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In allusion to the difficulty to obtain fault samples of multi-stage centrifugal pumps in practical engineering, three typical faults containing rubbing, misalignment and unbalance were simulated through the fault simulation test-bed of multi-stage centrifugal pumps. And a fault diagnosis model based on support vector machine (SVM) was established to realize the classification of three types of faults. High dimensional feature samples were constructed by extracting time-frequeney domain characteristies of vibration signal with ensemble empirical mode decomposition(EEMD). combined with characteristies of time domain, frequeney domain and information entropy. The efficient fault classification was achieved by optimizing the quality of input samples with principal component analysis (PCA). In addition, by comparing the classification effects of SVM and back propagation (BP) neural network, it shows that the SVM model has better classification effect and high applicability in fault diagnosis of multi-stage centrifugal pump.

Since 2018,scholars have proposed and studied a new topic of “concept reduction” in formal concept analysis.Including unnecessary concepts,core concepts,relatively necessary concepts,and the identification of three types of concepts,and research on concept reduction algorithm.In this paper,the same effect relation is proposed and its important properties are studied.It pre-sents a simple way to identify three types of concepts through the same effect relationship,and proposes a new algorithm for concept reduction which is based on the concept lattice of the complement set of subsets of the same effect relationship.For decades,the algorithm of “reduction topic” has adopted the method of conjunctive normal form and disjunctive normal form transformation.Many scholars even said that “reduction problem” was equivalent to the transformation of conjunctive paradigm and disjunctive paradigm.This paper studies a new method to solve the “reduction problem” without using the transformation between conjunctive normal form and disjunctive normal form.This new method is of significance both in theory and in practice.It is a new attempt.There are often many “concept reduction” in a background,so it is not very meaningful to find out all the results.Gene-rally,it is necessary to find out “concept reduction” containing some concepts,and the method in this paper has particular advantages in this respect.

Objective To explore the changes in root volume and root resorption in incisor arteries from adult patients with skeletal class Ⅲ malocclusion before and after camouflaged orthodontic treatment and to provide a reference for the clinic. Methods Thirty permanent dentition adult patients with skeletal class Ⅲ malocclusion were included from the Orthodontic Department. CBCT data of each patient at pretreatment and posttreatment were acquired, and 3D digital root models were reconstructed. The whole and segmented root volumes (cervical part, bodily part and apical part) of the right incisors were calculated. Results The root volumes (whole, cervical part, bodily part and apical part) posttreatment were smaller than those pretreatment (P0.05). Mandibular central incisors and lateral incisors showed more root resorption in the apical root than in the cervical root and bodily root (P0.05). The absorption ratio showed a significant difference in the mandibular lateral incisors (P = 0.028). Conclusion After camouflaged orthodontic treatment of adult skeletal class Ⅲ malocclusion, incisor root resorption occurred mainly in the apical part, but the cervical and bodily parts should also be considered. There was a high risk of root resorption in the mandibular incisors.

A cylindrical metastructure with chiral ring oscillators is proposed for broadband vibration isolation, and experimental studies are carried out. The vibration transmission characteristics of cylindrical chiral metastructure is calculated and analyzed. Vibration transmission of three prototypes of cylindrical chiral metastructure is tested, and the results by using numerical simulation method are validated by the experimental results. It can be found that the broad bandgap can be created by the coupling bandgap between the multiple locally resonant bandgaps and Bragg scattering bandgap. Therefore, the good low-frequency vibration isolation performance can be achieved by designing the suitable parameters of chiral ring oscillators. HIGHLIGHTS: A cylindrical chiral metastructure composed of chiral ring oscillators is proposed for broadband vibration isolation The coupling bandgap between multiple locally resonant bandgaps and Bragg scattering bandgap is produced in low frequency range Vibration isolation property can be greatly enhanced by vibration mode conversion between the axial and torsional deriction Broad low-frequency vibration isolation performance can be achieved by tuning the geometrical parameters of chiral ring oscillators [ABSTRACT FROM AUTHOR]

A high-speed multi-stage centrifugal pump building upon a transient investigation into the hydrodynamic characteristics, is conducted for 16 sets of clocking positions. The most significance of the pump head has a maximum increase of 3.6% at 0.8Qd. Phase differences emerge in the pressure pulsations at the impeller-guide vane gaps across stages. It results in waveform distortions that are primarily influenced by impeller clocking effects. Innovative average energy flux density analysis shows that impeller-guide vane clocking positions have the greatest influence on pressure pulsations near their gaps. The cumulative propagation of pressure pulsations has a relatively minor effect on fluid domains. Worst stability is observed when impellers rotated with a 3/4 maximum offset angle and guide vane positions remain unchanged. The best clocking position solution was adapted in a prototype pump for performance and operational stability measuring, achieving an efficiency of 53.67% and 1 mm/s vibration. This paper aims to provide valuable insights for enhancing the energy efficiency and operational safety of multi-stage pumps, offering beneficial guidance for engineering practices within the field of fluid machinery applications. [ABSTRACT FROM AUTHOR]

Calculating the shut-off head for centrifugal pumps poses significant challenges due to inaccuracies in existing empirical methods. This paper presents a predictive model based on extensive experimental data, employing a back propagation (BP) neural network optimized via grey theory and genetic algorithms (GAs). Data were collected from 141 single-stage volute centrifugal pumps, and grey theory was used to analyze nine critical parameters of the impeller and volute, yielding five optimal input schemes with correlation coefficients exceeding 0.6. The GA was utilized to optimize the weights and thresholds of the BP model. The training involved 121 samples, while 20 additional samples were used to evaluate the models against three established methods (throne, modified throne, and regression fitting). The results indicate that the optimal input scheme consists of four parameters (impeller diameter, blade wrap angle, inlet diameter, and rotational speed) with correlation coefficients greater than 0.7. Both the BP and GA-BP models achieved training regression coefficients approaching 0.999. Within the specific speed range of 22–215, the GA-BP model demonstrated superior performance to the BP model and the three established methods, with maximum testing errors of 10.0%, 20.6%, 20.7%, 19.9%, and 23.3%, and average relative errors of 3.9%, 5.0%, 8.4%, 8.1%, and 5.8%, respectively. This paper introduces a novel prediction model for the shut-off head with an accuracy of 96%, providing a valuable reference for hydraulic design and performance prediction in centrifugal pumps. [ABSTRACT FROM AUTHOR]

BackgroundThe high-temperature liquid lead-bismuth metal has a scouring and wear effect on the head of the axial flow lead-bismuth pump impeller blades in a lead-cooled fast reactor system, causing the protective layer on the blade surface to break down and material corrosion rate to accelerate.PurposeThis study aims to reduce the scouring wear effect of the high temperature liquid metals on blade surfaces.MethodsFirst of all, three types of leaf top clearance structures, i.e., plane, chamfered right angle, and chamfered rounded angle, were designed. Then, the reliability of the simulation results was verified by the scaling conversion method, and the commercial CFD software ANSYS CFX with SST k-ω turbulence model was employed to analyze the variation of flow velocity, shear force, and flow pattern with scouring and wear characteristics under different leaf top clearance structures. Finally, the energy loss of the high temperature liquid lead-bismuth metal on the material surface was analyzed using the wall entropy yield.ResultsAnalysis results show that the head and efficiency of the chamfered right angle model are reduced by 1.02% and 0.64%, respectively, compared with those of the flat surface under standard operating conditions, and the chamfered angle model shows a 0.51% reduction in the head and 0.51% efficiency increase. The impeller scouring wear effect occurs predominantly near the inlet edge of the blade rim, and the effect of the high temperature liquid metal on the blade head scouring wear is improved by the chamfered and rounded designs.ConclusionsThe chamfered and rounded designs reduces the mechanical energy loss on the blade surface by reducing the flow velocity at the top clearance and reducing the scouring wear effect at this location. Therefore, the rounded design and the right angle design could improve the influence of high-temperature liquid lead-bismuth metal on the erosion wear of the blade head.

The purpose of this article is to investigate the effect of different bending angles and traction directions of the traction arm on the stability of the titanium plate for bone-anchored maxillary protraction (BAMP). The titanium plate models with different bending angles of the upper and lower jaws were modelled in three dimensions, where the bending angles were 90°, 120°, 135°, 150°, 180° and recorded as U1-U5 and L1-L5 respectively. Finite element analysis was performed on the titanium plates with different structural parameters to complete the structural design selection study of the titanium plates. The displacement limit was defined and different angular tensile forces were applied to record the equivalent stress and displacement of the titanium plates under each working condition. A total of 120 sets of orthogonal simulation tests were designed, which showed that the stress values at U2, U3 and U4 are smaller at traction angles of 135° (66.152 MPa), 155° (59.015 MPa) and 175° (55.589 MPa) respectively. The displacement is correspondingly smaller at tensile angles of 135° (0.0073 mm), 150° (0.0056 mm) and 160° (0.0058 mm). L2 has the smallest stress value (50.491 MPa) and displacement (0.0062 mm) at a tension angle of 120°. Therefore, it is recommended to design a titanium plate with a mandibular traction arm bending angle of 120° for BAMP, and the traction arm bending angle of the maxillary titanium plate can be flexibly designed according to the clinical traction direction.