Laser Measurement Techniques Research Articles

PointDMS: An Improved Deep Learning Neural Network via Multi-Feature Aggregation for Large-Scale Point Cloud Segmentation in Smart Applications of Urban Forestry Management

Background: The development of laser measurement techniques is of great significance in forestry monitoring and park management in smart cities. It provides many conveniences for improving landscape planning efficiency and strengthening digital construction. However, capturing 3D point clouds in large-scale landscape environments is a complex task that generates massive amounts of unstructured data with characteristics such as randomness, rotational invariance, sparsity, and serious barriers. Methods: To improve the processing efficiency of intelligent devices for massive point clouds, we propose a novel deep learning neural network based on a multi-feature aggregation strategy. This network is designed to divide 3D laser point clouds in complex large-scale scenarios. Firstly, we utilize multiple terrestrial laser sensors to collect a large amount of data in open scenes such as parks, streets, and forests in urban environments. These data are integrated into a practical database called DMSdataset, which contains different information variables, densities, and dimensions. Then, an automatic block integrated with a multi-feature extractor is constructed to pre-process the unstructured point cloud data and standardize the datasets. Finally, a novel semantic segmentation framework called PointDMS is designed using 3D convolutional deep networks. PointDMS achieves a better segmentation performance of point clouds with a lightweight parameter structure. Here, “D” stands for deep network, “M” stands for multi-feature, and “S” stands for segmentation. Results: Extensive experiments on self-built datasets show that the proposed PointDMS achieves similar or better performance in point cloud segmentation compared to other methods. The overall identification accuracy of the proposed model is up to 93.5%, which is a 14% increase. Particularly for living wood objects, the average identification accuracy is up to 88.7%, which is, at least, an 8.2% increase. These results effectively prove that PointDMS is beneficial for 3D point cloud processing, division, and mining applications in urban forest environments. It demonstrates good robustness and generalization.

Validation of Filtered Rayleigh Scattering Optical Rake Measurement Techniques in Turbomachinery Applications and Boundary Layers

Abstract Filtered Rayleigh scattering (FRS) is a non-intrusive, laser-based optical technique for measuring three-component velocity, static temperature, and static density with high spatial resolution and low uncertainty. FRS can be used to derive total values as well as turbomachinery efficiencies. The Virginia Tech team has been developing this seedless technique for simultaneous planar (or line) measurements to overcome the limitations associated with seed-based laser measurement techniques such as laser Doppler velocimetry (LDV), particle image velocimetry (PIV), and Doppler global velocimetry (DGV) as well as limitations with physical probe rakes such as blockage and wake production. This technique is especially attractive in flow cases or environments where the aforementioned seed-based laser measurement techniques are limited or not possible. A combination of specially designed boundary layer total pressure probe rake measurements, FRS optical rake measurements, and computational fluid dynamics (CFD) results in the inlet of a Honeywell TFE731-2 turbofan are presented. Results show that all three techniques (FRS, probe, and CFD) match within approximately 2% root-mean-square error (RMSE). Inlet efficiency was derived and found to be within 2.3% difference for all three techniques.

Determination of dynamic material properties using laser measurement technique in split Hopkinson pressure bar

The split Hopkinson pressure bar (SHPB) is a commonly used technique to measure the stress-strain of materials at high strain rate. Using the strain records in the input and output bars, the average stress-strain and strain rate in the sample can be calculated by SHPB formulas based on the one-dimensional wave propagation theory. The accuracy of a SHPB test is based on this assumption. In this paper, first a laser measuring system is designed, implemented, and calibrated in order to obtain the dynamic properties of different materials using split Hopkinson pressure bar test. In this method which is a non-contact one, the displacements of bar/sample interfaces are measured directly using a laser extensometer technique, by using the provided equations, in addition to the strain, the stress of the tested sample can be calculated. Moreover, the operation of the method is evaluated using numerical simulation. Aluminum 7075 and copper C10200 samples were studied to evaluate the implemented measurement method. The comparison with other measurement methods shows good agreement of numerical and experimental results. Moreover, since the one-dimensional wave propagation is not used directly in this method, we show the proposed method can be used even with shorter pressure bars which can reduce the cost of manufacturing and maintenance of the SHPB apparatus.

Ultrafast laser spectroscopy uncovers mechanisms of light energy conversion in photosynthesis and sustainable energy materials

The invention of the laser in 1960 gave us the ruby laser, which generally produced chaotic pulses of light. Six years later, in 1966, a concept called passive mode-locking applied to neodymium-glass lasers produced reasonably well-behaving picosecond pulses. This triggered an intense activity, with respect to developing improved laser pulse sources, measurement techniques, and application to chemistry, physics, and biology. Initially, only ∼10 –ps-long pulses at a few wavelengths were available. Nevertheless, insight into the function of complex biological systems, like photosynthetic proteins, and molecules of chemical interest was gained in very early studies. Today, both duration and color of ultrashort pulses can be tuned to almost any value. This has of course opened up possibilities to study almost any atomic, molecular, or solid-state system and any dynamic process. This review focuses on the use of laser spectroscopy to investigate light energy conversion mechanisms in both natural photosynthesis and a topical selection of novel materials for solar energy conversion. More specifically, in photosynthesis we will review light harvesting and primary electron transfer; materials for solar energy conversion that we discuss include sensitized semiconductors (dye sensitized solar cells), polymer:fullerene and polymer:polymer bulk heterojunctions (organic solar cells), organometal halide perovskites, as well as molecular and hybrid systems for production of solar fuel and valuable chemicals. All these scientific areas, and in particular photosynthesis and the solar cell materials, have been extensively studied with ultrafast spectroscopy, resulting in a vast literature; a comprehensive review of the individual materials is, therefore, not feasible, and we will limit our discussion to work that we think has been of particular importance for understanding the function of the respective systems.

INSIGHTS INTO THE FLOW WITHIN THE WELL DOCK OF A MOTHERSHIP DURING FEEDER VESSEL DOCKING MANOEUVRES

An experimental campaign has been undertaken to explore the flow around a feeder vessel as it manoeuvres in and out of the well dock of a mothership. The parent hulls for this study are drawn from the floating harbour transhipper concept created by Sea Transport Corporation. Laser measurement techniques have been employed to analyse the flow field within the well dock while the feeder vessel both enters and departs. For the Master of the feeder vessel to safely perform these manoeuvres, the complex flows resulting from the highly confined nature of the well dock concept need to be understood and potentially mitigated. It is shown that the inclusion of vents in the well dock can significantly influence the flow and that their effectiveness is determined by the size of the vents. This study further progresses the authors’ recent work on the same novel concept where the confined water effect of the well dock and inclusion of vents is quantified for both the seakeeping behaviour and the docking/departure performance. It is concluded that the use of vents is very beneficial when a feeder vessel docks or departs the well dock, however a compromise on the vent size must be reached in order to reduce adverse effects on feeder vessel motions when docked and exposed to a seaway. It is likely that the optimum solution, that covers all operational parameters, only requires the inclusion of relatively small vents.

Improved laser measurement using advanced techniques: A review

AbstractLaser measurement technique has been widely explored and applied in various fields in recent years due to its advantages of high measurement precision and resolution. However, applications in frontier fields such as MEMS motion measurement and robotics control pose have requirement for higher precision and resolution, which promote further studies in improving the performance of this technique. Many advanced techniques have been proposed and applied in the laser measurement system to optimize its performance, and the optimized measurement system has found its way in state‐of‐the‐art applications. In this invited paper, we focus on the latest investigations and new applications of the improved laser measurement methods, especially present recent research works regarding the laser triangulation measurement and the laser heterodyne vibration measurement. At the end, we have discussed further developments and challenges of laser measurement technique.

Description of failure mechanism in placed riprap on steep slope with unsupported toe using smartstone probes

This article is aimed at investigating the influence of toe support conditions on stability aspects of placed ripraps on steep slopes exposed to overtopping flows. All past experimental model studies investigating placed riprap stability under overtopping conditions have been conducted with ripraps constrained at the toe section. However, ripraps constructed on the downstream slopes of rockfill dams are generally not provided with any form of toe support. Hence, it is of importance from stability and economical standpoints to understand the failure mechanism in placed ripraps with realistic toe support conditions. This article presents findings from experimental overtopping tests conducted on model placed ripraps unsupported at the toe section. Employing Smartstone probes, a new technology in stone movement monitoring, laser measurement techniques and Particle Image Velocimetry (PIV) techniques, detailed description of failure mechanism in placed ripraps under overtopping conditions is presented within this study. Study findings demonstrate sliding as the underlying failure mechanism in placed ripraps with unsupported toes. Further, comparison of experimental results with past findings revealed that placed ripraps with unrestrained toes experience a fivefold reduction in stability, characterized by the critical overtopping magnitude as compared with placed ripraps provided with fixed toe supports. Furthermore, toe support conditions were found to have no effects on either the failure mechanism nor the overall stability of dumped ripraps. Further research is recommended to arrive at well-defined methodologies for design and construction of toe supports for placed ripraps.

Insight into the Flow Within the Well Dock of a Mothership During Feeder Vessel Docking Manoeuvres

An experimental campaign has been undertaken to explore the flow around a feeder vessel as it manoeuvres in and out of the well dock of a mothership. The parent hulls for this study are drawn from the floating harbour transhipper concept created by Sea Transport Corporation. Laser measurement techniques have been employed to analyse the flow field within the well dock while the feeder vessel both enters and departs. For the Master of the feeder vessel to safely perform these manoeuvres, the complex flows resulting from the highly confined nature of the well dock concept need to be understood and potentially mitigated. It is shown that the inclusion of vents in the well dock can significantly influence the flow and that their effectiveness is determined by the size of the vents. This study further progresses the authors’ recent work on the same novel concept where the confined water effect of the well dock and inclusion of vents is quantified for both the seakeeping behaviour and the docking/departure performance. It is concluded that the use of vents is very beneficial when a feeder vessel docks or departs the well dock, however a compromise on the vent size must be reached in order to reduce adverse effects on feeder vessel motions when docked and exposed to a seaway. It is likely that the optimum solution, that covers all operational parameters, only requires the inclusion of relatively small vents.

Application of the steady-state and unsteady-state lasers in reconstructing the geometrical characteristic parameters of soot fractal aggregates

The unsteady-state laser, i.e. time-domain (TD) and frequency-domain (FD) lasers, and the steady-state (SS) laser are employed as the measurement lasers to reconstruct the geometrical characteristic parameters of soot fractal aggregates, i.e. the root mean square radius Rg and fractal dimension Df. The direct problems are solved by the finite volume method and Rayleigh-Debye-Gans fractal aggregate method, while an improved artificial bee colony algorithm is used as the inverse problem algorithm. The sensitivity analysis is employed to study the effective sampling region of the TD and FD laser measurement signals, and the results show that the time-resolved signals selected within [L, 0.5L + ctp] for the TD laser and the dimensionless frequency selected within [0.5, 5] for the FD laser are conducive to improving the retrieval accuracy. Then, the geometrical characteristic parameters of soot fractal aggregates are retrieved by using different measurement lasers, and the results reveal that the retrieval accuracy can be ensured by using the TD laser measurement technique. Moreover, the retrieval accuracy and robustness of Rg are better than those of Df. All the studies in the present manuscript supply an application plat of the laser measurement techniques in reconstructing the geometrical characteristic parameters of soot fractal aggregates.

A solid particle seeder for particle-based laser measurement techniques in low volume-flowrate gas streams

This article describes a device to seed solid micron-size particles into gases for particle-based laser diagnostic techniques. The particle seeder consists of a sealed vessel containing the particles, into which the gas to be seeded is introduced. Using an electric fan placed inside the vessel, a fine aerosol can be easily generated. It is demonstrated that (1) at a fixed fan speed the particle seeding density Np can be kept within the range 10–100 particles mm−3 across the gas volume flowrate range 0.05–5 LPM; and (2) at a fixed gas volume flowrate, the fan speed can be used for approximate adjustment of the particle seeding density in the range 1–100 particles mm−3. The device does not affect the volume flowrate of the gas stream. This simple method should prove useful for researchers wishing to generate solid particle aerosols in low volume flowrate gas streams.

Thermal performance enhancement of non-premixed syngas combustion in a partial combustion unit by winged nozzle: Experimental and CFD study

This paper presents the effect of nozzle assembly design on the performance of a partial combustion unit (PCU) using the scale-adaptive simulation (SAS) and non-intrusive laser measurement techniques. Four different configurations were tested, namely, nozzle without wing and three nozzles with wing, i.e., flat surface wing, semi-sphere hollow wing and bent wingtip. The syngas-oxygen reaction chemistry was calculated using non-premixed flame model incorporated with GRI-MECH 3.0 mechanism. The radiative heat transfer was modelled using the discrete ordinates (DO) model. The simulation was compared with the particle image velocimetry (PIV) and a two-dimensional laser doppler anemometry (LDA) measurement on a scaled-down PCU model. A good agreement between the SAS prediction and experimental measurement was obtained. It was found that the modified nozzle assembly design with a semi-sphere hollow wing yielded the highest combustion temperature owing to the intense turbulence-induced recirculation mixing of oxy-fuel. The modified nozzle assembly design introduced in this work increased the peak outlet combustion temperature up to 18% higher compared to the original design. The finding in this work may useful for design retrofits of a combustion system.

Error identification and verification of cycloid gear profile surfaces in precision forming grinding

ABSTRACT This paper presents an error identification method for directly related geometric errors of 4-axis forming grinding machine tool and some processing-induced errors from actual teeth profiles of a machined cycloid gear. Based on the developed 4-axis geometric error model, we build up an overall error model of cycloid gear-tooth profiles by forming grinding, which includes some directly related geometric errors of the machine tool and processing-induced errors. Error separation or identification methods are developed in correspondence with the form grinding process and are verified by some non-cutting identification or measurement techniques, including multi-lateration laser measurement technique and a laser rotary axis calibrator. The experiment results demonstrate that the separated geometric errors based on the machining test approach reach a better accuracy. In order to further improve the machining accuracy of the cycloid gear, two identified geometric errors and tooth-shaped error can be utilised for error compensation in the future.

Numerical and Experimental Analyses of Vibrations of Annular Plates with Multiple Eccentric Holes

This paper deals with the free transverse vibrations of annular plates with geometrical discontinuities in form of eccentric holes and rims. The finite element method and experimental studies are used. Solid and shell finite element models are employed in the numerical analysis using the commercial ANSYS software. The calculated results are verified by the original experimental data via innovative laser measurement techniques. Numerical and experimental results of this study adequately describe the phenomenon of dividing natural frequency values corresponding to the mode shapes, where the number of nodal diameters is a factor of the number of through holes. The proposed procedure of analysis of transverse vibrations of annular plates with eccentric through holes arranged over the specified radius is recommended for engineering applications.

Rain Drop Measurement Techniques: A Review

For over a century there have been many studies that describe the use of rain drop measurement techniques. Initial manual measurement methods evolved due to improved technology to include photographic and, more recently, automated disdrometer and laser measurement techniques. Despite these numerous studies, there have been few comparative reviews of the range of methodologies, and their relative performance. This review explores the raindrop measurement techniques available, and summarizes and classifies the techniques according to the method or principle involved. The requirements of a robust raindrop measurement technique are suggested, and these are reviewed against existing rain drop measurement techniques to provide a comparative guide to the use of the range of techniques available for any research study. This review revealed that while advances in technology have allowed many of the deficiencies of early techniques to be eliminated, challenges remain in relation to the precision of the measurement of the size, shape, and velocity of rain drops.

Nitric Oxide Chemistry Effects in Hypersonic Boundary Layers

Simulations of gas seeding into a hypersonic boundary-layer flow were performed using OpenFOAM® to investigate and quantify errors associated with quantitative planar laser-induced fluorescence thermometry and velocimetry techniques. A modified version of the compressible rhoCentralFoam solver was used to simulate multicomponent chemically reactive flows. Simulations replicated conditions used in NASA Langley Research Center’s 31 in. Mach 10 facility with a wedge model oriented at various angles of attack with respect to the freestream flow in the test section. Adverse chemistry effects from the reaction of nitric oxide with molecular oxygen were investigated at various facility running conditions. Specifically, the effect of heat release on velocity and temperature profiles that would be obtained using the nonintrusive laser measurement techniques was assessed. The effect of any potential adverse chemistry reactions was found to be negligible.

Novel adaptive laser measurement techniques

Novel adaptive laser measurement techniques

Applications of laser diagnostics to thermal power plants and engines

The demands for lowering the burdens on the environment will continue to grow steadily. It is important to monitor controlling factors in order to improve the operation of industrial thermal systems. In engines, exhaust gas temperature and concentration distributions are important factors in nitrogen oxides (NOx), total hydrocarbon (THC) and particulate matter (PM) emissions. Coal and fly ash contents are parameters which can be used for the control of coal-fired thermal power plants. Monitoring of heavy metals such as Hg is also important for pollution control. In this study, the improved laser measurement techniques using computed tomography-tunable diode laser absorption spectroscopy (CT-TDLAS), low pressure laser-induced breakdown spectroscopy (LIBS), and laser breakdown time-of-flight mass spectrometry (LB-TOFMS) have been developed and applied to measure 2D temperature and species concentrations in engine exhausts, coal and fly ash contents, and trace species measurement. The 2D temperature and NH3 concentration distributions in engine exhausts were successfully measured using CT-TDLAS. The elemental contents of size-segregated particles were measured and the signal stability increased using LIBS with the temperature correction method. The detection limit of trace species measurement was enhanced using low pressure LIBS and LB-TOFMS. The detection limit of Hg can be enhanced to 3.5 ppb when employing N2 as the buffer gas using low pressure LIBS. Hg detection limit was about 0.82 ppb using 35 ps LB-TOFMS. Compared to conventional measurement methods laser diagnostics has high sensitivity, high response and non-contact features for actual industrial systems. With these engineering developments, transient phenomena such as start-ups in thermal systems can be evaluated to improve the efficiency of these thermal processes.

Combustion and soot processes of diesel and rapeseed methyl ester in an optical diesel engine

In-cylinder combustion and soot processes for ultra-low sulphur diesel (ULSD) and rapeseed methyl ester (RME) fuels were investigated in an optically accessible high speed direct injection diesel engine (HSDI) using in situ optical and laser measurement techniques. High speed imaging techniques were used to study the spatial distribution of spray flames, soot formation and oxidation through simultaneous measurements of OH* chemiluminescence and natural soot luminosity, during the luminous combustion process. The amount of un-oxidised soot left in the cylinder after the end of luminous combustion for these fuels were investigated using planar laser induced incandescence (PLII). In addition to PLII, time resolved laser induced incandescence (TR-LII) technique was used simultaneously to explore crank angle resolved variation of primary soot particle size during the expansion stroke. The ignition for RME occurs earlier compared to ULSD, and the early phase of RME combustion proceeds quicker compared to ULSD. The flame lift off length (FLoL) and the length based on the first appearance of soot (SLoL) are longer for RME. The combined effect of relatively longer FLoL and the presence of fuel-bound oxygen reduced the overall soot formation process for RME. PLII data confirmed that the relative amount of soot left in the cylinder after the end of visible luminous combustion is less for RME, and the soot formed are oxidised well within the combustion chamber before it is exhausted out of the engine compared to ULSD. The measured in-cylinder primary soot particles are in the size range between 15 and 35nm and it decreases with crank angle. The sizes of particles generated from the combustion of RME were slightly smaller compared to ULSD.

Flow Field Investigations on the Effect of Rib Placement in a Cooling Channel With Film-Cooling

This paper presents experimental investigations on flat plate film-cooling in combination with a ribbed cooling channel. The effect of rib placement on the film-cooling injection and the flow in the cooling channel was studied. The velocity fields were measured using optical laser measurement techniques including LDA (laser doppler anemometry) and PIV (particle image velocimetry). A row of three cylindrical film holes is placed in the center rib segment of the cooling channel. The dimensionless rib-to-hole position s/D is varied from 4.5 to 10.5. The investigations are conducted at isothermal conditions for a variation of the coolant Reynolds number Rec,Dh from 10,000 up to 60,000 and for three blowing rates M = 0.5, 0.75, and 1.00. The flow field results for the film-cooling injection showed only a small influence of the rib placement. Due to different coolant-to-main flow pressure ratios across the row, a slight nonuniform share of coolant flow occurs. Intense streamwise mixing and decay of the turbulence in the film jet was observed within the first 10 hole diameters. Enhancement of the turbulence intensity inside the jet core was found with increasing coolant Reynolds numbers. Inside the internal cooling channel, the flow field showed significant influence of the rib position which is most pronounced at low Reynolds number (Rec,Dh = 10,000) and high blowing ratios (M = 1.0). The effect becomes significantly smaller when the Reynolds number is increased. This is mainly attributed to the strongly increasing channel mass flow which equals to a decreasing suction ratio SR = uh/uc of the holes. The experimental results are compared to comprehensive numerical simulations.

Fundamental investigation of fluidic optical devices: Transmission characteristics of laser beam in 1D temperature field of liquid medium

Laser measurement and laser processing techniques have been gaining strong attention from various applications. This research aims at the development of a novel optical device, and in order to fulfill the objective, characteristics of the thermal lens effect is studied. This phenomenon has the optical property of a divergent lens since the refractive index distribution on the optical axis is formed when the liquid medium is irradiated. One reason for the refractive index distribution is the temperature distribution in the liquid medium when it is irradiated. In this research, as a fundamental step to develop the fluidic optical devices, the interaction between a refractive angle of the probe beam and the temperature distribution on the thermal lens effect is investigated.