Effect Of Thermal Environment Research Articles

Unravelling the effects of dynamic urban thermal environment on utility-scale floating photovoltaic electricity generation

The utility-scale photovoltaic systems have been widely integrated for sustainable urban development. However, the varying photovoltaic conversion efficiency (PVCE) affected by dynamic urban thermal environment causes uncontrollable uncertainty in electricity generation, which challenges installed-capacity planning and load-balancing operations. To tackle this problem, this study develops a PVCE estimation model containing four hierarchical modules. First, photovoltaic surface temperatures (PVSTs) are retrieved from satellite imagery, and meteorological features are collected to represent the dynamic thermal environment. Second, the contribution of each feature to the PVST estimation is evaluated, referring to the Mean Decrease in Impurity, Permutation Importance, and SHapley Addictive exPlanations. Third, machine learning models using Support Vector Machine, Random Forest, and XGBoost are developed to establish robust regressions between PVSTs and the selected features, enabling an accurate estimation of PVST spatio-temporal heterogeneity. Finally, the spatio-temporally corresponding PVCEs are calculated, resulting in a refined estimation of annual electricity generation. The investigation of four floating PV systems in Singapore found that their PVCEs vary insignificantly throughout the year, which is probably because of its stable climate and the cooling effect of water. The proposed model is simple and effective, demonstrating its impact on PV potential estimation when the urban thermal effect becomes significant.

A Kirchhoff Plate Model for Longitudinal Vibration Analysis of Restrained Nanoplate Including Thermal Effects

This work attempts to apply the Kirchhoff plate theory to find out the vibrational analyses of a nanoplate incorporating thermal effects. The effects of thermal environments on the natural frequency of longitudinal vibration of restrained nanomaterials, especially for restrained nanoplates, have not been investigated, and most of the previous research has been carried out for unrestrained nanoplates. Therefore, it must be emphasized that the vibrations of restrained nanoplate, including thermal effects, are novel and applicable to the nanodevices, in which nanoplates act as the main structure of the nanocomposite. A novel motion and frequency equation are derived using the Kirchhoff plate model. The present study illustrates that a nanoplate’s longitudinal vibration characteristics strongly depend on the temperature change and stiffness coefficients. The numerical results clearly show that the longitudinal natural frequencies of the nanoplate are less than unity for both cases of low and high temperatures. This means that applying the Kirchhoff plate model for restrained nanoplate analysis would lead to an over-prediction of the frequency if the small thermal stress effect is neglected. Finally, the investigation of the restrained and thermal impact on longitudinal vibration of nanoplates may be used as a valuable reference for the application and the design of nanoelectronics and nano-drives devices, nano-oscillators, and nano-sensors, in which nanoplates act as essential elements.

Quantifying the Spatial Heterogeneity Relations Between Thermal Environment Effects and Influencing Factors Based on Geodetector in Central City of Chengdu

To address the current situation that urban thermal environment research lacked comprehensive assessment and analysis from natural-social multidimensional factors, this study analyzed the evolution characteristics of thermal environment effects in the central urban area of Chengdu from 2004 to 2019 based on multi-source data. A total of seven influencing factors of natural and social factors that were highly associated with the urban thermal environment were selected, and the influencing factors of spatial differentiation of land surface temperature (LST) and their interactions were studied by applying Geodetector. The results showed that: (1) the heat island in the central city of Chengdu from 2004 to 2019 was radiating outward from the center, and the spatial development spine of the thermal environment remained in the "southeast-northwest" direction, with a significant shift of the center of gravity of the thermal environment from 2011 to 2019; (2) the average LST from 2004 to 2019 increased from 36.57℃to 40.64℃, and the total area of heat island area increased from 641 km2 to 958 km2. overall, it showed a shift from sub-medium zone and medium temperature zone to sub-high temperature zone and high temperature zone, and the urban heat island effect tended to enhance; (3) the nighttime light intensity had the largest amount of contribution to the spatial differentiation of LST, and social factors had a more important position relative to natural factors in influencing the urban thermal environment but the amount of contribution from natural factors kept increasing.

Effects of thermal environment and air quality on outdoor thermal comfort in urban parks of Tianjin, China.

The comfort level of outdoor thermal environments is affected by several factors. Previous studies of thermal comfort have generally investigated the main microclimatic factors as dependent variables, such as the temperature, wind speed, humidity, and thermal radiation, but the influence of the air quality has rarely been explored. In this study, we acquired meteorological element observations and conducted questionnaire surveys in Peach Blossom Park, Hebei University of Technology, and Xigu Park in Tianjin. We analyzed the effects of the outdoor air quality and thermal environment on the thermal comfort in order to provide a theoretical basis for comprehensive evaluations of the outdoor environment and the mechanism. The results showed that thermal resistance of clothing and ambient temperature followed a negative step change, where people generally reduced the minimum amount of clothing when the temperature exceeded 28 °C. One unit change in the thermal sensation vote (TSV) occurred for every 11 °C rise in the physiological equivalent temperature (PET). The neutral PET was 21.68 °C, and the comfortable PET was about 23 °C. The air quality index (AQI) and air satisfaction were negatively correlated, and satisfaction decreased by 1 unit for every change of 230 AQI. The transitional season was most comfortable when the temperature felt slightly cool (TSV = -0.70). The neutral TSV was 0.507 in the summer and -0.334 in the winter. Air quality had a significant effect on the thermal comfort vote (TCV) (p = 0.0485 < 0.05). The effect of PET on TCV was highly significant (p < 0.01).

Magnetic field and thermal environment effects on sound transmission loss of double-walled cracked piezoelectric cylindrical nanoshells

Based on a non-local strain gradient theory (NSGT), this article analytically studies the sound transmission loss (STL) performance of a special type of double-walled partially cracked piezoelectric nanoshell structures of cylindrical shape undergoing initial electric potential and longitudinal magnetic field. The structure, which includes a specific number of axial and circumferential surface cracks, is struck by a plane wave in a thermal setting. Such cracks have minimal size compared to the nano-shell structure as a whole, minimizing the effects of curvature for this problem. The first-order shear deformation theory (FSDT) is utilized to explain the displacement components, and Hamilton’s concept is applied to obtain the coupled vibroacoustic equations that are used to generate the governing equations of the system for the two crack types, giving us an idea of the resulting structural stiffness in the presence of cracks using coefficients of crack compliance that are derived from the line spring model (LSM). The mechanical and acoustic properties are then checked to see their effect on the system response followed by a series of validation case studies. This evaluation also allows one to optimize a similar structure by selecting appropriate external parameters such as electric voltage, magnetic field intensity, different crack types, nonlocal and strain gradient parameters, variations of temperature, and incident angle of sound waves.

Nanostructure modeling for thermal properties of zigzag carbon nanotubes

In the nanotube design application, the case of dynamic damage is key problem attracted many engineering researchers. The thermal effect on the axial buckling of zigzag double walled carbon nanotubes (DWCNTs) embedded in an elastic medium is investigated in this article based on the nonlocal Timoshenko beam model. The effects of the van der Waals (vdW) forces between inner and outer tubes and the surrounding elastic medium are taken into account based on a Winkler model. Moreover, a modified molecular mechanics model is developed to study the effect of thermal environment on mechanical properties of zigzag double carbon nanotubes, in which the covalent bonds are traded as a truss. It is found that the axial buckling properties of zigzag DWCNTs increase with the increase of the temperature at room or low temperature, while the axial buckling properties of zigzag DWCNTs decrease with the increase of the temperature at high temperature. Moreover, the buckling strain considering the thermal effect is larger than the buckling strain ignoring the effect of temperature change, and increases with the increase of temperature change, which is contrary to the case of high temperature.

Combined effects of thermal and acoustic environments on outdoor human comfort in university campus

Urban outdoor public spaces are complex systems and the thermal and acoustic environments are the two main factors that affect their overall comfort. Many studies have analyzed the effects of the thermal environment and acoustic environment separately from different perspectives, while further research is required to understand the combined effects between two or more factors on the comfort in outdoor public spaces. In this study, we chose a university campus and assessed the combined effects of thermal and acoustic environments on human comfort at several spaces. Results showed that thermal evaluation is mainly affected by PET and acoustic evaluation is mainly affected by LAeq at most of the sites. Apart from that, interactive effects are only significant on TSV at PA, SQ and on OCV at AC. Prediction made by linear regression model revealed that there're obvious discrepancy on both thermal and acoustic evaluation between predictions and actual conditions. For overall comfort evaluations, linear regression analysis suggest that people feel “moderate” under ideal conditions where there're “no thermal stress” and LAeq =50 dB(A). The OCVeq chart analysis showed that the variation trend was separated by 0 with linear and centralized on each side, giving the hints that people judge their overall comfort and discomfort differently. This study concludes that it's possible to predict human comfort based on knowledge about the current thermal and acoustic environment, but due to limitations of this study, the reliability and accuracy requires further researches to confirm.

Evaluating the impact of sky view factor and building shadow ratio on air temperature in different residential and commercial building scenarios: A case study of Beijing, China

The urban building morphology is one of the most important effects of urban thermal environment (UTE). The sky view factor (SVF) is a crucial structure index of buildings and it combines height and density attributes. These attributes have impacts on the air temperature(Tair). However, there are few studies on the association between SVF and Tair across block scales. In this paper, we designed ten scenarios according to the characteristics of Beijing's commercial and residential buildings. Furthermore, we used ENVI-met, a microclimate simulation model, to simulate the Tair in designed scenarios and evaluate the impact of SVF on the Tair of each component. A number of significant observations were noted based on the experimental results: (1) from 10:00 to 17:00, there is a positive correlation between SVF and Tair; from 18:00 to 9:00 the next day, there is a negative correlation between SVF and Tair (2) the relationship between building shadow ratio (BSR) and Tair is not a single negative correlation: at sunrise, BSR is the maximum in a day, but the cooling effect of BSR on Tair is not obvious because of the weak solar radiation. In addition, the arrangement of building directions has a great influence on the relationship between BSR and Tair (3) for the same building scenario, BSR decreases with the increase of SVF (4) the synergistic effect of SVF and BSR on Tair in the daytime can be divided into two periods, the separation time points are 7:00 and 14:00. This study can provide instructions for urban design in optimizing building layout and mitigating the urban heat impact on human health.

Modeling and Free Vibration Analysis of Variable Stiffness System for Sandwich Conical Shell Structures with Variable Thickness

This paper presents modeling and free vibration analysis of variable stiffness system for the truncated sandwich conical shell made of porous aluminum foam core with variable thickness and carbon fiber face sheets under the simply supported boundary condition. The thickness of the core layer varies along the longitudinal direction. Five different types of porosity distribution of the aluminum foam core, which contains Type-X, Type-O, Type-U, Type-V and Type-[Formula: see text] along the direction of thickness, are considered. Considering the effect of thermal environment, we derive the nonlinear dynamic equations based on first-order shear deformation theory and Hamilton’s principle, and obtain the natural frequencies of the system by employing the Galerkin method. The comparison and validation are conducted by contrast with the determined results of the literature. The influences of porosity distribution pattern, porosity coefficient, the total number of layers, temperature increment, semi-vertex angle, the exponent of thickness function, the minimum radius-thickness and length-thickness ratio of the core layer on the natural frequencies, modal and mode shapes are studied comprehensively.

The effect of thermal and cryogenic environments on the impact performance of aluminum-glass fibers/epoxy laminated composites

In this research work, the effect of various environments on the impact properties of fiber metal laminates was investigated. To do so, in the first step, the 2024 aluminum layers were surface modified with the etching method. Then, the various glass fibers/epoxy composites with the configurations of (0°/0°/0°/0°, 90°/90°/90°/90°, +45°/−45°/−45°/+45° and 0°/90°/90°/0°) were sandwiched between two aluminum sheets. In the following, these samples were aged under thermal cycling (between 25 and 100 °C), isothermal aging at the temperature of 100°C, cryogenic cycling (between −196 and 25 °C), and cryogenic isothermal aging at the temperature of −196°C. To understand the effect of various aging methods on the mechanical features of these structures, the Charpy impact test was performed. Also, the failure mechanisms and related phenomena were assessed by visual observations and microstructural investigations. In the first steps of thermal aging, the impact strength of FMLs was improved, which the highest of that being 46.9%. In the higher cycles or exposing times, the impact strength showed reducing trends, due to thermal degradations of the epoxy matrix. The cryogenic cycling in the high cycles reduced the impact strength of FMLs. But in the cryogenic isothermal condition, in some cases, the improvement in the impact strength was seen, which the highest of that being about 43.4%.

Dynamical responses of variable generatrix profile and thickness ceramic-matrix composite shells under electro-thermo-mechanical effects

In this paper, new structures of shells have been proposed with complex profiles and thicknesses varying through the length direction subjected to a thermal environment. The inner and outer surfaces of the shells are bonded to the piezoelectric actuators with changes of various voltages. The nonlinear motion equations of variable generatrix profile and thickness (VGPT) shells are solved to investigate the nonlinear vibration and chaotic responses using the theory of elasticity and Von Karman-Donnell’s geometrical nonlinearity assumption. Four kinds of VGPT shells are combined by two types of complex profiles and two patterns of thickness distribution. The used materials are made of Silicon carbide (SiC) and Borosilicate. Galerkin’s method is applied to solve the systems of differential equations and then the fundamental frequencies and nonlinear dynamic behaviors can be found. The effects of material (coefficient k), geometrical parameters, thickness, piezoelectric layers, and thermal environment on the dynamic responses of VGPT shells are examined and presented in tables and graphs.

CFD Analysis of Solar Greenhouse Thermal and Humidity Environment Considering Soil–Crop–Back Wall Interactions

In the study of solar greenhouses, microclimate, soil, and back walls have an important influence on the greenhouse thermal environment because of their good heat storage and release characteristics. The transpiration of crops makes indoor humidity increase sharply, which is the main factor affecting indoor humidity distribution. Therefore, it is of great significance to grasp the microclimate change law of solar greenhouses and study the coupling effect of thermal and humidity environment. In this paper, based on computational fluid dynamics (CFD), a three-dimensional model of the thermal and humidity environment of a solar greenhouse is established, and the indoor temperature and humidity distribution under the influence of soil, crops, and back walls are considered. The CFD model initialization uses binary fitting functions to fit the temperature distribution of soil, back wall, and air. The distribution law of the temperature field and relative humidity field of the solar greenhouse under three different working conditions is simulated, that is, the insulation is uncovered and the ventilation window is closed during the day (G1), the insulation is uncovered and the ventilation window is opened during the day (G2), and the insulation is put down and the ventilation window is closed at night. (G3). The results show that the simulation results are in good agreement with the actual results under the three working conditions, and this paper can provide a reference for the improvement of the greenhouse structure and environmental regulation.

Experimental study on the effects of exercise intensity and thermal environment on thermal responses

Public exercise facilities have recently emerged across China. This study aims to investigate the impacts of exercise intensity and thermal environment on thermal responses as well as examine the dynamic changes and differences in thermal responses during exercise. Using a controlled thermal chamber, university students were assessed at varying walking speeds under six thermal conditions, from −15 to 35 °C. Their psychological and physiological responses were observed and recorded in real time during the thermal adaption, exercise, and rest phase. Firstly, the exercise intensity significantly affected heart rate and metabolic rate, whereas the thermal environment had no significant effect. The effect of the thermal environment on skin temperature, thermal sensation vote (TSV), and thermal comfort vote (TCV) was more pronounced than that of exercise intensity. Secondly, during exercise, the metabolic rate took 6–9 min to stabilise, and the psychological response lagged compared to the physiological response. Thermal sensation was closest to neutral at 15 °C, 5 °C, and −5 °C when walking at 3 km/h, 4.50 km/h, and 6 km/h, respectively. Thermal comfort vote (TCV) levels were greater for higher exercise intensities at −15 to 5 °C, lower for higher exercise intensities at 25–35 °C, and similar for varied exercise intensities at 15 °C. Finally, current thermal comfort guidelines underestimate the exercise metabolic rate by at least 9.7%. This study helps clarify the dynamic changes and influence factors of thermal responses during exercise and provides a reference for future research on exercisers’ thermal responses.

Free axisymmetric vibrations of heated non-uniform Bi-directional FGM Mindlin rings employing quadrature approaches

The present article investigates the axisymmetric vibrations of non-uniform bi-directional functionally graded rings under two-dimensional temperature distribution on the basis of first-order shear deformation theory. The linear variation of thickness along the radial direction is controlled by a taper parameter. The temperature-dependent mechanical properties are assumed to be graded in thickness as well as radial direction. The separation of variables method is applied to obtain the classical solution of two-dimensional heat conduction equation by imposing the thermal boundary conditions. The governing differential equations of thermoelastic equilibrium and axisymmetric motion together with boundary conditions are extracted from Hamilton’s principle. The quadrature technique is used to obtain the frequency equations and then the lowest three roots of these equations are calculated by MATLAB. After validating the results for the present approach, numerical results are given to analyze the effects of thermal environment, taper parameter, volume fraction index, heterogeneity and density parameters on the frequency parameter. Mode shapes for the specified rings are illustrated.

Plasticity in Na+/K+-ATPase thermal kinetics drives variation in the temperature of cold-induced neural shutdown of adult Drosophila melanogaster.

Most insects can acclimate to changes in their thermal environment and counteract temperature effects on neuromuscular function. At the critical thermal minimum, a spreading depolarization (SD) event silences central neurons, but the temperature at which this event occurs can be altered through acclimation. SD is triggered by an inability to maintain ion homeostasis in the extracellular space in the brain and is characterized by a rapid surge in extracellular K+ concentration, implicating ion pump and channel function. Here, we focused on the role of the Na+/K+-ATPase specifically in lowering the SD temperature in cold-acclimated Drosophila melanogaster. After first confirming cold acclimation altered SD onset, we investigated the dependency of the SD event on Na+/K+-ATPase activity by injecting the inhibitor ouabain into the head of the flies to induce SD over a range of temperatures. Latency to SD followed the pattern of a thermal performance curve, but cold acclimation resulted in a left-shift of the curve to an extent similar to its effect on the SD temperature. With Na+/K+-ATPase activity assays and immunoblots, we found that cold-acclimated flies have ion pumps that are less sensitive to temperature, but do not differ in their overall abundance in the brain. Combined, these findings suggest a key role for plasticity in Na+/K+-ATPase thermal sensitivity in maintaining central nervous system function in the cold, and more broadly highlight that a single ion pump can be an important determinant of whether insects can respond to their environment to remain active at low temperatures.

Static and Dynamic Analysis of Re-Entry Vehicle Nose Structures Made of Different Functionally Graded Materials

High-speed aerospace applications, such as re-entry vehicles, mostly involve thin-walled structural components with a high strength-to-weight ratio and high-temperature resistant. The present novel work comprises the structural and thermal analysis of re-entry vehicle nose structures made of four functionally graded materials (FGM). Four FGM shell structures made of aluminum/silicon carbide, aluminum/aluminum oxide, Ti-6Al-4V/silicon carbide and Ti-6Al-4V/aluminum oxide have been considered for the re-entry vehicle nose. The effect of various thermal environments, as well as the linear temperature rise from metal-rich to ceramic-rich on critical buckling temperature and natural frequency have been studied. The critical buckling temperature, as well as the natural frequency of the large, thin re-entry vehicle nose structures, decrease with an increase in a uniform thermal environment, as well as linear temperature rise. The effect of shell thickness on buckling and dynamic characteristics of an FGM shell is also studied, suiting the nose of the re-entry vehicle under various linear temperature rises. The critical buckling temperature and natural frequency are quantified for several cases, and it was observed that they are significantly influenced by the shell thickness. Thus, the research intends to determine the thickness required for such thin and large shells to withstand in the re-entry thermal conditions.

Investigation into effect of non-uniform thermal environment on thermal sensation under stratum ventilation for heating by using interpolation-based multi-level fuzzy comprehensive evaluation

Stratum ventilation for heating is applied to provide satisfactory indoor thermal environments with great potentials in winter. Indoor non-uniform environments are important for both overall and local thermal sensations in the same occupied subzone (i.e., vertical spaces) as well as different subzones of the occupied zone (i.e., horizontal spaces) under the effect of supply air jets. This study carried out field chamber experiments to consider the effect of non-uniform environments on both overall and local thermal sensations under stratum ventilation for heating using the multi-level fuzzy comprehensive evaluation (MFCE) method. This method has a multi-level structure to simultaneously investigate thermal sensation in both vertical spaces and horizontal spaces. The interpolation models of thermal sensation are helpful to enlarge the experimental sample size investigated by MFCE. The results showed that the interpolation-based MFCE method can quantitatively analyze the effect of non-uniform environments on thermal sensation in different subzones of the occupied zone from vertical spaces and horizontal spaces under the effect of supply air parameters. Compared with supply air temperature, supply air velocity has the opposite influence on the variation range of both integrated thermal sensations of feet, head and overall body and local thermal sensation of feet between the occupied subzones 1 and 2. Supply air temperature and velocity of 25–27 °C and no less than 1.1 m/s were recommended to improve the non-uniformity of thermal environments.

Research on the influence of indoor thermal environment and activity levels on thermal comfort in protective clothing

With the outbreak of infectious diseases such as Corona Virus Disease 2019, medical staff work intensively in isolated plots, medical disposable protective clothing (MDPC) has poor air condition and humidity permeability, which seriously reduces the thermal comfort of medical staff. In this paper, the effect of indoor thermal environment and activity levels on thermal comfort inside MDPC was studied by experiment. Five parts of the body were measured inside MDPC and the appropriate movements were chosen to simulate different levels of labor intensity. Meanwhile, physiological parameters and subjective thermal sensation were statistically analyzed. The results showed the influence range of different indoor temperatures on the temperature and humidity inside MDPC was about 1 °C and 10 %, respectively; it indicated that the environment inside MDPC could be improved by reducing indoor temperature, that is, a cross intelligent adjustment mode was proposed. The effect of labor intensity on the temperature inside MDPC was significantly less than that of humidity. Within 20 min, the humidity changes under moderate and heavy labor intensity were even more than 10 %, and the subjective discomfort threshold of the subjects increased by nearly 50 %. Furthermore, the maximum benefit could be obtained by concentrating cooling on back, forehead, chest and upper arm. Theoretical models of working time, labor intensity, and temperature and humidity inside MDPC under different indoor temperatures and different parts were given. In addition, acceptable regions inside MDPC which were approximately parallelogram in the enthalpy-humidity chart. These conclusions could be a reference for future thermal comfort inside MDPC research.

Study on indoor adaptive thermal comfort evaluation method for buildings integrated with semi-transparent photovoltaic window

Semi-Transparent Photovoltaic (STPV) windows have the potential of active energy-saving and have attracted more attention in recent years. Due to the selective absorption effect of solar cells on solar radiation, the indoor thermal environment and human thermal comfort of buildings integrated with STPV windows are considerably different from that with clear glass windows, and there are few studies on this. In this paper, the indoor human thermal comfort of buildings integrated with STPV window was investigated. Firstly, experiments and subjective questionnaires for the indoor environment were conducted in STPV and clear glass window buildings respectively. Secondly, the influence of illuminance on thermal sensation was statistically analyzed, with the consideration of visual effect, non-visual effect, as well as visual and non-visual coupling effect respectively. On this basis, an innovative thermal comfort evaluation method was provided. The thermo-physiological effect, light-physiological effect and light-psychological effect were comprehensively considered in this method. Finally, the reliability was verified by comparing with TSV. According to tests and questionnaires, it was found that the indoor thermal environment of the STPV window was an uneven thermal environment, and the subjective thermal sensation was more inclined to be slightly warm. When investigating the effect of illuminance on thermal sensation considering visual and non-visual coupling effect, it was found that illuminance had a significant influence on thermal sensation in different illuminance ranges. Meanwhile, it indicated the coupled effect of thermal environment and daylight environment on the thermal comfort of human.

Effect of humid and thermal environments on the performance of an epoxy resin pavement filling joint material

Modified epoxy resins have shown good results for the repair of pavement cracks. However, as the grouting material is directly exposed to the atmosphere, its performance is affected by humid and heat, resulting in a certain deterioration in its performance and service life. To explore the influence of humid and heat on an epoxy resin joint filling material (EPFM), EPFM was treated in humid and thermal environments for varying periods of time in this study, and the water absorption characteristics, mechanical properties, and road performance of the EPFM were tested. The stress relaxation index was used to evaluate the stress relaxation performance of the EPFM after humid and heat treatments. The results show that in a humid environment, EPFM undergoes a three-stage water absorption process, and the increase in water content reduces its glass transition temperature. In low-temperature environments, the tensile and shear strengths of the EPFM are reduced, but the deformation properties are enhanced under different stress patterns. In a high-temperature environment, the internal macromolecular structure of the EPFM is damaged, causing a significant reduction in its toughness. Under the −10 °C test conditions, the tensile strength reaches a maximum of 31 MPa, and the elongation at breaking decreases to less than 60 %. Through stress relaxation tests, it is found that compared with the thermal environment, water further weakens the stress relaxation performance of the EPFM.