Papers by Takashi OKAYASU
Journal of the Faculty of Agriculture, Kyushu University
Journal of the Faculty of Agriculture, Kyushu University
Journal of the Faculty of Agriculture, Kyushu University
Tractor stability predominantly determines operator's safety. For a tractor parking on lateral sl... more Tractor stability predominantly determines operator's safety. For a tractor parking on lateral slopes, overturning accidents have been frequently discussed using mathematical models. While the existing static models remarkably contribute tractor overturning mechanisms, few of them have considered the stability from the perspective of tractor sideslip. In our study, a relatively precise quasi-static model presented recently was adopted as the base model. We expanded it by introducing potential tractor sideslips. While the original model pointed out the lateral slope angle as the main factor influencing tractor overturns, we investigated tractor slipping stability under the influences of the slope angle and the coefficient of friction. The dimensional parameters of the example tractor for simulation were set the same as those in the original work. It was found that the allowable friction forces of both the front and rear tires primarily depended on the coefficient of friction rather than the slope angle. By comparing the surfaces of the allowable friction forces and the corresponding friction forces, tractor slipping thresholds for the front and rear tires were identified. Caution areas implying certain ground conditions that will definitely cause tractor sideslip were marked accordingly. The results shown in this study provide a relatively comprehensive way to understand tractor static stability when both tractor sideslip and overturn are concerned.
Agricultural and Forest Meteorology
農林水産省農林水産技術会議事務局研究成果, 2016
IEEE Conference Proceedings, 2017
Journal of the Japanese Society of Agricultural Machinery, 2001
Environmental and Experimental Botany, 2022
Journal of the Faculty of Agriculture, Kyushu University, 2018
The aim of this study was to analyze the fundamental lighting characteristics (spectrum distribut... more The aim of this study was to analyze the fundamental lighting characteristics (spectrum distribution and light intensity) of a low-light LED unit and its effect on gas exchange in strawberry leaves. This unit was newly developed to provide low-cost supplemental lighting for greenhouses. The low-light LED unit was made using 24 LED module chips, each of which were 1 m in length and 43.2 W. The electricity consumption of this unit was only 55% of that of the highlight LED previously reported by Hidaka et al. (2013). The spectrum characteristics of low-light LED were measured using a portable spectro-radiometer. The photosynthetic photon flux density (PPFD) was measured using a photon sensor, and its distribution was measured at five different heights from a reference plane (110 cm × 150 cm). Gas exchange in strawberry leaves under low-light LED (Low LED treatment) supplemental lighting and no lighting (Control treatment) were measured using a leaf chamber system. The results demonstrated that the spectrum distribution patterns of the low-light LED and the highlight LED were similar; we found that the relative light intensity of both LEDs peaked once near a wavelength of 450 nm and again near a wavelength of 550 nm. The PPFD and its horizontal distribution showed that, as the height of the light source increased, the PPFD and lighting regions decreased and increased, respectively. On the other hand, as the height of 20 cm, PPFD under supplemental lighting with the low-light LED increased by 2.1 times than natural condition. As a result, stomatal conductance and transpiration rate increased by 1.5 times and 1.2 times, respectively; further photosynthetic rate increased by 2.2 times. Thus, the low-light LED was demonstrated to have suitable wavelength for crop production. Furthermore, applying supplemental lighting with the low-light LED significantly improved light intensity and accelerated photosynthesis in strawberry.
Journal of the Faculty of Agriculture, Kyushu University, 2016
Bulletin of the Institute of Tropical Agriculture, Kyushu University, 2013
In Bangladesh, more than 70% of the population are engaged in agriculture, however, the income of... more In Bangladesh, more than 70% of the population are engaged in agriculture, however, the income of the farmer is still low compare to other professions due to lack of proper information related to advanced agricultural production techniques and poor marketing system. In order to improve such situation, Kyushu University, Japan along with three Bangladesh collaborative partners has conducted a 3 year long grass-root project supported by JICA. The aim of the project has been to generate income for small (low income, small or no land owners) BOP (Bottom of Pyramid) farmers by providing the knowledge of chemical free farming through ICT (Information Communication Technology). In this article, we introduce the challenges we faced and summarize the impact of the project on socioeconomic improvement of targeted farmers.
Journal of the Japanese Society of Agricultural Machinery, 2000
Journal of the Japanese Society of Agricultural Machinery, 2006
Transportation Geotechnics, 2021
Abstract With the ballast aging, the changes in the size and shape of the ballast particle reduce... more Abstract With the ballast aging, the changes in the size and shape of the ballast particle reduce the drainage capacity, as well as cause a greater permanent deformation of the railroad ballast. Therefore, it is meaningful to investigate the effect of aging on the mechanical behavior of unsaturated ballast, and to estimate the cyclic plastic deformation by considering the aging effects. Here, “aging effect” means the increase in fine fraction content and the particle shape becomes rounded and smooth as compared with fresh ballast. In this study, the influence of aging on the cyclic plastic deformation of unsaturated ballast was evaluated through a series of cyclic loading triaxial compression tests. Test results indicate that the cyclic plastic deformation of ballast is seriously affected by water content, fine fraction content and drainage condition, and the increasing trend becomes more remarkable at the water-rich aged ballast under the fully undrained condition since the effective confining pressure decreases due to the generation of excess pore water pressure. Furthermore, the applicability of two types of estimation models (i.e., a semi-empirical model named University of Illinois at Urbana-Champaign (UIUC) model, and an elasto-plastic model named subloading surface extension (SSE) model) to the prediction for cyclic plastic deformation of unsaturated ballast is also verified in this study by comparing with results of cyclic loading triaxial compression tests. As the result, it is revealed that the UIUC model is suitable for predicting the cyclic plastic deformation of fresh ballast (or slightly aged ballast) with different water contents under the fully drained condition, and the SSE model shows good potential to estimate the cyclic plastic deformation of fresh and aged ballasts by considering the effects of water content and drainage condition. The findings of this study indicate that drainage conditions have a significant effect on predicting the cyclic plastic deformation of aged ballast, and appropriate test conditions for triaxial compression tests (i.e., CD and CU tests) should be selected according to hydraulic properties (i.e., permeability and water retentivity) of the aged ballast.
Journal of the Faculty of Agriculture, Kyushu University, 2016
The purpose of this study was to evaluate fuel efficiency of tractor using working cycle. First, ... more The purpose of this study was to evaluate fuel efficiency of tractor using working cycle. First, baler operation was conducted in Italian ryegrass farmlands and engine torque and fuel consumption were measured as field data. Second, baler operation cycle was developed using the field data. The arbitrary working cycles were generated by randomly selected micro-trips, minimum working patterns. Some of the arbitrary working cycles were selected and baler operation cycle was determined considering sum of squared difference (SSD). The baler operation cycle was evaluated using performance value (PV) comparing with driving cycles. The results showed that PVs of the driving cycles were 67 ~ 109% of the baler operation cycle. Third, fuel efficiency of the baler operation was evaluated by dynamometer test using dynamometer system and the baler operation cycle. The fuel consumption and engine power were measured while the engine acted on the baler operation cycle and fuel efficiency was evaluated. The results of t-test showed no significant difference between fuel efficiency by the dynamometer test and fuel efficiency of each farmland by the field test. Considering all results of this study, the baler operation cycle is feasible to apply to evaluate fuel efficiency of tractor with dynamometer system.
Journal of Japan Society of Civil Engineers, Ser. B1 (Hydraulic Engineering), 2019
Journal of the Society of Materials Science, Japan, 2001
Various constitutive models have been applied to the analyses of localized deformation of solids.... more Various constitutive models have been applied to the analyses of localized deformation of solids. However, most of them fall within the framework of the conventional plasticity premising that the interior of yield surface is an elastic domain and obeys the plastic potential theory in which the plastic stretching is independent of the stress rate component tangential to the yield surface. Therefore, they predict a stiff elastic response until the stress reaches the yield state and further a stiff elastoplastic response after yielding. On the other hand, the subloading surface model falling within the unconventional plasticity would be only the model capable of describing pertinently the plastic deformation induced by the rate of stress within the yield surface in general loading process including the unloading, reloading and inverse loading. Further, the numerical calculation by this model is quite efficient disusing the special algorism, e.g. the mean normal method and the radial return method in order to make the stress lie just on the yield surface in the plastic loading process since it contains the controlling function to make the stress approach automatically the yield surface in the plastic loading process. Further, this model is recently extended so as to describe the tangential stress rate effect, i.e. the inelastic deformation induced by the stress rate component tangential to the subloading surface. In this article the post-localized deformation of metal due to the shear band formation is analyzed by the finite element method incorporating the subloading surface model with the tangential stress rate effect. Thus, the influence of the tangential stress rate effect on the shear band formation is discussed exhibiting several examples of the deformation patterns.
Journal of Structural and Construction Engineering (Transactions of AIJ), 2021
Recently, with the progress of research on earthquake ground motion, it has become necessary to i... more Recently, with the progress of research on earthquake ground motion, it has become necessary to increase the out-of-plane shear force used in the design of reinforced concrete flat plates such as foundation slabs and underground outer walls. There is a concern that out-of-plane shear failure occurs in these flat plates of existing buildings with insufficient amount of shear reinforcement. However, effective seismic retrofitting of foundation slabs or underground outer walls is difficult because the construction work can be completed only from the inside of building. In order to deal with this problem, a post-installed shear reinforcement (PSR) method was developed.
Journal of the Japanese Society of Agricultural Machinery, Sep 1, 2006
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Papers by Takashi OKAYASU