Experimental investigation of peening cylindrical workpieces utilizing a transducer with ring sonotrode

In industrial applications, the shafting components with high stress are easily damaged due to cyclic loads if there is no surface treatment. With the use of ultrasonic cavitation peening, the residual compressive stress and the surface hardness of these components can be improved. While tradi-tional longitudinal vibration transducers are used to treat cylindrical workpieces, the treated areas are limited, and the treatment period is relatively long. To solve these problems, we designed a novel configuration of the piezoelectric transducer as a type of the combination of rod and ring. During ultrasonic cavitation peening, we placed the cylindrical workpieces in the ring tool to improve the limitation. However, the treated surface properties were largely influenced by the input parameters (driving voltage and rod diameters). In this investigation, the cylindrical workpieces, which were covered with aluminum foils, were first treated by ultrasonic cavitation peening to detect the intensity and distribution of the cavitation bubbles on the treated surface. Then, the sonochemiluminescence method was utilized as an additional way to find the optimal operation parameters (190 V and 16 mm). Finally, the ultrasonic cavitation process was conducted with the optimal parameters. The treatment results showed that the surface hardness increased by about 36% without significant increase of the surface roughness. © 2020 by the authors. Licensee MDPI, Basel, Switzerland

Investigation of Low-Sidelobe Beampattern Controlling Methods for Acoustic Transmitting Array of Underwater Vehicles

In underwater unmanned vehicles, complex acoustic transducer arrays are always used to transmitting sound waves to detect and position underwater targets. Two methods of obtaining low-sidelobe transmitting beampatterns for acoustic transmitting arrays of underwater vehicles are investigated. The first method is the boundary element model optimization method which used the boundary element theory together with the optimization method to calculate the driving voltage weighting vector of the array. The second method is the measured receiving array manifold vector optimization method which used the measured receiving array manifold vectors and optimization method to calculate the weighting vector. Both methods can take into account the baffle effect and mutual interactions among elements of complex acoustic arrays. Computer simulation together with experiments are carried out for typical complex arrays. The results agree well and show that the two methods are both able to obtain a lower sidelobe transmitting beampattern than the conventional beamforming method, and the source level for each transmitting beam is maximized in constraint of the maximum driving voltage of array elements being constant. The effect of the second method performs even better than that of the first method, which is more suitable for practical application. The methods are very useful for the improvement of detecting and positioning capability of underwater unmanned vehicles

Aggregation of Nanochemical Microcrystals in Urine Promotes the Formation of Urinary Calculi

With the increasing incidence and recurrence rate of urinary calculi, urinary calculi have become a serious health risk, and the research on urinary calculi has become the focus of public attention. At present, the research results on the formation mechanism of urinary calculi are not ideal, and there is no unified conclusion. In order to further study the influencing factors of the formation of urinary calculi and provide new ideas for the prevention and clinical treatment of urinary calculi, the influence of agglomeration of nanochemical microcrystals in urine on urinary calculi was studied in this paper. In this study, fresh morning urine was collected from 10 urological stone patients and 10 healthy controls without urological stone in the urology department of a hospital. After processing the experimental specimens, we first use flame atomic absorption spectrometry and alcian blue colorimetric method to detect the content of Ca2+ and citrate in the urine and then use the nanoparticle size analyzer to detect the microcrystals in the urine. Diameter, distribution, degree of aggregation and potential, and finally HRTEM observation to observe the morphology, chemical composition, and element composition of the nanocrystals. The results showed that the content of Ca2+ and lemon hydrochloric acid in the urine of the experimental group was lower than that of the control group. The particle size of the nanocrystals increased with the increase in the pore size of the membrane. The average particle size of the experimental group increased gradually from 163 ± 31 nm to 3219 ± 863 nm, while the average particle size of the control group increased from 183 ± 65 nm to 997 ± 522 nm. The mean value of the potential decreased with the increase in the pore size of the filter membrane. The change amplitude of the experimental group was 6.57 mV, while the change amplitude of the control group was only 1.75 mV. In the composition of nanocrystals, element O accounts for the most, accounting for 42.54% of all elements. This indicates that the aggregation of nanocrystals in urine will lead to the rapid increase in the size of nanocrystals, which will eventually lead to the formation of stones

Seasonal Cycle of Background in the Tropical Pacific as a Cause of ENSO Spring Persistence Barrier

Statistical model results suggest that the declining growth rate from autumn to spring is the key to cause El Niño-Southern Oscillation (ENSO) spring persistence barrier (SPB). Using a dynamical approach, we develop the physical mechanisms responsible for ENSO SPB in the framework of recharge oscillator by adding a seasonally varying Bjerknes (BJ) stability index and linking it with ENSO growth rate. By decomposing BJ index, it is indicated that seasonal thermodynamic damping and thermocline positive feedback play an important role in determining the ENSO SPB. We further show that the increasing/decreasing upper-level cloud/low-level cloud and the deepening thermocline from autumn to spring are the main factors to control the SPB of ENSO. Our proposed mechanisms also have useful implications for the understanding of ENSO prediction

Finite Element Calculation with Experimental Verification for a Free-Flooded Transducer Based on Fluid Cavity Structure

A free-flooded transducer that couples the vibration of a longitudinal vibration transducer and the fluid cavity of an aluminum ring was investigated. Given the transducer is based on a fluid cavity structure and has no air cavity, it can resist high hydrostatic pressure when working underwater, which is suitable for application in the deep sea. At first, the structure and working principle of the transducer were introduced. Then, the axisymmetric finite element model of the transducer was established; and the transmitting voltage response, admittance, and radiation directivity of the transducer were simulated using the finite element method. According to the size of the finite element model, a prototype of the transducer was designed and fabricated, and the electro-acoustic performance of the prototype was measured in an anechoic water tank. The experimental results were consistent with the simulation results and showed a good performance of the transducer. Finally, the improvement of the radiation directivity of the transducer by the optimal design of the free-flooded aluminum ring was obtained using the finite element method and verified by experiments

A sidelobe suppressing near-field beamforming approach for ultrasound array imaging

A method is proposed to suppress sidelobe level for near-field beamforming in ultrasound array imaging. An optimization problem is established, and the second-order cone algorithm is used to solve the problem to obtain the weight vector based on the near-field response vector of a transducer array. The weight vector calculation results show that the proposed method can be used to suppress the sidelobe level of the near-field beam pattern of a transducer array. Ultrasound images following the application of weight vector to the array of a wire phantom are obtained by simulation with the Field II program, and the images of a wire phantom and anechoic sphere phantom are obtained experimentally with a 64-element 26MHz linear phased array. The experimental and simulation results agree well and show that the proposed method can achieve a much lower sidelobe level than the conventional delay and sum beamforming method. The wire phantom image is demonstrated to focus much better and the contrast of the anechoic sphere phantom image improved by applying the proposed beamforming method. (C) 2015 Acoustical Society of America.1193sciescopu

Sparse-View Neutron CT Reconstruction Using a Modified Weighted Total Difference Minimization Method

Indirect neutron imaging is an effective method for nondestructive testing of spent nuclear fuel elements. Considering the difficulty of obtaining experimental data in a high-radiation environment and the characteristic of high noise of neutron images, it is difficult to use the traditional FBP algorithm to recover the complete information of the sample based on the limited projection data. Therefore, it is necessary to develop the sparse-view CT reconstruction algorithm for indirect neutron imaging. In order to improve the quality of the reconstruction image, an iterative reconstruction method combining SIRT, MRP, and WTDM regularization is proposed. The reconstruction results obtained by using the proposed method on simulated data and actual neutron projection data are compared with the results of four other algorithms (FBP, SIRT, SIRT-TV, and SIRT-WTDM). The experimental results show that the SIRT-MWTDM algorithm has great advantages in both objective evaluation index and subjective observation in the reconstruction image of simulated data and neutron projection data