Model-based groupware solution for distributed real-time collaborative 4D planning via teamwork

Construction planning plays a fundamental role in construction project management that requires team working among planners from a diverse range of disciplines and in geographically dispersed working situations. Model-based four-dimensional (4D) computer-aided design (CAD) groupware, though considered a possible approach to supporting collaborative planning, is still short of effective collaborative mechanisms for teamwork due to methodological, technological and social challenges. Targeting this problem, this paper proposes a model-based groupware solution to enable a group of multidisciplinary planners to perform real-time collaborative 4D planning across the Internet. In the light of the interactive definition method, and its computer-supported collaborative work (CSCW) design analysis, the paper discusses the realization of interactive collaborative mechanisms from software architecture, application mode, and data exchange protocol. These mechanisms have been integrated into a groupware solution, which was validated by a planning team in a truly geographically dispersed condition. Analysis of the validation results revealed that the proposed solution is feasible for real-time collaborative 4D planning to gain a robust construction plan through collaborative teamwork. The realization of this solution triggers further considerations about its enhancement for wider groupware applications

Tactical fixed job scheduling with spread-time constraints

We address the tactical fixed job scheduling problem with spread-time constraints. In such a problem, there are a fixed number of classes of machines and a fixed number of groups of jobs. Jobs of the same group can only be processed by machines of a given set of classes. All jobs have their fixed start and end times. Each machine is associated with a cost according to its machine class. Machines have spread-time constraints, with which each machine is only available for L consecutive time units from the start time of the earliest job assigned to it. The objective is to minimize the total cost of the machines used to process all the jobs. For this strongly NP-hard problem, we develop a branch-and-price algorithm, which solves instances with up to 300 jobs, as compared with CPLEX, which cannot solve instances of 100 jobs. We further investigate the influence of machine flexibility by computational experiments. Our results show that limited machine flexibility is sufficient in most situations

Unlocking the flexibility of combined heat and power for frequency response by coordinative control with batteries

Owners of combined heat and power (CHP), e.g., industrial manufacturers, are motivated to provide frequency response to power grids due to clear financial benefits. Yet, the slow response speed of CHP limits its capability in providing such services. Moreover, frequent adjustments would cause a faster lifetime reduction of CHP and rapid pressure fluctuation in the gas network. To further unlock the flexibility of CHP, this paper integrates a battery unit with CHP via a power electronic interface. A filter-based coordinative controller is designed for smoothing short-term fluctuations in CHP outputs. Based on the filter parameters and frequency response requirements, the minimum required capacity of the battery is identified. The results show that the proposed system enhances the capability of CHP for frequency response and mitigates the associated adverse effects on the gas network. The required capacity of the battery is economically feasible considering the benefit it brings to the CHP

Tailoring magnetic hysteresis of Fe-Ni permalloy by additive manufacturing: Multiphysics-multiscale simulations of process-property relationships

Designing the microstructure of Fe-Ni permalloy by additive manufacturing (AM) opens new avenues to tailor the materials' magnetic properties. Yet, AM-produced parts suffer from spatially inhomogeneous thermal-mechanical and magnetic responses, which are less investigated in terms of process simulation and modeling schemes. Here we present a powder-resolved multiphysics-multiscale simulation scheme for describing magnetic hysteresis in materials produced via AM. The underlying physical processes are explicitly considered, including the coupled thermal-structural evolution, chemical order-disorder transitions, and associated thermo-elasto-plastic behaviors. The residual stress is identified as the key thread in connecting the physical processes and in-process phenomena across scales. By employing this scheme, we investigate the dependence of the fusion zone size, the residual stress and plastic strain, and the magnetic hysteresis of AM-produced Fe21.5Ni78.5 permalloy on beam power and scan speed. Simulation results also suggest a phenomenological relation between magnetic coercivity and average residual stress, which can guide the magnetic hysteresis design of soft magnetic materials by choosing appropriate AM-process parameters

A novel reflection removal method for acoustic emission wave propagation in plate-like structures

Acoustic emission (AE) is defined as the transient elastic wave generation due to a rapid release of strain energy within or on the surface of a material, which is well known as a highly sensitive technique to detect various types of damage, such as crack propagation in structure. In order to obtain the propagation characterizations of AE signals, simulation based on finite element method (FEM) is effective method. This paper attempts to present a new modeling method of AE by investigating the removal of unwanted reflections from the boundaries of the waveguides including plate and thin-walled cylinder structures. The principles of these techniques are described based on the theory of the infinite element and Rayleigh damping. Then FEM is implemented to simulate the properties of AE source mechanism, propagation and reflection, and the finite element (FE) models are established with reflections removal condition proposed in this paper. To validate accuracy of the FE technique, the AE simulation of an isotropic plate is carried out then compared with the result of pencil lead broken test on a steel plate. By the Choi-Williams transformation the analysis result of the simulation and experiment AE signals indicate that the former is consistent with the latter. Then the removal effect is validated by AE simulations in a thin-walled cylinder and an anisotropic plate too. All of the results demonstrate that the Rayleigh damping has significant influence on the removal effect of infinite elements. The results of this study clearly illustrate the effectiveness of using the FE method to model AE wave propagation problems and high accuracy removal of unwanted reflection can be realized by the infinite elements with appropriate Rayleigh damping

Mechanical tailoring of dislocation densities in SrTiO₃ at room temperature

Dislocation‐tuned functional properties such as electrical conductivity, thermal conductivity, and ferroelectric properties in oxides are attracting increasing research interest. A prerequisite for harvesting these functional properties in oxides requires successful introduction and control of dislocation density and arrangement without forming cracks, which is a great challenge due to their brittle nature. Here, we report a simple method to mechanically tailor the dislocation densities in single‐crystal perovskite SrTiO₃. By using a millimeter‐sized Brinell indenter, dislocation densities from ∼10¹⁰ to ∼10¹³ m⁻² are achieved by increasing the number of indenting cycles. Depending on tip radius and indenting load, large and crack‐free plastic zones over hundreds of micrometers are created. The dislocation multiplication mechanisms are discussed, and the work hardening in the plastic zone is evaluated by micro‐hardness measurement as a function of dislocation density. This simple approach opens many new opportunities in the area of dislocation‐tuned functional and mechanical studies