A simplified model for improving thermal stability of Lithium-ion batteries

Lithium ion batteries represent a well established technology in a range of applications (laptops, mobile phones, etc.) but they are becoming key factors in many other areas were reliability and safety are of paramount importance (e.g. the space and automobile industries). However, a number of drawbacks still raise concerns about their wider use and hamper a more structured introduction in these additional applications. In particular, the management of heat effects remains a challenge, as an excessive temperature rise can cause reduction of cycle life, battery failures and, above all, may lead to thermal runaway of individual cells or of an entire battery pack, with associated damages to the surrounding people or environment. In the present paper, a simplified model capable of predicting the thermal behaviour of a battery pack refrigerated with a cooling fluid, is presented. It allows to quickly estimating the efficiency of a given cooling system under specific working conditions, and thus identify the range of operation within which a given energy storage system can safely operate

Deformation patterns in a second-gradient lattice annular plate composed of "Spira mirabilis" fibers

In this paper, we aim to explore the mechanical potentialities of a material made of an orthogonal net of fibers arranged in logarithmic spirals. Therefore, an annular plate described with a second-gradient model is envisaged to evaluate the behavior of such material in a nonlinear elastic regime when large displacements and deformations occur. Several mechanical tests are performed numerically under the finite element method approximation obtained directly with a weak formulation based on the elastic energy that it is assumed to be predictive for this kind of network system of fibers. Plots reporting the mechanical characteristics in all the considered tests are provided to illustrate the overall mechanical behavior of the evaluated system

Towards targeted dietary support for shift workers with type 2 diabetes (Shift-Diabetes study): A mixed-methods case study protocol

BACKGROUND: Blood glucose is higher in people working night-shifts compared to day-workers. Changes to eating behaviour, activity, and sleep patterns in addition to circadian disruption are likely to impact glucose management in night-shift workers with Type 2 diabetes. AIM: To investigate current dietary intake and glucose variability during night work, including barriers and facilitators to dietary behavior in this context. METHODS: A mixed-methods case study will be conducted. Shift workers with Type 2 diabetes working in a hospital setting will be recruited to this two-part study. Part 1: 70 participants will complete a 10-day observational study collecting data on continuous glucose, diet (self-report diary), sleep and physical activity during a period covering night work, rest days and non-night workdays. Mean glucose concentration and variability, and the mean healthy diet index score, will be compared between days of night work, non-night work and rest, after adjusting for other individual factors (sleep/physical activity/demographics). Part 2: A sample (n~13) will complete semi-structured interviews based on behavioural science frameworks to explore barriers/enablers to dietary behaviour when working night shifts. This will inform a quantitative survey to explore the generalisability of interview findings. DISCUSSION: Findings from Part 1 and 2 will be triangulated to identify potential intervention strategies to address key barriers and enablers to healthier eating, and in turn improved glucose control, in shift workers with Type 2 diabetes. This will be facilitated through stakeholder consultation and application of behavioural science frameworks

qualitative thermal characterization and cooling of lithium batteries for electric vehicles

The paper deals with the cooling of batteries. The first step was the thermal characterization of a single cell of the module, which consists in the detection of the thermal field by means of thermographic tests during electric charging and discharging. The purpose was to identify possible critical hot points and to evaluate the cooling demand during the normal operation of an electric car. After that, a study on the optimal configuration to obtain the flattening of the temperature profile and to avoid hot points was executed. An experimental plant for cooling capacity evaluation of the batteries, using air as cooling fluid, was realized in our laboratory in ENEA Casaccia. The plant is designed to allow testing at different flow rate and temperatures of the cooling air, useful for the assessment of operative thermal limits in different working conditions. Another experimental facility was built to evaluate the thermal behaviour changes with water as cooling fluid. Experimental tests were carried out on the LiFePO4 batteries, under different electric working conditions using the two loops. In the future, different type of batteries will be tested and the influence of various parameters on the heat transfer will be assessed for possible optimal operative solutions

Design and evaluation of artificial controllers assisting voluntary balance performance in paraplegia and in stroke

The mobility impairment caused by a paralysis like a spinal cord injury or a stroke has, beside many other impacts, an influence on the transfer of signals between the muscles of the lower extremities and the brain. In a paraplegic person, this means that she or he can not stand without holding onto a support or standing in a standing frame while the impact on the ability to balance in a hemiplegic person can be less severe. Although the connection between the muscles and the brain is impaired by the injury, the muscles still retain the ability to contract if innervated. This thesis describes control approaches which combine the remaining voluntary control of the paraplegic and stroke patients with the artificially controlled stimulation of the muscles of the paralysed limbs to aid the subject in balancing. The aim was to develop new control approaches which would assist balance in paraplegic subjects and in stroke. To support standing in paraplegic subjects, the moment generated at the ankle using electrical stimulation of the shank muscles was integrated with the voluntary control of the upper body, resulting in the concept of Integrated Voluntary Control (IVC). In the outer loop the ankle moment produced by the paraplegic subject due to his voluntary upper body movement was estimated using a mathematical model based on the inclination angles of upper and lower body. This estimated ankle moment was then compared with the actual moment applied at the force plates the subject was standing on, and an appropriate stimulation signal was applied to the paralysed shank muscles. Experimental evaluation initially involved four able bodied volunteers in which base line results with stiffness and stiffness-viscosity controllers using a rotating standing platform were obtained. This was extended to the paraplegic subject, where electrical muscle stimulation was used to generate the required ankle moment. The IVC concept was then evaluated with the paraplegic subject and compared to the base line results. Due to the nature of the system and implied perturbation onto the control system controlling the posture of the paraplegic subject the known evaluation values (e.g. rise time, steady state value, overshoot value etc.) are not suitable. Therefore, the variance of a time signal around its mean value was used as an evaluation value which allowed to compare the achieved performance of the paraplegic subject employing the new control approach with the stiffness and stiffness-viscosity controllers directly. To assist balance in stroke patients, a new training approach was introduced based on the concept of integrating the voluntary abilities of the patient with mechanical balance support and sensory electrical stimulation. This concept was evaluated in a training program with one stroke subject which demonstrated the feasibility and potential balance improvement resulting from this approach.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Improving the linear stability of the visco-elastic Beck's beam via piezoelectric controllers

Control strategies for the visco-elastic Beck’s beam, equipped with distributed piezoelectric devices and suffering from Hopf bifurcation triggered by a follower force, are proposed in this paper. The equations of motion of the Piezo-Electro-Mechanical (PEM) system are derived through the Extended Hamilton Principle, under the assumption that the piezoelectric patches are shunted to the so-called zero-order network and zero-order analog electrical circuit. An exact solution for the eigenvalue problem is worked out for the PEM system, while an asymptotic analysis is carried out to define three control strategies, recently developed for discrete PEM systems, that are here adapted to improve the linear stability of the visco-elastic Beck’s beam. An extensive parametric study on the piezo-electrical quantities, based on an exact linear stability analysis of the PEM system, is then performed to investigate the effectiveness of the controllers

On the effectiveness of a rod-like distributed piezoelectric controller in preventing the Hopf bifurcation of the visco-elastic Beck’s beam

The linear stability of a piezo-electro-mechanical (PEM) system subject to a follower force is here discussed. The mechanical subsystem is constituted by a linear visco-elastic cantilever beam, loaded by a follower force at the free end. It suffers from the Hopf bifurcation, whose critical load is strongly affected by damping, according to the well-known Ziegler’s paradox. On the other hand, the electrical subsystem consists of a distributed array of piezoelectric patches attached to the beam and connected to a properly designed second-order analog circuit, aiming at possibly enhancing the stability of the PEM system. The partial differential equations of motion of the PEM system are discretized by the Galerkin method. Linear stability analysis is then carried out by numerically solving the associated eigenvalue problem, for different significant values of the electrical parameters. A suitable perturbation method is also adopted to detect the role of the electrical parameters and discuss the effectiveness of the controller

On the effects of a beam-like piezoelectric passive controller on the linear stability of the visco-elastic Beck's beam

The linear stability of the visco-elastic Beck's beam is investigated in this paper. The mechanical system is equipped with a piezoelectric distributed controller, whose governing equation of motion in linear dynamics resembles that of the beam, in except for the second-order spatial derivative term related to the follower force. Suitable passive control strategies are explored with the aim to increase the Hopf bifurcation critical load, triggered by the presence of the follower force in the mechanical sub-system. The equations of motion of the resultant Piezo-Electro-Mechanical (PEM) system are derived via a variational approach and discretized through the Galerkin method. The linear stability analysis of the PEM system is carried out by solving the descending eigenvalue problem. In this framework, parametric investigations are developed in order to investigate the effects of the electrical parameters on the stability of the system

A rod-like piezoelectric controller for the improvement of the visco-elastic Beck's beam linear stability

The linear stability of a cantilever beam subject to a follower force is investigated. A system of distributed piezoelectric devices is attached to the beam with the purpose of improving the dynamic stability of the structure. They are connected to a second-order network and second-order analog electrical circuit. The assembly of the mechanical and piezoelectric subsystems constitutes a coupled Piezo-Electro-Mechanical (PEM) system, whose equations of motion, derived within a variational approach, are discretized via the Galerkin weighted residual method and the stability of the trivial equilibrium is addressed by numerically solving the associated eigenvalue problem. A sensitivity analysis, carried out on a numerical ground, is thus conducted on a wide range of the electrical parameters to investigate the effectiveness of the proposed controller

On the failure of the ’Similar Piezoelectric Control’ in preventing loss of stability by nonconservative positional forces

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