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This paper investigates the tone noise generation by submarine propellers operating in nonuniform flows. A frequency domain numerical approach is proposed. The flow nonuniformities due to submarine wakes are obtained from Computational Fluid Dynamics method. The results show that the velocity field and its harmonics depend greatly on the hull geometry and its appendages. The prediction of the radiated far-field tone noise due to a seven-bladed, highly-skewed propeller has been performed. A prediction of the acoustic pressure level for various blade skew angles shows that the tone noise reduction amount increases as the inflow velocity increases. The predicted dependence of the radiated noise on the inflow velocity, propeller diameter and blade rotational speed shows that the mean square sound pressure at the first-order blade passing frequency varies as the 3.3 power of the characteristic inflow velocity, the third power of the propeller diameter and with the second power of the blade rotational speed. Effects of blade number on the propeller tone noise directivity are also discussed, which shows that the characteristic coupling order between the main inflow harmonic and the rotating blades is the key to determine the directivity pattern.

The competing risk model involving two Weibull distributions is characterized by four independent parameters. The shapes of the density and failure rate functions for the model depend on the parameter values. In this paper a complete parametric characterization of these shapes is presented.

Microwave cladding is one of the latest surface engineering techniques, which has been used to improve the surface properties of a material. This technique overcomes almost all limitations of the existing methods. In this study, Ni-based+10% Cr₃C₂ composite clads have been developed in domestic microwave oven of 2.45-GHz frequency and 900-W power. The developed composite clads have been characterized using various standard mechanical and metallurgical techniques like SEM/EDS, XRD and Vickers microhardness tester. Cavitation erosion resistance of developed composite clads has also been examined at different parametric conditions. The microstructure analysis exhibits that the developed composite clads of 730-$\mu$m thickness are free of cracks (solidification and interfacial) and less porous. The presence of various intermetallic and hard carbide phases like FeNi₃, CrSi₂, Cr₃Ni₂SiC, SiC and NiC is confirmed from the XRD analysis. The Vickers microhardness study reveals that the average microhardness of clad region is $430\pm 65$ HV${}_{0.3}$. The cavitation erosion study (at different parametric conditions using vibratory cavitation erosion testing) reveals that the developed composite clads perform much better under cavitation erosion environment than the SS-316 substrate. The stand-off distance is found to be the most dominating factor followed by amplitude and immersion depth.

The dynamic amplification of a bridge response due to moving vehicles has been the subject of numerous research efforts. The efforts indicate a common difficulty in treating the dynamic interaction. This paper presents a semi-analytical technique to solve the bridge/vehicle interaction problem. A skew bridge, idealized as a discretely stiffened thin isotropic plate, is considered. The natural frequencies and mode shapes of the bridge are computed by a pb-2 Rayleigh–Ritz method. The mode superposition principle is then applied. The dynamic response of the bridge to moving vehicle excitation is expressed in terms of mode shapes and normal coordinates. A three-dimensional three-axle vehicle model is developed and consists of 11 independent degrees of freedom. The bridge and the vehicle are treated as two separate systems connected only at the time-varying contact points. An iteration technique is used to deal with the true coupling between the bridge and the vehicle and to satisfy the compatibility of forces and displacements at the contact points. At last, a parametric study is conducted to investigate the dynamic amplification factor. The influences of vehicle type, axle spacing, traffic condition, span length, and skew angle are examined.

Pipelines are one of the most efficient means for transporting hydrocarbons from one point to the other. However, there is a great risk of pipelines operation failure due to the detrimental effects of corrosion. At the point of corrosion, the pipe wall becomes thinner and loses its mechanical resistance. In such cases, reliable defect assessment methods are necessary to decide whether to resume continual operation or to shut down for maintenance or replacement. However, the available assessment methods are over-conservative, which enforce either unnecessary maintenance or premature replacement. Furthermore, the defect assessment methods should not only ensure safe operation, but also optimized operation cost. Therefore, a new assessment method was developed based on the nonlinear finite element (FE) analysis and a parametric study of geometric parameters related to the corrosion defect. The new method was validated with burst test database, which can predict the burst pressure of corroded pipelines with better accuracy and consistency.

The U-shaped steel-concrete composite hollow waffle (CHW) floor is an innovative slender large-span floor composed of a thin slab and bidirectional orthogonal steel-concrete composite hollow beams. Large vibrations may occur under human excitations, and vibration guidelines for CHW floors are still lacking. Thus, this paper undertook a parametric and experimental study to explore the vibration performance of the CHW floors. First, the modal properties and vibration response under walking tests considering the varying frequencies and routes were obtained from the measurements, which validated the accuracy of the finite element analysis (FEA). Then, the influence of the structural parameters on the floor vibration was investigated by numerical modeling. The parametric study shows that the medium-sized long-span (MLS) (28m) CHW floors present the best vibration serviceability, the small-sized long-span (SLS) (14m) CHW floors vibrate substantially under walking excitation, and the large-sized long-span (LLS) (42m) CHW floors are vulnerable to resonance. Finally, this paper provides recommendations for design guidelines for CHW floors and indicates that controlling the span-to-height (SH) value and beam spacing (BS) at a small value are the most effective methods of vibration control.

The present work focuses on the evaluation of the dynamic behavior of a centenary steel arch bridge, located in Portugal, under light railway traffic loads. This works aims to assess the dynamic behavior of the bridge subjected to an alternative type of railway vehicle, more specifically, a typical underground vehicle that is currently in service in the Lisbon Metro. The dynamic response of the system has been evaluated using two distinct methodologies, namely a moving loads model and a vehicle–bridge interaction model. To achieve this goal, finite element (FE) models from both the bridge and the vehicle have been developed and a comprehensive study has been carried to evaluate the influence of distinct factors in the dynamic response of the bridge–train system, namely the methodology used to assess the dynamic response, the location of the response reference point in the deck, the train speed and the vehicle configuration (single or double vehicle). Moreover, both the traffic safety, passenger comfort and pedestrian comfort have also been evaluated using normative criteria based on acceleration responses. The results shown that the normative limits related to traffic safety and passenger comfort were never exceeded in any condition analyzed in the study. However, the pedestrian comfort was jeopardized when the train speed exceeded 20km/h.

When applying the Incremental Harmonic Balance (IHB) method to solve the limit cycle in a self-excited system, the practice of fixing one of the harmonic coefficients effectively solves the problem that there are more unknowns than algebraic equations due to the presence of unknown angular frequencies in the periodic response. However, an inappropriate value for this fixed harmonic coefficient can significantly affect the convergence of subsequent Newton–Poisson iterations. To address this issue, we propose a technique that dynamically adjusts the value of the fixed harmonic coefficient, effectively improving the convergence and stability of the traditional IHB method and providing an efficient solution for the parametric study of self-excited systems. The efficiency and performance of our method in accurately predicting periodic solutions are demonstrated by its application to Van der Pol oscillators and predicting vortex-induced vibrations in cable-stayed structures. Numerical simulations show that the results obtained by the proposed method are very close to those obtained by the Runge–Kutta method. This study opens up a robust and efficient approach for analyzing and studying the dynamic behavior of complex self-excited systems.

Low back pain is a common reason for activity limitation in people younger than 45 years old, and was proved to be associated with heavy physical works, repetitive lifting, impact, stationary work postures and vibrations. The study of load transferring and the loading condition encountered in spinal column can be simulated by finite element models. The intervertebral disc is a structure composed of a porous material. Many physical models were developed to simulate this phenomenon. The confounding effects of poroelastic properties and loading conditions on disc mechanical responses are, nevertheless, not cleared yet. The objective of this study was to develop an axisymmetric poroelastic finite element model of intervertebral disc and use it to investigate the confounding effect of material properties and loading conditions on the disc deformation and pore pressure. An axisymmetric poroelastic model of human lumbar L4–L5 motion segment was developed. The model was validated by comparing the height loss and intradiscal pressure of the L4–L5 intervertebral disc with in vitro cadaveric studies. The effect of permeability, void ratio, elastic modulus, and Poisson's ratio on disc height and pore pressure was investigated for the following three loading conditions: (1) 1334 N creep loading, (2) peak-to-peak, 1000-to-1600 N, 1 Hz cyclic loading, and (3) same loading magnitude, but at 5 Hz loading frequency. The disc height loss and pore pressure of the three loading conditions were analyzed. The predictions of the disc height loss and intradiscal pressure of the current FE model are well comparable with the results of in vitro cadaveric studies. After model validation, the parametric study of disc poroelastic properties on the disc mechanical responses shows that the increase of permeability and void ratio increases the disc height loss and decreases the pore pressure, and these effects are sensitive to external loading frequency. Higher elastic modulus reduces the disc deformation and the pore pressure, but this reduction is not sensitive to the loading frequency. The effect of Poisson's ratio on disc height loss and pore pressure is negligible. In conclusion, the hydraulic permeability describes the fluid flow capability within tissue matrix which has a higher sensitivity on the saturation time for disc deformation and pore pressure. Void ratio directly affects the amount of mobile water within disc and changes time-dependent response of disc. Increase in loading frequency reduces time for fluid inflow and outflow, which fades out the role of permeability and void ratio. Values of elastic modulus and Poisson's ratio, which demonstrates stiffness and bulging capacity, respectively, do not affect the overall dynamic response of disc.