This study investigates the effect of axial blade height (H) on the internal flow and aerodynamic performance of a biradial turbine in oscillating water column (OWC) wave energy converters. The axial-to-radial ratio (H/R) was varied from 0.98 to 1.23, with a focus on analyzing its effects on turbine efficiency (η), pressure fields, and vortex formation within the turbine. The results revealed that H/R = 1.23 delivered the highest efficiency (η ≈ 0.72), highlighting the significant impact of axial blade height on the aerodynamic behavior of the turbine. At this ratio, pressure distribution was more uniform, and vortical structures visualized via the λ₂ criterion were coherent and aligned along the axis, indicating improved flow stability. In contrast, the H/R = 0.98 case showed irregular vortices and reduced flow coherence. These results underscore the importance of internal flow behavior and suggest that maintaining H/R between 1.1 and 1.12 offers an optimal balance between efficiency, stability, and pressure recovery for design.

Numerical simulations of nitrogen flows passing through an orifice were performed to investigate the lowest temperature of the carbon steel piping. The piping temperature must be higher thant the minimum design metal temperature. The Joule-Thomson effect was considered in nitrogen flows for the first time. The simulation results showed that the temperature drop of the piping was more affected by the pressure ratio between the inlet and outlet than the heating from the piping outter wall.

Water flow measurement standards are established from 10 dm³/h to 2000 m³ with measurement uncertainty of 0.06 % (k = 2) in Korea. The water flow measurement standards can cover a part of flow ranges established by KOLAS laboratories; the flow range from 1 cm³/h to 12000 m³/h. Proficiency tests can relate the water flow measurement standards to the working standards established by the KOLAS laboratories. Degree of equivalence is used as a proof for accreditation of the laboratories by KOLAS. This study introduces the water flow measurement standards established by KRISS. After that, a proficiency test, which was held in 2024 with the flow range from 10 m³/h and 40 m³/h, is described. The degree of equivalence showed that 27 out of 28 KOLAS laboratories had measurement equivalence with the water flow measurement standards at KRISS.

Precise control of droplets within microchannels is essential for a wide range of droplet-based microfluidic applications. Multiple external force mechanisms, encompassing optical, magnetic, electrical, and acoustic fields, have been employed for on-chip manipulation of droplets containing cells. However, many of these approaches rely on prior labeling of the in-droplet contents, followed by detection, which can introduce artifacts, compromise sample integrity, or adversely affect cell viability. In this work, we present a label-free droplet separation method that utilizes the traveling surface acoustic wave-induced acoustic radiation force (ARF). Using a cross-type microfluidic platform integrated with a slanted-finger interdigital transducer on a lithium niobate substrate, we achieved precise and simultaneous droplet separation. This acoustofluidic approach exploits the distinct acoustophoretic responses of elastic and rigid microparticles within droplets, as these particles exhibit unique ARF resonance peaks governed by their size and material properties.

Thermal fluid-structure interaction (TFSI) arises in many critical applications, where the coupling between fluid flow, structural deformation, and heat transfer governs system behavior. Accurately capturing such multiphysics interactions remains challenging, particularly when dealing with complex geometries, large structural displacements, and moving interfaces. Immersed boundary (IB) methods provide a versatile and efficient framework for simulating TFSI problems by decoupling the fluid and solid meshes and enforcing interfacial conditions through momentum and thermal forcing terms. This review presents a comprehensive survey of recent advances in IB methods tailored for TFSI. We classify the methods based on their interface treatment into two main categories: direct forcing approaches, which use smoothed forcing to approximate boundary conditions, and reconstruction-based methods, which impose sharp interface conditions via interpolation. Applications to both rigid and elastic structures are discussed, including cases involving forced and natural convection, particle-laden flows, and bioheat transfer in vascularized tissues. Coupling strategies, including monolithic and partitioned frameworks, are reviewed with a focus on their stability and computational efficiency. Finally, open challenges and future directions are outlined, highlighting the need for robust coupling algorithms, adaptive time integration, and interface-aware discretizations to address the complexities of TFSI.

This study investigated the aerodynamic characteristics of a simplified high-speed train scale model, parameterized using Bézier surfaces, under crosswind conditions through computational fluid dynamics (CFD) simulations. The reliability of the simulation methodology was validated by comparison with experimental results. The overturning moment coefficient (C_Mx,lee) of the leading vehicle (V1) was, on average, 1.7 times higher than that of the trailing vehicle (V2) across all yaw angles. The results showed that the nose shape of high-speed train induced strong flow separation and significant pressure variations, which critically influenced the aerodynamic loads generated by crosswinds. In contrast, flow disturbances originating from the rear of the train dissipated rapidly and had a limited effect on the overall flow field. Theses findings highlighted the significant role of a nose shape in determining the aerodynamic performance and running stability of high-speed trains under crosswind conditions.

This study investigates the effects of wall temperature and condensation region variations on internal flow characteristics and helium distribution in the ISP-47 TOSQAN experiment. The time t = 16000s during Steady-State 4 of the ISP-47 TOSQAN experiment was selected as the initial condition for the simulation. Sensitivity analyses were performed by varying the condensation wall temperature and condensing wall region. The results revealed that in configurations with narrow condensation regions, helium volume fraction was primarily influenced by steam condensation driven by wall temperature. In contrast, when the condensation region expanded, enhanced natural circulation led to more uniform helium mixing. These observations were obtained through empirical assessment based on numerical simulations, offering insights into the relative importance of condensation-driven helium enrichment versus flow-induced mixing. This study provides a basis for understanding gas stratification behavior under variable boundary conditions in severe accident scenarios.

This paper examines the computational parameters for the numerical simulation of a ship advancing at constant forward speed in irregular waves. Numerical 2-D wave tank is utilized. Using the EOM and wave-damping approaches, the reflection waves are minimized to secure sufficient data. The computational domain and parameters are obtained from the Froude scale law based on the peak wave component. The shortest wave component and H1/3 are selected to determine grid density and time step. The time series and autocovariance analysis methods are utilized to predict the statistical variables and uncertainties in irregular head waves under SS 4, 5 and 6. The converged time has been examined as well.

This study investigates how shock patterns and initial particle location affect secondary breakup in high-pressure gas atomization (HPGA). Axisymmetric 2D numerical simulations were conducted using molten stainless streel and argon gas in an annular-slit, closed-coupled gas atomizer at inlet pressures of 1, 3, and 5 MPa. As the inlet pressure increased, the stagnation point shifted downstream and oblique shocks intensified with a normal shock (Mach disk) forming at 5 MPa. To examine its influence on breakup behavior, single-particle injection simulations were performed at 1 and 5 MPa, targeting two radial positions near the jet centerline. In both cases, the parent droplet injected into the jet center experienced rapid initial breakup, forming a smaller droplet. The Weber number (We) along the trajectory of the parent droplet revealed high initial values due to large gas-molten metal relative velocity, initiating intense breakup. At 5MPa, We decreased sharply beyond the first Mach disk and exhibited oscillatory behavior due to interactions with a secondary Mach disk, inducing local We peaks that are expected to promote continued droplet breakup. The final droplet size distributions, including both parent and child droplets, showed that a particle injected into the jet center produced finer droplets with narrower size distributions, particularly at higher pressures.

This study aimed to evaluate the leaching phenomena of radioactive cobalt (Co) ions from OPC-based waste forms through ANSI/ANS-16.1-2019 compliant experiments and to establish a validated computational model. Physical and chemical stability assessments showed negligible changes in compressive strength upon Co addition. BET analysis revealed a porosity reduction from 17% to 11%. Leaching tests indicated extremely low Co release (less than CFL 6.00×10^-4) and a low effective diffusion coefficient (D_e = 1.98×10^-23cm²/s), suggesting excellent immobilization performance. A CFD result using COMSOL Multiphysics accurately replicated experimental data, by optimizing physical parameters with RMS error analysis. The Co dissolution behavior was implemented through Noyes-Whitney model, validated by experimental BET data. Last, the present model also incorporated a saturation-limited dissolution mechanism, aligning with experimental cumulative leaching trends, these results demonstrate the model's capability to predict from short-term leaching to long-term radionuclide transport assessments.

In agrivoltaic systems, the structural safety of solar panels directly determines the long-term stable operation of the system. Among various factors, Wind is the main factor causing structural damage by imposing significant loads and vibrations on the panels. In this study, a structural safety analysis is performed using numerical simulation to investigate the pressures and corresponding frequencies experienced by solar panels with different tilt angles under wind speeds ranging from 1 to 30m/s. The agrivoltaic systems consists of eight panel arrays, and the potential resonance risks are further evaluated. The results indicate that, at a tilt angle of 30°, when the wind speed reaches 30m/s, the frequency of the pressure experienced by the panel (5.80 Hz) approaches its natural frequency (5.37 Hz), indicating a significant risk of resonance. At 30° condition, the front panel of the second array experiences strong vortex-induced vibrations and the largest pressure amplitude due to wake vortex shedding, resulting in the highest risk of fatigue damage at this location. The research results provide a theoretical reference to support the reliable operation of solar panels in agrivoltaic systems.

Covert feathers, flexible structures attached to both the upper (suction-side) and lower (pressure-side) surfaces of a bird's wing, are passively deployed in response to aerodynamic forces and contribute to lift enhancement and stall delay. Despite their functional significance and the influence of their attachment positions, most previous studies on bio-inspired flaps have investigated configurations with flaps on either the suction-side or the pressure-side, without considering their combined aerodynamic effects. In the present study, we perform numerical simulations of a NACA0012 airfoil equipped with flexible flaps on both the suction and pressure sides to explore the aerodynamic performance of dual-side configurations, systematically varying the suction-side (x_s) and pressure-side (x_p) flap positions. Compared to the clean airfoil, the dual-side flap system provides superior lift enhancement, stemming from the strengthening of primary vortices, the generation of secondary vortices on both sides, and the pressure dam effect induced by the suction-side flap.

This study investigates the unsteady dispersion characteristics of hydrogen jets under varying flow velocities and inert gas purging conditions using computational fluid dynamics (CFD). Simulations were performed for six cases with identical total hydrogen mass release but different jet velocities and nitrogen purging conditions. A two-dimensional axisymmetric domain and the SST k-ω turbulence model were employed to predict transient concentration fields and jet behavior. Results show that higher jet velocities extend jet penetration and enhance initial mixing, leading to a wider flammable region near the nozzle, but also accelerate subsequent dilution. After hydrogen release stops, buoyancy dominates jet dispersion, causing residual hydrogen to accumulate in upper regions. Nitrogen purging effectively reduces hydrogen concentrations below the lower flammability limit more rapidly by displacing hydrogen and enhancing entrainment. These findings provide quantitative insights into hydrogen jet dispersion and offer practical implications for safety assessment and mitigation in high-pressure storage systems.