A CFD Analysis of Wall-Effect Building Groups in a Curved Layout: A Study in Sha Tin, Hong Kong

Hong Kong’s building density is one of the highest in the world. Since ventilation is a key element in sustainable and environmental design, there is a need to evaluate local wind environments of high dense cities such as Hong Kong. In recent years non-standard curvilinear residential buildings that don’t follow conventional rectilinear block structures are becoming increasingly more popular. Though various studies of ventilation conditions of conventionally design buildings have been made, research of non-standard curvilinear building layouts is still limited. Previous research mainly explored rectilinear block-shaped layouts that typically cause a so called ‘Wall-Effect’ by blocking adequate ventilation on street- and mid-levels around buildings. Our paper presents and summarizes the analysis of airflow and ventilation of non-standard curvilinear buildings based on Computational Fluid Dynamics (CFD) simulations. The Flow Simulation of Solidworks has been used as our analysis software tools. Its technology is based upon the use of Cartesian based meshes and solving the Navier-Stokes equations. Nonstandard and curvilinear shaped building arrangements are categorized into various groups and analyzed in respect to their performance of ventilation on street and mid-levels using a case study of high rise buildings in Sha Tin, Hong Kong. Hong Kong’s climate is subtropical warm and humid in summer, subsequently a higher ventilation is needed and building design has to accommodate good airflow around the buildings. Our findings show that curvilinear buildings lead to a more favourable ventilation environment since they have a smaller wind resistance. Non-standard curvilinear designs perform better in terms of general ventilation since the airflow around the buildings is faster and less turbulent. Our simulations present that convex-shaped buildings have a better overall wind environment than concave-shaped ones. We conclude our paper with a classification of various nonstandard curvilinear buildings that offer a general better airflow and ventilation due to their shape. This classification allows designer to understand quickly wind resistance, airflow, and turbulences that a non-standard curvilinear design has on the immediate environment

A novel methodology for architectural wind environment study by integrating CFD simulation, multiple parametric tools and evaluation criteria

Nowadays wind environment research usually requires lots of comparisons of simulations to study influences on wind environment of building shapes and arrangements. This research aims to develop a novel methodology by integrating computational fluid dynamics (CFD) simulation, parametric tools and evaluation criteria. The integration of multiple tools can provide abundant functions and an efficient modelling-simulation-analysis solution for comparison studies. The methodology is consisted of parametric design, CFD simulation method and analysis method. It is further demonstrated in the case study of square form and scattered configuration to study the relationship between influences on winds and building variables through iterative analysis. For square form, the increase of edge length increases the influence, because more winds are obstructed by larger windward surfaces; the increase of rotation angle reduces the influence, because it is easier for winds to flow around non-vertical windward surfaces. For scattered configuration, the increase of building intervals reduces the influences on winds, because it is easier for winds to flow through larger intervals. In summary, the novel methodology provides an accurate and efficient integrated solution for wind environmental studies of contemporary buildings to explore basic laws for architects to improve their design on the early stage

Delay-dependent H∞ control of linear discrete-time systems with an interval-like time-varying delay

The free-weighting-matrix approach is developed to study the H control of linear discrete-time systems with an interval-like time-varying delay. First, a delay- and range-dependent criterion for a given H performance is derived. Second, a memoryless H state-feedback controller is designed based on a performance analysis. Finally, two numerical examples demonstrate the effectiveness of the proposed method and show that both the upper bound and range of an interval-like time-varying delay affect the stability and/or H performance of a system

Delay-dependent stabilization of linear systems with time-varying state and input delays

The integral-inequality method is a new way of tackling the delay-dependent stabilization problem for a linear system with time-varying state and input delays: ẋ(t)=Ax(t)+A1x(t-h1(t))+B1u(t)+B2u(t-h2(t)). In this paper, a new integral inequality for quadratic terms is first established. Then, it is used to obtain a new state- and input-delay-dependent criterion that ensures the stability of the closed-loop system with a memoryless state feedback controller. Finally, some numerical examples are presented to demonstrate that control systems designed based on the criterion are effective, even though neither (A,B1) nor (A+A1,B1) is stabilizable

Remedial role of financial development in corporate investment amid financing constraints and agency costs

The study investigates the role of financial development in boosting the investment efficiency of firms’ investments in China. Using a large sample of firm-level financial data and country level economic data over the period 2004-2015, present study creates a link between financial and real economy. Firms are priori classified into under- or over-invested and effect of financial development is analyzed individually on each classification by using panel data estimations. The research concludes that firms suffering from under- (over-) investment problem due to financing constraints (agency problem), are more likely to increase (decrease) their investment` in the response of underlying financial development in the economy. This study has demonstrated a novel approach by concurrently incorporating the monitoring and financing issues that disturb the optimal level of investments. Moreover, the findings give strong implications by suggesting and empirically proving the remedy that has the potential to balance the investment distortions by rectifying monitoring and financing deficiencies. © 2018 The Author(s)

Research on implication of convergence of interest hypothesis: Evidence from listed firms

© 2017 - IOS Press and the authors. All rights reserved. The purposefulness of the study is to test the convergence of interest hypothesis in Pakistan. Convergence of interest hypothesis illustrates that when the firm is owned by its own managers; it possesses lesser extent of agency cost. If the firm is largely owned by individuals who have not a role in the day to day management of the firm, then it has more cost of monitoring its management. It is because when ownership and management are in same hands, then owner-manager interests are converged. We examined this proposition employing the financial statistics of top 100 (capitalization wise) companies of KSE 100 index. The study has utilized fixed and random effect model of GLS Regression to deduce results. Results have emphasized that Agency Cost decreases in firms which have the significant proportion of insider ownership. Firms having more growth opportunities and larger amount of debt employed in their capital structure, exhibit lower agency problem but large sized firms have more agency cost. Results are important in a sense because it remained undiscovered before this study in the context of emerging economy like Pakistan. The study also gives strong suggestions to policy makers, investors and managers

Interactive effects of global change factors on soil respiration and its components: A meta-analysis

As the second largest carbon (C) flux between the atmosphere and terrestrial ecosystems, soil respiration (Rs) plays vital roles in regulating atmospheric CO2 concentration ([CO2 ]) and climatic dynamics in the earth system. Although numerous manipulative studies and a few meta-analyses have been conducted to determine the responses of Rs and its two components [i.e., autotrophic (Ra) and heterotrophic (Rh) respiration] to single global change factors, the interactive effects of the multiple factors are still unclear. In this study, we performed a meta-analysis of 150 multiple-factor (≥2) studies to examine the main and interactive effects of global change factors on Rs and its two components. Our results showed that elevated [CO2 ] (E), nitrogen addition (N), irrigation (I), and warming (W) induced significant increases in Rs by 28.6%, 8.8%, 9.7%, and 7.1%, respectively. The combined effects of the multiple factors, EN, EW, DE, IE, IN, IW, IEW, and DEW, were also significantly positive on Rs to a greater extent than those of the single-factor ones. For all the individual studies, the additive interactions were predominant on Rs (90.6%) and its components (≈70.0%) relative to synergistic and antagonistic ones. However, the different combinations of global change factors (e.g., EN, NW, EW, IW) indicated that the three types of interactions were all important, with two combinations for synergistic effects, two for antagonistic, and five for additive when at least eight independent experiments were considered. In addition, the interactions of elevated [CO2 ] and warming had opposite effects on Ra and Rh, suggesting that different processes may influence their responses to the multifactor interactions. Our study highlights the crucial importance of the interactive effects among the multiple factors on Rs and its components, which could inform regional and global models to assess the climate-biosphere feedbacks and improve predictions of the future states of the ecological and climate systems. © 2016 John Wiley & Sons Ltd

Grazing intensity significantly affects belowground carbon and nitrogen cycling in grassland ecosystems: A meta-analysis

Livestock grazing activities potentially alter ecosystem carbon (C) and nitrogen (N) cycles in grassland ecosystems. Despite the fact that numerous individual studies and a few meta-analyses had been conducted, how grazing, especially its intensity, affects belowground C and N cycling in grasslands remains unclear. In this study, we performed a comprehensive meta-analysis of 115 published studies to examine the responses of 19 variables associated with belowground C and N cycling to livestock grazing in global grasslands. Our results showed that, on average, grazing significantly decreased belowground C and N pools in grassland ecosystems, with the largest decreases in microbial biomass C and N (21.62% and 24.40%, respectively). In contrast, belowground fluxes, including soil respiration, soil net N mineralization and soil N nitrification increased by 4.25%, 34.67% and 25.87%, respectively, in grazed grasslands compared to ungrazed ones. More importantly, grazing intensity significantly affected the magnitude (even direction) of changes in the majority of the assessed belowground C and N pools and fluxes, and C : N ratio as well as soil moisture. Specifically,light grazing contributed to soil C and N sequestration whereas moderate and heavy grazing significantly increased C and N losses. In addition, soil depth, livestock type and climatic conditions influenced the responses of selected variables to livestock grazing to some degree. Our findings highlight the importance of the effects of grazing intensity on belowground C and N cycling, which may need to be incorporated into regional and global models for predicting effects of human disturbance on global grasslands and assessing the climate-biosphere feedbacks. © 2016 John Wiley & Sons Lt

Biochar increased soil respiration in temperate forests but had no effects in subtropical forests

© 2017 Elsevier B.V. As a climate change mitigation strategy, biochar application to soil has been demonstrated to increase soil carbon (C) sequestration and reduce greenhouse gas (GHG) emission. Although numerous manipulative studies have been conducted, it is still not fully understood how biochar application affects soil respiration (Rs) and its components (i.e., autotrophic [Ra] and heterotrophic respiration [Rh] ) in forest ecosystems, especially in subtropical forests. In this study, we performed a meta-analysis of forest ecosystems and a field experiment with biochar amendments of 0, 10, and 30 t ha −1 in a subtropical forest in Zhejiang, China to examine the effects of biochar application on Rs and its components. Our results showed that biochar application significantly increased Rs by 20.92% at the global scale with an increase of 20.25% in temperate forests and a nonsignificant effect in subtropical forests. Responses of Rs to biochar application varied with experimental methods and soil textures. Similarly, our field experiment showed that biochar amendment did not significantly affect Ra, Rh, and Rs in a subtropical forest in Eastern China. Specifically, the average Rs under biochar amendments of 0, 10, and 30 t ha −1 were 2.37, 2.06 and 2.15 μmol m −2 s −1 , respectively (P > 0.05). Both Rs and Rh were positively correlated with microbial biomass C (MBC) and negatively with dissolved organic C (DOC). Both apparent temperature sensitivity (Q 10 ) of Rh and Rs were significantly higher under biochar treatments than in the control. Our findings indicate the importance of the differential effects of biochar application on Rs in different forest types for C sequestration, which may inform ecosystem and regional models to improve prediction of biochar effects on forest C dynamics and climate-biosphere feedbacks

Effects of biochar application on soil greenhouse gas fluxes: A meta-analysis

Biochar application to soils may increase carbon (C) sequestration due to the inputs of recalcitrant organic C. However, the effects of biochar application on the soil greenhouse gas (GHG) fluxes appear variable among many case studies; therefore, the efficacy of biochar as a carbon sequestration agent for climate change mitigation remains uncertain. We performed a meta-analysis of 91 published papers with 552 paired comparisons to obtain a central tendency of three main GHG fluxes (i.e., CO2, CH4, and N2O) in response to biochar application. Our results showed that biochar application significantly increased soil CO2 fluxes by 22.14%, but decreased N2O fluxes by 30.92% and did not affect CH4 fluxes. As a consequence, biochar application may significantly contribute to an increased global warming potential (GWP) of total soil GHG fluxes due to the large stimulation of CO2 fluxes. However, soil CO2 fluxes were suppressed when biochar was added to fertilized soils, indicating that biochar application is unlikely to stimulate CO2 fluxes in the agriculture sector, in which N fertilizer inputs are common. Responses of soil GHG fluxes mainly varied with biochar feedstock source and soil texture and the pyrolysis temperature of biochar. Soil and biochar pH, biochar applied rate, and latitude also influence soil GHG fluxes, but to a more limited extent. Our findings provide a scientific basis for developing more rational strategies toward widespread adoption of biochar as a soil amendment for climate change mitigation