Bound Of Load Research Articles

Regional Residential Short-Term Load-Interval Forecasting Based on SSA-LSTM and Load Consumption Consistency Analysis

The electricity consumption behavior of the inhabitants is a major contributor to the uncertainty of the residential load system. Human-caused uncertainty may have a distributional component, but it is not well understood, which limits further understanding the stochastic component of load forecasting. This study proposes a short-term load-interval forecasting method considering the stochastic features caused by users’ electricity consumption behavior. The proposed method is composed of two parts: load-point forecasting using singular spectrum analysis and long short-term memory (SSA-LSTM), and load boundaries forecasting using statistical analysis. Firstly, the load sequence is decomposed and recombined using SSA to obtain regular and stochastic subsequences. Then, the load-point forecasting LSTM network model is trained from the regular subsequence. Subsequently, the load boundaries related to load consumption consistency are forecasted by statistical analysis. Finally, the forecasting results are combined to obtain the load-interval forecasting result. The case study reveals that compared with other common methods, the proposed method can forecast the load interval more accurately and stably based on the load time series. By using the proposed method, the evaluation index coverage rates (CRs) are (17.50%, 1.95%, 1.05%, 0.97%, 7.80%, 4.55%, 9.52%, 1.11%), (17.95%, 3.02%, 1.49%, 5.49%, 5.03%, 1.66%, 1.49%), (19.79%, 2.79%, 1.43%, 1.18%, 3.37%, 1.42%) higher than the compared methods, and the interval average convergences (IACs) are (−18.19%, −8.15%, 3.97%), (36.97%, 21.92%, 22.59%), (12.31%, 21.59%, 7.22%) compared to the existing methods in three different counties, respectively, which shows that the proposed method has better overall performance and applicability through our discussion.

Study on the Stiffness and Dynamic Characteristics of a Bridge Approach Zone: Tests and Numerical Analyses

This study focuses on the stiffness and dynamic characteristic rules of a bridge approach zone in a high-speed railway (HSR). Indoor and in situ tests were performed to explore the stiffness and dynamic characteristics of the roadbed filling. Based on the test results, an effective track-subgrade finite element model (FEM) of a high-speed train (HST) was established. The FEM simulated the train load and model boundaries based on the obtained loads and viscoelastic artificial boundaries. Suitable elements were then selected to simulate the various components of the system and the constraint equations were established and solved using multi-point constraints. The model was verified by comparing the time–history curve characteristics, the frequency-domain characteristics and the results obtained from different modeling methods with the measured results. The influence of stiffness on the dynamic characteristics of the bridge approach zone were subsequently analyzed based on the aforementioned tests and simulations. The results indicate that (i) the model produced reliable results using the proposed approach; (ii) the influence of train load on the embankment was generally reflected in the upper part of the structure, and thus, bed structures are recommended to be strengthened; and (iii) under stationarity, the stiffness ratio between the bridge and normal subgrade is recommended as 1:6, with a transition length of 25 m.

Method of strain analysis of pipelines under landslides: An improved semi-analytical method for softening bending moment-curvature

The accurate description of the elastic‒plastic stress‒strain of a pipeline is used to evaluate the risk that the pipeline will undergo failure during a landslide. This paper proposes a complete set of refined semi-analytical methods (SAMs) for pipeline elastic-plastic strain to accurately evaluate the safety of pipelines. First, a concise model for the calculation of landslide thrust is established based on the pipe-soil interaction mechanism as load boundaries of the SAMs. Secondly, the plastic softening bending moment-curvature relationship (BMCR) is derived to establish a difference equation for the deformation of the pipeline during the plastic stage based on the principle of internal force balance of the pipe section, and then the bending plastic strain is calculated accurately. Finally, the axial strain is fully calculated considering the interaction between axial force and bending of the pipeline. The comparison of the results of small-scale landslide tests, large-scale landslide tests, and SAM calculations shows that the improved SAM has good applicability, with 20% better accuracy than traditional methods. In conclusion, the SAM proposed in this paper can effectively guide the design and evaluation of the strain-based design pipeline.

Enhanced superlubricity of 1,3-diketone oil by doping polydopamine functionalized silica nano-additive

1,3-Diketone is a promising oil-based superlubricity material on steel surfaces. However, the achievement of its superlubricity is limited within a particular range of load and velocity. In this study, silica nanoparticles were modified by surface-coated polydopamine and stably dispersed in 1,3-diketone oil as the additive. It suggests that functionalized silica nanoparticles deposited on the steel substrate and repaired the surface pits, which enhanced the superlubricity of EPND with shorter running-in time and smaller wear. Such assistance became more significant for the operation at a higher load or a lower velocity. With the controlled size of wear debris, the superlubricity region of 1,3-diketone could break through its original load (e.g., 16–43 N) and velocity (200–100 mm/s) boundaries.

An explicit finite element approach for simulations of transient meshing contact of gear pairs and the resulting wear

A 3D time-domain modelling approach is developed with the explicit finite element method to simulate transient meshing contact of gear pairs and the resulting wear. Taking a helical gear pair used in a locomotive as an example, the dynamic contact states of gear teeth are predicted for different speeds in consideration of actual geometries (including those of damaged teeth), time dependent torques, and structural and continuum vibrations of the gear system. The friction between mating teeth is taken into account by a non-Newtonian EHL friction model. A tiny time step of 4.5 × 10−8 s determined by conditional stability of the explicit time integration ensures the capture of transient effects. Based on detailed contact solutions during meshing, the dynamic wear on teeth is further calculated using an Archard wear model to predict tooth profile evolvement. Taking initial involute profiles and a speed of 120 km/h, the model is first validated for dynamic contact solutions. More results show that structural vibrations and worn profiles influence the dynamic meshing contact significantly, tooth wear increases as lubrication fails, and tooth pitting's influence is localized. This approach provides key load boundaries for detailed studies on mating gears, and may be employed for studies on tooth damages and as a reference for lumped parameter dynamic models of gear pairs.

Long-Term Investigation of a Borehole Heat Exchanger (BHE) Array with the Influence of Same Inlet Temperature (SIT) and Same Heat Load (SHL) Boundaries

Borehole heat exchanger (BHE) array is a key element in the ground source heat pump system (GSHPS). The BHE array is traditionally simplified by assuming the same heat exchange rate for each BHE, which normally is not correspondent to the real applications. In this investigation, a TRT was firstly conducted for a site located in Shanxi Province (China) to get the local ground thermal properties. A numerical simulation framework was next verified by the TRT results. Subsequently, the ground thermal properties obtained by the TRT were used in the numerical simulation model to investigate the influence of two operation strategies on the ground temperature development of the surrounding soil and the BHE performance. The results showed that both ground temperature and BHE array performance decreased during the 8-year operation period of the BHE array in the heating mode. The ground temperature around the center BHE was lower in the same heat load (SHL) scenario (same heat load for the BHEs in the array) than in the same inlet temperature (SIT) scenario (same carrying fluid inlet temperature for the BHEs in the array), and this difference can be 2 °C in the 7th year. The annual average outlet temperature in the SHL scenario was also lower than that in the SIT scenario, especially in the long term. The investigation shows that SIT working strategy superiors the SHL strategy, providing a reference for the upcoming investigation on the design aspect of the GSHPS.

Load and velocity boundaries of oil-based superlubricity using 1,3-diketone

The clarification of the critical operating conditions and the failure mechanism of superlubricity systems is of great significance for seeking appropriate applications in industry. In this work, the superlubricity region of 1,3-diketone oil EPND (1-(4-ethyl phenyl) nonane-1,3-dione) on steel surfaces was identified by performing a series of ball-on-disk rotation friction tests under various normal loads (3.5–64 N) and sliding velocities (100–600 mm/s). The result shows that beyond certain loads or velocities superlubricity failed to be reached due to the following negative effects: (1) Under low load (≤ 3.5 N), insufficient running-in could not ensure good asperity level conformity between the upper and lower surfaces; (2) the high load (≥ 64 N) produced excessive wear and big debris; (3) at low velocity (≤ 100 mm/s), the weak hydrodynamic effect and the generated debris deteriorated the lubrication performance; (4) at high velocity (≥ 500 mm/s), oil migration occurred and resulted in oil starvation. In order to expand the load and velocity boundaries of the superlubricity region, an optimized running-in method was proposed to avoid the above negative effects. By initially operating a running-in process under a suitable combination of load and velocity (e.g. 16 N and 300 mm/s) and then switching to the target certain higher or lower load/velocity (e.g. 100 N), the superlubricity region could break through its original boundaries. The result of this work suggests that oil-based superlubricity of 1,3-diketone is a promising solution to friction reduction under suitable operating conditions especially using a well-designed running-in strategy.

Prediction and control of knock at high load boundary for HCCI engine based on neural network

Homogenous Charge Compression Ignition (HCCI) have drawn lots of attentions due to its high efficiency and low emissions. But HCCI engines are prone to random abnormal combustion phenomena at load boundaries. In this paper, innovatively implement online prediction and control of knock at high load boundary for HCCI utilizing only cylinder pressure as the diagnostic parameter based on neural networks. The results show that the neural network model with previous cycle heat release, previous cycle crank angle at 50 % cumulative heat release (CA50), peak cylinder pressure during previous and current cycle negative valve overlap (NVO) as inputs can realize the prediction of 87.5 % early combustion cycle in the intake phase before the early combustion occurs, and the diagnosis accuracy is 89.4 %. The frequency of early combustion can be reduced from 2.3 % to 0.3 % with the help of prediction model combining water injection and fuel injection reduction control, and no knocking occurs. The high load boundary of the HCCI engine is expanded by 7.1 % from 0.366 MPa to 0.392 MPa at 1500 r/min with the help of this control strategy.

Shakedown and limit analyses of a pressurised water reactor vessel nozzle under cyclic thermo-mechanical loadings

This paper has investigated cyclic plasticity of a reactor pressure vessel (RPV) nozzle subjected to cyclic thermo-mechanical loads thoroughly: cyclic thermal loads, cyclic bending moments, and cyclic internal pressures. By utilising an advanced direct numerical method known as the Linear Matching Method, elastic shakedown limit boundaries of the RPV nozzle are constructed to evaluate the effects of different load combinations on the cyclic plasticity behaviours. In additions, limit load boundaries of the RPV nozzle are constructed to confirm whether alternative plasticity or ratchetting response appear under the same loading combinations. Through comprehensive numerical studies, the effects of geometric parameters of the nozzle geometries on the cyclic plastic behaviour are identified and the parametric study results are formulated as semi-empirical equations to predict both limit load and elastic shakedown limit boundaries. Ultimately, this research provides reactor design engineer insight into the design of the RPV nozzle in consideration of cyclic plasticity.

Study on cyclic plastic behaviour of sandwich pipelines subjected to cyclic thermo-mechanical loads

Subsea pipelines are generally used to transfer hydrocarbons from ultra-deep seawater to facilities on the shore. Typically, sandwich pipelines are filled with polymeric cores for thermal insulation, with structural reinforcements also used as a deep-water application. Sandwich pipelines are subjected to either monotonic or cyclic loads, such as bending moment, buckling, internal and external pressures during their installation or operation. It is necessary to evaluate the cyclic plasticity of sandwich pipelines under complex loading combinations to prevent structural failures caused by applied loads. In this research, limit load and shakedown analyses of sandwich pipes subjected to complicated cyclic thermo-mechanical loadings are conducted using a Linear Matching Method (LMM). Temperature-dependent material properties are employed to simulate actual pipeline behaviour, and an elastic perfectly plastic model is considered with regard to geometric non-linearity issues. Numerical results are validated via a full cyclic incremental analysis, also known as a step-by-step analysis. Moreover, comprehensive parametric studies are conducted with respect to changes in the geometry of sandwich pipelines. This research presents valuable insights into the most severe loading types and combinations affecting the structural integrity of sandwich pipelines. In addition, allowable load boundaries against existing geometric parameters can be determined.

Study on the moving cross‐hatched textures under starved lubrication based on parallel calculation

AbstractThe oil storage effect of textures is beneficial for lubrication performance under starved lubrication. When the larger of the two surfaces in friction pairs is textured, the moving textures should be considered because the boundary conditions are transiently changed at each moment. This is especially for the cross‐hatched textures, which are manufactured on the cylinder liner while not on the piston ring. However, it means that the calculation cost will be very expensive for engineering friction pairs because the required calculation scale is very large and the required time step is very small. So the dynamic characteristics of moving textures on engineering surfaces are normally neglected in the existing researches. In this study, a starved lubrication model of the piston ring‐cylinder liner (PRCL) system is established considering the oil storage effect, local hydrodynamic effect and dynamic characteristics of the moving cross‐hatched textures. To speed up the calculation, an efficient parallel algorithm is developed. The results show that there is a significant difference in minimum oil film thickness (MOFT), wear load and oil film boundaries between stationary textures and moving textures, so the moving textures should not be simplified. This is helpful to find a better design of textures for engineering friction pairs.

Shakedown analysis of bounded kinematic hardening engineering structures under complex cyclic loads: Theoretical aspects and a direct approach

There exist two basic formulations of static shakedown theorem for bounded kinematic hardening (KH) model in literature. Whether the two formulations are equivalent, whether the conditions of loading-path-independence are satisfied, and how to employ the shakedown theorem to obtain the safety margin of realistic engineering structures under cyclic loading are some key issues to be solved and addressed. This paper presents theoretical aspects of the static shakedown theorem of KH and proposes a direct approach for shakedown analysis of KH structures. The presented direct approach allows for both the two shakedown formulations and considers the simultaneous influences of multiple load vertices. The two formulations are suitable for plastic models with different hardening laws and determine different shakedown load boundaries in the region of incremental collapse. Instead of dealing with a complicated problem of mathematical programming, the presented approach performs several linear elastic finite element iterative calculations, which ensures its high computational efficiency. Furthermore, the direct approach is implemented into Abaqus software platform so that it becomes a general tool to handle large-scale shakedown problems of engineering structures with complex geometry and loading conditions. An illustrative sample with analytical solution and three numerical examples from power plant engineering are adopted to validate these theoretical aspects and to present the potential of the direct approach.

Load Boundary Analysis of the Load-sensing Hydraulic System with Multi-way Valve and Pressure-compensated Valve

According to the analysis on the working principle of the load-sensing hydraulic system with multi-way valve and constant-difference relief pressure-compensated valve in the load-sensing circuit, it is concluded that there are two working conditions during the operation of the system, load-sensing condition and constant pressure supply condition. Without considering the effect of balance valves, the load boundaries of the forward and backward motion of two conditions were derived, as well as the whole load boundary. The selection principle of balance valves was studied and analyzed to expand the load boundaries. The above conclusions can be applied to this type of load-sensing hydraulic system with any valve-controlled cylinder structure and also provide the theoretical guidance for the design and apply of the system.

A support vector regression (SVR)-based method for dynamic load identification using heterogeneous responses under interval uncertainties

A support vector regression (SVR)-based method is presented in this paper, which aims to reconstruct the uncertain dynamic load using heterogeneous responses. Essentially, the technology of load identification can be regarded as an issue of nonlinear regression. Considering the incomplete limitation of the single response signal, the complicated relationship between the dynamic load and heterogeneous responses for a specific structure may be determined through some support vectors in simulated training samples based on the SVR algorithm. In view of multi-source uncertainties, an interval dimension-by-dimension (D–D) method is investigated, which can approximate the load changing concerning the each-dimensional uncertain parameter by Legendre orthogonal polynomials. Then, the dynamic load boundaries can be calculated through the maxima/minima of the approximation polynomial in the time history. The validity and specificity of the proposed methodology are clarified by 3 numerical examples. In addition, the results indicate that the proposed method can be utilized to identify the interval of dynamic load with outstanding accuracy and efficiency.

Generation of Plastic Collapse Load Boundaries of a Pressurized Cylindrical Vessel/Radial Nozzle Structure Subjected to Nozzle Bending Loadings Utilizing Various Plastic Collapse Load Techniques

This research focuses on generating the plastic collapse load boundaries of a cylindrical vessel with a radial nozzle via employing three different plastic collapse load techniques. The three plastic collapse load techniques employed are the plastic work curvature (PWC) criterion, the plastic work (PW) criterion, and the twice-elastic-slope (TES) method. Mathematical based determination of plastic collapse loads is presented and employed concerning both the PWC and the PW criteria. A validation study is initially conducted on a pressurized 90-degree pipe bend structure subjected to in-plane closing bending via finite element analyses along with an elaborate explanation of the mathematical approaches for determining the plastic collapse loads via the PWC and the PW criteria. Outcomes of the validation study revealed very good outcomes for the three techniques. Accordingly, the aforementioned three techniques are utilized to determine the plastic collapse load boundaries of a pressurized cylindrical vessel/nozzle structure subjected to in-plane (IP) and out-of-plane (OP) bending loadings applied on the nozzle one at a time. The TES method revealed considerate limitations when applied within the medium to the high internal pressure spectra. It is shown that both the PWC and the PW criteria outperform the TES method in computing the plastic collapse loads. The vessel/nozzle structure revealed relatively higher plastic collapse moment boundaries under IP bending as compared to OP bending. Conclusively, methodical steps are devised for determining the plastic collapse loads via the PWC and the PW criteria for the ease of systematic application on pressurized structures in general.

A novel method of distributed dynamic load identification for aircraft structure considering multi-source uncertainties

A series of work for distributed dynamic load identification is investigated in this paper considering unknown-but-bounded uncertainties in the aircraft structure. To facilitate the analysis, the complicated rudder structure is simplified to a plate structure based on the robust equivalence principle of mechanical property under multi-cases of flight environments. Aiming at the plate structure, a time domain–based model for distributed dynamic load identification is established through the acceleration response measured by sensors. Among them, the spatial distributed load is approximated by Chebyshev orthogonal polynomials at each sampling time, and load boundaries can be calculated by the Taylor-expansion-based uncertain propagation analysis. As keys to improve the reliability of recognition results, the optimization process for sensor placement is constructed by the particle swarm optimization algorithm, taking the robustness evaluation index and sensor distribution index into consideration. The validity and the feasibility of the proposed methodology are demonstrated by several numerical examples, and the results reveal that designer can make a rational tradeoff choice among the cost of sensor placement and the performance of load identification in a systematic framework.

Correlation of optically stimulated electron emission with failure mode of adhesively bonded epoxy composites

Carbon fiber reinforced polymers (CFRP) reduce weight in aerospace and automotive applications while maintaining or improving structural performance. Additional performance gains can be realized with composites if adhesive bonding is used in place of mechanical fasteners for structural assemblies. Surface preparation for adhesive bonding plays a critical role in the assembly process. Effective techniques for monitoring the pre-bonding surface conditions are crucial to obtain surfaces free from bond-degrading contaminants, e.g. mold release agents, which are widely used in CFRP manufacturing. In this work, optically stimulated electron emission (OSEE) was used prior to and after laser ablation to measure deposited levels of polydimethylsiloxane (PDMS) on CFRP (Torayca P2302-19). OSEE was also used to model the contamination layer thickness. After the specimens were adhesively bonded with a modified epoxy film adhesive (Loctite EA 9696 Aero), they were subjected to double cantilever beam (DCB) tests to investigate the hypothesis that surface contamination species and levels affect the fracture characteristics of adhesively bonded joints. This study relates OSEE photocurrent and the classification of the bond failure modes to their PDMS surface contamination levels prior to adhesive bonding. DCB test results show that (1) the region under the traces within the load and unloading boundaries consistently correlates with the bond strength and the probability of different failure modes, and (2) bond performance at fracture depends on the surface PDMS film thickness coating prior to laser surface treatment. The decrement in bond performance in this study correlates to the OSEE readings of contaminant levels on the adherent surfaces.

Inspection and Reconstruction of Metal-Roof Deformation under Wind Pressure Based on Bend Sensors.

Metal roof sheathings are widely employed in large-span buildings because of their light weight, high strength and corrosion resistance. However, their severe working environment may lead to deformation, leakage and wind-lift, etc. Thus, predicting these damages in advance and taking maintenance measures accordingly has become important to avoid economic losses and personal injuries. Conventionally, the health monitoring of metal roofs mainly relies on manual inspection, which unavoidably compromises the working efficiency and cannot diagnose and predict possible failures in time. Thus, we proposed a novel damage monitoring scheme implemented by laying bend sensors on vital points of metal roofs to precisely monitor the deformation in real time. A fast reconstruction model based on improved Levy-type solution is established to estimate the overall deflection distribution from the measured data. A standing seam metal roof under wind pressure is modeled as an elastic thin plate with a uniform load and symmetrical boundaries. The superposition method and Levy solution are adopted to obtain the analytical model that can converge quickly through simplifying an infinite series. The truncation error of this model is further analyzed. Simulation and experiments are carried out. They show that the proposed model is in reasonable agreement with the experimental results.

Impact of Retransmission Limit on Preamble Contention in LTE-Advanced Network

LTE-Advanced networks employ random access based on preambles transmitted according to multi-channel slotted Aloha principles. The random access is controlled through a limit $W$ on the number of transmission attempts and a timeout period for uniform backoff after a collision. We model the LTE-Advanced random access system by formulating the equilibrium condition for the ratio of the number of requests successful within the permitted number of transmission attempts to those successful in one attempt. We prove that for $W \leq 8$ there is only one equilibrium operating point and for $W \geq 9$ there are three operating points if the request load $\rho$ is between load boundaries $\rho_{1}$ and $\rho_{2} $ . We analytically identify these load boundaries as well as the corresponding system operating points. We analyze the throughput and delay of successful requests at the operating points and validate the analytical results through simulations.

A generalised method for ratchet analysis of structures undergoing arbitrary thermo‐mechanical load histories

SummaryA novel approach is presented based upon the Linear Matching Method framework in order to directly calculate the ratchet limit of structures subjected to arbitrary thermo‐mechanical load histories. Traditionally, ratchet analysis methods have been based upon the fundamental premise of decomposing the cyclic load history into cyclic and constant components, respectively, in order to assess the magnitude of additional constant loading a structure may accommodate before ratcheting occurs. The method proposed in this paper, for the first time, accurately and efficiently calculates the ratchet limit with respect to a proportional variation between the cyclic primary and secondary loads, as opposed to an additional primary load only. The method is a strain‐based approach and utilises a novel convergence scheme in order to calculate an approximate ratchet boundary based upon a predefined target magnitude of ratchet strain per cycle. The ratcheting failure mechanism evaluated by the method leads to less conservative ratchet boundaries compared with the traditional Bree solution. The method yields the total and plastic strain ranges as well as the ratchet strains for various levels of loading between the ratchet and limit load boundaries. Two example problems have been utilised in order to verify the proposed methodology. Copyright © 2015 John Wiley & Sons, Ltd.