Gear Sizes Research Articles

Enumeration of Feasible Clutching Sequences of Epicyclic Gear Mechanisms

A new methodology for enumeration of feasible clutching sequences of epicyclic gear mechanism (EGM) composed of two or more fundamental gear entities is presented. The method relies on previous work on algorithmic technique. It improves on existing techniques used for automatic transmission mechanisms in its ability to accurately solve the kinematics of geared mechanisms and estimating their velocity ratios and arranging them in a descending order in a simpler manner without depending on certain gear sizes. Twelve velocity-ratio-relations are derived for any four coaxial links of an epicyclic gear train. These velocity-ratio-relations are three more than the nine relations given in literature. In addition, the velocity ratios can be arranged in a descending sequence without using complicated artificial intelligence technique or complicated computer algorithm. The present methodology is judged to be more efficient for enumeration of all feasible clutching sequences of an EGM.

A comparison of four types of sampling gear used to collect shovelnose sturgeon in the Lower Missouri River

Summary We compared variability in catch per unit effort (CPUE) and size structure of shovelnose sturgeon Scaphirhynchus platorynchus collected in 2003 and 2004 with stationary winter gill nets, drifted trammel nets, hoop nets, and otter trawls in the Lower Missouri River, USA to determine the most precise types of gear to collect all sizes of sturgeon so that refinements of longterm monitoring protocols can be made. A total of 1947 net sets or trawls collected 8743 shovelnose sturgeon, with 67% of the fish collected during winter gill netting (16% of total samples). Mean coefficient of variation (CV) among all months for juvenile (age 3 and younger; <250 mm fork length) sturgeon was highest for gill nets and lowest for otter trawls (P = 0.0008). Mean CV of subadult and adult shovelnose sturgeon (‡250 mm) was highest in hoop nets compared to other gear types (P = 0.0002). All gear and mesh sizes collected the most common sizes of shovelnose sturgeon (500–600 mm), but only otter trawls and trammel nets collected fish <150 mm. The higher precision of winter gill nets and summer otter trawls led to fewer samples needed to detect changes in CPUE as compared to hoop and trammel nets. Sampling only with types of gear that do not collect younger shovelnose sturgeon may hinder management decisions that rely on recruitment trends to determine the effects of management actions (e.g. channel modifications).

Trophic signatures of small-scale fishing gears: implications for conservation and management

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 333:117-128 (2007) - doi:10.3354/meps333117 Trophic signatures of small-scale fishing gears: implications for conservation and management Konstantinos I. Stergiou1,2,*, Dimitrios K. Moutopoulos1,3, Hernando J. A. Casal4, Karim Erzini2 1Aristotle University of Thessaloniki, School of Biology, Department of Zoology, Box 134, Thessaloniki 54124, Greece 2CCMAR, Universidade do Algarve, 8005-139 Faro, Portugal 3University of Patras, Department of Biology, Section of Animal Biology, Rio-Patras 265 00, Greece 4Facultad de Ciencias del Mar, Departamento de Biologia, Grupo Dinamica de Poblaciones de Peces, Universidad de Cádiz, Avda. Republica Saharahui s/n, 11510 Puerto Real, Cádiz, Spain *Email: kstergio@bio.auth.gr ABSTRACT: We quantified the ecosystem effects of small-scale gears operating in southern European waters (Portugal, Spain, Greece), based on a widely accepted ecosystem measure and indicator, the trophic level (TL). We used data from experimental fishing trials during 1997 to 2000. We studied a wide range of gear types and sizes: (1) gill nets of 8 mesh sizes, ranging from 44 to 80 mm; (2) trammel nets of 9 inner panel mesh sizes, ranging from 40 to 140 mm; and (3) longlines of 8 hook sizes, ranging from Nos. 15 (small) to 5 (large). We used the number of species caught per TL class for constructing trophic signatures (i.e. cumulative TL distributions), and estimated the TL at 25, 50 and 75% cumulative frequency (TL25, TL50, TL75) and the slopes using the logistic function. We also estimated the mean weighted TL of the catches (TLW). Our analyses showed that the TL characteristics of longlines varied much more than those of gill and trammel nets. The longlines of large hooks (Nos. 10, 9, 7, 5) were very TL selective, and their trophic signatures had very steep slopes, the highest mean TL50 values, very narrow mean TL25 to TL75 ranges and mean TLW > 4. In addition, the mean number of TL classes exploited was smaller and the mean TL50 and TLW were larger for the longlines of small hooks (Nos. 15, 13, 12, 11) in Greek than in Portuguese waters. Trammel and gill nets caught more TL classes, and the mean slopes of their trophic signatures were significantly smaller than those of longlines as a group. In addition, the mean number of TL classes exploited, the mean TL50 and the TLW of gill nets were significantly smaller than those of trammel nets. We attribute the differences between longlines of small hooks to bait type, and the differences between all gear types to their characteristic species and size-selectivity patterns. Finally, we showed how the slope and the TL50 of the trophic signatures can be used to characterise different gears along the ecologically ‘unsustainable–sustainable’ continuum. KEY WORDS: Trophic level · Trophic signatures · Gill nets · Trammel nets · Longlines · Indicators · Northeast Atlantic Ocean · Mediterranean Sea Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 333. Online publication date: March 12, 2007 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2007 Inter-Research.

Quantifying the environmental impacts of artisanal fishing gear on Kenya’s coral reef ecosystems

The environmental impacts of artisanal fishing gear on coral reef ecosystems were studied in the multi-gear fishery of southern Kenya to evaluate which types of gear have the greatest impact on coral reef biodiversity. The gear types studied were large and small traps, gill nets, beach seines, hand lines and spear guns. Levels of coral damage, proportion of juvenile fish and discards, size and maturity stage at first capture were quantified and compared amongst the gear types. Results indicate that fishers using beach seines, spears and gill nets cause the most direct physical damage to corals. Spear fishers showed the highest number of contacts to live corals per unit catch followed by fishers using gill nets (12.6 ± 1.8 and 5.9 ± 2.0 coral contacts per kg fish caught per trip respectively). Apart from discarding 6.5% of their daily catch in the sea, as it was too small, beach seine fishers also landed the highest percentage of juvenile fish (68.4 ± 15.7%), a proportion significantly higher ( p < 0.001) than in any other gear. The size and maturity stage at first capture for 150 of 195 species caught by all gear types was well below the lengths at which they mature. For example, 100% of Lethrinus xanthochilus, 99% of Lethrinus nebulosus and 94% of Lethrinus harak caught were juveniles. Across all gear types, 50.1 ± 22.7% of the catch consisted of juvenile fish, indicating serious growth overfishing. Field assessment of levels of coral density showed that fishing grounds where beach seines were still in use had a significantly lower density than where beach seining was not used. This correlation is likely to arise in part because seines cannot be used in the most coral rich areas, and in part because coral loss is a consequence of seine use. On a per gear basis therefore, beach seines had the most impact on coral reef biodiversity. This study emphasizes the need to enforce restrictions on destructive gear and mesh sizes.

Graphical aid for planetary gear train design

A graphical overlay method is presented which can be used in the design of simple planetary gear trains when it is desired to establish gear sizes to produce given speed ratios. The technique can be used to establish both specific gear sizes and ratios as well as permissible size and ratio ranges.

Leaks in internal gaps in the pump in the flow-rate generator in a test system

There are three forms of gap in the flow of the medium between walls of annular form, of which one rotates with a constant velocity in its plane; radial(~n.~m), end(~el, 8e~, and interrotor (6i) (Fig. i). This flow is considered as plane-parallel because of the small geometrical dimensions of the gaps and the absence of a pressure gradient along the rotor rotation direction. Also, it is assumed that the speeds of the medium in the end and radial gaps are the same. These assumptions enable us to derive optimum relationships for the gear and measurement-chamber sizes.

Calculation of the Geometric Factor Using the Plate Formula for Bevel Gears with a Back Shoulder

Bevel gears with a back shoulder are considered to be stronger than straight through machined gears, in part, because of the excess web of material between the teeth. This strength has been theoretically shown to be significantly greater than similar conventional bevel gears. The equation derived for predicting the strength of the gears involves a geometric factor which is tabulated for different gear sizes. Its use in the design of this type of bevel gears is explained via an example problem.

A General Theory of Composite Gear Trains

Some basic gear arrangements which use a minimum number of gears are noted; the gear pairs in these composite gear trains are seen to be interdependent. A general and widely applicable method of gear train analysis is developed. Expressions and index numbers are deduced which define optimum designs and the gear sizes for optimum or other design points. The analysis is extended to include gears external to the composite gear sections, so providing a unified theory which covers all known and feasible minimum-gear arrangements based on three shafts. An example of application is included.

Involute-Gear Geometry: Nondimensional Analysis and Design of Tooth Forms, Tooth Thickness, and Mesh Relationships

Abstract Definition and discussion of recently discovered fundamental gear characteristic called “belt-length ratio,” to simplify gear design and generation computations, are given with necessary measurement procedures, formulas, and a graphical calculating chart. The concepts and methods are proposed as alternatives to use of conventional involute-function tables and formulas. Relationships are given in nondimensional (ratio) form so that a minimum of data are applicable to all gear sizes. A new standard for pin measurements of gears and involute splines is suggested.