Stability and Delay Compensation for Real-Time Substructure Testing

Real-time substructure testing is a method for establishing the dynamic behavior of structural systems. The method separates a complex structure into physical and numerically modeled substructures, which interact in real-time allowing time-dependent nonlinear behavior of the physical specimen to be accurately represented. Displacements are applied to the physical specimen using hydraulic actuators and the resulting measured forces are fed back to the numerical substructure. This feedback loop is implemented as a time-stepping routine. One of the key factors in obtaining reliable results using this method is the accurate compensation of the delayed response of the actuator. If this is not accounted for, instability of the feedback loop is likely to occur. This paper presents a method for estimating the delay while a test is in progress and accurately compensating for it during the test. The stability of both linear and nonlinear single-actuator systems is examined and the behavior of twin-actuator systems controlling two degrees-of-freedom at the substructure interface is presented. The effectiveness of the method is clearly demonstrated by comparisons between experimental and theoretical behavior.     

Linearly Implicit Time Integration Methods for Real-Time Dynamic Substructure Testing

The simulation in real time of heterogeneous systems has to guarantee that the time integration of the equations of motion is always successfully completed within an a priori fixed sampling time interval. Therefore, numerical and/or physical substructures as well as numerical solution methods have to be adapted to the needs of real-time simulations. Monolithic stable numerical methods are implicit and cannot be easily used in real-time applications because of their iterative strategies necessary to solve the nonlinear corrector equations. As an alternative, in the present paper, we consider linearly implicit Rosenbrock-based L-stable real-time (LSRT) compatible algorithms with both two-stage and three-stage. Moreover, other linearly implicit structural integrators used nowadays to perform coupled simulations in real time are introduced too. Successively, typical properties of monolithic algorithms are shown when large time steps are employed. The loss of stability and the reduction of accuracy of these algorithms, when applied to coupled systems caused by kinematically closed loops, are analyzed in-depth through a split-inertia substructured system. In this respect, the benefits of the L-stability property are shown. Finally, the performance of the algorithms under investigation appears in a number of more realistic tests considering both nonstiff and stiff substructures.     

Real-Time Watershed Delineation System Using Web-GIS

A Web-based geographic information system (GIS) that can delineate watersheds in real time was developed for use in hydrologic analysis and to support hydrologic model operation on the Internet. The system integrates a watershed delineation (WD) engine, common gateway interfaces, a Web-GIS user interface, and supports digital spatial data including vector and grid formats. The WD program utilizes a double-seed array-replacement algorithm to obtain a watershed boundary from point coordinates. The system provides a user interface for the selection of an outlet point from a map display in the Web browser using MapServer Web-GIS capability. The WD and data extraction system has been implemented for all of Indiana, with extensive verification conducted in the 2,082.7 km2 Wildcat Creek watershed in Indiana. The time to obtain results and the quality of results are acceptable for use as a real-time system for WD via the Web.     

Substructure strengthening mechanisms

The mechanisms which give rise to substructural strength originate in the dislocation character of the substructure boundary, in the size of sources for continued slip which the boundaries permit, and in the size of the cells or subgrains. The interrelation of these factors must be considered in obtaining a general view of the strengthening. Anthony W. Thompson, formerly with the Science Center, Rockwell International, Thousand Oaks, CA This paper is based on a presentation made at a symposium on “Mechanical-Thermal Processing and Dislocation Substructure Strengthening,” held at the Annual Meeting in Las Vegas, Nevada, on February 23, 1976, under the sponsorship of the TMS/IMD Heat Treating Committee.     

Reliability Verification Using Proof Pile Load Tests

Proof pile load tests are an important means to cope with uncertainties in the design and construction of pile foundations. In this paper, a systematic method to incorporate the results of proof load tests not conducted to failure into the design of pile foundations is developed. In addition, illustrative acceptance criteria for driven piles based on proof load tests are proposed for use in a reliability-based design. Finally, modifications to conventional proof test procedures are studied so that the value derived from proof tests can be maximized. Whether or not a proof test is conducted to failure, its results can be used to update the probability distribution of the pile capacity using the method proposed in this paper. Hence, contributions of the proof test can be included in foundation design in a logical manner by considering several load test parameters such as the number of tests, the test load, the factor of safety, and test results. This adds value to proof load tests and warrants improvements in the procedures for acceptance of pile foundations using proof load tests. A larger test load for proof tests, say 1.5 times the predicted pile capacity, is recommended since it will yield more information about the capacity statistics and thus allow for more economical designs.     

Bayesian Model Calibration Using Geotechnical Centrifuge Tests

The predicted performance using a geotechnical prediction model is expected to deviate from reality. A practical approach to assess the model error is through calibration with observed performances in physical model tests. In this paper, a Bayesian framework of model calibration using centrifuge modeling tests is proposed and the procedure of model calibration is illustrated. Two centrifuge tests conducted to investigate the performance of soil slopes under rainfall conditions are used to calibrate a coupled hydromechanical analysis model. It is found that for centrifuge tests with different levels of soil variability, the test with a smaller variability of soil properties is more efficient for model calibration. According to the concept of random field, a centrifuge model with a larger model size and accelerated to a lower acceleration is better for model calibration. When the discrepancy between the performance interpreted from the centrifuge model and the field performance is small, the improvement of the reliability estimation for a new slope is significant. However, when there is little information about the discrepancy, the reliability estimation cannot be significantly improved by the information from centrifuge modeling. The proposed procedure is shown to be able to quantify the calibration effects of centrifuge tests and may be used to achieve a more reliable calibration.     

Model Tests of Hydraulic Performance of Pit 6 Dam Stilling Basin

Pit 6 Dam, located on the Pit River in northern California, was constructed by Pacific Gas and Electric Company in San Francisco in 1965 for hydroelectric power generation. The gross head of the hydroelectric installation is 48.5 m for a rated generating capacity of 89 MW. Flow over the ogee spillway is regulated by two radial gates, and it discharges into a 33.5-m-wide and 19.5-m-long stilling basin. Since completion of the dam, there have been chronic problems with the floor blocks, some of which were dislodged more than once. To elucidate the primary cause of floor block failures and develop a new type of block, a 1:28-scale undistorted hydraulic model was constructed, and direct measurements of the longitudinal and lateral components of the forces acting on the model floor blocks were taken using a load cell. Extremely large fluctuating loads acting on the existing blocks in the lateral direction were found to be the primary cause of the block failures. Triangular hollow blocks, which substantially reduce the lateral loads, were then developed using the model.     

Teaching Hydraulic Design Using Equation Solvers

Civil engineering graduates need to be competent in hydraulic theory, as well as in the application of that theory to the solution of practical problems. Teachers of hydraulic design are faced with the dilemma that most realistic hydraulics problems are too complex to solve by hand, while most commercially available software packages obscure the theoretical background for program algorithms. Equation solvers provide a valuable tool for bridging these gaps. Students can develop an appropriate linear or nonlinear mathematical model to depict a realistic system, then use an equation solver package to solve that model for any combination of input data desired. Computer-based studio classrooms further enhance the learning experience by allowing students to solve problems under the instructor's supervision during class periods. This paper will describe how effective equation solvers and the studio classroom can be in teaching hydraulic design for water distribution systems and open-channel flow. The theory is developed in class through the use of printed notes. Students then develop the nonlinear mathematical model for a simple example, solve the model using an equation solver, and check the correctness of the solution. Students are able to investigate the dynamic response and the sensitivity of the model by varying the equation solver input variable values. Next they apply the theory and solution methods to a practical applications exercise. The final step is to complete a comprehensive, realistic design problem. Students are required to present their results to the class at all stages of the process. Course-end evaluation scores have risen significantly since the class has been converted to the studio format. Student comments indicate that they think equation solvers are a valuable engineering design tool, not only for learning, but in professional practice as well. The instructor has observed that students learn and retain the theory much better when they can apply it immediately to realistic problems. Much more realistic and sophisticated quizzes can be given when the students have computers available to assist with the analysis.     

Hydraulic Property Estimation Using Piezocone Results

Governing underground water flow, hydraulic properties such as hydraulic conductivity or coefficient of consolidation are major geotechnical parameters. Determination of hydraulic properties, however, is traditionally time consuming and expensive. This research proposes an easy and economical way of determining the hydraulic properties of soils through piezocone penetration tests. Pore pressure responses of soils from piezocone penetration tests are numerically analyzed herein by the coupled theory of mixtures, which is based on the large strain elastoplasticity. Using the numerical results, the effects of input parameters are evaluated. Simple equations are also derived for a faster estimation of the hydraulic conductivity or the coefficient of consolidation of soils. The hydraulic properties predicted by these derived equations agree reasonably with the measured results.     

Hydraulic Elements Chart for Pipe Flow Using New Definition of Hydraulic Radius

The Manning formula is used routinely to calculate the mean velocity of uniform flow. Although this empirical formula is effective when applied to uniform flow in simple rectangular or trapezoidal cross sections, the roughness coefficient of the formula is variable when examining flow in a pipe that is partially full. Thus, the coefficient must be altered depending on the relative depth of fluid in the pipe. As this seems to be due to the definition of the hydraulic radius, a new definition of hydraulic radius is proposed here that was used to calculate a hydraulic elements chart for flow in pipes with a constant roughness coefficient. The results of the calculations showed very good agreement with Camp’s chart. Furthermore, with adjustment of the “free-surface weight factor,” this method was also capable of expressing other hydraulic elements charts reported previously. This new definition of hydraulic radius can also be applied to flow in simple cross sections and may be developed further for use with compound channel flows in future studies.     

Constructing Hydraulic Robot Models Using Memory-Based Learning

Hydraulic machines used in mining and excavation applications are nonlinear systems. Apart from the nonlinearity due to the dynamic coupling between the different links there are significant actuator nonlinearities due to the inherent properties of the hydraulic system. Optimal motion planning for these machines, i.e., planning motions that optimize a user-selectable combination of criteria such as time, energy, etc., would help the designers of such machines, besides aiding the development of more productive robotic machines. Optimal motion planning in turn requires fast (computationally efficient) machine models in order to be practically usable. This work proposes a method for constructing hydraulic machine models using memory-based learning. We demonstrate the approach by constructing a machine model of a 25-ton hydraulic excavator with a 10 m maximum reach. The learning method is used to construct the hydraulic actuator model and is used in conjunction with a linkage dynamic model to construct a complete excavator model that is much faster than an analytical model. Our test results show an average bucket tip position prediction error of 1 m over 50 sec of machine operation. This is better than any comparable speed model reported in the literature. The results also show that the approach effectively captures the interactions between the different hydraulic actuators. The excavator model is used in a time-optimal motion planning scheme. We demonstrate the optimization results on a real excavator testbed to underscore the effectiveness of the model for optimal motion computation.     

Open-Channel Capacity Determination Using Hydraulic Performance Graph

A method for determining the flow carrying capacity of a channel system, capable of accounting for the interacting backwater effect among channel reaches and incoming lateral flow, is presented here. The method makes use of hydraulic performance graphs—a new tool for dealing with open-channel-flow problems. The hydraulic performance graph summarizes all the backwater profile information for a channel reach. As an illustration, the method is applied to evaluate the channel capacities of a portion of Boneyard Creek in the city of Urbana, Ill. The example demonstrates that the channel flow capacity is a function of the exit water level, of which the maximum normal flow capacity and the absolute maximum carrying capacity are special cases.     

运用PLC技术改进液压油滤油机性能

通过对现有滤油机的进一步改进、完善,运用PLC来进行自动控制,无需人员值守,达到了过滤、除水分同步进行。     

Determination of Hydraulic Conductivity Using Piezocone Penetration Test

An elastoplastic, finite-strain, coupled theory of mixtures in an updated Lagrangian reference frame is applied to the piezocone penetration test to estimate the hydraulic conductivity of the soil via analysis of the steady-state excess pore pressure generated during piezocone penetration. The results of this approach were compared with piezocone penetration test data. It showed that reliable hydraulic conductivities can be estimated conveniently without performing pore pressure dissipation tests. This study also shows that the change in the dimensionless excess pore pressure (excess pore pressure is normalized by the effective overburden pressure) at the cone tip is almost constant when the dimensionless hydraulic conductivity (hydraulic conductivity is normalized by the penetration speed and cone radius, hereafter called DLHC) is less than 10?7 or greater than 10?4. It is also shown that the drainage condition around the cone tip is close to a fully undrained condition when the DLHC of the soil is less than 10?7, while it is close to a fully drained condition when the DLHC of the soil is greater than 10?4.     

Laboratory and In Situ Tests for Long-Term Hydraulic Conductivity of a Cement-Bentonite Cutoff Wall

Slurry trench cutoff walls, constructed using self-hardening slag-cement-bentonite (Slag-CB), are the most common form of in-ground vertical contaminant barrier in the U.K., Europe, and Japan, and are increasingly being used in the United States. This paper presents a case study of the hydraulic conductivity evaluation of an 11-year-old Slag-CB wall material at a sulfate-contaminated site, using different in situ techniques and laboratory tests. The laboratory results suggest that the hydraulic conductivity of the samples, which vary in age from 4 weeks to 11 years, decreases with time for the first 3 years but then remains constant. The results indicate that the long-term performance of these containment walls is influenced by various parameters such as aging, the type/duration of contaminant exposure, mixing of surrounding soil during construction, and wall depth. Piezocone tests, packer tests, and self-boring permeameter tests were carried out in the field to determine the suitability of different in situ techniques and compare with the laboratory results. The hydraulic conductivity is affected by the type of in situ technique used and the geometric scale of the test section.     

Substructure strengthening in dispersion-strengthened nickel alloys

Pure nickel, 80 pct Ni-20 pct Cr, 98 pct Ni-2 pct ThO₂, and 78 pct Ni-20 pct Cr-2 pct ThO₂ were studied in a wide range of thermomechanical conditions to identify strengthening mechanisms in the dispersion-strengthened materials. An X-ray line profile technique was used to determine the distribution of lattice strain, the crystallite domain size and the incidence of twins and stacking faults. Transmission electron microscopy was carried out, and tensile tests were done at room temperature and at an elevated temperature. It was found that cold deformation of Ni?ThO₂ did not produce lattice strains as large as was the case with pure nickel and Ni?Cr. However, deformation of Ni?Cr?ThO₂ did generate high lattice strains, due it is thought to the influence of chromium on cross-slip. The materials containing high lattice strains recrystallized more readily on annealing or testing at high temperature. It was concluded that room temperature strength was related to domain size without regard to composition in the series investigated. Strengthening by particle-dislocation interaction was not thought to be applicable when the domain size was small compared to the interparticle spacing, or at elevated temperatures. High temperature strength was determined primarily by the presence of a polygonized dislocation substructure which was stabilized by the thoria dispersion.     

Substructure characteristics of titanium alloy weldments

The morphological characteristics of prior beta grain and subgrain boundaries in Ti-6 Al-6 V-2 Sn and Ti-6 Al-2 Sn-4 Zr-6 Mo fusion weldments have been studied using a unique decoration technique. Subgrain boundary characteristics were often found to differ from those of the more commonly observed microsegregation-revealed solidification substructure. Differences resulted both from alterations in the true cell boundary morphology and from the creation of secondary subgrain boundaries during weldment cooling. Decorated subgrain structures created during weldment cooling were often observed to be stable in weldments which had undergone super-transus post-weld heat treatment, and consequently which had experienced several allotropic transformations. Although a complete understanding of the decoration technique remains elusive, conclusions obtained concerning the validity of the subgrain decoration technique and weldment substructure characteristics were found to be complementary.     

Improved Estimation of ADCP Apparent Bed-Load Velocity Using a Real-Time Kalman Filter

An estimate of apparent bed-load velocity (v) can be derived from the difference between differential global positioning system (DGPSs) and acoustic Doppler current profiler (ADCP) bottom track (BT) measurements when BT is biased by a moving bottom. A Kalman filter has been developed to integrate GPS and bottom track data to improve estimation of boat velocity during ADCP measurements under moving bed conditions (Rennie and Rainville, 2008, J. Hydraulic Eng., in review). The boat velocity estimated using the Kalman filter is superior to boat velocity from raw GPS data. In this paper we assess the improvement in estimation of v using the Kalman filter as opposed to raw GPS data. Specifically, a synthetic moving bed bias was generated for 22 repeat transects of the Gatineau River, Quebec. The synthetic moving bed bias had mean, variance, and distribution across the section as typically observed during bed-load transport conditions, and had the advantage that it was known explicitly. The errors in estimated apparent bed-load velocity derived using either raw DGPS data or the Kalman filter boat velocity were compared. It was found that the improved boat velocity from the Kalman filter yielded significantly (α = 0.05) better estimates of v, (e.g., 61% reduction in error when the Kalman filter boat velocity was used instead of wide area augmentation system GGA), because boat velocity errors were reduced. Tests with real moving bed data confirmed the Kalman filter was able to significantly reduce errors in bed load calculated with stand alone GPS.