This work analyzes the applicability of the ASME Boiler and Pressure Vessel Code procedures to calculate fatigue crack initiation under multiaxial stresses and/or strains, in particular when caused by non-proportional loads that lead the principal directions at the critical point to vary with time, e.g. due to out-of-phase bending and torsion loads induced by independent sources. Classic uniaxial fatigue damage models are usually inappropriate for analyzing multiaxial loads, since they can generate highly inaccurate predictions. Moreover, it is shown that the ASME procedures can lead to non-conservative results for non-proportional load histories.

A cylinder array vibrating in a fluid exhibits multiple coupled frequencies and coupled mode shapes. For a square array of four cylinders with a pitch-to-diameter ratio of 1.25, one cylinder was excited. In order to obtain the coupled modes of the whole array without the influence of exciters, a new method named noncontact-measurement image processing system was used in this paper. This system can guarantee the consistency of the frequencies quantificationally. Due to noncontact-measurement, the flow field around cylinder arrays will not be disturbed and can be measured precisely. Experimental results show that if we want to obtain all the coupled mode shapes, the consistency of cylinder frequencies (within 2%) must be insured and the vibrated cylinder should be chosen with larger amplitude in the coupled mode shapes. Distinct coupled frequencies correspond to symmetric mode shapes, while repeated coupled frequencies correspond to asymmetric ones. Besides, the acoustic fluid-solid interaction numerical method was used to calculate the vibration process of multi objects in still water. The numerical simulation results were in good agreement with experimental ones. It is found that for the same number of cylinders, the bandwidth of coupled frequencies increases with the decrease of pitch-to-diameter ratio, and that for the same pitch-to-diameter ratio, the bandwidth of coupled frequencies increases with the increase of the number of cylinders. Detuning of the cylinder frequencies leads to changes of coupled frequencies and coupled mode shapes.

Due to the complex two phase flow, CFD simulation of liquid ring pump used to be extremely challenging. Using a recently developed Volume of Fluid (VOF) two phase flow model, this paper presents a 3D transient CFD model for a water ring vacuum pump. The test simulations show that the new VOF model is very robust and can catch most of the important physics when applied to a industrial water ring vacuum pump. Model formulation and problem setup will be presented in detail in the paper. Important issues that could affect the simulation results will be discussed. Water ring pump flow field characteristics revealed from simulation results will be summarized with explanation. And finally the simulation results will be compared with experiment test data.

Today there are numerous examples of collaborative online communities effectively creating innovative products (e.g., RepRap, Linux). But the potential of anonymous crowds to also engage in generative design, through the aggregation of many small contributions, is less clear. Although in recent years the “power of the crowd” has been repeatedly demonstrated in areas that range from image labelling to linguistic translation. The application of crowdsourcing in the fields of design research and creative innovation has been much slower to emerge. As a result, although there have been reports of systems and researchers using Internet crowdsourcing to carry out generative design, there are still many gaps in knowledge about the capability and limitations of the technology. For example on commercial crowdsourcing platforms, the relationship between remuneration and the final quality of designs has not been established, so it is unclear how much payment should be offered in order to ensure a particular standard of result. Key to investigating the relationship between the crowd’s remuneration and the value of their innovation is a robust method for quantifying the quality of the designs produced. This paper reports how payment for a design task (a 2D layout problem) was systematically varied and the quality of the output assessed through a separate crowdsourcing process. The work provides some interesting and valuable insight into how Crowdsourcing can be most effectively employed in design tasks.

The internal flow within a pressure swirl atomizer was numerically simulated and evaluated in the present investigation. To validate the numerical method, a large-scale atomizer with an orifice diameter 21mm has been simulated and compared with former experimental results in the literature. Then a production-scale atomizer with an orifice diameter 1mm was simulated and compared to the results of large-scale atomizer. The internal flow characteristics of the swirl chamber were evaluated mainly in terms of the film thickness at the exit of the orifice, the cone angle of the spray and the discharge coefficient of the nozzle. It was found that the numerical results of the large-scale atomizer with turbulent Reynolds Stress model yield more accurate solutions than the results with laminar flow model, which indicated that a turbulence flow has been formed within the large scale atomizer. Nevertheless, when the turbulent model was applied to a production-scale atomizer tested by Lacava (2004), its numerical results did not fit well with the experimental data any more. It was found that the Reynolds number of the flow in production-scale atomizer is about 2000, which is one order of magnitude lower than the Reynold’s number in the large-scale atomizer. As such a laminar flow model was successfully applied to its internal flow simulation and it is shown that the numerical results of the production-scale atomizer with laminar model yield more accurate solutions than the results with turbulent flow model. Finally, the effects of orifice contraction angle and mass flow rate were investigated in the production-scale pressure swirl atomizer using the laminar model. The numerical results showed that the discharge coefficient keeps almost constant with increasing orifice contraction angle, and the discharge coefficient, the film thickness at exit and the spray cone angle also almost keep constant with increasing the mass flow rate.

In this study, two kinds of two-dimensional (2D) complex gratings are proposed for a potential application as absorbing surfaces for solar cells in the visible and near-infrared wavelength regions, which are based on the superposition of multiple 2D simple gratings with different ridge heights for convex gratings or different groove depths for concave gratings, respectively. Silicon is selected as the complex grating material because it is common in micro/nanofabrication. Compared with one-dimensional (1D) gratings, the new structures present excellent radiative properties to rays from all directions. Besides, the new gratings can achieve satisfactory performance under both TM and TE waves, which cannot be easily obtained by 1D gratings. Furthermore, these two kinds of 2D complex gratings can both achieve higher absorptance in the whole of the interested spectral range by making full use of the microcavity resonance than 2D simple gratings with the same ridge height or groove depth. Taguchi method is employed as an efficient way of searching for the optimal profiles for the 2D complex gratings. The average spectral absorptance of the optimized structure for the 2D complex convex grating with two different ridge heights is above 0.93 within wavelength region from 0.3 to 1.1 μm for both TM and TE waves under normal incidence, which suggests that the proposed structures can be well suitable for solar absorber applications. The Finite-different time-domain (FDTD) method is used for all numerical calculations to obtain spectral absorptance of different structures.

The fatigue life of mechanical element is a random variable in nature following some kind of statistical distribution. In this paper, a method for reliability life prediction considering life randomness is proposed. Firstly, the Smith-Watson-Topper (SWT) model is used to describe the relationship of the maximum normal stress and strain range on the critical plane. Secondly, the maximum normal stress and strain range on the critical plane are calculated by finite element analysis. Thirdly, fatigue life samples are generated using Monte Carlo simulation method, and the mixed Weibull distribution is used to model the distribution of fatigue life of turbine discs. Finally, the proposed method is validated by comparing the prediction results from the proposed method, the observed cumulative failure probability based on median rank, and the standard two-parameter Weibull distribution.

Steady-state Reynolds Averaged Navier-Stokes (RANS) equations are solved in the present numerical investigation to simulate the reactive two-phase flow in a model aero-engine combustor, and the reactive flow field with NOx emissions is analyzed. The gaseous phase is modeled by the modified SST turbulence model, and the liquid phase is modeled by Lagrangian tracking method considering the droplet breakup, collision and evaporation. Turbulence-combustion interaction is modeled by the extended coherent flame model, and NOx emissions are modeled by solving the species transport equation based on the assumption of frozen temperature. The fuel system of the present simulated combustor is radially staged, with a main stage employing the principle of lean prevaporized and premixed (LPP) concept to reduce pollutant emission, and a pilot stage burning a diffusion flame for flame stability. For the exit temperature quality improvement, dilution air is assigned with little amount of airflow. Detailed numerical results including exit temperature distribution, dominant burning performances and species distributions are evaluated for the combustion with and without dilution air. The influence of upstream burning characteristics to downstream temperature distribution is assessed. Numerical prediction of NOx emission demonstrates its capability of a reasonable reduction, and the exit temperature pattern with the dilution air is also able to fulfill its design target.

Fractional calculus has been successfully applied to characterize the rheological property of viscoelastic materials, however, geomaterials were seldom involved in fractional order constitutive models (FOCM), and the issue of first loading and then unloading is rarely discussed through fractional calculus. It is considered that all materials are arranged in a queue and ideal solid and Newtonian fluid are located at both ends of the queue in FOCM. On the basis of FOCM, stress-strain relation under the condition of first loading and then unloading, besides creep, stress-relaxation and loading of constant strain rate are obtained. The stress-strain relation is utilized to fit triaxial test results of geomaterials under the corresponding conditions. The comparison between the test and fitting results reveals that FOCM can reasonably describe the stress-strain, stress-time or strain-time characteristics of geomaterials, which shows that fractional calculus is a good tool to constitutive model research of geomaterials.

Experimental investigations on a passive control method for suppressing VIV of long flexible riser are presented in this work. A riser model with L/D (slenderness ratio) of 1750 was horizontally installed on a carriage and uniform current was simulated by towing the riser using the carriage in a wave tank, which leads to the Reynolds numbers ranging from 10 3 to 10 4 . Four slender control rods with diameter d = 0.25 D were placed parallel to the riser at uniform angle (i.e. at 90° intervals around the riser circumference). Different pitch distances l/D = 0.813, 1 and 1.188 were considered in this work, where l is the center-to-center distance between control rod and riser model. Strain along the riser and tension were measured by Fiber Bragg Grating and tensionmeter, respectively. The experimental results indicate that the response characteristics of a riser model with multiple control rods are quite distinct from that of a bare riser. Multiple control rods can suppress VIV response significantly, and their performance is mainly dependent on the pitch distance. It is found that the spatial maximum standard deviation of strain decreases about 84% due to the existence of control rods. The optimal pitch distance is found to be l/D ≤ 1. Moreover, spectrum analysis shows that the dominate frequency increases linearly with the increasing of flow velocity, for both the bare riser and the riser with control rods, while the frequency band of the suppressed riser becomes broader compared with the bare riser. It is also observed that the tension of the riser is slightly increased due to the presence of four rods, but not sensitive to the pitch distance.

Managing the product realization process is a difficult endeavor in today’s global product development environment. Design project managers are required to form teams from geographically distributed designers as well as effectively manage the collaborative design process. In this paper, a computational method is proposed to aid design managers in allocating design tasks to geographically distributed designers and identify appropriate coordination mechanisms to manage the collaborative design process. The method involves three stages: i) arriving at an initial design task sequence using the design structure matrix through partitioning of design tasks into blocks of dependent, independent and interdependent tasks, ii) allocating of design tasks to design teams and the improvement of the design sequence accounting for the number of designers available and their competencies and iii) determination of design review meeting frequencies as a coordination mechanism for interdependent tasks using agent based modeling simulations.

Sidewall friction is of great significance for many MEMS devices such as micromotors, microgears and microhinges. Because sidewalls in MEMS devices are different from in-plane surfaces both chemically and topographically, friction and wear occurring on sidewalls are expected to have its own characteristics. A microtribotester has been developed with the bulk-fabrication technology to measure the sidewall friction and wear, and static friction and dynamic friction measurements have been reported previously. In this paper, experiment results of the microtribotester for a testing period of 55 hours are presented. It is found that the coefficient of dynamic friction reduces gradually with the increase in rubbing cycle, being similar to most macroscale tribopairs. The morphology and chemical components of the wear debris generated in the testing process were analyzed on scanning electron microscope and EDX. From the analysis results, it is concluded that the silicon sidewalls undergoes oxidation during the test.