Surface Thermal Field Research Articles

Real-time monitoring of the spatiotemporal thermal state of fused filament fabrication process for shape memory polymers

This study investigates a multi-sensor approach to estimate the surface thermal fields of Fused Filament Fabrication (FFF), an additive manufacturing process, at high spatial (4 μm) and temporal (0.1 msec) resolutions. The current state-of-the-art methods for quantifying the thermal, mechanical, and chemical state of the FFF processes are categorized into two main groups: numerical simulations and in-process thermal monitoring. Although numerical simulations can precisely estimate the process state for simple components, they are computationally demanding, become less accurate when complexity increases, and are therefore not suitable for real-time monitoring. In-process thermal monitoring, on the other hand, is becoming vital to track the process’ state, and offers a means to discern the underlying phenomena. While the current thermal sensors offer sub-mm scale spatial resolutions, their temporal resolutions (at best 1 msec) do not allow tracking of the thermal gradients necessary to determine the build geometry, microstructure, and the properties of the components. They are also limited by the cost and size, and need custom fixtures for mounting to a printer. The study proposes an approach based on pairing a primary high-tech thermal sensor with a secondary small footprint vibration sensor using a machine learning model to reconstruct the thermal fields at high time-resolutions from vibration signals. The key steps of this novel ML pipeline consisted of a singular value decomposition (SVD) of the ground truth of the thermal images and a time–frequency transformation with fast Fourier of the vibration signal. The overall model was able to make inferences and predict with 91.36 % accuracy the thermal state of the process using only vibration data as input. In addition, the ML pipeline filtered part of the experimental error contained in the ground truth data.

A scaling region identification method for the divider dimension of urban thermal environments

Abstract A scaling region identification method for divider dimensions using the coefficient of determination is proposed to improve the estimation accuracy of the divider dimension in the study of urban thermal environment differentiation characteristics. The effectiveness of this method was verified by analyzing the urban surface thermal field differentiation characteristics by applying the estimated divider dimensions of Nanjing’s thermal environment surfaces and transect lines. The research results show that the urban thermal environment has fractal characteristics only within a certain temperature threshold range. When the constraint of scaling regions is considered, the calculated divider dimension of the surface thermal field surface increases, reflecting the more complex fractal structure of the thermal field. For each temperature grade, the “trough” position of the thermal field divider dimension surface estimated by the line-divider method is near the determination level of the high-temperature region based on robust statistics, allowing the spatial extent of the urban heat island (UHI) to be determined based on the “trough” feature of the thermal field divider dimension surface.

Ultra-high pulse pressure induced particle surface thermal field assisted preparation of W–Al composite

Particle surface thermal field (PSTF) is an inhomogeneous thermal field that concentrates the heat effect on the surface of particles, and it can be utilized to fabricate composite materials with large differences in physical properties. However, it is difficult to form PSTF with large temperature gradients to meet the preparation requirement of materials with extreme differences in physical properties. In our work, a PSTF is proposed and realized by an ultra-high pulse pressure (UHPP) to prepare W–Al composite, the PSTF has a heating effect on the powder interface with a low-temperature interior of the powders. The combination of ex-situ microstructural observation and in-situ molecular dynamic simulation microstructural snapshot is used to demonstrate the densification mechanism. The PSTF is characterized as the temperature higher than 1200 °C on the W–Al powders interface but lower than 200 °C interior of the powders. The densification mechanisms are explained as interfacial jet penetration, interfacial friction welding and interfacial melting. In addition, interfacial temperature distribution creating gradient pressure on the W–Al interface illustrated the generation of gradient Al grains on the W surface, thus creating a high mechanical micro-hardness of 249.8 Hv and compressive strength of 473.2 MPa for the W–Al composite.

Spatial resolution enhancement of the land surface thermal field imagery based on multiple regression models on multispectral data from various space systems

The methodology has been developed for enhancing the spatial resolution of the land surface thermal field satellite imagery based on the following steps: coupling images in the visible, thermal, and radar ranges into the single multispectral data product; constructing regression models of the images’ relationship; performing the linear regression of the pseudo-thermal product with enhanced spatial resolution from the visible and radar ranges data. The methodology is implemented on the Google Earth Engine open cloud platform using the Earth Engine API and the software scripts created in the JavaScript language with the processing of multispectral image collections of various space systems at specified time intervals. The possibility of practical synthesis of the pseudo-thermal image with an enhanced spatial resolution of 10 m based on the thermal image with the resolution of 100 m and the multispectral composite with the layers’ resolution of 10 m and 30 m is shown. The technology has been developed for synthesis and calibration of the land surface temperature product with enhanced spatial resolution and daily data providing rate based on the brightness temperature product in the B10 band of Landsat 8 and linear regression on the MODIS, ASTER, and Sentinel 1 products with daily to moderate data providing rates. The software in JavaScript has been developed, and technology has been implemented in the interactive web service form with open access on the Google Earth Engine Apps cloud platform. The final data product provides the satisfactory relative root mean square error of the brightness temperature recovery of not more than 6 % according to the reference cross-calibration data of the B10 Landsat 8 band in the moderate thermal field (up to 100° C). The relative root mean square errors of the synthesized data according to the reference data on high-temperature sites (fire, hot lava) up to 28 % are due to the fact that the synthesized product contains information from high-temperature spectral bands (B07-B09 from ASTER), while the reference product (B10 from Landsat 8) does not contain such information. Technology implementation examples show that cross-calibration of the synthesized product can be performed during the year from March to October according to reference thermal images of natural or artificial objects. Objects selected for calibration must have stable thermal characteristics at the time of the satellite flight during the data acquisition period. Keywords: land surface temperature, brightness temperature, space resolution of imagery, multiply linear regression, heterogeneous multispectral data coupling, data providing rate, product cross-calibration, Google Earth Engine.

Impacts of Urban Canopy on Two Convective Storms With Contrasting Synoptic Conditions Over Nanjing, China

AbstractDiverse urban‐induced rainfall anomalies highlight the need for improved understanding on extreme rainfall in cities. In this study, we examine urban modification of rainfall over Nanjing, China. Our results are based on climatological analyses of hourly rainfall observations and high‐resolution Weather Research and Forecasting model simulations coupled with different urban physics schemes. A gridded dataset of urban canopy parameters (UCPs) was developed to better characterize the geometrical features of downtown Nanjing. Two convective storms were investigated to shed light on the impacts of urban canopy on spatial and temporal rainfall variabilities for storms with contrasting synoptic conditions. We show that the model simulations coupled with the multi‐layer urban physics scheme and the gridded UCPs can noticeably reduce biases in surface thermal and dynamic fields, but its performance in rainfall patterns varies with storm events. There is a strong convergence zone over the urban‐rural interface induced by building complexes, leading to intensified convection for the storm with strong synoptic conditions but bifurcated moisture fluxes for the storm with weak synoptic conditions. Lagrangian analysis of storm elements further illustrates the role of urban canopy in deflecting storm cells approaching the city for the storm under weak synoptic conditions. The magnitudes of positive rainfall anomalies induced by urban canopy range from 60% to 100% of the storm‐total rainfall. Our study highlights the necessity of improved characterization of urban canopy and the perturbed atmospheric boundary layer processes in examining urban convective rainfall.

3D Thermal Monitoring of Jointed Rock Masses through Infrared Thermography and Photogrammetry

The study of strain effects in thermally-forced rock masses has gathered growing interest from engineering geology researchers in the last decade. In this framework, digital photogrammetry and infrared thermography have become two of the most exploited remote surveying techniques in engineering geology applications because they can provide useful information concerning geomechanical and thermal conditions of these complex natural systems where the mechanical role of joints cannot be neglected. In this paper, a methodology is proposed for generating point clouds of rock masses prone to failure, combining the high geometric accuracy of RGB optical images and the thermal information derived by infrared thermography surveys. Multiple 3D thermal point clouds and a high-resolution RGB point cloud were separately generated and co-registered by acquiring thermograms at different times of the day and in different seasons using commercial software for Structure from Motion and point cloud analysis. Temperature attributes of thermal point clouds were merged with the reference high-resolution optical point cloud to obtain a composite 3D model storing accurate geometric information and multitemporal surface temperature distributions. The quality of merged point clouds was evaluated by comparing temperature distributions derived by 2D thermograms and 3D thermal models, with a view to estimating their accuracy in describing surface thermal fields. Moreover, a preliminary attempt was made to test the feasibility of this approach in investigating the thermal behavior of complex natural systems such as jointed rock masses by analyzing the spatial distribution and temporal evolution of surface temperature ranges under different climatic conditions. The obtained results show that despite the low resolution of the IR sensor, the geometric accuracy and the correspondence between 2D and 3D temperature measurements are high enough to consider 3D thermal point clouds suitable to describe surface temperature distributions and adequate for monitoring purposes of jointed rock mass.

Monitoring thermal field, humidity field and energy balance over heterogeneous surfaces in the typical valley-city

Land use and land cover (LULC) alteration has changed original energy balance and heat fluxes between land and atmosphere, and thus affects the structure characteristics of temperature and humidity fields over urban heterogeneous surfaces in different spatio-temporal scales. Lanzhou is the most typical river valley city of China, it is chosen as the case study. Typical river valley terrain, rapid urbanization and severe air pollution have caused unique urban climate and urban heat island (UHI) effects in Lanzhou. Firstly, the spatial structure characteristics and dynamic evolution of temperature and humidity fields in autumn are simulated by mobile measurement experiment and GIS spatial analysis method. The results show that temperature and humidity fields have significant dynamic change within a day, and have multiple center and multiple intensity level characteristics. Then, LULC and normalized difference vegetation index (NDVI) are extracted from remote sensing images, the distribution patterns of temperature and humidity fields have close relationships with LULC and NDVI. Moreover, there is a significant positive correlation between impervious surface area and thermal field intensity. A positive correlation between NDVI value and humidity field intensity has been found as well as a negative correlation between NDVI value and thermal field intensity. Finally, heat fluxes and energy balance characteristics between ground and atmosphere are analyzed based on the Bowen-ratio System experiments. This study could provide theoretical support and practical guidance for urban planning, urban eco-environment construction and air pollution prevention of river valley city.

Three-dimensional-imaging thermal surfaces of coal fires based on UAV thermal infrared data

ABSTRACT The quick and precise location of the burning zones of coal fires, which are continuously burning in abandoned coal mines worldwide, has long been a technical problem. The unmanned aerial vehicle (UAV) can reduce field work intensity, improve data collection efficiency, and ensure high accuracy at low cost. In order to visualize the distribution of burning points of coal fires, the UAV-based thermal infrared oblique photography is adopted. A 4-step 3D thermal imaging method is proposed in which the processing of thermal images is the most crucial. Furthermore, a software program is developed to improve the contrast and quality of batches of thermal images in one-click as well as to unify the temperature level and scale in each thermal image. This methodology is implemented in the Maoergou coal fires in China to reconstruct the surface thermal field in genuine 3D. The high-temperature zones are illustrated clearly in the 3D thermal model. The results indicate that this methodology can be used as a tool for the delineation of coal fires and other types of thermal anomaly scenario.

Permeability and voids influence on the thermal signal, as inferred by multitemporal UAV-based infrared and visible images

This work presents for the first time associated thermal anomalies and deformations over subsurface cavities/voids located within two harbour quays in Le Havre Harbourg, Normandy, France. An U.A.V. (Unmanned Aerial Vehicle) was used to acquire visible and thermal images over a diurnal cycle (from 7 a.m. to 5 p.m.). The visible images were processed to realize an altimetric model of the platforms by mean of the photogrammetric method, while the thermal infrared (TIR) images were used to study the evolution of their surface temperatures. The obtained 3D model shows the location of five topographic depressions on both quays. The analysis of the evolution of the surface thermal field leads to the detection of cold thermal anomalies that are (1) not correlated to surface properties, and (2) spatially associated to the flanks of the five topographic depressions. Using a 2D conductive-radiative model, we show that these anomalies are not directly due to the thermally insulating effect of an air-filled area. Finally, we conclude that preferential infiltration and subsequent evaporation in the micro-fracturation present within the flanks of the depressions may be responsible for the strong cooling of these zones.

Surface Temperature Multiscale Monitoring by Thermal Infrared Satellite and Ground Images at Campi Flegrei Volcanic Area (Italy)

Land Surface Temperature (LST) from satellite data is a key component in many aspects of environmental research. In volcanic areas, LST is used to detect ground thermal anomalies providing a supplementary tool to monitor the activity status of a particular volcano. In this work, we describe a procedure aimed at identifying spatial thermal anomalies in thermal infrared (TIR) satellite frames which are corrected for the seasonal influence by using TIR images from ground stations. The procedure was applied to the volcanic area of Campi Flegrei (Italy) using TIR ASTER and Landsat 8 satellite imagery and TIR ground images acquired from the Thermal Infrared volcanic surveillance Network (TIRNet) (INGV, Osservatorio Vesuviano). The continuous TIRNet time-series images were processed to evaluate the seasonal component which was used to correct the surface temperatures estimated by the satellite’s discrete data. The results showed a good correspondence between de-seasoned time series of surface ground temperatures and satellite temperatures. The seasonal correction of satellite surface temperatures allows monitoring of the surface thermal field to be extended to all the satellite frames, covering a wide portion of Campi Flegrei volcanic area.

Craters forming mechanism of high speed steel irradiated by intense pulsed ion beam

Intense pulsed ion beam (IPIB) is regarded as a material surface treatment technology due to its energy compression in temporal and spatial scales. However, the craters induced by IPIB irradiation limit its application. Therefore, the study about the forming mechanism of craters is crucial for the development of this technology. In this work, craters on the surface of high speed steel after IPIB irradiation were studied. The analysis revealed that the inclusions in steel was contributed to crater formation. It was found that the feature of inclusions in steel determined the topography of craters on material surface directly. The surface thermal field simulation showed that the inclusions will be vaporized prior to adjacent matrix. Partial evaporization of inclusions have been certified to drive the melt flow forming craters. The result is useful to understand the forming mechanism of a sort of craters induced by IPIB on steel surface.

Flying Laser Spot Thermography technique for the NDE of Fibre Metal Laminates disbonds

The present work investigates the features of an active Infrared-NDT Thermography technique derived from a Flying Laser Spot set-up for the analysis of interlaminar disbonds in layered structures in general and Fibre Metal Laminates in particular. The presented technique uses a laser-spot heat source, which moves at a constant speed, raster scanning the object surface. Interlaminar defects parallel to the surfaces act as barriers towards through-the-thickness heat diffusion. This produces some modifications over the surface thermal field which are well identified in the Standard Deviation calculated over a Reference Area following the heat source. The mechanisms leading to such defect signature are investigated in this work by means of Finite Element Analyses which model the dynamic thermal problem on a GLARE sample with triangular disbond defects at inner interfaces. An extended number of parameters is changed to study their influence on the defect signature, and the FEA analysis is also compared to an analytical and an experimental case studies for further validation.

Optical diagnostics of selective laser melting and monitoring of single-track formation

The article presents the optical diagnostics results of the selective laser melting process of single-track production. The track defects detection (such as balling effect, powder free zone formation, sparking) was shown, as well as the visualization of the independent particles consolidation in a solid track. The metal evaporation and the formation of the melt pool specific gas dynamic conditions were considered as important physical phenomena. The velocities of the particle emission from the melt pool, the rate of their involvement, and the velocity of the gas flow were estimated. The results make it possible to evaluate the kinetics of mass transfer under selective laser melting process. The surface thermal field of the laser-irradiated zone strongly influences the material qualitative characteristics after selective laser melting. The results becomes the basis for the development of optical monitoring and diagnostic systems for laser additive manufacturing processes based on the melt pool temperature online controlling.

Dynamics of surface urban biophysical compositions and its impact on land surface thermal field

Urban heat effects over Abeokuta city, Nigeria have raised interests by relevant scientific communities owing to the recent infrastructural and economic growth of the area. In this paper, the surface temperatures and land surface biophysical types retrieved from Landsat TM, and ETM+images of Abeokuta city for 1984, 2003 and 2014 were analyzed. The images acquired were classified into appropriate land cover types using supervised classification schemes and a change detection analysis was carried out on the classified imageries using land change modeller (LCM) to evaluate the extent of modification of surface features. A quantitative approach was used to explore the relationships among temperature, surface biophysical components and spectral indices. Results showed that impervious surface and water areas were found to be correlated positively with high temperatures. Conversely, vegetated areas and bare surfaces correlated positively with mid temperature zones. The overall metrics error between the regression-modeled LST and the retrieved LST for the study area is quite low, between 2.63 °C for root mean square error (RMSE) and 2.17 °C for mean absolute error (MAE). This study concluded that, areas with increasing built-up surfaces and surface reflectivity will bring about LST rise, and consequently leads to urban heat island development.

Pore-scale study of thermal fields during evaporation from drying porous surfaces

The drying of a porous surface and subsequent pore emptying resemble a sequence of drainage whereby pores are invaded according to their respective capillary size (large pores are invaded first). The emptying of pores modifies both the local evaporative fluxes and surface thermal fields adjacent to invaded pores. These local adjustments could result in a gradual decrease in evaporation rate and a potential increase in surface temperature thereby altering energy partitioning over the drying surface as described by the Pore-scale Coupled Energy Balance (PCEB) model of Aminzadeh and Or (2014). This study aims to observe and quantify these dynamic pore-scale mass and energy interactions to test key assumptions in the basis of the PCEB model and gain new insights into these important processes. We used a novel experimental system consisting of individual and clustered evaporating pores drilled into rough glass surfaces. Thermal fields around individual evaporating pores and their interactions were observed using highly resolved infrared imager under different radiative fluxes. Thermal observations and direct measurements of evaporative fluxes were in good agreement with predictions by the PCEB model. Drying of a glass beads surface was captured by optical and thermal imaging to provide links between pore emptying sequence and surface thermal adjustments. The results highlight the upscalability of pore-based representation of surface drying and the predictability of energy partitioning over drying porous surfaces.

Thermal field analysis of polymer/silica hybrid waveguide thermo-optic switch

The thermal field and the temperature change of the optical waveguide core of thermo-optic (TO) switch generated by heating the Al electrode are simulated using the finite-element method (FEM), and the steady-state temperature distribution and time response of TO switch are presented. Our research covers several conditions, including different electrode heater widths, upper cladding layer thicknesses, under cladding layer materials and different structures. The results turn out that the performance of the TO switch can be improved using the polymer/silica hybrid and the air trench waveguide structures. The TO switch was fabricated and the surface thermal field distribution was measured. A good agreement between the experimental results and theory analysis has been observed.

Application of CFD to Building Thermal Control Analysis

Building-integrated photovoltaic system is to import a photovoltaic panel system into the shell structure of a building by using building design techniques, so that the system constituents not only generate power, but are also a part of the building’s shell. If the photovoltaic panel is integrated with a sun shield, a power benefit could be obtained and both solar irradiation and the cooling load could be reduced. This study aimed to use CFD technology for analysis of building surface thermal control and flow field simulation, and further discuss the effects of the relative position of the sun and atmospheric wind flow field on the distribution of building surface temperatures and flow fields at different hours and in different seasons. Understanding the sun's position and other climatic conditions accurately is helpful for locating solar panels and solar collectors on buildings.

Effect of Porthole Design and Welding Chamber Dimensions on Material Flow and Weld Deformability of Extruded Aluminium Profiles

Aim of the work is to investigate different strategies in balancing material flow during direct extrusion through porthole dies. Two AA6082 hollow profiles were simultaneously extruded by a single die with different portholes extrusion ratio, dissimilar welding chambers and different bearing lengths. A strict process control was realized by measuring thermal conditions in the die by means of 6 thermocouples and on the profiles by a self calibrating pyrometer for aluminum alloy applications. Several billets were extruded at different ram speeds (2 to 7 mm/sec) and the effect of die design on surface quality, profile lengths and thermal field was recorded. The profiles were then sectioned and the position of the seam welds in the profiles identified and compared also with the profiles tip.

Plume-induced dynamic instabilities near cratonic blocks: Implications for P–T–t paths and metallogeny

Plume head–lithosphere interactions around cratonic blocks result in thermo-mechanical disturbances that lead to heating and burial phases of crustal rocks. We present results from numerical models of plume head–cratonic blocks interactions where a free upper surface condition and realistic rheologies are accounted for. These models include distinct cratonic blocks embedded within a continental lithosphere and separated by several hundreds of kilometers. Surface topography, thermal field and effective viscosity values are tracked for 20Myr of interactions. The modeled dynamic interaction of a plume head around cratonic blocks results in two main types of instabilities, each of them resulting in a distinct P–T–t path. The “slab-like” instability, focused on cratonic edges when plume head is away from the craton center, shows a near-isothermal burial phase, while the “drip-like” instability occurring above plume head material results in a near-isobaric heating phase. Consequently, both clockwise and counterclockwise P–T–t paths can be expected around cratons, as actually observed around the Tanzanian craton and other cratonic areas. Metallogenic data from gemstone-bearing rocks in south-east Africa and data from ultrahigh temperature and ultrahigh pressure metamorphism are compatible with our model. It appears that vertical mantle dynamics around cratons may also explain thermobarometric signatures that are often attributed to horizontal tectonics.

A Remote-Sensing Method of Selecting Reference Stations for Evaluating Urbanization Effect on Surface Air Temperature Trends

Abstract In the global lands, the bias of urbanization effects still exits in the surface air temperature series of many city weather stations to a certain extent. Reliable reference climate stations need to be selected for the detection and correction of the local manmade warming bias. The underlying image data of remote sensing retrieval is adopted in this study to obtain the spatial distribution of surface brightness temperature, and the surface air temperature reference stations are determined based on the locations of the weather stations in the remote sensing surface thermal fields. Among the 672 national reference climate stations and national basic weather stations of mainland China, for instance, 113 surface air temperature reference stations are selected for applying this method. Compared with the average surface air temperature series of the reference stations obtained by a more sophisticated method developed in China, this method is proven to be robust and applicable, and can be adopted for the evaluation and adjustment study on the urbanization bias of the currently used air temperature records of surface climate stations in the global lands.