This study introduces recent efforts of the Architectural Institute of Japan (AIJ) to develop guidelines for largeeddy simulation (LES) of pedestrian wind environments (PWEs). Reynolds-averaged Navier-Stokes (RANS) models have been widely used for predicting urban wind environments following best practice guidelines (BPGs) by Franke et al. [Int J Environ Pollut 44, 1-4 (2011)] and Tominaga et al. [J Wind Eng Ind Aerodyn 96 (10-11), 1749-1761 (2008)]. Although RANS models can predict mean wind velocity and some turbulence statistics based on empirical assumptions, LES provides higher accuracy in resolving transient turbulence structures larger than the grid scale. With increasing urbanization, understanding instantaneous complex wind and wind-related phenomena around buildings is essential for ensuring pedestrian wind comfort and safety. However, LES applications face challenges owing to a lack of BPGs. This study outlines key recommendations for simulation setups and post-processing, including domain size, building modeling, grid generation, boundary conditions, turbulence modeling, discretization, convergence criteria, and reliability evaluation. Additionally, new benchmark cases are provided to support validation for PWEs. The AIJ working group systematically evaluated LES performance across urban scenarios to ensure practical applicability while balancing computational costs. These guidelines aim to enhance prediction reliability, thereby contributing to the standardization of LES applications for PWE and advancement of computational wind engineering.
Seepage boundary conditions are commonly used in groundwater simulations to allow groundwater to discharge at the upper surface of the model when groundwater head exceeds atmospheric pressure. However, the extent and transient behavior of the seepage zone are often unknown a priori and difficult to predict. The standard mathematical representation of seepage boundaries defines head as equivalent to elevation only when groundwater pressure exceeds atmospheric pressure, which is a mixed conditional Dirichlet and Neumann boundary condition. While this representation has been widely implemented in groundwater models, it is rarely noted that convergence is guaranteed only when both the efflux and zero-pressure conditions are simultaneously satisfied, often requiring unnecessarily small timestep sizes, resulting in low computational efficiency. This study presents a continuous-differentiable seepage face (CDSF) equation that replaces the conventional mixed boundary condition (or traditional seepage face, TSF) with a head-dependent Robin boundary condition, improving numerical stability and computational performance. It is a refined adaptation of an existing seepage boundary condition approach previously used in integrated surface-subsurface hydrologic models, specifically optimized for saturated flow simulations. Through a series of verification models, we demonstrate that the refined method provides robust and efficient solutions for seepage boundary conditions in saturated flow models. The results suggest that this CDSF approach improves accuracy and computational performance compared to TSF methods, offering a more stable alternative for groundwater modeling. These findings contribute to the advancement of subsurface hydrology by providing a practical framework for handling seepage boundary conditions in groundwater simulations.
This study aims to establish a conceptual architecture for the electrical power system required to support human activities on the Moon such as exploration and utilization of water resources in the permanently shadowed regions (PSRs) of the lunar south pole and the subsequent production of hydrogen and oxygen. This study was initiated in 2021 by the Ministry of Economy, Trade and Industry (METI) of Japan and is being conducted with the participation of universities and private companies.Although the International Space Station (ISS) provides valuable experience for the spacecraft electrical power system, this study adopted terrestrial electrical power infrastructure as the primary reference of the architecture from the stand point of the human activities on the Moon. This approach is justified because the power system on the Moon must accommodate diverse power generation methods, transmission networks, and a wide range of consumers activities. The study concludes that an electrical power system similar to terrestrial infrastructure is required for sustained activities on the Moon. However, several critical differences must be addressed, including the vacuum environment, extreme temperature variations, the impact of lunar regolith, and the high transportation cost associated with system deployment. The technologies established by the ISS remain applicable in crewed and habitable areas.Various candidate technologies application for the Moon electrical power system was evaluated based on their characteristics under the lunar environment and their suitability for supporting human activities, and then applicable technologies and the system architectures for the electrical power infrastructure on the Moon were identified. Key issues examined in this study include, the necessity of orbit-based power generation systems, the feasibility and applicability of wireless power transmission (WPT) for long-distance power supply, and the requirement for a two-fault-tolerant (2FT) system to ensure human life. Finally, a phased development and deployment strategy for the electrical power system as based on the possible architecture consideration on the Moon is discussed, addressing both preparatory and operational stages of human exploration on the Moon.
To reduce conflicts and ensure safe and comfortable mobility for both pedestrians and cyclists, the development of dedicated bicycle lanes is crucial. However, compared to many European cities, Japanese roads are often narrower, making it challenging to allocate dedicated space for bicycles. Effectively prioritizing the installation of dedicated bicycle lanes requires a deep understanding of real-world street usage patterns. This study provides a quantitative assessment of how spatial separation, operationalized as the installation of dedicated bicycle lanes, affects cyclists’ safety and rideability, based on image analysis. The analysis utilizes camera data collected in Fukuyama City, focusing on dedicated bicycle lane before and after installation. The results indicate that while the introduction of dedicated lanes reduced the available space and subsequently decreased bicycle speeds (i.e., did not improve rideability), the physical separation between bicycle and pedestrian areas significantly reduced interactions between pedestrian and bicycle, leading to enhanced safety. Therefore, although no improvement in rideability was observed, the study suggests that the development of dedicated bicycle lanes has a positive impact on safety and supports their strategic implementation.
