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The poverty problem in China has an important connection with the precision sales of agricultural products. We are committed to providing farmers with all-round help, taking "farmers' income increase, agricultural growth, and rural stability" as our mission, and comprehensively helping farmers develop and become rich. Therefore, our team has developed a central APP called "Agricultural Helper", which provides a safe, reliable and convenient platform for farmers to sell agricultural products. Our platform eliminates many redundant steps and directly contacts with enterprises such as fruit processing plants and canning plants. The platform also provides a personal to personal marketing model to further simplify the transportation of agricultural products and ensure the quality of agricultural products, such marketing mode can reduce the purchase cost of enterprise users and individual users. This paper introduces the main functions, products and services of the "agricultural helper" APP, analyzes its marketing strategies, and analyzes its risk types and countermeasures.

In the current study, a 1-D phenomenological model is constructed to capture the temperature-induced hysteretic response in polycrystalline shape memory alloys (SMAs). The martensitic and austenitic transformations are regarded as the first-order transitions. A differential single-crystal model is formulated on the basis of Landau theory. It is assumed that the transformation temperatures follow the normal distribution among the grains due to the anisotropic stress field developed in the material. The polycrystalline hysteretic response is expressed as the integration of single-crystal responses. Besides, the prediction strategy for incomplete transitions is presented, and the first-order reversal curves are obtained via density reassignment. The proposed model is numerically implemented for validation. Comparisons between the modeling results and the experimental ones demonstrate the capability of the proposed model in addressing the hysteresis in thermally-induced phase transformations.

A kind of modified bismaleimide resin, with good processability, heat resistance, and impact strength was developed, using 4,4′-dipropargyloxydiphenyl ether (DPEDPE), N-(4-propargyloxyphenyl)maleimide (4-PPM), and 3-ethynylphenyl maleimide (3-EPM) as modifiers. The DPEDPE, 4-PPM, and 3-EPM were synthesized and characterized by Fourier transform infrared spectroscopy (FTIR) and 1H-nuclear magnetic resonance (1H NMR), and used to modify the N,N′-(4,4′-diphenylmethane)bismaleimide (BDM)/2,2′-diallyl bisphenol A (DABPA) resin system (BD) to obtain the different blend resin systems of DPEDPE-modified BD (BDD), 4-PPM-modified BD (BDP), and 3-EPM-modified BD (BDE). The curing temperature of BD resin increases with increase of the alkynyl-terminated modifier content. The processability of BD resin was improved with addition of the propargyloxy-terminated compounds. The temperature of 5% weight loss, residual yield at 800°C and glass transition temperature of the cured BD resin increase with increase of the alkynyl-terminated modifier content and can reach 443°C, 46.7% and higher than 380°C. The tensile strength of the cured BD resin decreases with increase of alkynyl-terminated modifier content. The impact strength of the cured BD resin increases with increase of the propargyloxy-terminated compound content and can increase by 65%. The tensile strength, elastic modulus, and impact strength of the cured BD resin blended with DPEDPE can be 73.7 MPa, 4.1 GPa, and 19.6 kJ m−2, respectively. Moreover, the cured BD resin blended with DPEDPE has good water absorption resistance.

Shape Memory Alloys (SMA) have become a material with great application prospects because of their unique characteristics and superior properties. A phenomenological constitutive model for SMA is constructed in the current paper. The proposed constitutive model is based on the phenomena observed in the experiment, and Artificial Neural Networks (ANN) are used to simulate part of the characteristics of SMA. The parameter identification method is also proposed, where Back-Propagation (BP) algorithm and the nonlinear optimisation algorithm are used at the same time. The numerical experiment has been carried out, which can well capture the constitutive relationship curve obtained from uniaxial tension and compression experiments of SMA, thus the model can be verified. The model can also describe the phase transformation characteristics of SMA well.

In this paper, a low-frequency vibration energy harvester based on magnetic shape memory alloys (MSMAs) is proposed to harvest the vibration energy. The principle of energy harvesting using the magnetic shape memory alloy is clarified, and the related experimental schematic diagram is designed. When the harvester is vibrated, the cantilever beam will exert force on the sample, which will make the martensite reorientation causing the axial magnetic polarization to change and leads to the change of magnetic flux. Therefore, when a pick-up coil is surrounded by the specimen, voltage will be induced according to Faraday's law. The magnetic field generated by the NdFeB magnet in the experimental device is simulated and verified, and the modal analysis of the cantilever beam is implemented to ensure that it can meet the requirements. Then the energy harvesting experiment is carried out and the induced voltage generated at low frequency (no more than 50 Hz) is depicted. The RMS values of the induced voltage at different frequencies are calculated. At low frequencies, the experimental results show that the proposed energy harvester has advantages in generating voltage compared with other devices, which further demonstrates the effectiveness of using magnetic shape memory alloy to capture low-frequency vibration energy and can provide references for the acoustic energy harvesting to some extent.

Magnetic shape memory alloys (MSMAs) are materials with strong nonlinearity, which will show hysteresis when it works. In the current paper, a differential model is proposed to describe the hysteresis in MSMAs caused by magnetic field induced martensite reorientation based on Landau theory of phase transitions. First, the three-dimensional model is simplified into a one-dimensional case, and the hysteresis in MSMAs is described by three martensite variant orientations. Then, a traditional Landau free energy is introduced, and the traditional Landau model is obtained by using the Euler–Lagrange equation. However, it is found that the prediction accuracy of the model is not ideal compared with the experimental data. Thus, an improved model is proposed, and the traditional Landau free energy is replaced by a function that can be determined by the easily measured physical quantities in the experimental curve. Numerical experiments show that the prediction effect of the improved model is much better than the traditional Landau model, and the stress dependence is also demonstrated. Moreover, the proposed improved model has the advantages for dynamic analysis and control with its differential form. Therefore, the frequency dependence of the improved model is demonstrated and a feedback linearization control methodology is proposed to make the system develops in the desired trajectory.

Liquid nitrogen (LN2), which can greatly improve the efficiency of hot dry rock (HDR) mining, is commonly used as a cooling material in the enhanced geothermal system (EGS). Physical property, triaxial compression, and permeability tests were undertaken on treated granite samples, for a better scientific understanding of the effect of the LN2 cooling method on the mechanical and permeability properties of the rocks after heat treatment. The experimental results indicated that the physical properties of the treated granite change significantly, such as the density and wave velocity are substantially reduced. Meanwhile, with the increase of treatment temperature, the macroscopic cracks on its surface are gradually generated and the volume is expanded clearly. In addition, the surface wettability of granite gradually increases with increasing temperature. Compared with the air/water cooling methods, under LN2 cooling condition, the mechanical properties decrease markedly. When the temperature exceeds 600°C, the granite strength decreases significantly to only 56.16% of the reference value. The deformation properties also change significantly, with a final strain of about 3% at failure for a sample at 800°C, showing an obvious ductile deformation characteristic. Further, an appreciable correlation also exists between the initial permeability of granite and temperature. Once the temperature exceeds 200°C, the increase in temperature contributes to the increase in initial permeability. In addition to the effect of temperature, the increase in load also leads to a change in the permeability coefficient. When the temperature reaches 600°C, the permeability of granite first decreases and then increases with the increases in axial stress. The results of this paper are valuable in understanding the effect of thermal shock by LN2 on the fracturing efficiency and permeability characteristics of dry hot rocks.

To explore the development mechanism of cracks in the process of rock failure, triaxial compression tests with simultaneous acoustic emission monitoring were performed on granite specimens using the MTS rock mechanics test system. The frequency-domain information of the acoustic emission signal was obtained by the fast Fourier transform. The Gutenberg–Richter law was used to calculate the acoustic emission signals and obtain the b-value dynamic curve in the loading process. Combined with the stiffness curve of granite specimens and acoustic emission signal in the time domain and frequency domain, the crack development characteristics in different stages were analyzed. The results showed that the acoustic emission signals of granite samples under triaxial compression can be divided into four stages: quiet period 1, active stage 1, quiet period 2, and active stage 2. b-value attained its maximum value in the active phase 2 when it is close to the sample loss, and then drops rapidly, which means the propagation of cracks and the formation of large cracks. The acoustic emission signal’s dominant frequency was not more than 500 kHz, mostly concentrated in the medium-frequency band (100–200 kHz), which accounted for more than 80%. The proportion of signals in each frequency band can reflect the distribution of the three kinds of cracks, while the change in low-frequency signals can reflect the breakthrough of microcracks and the formation time of macrocracks in granite samples. By fully analyzing the characteristics of acoustic emission signals in the time domain and frequency domain, the time and conditions of producing large cracks can be determined accurately and efficiently.

Shape memory alloy (SMA) is a very important smart material, which has been widely used in many fields, especially in vibration. Phase transformation can be induced by changing temperature and its stiffness changes accordingly. In this paper, the primary resonance vibration of a one-dimensional SMA oscillator is analyzed using the harmonic balance (HB) method. The amplitude-frequency curves of the SMA oscillator with different temperatures are drawn, and the effect of temperature and frequency on the amplitude is discussed. Then, the energy flow of SMA in the vibration process is researched by the power flow analysis (PFA) approach. The time-averaged input power (TAIP) is calculated using the analytical and numerical method, respectively, and the calculation time is compared. It is found that the difference between the analytical and numerical solutions is not significant in most cases, but the calculation time of analytical solution is only about one-tenth of that of the numerical solution, which is very important in saving computational cost, real-time control and so on. Finally, some other characteristics of energy flow in the SMA oscillator are identified.

The well completion and fracturing towards deep unconventional high-temperature (HT) petroleum or natural gas reservoirs is considerably strict to the packer especially packing elements. However, existing packing elements including swellable packers usually are made from Hydrogenated Nitrile (HNBR) or Fluorine rubber (FKM) with drawbacks of great expense and difficult tripping into the horizontal wellbore. This paper proposes a compact isolating solution using swellable Thermo-plastic Vulcanizates (TPVs), which is prepared by blending HNBR, low-cost Polyamide66 (PA66) and Porous Super Absorbent Resin (PSAR) with enhanced nanoparticles. The TPVs were characterized by experiments and the system with Plastic/Elastomer Ratio (PER) of 45:55, tensile strength of 18.6 MPa and elongation at break of 635% upon aging (150 °C) was qualified for the packing element material. A novel enhanced packing element is put forward with corrugated-profile structure to address large-size and over-extrusion issues. The numerical study on packer components was conducted based on TPV constitutive model. The prototype with element length of 2.5–2.6 m was validated in the lab and rated as the sealing of more than 70 MPa. An optional disintegrating casing is adopted to avoid the premature damage risk of packers. For the field trial, the multistage fracturing tubular with improved packers was deployed into the horizontal open hole without severe pipe stuck. The fracturing operation was successfully performed and all packers functioned normally with the maximum pressure differential of 73 MPa. It concludes that the new solution exhibited high strength, heat resistance and structure integrity with low cost over the traditional packers towards HT environment.

The Preisach model, which is formulated as a weighted superposition of hysteresis kernels, has been widely used for hysteresis modeling, especially in smart-material-based actuators. However, in the classical Preisach model, a trade-off is always required between the model accuracy and the number of the hysteresis kernels. To deal with this problem, a model order reduction technique based on the discrete empirical interpolation method (DEIM) has recently been proposed. The method can largely reduce the number of the hysteresis kernels while barely losing the model accuracy. It is noted that the kernel weight in the reduced DEIM-based model can be both positive and negative, which means that the monotonicity of the Preisach model could be lost. The monotonicity is a very important property especially when constructing the inverse Preisach model. Furthermore, the loss of the monotonicity can also deteriorate the model predictability. In the current paper, a modification strategy is proposed. In the modified reduced Preisach model, the DEIM is only employed to select the dominant hysteresis kernels while the corresponding weights of the selected hysteresis kernels are re-identified by solving a constraint optimization problem. Systematic simulation studies and experimental validation are carried out to demonstrate the effectiveness of the proposed strategy.

In this research, the propulsion of the proposed jellyfish-inspired mantle undulated propulsion robot (MUPRo) is optimized. To reliably predict the hydrodynamic forces acting on the robot, the proposed nonintrusive reduced-order model (NIROM) based on proper orthogonal decomposition (POD) additionally considers the POD basis that makes an important contribution to the features on the specified boundary. The proposed model establishes a mapping between the parameter-driven motion of the mantle and the evolution of the fluid characteristics around the swimmer. Moreover, to predict new cases where the input needs to be updated, the input of the proposed model is taken from the kinematics of the robot rather than extracted from full-order high-fidelity models. In this paper, it takes approximately 950 s to perform a simulation using the full-order high-fidelity model. However, the computational cost for one prediction with the proposed POD-NIROM is around 0.54 s, of which about 0.2 s is contributed by preprocessing. Compared with the NIROM based on the classic POD method, the proposed POD-NIROM can effectively update the input and reasonably predict the characteristics on the boundary. The analysis of the hydrodynamic performance of the MUPRo pinpoints that, over a certain period and with a certain undulation amplitude, the hydrodynamic force generated by the swinging-like mantle motion (k < 0.5) is greater, outperforming Aequorea victoria in startup acceleration. It is demonstrated that considering a certain power loss and a certain tail beat amplitude, the wave-like mantle motion (k > 0.5) can produce greater propulsion, which means higher propulsion efficiency.

Recently, a novel method for mechanical energy harvesting has been proposed, which is based on stress-induced polarization switching in ferroelectric materials. Compared with the traditional piezoelectric energy harvesters, a huge improvement in the output energy has already been theoretically demonstrated. In this article, the influence of different materials on the energy-harvesting performance associated with this new strategy is further studied. The state-of-the-art phase-field model is adopted to investigate the nonlinear hysteretic energy-harvesting process in two nanoscale ferroelectric energy harvesters, which are respectively based on two typical ferroelectric materials—single-crystal BaTiO3 and PbTiO3. In both cases, the effects of the bias voltage and bias resistance are carefully investigated and the optimum values are obtained. Later, the energy-harvesting process and energy flow details in both harvesters working at the optimum conditions are presented and carefully compared in the context of real applications. Furthermore, the energy-harvesting performance of a BaTiO3-based nanoscale piezoelectric energy harvester with equivalent material size is additionally simulated with the finite element method and compared with the corresponding results of the ferroelectric energy harvesters, where obvious advantages associated with the new strategy are demonstrated.

In the current paper, a macroscopic model is proposed to simulate the hysteretic dynamics of ferroelectric ceramics with creep phenomenon incorporated. The creep phenomenon in the hysteretic dynamics is attributed to the rate-dependent characteristic of the polarisation switching processes induced in the materials. A non-convex Helmholtz free energy based on Landau theory is proposed to model the switching dynamics. The governing equation of single-crystal model is formulated by applying the Euler–Lagrange equation. The polycrystalline model is obtained by combining the single crystal dynamics with a density function which is constructed to model the weighted contributions of different grains with different principle axis orientations. In addition, numerical simulations of hysteretic dynamics with creep phenomenon are presented. Comparison of the numerical results and their experimental counterparts is also presented. It is shown that the creep phenomenon is captured precisely, validating the capa...

In the current paper, energy dissipation via stress-induced polarization switching in ferroelectric material is investigated, and the feasibility of its application in sound wave absorption is analysed. For the system design and analysis, a phenomenological model based on the modified Landau phase transition theory is constructed to describe the polarization switching. A simple and robust energy dissipation prototype is introduced. The hysteretic dynamics associated with the polarization switching process and the energy dissipation process are investigated. The dependence of the energy dissipation on the bias voltage, frequency, and resistance is analysed in detail. The energy dissipation density in one cycle is calculated. It is shown that the resistance has a strong influence on the energy dissipation. Meanwhile, a better energy dissipation effect could be obtained by setting an appropriate resistance for the low-frequency excitation. The feasibility of using ferroelectric materials for low-frequency sound wave absorption is validated. For a specific acoustic energy dissipation device, corresponding design and analysis will be discussed in our future papers.

In this work, the hysteretic dynamics of a pseudoelastic shape memory alloy (SMA) spring is modeled and tested. A constitutive model of SMA spring is constructed by combining the theory of mechanical spring and the derived SMA constitutive relation. The SMA spring recovery force is modeled by employing the Euler–Lagrange equation based on a non-convex potential function. A macroscopic differential model is formulated to describe the hysteretic dynamics and the pseudoelasticity of the SMA spring. A theoretical method for estimating the equivalent stretch ratio at a specific temperature of SMA spring is given. Numerical simulations were presented in studying the influence of the stretch ratio at a temperature of 50, 70, and 90°C. The experimental tests are performed and presented together with their numerical counterparts. The comparison is made between numerical and experimental results to validate the proposed model for SMA spring.

In the current paper, the coupled hysteretic behaviors of ferroelectric ceramics subjected to combined electromechanical stimulations are modeled. For a single grain, the polarization orientation switching process is modeled by employing the Euler–Lagrange equations and formulated as a coupled differential equation system. For ferroelectric ceramics, the principle axis orientations of the individual grains are assumed to be distributed in a certain profile, the behaviors of the ceramics are modeled as a weighted combination of the response of each grain. The influence of intergranular interactions is carefully discussed. Numerical results for the minor hysteresis loops in strain and polarization are demonstrated. Comparisons between these results and their experimental counterparts are presented to illustrate the attributes of the proposed model.

In this study, pentacyclic triterpenoids (PTTs) were extracted from loquat leaves by subcritical water extraction (SWE) technique in a dynamic mode. The results revealed that PTTs yield increased up to 5.38±0.12 mg/g with the increasing temperature at 180 °C for corosolic acid (CA) and up to 7.20±0.11 mg/g at 200 °C for ursolic acid (UA) within experimental times. The optimum flow rates to obtain concentrated CA and UA extracts were found to be 33.33 and 41.67 mL/min, respectively. Furthermore, extraction temperatures strongly influenced the extraction rate as demonstrated by the rate constant of each temperature tested. Moreover, the kinetic rate constant decreased as the function of temperature indicating the yield of both CA and UA were significantly influenced by subcritical temperatures and extraction times.

In the current paper, a nonlinear differential algebraic approach is proposed for the modeling of hysteretic dynamics of polycrystalline ferromagnetic materials. The model is constructed by employing a phenomenological theory to the magnetization orientation switching. For the modeling of hysteresis in polycrystalline ferromagnetic materials, the single crystal model is applied to each magnetic domain along its own principal axis. The overall dynamics of the polycrystalline materials is obtained by taking a weighted combination of the dynamics of all magnetic domains. The weight function for the combination is taken as the distribution function of the principal axes. Numerical simulations are performed and comparisons with its experimental counterparts are presented. The hysteretic dynamics caused by orientation switching processes is accurately captured by the proposed model. Minor hysteresis loops associated with partial-amplitude loadings are also captured. Rate dependence of the hysteresis loops are inherently incorporated into the model due to its differential nature.

In the current paper, the ageing and de-ageing phenomena in ferroelectric ceramics are modelled by a Landau-type model based on the internal bias field theory. A new phenomenological term for the internal bias electrical field is added into the free energy function to simulate the phenomenon of lattice symmetry during the ageing phenomenon. The simulations for both ageing and de-ageing phenomena are successfully presented in the current paper. The hysteretic behaviours of the ageing and de-ageing phenomena are captured very well by the proposed model.

In the current paper, the coupled fatigue hysteretic behaviors in ferroelectric ceramics are modeled by a blending a phenomenological hysteresis model with point defects. The time-dependent phenomenological model is employed to capture the hysteresis loops associated with phase transitions. The fatigue hysteresis is modeled by combining the single-crystal model with time functions. The mechanism of fatigue in ferroelectric ceramics is interpreted as an accumulation of residual polarization in the proposed model. Numerical results of static and dynamic hysteretic behaviors are presented and compared to their experimental counterparts. The capability of the proposed model for capturing the fatigue phenomenon is validated.