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Editorial Complex Optimization and Simulation in Power Systems

Abstract The integrity of PWR pressure vessels is assured by keeping the crack tip stress intensity factor below the toughness of the material under monotonic isothermal loading. To study the effects of sudden cooling associated with a thermal gradient, a specially modified compact specimen has been developed. This has been used to carry out tests in the transition zone with different loading-temperature sequences liable to call the conventional criteria into question. The test is described in detail in Part I of this article [Chapuliot S, et al. Thermomechanical analysis of thermal shock fracture in the brittle/ductile transition zone. Part I: Description of the tests. Engng Fract Mech, 72, 2005, 661–73]. The second part describes numerical investigations to estimate the local mechanical fields at the crack tip and the overall parameters of the fracture mechanics. Finite element thermomechanical calculations are used to interpret the results of these new thermal shock tests using the master curve concept [ASTM E 1921–1997. Standard test method for determination of reference temperature To for ferritic steels in the transition range, 1997] and the Beremin statistical model [Beremin FM. A local criterion for cleavage fracture of a nuclear pressure vessel steel. Metall Trans A, 14A, November 1983, 2287–777].

Abstract This work aims to predict the general performances of a pilot parabolic trough collector during transient periods. To do so, a one-dimensional thermal model has been developed. It has been validated with experimental results from two different experimental setups, in steady-state conditions, with a transmitted power maximum error of 3.4%. Since the model only predicts the collector's thermal behavior, the parabolic trough collector has been first optically qualified. Then, optical efficiencies were used as input for the model. Experimental results were obtained in steady-state conditions and compared to the model. Then, experimental and numerical results were compared during two period of time with varying inlet conditions (i.e. dynamic condition tests): the first one with stable conditions, and the other one with harsh conditions. The developed model showed a good capability of predicting the thermal behavior of the parabolic trough collector with unstable environment (DNI, mass flow, inlet temperature), with a 9.6% relative standard error in the worst case. As a conclusion, while previous studies only focused on steady-state conditions, it has been showed that this kind of model can be used to precisely predict the dynamic behavior of large power plants.

Abstract Building-based active envelopes play an important role to reduce active heating supplies. Several techniques are developed to enhance the energy performances of active building envelopes; meanwhile, numerous numerical and mathematical models are also developed to conduct the performance analysis of these techniques. In this paper, we propose a state-space model for solar active wall-based Phase Change Materials (PCM). The advantage of this method remains in its simplicity to provide details of internal nodes and input/output parameters. The low-cost calculation is a supplementary advantage versus a heavy numerical method. The proposed numerical model is applied for a multi-layer wall with PCM Wallboards (PCMW) embedded between indoor and outdoor environments. The results show the ability of the state-space model to estimate the thermal behavior of the system, as well as the thermal characteristics of embedding PCM in the internal face of the wall. It significantly contributes to stabilize the indoor temperature and to ensure the thermal comfort.

Demand-Side Management systems aim to modulate energy consumption at the customer side of the meter using price incentives. Current incentive schemes allow consumers to reduce their costs, and from the point of view of the supplier play a role in load balancing, but do not lead to optimal demand patterns. In the context of charging fleets of electric vehicles, we propose a centralised method for setting overnight charging schedules. This method uses evolutionary algorithms to automatically search for optimal plans, representing both the charging schedule and the energy drawn from the grid at each time-step. In successive experiments, we optimise for increased state of charge, reduced peak demand, and reduced consumer costs. In simulations, the centralised method achieves improvements in performance relative to simple models of non-centralised consumer behaviour.

In order to know the origin of the noise generation when an impinging jet hit a specific geometry, an experimental setup was used allowing the generation of the flow and the adjustments of its parameters (such as Reynolds number, confinement, alignment, etc…). The vortex dynamics in case of a high acoustic level for two different Reynolds numbers Re = 5684 and Re = 6214 are considered here. Indeed, many configurations allow self-sustaining sound loop to take place in confined spaces between the nozzle and the impinged surface. This feedback loop optimizes the energy transfer between the aerodynamic field and the acoustic field and creates a source of noise that can become very noisy. Thus, to control these phenomena, it is necessary to understand the aero-acoustic coupling in such configurations. As a result, we measured the 2C kinematic instantaneous fields (vx, vy) of the flow by the technique of Particle Image Velocimetry (PIV) with a sampling rate of 1 KHz and the acoustic field is obtained using a B&K Microphone. For the two considered Reynold numbers, we can distinguish two patterns for the vortices travelling from the nozzle toward the plate of impact.

This paper details a numerical study of solid-liquid phase change heat transfer in a rectangular enclosure with the aim of optimizing the number, dimension, and positioning of fins in the enclosure. The enclosure is exposed on one side to a constant heat flux of 1000 W/m2 for 3 h and both the total fin mass and the PCM mass are kept constant in all simulated cases. The heat diffusion equation in the PCM uses the equivalent heat capacity method while natural convection driven PCM motion in the enclosure is modeled through the buoyancy force, using a modified viscosity and an additional volume force term in the Navier-Stokes momentum conservation equation. Three efficiency assessment parameters are used: (i) the height-averaged temperature of the front hot plate which should remain as low as possible for the longer possible time, (ii) the energy stored inside the PCM as a function of time, and (iii) the heat transfer rate and heat flux between the front plate and the PCM. For each simulated case, complementary data such as the standard deviation of temperature along the heated plate and the ratio of sensible heat to latent accumulation are also calculated. Results show that increasing the number of fins diminishes both the stabilization temperature and the stabilization time of the front plate during phase change, and accelerates the sensible and latent storage of energy in the PCM. Using thinner but longer fins provides the same impact except that the stabilization time also increases as the fin length is increased. Besides, at constant fin mass, varying fin spacing have marginal impact on the latent heat storage performance and on the hot plate temperature stabilization. The study also shows that the surface area plays the largest role in the increase of the heat transfer rate between the front plate and the PCM, while configurations which can promote stronger natural convection lead to higher heat flux. Finally, it was observed that systems allowing easier heat transfer to the back plate during melting provide a higher ratio of sensible heat to latent accumulation, while the standard deviation of the front plate temperature decreases as the number of fins or the spacing between fins increases.