Andrea Luigi Facci

Nonlinear hydrodynamic damping of sharp-edged cantilevers in viscous fluids undergoing multi-harmonic base excitation

In this paper, we investigate finite amplitude polychromatic flexural vibration of a thin beam oscillating in a quiescent viscous fluid. We consider a cantilever beam with rectangular cross section undergoing periodic base excitation in the form of a triangular wave. Experiments are performed on centimeter-size beams in water to elucidate the effect of the amplitude and the frequency of the base excitation on the fluid structure interaction. The fundamental frequency of the excitation is selected to induce structural resonance and the shape of the cantilevers is parametrically varied to explore different flow regimes. Experimental results demonstrate the presence of a frequency-dependent nonlinear hydrodynamic damping which tends to enhance higher frequency harmonics as compared to the fundamental harmonic. Such filtering effect produced by the encompassing fluid increases with both the frequency and amplitude of the base excitation. Experimental results are interpreted through available theoretical model...

SOFC Management in Distributed Energy Systems

Among the distributed generation emerging technologies, solid oxide fuel cells (SOFCs) seem to be the most promising for small and medium power (up to 1 MW) as they feature extremely high efficiency and low pollutant emissions, and the high-grade waste heat can be utilized for space heating, process steam, and/or domestic hot water demands. As their main drawbacks are high cost and relatively short lifetime, much research is devoted to solve technological problems and to develop less expensive materials and mass production processes. However, even if SOFCs are close to commercialization and several demonstration units are already running, only few researches have been performed on their integration in power plants for distributed power generation, which are complex systems made up of different components that have to satisfy energy requirements (heat, electricity, and cooling). In this paper, we investigate the behavior of SOFCs in distributed energy systems and how their operation in terms of load and fuel utilization factor could optimize fuel consumption and/or minimize energy costs. The potential advantages of SOFCs related to their excellent part-load operation and their ability to meet and follow the highly noncoincident electric and thermal loads in either grid-connected or stand-alone configurations are discussed.

Numerical Assessment of Similitude Parameters and Dimensional Analysis for Water Entry Problems

The prediction of impulsive loads deriving from the sudden impact of a solid body on the water surface is of fundamental importance for a wide range of engineering applications. The study of hull-slamming phenomena largely relies on laboratory scale experimental investigations and on simplified analytical models. The aim of this paper is to quantitatively assess the interplay between the relevant nondimensional parameters for the water entry of a two-dimensional body, evidencing the similitude conditions that allow the transition from scaled experiments to real size applications. This assessment is performed through the numerical study of the hydrodynamics induced by the water impact of a two-dimensional wedge. The fluid flow is considered incompressible. First of all numerical simulations are validated by comparison with experimental data from the literature and with the Wagner seminal theory. Afterwards, a thorough computational study is performed by systematically varying all the relevant parameters, such as the nondimensional entry velocity and acceleration. We conclude by evidencing some design prescriptions that should be adopted in order to facilitate the transition of laboratory scale experiments to real scale applications.

Comparing Energy and Cost Optimization in Distributed Energy Systems Management

Distributed generation, despite not being a new concept, is assuming a leading role in the field of energy conversion, as it should contribute to the enhancement of efficiency, flexibility, and reliability of national energy systems. However, it also noted that the effective performances of small and flexible power plants is critically influenced by their actual control strategy. Moreover, it is not trivial to identify a univocal parameter to evaluate the plant performance. For instance, cost evaluation clearly responds to an industrial view of the energy supply problem, while energy consumption or polluting emissions comply with a socio economic approach. In this scenario, the optimization of the plant management is a valuable instrument to gain insight on their behavior as the control strategy is varied, as well as to promote the distributed generation development, by maximizing the plants performances. In this paper, we further develop a graph based optimization methodology to optimize the set-point of an internal combustion engine based plant used to satisfy a hospital energy load, under different seasonal load conditions (winter, summer, and transitional seasons) and energy prices. Specifically, in order to dissect the effects of the objective function selection, two different optimization criteria are considered, namely economical optimization and primary energy consumption minimization. In particular, we focus on the features of the prime mover (i.e., the internal combustion engine) control strategy and on its drivers, as a function of the prescribed objective function. Results demonstrate that in the actual Italian energy market, cost minimization does not match primary energy consumption minimization, because the latter is only influenced by energy demand time series, and equipments performance, while the former is fundamentally driven by the electricity prices time series.

Optimization of CHCP Operation Strategy: Cost vs Primary Energy Consumption Minimization

An effective methodology to determine the optimal operational strategy for a complex CHCP plant is presented. The model is based on the minimization of a chosen variable and it is organically developed integrating thermodynamics and economics. The graph-based optimization algorithm is developed in order to find the optimal set-points of the energy system components in a sufficiently short-time. By this way the model is applicable to real industrial problems, especially when the energy is sold to the electricity market. The problem in study is discretized in time and plant states, represented as weighted graph, and the strategy that minimizes the total cost is determined using backward dynamic programming. The proposed methodology has been applied to the optimization of the set-point of an internal combustion engine based plant used to satisfy an hospital energy load, under different seasonal load conditions (winter, summer and transitional seasons) and energy prices. Two different optimization criteria are considered, namely economical optimization and primary energy consumption minimization. It is then demonstrated that the model can be effectively applied to analyze the cost and profit in energy conversion in power plants, related to electricity price, fuel price, running of turbine and auxiliary equipment, service power consumption. In particular, the chosen test case demonstrates not only the model reliability but also the economical and thermodynamic convenience of using the model itself to optimize the plant.Copyright

Three-Dimensional Simulation of Gaseous Fuel Injection Through a Hybrid Approach

Direct injection of gaseous fuel has emerged to be a high potential strategy to tackle both environmental and fuel economy requirements. However, since the electronic gaseous injection technology is rather new for automotive applications, limited experience exists on the optimum configuration of the injection system and the combustion chamber. To facilitate the development of these applications computer models are being developed to simulate gaseous injection, air entrainment, and the ensuing combustion. This paper introduces a new method for modeling the injection process of gaseous fuels in multidimensional simulations. The proposed model allows holding down grid requirements, thus, making it compatible with the three-dimensional simulation of an internal combustion engine.

Multidimensional Modelling of Gaseous Injection in Modern Direct Injection Internal Combustion Engines: Analisys of Different Fuel Injection Strategies.

In the short medium term natural gas has emerged as one of the most promising energy sources for internal combustion engines because its usage leads to cleaner combustion, lower CO2 emissions, and energy source diversification. However, considering that automotive DI gas engines are rather new, only limited experience exists on the optimum configuration of the injection system and the related strategy. To facilitate the development of these applications computer models are being developed. In a previous paper, a phenomenological-3D combined approach to simulate gas injection has been presented. This model has been implemented in a modified version of the KIVA 3V code and the simulation of a gas engine is here presented. After having validated both the injection model and the whole 3D code, an analysis of different injection strategies have been carried out in order to demonstrate that these tools are suitable for optimization of direct injection gas engines. To this aim a research engine has been simulated in under stratified charge conditions.

Control strategy optimization of HVAC plants

In this paper we present a methodology to optimize the operating conditions of heating, ventilation and air conditioning (HVAC) plants to achieve a higher energy efficiency in use. Semi-empiric numerical models of the plant components are used to predict their performances as a function of their set-point and the environmental and occupied space conditions. The optimization is performed through a graph-based algorithm that finds the set-points of the system components that minimize energy consumption and/or energy costs, while matching the user energy demands. The resulting model can be used with systems of almost any complexity, featuring both HVAC components and energy systems, and is sufficiently fast to make it applicable to real-time setting.

Influence of sensors layout in damage monitoring of cylindrical bodies under impulsive hydrodynamic loading

The problems related to solid bodies impacting the water surface often result of difficult approach, but the possibility of monitoring the structural behavior in real time represents an important scientific challenge for damage and critical condition detection. The availability of sensing system technologies able to operate at very large sampling frequencies, with high resolution and very low noise, moves the issue to the development of modelling tools and processing codes that can manage signals. An enhanced method for real time structural health monitoring of cylindrical bodies has been presented by the authors in previous works. In this paper is tested the capability of the procedure to detect damage presence, extension and position with different sensing system dispositions.The problems related to solid bodies impacting the water surface often result of difficult approach, but the possibility of monitoring the structural behavior in real time represents an important scientific challenge for damage and critical condition detection. The availability of sensing system technologies able to operate at very large sampling frequencies, with high resolution and very low noise, moves the issue to the development of modelling tools and processing codes that can manage signals. An enhanced method for real time structural health monitoring of cylindrical bodies has been presented by the authors in previous works. In this paper is tested the capability of the procedure to detect damage presence, extension and position with different sensing system dispositions.

Strongly coupled partitioned approach for fluid structure interaction in free surface flows

In this paper we describe and validate a methodology for the numerical simulation of the fluid structure interaction in free surface flows. Specifically, this study concentrates on the vertical impact of a rigid body on the water surface, (i.e. on the hull slamming problem). The fluid flow is modeled through the volume of fluid methodology, and the structure dynamics is described by the Newton’s second law. An iterative algorithm guarantees the tight coupling between the fluid and solid solvers, allowing the simulations of lightweight (i.e. buoyant) structures.The methodology is validated comparing numerical results to experimental data on the free fall of different rigid wedges. The correspondence between numerical results and independent experimental findings from literature evidences the reliability and the accuracy of the proposed approach.In this paper we describe and validate a methodology for the numerical simulation of the fluid structure interaction in free surface flows. Specifically, this study concentrates on the vertical impact of a rigid body on the water surface, (i.e. on the hull slamming problem). The fluid flow is modeled through the volume of fluid methodology, and the structure dynamics is described by the Newton’s second law. An iterative algorithm guarantees the tight coupling between the fluid and solid solvers, allowing the simulations of lightweight (i.e. buoyant) structures.The methodology is validated comparing numerical results to experimental data on the free fall of different rigid wedges. The correspondence between numerical results and independent experimental findings from literature evidences the reliability and the accuracy of the proposed approach.