Water Hammer and Piping Stresses

TutorialThis tutorial provides guidance to help understand the causes, and to prevent or mitigate the effects of water hammer, or fluid transients, in piping and pipeline systems. The text of this paper is based on early drafts of ASME B31D, which is still under consideration (The American Society of Mechanical Engineers, ASME Code for Pressure Piping, ASME B31D, Design of Piping Systems for Dynamic Loads from Fluid Transients). Drafts of B31D were, in turn, based on an ASME Press text book, titled Fluid Mechanics, Water Hammer, Dynamic Stresses, and Piping Design which was written by this author. The information presented here is not necessarily new, but it is provided in a format to provide an overview of fluid transient topics that are important to practicing engineers who work with piping systems

CHARACTERISTICS AND TRENDS IN BARIATRIC SURGERY IN THE U.S., 1999-2004, AND A COMPARISON OF SURGICAL PATIENTS TO THOSE ELIGIBLE FOR SURGERY

Severe obesity (BMI >= 40 kg/m2) increases risk for many diseases (e.g., hypertension, diabetes). Bariatric surgery is the treatment with the greatest long-term success for severe obesity, sustaining weight loss and improving health. The number of bariatric surgeries has increased tremendously in recent years, although the percentage of adults eligible for surgery that receive the surgery is very small. Using the National Hospital Discharge Survey (1999-2004), patient, surgical, and hospital characteristics were analyzed over this six year time period. Using the National Health and Nutrition Examination Survey (NHANES), severely obese adults were compared to bariatric surgical patients with respect to age, sex, and health insurance for the years 2003 and 2004. Chi-square tests were used to test for differences in characteristics, and tests for trend were performed to test for temporal trends. Poisson regression was used to model length of hospital stay. From 1999 to 2004, most bariatric surgical patients were 30-49 years old, female, and were expected to pay with private insurance only. The most common comorbidities among bariatric surgical patients were hypertension (45.5%), sleep apnea (25.8%), and diabetes (21.8%). The majority of bariatric surgeries performed were high gastric bypasses. The number of bariatric surgeries increased more than 15-fold from 2000 to 2003. Length of hospital stay decreased from 1999 to 2004. Those who had gastroplasty were more likely to have a shorter hospital stay compared to other procedures.Only about 2.3% of severely obese individuals in the United States received bariatric surgery in 2003-2004. Males, younger and older adults, and those with public insurance were under-represented among bariatric surgical patients in 2003 and 2004. Because obesity is a major public health concern, discrepancies in characteristics of adults who are eligible for bariatric surgery compared to those receiving the surgery need to be addressed. Clinical practices should make sure everyone eligible is aware and well-informed of bariatric surgery. Healthcare policies should eventually allow every candidate the choice of having bariatric surgery, to improve health and reduce healthcare costs

Changes in Vitamin B12, Homocysteine, and Neurological Function in Older Adults

Vitamin B12 deficiency affects 5-20% of older adults, with up to 40% with low B12 levels [271nmol/L & MMA>2-methylcitrate] B12 were associated with peripheral sensory and motor nerve function, and evaluated whether there was a threshold effect of serum B12 levels on peripheral nerve function in older black and white adults. We found poor B12 were associated with greater insensitivity to 1.4g monofilament and worse nerve conduction velocity [NCV] and there was a significant serum B12 threshold level of 390 pmol/L for NCV. To consider cognitive function, we examined whether low B12 or 7-year change in B12 were associated with decline in Digit Symbol Substitution Test [DSST] scores over 6-years. We found low B12 was associated with greater DSST decline and a serum B12 level of 410 pmol/L was associated with lower DSST decline. These results have important public health significance, because low B12 levels, above clinical deficiency [<148 pmol/L], were associated with worse peripheral nerve function and decline in information processing speed, which may lead to decreased cognitive and physical function, and disability in older adults. Vitamin B12 supplementation is widely available, adequately absorbed, well-tolerated, and potentially may prevent declines in neurological function

IMECE2005-79178 STRESSES DURING IMPACTS ON HORIZONTAL RODS

ABSTRACT The impact of an object striking the tip of a horizontally mounted bar provides some insight into the dynamics of structural impact in general. Modeling a cylindrical bar provides significant simplifications to enable comparison between experiment and theory. In particular, experimental results available in the literature are compared herein to both elastic wave theory and vibration theory. Relating these two theories is the focus of this paper. Vibrations can be directly related to the time of impact, the maximum stress at the tip of the bar, and the frequencies of the struck bar. Once these stresses and frequencies are found, elastic wave theory can then be used to describe the stresses throughout the bar

Comparison of Experimental to Theoretical Strains During Water Hammer

Experimental strains during water hammer were compared to theoretical equations for strain. These equations were derived from the basic equations of motion, which lead to equations for the hoop stress and hoop strain. In this particular case, a sudden pressure increase increase traveling in a pipe was measured, and the hoop strains resulting from this fluid transient were also measured. Measuring the strains at numerous locations along the pipe permitted comparison of the strains as a function of position with respect to the fluid shock wave. This comparison of strains at different positions along the pipe permits analysis the vibratory nature of the strain in the pipe wall. Essentially, the equations of motion provide an approximate technique to find the maximum stress and strain due to water hammer

Application of a Dynamic Stress Theory to Pike Leaks

This report talks about Application of a Dynamic Stress Theory to Pike Leak

EXCITATION OF STRUCTURAL RESONANCE DUE TO A BEARING FAILURE

Vibration due to a bearing failure in a pump created significant vibrations in a fifteen foot by fifteen foot by eight feet tall mounting platform due to excitation of resonant frequencies. In this particular application, an 18,000 pound pump was mounted to a structural steel platform. When bearing damage commenced, the platform vibrated with sufficient magnitude that conversations could not be heard within forty feet of the pump. Vibration analysis determined that the frequency of the bearing was coincident to one of the natural frequencies of the pump, which was, in turn, coincident to one of the natural frequencies of the mounting platform. This coincidence of frequencies defines resonance. Resonance creates excessive vibrations when the natural frequency of a structure is coincident to an excitation frequency. In this well documented case, the excitation frequency was related to ball bearing failures. The pump is a forty foot long vertical pump used to mix nuclear waste in 1,300,000 gallon tanks. A 300 horsepower drive motor is mounted to a structural steel platform on top of the tank. The pump hangs down into the tank from above to mix the waste and is inaccessible after installation. Initial awareness of the problem was due to increased noise from the pump. Initial vibration analysis indicated that the vibration levels of the bearing were within the expected range for this type of bearing, and the resonant condition was not obvious. Further analysis consisted of disassembly of the motor to inspect the bearings and extensive vibration monitoring. Vibration data for the bearings was obtained from the manufacturer and compared to measured vibration plots for the pump and mounting platform. Vibration data measured along the length of the pump was available from full scale testing, and vibrations were also measured at the installed pump. One of the axial frequencies of the pump, the platform frequency in the vertical direction, and the ball spin frequency for the bearing were multiples of each other. This resonant condition was detected before other damage occurred, and further damage due to the resonant condition was prevented through vibration analysis

BLENDING STUDY FOR SRR SALT DISPOSITION INTEGRATION: TANK 50H SCALE-MODELING AND COMPUTER-MODELING FOR BLENDING PUMP DESIGN, PHASE 2

The Salt Disposition Integration (SDI) portfolio of projects provides the infrastructure within existing Liquid Waste facilities to support the startup and long term operation of the Salt Waste Processing Facility (SWPF). Within SDI, the Blend and Feed Project will equip existing waste tanks in the Tank Farms to serve as Blend Tanks where 300,000-800,000 gallons of salt solution will be blended in 1.3 million gallon tanks and qualified for use as feedstock for SWPF. Blending requires the miscible salt solutions from potentially multiple source tanks per batch to be well mixed without disturbing settled sludge solids that may be present in a Blend Tank. Disturbing solids may be problematic both from a feed quality perspective as well as from a process safety perspective where hydrogen release from the sludge is a potential flammability concern. To develop the necessary technical basis for the design and operation of blending equipment, Savannah River National Laboratory (SRNL) completed scaled blending and transfer pump tests and computational fluid dynamics (CFD) modeling. A 94 inch diameter pilot-scale blending tank, including tank internals such as the blending pump, transfer pump, removable cooling coils, and center column, were used in this research. The test tank represents a 1/10.85 scaled version of an 85 foot diameter, Type IIIA, nuclear waste tank that may be typical of Blend Tanks used in SDI. Specifically, Tank 50 was selected as the tank to be modeled per the SRR, Project Engineering Manager. SRNL blending tests investigated various fixed position, non-rotating, dual nozzle pump designs, including a blending pump model provided by the blend pump vendor, Curtiss Wright (CW). Primary research goals were to assess blending times and to evaluate incipient sludge disturbance for waste tanks. Incipient sludge disturbance was defined by SRR and SRNL as minor blending of settled sludge from the tank bottom into suspension due to blending pump operation, where the sludge level was shown to remain constant. To experimentally model the sludge layer, a very thin, pourable, sludge simulant was conservatively used for all testing. To experimentally model the liquid, supernate layer above the sludge in waste tanks, two salt solution simulants were used, which provided a bounding range of supernate properties. One solution was water (H{sub 2}O + NaOH), and the other was an inhibited, more viscous salt solution. The research performed and data obtained significantly advances the understanding of fluid mechanics, mixing theory and CFD modeling for nuclear waste tanks by benchmarking CFD results to actual experimental data. This research significantly bridges the gap between previous CFD models and actual field experiences in real waste tanks. A finding of the 2009, DOE, Slurry Retrieval, Pipeline Transport and Plugging, and Mixing Workshop was that CFD models were inadequate to assess blending processes in nuclear waste tanks. One recommendation from that Workshop was that a validation, or bench marking program be performed for CFD modeling versus experiment. This research provided experimental data to validate and correct CFD models as they apply to mixing and blending in nuclear waste tanks. Extensive SDI research was a significant step toward bench marking and applying CFD modeling. This research showed that CFD models not only agreed with experiment, but demonstrated that the large variance in actual experimental data accounts for misunderstood discrepancies between CFD models and experiments. Having documented this finding, SRNL was able to provide correction factors to be used with CFD models to statistically bound full scale CFD results. Through the use of pilot scale tests performed for both types of pumps and available engineering literature, SRNL demonstrated how to effectively apply CFD results to salt batch mixing in full scale waste tanks. In other words, CFD models were in error prior to development of experimental correction factors determined during this research, which provided a technique to use CFD models for salt batch mixing and transfer pump operations. This major scientific advance in mixing technology resulted in multi-million dollar cost savings to SRR. New techniques were developed for both experiment and analysis to complete this research. Supporting this success, research findings are summarized in the Conclusions section of this report, and technical recommendations for design and operation are included in this section of the report

TANK 21 AND TANK 24 BLEND AND FEED STUDY: BLENDING TIMES, SETTLING TIMES, AND TRANSFERS

The Salt Disposition Integration (SDI) portfolio of projects provides the infrastructure within existing Liquid Waste facilities to support the startup and long term operation of the Salt Waste Processing Facility (SWPF). Within SDI, the Blend and Feed Project will equip existing waste tanks in the Tank Farms to serve as Blend Tanks where salt solutions of up to 1.2 million gallons will be blended in 1.3 million gallon tanks and qualified for use as feedstock for SWPF. In particular, Tanks 21 and 24 are planned to be used for blending and transferring to the SDI feed tank. These tanks were evaluated here to determine blending times, to determine a range of settling times for disturbed sludge, and to determine that the SWPF Waste Acceptance Criteria that less than 1200 mg/liter of solids will be entrained in salt solutions during transfers from the Tank 21 and Tank 24 will be met. Overall conclusions for Tank 21 and Tank 24 operations include: (1) Experimental correction factors were applied to CFD (computational fluid dynamics) models to establish blending times between approximately two and five hours. As shown in Phase 2 research, blending times may be as much as ten times greater, or more, if lighter fluids are added to heavier fluids (i.e., water added to salt solution). As the densities of two salt solutions converge this effect may be minimized, but additional confirmatory research was not performed. (2) At the current sludge levels and the presently planned operating heights of the transfer pumps, solids entrainment will be less than 1200 mg/liter, assuming a conservative, slow settling sludge simulant. (3) Based on theoretical calculations, particles in the density range of 2.5 to 5.0 g/mL must be greater than 2-4 {micro}m in diameter to ensure they settle adequately in 30-60 days to meet the SWPF feed criterion (&lt;1200 mg/l). (4) Experimental tests with sludge batch 6 simulant and field turbidity data from a recent Tank 21 mixing evolution suggest the solid particles have higher density and/or larger size than indicated by previous analysis of SRS sludge and sludge simulants. (5) Tank 21 waste characterization, laboratory settling tests, and additional field turbidity measurements during mixing evolutions are recommended to better understand potential risk for extended (&gt; 60 days) settling times in Tank 21