Oscillating water column (OWC) devices for wave power extraction are appealing, but are still in need of research. In this study, a series of wave-flume experiments was conducted to examine the hydrodynamic performance of a rectangular OWC device fixed in regular waves. Two types of orifices, slot orifices and circular orifices, were used to simulate the nonlinear power take-off (PTO) mechanism, and the effects of orifice geometry were examined. A two-point measurement method was proposed to reconstruct the instantaneous spatial profile of the water surface inside the OWC chamber for reducing bias in the measured wave power extraction efficiency. The flow characteristics of PTO were described by a quadratic loss coefficient, and our experimental results showed that the quadratic loss coefficient of the slot orifices varied with wave period and slot geometry. Empirical formulas were proposed for the quadratic loss coefficients of the two types of orifices. The ability to determine the quadratic loss coefficient of an orifice will allow us to design orifices for small-scale tests and calculate the power extraction using only pressure measurement. Our results also suggested that the pressure coefficient should be more reliable than the amplification coefficient as an indicator of the power extraction performance of an OWC device.

Initial fabric anisotropy can greatly affect the shear behavior of particulate materials during shear. The bedding plane effect induced by particle orientation is one of the main fabric anisotropic factors that may affect other factors. It is hard to experimentally examine the effect of bedding direction of particles on the shear behavior of particulate materials, such as sand. A 2D discrete element method (DEM) is employed in this paper to study the influence of different orientations of oval particles on the behavior of dense assemblies under simple shear. As well as the macroscopic shear behavior, the evolution of particle orientation, contact normal, and inter-particle contact forces within the samples with different initial bedding angles during shear have been extensively examined. It was found that the initial bedding direction of the particles has great influence on the non-coaxiality between the directions of principal stress and principal strain increment. The bedding direction also affects the strength and dilatancy responses of DEM samples subjected to simple shear, and the samples with larger bedding angles exhibit higher shear strength and larger volume dilation. A modified stress-force-fabric relationship is proposed to describe the effect of particle bedding direction on the shear strength of samples, and the new equation can better describe the stress-force-fabric relationship of assemblies with initial anisotropic fabrics compared with the existing model.

Based on the explicit finite element (FE) software ANSYS/LS-DYNA, the FE model for a sliding lead rubber bearing (SLRB) is developed. The design parameters of the laminated steel, including thickness, density, and Young’s modulus, are modified to greatly enlarge the time step size of the model. Three types of contact relations in ANSYS/LS-DYNA are employed to analyze all the contact relations existing in the bearing. Then numerical simulations of the compression tests and a series of correlation tests on compression-shear properties for the bearing are conducted, and the numerical results are further verified by experimental and theoretical ones. Results show that the developed FE model is capable of reproducing the vertical stiffness and the particular hysteresis behavior of the bearing. The shear stresses of the intermediate rubber layer obtained from the numerical simulation agree well with the theoretical results. Moreover, it is observed from the numerical simulation that the lead cylinder undergoes plastic deformation even if no additional lateral load is applied, and an extremely large plastic deformation when a shear displacement of 115 mm is applied. Furthermore, compared with the implicit analysis, the computational cost of the explicit analysis is much more acceptable. Therefore, it can be concluded that the proposed modeling method for the SLRB is accurate and practical.

In this paper, we present a method for the global optimization of the tooth contact pattern and transmission error of spiral bevel and hypoid gears, which includes three optimization objectives, three control parameters, and a complex-constrain genetic algorithm solving method. A new set of fundamental equations for pitch cone parameters of hypoid gear drives are established, as well as the relationships between pitch cone and curvature parameters. Based on this theory, three control parameters are selected to determine the pinion tooth surface. A hypoid gear drive is chosen for case studies. The results verify that the optimization methodology can achieve the expected optimization objectives and has good convergence. Correlations between optimization objectives and control parameters are discussed. Furthermore, a finite element model of a simplified hypoid gear drive system is established and its quasi-static meshing characteristics analyzed. The results again confirm the correctness of the optimization method. The effects of torque load on the contact pattern and transmission error are discussed. The results provide a theoretical reference for geometric calculations, quasi-static analysis, and optimal design of spiral bevel and hypoid gears.

It is crucial to conduct a study of vehicle ride comfort using a suitable physical model, and a precise and effective problem-solving method is necessary to describe possible engineering problems to obtain the best analysis of vehicle vibration based on the numerical model. This study establishes different types of vehicle models with different degrees of freedom (DOFs) that use different types of numerical methods. It is shown that results calculated using the Hamming and Runge-Kutta methods are nearly the same when the system has a small number of DOFs. However, when the number is larger, the Hamming method is more stable than other methods. The Hamming method is multi-step, with four orders of precision. The research results show that this method can solve the vehicle vibration problem. Orthogonal experiments and multi-objective optimization are introduced to analyze and optimize the vibration of the vehicle, and the effects of the parameters on the dynamic characteristics are investigated. The solution F₁ (vertical acceleration root mean square of the vehicle) reduces by 0.0352 m/s², which is an improvement of 7.22%, and the solution F₂ (dynamic load coefficient of the tire) reduces by 0.0225, which is an improvement of 6.82% after optimization. The study provides guidance for the analysis of vehicle ride comfort.