Dissipative Scheme Research Articles

A comprehensive numerical study based on topology optimization for cooling plates thermal design of battery packs

This article focuses on the problem of fluctuating cooling system flow caused by different working states such as acceleration and braking during the actual operation of electric vehicles, which prevents the system from effectively dissipating heat from the battery for a long time. In the past, liquid cooling heat dissipation schemes designed based on structural parameters often relied on the experience of CFD engineers. There is no in-depth study of the heat propagation characteristics. At present, research on the application of topology optimization method in cooling plate design mainly focuses on the relative positions of single inlet and outlet, objective functions, and constraint conditions. There are very few studies evaluating the adaptability of different cooling plate structures at different flow rates. In this perspective, this work proposes a two-dimensional topology optimization method for obtaining the cooling plates with different topological structures such as the series of cooling plate structures with dual entrances and exits. The method comprises of a comprehensive study on variations of the inlet flow rate under different average fluid volume fraction, outlet width, and temperature weight conditions. The results indicate that setting an excessive inlet flow rate can actually lead to an increase in the average temperature of the optimized cooling plate. Subsequently, the cooling plate structure obtained through topology optimization at inlet flow rates of 0.015 m/s, 0.02 m/s, and 0.025 m/s was selected, and a three-dimensional electrothermal fluid coupling model was established based on its two-dimensional channel structure. Its cooling performance, flow characteristics, and heat transfer characteristics were analyzed, and compared with two straight channel reference models. The results indicate that the optimized cooling plate structure under low flow conditions has better heat dissipation performance. At a flow rate of 0.56 × At 10-6m3/s, compared to traditional cooling plates(CASE D, CASE E), the highest temperature of the battery using topology optimized cooling plates (CASE A) decreased by 3.5 K and 1.79 K, respectively, and the standard deviation of temperature decreased by 48% and 14%, respectively. Under the same inlet flow velocity, the area of the fluid region increases with the increase of the mean fluid volume fraction, and the width of the flow channel increases gradually and the branches increase significantly, from the concentrated solid region to the dispersed isolated region. At a low flow rate, the normalized temperature of the cooling plate increases with the increase of the flow rate of the coolant inlet, and when the flow rate reaches a certain value, in order to reduce the power loss of the cooling plate, the flow path is gradually concentrated on both sides of the cooling plate. This leads to the decline of the normalized temperature of the cooling plate.

Resolving entropy growth from iterative methods

We consider entropy conservative and dissipative discretizations of nonlinear conservation laws with implicit time discretizations and investigate the influence of iterative methods used to solve the arising nonlinear equations. We show that Newton’s method can turn an entropy dissipative scheme into an anti-dissipative one, even when the iteration error is smaller than the time integration error. We explore several remedies, of which the most performant is a relaxation technique, originally designed to fix entropy errors in time integration methods. Thus, relaxation works well in consort with iterative solvers, provided that the iteration errors are on the order of the time integration method. To corroborate our findings, we consider Burgers’ equation and nonlinear dispersive wave equations. We find that entropy conservation results in more accurate numerical solutions than non-conservative schemes, even when the tolerance is an order of magnitude larger.

Optimization of Heat Dissipation and Control Scheme for Wind Turbine Gearbox Based on FloMaster-Simulink co-Simulation

Due to favorable wind conditions and steadily rising temperatures, the demand for heat dissipation for the gearbox of wind turbines rises every spring and summer, and the energy consumption of the heat dissipation system rises as well. In cases where the gearbox oil temperature is excessively high due to poor heat dissipation, the wind turbine unit may only operate at a limited load or shut down. This article suggests a restoration strategy that uses seawater to cool the gearbox lubrication system, based on the operation of the gearbox cooling system of wind turbines. The original wind turbine gearbox cooling system and the enhanced seawater cooling system simulation models are built at the same time, and dynamic working conditions simulation research is done by utilizing the FloMaster simulation platform. To achieve automatic management of the gearbox temperature, we alter the fan or pump’s speed by the oil temperature at the gearbox’s outlet. We design a control scheme based on the working principle and use the FloMaster-Simulink co-simulation to calculate the operating characteristics of the system under dynamic working conditions. The results show that by simultaneously controlling the speed of the pump and the speed of the fan, the cooling system has the best control effect and the lowest energy consumption, providing a reference for the development of the gearbox cooling system of wind turbines.

Quantum metrology with critical driven-dissipative collective spin system

We propose two critical dissipative quantum metrology schemes for single parameter estimation which are based on a quantum probe consisting of a coherently driven ensemble of N spin-1/2 particles under the effect of a collective spin decay. The collective spin system exhibits a dissipative phase transition between thermal and ferromagnetic phases, which is characterized by a nonanalytical behavior of the spin observables. We show that thanks to the dissipative phase transition the sensitivity of the parameter estimation can be significantly enhanced. Furthermore, we show that our steady state is a spin squeezed state which allows one to perform parameter estimation with sub shot-noise limited measurement uncertainty.

On designing and developing single‐step second‐order implicit methods with dissipation control and zero‐order overshoots via subsidiary variables

AbstractHilber and Hughes gave several competitive demands on the implicit methods in 1978. However, there are no such integration methods in the traditional algorithm design. Via imposing subsidiary variables, this article proposes two novel implicit methods to splendidly achieve these competitive demands without increasing computational costs. The two novel methods are self‐starting, unconditionally stable, single‐solve, identically second‐order accurate, controllably dissipative, and non‐overshooting. The novel methods achieve the maximal dissipation of auxiliary variables in the high‐frequency limit, although such the design is not a must. The first novel method uses auxiliary velocity and acceleration variables, whereas the second one employs two auxiliary acceleration variables. After embedding desired numerical characteristics, the novel methods employ four eigenvalues of amplification matrices in the high‐frequency limit as user‐specified parameters to flexibly control numerical high‐frequency dissipation. To reduce the number of use‐specified parameters, this article gives some recommended sub‐families of algorithms, such as optimal low‐frequency dissipation schemes. The article further refines the error analysis to analytically calculate amplitude and phase errors for some implicit methods. The error analysis technique can be applied to almost all direct time integration methods. Comparisons of amplitude and phase errors highlight the superiority of the novel methods over the published algorithms. In addition, some classical measures, such as numerical damping ratios and relative period errors, are analyzed and compared. Numerical examples are solved to show the novel methods' superiority.

Effect of gas–liquid phase change of axial rotating heat pipe on fluid-thermal-solid behaviors of high-speed spindle

The thermal deformation control (TDC) of the high-speed spindle (HSS) is difficult to be realized because the nonlinear, non-steady, and varying influencing factors, and traditional cooling system cannot effectively dissipate the internal heat and realize TDC. It is expected to effectively export the internal heat of HSS with a reasonable design and manufacturing. To effectively realize HSS cooling and TDC, the effect of gas–liquid phase change of axially rotating heat pipe (ARHP) on fluid-thermal-solid behaviors of HSS is investigated. The ARHP, which is suitable for HSS cooling and TDC, is designed. Then an experimental platform is constructed to study the operation performance and heat dissipation performance (HDP) of the designed ARHP under different working conditions. The effects of the rotational speed, heat flux, and cooling air flow rate on HDP of ARHP are investigated. The designed ARHP is embedded into the original HSS (O-HSS) to dissipate the internal heat, and the silicone grease (SG) is used to fill the gap between the ARHP and shaft core of HSS, increasing the contact area and enhancing heat transfer. Then the fluid-thermal-solid coupling behavior of HSS is simulated and experimentally studied. To verify the effectiveness of the designed ARHP and the proposed heat dissipation scheme, the fluid-thermal-solid coupling behaviors of O-HSS, HSS with ARHP (ARHP-HSS), and HSS with ARHP and SG (ARHP-SG-HSS) are compared. The results show that the maximum temperatures of ARHP-SG-HSS and ARHP-HSS are reduced by 50% and 43.5% compared with that of O-HSS, respectively. Moreover, the maximum thermal balance time of O-HSS, ARHP-HSS, and ARHP-SG-HSS is 1450 s, 800 s, 500 s, respectively. The maximum thermal deformation (TD) ranges of O-HSS, ARHP-HSS, and ARHP-SG-HSS are [-35 μm, 25 μm], [-20 μm, 10 μm], and [-20 μm, 10 μm], respectively. The maximum TDs of ARHP-SG-HSS and ARHP-HSS are reduced by 76.5% and 58.8% compared with maximum TD of O-HSS, respectively.

Structure design and hydraulic performance analysis of drip emitters based on vortex energy dissipation

AbstractThe centre of the vortex within the drip irrigation emitter easily forms a low‐speed or zero‐velocity zone, which easily causes sediment deposition and blocks the narrow channel of the emitter. To solve this problem, a funnel‐shaped drip irrigation emitter was designed and optimized. Numerical simulations and field tests were conducted to compare and analyse the flow index, energy dissipation coefficient and relative energy dissipation ratio of the emitter. The results showed: (1) When the incident angle (θ) of the diversion channel increased from 0 to 37.4°, the energy dissipation increased from 20% to 64%. The main way of energy dissipation in the emitter changed from impingement of water to viscous drag in the vortex. (2) Under normal pressure, the energy dissipation coefficient of the vortex energy dissipation scheme (F5) was 60% higher than that of the impingement energy dissipation scheme (F1). The flow index of F5 was lower than that of F1 in both the high‐pressure and low‐pressure regions, which was in the range of 0.433–0.466. (3) Due to the spiral flow, there was a vortex with a large axial velocity inside the conical cavity, which can effectively avoid sediment deposition in the vortex centre.

Stabilization and Dissipative Information Transfer of a Superconducting Kerr-Cat Qubit

Today, the competition to build a quantum computer continues, and the number of qubits in hardware is increasing rapidly. However, the quantum noise that comes with this process reduces the performance of algorithmic applications, so alternative ways in quantum computer architecture and implementation of algorithms are discussed on the one hand. One of these alternative ways is the hybridization of the circuit-based quantum computing model with the dissipative-based computing model. Here, the goal is to apply the part of the algorithm that provides the quantum advantage with the quantum circuit model, and the remaining part with the dissipative model, which is less affected by noise. This scheme is of importance to quantum machine learning algorithms that involve highly repetitive processes and are thus susceptible to noise. In this study, we examine dissipative information transfer to a qubit model called Cat-Qubit. This model is especially important for the dissipative-based version of the binary quantum classification, which is the basic processing unit of quantum machine learning algorithms. On the other hand, Cat-Qubit architecture, which has the potential to easily implement activation-like functions in artificial neural networks due to its rich physics, also offers an alternative hardware opportunity for quantum artificial neural networks. Numerical calculations exhibit successful transfer of quantum information from reservoir qubits by a repeated-interactions-based dissipative scheme.

Fast High Order and Energy Dissipative Schemes with Variable Time Steps for Time-Fractional Molecular Beam Epitaxial Growth Model

Fast High Order and Energy Dissipative Schemes with Variable Time Steps for Time-Fractional Molecular Beam Epitaxial Growth Model

Event-Triggered Finite-Time Dissipative Filtering for Interval Type-2 Fuzzy Complex Dynamical Networks With Cyber Attacks

This article aims to resolve the event-based finite-time dissipative filtering issue for interval type-2 fuzzy complex dynamical networks with coupling delays and cyber attacks. An event-triggered scheme introducing the estimation error is designed, which is a tradeoff between state estimator performance and network communication bandwidth in accordance with the practical requirements. Moreover, the cyber attack model is established, which consists of randomly occurring deception attacks. The stochastic variable obeying the Bernoulli distribution is utilized to describe the attack condition. Through handling the linear matrix inequalities (LMIs) with some slack matrices, the event-triggered finite-time filter is designed to guarantee that the resulting systems are finite-time bounded and strictly dissipative. The proposed filter design parameters are obtained by solving LMIs. Finally, a numerical example and a practical example of a tunnel diode circuit system are used to show the effectiveness and applicability of the proposed event-based dissipative filtering scheme.

Optimization design of heat dissipation scheme for submarine data center based on analytic hierarchy process

Aiming at the problem of heat dissipation optimization design of submarine data center, firstly, the placement mode of server is designed, and on this basis, the heat generation power of server is analyzed by Newton cooling method of convective heat transfer to determine its feasibility. Secondly, based on the relationship between fluid velocity and pressure and the relationship between fluid velocity and heat dissipation through the container surface, the container structure design and its placement direction are clarified. Then, the optimal container shell material is determined by using multi-attribute decision-making model and analytic hierarchy process. Finally, the quadratic composite function of shell cost and seawater depth with respect to shell thickness is constructed to calculate the appropriate seawater depth. According to the research, considering the structure, placement method, heat dissipation effect and seawater temperature of the container, on the basis that a single container shell can be placed with up to 609 servers, Maraging 300 Steel is selected as the most suitable container shell material.

A unified framework for non-linear reconstruction schemes in a compact stencil. Part 1: Beyond second order

Discretization of the convection term in a three-cell compact stencil has been widely used in Computational Fluid Dynamics (CFD) of engineering because the second-order interpolation scheme is considered to be more robust and algorithmically simple than very high-order schemes. However, according to Godnunov's theorem, it has never been trivial to design an accurate and oscillation-free discretization scheme in a compact stencil. Over decades, various kinds of schemes have been proposed to increase accuracy beyond second-order without producing non-physical numerical oscillations. Representative schemes are polynomial-based non-linear interpolations such as TVD (Total Variation Diminishing), NVD (Normalized Variable Diagram) and third-order WENO (Weighted Essentially Non-oscillatory); and non-polynomial-based interpolations including RBF (Radial Basis Functions), LDLR (Local Double Logarithmic Reconstruction) and Tangent of Hyperbola for INterface Capturing (THINC). Within the semi-discretization finite volume method, existing reconstruction schemes suffer from different issues to some extent. For example, existing TVD schemes tend to cause smearing, clipping and squaring effects. Most WENO schemes and inconsistent RBF schemes are not scale-invariant. Especially, the improved WENO-Z scheme is neither scale-invariant nor mesh-size-independent. Computationally expensive non-polynomial-based interpolations usually have singularity and are dependent on tunable parameters. Thus, this work reviews reconstruction schemes by reformulating or calculating the reconstructed boundary value in the normalised-variable space where the characteristics of reconstruction schemes can be read directly. Through the accuracy analysis and the induction of existing schemes, this work proposes a Unified Normalised-variable Diagram (UND) where the following properties of a reconstruction scheme can be given diagrammatically: 1) the second-order and the third-order accuracy condition, 2) the TVD and CBC (Convection Boundedness Criterion) constrain, 3) the ENO condition, 4) the High Resolution (HR) property, 5) and the numerical dissipation and anti-dissipation error.The proposed UND framework is firstly demonstrated by the improvement of the existing schemes with a shape-preserving TVD limiter and a scale-invariant WENO scheme. Then, by defining the normalised reconstruction operator, a brand-new scheme named ROUND (Reconstruction Operator on Unified Normalised-variable Diagram) is proposed. The ROUND scheme is devised by directly configuring the normalised reconstruction operator of favourable properties on UND. This work presents a dissipative ROUND scheme in which normalised reconstruction operators are fully in the dissipative region of UND, and a low-dissipative ROUND scheme where rigorously adjusted anti-dissipation errors are introduced. Different formulations of ROUND schemes are presented to show the flexibility of designing schemes within the UND framework. The proposed dissipative and low-dissipative ROUND schemes are evaluated via benchmark tests which show the superior performance of ROUND on accuracy and resolution. Especially, in some cases, the low-dissipative ROUND schemes obtain comparable and even better resolution than classic fifth-order WENO. The significance of this work is further demonstrated by the preliminary results of applying ROUND on the FDM-IBM (Finite Difference Method and Immersed Boundary Method) framework.

Research on Heat Dissipation Characteristics of Protective Fluid for Immersed Lithium-ion Battery Module

In this article, the immersed lithium-ion battery module’s liquid cooling and heat dissipation scheme are studied, and the heat dissipation characteristics of the large-capacity battery module after the battery is grouped are analyzed. The simulation models of the liquid cooling system’s five inlet and outlet layouts are established. The numerical results show that immersed liquid cooling method can effectively prevent and reduce the temperature rise of large-capacity battery modules. The layout of the imports and exports can influence the heat transfer effect, which is of guiding significance for the design of immersed protective fluid heat dissipation of lithium-ion battery modules.

Analysis of a heat dissipation scheme for a space manipulator joint

A space manipulator is an important tool that assists humans in space exploration. The thermal control of the joint is important to the normal operation of the space manipulator. This paper proposes an effective scheme for the thermal design of a space manipulator in view of thermal characteristics of the manipulator joint, such as the harsh external thermal environment, complex flight attitude and large internal power dissipation. The adaptability of the size of the radiating surface under various extreme operating conditions is compared and analyzed. The results show that in extreme high- and low-temperature running modes, when the radiating surface has dimensions of 100 mm × 120 mm, the temperature of each component obtained by NX/TMG and a heat balance test meets thermal requirements. Additionally, the simulation results of the joint shell and electricity box differ from the experimental results within 4.2 °C. The dimensions of the radiating surface are thus designed as 100 mm × 120 mm, which well meets the needs of thermal control. The present study thus provides a theoretical basis for improving the reliability and thermal optimization of manipulator joints.

Quantum collisional classifier driven by information reservoirs

We investigate the open dynamics of a probe qubit weakly interacting with distinct qubit environments bearing quantum information. We show that the proposed dissipative model yields a binary classification of the reservoir qubits' quantum information in the steady state in the Bloch qubit parameter space, depending on the coupling rates. To describe the dissipation model dynamics, we have adopted the collision model, in which the input information parameters of the reservoir qubits are easily determined. We develop a generalized classification rule based on the results of the micromaserlike master equation where the classification can be described in terms of the Bloch parameters. Moreover, we show that the proposed classification scheme can also be achieved through quantum parameter estimation. Finally, we demonstrate that the proposed dissipative classification scheme is suitable for gradient descent-based supervised learning tasks.

A family of second-order dissipative finite volume schemes for hyperbolic systems of conservation laws

We propose and study a family of formally second-order accurate schemes to approximate weak solutions of hyperbolic systems of conservation laws. Theses schemes are based on a dissipative property satisfied by the second-order discretization in space. They are proven to satisfy a global entropy inequality for a generic strictly convex entropy. These schemes do not involve limitation techniques. Numerical results are provided to illustrate their accuracy and stability.

Analysis and Optimization of Heat Dissipation Module in the Motor Grader Engine Compartment

Abstract To solve the problem of heat reflow in the fan rotation center of the forced convection cooling system in the engine compartment, this study established a calculation model of the external flow field of the engine compartment’s cooling module. It then used the CFD numerical simulation method to calculate and analyze the heat flow characteristics of the existing radiator and compared these with the experimental results. Accordingly, the region where the heat reflux occurred and the reason for the heat reflow were found. The existing heat dissipation scheme was recalculated by using the secondary heat dissipation model, and an optimized and improved scheme was proposed to introduce a deflector cone structure to eliminate heat reflow. The research results showed that the secondary heat dissipation model could more accurately describe the heat reflow problem of the engine compartment, the heat flow organization of the improved structure was more reasonable, and the temperature distribution was more uniform. Moreover, the theoretical heat dissipation effect of the improved structure was more than 10% higher than that of the existing structure.

Adaptive energy stable artificial dissipation for preserving scalar boundedness in turbulent flows

An adaptive dissipation scheme is developed that preserves scalar boundedness in a high-order finite difference framework satisfying the summation-by-parts (SBP) property. A sensor is introduced that switches from an SBP dissipation operator based on a high derivative order that is efficient at absorbing the highest energy modes to a second order derivative that targets energy across scales. Conditionally- and unconditionally-stable formulations are presented. Numerical experiments of a one-dimensional advection equation and a three-dimensional turbulent round jet demonstrate that scalar boundedness can be achieved within an acceptable threshold while retaining overall high-order accuracy. Although not demonstrated here, the same approach could be employed for shock capturing as well.

“A posteriori” limited high order and robust schemes for transient simulations of fluid flows in gas dynamics

In this paper, we propose a novel approximation strategy for time-dependent hyperbolic systems of conservation laws for the Euler system of gas dynamics that aims to represent the dynamics of strong interacting discontinuities. The goal of our method is to allow an approximation with a high-order of accuracy in smooth regions of the flow, while ensuring robustness and a non-oscillatory behaviour in the regions of steep gradients, in particular across shocks.Following the Multidimensional Optimal Order Detection (MOOD) ([15,17]) approach, a candidate solution is computed at a next time level via a high-order accurate explicit scheme ([3,5]). A so-called detector determines if the candidate solution reveals any spurious oscillations or numerical issue and, if so, only the troubled cells are locally recomputed via a more dissipative scheme. This allows to design a family of “a posteriori” limited, robust and positivity preserving, as well as high accurate, non-oscillatory and effective scheme. Among the detecting criteria of the novel MOOD strategy, two different approaches from literature, based on the work of [15,17] and on [35], are investigated. Numerical examples in 1D and 2D, on structured and unstructured meshes, are proposed to assess the effective order of accuracy for smooth flows, the non-oscillatory behaviour on shocked flows, the robustness and positivity preservation on more extreme flows.

A many-body dissipative particle dynamics parametrisation scheme to study behaviour at air-water interfaces.

In this article, we present a general parametrisation scheme for many-body dissipative particle dynamics (MDPD). The scheme is based on matching model components to experimental surface tensions and chemical potentials. This allows us to obtain the correct surface and mixing behaviours of complex, multicomponent systems. The methodology is tested by modelling the behaviour of nonionic polyoxyethylene alkyl ether surfactants at an air/water interface. In particular, the influence of the number of ethylene oxide units in the surfactant head group is investigated. We find good agreement with many experimentally obtained parameters, such as minimum surface area per molecule; and a decrease in the surface tension with increasing surfactant surface density. Moreover, we observe an orientational transition, from surfactants lying directly on the water surface at low surface coverage, to surfactants lying parallel or tilted with respect to the surface normal at high surface coverage. The parametrisation scheme is also extended to cover the zwitterionic surfactant lauryldimethylamine oxide (LDAO), where we provide good predictions for the surface tension at maximum surface coverage. Here, if we exceed this coverage, we are able to demonstrate the spontaneous production of micelles from the surface surfactant layer.