In a sustainable city, public transportation is prohibited from emitting greenhouse gases. A vehicle running on electric power generated from a green energy source does not emit carbon dioxide (a major greenhouse gas) and is thus optimal for reducing greenhouse gas emissions. To pursue this goal, we propose a public transport system consisting of electric buses that are quickly charged at every bus stop, using electric power generated from green energy sources. Such a system resolves the problem of low mileage per charge for heavy batteries. This system would also be able to effectively use low density and widely available solar energy to generate power at bus stops, which are widely distributed throughout a city. In this paper, an electric bus system that is rapidly charged at every bus stop, using electric power generated from green energy sources is introduced first. Next, the simple full-size electric bus simulator is constructed by extrapolating the parameters obtained from the single-passenger electric vehicle. Then, the simulations in some characteristic cases are performed, and the results are examined, especially the change of the state of charge (SOC) of the battery mounted on the bus, the energy charging to the bus at the bus stop and the travel time including the stoppages of 20 s at each bus stop. Last, the storage equipment capacity of the full-scale electric bus and the specifications of the bus stop, in particular the capacity of the solar modules, are estimated using the constructed simulator.
Direct current systems that lack an inertial force, such as fuel cells or photovoltaics, are expected to be used for electrical power in advanced sustainable cities. A small-capacity transmission network (microgrid) without inertial force has difficulties for converging short-term electric power fluctuations. Consequently, the frequency of transmission on such networks frequently diverges. Therefore, the electric power fluctuation due to cyclic fluctuation of an interconnected system of clean and renewable power sources (namely a solid oxide fuel cell (SOFC)-hydraulic generator, photovoltaics, and a wind-power generator) is investigated by numerical analysis in this study, together with means of controlling it. The characteristics of this fluctuation are clarified, and the setting range required to control the cyclic fluctuation of the transmission network is illustrated based on the relation between the inertial force of the hydraulic generator and battery (lithium ion) capacity.
In previous studies, questionnaire surveys were used to investigate the current circumstances of vehicle horn use and its effects on drivers and pedestrians in Japan. Several cities in other countries face more serious noise problems related to the use of car and motorbike horns. In urban areas of South Korea, frequent vehicle horn use on roads was found through onsite inspections. Measurements of noise at crossroads with heavy traffic revealed frequent horn use with high sound pressure level. In such areas, it is necessary to clarify the current circumstances of vehicle horn use, including its effects. Therefore, a survey on such use, similar to the previous work, was carried out. The survey included questions on the latest or last-remembered case of horn use in various situations in which the respondent was a driver or pedestrian. It was found that many pedestrians had experiences of being honked at by a single honk, two short honks and a long honk. Such honking mostly aroused negative psychological reactions such as feeling startled, a sensation of noisiness and feeling irritated. There were no significant relationships between questionnaire items regarding the driver's own horn use, suggesting there is no particular manner of such use. Relationships between driver awareness of their own horn use and its mode suggested that drivers who did not usually honk had feelings of reluctance to use the horn, and that they briefly honked out of necessity.
A novel method for automatically monitoring the preload degradation of linear guideway type (LGT) recirculating linear ball bearings of an X-Y table is proposed. Both simulations and experiments revealed that the reduction in the natural frequency corresponding to the yawing mode of the worktable was extremely sensitive to and varied linearly with the degradation of the LGT linear bearing preload. By attaching three accelerometers to the worktable of a machine tool and then exciting the worktable with a pulse from the servo motor of a feed drive, this study identified the natural frequencies of the worktable and their corresponding mode shapes by using operational modal analysis (OMA). Among all the natural frequencies obtained by OMA, the natural frequency corresponding to the specific yawing mode of the worktable was extracted using the modal assurance criteria, and the change in the extracted frequency was tracked; thus, the degradation of LGT linear bearing preload could be monitored automatically without exciting the worktable manually. In this study, the performance of this method was assessed experimentally, and this paper presents the method in detail.
The conventional phase-field topology optimization (PFTO) models minimize not only the objective function but also the interface energy. In the present study, a new PFTO model, which minimizes only the objective function, is developed by removing the curvature effect from the conventional PFTO model. Simulations of elastic strain energy minimization under a constant-volume constraint condition of a cantilever are performed using the developed and conventional PFTO models. From the simulation results, we confirm that the developed PFTO model that removes the curvature effects can efficiently optimize only the objective function.
The US-Advanced Boiling Water Reactor (ABWR), certified by the USNRC, is a third generation, evolutionary boiling water reactor design which is the reference for the South Texas Project Units 3 and 4 (STP3&4) Combined License Application (COLA) and incorporates numerous design and technology enhancements for improved safety performance. Nuclear Innovation North America (NINA) is the License Applicant for this new build project, and Toshiba is the selected primary technology contractor. The STP3&4 project has finished the USNRC technical review of the COLA and the final safety evaluation report (FSER) was issued by the USNRC in September 2015. Following the accident at the Fukushima Dai-ichi plant, the US-ABWR has been further reviewed for Beyond Design Basis Event (BDBE) safety using industry and regulatory guidance for USNRC Order EA-12-049 “Order Modifying Licenses with Regard to Requirements for Mitigation of Beyond Design Basis External Events (BDBEE)”. By virtue of the design approach, the US-ABWR is capable of providing an indefinite coping period for a station blackout. The use of installed systems with extended coping times is a significant advantage of the US-ABWR compared to most of the plants currently operating in the U.S. In addition, STP3&4 design incorporates enhancements consistent with the current US industry Diverse and Flexible Coping Strategies (FLEX) initiative. This paper summarizes the progress of the US-ABWR licensing and describes the technology and features of the US-ABWR design that contribute to safety post-Fukushima.
We treated numerically premixed flames at high Lewis numbers under the adiabatic and non-adiabatic conditions to elucidate the effects of unburned-gas temperature on intrinsic instability. Numerical calculations of two-dimensional unsteady reactive flow were performed, based on the compressible Navier-Stokes equation including one-step chemical reaction. Lewis numbers higher than unity were adopted, and radiative heat loss was employed. Superimposing a sinusoidal disturbance with sufficiently small amplitude on a stationary planar flame, we obtained the relation between the growth rate and wave number, so-called dispersion relation. When the Lewis number was higher than unity, the growth rate was small and the unstable range was narrow, compared with premixed flames at Lewis number of unity, which was because of the weakness of intrinsic instability due to diffusive-thermal effects. As the unburned-gas temperature became higher, the growth rate increased and the unstable range widened. This was because of the increase of the burning velocity of a planar flame. Taking account of radiative heat loss, we obtained small growth rates and narrow unstable range. To study the characteristics of cellular flames generated by intrinsic instability, we superimposed a disturbance with the critical wave number corresponding to the maximum growth rate. The superimposed disturbance evolved, and a cellular flame formed. The burning velocity of a cellular flame normalized by that of a planar flame decreased as the unburned-gas temperature became higher. As the heat loss became larger, the normalized burning velocity of a cellular flame decreased. This indicated that the heat loss inhibited the instability of premixed flames at high Lewis numbers.
We studied shaft tillage cultivation as practiced by an autonomous robot. Through previous studies, we determined that leg locomotion has a higher compatibility with the shaft tillage method than wheeled locomotion. Therefore, we are currently developing a legged robot for shaft tillage cultivation. In general, robots require a positioning system to autonomously travel in fields. The objectives of this study are the development of a localization method for an agricultural legged robot and an evaluation of the localization method. We assumed that an agricultural legged robot exhibits its slowest wave gait when walking. In this gait, after each leg is sequentially moved, the body is moved forward to complete one movement. This means that the body stops for a long time despite the robot is walking. The proposed localization method utilizes this unique characteristic of the legged robot. This study first reports on the development of localization using a laser distance sensor and a pan-tilt unit. Secondly, we report on a localization experiment to evaluate the localization accuracy of the proposed method. In this experiment, a total station with automatic target recognition was used as a ground truth. From the experimental results, we found that the measurement error between the proposed method and the total station data was approximately 14mm and 0.232°. Additionally, we found that we could improve the localization accuracy if we could fix the reflector sheet with higher accuracy and replace the laser distance sensor with a more precise resolution. Therefore, we determined that the legged robot will be able to autonomously travel with a positioning accuracy of approximately 10mm when using the proposed localization method.
In this paper, we present a parameter-free free-form optimization method for the strength design problem of a frame structure. The maximum von Mises stress is minimized under a given volume constraint. The strength design problems are formulated as distributed-parameter optimization problems under the assumptions that each member is varied in the off-axis direction to the centroidal-axis and the cross section is not varied with respect to the iteration process. The issue of non-differentiability inherent in this min-max problem is avoided by transforming the singular local measure to a smooth differentiable integral functional by using the Kreisselmeier-Steinhauser function. The shape gradient functions and optimality conditions theoretically derived are applied to the free-form optimization method for frames. With this method, the smooth optimal free-form of a frame structure is determined without any shape design parameterization, while minimizing the objective functional. Design examples are presented to demonstrate the validity of this free-form optimization method for strength design problems of a frame structure.
Small and major accidents and near misses are still occurring in nuclear power plants (NPPs). Risk level has increased with the degradation of NPP equipment and instrumentation. In order to achieve NPP safety, it is important to continuously evaluate risk for all potential hazard and fault propagation scenarios and map protection layers to fault / failure / hazard propagation scenarios to be able to evaluate and verify safety level during NPP operation. There are major limitations in current real time safety verification tools, as it is mainly offline and with no integration to NPP simulation tools. The main goal of this research is to develop real time safety verification with co-simulation tool to be integrated with plant operation support systems. This includes the development of static and dynamic fault semantic network (FSN) to model possible fault propagation scenarios and the interrelationships among associated process variables. The detailed methodology involves the integration of process models, construction of static FSN with fault propagation scenarios, and evaluation and tuning of dynamic FSN with probabilistic and process variable interaction values. The focus however of the present study is to highlight the need to incorporate error reduction in performing safety verification of NPPs. Two selected case studies were used to demonstrate the proposed methodology; one on a turbine trip and the other on steam generator tube rupture. In the former case, the error reduction concept was shown while the safety verification method was demonstrated in the latter case. The results confirmed the importance of error reduction as well as the need to constantly undertake safety verification of safety critical systems such as a NPP.