Multi-row Arrays Research Articles

Experimental study on wind-induced vibration and aerodynamic interference effects of flexible photovoltaics

This study investigates the wind-induced vibrations (WIVs) of photovoltaic (PV) modules possessing unique characteristics such as lightweight construction, low frequency, and susceptibility to wind loads, in contrast to stationary PV systems installed on rooftops and ground surfaces. The complex interference effects within rows of flexible PV arrays were investigated under varying angles of wind attack (AOAs) and inter-row distances, specifically focusing on wind directions of 0° and 180°. A comparative analysis of the WIV of a single row was also conducted. The findings indicated that both single- and multi-row PV modules experience flutter instability as wind speeds increase, resulting in significant vibrations at wind directions of 0° and 180°. Vertical vortex-induced vibrations (VIVs) were observed in multi-row arrays at lower wind speeds prior to the onset of flutter instability, whereas no VIVs occurred in the single-row configuration. Within the three-row array, the middle row exhibited the most significant VIVs. An increase in AOA was found to correlate with elevated maximum VIV responses, wind speed, and vortex amplitude. Throughout various flutter instability scenarios, the third row consistently maintained stable. Notably, the critical wind speed for flutter was lower at a wind direction of 180°, and the VIV response was more pronounced compared to that observed at 0°.

An adaptation of the ultrasound transducer element test for multi-row arrays.

A simple "paperclip test" for the function of individual elements in a diagnostic ultrasound transducer array is widely performed and has been adapted for phased arrays. The aim of this study was to adapt the test further for multi-row transducer arrays. An embossing tool was used in place of the usual paperclip or metal rod and was slowly moved along the transducer array, attempting to isolate the signal from each row in turn. Phased array transducers were operated in M-mode. Non-functioning elements were identified by a reduction in amplitude of the reverberation line. The test was repeated several times for each transducer, ensuring that all non-functioning elements were identified and looking for consistency of results. 28 phased arrays and 5 linear/curvi-linear arrays in clinical use and 1 phased array and 1 linear array already identified as faulty by electronic transducer testing, and not in clinical service, were available for testing. 8 of the clinical phased arrays were found to have 1 or more faulty elements; 3 had only minor defects and 5 were replaced under warranty or service contract. The linear/curvi-linear arrays showed no fault. The adapted test showed the failed elements in the known faulty phased array, except at the end of the array, but weak elements were not detected. The faulty linear array had a block of failed outer elements which was identified by the test. The adapted test is capable of detecting non-functioning elements in multi-row arrays, but weak elements were not detected.

The Imaging Performance of Diagnostic Ultrasound Scanners Using the Edinburgh Pipe Phantom to Measure the Resolution Integral - 15Years of Experience.

The grayscale imaging performance of a total of 368 different scanner/transducer combinations from 39 scanner manufacturers measured over a period of 15 years is presented. Performance was measured using the resolution integral, a single figure-of-merit to quantify ultrasound imaging performance. The resolution integral was measured using the Edinburgh Pipe Phantom. Transducers included single element, linear, phased, curvilinear and multi-row arrays. Our results demonstrate that the resolution integral clearly differentiates between transducers with varying levels of performance. Two further parameters were also derived from the resolution integral: characteristic resolution and depth of field. We demonstrate that these two parameters can successfully characterize individual transducer performance and differentiate between transducers designed for different clinical and preclinical applications. In conclusion, the resolution integral is an effective metric to quantify and monitor grayscale imaging performance in clinical practice.

Hybrid pressure integration and buffeting analysis for multi-row wind loading in an array of single-axis trackers

Unrestrained single-axis solar trackers are uniquely flexible structures that can withstand more deflections than typical aeroelastic structures such as long-span bridges or aircraft wings. These distinctive features and the aerodynamics of multi-row arrays lead to the requirement of novel techniques for design wind loads. The present study presents a hybrid technique using two separate wind tunnel tests: (i) a pressure model at a relatively small scale, and (ii) a sectional model at a larger scale. The pressure model test is used to measure the buffeting forces acting on each row of the array and the sectional model study is used to extract the variation in aerodynamic stiffness and damping as a function of wind speed. The results of these separate studies are combined to numerically simulate the buffeting response of the tracker, which predicts significant inertial and self-excited forces. Comparisons between the proposed hybrid method and wind loads estimated using a dynamic amplification approach are performed. It is shown that at high wind speeds, the self-excited forces become significant and the peak design moments exceed those predicted using pressure data alone. The proposed methodology is expected to complement aeroelastic modeling as a convenient and efficient design tool.

Effects of Mainstream Turbulence Intensity and Coolant-to-Mainstream Density Ratio on Film Cooling Effectiveness of Multirow Diffusion Slot Holes

Abstract Multirow film cooling is widely used in gas turbine airfoils cooling to cope with extremely high inlet temperature. The film cooling effectiveness of diffusion slot holes was measured in multirow arrays at a flat plate experimental facility using the pressure sensitive paints (PSP) technique. Emphasis was focused on the influence mechanism of mainstream turbulence intensity (Tu) and coolant-to-mainstream density ratio (DR) on film cooling effectiveness of multirow arrays with wide exit holes. The diffusion slot hole with exit width of 3.7D and 4.0D was, respectively, tested in three staggered arrays of P/D = 6 and S/D = 30, P/D = 6 and S/D = 20, and P/D = 9 and S/D = 20. Four blowing ratios varied from M = 0.5 to 2.0. The baseline condition (Tu = 3.5%, DR = 1.38) was compared with an increased Tu condition (Tu = 8.4%) and a decreased DR condition (DR = 0.97). The results showed that in two P/D = 6 arrays, increasing Tu decreased the multirow effectiveness considerably under all blowing ratios, but increasing Tu prominently restrained the film coalescence. The influences of Tu were more intense for the arrays with larger exit width holes and larger S/D. Decreasing DR increased multirow effectiveness obviously. The influences of DR tended to consistent for all arrays and the influences were relatively weak for high blowing ratios. In the P/D = 9 array, the superiority of large exit width hole disappeared completely, regardless of Tu and DR variations.

Microfluidic pumping using artificial magnetic cilia

One of the vital functions of naturally occurring cilia is fluid transport. Biological cilia use spatially asymmetric strokes to generate a net fluid flow that can be utilized for feeding, swimming, and other functions. Biomimetic synthetic cilia with similar asymmetric beating can be useful for fluid manipulations in lab-on-chip devices. In this paper, we demonstrate the microfluidic pumping by magnetically actuated synthetic cilia arranged in multi-row arrays. We use a microchannel loop to visualize flow created by the ciliary array and to examine pumping for a range of cilia and microchannel parameters. We show that magnetic cilia can achieve flow rates of up to 11 μl/min with the pressure drop of ~1 Pa. Such magnetic ciliary array can be useful in microfluidic applications requiring rapid and controlled fluid transport.

Estimation of the Alignment Parameters of a Scanning Device with a Multirow Focal Plane Array

Scanning devices based on multirow focal plane arrays providing increased resolution impose much more stringent requirements on alignment than single-row arrays. This paper presents a new method for measuring and estimating the scanning speed and the angle of orientation of a multirow focal plane array relative to the scanning direction — the parameters that determine the quality of the discrete image formed. The method is based on an analysis of the image of a simple test object — an optical slit. An algorithm for estimating these parameters is proposed which provides high-accuracy estimates under fairly weak requirements for the image quality of the test object. The estimation accuracy was calculated analytically and confirmed by simulation modeling.

Adiabatic Film Cooling Effectiveness Measurements Throughout Multirow Film Cooling Arrays

Adiabatic film cooling effectiveness measurements are obtained using pressure-sensitive paint (PSP) on a flat film cooled surface. The effects of blowing ratio and hole spacing are investigated for four multirow arrays comprised of eight rows containing 52 holes of 3.8 mm diameter with 20 deg inclination angles and hole length-to-diameter ratio of 11.2. The four arrays investigated have two different hole-to-hole spacings composed of cylindrical and diffuser holes. For the first case, lateral and streamwise pitches are 7.5 times the diameter. For the second case, pitch-to-diameter ratio is 14 in lateral direction and 10 in the streamwise direction. The holes are in a staggered arrangement. Adiabatic effectiveness measurements are taken for a blowing ratio range of 0.3–1.2 and a density ratio of 1.5, with CO2 injected as the coolant. A thorough boundary layer analysis is presented, and data were taken using hotwire anemometry with air injection, with boundary layer, and turbulence measurements taken at multiple locations in order to characterize the boundary layer. Local effectiveness, laterally averaged effectiveness, boundary layer thickness, momentum thickness, turbulence intensity, and turbulence length scale are presented. For the cylindrical holes, at the first row of injection, the film jets are still attached at a blowing ratio of 0.3. By a blowing ratio of 0.5, the jet is observed to lift off, and then impinge back onto the test surface. At a blowing ratio of 1.2, the jets lift off, but reattach much further downstream, spreading the coolant further along the test surface. A thorough uncertainty analysis has been conducted in order to fully understand the presented measurements and any shortcomings of the measurement technique. The maximum uncertainty of effectiveness and blowing ratio is 0.02 counts of effectiveness and 3%, respectively.

Towards a Low-Cost Modelling System for Optimising the Layout of Tidal Turbine Arrays

In the long-term, tidal turbines will most likely be deployed in farms/arrays where energy extraction by one turbine may significantly affect the energy available to another turbine. Given the prohibitive cost of experimental and/or field investigations of such turbine interactions, numerical models can play a significant role in determining the optimum layout of tidal turbine arrays with respect to energy capture. In the present research, a low-cost modelling solution for optimising turbine array layouts is presented and assessed. Nesting is used in a far-field model to telescope spatial resolution down to the scale of the turbines within the turbine array, allowing simulation of the interactions between adjacent turbines as well as the hydrodynamic impacts of individual turbines. The turbines are incorporated as momentum sinks. The results show that the model can compute turbine wakes with similar far-field spatial extents and velocity deficits to those measured in published experimental studies. The results show that optimum spacings for multi-row arrays with regard to power yield are 3–4 rotor diameters (RD) across-stream and 1–4 RD along-stream, and that turbines in downstream rows should be staggered to avoid wake effects of upstream turbines and to make use of the accelerated flows induced by adjacent upstream turbines.

Closely-spaced double-row microstrip RF arrays for parallel MR imaging at ultrahigh fields.

Radiofrequency (RF) coil arrays with high count of elements, e.g., closely-spaced multi-row arrays, exhibit superior parallel imaging performance in MRI. However, it is technically challenging and time-consuming to build multi-row arrays due to complex coupling issues. This paper presents a novel and simple method for closely-spaced multi-row RF array designs. Induced current elimination (ICE) decoupling method has shown the capability of reducing coupling between microstrip elements from different rows. In this study, its capability for decoupling array elements from the same row was investigated and validated by bench tests, with an isolation improvement from -8.9 dB to -20.7 dB. Based on this feature, a closely-spaced double-row microstrip array with 16 elements was built at 7T. S21 between any two elements of the 16-channel closely-spaced was better than -14 dB. In addition, its feasibility and performance was validated by MRI experiments. No significant image reconstruction- related noise amplifications were observed for parallel imaging even when reduced factor (R) achieves 4. The experimental results demonstrated that the proposed design might be a simple and efficient approach in fabricating closely-spaced multi-row RF arrays.

Effects of stream turbine array configuration on tidal current energy extraction near an island

Enhanced tidal currents around islands appear to present the potential for power extraction. In this research, a three-dimensional numerical model is applied to investigate the naturally occurring tidal dynamics and the extractable energy from turbines close to Zhaitang Island, located off the east coast of China. In the model, the effect of tidal turbine is represented by a horizontal thrust and added to the momentum equations. To determine a better configuration of turbine array, a detailed work has been undertaken to investigate the combined influences of the topographic features and array arrangement on the performance of power generation. First, three single row arrays are examined with lateral spacing being 2, 3 and 4 times rotor diameters. Then, corresponding to each lateral spacing, three multi-row arrays in a staggered manner with longitudinal spacing being 5, 10 and 15 times rotor diameters are developed. It has been found that single row arrays with higher local blockage outperform arrays with lower blockage. While for multi-row arrays, the performance of inside turbine is significantly experienced the wake influence of upstream turbines, which can be weakened with an increment of turbine spacing. And a remarkable improvement of turbine performance is observed as the longitudinal spacing increases to 10 times rotor diameters. However, the change pattern of power extraction is mainly dependent on that of naturally kinetic energy when the turbine density is further decreasing in the given region.

Longest Increasing Subsequences of Randomly Chosen Multi-Row Arrays

A two-row array of integers \[ \alpha_{n}= \begin{pmatrix}a_1 & a_2 & \cdots & a_n\\ b_1 & b_2 & \cdots & b_n \end{pmatrix} \] is said to be in lexicographic order if its columns are in lexicographic order (where character significance decreases from top to bottom, i.e., either ak < ak+1, or bk ≤ bk+1 when ak = ak+1). A length ℓ (strictly) increasing subsequence of αn is a set of indices i1 < i2 < ⋅⋅⋅ < iℓ such that ai1 < ai2 < ⋅⋅⋅ < aiℓ and bi1 < bi2 < ⋅⋅⋅ < biℓ. We are interested in the statistics of the length of a longest increasing subsequence of αn chosen according to ${\cal D}$n, for different families of distributions ${\cal D} = ({\cal D}_{n})_{n\in\NN}$, and when n goes to infinity. This general framework encompasses well-studied problems such as the so-called longest increasing subsequence problem, the longest common subsequence problem, and problems concerning directed bond percolation models, among others. We define several natural families of different distributions and characterize the asymptotic behaviour of the length of a longest increasing subsequence chosen according to them. In particular, we consider generalizations to d-row arrays as well as symmetry-restricted two-row arrays.

Fabrication and performance of a 64 × 5 element 1.5D active matrix array transducer for medical imaging

Compared to 1D phased array probes with a fixed focus in elevation, multi-row arrays can significantly improved the slice thickness throughout image by expanding aperture and dynamic focusing in elevation. This paper describes the design and measurement of a 64×5 element 1.5D ultrasonic transducer that enables dynamic focusing and apodization in the elevation direction. We manufactured a transducer with an aperture size of 24mm×16mm using a widely used piezoelectric ceramic (PZT-5H) as the piezoelectric vibrator. The measured center frequency and −6dB fractional bandwidth of the 1.5D transducer were 3MHz and 79%, respectively. A two-way insertion loss of −58dB was obtained at the average center frequency. We carried out a sound field simulation and measured the actual transmitting (one-way) sound field data by using a hydrophone. In this way the sound beam profile in elevation direction was obtained, showing the −6dB slice thickness measured was about 2mm throughout the whole range of interest (from near to far field). This provided a much greater focal depth and much better imaging resolution in the elevation direction than can be achieved by using 1D probe.

Element size effect on phase aberration correction.

The distortion effect of tissue on ultrasonic beamforming is simplified as a 2-D time-shifting screen placed against the array surface. The ideal correction of such distortion requires a 2-D array with infinitesimally small elements. However, elements of finite sizes must be utilized in practice, causing the so-called residual phase error (RPE). As element size is reduced, the magnitude of the RPE is reduced, and its spatial feature becomes finer. Analyses have been performed to reveal that the magnitude of the RPE is proportional to the imaging frequency, the rms magnitude of the original time-delay error, and the diagonal size of individual rectangular elements, and is inversely proportional to the correlation length of the original time-delay error. Simulations have been performed to study the peak sidelobe level caused by the RPE as the element sizes are reduced. The sidelobe is defined here as the difference between the ideal beam (with no phase error) and the beam obtained in the presence of the RPE. For a multi-row array in which a conventional 1-D array is divided into N rows of independent elements in the elevation direction, the peak sidelobe level is found to vary approximately as N(-1) instead of the anticipated N(-2). The reduction is caused by the reduced magnitude of the RPE, and the finer spatial feature of the RPE, although apparent in the reduced spatial correlation length, does not result in additional reduction of the sidelobe level. The reason for this has been analyzed. The results of this study provide guidance for designing multi-row arrays suitable for phase aberration correction.

Examples of design curves for multirow arrays used with time-shift compensation.

The effect of 1.75-D array element height on time-shift compensation is analyzed using a two-dimensional array system and a distributed aberration phantom. The analysis uses hydrophone measurements of transmit beams. The results indicate that, for imaging at 3 MHz through aberration representative of the abdominal wall, similar focus compensation performance can be expected from arrays with element pitches less than or equal to 3.0 mm.

Spatio-temporal dynamics in large arrays of fluid-elastic, Toda-type oscillators

New experiments on the dynamics of 300 elastic oscillators in a steady cross flow are described. Impact constraints between the rods mimic Toda-type exponential potentials. Unlike single row dynamics, which lead to limit cycle behavior, multi-row arrays seem to exhibit chaotic though not necessarily, low-dimensional dynamics, at a critical flow value. With increasing flow velocity, organized wave-like structures appear to develop as the impact rate between rods increases. Experimental models of this type may serve to help understand complex dynamics in large array heat exchange systems. It may also be a model to understand wind crop dynamics and damage.

Time-shift estimation and focusing through distributed aberration using multirow arrays.

The effects of element height on time-shift estimation and transmit focus compensation are demonstrated experimentally. Multirow ultrasonic transducer arrays were emulated by combining adjacent elements of a 3.0-MHz, 0.6-mm pitch, two-dimensional array to define larger virtual elements. Pulse-echo data were acquired through tissue-mimicking distributed aberrators, and time-shift maps estimated from those data were used for transmit focus compensation. Compensated beams formed by arrays with fine row pitches were similar, but focus restoration was significantly less effective for "1.75-D" arrays with a coarse row pitch. For example, when focus compensation was derived from strongly aberrated random scattering data [70-ns nominal rms arrival time fluctuation with 7 mm FWHM (full-width at half-maximum) correlation length], the mean -20 dB lateral beamwidths were 5.2 mm for f/2.0 arrays with 0.6- and 1.8-mm row pitches and 9.5 mm for an f/2.0 array with 5.4-mm pitch. Time-shift maps estimated from random scattering data acquired with 5.4-mm pitch arrays included large discontinuities caused by low correlation of signals received on vertically and diagonally adjacent emulated elements. The results indicate that multirow arrays designed for use with aberration correction should have element dimensions much less than 75% of the correlation length of the aberration and perhaps as small as 25 to 30% of the correlation length.

Calculation of coupling to slow and fast waves in the LHRF from phased waveguide arrays

A previously reported algorithm for solving the problem of coupling electromagnetic energy in the LHRF from a phased array of identical rectangular waveguides to a plane-stratified, magnetized cold plasma is numerically implemented. The resulting computer codes are sufficiently general to allow for an arbitrary number of waveguides with finite dimensions in both poloidal and toroidal directions and are thus capable of computing coupling to both slow and fast waves in the plasma. Some of the details of the implementation and the extension of the algorithm to allow study of the Fourier spectrum of slow and fast waves launched by the array are discussed. Good agreement is found with previously reported, less general work for the slow wave launching case. The effect of phasing multirow arrays in the poloidal direction is studied, and an asymmetric between phasing ‘up’ and ‘down’ is found that persists in the case where the plasma adjacent to the array is uniform. A 4 × 3 array designed to launch fast waves of high phase velocity is studied. By using the optimal poloidal phasing, low reflection coefficients (|R|2 ⪅ 20%) are found under some not unrealistic edge plasma conditions, but most of the input power is trapped in the outermost layer of the plasma. Implications of our results for fast wave current drive experiments are discussed.