Wind Loading on Scaled Down Fractal Tree Models of Major Urban Tree Species in Singapore

Estimation of the aerodynamic load on trees is essential for urban tree management to mitigate the risk of tree failure. To assess that in a cost-effective way, scaled down tree models and numerical simulations were utilized. Scaled down tree models reduce the cost of experimental studies and allow the studies to be conducted in a controlled environment, namely in a wind or water tunnel, but the major challenge is to construct a tree model that resembles the real tree. We constructed 3D-printed scaled down fractal tree models of major urban tree species in Singapore using procedural modelling, based on species-specific growth processes and field statistical data gathered through laser scanning of real trees. The tree crowns were modelled to match the optical porosity of real trees. We developed a methodology to model the tree crowns using porous volumes filled with randomized tetrahedral elements. The wind loads acting on the tree models were then measured in the wind tunnel and the velocity profiles from selected models were captured using particle image velocimetry (PIV). The data was then used for the validation of Large Eddy Simulations (LES), in which the trees were modelled via a discretized momentum sink with 10–20 elements in width, height, and depth, respectively. It is observed that the velocity profiles and drag of the simulations and the wind tunnel tests are in reasonable agreement. We hence established a clear relationship between the measured bulk drag on the tree models in the wind tunnel, and the local drag coefficients of the discretized elements in the simulations. Analysis on the bulk drag coefficient also shows that the effect of complex crown shape could be more dominant compared to the frontal optical porosity.

Marble Durability Assessment by Means of Total Optical Porosity and Adjacent Grain Analysis

The presence of pores, cracks and microcracks in marble is one of the main features that govern the processes of decay of this stone material and, although marble is characterised by a modest porosity, there is a clear correlation between the presence and movement of fluids, and the phenomena of alteration. Through the study of porosity, it is possible to better understand the phenomena of alteration and degradation in order to obtain useful information, not only in the field of modern building, but also for the protection and recovery of historical and artistic heritage goods. This study was conducted through the characterisation of parameters directly related with the degree of alteration of the materials: water absorption at atmospheric pressure (EN 13755), open porosity (EN 1936), flexural strength (EN 12372) and bowing (EN 16306 par. 8.2). The physical and mechanical measurements have been compared with the Total Optical Porosity method (TOP) and the Adjacent Grain Analysis (AGA) index (a suggested method to evaluate the marbles’ tendency to bow, in EN 16306 annex C); two different methodologies both based on image analysis. The purpose of this study is to demonstrate the effectiveness, for the assessment of marble durability, of the two techniques of microscopic image analysis, the first correlating to the grain shape and the second to the open porosity index. This was done by comparing the microscopic image analysis results with the physical and mechanical properties, both after artificial ageing and after ten years of natural ageing. The results obtained with the TOP method seem to represent the tendency to decay better than the AGA index. The comparison of image analysis of the thin sections, in different portions of the marble specimens, shows the development of degradation due to atmospheric agents, from the surface to the inside, of naturally aged specimens, confirming recent studies made on different marbles.

Drones and windbreaks

The article presents a possibility of applying the techniques specific to the drones (UAV) in order to estimate the efficiency, and optimize the windbreaks (vegetative barriers, forest curtains).In the first part the article presents a variant of determination of the dynamic and optical porosities of forest protection curtains using one or two drones simultaneously. In the second part, ascertaining some language inaccuracies, it observes that the issue of the efficiency of the forest curtains became a problem of mitigation of wind intensity. Finally, the last proposed application shows that using the drones, you can estimate the protected volumes behind the curtains, basically giving up the optical porosity. In order to achieve these applications, there is an essential condition: records of the magnitude of the wind speed and of the coordinates must not be excessively affected by the wind.

Effect of windbreaks on wind speed reduction and soil protection against wind erosion

Windbreaks form efficient soil protection against wind erosion particularly at the time when soil cover is not protected by the cultivated plant vegetation cover. The objective of this research was to evaluate windbreaks efficiency in terms of wind speed reduction. Wind speed along the windbreaks was measured in the cadastral areas of Dobrovíz and Středokluky (Czech Republic, Central Europe). The measurement was carried out by 4 stations placed at windward side (1 station at the distance of 3 times the height of the windbreak) and at leeward side of the windbreak (3 stations at the distance of 3, 6, and 9 times the height of the windbreak). Each station contained 2 anemometers situated 0.5 and 1 m above surface. The character of windbreak was described by terrestrial photogrammetry method as the value of optical porosity from the photo documentation of the windbreak at the time of field measurement. A significant dependence between the value of optical porosity and efficiency of windbreak emerged from the results. The correlation coefficient between optical porosity and wind speed reduction was in the range of 0.842 to 0.936 (statistical significance more than 95%). A significant effect of windbreak on airflow reduction was proven on the leeward side of windbreak in a belt corresponding to approximately six times the height of the windbreaks depending on the optical porosity and it was expressed by a polynomial equation.

The character of windbreaks and their influence on mitigation of soil erosion

Windbreaks create efficient soil protection against wind erosion particularly at the time when soil cover is not protected by vegetation cover of cultivated plant. The objective of this research was to find correlation between qualitative parameters of windbreaks and their efficiency in terms of wind speed reduction. The wind speed measurement was carried out by 4 stations along windbreak. The station contains 2 anemometers at heights 0.5 and 1 m above the surface. The character of windbreak was described by photogrammetry method as the value of optical porosity from the photo documentation of the windbreak at the time of ambulatory measurement. Important dependency between the value of optical porosity and efficiency of windbreak emerged from the results. An important protective effect of windbreak on soil was proven on the leeward side of the windbreak in the belt corresponding with approximately six times the height of the windbreaks.

Impact of protective shelterbelt microclimate characteristics

Evaluation of microclimate characteristics of a protective shelterbelt in Obelisk enclosure in 2010. Vegetation performs indispensable functions in the landscape. Protective shelterbelts are important landscape elements. Individual interventions to these ecosystems should be made with the intention to increase the retention capacity of the landscape, the biodiversity, and the stability of individual landscape elements and the landscape as a whole. This article presents the results of the measuring of the effect of model forest vegetation in the proximity of Obelisk in the Lednice-Valtice area on the microclimate. The protective shelterbelt, declared as a forest stand, is located in the cadastral area of Lednice, Podivin and Rakvice. A set of weather stations, supplied by AMET- Litschmann and Suchy Velke Bilovice, was used for the measuring. The stations measured wind velocity (m/s), soil temperature in depths of 5 and 10 cm (°C), air temperature (°C), radiation (W.m-2) and precipitation (mm) from January 1 to December 31, 2010. The ImageTool application was used to establish optical porosity, based on photos taken in summer and winter. Optical porosity was established as a ratio of white spots to their total number in a specific section of a photograph. The optical porosity was 5% during the growing season and 23% outside the growing season. These values significantly differ from the optimum values for efficient semi-permeable PS, whose porosity is set to 40-50%.

Quantitative Porosity Studies of Archaeological Ceramics by Petrographic Image Analysis

ABSTRACTPores in archaeological ceramics can form in a number of different ways, and reflect both deliberate choices and uncontrollable factors. Characterizing porosity by digital image analysis of thin sections holds a number of advantages as well as limitations. We present the results of experiments aimed at improving this method, focusing on high-resolution scans of entire thin sections. We examine the reproducibility of pore measurements by petrographic image analysis of ceramic thin sections using laboratory-prepared specimens of clay mixed with sand of known amount and size. We outline protocols for measuring Total Optical Porosity, using the Image-Pro Premier software package. We also briefly discuss use of pore size and pore shape (aspect ratio and roundness) in characterizing archaeological ceramics. While discerning reasons for observed amounts, sizes, and shapes of pores is an extremely complex problem, the quantitative analysis of ceramic porosity is one tool for characterizing a ware and comparing a product to others. The methods outlined here are applied to a case study comparing historic bricks from the Read House in New Castle, Delaware; the porosity studies indicate that different construction campaigns used bricks from different sources.

Thermal comfort properties of Kevlar and Kevlar/wool fabrics

Recent research on ballistic vests has focused on comfort performance by enhancing thermal comfort and moisture management. Kevlar/wool fabric has been developed as a potential material for ballistic vests. This study investigates the thermal comfort properties of woven Kevlar/wool and woven Kevlar ballistic fabrics. In this context, the thermal resistance, water-vapor resistance, moisture management performance, air permeability and optical porosity of 100% Kevlar and Kevlar/wool ballistic fabrics were compared. The effects of fabric physical properties on laboratory-measured thermal comfort were analyzed. This study also presents the fabric bursting strength and tear strength for comparison. Experimental results showed a clear difference in thermal comfort properties of the two fabrics. It was found that Kevlar/wool possesses better moisture management properties and improved mechanical properties than Kevlar fabric.