Dynamics modeling and experimental modal analysis of bolt loosening for lightning rod

Lightning rods are effective to prevent lightning damage in power systems. However, under the influence of severe weather conditions, they often face failure problems, mainly manifested as tilt and fracture caused by bolt loosening which can result in significant economic losses. Therefore, it is very meaningful to detect the loosening of the lightning rod. The vibration-based method is an effective method for bolt loosening detection and is suitable for use on large lightning rods. This paper built a finite element model of the lightning rod Flange-Bolt Structure Unit (FBSU) based on the virtual material method, designed an effective acquisition test of the vibration signal under different loosening conditions of the lightning rod FBSU. The experimental results showed that it was effective to establish the dynamic model of the lightning rod FBSU by using the virtual material method. According to the measured vibration signal, the frequency response function was obtained by TIME MDOF method, and the preliminary judgment of bolt loosening can be realized. This study lays the foundation for the precise positioning and the extent of loosening detection of lightning rod bolt loosening, and also provides a guideline for the vibration test design of large bolted structures similar to lightning rods

Research on Parametric Model for Surface Processing Prediction of Aero-Engine Blades

This paper presented a method for establishing a blade surface machining prediction model based on a parametric model. The abrasive grain state of the grinding tool was divided into initial wear stage, stable wear stage and sharp wear stage. Based on this, a parametric prediction model of engine blade surface material removal was established. In this paper, the simulation of blade surface machining was carried out. In this work, the blade was divided into several sections according to the direction from the blade root to the blade tip. A certain curve of the outer contour was fitted with a specific arc to reduce the calculation amount. Through a series of simulation calculations, the expressions of the above parametric prediction model were obtained, and several experiments were carried out to verify the feasibility of the prediction model, and the results were analyzed

Research on Combustion Chamber Structure Improvement and Ignition System of Missile Turbojet Engine for Diesel Fuel

To meet the conditions of diesel ignition, this paper presents several structural improvements of a small missile turbojet engine for diesel fuel. The engine starts motor-assisted, and its fuel is ignited by silicon nitride ceramic ignitor. Theoretical analysis is performed by establishing a mathematical model of the combustion model and combustion conditions. The feasibility of diesel used as a small turbojet fuel is analyzed by using numerical simulation software. Research is carried out based on the following points: the improvement of combustion chamber and evaporator, selection of ignitor position and sustainability of fire. This paper proposed the method of linking the engine-assisting startup system and selected the right type of ignitor, and on the advanced experimental platform several groups ignition tests were carried out

Reliability and Validity of the Chinese Version of the Partners in Health Scale in Patients with Chronic Heart Failure

BackgroundChronic heart failure (CHF) is a common cardiovascular disease. Improving the self-management ability of CHF patients will contribute to quality of life improvement and reduction of rehospitalization and mortality rates. The Partners in Health (PIH) Scale is a measure designed by Flinders University, Australia, to assess the generic knowledge, attitudes, behaviors, and impacts of self-management in chronic disease patients, and is mainly used to assess the implementation effect of self-management projects in chronic disease patients.ObjectiveTo translate the PIH Scale into Chinese, then test the reliability and validity of the Chinese version in CHF patients, providing CHF patients with a tool for precisely assessing their self-management abilities.MethodsThe PIH was translated into Chinese with the guidance of the Brislin's translation model, then was revised according to the results of the review of a panel of experts, and a pre-test, and then the Chinese version of PIH (C-PIH) was developed. The demographic questionnaire, C-PIH, and Minnesota Living with Heart Failure Questionnaire (MLHFQ) were used in two surveys (one was conducted between April and June 2010, and another between April and June 2011) with 410 CHF patients selected from two grade A tertiary hospitals in Beijing using convenience sampling. Measurement of ceiling and floor effects, and item-total correlation were used for item analysis. Expert evaluation was used to evaluate the content validity analysis. Spearman's rank correlation coefficient was used to measure the criterion-related validity. KMO test, Bartlett's test of sphericity, exploratory factor analysis and confirmatory factor analysis were used for construct validity analysis. Monofactor analysis was used for validity analysis of known-groups. Reliability analysis was estimated by using the Cronbach's α.ResultsItem analysis indicated that only item 3 (level of adhering to medication) of the C-PIH showed ceiling effect. Item-total correlation coefficients of the scale ranged from 0.424 to 0.761 (P<0.001) . The scale-level content validity index of the scale was 0.966. Item-level content validity indices ranged from 0.800 to 1.000. C-PIH was positively correlated with MLHFQ in terms of total score (rs=0.200, P<0.05) . The KMO value was 0.872 and Bartlett's test of sphericity was χ2=1 139.142 (P<0.001) , indicating that the sample size was appropriate for factor analysis. By exploratory factor analysis, 3 factors with an eigenvalue greater than 1.000 were extracted, including knowledge (7 items) , coping (3 items) and adherence (2 items) , explaining 66.514% of the total variance. The loadings of items on each factor ranged from 0.571 to 0.869. The original model fit indices did not reach the critical value. After adding the suggested covariance correlation between errors-in-variables e1 and e2, e6 and e7, the fitting indices of the modified model were acceptable (χ2/df=2.393, RMSEA=0.0851, CFI=0.968, NFI=0.953, NNFI=0.963, GFI=0.905, AGFI=0.854, RFI=0.932, IFI=0.966) . Known-groups analysis demonstrated that the C-PIH total score varied significantly by level of education, economic income, NYHA class, and treatment (inpatient or outpatient) in CHF patients (P<0.001) . Good internal consistency was indicated with a scale Cronbach's α of 0.890, and three factors' (knowledge, coping and adherence) Cronbach's α of 0.894, 0.807, and 0.511.ConclusionThe C-PIH exhibited good reliability and validity, which may be used as a general self-management assessment tool in patients with CHF

Research on Abrasive Belt Based Machining Technology for Milling Shaped Aero-Engine Blades

This paper proposes an automatic surface treatment method for CNC milled blades. The surface texture characteristics of the blade after milling were analyzed. The contact area between the contact wheel and the blade surface was analyzed theoretically, and then the contact wheel and the blade edge were analyzed. The contact area between the intake side and the exhaust side was theoretically analyzed, and one micro-element in the contact area was selected, and the simulation analysis under multiple sets of parameters was carried out. In the experimental aspect, this paper has assembled a set of relatively reliable experimental systems, and carried out an in-depth analysis of a certain area of the engine blade obtained from the experiment to verify the feasibility and reliability of the proposed method

The Ninth Visual Object Tracking VOT2021 Challenge Results

acceptedVersionPeer reviewe

Parameters Optimization and Numerical Simulation for Soft Abrasive Flow Machining

In allusion to the shortcomings of CFD simulation for high volume fraction of abrasives flow, a new and high efficient scheme is developed to calculate the collision velocity between the abrasive and the wall surface. The V shaped gradually variable channel is regarded as a kind of typical and effective machining flow channel and the soft abrasive flow machining for this channel is researched. Based on Eulerian-Lagrangian multiphase flow model, an analytical method was proposed to optimize the parameters of the soft abrasive flow machining. The simulation shows that the initial velocity of the abrasive flow influences much on the pressure distribution but little on the abrasive volume fraction distribution, while the abrasive volume fraction influences much on the flow pressure, but little on the velocity. The experiment is taken to verify the simulation. The experiment results show that the computation scheme and the analytical method are useful