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With the current demand of wood products and industrial requirements, plantation owners need to re-think ways in which harvesting is carried out and identify the most efficient harvesting system that also utilizes small diameter parts of stem per industry's product specifications. This paper contributes to the discussion by comparing the harvesting productivity and stem recovery between conventional harvesting (CH) and integrated harvesting (IH) systems. CH is harvesting which does not necessarily align with the log dimensional requirements of the customer and only recovers logs with big diameters while IH is based on harvesting and sorting logs according to need in a single operation so that as much volume and value as possible of the stands is realized. The study was carried out at the Sao Hill Forest Plantation in the Southern Highlands of Tanzania. The harvested compartment was purposively selected and divided into IH and CH plots. A total of 39 trees were randomly selected to be harvested from each plot. The findings portray a significant difference in the stem recovery of 75% for IH and 60% for CH. CH had an average cutting productivity of 16 m3/h as compared to 14 m3/h for IH while skidding productivity was 15.3 m3/h and 24.9 m3/h for IH and CH, respectively. In this study, the IH system resulted in higher production in terms of volume recovered, meaning IH had a significant impact on the production and stem recovery of the standard stem-wood for use in different industries. [ABSTRACT FROM AUTHOR]

Skid trails are a major management‐induced disturbance in temperate forest ecosystems with considerable impact on soil ecological processes that are so far poorly understood. In German forests, skid trails comprise 10%–20% of the forest area that is potentially affected by soil compaction through heavy machinery. We systematically investigated the influence of skid trails on physical, chemical and microbiological soil parameters at 84 paired plots across four Central European forest types.In low mountain forests with steeper topography, skid trails had more drastic effects than in lowland forests. Skid trails in low mountain areas showed a decrease in the C to N ratio of microbial biomass (MBC/MBN), as well as increased microbial (MBC/SOC) and enzyme activities leading to faster carbon turnover (lower C/N, EOC/EN) and increased CO2 losses (CO2/SOC) from the soil.The overall effects of the skid trails in lowland forests were small. On base‐poor soils, we found an increase in the MBC/MBN ratio, while skid trails in base‐rich lowland soils showed a reduction in CO2/SOC, suggesting a proportional increase in soil carbon storage.Regardless of region‐specific effects, the relative increase in the bulk density of the fine soil was identified as a 'golden trait' that determined the effects of skid trails on many soil parameters, as shown by negative correlations with SOC, N, MBC, MBN, MBP, MBC/SOC and CO2/SOC and positive ones with the activities of certain hydrolytic enzymes.Synthesis and applications: Our data clearly showed that carbon conversion processes and soil respiration leading to significant carbon and nutrient losses increased significantly on skid trails in low mountain regions with relatively steep slopes, which was in sharp contrast to lowland sites. The strong context dependence of our findings suggests that the mapping of soil conditions in terms of slope, substrate and moisture with high spatial resolution is mandatory to assess the vulnerability of sites to soil compaction by heavy machinery. Based on such vulnerability analysis, negative impacts can be minimised through the designation of permanently fixed skid trails, technical adaptation of vehicles (e.g. wide base tyres) as well as careful planning and timing of management operations that should be restricted to dry weather and soil moisture conditions or periods of frost. [ABSTRACT FROM AUTHOR]

The general objective of this research project is to determine the effectiveness of ancient medicine for respiratory diseases in older adults in the El Chorrillos sector of Babahoyo Canton. The sample was drawn from a survey of community citizens. Mainly men (75%), which is more than half of all and the difference (5%) represents the female sex, the most common respiratory illness is influenza (53%) or flu, the results also show (8%) that it is in a mild stage; Most respondents (87%) believe that ancient medicine contributed to their recovery; The treatments used vary from person to person, the most appropriate means to treat respiratory diseases are infusions (8%), creams (10%) and vapors (99%).In summary, it can be stated that the community (107%) supports the use of traditional medicine prescriptions for respiratory diseases and the implementation of respiratory physiotherapy as a preventive measure so that the elderly do not worsen respiratory infections and can maintain their traditions using a treatment that recognizes that they have cultural roots and ethnic identities specific to their field. [ABSTRACT FROM AUTHOR]

Copyright of Lubrication Engineering (0254-0150) is the property of Editorial Office of LUBRICATION ENGINEERING and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Featured Application: Penetration resistance is a descriptor of soil compaction. In this study, we have exercised control over the weight of the payload of three timber extraction options, therefore the results may be used to estimate the contribution to soil compaction of each pass, as well as for comparison and for planning of operations, given the trends and the magnitude of penetration resistance between the passes. Local effects of ground-based timber harvesting, such as soil compaction, are often important for forest management and resilience of forests. One way to evaluate the compaction of the forest soils is by the penetration resistance. Most often, however, the control over the weight of the means used to extract the wood is difficult to maintain, influencing therefore the outcomes of the comparison studies. In this study, a controlled experiment was set up to see how the penetration resistance is affected by the number of passes of three wood extraction methods. A first objective of the study was to characterize the undisturbed soils by the mean values of penetration resistance along the profile. The second objective of the study was to compare the changes in penetration resistance induced by the number of passes along the soil profile. The extraction means were selected based on their typical use in flat-land operations, namely horse logging, skidding and forwarding, and the weight of their loads was determined before the experiment; then, each one was tested in a different area by operating in a closed loop on flat land, with 15 passes over the respective testing area. Penetration resistance was sampled up to 80 cm in depth in 10 control points, as well as in 10 sampling points over the wheels' footprints. Ten samples were taken on the latter after the first, second, third, fourth, fifth, tenth and fifteenth passes, and comparisons were set up based on natural changing points in penetration resistance found in the control areas. The comparisons found significant differences by an increase in penetration resistance for all three extraction means, and there was a difference by an order of magnitude and depth; horse logging affected it the least and forwarding the most in magnitude, while skidding seemed to produce more significant changes in depth. However, the magnitude and depth of these changes may have depended on the characteristics of the soils from the test areas, and it cannot be concluded that the found levels of penetration resistance will affect the trees located nearby the experimental trails. The problem of soil compaction should be further examined by dedicated studies, given the variability in soil characteristics and diversity in means used to extract timber. [ABSTRACT FROM AUTHOR]

The efficient planning and control of timber harvesting operations is crucial to growth productivity and reducing costs, and different systems or methods are applied to obtain elevated performance. In particular, cable yarding is a highly appreciated and very efficient wood extraction method in areas that are difficult to access with ground-based extraction machines. Combined logging systems are not diffuse and not often implemented. For this reason, the use and the application of innovative methods are limited. However, some combinations have recently been observed in forest operations. This study, conducted in a deciduous stand in Bulgaria, paid attention to the combination of a tractor-mounted tower yarder (Valentini V400) with a clambunk skidder (Timberjack 1010D), aiming to examine the viability and develop the operational efficiency of the two-stage extraction system and to define the time, log volume extracted per unit by the yarder and the clambunk, and the yarding and skidding costs. The researchers carried out a time-motion study and performed a regression analysis to identify those variables that are most likely to affect the duration of work elements and productivity. For cost analysis, the COST model was used. The mean productivity of the tower yarder was 10.34 m3/PMH and 8.11 m3/SMH, while for the clambunk skidder, the productivity was 6.23 m3/PMH and 4.93 m3/SMH. The net costs for the combined logging system were calculated as 120.87 €/PMH and 14.93 €/m3. This study adds new data about the correct use of both machines, supporting their application in beech forests. [ABSTRACT FROM AUTHOR]

he mechanized tillage systems of agricultural soils for the cultivation of quinoa in the central Ecuadorian highlands are influenced by several factors, among them: the skidding that occurs in soil tillage, with different implements used both in conventional tillage and in minimum or reduced tillage, in plowing, harrowing, furrowing, which are executed for the cultivation of quinoa, without considering the slope, humidity, soil compaction and the increase in cost and time. The objective of the study was to determine the percentage of skidding in sandy textured soils for quinoa cultivation, with slope ranges from 5 to 12% with moisture contents from 13 to 18% under conventional and minimum or reduced tillage systems in plowing, harrowing, furrowing, using disk plow, chisel plow, disk harrow, furrower coupled to an agricultural tractor of 95 KW of power with assisted traction. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Forestry Society of Croatia / Sumarski List Hrvatskoga Sumarskoga Drustva is the property of Forestry Society of Croatia and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Fine roots are an important component of forest soil as they play a key role in fundamental processes like plant nutrition and water supply. As with all the features of forest soil, the compaction related to the forest operations and, in particular, to the wood extraction via ground‐based technologies could lead to a significant impact on the presence of fine roots in the soil affected by the passage of the machines. Considering the lack of a review, we used a meta‐analytic approach to synthesise effect sizes of ground‐based extraction technologies affecting the presence of fine roots in the soil, using a multivariate mixed‐effects meta‐analytic model. The obtained results revealed that the presence of fine roots in the soil affected by the passage of the machines was significantly reduced by both skidding (g = −1.23, 95%CI ‐1.87, −0.60) and forwarding (g = −1.37, 95%CI ‐2.01, −0.74). Due to the higher soil compaction caused by forwarding, this method had a marginally but statistically significant greater impact than skidding. We further confirmed the hypothesis that soil compaction and the presence of fine roots were strongly correlated, with the latter being greatly reduced in compacted soils characterised by higher bulk density. What is more, even more than 20 years after a harvesting intervention, the presence of fine roots was significantly lower in both strip roads (forwarding) and skid trails (skidding) as compared to areas which were not impacted by the machine passage. This shows that fine roots are particularly vulnerable to forest operations. On the other hand, the majority of the trails in the database used for the meta‐analysis were created in countries that favour the creation of a small number of widely used trails. Therefore, it would be scientifically valuable to do a comparative evaluation in various forestry contexts, such as in the Mediterranean area, where the development of the forest trails network is oriented on creating a large number of trails with low traffic volumes. Because machinery‐induced soil compaction is the major driver of the decrease in fine roots in skid trails and strip roads, both the application of best management practices as well as of a smarter planning of the trail network to limit soil compaction are strongly recommended. Both applications are highly recommended to be used in the planning phase and in the practical implementation of logging activities. [ABSTRACT FROM AUTHOR]

Examination of the technical and economic dimensions of skidding operations is imperative for sustainable forest management, offering invaluable insights crucial for the formulation of sustainable forestry strategies. In many countries, the shift from modified agricultural machinery to purpose-built forest machinery has become apparent in forest operations. However, this transition often accompanies a reduction in logging crew size, raising new questions about productivity, costs, and ergonomics of the introduced harvesting systems. This study investigates two skidding systems utilizing the cable-grapple skidder Welte 115/5L, differing in work team size: one with one skidder operator and two chainsaw operators (WT3) and the other with one skidder operator and one chainsaw operator (WT2). Conducted in natural European beech forests in southern Bulgaria, the research focused on the group shelterwood system within the Natura 2000 network. Both WT3 and WT2 exhibited net skidding productivity of 9.96 m3 PMH−1 over a mean skidding distance of 300 m and a mean winching distance of 20 m, outperforming conventional systems in the area. Despite this, there were notable differences in gross skidding productivity (8.64 m3 SMH−1 for WT3 vs. 7.30 m3 SMH−1 for WT2), affecting skidding cost (EUR 5.41 m−3 for WT3 vs. EUR 6.62 m−3 for WT2) and unit production cost (EUR 9.33 m−3 vs. EUR 11.53 m−3). This study highlights that the cable-grapple skidder can be effectively employed by smaller teams, providing higher productivity, lower unit cost, and increased flexibility during piling, primarily due to the presence of the knuckle-boom loader. While WT2 experienced more delays and production pressure, the findings suggest that WT3 represents a balanced option for small logging crews, ensuring sustainable forest operations in the face of workforce challenges. [ABSTRACT FROM AUTHOR]

Felling and skidding are essential in the timber extraction process. But on the other hand, residual stand damage can't be avoided. This study aimed to analyze the impact of conventional and improved felling and skidding techniques on residual stands in natural forests. Three observation plots were developed to identify the types, numbers, and criteria of residual stand damage due to both techniques. The criteria were categorized as a) minor damage (<25%), b) moderate damage (25--50%), and c) major damage (>50%). It showed that the conventional felling and skidding techniques caused damages of 14.92% dominated by tree crown damage and 16.70% dominated by stem wounds, respectively. The residual stand damage due to conventional felling and skidding techniques was 31.62% categorized as medium damage. Meanwhile, improved felling and skidding techniques caused damage of 9.89% dominated by broken trees and 10.27% dominated by stem wounds, respectively. The residual stand damage due to improved felling and skidding technique was 20.16% categorized as minor damage. The improvement techniques can minimize residual stand damage by 36.24%. Therefore, a good understanding of forest concessionaires regarding RIL principles is necessary for achieving sustainable timber harvesting [ABSTRACT FROM AUTHOR]

Thirty-five years post-harvest, effects of harvest disturbances upon tree composition and aboveground biomass were evaluated in a water-tupelo (Nyssa aquatica)- baldcypress (Taxodium distichum) bottomland. The forested wetland, along the Tensaw River, is within the Mobile-Tensaw River Delta in southwest Alabama. Nine replications of four disturbances were evaluated: no harvest reference (REF), clearcutting with helicopter removal (HELI), HELI combined with skidder extraction simulation (SKID), and HELI combined with broadcast herbicide application (glyphosate) to sprouts and seedlings for two years (GLYPH). Thirty-five years post-treatment, species, diameter at breast height (DBH; 1.37 m or above swell) and tree height were measured within treatments and converted to aboveground dry weight biomass. Clip plots were installed for herbaceous and woody stems < 1.37 m. Density and biomass results indicate HELI and SKID are on a trajectory to produce species, densities and biomass similar to REF. GLYPH coppice and seedlings were removed, so GLYPH regenerated from seedbanks and flood disseminated seed. GLYPH has transitioned from an herbaceous freshwater marsh to an open woodland/savanna community. GLYPH exemplifies advantages of coppice for rapid tree regeneration and growth on sites with long hydroperiods. This research demonstrates the capacity for long-term recovery of forested wetland ecosystems following harvest where multiple site/stand factors favored recovery. Adequate stocking of flood tolerant species capable of stump sprouting favored survival of original species. Floods provided annual sediment deposits to offset rutting. Compaction was additionally ameliorated by shrink-swell clays. Finally, nearby forests provided seed sources for areas. Collectively, these factors favored rapid recovery from disturbances. [ABSTRACT FROM AUTHOR]

The article presents constraining factors of the use of traditional approaches for timber skidding in the winter logging period in the North-West Federal District of the Russian Federation. Based on the study of scientific literature, the classification of cable-railways is given, methods of fastening the platform or cable car to the traction cable, the peculiarities of cable selection are considered. The modes of operation of cable-railways are described (without an engine – as a timber slide, with an engine without a trailing cable, with an engine with a trailing cable), the basic requirements for cable-railways and factors limiting the scope of application of such roads are considered. A methodology for determining the driving forces is proposed. It takes into account the weight of the car moving on the slope, the number of cars, the angle of inclination of the track section, the resistance to car movement, additional resistance to car movement when passing curves, the weight of the cable, its length, the friction of the cable on the ground, sleepers and other obstacles, which depends on the condition of the track structure, the density of sleeper laying, ballast protruding on the surface, cable lubrication and other factors. In addition to the above, power losses from the resistance of track rollers when they are enveloped by the running down branch of the cable, friction losses in the trunnions of the winch drums and friction losses from the cable enveloping the winch drums were considered. The article discusses the conditions under which it is possible to move the car down the slope, as well as prevent slipping and provide cable braking in the grooves of the drums. Limitations for the use of cable-railways, depending on the nature of the track, rolling stock, slope angle of the track, average skidding distance, are determined. A technical solution to improve the existing cable-railways using an articulated carriage that increases the operational properties of cable-railways, is proposed. The proposed design allows to reduce the wear of cables and to organize timber harvesting, including on nonstraight skidding trails with rotation angles up to 45 degrees. At the same time, the design of the articulated carriage can be effectively applied on cable-railways already in operation. For citation: Svoykin F.V., Svoykin V.F., Sokolova V.A., Voinash S.A., Ariko S.Ye. Application of Cable-Railways for Timber Skidding. Lesnoy Zhurnal = Russian Forestry Journal, 2023, no. 5, pp. 115–125. (In Russ.). https://doi.org/10.37482/0536-1036-2023-5-115-125

Local effects of ground-based timber harvesting, such as soil compaction, are often important for forest management and resilience of forests. One way to evaluate the compaction of the forest soils is by the penetration resistance. Most often, however, the control over the weight of the means used to extract the wood is difficult to maintain, influencing therefore the outcomes of the comparison studies. In this study, a controlled experiment was set up to see how the penetration resistance is affected by the number of passes of three wood extraction methods. A first objective of the study was to characterize the undisturbed soils by the mean values of penetration resistance along the profile. The second objective of the study was to compare the changes in penetration resistance induced by the number of passes along the soil profile. The extraction means were selected based on their typical use in flat-land operations, namely horse logging, skidding and forwarding, and the weight of their loads was determined before the experiment; then, each one was tested in a different area by operating in a closed loop on flat land, with 15 passes over the respective testing area. Penetration resistance was sampled up to 80 cm in depth in 10 control points, as well as in 10 sampling points over the wheels’ footprints. Ten samples were taken on the latter after the first, second, third, fourth, fifth, tenth and fifteenth passes, and comparisons were set up based on natural changing points in penetration resistance found in the control areas. The comparisons found significant differences by an increase in penetration resistance for all three extraction means, and there was a difference by an order of magnitude and depth; horse logging affected it the least and forwarding the most in magnitude, while skidding seemed to produce more significant changes in depth. However, the magnitude and depth of these changes may have depended on the characteristics of the soils from the test areas, and it cannot be concluded that the found levels of penetration resistance will affect the trees located nearby the experimental trails. The problem of soil compaction should be further examined by dedicated studies, given the variability in soil characteristics and diversity in means used to extract timber.

The efficient planning and control of timber harvesting operations is crucial to growth productivity and reducing costs, and different systems or methods are applied to obtain elevated performance. In particular, cable yarding is a highly appreciated and very efficient wood extraction method in areas that are difficult to access with ground-based extraction machines. Combined logging systems are not diffuse and not often implemented. For this reason, the use and the application of innovative methods are limited. However, some combinations have recently been observed in forest operations. This study, conducted in a deciduous stand in Bulgaria, paid attention to the combination of a tractor-mounted tower yarder (Valentini V400) with a clambunk skidder (Timberjack 1010D), aiming to examine the viability and develop the operational efficiency of the two-stage extraction system and to define the time, log volume extracted per unit by the yarder and the clambunk, and the yarding and skidding costs. The researchers carried out a time-motion study and performed a regression analysis to identify those variables that are most likely to affect the duration of work elements and productivity. For cost analysis, the COST model was used. The mean productivity of the tower yarder was 10.34 m3/PMH and 8.11 m3/SMH, while for the clambunk skidder, the productivity was 6.23 m3/PMH and 4.93 m3/SMH. The net costs for the combined logging system were calculated as 120.87 €/PMH and 14.93 €/m3. This study adds new data about the correct use of both machines, supporting their application in beech forests.

The occurrence and aggravation of local defects in ball bearings are closely linked to the skidding behavior of the ball. Previous studies have given less attention to investigating the impact of localized defects on the problem of bearing skidding. To investigate the dynamic response of defective bearings due to skidding, a dynamic model of the ball bearing is developed that considers various factors, including self-rotation, revolution, and radial motion of the ball, as well as the contact forces and friction forces of ball/cage and ball/race, time-varying displacement excitation, and elastohydrodynamic lubrication (EHL). Experimental signals collected from a machinery fault simulator test rig are used to validate the accuracy of the proposed model. The impact of race defects on the vibration characteristics of the bearing is analyzed, and the patterns of variation in contact and friction forces within one cycle of inner race rotation are described. The results indicate that the presence of defects intensifies the force fluctuation of the ball and causes it to deviate from its normal rolling condition. By comparing the skidding characteristics of a healthy bearing with a defective one under slippage, local defects will increase the skidding ratio of bearings. The proposed model can investigate the impact of race defects on the vibration response of ball bearings under the skidding condition. [ABSTRACT FROM AUTHOR]

Sliding and spinning behaviors significantly affect the performance of rolling bearings, especially for dry-lubricated bearings, micro and macro sliding may lead to increased wear of the solid lubricating film. A unified rolling contact tribology analytical model is proposed for dry-lubricated angular contact ball bearings (ACBBs) considering the extreme conditions including high combined loads and rolling contact effects. A comprehensive solution framework is proposed to ensure the robustness of the model under different loading conditions. Equilibrium equations are solved to study the effects of friction coefficients, rotating speeds, and combined loads on the skidding and spinning characteristics of the ACBB. The results show that the rolling contact effects and combined loads significantly affect the skidding and spinning performance of the ACBB. Further analysis reveals that the skidding mechanism is related to the interaction between ball kinematical motion and traction forces. The developed analytical model is proved to more accurately predict the bearing kinematical and tribological behavior as it discards the raceway control hypothesis and considers the macro/micro-slipping, creepage, and self-spinning motions of the ball, which is validated using both the existing pure axial loading dry-lubricated ACBB model and the classical Jones—Harris model. The study would provide some guidance for the structure and lubrication design of dry-lubricated ACBBs. [ABSTRACT FROM AUTHOR]

Copyright of Rolling Stock (1002-7602) is the property of Rolling Stock Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Lubrication Engineering (0254-0150) is the property of Editorial Office of LUBRICATION ENGINEERING and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This paper develops a coupling model of cam-roller contact and roller-pin contact considering thermal effects based on the exhaust cam-roller unit of an internal combustion engine. For the steady/startup running processes, the skidding and the lubrication performance are obtained in a complete cam rotation cycle, and the effects of oil viscosity or modified load are also discussed. The results show that the most significant effect of skidding on the cam-roller unit is the increase in friction between the cam and the roller. In a cam rotation cycle, the slide-roll ratio is not constant, and its value may even be negative. Compared with the steady running process, skidding is more pronounced during the startup running process, especially at the beginning of the acceleration stage (0–18°). Reducing oil viscosity or increasing modified load can effectively reduce the skidding situation, and its effect is more obvious in the steady running process than in the startup running process. [ABSTRACT FROM AUTHOR]

The vibration characteristics and skidding behaviour of deep groove ball bearings (DGBBs) are significantly influenced by the evolution of local defects and thermal effects. In previous studies, the influences of skidding and thermal effects were not considered in order to simplify the model of defective bearings. But the presence of skidding and thermal should not be ignored to accurately simulate the operation of bearing. To gain a comprehensive understanding of the operational mechanism of defective bearings, it is crucial to examine the skidding and thermal characteristics of various defect types using dynamic modelling approaches. In this study, the DGBB dynamic model for seven types of defects is established, which considers the self-rotation, rotation, and radial motion of ball, the contact force, ball/cage and ball/raceway skidding, and the effects of thermal elastohydrodynamic lubrication (TEHL). Experimental data from a machine fault simulator test rig is utilized to validate the accuracy of the proposed modelling methods. The results indicate that compound defects (CDs) result in higher vibration amplitudes and more severe skidding phenomena compared to single defects (SDs). Furthermore, compound defects exhibit a greater thermal effect on the oil film in the contact area than SDs, significantly impacting the operational performance of the bearing. [ABSTRACT FROM AUTHOR]

Abstract Sliding and spinning behaviors significantly affect the performance of rolling bearings, especially for dry-lubricated bearings, micro and macro sliding may lead to increased wear of the solid lubricating film. A unified rolling contact tribology analytical model is proposed for dry-lubricated angular contact ball bearings (ACBBs) considering the extreme conditions including high combined loads and rolling contact effects. A comprehensive solution framework is proposed to ensure the robustness of the model under different loading conditions. Equilibrium equations are solved to study the effects of friction coefficients, rotating speeds, and combined loads on the skidding and spinning characteristics of the ACBB. The results show that the rolling contact effects and combined loads significantly affect the skidding and spinning performance of the ACBB. Further analysis reveals that the skidding mechanism is related to the interaction between ball kinematical motion and traction forces. The developed analytical model is proved to more accurately predict the bearing kinematical and tribological behavior as it discards the raceway control hypothesis and considers the macro/micro-slipping, creepage, and self-spinning motions of the ball, which is validated using both the existing pure axial loading dry-lubricated ACBB model and the classical Jones—Harris model. The study would provide some guidance for the structure and lubrication design of dry-lubricated ACBBs.

Logging is essential to provide society with fuel, building materials, furniture and myriad other needs. At the same time, the ecosystem must be conserved so that the resources are sustainable. This paper considers the impact of forestry activities on forest vegetation and soil indicators: mean height, mean diameter, mean age, tree stock, plant density, soil density, thickness and porosity. The authors analyse the effect of five types of forest machinery operating three extraction (skidding) procedures: butt-first, top-end first, and untrimmed trees. Butt-first skidding using the Amkodor 2242B wheeled tractor was found to have a minimal effect on plant valuation indices; the least damage to soil attributes was inflicted by crawler tractors skidding untrimmed trees. [ABSTRACT FROM AUTHOR]

Despite enormous research, material, and manufacturing advancements in bearings, these continue to fail in critical aerospace applications. Material and processing aspects of bearing, which are often secondary, then become the central theme of investigation in place of a systemic and holistic view. Therefore, unlike conventional failure analysis, the present review critically examines potential issues in functionality, operation, unusual assembly configurations resulting in opposing inputs to the rolling elements, high DN (diameter × rpm) situations, distress due to slip, skid, and fatigue. Contra-rotating bearing can alleviate the effect of opposing inputs in aeroengine bearings where both the races rotate. It covers both state-of-the-art and conventional concepts. A brief on bearing materials, both conventional and unconventional, is also presented. Various techniques for monitoring bearing health and fault diagnosis are outlined. Life testing of bearing is mandatory to improve the design, material selection, manufacturing, and analysis. While prediction of the B10 life of bearings using Weibull analysis is more prevalent among industries, aerospace industry prefers B1.0 life. A brief on future possibilities is also presented. The present review aims to bring an application perspective on aerospace bearings to prevent their failures and enhance life. [ABSTRACT FROM AUTHOR]

In many applications, mobile vehicles operate over rough terrains to handle certain tasks and missions. Therefore, they are designed with tracks to deal with such irregular surfaces. Motion control and steering of tracked vehicles under the influence of slipping while skidding are still an interesting topic for many specialists and researchers and need further investigation. In fact, modelling and control of skid-steered tracked vehicles with slipping are very challenging. In this paper, various control schemes are proposed to investigate the closed-loop dynamical performance of tracked vehicles using different desired trajectories. Three control strategies are formulated and tuned to handle the undesirable effect of slipping while skidding: (i) robust nonlinear controller, (ii) speed compensation-based fuzzy logic controller, and (iii) speed compensation-based proportional–integral controller. The proposed control schemes are designed to explore new methods of skid-steering control with slipping. Preliminary simulation results are introduced to verify the effectiveness of the proposed controllers, using different desired trajectories, and to demonstrate the feasibility of utilizing such controllers.

Knowledge about wood transportation distances is essential for sustainable forest management and related decision making in forest protection against fire or flood events. In this context, we developed the geoprocessing tool TraDis to allow for the calculation of two-dimensional (2D) and three-dimensional (3D) distance between a forest stand and the nearest forest road (i.e., pre-skidding distance) and the distance between this road and the nearest hauling place (i.e., skidding distance). The first aim of this study is to present the workflow for the calculation of the primary wood transportation distance using the TraDis tool. A detailed description, flowchart, and scheme are provided for these purposes. The second aim is to present the applicability of this workflow through a case study. The study area included 391 ha of forest stands, 58 km of forest roads, and 18 hauling places, and the transportation distances were calculated for various target objects, such as 366 forest stands, 10,341 square cells, 7220 hexagon cells, and 83,120 tree crowns. The results show that, while there is the ability to calculate the 2D distances for six forests, eight cells, and three crowns in one second, the calculation time for 3D distances is 1.6 times longer. Moreover, the pre-skidding distance and skidding distance at the 3D level were 3.6% and 0.9% greater than these distances at the 2D level, respectively. [ABSTRACT FROM AUTHOR]

Based on the cam-roller pair of an internal combustion engine, a mathematical model of transient thermal elastohydrodynamic lubrication under finite line-contact and the corresponding numerical solver have been established. Under an actual load spectrum and other working parameters from an industry partner, the detailed lubrication performance of the cam-roller pair has been obtained in a cam rotation cycle. Particularly, the influences of the roller convexity, the roller tilting and the skidding between cam and roller on the contact pair lubrication are presented. The lubrication performance of the cam-roller pair depends on the roller convexity markedly, and an optimal roller convexity can effectively reduce the probability of the lubrication film rupture and improve the uniformity of pressure distribution in the contact zone. The roller tilting can worsen the lubrication of the contact zone, and increase the possibility of lubrication failure. If the tilting is taken into consideration at the beginning of the roller convexity design, its negative effect can be effectively alleviated to a certain extent. The skidding results in noticeable increase in temperature and friction coefficient, which can deteriorate the contact zone lubrication. The results provide some theoretical data basis for the lubrication design of cam-roller pairs. [ABSTRACT FROM AUTHOR]

Beech (Fagus spp.) is one of the most common tree species in Europe and Western Asia. The implementation of sustainable forest Operations (SFOs) in beech forests is therefore crucial in terms of sustainable forest management. This review summarises the state of the art concerning time-motion studies carried out in beech forests, defining the work productivity and the related costs of different harvesting systems applied in these stands. The main focus in recent years on felling and processing operations has been the introduction of fully mechanised systems in beech forests, obtaining satisfactory results in terms of work productivity. However, the working performance is still lower than in coniferous stands. Skidding and forwarding resulted in suitable techniques for ground-based extraction, both showing a clear inclination towards increasing working performance when applying higher levels of mechanisation. Aerial extraction by cable yarders is particularly important in beech forests, considering that these are often located in steep terrains. Further efforts should be dedicated to enhancing the training for operators to extend the application of aerial extraction systems, which ensures good levels of work productivity and limited soil disturbances. In summary, this review aimed to give a clear insight into forest operations in beech forests which could be useful for forest managers, forest engineers and researchers in the sector of sustainable forest operations. [ABSTRACT FROM AUTHOR]

Roller bearings operating under light loads may suffer from skidding. The latter is more pronounced as the speed increases and may result in extensive wear and reduced service life of the bearing. The main objective of this study is to analyze skidding occurrence in a custom-made all-steel M50 bearing and a hybrid roller bearing subjected to the same operating conditions. The test bearings have a bore diameter of 90 mm, an outer diameter of 125mm and 26 rollers. The hybrid bearing features silicon nitride (Si3N4) rollers and steel rings (M50 outer ring and M50-NIL inner ring). The bearings feature special channels to allow for under race lubrication of the bearing components in relative motion. A suite of sensors were used and installed to detect skidding and monitor the overall performance of the test bearing such as vibrations and temperature. The effect of the radial applied load, shaft rotational speed, and oil flowrate on roller skidding has been investigated and discussed. Slip ratio for each of the bearings under various speed-load combinations was also determined and analyzed. Turbo-Oil 2380 was used to lubricate the test bearings at a constant temperature of 77 °C. Tests were conducted on a high-speed rolling bearing test rig, and data were recorded using a 24-bit data acquisition system. [ABSTRACT FROM AUTHOR]

In many applications, mobile vehicles operate over rough terrains to handle certain tasks and missions. Therefore, they are designed with tracks to deal with such irregular surfaces. Motion control and steering of tracked vehicles under the influence of slipping while skidding are still an interesting topic for many specialists and researchers and need further investigation. In fact, modelling and control of skid-steered tracked vehicles with slipping are very challenging. In this paper, various control schemes are proposed to investigate the closed-loop dynamical performance of tracked vehicles using different desired trajectories. Three control strategies are formulated and tuned to handle the undesirable effect of slipping while skidding: (i) robust nonlinear controller, (ii) speed compensation-based fuzzy logic controller, and (iii) speed compensation-based proportional–integral controller. The proposed control schemes are designed to explore new methods of skid-steering control with slipping. Preliminary simulation results are introduced to verify the effectiveness of the proposed controllers, using different desired trajectories, and to demonstrate the feasibility of utilizing such controllers. [ABSTRACT FROM AUTHOR]

The objectives of this investigation were to experimentally examine the cage motion and ball-cage contact forces for an angular contact ball bearing (ACBB) operating under various load and speed combinations. In order to achieve the objectives, a Counter Rotating Angular Contact Ball Bearing Test Rig (CRACTR) was designed and developed such that both the races of an ACBB can be rotated simultaneously in opposite directions, providing valuable insights into the ball-cage interaction. Five proximity probes were used concurrently to measure the in-plane (radial) and out-of-plane (axial) motion for three commercially available cage designs. Two load cells were used to measure the contact forces between the balls and cage pocket. The experimental results demonstrate that high inner race speeds and high axial loads develop the smallest and most circular cage whirl motions. Additionally, cage radius, cage pocket clearance, cage pocket area and cage inertia were the prominent factors affecting the magnitude of cage whirl. Experimental results also indicate that contact forces between the ball and cage pocket increase linearly with the increased race speeds. Ball-cage contact force was shown to be different for the three cages and was primarily governed by the cage pocket area and the cage radius. Results from this investigation can be utilized to predict the correlation between the ball-cage contact forces and the race speeds, and identify the key parameters governing the stable cage motion during bearing operation. [ABSTRACT FROM AUTHOR]

Farm tractors have been applied in forest operations to carry out several tasks such as tree/felling/process-ing, forwarding, loading, skidding and cable yarding. Farm tractors can be equipped with special logging equipment that allows for their safe and efficient work in the harvesting of forest stands. This research is aimed to collect and review available literary sources on the productivity of farm tractors during skidding operations. The study results showed that work productivity of farm tractors for timber skidding has been studied by several researchers around the world. According to the results, the reported work productivity of skidding with farm tractors varied from 1.2 m3/PMH0 to 15.8 m3/PMH0 among international studies. Main variables impacting the work productivity of skidding included skidding distance, load volume, number of pieces per turn, tree diameter, tree length, slope of skid trails and engine power. Proper skid trail planning, applying suitable skidding equipment (e.g. winches, sulkies etc.), considering suitable engine size and prop-er safety standards can all help improving the work efficiency of the farm tractors during timber extracting. The information provided in this research can help the forest industry users and researchers gain proper knowledge on the work productivity of farm tractors applied for timber skidding. The study results can be also useful for planning and development purposes within small-scale forest operations.

In view of the skidding of aero-engine spindle bearings under high speed and light load and based on the construction of a simulation model of an aero-engine cylindrical roller bearing，the effects of structural parameters such as roller number，roller length，initial radial clearance and cage guide clearance on bearing skidding and fatigue life are studied . The results show that the rate of bearing skidding can be effectively reduced by increasing the number of rollers，cage guide clearance，and reducing roller length and initial radial clearance. By using the orthogonal design method，the influence weights of roller number，roller length，initial radial clearance and cage guide clearance on bearing skidding，bearing fatigue life and inner raceway wear rate are obtained. Through comprehensive balance and optimization，it is obtained that when the number of rollers，roller length，initial radial clearance and cage guide clearance are 13，6 mm，-2 μm and 1 mm respectively，the cage skidding rate is 0.29%，and the inner raceway wear rate is 5.9×10-13 m3/s，which reduce the probability of skidding and abrasion failure of the bearings while ensuring the bearing life.

Forest soils are complex ecosystems including a huge biodiversity including different microbial communities that are responsible for soil nutrient cycling and organic matter decomposition. One of the main threats to forest soil health is soil compaction caused by forest exploitation activities and, in particular, by wood extraction operations. These latter may change the physical, chemical and, in turn, biological properties of soil, eventually impacting tree growth and regeneration. However, there is a significant lack of knowledge in understanding the response of soil microbial communities to soil compaction. Furthermore, most of previous studies did not properly frame the short-term response of soil microbiota to compaction, which could serve as an early indicator of soil health. This study aims to investigate and monitor the short-term response of forest soil to severe compaction stress integrating soil physico-chemical analysis with biological and biochemical analysis. To investigate the early response of soil microbial communities to compaction over time, forest soil was analyzed 8 and 12 months after the repeated passage of a tractor pulling some logs simulating skidding operations in a heavily trafficked area for wood extraction. Despite the initial strong increase in bulk density (up to 42 %), the soil almost recovered from compaction after just one year. Most of the soil chemical parameters (i.e. pH, C, and N content) were not affected by soil compaction, while the analysis of enzymatic activity showed a change of some functions upon soil compaction in the first 8 months, followed by a substantial recovery after one year. The microbial communities showed different responses to compaction, highlighting a greater bacterial community resilience in the short term compared to the fungal community, which showed persistent and significant shifts between compacted and not-compacted soil. We also identified some indicator species that may be useful for monitoring early changes in microbial communities and activities following soil compaction. • Machinery induced soil compaction was intense but transient. • Most of the physico-(bio)chemical soil properties already recover after 12 months. • Higher bacterial community resilience in the short term than fungal one. • Species possibly useful as early indicators of soil degradation were identified. [ABSTRACT FROM AUTHOR]

Due to the growing demand for timber, forest soils are increasingly exposed to mechanical disturbances, caused by forestry equipment. Even though using skidding machines to transport wood is detrimental to the physical state of the soil, this method remains the most common. Hence, there is a need to model the impact of skidding systems on the upper (fertile) layer of the soil. This study aims to develop such a model using the D'Alembert principle, the method of Laplace transforms, and a modified Kelvin-Voigt model. The work shows that subdividing the tractor-bundle-soil system makes it possible to consider the dynamic effect of the vibrating tractor on the soil and soil's ability to undergo deformation separately. In addition, the study developed individual models for the first subsystem that determine vibration effects on soil caused by an unloaded tractor and two loaded skidding systems using different methods of semi-suspended skidding. The present findings can be used to predict the degree of dynamic soil compaction without conducting direct on-site experiments and thus minimize the negative impact of forestry operations on the local ecosystem. The current data also allow simplifying design models for complex forwarders.

The paper considers a method for calculating the skidding in cylindrical roller bearings under contact hydrodynamic friction and confirms its compliance with experimental data on skidding at various values of radial load and radial clearance. Dependences of the skidding value of bearings 2672934 and 1032930 on the radial load and bearing clearance, which are critical for the occurrence of seizing, are determined. [ABSTRACT FROM AUTHOR]

This paper develops a coupling model of cam-roller contact and roller-pin contact considering thermal effects based on the exhaust cam-roller unit of an internal combustion engine. For the steady/startup running processes, the skidding and the lubrication performance are obtained in a complete cam rotation cycle, and the effects of oil viscosity or modified load are also discussed. The results show that the most significant effect of skidding on the cam-roller unit is the increase in friction between the cam and the roller. In a cam rotation cycle, the slide-roll ratio is not constant, and its value may even be negative. Compared with the steady running process, skidding is more pronounced during the startup running process, especially at the beginning of the acceleration stage (0–18°). Reducing oil viscosity or increasing modified load can effectively reduce the skidding situation, and its effect is more obvious in the steady running process than in the startup running process.

One of the basic requirements for sustainable forest management in mixed broadleaved stands is to provide suitable conditions for natural regeneration of trees. These conditions include, but are not limited to, the frequency, quality and the composition of seedling species. Compacted soil layers caused by forest machinery traffic are the most common problem affecting seedling establishment and growth after skidding operations. In this study, we evaluated the frequency, quality, diversity of seedling species and physicochemical properties of soil on 10-, 20- and 30-year-old abandoned skid trails. Further comparison to the values of the mentioned above parameters in control areas allowed for the evaluation in terms of natural recovery processes, under varying traffic intensity and the longitudinal slope of the skid trails in a mixed broadleaved forest. Results showed that there is a significant positive trend of recovery for soil physicochemical properties and ecological characteristics (density and quality) of seedling growing on the skid trails. The time required to recover soil properties and ecological attributes of seedlings increased with increasing traffic intensity and slope of the skid trail. Our results showed that it takes 20 and 30 years to fully recover the chemical and physical properties of the soil, respectively. On the 30-year-old skid trails, density and species diversity indices were fully recovered, but the quality of the seedlings was not restored to the control conditions. The results suggest the importance of a proper planning of the skid trail network, avoiding in particular skid trails with a slope gradient higher than 20%. [ABSTRACT FROM AUTHOR]

The results obtained in this article relate to the scientific and technological development of the timber industry. The main idea of the article is based on the possibility of concentrating several forest plots designated for felling with different percentages of cut components within a single cutting area. On the logging site created in this way, single main skidding and skidding trails were laid, allowing the entire range of logging operations to be carried out. The shape of such combined cutting areas can be a complex geometric figure. The purpose of this article is to improve existing methods and mathematical dependencies to justify the average skidding distance of timber when combining adjacent forest areas into a single cutting area. The article uses the methods of mathematical analysis, in particular, the methods of differential and integral calculus. The developed algorithm made it possible to create a unified methodological approach to find the average skidding distance, regardless of the shape of the cutting area. An important distinguishing characteristic of the created mathematical dependencies is that they can be used in cutting areas consisting of several forest plots characterized by different wood stocks. The forest areas included in the cutting area may differ in the presence of a branched structure of the main skidding and skidding trails. The results obtained can be used effectively by logging enterprises in substantiating the production rates and planning the work for future periods. As a result of using the obtained mathematical dependencies, it becomes possible to effectively place loading points and skidding trails on the territory of the cutting area. [ABSTRACT FROM AUTHOR]

While polymer‐bonded explosives, PBX, have reduced sensitivity to ignition from mechanical shock or heating compared to conventional explosives, the investigation of the mechanical ignition mechanisms for PBX remains vital to assessing the safety during machining and general handling. Under frictional heating, hot spot generation due to high melting point contaminants in the interface is a suspected source for increased probability of ignition. To investigate such frictional heating, samples of PBX 9501 and PBX 9502 were impacted and skidded against a tangentially moving target and thermally imaged. Temporally resolved temperature and forces were simultaneously measured with and without 300 μm silica grit at the frictional interface. A trend of increasing temperature was observed as the speed and tangential force on the sample increased. Grit particles in the frictional interface were found to act as frictional heat concentration spots owing to the grit's protrusion from the surface and lesser susceptibility to melting compared to the PBX. The coefficient of friction between PBX 9501 and the skidding surface was observed to be largely constant for forces and speeds at the lower end of the test range. In contrast, at high tangential speeds, the coefficient was found to be significantly lower. [ABSTRACT FROM AUTHOR]

• The present work seeks to construct a mathematical model of soil compaction. • The high demand for forest products stimulate the logging activity. • The primary impact of machinery is soil compaction. Soil compaction from wheeled vehicles poses a huge challenge for the forest ecosystems. Modeling the impact of skidding machines on the soil could help solve the problem. The present work seeks to construct a mathematical model of soil compaction under the cyclic dynamic loading of wheeled skidding machines using the vibration analysis method for elastic dynamic systems. The study found that 4 × 4, 6 × 6 and 8 × 8 forestry vehicles have similar amplitude-frequency characteristics regardless of driving speed and load. The analysis of soil compaction from dynamic loading revealed that loaded and unloaded skidder passes cause the least damage (21–31%) to forest roads compared to skid trails. As regards skid trails, 4 × 4 and 6 × 6 tractors were found to compact the soil by 23–50% in the first four passes. The subsequent passes will lead to 60–66% of compaction. Finally, 8 × 8 trucks cause 98–99% of soil compaction. The difference between the experimental and theoretical values of soil density does not exceed 12%. The unevenness coefficient of the soil compaction and the confidence interval fall within the acceptable range. The mathematical models are in good agreement with the experimental data and can be used to calculate the operating modes of wheeled forestry equipment. [ABSTRACT FROM AUTHOR]

The aim of this study was to evaluate skidding techniques, which result in minimal damage to the soil, depending on the slope and stand type. Thus, three skidding techniques with tractor for harvesting (suspended skidding [SS], using a skidding cone [SC], and cable-pulling [CP]) were used in six different study sites and the variations in soil properties were examined at three different slopes (0%–20%, 20%–33%, >33%), 2 different stand types (A, B), and 2 different soil depths (0–5 cm, 5–10 cm). Soil bulk density, soil organic matter, soil compaction, organic carbon (C), and total nitrogen (N) were determined. The Entropy and TOPSIS methods were used among the multiple-criteria decision-making methods for six different coniferous stands. With the combination of the Entropy and TOPSIS methods, we found that slope was an important factor in determining the preferred skidding technique. Suspended skidding was seen as the preferred method of skidding technique in the 0–20% slope group. For the 20%–33% slope group, the usability of the three methods varied depending on stand type and soil depth, whereas the technique using a skidding cone was found to be the preferred skidding technique in the > 33% slope group. [ABSTRACT FROM AUTHOR]

Animal logging is one of the most ancient wood extraction methods and it is still applied in different parts of the world, including industrialised countries. Animal logging is often imagined as a low-impact method and sometimes, or rather often, it is recommended as a best-management practice. However, the literature findings depict a more complex scenario, and the goal of the present review is to shed light on the topic of environmental sustainability of logging operations performed by animals. Usually, animal logging causes less pollutant emissions and less damage to the residual stand in comparison to ground-based mechanised extraction methods. However, when applied in commercial forestry interventions such as coppicing, animal logging showed levels of soil compaction in line with those of ground-based machinery like tractors, skidders and forwarders. Specifically developed trials revealed that in the animal skid trails a strong disturbance to the soil microarthropod community occurred. Furthermore, the soil features in the animal trails seemed to get worse over time after logging, thus suggesting the possible presence of strong localised erosion along these trails. Despite the strong need to further investigate this topic, concerning the ecological aspects of forest soil which were generally neglected by the literature, the use of animal logging can be recommended in the case of small-scale forestry with wooden material sparsely located throughout the logging site. In the case of commercial logging on steep slopes instead it is recommended to replace animal logging with cable-based extraction systems. • Logging operations by the use of animals are still very common. • Animal logging causes lower emission and less damage to the residual trees than machinery. • Animal logging can cause disturbance to soil physicochemical and biological features. • Animal logging is recommended for isolated pockets of timber to be harvested. • Cable systems should be preferred to animal logging on steep slopes. [ABSTRACT FROM AUTHOR]

• The dynamic model of angular contact ball bearing is established. • The cage instability is investigated from aspects of impact and friction. • The cage instability behavior is different with/without gross skidding. • The effect of cage material and clearance ratio on the cage stability are explored. As a key component of machines, angular contact ball bearings are continuously required to operate at high speeds, cage instability has become a prominent problem, which will seriously affect the performance and service life of bearings. In this study, cage instability is investigated based on the dynamic model considering gross skidding and the interaction between balls and raceways, cage, and guiding surfaces. The impact force and friction between the ball and cage pocket, as well as the cage instability under varying situations, are studied. The results indicate that a lower friction coefficient and a lower elastic modulus of the cage may improve cage stability, but a bigger cage pocket clearance will result in cage instability under high-speed conditions. This study may offer recommendations for enhancing the motion stability of the cage. [ABSTRACT FROM AUTHOR]