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Computational and experimental analysis of trawl winches barrels deformations Vladimir Solovyov a, Alexandr Cherniavskyb, aKamchatka Polytechnic College, 37 Leningradskaya St., Petropavlovsk-Kamchatsky 683003, Russia bSouth-Ural State University, Applied Mechanics Dept., 76 Lenin Ave., Chelyabinsk 454080, Russia a r t i c l ei n f o Article history: Received 10 May 2012 Accepted 8 October 2012 Available online 2 November 2012 Keywords: Trawl winch Strength Durability Rope tension gauge a b s t r a c t The necessary use of heavy duty trawl winches can cause plastic deformation of winch bar- rels, known as rolling. Numerical analysis shows that the main reason for such deforma- tion is pressure from layers of cable, while other reasons a rolling spot of stress near the rope-barrel contact point, barrel bending and torsion play a small role. The infl uence of different factors (barrel sizes, material properties, rope properties, and load levels) on the strain accumulation rate is analyzed. The described method provides a barrel design for new winches and load constraints for existing winches. New rope tension gauge and spe- cial software are developed to help the trawler master predicts situation that can lead to barrel plastic deformation. ? 2012 Elsevier Ltd. All rights reserved. 1. Introduction Industrial fi shing requires increasing trawling speed and depth. Depths of 600800 m are often necessary, and some sea- food catch demands depths up to 2000 m. Desired trawling speed increases from, for example, 46 knots (about 11 km/h). Increased hydrodynamic resistance and weight of trawling systems produce heavy loads on deck machinery, forcing it to work at the limits of its capacity. One of the critical pieces of equipment on a trawler is the winch barrel. These barrels are quite large, holding up to 3 km of rope with a 2530 mm diameter, so a deformed barrel cannot be repaired or changed out at sea. Despite some design and technological differences, all examined barrels (of Russian-built winches LETR 23 and LETR 25, Polish WTJ-12.5, etc.) can be reduced to a single scheme. Fig. 1 shows a barrel of WTJ-12.5 winch with a 12.5 ton pulling force installed on a trawler- freezer of 5500 tons displacement. The barrel consists of a spindle (a pipe with an outer diameter of 495 mm and inner of 420 mm) and two fl anges. Cyclic loading caused by trawling and trawler hoisting leads to increasing barrel deformation with the number of cycles. Suchdeformation,shown schematically in Fig.1 by the dotted line,results in contactwith the barrel and surrounding structures (brake, supports, etc.), destruction of the barrel bearings, and cracks between the barrel spindle and fl anges. Warping was observed on all of Kamchatkas fi shing vessels, demanding repair (or replacement) of the barrel about every year to prevent contact and fracture of brake, bearings, etc., about 10% of necessary barrel repairs are for cracking. 2. Calculations and results Rope tension causes torsion and bending of the barrel spindle. The bending is at maximum when the rope is at the middle of the spindle length. Mechanical stresses related to this bending and torsion vary cyclically in any barrels point due to the 1350-6307/$ - see front matter ? 2012 Elsevier Ltd. All rights reserved. /10.1016/j.engfailanal.2012.10.007 Corresponding author. Tel./fax: +7 351 2679306. E-mail address: a.o.chermail.ru (A. Cherniavsky). Engineering Failure Analysis 28 (2013) 160165 Contents lists available at SciVerse ScienceDirect Engineering Failure Analysis journal homepage: /locate/engfailanal barrel rotation and the fact that the brake and gear clutch driving the barrel are located on its opposing sides (Fig. 1). Besides this, additional stresses due to contact interaction of the rope and barrel can be expected: peak stresses form in relatively small contact spots near the contact point and stresses produced by uniform pressure of rope wound under tension (the entire coil can contain up to 25 rope layers). Numerical estimation of stresses and strength given below are made for a 12.5-ton winch made of steel with 216 MPa yield stress and an ultimate strength of 432 MPa. Simple estimations performed by well-known strength-of-materials formulas (see, for example 1) show that maximum bending stresses do not exceed 18 MPa, so the bending cannot be the main source of plastic deformation. The same can be said about torsion, which produces about 5 MPa. Contact stresses calculation is much harder and demands usage of numerical analysis. The danger of these types of stres- ses is connected with the motion of the contact spot in the circumferential direction due to rotation of the barrel and in the axial direction due to the gradual fi lling of the barrel with the rope; such motion could cause plastic deformation of the bar- rel upon rolling if stresses are great enough. The numerical model consisted of the barrel, layers of wrapped rope and the rope piece under load (Fig. 2). These were investigated with the aid of fi nite-element analysis. The barrel was treated as a linear elastic isotropic body and the rope as a linear-elastic anisotropic. Elastic modulus of steel rope in the axial direction was chosen on the basis of measured elongation under a workload (1% elongation was used; experimental results in 2,3 give values of 0.41.6%); elastic modulus in the transverse direction was taken up 510 times lower than in the axial direc- tion. The exact value of this quantity has little effect on the calculation results. Wrapped layers of rope were modeled by an elastic solid cylinder with appropriate anisotropy. ANSYS fi nite-element code was used for calculations. Calculated stresses appear surprisingly small not greater than 5 MPa, mainly due to relatively little stiffness of the wound rope compared to a steel barrel (note that in accordance to the winch manual, at least two wound layers must be kept on the barrel). Therefore, the infl uence of these stresses on barrel deformation cannot be noticeable. The main source of high stress and plastic deformation in this case is pressure on the barrel from layers of pre-stretched rope. In the computational sense this task is analogous to the problem of uneven heating where pre-tension of the rope is modeled by thermal shrinkage. This shrinkage varies from layer to layer because shorter trawl rope in water has less hydraulic resistance and weight, so during trawl hoisting the rope traction decreases up to 23 times 4. Thus, the compu- barrel axle bearing brake 2500 1600 deformed shape gear clutch torque from engine Fig. 1. Barrel and its deformation scheme. Fig. 2. Computer model of rope wound layers spindle and stress distribution in spindle (darker shading corresponds to higher stresses). V. Solovyov, A. Cherniavsky/Engineering Failure Analysis 28 (2013) 160165161 tational scheme is a two-layer cylinder: the inner one is a steel barrel while the outer is wound rope cooled to imitate pre-stress conditions. Cooling was calculated on the basis of maximum pulled force taken from the winch manual and exper- imental data 4 on decreasing this force in trawl hoisting. Assuming both barrel and rope are perfectly elastic, this task can be solved analytically on the basis of known Lame solu- tion (see, for example 5). Fig. 3 shows results of the solution: as soon as after winding six layers with maximum winch nameplate momentum, some plastic deformation must appear. Subsequent elasticplastic analysis cannot be fulfi lled analytically and ANSYS software was again used for the numerical solution. The main feature of the systems behavior is that high stresses do not mean immediate fracture; even a small de- crease in the barrel radius due to plastic deformation reduces pressure produced by the rope; corresponding reduction of stresses stop plastic deformation when pressure and barrel resistance are balanced. In subsequent cycles the rope is wound on an already reduced barrel, but pulling force and thus pre-tension is independent of the barrel radius. In elastic short- ening of the barrel radius and connected elongation of its axial length are restricted in one cycle of trawl hoisting. However, such changes would accumulate with the number of cycles. Fig. 4 shows an example of calculated elongation of the barrel with cycle numbers. Stabilization after some cycles occurs if deformation strengthening of barrel material is great enough, i.e. if the ultimate strength of the material is appropriately high. Calculated results were checked using deformation measuring on barrels of trawl winches WTJ-12.5, submitted for repair to the shipyard of Petropavlosk-Kamchatsky from February to June 2010. Barrel elongation, which demands replacement, is at about 20 mm. Investigation of winches in repair show that the distance increases between the outer points of the barrel fl anges is higher than elongation of the inner part of the barrel (about 1.5 times) because of the fl anges bending see Fig. 1. There were some cases of cracks between the barrel and fl anges. Deformation differences between barrels are quite high, the main reason seemingly being the absence of accurate load fi xation during winch exploitation. Moreover, the shrinkage of the barrel is neither strictly axisymmetric nor symmetric with respect to barrel mid-plane (two barrel measurement results are represented in Fig. 5 by thin lines; segments shows max- imum deviation from symmetry). However, in the middle part of the barrels calculated radius decrease is near to the mea- sured ones (the bold solid line on Fig. 5 represents calculations whereas thin lines represent measured barrel profi les). Deviations near the barrel fl ange are connected with specifi c loading factors pressure on the fl ange from the rope wrap that fi nishes layer (see Fig. 6). Despite special devices for forming rope layers, the fi nishing wrap falls into a gap between the preceding wrap and fl ange, leading to additional force on the fl ange and bending the barrel. This force and corresponding stress was computed using fi nite-element analysis (contact tasks capabilities of ANSYS/LS-DYNA in implicit formulations). It is necessary to remember that in different layers of rope these loads are applied to different points. An improved numerical 51015 N0 200 eqv, MPa 300 100 yield Fig. 3. The dependence of the maximum equivalent stresses in the barrel on the number of layers of wound cable (analytical solution). l, mm -30 -20 -10 050100 N, cycle Fig. 4. Barrel elongation vs. cycle numbers. 162V. Solovyov, A. Cherniavsky/Engineering Failure Analysis 28 (2013) 160165 model, taking into account these additional loads and stresses, give good agreement with the experiment (bold dotted line in Fig. 5). Besides agreement in deformation, the model predicts maximum stresses in just the same points where cracks in used barrels were found. A tested numerical model allows accurate enough estimation of barrel strain accumulation versus the number of cycles as shown in Fig. 4. The main questions about such results are whether the elongation stops after a number of cycles and what length increase will be accumulated to this moment. Finite-element calculations are very time-consuming; a more conve- nient way is using the shakedown theory 6,7, which gives a direct way to estimate load-carrying capacity without cy- cle-by-cycle calculations. One advantage of the theory is relatively simple calculations that allow study of the dependence of the accumulated strain (in this case barrel elongation and radius reduction) on the material properties and dimensions of the structure. The disadvantage comparing to cycle-by-cycle calculation is an unknown rate of strain accumu- R, mm -6 -4 -2 00.8 x, M calculated measured corrected calculations x Fig. 5. Barrel radius decrease. Fig. 6. Finite-element model of barrel with fl ange and wound rope (a) and calculated stress distribution (b). E1, GPa 0 10 20 30 lmax, mm E1, GPa 0 2 4 l1, mm 20302030 048 200 400 , MPa , % y u (c)(b)(a) Fig. 7. Stressstrain diagram of the barrel material (a), dependence of accumulated strain on these diagrams and rope elastic modulus (b and c). V. Solovyov, A. Cherniavsky/Engineering Failure Analysis 28 (2013) 160165163 lation; only strain after numerous cycles can be found, necessary number of cycles remains unknown. This is useful, how- ever, if we try to make a barrel with a suffi ciently long lifespan. Omitting calculation details, the solid line on Fig. 7a corresponds to a stressstrain diagram of the material used in the analyzed barrel. A dotted line gives hypothetic 1.5-times stronger material, and the dashed line indicates two times more strength. Fig. 2b illustrates calculated elongation of the barrel (using the shakedown approach) after numerous cycles depending on rope elasticity E1(higher E1corresponds to stiffer rope); the solid line shows results for present material while the dotted and dashed for stronger ones (see Fig. 7a). For comparison, Fig. 7c shows barrel elongation after the fi rst cycle, calculated via fi nite-element analysis. 3. Discussion Calculation results similar to those shown in Fig. 7b can be used to fi nd barrel material of minimal strength (i.e. the least expensive) while providing properly limited elongation. It also proves that surface hardening of the barrel does not help to solve elongation problem: all material must be equally as strong because of high stresses in the inner (closest to axle) points of the barrel. Increasing the barrels wall thickness is also ineffective: if the material remains unchanged, deformations cal- culated for a 25 mm (double) thickness increase are still greater than those demanding repair. It is interesting to compare elongation after the fi rst cycleDl1(Fig. 7c) with elongation after numerous cyclesDlmax (Fig. 7b). The fi rst (Dl1) decreases with increasing stiffness of the rope, while the second (Dlmax), contrarily, increases. The reason is that maximum pressure that can be produced by stiff rope is greater than by stretched rope, but stiff rope tension decreases with deformation of the barrel (radius decrease) faster than of compliant rope. Taking into consideration barrel deformation in every cycle, it is possible to show that stiff rope strain accumulation in the fi rst cycles will be less, but will continue during increasing number of cycles. Note that the stiffness of rope increases during operation along with rope elongation. Calculations like those shown above can be used in winch design (or repair) to choose proper materials for winch barrels. There are cases, however, when barrels are already made from steel insuffi ciently strong to eliminate strain accumulation under maximum load. As a palliative, it is possible to offer to constraint maximum load but in some circumstances max- imum load capacity may be sill needed. To help the trawl master to solve this problem, a special combination of hardware and software was developed 8. It consists of rope tension gauge, software that predicts pressure on the barrel after all rope is hauled in, and calculations to determine whether the barrel will deform at a given pressure. Rope tension gauges use strain sensors (tensometers) mounted inside the hollow axle of the upper pulley (Fig. 8). Gauges placed there are well protected against environmental action (salt water, ice, etc.) and do not disturb the crew during their work. Eight sensors with special connection patterns give information about rope tension even in the case of an unknown angle between rope and deck this unknown angle is also computed using the sensor signal. An amplifi er and transmitter mounted inside the hollow axle transfers the signal in digital form to a receiver in the deckhouse. Software that predicts plastic deformation occurrence does not use only measured rope tension it includes a model for tension calculation taking into account water resistance and the weight of the trawl system and ropes. As well as prediction of plastic deformation, the software solves one more important task: it defi nes if it is possible to use the trawl at a given depth and speed with given pulling force providing by the trawler. 4. Conclusion Numerical analysis reveals the reason for heavy-duty winch barrel deformation: evenly distributed pressure of wound rope cause plastic strains that covers the whole volume of the barrel material. Running spots of contact stresses near the point of contact between the rope and barrel, barrel bending and torsion have less importance. Strain (barrel elongation) rope pulley axle gauges amplifier and transmitter Fig. 8. Rope tension measuring system. 164V. Solovyov, A. Cherniavsky/Engineering F