209 research outputs found
Exploring the trend of New Zealand housing prices to support sustainable development
The New Zealand housing sector is experiencing rapid growth that has a significant impact on society, the economy, and the environment. In line with the growth, the housing market for both residential and business purposes has been booming, as have house prices. To sustain the housing development, it is critical to accurately monitor and predict housing prices so as to support the decision-making process in the housing sector. This study is devoted to applying a mathematical method to predict housing prices. The forecasting performance of two types of models: autoregressive integrated moving average (ARIMA) and multiple linear regression (MLR) analysis are compared. The ARIMA and regression models are developed based on a training-validation sample method. The results show that the ARIMA model generally performs better than the regression model. However, the regression model explores, to some extent, the significant correlations between house prices in New Zealand and the macro-economic conditions
Optimization of the supplier selection process in prefabrication using BIM
Prefabrication offers substantial benefits including reduction in construction waste, material waste, energy use, labor demands, and delivery time, and an improvement in project constructability and cost certainty. As the material cost accounts for nearly 70% of the total cost of the prefabrication project, to select a suitable material supplier plays an important role in such a project. The purpose of this study is to present a method for supporting supplier selection of a prefabrication project. The proposed method consists of three parts. First, a list of assessment criteria was established to evaluate the suitability of supplier alternatives. Second, Building Information Modelling (BIM) was adopted to provide sufficient information about the project requirements and suppliers’ profiles, which facilitates the storage and sharing of information. Finally, the Analytic Hierarchy Process (AHP) was used to rank the importance of the assessment criteria and obtain the score of supplier alternatives. The suppliers were ranked based on the total scores. To illustrate how to use the proposed method, it was applied to a real prefabrication project. The proposed method facilitates the supplier selection process by providing sufficient information in an effective way and by improving the understanding of the project requirements
New Zealand Building Project Cost and Its Influential Factors: A Structural Equation Modelling Approach
Construction industry significantly contributes to New Zealand's economic development. However, the delivery of construction projects is usually plagued by cost overruns, which turn potentially successful projects into money-losing ventures, resulting in various other unexpected negative impacts. The objectives of the study were to identify, classify, and assess the impacts of the factors affecting project cost in New Zealand. The proposed research model was examined with structural equation modelling. Recognising the lack of a systematic approach for assessing the influencing factors associated with project cost, this study identified 30 influencing factors from various sources and quantified their relative impacts. The research data were gathered through a questionnaire survey circulated across New Zealand construction industry. A total of 283 responses were received, with a 37% response rate. A model was developed for testing the relationship between project cost and the influential factors. The proposed research model was examined with structural equation modelling (SEM). According to the results of the analysis, market and industry conditions factor has the most significant effect on project cost, while regulatory regime is the second-most significant influencing factor, followed by key stakeholders' perspectives. The findings can improve project cost performance through the identification and evaluation of the cost-influencing factors. The results of such analysis enable industry professionals to better understand cost-related risks in the complex environment
Meshing Force of Misaligned Spline Coupling and the Influence on Rotor System
Meshing force of misaligned spline coupling is derived, dynamic equation of rotor-spline coupling system is established based on finite element analysis, the influence of meshing force on rotor-spline coupling system is simulated by numerical integral method. According to the theoretical analysis, meshing force of spline coupling is related to coupling parameters, misalignment, transmitting torque, static misalignment, dynamic vibration displacement, and so on. The meshing force increases nonlinearly with increasing the spline thickness and static misalignment or decreasing alignment meshing distance (AMD). Stiffness of coupling relates to dynamic vibration displacement, and static misalignment is not a constant. Dynamic behaviors of rotor-spline coupling system reveal the following: 1X-rotating speed is the main response frequency of system when there is no misalignment; while 2X-rotating speed appears when misalignment is present. Moreover, when misalignment increases, vibration of the system gets intricate; shaft orbit departs from origin, and magnitudes of all frequencies increase. Research results can provide important criterions on both optimization design of spline coupling and trouble shooting of rotor systems
Caracterização de moduladores RSOA em ligações de radio sobre fibra
Doutoramento em Engenharia ElectrotécnicaIn this work physical and behavioral models for a bulk Reflective Semiconductor
Optical Amplifier (RSOA) modulator in Radio over Fiber (RoF) links
are proposed. The transmission performance of the RSOA modulator is predicted
under broadband signal drive.
At first, the simplified physical model for the RSOA modulator in RoF links
is proposed, which is based on the rate equation and traveling-wave equations
with several assumptions. The model is implemented with the Symbolically
Defined Devices (SDD) in Advanced Design System (ADS) and validated
with experimental results. Detailed analysis regarding optical gain,
harmonic and intermodulation distortions, and transmission performance is
performed. The distribution of the carrier and Amplified Spontaneous Emission
(ASE) is also demonstrated.
Behavioral modeling of the RSOA modulator is to enable us to investigate
the nonlinear distortion of the RSOA modulator from another perspective
in system level. The Amplitude-to-Amplitude Conversion (AM-AM) and
Amplitude-to-Phase Conversion (AM-PM) distortions of the RSOA modulator
are demonstrated based on an Artificial Neural Network (ANN) and
a generalized polynomial model. Another behavioral model based on Xparameters
was obtained from the physical model.
Compensation of the nonlinearity of the RSOA modulator is carried out
based on a memory polynomial model. The nonlinear distortion of the RSOA
modulator is reduced successfully. The improvement of the 3rd order intermodulation
distortion is up to 17 dB. The Error Vector Magnitude (EVM) is
improved from 6.1% to 2.0%.
In the last part of this work, the performance of Fibre Optic Networks for
Distributed and Extendible Heterogeneous Radio Architectures and Service
Provisioning (FUTON) systems, which is the four-channel virtual Multiple
Input Multiple Output (MIMO), is predicted by using the developed physical
model. Based on Subcarrier Multiplexing (SCM) techniques, four-channel
signals with 100 MHz bandwidth per channel are generated and used to drive
the RSOA modulator. The transmission performance of the RSOA modulator
under the broadband multi channels is depicted with the figure of merit, EVM
under di erent adrature Amplitude Modulation (QAM) level of 64 and 254
for various number of Orthogonal Frequency Division Multiplexing (OFDM)
subcarriers of 64, 512, 1024 and 2048.Nesta tese são propostos modelos físicos e comportamentais para o amplificador
óptico semicondutor reflectivo (RSOA), tendo como objectivo a avaliação
do seu desempenho quando utilizado como modulador em ligações de
rádio sobre fibra (RoF). Os modelos propostos são capazes de prever o comportamento
do dispositivo quando utilizado com sinais de banda larga bem
como quando estimulado por sinais de elevada potência.
Inicialmente propõe-se um modelo físico simplificado para o RSOA baseado
nas equações de taxa e nas equações de propagação electromagnética. A implementação
do modelo utiliza o ADS (Advanced Design Systems) e o bloco
designado por dispositivo definido simbolicamente (SDD) para descrever as
equações de taxa, assim como a propagação de fotões ao longo da cavidade.
O modelo permite uma análise detalhada do ganho óptico, distorções harmônicas,
intermodulação e seu desempenho de transmissão com portadoras
RF modeladas.
Foram também considerados modelos comportamentais. Um modelo
baseado em rede neural artificial (ANN) e um modelo polinomial generalizado
para banda base foram considerados tendo os parâmetros respectivos
sido extraídos utilizando, para o efeito, dados obtidos experimentalmente.
São demonstradas a característica da distorção resultante da conversão amplitude
- amplitude (AM-AM) e conversão da fase - amplitude (AM-PM) no
modulador RSOA. Um modelo baseado em parametros X, obtidos a partir do
modelo físico, foi também analisado.
Compensação da não-linearidade do modulador RSOA é realizada com base
num modelo polinomial com memória. Demonstra-se que a distorção não
linear do modulador RSOA pode ser compensada com sucesso. Com a compensação
obtem-se uma redução de 17 dB da distorção introduzida pelos
produtos de intermodulação de terceira ordem. O EVM (Error Vector Magnitude)
apresenta uma melhoria de 6,1% para 2,0%.
Na última parte deste trabalho considera-se uma configuração que representa
a ligação ascendente por fibra de um sistema de antenas remoto a
uma estação central de processamento. Com esta configuração pretendese
demonstrar a possibilidade de implementação de uma tecnologia MIMO,
suportada num sistema RoF. Baseado numa técnica de multiplexação subportadora
(SCM), os sinais de quatro canais com largura de banda de 100 MHz
por canal são multiplexados e utilizados para modelar o ganho do RSOA. O
desempenho deste link óptico é caracterizado para modulações OFDM considerando
diferentes números de sub-portadoras por símbolo (64, 512 , 1024
e 2048) assim como o formato QAM imposto sobre cada sub-portadora
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