摘要:
Purpose This paper is concerned with the H-infinity optimization design of passive and active dynamic vibration absorbers (DVAs) attached to an undamped or damped primary system.Methods The proposed optimization method is an efficient non-smooth H-infinity-synthesis algorithm that is utilized to solve structured H-infinity-synthesis in control engineering. This method can conveniently achieve the optimal design for the amplitude magnification factors of both the absolute and the relative displacements of a DVA using the proposed dual H-infinity design, and implement co-design of H-infinity-optimal proportional-integral-differential controllers and passive parameters of an active DVA.Results Two active DVAs and two variant passive DVAs reported in the literature are taken as examples for design improvement. The optimization results indicate that the proposed method has significant advantages over the conventional fixed points-theory-based methods and many numerical global optimization methods.Conclusions The proposed H-infinity optimization design yields much better vibration suppression result for proportional-integral differential control based active DVAs and variant passive DVAs with complicated structures. It is directly based on their equations of motion in state-space forms, and explicit formulations of various amplitude magnification factors, such as those on the absolute and the relative displacements and active force, need not be derived in the MATLAB environment. A possible situation of occurrence of large amplitude of the relative displacement in DVAs rarely considered in the literature can be handled by using the proposed dual H-infinity design.
通讯机构:
[Li, B ] W;Wuhan Polytech Univ, Sch Mech Engn, Wuhan 430023, Hubei, Peoples R China.
关键词:
continuous movement;microwave drying;numerical simulation;rice grains;temperature and moisture
摘要:
This study proposes a simulation strategy that facilitates the continuous movement of rice grains. The study establishes a three‐dimensional model concerning multiple physical fields, including electromagnetism, heat, and mass transfer. It examines the effects of rice grain layer thickness and microwave intensity on the moisture and temperature of rice grains. The drying process is analyzed and studied through mathematical modeling, aiming to improve the efficiency of microwave drying of materials and the quality after drying. Abstract To comprehensively understand temperature and moisture changes in a continuous microwave rice grain drying system, this study proposes a simulation strategy that facilitates the continuous movement of rice grains. The study establishes a three‐dimensional model concerning multiple physical fields, including electromagnetism, heat, and mass transfer. It examines the effects of rice grain layer thickness and microwave intensity on the moisture and temperature of rice grains. The results indicate that the drying rate is negatively correlated with material thickness but positively correlated with temperature. The optimal thickness for the rice grain layer is 8 mm. Furthermore, both the microwave drying rate and temperature increase with microwave intensity. These findings contribute to a deeper understanding of the hydrothermal change mechanisms in rice grains during microwave drying. Practical applications Microwave drying, as an emergent drying technology, has garnered widespread attention for its selective heating, efficient drying, energy savings, and environmental protection. Nevertheless, enhancing uniformity during the microwave heating process constitutes an important research topic in scientific research and technological applications. Numerical simulation methods can visually analyze electric field distribution, thereby optimizing microwave heating uniformity and improving drying effects. This article aims to accurately predict the continuous microwave drying time of paddy and maximize energy usage by optimizing drying thickness and microwave power parameters establishing a mathematical model for the process. The study not only provides a solid theoretical basis for microwave dryer design but also scientifically guides the continuous microwave drying of rice and other food crops.
摘要:
adipate terephthalate (PBAT) as matrix and zinc oxide nanoparticles (ZnONPs) and silver nanoparticles (AgNPs) as antibacterial agents, a series of antibacterial PLA/PBAT films were prepared by melt blending. The weight ratio of PLA, PBAT and nanoparticles in composite films was 70:900:10 (lower loading) or 70:900:20 (higher loading). The results showed that comparing with the PLA/PBAT films, the hydrophilicity, oxygen barrier properties, mechanical performance and antibacterial activities of PLA/PBAT/nanoparticles films were significantly improved (P < 0.05), and influenced by the content and type of nanoparticles. After the addition of nanoparticles, the maximum change of films performance was from 71.3 degrees to 35.8 degrees for water contact angle, from 7.4 x 10(-14) cm(3) cm.cm(-2). s(-1). Pa-1 to 5.5 x 10(-14) cm(3) cm.cm(-2). s(-1). Pa-1 for oxygen transmission permeability, from 26.4 MPa to 31.4 MPa for tensile strength, and from 0% to 57.8% (Escherichia coli) or 58.6% (Staphylococcus aureus) for antibacterial ratio. The films with higher loading content of nanoparticles showed a better antibacterial activity. For the same nanoparticles content, the antibacterial activity of PLA/PBAT/AgNPs was better than PLA/PBAT/ZnONPs. The overall migration in food simulants involving acetic acid (3%) ethanol (10% and 95%) was below 10 mg/dm(2) for most films, however, the overall migration for the films with higher content of AgNPs exceeded the limit value. The fresh noodles packaged by PLA/PBAT/AgNPs films showed the significant lowest total viable count with 4.6 lg (CFU/g) and the best appearance color characterized by L* (lightness), a*(red-green) and b*(yellow-blue) at storage time of 7 d in contrast with PLA/PBAT and PLA/PBAT/ZnONPs films, indicating the potential application of prepared films in active packaging to prolong the shelf life of food.
通讯机构:
[Wu, Y ] W;Wuhan Polytech Univ, Coll Mech Engn, Wuhan 430048, Peoples R China.
关键词:
AZ31 magnesium alloy;Stamping forming;GA;DBO algorithm;BP neural network;RF regression model
摘要:
To study the formability of AZ31 magnesium alloy under different temperature conditions and improve the forming quality of its parts, this paper aims to solve the minimization problem of pursuing the "maximum thinning rate". This study obtained the mechanical properties of AZ31 magnesium alloy at 25 degrees C, 150 degrees C, 250 degrees C, and 350 degrees C through uniaxial tensile tests and explored the stamping formability of AZ31 magnesium alloy mobile phone cases using the finite element inverse calculation method (MSTEP). Based on the hot stamping of AZ31 magnesium alloy at 250 degrees C, the Monte Carlo Simulation (MCS) method was used to randomly sample the blank holder force, stamping speed, friction coefficient, and resistance coefficient, and then simulate to obtain the corresponding "maximum thinning rate". In addition, a hybrid prediction model optimized by Genetic Algorithm (GA) and Dung Beetle Optimization (DBO) based on the Back Propagation Neural Network (BPNN) - Random Forest (RF) was used to explore the nonlinear relationship between blank holder force, stamping speed, friction coefficient, resistance coefficient, and the "maximum thinning rate". The results show that the plasticity of AZ31 magnesium alloy enhances with the temperature increase, especially exhibiting the best stamping formability at 250 degrees C. Feature importance indicates that the resistance coefficient and stamping speed have a greater impact on the maximum thinning rate, while the influence of blank holder force and friction coefficient is relatively smaller. Mean Square Error (MSE) shows that the predictive capability of the hybrid model is significantly superior to that of the single BP neural network and Random Forest model, displaying optimal efficiency. The predicted maximum thinning rate by the model is 15.39 %, with an error rate of only 0.32 % compared to the DYNAFORM finite element software simulation results, confirming the correctness, accuracy, and effectiveness of the prediction model. Overall, this study provides practical optimization strategies for metal stamping forming processes, with significant practical application value.
摘要:
The welding process and the properties of welding instruments may improve the mechanical performance of an item. One of these properties is the length of the welding tool. This approach has a substantial effect on the mechanical strength of the metallic matrix. The current study used molecular dynamics modeling and LAMMPS software to evaluate the effect of welding tool length on the mechanical properties of a welded Cu-Ag metallic matrix. This simulation makes use of the Lennard-Jones potential function and the embedded atom model. First, the equilibrium phase of modeled samples was verified by changing the computation of kinetic and total energies. Next, the mechanical properties of the welded matrix were studied using the stated Young's modulus and ultimate strength. The stress-strain curve of samples demonstrated that the mechanical strength of atomic samples increased as the length of the welding tool (penetration depth) increased. Numerically, by increasing the tool penetration depth of Fe tools from 2Å to 8Å, Young's modulus and ultimate strength of the matrixes sample increase from 34.360GPa to 1390.84MPa to 38.44GPa and 1510MPa, respectively. This suggested that the length of the Fe welding tool significantly affected the mechanical properties of the welded metallic matrix. The longer the length of Fe welding tools, the more particles were involved, and consequently, more bonds were formed among the particles. Bonding among the particles caused changes in mechanical properties, such as greater ultimate strength. This method can optimize mechanical structures and be useful in various industries.
作者机构:
[He, Dongping; Zhou, Li; Lei, Fenfen; Zheng, Meiyu; Zheng, Jingcheng; Zhang, Tianyu; Nie, Qiangsheng; Zhang, Qinfeng; Hu, Chuanrong] Key Laboratory of Edible Oil Quality and Safety for State Market Regulation, School of Food Science and Engineering, Wuhan Polytechnic University, Wuhan, 430023, China;[He, Dongping; Zhou, Li; Lei, Fenfen; Zheng, Meiyu; Zheng, Jingcheng; Zhang, Tianyu; Nie, Qiangsheng; Hu, Chuanrong] Grain and Oil Resources Comprehensive Exploitation and Engineering Technology Research Center of State Administration of Grain, School of Food Science and Engineering, Wuhan Polytechnic University, Wuhan, 430023, China;[He, Dongping; Wang, Shu] Wuhan Institute for Food and Cosmetic Control, Wuhan, 430012, China;[Hu, Zhigang; Li, Bin] School of Mechanical Engineering, Wuhan Polytechnic University, Wuhan, 430023, China;[Lei, Fenfen] Wuhan Institute for Food and Cosmetic Control, Wuhan, 430012, China. Electronic address: fenfenlei@whpu.edu.cn
通讯机构:
[Lei, Fenfen] W;[Zhang, Qinfeng] H;Wuhan Institute for Food and Cosmetic Control, Wuhan, 430012, China. Electronic address:;Hubei Key Laboratory of Resources and Eco-Environment Geology, Hubei Geological Research Laboratory, Hubei Geological Bureau, Wuhan, 430034, China. Electronic address:
摘要:
Dry fractionation represents a significant technique for separation of diverse fractions from beef tallow. The objective of this study was to undertake a systematic investigation of alterations in physicochemical properties, crystallization behavior, thermal properties, and flavor compounds that occur during the beef tallow dry fractionation process. The solid component yielded at 40, 30, and 15°C were 44.88%, 33.72%, and 13.04% respectively, with an 8.36% liquid content at 15°C, which was consistent with the characteristics of saturated fatty acids content. The β - β' transformation in the dry fractionation process was clearly revealed by X-ray diffraction. Differential scanning calorimetry curves exhibited alterations in exothermic and endothermic peak, as well as enthalpy. Electronic nose identified short-chain compounds, aldehydes, ketones, and nitrogen-containing substances as flavor compounds. Volatile compounds were quantified using HS-SPME-GC-MS. Overall, dry fractionation produces beef tallow fractionated compounds with diverse physicochemical properties and aromatic-active substances, thereby expanding its potential utilization.
通讯机构:
[Shen, SN ; Li, H ; Li, H] W;Wuhan Univ, Sch Power & Mech Engn, Wuhan 430072, Peoples R China.;Wuhan Polytech Univ, Sch Mech Engn, Wuhan 430048, Peoples R China.
关键词:
Laser powder bed fusion;Laser ultrasonic detection;Surface roughness;Internal holes;Longitudinal wave
摘要:
In view of the non-destructive and non-contact features, laser ultrasonic (LU) technology has long been the effective method to detect tiny defects for laser powder bed fusion (LPBF) additive manufactured specimens. Of larger concern is the variation and the corresponding mechanism on tested results of LU detection as the property of LPBF additive manufactured specimen is changed. Aiming at the property of surface roughness, this work investigated the propagation characteristics of excited ultrasonic waves in LPBF additive manufactured 316L stainless steel with different surface roughness, as well as the interaction between ultrasonic waves and artificial submillimeter holes. Both numerical simulated and experimental study were conducted. Simulated results revealed that the amplitudes of longitudinal wave (L wave) and its echo wave L1 at the holes exhibited a discernible increase as the surface was coarser. The increase in surface roughness was detrimental to the resolution of defect detection as was expected from the increased amount of noise. LPBF fabrication and the subsequent LU pulse-echo detection were conducted for 316L stainless steel. Both B-scan and C-scan were able to detect the holes with the diameter of 0.6 mm. The speckle phenomenon deriving from the increase in surface roughness emerged, corresponding to the increased ultrasonic signal energy but deteriorated resolution of detected images. It is feasible to optimize LU detected effect by minimize the surface roughness of tested specimens.
关键词:
Beam shaping;Femtosecond lasers;Lithium niobate;Nonlinear frequency conversion;Nonlinear photonic crystals;Ultrafast lasers
摘要:
<jats:p>We experimentally extend the nonlinear Gaussian to flat-top beam shaping from one to two dimensions through a three-dimensional nonlinear photonic crystal. Employing a near-infrared femtosecond laser, we induce a modification inside lithium niobate to achieve a second-order nonlinear optical coefficient modulation in three dimensions. The flat-topped truncation of wavefront has been adjusted in a mutual perpendicular coordinate separately. Among the generated flat-topped beams, the optimal flatness is 97.1%, and the nonlinear conversion efficiency is 10<jats:sup>−2</jats:sup> at the peak power of 37 kW with the interaction length of 630 µm. By adding an extra dimension, our work simultaneously enables full-wavefront flat-top distribution and nonlinear frequency conversion.</jats:p>
摘要:
<jats:p>Anthocyanin extracts from purple tomato (PTA) were incorporated with polyvinyl alcohol (PVA), resulting in a series of colorimetric PVA/PTA films with PTA concentrations of 0%, 1%, 3%, and 5% (based on PVA). The role of anthocyanin on color response, Fourier-transform infrared (FTIR), thickness, water content, mechanical properties, antioxidant activity, and water vapor permeability (WVP) through the films was examined. In addition, its application in smart packaging to assess the freshness of shrimp was studied. It was found that the tensile strength, contact angle and WVP of PVA/PTA films increases with the addition of more PTA, while the elongation at break and water content decreased. FTIR analysis showed that there are interactions between PTA and the PVA matrix. The addition of anthocyanins caused significant improvement in the antioxidant properties of PVA films. Furthermore, the total volatile alkaline nitrogen (TVB-N), total plate count (TPC), and pH value of shrimp were monitored after 4 days of refrigeration, and the color change of the indexes was recorded. The PVA/PTA films changed color from purple to yellow-green during the storage time of 0–4 days for shrimp. This suggests that the film could be used in smart packaging as a real-time freshness indicator for shrimp.</jats:p>
摘要:
To develop novel intelligent indicator films, the mixture of anthocyanin (BWA), polyvinyl alcohol (PVA) and sodium alginate (SA) were spun into PVA/SA/BWA nanofiber films with BWA concentration of 0%, 5%, 10%, and 15% (based on PVA and SA) via electrospinning technology. The results showed that the BWA was sensitive to pH and was controlled release from films. With increasing BWA concentration, the fiber diameter, tensile strength, and elongation at break gradually decreased, while water contact angle, thickness, moisture content, and antioxidant properties gradually increased. The electrospinning films exhibited high sensitivity to ammonia with rapid color changes in 1s and excellent color reversibility and color stability within 21 d. The application for shrimp packaging showed that the colorimetric response of the films was closely related to the changes in pH, total volatile basic nitrogen (TVB-N), and total viable count (TVC) of shrimp. This suggests that the prepared films are promising in application for intelligent packaging.
摘要:
In this research, we present the pure open multi -processing (OpenMP), pure message passing interface (MPI), and hybrid MPI/OpenMP parallel solvers within the dynamic explicit central difference algorithm for the coining process to address the challenge of capturing fine relief features of approximately 50 microns. Achieving such precision demands the utilization of at least 7 million tetrahedron elements, surpassing the capabilities of traditional serial programs previously developed. To mitigate data races when calculating internal forces, intermediate arrays are introduced within the OpenMP directive. This helps ensure proper synchronization and avoid conflicts during parallel execution. Additionally, in the MPI implementation, the coins are partitioned into the desired number of regions. This division allows for efficient distribution of computational tasks across multiple processes. Numerical simulation examples are conducted to compare the three solvers with serial programs, evaluating correctness, acceleration ratio, and parallel efficiency. The results reveal a relative error of approximately 0.3% in forming force among the parallel and serial solvers, while the predicted insufficient material zones align with experimental observations. Additionally, speedup ratio and parallel efficiency are assessed for the coining process simulation. The pure MPI parallel solver achieves a maximum acceleration of 9.5 on a single computer (utilizing 12 cores) and the hybrid solver exhibits a speedup ratio of 136 in a cluster (using 6 compute nodes and 12 cores per compute node), showing the strong scalability of the hybrid MPI/OpenMP programming model. This approach effectively meets the simulation requirements for commemorative coins with intricate relief patterns.
关键词:
Near -Infrared spectroscopy;Rapid non-destructive detection;Grass carp fillets;Total volatile basic nitrogen;Machine learning;Orthogonal signal correction (OSC);Particle swarm optimization algorithm;optimized BP neural network (PSO-BP)
摘要:
This research aims to accurately forecast the freshness indicators (TVB-N) of skinned and skinless grass carp fillets by integrating near-infrared spectroscopy (NIR) with machine learning algorithms. By comparing the predictive accuracy of machine learning models for the two types of grass carp fillets, the most effective modeling method is identified. Methodologically, the study first applies orthogonal signal correction (OSC) and the first derivative among other algorithms for spectral pre-processing. Subsequently, competitive adaptive reweighted sampling (CARS), moving window partial least squares (MWPLS), and random frog (RF) are used for the selection of variables. Lastly, partial least squares regression (PLSR), support vector regression (SVR), backpropagation neural networks (BPNN), and particle swarm optimization-enhanced BP neural networks (PSO-BP) are employed to quantitatively analyze the NIR data. The most relevant results reveal that the (OSC+D1)-CARS-PSO-BP model exhibits superior predictive capabilities. Especially when applied to skin-on fish fillets (R2P =0.988, RMSEP=0.092), this model surpasses that for skinless fish fillet data (R2P =0.987, RMSEP=0.096). Therefore, combining near-infrared with machine learning to predict the freshness (TVB-N) of grass carp fillets based on skin-on samples is a more effective non-destructive testing method.
关键词:
Freshwater fish;head and tail;ICNet;image segmentation;manipulator
摘要:
Pre-treatment processing technology plays a crucial role in the overall freshwater fish processing procedure, and automatic head and tail cutting stands out as a significant pre-treatment technique within the industry. The system for removing the head and tail of freshwater fish comprised a Cartesian coordinate manipulator, a fish transfer device, a control system, and an image acquisition device. In the vision system, five image segmentation methods were utilized for fish head and tail image segmentation comparison tests. These methods include U-Net (U-shaped Deep Neural Network), DeeplabV3, PSPNet (Pyramid Scene Parsing Network), FastSCNN (Fast Semantic Segmentation Network), and ICNet (Image Cascade Network), all of which were employed to evaluate their performance. Among the tested segmentation methods, the ICNet demonstrated the most excellent segmentation capability. The experimental results indicated a segmentation accuracy of 99.01%, a mean intersection over union (MIoU) of 82.50%, and an image processing time of 15.25 ms. The results showed that the fish head and tail were successfully cut off using this model for recognition with a circular knife. Consequently, the segmentation model employed in the machine vision system within this study has demonstrated successful applicability in automatically cutting the heads and tails of freshwater fish of various sizes.