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BACKGROUND Acute myocarditis is an acute myocardium injury that manifests as arrhythmia, dyspnea, and elevated cardiac enzymes. Acute myocarditis is usually caused by a viral infection but can sometimes be caused by autoimmunity. Graves’ disease is an autoimmune disease that is a rare etiology of acute myocarditis. Accelerated junctional rhythm is also a rare manifestation of acute myocarditis in adults. CASE SUMMARY A rare case of new-onset Graves’ disease combined with acute myocarditis and thyrotoxic periodic paralysis is reported. The patient was a 25-year-old young man who suddenly became paralyzed and felt palpitations and dyspnea. He was then sent to our emergency department (ED). Upon arrival, electrocardiography revealed an accelerated junctional rhythm and ST-segment depression in all leads, and laboratory findings showed extreme hypokalemia and elevated troponin I, with the troponin I level being 0.32 ng/mL (reference range, 0-0.06 ng/mL). Coronary computer tomography angiography was performed, and there were no abnormal findings in the coronary arteries. Subsequently, the patient was admitted to the ED ward, where further testing revealed Graves’ disease, along with continued elevated cardiac enzyme levels and B-type natriuretic peptide (BNP) levels. The troponin I level was 0.24 ng/mL after admission. All of the echocardiography results were normal: Left atrium 35 mm, left ventricle 48 mm, end-diastolic volume 102 mL, right atrium 39 mm × 47 mm, right ventricle 25 mm, and ejection fraction 60%. Cardiac magnetic resonance was performed on the fifth day of admission, revealing myocardial edema in the lateral wall and intramyocardial and subepicardial late gadolinium enhancement in the lateral apex, anterior lateral, and inferior lateral segments of the ventricle. The patient refused to undergo an endomyocardial biopsy. After 6 d, the patient’s cardiac enzymes, BNP, potassium, and electrocardiography returned to normal. After the patient’s symptoms were relieved, he was discharged from the hospital. During a 6-mo follow-up, the patient was asymptomatic and subjected to thyroid function, liver function, kidney function, troponin I, and electrocardiograph routine tests for medicine adjustments. The hyperthyroid state was controlled. CONCLUSION Acute myocarditis is a rare manifestation of Graves’ disease. Accelerated junctional rhythm is also a rare manifestation of acute myocarditis in adults. When the reason for hypokalemia and elevated cardiac enzymes in patients is unknown, cardiologists should consider Graves’ disease and also pay attention to accelerated junctional rhythm.

Blade is one of the basic and key components in wind turbines. To get closer to the actual loading condition of blade under complex and extreme wind conditions to more accurately analyse the structural failure characteristics of large wind turbine blades. The structural collapse test of a 52.5 m wind turbine blade under combined loading was carried out. The entire process of damage under ultimate load was recorded and analysed in detail. The joint analysis of the failure region after the blade collapse and the failure mode during the test process were performed. The research shows that the geometrical nonlinear buckling of spar cap and shear web, the delamination result from non-uniform stress distribution and further fracture of Aft panel cause catastrophic failure of the blade. The torsional moment cause oblique cracks and oblique bulges, aggravates the expansion of the internal and external composite cracks of blade, affects the final failure mode after blade collapses (critical failure mode), and make the spar cap at suction side to clockwise twist from blade tip to root. The research results lay a theoretical foundation for subsequent model establishment and simulation analysis of large wind turbine blades under combined loading.

This paper presents an in-depth analysis of the failure mechanism for the blade trailing edge from the viewpoint of material damage. A 3 m long blade segment is made and subjected to the static load in the subcomponent test through a specially designed test rig. A finite element model is set up to predict the progressive failure in the trailing edge region. The simulation results are used for setting up the on-site test and further, compared with the test results. The initial damage location and evolution of each defect are elucidated by cutting the test subcomponent into slices. The damage details of the test subcomponent and sensors data show that the end force leads to the local buckling of the PS and SS surface near the blade tip side. The buckling induces the damage to trailing edge materials, especially the sandwich structure in SS, and further bonding failure of the adhesive joint, which reduces the global strength of the subcomponent structure. The fracture of the sandwich caused by continued pressure leads to the final collapse of the test subcomponent.

To further study the structural failure mechanism and response characteristics of large wind turbine blades under extreme conditions, a full-scale 48.8 m blade collapse test was carried out. The strong coupling action of different damage modes are descripted by the gradual collapse process recorded by cameras. The damage behavior of suction side and pressure side, and interior and skin behavior of test blade are analysed. The test shows that the buckling of the suction side spar cap at about 21 m and cracks of the root shear web are the essential factor leading to the catastrophic failure of the entire blade, the test result is consistent with the finite element analysis. The load-deformation curve of the suction side spar cap, the deflection curves at 24 m, 36 m and tip, and the strains curves along the blade span are plotted to perform the data analysis. The critical load of 78% and deflection behavior in collapse process are determined by data analysis. The research results have great significance for improving the ultimate strength of entire blade, and provide a theoretical basis for the structural improvement of the weak points of blade.

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In the case of the stiffness of offshore wind turbine blade is relatively large, the joint excitation device solves the problem of low accuracy of bending moment distribution, insufficient driving ability and long fatigue test period in single-point loading. In order to study the synchronous characteristics of joint excitation system, avoid blade vibration disturbance. First, on the base of a Lagrange equation, a mathematical model of combined excitation is formulated, and a numerical analysis of vibration synchronization is performed. Then, the model is constructed via MATLAB/Simulink, and the effect of the phase difference on the vibration synchronization characteristics is obtained visually. Finally, a set of joint excitation platform for the fatigue test of offshore wind turbine blades are built. The parameter measurement scheme is given and the correctness of the joint excitation synchronization in the simulation model is verified. The results show that when the rotational speed difference is 2 r/min, 30 r/min, the phase difference is 0, π/20, π/8 and π/4, as the rotational speed difference and the phase difference increase, the time required for the blade to reach a steady state is longer. When the phase difference is too large, the electromechanical coupling can no longer make the joint excitation device appear self-synchronizing phenomenon, so that the value of the phase difference develops toward a fixed value (not equal to 0), and the blade vibration disorder is serious, at this time, the effect of electromechanical coupling must be eliminated. The research results provide theoretical basis for the subsequent decoupling control algorithm and synchronization control strategy, and have good application value.