Sagging damage characteristics of hull girder with trapezoidal cross-section subjected to near-field underwater explosion

To investigate the overall damage characteristics and failure modes of a warship subjected to an underwater non-contact near-field explosion,a hull girder with a trapezoidal cross-section was designed,manufactured,and tested.The design criteria and parameters were determined according to the similarity criterion.Dynamic responses of the girder freely floating on water were obtained under varying conditions,including stand-off distance,charge mass,and position of attack.Damage morphologies of the girder model were obtained.Based on our analysis,basic conditions for sagging damage of the hull girder are proposed.The aim of this study was to determine an efficient method of attack resulting in the most severe damage to the ship hull.The experimental results show that the girder mainly exhibits a first-order response when the first wet frequency of the girder is close to the frequency of the explosion bubble pulsation.The largest deformation was observed when the underwater explosion occurred directly below the midspan of the girder compared to other explosions of the same intensity at different attack positions.When the ratio of stand-off to maximum bubble radius(λ)satisfies 0.7≤λ<2,the bubble mainly causes sagging damage instead of hogging.Asλdecreases(1≤λ<2),the sagging damage increases under the same charge mass.However,asλdecreases further(0.7≤λ<1),the sagging deformation decreases.This is likely due to the impact of the liquid jet formed by the collapsing bubble,which causes the girder deformation to shift from sagging back to hogging deformation.The initial shock wave excites the high-frequency response of the girder structure but contributes very little to the overall velocity and displacement.However,bubble pulsation typically causes a low-frequency response,which will affect the velocity and displacement of the girder.The low-pressure region of the flow field formed by bubble pulsation and resonant coupling between the girder and the bubble are the predominant causes of damage to the overall girder structure.

Association between Mycoplasma pneumoniae infection and acute coronary syndrome

Objective: To investigate the association between Mycoplasma pneumoniae (MP) infection and the occurrence of acute coronary syndromes (ACS), and its associated mechanism in ACS development. Methods: A total of 134 patients with confirmed ACS were selected as the ACS group, and another 102 healthy subjects were enrolled as the control group. Serum triglycerides (TG), cholesterol (TC), high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C), apolipoprotein A1 (ApoA1), and apolipoprotein B (ApoB) were detected using immuno-transmission turbidimetry in the ACS and control groups. An enzyme-linked immunosorbent assay was used to detect MP-specific IgG antibodies in the serum. Results:The MP infection rate in the ACS group was significantly higher than that in of the healthy control group. Although there were significant differences in the expression of TC, HDL, LDL, and ApoB between the ACS and control groups, there were no significant differences between the MP IgG-positive and negative groups for any the six serum lipid indexes in the ACS patients. The level of high-sensitivity C-reactive protein (hs-CRP) expression in ACS patients was significantly higher in the MP IgG-positive group compared with the negative group. Conclusions: MP infection is associated with ACS and may be a risk factor for ACS. MP infection may not affect blood lipid levels but rather induce the development of ACS by affecting the long-term inflammatory environment.