Assessment of the curving performance of heavy haul trains under braking conditions

To study the curving performance of trains, 1D and 3D dynamic models of trains were built using nu- merical methods. The 1D model was composed of 210 simple wagons, each allowed only longitudinal motion; whereas the 3D model included three complicated wagons for which longitudinal, lateral, and vertical degrees of freedom were considered. Combined with the calculated results from the 1D model under braking conditions, the behavior of draft gears and brake shoes were added to the 3D model. The assessment of the curving performance of trains was focused on making comparisons between idling and braking conditions. The results indicated the following： when a train brakes on a curved track, the wheel-rail lateral force and derailment factor are greater than under idling conditions. Because the yawing movement of the wheelset is limited by brake shoes, the zone of wheel contact along the wheel tread is wider than under idling conditions. Furthermore, as the curvature becomes tighter, the traction ratio shows a nonlinear increasing trend, whether under idling or braking conditions. By increasing the brake shoe pressure, train steering becomes more difficult.

Exploiting demand-side heterogeneous flexible resources in risk management of power system frequency

More demand-side flexible resources(DFRs)are participating in the frequency regulation of renewable power systems,whose heterogeneous characteristics have a significant impact on the system frequency response.Consequently,selecting suitable DFRs poses a formidable challenge for independent system operators(ISO).In this paper,a reserve allocation methodology for heterogeneous DFRs is proposed to manage the risk of power system frequency.Firstly,a performance curve is developed to describe the cost,capacity,and response speed of DFRs.Moreover,a clustering method for multiple distributed DFRs is conducted to calculate the aggregated performance curves and uncertainty coefficients.Then,the frequency security criterion considering DFRs’performance is constructed,whose linearity makes it can be easily coupled into the system scheduling model and solved.Furthermore,a risk management model for DFRs considering frequency-chance-constraint is proposed to make a trade-off between cost and frequency security.Finally,the model is transformed into mixed integer second-order cone programming(MISOCP)and solved by the commercial solver.The proposed model is validated by the IEEE 30 and IEEE 118 bus systems.

Satellite Constellation Configuration Design with Rapid Performance Calculation and Ordinal Optimization

Satellite constellation configuration design is a complicated and time-consuming simulation optimization problem. In this paper, a new method called the rapid method for satellite constellation performance calculation is developed by the Hermite interpolation technique to reduce the computing complication and time. The constellation configuration optimization model is established on the basis of the rapid performance calculation. To reduce the search space and enhance the optimization efficiency, this paper presents a new constellation optimization strategy based on the ordinal optimization （00） theory and expands the algorithm realization for constellation optimization including precise and crude models, ordered performance curves, selection rules and selected subsets. Two experiments about navigation constellation and space based surveillance system （SBSS） are carried out and the analysis of simulation results indicates that the ordinal optimization for satellite constellation configuration design is effective.

Predation changes the shape of thermal performance curves for population growth rate

Ectotherms generally demonstrate nonlinear changes in performance （e.g., movement speed, indi- vidual growth, population growth） as a function of temperature that are characterized by thermal performance curves （TPC）. Predation risk elicits phenotypic and behavioral changes that likewise impact performance measures. We tested whether exposure to predation Orthocyclops modestus impacts the maximum population growth rate （rmax） TPC of the protist Paramecium aurelia. We fit predator and non-predator exposed P. aurelia population growth rates to a function previously shown to best describe Paramecium population growth rate TPC＇s （Lactin-2） and compared subse- quent parameter estimates between curves. For Paramecium exposed to predation risk, maximum population growth increased more rapidly as temperatures rose and decreased more rapidly as temperatures fell compared to the initial temperature. The area under each TPC curve remained ap- proximately the same, consistent with the idea of a trade-off in performance across temperatures. Our results indicate TPCs are flexible given variation in food web context and that trophic inter- actions may play an important role in shaping TPCs. Furthermore, this and other studies illustrate the need for a mechanistic model of TPCs with parameters tied to biologically meaningful properties.

Divergence and constraint in the thermal sensitivity of aquatic insect swimming performance

Environmental temperature variation may play a significant role in the adaptive evolutionary divergence of ectotherm thermal performance curves(TPCs).However,divergence in TPCs may also be constrained due to various causes.Here,we measured TPCs for swimming velocity of temperate and tropical mayflies(Family:Baetidae)and their stonefly predators(Family:Perlidae)from different elevations.We predicted that differences in seasonal climatic regimes would drive divergence in TPCs between temperate and tropical species.Stable tropical temperatures should favor the evolution of"specialists"that perform well across a narrow range of temperatures.Seasonally,variable temperatures in temperate zones,however,should favor"generalists"that perform well across a broad range of temperatures.In phylogenetically paired comparisons of mayflies and stoneflies,swimming speed was generally unaffected by experimental temperature and did not differ among populations between latitudes,suggesting a maintenance of performance breadth across elevation and latitude.An exception was found between temperate and tropical mayflies at low elevation where climatic differences between latitudes are large.In addition,TPCs did not differ between mayflies and their stonefly predators,except at tropical low elevation.Our results indicate that divergence in TPCs may be con strai ned in aquatic in sects except under the most differe nt ther・mal regimes,perhaps because of trade-offs that reduce thermal sensitivity and increase performance breadth.

Monitoring and evaluation of building ventilation system fans operation using performance curves

Ventilation fans are an important component of any mechanically ventilated building.Poor fan performance could significantly affect the whole building performance metrics.There are several issues such as dirty blades,mechanical wear,aging of fans could impact the fan’s performance.In present work,a novel,indirect and data-driven methodology is introduced to monitor the ventilation fan unit performance.The proposed method is able to perform continuous monitoring of ventilation fan unit in real-time.The real-time performance of 3 Air handling unit(AHU)fans is examined in an academic building.Expected fan performance is modeled with the help of manufacturer data and compared against the real-time performance.Two data-driven models are developed and implemented.The first model is used to compute expected total fan pressure at a given airflow rate while second is a Support Vector Regression(SVR)model,to predict the fan efficiency.The performance monitoring of the ventilation fan unit is determined in terms of expected and actual fan energy consumption.Findings indicated a significant performance gap in three ventilation fan unit in a case building known as OU44,located in city Odense,Denmark.The advantage of this method comprises simplicity,no direct human intervention and scalability to the series of ventilation units.

Experimental investigation of the flow characteristics of jet pumps for zero flow-ratio conditions

Experimental research was conducted on the performance curves and the cavity evolution for different flow and geometric parameters in jet pumps for zero flow ratio(ZFR)conditions.New pressure ratio,Pr,flow ratio,qr,were used in place of the conventional performance parameters h,q,to characterize the jet pump flow performance.A super cavitation cavity in the jet pump was observed to fill most of the flow channel,which hindered further increases of the flow rate and increased qr to one,thus,created a critical point on the new P_(r)-q_(r)^(2)curve.Before the critical point,P_(r)was proportional to q_(r)^(2)with a coefficient that was much more sensitive to the area ratio than the relative throat length and the diffusion angle.After the critical point,the flow rate reached its maximum,the limiting flow rate,which only depended on the total inlet pressure and the area ratio.The total inlet pressure was proportional to the square of the limiting flow rate with a flow coefficient that was only a quadratic function of the area ratio.