Strong Scale Effect Research Articles

Application of CFD on VIM of semi-submersible FOWT: A Case Study

This study examines the Vortex Induced Motions (VIM) of the INO WINDMOOR 12 MW semi-submersible Floating Offshore Wind Turbine (FOWT) platform using three-dimensional Computational Fluid Dynamics (CFD). The results from both model- and full-scale simulations are presented. The model scale results reveal varying VIM performances at different current headings, with detailed flow visualizations and analyses of hydrodynamic loads on FOWT components providing insights into the underlying wake interaction scenarios. One simulation shows bifurcated VIM, where regular motions are intermittently interrupted due to simultaneous suppression of vortex shedding on all FOWT columns. Preliminary full-scale CFD results suggest a strong scale effect. The paper concludes with a discussion on how CFD simulation can be more effectively used in VIM research.

Laboratory investigation of scale effects in bursting failure of quasi-brittle materials

Understanding the scale effect in the behavior of solid materials is important when small-scale models are used to predict the behavior of real structures. Tremendous efforts have been devoted to investigating the scale effect in the strength of quasi-brittle materials. However, limited studies have focused on the whether there is a scale effect in bursting failure, which is a typical failure pattern of quasi-brittle structures. Here, we conduct a series of unconfined compression tests on coal samples using a specialized designed loading machine to produce bursting failure in the laboratory. We use cubic coal samples with a large range of sizes from 50 to 300 mm to investigate the scale effect in bursting failure of quasi-brittle materials. We use acoustic emission technology to monitor microcreaking within the samples and a high-speed camera to capture the bursting failure process. We demonstrate that there is a strong scale effect in bursting failure of quasi-brittle materials in terms of mechanical properties including compressive strength and deformability, strain energy density, bursting severity, and precursor time. We found that ejection of localized pieces from the skin of the structure is a precursor of catastrophic bursting failure of quasi-brittle materials. We conclude that the relationship between the precursor time (T) and structure size (M) of bursting failure is logarithmic and can be described as logT = a + bM where a and b are constants. This relationship provides a guideline when models obtained from laboratory tests are used to predict strength and behavior at the intermediate (mines and rock slopes) and large scales (earthquakes).

The coordinated impact of forest internal structural complexity and tree species diversity on forest productivity across forest biomes

Forest structural complexity can mediate the light and water distribution within forest canopies, and has a direct impact on forest biodiversity and carbon storage capability. It is believed that increases in forest structural complexity can enhance tree species diversity and forest productivity, but inconsistent relationships among them have been reported. Here, we quantified forest structural complexity in three aspects (i.e., horizontal, vertical, and internal structural complexity) from unmanned aerial vehicle light detection and ranging data, and investigated their correlations with tree species diversity and forest productivity by incorporating field measurements in three forest biomes with large latitude gradients in China. Our results show that internal structural complexity had a stronger correlation (correlation coefficient = 0.85) with tree species richness than horizontal structural complexity (correlation coefficient = -0.16) and vertical structural complexity (correlation coefficient = 0.61), and it was the only forest structural complexity attribute having significant correlations with both tree species richness and tree species evenness. A strong scale effect was observed in the correlations among forest structural complexity, tree species diversity, and forest productivity. Moreover, forest internal structural complexity had a tight positive coordinated contribution with tree species diversity to forest productivity through structure equation model analysis, while horizontal and vertical structural complexity attributes have insignificant or weaker coordinated effects than internal structural complexity, which indicated that the neglect of forest internal structural complexity might partially lead to the current inconsistent observations among forest structural complexity, tree species diversity, and forest productivity. The results of this study can provide a new angle to understand the observed inconsistent correlations among forest structural complexity, tree species diversity, and forest productivity.

Assessing energy resilience and its greenhouse effect: A global perspective

A sound and resilient global energy system can effectively guarantee normal production and green research and development activities, which have uncertain global greenhouse effect. Thus, to accurately investigate the potential impact of energy resilience on carbon dioxide (CO2) emissions, we first construct an energy resilience composite index based on three components (i.e., energy access, renewable energy, and energy efficiency) by employing cross-sectional data of 107 countries in 2016. Then, to explore the internal impact mechanism in the energy resilience-CO2 nexus, we divide the total effect of energy resilience on CO2 emissions into three effects: scale effect, technical effect, and composition effect. The main findings of this study show that: (1) increased energy resilience across the globe is positively associated with CO2 emissions, and three sub-indexes of energy resilience (i.e., energy access, renewable energy, and energy efficiency) affect greenhouse effect positively; (2) strong energy resilience and CO2 emissions show significant asymmetric and regional heterogeneous relationships; and (3) the positive energy resilience-CO2 nexus stems from the fact that the negative technical and composition effects of energy resilience on CO2 emissions are fully offset by the strong positive scale effect. Following the above conclusions, we propose several policy implications of strengthening energy resilience and mitigating the greenhouse effect.

Photogrammetric Prediction of Rock Fracture Properties and Validation with Metric Shear Tests

An accurate understanding of jointed rock mass behavior is important in many applications ranging from deep geological disposal of nuclear waste, to deep mining, and to urban geoengineering projects. The roughness of rock fractures and the matching of the fracture surfaces are the key contributors to the shear strength of rock fractures. In this research, push shear tests with three normal stress levels of 3.6, 6.0, and 8.5 kPa were conducted on two granite samples with artificially induced well-matching tensile fractures with sizes of 500 mm × 250 mm and 1000 mm × 500 mm. The large sample reached on average a −60% weaker peak shear stress than the medium-sized sample, and a strong negative scale effect was observed in the peak shear strength. The roughness of the surfaces was measured using a profilometer and photogrammetry. The scale-corrected profilometer-based method (joint roughness coefficient, JRC) underestimates the peak friction angle for the medium-sized slabs by −27% for the medium sample and −9% for the large sample. The photogrammetry-based (Z′2) method produces an estimate with −7% (medium) and + 12% (large) errors. The photogrammetry-based Z′2 is an objective method that consistently produces usable estimates for the JRC and peak friction angle.

Dynamics of Space-Fractional Euler–Bernoulli and Timoshenko Beams

This paper investigates the dynamics of the beam-like structures whose response manifests a strong scale effect. The space-Fractional Euler–Bernoulli beam (s-FEBB) and space-Fractional Timoshenko beam (s-FTB) models, which are suitable for small-scale slender beams and small-scale thick beams, respectively, have been extended to a dynamic case. The study provides appropriate governing equations, numerical approximation, detailed analysis of free vibration, and experimental validation. The parametric study presents the influence of non-locality parameters on the frequencies and shape of modes delivering a depth insight into a dynamic response of small scale beams. The comparison of the s-FEBB and s-FTB models determines the applicability limit of s-FEBB and indicates that the model (also the classical one) without shear effect and rotational inertia can only be applied to beams significantly slender than in a static case. Furthermore, the validation has confirmed that the fractional beam model exhibits very good agreement with the experimental results existing in the literature—for both the static and the dynamic cases. Moreover, it has been proven that for fractional beams it is possible to establish constant parameters of non-locality related to the material and its microstructure, independent of beam geometry, the boundary conditions, and the type of analysis (with or without inertial forces).

Enhanced scaling effects significantly lower the ability of MODIS normalized difference snow index to estimate fractional and binary snow cover on the Tibetan Plateau

MODIS fractional (FSC) and binary (BSC) snow-cover data are important for obtaining accurate spatiotemporal snow-cover information for the Tibetan Plateau (TP) where rapid warming is closely related to snow-cover changes. However, FSC and BSC data are no longer provided in the newly released version (v6) of the MODIS snow cover product, having been replaced with normalized difference snow index (NDSI) data. Recent studies have observed clearly lower accuracy of MODIS snow cover data on the TP than in other areas, possibly implying that there are strong scaling effects due to the complex terrain and land cover which are not well understood. A total of 353 Landsat-8 scenes covering most parts of the TP are used to establish a new empirical relationship between FSC and MODIS NDSI for FSC estimation and a new NDSI threshold for BSC estimation. The results indicate that the new regression model (mean root-mean-squared-deviation (RMSD): 0.22) has a better FSC estimation accuracy than the previously used global reference equation (mean RMSD: 0.24) and that the new NDSI threshold of 0.29 (mean Cohen’s Kappa (CK): 0.49) outperforms the global reference NDSI threshold of 0.4 (mean CK: 0.40) in BSC estimation. The relatively low accuracy could be due to an enhanced scaling effect. The 30-m Landsat-8 NDSI data are upscaled to 500-m (MODIS) to analyze the scaling effects on FSC and BSC estimates made using MODIS NDSI. We find that the methods using MODIS NDSI have much lower estimation accuracy, for both FSC and BSC, compared with those using upscaled Landsat-8 NDSI. An analysis of variance (ANOVA) test which considers 512 combinations of aspect, slope and normalized difference vegetation index (NDVI) further demonstrates that the enhanced scaling effects are mainly caused by terrain factors (i.e. aspect and slope). The optimal NDSI threshold for estimating BSC generally increases with slope and decreases as the aspect varies from the southeast to northwest. This study has important implications for the optimal use of MODIS NDSI snow cover data on the TP and highlights the importance of developing more advanced methods which take more factors into account.

Issues of financial liquidity of small and medium-sized trading companies: a case study from Poland

Most often, the victims of financial crises are small and medium-sized enterprises. Very often, even short-term payment gridlocks can lead to their bankruptcy. All over the world, managers of such enterprises are trying to introduce solutions that will improve their financial security. Branch group purchasing organizations (GPOs) are a very popular method to improve the financial security and financial situation of small and medium enterprises. They are multi-stakeholder organizations using the effect of scale. It allows them to reduce costs, increase sales and gives many opportunities to build a policy of managing liquidity. The purpose of the article is to present the impact of branch GPOs on the financial liquidity of small and medium-sized enterprises. The research was conducted on a group of 96 Polish small and medium-sized commercial enterprises operating in the construction industry. The study showed that the analyzed units do not have problems with financial liquidity, due to the use of a strong scale effect.

Identifying dominant factors of waterlogging events in metropolitan coastal cities: The case study of Guangzhou, China

Urban waterlogging disasters are affected by environmental conditions and human activities. Previous studies had explored the effect of land-use type on waterlogging in relatively small watersheds. Few, however, have comprehensively revealed the relative contributions of the environmental and anthropogenic factors to urban waterlogging concerning different scales of analysis. Indeed what is less known, are the dominant factors and the appropriate scale of analysis. To overcome this limitation, a novel method that integrates the stepwise regression model with hierarchical partitioning analysis is presented. The purpose is to investigate the complex mechanism of urban waterlogging by identifying the relative contribution of each environmental and anthropogenic factor and the stability linking waterlogging to influencing factors at multiple scales of analysis (i.e. 1 km, 2 km, 3 km, 4 km, and 5 km). We consider waterlogging events in the central urban districts of Guangzhou (PR China) from 2009 to 2015 as a case study. The results show that the spatial distribution of waterlogging events in the central urban area presents a strong agglomeration pattern. The waterlogging hot spots are mainly concentrated in the historical area of Guangzhou. Under all analysis scales, we find that the percent cover of urban green spaces (44.74%), percent cover of residential area (41.03%), and slope.std (36.85%) both have a dominant contribution to urban waterlogging, which suggests the importance of land cover composition in determining urban waterlogging. However, the relative contribution and dominant factors of waterlogging varied across different analysis scales, presenting a strong scale effect. Under a small analysis scale (1 km), the topography factors (slope.std and relative elevation) are confirmed as the dominant variables; however, with the increase of analysis scale, the influence of land cover composition (greenspace, residence area, grassland) and land cover spatial configuration (LPI, AI, Cohesion index) on waterlogging magnitude is greater than other factors. This finding provides additional insights that the urban waterlogging can be alleviated by balancing the relative composition of land cover features as well as by optimizing their spatial configuration. Since the optimal statistical scale for urban waterlogging studies only worked for specific influencing factors, the appropriate analysis scale for urban waterlogging study should be determined by the characteristics of study areas. This study has the capability to extend our scientific understanding of the complex mechanisms of waterlogging in the highly urbanized coastal city, providing useful support for the prevention and management of urban waterlogging.

Length-scale dominated thermal fatigue behavior in nanocrystalline Au interconnect lines

Thermal fatigue behavior of nanocrystalline Au lines with different thicknesses (50, 100, and 200 nm) and line widths (5, 10, and 15 µm) was investigated by applying alternating current to generate thermal cyclic stain. The thermal fatigue life was found to show a strong scale effect, i.e., thinner films had higher thermal fatigue resistance and sustained higher temperature oscillation. However, no obvious line width effect was found. Besides, the thermal fatigue damage behavior also shows evident dependence on the line thickness and the applied strain range. A thermal fatigue mechanism map of nanocrystalline films is proposed based on the experimental evidence and theoretical evaluation. Atom diffusion and dislocation activity were found to be two important mechanisms in thermal fatigue, and atom diffusion is the main factor to control the fatigue failure.

Micromechanical analysis of sand production

SummaryWe present a micromechanical approach based on zero‐thickness interface elements for modelling advanced localization and cracking states of cemented granular materials, such as reservoir sandstones. The proposed methodology is capable of reproducing the complex behaviour of intergranular and intragranular localization, cracking, and fracturing of rock formation that leads to sanding in hydrocarbon production. The model is calibrated at the macroscale, using only a few physical parameters, by reproducing the typical behaviour of compression element tests. The model exhibits clear transition behaviour from brittle dilatant to ductile compactant behaviour with increasing confining stress. The methodology is implemented for sand production prediction analysis based on the simulation of 2D micromechanical models of hollow cylinder cross sections. The obtained results are compared well with published experimental data from hollow cylinder tests characterized by strong scale effect in the range of small perforations.

Tradeoffs between US national forest harvest targets and fuel management to reduce wildfire transmission to the wildland urban interface

US public land management agencies are faced with multiple, often conflicting objectives to meet management targets and produce a wide range of ecosystem services expected from public lands. One example is managing the growing wildfire risk to human and ecological values while meeting programmatic harvest targets for economic outputs mandated in agency budgets. Studies examining strategic management tradeoffs on federal lands and program efficiencies are rare. In this study we used the 79 western US national forests to examine tradeoffs between forest management scenarios targeting wildfire risk to the wildland urban interface (WUI) and those meeting agency convertible volume production targets. We quantified production frontiers to measure how the efficiency of meeting harvest volume targets is affected by prioritizing treatments to areas that transmit fire to the WUI. The results showed strong tradeoffs and scale effects on production frontiers, and more importantly substantial variation among planning areas and national forests. Prioritizing treatments to reduce fire transmission to the WUI resulted in an average harvest volume reduction of about 248 m3 per ha treated. The analysis also identified opportunities where both management objectives can be achieved. This work represents the first large-scale tradeoff analysis for key management goals in forest and fuel management programs on national forests.

Uncertainty in the effects of the modifiable areal unit problem under different levels of spatial autocorrelation: a simulation study

ABSTRACTThe objective of this paper is to investigate uncertainties surrounding relationships between spatial autocorrelation (SA) and the modifiable areal unit problem (MAUP) with an extensive simulation experiment. Especially, this paper aims to explore how differently the MAUP behaves for the level of SA focusing on how the initial level of SA at the finest spatial scale makes a significant difference to the MAUP effects on the sample statistics such as means, variances, and Moran coefficients (MCs). The simulation experiment utilizes a random spatial aggregation (RSA) procedure and adopts Moran spatial eigenvectors to simulate different SA levels. The main findings are as follows. First, there are no substantive MAUP effects for means. However, the initial level of SA plays a role for the zoning effect, especially when extreme positive SA is present. Second, there is a clear and strong scale effect for the variances. However, the initial SA level plays a non-negligible role in how this scale effect deploys. Third, the initial SA level plays a crucial role in the nature and extent of the MAUP effects on MCs. A regression analysis confirms that the initial SA level makes a substantial difference to the variability of the MAUP effects.

Spatial patterns in natural Picea crassifolia forests of northwestern China, as basis for close-to-nature forestry

Close-to-nature forest management has been proposed as an effective method for improving the quality of plantation forests. Knowledge of spatial distribution patterns, structure, and succession trajectories in natural forests can provide guidelines for the establishment of close-to-nature forest plantations. Such knowledge is lacking in natural spruce (Picea crassifolia) forests in the Qilian Mountains of China, impeding the establishment of production forests. We conducted a case study in the Qilian Mountains to analyze the relationships between the naturally-formed forest patches and terrain factors, spatial heterogeneity of stand characteristics, and stand structure following harvesting disturbance. Our results suggested that spruce plantations will be effective on the N, NE, and NW slopes, at elevations between 2700 and 3300 m, and on slopes ranging from 15° to 45°. Further, planted forest patches should occupy 64% of the slope area on semi-shady slopes (NE, NW). Spatial patterns in the studied forest exhibited a strong scale-effect, and an area of 0.25 ha could be used as the most efficient plot scale for the management of spruce plantations. Partial logging is an effective method for the conversion of spruce planted forests into nearnatural forests, and the intensity of partial logging can be determined from the negative exponential function relationship between stand density and DBH. Our results provided critical information for the development of spruce plantations and conversion of existing plantations.

Identification of mechanical properties of 1D deteriorated non-local bodies

Deterioration, understood as a change of mechanical properties of devices exhibiting a strong scale effect, is a phenomenon of great importance in modern industry. This effect is simultaneously an open question in theoretical mechanics, due to the fact that none of existing non-local theories (which are necessary to describe the scale effect) seem to be universal - thus constant development of new mathematical models is necessary. This paper presents the study of the above emphasised problem in the framework of fractional continuum mechanics, as an optimization (identification) task. In the identification routine, the steering parameters are: density of material, order of material, and material length scale.

Life Cycle Assessment of hydrogen transport and distribution options

Renewably produced hydrogen offers a solution for mobility via fuel cell electric vehicles without emissions during driving. However, the hydrogen supply chain, from hydrogen production to the fueling station – incorporating seasonal storage and transport – varies in economic and environmental aspects depending on the technology used, as well as individual conditions, such as the distance between production and demand. Previous studies have focused on the economic aspects of varying technologies and elaborated application areas of each technology, while environmental issues were not specifically considered. To address this shortcoming, this paper presents a life cycle assessment of three supply chain architectures: (a) Liquid Organic Hydrogen Carriers (LOHCs hereinafter) for transport and storage; as well as (b) compressed hydrogen storage in salt caverns, together with pipelines; and (c) pressurized gas truck transport. The results of this study show that the pipeline solution has the least environmental impact with respect to most of the impact categories for all analyzed cases. Only for short distances, i.e., 100 km, is truck transport better in a few impact categories. When considering truck transport scenarios, LOHCs have higher environmental impacts than pressurized gas in seven out of 14 impact categories. Nevertheless, for longer distances, the difference is decreasing. The seasonal storage of hydrogen has almost no environmental influence, independent of the impact category, transport distance or hydrogen demand. In particular, strong scaling effects underlie the good performance of pipeline networks.

Tudy on the Scale Effect of Nan scale Indentation on Yield Strength and Modulus of Elasticity

In recent decades, many micromechanics experiments have proved that the mechanical behavior of metal materials at the scale of micron or submicron scale is quite different from that of materials under macroscopic scale (above millimeter order). When the characteristic length of the no uniform plastic deformation reaches the magnitude of micrometer or submicron, the material will show a very strong scale effect. In this paper, we mainly study the scale effect of the two parameters, the yield strength and the modulus of elasticity, which are very important in the mechanical constitutive equation. The scale effect of yield strength can be studied by using the H-P formula. With the further research, it is found that the modulus of elasticity have obvious scale effect.

Tudy on the Scale Effect of Nan scale Indentation on Yield Strength and Modulus of Elasticity

In recent decades, many micromechanics experiments have proved that the mechanical behavior of metal materials at the scale of micron or submicron scale is quite different from that of materials under macroscopic scale (above millimeter order). When the characteristic length of the no uniform plastic deformation reaches the magnitude of micrometer or submicron, the material will show a very strong scale effect. In this paper, we mainly study the scale effect of the two parameters, the yield strength and the modulus of elasticity, which are very important in the mechanical constitutive equation. The scale effect of yield strength can be studied by using the H-P formula. With the further research, it is found that the modulus of elasticity have obvious scale effect.

A Model for the Characterization of the Polarizability of Thin Films Independently of the Thickness of the Film.

The dielectric properties of thin films can be modified relative to the bulk material because the interaction between film and substrate influences the mobility of the atoms or molecules in the first layers. Here we show that a strong scale effect occurs in nanometer size octadecylammine thin films. This effect is attributed to the different distribution of molecules depending on the size of the film. To accurately describe this effect, we have developed a model which is a reinterpretation of the linearized Thomas-Fermi approximation. Within this model, we have been able to characterize the polarizability of thin films independently of the thickness of the film.

Stochastic analysis of the efficiency of coupled hydraulic-physical barriers to contain solute plumes in highly heterogeneous aquifers

The expected long-term efficiency of vertical cutoff walls coupled to pump-and-treat technologies to contain solute plumes in highly heterogeneous aquifers was analyzed. A well-characterized case study in Italy, with a hydrogeological database of 471 results from hydraulic tests performed on the aquifer and the surrounding 2-km-long cement-bentonite (CB) walls, was used to build a conceptual model and assess a representative remediation site adopting coupled technologies. In the studied area, the aquifer hydraulic conductivity Ka [m/d] is log-normally distributed with mean E(Ya)=0.32, variance σYa2=6.36 (Ya=lnKa) and spatial correlation well described by an exponential isotropic variogram with integral scale less than 1/12 the domain size. The hardened CB wall’s hydraulic conductivity, Kw [m/d], displayed strong scaling effects and a lognormal distribution with mean E(Yw)=-3.43 and σYw2=0.53 (Yw=log10Kw). No spatial correlation of Kw was detected. Using this information, conservative transport was simulated across a CB wall in spatially correlated 1-D random Ya fields within a numerical Monte Carlo framework. Multiple scenarios representing different Kw values were tested. A continuous solute source with known concentration and deterministic drains’ discharge rates were assumed. The efficiency of the confining system was measured by the probability of exceedance of concentration over a threshold (C∗) at a control section 10years after the initial solute release. It was found that the stronger the aquifer heterogeneity, the higher the expected efficiency of the confinement system and the lower the likelihood of aquifer pollution. This behavior can be explained because, for the analyzed aquifer conditions, a lower Ka generates more pronounced drawdown in the water table in the proximity of the drain and consequently a higher advective flux towards the confined area, which counteracts diffusive fluxes across the walls. Thus, a higher σYa2 results in a larger amount of low Ka values in the proximity of the drain, and a higher probability of not exceeding C∗.