimizing the energy of deformation of the mesh considered as a lattice. The proposed method is validated on a complex shape. Finally, this method is applied to an industrial part in order to highlight interest for balancing issues.

The effect of monofilament thickness on the catches of gillnets for common sole in the Mediterranean small-scale fishery

Experimental fishing trials were carried out on an Italian commercial vessel to test gillnets of different monofilament diameters targeting common sole (Solea solea). The gillnets only differed in the nominal monofilament diameter: 0.18, 0.20, 0.22, 0.25, and 0.30mm. The nominal mesh size (stretched) was 72mm. A total of 47 taxa were caught. The mean number of species caught with 0.30mm monofilament was significantly lower than those obtained with the three thinnest diameters. Total number, number of commercial and discard of non-commercial species significantly decreased with the increase of monofilament diameter. The number of common sole and tub gurnard caught was not statistically different amongst diameters. No statistical differences were observed for the length–frequency distributions of common sole and tub gurnard caught with the different monofilament diameters. The analysis of the mechanism of capture for the common sole showed that for all diameters the main type of retention was snagging, and the percentage of individuals retained in such way decreased with the increase of diameters, while an opposite trend was observed for the common sole that were gilled. Monofilament thickness had a substantial effect upon the catch rates of the gillnets.

A time domain approach to diagnose gearbox fault based on measured vibration signals

Abstract Spectral analysis techniques to process vibration measurements have been widely studied to characterize the state of gearboxes. However, in practice, the modulated sidebands resulting from the local gear fault are often difficult to extract accurately from an ambiguous/blurred measured vibration spectrum due to the limited frequency resolution and small fluctuations in the operating speed of the machine that often occurs in an industrial environment. To address this issue, a new time-domain diagnostic algorithm is developed and presented herein for monitoring of gear faults, which shows an improved fault extraction capability from such measured vibration signals. This new time-domain fault detection method combines the fast dynamic time warping (Fast DTW) as well as the correlated kurtosis (CK) techniques to characterize the local gear fault, and identify the corresponding faulty gear and its position. Fast DTW is employed to extract the periodic impulse excitations caused from the faulty gear tooth using an estimated reference signal that has the same frequency as the nominal gear mesh harmonic and is built using vibration characteristics of the gearbox operation under presumed healthy conditions. This technique is beneficial in practical analysis to highlight sideband patterns in situations where data is often contaminated by process/measurement noises and small fluctuations in operating speeds that occur even at otherwise presumed steady-state conditions. The extracted signal is then resampled for subsequent diagnostic analysis using CK technique. CK takes advantages of the periodicity of the geared faults; it is used to identify the position of the local gear fault in the gearbox. Based on simulated gear vibration signals, the Fast DTW and CK based approach is shown to be useful for condition monitoring in both fixed axis as well as epicyclic gearboxes. Finally the effectiveness of the proposed method in fault detection of gears is validated using experimental signals from a planetary gearbox test rig. For fault detection in planetary gear-sets, a window function is introduced to account for the planet motion with respect to the fixed sensor, which is experimentally determined and is later employed for the estimation of reference signal used in Fast DTW algorithm.

Assessment of the Selective Properties and Optimization of Mesh Size of Pelagic Trawl Codends, Used for Fishing Mackerel (Trachurus Spp) in the Gulf of Guinea

Over the past few decades, it has become widely recognized that the management strategies of world fisheries must ensure sustainability of target species. The intervening years have seen many improvements to the concept of gear selectivity and methods for measuring the selectivity of fishing towed gears. Improved understanding of the principles of the selection of fish by gears has changed the list of parameters which are known to have a significant effect upon selection. The recent development of new mathematical models and the increased availability of powerful computers have resulted in improvements in the analysis procedures for the data produced to measure a gear’s selectivity. The catch of mackerel in the gulfofGuineahas steeply declined during the last two decades, and resource management is clearly required. Therefore, the need for evaluation of trawl codends used in this fishery and the potential improvements to their selectivity are of prime importance. In this paper, we use semi-empirical models to define selective properties of pelagic trawl codends targeting black mackerel (Trachurus spp) in theGulfofGuinea. These properties are determined using the experimental and theoretical methods of assessing the parameters of the selectivity curve, and by plotting the curve. Selection parameters were obtained by fitting a logistic equation using a maximum likelihood method. Trawl codend selectivity is estimated for 17 internal diamond mesh sizes in the range 47 - 79 mm. Using the basic selectivity equations, we determine the needed mesh size A = 58 mm for fishing mackerel in the gulf of Guinea. This nominal mesh size gives room for nj = 0.1 catch of juveniles, which not exceeds the allowable proportion [nj] = 0.1. To provide resource conservation, there is the need to make amendments in the fishery regulations for more rational exploitation of mackerel stoks, because the currently use nominal mesh size A = 56 mm is rather unselective.

Gillnet Selectivity for Bluefish (Pomatamus saltatrix, L. 1766) in Çanakkale Strait, Turkey

To determine the selectivity of gill nets with 22, 23, 25 and 28 mm nominal mesh size (bar length) for bluefish (Pomatamus saltatrix, L. 1766), the study was conducted at three different stations between 20 and 30 m water depths at Canakkale Strait, Turkey, between February 2007 and April 2012. Gill net with 22, 23, 25 and 28 mm mesh size (bar length) each having same twine thickness (210 denier / 3) and 100 mesh depth vertically were rigged for this purpose. The fish samples were obtained by drive-in fishery method during winter season. The SELECT method was used in determining selectivity parameters. By comparing the deviances of five different models of SELECT method, lognormal model gave the best fit. The modal lengths of the gill nets with 22, 23, 25, and 28 mm mesh size were estimated 22.24, 23.25, 25.27 and 28.30 cm, respectively. The results of the trials indicated that minimum gill net mesh size for this fish should use larger than 25 mm

Southern occurrence of the sand sole (Psettichthys melanostictus)

The geographic and depth ranges of marine fishes commonly reflect their physiological preferences (Portner et al., 2010). Given the wide availability of habitats along the California coastline, biogeographic range extensions of many species have been observed to occur periodically, most frequently during periods of short-term oceanographic temperature fluctuation. Over the last 30 years, these range extensions in California have mostly been poleward expansions as ocean temperatures have warmed or through largescale oceanographic anomalies such as Californian-El Nino conditions (Lea and Rosenblatt, 2000). Many of the recently documented range extensions in southern California have been associated with thermal power plant cooling water intakes or discharges, often due to the increased sampling and/or the presence of greater-thanambient water temperatures near the discharges (Pondella, 1997; Lea and Rosenblatt, 2000; Miller and Curtis, 2008). In addition to the thermal discharge, the cooling water system entrains material, including fishes, with the cooling water drawn into the system. The cooling water is filtered through traveling screens with a nominal square mesh of 10-mm to prevent debris from passing farther into the system and potentially clogging downstream condensers. Fish impingement upon these traveling screens is routinely monitored to provide a representative accounting of the fishes taken in by the cooling water system, and an opportunity to collect random tourist species. Sand sole (Psettichthys melanostictus) reportedly ranges from the Southeastern Bering Sea, Alaska to Newport Beach, California in depths ranging from the intertidal zone out to 325 m (Love et al., 2005). Museum records contain numerous specimens taken in northern California with only three lots collected offshore of Ventura County, California at the southernmost extent (Fishnet2 2011). Surprisingly, no records were found for collections in the Santa Barbara, California area despite substantial areas of suitable habitat. Reviews of the Santa Barbara Natural History Museum (SBNHM 2011) ichthyology records found no sand soles in the collection. Fitch and Schultz (1978) detailed two fish taken in the southern Santa Monica Bay in the mid-1970s during impingement sampling at Scattergood Generating Station in El Segundo, California and the Redondo Beach Generating Station in Redondo Beach, California. The Redondo Beach sample had set the southern range limit for this species at the time. Slightly farther southwards, several sand sole were caught by recreational anglers fishing off the Balboa Pier during the 1980s (M. Love, unpubl. data), which had served as the impetus for the current southern range endpoint. One collection that has gone largely unreported is recorded in the Museum of Comparative Zoology (MCZ 2011) as collected in San Diego County, California during the mid-1800s (Lot 25988) and has not been previously included in the biogeographic distribution of the sand sole (Love et al., 2005; Horn et al., 2006). This sample, however, has limited information regarding its collection. Careful

Effect of twine thickness on selectivity of gillnets for bogue, Boops boops,in Turkish waters

To investigate the effect of twine thickness on the selectivity of multifilament gillnet targeting bogue,Boops boops L., four different stations were sampled between March and November 2008 in the northern Aegean Sea. Gillnets with 22, 23, and 25 mm nominal mesh size (bar length) each having two different twine thicknesses (approximately 0.45 mm and 0.54 mm ∅) were applied for this purpose. The deviances from the SELECT method revealed that lognormal models provided the best fits for both of the twine thicknesses. Results from the two-way ANOVA analyses revealed that the mean total lengths increased with the mesh size (F = 87.36; df = 2; P < 0.0001) and decreased with the twine thickness (F = 46.12; df = 1; P < 0.0001). The 22 mm mesh size net (0.45 mm ∅) captured significantly larger fish than the 23 mm mesh size net (0.54 mm ∅) probably due to the higher elasticity and flexibility of the thinner twine. Thus, fisheries managers should take into consideration the twine thickness while advising mesh size regulations in gillnet fisheries.

Selectivity of 40 mm square and 50 mm diamond mesh codends for five species in the Eastern Mediterranean demersal trawl fishery

The aim of this study was to determine the selectivity of 40 mm square (40S) and 50 mm diamond (50D) mesh codend for five species, red mullet ( Mullus barbatus ), annular sea bream ( Diplodus annularis ), common Pandora ( Pagellus erythrinus ), axillary sea bream (Pagellus acarne ) and blotched picarel ( Spicara maena ) in the Eastern Mediterranean. Selectivity data were collected by the covered codend method and analyzed. Mean selection curves were analyzed and compared using the between haul variations model for red mullet and annular sea bream. Pooled data were used for common Pandora, axillary sea bream and blotched picarel. In total, 22 valid hauls, 10 with 40S and 12 with 50D codends were carried out. The 50% retention lengths (L 50 ) of 40S and 50D codend were found as 14.5 and 15.3 cm for red mullet, 9.5 and 11.3 cm for annular sea bream, 13.1 and 15.0 cm for common Pandora, 14.4 and 15.3 cm for axillary sea bream, 14.5 and 17.2 cm for blotched picarel, respectively. This study showed that codends with 40S and 50D L 50 results improve the selectivity when considering commercially used 40 mm nominal diamond mesh codend in Turkish seas for given species. However, in multi-species, it seems likely that a separation of species system would potentially be of more value than size-selective systems. Therefore, different selective techniques such as grid and separation panel and behaviour of the species against the gear need to be investigated. Key words: Codend selectivity, 40 mm square mesh, 50 mm diamond mesh, Eastern Mediterranean, demersal trawl.

Effect of mesh size and codend circumference on selectivity in the Mediterranean demersal trawl fisheries

The effects of mesh size and codend circumference on selectivity of some commercially important species were evaluated. Four different codends were used in the sea trials. The nominal mesh sizes tested were 48 mm and 56 mm and two different nominal circumferences were associated with each mesh size. Selectivity experiments were carried out in the Central Adriatic Sea, in the course of two different periods of the year (May and September 2005) on two different fishing grounds normally exploited by local fishermen. Reliable selectivity results were obtained for red mullet ( Mullus barbatus), little squid ( Alloteuthis media) and European hake ( Merluccius merluccius). For all the species, the codend circumference plays a role which is as important as mesh size. The positive effect of increasing mesh size, from 48 mm to 56 mm, could be made fruitless by an increase in codend circumference. According to species, the change only in the mesh size from 48 mm to 56 mm significantly increases L50 by +15–42%, while by increasing only the codend circumference of around 13–17%, L50 decreases by 9–41%, thus being effective as by increasing mesh size. As a consequence the selection factor (i.e. SF is the ratio of L50 and the codend mesh size) depends on the codend circumference and does not result mesh-size-independent. We confirm that it is not sufficient to regulate selectivity in multispecies fisheries just by setting a minimum mesh size and that there is a need in mixed fisheries to improve selectivity by using additionally mechanisms. Possible solution would be to design policies and management programmes that seek to minimise discards, which include active rather than static management, obligations to land all catches, and no MLS and reduced benefits from landings of juvenile fish.

The effect of forced mesh opening in the upper panel of a Nephrops trawl on size selection of Nephrops, haddock and whiting

In an attempt to reduce catches of juvenile fish in the Icelandic Nephrops norvegicus fisheries, the mesh sizes in the upper part of a commercial Nephrops trawl were increased and the netting hung to force wide mesh opening. Two different designs, each with 135 mm nominal mesh upper panel were compared to an unmodified commercial trawl in June 2009. Design A had a 23.2 m long panel and design B had a 16.1 m long panel, extending respectively to 9.7 and 15.0 m from the cod-line. The panels in both designs were one third narrower and longer than the matching lower panel. With design A, about half of Nephrops, haddock ( Melanogrammus aeglefinus) and whiting ( Merlangius merlangus) catches were lost, while with design B, the losses were restricted to smaller specimen of fish and Nephrops, i.e. a marked size selection was observed. These trials demonstrate the potential for size selection by a simple manipulation of a Nephrops trawl to reduce discarding.