Various prominent methods for structural topology optimization have been developed, especially since the late 1980s when the homogenization method was proposed. However, knowledge in the topology of mathematics was nearly not applied in structural optimization. With the application of the homology theory in the topology, this study proposed an original method of optimizing the topology of a structure consisting of elastic triangular plates sustaining a static load. The total volume of the structure was minimized under the constraint that the strain energy density in all elements is equal to a prescribed value. Although apparent design variables are the material density of triangular plates, the coefficients of boundary cycles of 3-simplexes are utilized as auxiliary variables that express inner forces in the plates. The arbitrary values of the auxiliary variables always satisfy the equilibrium among inner forces in triangular plates and do not generate useless elements with no stress throughout the optimization process. Simultaneous linear equations for stress analysis need not be solved repeatedly because the volume minimization process is concurrently involved in the analysis. The number of variables can be reduced to less than that of triangular plates with eigenvalue decomposition. The validity of the proposed method was verified by applying it to several numerical examples.
Analytical theories related to the buckling criterion and strength of thin-walled structures are classified into flat plate and cylindrical shell theories and others (conical shell and spherical shell). To discuss the accurate predictions for the ultimate load-bearing capacities (ULBCs) of thin-walled steel (TWS) composite members under longitudinal compression and solve the long-standing problem of the different effective width (EW) definitions under different main TWS structural specifications, a simple model of a flat element supported in parallel by two cylindrical shell elements (corner ridgelines) on both longitudinal sides was analyzed. In addition, a simplified method to evaluate the reduction factor of the postbuckling ULBC caused by the initial imperfections was developed. The rational results for releasing additional anti-buckling functions of the ridgeline revealed herein are expected to be beneficial to the structural lightweight optimization for not only civil and construction engineering but also other broad areas such as spacecraft and aircraft engineering.
Water jet work is used in a variety of settings, including material processing and washing. Protective clothing currently used in water jet work is made from metal and other rigid materials. Areas near joints, where flexibility is required, remain insufficiently protected. To contribute to the goal of developing flexible protective materials that can be used to produce protective gloves for water jet work, we propose a method for evaluating the protective performance of candidate materials along with a testing apparatus, of which we create a prototype. The effectiveness of the proposed method is verified through testing of rubber and other materials. An investigation of the destructive mechanism at work in flexible materials reveals that the mode of destruction in thin, flexible materials suitable for use in protective gloves differs significantly from that affecting ordinary materials.
Copper (Cu) particles volume fraction in Aluminum-Copper (Al-Cu) have been detected by multiple-amplitude modulation which is implemented into an impedance measurement system (mAM-IMS). The mAM-IMS has an evaluation section and a measurement section. The evaluation section is composed of three steps which are 1) The evaluation step of single modulation frequency fm for Cu particles volume fraction φCu detection in static Al-Cu mixtures, 2) The evaluation step of multiple fm for φCu detection in vibrating Al-Cu mixtures, 3) The determination step of multiple-AM for the best modulation and carrier frequencies fm/fc combination for φCu detection in vibrating Al-Cu mixtures under vibration frequency fp. All steps in the evaluation section are investigated by a simulation study. After the evaluation step, the best fm/fc combination is tested and evaluated in the measurement section by the wet-type gravity vibration separator (WGS) deck for the experimental φCu detection in vibrating Al-Cu mixtures under constant vibration frequency fp. As a result, the mAM-IMS with the best fm/fc combination should satisfy the requirement of fm ≤ fp ＜ fc where fc = 2.5fp. By evaluating the normalized measured impedance Z′^expm in the range of 0% ≤ φCu ≤ 57.14%, the mAM-IMS with the best fm/fc combination is able to detect the experimental φCu in vibrating Al-Cu mixtures by spatial-mean error deviation 〈ε〉=8.12%.
In recent years, advanced combustion technologies, such as highly dilute and highly boosted technologies were employed in the internal combustion engine to improve the fuel economy and reduce exhaust emissions. However, there are still many challenges in these advanced combustion technologies for the purpose of ignition control. Developing a next-generation spark ignition system is strongly required for the spark-ignition engine. In this study, three types of ignition coils were used to understand the impact of different ignition strategies on discharge channel stretching and shortening behaviors. A high-speed infrared imaging and a high-speed direct photography method were used to capture the images simultaneously to investigate the influence of discharge channel behaviors on the initial flame formation. Results show that the discharge current is the main factor affecting the discharge channel stretching as compared with the discharge duration. Short-cut and restrike are two kinds of discharge channel shortening behaviors that affect early flame overlap and growth, short-cut shortening behavior is better than restrike shortening behavior for the flame development and enlarges the early flame during the discharge duration.
The vibration of liquid in an axisymmetric tank covered by an elastic diaphragm is analyzed and an equivalent mechanical model for the coupled oscillation of the liquid and the diaphragm is developed. As a preliminary step to the vibration analysis, the static shape of the diaphragm is determined by solving nonlinear differential equations. The characteristic function for the liquid motion applicable to arbitrary axisymmetric tanks is analytically expressed in terms of the Gaussian hypergeometric series by introducing spherical coordinates. This expression enables reduced-order modeling for sloshing in arbitrary axisymmetric convex tanks, for which time-consuming and expensive numerical methods have been used in the past. The decreasing effects of the diaphragm on the sloshing force and moment are explained by developing a mechanical model for the coupled liquid-diaphragm system and comparing the model with that for free-surface sloshing.
A quasi-static indentation (QSI) test analysis equivalent to the low-velocity impact test and the subsequent compression-after-impact (CAI) test analysis of the carbon fiber reinforced plastics skin-stringer specimen were performed by FEM using interface elements considering the zig-zag cohesive zone model, which models delamination and matrix cracking. Damage propagation analyses were performed by the implicit method considering nonlinearity, such as materials, large deformations, and contact phenomenon. The numerical models were validated through comparison with experimental results, including the indentation load-displacement relationship and delamination area in the QSI test and the compression load-displacement relationship and strain-displacement relationships in the CAI test. Moreover, the effects of dents due to impact test and the initial imperfection were also examined.
Wheelchair sports have an important role as a tool of rehabilitation for people with physical disabilities in lower limbs, and have been a driving force for innovation in wheelchair technology and practice as well. In wheelchair tennis, it is important to evaluate the pushing motion by players as well as the performance of the wheelchair when pushing. The objective of this study was to construct a comprehensive simulation model which was capable of evaluating the design parameters of a wheelchair as well as the pushing motion by a player in wheelchair tennis, and to investigate the effect of seat height of a wheelchair on the joint torques of the player as an example of analysis. The pushing motion during short distance dash was focused in the present study. The simulation model was constructed based on a multibody dynamics analysis software. Pushing motions by a player were acquired in the experiment by using a motion capture system and a specially developed wheelchair ergometer. Simulations reproducing the experimental conditions were conducted using the acquired pushing motions. The simulation model was validated since it could predict the propulsion torque and angular velocity overall within 10% error, although there was a room for improvement especially for the instantaneous characteristics around the timing of initial contact between the hand and hand rim. A parameter study changing the seat height of the wheelchair was conducted using the constructed simulation model. It was found that the joint torques of the thorax and shoulder decreased according to the decrease in the seat height, while joint torque of the elbow increased. It suggests that there is a trade-off relationship between the joint torques of the thorax and shoulder and that of the elbow with respect to the seat height.