Search

Based on the zig-zag theory and Hamiltonian principle, the electromechanical coupling dynamic finite element(FE) model of piezoelectric damping laminated structure is established, the natural frequency and loss factor of the structure is accurately calculated. The eight nodes quadratic element is adopt for FE modeling, each node with seven DOFs, which considers the complex elastic modulus of damping layer. The correctness of model is verified by the calculation and simulation of an example in the literature. The effects of reinforcement orientation angle, thickness of damping layer and structure curvature on the frequency and loss factor of piezoelectric damping laminated structure are investigated. This study can provide references for vibration control and optimization design of piezoelectric damping laminated structures.

Electrical stimulation is widely used in nerve regulation and treatment. The detection of the distribution of stimulation current in tissues is of great significance to improve the accuracy of electrical stimulation, but the current technical means are still difficult to achieve the non-invasive detection of stimulation current. This study proposes a non-invasive detection method of electrical stimulation current based on the magneto-acoustic (MA) effect, which has the advantages of high spatial resolution and high spatial contrast. In this study, continuous sine waves with the frequency of 20kHz are used to stimulate samples. The MA signal generated by the stimulation current in the samples in a stable magnetic field is detected by lock-in amplifier, and the two-dimensional distribution of sound source is extracted. The current density distribution of samples is simulated by the method of finite element analysis, and the simulation results are verified by experiments. The results show that under the electrical stimulation of the order of 0.01A, the location measurement of two-dimensional surface sound source with millimeter accuracy can be achieved non-invasively in isolated pork and pig brain, and the measurement accuracy of weak MA signal can reach 10

Daily start-up is a typical feature of concentrated solar power plants (CSPs) due to solar energy intermittency. Therefore, appropriate start-up operation strategies are significant for CSPs. A parabolic trough concentrated solar power plant (PTCSP) with molten salt (MS) is a potential technical route. However, little attention has been paid to the dynamic start-up performance of PTCSP using MS. To mend the research gap, the dynamic start-up simulation of PTCSP using MS is conducted. Main contributions of this study are the dynamic start-up simulation of PTCSP using MS and evaluation of two MS anti-freezing solutions. Results indicate that the outlet MS temperature of solar field transiently exceeds nominal values during start-up processes. The inlet feedwater temperature of the preheater is much lower than MS freezing temperature during start-up processes. Therefore, two anti-freezing solutions were used to avoid MS solidification. Compared with utilizing the recirculating pump, utilizing the low-load regenerative heater can enhance anti-freezing performance, which could reduce the maximum control deviation of the preheater inlet feedwater temperature by 2.0 °C and increase the average outlet MS temperature of the preheater by 2.4 °C. This study may provide guidance for the dynamic simulation and operation optimization of CSPs during start-up processes.

Magneto–acoustic signals reflect the electrical properties of tissues, which is meaningful for the diagnosis of tumors, bleeding and other diseases. The low signal-to-noise ratio (SNR) of the magneto–acoustic signals limits the image quality of the magneto–acoustic imaging. A chirp coded excitation signal processing method for magneto–acoustic imaging is proposed in this paper. The SNR of magneto–acoustic signal is improved. In this paper, magneto–acoustic signals under different pulse widths chirp coded excitation are studied by simulation and experimental measurement. The SNRs of the magneto–acoustic signals are increased by 7.5, 16.3, 42.2, and 90.1 times under 10, 20, 50 and 100[Formula: see text][Formula: see text]s chirp excitation, respectively, for the beef and copper ring sample. At the same time, the processing time was significantly shortened to 1.2% of the average method under the single pulse excitation. The chirp coded method is of great significance to improve the SNR of magneto–acoustic signals, image quality and imaging efficiency.

Compared with static shape control, dynamic shape control is more difficult due to its time-varying nature. To improve the control precision and reduce the number of actuators needed, an integrated design optimization model of structure and control is proposed. The following three sets of design variables are considered to minimize the time domain variance between the controlled and desired dynamic shapes: the time-varying actuator voltages, the actuator layout and the structural ply parameters. To satisfy the engineering performance requirements to the greatest extent possible, constraints on the structural mass, the energy, the maximum transient voltage and the number of actuators are considered. Because the control voltages are varying in time, a two-level optimization strategy is adopted. In the inner optimization problem, the Newmark integral method is applied to derive discrete time domain expressions for the shape control equations, and then, the Kuhn-Tucker condition is introduced to calculate the optimal time-varying voltage distribution. To solve the outer optimization problem, because of the coexistence of discrete variables and continuous variables, a simulated annealing algorithm is used. To address the shape control of complicated curved shells, a finite element formulation for an eight-node laminated curved shell element with piezoelectric actuators is derived. Numerical examples show that the proposed integrated design optimization method can significantly improve the control effect and that the optimization of the structural ply parameters plays an important role. Moreover, the control system can be simplified by taking the minimum number of actuators as the objective function when the control accuracy allows.

Magneto-acoustic-electrical tomography (MAET) combines the advantages of ultrasound and electrical impedance functional tomography methods and has important research value in the early diagnosis of tumors and biocurrent monitoring. In this study, we propose a MAET method combining liquid metal image enhancement and maximum length sequence (MLS)-coded excitation to improve the signal-to-noise ratio (SNR) of MAET. The results indicate that liquid metal can achieve image enhancement of tissue MAET. When 7-, 15-, 31- and 63-bit MLS-coded excitations were applied to the samples, the SNR was improved by 28, 34, 40 and 45 dB, respectively. For a similar SNR improvement, the total used time under 31-bit MLS-coded excitation can be shortened to 23% under single-pulse excitation. The experimental results prove the feasibility of applying the MLS code to rotational MAET and reveal the significance of liquid metal as an image intensifier to improve the quality of MAET.

Most previous studies of viscoelastic sandwich plates were based on the assumption that damping was only resulting from shear deformation in the viscoelastic core. However, extensive and compressiv...

Magneto-acoustic imaging is a novel functional imaging method to electrical characteristics of tissue. It provides valuable tools for diagnosing early stage tumor and monitoring bioelectrical current. Common single short-pulse excitation limits SNR due to the short-pulse duration and low power of magneto-acoustic signal. In this study, we propose M-sequence-coded excitation and pulse compression approach to improve SNR of magneto-acoustic imaging. Simulations on the magneto-acoustic signal under different bit lengths M-sequence-coded excitation are performed. Experiments on the samples made of pork and graphite slices are done to validate the proposed coded excitation method. The SNR and sidelobe levels were investigated. The results showed when 7, 15, 31, 63, 127 bits M-sequence-coded excitations were applied onto the samples, SNR was improved by 17.4 dB, 24.2 dB, 30.6 dB, 37.6 dB, and 40.1 dB, respectively. For a similar SNR improvement, the total used time under coded excitation can be shortened to 9.4% under the single pulse excitation. The result indicates the M-sequence-coded excitation approach is effective to improve the magneto-acoustic signal SNR and shorten the imaging time. Graphical abstract SNR of the magneto-acoustic signal is significantly improved by the coded excitation than the pulse excitation, the reconstructed image of the front and back boundary of the pork can be seen clearly under the 7, 15, 31, 63, 127 bit M-sequence-coded excitations.

Functional imaging method of biological electrical characteristics based on magneto-acoustic effect gives valuable information of tissue in early tumor diagnosis. Common exciting and measuring method is to use single pulse. The imaging quality and the imaging speed are limited by the signal to noise ratio (SNR). In this study, we propose a processing method based on coded excitation and pulse compression to improve SNR of magneto-acoustic imaging. Barker code is widely used in ultrasonic signal processing, which can effectively improve the signal to noise ratio. It is introduced to increase SNR of the magneto-acoustic signal. Simulations on magneto-acoustic signal and pulse compressed signal under Barker coded excitation with a group of bit lengths are computed. Experiments on sample made of pork and graphite slices are done to validate the proposed coded excitation method. The pork sample is imaged to validate this method. SNR is investigated using Barker codes with different bits. The results showed, the SNR of magneto-acoustic signal is improved by the coded excitation. When 13 bit Barker code mode is adopted as the exciting signal, SNR improved by 21.5 dB. For a similar SNR improvement, the processing time of coded excitation method can be shortened by 95.8% compare with single pulse excitation method. In a conclusion, the coded excitation method is effective to improve the magneto-acoustic signal SNR and imaging quality. It also improves the magneto-acoustic imaging speed.

Integrating a regenerative turbine (RT) is a significant modification to improve the Rankine cycle efficiency by reducing the superheat degree of extraction steam. This work evaluates the short-term operational flexibility of the modified cycle, emphasizing the evaluation of recuperative heater shutdown as a method to rapidly increase the power generation. A number of scenarios were modeled that included a shutdown of recuperative heaters, and the power change was observed. Results indicate that the utilization of an RT decreases the operational flexibility of the power plant with the high-pressure recuperative heater (HPH) shutdown. It shows that the adjusting time of total power generation increases by 492.9–550.6 s and the maximal output power increment reduces by 6.0–28.1 MW compared to that of the conventional Rankine cycle (CRC). Control strategies are proposed and evaluated to improve response performance and limit the deaerator (DTR) pressure. The results reveal that the adjusting time of the total power and maximum negative overshoot value could be reduced by 342.8 s and 7.79 MW, respectively, with a normal DTR pressure under the condition of No.3 and No.4 HPH shutdowns.

Both the linear leg spring model and the two-segment leg model with constant spring stiffness have been broadly used as template models to investigate bouncing gaits for legged robots with compliant legs. In addition to these two models, the other stiffness leg spring models developed using inspiration from biological characteristic have the potential to improve high-speed running capacity of spring-legged robots. In this paper, we investigate the effects of “J”-curve spring stiffness inspired by biological materials on running speeds of segmented legs during high-speed locomotion. Mathematical formulation of the relationship between the virtual leg force and the virtual leg compression is established. When the SLIP model and the two-segment leg model with constant spring stiffness and with “J”-curve spring stiffness have the same dimensionless reference stiffness, the two-segment leg model with “J”-curve spring stiffness reveals that (1) both the largest tolerated range of running speeds and the tolerated maximum running speed are found and (2) at fast running speed from 25 to 40/92 m s−1both the tolerated range of landing angle and the stability region are the largest. It is suggested that the two-segment leg model with “J”-curve spring stiffness is more advantageous for high-speed running compared with the SLIP model and with constant spring stiffness.

Objective Magnetoacoustic imaging provides valuable information for monitoring bioelectricity and early tumor diagnosis. However, the low signal-to-noise ratio (SNR) of the magnetoacoustic signal, resulting from the single pulsed excitation, limits the imaging quality. A signal processing method of frequency coding excitation is proposed to increase the SNR of the magnetoacoustic signal. Methods Chirp signal frequency coding is studied by simulation. M-sequence phase coding and wave averaging are also adopted in the studies. The experiments are conducted using a phantom of beef and fat with embedded copper rings. Two evaluation parameters, SNR improvement per unit pulse duration and SNR improvement per unit pulse duration per unit time, as well as the processing speed, are proposed to evaluate the SNR improvement. Results The results show that the frequency coding approach can rapidly improve the SNR of the magnetoacoustic signal as well as phase coding excitation, compared with the wave averaging approach. Conclusions A method of combining the coding and waveform averaging to improve the SNR of magnetoacoustic signal has been developed. A higher SNR improvement in the magnetoacoustic signal, up to 235×, with a short processing time of 0.867 s, can be obtained. Significance This study provides an effective method to improve the SNR in magnetoacoustic imaging.

Parabolic trough concentrating solar power with indirect thermal energy storage, as a promising application of solar energy, has been widely used in concentrating solar power plants. The exergy efficiency of thermal energy storage system and plant parasitic power consumption could change under cloudy conditions when the thermal oil distribution was adjusted to the live steam branch and reheat steam branch. However, the operating condition optimization of steam generation system has received insufficient attention. This study designed a detailed fixed-power-supply model of parabolic trough concentrating solar power plants to optimize the operation strategies under various conditions. The parametric constraints, which worked on the optimization, were investigated under various direct normal irradiation values. Simulation results indicated that the low reheat steam temperature, thermal oil mass flow rate of the live steam branch, and live steam pressure reduced the molten salt temperature at the discharging exchangers and plant parasitic power consumption. The distribution mode of preferentially satisfactory distribution of reheat steam branch demand had low molten salt consumption and high exergy efficiency of thermal energy storage. The molten salt consumptions under optimal conditions were 0.98%–13.68% lower than the consumption under original conditions with the decreasing direct normal irradiation from 300 W/m2 to 210 W/m2.

Micro pin fin heat sinks are an indispensable component in high-power electronic devices that are intended to enhance the device's thermal performance. In this study, the combination of conventional pin fin and lattice structure are used to propose a new design of micro latticed pin fin. The thermal performance and the impacts of the flow states and morphological types on the new design are investigated through fluid-thermal coupled numerical approach. The results reveal that overall pressure loss shows a slight improvement by using the latticed pin fin when compared with a solid pin fin. However, only a cubic body-centered-cubic pin fin has a positive influence on hydraulic and thermal performance, using a vertex cube achieves the opposite results. In terms of weight reduction, using the latticed pin fin can reduce the volume of the heat sink by approximately 14%-17%. Considering both pressure loss and Nusselt number (Nu), the improvement of the thermal-hydraulic performance index (η) of the BCC-PF (cubic body-centered-cubic pin fin) heat sink is more than 140% compared with the conventional pin fin heat sink.

Composite structures integrated with viscoelastic materials are becoming more and more popular in the application of vibration suppression. This paper presents a comprehensive approach for analyzing this class of structures with an improved Burgers model, from material constitutive modeling, finite element formulation to solution method. The refined model consists of a spring component and multiple classical Burgers components in parallel, where the spring component converts the viscoelastic fluid model to a viscoelastic solid model and the multiple Burgers components increase the accuracy. Through the introduction of auxiliary coordinates, the model is applied to the finite element formulation of composites structures with viscoelastic materials. Consequently, a complicated Volterra integro-differential equation is transformed into a standard second-order differential equation and solution techniques for linear elastic structures can be directly used for elastic–viscoelastic composite structures. The improved Burgers model is a second-order mini-oscillator model, in which every mini-oscillator term has four parameters. The model parameters determination is performed by optimization algorithm. By comparison of model fitting results for a typical viscoelastic material, the refined model is better in accuracy than Golla–Hughes–McTavish (GHM) model and original Burgers model. Finally, several numerical examples are presented to further verify the effectiveness of the improved Burgers model.

Magnetoacoustic Tomography (MAT) is a non-invasive imaging modality for electrical conductivity with good contrast and high spatial resolution. We have analyzed the acoustic source generation mechanism of MAT and presented its physical model, including the simulations and experiments in this paper. In MAT, acoustic sources are generated in a conductive object placed in a static magnetic field. Pulsed current is injected into the object and produces a Lorentz force due to the static magnetic filed. Acoustic vibration was excited by the Lorentz force, and hence, ultrasound waves propagate in all directions and are collected with transducers placed around the object. The conductivity image can then be reconstructed with acoustic waves using some reconstruction algorithms. Because the acoustic source generation mechanism of MAT is the key problem of forward and inverse problems, we analyzed the physical process of acoustic source generation and presented the acoustic dipole source model according to the Lorentz force imposed on the object. In addition, computer simulations and experiments were also conducted. The results of simulations applying an acoustic dipole source model are consistent with experimental results. This study has cardinal significance for the accurate algorithm of MAT and provides a methodology and reference for acoustic source problems.

Payload capacity of running robots with compliant legs is a very important subject for robotic researchers, with the fact that SLIP model, two-segment leg model with constant spring stiffness and with ‘J’-curve spring stiffness are regarded as an effective tool as well as a good basis for the study of running robots with compliant legs. However, in fast locomotion, little work has been done on the relationship between leg compliance and payload capacity based on these three models. Thus, at high speed we adopt the steps-to-fall method and the apex return map to investigate the influence of leg stiffness on payload capacity in all three models. Simulation results reveal that in all three models the two-segment leg model with J-curve spring stiffness shows the largest stability region, and for the same payloads the tolerated minimum reference stiffness is the lowest. In other words, for the same leg stiffness, it provides the maximum payload capacity in all three models. Thus, at high speed two-segment leg model with ‘J’-curve spring stiffness is more propitious for high-payload running compared with the other two models.

Nano reinforcement of metals cannot escape the attention of designers who seek to improve overall performance of engineering structures from automotive components to biomedical devices. Since many engineering structures are susceptible to variable cyclic load, presenting shakedown design of them is of the present research interest. So that, in the present research the shakedown loading capacity of metal based nanocomposite is estimated through finite element discretization and interior point optimization method. Finally, the results are obtained for plate structures subjected to two independent biaxial loads. A maximum improvement of 71.2% is achieved for shakedown load factor of the structure, which means a remarkable improvement in load bearing capacity of the structure.

Acoustic and electrical characteristics of biological tissue are important factors in magnetoacoustic tomography with magnetic induction (MAT-MI). Acoustic inhomogeneity significantly affects the propagations of sound waves. Differences in sound speed lead to distortions of the sound sources in the reconstruction process. The objective of this study is to develop a novel algorithm to reconstruct the sound source distribution in an acoustically inhomogeneous medium. The proposed algorithm is developed on the basis of the finite-difference time-domain method and time-reversal acoustic theory; it combines the relationship among symmetrical transducers with the back-projection algorithm. An acoustically inhomogeneous model with different regions of variable sound speeds is established to validate the proposed algorithm. From the data collected by a rotated focused transducer, first, the sound speed distribution is reconstructed, and then, the sound sources of the model are reconstructed. The reconstructed sound sources are obviously distorted when the speed differences are not considered. In contrast, the proposed algorithm yields reconstructed sound sources that are consistent with the model in terms of shape and size. Thus, the proposed algorithm is capable of accurately reconstructing the acoustic sources distribution in an acoustically inhomogeneous medium. This method provides a solution reducing the influence of acoustic inhomogeneity in MAT-MI. The distributions of sound speed can be obtained during the process of reconstructing the sound source. Consequently, the imaging of the acoustic speed and the electrical conductivity of biological tissues can be implemented simultaneously in MAT-MI.

Functional imaging method of biological electrical characteristics based on magneto-acoustic effect gives valuable information of tissue in early tumor diagnosis, therein time and frequency characteristics analysis of magneto-acoustic signal is important in image reconstruction. This paper proposes wave summing method based on Green function solution for acoustic source of magneto-acoustic effect. Simulations and analysis under quasi 1D transmission condition are carried out to time and frequency characteristics of magneto-acoustic signal of models with different thickness. Simulation results of magneto-acoustic signal were verified through experiments. Results of the simulation with different thickness showed that time-frequency characteristics of magneto-acoustic signal reflected thickness of sample. Thin sample, which is less than one wavelength of pulse, and thick sample, which is larger than one wavelength, showed different summed waveform and frequency characteristics, due to difference of summing thickness. Experimental results verified theoretical analysis and simulation results. This research has laid a foundation for acoustic source and conductivity reconstruction to the medium with different thickness in magneto-acoustic imaging.

A new method to improve the focalization and efficiency of the Figure of Eight (FOE) coil in rTMS is discussed in this paper. In order to decrease the half width of the distribution curve (HWDC), as well to increase the ratio of positive peak value to negative peak value (RPN) of the induced electric field, a shield plate with a window and a ferromagnetic block are assumed to enhance the positive peak value of the induced electrical field. The shield is made of highly conductive copper, and the block is made of highly permeable soft magnetic ferrite. A computer simulation is conducted on ANSYS® software to conduct the finite element analysis (FEA). Two comparing coefficients were set up to optimize the sizes of the shield window and the block. Simulation results show that a shield with a 60 mm $\,\times\,$ 30 mm sized window, together with a block 40 mm thick, can decrease the focal area of a FOE coil by 46.7%, while increasing the RPN by 135.9%. The block enhances the peak value of the electrical field induced by a shield-FOE by 8.4%. A real human head model was occupied in this paper to further verify our method.

Magnetoacoustic tomography (MAT) has some advantages such as high sensitivity and high spatial resolution. The generating mechanism of acoustic source is the research foundation of forward and inverse problems. A coustic signals were respectively simulated by using monopole and dipole radiation theory in the experimental conditions, then the differences between their acoustic pressures were discussed, and furthermore the contrast and validation were conducted by physical experiments in this study. The physical experimental results showed that acoustic waveform of MAT had a certain directivity and therefore they indicated that dipole model showed higher approximation to the real facts than monopole model. It can be well concluded that this research has cardinal significance for the accurate algorithm of MAT.

Reconstruction of absorption coefficient \mu_{a} and scattering coefficient \mu_{s} is very important for applications of diffuse optical tomography and near infrared spectroscopy. Aiming at the early cancer detection of cervix and stomach, we present a fast inverse Monte-Carlo scheme for extracting \mu_{a} and \mu_{s} of a tubular tissue from the measurement on frequency domain. Results show that the computation time for reconstructing one set of \mu_{a} and \mu_{s} is less than 1 min and the relative errors in reconstruction are less than +-10% for the optical properties of normal cervical tissue and precancerous lesions.

Magnetoacoustic tomography (MAT) is an emerging noninvasive electrical conductivity imaging that combines the high dielectric contrast of tissues and excellent resolutions of ultrasonography. In this paper, we have found the thermoacoustic (TA) effect in the measurement of MAT. Several materials with different conductivities have been measured by a MAT system with and without a static magnetic field. The acoustic signals have been analyzed and compared in the time domain and the frequency domain, respectively. It is found that the TA effect is related to the material characteristics. For the tissue-like materials with low conductivities, the TA signals caused by the TA effect are observable and cannot be ignored in the time and frequency domains. It means that the TA effect of biological tissues should be considered in MAT system in the future.

This article aims at the optical parameter reconstruction technology for the frequency- domain measurement of near-infrared diffused light. For mimicking the cervix, a cylindrical model with hole in the middle is used in the simulation and experiments. Concerning the structure of the cervix, Monte-Carlo simulation is adopted for describing the photon migration in tissue and Perturbation Monte-Carlo is used for the reconstruction of the optical properties of cervix. The difficulties in the reconstruction of cervical optical properties with frequency domain measurement are the description of the tissue boundary, expression of the frequency-domain signal, and development of rapid reconstruction method for clinical use. To get the frequency domain signal in Monte Carlos simulation, discrete Fourier transformation of the photon migration history in time-domain is employed. By combining the perturbation Monte-Carlo simulation and the LM optimization technology, a rapid reconstruction algorithm is constructed, by which only one Monte-Carlo simulation is needed. The reconstruction method is validated by simulation and experiments on solid phantom. Simulation results show that the inaccuracy in reconstruction of absorption coefficient is less than 3% for a certain range of optical properties. The algorithm is also proved to be robust to the initial guess of optical properties and noise. Experimental results showed that the absorption coefficient can be reconstructed with inaccuracy of less than 10%. The absorption coefficient reconstruction for one set of measurement data can be fulfilled within one minute.