Hyo-Hyun Lee

Damage detection using the Lipschitz exponent estimated by the wavelet transform: applications to vibration modes of a beam

Damage detection by the wavelet transform of the fundamental vibration mode receives much attention recently. Many investigations report successful applications of the wavelet transform in damage detection, but most of them appear to lack theoretical justifications. The objective of this contribution is to show the effectiveness of the wavelet transform by means of its capability to estimate the Lipschitz exponent. It is also addressed that the magnitude of the Lipschitz exponent can be used as a useful indicator of the damage extent. As a specific example, damaged beams are investigated both numerically and experimentally. The continuous wavelet transform (CWT) by a Mexican hat wavelet having two vanishing moments is utilized for the estimation of the Lipschitz exponent. The analysis by the CWT also gives a guideline to choose appropriate discrete wavelet transforms.

Validation of clothing insulation estimated by global and serial methods

Purpose – The purpose of this paper is to examine differences between thermal insulation calculated by a global and a serial method using a thermal manikin, in comparison with human trials.Design/methodology/approach – A total of 150 single garments and 38 clothing ensembles were assessed using the manikin; 26 seasonal clothing ensembles were selected for human trials.Findings – The results showed that total insulation of single garments was 16 percent higher in the serial method than in the global method. The difference was higher in garments with smaller covering area per unit garment mass (e.g. winter garments). For seasonal clothing ensembles, the serial values were 39.2 percent (0.18 clo) for spring/fall wear, 62.6 percent (0.15 clo) for summer wear and for winter wear 64.8 percent (0.69 clo) greater than the global values. The clothing insulation by the global method was systemically lower in all 26 seasonal ensembles than values by human trials, which suggests that the values by the global calculat...

Diving bradycardia of elderly Korean women divers, haenyeo, in cold seawater: a field report

The purpose of the present field study was to explore diving patterns and heart rate of elderly Korean women divers (haenyeo) while breath-hold diving in cold seawater. We hypothesized that the decreasing rate in heart rate of elderly haenyeos during breath-hold diving was greater and total diving time was shorter than those of young haenyeos from previous studies. Nine haenyeos participated in a field study [68 ± 10 yr in age, ranged from 56 to 83 yr] at a seawater temperature of 10 to 13 °C. Average total diving time including surface swimming time between dives was 253 ± 73 min (155–341 min). Total frequency of dives was 97 ± 28 times and they dived 23 ± 8 times per hour. All haenyeos showed diving bradycardia with a decreased rate of 20 ± 8% at the bottom time (101 ± 20 bpm) when compared to surface swimming time (125 ± 16 bpm) in the sea. Older haenyeos among the nine elderly haenyeos had shorter diving time, less diving frequencies, and lower heart rate at work (p<0.05). These reductions imply that haenyeos voluntarily adjust their workload along with advancing age and diminished cardiovascular functions.

Evaluation of Thermoregulatory Properties of Thermal Underwear Named as `Heating Underwear` using Thermal Manikin and Human Performance Test

This study evaluated the thermoregulatory properties of functional thermal underwear (‘heating underwear’) in markets using a thermal manikin and human wear trials. One ordinary thermal underwear (ORD) and two functional thermal underwear (HEAT1 and HEAT2; manufactured goods, HEAT1: moisture absorbing heat release mechanism, HEAT2: heat storage, release mechanism) were chosen. Thermo-physiological and subjective responses were evaluated at an air temperature of 5.0±0.5 o C and air humidity of 30±5%RH with five male subjects (21.6±1.3yr in age, 178.0±5.9cm in height, 68.2±5.9kg in body mass). Experimental conditions consisted of four ensembles that included winter clothes (Control: no underwear, ORD, HEAT1, HEAT2). Water-vapor resistance was greater in fabric of HEAT1 than others. The results were: 1) Total thermal insulation (IT) using a thermal manikin were not greater for HEAT1 (0.860clo) and HEAT 2 (0.873clo) than for ORD (0.886clo). 2) There were no significant differences in rectal temperature, mean skin temperature, heart rate and total body mass loss between the four conditions. Microclimate clothing temperature on the back was greater for ORD than for HEAT1 and HEAT2. Subjects felt more comfortable with HEAT1 than for others at rest. HEAT2 was higher in microclimate humidity when compared to other conditions. The results suggest that thermoregulatory properties of ‘heating underwear’ in market did not differ from those of ordinary thermal underwear in terms of total thermal insulation and thermoregulatory responses in a cold environment.

Survey on the Actual Wearing Conditions of Naval Duty Uniforms in Naval Vessels

Abstract : This study investigates the conditions of Korean naval duty and combat uniforms to develop a new design.Survey participants consisted of, 723 Sailors (25.3±6.9yr in age, 43±53 months in work experience, 174±6cm in height,71±9kg in body mass) serving in the Korean Navy for over 12 months. The questionnaire consisted of 72 questions aboutanthropometric characteristics, preferred design, textiles, wear mobility, and subjective perceptions. The results showedthat the preferred colors for future naval duty uniforms were blue in summer (69%) and black in winter (62%). Digitalcamouflage pattern (60%) and darker colors on the inside of shirt collar (87%) and the edge of sleeves (84%) were pre-ferred. They favored more than one pocket on the upper arm and chest of the shirts (58%), narrower width around pantlegs and hems than the current clothing (63%), self-controlled elastic waist (55%) and no cargo type pocket on the pants(45%). There were requirements to alleviate excessive heat stress in summer and to protect from the cold and wind inwinter. Wrinkle-free (85%), anti-bacterial (78%), water-proof (75%), oil-proof (90%), and elastic (67%) textiles were pre-ferred for Korean navy uniforms. These results will be applied to develop the next generation Korean navy uniforms.Key words :naval duty uniform(함상 근무복), questionnaire(설문 조사), navy combat uniform(해군 전투복), wearermobility(동작 적합성), thermal comfort(온열 쾌적)

Frequency of firefighters’ heat-related illness and its association with removing personal protective equipment and working hours

The purpose of this study was to examine the frequency of firefighters’ heat-related illness (HRI) in the line of duty with relation to resting/working hours and the behaviour of taking off PPE during rest periods based on nationwide survey (N=674). The results showed that 74.8% of firefighters experienced HRI symptoms and 5% of firefighters suffered from symptoms of HRI 20 times or more in a year. This study also showed a statistically significant correlation between working hours and removing PPE with the experience of HRI symptoms (p<0.05). In addition, removing PPE except the helmet was correlated with resting hours (p<0.001; Gloves: p=0.051), which indicates that removing PPE is related to resting time. This study revealed that firefighters routinely experienced mild HRI symptoms and the fatalities were just a tiny fraction. It is also emphasized that attention should be given on the significant role of taking off PPE during rest and on the standardized firefighters’ rehabilitation followed by its application.