Search results

Constructing porous wind barriers is one of the most effective approaches to increase the running safety of trains on viaducts in crosswinds. This paper aims to further improve the wind-sheltering performance of the porous wind barriers.

Improved delayed detached eddy simulations based on the k-ω turbulence model were carried out, and the results were validated with wind tunnel tests. The effects of the hole diameter on the flow characteristics and wind-sheltering performance were studied by comparing the wind barriers with the porosity of 21.6% and the hole diameters of 60 mm–360 mm. The flow characteristics above the windward and leeward tracks were analyzed, and the wind-sheltering performance of the wind barriers was assessed using the wind speed reduction coefficients.

The hole diameters affected the jet behind the wind barriers and the recirculation region above the tracks. Below the top of the wind barriers, the time-averaged velocity first decreased and then increased with the increase in the hole diameter. The wind barrier with the hole diameter of 120 mm had the best wind-sheltering performance for the windward track, but such barrier might lead to overprotection on the leeward track. The wind-sheltering performance of the wind barriers with the hole diameters of 240 mm and 360 mm was significantly degraded, especially above the windward track.

The effects of the hole diameters on the wake and wind-sheltering performance of the wind barriers were studied, by which the theoretical basis is provided for a better design of the porous wind barrier.

Catastrophe of steel-structured bridges due to progressive localized corrosion may lead to a major loss in terms of life and cost if not monitored continuously or periodically. The purpose of this paper is to present a vibration-based strategy to assess the severity and monitor the deterioration caused by corrosion-induced localized damage in a simply-supported steel beam.

The threshold damage level is defined up to the yield limit of a simply supported steel beam of size ISMB 150 × 8 × 5 under three-point bending test and the progressive damage is induced through a continuous accelerated corrosion test. Change in the fundamental natural frequency due to localized damage in the experimental beam and the modulus of elasticity (E) in the corroded zone of an updated finite element (FE) model is evaluated.

The updated FE model of the damaged beam shows a clear trend with the progressive damage of the beam and, hence, can be used to monitor the severity of damage and remaining capacity assessment of the monitored beam.

Steel-structured bridges are prone to localized corrosion attack, and there are no standardized process or predictive model available by international steel design codes on how to consider corrosion damage in the condition assessment analysis. The vibration-based methods have gained popularity for condition assessment, and are mostly confined to damage assessment of corroded reinforced concrete (RC) beams. In this work, a vibration-based approach is presented for degradation assessment of steel beam due to progressive localized corrosion using modal hammer test.

The purpose of this paper is to develop an effective treatment to analyze and diagnose urban rail transit (URT) vehicle maintenance strategy.

In this paper, the technique of Failure Mode and Effects Analysis (FMEA) is introduced into the examination of URT trains, first. Then the method of fuzzy-set-based assessment for FMEA is presented, which is the quantitative tool of Fuzzy-Set-based treatment for FMEA in analysis and diagnoses to URT maintenance strategy. Moreover, recommendations for further improvement of the proposed approach are also provided. Initial application into the vehicle maintenance of Shanghai URT System shows, that the proposed approach has a good performance and consequently is worth further development.

The paper presents a FMEA and fuzzy-set-based theoretical approach for analyzing and diagnosing current methods in URT vehicle maintenance strategy.

With rapid development of URT systems in the world especially in those highly populated areas, much more attentions are turning to researches on URT maintenance, nevertheless, few quantitative research achievement are mentioned or applied. This paper is a tentative attempt at introducing fuzzy-set theory into quantitative analysis and diagnoses of URT maintenance strategy.

The study in this paper is helpful in theory and practice of URT maintenance and its methodology could be further applied into a broad family of facility group or system in other engineering fields.

This paper aims to present the main factors affecting the mechanical drilling of the printed circuit board (PCB for short) micro-holes and method of micro-ultrasonic powder molding (micro-UPM for short) by utilizing PCB micro-hole array.

To optimize the drilling process, the paper proposes the on-line monitoring methods for the drilling process including drilling force, drilling temperature, high-speed photography and vibration signals. Taking 0.10 and 0.15 mm micro-drilling as examples, the paper analyzes the drilling process of ultra-small micro-holes. Finally, by taking the PCBs with 0.10 and 0.15 mm micro-hole arrays as the micro-cavity inserts, utilizing ultra-high-molecule weight polyethylene powder with the average particle size of about 150 μm as raw material, two sizes of micro-cylinder array polymer parts are fabricated through micro-UPM process.

PCB micro-cavity inserts with micro-hole arrays fabricated by mechanical drilling has the advantages of low costs, high efficiency and good consistency. Taking 0.10 and 0.15 mm micro-drilling as examples, it is found that the both measured apertures are about 10.0 μm more than the diameter of the micro-drill bits on average. The average diameter of the micro-cylinders by micro-UPM process is smaller than that of the micro-hole with the same specification, while the value of the roughness of the cylinder surface is more than that of the hole-wall surface with the same specification.

This paper describes the challenges and the developments of mechanical drilling and by using PCB micro-cavity inserts with micro-hole arrays fabricated by mechanical drilling, two different micro-cylinder array polymer parts are successfully made and thus the application area of PCB micro-drilling is broadened.

The purpose of this paper is to study the insulation structure optimization method of multiwinding high-frequency transformer (HFT).

This paper takes 100 kW, 10 kHz multiwinding HFT as the research object. First, the distribution of electric field strength within the core window of multiwinding HFT with different winding configurations is simulated by the electrostatic field finite element method. The symmetrical hybrid winding structure with minimum electric field strength is selected as the insulation design. To reduce the electric field strength at the end region of the winding, the electrostatic ring and angle ring are designed based on the response surface method.

The optimal results show that the maximum electric field strength can be reduced by 15.4%, and the low voltage stress can be achieved.

The above research provides guidance and basis for the optimal design of insulation structure of multiwinding HFT.

This paper aims to develop a multi-hazard risk assessment method based on probability theory and a set of economic, social and environmental indicators, which considers the increase in hazards when they occur concurrently or consecutively.

Disaster risk assessment generally considers the impact and vulnerability of a single hazard to the affected location/object without considering the combination of multiple hazards occurring concurrently or consecutively. However, disasters are often closely related, occurring in combination or at the same time. Probability theory was used to assess multi-hazard, and a matrix method was used to assess the interaction of hazard vulnerabilities.

The results of the case study for the Mid-Central Coastal Region show that the proportions of districts at a very high class of multi-hazard, multi-vulnerabilities and multi-hazard risk are 81%, 89% and 82%, respectively. Multi-hazard risk level tends to decrease from North to South and from East to West. A total of 100% of coastal districts are at high to very high multi-hazard risk classes. The research results could assist in the development of disaster risk reduction programs towards sustainable development and support the management to reduce risks caused by multi-hazard.

The multi-risk assessment method developed in this study is based on published literature, allowing to compare quantitatively multiple risk caused by multi-hazard occurring concurrently or consecutively, in which, a relative increase in hazard and vulnerability is considered. The method includes the assessment of three components of disaster risk including multi-hazard, exposure and multi-vulnerability. Probability and Copula theories were used to assess multi-hazard, and a matrix method was used to assess the interaction intensity of multi-vulnerabilities in the system.

The purpose of this paper is to investigate and evaluate the new performance measurement model for the Thai frozen shrimp chain.

The performance measurement model was developed by the combination method between a structural equation modeling and an analytical hierarchy process, which the method confirmed and proved the construction of the framework and identified the important key performance indicators of the chain from different supply chain members’ point of views.

The results showed that the model is reliable and valid as well as being theoretically acceptable on the basis of performance measurement foundations. Furthermore, the financial and the customer perspectives are demonstrated as the first to be prioritized in order to evaluate the performance.

Two limitations should be considered. First, small sample size of this study is a limitation. Hence, further study should consider on enough sample size. A next limitation, different points of view from participants has effect on factor loading which represented minus value on the research model. Therefore, the future research should apply several techniques, such as the fuzzy set and data envelopment analysis.

The contribution of this study is the new performance measurement model which based on the integrated conceptual ideas and the synthesizing methods for evaluating the Thai frozen shrimp chain.