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Royal Society Open Science RSS feed -- recent Engineering articles2054-5703Royal Society Open Science<![CDATA[Waterjet and laser etching: the nonlinear inverse problem]]>
http://rsos.royalsocietypublishing.org/cgi/content/short/4/7/161031?rss=1
In waterjet and laser milling, material is removed from a solid surface in a succession of layers to create a new shape, in a depth-controlled manner. The inverse problem consists of defining the control parameters, in particular, the two-dimensional beam path, to arrive at a prescribed freeform surface. Waterjet milling (WJM) and pulsed laser ablation (PLA) are studied in this paper, since a generic nonlinear material removal model is appropriate for both of these processes. The inverse problem is usually solved for this kind of process by simply controlling dwell time in proportion to the required depth of milling at a sequence of pixels on the surface. However, this approach is only valid when shallow surfaces are etched, since it does not take into account either the footprint of the beam or its overlapping on successive passes. A discrete adjoint algorithm is proposed in this paper to improve the solution. Nonlinear effects and non-straight passes are included in the optimization, while the calculation of the Jacobian matrix does not require large computation times. Several tests are performed to validate the proposed method and the results show that tracking error is reduced typically by a factor of two in comparison to the pixel-by-pixel approach and the classical raster path strategy with straight passes. The tracking error can be as low as 2–5% and 1–2% for WJM and PLA, respectively, depending on the complexity of the target surface.
]]>2017-07-05T00:08:12-07:00info:doi/10.1098/rsos.161031hwp:master-id:royopensci;rsos.1610312017-07-05Engineering47161031161031<![CDATA[A frequency quantum interpretation of the surface renewal model of mass transfer]]>
http://rsos.royalsocietypublishing.org/cgi/content/short/4/7/170103?rss=1
The surface of a turbulent liquid is visualized as consisting of a large number of chaotic eddies or liquid elements. Assuming that surface elements of a particular age have renewal frequencies that are integral multiples of a fundamental frequency quantum, and further assuming that the renewal frequency distribution is of the Boltzmann type, performing a population balance for these elements leads to the Danckwerts surface age distribution. The basic quantum is what has been traditionally called the rate of surface renewal. The Higbie surface age distribution follows if the renewal frequency distribution of such elements is assumed to be continuous. Four age distributions, which reflect different start-up conditions of the absorption process, are then used to analyse transient physical gas absorption into a large volume of liquid, assuming negligible gas-side mass-transfer resistance. The first two are different versions of the Danckwerts model, the third one is based on the uniform and Higbie distributions, while the fourth one is a mixed distribution. For the four cases, theoretical expressions are derived for the rates of gas absorption and dissolved-gas transfer to the bulk liquid. Under transient conditions, these two rates are not equal and have an inverse relationship. However, with the progress of absorption towards steady state, they approach one another. Assuming steady-state conditions, the conventional one-parameter Danckwerts age distribution is generalized to a two-parameter age distribution. Like the two-parameter logarithmic normal distribution, this distribution can also capture the bell-shaped nature of the distribution of the ages of surface elements observed experimentally in air–sea gas and heat exchange. Estimates of the liquid-side mass-transfer coefficient made using these two distributions for the absorption of hydrogen and oxygen in water are very close to one another and are comparable to experimental values reported in the literature.
]]>2017-07-05T00:08:12-07:00info:doi/10.1098/rsos.170103hwp:master-id:royopensci;rsos.1701032017-07-05Engineering47170103170103<![CDATA[Chromium oxide coatings with the potential for eliminating the risk of chromium ion release in orthopaedic implants]]>
http://rsos.royalsocietypublishing.org/cgi/content/short/4/7/170218?rss=1
Chromium oxide coatings prepared by radiofrequency reactive magnetron sputtering on stainless steel substrates were exposed to Ringer's physiological solution and tested for their electrochemical corrosion stability using an open circuit potential measurement, potentiodynamic polarization, electrochemical impedance spectroscopy and Mott–Schottky analysis. The coatings were found to be predominantly Cr_{2}O_{3}, based on the observation of the dominance of A1g and E_{g} symmetric modes in our Raman spectroscopic investigation and the E_{u} vibrational modes in our Fourier transform infrared spectroscopic measurements on the coatings. We investigated for the presence of chromium ions in Ringer's solution after all of the above electrochemical tests using atomic absorption spectroscopy, without finding a trace of chromium ions at the ppm level for coatings tested under open circuit and at the lower potentials implants are likely to experience in the human body. The coatings were further exposed to Ringer's solution for one month and tested for adhesion strength changes, and we found that they retained substantial adhesion to the substrates. We expect this finding to be significant for future orthopaedic implants where chromium ion release is still a major challenge.
]]>2017-07-05T00:08:13-07:00info:doi/10.1098/rsos.170218hwp:master-id:royopensci;rsos.1702182017-07-05Engineering47170218170218<![CDATA[Terahertz time-domain spectroscopy of edible oils]]>
http://rsos.royalsocietypublishing.org/cgi/content/short/4/6/170275?rss=1
Chemical degradation of edible oils has been studied using conventional spectroscopic methods spanning the spectrum from ultraviolet to mid-IR. However, the possibility of morphological changes of oil molecules that can be detected at terahertz frequencies is beginning to receive some attention. Furthermore, the rapidly decreasing cost of this technology and its capability for convenient, in situ measurement of material properties, raises the possibility of monitoring oil during cooking and processing at production facilities, and more generally within the food industry. In this paper, we test the hypothesis that oil undergoes chemical and physical changes when heated above the smoke point, which can be detected in the 0.05–2 THz spectral range, measured using the conventional terahertz time-domain spectroscopy technique. The measurements demonstrate a null result in that there is no significant change in the spectra of terahertz optical parameters after heating above the smoke point for 5 min.
]]>2017-06-28T00:08:13-07:00info:doi/10.1098/rsos.170275hwp:master-id:royopensci;rsos.1702752017-06-28Engineering46170275170275<![CDATA[Sticking to rough surfaces using functionally graded bio-inspired microfibres]]>
http://rsos.royalsocietypublishing.org/cgi/content/short/4/6/161105?rss=1
Synthetic fibrillar adhesives inspired by nature, most commonly by the gecko lizard, have been shown to strongly and repeatedly attach to smooth surfaces. These adhesives, mostly of monolithic construction, perform on par with their natural analogues on smooth surfaces but exhibit far inferior adhesive performance on rough surfaces. In this paper, we report on the adhesive performance of functionally graded microfibrillar adhesives based on a microfibre with a divergent end and a thin soft distal layer on rough surfaces. Monolithic and functionally graded fibre arrays were fabricated from polyurethanes and their adhesive performance on surfaces of varying roughness were quantified from force–distance data obtained using a custom adhesion measurement system. Average pull-off stress declined significantly with increasing roughness for the monolithic fibre array, dropping from 77 kPa on the smoothest (54 nm RMS roughness) to 19 kPa on the roughest (408 nm RMS roughness) testing surface. In comparison, pull-off stresses of 81 kPa and 63 kPa were obtained on the same respective smooth and rough surfaces with a functionally graded fibre array, which represents a more than threefold increase in adhesion to the roughest adhering surface. These results show that functionally graded fibrillar adhesives perform similar on all the testing surfaces unlike monolithic arrays and show potential as repeatable and reusable rough surface adhesives.
]]>2017-06-07T00:07:57-07:00info:doi/10.1098/rsos.161105hwp:master-id:royopensci;rsos.1611052017-06-07Engineering46161105161105<![CDATA[On the formation of fold-type oscillation marks in the continuous casting of steel]]>
http://rsos.royalsocietypublishing.org/cgi/content/short/4/6/170062?rss=1
Asymptotic methods are employed to revisit an earlier model for oscillation-mark formation in the continuous casting of steel. A systematic non-dimensionalization of the governing equations, which was not carried out previously, leads to a model with 12 dimensionless parameters. Analysis is provided in the same parameter regime as for the earlier model, and surprisingly simple analytical solutions are found for the oscillation-mark profiles; these are found to agree reasonably well with the numerical solution in the earlier model and very well with fold-type oscillation marks that have been obtained in more recent experimental work. The benefits of this approach, when compared with time-consuming numerical simulations, are discussed in the context of auxiliary models for macrosegregation and thermomechanical stresses and strains.
]]>2017-06-07T04:09:43-07:00info:doi/10.1098/rsos.170062hwp:master-id:royopensci;rsos.1700622017-06-07Engineering46170062170062<![CDATA[A superlinear iteration method for calculation of finite length journal bearing's static equilibrium position]]>
http://rsos.royalsocietypublishing.org/cgi/content/short/4/5/161059?rss=1
Solving the static equilibrium position is one of the most important parts of dynamic coefficients calculation and further coupled calculation of rotor system. The main contribution of this study is testing the superlinear iteration convergence method—twofold secant method, for the determination of the static equilibrium position of journal bearing with finite length. Essentially, the Reynolds equation for stable motion is solved by the finite difference method and the inner pressure is obtained by the successive over-relaxation iterative method reinforced by the compound Simpson quadrature formula. The accuracy and efficiency of the twofold secant method are higher in comparison with the secant method and dichotomy. The total number of iterative steps required for the twofold secant method are about one-third of the secant method and less than one-eighth of dichotomy for the same equilibrium position. The calculations for equilibrium position and pressure distribution for different bearing length, clearance and rotating speed were done. In the results, the eccentricity presents linear inverse proportional relationship to the attitude angle. The influence of the bearing length, clearance and bearing radius on the load-carrying capacity was also investigated. The results illustrate that larger bearing length, larger radius and smaller clearance are good for the load-carrying capacity of journal bearing. The application of the twofold secant method can greatly reduce the computational time for calculation of the dynamic coefficients and dynamic characteristics of rotor-bearing system with a journal bearing of finite length.
]]>2017-05-31T00:08:24-07:00info:doi/10.1098/rsos.161059hwp:master-id:royopensci;rsos.1610592017-05-31Engineering45161059161059<![CDATA[Emergence of leadership in a robotic fish group under diverging individual personality traits]]>
http://rsos.royalsocietypublishing.org/cgi/content/short/4/5/161015?rss=1
Variations of individual’s personality traits have been identified before as one of the possible mechanisms for the emergence of leadership in an interactive collective, which may lead to benefits for the group as a whole. Complementing the large number of existing literatures on using simulation models to study leadership, we use biomimetic robotic fish to gain insight into how the fish’s behaviours evolve under the influence of the physical hydrodynamics. In particular, we focus in this paper on understanding how robotic fish’s personality traits affect the emergence of an effective leading fish in repeated robotic foraging tasks when the robotic fish’s strategies, to push or not to push the obstacle in its foraging path, are updated over time following an evolutionary game set-up. We further show that the robotic fish’s personality traits diverge when the group carries out difficult foraging tasks in our experiments, and self-organization takes place to help the group to adapt to the level of difficulties of the tasks without inter-individual communication.
]]>2017-05-24T00:08:00-07:00info:doi/10.1098/rsos.161015hwp:master-id:royopensci;rsos.1610152017-05-24Engineering45161015161015<![CDATA[Graphic kinematics, visual virtual work and elastographics]]>
http://rsos.royalsocietypublishing.org/cgi/content/short/4/5/170202?rss=1
In this paper, recent progress in graphic statics is combined with Williot displacement diagrams to create a graphical description of both statics and kinematics for two- and three-dimensional pin-jointed trusses. We begin with reciprocal form and force diagrams. The force diagram is dissected into its component cells which are then translated relative to each other. This defines a displacement diagram which is topologically equivalent to the form diagram (the structure). The various contributions to the overall Virtual Work appear as parallelograms (for two-dimensional trusses) or parallelopipeds (for three-dimensional trusses) that separate the force and the displacement pieces. Structural mechanisms can be identified by translating the force cells such that their shared faces slide across each other without separating. Elastic solutions can be obtained by choosing parallelograms or parallelopipeds of the appropriate aspect ratio. Finally, a new type of ‘elastographic’ diagram—termed a deformed Maxwell–Williot diagram (two-dimensional) or a deformed Rankine–Williot diagram (three-dimensional)—is presented which combines the deflected structure with the forces carried by its members.
]]>2017-05-24T00:08:06-07:00info:doi/10.1098/rsos.170202hwp:master-id:royopensci;rsos.1702022017-05-24Engineering45170202170202<![CDATA[Thin Al1-xGaxAs0.56Sb0.44 diodes with extremely weak temperature dependence of avalanche breakdown]]>
http://rsos.royalsocietypublishing.org/cgi/content/short/4/5/170071?rss=1
When using avalanche photodiodes (APDs) in applications, temperature dependence of avalanche breakdown voltage is one of the performance parameters to be considered. Hence, novel materials developed for APDs require dedicated experimental studies. We have carried out such a study on thin Al_{1–x}Ga_{x}As_{0.56}Sb_{0.44} p–i–n diode wafers (Ga composition from 0 to 0.15), plus measurements of avalanche gain and dark current. Based on data obtained from 77 to 297 K, the alloys Al_{1–x}Ga_{x}As_{0.56}Sb_{0.44} exhibited weak temperature dependence of avalanche gain and breakdown voltage, with temperature coefficient approximately 0.86–1.08 mV K^{–1}, among the lowest values reported for a number of semiconductor materials. Considering no significant tunnelling current was observed at room temperature at typical operating conditions, the alloys Al_{1–x}Ga_{x}As_{0.56}Sb_{0.44} (Ga from 0 to 0.15) are suitable for InP substrates-based APDs that require excellent temperature stability without high tunnelling current.
]]>2017-05-17T00:07:48-07:00info:doi/10.1098/rsos.170071hwp:master-id:royopensci;rsos.1700712017-05-17Engineering45170071170071<![CDATA[Using Fisher information to assess stability in the performance of public transportation systems]]>
http://rsos.royalsocietypublishing.org/cgi/content/short/4/4/160920?rss=1
Public transportation systems (PTS) are large and complex systems that consist of many modes operated by different agencies to service entire regions. Assessing their performance can therefore be difficult. In this work, we use concepts of Fisher information (FI) to analyse the stability in the performance of PTS in the 372 US urbanized areas (UZA) reported by the National Transit Database. The key advantage of FI is its ability to handle multiple variables simultaneously to provide information about overall trends of a system. It can therefore detect whether a system is stable or heading towards instability, and whether any regime shifts have occurred or are approaching. A regime shift is a fundamental change in the dynamics of the system, e.g. major and lasting change in service. Here, we first provide a brief background on FI and then compute and analyse FI for all US PTS using monthly data from 2002 to 2016; datasets include unlinked passenger trips (i.e. demand) and vehicle revenue miles (i.e. supply). We detect eight different patterns from the results. We find that most PTS are seeking stability, although some PTS have gone through regime shifts. We also observe that several PTS have consistently decreasing FI results, which is a cause for concern. FI results with detailed explanations are provided for eight major UZA.
]]>2017-04-26T00:05:43-07:00info:doi/10.1098/rsos.160920hwp:master-id:royopensci;rsos.1609202017-04-26Engineering44160920160920