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This paper investigates the performance of a novel semiactive damping device at mitigating nonsimultaneous multihazard loads. The device, termed modified friction device (MFD), has been previously proposed by the authors. It consists of a variable friction system based on automotive drum brake technology. The device has been demonstrated in a laboratory environment, and its dynamic behavior has been modeled. This model is used to conduct numerical simulations on two representative structures, one short building located in Japan and the other tall building located in Boston, MA. Simulated hazards include wind, blast, and seismic loads. Various control cases are considered, including semiactive control under five different sets of control weights, and passive viscous and passive friction to benchmark performance. Results show that the semiactive control cases outperforms all of the other cases for the vast majority of hazards and performance indices, provided that the right control weights are utilized. [ABSTRACT FROM AUTHOR]

Project-specific dispute resolution ladders (DRLs) are typically implemented in construction projects to resolve issues arising between the project participants. The DRL typically consists of single or multiple alternative dispute resolution (ADR) techniques to address construction issues at the three levels of escalation: conflicts; disputes; and claims. However, a DRL requires significant investments to cover the direct costs incurred in-house by the project participants or, externally, if construction specialists and lawyers are recruited to assist in the resolution. Thus, the benefits of the DRL implementation in a construction project must outweigh its costs for the implementation to be worthwhile. This paper presents a methodology to study the effect of different resolution strategies on the value of the investment in a DRL using option/real option theories from financial engineering, process centric modeling, and system dynamics methodology. Of particular interest in this paper is the integration of these research methodologies into a computer model to support the evaluation of the DRL investment in a particular construction project by taking into account the characteristics of (1) the project and (2) the different ADR techniques chosen for the DRL implementation. Finally, an example is presented to illustrate the application of the computer model in a real construction project. The results of the simulation serve two main purposes. First, the results of the simulation are used to verify the intended model behavior in terms of proper integration of the three methodologies (i.e., real options, process centric, and system dynamics) in one computer system. Second, the model application to a real construction project using actual project data illustrates the potential of the model in providing the project participants with information related to the expected number of claims and change orders resolved at each level of the DRL, the change in the expected savings during the construction phase, and finally the value of the investment from the perspective of the project owner. [ABSTRACT FROM AUTHOR]

The level-furrow irrigation system consists of furrowing a level basin. In level furrows, irrigation proceeds just like in level basins: the field is flooded from one point and water spreads to irrigate each furrow. Several writers have reported that this irrigation system has the potential to conserve water as compared to level-basin irrigation. However, no comparative studies on the performance of both irrigation systems are available, and the simulation of level furrows has not been attempted. In this work, two field experiments are reported. Both of them were performed in the same soil and in the same conditions. In the first experiment, infiltration was estimated for a series of furrow irrigation discharges and for a level basin. In the second experiment, a level furrow irrigation event was evaluated. A simulated level basin irrigation event in the level furrow experimental field required six times more time and water to complete advance. Infiltration equations including the irrigation discharge or the wetted perimeter as independent variables were proposed for the experimental furrow conditions. Application of a furrow simulation model to the level–furrow experiment resulted in an underestimation of the time of advance. To overcome this problem, a simulation model for level furrows was developed and is presented in a companion paper. The reported field experiments were used to validate the model, which was applied (in a companion paper) to explore adequate conditions for level furrow irrigation performance. [ABSTRACT FROM AUTHOR]

In a companion paper, experimental evidence was elaborated to confirm that in particular circumstances the performance of level-furrow irrigation can exceed that of level-basin irrigation. The application of a single furrow simulation model to an irrigation event in a level-furrow field resulted in large estimation errors. To overcome them, the development and validation of a numerical model of level-furrow irrigation is reported in this work. The model is based on the interconnection of a number of one-dimensional channels. The individual channels are connected using confluence or bifurcation points. Furrow infiltration is modelled through a Kostiakov infiltration equation including the furrow discharge as an independent variable. The proposed model is validated using the experimental level furrow evaluation presented in the companion paper. Finally, the model is applied to explore the conditions in which level furrow irrigation can outperform level basin irrigation. The proposed model stands as a valuable tool in the design and management of level furrow irrigation systems. [ABSTRACT FROM AUTHOR]

Distributed hybrid simulation is an approach to large-scale testing in which the system under test is split into several sub-structures which are tested or simulated in different locations. Data are passed between the sub-structures at each timestep so as to ensure that the distributed experiment realistically simulates the full system under test. This approach optimises the use of resources at different locations to achieve a more representative experiment. While different software to conduct distributed simulations exists, there are no standards and specifications to organise and plan the experiments, and as a result the different systems lack inter-operability. To address these issues, we have developed a high-level specification called Celestina, which provides a framework for conducting a distributed experiment. Celestina specifies the services to be implemented, under three main headings of networking, definition and execution, and supports the data exchange during a simulation. It does not force any particular implementation or method of data exchange. This paper summarises the Celestina specification and describes one implementation. Lastly, a validation experiment is presented, involving distributed numerical simulations of an earlier local hybrid experiment, in which Celestina controls the experiment planning and data exchange effectively and with minimal computational overhead. [ABSTRACT FROM AUTHOR]

In this paper, a new kind of activation function using a particular combination of stop and play operators is proposed and used in a feedforward neural network to improve its learning capability in the identification of nonlinear hysteretic material behavior with both stiffness and strength degradation. The new neuron and neural network are referred to as a deteriorating stop and generalized Prandtl neural network, respectively. To show the generality of the proposed neural network, it is trained on several data sets generated by various mathematical models of material hysteresis with and without deterioration as well as on a set of experimental data with very high nonlinearity, including severe damage. In each case, the training is successful, and the generalized Prandtl neural network response precision is very high. Also, using the proposed neural network, a neuro-modeler is designed and used in the dynamic analysis of a one-story shear frame under seismic loads with severe damage. A comparison of the results shows that the generalized Prandtl neural network type of the neuro-modeler is more successful than the previously proposed Prandtl neural network type. [ABSTRACT FROM AUTHOR]

Because of the ongoing expansion of urban areas, transportation systems are being increasingly moved beneath the ground into tunnels. However, the construction of tunnels is very challenging regarding unexpected geological conditions, the protection of existing buildings from damage, and the control of financial and safety risks. During the tunnel construction process, different simulations are performed to predict, for example, settlements, soil excavation, or grouting behavior. Although these simulations should strongly interact, they often use independent heterogeneous geological data models and resources, thus resulting in unreliable predictions. This paper presents a hybrid ground data model along with necessary access concepts to support the automated management and exchange of continuously updated geological information among interacting simulations. The ground data model uses a boundary and a decomposition representation of the ground geometry with material information attached to each representation. These representations are converted to one another on demand to make up-to-date ground information available for participating tunneling simulations. To validate the proposed model and concepts, a case study is presented in which two typical simulations are coupled using the prototypically implemented hybrid ground data model. [ABSTRACT FROM AUTHOR]

In this paper, the friction generated in gas-flow regulation of ducted rockets is considered, and a compensation method is discussed to eliminate its effect. First, the dynamic mathematic model of gas flow-regulating system considering friction is established and analyzed. Then, the mechanism of friction-compensation method based on additional dither signal is proposed, and the compensation loop with adaptive-amplitude dither signal is added to the original system to overcome the effect of the varied friction. The simulation results show the validation of the adaptive dither signal in solving the problems caused by the variable friction in gas-regulation system of ducted rockets. [ABSTRACT FROM AUTHOR]

This paper proposes a simple analytical approach for nonlinear analyses of the load-displacement response of single piles and pile groups. Two models were adopted in the proposed approach. One model is based on a hyperbolic nonlinear relationship to simulate the behavior between unit skin friction and pile displacement developed along the pile-soil interface. The other model uses a bilinear hardening model to simulate the load-settlement response developed at the pile base. Based on the two proposed models, a highly effective iterative computer program was developed for nonlinear analysis of the load-settlement behavior of a single pile. Concerning analysis of the response of pile groups, the interaction between two piles was assumed to be composed of two aspects: interaction between pile shafts and interaction between pile bases. Based on this assumption, a reduction coefficient was introduced into the discussion of pile-pile interaction to account for the reinforcing effect between piles. Comparisons of the load-settlement response for three well-instrumented tests were given to demonstrate the effectiveness and accuracy of the proposed simple method. [ABSTRACT FROM AUTHOR]

Current processes for design and detailing in structural engineering are often broken up into a sequence of partial processes because of the complexity of the problem. But sequential additions of separate solutions rarely lead to an optimal design. For example, the basic structural system is often developed with its geometry and topology but without consideration of important aspects of structural performance, like robustness, redundancy, ductility. Decisions on performance are left for later design stages, when it is still possible to change details but too late to improve the structural system. A design that takes into account multiple objectives, such as safety, functionality, and aesthetics, requires a complete reconsideration of the authors' conventional sequential structural design process. Most engineering tools were developed many years ago as technology was much more limited, resulting in separate tools for separate objectives to be used in succession. In this paper, a new approach is presented as integrative structural design (ISD), where separate state-of-the-art solutions are synchronized in such a way that designers are not confined to predetermined solution paths but rather are enabled to consider different objectives concurrently including interactions between objectives. The resulting design tool for the conceptual, interactive modeling, simulation, and visualization of structural design or integrative design is presented under the term integrative structural design system (ISDS). [ABSTRACT FROM AUTHOR]

A water distribution network is said to be under pressure-deficient condition when hydraulic-head or pressure-head at any of its nodes fall below the required level. The demands at these pressure-deficient nodes cannot be fully satisfied. To make the analysis simple, it is generally assumed that the demand is fully satisfied irrespective of the pressure-head available and this approach is referred as demand-driven analysis. For simplicity, demand-driven analysis received great attention in the past and several computer packages are readily available for the analysis of normal operational water distribution network. On the other hand, head-driven or pressure-driven analysis could be effectively used to analyze the pressure-deficient condition as these methods consider the head-discharge relationship at every node. This paper presents a pressure-deficient analysis algorithm using the widely used demand-driven analysis-based solver. The proposed algorithm is validated through benchmark water distribution network and then extended period simulation is carried out for a multiple source pumped network. The analysis shows that the proposed algorithm could find the partial nodal outflows and corresponding hydraulic-head values in a single hydraulic simulation run. [ABSTRACT FROM AUTHOR]

In Part I of this two-part study, a theory is provided for the extension of the lattice discrete particle model (LDPM) to include fiber reinforcing capability. The resulting model, LDPM-F, is calibrated and validated in the present paper by comparing numerical simulations with experimental data gathered from the literature. The analyzed experiments include direct tension, confined and unconfined compression, and notched three-point bending tests. [ABSTRACT FROM AUTHOR]

When selecting construction design-build teams, subjective multi-evaluator decision making can be controversial and can lead to project delay, loss of public trust, and increased legal fees. This paper introduces a mathematical algorithm that supports multi-evaluator selection decisions by detecting and reducing the effect of possible uncertainty in the scores given by the evaluators. The algorithm was coded and tested using several scenarios. The study results show that the model is robust and capable of extracting the maximum knowledge from the scores given by evaluators with varying degrees of expertise. Simulation results show that the proposed model performed better than the simple averaging method 89% of the time. The outcome of this research provides the decision maker with a justified basis to proceed with the selection decision. [ABSTRACT FROM AUTHOR]

As construction projects get larger and more complex, it has become clear that no single entity can have complete knowledge of or the abilities to handle all matters. Therefore, collaborative practices among heterogeneous individuals, which are temporarily congregated to perform a project, are required to accomplish common project objectives. On the basis of this premise, this paper introduces an agent-based simulation of the evolution of collaboration within interorganizational networks of construction project teams from game theory and social network perspectives. The simulation confirmed that the fewer individuals are familiar with others in the network, and thereby aware of networks they are involved in, the more time it takes for networks to reach stable states. It was also found that the tendency of cohesion increased as the effort to form relationships with outside partners rose. Furthermore, the results indicated that the more effort needed to form relationships with those from other organizations, the less efficient the networks were. The model of organizational processes developed in this study explicitly incorporated a representation of individual decision makers and their interactions from both active and dynamic standpoints. This model represents a contribution to enhancing the understanding of the affect of organizational aspects on project management and to facilitating the development of tools for investigating organizations in construction. [ABSTRACT FROM AUTHOR]

Managing heavy-pressure vessel lifts on construction sites requires planning, arranging adequate crane support, and preparing collision-free rotation (from a horizontal position to a vertical position) of the vessel. Generally, selecting mobile cranes and developing engineered lift studies for vessels are done using two cranes and analyzing the lift for each crane individually on the basis of the selected cranes' lift-capacity specifications provided by crane manufactures. This practice is relatively costly and time-consuming. Optimizing the mobile cranes' use and location is also difficult. To assist in the field operation of mobile cranes and to provide engineers with a planning tool, this paper presents a methodology to carry out such a lift utilizing only one crane. Using the developed methodology and mechanism, heavy vessels can be rotated off the ground (in the air) with one crane. The proposed mechanism is supported with a mathematical model that has been developed into a computer system and has been integrated with a previously developed crane selection and ground pressure calculation system and crane database. The developed system provides users with a lift study analysis for a given configuration as well as simulation results with interactive graphics to assist in the selection of an optimum configuration. This research is important as projects involving heavy lifts need to reduce the cost and time associated with construction operations. [ABSTRACT FROM AUTHOR]

The research into modeling walking-induced dynamic loading and its effects on footbridge structures and people using them has been intensified in the past decade after some high profile vibration serviceability failures. In particular, the crowd induced loading, characterized by spatially restricted movement of pedestrians, has kept attracting attention of researchers. However, it is the normal spatially unrestricted pedestrian traffic, and its vertical dynamic loading component, that is the most relevant for vibration serviceability checks for most footbridges. Despite the existence of numerous design procedures concerned with this loading, the current confidence in its modeling is low due to lack of verification of the models on as-built structures. This is the motivation behind reviewing the existing design procedures for modeling normal pedestrian traffic in this paper and evaluating their performance against the experimental data acquired on two as-built footbridges. Additionally, the use of Monte Carlo simulations is also investigated. Possible factors that cause discrepancies between measured and calculated vibration responses, including possibility of existence of pedestrian-structure dynamic interaction, are discussed. [ABSTRACT FROM AUTHOR]

The pipe jacking method pushes a tunneling machine through concrete pipes ahead of the jacks. The main factors influencing the thrust force are friction around the pipe and face resistance. Both of these forces can be estimated by the analytical or empirical calculation models established by various researchers. So far, most of the models do not consider the overcutting distance; thus, the pipe behavior is still not clarified. Therefore, this paper introduces a developed stack pipe model with the overcutting effect to describe pipe behavior and evaluate the thrust force using the surrounding ground spring model and pipe positioning model with phase analysis in the finite-element method. A simulation of the pipe behavior was carried out to examine the model’s validity and performance. As a result, it was found that the developed model can simulate the soil-pipe interaction behavior and the thrust force reasonably well. Furthermore, it can be pointed out that the thrust force is greatly influenced by the developed friction around the pipe and the moment distribution at the cushion. [ABSTRACT FROM AUTHOR]

This research proposes a hybrid simulation approach based upon the principles of system dynamics (SD) and discrete event simulation (DES), which facilitates a better understanding of complex interactions among various processes in large-scale construction. The significance of the construction context that interacts with construction operations is highlighted, and a hybrid SD-DES approach is proposed as a means to capture the feedback between the two. In particular, this paper focuses on how to seamlessly integrate SD and DES within the framework of a modeling perspective. For the purpose of substantiating the discussion, a pipeline installation process is modeled using the proposed hybrid approach, with specific consideration given to how the approach can serve to address complex interactions between operation and context. [ABSTRACT FROM AUTHOR]

In this paper a review of impact mechanics and high-energy absorbing materials is presented. We review different theoretical models (rigid-body dynamics, elastic, shock, and plastic wave propagation, and nonclassical or nonlocal models) and computational methods (finite-element, finite-difference, and mesh-free methods) used in impact mechanics. Some recent developments in numerical simulation of impact (e.g., peridynamics) and new design concepts proposed as high energy absorbing materials (lattice and truss structures, hybrid sandwich composites, metal foams, magnetorheological fluids, porous shape memory alloys) are discussed. Recent studies on experimental evaluation and constitutive modeling of strain rate-dependent polymer matrix composites are also presented. Impact damage on composite materials in aerospace engineering is discussed along with future research needs. A particular example for the design of a sandwich material as an impact mitigator is given in more detail. This brief review is intended to help the readers in identifying starting points for research in modeling and simulation of impact problems and in designing energy absorbing materials and structures. [ABSTRACT FROM AUTHOR]

A significant number of large-scale civil infrastructure projects experience cost overruns and schedule delays. To minimize these disastrous consequences, management actions need to be carefully examined at both the strategic and operational levels, as their effectiveness is mainly dependent on how well strategic perspectives and operational details of a project are balanced. However, current construction project management approaches have treated the strategic and operational issues separately, and consequently introduced a potential conflict between strategic and operational analyses. To address this issue, a hybrid simulation model is presented in this paper. This hybrid model combines system dynamics and discrete event simulation which have mainly been utilized to analyze the strategic and operational issues in isolation, respectively. As an application example, a nontypical repetitive earthmoving process is selected and simulated. The simulation results demonstrate that a systematic integration of strategic perspective and operational details is helpful to enhance the process performance by enabling construction managers to identify potential process improvement areas that traditional approaches may miss. Based on the simulation results, it is concluded that the proposed hybrid simulation model has great potential to support both the strategic and operational aspects of construction project management and to ultimately help increase project performance. [ABSTRACT FROM AUTHOR]

Emergency rooms are critical infrastructures that provide acute care and rapid treatment of sudden illnesses and trauma. These life saving services must remain in continuous operation. An internal chemical attack on an emergency room would interrupt these essential services and severely impact the capabilities of the health care professionals and staff. In this paper, a combination of multizone simulation and statistical modeling are used as tools to assess emergency room designs for protection against an internal chemical threat. Design options include: the use of dilution ventilation, additional air handling equipment, gas phase filtration, building segmentation, and a sensor system to improve response time. Protection levels are placed into discrete categories and an ordered probability model (with random effects) is estimated. This model identifies factors, such as the design option, chemical type, elapsed time after chemical release, and the air handling unit’s operational and maintenance costs that significantly influence protection levels. Marginal effects are also computed to measure the impact of these factors on the protection-category probabilities. The results of this study can assist owners, designers, and decision makers by providing a quantitative methodology to assess building designs for protection against chemical threats. [ABSTRACT FROM AUTHOR]

Construction operations often face time constraints that influence the execution of activities, which are not addressed enough when modeling through general discrete-event simulation. This paper describes a simulation-based methodology to handle the time constraints including the cyclical break, preemption, and overtime use. In consideration of the variable number of breaks or variable break duration for different activities, an algorithm to determine the execution of the time-constrained activities is proposed, in which the concepts of time cycle and time window are introduced. The proposed algorithm is incorporated with an activity scanning simulation strategy to develop a construction simulation for modeling the time-constrained construction operations. Some examples are presented to illustrate and validate the algorithm, and highlight the effectiveness of the developed construction simulation. The study provides an alternative to improve construction simulation in modeling of the time-constrained construction operations and is expected to assist researchers or practitioners at analyzing or planning construction operations. [ABSTRACT FROM AUTHOR]

This paper presents an observer designed under the assumption that differences between predicted and measured outputs arise from discrepancies between the real structural system and the nominal model used to represent it. The observer gain is independent of the assumed model error parametrization and proves to be the transpose of the state to output matrix of a state space formulation. The estimated state with the proposed observer is shown to be identical to that obtained by exciting the nominal model with the known input while adjusting the measured portion of the state to match the measurements at the start of every step. Numerical experiments suggest that the proposed observer can provide state estimates that are substantially more accurate than results predicted by projecting the measurements in a truncated modal space. [ABSTRACT FROM AUTHOR]

In the last few decades, piezoceramic (PZT) transducers have been extensively used either as actuators or as sensors in the vibration and noise control of aero, civil, and mechanical (ACM) systems. Only in the last decade, PZT transducers have been used in the electromechanical impedance (EMI) models as both sensor and actuator for the structural health monitoring of ACM systems. In the EMI models, the PZT transducers are generally surface bonded to the host structure and are then subjected to one-dimensional (1D) voltage to interrogate the structure for the desired frequency range. The interrogation results in the prediction of electromechanical admittance signatures. These signatures serve as indicators of the health/integrity of the structure. However, the existing single PZT–structure interaction models consider the PZT transducer to be negligible in mass and thus ignored. Moreover, they impose restrictions on the PZT shape, size, and isotropy. This paper presents a novel semianalytical multiple three-dimensional PZT–structure interaction model which considers the “mass” of the PZT transducers, and the transducers are subjected to parallel (1D) sinusoidal voltage. Further, the model does not impose restriction on the shape (square or rectangular), size (thin or thick), and electrical properties (isotropic or anisotropic) of PZT. The derived model is also experimentally verified using lab-sized aluminum plate. As it is generic, the model is expected to be applicable for the nondestructive evaluation of most ACM systems. [ABSTRACT FROM AUTHOR]

This paper presents a newly developed simulation-based approach for Bayesian model updating, model class selection, and model averaging called the transitional Markov chain Monte Carlo (TMCMC) approach. The idea behind TMCMC is to avoid the problem of sampling from difficult target probability density functions (PDFs) but sampling from a series of intermediate PDFs that converge to the target PDF and are easier to sample. The TMCMC approach is motivated by the adaptive Metropolis–Hastings method developed by Beck and Au in 2002 and is based on Markov chain Monte Carlo. It is shown that TMCMC is able to draw samples from some difficult PDFs (e.g., multimodal PDFs, very peaked PDFs, and PDFs with flat manifold). The TMCMC approach can also estimate evidence of the chosen probabilistic model class conditioning on the measured data, a key component for Bayesian model class selection and model averaging. Three examples are used to demonstrate the effectiveness of the TMCMC approach in Bayesian model updating, model class selection, and model averaging. [ABSTRACT FROM AUTHOR]

This paper addresses the modeling problem of nonlinear and hysteretic dynamic behaviors through a constructive modeling approach which exploits existing mathematical concepts in artificial neural network modeling. In contrast with many neural network applications, which often result in large and complex “black-box” models, here, the writers strive to produce phenomenologically accurate model behavior starting with network architecture of manageable/small sizes. This affords the potential of creating relationships between model parameter values and observed phenomenological behaviors. Here a linear sum of basis functions is used in modeling nonlinear hysteretic restoring forces. In particular, nonlinear sigmoidal activation functions are chosen as the core building block for their robustness in approximating arbitrary functions. The appropriateness and effectiveness of this set of basis function in modeling a wide variety of nonlinear dynamic behaviors observed in structural mechanics are depicted from an algebraic and geometric perspective. [ABSTRACT FROM AUTHOR]

Based on the basic formulation developed in a companion paper, the writers now present the application of an artificial neural network approach to designing streamlined network models to simulate and identify the nonlinear dynamic response of single-degree-of-freedom oscillators using the restoring force-state mapping interpretation. The neural networks which use sigmoidal activation functions are shown to be highly robust in modeling a wide variety of commonly observed nonlinear structural dynamic response behaviors. By streamlining the networks, individual network model parameters take on physically or geometrically interpretable meaning, and hence, the network initialization can be achieved through an engineered approach rather than through less physically meaningful numerical initialization schemes. Although not proven in general, examples show that by starting with a more meaningful initial design, identification convergence is improved, and the final identified model parameters are seen to have a more physical meaning. A set of model architecture prototypes is developed to capture commonly observed nonlinear response behaviors. [ABSTRACT FROM AUTHOR]

The integration of modeling and simulation tools with robust and efficient methods of optimal design offers a rational approach to explore new concepts and designs. However, a widespread adaptation of these tools in the industry design environment will require that they incorporate a systematic analysis of uncertainty in all aspects of the design process. A lack of confidence in designs generated in a simulation-based approach is the result of uncertainties in the predictive capabilities of physics-based models used in the simulations, and poor representation of uncertainties and their propagation in a coupled systems engineering design problem. A data- and knowledge-lean environment, typical of a design process involving novel concepts, further exacerbates the situation; design engineers often make gross assumptions about distributional information of random variables and parameters, thereby adding to the uncertainty associated with the design results. The paper focuses on numerical and analytical tools by which to model uncertainty and risk in a simulation-based design environment, including cases where the uncertainty does not conform to standard probabilistic distributions. A specific focus of the modeling effort is an approach to establish confidence intervals for response predictions available from analytical and numerical models, as well as surrogate approximations used in the design process. Innovative adaptations of formal optimization methods in a nondeterministic design setting are discussed, including design problem formulations that examine the nondeterministic design problem in a multicriteria optimization framework. Simple design problems are used to illustrate the concepts and to underscore the deficiencies in a purely deterministic approach to the design problem. [ABSTRACT FROM AUTHOR]

Multiphase and multidomain fluid flows associated with interfacial dynamics, steep jump in fluid properties, and moving boundaries between different phases and materials pose substantial computational challenges. In this paper, recent progresses made in numerical simulation using continuum and lattice–Boltzmann methods are highlighted, with special attention paid to issues related to time varying geometries, adaptive grid refinement, interfacial and geometric tracking, topological changes, and reduced numerical dispersion and dissipation. Illustrative physical applications including: (1) multiple rising bubbles interacting with carrier phase and with each other; (2) wave reflected on an inclined wall; and (3) the Rayleigh–Taylor instability problem, are presented to highlight the various aspects of the techniques developed. [ABSTRACT FROM AUTHOR]

The focus of this paper is to demonstrate the application of a recently developed Bayesian state estimation method to the recorded seismic response of a building and to discuss the issue of model selection. The method, known as the particle filter, is based on stochastic simulation. Unlike the well-known extended Kalman filter, it is applicable to highly nonlinear systems with non-Gaussian uncertainties. The particle filter is applied to strong motion data recorded in the 1994 Northridge earthquake in a seven-story hotel whose structural system consists of nonductile reinforced-concrete moment frames, two of which were severely damaged during the earthquake. We address the issue of model selection. Two identification models are proposed: a time-varying linear model and a simplified time-varying nonlinear degradation model. The latter is derived from a nonlinear finite-element model of the building previously developed at Caltech. For the former model, the resulting performance is poor since the parameters need to vary significantly with time in order to capture the structural degradation of the building during the earthquake. The latter model performs better because it is able to characterize this degradation to a certain extent even with its parameters fixed. For this case study, the particle filter provides consistent state and parameter estimates, in contrast to the extended Kalman filter, which provides inconsistent estimates. It is concluded that for a state estimation procedure to be successful, at least two factors are essential: an appropriate estimation algorithm and a suitable identification model. [ABSTRACT FROM AUTHOR]

Permeability is an important property that influences the performance of hot-mix asphalt (HMA). It is a function of compaction effort, and several properties of HMA such as asphalt content, and the shape and size distribution of aggregates. Due to the different laboratory and field methods for measuring permeability, and the interaction among the factors that influence its value, it would be difficult to develop an analytical equation that accurately relates permeability to all factors contributing to HMA permeability. This paper presents a simple equation for approximating the permeability of asphalt mixes. It utilizes the percent air voids and surface area of aggregates. The equation is empirical but it is derived based on the well-known Kozeny–Carman equation for calculating the permeability of granular materials. The developed equation was used successfully to fit permeability data collected from several studies that carried field and laboratory measurements of HMA permeability. A finite element model was developed to investigate the influence of the gradient of percent air voids in HMA on water flow patterns. The x-ray computed tomography was used to measure the percent air void gradients among sublayers of the asphalt mix. The permeability of these sublayers was calculated using the developed equation, and used as an input to the finite element model. The simulation results show that air void gradients in HMA encourage lateral flow in the horizontal direction and reduce the flow in the vertical direction. [ABSTRACT FROM AUTHOR]

A new design of a reconfigurable multirotor is developed by employing a novel active–passive motor scheme. The scheme is based on quadrotor configuration with four additional motors placed in coaxial setup along a single axis. This unconventional design seeks to improve the general response of the system and increase the payload carrying capacity of the aerial vehicle. This paper presents an extensive mathematical model to establish the stability of the design, along with simulation and various real time tests. Simulation of the mathematical model with a proportional–integral–derivative (PID) controller shows the stability and responsiveness of the system in different configurations. Throttle response is also compared for different configurations. Finally, preliminary experimental test results with a prototype employing the same design are discussed. It is analytically and experimentally a stable system with a general improvement in throttle response. [ABSTRACT FROM AUTHOR]

Operational performance in residential construction production systems is assessed based on measures such as average house-completion time, number of houses under construction, lead time, and customer service. These systems, however, are prone to nonuniformity and interruptions caused by a wide range of variables such as inclement weather conditions, accidents at worksites, fluctuations in demand for houses, and rework. The availability and capacity of resources therefore are not the sole measures for evaluating construction production systems capacity, especially when rework is involved. The writers' aim is to investigate the effects of rework timeframe and frequency/length on tangible performance measures. Different call-back timeframes for rework and their impact on house-completion times are modeled and analyzed. Volume home-building was chosen as the industry sector studied in the research reported in this paper because it is a data-rich environment. The writers designed several experiments to model on time, late, and early call-back timeframes in the presence of rework with different length and frequency. Both mathematical modeling and discrete-event simulation were then used to compare and contrast outputs. The measurements showed that the average completion time is shorter in systems interrupted by frequent but short rework. In other words, a smaller downstream buffer between processes is required to avoid work starvation than those systems affected by infrequent but long interruptions. Early call-backs for rework can significantly increase the number of house completions over the long run. This indicates that there is an opportunity for the mass house-building sector to improve work practice and project delivery by effectively managing rework and its related variables. The research reported in this paper builds on the current body-of-knowledge by applying even-flow production theory to the analysis of rework in the residential construction sector, with the intention of ensuring minimal disruption to construction production process and improving productivity. [ABSTRACT FROM AUTHOR]