Search results

The purpose of this paper is to present an overview of the aircraft design problems which can be efficiently solved using a special solid finite‐element model of variable density.

Optimization algorithms based on fully‐stressed design philosophy, sensitivity coefficients, and employing material density as a design variable provide means to generate optimal topology layouts, subject to a wide range of design constraints. A novel non‐dimensional criterion is used for assessment of load‐carrying efficiency of structures and knowledge accumulation.

Variable density model, together with non‐dimensional criterion of structural efficiency, yields a new versatile approach to a structural weight estimation at early design stages. New weight equations are used. The approach is a powerful tool for addressing complex multidisciplinary design optimization (MDO) problems such as aerodynamic load prediction taking aeroelastic deformations into account and aerodynamic‐structural design optimization of unconventional aircraft configurations.

For accurate estimation of wing weight and deflections, the method should be tuned by regression analysis of existing aircraft to properly account for secondary structural weight.

The developed software tools for aeroelastic behaviour prediction and coupled aerodynamic‐structural design optimization are ready for integration into the complex MDO framework.

The variable density model is shown to have broad predictive opportunities for design problems at early stages of a product development.

The purpose of this paper is to propose an improved proportional topology optimization (IPTO) algorithm for tackling the stress-constrained minimum volume optimization problem, which can meet the requirements that are to get rid of the problems of numerical derivation and sensitivity calculation involved in the process of obtaining sensitivity information and overcome the drawbacks of the original proportional topology optimization (PTO) algorithm.

The IPTO algorithm is designed by using the new target material volume update scheme and the new density variable update scheme and by introducing the improved density filter (considering the weighting function based on the Gaussian distribution) and Heaviside-type projection operator on the basis of the PTO algorithm. The effectiveness of the IPTO algorithm is demonstrated by solving the stress-constrained minimum volume optimization problems for two numerical examples and being compared with the PTO algorithm.

The results of this paper show that the uses of the proposed strategies contribute to improving the optimized results and the performance (such as the ability to obtain accurate solutions, robustness and convergence speed) of the IPTO algorithm. Compared with the PTO algorithm, the IPTO algorithm has the advantages of fast convergence speed, enhancing the ability to obtain accurate solutions and improving the optimized results.

This paper achieved the author’s intended purpose and provided a new idea for solving the stress-constrained optimization problem under the premise of avoiding obtaining sensitivity information.

Reviews the literature on trade union membership in OECD countries. After considering the ways in which trade union membership is measured, trends in both membership and density since 1970 are examined. When cross‐sectional determinants are considered, density is found to be unrelated to size of employment in the manufacturing sector and the share of female employment, but it is related to the level of collective bargaining and the size of the public sector. An examination of individual and job‐related characteristics finds membership is higher among males, those with family responsibilities, those with lower occupational status and those with low educational achievements and that job dissatisfaction and left‐wing views are also important. Time‐series studies find that while union growth and decline are linked to the business cycle, with wages, prices and unemployment affecting membership, economic factors are not the sole explanation. Concludes by surveying the causes of union decline since 1980, together with recent error‐correction and cointegration approaches to modelling trade union membership.

A long tradition in social science research emphasizes the potential for knowledge to flow among firms colocated in dense areas. Scholars have suggested numerous modes for these flows, including the voluntary transfer of private knowledge from one firm to another. Why would the holder of valuable private knowledge willingly transfer it to a potential and closely proximate competitor? In this paper, we argue that geographic concentration has an effect on the expected compliance with norms governing the use of transferred knowledge. The increased expected compliance favors trust and initiates a process of reciprocal exchange. To test our theory, we use a scenario-based field experiment in gourmet cuisine, an industry in which property rights do not effectively protect knowledge and geographic concentration is common. Our results confirm our conjecture by showing that the expectation that a potential colocated firm will abide by norms mediates the relationship between geographic concentration and the willingness to transfer private knowledge.

This paper examines the impact of urban form on disaster resiliency. The literature shows a complex relationship between urban form factors such as density and diversity and disaster recovery. The empirical analysis in this paper tests the impact of land use mix, population density, building type and diversity on the reconstruction progress in three, six and nine months after the 2010 flood in Brisbane and Ipswich as proxies of disaster resilience. Considerable debate exists on whether urban form factors are the causal incentive or are they mediating other non-urban form causal factors such as income level. In view of this, the effects of a series of established non-urban form factors such as income and tenure, already known as effective factors on disaster resilience, are controlled in the analysis.

The structure of this paper is based on a two-phase research approach. In the first phase, for identification of hypothetical relationships between urban form and disaster resiliency, information was gathered from different sources on the basis of theory and past research findings. Then in phase two, a database was developed to test these hypothetical relationships, employing statistical techniques (including multivariate regression and correlation analysis) in which disaster recovery was compared among 76 suburbs of Brisbane and Ipswich with differing levels of population density and land use mix.

The results indicate that population density is positively related to disaster resilience, even when controlling for contextual variables such as income level and home ownership. The association between population density and disaster reconstruction is non-linear. The progress of reconstruction to population density ratio increases from low, medium to high densities, while in very low and very high density areas the reconstruction progress does not show the same behavior, which suggests that medium-high density is the most resilient.

The originality of this paper is in extracting hypothetical relationships between urban form and resiliency and testing them with real world data. The results confirmed the contribution of density to recovery process in this case study. This illustrates the importance of attention to disaster resiliency measures from the early stages of design and planning in development of resilient urban communities.

The primary purpose of this study is to identify whether there is a price premium and consumers’ preferences for higher housing density, and whether there is a relationship between housing densities and sales prices. The second purpose was to identify if there is a non-linear relationship between housing density and prices even though housing density is directly associated with housing prices.

This paper applies hedonic modeling techniques to measure the value of development density of apartments in the metropolitan area of Seoul, South Korea. The regression of the sale price is a function of different types of variables such as density, market, location and other control variables.

For the first question, this paper concludes that the higher densities cause housing prices to decrease in Seoul. The summary of the results presents that housing density, floor area ratio (FAR), building coverage ratio and floor level are all important components affecting housing prices. Generally, consumers tend to buy housing with central heating systems, more parking spaces, smaller portion of rental housing within an apartment and buildings that have more of a mixed-use function. Consumers are also found to pay higher premiums for housing in areas with high population growth and less housing supply. It is conclusive that people are inclined to live in populated areas but do not want more density. For the second question, the results show that generally FAR has quadratic effects, but most housing density variables tend to have a non-linear relationship depending on the different quantile groups.

There is a knowledge gap in the area of estimating development density of apartments. Generally, studies investigating property value impacts of multifamily housing focus on external effects of the multifamily housing on home values to examine whether high density development could result in a decrease in nearby property values. These studies found that there are some positive effects. A study found that high-density housing increases property values of existing single-family homes (Joint Center for Housing Studies, 2011). More specifically, developments that are of a high design quality and superior landscaping increase values of single-family homes as well. Also, those residents who live in these high-density apartments can be good potential buyers for the existing single-family homes. The greater the number of buyers, the greater the housing market becomes. Similarly, according to a report by the Joint Center for Housing Studies (2011) at Harvard University, the presence of multifamily residents correlates with higher home values in “working communities”. Indeed, density can be an important factor determining value of apartments because of its unique characteristics. However, no empirical evidence has been provided in the literature with regard to the value of the development density. This study contributes toward improving this knowledge gap.

Crowded urban regions pose a complex urban challenge that can adversely affect urban residents, encompassing aspects like mental and physical well-being, overall livability and quality of life. The complexity in determining the factors influencing the crowding perception, which encompass subjective and situational psychological factors alongside physical and environmental attributes, imparts ambiguity to planners' approach. This study aims to unravel the intricate interplay between crowding and the physical attributes inherent in the built environment.

This literature review analyses theories linking urban planning and environmental psychology to uncover gaps in the relationship between urban design principles and residents' perceptions of crowding. It also explores influential variables affecting crowding perception and diverse methodologies across contexts.

The study built upon a broad literature review which is expected to summarise and classify the variables of urban planning components and approaches according to their impacts on the psychological perception of crowding. Furthermore, highlighting a number of recommendations that can be considered a guide for planners and urban designers to enhance the urban experience and reduce the perception of crowding.

This study seeks to improve the overall experience of crowding in densely populated urban areas. It accomplishes this by identifying influential factors and comprehending the associated outcomes in such contexts. Furthermore, it bridges perspectives from various fields to examine relevant policies and strategies to mitigate crowding consequences.

The purpose of the paper is to propose a homogenization-based topology optimization method to optimize the design of variable-density cellular structure, in order to achieve lightweight design and overcome some of the manufacturability issues in additive manufacturing.

First, homogenization is performed to capture the effective mechanical properties of cellular structures through the scaling law as a function their relative density. Second, the scaling law is used directly in the topology optimization algorithm to compute the optimal density distribution for the part being optimized. Third, a new technique is presented to reconstruct the computer-aided design (CAD) model of the optimal variable-density cellular structure. The proposed method is validated by comparing the results obtained through homogenized model, full-scale simulation and experimentally testing the optimized parts after being additive manufactured.

The test examples demonstrate that the homogenization-based method is efficient, accurate and is able to produce manufacturable designs.

The optimized designs in our examples also show significant increase in stiffness and strength when compared to the original designs with identical overall weight.

The purpose of this study is to examine the impact of crime on apartment prices for Hamburg, Germany, for the years 2012 to 2017.

The authors use a panel data setting with fixed effects estimators and temporal lags to moderate the endogeneity concerns related to crime. The authors consider the effect of total crime, violent and property crime and some sub-categories of crime.

The estimates show that it takes two to three years for prices to react, with the longer run elasticity reaching −0.12 for total crime, −0.15 for property crime and −0.06 for violent crime. The elasticities are much larger in high-crime areas (−0.22 for total crime, −0.28 and −0.09 for property and violent crime) and elevated also in low-income areas.

The finding that property crime matters more in terms of quantitative impact for housing values than violent crime provides reasonable grounds for rethinking the resource allocation of public spending on crime clearance and prevention in Germany. Far more emphasis on preventing property crime appears in order and especially so in the lower income or higher crime areas, which are significantly more affected by crime and in particular property crime than those in high income or low crime areas.

The estimates for Hamburg provide the first detailed results of the impact of crime on real estate prices in Germany. It is also the first study for Continental Europe using panel data.

This chapter reviews recent developments in the density discontinuity approach. It is well known that agents having perfect control of the forcing variable will invalidate the popular regression discontinuity designs (RDDs). To detect the manipulation of the forcing variable, McCrary (2008) developed a test based on the discontinuity in the density around the threshold. Recent papers have noted that the sorting patterns around the threshold are often either the researcher’s object of interest or may relate to structural parameters such as tax elasticities through known functions. This, in turn, implies that the behavior of the distribution around the threshold is not only informative of the validity of a standard RDD; it can also be used to recover policy-relevant parameters and perform counterfactual exercises.