Improved multi-objective artificial bee colony algorithm-based path planning for mobile robots.

Mobile robots are widely used in various fields, including cosmic exploration, logistics delivery, and emergency rescue and so on. Path planning of mobile robots is essential for completing their tasks. Therefore, Path planning algorithms capable of finding their best path are needed. To address this challenge, we thus develop improved multi-objective artificial bee colony algorithm (IMOABC), a Bio-inspired algorithm-based approach for path planning. The IMOABC algorithm is based on multi-objective artificial bee colony algorithm (MOABC) with four strategies, including external archive pruning strategy, non-dominated ranking strategy, crowding distance strategy, and search strategy. IMOABC is tested on six standard test functions. Results show that IMOABC algorithm outperforms the other algorithms in solving complex multi-objective optimization problems. We then apply the IMOABC algorithm to path planning in the simulation experiment of mobile robots. IMOABC algorithm consistently outperforms existing algorithms (the MOABC algorithm and the ABC algorithm). IMOABC algorithm should be broadly useful for path planning of mobile robots.

Modeling and Optimization of Water Distribution in Mineral Processing considering Water Cost and Recycled Water.

Reducing mineral processing water costs and freshwater consumption is a challenging task in the mineral processing water distribution (MPWD). The work presented in this paper focuses on two aspects of the MPWD optimization model and the MPWD optimization method. To achieve MPWD optimization effectively, a nonlinear constrained multiobjective model is built. The problem is formulated with two objectives of minimizing the mineral processing water costs and maximizing the amount of recycled water. In this paper, an optimization method named enhancing the multiobjective artificial bee colony (EMOABC) algorithm is proposed to solve this model. The EMOABC algorithm uses four strategies to obtain the Pareto-optimal solutions and to achieve the MPWD optimal solutions. With the three benchmark functions, the EMOABC algorithm outperforms the other two widely used algorithms in solving complex multiobjective optimization problems. The EMOABC algorithm is then applied to two cases. Results have shown that the proposed algorithm has the ability to solve the MPWD optimization model. The developed model and the proposed algorithm provide decision support for the actual MPWD problem.

Artificial bee colony algorithm based PID controller for steel stripe deviation control system.

To improve the performance of the PID controller for a steel strip deviation control system (SSDCS), an enhanced artificial bee colony algorithm (EABC) is proposed to optimize PID controller gains (EABC-PID). The proposed EABC changes the candidate solution equation to balance its explorative and exploitative capabilities. The experiment presents a detailed comparison of EABC-PID and four bio-inspired algorithms based PID controllers considering four types of objective functions. Simulation results show that EABC-PID proves to be superior for SSDCS compared to four bio-inspired algorithms based PID controller in terms of convergence, dynamic adjustment, and robustness.

Characterization of microstructural anisotropy using the mode-converted ultrasonic scattering in titanium alloy.

The mode-converted (Longitudinal to Transverse, L-T) ultrasonic scattering was utilized to characterize the microstructural anisotropy on three surfaces of samples cut from the low-scattering and high-scattering regions of a raw titanium alloy Ti-6Al-4V billet, respectively. The L-T ultrasonic measurements were performed in two perpendicular directions using two focused transducers with a 15 MHz center frequency in a pitch-catch configuration. The root mean square (RMS) of ultrasonic scattering was calculated for each L-T measurement and a Gaussian function was used to fit each RMS to determine the RMS amplitude. The ratio of RMS amplitudes for L-T measurements performed in two perpendicular directions was calculated to characterize the microstructural anisotropy on the measured surface of a sample. The results show that the amplitude of L-T ultrasonic scattering is highly dependent on the microstructural anisotropy. The microstructural isotropy was considered on the x-y planes of all samples, while the high anisotropy was seen on the x-z and y-z planes of all low-scattering and high-scattering samples. In addition, the microstructural anisotropy measured on the x-z planes of the low-scattering and high-scattering samples gradually increases and decreases, respectively, from the outside diameter (OD) to the centerline (CL) of the billet. The anisotropy measured on the y-z planes of the low-scattering samples slightly decreases and then increases towards the center, while the anisotropy measured on the y-z planes of the high-scattering samples continuously increases towards the center. The variation of microstructural anisotropy in the titanium alloy Ti-6Al-4V billet with duplex microstructure was quantified with the L-T ultrasonic method and the results agree well with micrographs shown in Ref. [18]. The mode-converted ultrasonic scattering method provides a NDE method to characterize microstructural anisotropy, which can be used as an NDE tool for quality control.

Evaluation of Structural Anisotropy in a Porous Titanium Medium Mimicking Trabecular Bone Structure Using Mode-Converted Ultrasonic Scattering.

The mode-converted (longitudinal to transverse, L-T) ultrasonic scattering method was utilized to characterize the structural anisotropy of a phantom mimicking the structural properties of trabecular bone. The sample was fabricated using metal additive manufacturing from high-resolution computed tomography (CT) images of a sample of trabecular horse bone with strong anisotropy. Two focused transducers were used to perform the L-T ultrasonic measurements. A normal incidence transducer was used to transmit longitudinal ultrasonic waves into the sample, while the scattered transverse signals were received by an oblique incidence transducer. At multiple locations on the sample, four L-T measurements were performed by collecting ultrasonic scattering from four directions. The amplitude of the root mean square (rms) of the collected ultrasonic scattering signals was calculated for each L-T measurement. The ratios of rms amplitudes for L-T measurements in different directions were calculated to characterize the anisotropy of sample. The results show that the amplitude of L-T converted scattering is highly dependent on the direction of microstructural anisotropy. A strong anisotropy of the microstructure was observed, which coincides with simulation results previously published on the same structure as well as with the anisotropy estimated from the CT images. These results suggest the potential of mode-converted ultrasonic scattering methods to assess the anisotropy of materials with porous, complex structures, including trabecular bone.

Microstructural characterization of trabecular bone using ultrasonic backscattering and diffusion parameters.

Finite differences time domain methods were utilized to simulate ultrasound propagation and scattering in anisotropic trabecular bone structures obtained from high resolution Computed Tomography (CT). The backscattered signals were collected and the incoherent contribution was extracted. The diffusion constant was calculated for propagations along and across the main direction of anisotropy, and was used to characterize the anisotropy of the trabecular microstructures. In anisotropic structures, the diffusion constant was significantly different in both directions, and the anisotropy of the diffusion constant was strongly correlated to the structural anisotropy measured on the CT images. These results indicate that metrics based on diffusion can be used to quantify the anisotropy of complex structures such as trabecular bone.

Dependence of diffuse ultrasonic backscatter on residual stress in 1080 steel.

In this article, the effects of residual stress on the ultrasonic scattering in a quenched steel sample are investigated by calculating the change of spatial variance amplitudes of ultrasonic signals after removing residual stress via annealing. The experimental results show that the average spatial variance amplitude decreases by about 11.89% for a scan area on the quenched surface after removing residual stress. This quantity was used to estimate the residual stress based on the developed stress-dependent backscatter model. In addition, the residual stress on the whole scan area was mapped by calculating the change of the spatial variance amplitude for each subarea after annealing, respectively. Diffuse ultrasonic backscatter signals show a high sensitivity to residual stress such that this technique has potential as a non-destructive method for measuring residual stress.

Ultrasonic attenuation in pearlitic steel.

Expressions for the attenuation coefficients of longitudinal and transverse ultrasonic waves are developed for steel with pearlitic microstructure. This type of lamellar duplex microstructure influences attenuation because of the lamellar spacing. In addition, longitudinal attenuation measurements were conducted using an unfocused transducer with 10 MHz central frequency on the cross section of a quenched railroad wheel sample. The dependence of longitudinal attenuation on the pearlite microstructure is observed from the changes of longitudinal attenuation from the quenched tread surface to deeper locations. The results show that the attenuation value is lowest and relatively constant within the quench depth, then increases linearly. The experimental results demonstrate a reasonable agreement with results from the theoretical model. Ultrasonic attenuation provides an important non-destructive method to evaluate duplex microstructure within grains which can be implemented for quality control in conjunction with other manufacturing processes.

Stress-dependent changes in the diffuse ultrasonic backscatter coefficient in steel: experimental results.

In this article, the effects of uniaxial compressive loading on the ultrasonic scattering from polycrystalline grains are shown for 10 MHz ultrasound in annealed, 1018 steel. The results show a decreasing value of the stress-dependent backscatter coefficient for normal incident ultrasound when the compression loading is perpendicular to the scattering direction. The change due to scattering is about 2 orders of magnitude greater than changes observed by others using ultrasonic wavespeed measurements. It is anticipated that this research can serve as the basis for many methods associated with nondestructive determination of stress in structural materials.

Study on the vibration characteristics of a finite-width corrugated cylindrical shell piezoelectric transducer.

Coupled extensional and flexural vibrations of an ultrasonic piezoelectric transducer are studied in the paper. The ultrasonic piezoelectric transducer is made of piezoelectric polymer PVDF films and modeled as a corrugated cylindrical shell with a finite width in the ridge direction, which consists of multiple pieces of circular cylindrical surfaces smoothly connected along their ridges. The classical shell theory is used to obtain the theoretical solution. Effects of the edge constraints on vibrational characteristics of the resonant frequencies, mode shapes, and internal forces are investigated for a corrugated ultrasonic piezoelectric transducer consisting of a few circular pieces each with a thickness of about 40 microm, radius of 5 mm, and span angle of 120 degrees.

Analysis of multilayered thin-film piezoelectric transducer arrays.

We study coupled extensional and flexural vibrations of a 1-D array of partially electroded, multilayered piezoelectric transducers. The classical theory for laminated plates is used. A theoretical solution is obtained. Based on the solution, basic vibration characteristics of resonant frequencies, mode shapes, and admittance are calculated. Their dependence on geometric parameters is examined. The present analysis represents a significant progress of existing analyses on a single cell of a transducer array.

Size optimization of a piezoelectric actuator on a clamped elastic plate.

We determine by a theoretical analysis the optimal dimension of a piezoelectric actuator attached to a multilayered elastic plate clamped at both ends. The dimension is optimal in the sense of producing maximal plate center flexural displacement. The first-order theory for laminated piezoelectric plates is used. A theoretical solution is obtained. Numerical results calculated from the solution show that when the actuator length takes a particular value, the center flexural displacement of the elastic plate reaches a maximum. For PZT4 and PZT5A actuators this happens when the actuator length is about 55% of the plate length. Basic vibration characteristics of the structure at the first resonance near the optimal actuator length are also calculated. It is found that the admittance is also maximal when the electrode length is optimal.

Optimization of a circular thin-film piezoelectric actuator lying on a clamped multilayered elastic plate.

A system consisting of a circular multilayered thin-film elastic plate and a piezoelectric actuator, which is generally used for ultrasound generation in air, is studied in this paper. Effects of the electrode dimension of a circular thin-film piezoelectric actuator lying on a clamped multilayered elastic plate are discussed theoretically, while the first-order theory of asymmetrically laminated piezoelectric plates with consideration of coupled extension and flexure of the reference plane is used. Numerical results show that the deflection of the elastic plate can be optimized by adjusting the radius of the top electrode.

Vibration characteristics of a corrugated cylindrical shell piezoelectric transducer.

We study coupled extensional and flexural cylindrical vibrations of a corrugated cylindrical shell piezoelectric transducer consisting of multiple pieces of circular cylindrical surfaces smoothly connected along their generatrices. Using the classical shell theory, a theoretical solution is obtained. Based on the solution, basic vibration characteristics of resonant frequencies, mode shapes, and internal forces are calculated and examined for the corrugated transducers, consisting of a few circular pieces each about 50 mum thick, with radius of 5 mm and span angle of 120 degrees. For these transducers the first resonance is of the order of 10-100 Hz.