Survey and investigation of performance of superstructure of long span bridges in China

With the rapid development of China’s economy in the past three decades, requirements for construction of infrastructure for transportation have been enhanced and a great many long-span bridges have been built. Internationally, it can be boasted that China is one of the countries with the most long-span bridges. However, inadequate performance in long span bridges is often observed in field investigations, such as, excessive deflection in the mid-span, cracking of the concrete, cable corrosion in cable-stayed bridges, suspender cable corrosion in suspension bridges, and the corrosion of reinforced steel in the concrete resulting in the scaling and spalling of the concrete cover. This arouses the concern for the safety, serviceability, durability, service life, life cycle cost of maintenance and rehabilitation of long span bridges. A survey was made on the working condition of long span bridges in China. The causes resulting in deterioration of long span bridges are examined and measures for prolonging the service life of long span bridges in view of design, construction and maintenance are proposed

Application of flame image velocimetry for flow field and turbulence analysis in an optical diesel engine

Measurements of flow and turbulence within the flames are important to enhance fundamental knowledge of air-fuel mixing required to achieve high efficiency and low emissions in diesel engines. However, interferences from broadband soot luminosity signals pose a significant diagnostic challenge. To overcome this hurdle, the present study implements a new diagnostic method based on tracking of flame pattern changes detected in high-speed soot luminosity movies, namely, flame image velocimetry (FIV). In a small-bore optical diesel engine, time-resolved particle image velocimetry (PIV) is firstly performed to understand the in-cylinder flow field and turbulence in a motored engine condition, which shows an expected swirl structure and well distributed turbulence. With the direct fuel injection and flame development, the FIV is applied to show flow field evolution during the combustion event and its influence on in-flame turbulence distribution. A total of 100 engine cycles are recorded and processed for the FIV to address the inherent cyclic variations. The ensembleaveraged flow fields and turbulence intensity distribution extracted from individual cycles via the spatial filtering method are discussed with variations in injection pressure, inter-jet spacing, jet-swirl interaction and after injection condition. The FIV-derived flow fields show that increased injection pressure causes increased flow magnitude and turbulence intensity at the expense of cyclic variations. When the inter-jet spacing angle is narrower, an interesting flow suppression effect is found within the jet-jet interaction region due to flow collision. Regarding the jet-swirl interaction, the counter-flow condition on the up-swirl side leads to higher turbulence intensity suggesting better mixing. With the after injection, increased flow magnitude and turbulence intensity is found to be more effective when the injection timing is set close to the main injection. New knowledge developed from these FIV measurements provides guidance for engine developers to further optimise fuel injection conditions and injector geometry

Processing-structure-protrusion relationship of 3D Cu TSVs: control at the atomic scale

A phase-field-crystal model is used to investigate the processing-structure-protrusion relationship of blind Cu through-silicon vias (TSVs) at the atomic scale. A higher temperature results in a larger TSV protrusion. Deformation via dislocation motion dominates at temperatures lower than around 300∘C, while both diffusional and dislocation creep occur at temperatures greater than around 300∘C. TSVs with smaller sidewall roughness Ra and wavelength λa exhibit larger protrusions. Moreover, different protrusion profiles are observed for TSVs with different grain structures. Both protrusions and intrusions are observed when a single grain is placed near the TSV top end, while the top surface protrudes near both edges when it contains more grains. Under symmetric loading, coalescence of the grains occurs near the top end, and a symmetric grain structure can accelerate this process. The strain distributions in TSVs are calculated, and the eigenstrain projection along the vertical direction can be considered an index to predict the TSV protrusion tendency

Protrusion of Cu-TSV under different strain states

A phase-field-crystal (PFC) model is used to investigate the protrusion of blind TSVs under different strain states. The direction of loading applied to the TSVs has an effect on the protrusion, which is closely related to the copper grains and their orientations at the TSV edges. A nonlinear relation between protrusion and strain rate has been found, which can be explained by different mechanisms of deformation. A higher strain occurring near the top end of the TSVs leads to a larger protrusion of the bind TSVs