Aging social infrastructures necessitate increasing maintenance and management efforts. Accurate deflection measurement is essential for evaluating bridge integrity. The sampling moiré method, using digital cameras to capture grating patterns on structures, typically requires a rigidly fixed camera. However, locating suitable fixed points for photographing bridges overseas or mountains is often impractical. Recently, drone-mounted cameras have emerged as a promising inspection technology for bridges and transportation infrastructure. This study introduces a novel displacement measurement method with drone aerial photography and moiré phase analysis. Laboratory tests on a 50-mm-pitch grid pattern demonstrated its effectiveness, alleviating the need for fixed cameras and enabling deflection measurement in diverse real-world scenarios.

Capturing the dynamics of rapidly changing fluids presents a major challenge in fluid mechanics. In this paper, we introduce a high-speed digital holographic tomography system designed to advance fluid dynamics research. The proposed system enables three-dimensional (3-D) visualization of fast and irregular airflow. It combines two lasers with different wavelengths, which significantly reduce interference from object beams using off-axis multiplexing. A single high-speed camera simultaneously captures holograms generated by the interference of reference and object beams from six different perspectives. In our experiments, the system successfully achieved 3-D visualization of asymmetrical airflow caused by high-pressure air breakdown, collecting data at a rapid rate of 2,000 frames per second. This enabled us to effectively track the 3-D path of the air breakdown phenomenon during discharge. Additionally, we achieved 3-D visualization of the density field of an asymmetric jet gas. This fast holographic tomography system not only provides the capability for 3-D visualization of asymmetric airflow but also holds significant importance for understanding the behavior of fluids under high-speed dynamic conditions.

In this study, we propose a method to obtain the strain and stress distributions of a viscoelastic body by combining digital image correlation and finite element analysis, based on the principle of superposition. In this method, the boundary conditions of the measurement area are determined by inverse analysis so that the displacement distributions as those obtained by measurements are obtained. A regularization scheme is introduced to reduce the influence of measurement errors near boundaries. The strain distributions are simultaneously obtained with the displacements. Meanwhile, the stress distributions are obtained from the variation of the strain components by taking into account the time-dependent mechanical properties of the viscoelastic body. The effectiveness of the proposed stress analysis method for viscoelastic bodies is demonstrated through simulation. Furthermore, as an example of the application of the proposed method, the stress analyses around the contact surfaces are shown. The proposed method can overcome difficulties of data processing in measurement and is effective for stress and strain analysis of viscoelastic bodies.

Plasma actuators are fluid control tools that utilize induced flow from non-equilibrium plasma and are capable of actively controlling surface fluid flow, such as suppression of separation. Their applications are expected to expand into various fields, including reducing wind turbine blade drag and minimizing air resistance in unmanned aerial vehicles. However, the low velocity of plasma-induced flow remains a significant research challenge for plasma actuators. This study aims to accelerate induced flow by changing the exposed electrode shape of the plasma actuator from a common straight shape to a combined shape composed of rectangular and serrated configurations. Observations from Particle Image Velocimetry (PIV) reveal that the use of combined electrodes induces three-dimensional turbulence in the flow, reducing the influence of frictional resistance from the wall surface and thus improving velocity compared to straight electrodes.

In this study, we proposed and verified a non-contact method for measuring the vibration state of the body to improve the measurement accuracy of body vibrations in vehicle comfort research, particularly regarding seat comfort. Previous studies measured vibrational acceleration by directly attaching sensors to the body, which could affect occupant comfort and increase psychological stress. To address this issue, we employed a non-contact measurement method using a laser displacement sensor, chosen for its high temporal and spatial resolutions. The vibrational acceleration of the body was calculated by taking the difference between the second derivative of the measured displacement and the vibrational acceleration of the sensor. The results show that in the low-frequency range, the vibrational acceleration obtained was nearly identical to that measured using directly attached sensors. This suggests that the proposed non-contact method is a viable alternative to traditional methods, potentially leading to more accurate and less invasive measurements in vehicle comfort research.

Over time, material degradation and structural aging (e.g. creep and shrinkage in concrete bridges) can affect the performance and health of a structure. These changes can be reflected in vertical deflection, a critical yet challenging physical quantity to measure. Measuring vertical deflection on existing bridges remains a challenge for current measurement technology. This paper introduces a method that uses a novel laser and video-based displacement transducer (LVBDT) to monitor the relative displacement changes simultaneously at different points within a certain distance of the structure. The proposed solution employs a linear laser to provide a consistent horizontal position reference at various locations simultaneously, so that the deflection difference between the mid-span and supports of the target bridge can be considered. To investigate the feasibility and accuracy of the LVBDT method, a four-point cyclic loading bending test was conducted in the laboratory which ensured a relatively controllable environment and exposed potential issues that could arise in actual field measurements in advance, thereby enhancing the feasibility of this measurement method for practical applications.

Cavitation bubbles grow and collapse due to impulsive pressure change in liquids and the damage could be imposed on the interfaces between liquid and solid walls. Liquid heavy metals are applied as high-intensity spallation neutron sources, e.g., mercury targets in SNS (spallation neutron source in ORNL) and MLF/J-PARC, etc. The cavitation damage gets to be one of crucial issues from the viewpoint of structural integrity, i.e., durability under high power operation. The relationship between the dynamic behavior of cavitation bubbles and the local impact which generated by the bubble collapse was systematically investigated using the element model on the interaction between solid wall and liquid where the direct visualization technique with a high-speed camera and electric spark thermal loading technique were used. The results show that the maximum bubble radius and the local impacts caused by bubble collapse can be estimated from the time information on the bubble dynamics (e.g., the time duration between bubble growth and collapse), which could be applicable to predict the cavitation damage in the structure with the interface between the liquid and solid, such as the mercury targets.