The Fracture Mechanics Concept of Creep and Creep/Fatigue Crack Growth in Life Assessment

There is an increasing need to assess the service life of components containing defect which operate at high temperature. This paper describes the current fracture mechanics concepts that are employed to predict cracking of engineering materials at high temperatures under static and cyclic loading. The relationship between these concepts and those of high temperature life assessment methods is also discussed. A model for predicting creep crack growth initiation and growth in terms of C* and the creep uniaxial ductility is presented and it is shown that this model gives good agreement with the experimental results. The effects of cyclic loading on crack growth behaviour are considered and fractography evidence is shown to back a simple cumulative damage concept when dealing with creep/fatigue interaction. Finally a discussion is presented which highlights the important aspect of life assessment methodology for high temperature plant

Toward Improved Urban Building Energy Modeling Using a Place-Based Approach

Urban building energy models present a valuable tool for promoting energy efficiency in building design and control, as well as for managing urban energy systems. However, the current models often overlook the importance of site-specific characteristics, as well as the spatial attributes and variations within a specific area of a city. This methodological paper moves beyond state-of-the-art urban building energy modeling and urban-scale energy models by incorporating an improved place-based approach to address this research gap. This approach allows for a more in-depth understanding of the interactions behind spatial patterns and an increase in the number and quality of energy-related variables. The paper outlines a detailed description of the steps required to create urban energy models and presents sample application results for each model. The pre-modeling phase is highlighted as a critical step in which the geo-database used to create the models is collected, corrected, and integrated. We also discuss the use of spatial auto-correlation within the geo-database, which introduces new spatial-temporal relationships that describe the territorial clusters of complex urban environment systems. This study identifies and redefines three primary types of urban energy modeling, including process-driven, data-driven, and hybrid models, in the context of place-based approaches. The challenges associated with each type are highlighted, with emphasis on data requirements and availability concerns. The study concludes that a place-based approach is crucial to achieving energy self-sufficiency in districts or cities in urban-scale building energy-modeling studies

Quantifying the impacts of urban morphology on modifying microclimate conditions in extreme weather conditions

It is well-known that the morphology of urban areas modifies the variations of climate variables at microscale; known as microclimate conditions. The complexity of urban morphology can lead to undesired wind conditions or excessive air temperature; particularly in extreme weather conditions. This study attempts to quantify the impacts of urban morphology on the evolution of wind speed and air temperature at the urban canopy layer using Computational Fluid Dynamic (CFD) simulations. In this regard, three urban neighbourhoods are generated based on a novel urban morphology parameterization method and assessed in two extreme low and high wind conditions. Results showed that wind speed (up to 75%) and air temperature (up to 28%) at the microscale can get amplified or dampened in extreme conditions. A negative correlation was observed between wind speed and air temperature variations indicating a great potential to reduce outdoor air temperature through heat removal in urban canyons. The findings of the study are categorized based on the morphological parameters to present a series of design-based strategies for the newly-built urban neighbourhoods

Urban cells: Extending the energy hub concept to facilitate sector and spatial coupling

The rapid growth of urban areas and concerns over climate change make it vital to improve the energy sustainability of cities. Understanding the complex interactions within different sectors (sectoral) and localities (spatial) of cities plays a crucial role in improving efficiency and sustainability, which is extremely challenging due to the complex urban morphology. State-of-the-art energy concepts do not facilitate a detailed consideration of both sectoral and spatial coupling that energy infrastructure maintains at the urban scale. This has become a significant challenge when designing interconnected urban energy infrastructure. The Urban Cell concept is introduced to address this bottleneck. A novel computational model using a modular approach is introduced to create an interconnected urban infrastructure, including the energy, building, and transportation sectors. Optimal sizing of the distributed energy system (including renewables, energy storage, and dispatchable sources) and optimal urban morphology is determined within a modular unit. A game-theoretic approach is used to model the interactions between urban cells (modular units). The study revealed that the urban cell concept can reduce the net present value of the interconnected energy infrastructure by 37% while increasing the installed renewable energy capacity by 25%. This demonstrates the benefit potential of urban cells and the importance of considering interactions between different sectors and different parts within a city. The Urban Cell concept can be used to present the complex interactions maintained within a city

A multi-objective optimization framework for designing climate-resilient building forms in urban areas

With the increasing global awareness about the impacts of climate change on the built environments, the need for improving the climate resilience of buildings is being more acknowledged. Despite the high number of relevant studies, there is a lack of frameworks to assess the resiliency of buildings and urban areas. This study presents a multi-objective framework to optimize the form of buildings against its energy performance and thermal comfort considering its resiliency to the uncertainties of climate change during three thirty-years periods (2010-2099) of a warm region. Three performance sections related to building's form are identified and categorized for the impact assessment including (1) urban form, (2) orientation, and (3) transparency with ten influencing parameters. The analysis of non-dominated solutions out of the optimization process showed that the annual energy performance (cooling and heating demand) of the urban areas can improve about 34% in both typical and extreme weather conditions whilst maintaining thermal comfort by optimizing the overall form of the buildings with similar built density and heights. Moreover, Buildings with 15 to 30-degree rotations and 33% glazing ratio showed the highest energy performance. Finally, the top 20 resilient building forms with the highest energy performance and climate resiliency were selected out of the database of results to derive design suggestions