Finite element analysis of tensegrity structures in offshore aquaculture installations

Aquaculture is the fastest growing food producing sector in the world. Considerable interest exists in developing open ocean aquaculture in response to a shortage of suitable, sheltered inshore locations and possible husbandry advantages of oceanic sites such as increased water quality and oxygen supply, which improve production efficiency and the quality of fish. The extreme weather conditions experienced offshore leads to a focus on new structure concepts, remote monitoring and a higher degree of automation in order to keep the cost of constructions with an economically viable range. This paper proposes tensegrity structures in the design of wave compliant structures for offshore aquaculture. The objective of this paper is to study several different combinations of pre-stress and stiffness and determine how they influence the stiffness of the tensegrity structure. The finite element analysis program ABAQUS™ has been used to investigate the load carrying capacity of a tensegrity beam structure. The stiffness properties of the tensegrity beam were observed to be highly non-linear and dependent on pre-stress and spring stiffness. When designing a tensegrity beam, both pre-stress and spring stiffness should be considered to ensure the desired structural properties. A large strength to mass ratio and promising properties with respect to control of geometry, stiffness and vibration could make tensegrity an enabling technology for future developments. The suggested concept, the tensegrity beam, shows promising stiffness properties in tension, compression and bending, which are relevant for development of open ocean aquaculture construction for high energy environments.     

Effects of compaction on soil hydraulic properties,penetration resistance and water flow patterns at the soil profile scale

The aim of this study was to quantify the effects of compaction on water flow patterns at the soil profile scale. Control and trafficked plots were established in field trials at two sites. The trafficked treatment was created by four passes track‐by‐track with a three‐axle dumper with a maximum wheel load of 5.8 Mg. One year later, dye‐tracing experiments were performed and several soil mechanical, physical and hydraulic properties were measured to help explain the dye patterns. Penetration resistance was measured to 50 cm depth, with saturated hydraulic conductivity (K_s), bulk density, and macroporosity and mesoporosity being measured on undisturbed soil cores sampled from three depths (10, 30 and 50 cm). Significant effects of the traffic treatment on the structural pore space were found at 30 cm depth for large mesopores (0.3–0.06 mm diameter), but not small mesopores (0.06–0.03 mm) or macroporosity (pores > 0.3 mm). At one of the sites, ponding was observed during the dye‐tracing experiments, especially in the trafficked plots, because of the presence of a compacted layer at plough depth characterized by a larger bulk density and smaller structural porosity and K_s values. Ponding did not induce any preferential transport of the dye solution into the subsoil at this site. In contrast, despite the presence of a compacted layer at 25–30 cm depth, a better developed structural porosity in the subsoil was noted at the other site which allowed preferential flow to reach to at least 1 m depth in both treatments.     

Correction to: Precision agriculture research in sub-Saharan Africa countries: a systematic map

Precision Agriculture - A correction to this paper has been published: https://doi.org/10.1007/s11119-021-09796-w     

Production strategies in the Swedish softwood sawmilling industry

The strategic production decisions to improve profits for sawmills can be described in three main dimensions. More value-added production increases unit revenues, larger volumes reduce fixed costs per produced unit, and improved productivity reduces unit costs. Using data about the Swedish sawmills and cluster analysis, six groups of sawmills were defined with these strategy dimensions. Characteristics of each strategy are presented concerning ownership, location, technology, and economic indicators. The results indicate that different groups of Swedish sawmills employ different production strategies, which are reflected both in the dimensions, value-added shares, size, productivity, and by other technical and economic characteristics of the sawmills. The relationships between production strategy and profitability is also analysed and discussed.     

Protein-based adhesives for particleboards—Effect of application process

The main purpose of this study was to investigate wheat gluten (WG) dispersions as adhesives for particleboard. The effect of the dispersion concentration and two application methods were studied. When application method 1 was employed all the dispersion was added to the particles in one step, the particles were dried after the gluing. When using application method 2, the dispersion was added in two steps with drying of the glued chips between the first and the second addition of the dispersion. The amount of dry wheat gluten on dry particles was kept constant for all the experiments as was the pressing conditions. The performance of the wheat gluten dispersions was evaluated based on the following board properties: internal bond (IB), thickness swelling (TS) and water absorption (ABS). It is desirable to have high IB values, however, in the case of the TS and ABS lower values are preferable. The experiments were conducted according to a factorial screening design and SIMCA-P+ was employed as a multivariate analyzing tool. The results reveal that application method 2 seems to be beneficial, with regard to the board properties. Furthermore, it appears as, regarding the IB of the boards, the preferable dispersion concentration depends on the employed application method. When application method 1 is used a higher concentration seems to be better, in contrast for application method 2 a lower concentration of the dispersion may be beneficial. The improved properties obtained using application method 2 is proposed to be due to a more optimal penetration of the dispersion into the wood particles.