There are many requirements, issues and complexities that engineering design problems must take into account, and these engineering items are often treated as constraints in optimization problems. The constraint optimization problems (COPs) are the most popular type of problems, therefore, optimization algorithms for the COPs have been attracted more and more attention. Particle swarm optimization is one of the most popular algorithms for solving the COPs due to the simplicity and efficient convergence performance, and various types of PSO are actively developed in recent years. However, despite the popularity, they still have limitations in terms of search efficiency. Notably, it takes a lot of calculation costs to obtain the optimal solution on the boundary of constraints or the complicated feasible area. To overcome the difficulties, this paper presents a novel particle swarm optimization algorithm named independent 2-group particle swarm optimization (I2GPSO). I2GPSO is based on the following ideas - a constraint handling method, a novel structure of particles and a novel local search operator. The constraint handling method uses the existing penalty function method. The structure of particles defines two particle groups that have original roles, efficiently enabling PSO to search globally and locally. The local search operator is introduced into one group and enables particles to search near the boundary of constraints efficiently or candidates of the optimal solution. These novel approaches effectively reinforce the optimization efficiency of the PSO algorithm. The optimization capability and character of I2GPSO is illustrated in 11 benchmark problems. The results are compared with other state-of-the-art PSOs, and it is shown that the proposed algorithm possesses competitive search efficiency.

We expect that gait will be useful information for detecting wandering and managing the health of elderly people utilizing a monitoring support robot. However, some kind of sensor is needed to extract pedestrian gait features. In this paper, we proposed a privacy-aware method of extracting gait features from pedestrians’ feet only. This paper describes methods for detecting frames in which heel-strike and toe-off events occurred in foot video, and for extracting the heel contact position in the image. Firstly, dynamic regions were extracted utilizing edge detection and optical flow, and then clustering was used to extract pedestrians’ feet regions. Subsequently, the acceleration field was estimated using optical flow, the acceleration was decomposed into tangential and radial components, and the radial component acceleration was used to detect heel-strike frame. Next, we extracted static regions in the pedestrians’ feet region by utilizing edge detection, optical flow, clustered foot regions, and motion characteristics during gait, and finally performed toe-off frame detection. The heel contact position in the image was extracted by using Otsu’s binarization and static region. We conducted gait experiments with several camera direction conditions and applied it to the system. The RMSE of the estimated and true values for heel-strike and toe-off frame detection were within about one frame in all conditions, and the F-measure was above 80 % in all conditions. The F-measure for heel contact position detection also exceeded 80 % in all conditions.

Tensegrity structures are lightweight structures, often deployable, consisting of axial members (rods and cables). One of their design problems is to determine the minimum member mass to support an external force under the buckling and yielding conditions. In the previous work, the deformation of the structure is not considered, and the equilibrium position is assumed to be known in advance. However, when the structure is subjected to an asymmetric force, for example, the equilibrium position is not obvious and is typically unknown. As a more realistic problem setting, this study discusses a minimal mass design considering the deformation by an asymmetric external force. The self-equilibrated configuration is chosen as the initial configuration for the optimization. The internal force at this configuration is called the prestress, and is often utilized to improve structural stability and stiffness. The problem setting in this paper also allows us to introduce the prestress in the design. Mechanical formulae considering the deformation without the prestress are first derived. A minimal mass design problem allowing the deformation can be formulated by using these formulae. The problem is a nonlinear problem with many variables, and requires proper initial estimates. The paper also addresses this issue by employing dynamical simulation. The prestress can be introduced by modifying the member force calculation in the above formulae. Numerical examples are conducted to show the efficiency of the proposed method.

The damping performance of a rolling-ball damper was examined experimentally and numerically. The damper consists of multiple rolling balls on a circular track attached to the main vibration body. Since, unlike mass-spring-tuned mass dampers, it does not use a spring, it is far superior in durability. Moreover, the cover of the damper ensures that the rolling balls will not jump out from the track. However, determining the combination of parameters that maximize performance remains challenging. In this study, we used a novel evolutionary algorithm and the discrete element method. In terms of convergence and calculation time, we compared the particle swarm optimization (PSO) and cuckoo search algorithms and chose PSO as the evolutionary algorithm. To verify the validity of the numerical method, an experimental apparatus that acts as an equivalent horizontal single-degree-of-freedom system was used. The main vibration body is excited sinusoidally at the support using a motor and a slider-crank mechanism. Steel balls were used as rolling balls. The displacement of the support and the main vibration body was measured using two laser displacement sensors. The numerical results were compared with the experimental results for the relationship between amplitude and frequency to verify the validity of the numerical method.

This paper deals with an advanced version of eMDVA (embedded Mass Dynamic Vibration Absorber), which is a passive multi-modal damping device that was proposed by the authors. The eMDVA consists of a mass embedded in a viscoelastic material, and the mass can vibrate freely in all directions. The authors showed in their former works that the eMDVA consisting of a single mass sphere embedded in a spherical or elliptical viscoelastic material with a constrained outer shape is valid for multiple vibration control target frequencies. Considering practical use, the authors are developing another configuration of the eMDVA where many masses are dispersed and embedded in a sheet-like viscoelastic material. While the original eMDVA utilizes the multi-directional vibrations of the embedded mass as a multi-modal dynamic vibration absorber, the sheet-like configuration achieves multi-modal vibration damping by using different sizes of masses. In this work, we take up an eMDVA in which a mass sphere is embedded in a cuboid viscoelastic material, assuming a partial element of the sheet-like eMDVA and the influence of the external shape of the viscoelastic material on the vibration of the embedded mass is investigated using finite element analysis. It is shown that the peak frequencies of the frequency response function (corresponding to natural frequencies of the embedded masses) can be adjusted by changing the diameter of the mass sphere and the thickness of the viscoelastic material, and this means the sheet-like eMDVA can be designed by the size of the embedded mass sphere. The numerical and experimental results are described in this paper, including the configuration of multiple masses embedded in the viscoelastic material side by side. In addition, a series of excitation tests are conducted using a plate-like structure, a 1:10 scale model of a railway vehicle’s underframe, and the multi-modal vibration reduction effect by the eMDVA has been confirmed.

This paper proposes a simple passive device with an adjustment mechanism for spring constant and damping coefficient to realize a dynamic vibration absorber (DVA) that can be used for various vibration control target frequencies. The proposed device consists of a coil spring and an air spring with an auxiliary reservoir and orifice. The active coil of the device's coil spring can be varied to adjust the spring constant. The main tank and reservoir tank are separated by an "orifice disk" with several orifices of different diameters, and the damping coefficient can be changed by selecting one of these orifices. A numerical model was constructed to design the spring constant and damping coefficient, and a DVA equipped with the proposed adjustment mechanism was developed. The results of stand-alone vibration tests showed that the changing trend of vibration response property agreed well with the numerical results, and the proposed adjustment mechanism worked well. Then, vibration control tests were conducted by mounting a dynamic vibration absorber on a plate-like structure that simulates the underframe of a railroad car at approximately 1/10 scale. As a result, a significant vibration reduction was successfully achieved for the bending mode of elastic vibration, and the usefulness of the proposed spring constant and damping coefficient adjustment mechanism was confirmed by adjusting the optimum spring constant and damping coefficient values, which varied at each measurement point.

Helical springs are used for many mechanisms. Rectangular wire helical springs are used in machines that require large spring loads, such as press machines, die machines, injection molding machines, construction machines, and load testing machines. Design formulas for the rectangular wire helical springs were given by Liesecke. However, pitch angle of the helical spring is neglected in his formulas, and they are inconvenient because we have to read factors used in the formulas from graphs. And, Shimizu et al. derived a theoretical equation, but there are still differences between values calculated by the equations and the FEM analysis results although a trend is consistent. And, the practical design equations are desired to be simple. Therefore, in this paper, simple practical design equations of the spring constant and the maximum shear stress are derived by using a fractional expression to FEM results by focusing on that the displacement and the stress generated in the helical spring are mainly caused by a tortional moment to the spring wire. Errors of the spring constant equations to the FEM results are less than 3 percents and errors of the maximum shear stress equation to the FEM results are less than 3.5 percents. Therefore, these equations are very useful for the practical design of the rectangular wire helical springs.