Growing Urban Roads

We present a simple simulation of road growing dynamics that can generate global features as belt-ways and star patterns observed in urban transportation infrastructure. The road growing dynamics consist of two steps: Identifying the maximum transportation potential bewteen two locations within the city, followed by the generation of the least expensive road between these two locations. The simulation defines a previously missing component for modeling the co-evolution of urban settlement- and road systems as it can directly be coupled to existing urban settlement simulations.     

Effect of complexity on learning ability of recurrent neural networks

This paper demonstrates that recurrent neural networks can be used effectively to estimate unknown, complicated nonlinear dynamics. The emphasis of this paper is on the distinguishable properties of dynamics at the edge of chaos, i.e., between ordered behavior and chaotic behavior. We introduce new stochastic parameters, defined as combinations of standard parameters, and reveal relations between these parameters and the complexity of the network dynamics by simulation experiments. We then propose a novel learning method whose core is to keep the complexity of the network dynamics to the dynamics phase which has been distinguished using formulations of the experimental relations. In this method, the standard parameters of neurons are changed by the core part and also according to the global error measure calculated by the well-known simple back-propagation algorithm. Some simulation studies show that the core part is effective for recurrent neural network learning, and suggest the existence of excellent learning ability at the edge of chaos. This work was presented, in part, at the Second International Symposium on Artificial Life and Robotics, Oita, Japan, February 18–20, 1997     

基于物理模型的实时喷泉水流运动模拟

本文基于流体动力学和粒子系统给出了一个模拟实时喷泉水流运动的方法。     

Computation of vortex-induced vibrations of long structures using a wake oscillator model: Comparison with DNS and experiments

We consider here the dynamics of flexible slender systems undergoing vortex-induced vibration (VIV). This type of motion results from the coupling between the oscillating wake due to cross-flow and the structure motion. Practical applications are mainly found in the field of ocean engineering, where long flexible structures such as risers or mooring cables are excited by sea currents. The wake dynamics is here represented using a distributed wake oscillator coupled to the dynamics of the slender structure, a cable or a tensioned beam. This results in two coupled partial differential equations with one variable for the solid displacement and one for the wake fluctuating lift. This simplified model of the wake dynamics has been previously validated on simple experiments. Here, comparisons with direct numerical simulation results are done for both uniform and non-uniform flow. Comparison is also performed between the wake oscillator predictions and some experimental results on long cables. The results of those comparisons show that the proposed method can be used as simple computational tool in the prediction of some aspects of vortex induced vibrations of long flexible structures.     

Stochastic simulations of fermionic dynamics with phase-space representations

A Gaussian operator basis provides a means to formulate phase-space simulations of the real- and imaginary-time evolution of quantum systems. Such simulations are guaranteed to be exact while the underlying distribution remains well-bounded, which defines a useful simulation time. We analyse the application of the Gaussian phase-space representation to the dynamics of the dissociation of an ultra-cold molecular gas. We show how the choice of mapping to stochastic differential equations can be used to tailor the stochastic behaviour, and thus the useful simulation time. In the phase-space approach, it is only averages of stochastic trajectories that have a direct physical meaning. Whether particular constants of the motion are satisfied by individual trajectories depends on the choice of mapping, as we show in examples.     

Deterministic event-based simulation of quantum phenomena

We propose and analyse simple deterministic algorithms that can be used to construct machines that have primitive learning capabilities. We demonstrate that locally connected networks of these machines can be used to perform blind classification on an event-by-event basis, without storing the information of the individual events. We also demonstrate that properly designed networks of these machines exhibit behavior that is usually only attributed to quantum systems. We present networks that simulate quantum interference on an event-by-event basis. In particular we show that by using simple geometry and the learning capabilities of the machines it is possible to simulate single-photon interference in a Mach-Zehnder interferometer. The interference pattern generated by the network of deterministic learning machines is in perfect agreement with the quantum theoretical result for the single-photon Mach-Zehnder interferometer. To illustrate that networks of these machines are indeed capable of simulating quantum interference we simulate, event-by-event, a setup involving two chained Mach-Zehnder interferometers, and demonstrate that also in this case the simulation results agree with quantum theory.     

Learning to Transfer In-Hand Manipulations Using a Greedy Shape Curriculum

In-hand object manipulation is challenging to simulate due to complex contact dynamics, non-repetitive finger gaits, and the need to indirectly control unactuated objects. Further adapting a successful manipulation skill to new objects with different shapes and physical properties is a similarly challenging problem. In this work, we show that natural and robust in-hand manipulation of simple objects in a dynamic simulation can be learned from a high quality motion capture example via deep reinforcement learning with careful designs of the imitation learning problem. We apply our approach on both single-handed and two-handed dexterous manipulations of diverse object shapes and motions. We then demonstrate further adaptation of the example motion to a more complex shape through curriculum learning on intermediate shapes morphed between the source and target object. While a naive curriculum of progressive morphs often falls short, we propose a simple greedy curriculum search algorithm that can successfully apply to a range of objects such as a teapot, bunny, bottle, train, and elephant.     

SOFTWARE PROCESS FLIGHT SIMULATION Dynamic Modeling Tools and Metrics

Process flight simulation tools can help managers understand the dynamics of new processes and technologies before they are introduced. This article tells how these exploratory tools can be used for IS project management, simple modeling of the software process, and modeling the dynamics of the IS organization in transition.     

A Novel Method of Gait Synthesis for Bipedal Fast Locomotion

Common methods of gait generation of bipedal locomotion based on experimental results, can successfully synthesize biped joints’ profiles for a simple walking. However, most of these methods lack sufficient physical backgrounds which can cause major problems for bipeds when performing fast locomotion such as running and jumping. In order to develop a more accurate gait generation method, a thorough study of human running and jumping seems to be necessary. Most biomechanics researchers observed that human dynamics, during fast locomotion, can be modeled by a simple spring loaded inverted pendulum system. Considering this observation, a simple approach for bipedal gait generation in fast locomotion is introduced in this paper. This approach applies a nonlinear control method to synchronize the biped link-segmental dynamics with the spring-mass dynamics. This is done such that while the biped center of mass follows the trajectory of the mass-spring model, the whole biped performs the desired running/jumping process. A computer simulation is done on a three-link under-actuated biped model in order to obtain the robot joints’ profiles which ensure repeatable hopping. The initial results are found to be satisfactory, and improvements are currently underway to explore and enhance the capabilities of the proposed method.     

Safe Landing Analysis of a Quadrotor Aircraft With Two Legs

We proposed a multi-propeller multifunction aerial robot (MMAR) that is composed of a quadrotor with two legs. The legs can increase the function of the robot. We found that the legs can increase the safety region of the robot during the landing. To study the safety problem, the dynamics of MMAR interacting with environment should be solved. On the basis of the interaction dynamics, this paper investigates the velocity constraint for safe landing of MMAR. The investigation begins from the kinematics and dynamics of MMAR in flight mode. Then the impact dynamics of MMAR during landing is developed. Furthermore, the landing safety problem is formulated by a series of constraint equations which can give a safety region of the velocity during landing. The safety region can give the safe velocity of the aerial robot before landing. Finally, simulation examples are presented using the proposed methodology. In the examples, a detailed safety region of a simulated MMAR is constructed and shown.     

Dynamic control and coupling of a free-flying space robot system

In this article we discuss the problem of dynamic coupling and control of a space robot with a free-flying base, which could be a spacecraft, space station, or satellite. We formulate the dynamics of the system systematically and demonstrate nonlinearity of parameterization of the dynamics structure. We study the dynamic coupling of the robot and base system, and propose a concept, i.e., coupling factor, to illustrate the motion and force dependencies. Based on the coupling factor, we define a measure to characterize the degree of the dynamic coupling. The measure can be considered as a performance index in planning robot motion, or in evaluating robot trajectory for minimizing base motion, or in optimizing the robot configuration design and selecting the robot base location. Based on the dynamics analysis, we propose control schemes for position regulation and trajectory tracking problems. The regulation controller is simple to implement and will be useful in regular material transporting tasks. The tracking controller uses a dynamic model and provides more accurate and faster motion, and will be feasible for tracking moving objects or structural inspection tasks. A simulation study is shown at the end of the article. © 1994 John Wiley & Sons, Inc.     

Toward a human-like biped robot with compliant legs

Conventional models of bipedal walking generally assume rigid body structures, while elastic material properties seem to play an essential role in nature. On the basis of a novel theoretical model of bipedal walking, this paper investigates a model of biped robot which makes use of minimum control and elastic passive joints inspired from the structures of biological systems. The model is evaluated in simulation and a physical robotic platform by analyzing the kinematics and ground reaction force. The experimental results show that, with a proper leg design of passive dynamics and elasticity, an attractor state of human-like walking gait patterns can be achieved through extremely simple control without sensory feedback. The detailed analysis also explains how the dynamic human-like gait can contribute to adaptive biped walking.     

Visual simulation of water currents using a particle-based behavioural model

Several CG researchers have simulated impressive ocean waves so far. Recently, other researchers have succeeded in simulating waterfalls by employing a mass of particles. However, visual simulation of water currents having complex surfaces, such as mountain streams and turbulent water, still remains a challenging problem thanks to their complicated patterns of behaviour. Effective simulation methods for water currents are expected to have abilities to represent the following remarkable behavioural visual features of water: the appearance of a pool, an obstacle avoidance flow, a fluent flow, a flow into an open space, the collision and the confluence of flows and the occurrence of splashes. In this paper, we present a new type of particle-based simulation method for complex water currents which is not based on strict fluid dynamics but rather classified into a ‘quasi-physically-based’ simulation method constructed on the basis of algorithmic approaches. We first present a simple behavioural model of a ‘water-particle’. Next, we propose a method for generating CG images of water currents from a set of water-particles. Finally, we demonstrate the ability of our method by showing several examples of the simulation.     

Dynamic modeling of a wave glider

We propose a method to establish a dynamic model for a wave glider, a wave-propelled sea surface vehicle that can make use of wave energy to obtain thrust. The vehicle, composed of a surface float and a submerged glider in sea water, is regarded as a two-particle system. Kane’s equations are used to establish the dynamic model. To verify the model, the design of a testing prototype is proposed and pool trials are conducted. The speeds of the vehicle under different sea conditions can be computed using the model, which is verified by pool trials. The optimal structure parameters useful for vehicle designs can also be obtained from the model. We illustrate how to build an analytical dynamics model for the wave glider, which is a crucial basis for the vehicle’s motion control. The dynamics model also provides foundations for an off-line simulation of vehicle performance and the optimization of its mechanical designs.     

Spreadable cellular automata: modelling and simulations

The spreadable phenomena which describes the expansion in time of a given spatial property has been studied using models based on partial differential equations. These spreadable dynamics are generally non-linear and then difficult to simulate particularly in two dimensions. In this article, we propose cellular automata (CA) models as an alternative modelling tool that can easily simulate spreadable systems. CA are capable of describing complex systems based on simple evolution rules, which provide numerical schemes directly implemented on computers without approximation or rounding errors. We design local CA dynamics which allow us to maintain a spatial property on non-decreasing subdomains. Several numerical results are performed to illustrate spreadable phenomena. The simulation results corroborate the general shape theory that exhibits the convergence to a specific domain independently on initial conditions.     

Distributed Adaptive Cooperative Tracking of Uncertain Nonlinear Fractional-order Multi-agent Systems

In this paper, the leader-following tracking problem of fractional-order multi-agent systems is addressed. The dynamics of each agent may be heterogeneous and has unknown nonlinearities. By assumptions that the interaction topology is undirected and connected and the unknown nonlinear uncertain dynamics can be parameterized by a neural network, an adaptive learning law is proposed to deal with unknown nonlinear dynamics, based on which a kind of cooperative tracking protocols are constructed. The feedback gain matrix is obtained to solve an algebraic Riccati equation. To construct the fully distributed cooperative tracking protocols, the adaptive law is also adopted to adjust the coupling weight. With the developed control laws, we can prove that all signals in the closed-loop systems are guaranteed to be uniformly ultimately bounded. Finally, a simple simulation example is provided to illustrate the established result.      

基于分形的三维波浪仿真

随着计算机游戏、三维动画、影视及广告的普及,波浪、水、云、烟、雨、雪等自然景物的模拟受到越来越多的重视。其中自然景观的波浪模拟可以大大提高三维场景的逼真度和可观赏性,论文基于海浪谱在分形系统的基础上,采用一种简单的分形模型,实现对波浪自然现象的实时模拟。     

基于热力系统动力学的冷凝器动态仿真建模

冷凝器中进行的是一个融合了传热、传质、流动的复杂热力过程，仿真分析是其动态特性研究的有效手段。传统上对冷凝器进行仿真建模是基于“热静力学”的观点和方法，其揭示的内容与深度都是不够的。为深入理解动态特性，基于热力系统“热动力学”的观点和方法，视对象各参数之间是定量耦合的。采用一组常微分方程，建立起能够有效反映冷凝器工作过程和动态特性的仿真模型。仿真模型能够给出以往的仿真模型所不能揭示的系统参数之间的耦合关系。模型形式简洁，便于数值计算。