Image Motion Extraction of Structures Using Computer Vision Techniques: A Comparative Study

Vibrational measurements play an important role for structural health monitoring, e.g., modal extraction and damage diagnosis. Moreover, conditions of civil structures can be mostly assessed by displacement responses. However, installing displacement transducers between the ground and floors in real-world buildings is unrealistic due to lack of reference points and structural scales and complexity. Alternatively, structural displacements can be acquired using computer vision-based motion extraction techniques. These extracted motions not only provide vibrational responses but are also useful for identifying the modal properties. In this study, three methods, including the optical flow with the Lucas–Kanade method, the digital image correlation (DIC) with bilinear interpolation, and the in-plane phase-based motion magnification using the Riesz pyramid, are introduced and experimentally verified using a four-story steel-frame building with a commercially available camera. First, the three displacement acquiring methods are introduced in detail. Next, the displacements are experimentally obtained from these methods and compared to those sensed from linear variable displacement transducers. Moreover, these displacement responses are converted into modal properties by system identification. As seen in the experimental results, the DIC method has the lowest average root mean squared error (RMSE) of 1.2371 mm among these three methods. Although the phase-based motion magnification method has a larger RMSE of 1.4132 mm due to variations in edge detection, this method is capable of providing full-field mode shapes over the building.

Performance study on mounting system for displacement transducer in mechanical tests of timber samples using photogrammetry method

This paper presents a unique study to reveal the effect of the mounting system of the linear variable differential transformer (LVDT) on the mechanical property tests of timber materials. This effect has been overlooked in the past but proven to be significant enough that will distort the measurements completely if the displacement is relatively small. The reason for causing this error is because the LVDT is not directly measuring targeting points on a sample, instead, the LVDT is measuring the distance between one point on the stop-end (where the tip rested on) and the holder. The wrong common sense hopes that this point on the stop-end and holder reliably following the movement of the sample points. But this study reveals that it is not always the case with the aid from the photogrammetry method. The messages of this paper are simple but alertly useful and, important: 1) the mounting system and the method of installation of the LVDTs have a significant impact on the actual displacement measurement in a mechanical properties test of timber materials. It should be carefully designed and validated before the actual test; 2) the displacement distribution is not uniform across the timber sample. This should be taken into account when selecting the mounting points of the LVDTs. Testing standards should consider this effect when recommending displacement transducers to be used in a timber-related test.

Energy Absorption in Actual Tractor Rollovers with Different Tire Configurations

In order to better understand the complexities of modern tractor rollover, this paper investigates the energy absorbed by a Roll-Over Protective Structure (ROPS) cab during controlled lateral rollover testing carried out on a modern narrow-track tractor with a silent-block suspended ROPS cab. To investigate how different tractor set-ups may influence ROPS and energy partitioning, tests were conducted with two different wheel configurations, wide (equivalent to normal ‘open field’ operation) and narrow (equivalent to ‘orchard/vineyard’ operation), and refer to both the width of the tires and the corresponding track. Dynamic load cells and displacement transducers located at the ROPS-ground impact points provided a direct measurement of the energy absorbed by the ROPS cab frame. A trilateration method was developed and mounted onboard to measure load cell trajectory with respect to the cab floor in real-time. The associated video record of each rollover event provided further information and opportunity to explain the acquired data. The narrow tire configuration consistently subjected the ROPS cab frame to more energy than the wide tire arrangement. To better evaluate the influence of the ROPS cab silent-blocks in lateral rollover, static and dynamic tests were performed. The results confirm that tires influence the energy partition significantly and that further understanding of silent-blocks’ dynamic performance is warranted.

Xylem, phloem and transpiration flows in developing European plums

Neck shrivel is a quality disorder of European plum (Prunus × domestica L.). It has been suggested that backflow in the xylem (from fruit to tree) could contribute to the incidence of neck shrivel in plum. The objective was to quantify rates of xylem, phloem and of transpiration flow in developing plum fruit. Using linear variable displacement transducers, changes in fruit volume were recorded 1) in un-treated control fruit, 2) in fruit that had their pedicels steam-girdled (phloem interrupted, xylem still functional) and 3) in detached fruit, left in the canopy (xylem and phloem interrupted). Xylem flow rates were occasionally negative in the early hours after sunrise, indicating xylem sap backflow from fruit to tree. Later in the day, xylem flows were positive and generally higher in daytime and lower at night. Significant phloem flow occurred in daytime, but ceased after sunset. During stage II (but not during stage III), the rates of xylem flow and transpiration were variable and closely related to atmospheric vapor pressure deficit. The relative contribution of xylem inflow to total sap inflow averaged 79% during stage II, decreasing to 25% during stage III. In contrast, phloem sap inflow averaged 21% of total sap inflow during stage II, increasing to 75% in stage III. Our results indicate that xylem backflow occurs early in the day. However, xylem backflow rates are considered too low to significantly contribute to the incidence of neck shrivel.

Investigating the Effect of the Tractor Drive System Type on Soil Behavior under Tractor Tires

To determine the effect of the tractor driving system type on the soil compaction and soil behavior a series of tests was conducted using Goldoni 240 tractor with a power rate of 30.8 kW and included four similar tires at three different driving systems (4WD, rear-wheel drive (RWD) and front-wheel drive (FWD)). To evaluate these systems’ effects on soil compaction, tests were conducted at three soil moisture contents (10, 15 and 20% d.b.), three tire inflation pressures (170, 200 and 230 kPa), and three tractor speeds (1.26, 3.96 and 6.78 km/h). Soil bulk density was measured at three average depths of 20, 30 and 40 cm. To evaluate soil compaction, cylindrical cores were used and to assess soil behavior during this process, the soil displacement in a three coordinate system was measured using three displacement transducers. It was found that the 4WD system created the least bulk density of 1155 kg/m3, while the FWD system led to the highest density of 1241 kg/m3. Maximum vertical soil compression of 55 mm occurred for the FWD system and it declined to 43 and 36 mm in RWD and 4WD systems, respectively. Soil displacement in the horizontal and lateral directions was larger for the FWD system in comparison to the other systems. With increment of speed and depth soil compaction decreased. Minimum bulk density of 1109 kg/m3 was occurred at velocity of 6.78 Km/h using the 4WD system, also with this system at the depth 40 cm density was 1127 kg/m3. While at velocity of 1.26 Km/h and depth of 20 cm soil density was 1190 kg/m3.

Investigating the effect of farmyard manure on clay soil compactibility

One of the important factors that can control and decrease soil compaction is incorporation farmyard manure to the soil. It increases soil elasticity and soil tolerance to the imported load. To evaluate the farmyard manure effect on the soil compaction, it was incorporated in the clay soil at different rates of 0, 45, 60, and 90 Mg ha^-1. Tests were conducted at different tire passes of 1, 6, 11 and 16 on the same track at three soil moisture contents of 8%, 11% and 14% (dry base); soil bulk density was measured at depths of 10, 20, and 30 cm. To evaluate soil compaction, cylindrical cores were employed to measure the soil bulk density. To assess soil behavior during the soil compaction process, three displacement transducers were placed in the soil in three coordinate directions of x, y and z. The soil volumetric change was measured using the transducers and soil sinkage was also measured. A single-wheel tester was used in a soil bin with a Barez 8.25-16 (8) P.R HLF agricultural tractor tire operated at a forward velocity of 0.8 m s^-1 under a vertical load of 4 kN and an inflation pressure of 300 kPa. Incorporating the farmyard manure noticeably decreased the final vertical and longitudinal displacement below the tire track, while the lateral displacement increased. Bulk density decrements of 14.7%, 9.7% and 6.3% were occurred via farmyard manure application rates of 90, 60 and 45 Mg ha^-1, respectively. Maximum soil sinkage occurred at 14% moisture, 16 passes of tire and with no manure condition.

Benefits of using digital image correlation systems for advanced structural assessment

<p>New developments in civil engineering in the area of innovative high-performance materials and sophisticated geometrical designs generate the need for advanced measurement and monitoring systems. Based on years of utilizing digital image correlation (DIC) in a diverse field of applications, the advantages and disadvantages of DIC measurements are highlighted, by means of a selection of various experimental tests conducted by the authors. Recommendations for a general methodology for the utilization of DIC systems are presented. For this purpose, the beneficial advantages in the case of a variety of different chosen test setups, as well as the originated evaluation data, are shown. Such a type of non invasive optical measurement system enables the user to gather data even in challenging conditions, where a brittle failure of the specimen has to be expected and conventional measurement equipment, like LVDTs or displacement transducers, reach their limit. In addition, a simplified model for a 3D measurement setup calculation is presented.</p>