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The Free Euler Rigid Body Revisited 重新审视自由欧拉刚体
Pub Date : 2023-09-18 DOI: 10.3390/dynamics3030032
Lidia Jiménez-Lara, Jaume Llibre
We review from a different perspective the approach and solution to the torque-free Euler equations, also called the free asymmetric top equations. We aim to simplify and broaden the study of the asymmetric free rigid body. This is an old but important integrable problem that has two first integrals: the energy and the angular momentum. We reduce this problem by eliminating the time as the independent variable in the three autonomous Euler equations written in cylindrical dimensionless variables, which allows a geometric study of the solution as a function of the cylindrical angle variable ψ, by means of continuous deformations dependent on the two independent parameters κ and e0. The parameter space is divided into six disjoint regions, whose boundaries are the separatices and degenerated cases. The solutions are given in terms of trigonometric functions of the independent cylindric angle ψ.
我们从不同的角度回顾了无扭矩欧拉方程的方法和解,也称为自由不对称顶方程。我们的目的是简化和拓宽非对称自由刚体的研究。这是一个古老但重要的可积问题,它有两个前积分:能量和角动量。我们通过消除以柱面无量纲变量表示的三个自治欧拉方程中的自变量时间来减少这个问题,这使得通过依赖于两个独立参数κ和e0的连续变形,可以将解作为柱面角变量ψ的函数进行几何研究。将参数空间划分为6个不相交的区域,这些区域的边界为分离和简并情况。解是用独立圆柱角ψ的三角函数给出的。
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引用次数: 0
Dynamical and Probabilistic Approaches to Irreversibility 不可逆性的动态和概率方法
Pub Date : 2023-09-15 DOI: 10.3390/dynamics3030031
Fernando C. Pérez-Cárdenas
Boltzmann’s H-theorem is considered a great triumph of science. Though some modifications are necessary to adapt it to modern dynamical theories, it is well established that one of its main tenets remains widely accepted: the introduction of probability is a key element in achieving a transition from time-reversible, deterministic dynamical laws at the microscopic level to irreversible laws describing the approach to equilibrium of isolated macroscopic systems. Thus, it is somehow surprising that we still find instances where this subject is labeled as paradoxical and elusive. More remarkable is the fact that this often happens in texts that succeed in presenting Boltzmann’s ideas with clarity. In order to shed light on how probability allows us to go form microscopic reversibility to macroscopic irreversibility, we use numerical results from a two-dimensional lattice gas composed of distinguishable particles. We discuss the roles played by noise, coarse graining, and probability. The simplicity of our model might help the newcomer to this area in better grasping Boltzmann’s fundamental breakthrough.
玻尔兹曼的h定理被认为是科学的伟大胜利。虽然有些修改是必要的,以适应现代动力学理论,它是公认的,它的主要原则之一仍然被广泛接受:概率的引入是实现从时间可逆的,确定性的动力学定律在微观水平上的过渡到不可逆的定律描述的方法,孤立的宏观系统的平衡的关键因素。因此,令人惊讶的是,我们仍然发现这个主题被贴上矛盾和难以捉摸的标签。更值得注意的是,这种情况经常发生在那些成功地清晰地呈现玻尔兹曼思想的文本中。为了阐明概率如何使我们从微观可逆性到宏观不可逆性,我们使用由可区分粒子组成的二维晶格气体的数值结果。我们讨论了噪声、粗粒度和概率所起的作用。我们模型的简单性可能会帮助这个领域的新手更好地理解玻尔兹曼的根本突破。
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引用次数: 0
Editorial on the New Scope of Dynamics 关于动力学新范围的社论
Pub Date : 2023-09-06 DOI: 10.3390/dynamics3030030
Christos Volos
We are thrilled to introduce the new scope of the Dynamics, a platform that will unravel the captivating world of diverse dynamics and their multifaceted applications [...]
我们很高兴地介绍动态的新范围,一个平台,将解开不同的动态及其多方面的应用程序的迷人的世界[…]
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引用次数: 0
Korteweg-Type Fluids and Thermodynamic Modelling via Higher-Order Gradients 基于高阶梯度的korteweg型流体和热力学建模
Pub Date : 2023-09-04 DOI: 10.3390/dynamics3030029
Angelo Morro
This paper investigates the modelling of Korteweg-type fluids and hence the dependence of the stress tensor on gradients of mass density. This topic, originating from the need for describing capillarity effects, is mainly of interest in connection with nanosystems where the mean free path may be comparable with the geometric dimensions of the system. In addition to the Korteweg fluid model, the paper gives a review of the stress tensor function arising in quantum fluid hydrodynamics. Next, thermodynamic consistency is established for a fluid involving first- and second-order density gradients. The modelling investigated is a generalization of the classical Korteweg fluid and allows a better understanding of previous thermodynamic restrictions. The restrictions determined for the general scheme with second-order gradients are applied to the particular cases of the Korteweg fluid and the quantum fluid. Further, to allow for discontinuity wave solutions with finite speed of propagation, a model is established which involves higher-order derivatives and reduces to the Korteweg fluid in stationary conditions.
本文研究了korteweg型流体的建模,并由此研究了应力张量对质量密度梯度的依赖性。本主题源于描述毛细效应的需要,主要与纳米系统相关,其中平均自由程可能与系统的几何尺寸相当。除了Korteweg流体模型外,本文还对量子流体力学中出现的应力张量函数进行了综述。其次,建立了涉及一阶和二阶密度梯度的流体的热力学一致性。所研究的模型是经典Korteweg流体的推广,可以更好地理解以前的热力学限制。对于二阶梯度的一般格式所确定的限制适用于Korteweg流体和量子流体的特殊情况。此外,为了考虑具有有限传播速度的不连续波解,建立了一个涉及高阶导数的模型,并简化为静止条件下的Korteweg流体。
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引用次数: 0
On Solutions of the Third-Order Ordinary Differential Equations of Emden-Fowler Type Emden-Fowler型三阶常微分方程的解
Pub Date : 2023-09-03 DOI: 10.3390/dynamics3030028
Felix Sadyrbaev
For a linear ordinary differential equation (ODE in short) of the third order, results are presented that supplement the theory of conjugate points and extremal solutions by W. Leighton, Z. Nehari, M. Hanan. It is especially noted the sensitivity of solutions to the initial data, which makes their numerical study difficult. Similar results were obtained for the third-order nonlinear equations of the Emden-Fowler type.
对于一类三阶线性常微分方程,给出了对W. Leighton, Z. Nehari, M. Hanan的共轭点和极值解理论的补充结果。特别要注意的是解对初始数据的敏感性,这使得它们的数值研究变得困难。对于Emden-Fowler型三阶非线性方程也得到了类似的结果。
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引用次数: 0
A Dynamic Model of Human Limb Selection 人体肢体选择的动态模型
Pub Date : 2023-09-01 DOI: 10.3390/dynamics3030027
Ralf F. A. Cox
Two experiments and a dynamic model forhuman limb selection are reported. In Experiment 1, left-handed and right-handed participants (N = 36) repeatedly used one hand for grasping a small cube. After a clear switch in the cube’s location, perseverative limb selection was revealed in both handedness groups. In Experiment 2, the cubes were presented in a clockwise and counter-clockwise sequence to right-handed participants (N = 15). A spatial shift in the switch point between right-hand use and left-hand use was observed. The model simulates the experiments by implementing the nonlinear multiple-timescale dynamics of the action-selection process underlying limb selection. It integrates two mechanisms that were earlier proposed to underlie this selection aspect of manual activity: limb dominance and attentional information. Finally, the model is used to simulate an influential earlier experiment, by establishing a conceptual link between cross-lateral inhibition asymmetry and the direction and strength of handedness.
本文报道了人体肢体选择的两个实验和一个动态模型。在实验1中,左撇子和右撇子参与者(N = 36)反复用一只手抓一个小立方体。在立方体位置发生明显改变后,两个惯用手组都出现了持续性肢体选择。在实验2中,立方体以顺时针和逆时针的顺序呈现给右撇子参与者(N = 15)。在右手使用和左手使用之间的切换点的空间移动被观察到。该模型通过实现肢体选择下动作选择过程的非线性多时间尺度动力学来模拟实验。它整合了先前提出的两种机制,这两种机制是手工活动选择方面的基础:肢体优势和注意信息。最后,通过建立横向抑制不对称性与利手性方向和强度之间的概念联系,该模型被用于模拟一个有影响力的早期实验。
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引用次数: 0
Exploiting the Abstract Calculus Pattern for the Integration of Ordinary Differential Equations for Dynamics Systems: An Object-Oriented Programming Approach in Modern Fortran 利用抽象微积分模式求解动力学系统常微分方程的积分:现代Fortran中面向对象的编程方法
Pub Date : 2023-08-28 DOI: 10.3390/dynamics3030026
S. Zaghi, Cristiano Andolfi
This manuscript relates to the exploiting of the abstract calculus pattern (ACP) for the (numerical) solution of ordinary differential equation (ODEs) systems, which are ubiquitous mathematical formulations of many physical (dynamical) phenomena. We present FOODIE, a software suite aimed to numerically solve ODE problems by means of a clear, concise, and efficient abstract interface. The results presented prove manifold findings, in particular that our ACP approach enables ease of code development, clearness and robustness, maximization of code re-usability, and conciseness comparable with computer algebra system (CAS) programming (interpreted) but with the computational performance of compiled programming. The proposed programming model is also proven to be agnostic with respect to the parallel paradigm of the computational architecture: the results show that FOODIE applications have good speedup with both shared (OpenMP) and distributed (MPI, CAF) memory architectures. The present paper is the first announcement of the FOODIE project: the current implementation is extensively discussed, and its capabilities are proved by means of tests and examples.
本文涉及利用抽象微积分模式(ACP)求解常微分方程(ode)系统的(数值)解,这是许多物理(动力)现象的普遍数学公式。我们提出了FOODIE,一个软件套件,旨在通过一个清晰,简洁,高效的抽象界面,在数值上解决ODE问题。提出的结果证明了多方面的发现,特别是我们的ACP方法可以简化代码开发,清晰和健壮性,最大化代码可重用性,以及与计算机代数系统(CAS)编程(解释)相媲美的简洁性,但具有编译程序的计算性能。所提出的编程模型也被证明与计算架构的并行范式无关:结果表明,FOODIE应用程序在共享(OpenMP)和分布式(MPI, CAF)内存架构下都有很好的加速。本文是FOODIE项目的首次公告,对目前的实现进行了广泛的讨论,并通过测试和实例证明了其功能。
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引用次数: 0
Investigation of Dynamic Behavior of Ultra-Large Cold-Water Pipes for Ocean Thermal Energy Conversion 大型海洋热能转换冷水管道动力特性研究
Pub Date : 2023-08-18 DOI: 10.3390/dynamics3030025
Yanfang Zhang, Miaozi Zheng, Li Zhang, Chaofei Zhang, J. Tan, Yulong Zhang, Menglan Duan
Ocean Thermal Energy Conversion (OTEC) is a process that can produce electricity by utilizing the temperature difference between deep cold water and surface warm water. The cold-water pipe (CWP) is a key component of OTEC systems, which transports deep cold water to the floating platform. The CWP is subjected to various environmental and operational loads, such as waves, currents, internal flow, and platform motion, which can affect its dynamic response and stability. In this paper, we establish a computational model of the mechanical performance of the CWP based on the Euler–Bernoulli beam theory and the Morrison equation, considering the effects of internal flow, sea current, and wave excitation. We use the differential quadrature method (DQM) to obtain a semi-analytical solution of the lateral displacement and bending moment of the CWP. We verify the correctness and validity of our model by comparing it with the finite element simulation results using OrcaFlex software. We also analyze the effects of operating conditions—such as wave intensity, clump weight at the bottom, and internal flow velocity—on the dynamic response of the CWP using numerical simulation and the orthogonal experimental method. The results show that changing the wave strength and internal flow velocity has little effect on the lateral displacement of the CWP but increasing the current velocity can significantly increase the lateral displacement of the CWP, which can lead to instability. The effects of waves, clump weight, internal flow, and sea current on the maximum bending moment of the CWP are similar; all of them increase sharply at first and then decrease gradually until they level off. The differences in the effects are mainly reflected in the different locations of the pipe sections. This paper suggests some design guidance for CWP in terms of dynamic responses depending on the operating conditions. This paper contributes to the journal’s scope by providing a novel and efficient method for analyzing the mechanical performance of CWP for OTEC systems, which is an important ocean energy resource.
海洋热能转换(OTEC)是利用深层冷水和表面温水之间的温差来发电的过程。冷水管(CWP)是OTEC系统的关键部件,它将深水输送到浮式平台。CWP受到各种环境和运行载荷的影响,如波浪、水流、内部流动和平台运动,这些都会影响其动态响应和稳定性。本文基于欧拉-伯努利梁理论和莫里森方程,考虑内流、海流和波浪激励的影响,建立了CWP的力学性能计算模型。利用微分正交法(DQM)得到了CWP的侧向位移和弯矩的半解析解。通过与OrcaFlex有限元仿真结果的对比,验证了模型的正确性和有效性。采用数值模拟和正交实验方法分析了波浪强度、底部团块重量和内部流速等工况对CWP动力响应的影响。结果表明:波浪强度和内部流速的变化对水轮机的侧向位移影响不大,但流速的增加会显著增加水轮机的侧向位移,从而导致水轮机的失稳。波浪、团块重量、内部流量和海流对CWP最大弯矩的影响相似;它们都在开始时急剧增加,然后逐渐减少,直到趋于平稳。效果的差异主要体现在管段位置的不同。本文从运行工况的动态响应角度对水轮机的设计提出了一些指导意见。本文提供了一种新颖而有效的方法来分析OTEC系统的CWP力学性能,这是一种重要的海洋能源。
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引用次数: 0
Exact Solutions of Nonlinear Second-Order Autonomous Ordinary Differential Equations: Application to Mechanical Systems 非线性二阶自治常微分方程的精确解:在机械系统中的应用
Pub Date : 2023-08-14 DOI: 10.3390/dynamics3030024
Murillo V. B. Santana
Many physical processes can be described via nonlinear second-order ordinary differential equations and so, exact solutions to these equations are of interest as, aside from their accuracy, they may reveal beforehand key properties of the system’s response. This work presents a method for computing exact solutions of second-order nonlinear autonomous undamped ordinary differential equations. The solutions are divided into nine cases, each depending on the initial conditions and the system’s first integral. The exact solutions are constructed via a suitable parametrization of the unknown function into a class of functions capable of representing its behavior. The solution is shown to exist and be well-defined in all cases for a general nonlinear form of the differential equation. Practical properties of the solution, such as its period, time to reach an extreme value or long-term behavior, are obtained without the need of computing the solution in advance. Illustrative examples considering different types of nonlinearity present in classical physical systems are used to further validate the obtained exact solutions.
许多物理过程可以通过非线性二阶常微分方程来描述,因此,这些方程的精确解是有趣的,因为除了它们的准确性之外,它们可以预先揭示系统响应的关键属性。本文提出了一种二阶非线性自治无阻尼常微分方程精确解的计算方法。解分为九种情况,每种情况取决于初始条件和系统的第一个积分。通过对未知函数进行适当的参数化,构造出精确的解,使其成为能够表示其行为的一类函数。对于一般非线性形式的微分方程,证明了在所有情况下解的存在性和良好的定义性。解的实际性质,如周期、达到极值的时间或长期行为,无需事先计算解即可获得。通过考虑经典物理系统中不同类型非线性的实例,进一步验证了所得到的精确解。
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引用次数: 0
Dynamics Differences between Minimal Models of Second and First-Order Chemical Self-Replication 二阶和一级化学自复制极小模型的动力学差异
Pub Date : 2023-08-03 DOI: 10.3390/dynamics3030023
Lauren A. Moseley, E. Peacock-López
To further explore the origins of Life, we consider three self-replicating chemical models. In general, models of the origin of Life include molecular components that can self-replicate and achieve exponential growth. Therefore, chemical self-replication is an essential chemical property of any model. The simplest self-replication mechanisms use the molecular product as a template for its synthesis. This mechanism is the so-called First-Order self-replication. Its regulatory limitations make it challenging to develop chemical networks, which are essential in the models of the origins of Life. In Second-Order self-replication, the molecular product forms a catalytic dimer capable of synthesis of the principal molecular product. In contrast with a simple template, the dimers show more flexibility in forming complex chemical networks since the chemical activity of the dimers can be activated or inhibited by the molecular components of the network. Here, we consider three minimal models: the First-Order Model (FOM), the Second-Order Model (SOM), and an Extended Second-Order Model (ESOM). We construct and analyze the mechanistic dimensionless ordinary differential equations (ODEs) associated with the models. The numerical integration of the set of ODEs gives us a visualization of these systems’ oscillatory behavior and compares their capacities for sustained autocatalytic behavior. The FOM model displays more complex oscillatory behavior than the ESOM model.
为了进一步探索生命的起源,我们考虑了三种自我复制的化学模型。一般来说,生命起源的模型包括可以自我复制和实现指数增长的分子成分。因此,化学自复制是任何模型的基本化学性质。最简单的自我复制机制使用分子产物作为其合成的模板。这种机制就是所谓的一阶自我复制。它的监管限制使得开发化学网络具有挑战性,而化学网络在生命起源模型中至关重要。在二级自我复制中,分子产物形成催化二聚体,能够合成主分子产物。与简单的模板相比,二聚体在形成复杂的化学网络方面表现出更大的灵活性,因为二聚体的化学活性可以被网络的分子成分激活或抑制。在这里,我们考虑三种最小模型:一阶模型(FOM),二阶模型(SOM)和扩展二阶模型(ESOM)。我们构造并分析了与这些模型相关的机械性无量纲常微分方程。通过对ode集合的数值积分,我们可以直观地看到这些系统的振荡行为,并比较它们持续自催化行为的能力。FOM模型比ESOM模型表现出更复杂的振荡行为。
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引用次数: 0
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