Considerable research has been carried out to establish a rational assessment method for nuclear power plants against external projectile impact. Most of the empirical formulas have been proposed to quantitatively investigate local damage to reinforced concrete (RC) structures caused by rigid projectile impact. These formulas were derived based on impact tests performed normal to the target structure, while only a few impact tests oblique to the target structure were studied. This work aims to propose a new formula for evaluating local damage to RC structures caused by oblique impact based on experimental and simulation results. At present, we have validated an analytical method via comparison with experimental results and have conducted simulation analyses of oblique impact assessments on RC slabs using projectile with flat nose shape. In this study, the same analytical method will be used to investigate perforation damage to RC slabs subjected to oblique impact by projectiles with hemispherical nose shape. The effect of projectile nose shape on perforation damage to RC slabs, the residual velocity of projectiles and the time history of energy transmission will be discussed.

Effective utilization of biomass, including wood, is necessary for environmental sustainability. Bio-coke is a solid biofuel made from plant biomass. Bio-coke has been proposed as an alternative energy source to coal due to its high density and compressive strength. Bio-coke is produced by subjecting wood biomass to the hot press method, and the softening properties of hemicellulose and lignin in the raw biomass affect the formation, physical and mechanical characteristics of Bio-coke. In prior studies, we investigated the effect of raw material biomass composition and moisture content on flow-starting temperature, and compressive strength of the resulting Bio-coke. The purpose of the present study was to quantitatively determine the effect of biomass composition changes on flow-starting temperature and compressive strength on using cellulose-rich cedar trunk and lignin-rich cedar bark as raw materials. Due to the difficulty collecting a single form of biomass, the study of mixed raw biomasses is more relevant when evaluating practical applications of produced from these materials. The present study revealed that as lignin ratio increased, flow-starting temperature and Bio-coke compressive strength decreased. Furthermore, we developed a potential equation for estimating the maximum compressive strength of Bio-coke from the raw biomass chemical composition ratio and moisture content.

Throwing by a powered manipulator is an effective way for wide range transportation of an object and carrying an object in unmanned environments. The main problems of throwing are (i) how far the manipulator can throw the object and (ii) the accuracy of the landing position. Focusing on (ii), this paper proposes sensitivity analysis of the landing position with respect to the error covariance of dynamic parameters. Focusing on a planar 3-DOF manipulator, (1) the minimum set of dynamic parameters is introduced and identified based on a frequency weighted method for a nonlinear system, and its error covariance is also identified. (2) The calculation algorithm for sensitivity of landing position with respect to the minimum set of dynamic parameters is proposed. (3) By considering the error covariance of identification, an optimal throwing is designed and evaluated by simulations and/or experiments. Moreover, (4) the principal of sensitivity analysis is discussed from error ellipsoid point of view, and zero error throwing is designed.

A driver steering assistance control algorithm for a vehicle with an active front steering system is proposed in this paper. The control algorithm is designed so as to optimize turning performance and realize collision avoidance simultaneously under magnitude constraints on the front wheel turn angle and the lateral tire force. The control algorithm is developed based on a model predictive control law for tracking a time-varying reference signal. The proposed control algorithm is reduced to a convex quadratic programming problem. The effectiveness of the proposed method is shown by human-in-the-loop simulations.

This paper describes the optimum tuning of damped side-branch silencers. As is well known, a side-branch silencer is a type of vibration absorber; however, damped side-branch silencers have not yet been sufficiently studied. In this study, to derive the optimum tuning conditions of a side-branch silencer, modal analysis was applied to wave equations of a host acoustic field and a side-branch silencer. Using the equations of motion with the modal coordinate system, an equivalent discrete model of the coupled vibration system between the host acoustic field and side-branch silencer was obtained. The degrees of freedom of the equivalent discrete model were reduced to two by ignoring the non-related acoustic modes, and the two fixed point method was applied to the two degree of freedom vibration system to derive the optimum natural frequency ratio and optimum loss factor of the side-branch silencer. In addition, open-end correction of the side-branch silencer was formulated considering the effect of residual acoustic modes of the host acoustic field. A theoretical analysis with respect to the optimum tuning conditions and open-end correction was validated through simulations and experiments.

The “Flutter-mill” is a power generation device that can be parallelized and downsized more easily than conventional wind-power generators with the added advantage of lower manufacturing costs. Flutter-mills comprise a flexible sheet with an electric power generator at its leading edge. Flutter-mills exhibit complex power generation performance characteristics that are highly dependent on the specifications of the flexible sheet and the inlet flow velocity. In particular, the span width of the sheet affects the stability and flapping behavior significantly. Using the numerical analysis model, these complex flutter-mill characteristics can be estimated without experiments, and thereby numerical model inform the choice of the sheet dimensions, which are critical for designing an effective flutter-mill. Here, we present a numerical model that can provide a preliminary survey of the power generation performance and attempt to clarify the relationship between the aspect ratio of the sheet and the harvested power. The equation of motion for a flexible sheet includes rotational damping at the leading edge of the sheet to emulate the coupling effect between the sheet and the energy harvesting circuit. We verified the validity of our numerical model by evaluating its performance against previously published experimental results, and thus established the relationship between the aspect ratio of the sheet and the harvested power. We found that the local minimum value of the harvested power of the flutter-mill may be caused by the vibration amplitude at the leading edge of the sheet decreasing in the transition domain of the flapping vibration mode if the aspect ratio is large.

Living machines are expected to expand the limits of silicon microtechnology. Vorticella convallaria is a ciliated protozoa and a promising linear actuator. The use of Vorticella as a Ca²⁺-responsive actuator, in a small system, requires a reduction in the size of the membrane treatment of selectively patterned Vorticella. However, selective cell patterning and the electrolysis of cell membranes have not yet been combined; therefore, the development of a combined method is essential. The objective of this study is to develop a method for combining selective cell patterning and the electrolysis of cell membranes. A two-layer pneumatic device was fabricated in polydimethylsiloxane (PDMS), and the device and electrodes were clamped with acrylic plates. The deformation of the PDMS membrane was controlled by compressed air. The electrochemical reactions were visualized with fluorescein, and the temporal pH change was evaluated. Vorticella cells were introduced into a microfluidic device and were captured in chambers at a pressure of 21 kPa. They were immobilized in the chambers after incubation for 6 h. Further, OH^– was generated from the cathode by the electrolysis of water, and the bell-shaped bodies of Vorticella became spherical. This permeabilization treatment stopped both spontaneous contraction and cilia movement. The application of DC 3 V was sufficient for the electrolysis of Vorticella. Selective patterning and electrochemical membrane treatments are beneficial for facilitating the use of Vorticella as a Ca²⁺ responsive actuator in a small system.

This paper presents a numerical method for analyzing elastic wave scattering by multi-layered periodic structures in two dimensions. The proposed method is based on the boundary element method (BEM) and scattering matrix representing a relationship between incoming and outgoing waves in the vicinity of a periodic structure. First, we define the scattering matrix using a plane-wave expansion of the solution of the elastic problem. Then, we show the integral formulae that convert the solution of a system of boundary integral equations into elements of the scattering matrix. The proposed scattering matrix method with the BEM enables us to reduce the scattering problem in a multi-layered structure to a purely algebraic one in terms of the scattering matrix of each layer, resulting into less requirement in computational resources than in the methods which are based on the meshing of an entire boundary and solution of the corresponding boundary integral equations. Such a procedure called layer-doubling method is implemented in a numerically stable manner based on the eigendecomposition of a relevant matrix. Moreover, some scattering properties and phononic band structures of semi-infinite phononic crystals are yielded through an asymptotic analysis on the scattering matrix. Some numerical examples are presented to demonstrate that the proposed method can solve accurately scattering problems and also can calculate some related eigenmodes including the Bloch modes and guided waves within stacked structures.

Inconel 718 is a Ni-based superalloy, which shows excellent mechanical properties such as tensile strength, fatigue strength, and creep strength at high temperatures up to 700 ℃. However, as Inconel 718 is a difficult-to-cut material, it causes severe wear of machining tools. Fabricating Inconel 718 by Selective laser melting (SLM), a type of additive manufacturing (AM), is therefore expected as the manufacturing method to deal with this problem. However, it is impossible to completely prevent the occurrence of the internal defects in SLM parts. These internal defects deteriorate the mechanical properties such as the fatigue strength of SLM parts. Though the effect of the internal defect size on the fatigue limit of SLM alloys such as Ti6Al4V and AlSi10Mg has been extensively investigated, its effect on SLM Inconel 718 has not yet been investigated. In this study, Inconel 718 specimens with various internal defect sizes were fabricated by SLM and the effect of the internal defect size on their fatigue strength was investigated. Internal defect size distribution in as built specimen can be approximated by Gumbel distribution. The specimens containing internal defects with a diameter of about 400 μm showed no significant decrease in the fatigue strength. In the case of the plane specimen, the fatigue limit predicted using the statistic of extremes and the √area parameter model was 40% higher than that obtained experimentally.

Mathematical modeling of the thoracic aorta is important for detecting extraordinary and unusual stress or strain distributions of the hypertensive aortic wall, even in early stages, and for understanding the development and progression of various cardiovascular diseases. In a freshly isolated aortic media, which mainly comprises elastic laminas (ELs) and smooth muscle layers (SMLs), circumferential EL waviness and longitudinal EL undulation are often observed because of the buckling of ELs, which is closely associated with residual stresses of ELs and SMLs in the aortic wall. However, the mechanism underlying EL buckling or specific mechanical interactions between EL and SML remains unclear. We hypothesized that the longitudinal EL undulation is likely formed by the superposition of the circumferential EL waviness along the aortic axis. Hence, a series of numerical simulations were conducted based on a design of experiments approach by implementing residual stresses. We identified that the prestress initially administered to ELs in the circumferential and axial directions, and the predefined internodal gap, which couples the EL and SML, are essential mechanical parameters to computationally reconstruct the circumferential EL waviness and the longitudinal EL undulation at an unloaded state. In addition, a mechanical balance between the assigned prestresses along the circumferential and axial directions is crucial for successful representation of structural buckling of EL in the unloaded aortic media. Although further study is required, we have verified that our hypothesis is reasonable in the current work. Moreover, the information we obtained here will greatly help improve understanding the roles of EL and SML in the aortic medial wall at the in vitro and in vivo states, while simultaneously providing a basis for more sophisticated computational modeling of the aorta.

In present study, human subject experiment including sensory evaluation was conducted to investigate gripping comfort during gripping spherical and columnar objects and to identify important factors that affect gripping comfort score. Contact pressure measurement using a pressure sensor sheet and fingers posture measurement using a motion capture system during each gripping task were then carried out to investigate the individual differences in gripping style and to reveal the differences in fingers posture according to the shapes of the test objects. As a result, significant differences in the gripping comfort score between male and female could not be found in all test objects. Additionally, the coefficients of determination of the relationship between the gripping comfort score and hand length and between the gripping comfort score and hand breadth were considered low in all test objects. Furthermore, a hierarchical cluster analysis of contact pressure distribution demonstrated that two gripping styles during gripping a cylinder existed in present study. Joint angles around x-axes of PIP joints of the middle finger and the ring fingers, around y-axis of CM joint of the thumb and around y-axes of MCP joints of the five fingers varied according to the gripping styles. Moreover, significant differences in 11 joint angles among test objects were confirmed based on the analysis result of fingers posture. This result indicates that fingers posture during gripping changes with the change of the shape of the test object. The results of present study provide information regarding important factors that should be considered or may not be considered during the evaluation and improvement of the gripping comfort of a manufactured product.

To evaluate tasks that have low physical workloads or small variations in the working postures, a method that can be used to analyze slight differences in postures and movements based on human motion characteristics is required. The interjoint coordination, which produces multijoint movements by organizing the redundant degrees of freedom into fewer major covarying relationships, is one of the primary characteristics of human motion. This work proposes a novel evaluation method for interjoint coordination using the graphical lasso and clarifies its efficacy for evaluations of interjoint coordination in complete tasks as well as time-varying interjoint coordination and working postures. In a subject experiment, eleven male participants performed lightweight material-handling tasks under different working conditions and paces, and an electromagnetic motion-tracking system was used to measure their working postures. The principal interjoint coordination for measured joint angles was extracted using the graphical lasso tool as a sparse precision matrix. Further, the contribution of each joint angle to the changes in the working postures in the time series was calculated by correlation anomaly using the graphical lasso. The estimated sparse precision matrix using the graphical lasso suggested that the principal interjoint coordination reflecting the differences in movement strategies by task type can be extracted in comparison with the covariance matrix. The time-varying correlation anomaly score suggested that the joint angle that contributes to differences between interjoint coordination at the onset and termination of tasks could be determined according to the final score. Therefore, our study shows the efficacy of the graphical lasso for evaluation of interjoint coordination and working postures from the time series for repetitive lightweight material-handling tasks.

Static weight estimation of a vehicle in motion is challenging, especially when the vehicle is accelerating and decelerating. This paper presents a new estimation method for accelerating and decelerating vehicles. This method uses at least two miniature load measurement devices cascaded in traffic lane and consideration of transfer load between the front and rear wheels of a motorbike. Both individual axle load and the gross mass of the motorbike are estimated with accuracy under field conditions.