Load Shape Research Articles

A finite element model of shape memory polymer composite beams for space applications

SummaryStructures made of shape memory polymer composite (SMPC), due to their ability to be formed into a desired compact loading shape and then transformed back to their original aperture by means of an applied stimulus, are an ideal solution to deployment problems of large and lightweight space structures. In the literature, there is a wide array of work on constitutive laws and qualitative analyses of SMP materials; dynamic equations and numerical solution methods for SMPC structures have rarely been addressed. In this work, a macroscopic model for the shape fixation and shape recovery processes of SMPC structures and a finite element formulation for relevant numerical solutions are developed. To demonstrate basic concepts, a cantilever SMPC beam is used in the presentation. In the development, a quasi‐static beam model that combines geometric nonlinearity in beam deflection with a temperature‐dependent constitutive law of SMP material is obtained, which is followed by derivation of the dynamic equations of the SMPC beam. Furthermore, several finite element models are devised for numerical solutions, which include both beam and shell elements. Finally, in numerical simulation, the quasi‐static SMPC beam model is used to show the physical behaviors of the SMPC beam in shape fixation and shape recovery. Copyright © 2015 John Wiley & Sons, Ltd.

Enhancing the clustering process in the category model load profiling

Load profiling based consumer categorisation is a procedure that involves stages such as the proper representation of the load data, the selection of one or more pattern recognition algorithms, the assessment of their performance, the formation of daily load curve clusters for each consumer and the formation of the final consumer clusters. This study proposes improvements for every stage, while a new stage is introduced to enhance the whole procedure. All the pattern representation techniques of the load profiling related literature are examined together with the most widely used clustering algorithm, namely the K-means. Two novel modified forms of the algorithm are introduced, specially designed by the authors for the problem under study. The aim is to optimally group together similar daily demand patterns to provide exploitable information to the utilities and the retailers for the efficient design and implementation of innovative energy services, targeted to the different consumer categories. Moreover, all the pattern representation techniques that have been proposed in the literature are examined. These techniques can be divided in three major categories, namely time-domain indices, load shape indices and frequency-domain indices. Furthermore, four proposed dimensionality reduction techniques are investigated, namely the principal components analysis (PCA), Sammon mapping (SM), curvilinear component analysis (CCA) and canonical variate analysis (CVA) (6, 7). To enhance the clustering performance, we examined reduction schemes from 0-98% of the initial patterns dimension. Therefore, this paper aims to help the user to select the most efficient load profiling approach in terms of minimising the clustering error, by presenting a detailed comparative analysis of existing algorithms and techniques.

On the introduction of a mean stress in kinetic damage evolution laws for fatigue

An evolutive mean value z̆ is defined for complex loadings. It is shown to be independent from the loading shape and it tends toward the classical mean value zmean=z‾=12zmin+zMax for a periodic loading. The proposed definition applies to quantities encountered in the fatigue modeling of different materials: mean stress or mean hydrostatic stress for metals, mean damage driving force or mean equivalent strain for quasi-brittle materials or for composites. It gives the possibility to introduce the adequate mean stress effect in kinetic (rate) damage evolution laws. This point is illustrated for woven interlock composites in two steps, (i) by proposing an original modeling of the asymptotic Haigh diagram and (ii) by the description of full mean stress effect from kinetic damage evolution laws. The concept of evolutive mean stress gives the possibility to model fatigue under complex loading with no need to define a cycle. It applies to random fatigue as shown in different examples.

Fundamental framework toward optimal design of product platform for industrial three-axis linear-type robots

Abstract This paper discusses an optimization-based approach for the design of a product platform for industrial three-axis linear-type robots, which are widely used for handling objects in manufacturing lines. Since the operational specifications of these robots, such as operation speed, working distance and orientation, weight and shape of loads, etc., will vary for different applications, robotic system vendors must provide various types of robots efficiently and effectively to meet a range of market needs. A promising step toward this goal is the concept of a product platform, in which several key elements are commonly used across a series of products, which can then be customized for individual requirements. However the design of a product platform is more complicated than that of each product, due to the need to optimize the design across many products. This paper proposes an optimization-based fundamental framework toward the design of a product platform for industrial three-axis linear-type robots; this framework allows the solution of a complicated design problem and builds an optimal design method of fundamental features of robot frames that are commonly used for a wide range of robots. In this formulation, some key performance metrics of the robot are estimated by a reduced-order model which is configured with beam theory. A multi-objective optimization problem is formulated to represent the trade-offs among key design parameters using a weighted-sum form for a single product. This formulation is integrated into a mini–max type optimization problem across a series of robots as an optimal design formulation for the product platform. Some case studies of optimal platform design for industrial three-axis linear-type robots are presented to demonstrate the applications of a genetic algorithm to such mathematical models.

The Computer Simulation of the Dynamic Buckling of Cyclindrical Shells under Pulse Load

The computer simulation of the dynamic buckling on the cylindrical shell subjected to pulse load was carried out by ABAQUS/Expliect. The value of the rectangle and triangle pulse load is the same and the shape is different, and they are applied on the impact end of the cyclindrical shell. The influence of the load amplitude, the shape of load and the effect of the stress wave on the critical buckling time of cylindrical shell were discussed. The radial displacement curve was obtained which indicates that stress wave propagate along the length of the cylindrical shells, and the curve of strain time history is also acquired which is used to judge bifurcation and give the critical time.

Minimum mass design of thin tubular structures under eccentric compressive loading

A minimum mass design study applicable to thin circular tube is performed for various modes of eccentric compressive loading. Axial crushing failure mode, frequently noticeable in uniform axial compressive loading of thin circular tube, does not appear in eccentric compression. Hence, other compressive failure modes, e.g., global buckling, yield and local buckling are studied with respect to non-dimensional load and geometric shape factors for a fixed-free condition. These modes are predominant in ductile engineering alloys. A failure mode map in terms of non-dimensional load and shape-factor for a given load-eccentricity are obtained and the prescription for minimum mass is given.

A market-oriented hierarchical framework for residential demand response

The integration of a great deal of uncertain renewable sources in future grids will require more operational flexibility. Demand response (DR) can provide the load shaping potentials thereby assuaging the need for operational flexibility. To this end, this paper intends to develop a framework focusing on realization of domestic storage space heating DR capability in balancing market. The developed framework consists of two hierarchical stages named energy market stage and balancing power market stage. The first stage deals with customers’ day-ahead decisions in energy market. In this stage, the system operator releases day-ahead energy prices in response to which customers optimize their electricity usage to minimize their energy expenses. The second stage optimizes customers’ intra hour load scheduling decisions in balancing power market. In the second stage, up/down power regulation incentives are offered to customers who, in the hope of achieving monetary gains, modify their promised day-ahead decisions. Performance of the framework is verified through simulations on Finnish case studies. According to the obtained results, the framework allows the customers to make savings in energy expenses as well as the system operator to benefit from DR.

Acoustic Emission Assessment of Through-Thickness Fatigue Crack Growth in Steel Members

The understanding of crack behavior under fatigue remains a critical issue in addressing the performance of steel bridges. Single edge notches in general provide a very well defined load and fatigue crack size and shape environment for estimation of the stress intensity factor K, which is not found in welded elements. ASTM-E647 SE(T) specimens do not appear to provide ideal boundary conditions for proper recording of acoustic wave propagation and crack growth behavior observed in steel bridges, but do provide standard fatigue crack growth rate data. Acoustic emission (AE) has been increasingly used for assessment and prediction of fatigue cracks in steel bridge members. In steel bridge members, AE transducers are commonly attached to the surface of the plate from which the crack is initiated, hence producing a through-thickness crack growth monitored by the transducer. A modified version of the SE(T) specimen was developed in order to maintain similitude with the field crack propagation orientation and to provide a small-scale specimen with improved AE characteristics while maintaining accuracy of fatigue crack growth rate ( da/dN) versus stress intensity factor range (Δ K). The specimen simulates fatigue cracks in flanges or early stage of crack growth in webs of steel bridge members. Effects of load ratio (R) and material on AE data recorded during the crack growth was addressed. Applicability of AE to capture, locate and predict the behavior of the growing crack was positively verified. R ratio showed to have a significant effect on evolution of AE data captured during the test.

Influence of Blank Holding Force on Stretch Flange Forming of Aluminum Alloy

The effect of blank holding force on the stretch flanging process was investigated using finite element simulation and experimental analysis. Finite element model was used to study the effect of blank holding forces on punch load and forming kinematics. An aluminum alloy 5052 sheet of 0.5mm thickness was employed for this work. Blank holding force has a great effect on punch load and significant influence on forming kinematics. Validation of FEM results were obtained by conducting experiments. A very good agreement was obtained between FEM simulation results in terms of punch load and final shape which shows the accuracy of present finite element model.

Subspace Projection Method Based Clustering Analysis in Load Profiling

Customers of different contract types have different shapes in daily load profiles in the manner of different characteristics. Therefore, maximally capture local and global shape variability is essential in load profiling which exhibits the customers' different behaviors and characteristics. Existing approaches are focusing on the global property by considering all dimensions in the data set. However, the load shapes are determined by subspace of dimensions in most of the time. In this paper, we use subspace projection methods (subspace clustering and projected clustering) to capture such subspaces of load diagrams which maximize the difference between particular load shapes in different groups of customers. Also, we have treated clustering as classification to select most appropriate cluster numbers. The contribution of our study is that we have interpreted the strength and weakness of subspace projection method in load profiling. The result shows that subspace projection based method outperforms traditional clustering algorithms.

Load Shaping Strategy Based on Energy Storage and Dynamic Pricing in Smart Grid

Load shaping is one of important and challenging issues in power grid. In this paper, we propose a novel load shaping strategy based on energy storage and dynamic pricing in smart grid. In the proposed strategy, a consumer is encouraged to draw a certain amount of energy (i.e., quota) from the grid. When the actual energy demand is deviated from the quota, the consumer is faced with a higher electricity price. With the help of energy storage, the consumer can draw less electricity from the grid at a lower price by discharging energy when the demand is higher than the quota and draw more electricity from the grid at a lower price by charging energy when the demand is lower than the quota. As a result, the utility can implement load shaping and consumers can save energy cost simultaneously. Moreover, the proposed strategy can be implemented with low complexity and in a distributed fashion, which offers scalability to large number of consumers. Simulations results show the effectiveness of the proposed load shaping strategy.

Dynamic frequency regulation resources of commercial buildings through combined building system resources using a supervisory control methodology

Frequency regulation (FR) is the electric grid service responsible for maintaining the system frequency at its nominal value of 60Hz in the United States — an indicator of energy balance on the grid. In cases of mismatch between power supply and demand, FR resources either on the generation or the demand side, responding rapidly to restore system frequency to its nominal value. Due to the limited responsiveness of generators, fast and accurate demand side resources (DSR) have recently been encouraged to participate in FR. However, the tested DSRs typically require high initial equipment investment (e.g., flywheels and batteries). Large commercial buildings can provide effective load shaping with little impact to occupants’ comfort and have significant amount of available capacity for FR participation. In addition, commercial buildings are characterized by numerous interdependent HVAC subsystems and control systems. Therefore, a high-level supervisory control strategy is needed that directs the interdependent HVAC systems for FR with strengthened interactions and depressed counteractions. Simulation results suggest that large commercial buildings can provide significant FR capacity and high performance scores. Dynamic building-to-grid integration automatically and continuously provides solutions maintaining energy balance on the gird. The benefit to the power system reliability would be significant.

Shape Recovery of Viscoelastic Beams After Stowage

The deployment of viscoelastic structures that have been held stowed for a given time duration can be formulated as a viscoelastic boundary value problem in which the prescribed condition switches from constant displacement to constant traction. This paper presents closed-form expressions for the load relaxation and shape recovery of a linear viscoelastic beam subject to such time-varying constraints. It is shown that a viscoelastic beam recovers to its original shape asymptotically over time. The analytical solutions are employed to investigate the effect of temperature and stowage time on the time required to achieve recovery with a specified precision. Based on the time-temperature equivalence principle, the relationship between recovery time and holding duration is concisely presented on a single plot. It is found that recovery time increases with holding duration but with a diminishing effect.

패치 로딩을 받는 알루미늄 합금 A6082-T6 사각형 판의 임계 탄성좌굴하중 검토

In this paper, we examined the problem of the structural stability according to the patch load of a rectangular plate that reflects the material properties of A6082-T6 is used primarily for marine plant structure. it applied to the four patch loading shapes, the effect of aspect ratio, a boundary condition and calculated the critical elastic buckling load. Calculating the critical elastic buckling load, During the eigenvalue buckling analysis it is applied to the shell181 as 4 node shell element. when the plate subjected to patch loading compare to the plate under a uniform axial compression load, it is possible observed to occur the different elastic buckling behaviour and it could be confirmed that it is affected significantly on a variable position and type of loadings, such as the effect of the aspect ratio. Also, Critical elastic buckling load according to th patch loading type in simply supported rectangular plate ,  are calculated 67%(Loading type I), 119 %(Loading type II), 76 %(Loading type III), 160 %(Loading type IV), respectively. Loading type I and III could be determined with the strong elastic buckling behavior much more than Loading type II and IV.

The concept and evaluation of demand side programmes

The concern of utilities about meeting energy demand and the customers' interest in energy efficiency have resulted in the development of the demand side management (DSM) concept. DSM deals with the planning, implementation, and monitoring of those activities that change the time pattern and magnitude of customers' load curve. This is done by adopting efficient technologies and processes that can be directly substituted for less efficient ones and also managerial techniques and alternative energy sources like co–generation resulting in significant overall reductions in energy use. This paper discusses the conceptual framework of DSM and its evaluation for electricity conservation and load management. It identifies the issues by describing the general mechanisms by which DSM programmes effect load shape change and balance the needs of utility and customer.

Nonlinear Load and RLC Pulse Shaping Surge Generator Models in Simulation Environment

The present study was performed in order to understand how a nonlinear load affects the characteristics of the RLC pulse shaping surge generator waveforms under simulation studies. The obtained results were compared when analytical equations were used as source models for both 1.2/50 µs voltage & 8/20 µs current impulses. Three circuit models; Capacitor Bank generator, Combination waveform generator and Schaffner generator were evaluated under nonlinear loads varied from 10Ω to 106 Ω for voltage impulses and for current impulses it was from 10-4 Ω to 1 Ω. As it can perceive from the analysis, delay time, rise time and FWHM remain unchanged throughout the tested impedance range when used model equations as generator sources. It was found that for voltage impulses, these values were 4.95 μs, 1.20 μs and 81.8 μs respectively. For current impulses, these values were 16.2 μs, 8.02 μs and 20.7 μs respectively. However results obtained for generator circuit models shows that delay time, rise time and FWHM deviated from above values up to maximum of 35.15 %, 106.67 % & 115.16 % respectively for voltage impulses. For current impulses these deviations were up to maximum of 79.63 %, 48.75 % & 39.61 % respectively. The deviations were due to influence caused by the nonlinear load to the generator circuit parameters and effective internal impedance.

Nonlinear Load and RLC Pulse Shaping Surge Generator Models in Simulation Environment

The present study was performed in order to understand how a nonlinear load affects the characteristics of the RLC pulse shaping surge generator waveforms under simulation studies. The obtained results were compared when analytical equations were used as source models for both 1.2/50 µs voltage & 8/20 µs current impulses. Three circuit models; Capacitor Bank generator, Combination waveform generator and Schaffner generator were evaluated under nonlinear loads varied from 10Ω to 106 Ω for voltage impulses and for current impulses it was from 10-4 Ω to 1 Ω. As it can perceive from the analysis, delay time, rise time and FWHM remain unchanged throughout the tested impedance range when used model equations as generator sources. It was found that for voltage impulses, these values were 4.95 μs, 1.20 μs and 81.8 μs respectively. For current impulses, these values were 16.2 μs, 8.02 μs and 20.7 μs respectively. However results obtained for generator circuit models shows that delay time, rise time and FWHM deviated from above values up to maximum of 35.15 %, 106.67 % & 115.16 % respectively for voltage impulses. For current impulses these deviations were up to maximum of 79.63 %, 48.75 % & 39.61 % respectively. The deviations were due to influence caused by the nonlinear load to the generator circuit parameters and effective internal impedance.

Analytical and Numerical Observations on the Hetényi Solution for Buckling of Beams on Elastic Foundations

AbstractThis paper considers the minimum buckling load and mode shape of a simply supported beam on an elastic foundation. Solutions are obtained by solving the eigenvalue problem delivered by a finite-element formulation and by using the analytical solutions involving (1) trials and (2) rounding of real numbers to integers as described by Hetenyi [Hetenyi, M. (1946). Beams on Elastic Foundations, University of Michigan Press, Ann Arbor, MI]. The comparison shows that the solution by rounding can lead to overestimation of the buckling load close to the transition zone between mode shapes. The paper explains the reason for the overestimation and offers a simple direct algorithm that always leads to the correct mode shape and minimum buckling load.

Extending one-dimensional models for deep lakes to simulate the impact of submerged macrophytes on water quality

Submerged macrophytes can stabilise clear water conditions in shallow lakes. However, many existing models for deep lakes neglect their impact. Here, we tested the hypothesis that submerged macrophytes can affect the water clarity in deep lakes. A one-dimensional, vertically resolved macrophyte model was developed based on PCLake and coupled to SALMO-1D and GOTM hydrophysics and validated against field data. Validation showed good coherence in dynamic growth patterns and colonisation depths. In our simulations the presence of submerged macrophytes resulted in up to 50% less phytoplankton biomass in the shallowest simulated lake (11 m) and still 15% less phytoplankton was predicted in 100 m deep oligotrophic lakes. Nutrient loading, lake depth, and lake shape had a strong influence on macrophyte effects. Nutrient competition was found to be the strongest biological interaction. Despite a number of limitations, the derived dynamic lake model suggests significant effects of submerged macrophytes on deep lake water quality.

Abstracts fromThe 32nd AnnualNational Neurotrauma SymposiumJune 29–July 2, 2014San Francisco, California

Abstracts fromThe 32^nd AnnualNational Neurotrauma SymposiumJune 29–July 2, 2014San Francisco, California