Aeroelastic stability of combined plunge-pitch mode shapes in a linear compressor cascade

Modern aeroengine designs strive for peak specific fuel and thermal efficiency. To achieve these goals, engines have more highly loaded compressor stages, thinner aerofoils, and blended titanium integrated disks (blisks) to reduce weight. These configurations promote the occurrence of aeroelastic phenomena such as flutter. Two important parameters known to influence flutter stability are the reduced frequency and the ratio of plunge and pitch components in a combined flap mode shape. These are used as design criteria in the engine development process. However, the limit of these criteria is not fully understood. The following research aims to bridge the gap between semi-analytical models and modern compressors by systematically investigating the flutter stability of a linear compressor cascade. This paper introduces the plunge-to-pitch incidence ratio, which is defined as a function of reduced frequency and pitch axis setback for a first flap (1F) mode shape. Using numerical simulations, in addition to experimental validation, aerodynamic damping is computed for many modes to build stability maps. The results confirm the importance of these two parameters in compressor aeroelastic stability as well as demonstrate the significance of the plunge-to-pitch incidence ratio for predicting the flutter limit

INCIDENCE OF TRAVELERS’ DIARRHEA AMONG JAPANESE VISITING THAILAND

A cross-sectional survey of 327 Japanese short-term travelers (≤3 weeks) arriving in Bangkok, Thailand was conducted to assess the incidence of travelers’ diarrhea (TD) as well as their symptoms and treatment-seeking behaviors. The incidence of the first episode of TD (FTD) was ascertained retrospectively by questionnaire. Reported by 69 travelers, FTD clustered within the first 8 days of arrival in Thailand, and the incidence rate varied from 2% to 8% with the highest incidence on the third day.Cumulative probability of FTD was 19% for those arriving in Thai directly from Japan, 42 % for those arriving via Southeast Asia, and 25% for those arriving via other regions at Day 7 by the Kaplan-Meier survival analysis. Log rank test revealed a higher FTD risk for travelers arriving via other Southeast Asian countries than for those arriving directly from Japan (P < 0.005). Of all the 69 FTD episodes, 33% had classic TD defined as ≥3 unformed stools per 24 hours with at least one accompanying symptom, 49% had moderate TD defined as ≤2 unformed stools with at least one additional symptom or more unformed stools without additional symptoms, and 17% had mild TD defined as with ≤ 2 unformed stools without additional symptoms. Cumulative probability of FTD at Day 7 was 12% for classic TD, 25% for classic plus moderate TD and 30% for all the TD. More than 38% of travelers with diarrhea took medicine brought from Japan. Among travelers with classic TD, 35% bought medicine in Thailand, whereas 47-50% of travelers with moderate and mild TD took only rest without any treatment