Load Shape Research Articles

Indirect Load Shaping for CHP Systems Through Real-Time Price Signals

Direct or centralized loading shaping in smart grid has been heavily investigated. However, it is usually not clear how the users are compensated by providing load shaping services. In this paper, we will discuss indirect load shaping in a distributed manner. On one hand, we aim to reduce the users’ energy cost by investigating how to fully utilize the battery pack and the water tank for the combined heat and power (CHP) systems. We first formulate the queueing models for the CHP systems and then propose an algorithm based on the Lyapunov optimization technique, which does not need any statistical information about the system dynamics. The optimal control actions can be obtained by solving a nonconvex optimization problem. We then discuss when it can be converted into a convex optimization problem. Since the CHP battery pack queue and water tank queue are correlated, the capacity relationship between them is further explored considering different queue weights. On the other hand, based on the users’ reaction model, we propose an algorithm with a time complexity of ${O}$ (log ${n}$ ) to determine the real-time price for the power company to effectively coordinate all the CHP systems and provide distributed load shaping services.

Development of a Test Protocol to Measure Uniaxial Fatigue Damage and Healing

Various laboratory testing methods have been developed to characterize the fatigue response of asphalt concrete mixtures. These test methods attempt to simulate in-service conditions or formulate constitutive models. Experiments such as the four-point beam fatigue test have attempted to simulate in-service conditions. The prediction accuracy of such experiments depends on their effectiveness in simulating actual field conditions such as loading, support, stress state, and environment. Constitutive modeling experiments have aimed at measuring fundamental stress–strain relationships so that rigorous constitutive models can be formulated. The results from these experiments are used as input for field performance prediction algorithms. The uniaxial fatigue test is a promising method in this category because of the constant stress state across the specimen section. A few documents have focused on standard test methods for the uniaxial fatigue test; however, there are no AASHTO or ASTM protocols available that include the healing of asphalt concrete mixtures. The main objective of this study was to report on the development of a uniaxial fatigue test protocol that measures fatigue damage and healing of asphalt concrete mixtures. The documented work includes surrogate studies to identify appropriate sample fabrication procedures, gluing materials and procedures, alignment, machine compliance, type of strain wave shape, and strain-control mode of loading. It was found that the use of a gluing jig and 180-mm compaction height was essential to achieve successful mid-specimen failures. In addition, the sinusoidal strain wave shape and on-specimen strain-controlled mode of loading are appropriate test conditions for fatigue damage and healing characterization of asphalt concrete mixtures.

Harmonic Impact of Plug-In Hybrid Electric Vehicle on Electric Distribution System

This paper presents the harmonic effects of plug-in hybrid electric vehicles (PHEV) on the IEEE 37-bus distribution system at different PHEV penetration levels considering a practical daily residential load shape. The PHEV is modeled as a current harmonic source by using the Open-Source Distribution System Simulator (OpenDSS) and DSSimpc software. Time series harmonic simulation was conducted to investigate the harmonic impact of PHEV on the system by using harmonic data obtained from a real electric vehicle. Harmonic effects on the system voltage profile and circuit power losses are also investigated by using OpenDSS and MATLAB software. Current/voltage total harmonic distortion (THD) produced from the large scale of PHEV is investigated. Test results show that the voltage and current THDs are increased up to 9.5% and 50%, respectively, due to high PHEV penetrations and these THD values are significantly larger than the limits prescribed by the IEEE standards.

Integration of Demand-Side Management Programs and Supply-Side Alternatives for Decentralized Energy Planning

Optimally selection of an appropriate mix of renewable sources for supplying electricity of remote areas has been always an important challenge for policy makers. Also, in recent years, the great advantages of Demand Side Management (DSM) programs such as postponing investments in construction of new plants and/or desirably modification of electricity consumption pattern has turned great attention of energy planners to these programs. Moreover, the issue of global warming has caused the need for reduction of human use of fossil fuels and switching to employing green energy sources. To address the mentioned concerns, in this paper, an integrated mathematical formulation for selecting the best mix of renewable energy technologies is proposed. In this study, DSM considered as a competitive option against supply-side alternatives for making energy planning decisions. Additionally, by considering real data from a case in Iran, the effects of considering energy import and export has been taken into account. To validate the model, for smaller-scaled test problems the model has been solved by Lingo 8.0 software while for solving larger instances of problems (real scale of case study) a novel genetic algorithm (GA) is devised. The numerical results indicate that DSM policies have made use of their maximum capacity and resulted in significant improvements, especially in terms of reducing consumption and suitably changing the load shape.

An Influence of Gas Explosions on Dynamic Responses of a Single Degree of Freedom Model

Explosion risk analysis (ERA) is widely used to derive the dimensioning of accidental loads for design purposes. Computational fluid dynamics (CFD) simulations contribute a key part of an ERA and predict possible blast consequences in a hazardous area. Explosion pressures can vary based on the model geometry, the explosion intensity, and explosion scenarios. Dynamic responses of structures under these explosion loads are dependent on a blast wave profile with respect to the magnitude of pressure, duration, and impulse in both positive and negative phases. Understanding the relationship between explosion load profiles and dynamic responses of the target area is important to mitigate the risk of explosion and perform structural design optimization. In the present study, the results of more than 3,000 CFD simulations were considered, and 1.6 million output files were analyzed using a visual basic for applications (VBA) tool developed to characterize representative loading shapes. Dynamic response of a structure was investigated in both time and frequency domains using the Fast Fourier Transform (FFT) algorithm. In addition, the effects of the residual wave and loading velocity were studied in this paper.

A pattern-based automated approach to building energy model calibration

Building model calibration is critical in bringing simulated energy use closer to the actual consumption. This paper presents a novel, automated model calibration approach that uses logic linking parameter tuning with bias pattern recognition to overcome some of the disadvantages associated with traditional calibration processes. The pattern-based process contains four key steps: (1) running the original pre-calibrated energy model to obtain monthly simulated electricity and gas use; (2) establishing a pattern bias, either Universal or Seasonal Bias, by comparing load shape patterns of simulated and actual monthly energy use; (3) using programmed logic to select which parameter to tune first based on bias pattern, weather and input parameter interactions; and (4) automatically tuning the calibration parameters and checking the progress using pattern-fit criteria. The automated calibration algorithm was implemented in the Commercial Building Energy Saver, a web-based building energy retrofit analysis toolkit. The proof of success of the methodology was demonstrated using a case study of an office building located in San Francisco. The case study inputs included the monthly electricity bill, monthly gas bill, original building model and weather data with outputs resulting in a calibrated model that more closely matched that of the actual building energy use profile. The novelty of the developed calibration methodology lies in linking parameter tuning with the underlying logic associated with bias pattern identification. Although there are some limitations to this approach, the pattern-based automated calibration methodology can be universally adopted as an alternative to manual or hierarchical calibration approaches.

Demand Response Programs in Optimal Operation of Multi-Carrier Energy Networks

Smart grid worldwide project provides integration of Distributed Energy Resources (DERs) to electrical power systems, especially electrical distribution networks. Combined Heat and Power (CHP) and Demand Response (DR) programs are considered as prominent resources of DERs. CHP allows integration of different energy infrastructures and DR enables customers to participate in energy market. In this paper, effect of DR programs is evaluated on multi-carrier energy networks based on the Energy Hub (EH) approach. Time-based and incentive-based programs of DR are taken into account. GAMS software is used to solve Mixed Integer Linear Programming (MILP) models of the proposed EH. Results demonstrate that different DR programs have different effects on load shape and hub operation costs. The results confirm that load participation factors by customers provide more operation cost reductions for EH owners. The results also demonstrate possible purchasing distributions of energy carriers from the networks for operation cost minimization in the presence of DR programs. In addition, the results show, in order to operation costs reduction, which technology should be optimally operated when different DR programs are applied on the multi-carrier network.

An analytical approach for buckling analysis of generally laminated conical shells under axial compression

In the present investigation, the buckling of generally laminated conical shells with various boundary conditions subjected to axial pressure is studied using an analytical approach. The governing equations are obtained using classical shell theory with Donnell assumptions in strain–deformation relations and the principle of minimum potential energy. The differential equations are solved using trigonometric functions in circumferential and power series in longitudinal directions. All types of boundary conditions can be applied in this method. The results are compared and validated with the results available in the literature, and good agreement is observed. Finally, the effects of the length, semi-vertex angle, and lamination sequences on the buckling load and mode shapes of generally laminated conical shells are presented.

Indentation creep analysis of T22 and T91 chromium based steels

Classical creep tests are very time-consuming, they usually take more than one year for steels, whereas creep analysis by instrumented indentation tests (IIT) only requires few hundred minutes. By IIT, creep is observed when the indenter continues to penetrate into the material at constant indentation load which leads to a horizontal plate in the load–depth curve. However, an indentation test cannot reasonably replace the conventional creep test. This is the reason why the objective of this work is to propose a methodology to classify the materials according to their creep sensitivity by means of the indentation test. Within this objective, the indentation testing conditions (dwell-time, maximum indentation load, loading rate and indenter shape) are optimized regarding the ability of the different models to adequately represent the time-indenter displacement variation. Applied to the study of T22 and T91 chromium based steels, the proposed methodology by indentation allows the identification of the creep behavior of these two materials. Furthermore, it is found an analogy with classical creep test through the stress exponent.

Orchestration of Renewable Generation in Low Energy Buildings and Districts Using Energy Storage and Load Shaping

There is increasing penetration of renewable generation in buildings and districts. There are challenges in making the effective use of this generation. The objective of the ORIGIN project (Orchestration of Renewable Integrated Generation In Neighborhoods) is to shape loads so that the fraction of energy consumed that is from local renewable generation is maximized, and energy imported from outside sources is minimized. This paper presents the overall approach taken in the ORIGIN project and explores building physics aspects of solar thermal storage system orchestration. The case study districts are briefly introduced and characteristics of their generation, buildings, districts and shiftable loads described. The orchestration approach taken in ORIGIN is then presented. At the core of the ORIGIN system is the orchestration algorithm which generates informational and control outputs to shape future loads to best meet the objectives. The model based approach used to quantify thermal and electrical load shifting opportunities for pre-charging, coasting or avoiding loads, while meeting thermal comfort and other demands, is described using a solar thermal storage system as an example. The future steps for the ORIGIN project; retrofit of the ORIGIN system into existing districts and potential for other future applications is briefly discussed.

Advanced building energy management based on a two-stage receding horizon optimization

The continuous increase in energy demand and the integration of a large number of renewable energy sources with intermittent production require an advanced energy management to guarantee an uninterrupted supply. Deployment of smart meters in wide areas of power networks and availability of affordable storage systems encourage development and implementation of local energy management systems. Local energy management is considered a feasible and inexpensive approach to reduce the impact of load variations and intermittent generation. Demand response and load shaping techniques provide customers with the facility to contribute to system balancing and improve power quality. This paper presents a building energy management which determines the optimal scheduling of the components of the local energy system. The developed two-stage optimization is based on a receding horizon strategy and minimizes the energy costs under consideration of the physical system constraints. The proposed building energy management has been implemented and tested with a medium-size hotel emulated in a microgrid testbed using power-hardware-in-the-loop techniques. The obtained results underline that energy management strategies can be validated under realistic conditions using flexible power scenarios.

Commercial Building Energy Saver: An energy retrofit analysis toolkit

Small commercial buildings in the United States consume 47% of the total primary energy of the buildings sector. Retrofitting small and medium commercial buildings poses a huge challenge for owners because they usually lack the expertise and resources to identify and evaluate cost-effective energy retrofit strategies. This paper presents the Commercial Building Energy Saver (CBES), an energy retrofit analysis toolkit, which calculates the energy use of a building, identifies and evaluates retrofit measures in terms of energy savings, energy cost savings and payback. The CBES Toolkit includes a web app (APP) for end users and the CBES Application Programming Interface (API) for integrating CBES with other energy software tools. The toolkit provides a rich set of features including: (1) Energy Benchmarking providing an Energy Star score, (2) Load Shape Analysis to identify potential building operation improvements, (3) Preliminary Retrofit Analysis which uses a custom developed pre-simulated database and, (4) Detailed Retrofit Analysis which utilizes real-time EnergyPlus simulations. CBES includes 100 configurable energy conservation measures (ECMs) that encompass IAQ, technical performance and cost data, for assessing 7 different prototype buildings in 16 climate zones in California and 6 vintages. A case study of a small office building demonstrates the use of the toolkit for retrofit analysis. The development of CBES provides a new contribution to the field by providing a straightforward and uncomplicated decision making process for small and medium business owners, leveraging different levels of assessment dependent upon user background, preference and data availability.

Understanding and predicting the impact of location and load on microgrid design

This paper examines the impact of location and load shape selection on microgrid optimal design. 96 unique combinations of location and load shape are considered to provide a broader scope than any previous work in microgrid design sensitivity analysis. In addition, the level of autonomy from the macrogrid is considered as a tunable parameter in the optimization. A generic system is considered consisting of photovoltaics, wind turbine, microturbines, electric and natural gas boilers, thermal storage, and a battery bank. The microgrid is grid-connected and designed to supply both heat and power. A mixed integer linear program is used to minimize the expected cost of energy supply over a 20 year horizon. Trends in the design results are discussed and important input parameters that depend on the location and load shape are identified. Finally, a procedure to quantify these trends and predict optimal design results in new locations is proposed.

Structural performance of final lining according to the rock load shape

The purpose of this study is to analyze the structural performance of the lining according to the magnitude as well as shape of rock load. Four cases of rock load shape were applied on the final lining (concrete lining) to perform structural analysis using beam spring model. This study includes two contents; firstly, the stability of the lining was analyzed using capacity diagrams. Secondly, the serviceability of the lining was analyzed using the cracked hinge model. While assessing the stability of the lining, FS = 2.45 was used according to LRFD specifications. The stress-crack opening relationship, represented by g(w) function, was used to assess the serviceability of the lining. The critical parameters used in this study are the K0 condition, load direction and application of the wedge load. Based on the results obtained after analysis, it was concluded that the K0 condition could change the thrust force-bending moment relationship which affects the stability and serviceability of the lining. Rock load in vertical direction affected the lining more than that in horizontal direction. Lastly, the development of wedge load proved to be more adverse than the application of larger uniform rock load on the lining.

Evaluation of resilient behavior of flexible pavement asphalt layers

Asphalt concrete is a viscoelastic material that has a resilient behavior during cyclic loads. One of the important features for defining this behavior is resilient modulus (MR). Usually, asphalt mixture is laid down in two layers known as binder and surface layers at different depth beneath the road surface. The current test methods use only one loading pulse shape, namely, haversine that represents the shape of loading exerted to the binder layer. Thus, this paper investigates resilient behavior of asphalt material in different depths. Indirect tensile test was employed for determination of MR using universal testing machine. The modulus of asphalt mixture was measured by applying the two pulse shapes in a range of temperatures and pulse widths. The pulse shapes were haversine and square, describing the behavior of mixture in binder and surface layers, respectively. The test results showed that difference between resilient behavior of binder and surface layers is more apparent at high temperatures and under fast traffic loadings. In addition, using the best-fitted functions to MR results and mathematical calculations, haversine pulse widths for surface layer were specified. The MR testing under haversine pulse should be performed with longer pulse widths compared to square loading to fulfill resilient behavior of surface layer accurately. The MR test under haversine pulse was more accurate and beneficial than square one.

Optimal real time cost-benefit based demand response with intermittent resources

Ever-increasing price of conventional energy resources and related environmental concern enforced to explore alternative energy sources. Inherent uncertainty of power generation and demand being strongly influenced by the electricity market has posed severe challenges for DRPs (Demand Response Programs). Definitely, the success of such uncertain energy systems under new market structures is critically decided by the advancement of innovative technical and financial tools. Recent exponential growth of DG (distributed generations) demanded both the grid reliability and financial cost–benefits analysis for deregulated electricity market stakeholders. Based on the SGT (signaling game theory), the paper presents a novel user-aware demand-management approach where the price are colligated with grid condition uncertainties to manage the peak residential loads. The degree of information disturbances are considered as a key factor for evaluating electricity bidding mechanisms in the presence of independent multi-generation resources and price-elastic demand. A correlation between the cost–benefit price and variable reliability of grid is established under uncertain generation and demand conditions. Impacts of the strategies on load shape, benefit of customers and the reduction of energy consumption are inspected and compared with Time-of-Used based DRPs. Simulation results show that the proposed DRP can significantly reduce or even eliminate peak-hour energy consumption, leading to a substantial raise of revenues with 18% increase in the load reduction and a considerable improvement in system reliability is evidenced.

Numerical Studies on Stability Problems in Thin Walled Laminated Composite Box Beams with Emphasis on Stiffeners

The presence of in-plane loading may cause buckling of laminated composite box beams. An accurate knowledge of critical buckling load and mode shapes are essential for reliable and lightweight structural design. This paper presents some parametric studies on stability problems in thin walled laminated composite box beams. Many models were analysed using ANSYS 15. Studies are carried out by changing the fiber orientation in web, laminate thickness. Rotational restraint which prevents distortional buckling an important parameter in this paper. The stiffeners in the box beam reduces the buckling effect.

Finite element simulation of buckling-induced failure of carbon fibre-reinforced laminated composite panels embedded with damage zones

This work is concerned with the buckling-induced failure prediction of aerospace grade carbon fibre-reinforced laminated composite panels embedded with pre-assumed damage. Fibrous composites are being broadly used in aircraft and aerospace vehicle components. However, a major drawback in widespread use is their susceptibility to drop tool impacts and ground equipment collisions. Such incidents could inflict invisible internal damage and delamination that divides laminate into sub-laminates of lower bending stiffness/resistance to buckling load that might result in catastrophic consequences during later operations. This situation is a major concern for aircraft/aerospace industry and necessitates thorough understanding of damage tolerance capabilities of structural members for safety of human lives and structural assets. Extensive studies, based on experimental testing, were conducted on the topic. Since physical testing consumes time and resources, generate limited data, and lack in ply level effect of mixed-modes buckling hence development of a computational model is required. The present study consists of simulation models developed using ABAQUS™ software. Impact-induced damage was introduced as an area of reduced stiffness (soft-inclusion) or hole. Overall damage zones of known size and shape were inserted at various locations in the volumes of various laminates to predict critical buckling load based on global and local buckling with emphasis on mixed-mode buckling. Simulated cases of single and multiple damage zones/holes, switching and coupling of local–global buckling modes were investigated. Damage size, location, type, and penetration depth against critical buckling load and mode shape were investigated. The critical buckling load is found to correlate well corresponding to soft-inclusions to predict ply-level failure. Selected results of eight-, sixteen, and twenty-four ply laminates were compared against the data available in the literature and found to be in agreement up to 90%. The model could also be useful to efficiently study various lay-ups, loading, and material properties for the similar cases.

A Dynamic Water-Filling Method for Real-Time HVAC Load Control Based on Model Predictive Control

Heating ventilation and air-conditioning (HVAC) system can be viewed as elastic load to provide demand response. Existing work usually used HVAC to do the load following or load shaping based on given control signals or objectives. However, optimal external control signals may not always be available. Without such control signals, how to make a tradeoff between the fluctuation of non-renewable power generation and the limited demand response potential of the elastic load, while still guaranteeing user comfort level, is still an open problem. To solve this problem, we first model the temperature evolution process of a room and propose an approach to estimate the key parameters of the model. Second, based on the model predictive control, a centralized and a distributed algorithm are proposed to minimize the fluctuation and maximize user comfort level. In addition, we propose a dynamic water level adjustment algorithm to make the demand response always available in two directions. Extensive simulations based on practical data sets show that the proposed algorithms can effectively reduce the load fluctuation.

Reverse Bending을 통한 CTOD 시험 예비균열 형상균일화에 관한 연구

This study investigates the appropriate range of reverse bending load for the CTOD test of thick weld by observing improvement of pre-crack shape and determination of the limit applicable load. In order to do it, the effect of the amount of the reverse bending load on the maximum deviation of the pre-crack length was investigated by the extensive tests, and the variation of plastic zone size in way of the crack tip under reverse bending load were evaluated by FEA. With the results obtained by the experiments and FEA, the proper range of reverse bending load was suggested. The effectiveness of the reverse bending method was verified by examining the pre-crack straightness after CTOD tests of thick weld specimens with various thickness and strength.