Repair Costs Research Articles

Analysis of Vibration Signals Based on Machine Learning for Crack Detection in a Low-Power Wind Turbine.

Currently, renewable energies, including wind energy, have been experiencing significant growth. Wind energy is transformed into electric energy through the use of wind turbines (WTs), which are located outdoors, making them susceptible to harsh weather conditions. These conditions can cause different types of damage to WTs, degrading their lifetime and efficiency, and, consequently, raising their operating costs. Therefore, condition monitoring and the detection of early damages are crucial. One of the failures that can occur in WTs is the occurrence of cracks in their blades. These cracks can lead to the further deterioration of the blade if they are not detected in time, resulting in increased repair costs. To effectively schedule maintenance, it is necessary not only to detect the presence of a crack, but also to assess its level of severity. This work studies the vibration signals caused by cracks in a WT blade, for which four conditions (healthy, light, intermediate, and severe cracks) are analyzed under three wind velocities. In general, as the proposed method is based on machine learning, the vibration signal analysis consists of three stages. Firstly, for feature extraction, statistical and harmonic indices are obtained; then, the one-way analysis of variance (ANOVA) is used for the feature selection stage; and, finally, the k-nearest neighbors algorithm is used for automatic classification. Neural networks, decision trees, and support vector machines are also used for comparison purposes. Promising results are obtained with an accuracy higher than 99.5%.

Propeller-Induced Jet Impact on Vegetated Flow Fields: Complex Coupled Effect towards the Velocity Profile

The failure of swirling ship propellers in marine environments can lead to huge repair costs. One of the main causes of such failure is when propellers tangle with vegetation, especially in shallow flow environments like ports, harbours, or shipyards. In order to understand the above-mentioned issue, this study proposes an analytical approach to explore efficient predictions and provide a flow guideline with respect to the co-existence of vegetation and propeller swirling effects. More specifically, we intend to investigate the full-depth theoretical velocity profile to represent propeller-induced flow under submerged vegetation conditions. This paper first investigates the modified logarithmic law approach to determine its suitability to represent the regional vegetated flow zone before implementing it into a three-layer analytical model. It was found, using the benchmark of literature measurements, that the modified log law improved the near-bed velocity calculation by nearly 70% when compared to an existing model. A propeller jet impact computation coupled into the vegetation analytical model was then investigated in different locations within the vegetated flow, i.e., at free-flow, water–vegetation interface, and vegetation-hindered zones, to study their complex velocity distribution patterns. The results demonstrate adequate validation with the vegetated flow and measured propeller jet data from the literature. This proves the potential of the proposed analytical approach in representing a real-world propeller jet event submerged in water flow with the existence of vegetation. The proposed novel method allows costless computation, i.e., as compared to conventional numerical models, in representing the complex interaction of the propeller jet and vegetated flow.

An approach to modeling residual life of a renewal process for reliability analysis and maintenance planning

This paper extends and relaxes the structure of a mean remaining time to renewal model for a failure prone system subject to minimal repairs. Compared to existing related works, the contributions of our model are threefold. It not only accounts for changes in operating states and age factor, but also can adapt itself to minimal repair process history. It is implemented through the use of a damage process X(t) coupled with a supplementary variable N(t) counting the number of failures. The bivariate approach allows a wide class of models to be considered including age-based models and those ignoring the repair effect. Another feature enhancing the domain of its applicability is to predict failures and quantify some reliability indexes. These impose a challenge when coping with models either characterized by inter-correlated failure times or developed under varying operating conditions. Further, the structure of the devised model called state-dependent mean remaining time to renewal (in short SD-MRTR) enables the implementation of maintenance policy on the basis of renewal–reward arguments. In present setting, a renewal is defined with respect to the supplementary variable. That means, a renewal (perfect repair) is carried out as soon as the number of failures reaches a give value j. Using the renewal–reward theorem argument and the explored SD-MRTR, the practical contribution of the model is enhanced by proposing a j-based preventive replacement policy achieving minimum repair costs. The proposed model and the behavior of the optimal solution as the model parameters change are illustrated through numerical examples.

Boosting Erasure-Coded Multi-Stripe Repair in Rack Architecture and Heterogeneous Clusters: Design and Analysis

Large-scale distributed storage systems have introduced erasure codes to guarantee high data reliability, yet inevitably at the expense of high repair costs. In practice, storage nodes are usually divided into different racks, and data blocks in storage nodes are often organized into multiple stripes independently manipulated by erasure code. Due to the scarcity and heterogeneity of the cross-rack bandwidth, the cross-rack network transmission dominates the entire repair costs. We argue that when erasure code is deployed in a rack architecture, existing repair techniques are limited in different aspects: neglecting the heterogeneous cross-rack bandwidth, less consideration for multi-stripe failure, and no special treatment on repair link scheduling. In this paper, we present CMRepair, a <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Cross-rack Multi-stripe Repair</i> technique that aims to reduce the repair time for multi-stripes failure repair in heterogeneous erasure-coded clusters. CMRepair first carefully chooses the nodes for reading/repairing blocks and searches for the multi-stripe repair solution. It adopts different algorithms to adjust per stripe solution, including the Computation Time Priority (CTP) algorithm based on the greedy idea and the Repair Time Priority (RTP) algorithm based on the meta-heuristics idea. Furthermore, CMRepair selectively schedules the execution orders of cross-rack links, with the primary objective of saturating the unused upload/download bandwidth resources and avoiding network congestion. The experiments show that CMRepair with the CTP algorithm can reduce 27.59%-58.12% of the repair time while only introducing negligible computation overhead, and CMRepair with the RTP algorithm can reduce 33.52%-97.75% of the repair time in an acceptable computation time, over existing repair techniques.

Maintenance modeling and cost assessment for repaired reinforced concrete structures exposed to chloride attack in coastal areas in Vietnam

One of the primary causes that can reduce the lifespan of concrete structures is chloride-induced corrosion of reinforcing steel. Recent research has shown that material properties, exposure conditions and climatic conditions have a significant influence on the structural deterioration of reinforced concrete (RC) structures, especially in marine environments. The objective of this paper is to predict the durability of RC structures damaged by chloride-induced corrosion in near-shore environments in Vietnam, considering regular repair activities. A two-dimensional model of chloride penetration in square cross-section RC columns repaired by cover replacement techniques is studied. Two repair methods with different shapes (orthogonal and circular) are considered. The effects of the different repair methods on the life span of structures are investigated in case studies in Vietnam that consider the variations of annual temperature and humidity in three coastal areas such as Danang, Haiphong, and Ho Chi Minh City. Finally, maintenance and repair costs during the lifetime of structures are calculated for each case. The study suggests that for RC structures exposed to two-dimensional chloride ingress, the most critical areas for assessing chloride concentration, predicting corrosion initiation, and planning repair schedules are the corners of the columns. In addition, the chloride-induced corrosion process is strongly influenced by the local weather conditions, especially in areas with high humidity. The repair method with circular concrete replacement seems to be more efficient in terms of maintenance schedule and cost than the repair method with orthogonal concrete replacement.

A WebGPU-based acoustic wave simulator for ultrasound NDT

Ultrasound NDT is a standard industrial technique for health monitoring and flaw identification in several structures, such as subsea oil pipelines. Its primary purpose is to form a representative image of the internal structure of the inspected object, which provides, in many cases, early warning of structure discontinuities, making it possible to reduce repair costs and mitigate risks. One of the imaging methods that has been receiving increasing attention in the ultrasound and seismology communities is the Full Waveform Inversion (FWI), which estimates the velocity model for the inspection area by confronting the acquired information obtained by the NDT system with theoretical simulated data. Since FWI algorithms rely on successive ultrasonic wave simulations, it is essential to ensure that each simulation is optimized and contributes little to the total running time. Acoustic wave simulations can be optimized using a graphical processing unit (GPU), which provides hardware acceleration through parallelism, where each point of the simulated area can be computed simultaneously. Among all available GPU APIs, WebGPU is the next-generation standard graphics Web API that exposes modern computer graphics capabilities by giving the user low-level, general-purpose access to the GPUs. This API is designed to efficiently map to native GPU APIs, which enables applications to run on different GPUs, making implementations more scalable and interchangeable. Motivated by this flexibility, we explore the acceleration capabilities of the WebGPU API by implementing a WebGPU-based acoustic wave simulator for ultrasound NDT.

Pemodelan Estimasi Kerusakan Jalan Metode Markov

Roads with damaged conditions can cause traffic accidents and hinder society's economic and social progress. Roads that are left hurt and no repairs will further worsen the condition of these roads. For this reason, it is necessary to analyze the modeling of estimated road damage, which is needed to get an informed picture of future road pavement changes. This study aims to predict road conditions for five years, with the research location being on six roads in Malang Regency. This research method uses interviews and secondary data collection using Markov chain analysis. The method used in this study is the Markov Chain method, which is a method that studies the properties of a variable in the present based on its past properties to determine the properties of these variables in the future. The results of modeling road damage are when road repairs are not carried out, and the injury worsens yearly. On the roads studied, road damage increased from year 0 to year 1, and there were many increases ranging from 2% -7%, and for years 1 to 5, there was an increase of 1%. The conclusion of this study is that road damage is increasing because there is no repair at all, so more funds are needed for road repair costs.

Virus–pathogen interactions improve water quality along the Middle Route of the South-to-North Water Diversion Canal

Bacterial pathogens and viruses are the leading causes of global waterborne diseases. Here, we discovered an interesting natural paradigm of water “self-purification” through virus–pathogen interactions over a 1432 km continuum along the Middle Route of the South-to-North Water Diversion Canal (MR-SNWDC) in China, the largest water transfer project in the world. Due to the extremely low total phosphorus (TP) content (ND-0.02 mg/L) in the MR-SNWDC, the whole canal has experienced long-lasting phosphorus (P) limitation since its operation in 2015. Based on 4443 metagenome-assembled genomes (MAGs) and 40,261 nonredundant viral operational taxonomic units (vOTUs) derived from our recent monitoring campaign, we found that residential viruses experiencing extreme P constraints had to adopt special adaptive strategies by harboring smaller genomes to minimize nucleotide replication, DNA repair, and posttranslational modification costs. With the decreasing P supply downstream, bacterial pathogens showed repressed environmental fitness and growth potential, and a weakened capacity to maintain P acquisition, membrane formation, and ribonucleotide biosynthesis. Consequently, the unique viral predation effects under P limitation, characterized by enhanced viral lytic infections and an increased abundance of ribonucleotide reductase (RNR) genes linked to viral nuclear DNA replication cycles, led to unexpectedly lower health risks from waterborne bacterial pathogens in the downstream water-receiving areas. These findings highlighted the great potential of water self-purification associated with virus–pathogen dynamics for water-quality improvement and sustainable water resource management.

Optimizing facility maintenance planning under uncertainty

Maintenance of civil infrastructure is necessary to ensure assets perform as intended over their service life. As these elements age and degrade, appropriate repair planning helps ensure continued operation. Unfortunately, optimal repair planning can be complex due to uncertainty regarding component conditions. This uncertainty also makes budgeting difficult. This paper presents a novel methodology for optimizing maintenance planning of facility components under uncertainty. The proposed methodology integrates a Markov chain Monte Carlo process to capture the uncertainty inherent in equipment degradation, and a mixed integer programming model to generate an optimal repair plan and an associated minimized budget. This approach identifies an optimal set of facility components that need to be repaired to minimize the total facility repair cost required to meet or exceed a user-defined goal for facility health. The proposed method has distinct advantages over many non-linear approaches in literature as it can guarantee an optimal solution with significantly lower computational time. This computational advantage enables the technique to scale to more significant problems, such as determining repair plans across a portfolio of facilities. The method outperforms basic decision heuristics used to define repair plans and existing non-linear optimization methods in terms of consistently meeting a facility health metric at a minimal cost. Data obtained from the U.S. Army Corps of Engineers is used within a case study to demonstrate the feasibility of the proposed approach as it applies to building infrastructure maintenance.

Post-Handover Housing Quality Management and Standards in Korea

Housing quality is a subject of dispute worldwide, and these disputes are increasing due to the significant differences in the views of producers and consumers on quality standards. To arbitrate disputes, an objective evaluation of housing quality is necessary. In Korea, disputes over housing quality in the post-handover stage result in lawsuits, thus becoming a social issue. This study analyzed the results of lawsuits against housing complexes in Korea. The ratio of defect repair cost to construction cost (DRCCC) was adopted as an indicator, and the quality level of the building was evaluated using a control chart to select failures. The findings showed that there were more cases where the construction cost was small, the housing quality was poor, the deviation was wide, and the quality defect exceeded the limit level of the control chart. To improve housing quality, it is necessary to strengthen quality management, to control the quality within the management limit, and to adjust standards by reflecting the consumer’s viewpoint.

Designing price-service menus in a product-service system

We study contract menu design by a vendor leasing production equipment to its clients who serve customers. The equipment can fail which can cause delays to clients' customers. The equipment vendor can offer its clients three types of lease-and-repair contracts: equipment lease with an immediate replacement upon failure, repair with a redundant unit on client premises (parallel layout), and repair without a backup unit on the premises. The vendor does not have full information about each client but knows that clients fall into two types. ‘High’ (vs. ‘Low’) type clients have a higher (vs. lower) willingness to pay but have customers who are more (vs. less) delay-sensitive. Modeling the interaction between the vendor and its clients as a leader-follower game and using queueing theory, we show that a monopolistic vendor can increase its expected profit through second-degree price discrimination by offering a menu of contracts to its clients. We find that when the distribution of customers with low and high willingness to pay is not skewed (one-sided) and either the cost of repair or cost of equipment is low the vendor can increase its profit by inducing price discrimination through offering the menus proposed in the paper.

Input parameters and nomograms for service life-based design of reinforced concrete structures exposed to chlorides

Civil engineers are trying to promote the service-life-based design of reinforced concrete (RC) structures to ensure long corrosion-free service life with minimal maintenance, repair, rehabilitation, and life cycle costs. This paper highlights the difficulties in adopting the existing tools as a general practice, especially for high-performance concrete with novel materials. To overcome these difficulties, “SL-Chlor,” a MATLAB® computer program is developed to estimate service life, which uses Fick’s 2nd Law of Diffusion to model chloride ingress, a major factor causing corrosion. Based on SL-Chlor, user-friendly nomograms are then developed to estimate the service life of RC structures located at various distances from the seashore. With the development of nomograms, this paper attempts to bring a new perspective to promote service life-based design with the help of user-friendly tools. The use of nomograms is demonstrated using case studies with multiple input parameters. The effect of different input parameters on service life is found to be synergistic, in the following descending order of influence: cover depth (d) > chloride diffusion coefficient (DCl) > ageing coefficient (m) [maturity constant ofDCl)] > chloride threshold of the steel-cementitious system (Clth). These findings encourage not only the use of blended cements but also the implementation of 3C’s (adequate cover depth, compaction, and curing, which inherently influences d, DCl, and m) to help structures achieve the desired service life.

Estimating the Cost of Wildlife Strikes in Australian Aviation Using Random Forest Modeling

Wildlife strikes in aviation represent a serious economic concern; however, in some jurisdictions, the costs associated with this phenomenon are not collected or shared. This hampers the industry’s ability to quantify the risk and assess the potential benefit from investment in effective wildlife hazard management activities. This research project has applied machine learning to the problem by training a random forest algorithm on wildlife strike cost data collected in the United States and predicting the costs associated with wildlife strikes in Australia. This method estimated a mean annual figure of AUD 7.9 million in repair costs and AUD 4.8 million in other costs from 2008 to 2017. It also provided year-on-year estimates showing variability through the reporting period that was not correlated with strike report numbers. This research provides a baseline figure for the Australian aviation industry to assess and review current and future wildlife hazard management practices. It also provides a technique for other countries, airlines, or airports to estimate the cost of wildlife strikes within their jurisdictions or operational environments.

Experimental investigation on the seismic behavior of a novel self-centering friction damper

A new type of self-centering friction damper using Shape Memory Alloy (SMA) bars is developed. The proposed damper is composed of a friction energy dissipation system and a self-centering system. Its self-centering capacity and low repair cost after earthquake make it have great advantages when applied to earthquake resistant structures. The mechanical properties of SMA bars at different heating temperatures and the seismic performance the proposed damper were experimentally investigated. Results indicated that the damper exhibits a flag-shaped hysteretic behavior under cyclic loadings. As the friction force increases, the stiffness, bearing capacity, and residual deformation of the damper increase. As the loading rate increases, the energy dissipation and residual displacement of the damper decrease. A theoretical model is presented and compared with the test results. Nonlinear numerical models were developed in ANSYS software and parametric analysis were conducted. Results showed that as the diameter of the SMA bar increases, the bearing capacity and energy dissipation of the damper increase, and the residual displacement decreases. As the preload of the SMA bar increases, the residual displacement of the damper decreases, but the dissipated energy changes slightly.

An evaluation of the effectiveness of implementing technological solutions based on digital technologies to improve well casing quality

The article presents the process of forming measures based on digital technologies to improve the quality of well cementing at the fields of Western Siberia. The problem associated with the low quality of input information due to the use of several independent sources was identified and solved. The economic efficiency of the developed methods for reducing the labour costs of data collection for modelling using machine learning algorithms is demonstrated. If the solutions developed are implemented, there is a prospect of reducing the cost of repair and insulation work. Key information is provided about the hypotheses generated and their objectives. The authors of the article describe the method of using various mathematical algorithms to analyze the results of industrial experimental work. The efficiency of the developed solutions is evaluated by comparing the results of cementing experimental wells and wells built using the basic technology. The dynamics of cement quality growth in the fields of Western Siberia are summarised as a general result. As a result of the experience gained, the solutions have been adapted and are in the process of being re-implemented in order to make a final assessment of their effectiveness.

Experimental validation of multiaxial fatigue theories to estimate fatigue life of helical compression spring

High-stress amplitudes and mean stress cycles are expected to be endured by helical compression springs utilized in a two-suspension wheeler's system. Fatigue failure of all these springs brings enormous eventual repair and replacement costs. A fatigue test is conducted to ascertain fatigue strength. The spring test plan is rather extensive due to the limited time and numerous test spring versions. Efforts were made to anticipate the helical spring's fatigue life. Multiaxial fatigue theories are examined in this work. The research paper aims to scrutinize the appropriate techniques that spring manufacturers should employ in the planning stage to calculate the fatigue life of helical compression springs. The criteria of Wang &amp; Brown, Fatemi &amp; Socie, Mitchell, Baumel &amp; Seeger, and Smith &amp; Watson are used in the present investigation. The results of the experiment and the predicted life are compared. Spring fatigue life is overvalued by the Wang-Brown criterion, while the Fatemi-Socie model offers a precise forecast of fatigue life.

Fatigue Crack Growth Mitigation by In Situ Healing in Thermoset CFRP Composite

Delamination due to fatigue loading in laminated composites is difficult to detect and, therefore, could lead to catastrophic failure if left undetected. Hence, it is important to be able to detect and quantify the delamination crack growth behavior due to fatigue loading and explore methods to heal the delamination in situ, without the need for mechanical fasteners. To this end, double cantilever beam specimens of carbon-fiber-reinforced polymer composite containing thermoplastic healants were manufactured, and mode I fatigue delamination experiments were carried out for the virgin and healed cases for oven healing, and in situ macro fiber composite healing cases. The primary purpose of using thermoplastic healants (polycaprolactone and shape memory polymer) was to heal the cracks formed during fatigue loading and regain the load-carrying capacity of the composite structure. The in situ healing was carried out by activating the macro fiber composite actuators attached to the double cantilever beam specimen after 5000 cycles of loading to generate heat. After in situ healing, significant reduction in crack growth compared to the virgin cycle was observed, and healing was repetitive. We envision that these findings will be immensely helpful in extending the service life of composites and may also result in significant repair cost savings.

Probabilistic seismic damage and loss assessment methodology for wastewater network incorporating modeling uncertainty and damage correlations

Maintaining the functionality of wastewater networks is critical to individual well-being, business continuity, public health, and safety. However, seismic damage and loss assessments of wastewater networks traditionally use fragility functions based on median repair rates without considering relevant sources of uncertainty and correlations of damage when estimating potential damage states and pipe repairs. This study presents a probabilistic methodology to incorporate modeling uncertainty (e.g. model parameter and model class uncertainty) and spatial correlations (e.g. spatial auto- and cross-correlation) of pipe repairs. The methodology was applied to a case study backbone system of a wastewater network in Portland, OR, using the expected hazard intensity maps for multiple deterministic earthquake scenarios, including a moment magnitude M6.8 Portland Hills Fault and M8.1, M8.4, M8.7, and M9.0 Cascadia Subduction Zone (CSZ) events. As spatial-correlation models of pipeline damage were non-existent in the literature and local information on costs to repair the pipes was limited at the time of this study, correlation methods and repair costs were proposed to estimate lower and upper bounds of pipe damage and loss. The results show how the consideration of different levels of uncertainty and spatial correlation for pipe repair rate could lead to different probabilistic estimates of damage and loss at the system level of the wastewater network, even though the point estimates, such as the mean and median, remain essentially unaltered.

Surface Waterproofing Techniques: A Case Study in Nova Lima, Brazil

Considering the various problems caused by infiltration in civil construction, this study aimed to identify the most appropriate waterproofing methods for different types of surfaces. A study was conducted on the mechanisms of water infiltration on surfaces and the waterproofing methods available on the market, focusing on asphalt blankets, in addition to a literature review highlighting state-of-the-art methods on this topic. A case study was also conducted in a residence in Nova Lima, Brazil, analyzing different waterproofing techniques, including their characteristics and stages. Among the conclusions, it is highlighted that the implementation of adequate project, installation, inspection, and maintenance techniques can significantly reduce the waterproofing failure rate and repair costs, and that the excellent choice of materials, along with the skill of the labor force in the application, is fundamental to guarantee the adequate performance of these materials in buildings.

Cost–Benefit Assessment of Offshore Structures Considering Structural Deterioration

Offshore facilities are essential infrastructure systems for many nations because their partial or total interruption causes diverse consequences in the economic, political, environmental, and social sectors. With the aim to preserve such structures at acceptable reliability levels, an approach is proposed to calculate the optimal instant of time in which inspection and maintenance works can be performed. The optimal time instant is estimated following the cost benefit criterion (CB) considering the cost of inspection, repair and failure. The inspection cost is given by an inspection quality, while fatigue crack size at different critical joints is calculated to estimate repair costs. In this paper, the concept of demand exceedance rates is introduced to evaluate the failure cost. Uncertainties related to both storm and operational waves are considered. The optimal time instant is associated with the lowest cost of inspection, repair and failure. For this purpose, the approach is exemplified in an offshore jacket structure situated in the Gulf of Mexico. The optimal instant of time corresponds to 6 years after the offshore jacket installation. If maintenance actions are implemented every six years during the lifespan of the system, an economic reduction of 58% is achieved, compared to the case in which no inspection and maintenance works are performed over time. The approach helps decision-makers ensure the best use of economic resources.