Applied Mechanics and Materials Vol. 775

Abstract: As Failure evolution processes algorithms of brittle rocks usually comply with the Single Instruction Multiple Data (SIMD) model, implementation efforts using such hardware resources are suitable. Graphics processor (GPU) is available SIMD hardware component nowadays, which can lead to substantial increase of computing performance. In this paper we propose a novel parallel cellular automaton algorithm for failure evolution processes of brittle rocks based on GPU. The details of implementation and optimized methods are presented. The performance results show that our GPU implementation achieves 39 times faster than original algorithm on common general purpose processor (CPU).

Abstract: An efficient seismic fragility assessment method is proposed for underground tunnel structures in this paper. The ground response acceleration method for buried structure (GRAMBS), an efficient quasi-static method considering soil-structure interaction (SSI) effect, is used in the proposed approach to estimate the dynamic response behavior of the underground tunnels. In addition, the pushover analyses are conducted to identify the damage states of tunnels and Latin Hypercube sampling technique is used to consider uncertainties in the design variables. A large set of artificially generated ground motions satisfying a design spectrum for specific earthquake intensity are generated and fragility curves are developed. The seismic fragility curves are represented by two-parameter lognormal distribution function and its two parameters, namely the median and log-standard deviation, are estimated using the maximum likelihood estimates method.

Abstract: Regardless of material regulations at the supply source or post-construction quality inspection systems, certain levels of model management systems have been developed. However, in the hospital waiting room, the measured formaldehyde concentration in the air reached 0.99 ppm, which is 12 times higher than that of the standard value. The formaldehyde emission rates measured in the building materials of the private housings or hospital waiting room ranged from 158 to 238 μg/m²∙h, which exceed both the ABSL and BSMI standards. Moreover, the decoration locations, construction staff, and construction behaviors varied despite their claims of using low formaldehyde-emitting materials. This study compiled the current objectives and regulations established by various supervising authorities and implemented a supporting management system in material grading, amount of material usage, ventilation path control, and ventilation effectiveness for facilitating the promotion of healthy indoor air quality, thereby enhancing public health.

Abstract: Damping of geo-materials in resonant column test is commonly evaluated with two alternative experimental methods; during a steady-state vibration (SSV) and during free-vibration decay (FVD). Damping is an important dynamic property necessary to capture the complete behavior of soils. In the study, representative test results on crushed rock are discussed with a focus on material damping derivations along with stiffness degradation test results derived from torsional resonant column tests. A comparison between material damping derived from the SSV and FVD methods and from small to medium shear strains is presented and discussed. In the first part of the paper, the definition of material damping by means of a closed loop in the shear stress - shear strain plane is presented along with a report on literature data associated with damping of coarse-grained soils and the important factors that control material damping of sands and gravels. In the second part, the materials and experimental techniques of the study are described briefly and the background of determining material damping in a resonant column test is also presented along with the analytical formulae. Finally, in the third part representative test results are given including both stiffness and damping, and a comparison of damping derivations using different methods is also highlighted.

Abstract: Aim at the slow and complicated hydration process of straw-cement mixed system and the retarding coagulation of cement-based biomass material in C₃S reaction. To investigate the improving effect of early-strength agents on the hydration process of straw-cement mixed system by adding CaCl₂, FeCl₃ and Al₂(SO₄)₃ which could increase the release of hydration heat, accelerate the hydration of cement and weaken the retarding effect of dissolved substances from straw. By testing the variation of temperatures in hydration process to analyze the highest hydration temperature (T_max), the time of reaching the highest hydration temperature (t), the maximum temperature difference (△T) and the compatibility coefficients (C_A) of cement-based biomass materials with modified agents and with no modified agents, and evaluate the compatibility of straw-cement mixed system. Experimental results show that T_max, t and △T these indexes can intuitively reflect the changing characteristics of early hydration heat of cement-based biomass materials, while C_A could reflect the early hydration behavior comprehensively and objectively. Meanwhile, when the dosage of early-strength agents is between 3%~8%, the growth of C_A shows as follows: CaCl₂ is the best, and FeCl₃ is better than Al₂(SO₄)₃.

Abstract: The resonant column method is established as a standard laboratory method for the study of the elastic properties of soils. The study presents low-amplitude resonant column test results on volcanic sands with intra-particle voids. The experiments were performed on dry samples prepared at variable relative densities and tested in torsional mode of vibration. In the first part of the article, the important factors that control the elastic stiffness of uncemented sands are described shortly and recent findings on granular soils dynamic properties are presented briefly. The second part describes the basic features of the resonant column used in the investigation and the materials of the study and in the third part representative results of an extensive experimental testing program on volcanic granular soils are presented and discussed with a focus on comparisons between the elastic stiffness of volcanic and quartz granular soils. The importance of the effect of the presence of intra-particle voids within the particle mass of the volcanic soils is emphasized, which in turn affects markedly the global void ratio of the samples.

Abstract: The aim of this study is to examine the complicated dynamics behavior of nonlinear vibrations of bistable cantilevered piezoelectric beam. The base excitation on the beam is assumed to be harmonic load. The Galerkin’s approach is adopted to disperse the energies and the virtual work. Dynamic equation of the bistable piezoelectric system is established by using Hamilton’s principle. The averaged equations in the polar form is obtained by using the method of multiple scales. Based on the actual work situation of the cantilevered piezoelectric beam, it is known that base excitation and the size parameter of the beam play the important roles in the nonlinear vibration of the cantilevered piezoelectric beam. The quality of the permanent magnet, the thickness of the base layer and the length of the beam all affect the amplitude of the beam. The thickness of the piezoelectric layer can make the frequency response curve shift in frequency domain.

Abstract: To solve the presence of the phantom phenomenon when single ultrasonic sensor detects obstacles, this paper proposes a multi-ultrasonic sensors design using grouping cycle emission. Using the fuzzy control algorithm in the obstacle avoidance simulation, the quadrotorflies through an unknown environment. The simulation results show that the algorithm can meet the requirements of the quadrotor obstacle avoidance , and have the characteristics of real-time and accuracy , provide the foundation for further practical application.

Abstract: Response of a simplest servo system to an input perturbation is considered for two variants of correction of a servo drive to provide its stability and controllability. Numerical computations made it possible to find out the effect of the main parameters of the system on the dynamic characteristics of the controlling system.

Abstract: In order to solve the mobile robot trajectory tracking problem better, an iterative learning control (ILC) was applied. And the efficiency of mobile robot trajectory tracking was improved. From the simulation result, ILC with forgetting factor has very good performance for solving mobile robot trajectory tracking problem, and the smooth of trajectory tracking process also improved well.