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As prefabrication of timber structures in the construction sector becomes part of the solution to overcome the housing and environmental crisis, the lack of efficiency of this industry needs to be addressed. This inefficiency, characterized by low production capacity, high costs, and large workforce, are in part due to the low adoption of automation and robotic technologies, caused by insufficient knowledge and research measuring the impact of these technologies. This paper aims to measure the efficiency of introducing automation in a prefabrication environment of timber-frame structures, through a decision analysis tool. Four layout types with varying automation levels are explored using simulation modeling, while KPIs are exploited to measure the efficiency of each production environment. A sensitivity analysis is conducted to assess the most performing layout if a new type of wall, requiring fewer tasks, is introduced in the product mix. A design of experiments (DOE) is also performed on the fourth layout, a fixed robotic cell with the highest level of automation, to assess the most influential variables. Results show a positive increase in worker, space, and production efficiency as the level of automation increase. This research contributes to the body of knowledge by providing a decision analysis tool supporting the choice of an optimized layout for the prefabrication of timber-frame walls (TFW). The findings and the decision analysis tool should provide solid grounds for future exploration of automation and practice in the field. [ABSTRACT FROM AUTHOR]

This paper deals with the formulation and validation of the discrete fresh concrete (DFC) model to simulate the rheological behavior of self-consolidating, ordinary, and printable concrete in the fluid state immediately after mixing. The DFC model is formulated within the framework of the discrete-element method (DEM), and it models the interaction among coarse aggregate particles embedded in a fine mortar. The formulation is based on stress-strain constitutive equations through which the behavior of fresh concrete can be described by parameters with clear physical meaning. This study presents a rigorous methodology for estimating the model key input parameters by the comparison of numerical simulations with experimental data. This methodology includes (1) a series of sensitivity analyses and simulations to establish the relationship between constitutive parameters and macroscopic properties; and (2) numerical simulations of experimental tests commonly used to characterize the fresh state behavior of concrete. Finally, the paper discusses the application of the DFC model to the simulation of concrete additive manufacturing. [ABSTRACT FROM AUTHOR]

This paper addresses the first passage problem of linear systems subjected to non-Gaussian excitations by means of simulation. A non-Gaussian simulation technique based on the unified Hermite polynomial model (UHPM) is adopted to model input excitations, and then the output responses are further obtained through time-domain analysis. The novel contribution of this paper is to construct an efficient importance sampling (IS) density function based on UHPM and the first-order reliability method (FORM) to release the computational burden. A simple and efficient sampling procedure is also provided for convenient implementation. Such an approach allows the failure probabilities in the order of 10−3 or lower to be estimated reliably with a reduced computational cost. The accuracy and efficiency of the proposed method are demonstrated by three examples, including a single-degree-of-freedom oscillator, a 3-story linear shear frame, and a relatively large-scale finite-element model. [ABSTRACT FROM AUTHOR]

This paper focuses on the simulation of irregular stone masonry by the lattice discrete particle model (LDPM), which simulates the fracture and failure behavior of quasi-brittle heterogeneous materials by modeling the interaction among coarse material heterogeneities. LDPM is formulated at the length scale of the masonry stones whose interaction is described through constitutive equations featuring softening in tension and strain hardening in compression. The numerical results relevant to diagonal compression tests show that the intrinsic stochastic character of LDPM can quantify the variation of the mechanical properties of irregular masonry resulting from random stone size and stone-size distribution. Furthermore, the paper presents an analysis of the size effect on irregular stone masonry structures. This was obtained by simulating the shear behavior of geometrically similar samples of different sizes. The simulations demonstrate that increasing structural size leads to a significant reduction of both structural strength and structural ductility. The magnitude of the predicted size effect suggests that, contrary to typical experimental results on reduced size samples, real irregular masonry structures must be considered as perfectly brittle. [ABSTRACT FROM AUTHOR]

The growing applications involving unmanned aerial vehicles (UAVs) are requiring more advanced control algorithms to improve rotary-wing UAVs' performance. To preliminarily tune such advanced controllers, an experimental approach could take a long time and also be dangerous for the vehicle and the onboard hardware components. In this paper, a simulation model of a quadcopter is developed and validated by the comparison of simulation results and experimental data collected during flight tests. For this purpose, an open-source flight controller for quadcopter UAVs is developed and a linear quadratic regulator (LQR) controller is implemented as the control strategy. The input physical quantities are experimentally measured; hence, the LQR controller parameters are tuned on the simulation model. The same tuning is proposed on the developed flight controller with satisfactory results. Finally, flight data and simulation results are compared showing a reliable approximation of the experimental data by the model. Because numerous state-of-the-art simulation models are available, but accurately validated ones are not easy to find, the main purpose of this work is to provide a reliable tool to evaluate the performance for this UAV configuration. [ABSTRACT FROM AUTHOR]

The publisher is issuing an Expression of Concern to inform readers that a claim has been made that this paper was part of work done in association with Engineering and Software System Solutions, Inc. (ES3) and the US Army Corps of Engineers. The authors claim the publication approval was not required because the presented material was obtained after the end of the project and was not part of the project deliverables. There exists an outstanding claim that the funding agencies had final approval before publication and this was not sought; however, the authors dispute this claim. [Extracted from the article]

The numerical simulations were performed with the MARS software prior to January 2020. The following "Acknowledgments" section should be added to the original paper: Acknowledgments This effort was partially sponsored by the US Army Engineer Research and Development Center (ERDC) via Engineering and Software System Solutions, Inc. (ES3). [Extracted from the article]