Extreme Thermal Environments Research Articles

Physical demands and physiological strain of American football referees while officiating

ABSTRACT Objectives Certain occupations are associated with greater risk of triggering a sudden cardiac event because of high levels of physical exertion and extreme thermal environments in which they occur. The extent to which sports officials––particularly high school (HS) American football referees––experience these conditions is unknown. Forty-six male HS officials (72% White/Caucasian; age = 48 ± 12 years, body mass index = 31.7 ± 6.6 kg·m−2) were studied to quantify the physiological strain and physical demands of officiating. Methods Referee demographics (e.g., experience, habitual exercise), pre-game urine specific gravity (USG), thermal (peak core temperature [Tcore]) and cardiovascular (average heart rate [HR]) strain, kinematic activity (e.g., total distance, speed, mechanical intensity), and environmental conditions were measured during 10 regular season varsity HS football games (≈2.5 h each) in the Southeastern United States (average wet bulb globe temperature and relative humidity: 18.9 ± 6.0 °C and 78.2% ± 12.1%). Analyses included descriptive statistics, bivariate correlations, and linear regression. Results Referees covered 5.2 ± 1.2 km per game, eliciting average HR and peak Tcore of 71.5% ± 8.0% HRmax and 38.3 ± 0.5 °C, respectively; 38% began games dehydrated (USG = 1.026 ± 0.004). Multiple regression analyses revealed that obesity (β = 0.34), not participating in regular exercise (β = −0.36), and officiating at lower mechanical intensity (β = −0.33) predicted greater cardiovascular strain (all p ≤ 0.03). White/Caucasian race/ethnicity (β = 0.59), younger age (β = −0.46), and obesity (β = 0.28) predicted greater thermal strain (all p ≤ 0.01). Conclusion HS football referees experienced elevated levels of physiological strain while officiating, with individual factors modulating the magnitude of strain. Strategies aimed at reducing obesity, increasing exercise participation, and improving cardiovascular health should be emphasized to mitigate strain and prevent cardiac events.

The Complete Set of Thermo-mechanical-Radiation Methods, Simulations and Results for a Swarm of Nanorovers Deployed on the Moon’s Surface (Lunar Zebro Mission)

Lunar Zebro’s mission is heading the race for deploying the world’s smallest and lightest swarm of nanorovers on the surface of Moon. The concept validation of a single nanorover is of crucial importance, as it will be the launching pad for deploying a swarm of those nanorovers thereafter. Then, they will get connected in a network, acting as a single device and performing scientific missions analyzing data from remote points on the Moon’s surface. In the current study, the complete set of thermo-mechanical-radiation analyses for Lunar Zebro nanorovers are carried out. These range from the Ground Segment to the Moon environment, taking also into account the extreme mechanical and thermal environment at launch-transit conditions when the nanorover is attached to the lander. An innovative ray tracing method to evaluate the effect of the thermal environment on the Lunar Zebro nanorovers is explained in this paper. Material choices, structural design, and mechanical/thermal strategies for the nanorover to overcome the launch, space and Moon’s conditions are shown. The different analyses methods used, expected loads and results obtained should serve as a baseline for evaluating the behaviour of other small devices attached to a lander when aiming for any space mission. More specifically, for those aiming to go to the Moon, the environmental and mechanical expectations here can also be implemented. The ultimate outcome of the paper is the environmental survivability assurance from an analytical perspective of these nanorovers when being sent to the Moon. The validation of the survivability of a single nanorover will be a breakthrough in the space swarm robotics’ field, resulting in the successful performance of the lightest swarm of nanorovers ever deployed on the Moon’s surface.

The microstructure evolution, damage behavior and failure analysis of fine-grained W-Y2O3 composites under high transient thermal shock

Extreme thermal environment, especially transient high thermal load, is one of the great challenges for plasma facing tungsten materials. In this work, the fine-grained W-Y2O3 composites fabricated by nano in-situ composite method were exposed to transient heat loading using electron beams. The microstructure evolution, damage behavior and failure analysis were investigated by experimentally combing with finite element modelling (FEM). Besides, the correlation among thermal shock resistance, microstructure and mechanical properties of the W-Y2O3 composites were initially analyzed. Results show the W-Y2O3 composites obtains superfine microstructure and coherent interface. The surface morphology evolves from smooth to roughness, cracks and melting as the power density increases. Simultaneously, four crack patterns of surface micro-cracks, crack networks, longitudinal cracks and internal transverse cracks were observed. The W-0.3 wt%Y2O3 composites exhibit superior resistance to crack formation attributed to excellent interfacial performance and diffuse Y2O3 hindrance. No obvious damage was found on the surfaces when the power density reached 600 MW/m2. With the increasing Y2O3 contents, the thermal resistance of W-Y2O3 composites significantly decreases. Finite element modelling (FEM) analysis shows that the surface damage is the most serious compared to the interior after thermal shock. The damage, especially cracks, are preferentially formed on the surface, and then migrate and expand to the interior. The damage and its evolution are attributed to the palstic thermal strain on the surface caused by thermal stress. Moreover, the higher the mechanical properties of W-Y2O3 composites, especially the high temperature yield stress and elongation, the better high thermal load resistance. These results should be of relevance for the optimum design of W plasma facing materials in future nuclear fusion reactors.

Numerical investigation on the generation mechanism of aero-heating of rudder shaft from three-dimensional flow separation and vortices

The hypersonic flow past a controlled rudder mounted at a gap to the aircraft fuselage is numerically investigated by solving three-dimensional (3D) Reynolds-averaged Navier–Stokes equations. This paper aims to explain the mechanism of production of extreme thermal environment faced by a rudder shaft from the view of physics of flow in the mounting gap. Simulations are conducted at Mach number of 10, and the gap ratio h/δ varies from 0 to 1.42, where h denotes the gap height and δ represents the thickness of the incoming turbulent boundary layer. Topological theory is utilized to identify the separation types. The formation of vortices is traced by extracting volume streamlines in the 3D space. The results indicate that the types of 3D separation appear in the gap shifts from the coexistence of horseshoe-type and tornado-type separations to only horseshoe-type separation that persists with the increase of h/δ. It is found that high heat flux is generated by the high-momentum fluid transported toward the surface by the horseshoe vortices. The tornado-type vortex prevents the incoming flow from arriving at the rudder shaft, which avoids the generation of high heat flux at the center of the rudder shaft. The rate of local heat transfer increases with h/δ as a result of the shrink and disappearance of the tornado-type vortices, which means that the region of low-speed backflow in front of the rudder is reduced and vanished. This study contributes to a clearer understanding of the flow physics in the complex disturbance area.

Relationship between environmental indoor conditions of a classroom and the performance of undergraduate students

PurposeThis research aims at studying the influence of a classroom’s inner environmental conditions on undergraduate students’ performance using an experimental methodology.Design/methodology/approachThe Uchida-Kraepelin test (U-K test) was applied to measure the performance of a group of 47 students in a selected classroom that was arranged according to the following experimental conditions: air-conditioning on, and doors and windows closed (D1); doors and windows open, and air-conditioning off (D2); air-conditioning off, and doors and windows closed (D3). After completing the tests, questionnaires were distributed to evaluate the students’ assessment of each set of environmental conditions.FindingsOn-site measurements of humidity and carbon dioxide levels stress the importance of ensuring good natural ventilation through open doors and windows, independently of whether the air-conditioning system is operated or not. Also, the authors find that the students’ self-assessment regarding the inner environmental conditions for each studied set was entirely accurate, with set D3 being assessed as the worst. The U-K test scores for each environmental set did not show statistically significant differences, which means that, in the studied conditions, the student’s performance in the tests was not affected by the inner environmental conditions.Practical implicationsThere is a direct relationship between the building’s indoor conditions and an occupant’s health. Factors such as poor maintenance, bad indoor environmental quality (IEQ) and building age will worsen the building’s condition and negatively impact the occupant’s health. Educational buildings with poor IEQ can reduce the concentration and performance of occupants.Social implicationsSchool is an important place to help students grow in their various capabilities. They spend approximately 30% of their daily lives in schools for their educational activities. Since most of their activities are performed indoors, indoor environmental attributes, such as light, heat, air and sound, should be maintained as required. In general, schools are not thermally comfortable. The extreme thermal environment of classrooms affects students’ concentration. Thermal discomfort may also cause irritation. In addition to reduced concentration, such an environment could also cause tiredness, sluggishness and health problem.Originality/valueDespite the importance of the issue, scientific investigations of the correlations between students’ performance and the quality of scholar buildings’ inner environmental conditions are still relatively recent. In this context, this research further explores the effect of a classroom’s different environmental inner conditions on the performance of undergraduate students at a university in São Paulo/Brazil.

Numerical investigation of effects of cooling structure parameters on performance of flameholder in an integrated afterburner

The integration of components is an important trend at present in the development of the afterburner. This study proposes a cooling structure of the guide plate to cope with the extreme thermal environment to which the flameholder is subjected. A numerical investigation is carried out to examine the effects of the cooling structure with different characteristic parameters on the cooling performance of the flameholder. The results show that the proposed cooling structure can reduce the peak temperature and improve the cooling efficiency of the flameholder while not affecting the operation of the remaining components. Furthermore, the characteristic parameters were found to influence cooling performance by changing the state of formation of and the distribution of locations of vortices in the flameholder. The optimum model was obtained by comparing the results of models with different characteristic parameters. It can reduce the peak temperature by 2.1% and increase the average efficiency of cooling by 15.3% compared with the baseline model.

Novel strong and tough Ta/TaHfC2 composites with multi‐scale laminated structure

AbstractTa‐Hf‐C ternary ceramics are good candidates for structural components used in extreme thermal environment. However, intrinsic brittleness greatly restricts their applications in reality. Here, we report a novel TaHfC2‐based composite with superior strength and toughness by employing Ta foil as interlayers to generate a multi‐scale laminated structure together with the in situ formed Ta2C MXene during sintering. Owing to the unique composition and microstructure, the tensile strength, shear strength, fracture toughness (KIC), and work of fracture of Ta/TaHfC2 have reached 233 ± 12 MPa, 64 ± 6 MPa, 13.16 ± 0.03 MPa·m1/2, and 1726 ± 448 J/m2 simultaneously, and all showed substantial increments when compared with TaHfC2 monolithic ceramic and related Ta‐Hf‐C materials as showed in literatures. This study significantly improved the toughness of TaHfC2, and it provides a new high‐performance thermal structural material for the aerospace industry as well as a new idea for toughening ultra‐high temperature ceramics (UHTCs) of transition metal carbides.

Verification at Mach 4 heat conditions of an annular microtube-typed precooler for hypersonic precooled engines

• A high performance microtube-typed precooler is designed and manufactured. • A sophisticated high-temperature test platform for the precooler is established. • A parameter matching method for operating the test platform is proposed. • The heat transfer performance and operating reliability of the precooler are verified. The precooler with high power-to-weight ratios and robustness is a core component of hypersonic precooled engines to operate efficiently at the full speed range. In order to figure out the feasibility of precooler technology, an annular microtube-typed precooler was designed and manufactured. A high temperature test platform consisting of an extreme thermal environment system and a closed S-Helium loop system was built to experimentally verify the operating performance and reliability of this novel precooler. Moreover, a parameter matching method was proposed for stably operating the test platform. On these basis, an 1800-seconds longtime precooler performance test simulating Mach4 heat conditions and constantly supplying S-Helium at 8 MPa was successfully conducted. The test results are in a great agreement with the model results and the maximum error of the heat transfer rate is within ± 10%. The manufactured microtube-typed precooler exhibits its long-term resistance to harsh operating environment (at temperature of nearly 1000 K and pressure of over 8 MPa) and maintains its structural integrity after thermal cycles with an acceptable leakage rate of below 3vol%/h. The airflow temperatures were quenched in excess of 600 K in the test which demonstrates the precooler’s ability to cool airflow at speeds significantly beyond the limit of any jet-engine powered aircraft. In addition, the measured power/weight ratio is up to 100 kW/kg, which is in the lead in precooler technology to the authors’ knowledge.

181 Impact of Extreme Temperatures on Hemostatic Gauzes Using Thromboelastography

In both military and wilderness/extreme civilian settings, life-threatening hemorrhage can be difficult to control. Hemostatic gauzes provide an excellent option for wounds not amenable to tourniquets. In this study, thromboelastography (TEG) was utilized to evaluate the effect of extreme temperature storage environments on the efficacy of three gauze products. Blood from 30 healthy active duty military adults was diluted by 30% with hetastarch to mimic trauma-induced coagulopathy. Temperatures were chosen because they represented thermal extremes that could be encountered in the tactical setting. Kerlix, Combat Gauze, and Chito Gauze stored for 3 weeks in cold (- 10C), hot (70C), and room-temperature (22C) environments were compared in the TEG parameters of R (time to initiation of clot formation), K (clot amplification), α angle (clot formation rate), and MA (maximum amplitude of clot) using repeated measures ANOVA with the p<.05 statistical significance threshold. Compared to whole blood, diluted blood had weaker clots with slower clot formation kinetics (MA- 58.00 vs 43.00, p<.0001; K- 2.58 vs 4.00, p<.0001; α angle- 54.98 vs 47.36, p<.0003) but faster clot initiation times (R- 8.66 vs 7.14, p<.0001). Addition of any gauze improved clot initiation times (R; Kerlix- 7.14 vs 4.98, p<.0001; Chito Gauze- 7.14 vs 5.22, p<.0001; Combat Gauze- 7.14 vs 2.71, p<.0001), with Combat Gauze significantly improving R over Chito Gauze and Kerlix. Reductions in R values were consistent across temperature extremes (p<.05) The other parameters were consistently unaffected (p>.05) Hemostatic gauze, regardless of temperature storage conditions, improved the rate of initiation of clot formation when compared to diluted blood. Additionally, our results suggest that Combat Gauze may be the best choice for extreme thermal environments.

Ultrahigh-temperature decompression of sapphirine-granulites from the southern Madurai block (South India): Insights from geothermobarometry, pseudosection modelling and U-Pb geochronology

Madurai block in South India stands as an excellent example of ultrahigh temperature metamorphic terranes being studied globally to understand the extreme thermal capacities of crustal rocks and the processes that cause these extreme thermal environments. The granulites of the Madurai block were subjected to extreme crustal metamorphism during the Late Neoproterozoic, as evidenced by the texture of the sapphirine + quartz association registered as peak metamorphic assemblage. The metamorphic zircon from sapphirine-granulites produces a U-Pb age of 546.5 ± 7.8 Ma which is interpreted as a global Pan-African crustal evolution event and the dominant zircon population indicates multiple sources of Neoarchean to Paleoproterozoic age in the southern Madurai block. Decompression textures other than orthopyroxene-cordierite ± sapphirine symplectites are indicative of retrograde / exhumation in the granulites metamorphic cycle. P–T pseudosections have been constructed for sapphirine-granulites in relation to the NCKFMASHTO system (Na2O-CaO-K2O-FeO-MgO-Al2O3–SiO2-H2O-TiO2-O2) using Perple_X software (version 6). The limitations in the interpretation of mineral reactions and the metamorphic history provided by pseudosection modelling for mineral proportions suggest that the peak metamorphic temperature is ~960 °C and pressure is ~9.2 kbar.

Enhancing the heat tolerance of reef-building corals to future warming.

Reef-building corals thriving in extreme thermal environments may provide genetic variation that can assist the evolution of populations to rapid climate warming. However, the feasibility and scale of genetic improvements remain untested despite ongoing population declines from recurrent thermal stress events. Here, we show that corals from the hottest reefs in the world transfer sufficient heat tolerance to a naïve population sufficient to withstand end-of-century warming projections. Heat survival increased up to 84% when naïve mothers were selectively bred with fathers from the hottest reefs because of strong heritable genetic effects. We identified genomic loci associated with tolerance variation that were enriched for heat shock proteins, oxidative stress, and immune functions. Unexpectedly, several coral families exhibited survival rates and genomic associations deviating from origin predictions, including a few naïve purebreds with exceptionally high heat tolerance. Our findings highlight previously uncharacterized enhanced and intrinsic potential of coral populations to adapt to climate warming.

On-orbit thermal deformation prediction for a high-resolution satellite camera

Thermal-structural analysis of satellite camera in the early design phase as well as during the later experimental verification is important due to the extreme thermal environment. The purpose of this work is to numerically investigate the thermal deformation for a high-resolution satellite camera under solar radiation. Based on the on-orbit thermal environment of the geosynchronous orbit, thermal-structural finite element model of the satellite camera is developed and opto-thermo-mechanical analysis of the optical system is proposed. Transient temperature distributions of the satellite camera under different extreme heat loads are obtained. Mirror deformations, translation and rotation have been introduced to the optical analysis and modulation transfer function analysis has been performed. Numerical simulation results reveal the dynamic response of the optical system under transient temperature and the thermal vacuum test predicts the imagery quality of the satellite camera, which can provide guidance for designers to analyze the on-orbit stability for the optical camera.

Detailed thermal indicators analysis based on outdoor thermal comfort indices in construction sites in South China

Extreme thermal environment harms the health of outdoor workers and poses a potential threat to workplace safety. A field survey, including thermal parameter measurements, was conducted at construction sites in South China during the summer of 2019. The relationship between health risk and thermal parameters was obtained. The thermal sensation and satisfaction rate of the workers at different outdoor environmental conditions were analyzed, and recommendations were made based on the comparison of thermal indices. The thermal stress categories of the thermal indices were also investigated. The results suggest that the intensity of working conditions should be reduced when the air temperature is higher than 34 °C; the satisfaction rate of workers was found to be relatively high when the outdoor temperature is lower than 34 °C and the wind speed is greater than 1.3 m/s. Thermal indicators used to evaluate the comfort level of outdoor workers need to be modified according to the local climate and working environment to avoid excessive exposure to high-temperature work environments.

Study on the ablation resistance of plasma sprayed La2(Zr0·7Ce0.3)2O7/YSZ and La1·9Ca0·1(Zr0·7Ce0.3)1.9Cr0·1O6.9/YSZ thermal protection coatings

Metal materials have been widely used in hypersonic aircrafts due to their unique advantages, while none of the alloys can withstand the extreme aerodynamic thermal environment without ablation failure. Thermal protection coatings with low thermal conductivity or high infrared radiation are usually used to prevent heat from entering metal matrix, and at the same time, prolong or avoid the occurrence of ablation failure. Our previous study has shown that co-doping of Ca2+ and Cr3+ ions could effectively improve the infrared radiation performance of La2(Zr0·7Ce0.3)2O7(LZ7C3) ceramic. In this paper, plasma spraying method was adopted to prepare LZ7C3/YSZ and La1·9Ca0·1(Zr0·7Ce0.3)1.9Cr0·1O6.9(LZ7C3Cr)/YSZ coatings on steel substrate, and the anti-ablation and thermal protection performance evaluation experiment were carried out with oxyacetylene flame. The results showed that the LZ7C3/YSZ coating could protect the steel substrate from ablation damage with ablation surface temperature of 1650 °C and ablation time of 300 s. Under the same evaluation condition, the LZ7C3Cr/YSZ coating showed better ablation resistance than the LZ7C3/YSZ coating to some extent, the reason for this was that LZ7C3Cr/YSZ coating could reduce the ablation surface temperature by 100 °C due to the high infrared radiation performance, and LZ7C3Cr material had higher thermal expansion coefficient than LZ7C3 material, which led to lower thermal mismatch stress between the coating and the metal matrix in the ablation process. In addition, the formation of surface vertical microcracks on LZ7C3Cr/YSZ coating during the ablation process also played an important role in the improvement of ablation resistance of LZ7C3Cr/YSZ coating.

Microbiome of juvenile corals in the outer reef slope and lagoon of the South China Sea: insight into coral acclimatization to extreme thermal environments.

Environmental conditions between the outer reef slope (ORS) and lagoon in tropical atolls are significantly different, but the variations of juvenile coral-microbiomes in the two environments and their relationship with coral thermal acclimatization are poorly understood. We explored this issue based on local water conditions and the microbiome of juvenile corals in the ORS and lagoon in the central South China Sea. Coral-symbiotic Symbiodiniaceae showed significant differences among coral species; Pocillopora verrucosa and Pachyseris rugosa in the ORS, and Acropora formosa in the lagoon were dominated by Durusdinium, but other corals were dominated by Cladocopium. Although A. formosa in the ORS were dominated by Cladocopium (C3u), they were dominated by Durusdinium (D1/D1a) and Cladocopium (C50) in the lagoon. Other coral species were both dominated by Cladocopium in the lagoon and ORS. The relative abundance of bacteria in the Deinococcus-Thermus was generally higher in the lagoon corals than in the ORS corals. Our study indicates that P. verrucosa, P. rugosa and Porites lutea may have high thermal tolerance based on the relatively high abundance of heat-tolerant Durusdinium and Thermus scotoductus. Likewise, A. formosa in the lagoon may acclimatize to the thermal environment based on a high relative abundance of heat-tolerant Durusdinium.

A synchronous placement and size-based multi-objective optimization method for heat dissipation design on antenna module of space solar power satellite

As a potential space building for supplying solar energy, space solar power satellite (SSPS) has become an important aspect of its feasibility study. For such a high-power system, the heat dissipation problem caused by the large external heat flux and internal heat source must be resolved. This study investigates an optimum layout for heat dissipation of an antenna module in SSPS exposed to an extreme thermal environment using optimization with an iterative two-layer design. A synchronous placement and size-based multi-objective optimization problem is constructed with temperature constraints to balance the module’s mass and temperature distribution with the optimum location, placement, and size. To improve the solution efficiency, an iterative two-layer heat dissipation design is developed to avoid the limitations of directly solving the high-dimensional optimization. The first-layer design optimizes the placement and basic size of the thermal control equipment using the constrained NSGA-II, and the size factors are continually optimized in the second-layer design. This innovative design can not only overcome the large-scale calculation, but also meet the actual engineering needs, which optimize the key indicators and balance accuracy and efficiency. The proposed method with statistical analysis is applied to realize 2.6% weight reduction and acceptable temperature distribution with effectiveness.

Thermal response during volumetric ablation of carbon fiber composites under a high intensity continuous laser irradiation

The phenomenon of volumetric ablation of carbon fiber composites by a continuous high power density laser was investigated theoretically and numerically. The main goal of this study was to investigate the thermal responses of the heat shields of re-entry vehicles in the extreme thermal environment. The composite was considered as a homogenized block in geometry. And a one-dimensional transient model was proposed. The laser power density varied from 50W/cm2 to 500W/cm2 and the laser irradiation time varied from 0 to 5 s. During volumetric ablation, the composite could be separated into three zones: the virgin zone, the pyrolysis zone and the char zone. It was found that a higher laser power density led to a smaller pyrolysis zone. The peak pressure of pyrolysis gases in the composite appeared in the region with a low degree of pyrolysis reaction, which had a significantly low porosity and permeability. When the initial porosity of the composite was low, a small amount of gas generation might lead to a high gas pressure, causing mechanical failure of the composite. And the magnitude of the peak pressure decreased quickly with the initial porosity increasing. Therefore, the porous structure and the honeycomb sandwich structure used inside of the composite should decrease the internal gas pressure to prevent the material from mechanical damage. The simulation result of this study was helpful for the design of high temperature thermal protection systems.

The influence of inlet swirl intensity and hot-streak on aerodynamics and thermal characteristics of a high pressure turbine vane

In modern gas turbines, the High Pressure Turbine (HPT) is exposed to an extreme thermal environment due to the burned gases leaving the combustor. The burned gases are characterized by flow and temperature distortions that effect the aerodynamics and heat transfer of the turbine. The purpose of this paper is to investigate numerically the effect of the intensity of the swirling flow combined with the temperature non-uniformity “Hot-Streak” (H-S) on the aerothermal performances of a HPT Nozzle Guide Vane (NGV). The investigations are conducted on the solid untwisted NGV annular cascade developed in NASA Lewis Research Center. Four swirl intensities (|Sn| = 0, 0.1, 0.25 and 0.5), two swirl orientations (positive and negative) and two hot-streaks (rounded and radial) at the NGV inlet are considered. The simulations are done by solving the Reynolds Averaged Navier-Stokes (RANS) equations using ANSYS-CFX software. The results show that the H-S with swirl undergoes twisting following the orientation of the swirl. The H-S twist is aggressive under positive swirl compared to the negative swirl case. The inlet swirl generates a new secondary flow structure, so called Swirl Vortex (SV), which induces more aerodynamic losses. The aerodynamic efficiency under negative swirl found to be higher than that under positive swirl. The maximum temperature on the vane surface is controlled by the radial transport of the SV towards the endwalls.

Thermal responses of workers during summer: An outdoor investigation of construction sites in South China

Extreme thermal environments harm the health and reduce the productivity of outdoor workers. Variations in human physiological indices and the thermal exposure time limit are the main factors in evaluating heat safety in an extreme thermal environment. Therefore, it is necessary to determine the relationships between human physiological indices, psychological responses, and thermal parameters to accurately predict and evaluate human thermal safety in extreme thermal environments. A field survey, including thermal parameter measurements, was conducted at construction sites in South China during the summer of 2019. The relationship between health risk and thermal parameters was obtained, and the adaptability and sensitivity of workers to i) thermal parameters (outdoor ambient temperature (Ta), mean radiant temperature (Tmrt), wind speed (Va), and relative humidity (RH)) and ii) physiological indicators (heart rate (HR) and auditory canal temperature (ACT)), as well as the variations in their cognitive ability, were analyzed. The results indicate that 40 % of workers experienced discomfort and that when Ta > 34 °C, the working intensity of workers needs to be reduced in construction sites. The HR and ACT increased with increasing working hours, and the thermal parameters and cognitive ability decreased. To avoid discomfort, it is suggested that the HR may be kept near 94 beats/min. The effects of physiological indicators and cognitive ability on the physical and mental state of the workers were significant; with an increase in thermal environment parameters, the efficiency decreased by approximately 8%. The results of this investigation are beneficial for ensuring the occupational safety of workers and reducing the risk of heat exposure.

Axially functionally graded design methods for beams and their superior characteristics in passive thermal buckling suppressions

Thin-wall structures on high-speed spacecrafts are usually exposed to extreme thermal environments during their service life. This problem will lead to the buckling and instability of structures, which can seriously affect the integrity and reliability of spacecrafts. Therefore, it is significant to study the suppression methods for the thermal buckling. It is well known that temperature change will produce a negative stiffness, which may eventually lead to the thermal buckling of structures. Based on this mechanism of thermal buckling, it is reasonable and effective to construct the equivalent positive thermal stiffness by changing the geometrical sizes and material properties of the structure along the axial direction. Inspired from this, in this paper, two passive ways, i.e. the axially functionally graded (AFG) design and adding torsional springs, are investigated. For the AFG design, both the thickness and material properties are functions of the axial spatial variable. In order to obtain the optimal functions for the thickness and volume fraction, an incremental structural stiffness method is proposed, and the genetic algorithm (GA) is also introduced. Numerical results show that through the AFG design, the thermal buckling characteristics of the structures are improved significantly. On the other hand, when the torsional springs are added to the main structure, under appropriate stiffness coefficients, the structural stiffness reduction caused by the temperature change can be offset to the maximum extent by the passive stiffness generated by the torsional springs. The present study is significant in the structural design of aerospace vehicles.