Analysis Of Performance Degradation Research Articles

Multiscale analysis of shrinkage-induced performance degradation of shear wall and application to structural analysis

Shrinkage-induced cracks reduce the stiffness of concrete structures. Shear walls are more sensitive to drying shrinkage than other members because of their fully restricted condition and large surface areas exposed to air. This study examines how concrete structural performance is affected by shrinkage due to moisture loss via hydration or dissipation by applying multiscale integrated finite element analysis. First, a cyclic shear loading test on shear wall specimens subjected to drying in a previous study was reproduced. Based on the reproduction analysis model, parametric analysis was conducted, focusing on the member scale, mix proportion, and surface treatment of concrete. Shrinkage-induced cracks reduced member stiffness, and the effects of the member scale on drying speed were shown. The dominance of autogenous shrinkage in the case of high-strength concrete was also observed. The sealing of the concrete surface effectively prevented moisture dissipation, but moisture supply from ambient air was also blocked when the humidity inside the concrete was low. Thus, a proper surface protection method should be selected considering water consumption via hydration. Finally, the use of equivalent material properties for considering initial damage due to shrinkage was proposed as a simple way to account for drying effects in structural analyses.

Quantitative analysis of performance degradation in movable MEMS devices by a multiscale approach

The rapid advancements in AI and 5G/6G communication technologies have intensified the demand for MEMS devices characterized by exceptional performance and diversity. Simultaneously, the imperative for enduring stability in these devices has become increasingly critical. Unforeseen reliability issues pose substantial challenges to the full-scale application of these advanced MEMS devices, underscoring the importance of understanding their failure mechanisms. Presently, there is a scarcity of comprehensive research in reliability computation and analysis. In this study, we adopt cross-scale damage variables as a nexus, linking responses across three scales: material, structural, and performance. We implement a synergistic finite element-molecular dynamics approach for multiscale analysis. Using a prototypical MEMS resonator structure as a case study, we establish quantitative interrelations among these three scales, enabling precise depiction of atomic failure behavior and its impact on resonant frequency degradation. This approach offers an atomically grounded explanation for the fundamental material processes underlying frequency degradation. Our numerical analyses explore the failure mechanisms responsible for the frequency degradation in MEMS resonators. Additionally, we propose several optimized strategies for the design and preparation phases aimed at enhancing fatigue performance. These findings are particularly relevant in light of the growing necessity for devices that maintain long-term stability.

Cause Analysis of Whole Vehicle NVH Performance Degradation under Idle Conditions

Cause Analysis of Whole Vehicle NVH Performance Degradation under Idle Conditions

Numerical analysis of PEMFC stack performance degradation using an empirical approach

This paper proposes a performance degradation model based on empirical approaches, which can break down the power loss and quantify the influence of each aging phenomena from the overall performance degradation. With the presence of primary degradation mechanisms, the approach can be used to analyze the performance degradation of fuel cells under different degradation conditions. The aging parameters that represent hydrogen crossover, membrane resistance increase, and electrochemical active surface area (ECSA) loss are introduced to characterize the performance degradation. Based on the polarization behavior of proton exchange membrane fuel cells (PEMFCs), the variations of degradation stressors are determinated by fitting the aging parameters to the measuring polarization curves. The empirical approach is validated by a 150 h durability experiment and agrees well with all polarization curves. The results show that ECSA loss always maintains an apparent influence and hydrogen crossover accounts for 56% of the performance degradation in OCV.

Performance degradation and reliability analysis of a MEMS flow sensor with accelerated degradation testing

In this article, we research the performance degradation of a MEMS flow sensor with accelerated degradation testing (ADT). The degradation of temperature stress (Ts) on sensor is studied. Based on the performance in the aging test, resistance degradation ∆R is selected as a more suitable degradation characteristic parameter. Furthermore, the degradation process of the characteristic parameter results from resistivity decreases, in which Ts leads to stress relief within the bulk of the resistor. By implementing the Constant-stress accelerated degradation test (CSADT), we estimate the lifetime of this MEMS flow sensor based on the Arrhenius model. The calculated lifetime is 6.833 years for the 120°C group, 3.942 years for the150°C group, and 2.492 years for the180°C group. In addition, using statistics analysis, the Weibull distribution (WD) is proved to be the better mode for the MEMS flow sensor acceleration life with the Anderson-Darling (AD) being 235.910. The scale and shape of WD was evaluation. On the other hand, to verify the rationality of the distribution, the Standard residual error method and the Cox-Snell residual error method have been used separately, to perform the Goodness-of-fit tests. The AD value of Standard residual error and Cox-Snell residual error is 3.476. It proves that the selected life distribution model of this MEMS flow sensor is befitting. Finally, in this research the CSADT results are original and novelty. The lifetime distribution results reveal that considering the Goodness-of-fit tests can significantly improve the accuracy of reliability analysis of this MEMS flow sensor. Based on those results, a reliability method for this MEMS flow sensor is established.

Analysis of performance degradation in the dead-ended anode proton exchange membrane fuel cell under different load profiles

This paper addresses the load profile effect on the long-term performance of dead-ended anode proton exchange membrane fuel cells (DEA-PEMFC). Two fuel cells were fabricated with an identical structure and they were activated using the same methods. Next, they were subjected to the constant and varying load profiles in the DEA mode. Examination of the frequency-dependent resistances, the cathode electrochemical active surface area (ECSA), and the polarization curves of the fuel cells at the same time points showed that, despite the same initial performance, a gradual decrease in performance was observed in both fuel cells, which was mainly due to the degradation of the catalyst layer. The test results showed a sharper drop in the performance parameters at the constant load profile. For example, the charge transfer resistance after 60 h increased by 86% and 17% at the constant and varying load profiles, respectively. The transmission electron microscopy (TEM) images of the cathode catalyst at the end of the tests showed that the more severe corrosion of the carbon substrate and the larger agglomerates of platinum nanoparticles in the constant load profile were the main causes of the reduction in the ECSA and the performance of the fuel cell.

Analysis of Performance Degradation in Lithium-Ion Batteries Based on a Lumped Particle Diffusion Model.

The analysis of performance degradation in lithium-ion batteries plays a crucial role in achieving accurate and efficient fault diagnosis as well as safety management. This paper proposes a method for studying the degradation pattern of lithium-ion batteries and establishing the structure-activity relationship between internal and external parameters by employing a lumped particle diffusion model. To simulate real-world operating conditions, a cycle life test was conducted with the constant current-constant voltage (CC-CV) charge mode and the discharge mode under New European Driving Cycle (NEDC) working condition. The test aimed to analyze the variations in the external macroscopic characteristic parameters of the battery. Building upon this analysis, a lumped particle diffusion model was constructed, and the model parameters were identified using the Levenberg-Marquardt (L-M) algorithm. Subsequently, the ohmic, activation, and concentration losses of the battery under different aging conditions were determined, revealing the internal state evolution during the degradation process of lithium-ion batteries. The findings indicate that the lumped particle diffusion model provides a comprehensive explanation of the internal mechanisms contributing to the performance degradation of lithium-ion batteries. Moreover, the proposed method offers a novel perspective for the real-time quantitative analysis of lithium-ion battery performance degradation.

Dynamic causal modeling for nonstationary industrial process performance degradation analysis and fault prognosis

Performance degradation analysis and fault prognosis of industrial processes refer to distinguish different degradation stage and raise warnings before a failure occurs, which are crucial to ensure the operation efficiency and safety. However, processes usually have nonstationarity caused by operating condition switching, which may be confused with the underlying temporal variations in the degradation process. Considering that the degradation process is essentially the changes in short-term temporal information transmission between variables, we propose a dynamic causal graph-driven performance degradation analysis and fault prognosis framework (DCG-PDA), which can reveal the intrinsic connection between causality and degradation mechanism. First, a dynamic causal graph framework is constructed, in which the nonstationarity is removed by transfer entropy-guided symbolization, to extract significant short-term causal information transmission. Second, changes in causality are effectively captured and quantified, and the causal graphs corresponding to some time points with larger changes in causality are selected to characterize the representative causal patterns in the degradation process. Finally, a node anomaly score is designed to consider the accumulation of causal structural changes at anomaly time points and measure variable-wise degradation contributions, so as to realize accurate locations for key variables in the degradation process. The validity of the proposed method is illustrated through a real compressor fouling process.

Performance degradation analysis and fabrication guidance of μ-TEG from material to device

Micro thermoelectric generator (μ-TEG) attracts more and more attention due to its small size and high power density. Many two-dimensional thermoelectric materials with high performance have facilitated the development of μ-TEG. However, the performance of μ-TEG fabricated by these great thermoelectric materials is significantly degraded due to size effect, interfacial effects (include contact effect and boundary effect) and structure effect. To accurately assess the performance degradation degree from material to μ-TEG and guide the device fabrication, an experiment-verified mathematical model considering interfacial and size effects is proposed. Firstly, the phonon/electron temperature distribution in thermoelectric leg of μ-TEG is analyzed to investigate the device-level thermoelectric properties of material. Then based on the device-level thermoelectric properties, the actual power generation performance model of μ-TEG is established to conduct the influence analysis of these effects (boundary, size, contact and structure effects) on material and device. Finally, the thermoelectric leg thickness (Hte) is optimized to realize optimal power generation. The study results reveal that boundary and size effects weaken the device-level thermoelectric properties, and the reduction trend is more obvious when Hte is smaller, especially when Hte ≤ 20 μm. The decrease from the material intrinsic figure of merit ((ZT)m) to the device figure of merit ((ZT)D) is owing to the boundary effect, structure effect and contact effect, and the dominant factor of this decrease changes from structure effect (Hte＜7 μm)to contact effect (Hte ≥ 7 μm) as Hte increases, which points to a main optimization direction for (ZT)D for different Hte. As for contact effect, the electrical contact resistivity (re,c) has a more significant impact on weakening the performance of μ-TEG than thermal contact resistivity (rk,c), and their optimization goals are explored (re,c ≤ 5.1 × 10−12 Ω·m2, rk,c ≤ 9.3 × 10−8 K·m2/W). At given electrical and thermal contact resistivity, there exists an optimal Hte for achieving the optimal power generation (Popt) and a large range of Hte for achieving 95%Popt, and the optimal Hte increases with increasing electrical and thermal contact resistivity. This study can reduce the processing difficulty and save time and economic costs of μ-TEG fabrication, which can avoid the blind fabrication of μ-TEG.

Performance degradation analysis of a medium pressure superheater due to tube deactivation

Steam is essential in petrochemical industries for the transportation of thermal energy and usage in some reforming process. Superheaters are heat exchangers that convert saturated steam to dry steam by utilizing waste heat from the flue gas stream. Medium pressure steam superheaters are prone to tube deterioration due to service at elevated temperatures and erosion from the presence of liquid phase in the steam, leading to tube plugging after tube failure. This reduces the overall surface heating area of the superheater. Relations between the tube plugging practice and the energy dynamics of the superheaters are important for engineers to identify the responses of the superheater for operation planning, and this issue has not been extensively explored academically. This article analyses the deterioration of superheater performance due to reduction of surface heating area based on operational data of a petrochemical steam generation line. The objective is to find relations between the effect of tube plugging on the states of both steam and flue gas streams, as well as its impact on the overall energy exchange. The operating conditions of a superheater at two separate service years, before (year 2014) and after (year 2017) tube plugging, were compared through the first law energy analysis. The average steam inlet temperatures were between 248 °C and 250 °C, at flow rates between 70 and 90 ton/hour. The analysis indicated that 0.3 to 0.8 % increase in inlet energy is required for every plugged tube to compensate for the reduction of heating surface. At 3 % reduction of heating surface area, the heat exchanger effectiveness decreases by an average of 11 % that also leads to a lower steam temperature output by approximately 6% from the design operating temperature. These results would assist steam engineers to analyse changes to the energy economics of the whole plant and decide the feasibility of replacing existing superheaters with new ones. Also, another significant finding to be considered by steam engineers is that the current practice of increasing the steam flow rate does not offset the loss of energy effectiveness due to tube plugging.

Power losses in PV arrays of field-aged modules

Most of studies are focused mainly on performance degradation analysis of solar cell or categorizing PV failure modes concerning solely climate or cell-technology. However, the impact of degradation modules on output power of PV arrays remains somewhat unclear and has not been reported so far. Therefore, main task of the present work is to get a general view of mismatch effect on PV arrays output for aged panels. Photovoltaic current-voltage characteristics of the 10 individual modules at Research Unit in Renewable Energies in Saharan Medium were measured and recorded. Measurements are based on the analysis of mismatch losses due to series and parallel connection of aged PV modules. Degradation data and the analysis of the I-V characteristics indicate that the tested modules have suffered in the hot desert. Both of visual and electrical degradation data reaffirm the direct relation between observed physical degradation and output power drop. Results and analysis of the I-V characteristics and degradation data indicate that Power losses in crystalline PV modules are also due to mismatch in the I-V characteristics of these modules. The paper provides many findings that can be beneficial in further studies on design of aged PV array and development of a crystalline silicon PV module and can enable the manufacturers to prevent premature failure in desert climates.

The aerodynamic performance degradation analysis of a small high bypass turbofan engine compression system with fan rotor blade leading edge erosion

Abstract The entire compression system of DGEN380 was selected to study the degradation of aerodynamic characteristics caused by erosion of the leading edge. Numerical simulations under different degrees of leading edge erosion were performed. It was found that the leading edge erosion causes a significant decrease in operability from 70 % of the blade height to the tip, and mainly affects the subsequent flow field in the bypass. At 90 % of blade height, the isentropic efficiency and total pressure ratio of the blade with leading edge erosion are reduced compared to the origin blade. Afterwards, the thrust equation was introduced to analyze the effect of leading edge erosion on the thrust loss under different operating conditions of the aircraft. Among the three operating conditions, the thrust loss rate of the cruise condition was the largest, which provided a reference for the subsequent evaluation of the blade repair condition.

Multi‐pronged degradation analysis of a photovoltaic power plant after 9.5 years of operation under hot desert climatic conditions

AbstractLong‐term reliability assessment of photovoltaic (PV) modules is key to ensuring the economic viability of PV systems. This paper presents a multi‐pronged performance degradation analysis of a 62.1 kWp solar PV power plant after 9.5 years of operation. For this purpose, various diagnosis techniques, namely, visual inspection, infrared thermography (IR), ultraviolet fluorescence (UVFL) and current‐voltage (I‐V) characterization, have been performed to evaluate the performance and degradation of the solar PV power plant. The visual characterization results show that the PV strings are affected by different mechanisms with different degrees of occurrences. The degradation mechanisms observed and the level of occurrence among the modules were found to be, encapsulant discolouration (100%), degraded frame adhesive (57%), degraded junction box adhesive (39%), snail trails (30%), burn marks (3%), cell cracks (2%) and delamination (0.4%). Although discolouration of the encapsulant was the most common possible degradation mechanism observed, the main causes of the power loss were snail trails and cracks in the PV cells. Furthermore, the IR thermography and UVFL analysis provided better understanding on snail trails phenomenon and crack mechanism on the affected PV modules. Besides imaging techniques, to assess the electrical performance of the system, we performed current‐voltage (I‐V) and power‐voltage (P‐V) characterization of the entire PV plant from which the degradation rates of the electrical parameters were determined. Our results show that the degradation rates for the maximum power and the fill factor are 0.84%/year and 0.66%/year, respectively, over the operating period of the installation. The estimated maximum power degradation rate for this installation could be considered as a realistic degradation rate for PV modules installed in harsh and hot desert climatic conditions. Additionally, our work has raised doubts about the validity of the warranties proposed by the manufacturers.

Probabilistic analysis of wind turbine performance degradation due to blade erosion accounting for uncertainty of damage geometry

Geometry alterations of wind turbine blades due to erosion reduce the blade aerodynamic performance, yielding turbine power and energy losses. This study proposes a novel probabilistic analysis framework combining computational fluid dynamics, probabilistic and deterministic uncertainty propagation, and high-performance computing to assess this performance degradation accounting for the unavoidable uncertainty on field records of blade erosion. This uncertainty presently prevents using erosion records for improving wind turbine maintenance planning, increasing energy yield, and thus further reducing the wind energy cost. The technology is demonstrated by quantifying the statistical moments of power and energy yield losses of an eroded utility-scale turbine at a North Sea offshore site and a southern European onshore site. The expectations of the offshore and onshore annual energy production losses are found to be 2 and 3% of the corresponding nominal values, respectively, with corresponding standard deviations of 0.1 and 0.15%. In the realistic scenario of erosion varying with high radial frequency, these low standard deviations result from partial compensation of the impact of mild and severe damages. These low standard deviations indicate that present uncertainty levels of erosion geometry records can be handled with uncertainty analysis in predictive maintenance for further reducing wind energy costs. With the frequent assumption of small or no radial variation of erosion, the standard deviation of the loss is misleadingly higher. For the first time, the study reports on the significant impact of turbulence intensity of the installation site on the turbine loss variability with the site wind characteristics.

Photovoltaics literature survey (no. 182)

Photovoltaics literature survey (no. 182)

Comprehensive Analysis of Solid Oxide Fuel Cell Performance Degradation Mechanism, Prediction, and Optimization Studies

Solid oxide fuel cell (SOFC) performance degradation analysis and optimization studies are important prerequisites for its commercialization. Reviewing and summarizing SOFC performance degradation studies can help researchers identify research gaps and increase investment in weak areas. In this study, to help researchers purposely improve system performance, degradation mechanism analysis, degradation performance prediction, and degradation performance optimization studies are sorted out. In the review, it is found that the degradation mechanism analysis studies can help to improve the system structure. Degradation mechanism analysis studies can be performed at the stack level and system level, respectively. Degradation performance prediction can help to take measures to mitigate degradation in advance. The main tools of prediction study can be divided into model-based, data-based, electrochemical impedance spectroscopy-based, and image-based approaches. Degradation performance optimization can improve the system performance based on degradation mechanism analysis and performance prediction results. The optimization study focuses on two aspects of constitutive improvement and health controller design. However, the existing research is not yet complete. In-depth studies on performance degradation are still needed to achieve further SOFC commercialization. This paper summarizes mainstream research methods, as well as deficiencies that can provide partial theoretical guidance for SOFC performance enhancement.

Experiment and Analysis of Performance Degradation of CCD Image Sensors Induced by Proton Radiation with Different Energy

Experiment and Analysis of Performance Degradation of CCD Image Sensors Induced by Proton Radiation with Different Energy

Failure Mechanism of pHEMT in Navigation LNA under UWB EMP.

With the development of microelectronic technology, the integration of electronic systems is increasing continuously. Electronic systems are becoming more and more sensitive to external electromagnetic environments. Therefore, to improve the robustness of radio frequency (RF) microwave circuits, it is crucial to study the reliability of semiconductor devices. In this paper, the temporary failure mechanism of a gallium arsenide (GaAs) pseudomorphic high electron mobility transistor (pHEMT) in a navigation low-noise amplifier (LNA) under the jamming of ultra-wideband (UWB) electromagnetic pulses (EMP) is investigated. The failure process and failure mechanism of pHEMT under UWB EMP are elaborated by analyzing the internal electric field, current density, and temperature distribution. In detail, as the amplitude of UWB EMP increases, the output current, carrier mobility, and transconductance of pHEMT decrease, eventually resulting in gain compression. The injection experiment on LNA, which effectively verified the failure mechanism, indicates that the gain of pHEMT is suppressed instantaneously under the jamming of UWB EMP and the navigation signal cannot be effectively amplified. When UWB EMP amplitude increases to nearly 10 V, the BeiDou Navigation Satellite System (BDS) carrier signal is suppressed by nearly 600 ns. Experimental results accord well with the simulation of our model. UWB EMP jamming is a new and efficient type of electromagnetic attack system based on the device saturation effect. The performance degradation and failure mechanism analysis contribute to RF reinforcement design.

A performance degradation analysis method for a reciprocating rod seal in the wear process under mixed lubrication conditions

The sealing performance of a reciprocating seal degrades during service. The analyses developed based on the initial state of a seal cannot express the performance degradation due to seal wear in detail. In this research, the Archard model in dry friction is extended to mixed lubrication by introducing the lubrication coefficient verified by an experiment. The nonlinear adaptive meshing technique is used in finite element analysis (FEA) to simulate the material removal to obtain the static contact pressure during the wear process. Hence, a sealing performance degradation analysis method is proposed based on the modified Archard model for reciprocating seals under mixed lubricating conditions. This method can be used to analyse the sealing, lubrication, and wear characteristics of seals at any service time. The simulation results indicate that the static pressure becomes more uniform with the occurrence of seal wear, and the lubricating property of the oil film reduces the seal wear. The variation trends of the sealing performance parameters such as contact pressure, friction, and net leakage at different service times under specific operating conditions are obtained.

Analysis of performance degradation on the components in polymer electrolyte membrane fuel cell by dissecting the oxygen diffusion region

Performance degradation due to mechanical effect is an important durability issue for polymer electrolyte membrane fuel cells (PEMFCs). Mechanical degradation mainly occurs during the startup/shutdown mode at subzero temperature. However, studies about the contribution of mechanical degradation to the main PEMFC components of the gas diffusion layer (GDL) and catalyst-coated membrane (CCM) have not been analyzed quantitatively under various operating conditions. In this study, the freeze-thaw accelerated stress test (AST) is newly developed and performed to identify the exclusive effect of mechanical degradation on the GDL and CCM under normal and subzero conditions. Under normal conditions, the PEMFC performance result indicates that CCM has a larger degradation than the GDL owing to an increase in oxygen transport resistance and low water saturation point. Under subzero conditions, a cold start is experimentally investigated using the constant voltage method, revealing that the oxygen transfer coefficient dominantly affects the heat generation term in the 0-D model. Therefore, this study provides design guidelines for high-durability PEMFC components (GDL and CCM) and new insights into the interactive effects between heat and oxygen transport under normal and subzero conditions.