The Steiner Linear Ordering Problem: Application to resource-constrained scheduling problems

When examined through polyhedral study, the resource-constrained scheduling problems have always dealt with processes which have the same priority. With the Steiner Linear Ordering problem, we can address systems where the elements involved have different levels of priority, either high or low. This allows us greater flexibility in modeling different resource-constrained scheduling problems. In this paper, we address both the linear ordering problem and its application to scheduling problems, and provide a polyhedral study of the associated polytopes

Modeling Supply Chain Acquisitions

Companies that are considering an acquisition are generally concerned with combining businesses successfully. Acquisitions are strategic decisions, aimed at increasing the current operations as well as posi-tioning themselves for future success. The aim of this dissertation research reflects that ambition: providing decision support models and methodologies for making network design decisions that enable successful current and future supply chain operations. These businesses operate in an uncertain world, where de-cisions regarding supply chain network design must be made despite the possibility of unforeseen future events that may disrupt or damage the supply chain. In an effort to aid decision makers in designing sup-ply chain networks that can operate well in the uncertain future, we offer both a deterministic and a robust optimization model that consider both cost and network connectivity as objective functions. Decision mak-ers are able to evaluate several solutions with different cost and connectivity values, choosing the levels that best serve the needs of their newly merged company. The proposed robust optimization model also allows decision makers to control the conservativeness of the model while making good decisions despite uncertain or incomplete data, which is not uncommon in acquisition scenarios

Testing Mobile Chippers for Chip Size Distribution

Nine chippers were tested for particle size distribution, in order to a) see how chips produced with these machines matched the quality specifications set by the district heating plants of Northeastern Italy and b) detect significant differences between machines. The benchmark was set by collecting chip samples from fourteen district heating plants in the region of interest. The effect of operator skill was minimized and all machines were fed with the same assortment: logs, supplied in lengths varying between 2.4 and 6 m. All logs had similar moisture contents, which typically ranged between 33 and 37 % on a fresh weight base. Mobile in-woods chippers fed with limb-free logs produce high-quality chips, whose particle size distribution matches that of the best chips normally fed to the Italian district heating plants. Indeed, all the tested machines produced chip samples containing almost no oversize particles, very little fines (0.5 to 1 %), and a large majority of chips within the 3-45mm range (95 to 99 %), except the auger-equipped Laimet, which is designed to produce larger chips. There were statistically significant differences between machines and machine types, which were not affected by possible variations of the tree species processed

The Effect of New Silvicultural Trends on Mental Workload of Harvester Operators

Close-to-nature (CTN) forestry offers many advantages, but makes management more complex and generally results in lower harvesting productivity and higher harvesting cost. While the higher harvesting cost of CTN is widely acknowledged, few ever consider the potential impact on operator workload, as the harvesting task becomes more complex. This study aimed to determine the mental workload of harvester operators under two silvicultural regimes: »pure conifer« stand and »mixwood« stand. In total, 13 harvester operators with varying experience levels were monitored for work performance and mental workload when operating a harvester simulator in two virtual stands designed according to the above-mentioned silvicultural regimes. Mental workload was assessed using the NASA Task Load Index (NASA-TLX) interview method and heart rate variability measurements, during two 30-minute test sessions performed in the »pure conifer« and the »mixwood« stand, respectively. As expected, operating in a more diversified »mixwood« stand resulted in a marked productivity loss, estimated between 40 and 57%. The study also confirmed the increased aggravation of mental demand, effort and frustration experienced by the operators when passing from the »pure conifer« stand to the »mixwood« stand. Such increase in mental workload was independent of the age and experience of the operators. Results can be used to paint a more holistic picture of CTN forestry and its implications for harvester operators. Besides increasing the number of subjects being monitored, future studies should focus on live forest operations

Quantitative and qualitative workload assessment in steep terrain forest operations: fostering a safer work environment through yarder automation

Many forestry roles have changed from being manual tasks with a high physical workload to being a machine operator task with a high mental workload. Automation can support a decrease in mental fatigue by removing tasks that are repetitive and monotonous for the operators. Cable yarding presents an ideal opportunity for early adoption of automation technology; specifically the carriage movement along a defined corridor. A Valentini V-850 cable yarder was used in an Italian harvesting setting, in order to gauge the ergonomic benefit of carriage control automation. The study showed that automating yarder carriage movements improved the ergonomic situation of the workers directly involved in the related primary tasks. However, the caveat is that improving one work task may negatively affect the other work tasks, and therefore introducing automation to a worksite must be done after considering all impacts on the whole system. Practitioner summary: Automation decreased the winch operator’s mental workload while improving overall productivity. At the same time, the mental and physiological workload of the operator tasked with bucking were slightly increased. Ideally, winch automation should be coupled with bucking mechanisation to balance the intervention and boost both operator well-being and productivity.publishedVersio

Manipulating Chain Type and Flail Drum Speed for Better Fibre Recovery in Chain-Flail Delimber-Debarker-Chipper Operations

A chain-flail delimber-debarker-chipper (CFDDC) was adapted for treating smaller trees than normal by replacing the standard flails with lighter ones, and by reducing flail drum rotation speed. The machine produced 16 full containers (24 t each) for the standard configuration and 24 full containers for the innovative one. For each container the researchers measured: original tree mass, chip mass, time consumption and fuel use. Results indicated that the innovative setting accrued a 12% improvement on fiber recovery compared with the standard setting (control). At the same time, productivity increased by 20% and fuel consumption was reduced by 30%. Product quality was largely unaffected, with bark content remaining below the 1% threshold specification. If at all, product quality was improved through the reduction of fine particles, possibly derived from less diffused fraying. These results have triggered the real scale adoption of the new setting by contractors who participated in the study. The success of the innovative treatment is likely explained by its better alignment with the weaker structure of small trees from low-yielding stands

Production de biomasse à usage énergétique par la gestion des pineraies du Frioul

Dans la région montagneuse du Frioul, au nord-est de l'Italie, les pineraies à dominante de pin noir et pin sylvestre couvrent quelques 36 000 hectares. Le Centre national de recherche italien a mené trois essais de récolte dans ces peuplements, pour vérifier si la récupération de la biomasse à usage énergétique était intéressante. Bien que décrivant une technique non pratiquée, pour l'instant, en France, la valorisation énergétique de la biomasse est un sujet qui attire l'attention de beaucoup de propriétaires forestiers, à la recherche de nouveaux marchés pour le bois, en région méditerranéenne aussi

Comparison of Cost Efficiency of Mechanized Fuel Wood Thinning Systems for Hardwood Plantations on Farmland

A harwarder is a machine used for both wood harvesting and extraction. A small and a large harwarder (SH and LH) were time studied whilst thinning hardwood plantations established on agricultural land in Italy. Two treatments were studied: whole tree sections (WT) or firewood logs integrated with tree tops (IH) were harvested and forwarded to the roadside. The selective thinning yielded 45 tonnes of fresh biomass (t) per hectare. The average productivity of the SH and LH with the WT harvesting treatment were 3.46 and 2.77 t per gross productive work hour, respectively. The SH was more efficient for felling and loading, while the LH was more efficient in the terrain transport work. The productivity of both machines was about 15% lower for IH treatment. The harwarder based thinning operation gave a harvesting cost between 18 and ‘ €/t under the conditions studied. Thus, the operational cost per t of the SH was less than for the LH. The harvesting cost decreased with increasing size of harvested trees for both machines. The level of stand damage caused by both harwarders was almost as low as the levels recorded in the literature for motor-manual thinning. The LH was able to handle larger trees than the SH in the studied conditions. The LH gives higher flexibility, since it can be used more efficiently in thinning of larger trees and in larger plantations than in the present study

Trends and Perspectives in Coppice Harvesting

Coppice management is applied to many species, in many countries and in many ways, so that several harvesting techniques have been developed depending on specific local conditions. However, all techniques designed for handling coppice stands must be suitable for coping with small stem size and stump crowding, and often with steep and generally difficult terrain. Traditional harvesting systems are labor intensive because they usually include motor-manual felling and processing into one-meter lengths at the stump site, and manual loading of the short logs onto pack animals or tractors. Thus, in industrialized countries, these systems are no longer viable and they are being replaced with mechanized cut-to-length and whole-tree harvesting, depending on site conditions. Mechanization dramatically improves worker safety, and compensates for the reduced availability of rural labor, with their propensity to perform heavy and low-paying jobs. Much progress has already been made, with the massive introduction of modern harvesters, forwarders and tower yarders in coppice harvesting operations. The presence of multiple stems on the same stump offers a serious challenge to the introduction of mechanized felling to coppice harvesting operations, because stump crowding hinders felling head movements. However, new machines have been designed that can handle coppice stumps. Further research should address the relationship between stump damage and regeneration vigor, in order to define new standards for cut quality. Silvicultural practice may need adapting to the new harvesting technology and to the products required by the modern bio-economy