Long Dominating Cycles in Graphs

All graphs considered in this paper will be finite and simple. We use Bondy & Murty for terminology and notations not defined here

Dynamic humanoid locomotion: Hybrid zero dynamics based gait optimization via direct collocation methods

Hybrid zero dynamics (HZD) has emerged as a popular framework for dynamic and underactuated bipedal walking, but has significant implementation difficulties when applied to the high degrees of freedom present in humanoid robots. The primary impediment is the process of gait design–it is difficult for optimizers to converge on a viable set of virtual constraints defining a gait. This dissertation presents a methodology that allows for the fast and reliable generation of efficient multi-domain robotic walking gaits through the framework of HZD, even in the presence of underactuation. To achieve this goal, we unify methods from trajectory optimization with the control framework of multi-domain hybrid zero dynamics. We present a novel optimization formulation in the context of direct collocation methods and HZD where we rigorously generate analytic Jacobians for the constraints. Two collocation methods, local collocation and pseudospectral (global) collocation, are developed within an unified framework, and their performance in different circumstances is comparatively studied. As a result, solving the resulting nonlinear program becomes tractable for large-scale NLP solvers, even for systems as high-dimensional as humanoid robots. We experimentally validate our methodology on the spring-legged prototype humanoid, DURUS, showing that the optimization approach yields dynamic and stable walking gaits for different walking configurations, including unrestricted 3D dynamic walking.Ph.D

Simulation Research on the Heating Performance of the Combined System of Solar Energy and Heat-Source Tower Heat Pump in a Hot Summer and Cold Winter Area

Three connection methods for the combined heating systems of a closed-type heat-source tower heat pump (CHTHP) and solar collector (SC) were proposed in this paper: the heat-source tower (HST) and solar collector were connected in series (HST+SC), and the solar collector and heat pump (HP) condenser were connected in series (SC+HP) and in parallel (SC//HP). The calculation module of the closed heat-source tower was built using programming software based on C++ language, and three corresponding calculation models of the combined heating systems were established in the TRNSYS. Under the climatic conditions of the cold season in Changsha, the combined heating performance of the three systems was simulated and analyzed. The results indicate that the simulation results of the established models are in good agreement with the test results, and the simulation results can be used for the research of the system’s combined heating performance. When the outdoor air temperature and solar radiation intensity are low, the HST+SC system has the best heating performance; however, when the solar radiation intensity and ambient temperature are high, the heating performance of the SC//HP system is the best. When the solar radiation intensity and outdoor air temperature are between the previous two working conditions, the SC+HP system is the best performer for heating among the three systems. On the basis of the collector area and heat pump power designed in this study, the best operating condition interval diagrams of the three combined heating systems are established

Heating Performance of Solar Building Integrated Wall under Natural Circulation

This paper presented a building façade combined with photothermal technology where a water circulation system, including a thermal radiation plate and a solar collector, was installed. When heated by solar radiation, the water in the system transfered part of the solar heat to the room through natural circulation by buoyancy caused by density difference. During the cold season, the solar heat efficiency of the façade under natural circulation was studied through experiments and numerical simulations. The results show that the simulated values of the model established by MATLAB were in good agreement with the experimental values. Under the action of natural circulation, good solar energy utilization efficiency could be obtained by the façade. When solar irradiance was 1100 W/m2, the heat gain of the solar collector was 1672 W, of which the heat delivered to the recycled water and supplied to indoor was 1184 W, and the solar heat efficiency could reach 71%. Both the pipeline impedance and the height difference between radiation plate center and solar collector center had a great influence on temperature change of water supply in this system, whereas had little impact on thermal supply and solar heat efficiency of this system

The Evaluation of the Corrosion Rates of Alloys Applied to the Heating Tower Heat Pump (HTHP) by Machine Learning

The corrosion rate is an important indicator describing the degree of metal corrosion, and quantitative analysis of the corrosion rate is of great significance. In the present work, the support vector machine (SVM) and the artificial neural network (ANN) integrating the k-fold split method and the root-mean-square prop (RMSProp) optimizer are used to evaluate the corrosion rates of alloys, i.e., copper H65, aluminum 3003, and 20# steel, applied to the heating tower heat pump (HTHP) in various anti-freezing solutions at different corrosion times, flow velocities, and temperatures. The mean-square error (MSE) versus the epoch of the ANN model shows that the result breaks the local minimum and is at or close to the global minimum. Comparisons of the SVM-/ANN-evaluated corrosion rates and the measured ones show good agreements, demonstrating the good reliability of the obtained SVM and ANN models. Moreover, the ANN model is recommended since it performs better than the SVM model according to the obtained R2 value. The present work can be further applied to predicting the corrosion rate without any prior experiment for improving the service life of the HTHP

Modeling solar radiation on a human body indoors by a novel mathematical model

Solar radiation affects occupant comfort and building energy consumption in ways that have received relatively little attention in environmental design and energy simulation. Direct, diffuse, and reflected irradiation on the body have warming effects that can be equated to increases in the mean radiant temperature (MRT) of the occupant’s surroundings. A simplified occupant-centered model (SolarCal Model, i.e., SC Model) has recently been adopted in ASHRAE Standard 55, followed by a comprehensive simulation procedure combining detailed room- and manikin geometries using the Daylight Coefficient Model (DC Model). This paper presents an intermediate-level mathematical model (the HNU Solar Model) capable of rapid annual calculations of the MRT increases. Both the room and occupant geometries are simplified but consistent with those of the SC Model. Novel strategies of the calculation include a sky-annulus fraction, virtual body shadow, and equivalent window. Modeled results are compared with those simulated by the DC Model using Radiance software, which is assumed to be accurate. The differences in the Delta MRT by diffuse, direct, and reflected solar radiation are usually less than 1, 2, and 0.5°C between the DC and HNU Solar Models, respectively. For a given occupant position indoors, the HNU Solar Model only needs five seconds to obtain the annual Delta MRT, while the DC Model needs about seven minutes. The HNU Solar Model provides a simple and practical way to evaluate indoor environments at the room scale, to design fenestration, and to predict set-point changes in annual energy simulation of HVAC systems

Modeling solar radiation on a human body indoors by a novel mathematical model

Solar radiation affects occupant comfort and building energy consumption in ways that have received relatively little attention in environmental design and energy simulation. Direct, diffuse, and reflected irradiation on the body have warming effects that can be equated to increases in the mean radiant temperature (MRT) of the occupant’s surroundings. A simplified occupant-centered model (SolarCal Model, i.e., SC Model) has recently been adopted in ASHRAE Standard 55, followed by a comprehensive simulation procedure combining detailed room- and manikin geometries using the Daylight Coefficient Model (DC Model). This paper presents an intermediate-level mathematical model (the HNU Solar Model) capable of rapid annual calculations of the MRT increases. Both the room and occupant geometries are simplified but consistent with those of the SC Model. Novel strategies of the calculation include a sky-annulus fraction, virtual body shadow, and equivalent window. Modeled results are compared with those simulated by the DC Model using Radiance software, which is assumed to be accurate. The differences in the Delta MRT by diffuse, direct, and reflected solar radiation are usually less than 1, 2, and 0.5°C between the DC and HNU Solar Models, respectively. For a given occupant position indoors, the HNU Solar Model only needs five seconds to obtain the annual Delta MRT, while the DC Model needs about seven minutes. The HNU Solar Model provides a simple and practical way to evaluate indoor environments at the room scale, to design fenestration, and to predict set-point changes in annual energy simulation of HVAC systems