RESUMO
Large floating raft vibration isolation systems (FRVISs) based on high-static-low-dynamic stiffness (HSLDS) technology offer excellent low frequency vibration isolation performance with broad application prospects. However, the design process for these complex high-dimensional coupled nonlinear systems remains poorly developed, particularly when applied for ocean-going vessels that experience rolling and pitching motions. The present work addresses this issue by establishing a six-degree-of-freedom HSLDS vibration isolation model for FRVISs composed of eight isolators, and the model is applied to fully analyze the swing stability and multidimensional vibration isolation performance of these systems. The influence of nonlinearity on the mechanical properties of the vibration isolators is analyzed more clearly by assuming that each vibration isolator realizes nonlinear HSLDS characteristics in the z direction and linear characteristics in the x and y directions. The results demonstrate that the swing displacement responses of the system are greatly reduced under weak nonlinearity, which reflects the high static stiffness and high static stability characteristics of an HSLDS system. The multidimensional vibration isolation performance of the system is evaluated according to the impacts of nonlinearity, the installation height Hz of the isolators, and the relative position Dr of the two middle isolators. The results of analysis demonstrate that applying a value of Hz = 0 produces the best vibration isolation performance overall under strong nonlinearity by avoiding unnecessary secondary peaks in the force transmission rate under harmonic mechanical excitation and ensuring a maximum high-frequency vibration isolation effect. However, applying a weak nonlinearity is better than a strong nonlinearity if Hz is not zero. In contrast, Dr has little effect on the vibration isolation effect of the raft in the x, y, and z directions. Therefore, an equidistant installation with Dr = 0.5 would be considered ideal from the standpoint of installation stability.
RESUMO
OBJECTIVE: This research reported the experience of early surgical treatment for infants with large atrial septal defects (ASD) or ventricular septal defects (VSD) complicated by pneumonia. METHODS: Between January 2003 and January 2008, 39 infants with large ASD or VSD complicated by pneumonia were admitted to the Second Xiangya Hospital. Thirty-six patients underwent surgical repair within 7-10 days after pneumonia had been controlled. Mean age was 5.4+/-3.4 months and mean weight was 4.7+/-1.6 kg in the 36 patients. Three patients received conservative treatment due to uncontrolled lung infections. RESULTS: Of the 36 patients, 33 had successful surgery and 3 (8.3%) died of serious low cardiac output (n=1) or respiratory failure due to congenital tracheostenosis (n=2). The 33 survivors showed normal growth and development in a 6 month-5 year follow-up. Of the 3 patients receiving conservative treatment, 1 died of cardiopulmonary failure and 2 were discharged after the symptoms had been improved. CONCLUSIONS: With increasing medical experience and technique, early surgical operation may be performed with good outcomes in infants with large ASD or VSD complicated by pneumonia.