Validation of the CHARM Software Module Including Near-Field Dispersion With Varying Roughness

Transcription

1 Valdaton of the CHARM Software Module Includng Near-Feld Dsperson Wth Varyng Roughness Paper Number # By Mark W. Eltgroth, PhD URS Corporaton Austn, Texas Ron Petersen, PhD CPP, Inc. Fort Collns, Colorado James Sanders Eastman Kodak Company Rochester, New York

2 ABSTRACT As personal computers get faster and more powerful ar dsperson models can ncrease n complexty. Ths paper brefly dscusses modfcatons made to the CHARM software package for ar dsperson from a Lagrangan puff model to an Euleran grd model and presents comparsons of the modfed model wth new wnd tunnel (60 ponts presented here) and exstng feld data. The wnd tunnel data ncludes near-feld data from 3 to 50 meters downwnd dstance at three surface roughness values. The feld data s from prevously publshed reports. The wnd tunnel data s presented n tabular form. The comparson of maxmum concentraton predctons from the modfed model gves a Fractonal Bas of and a Factor of fracton of 0.8. The comparson of offcenterlne ponts gves a Fractonal Bas of 0.3 and a Factor of fracton of BACKGROUND Personal computers have evolved nto beng capable of much more than just word processng and spreadsheet applcatons. The PC of today s capable of carryng out calculatons so complex that 0 years ago they would have been left to super computers. Ths paper descrbes modfcatons that have been made to a computer model that s desgned to predct movement and concentratons of arborne plumes from released chemcals as well as to determne thermal radaton, and exploson overpressures mpacts. Comparsons of the modfed model s predctons wth feld data are presented to gve an ndcaton of the realsm of the estmates. These comparsons wth measured data were done after the model modfcatons were done. These comparsons act as the ntal test of the code. The model was not tuned to the measured value. Codng errors were corrected as they appeared durng the smulatons and prevous smulatons re-run. For example, when the surface roughness was greater than meter a varable was not beng set and the dffuson coeffcent was calculated ncorrectly. There s specal treatment for hydrogen fluorde to account for the olgomerzaton of hydrogen fluorde. Ths effect s smulated by changng the apparent molecular weght of the chemcal n calculatons. The degree of the effect s a functon of the concentraton and temperature of the hydrogen fluorde. Because of the length of the output and nput tables, they are presented n an Appendx to ths paper. THE MODEL The CHARM software package, (Complex Hazardous Ar Release Model) began development n 98 when personal computers began to become popular. Snce then, t has gone through contnuous development n both functonalty and mplementaton.

3 Descrpton Intally, the model was wrtten to smulate the advecton and dffuson of a gaseous release. A puff model was used as the core of the calculaton. Over tme, source-term calculatons were added to ad n determnng emsson rates and release-state parameters. Calculatons for smulatng jet fres, pool fres, BLEVEs, contaner explosons, and vapor cloud explosons were also added. The ntal mplementaton of the program was wrtten n FORTRAN. Graphcs were added usng the Basc language and Intel Assembler. It was rewrtten n C to reduce the mantenance requred for a number of languages. Currently, the code s entrely wrtten n C and desgned for use n Mcrosoft Wndows. The software s a hghly nteractve program desgned to gve output as tables, D, and 3D dsplays. Modfcatons The major modfcaton to the latest verson of the model s the replacement of the advecton/dffuson Lagrangan approach wth a Euleran grd approach. Movng to a grd model allowed for the addton of many other mechansms to be consdered n a release and ts subsequent mpacts. Because of the mplementaton of a grd framework for the calculaton, the followng consderatons have been added: o Varyng terran alttude n each grd column o Varyng surface roughness n each grd column o Wnd feld calculaton nteracts wth terran to mnmze dvergence o Lqud releases can flow over the terran to become polymorphous sources Other addtons were made to the model at the same tme. These changes nclude: o Multple releases n one smulaton o Calculaton of coagulaton, evaporaton, and deposton of partcles/droplets The model has the capablty to set up nested grds automatcally around a source to ensure a more detaled calculaton n the volume where thngs are changng the quckest. Ths opton was not turned on for these results. Most data sets for dsperson of releases n the atmosphere are for releases n flat terran. In model comparsons, the advecton and dffuson terms are the largest determners n the goodness of agreement. The model software was modfed to use the West Wnd Feld 3. The West Wnd Feld consders the effects of vertcal temperature stratfcatons on the wnd and dffuson felds and shear flows caused by the atmospherc boundary layer or by terran effects. 3

4 4 The wnd feld calculaton uses an teratve procedure to mnmze the dvergence n the feld. The advecton/dffuson porton of the model uses a flux-corrected verson of Crowely s 4 second-order advecton scheme, as mplemented by Sklarew and Wlson 5. The flux corrector method prohbts the calculaton of negatve concentratons. The form of the calculaton for the advecton/dffuson for the n th tme step of the concentraton (C) of the th speces n the x drecton s: x t F F C C n n n n = () where ( ) ( ) α α = x C C K C C C C t x F n n x n n n n n () and x t u = α (3) The ar parameters used n the advecton/dffuson calculaton are those from the West Wnd Feld wth modfcatons from effects of mass, momentum, and energy from the releases. The frst modfcaton s due to the emtted momentum n each drecton: t e a m p u m u' = (4) where u' s the new wnd speed u s the atmospherc wnd speed m a s the mass of ar n a cell m t s the total mass n a cell p e s the momentum n a cell from an emsson The mass from an emsson s tracked for each cell as well as the fracton that mght be n

5 droplet form. The volume occuped by the mass from an emsson can then be calculated. Whatever volume remans n a cell s assumed to be ar. The next modfcaton s only to the vertcal component of the velocty and s due to buoyancy. If the dfference of the cell s densty (ρ) wth the ambent densty (ρ a ) s greater than one percent of ρ a, then the vertcal velocty may be modfed. If the cell s bottom s not n contact wth terran, the vertcal velocty changng by: dw dt ρa = g ρ (5) where g = gravtatonal acceleraton = 9.8 m/sec If the bottom of the cell s n contact wth the ground and the densty dfference s less than 0.0, the vertcal moton caused by slump s assumed to be transferred to horzontal moton. The horzontal velocty caused by the downward moton s gven by: where z = vertcal grd spacng (m) ρa u' = g z (6) ρ The emtted momentum and energy are allowed to advect and dsperse usng the same formulaton as used for concentraton. EXPERIMENTAL DATA There have been a number of controlled releases over the years. These were done to provde a database for evaluatng models. The model results have been compared wth the measurements from some of those controlled releases. Normally, the results from a feld release are gven as a number of maxmum concentratons measured at varous dstances downwnd from the release ste. In addton to the feld releases, a new data set of a number of releases n a wnd tunnel has been developed. The mportance of ths data set s that not only are the maxmum 5

6 concentratons at varous downwnd dstances provded but also concentratons at off centerlne locatons. Wnd Tunnel Database Wnd tunnel testng was carred out at the facltes of CPP, Inc. n Fort Collns, Colorado. The purpose of the wnd tunnel testng was to collect a set of ground-level concentraton measurements for full-scale dstances out to 50 m for varous roughness confguratons for use n valdatng the model. Wnd tunnel operatng condtons were set usng smlarty requrements descrbed n the EPA flud modelng gudelne 6. To meet the wnd tunnel modelng objectves, a :00 scale model of the varous roughness confguratons and m surface release were constructed and placed n CPP s wnd tunnel. Three dfferent roughness confguratons were evaluated durng ths study as summarzed below: Confguraton A -- Ths confguraton conssted of a pattern of nch hgh roughness desgned to gve a full-scale surface roughness length of 5. cm. Confguraton B -- Ths confguraton conssted of a pattern of nch hgh roughness desgned to gve a full-scale surface roughness length of cm. Confguraton C -- Ths confguraton conssted of a pattern of and 8-nch hgh roughness desgned to gve a full-scale surface roughness length of 3 cm. For all tests, a m crcular release at ground level was smulated. The release was constructed of a brass tube wth steel wool and a screen nstalled nsde to ensure a unform flow upon ext. The release was suppled wth a tracer gas (methane or ethane and helum) wth a densty dentcal to methane. Precson mass flow controllers were used to montor and regulate the dscharge veloctes. Concentraton measurements were taken n a horzontal/vertcal samplng array at four downwnd dstances (x = 3, 7.5, 5 and 50 m). The test procedure conssts of: ) settng the proper tunnel wnd speed; ) releasng a metered mxture of source gas of the requred densty from the release pont; 3) wthdrawng samples of ar from the wnd tunnel at desgnated locatons; and 4) analyzng the samples wth a flame onzaton gas chromatograph (FIGC). The samples are collected smultaneously over a 00 second (approxmate) tme usng CPP s samplng system and consecutvely njected nto the FIGC. Results Table through Table 4 present the results of the wnd tunnel experments for dfferent surface roughness values. Included n the tables s a column labeled Adjusted Wnd Tunnel. Gven a contnuous-constant release wth a constant wnd speed, the model predcted an axally symmetrc concentraton feld. The wnd tunnel data does not exhbt 6

7 the same symmetry, although the data ndcates that such symmetry exsts but somewhat off from the centerlne of the tunnel. The wnd tunnel results at each downwnd dstance were ftted to a Gaussan dstrbuton to estmate what the concentraton dstrbuton would be f t were symmetrc. These estmates are n the Adjusted Wnd Tunnel column. The ft was performed to mnmze the amount of error n the ft to actual results. The soluton s teratve and somewhat dependent upon the ntal guess of what the parameters should be. A few of the fts resulted n lower maxmum concentratons than those actually measured. Feld Data To provde range for the comparson readly avalable data sets were selected. The wnd tunnel data s newly avalable and only covers the near-feld regon. Other data sets were selected that had releases other than methane, had measurement values further downwnd, or were from elevated sources. The feld data used s for the Burro, Desert Tortose, Goldfsh, and Lllestrom releases. The Burro LNG releases occurred at the Naval Weapons Center at Chna Lake, Calforna, n the summer and fall of 98. The Desert Tortose and Goldfsh experments releases were at Lquefed Gaseous Spll Test Faclty n Nevada. Ammona was released n the Desert Tortose experments n 983. Hydrogen fluorde was released n the Goldfsh experments n 986. The Lllestrom releases were of SF 6 n Lllestrom near Oslo, Norway n 987. The release descrptons and results were found on the Transoft Internatonal ( and The Albany County Research Corporaton ( web stes. The Transoft papers compared ther models Fludyn-PANACHE- PANEPR 7 (Burro, Desert Tortose, Goldfsh) and Fludyn-PANACHE 8 (Lllestrom) to the expermental data, as well as other models, ncludng an earler verson of the CHARM model. The ACRC paper 9 provded descrptons and some of the release nformaton of the experments. Results The results of the model calculatons for the varous releases are gven n Table 6. MODEL INPUT The model requres three types of nput. The frst type s the release descrpton (e.g., emsson rate, temperature, locaton, source sze, etc.). The second type s the meteorologcal condtons. The thrd type s the grd over whch the calculaton wll take place. The nputs to the model are gven n Table 8 through Table 4. 7

8 Wnd Tunnel The emsson rates, meteorology, and grd nput to the software for the wnd tunnel experments are gven n Table 8 and Table 6. Table 8 contans the nput that was vared for each expermental run. Table 6 contans the nput that was assumed for every smulaton. The grd used for the wnd tunnel smulatons had a zero elevaton at all grd cells. Its largest extent was n the x drecton (east-west) wth the source near the west end of the grd and the wnd from the west. Feld Data The emsson rates, meteorology, and grd nput to the software for the feld experments are gven n Table 8 through Table 4. For the Desert Tortose and Goldfsh releases, the elevatons of the grd cells were set usng USGS DEM data for each area. An edtor comes wth the model software for processng the DEM data, as well as other nformaton (e.g., maps and chemcal data) for use n the man program. Two grds were used for the Goldfsh experments. One was used for the near feld (300 m downwnd) wth a fne mesh and the other for estmatng concentratons beyond 300 m downwnd wth a coarser mesh. Ths was done to ncrease the lkelhood that the effects of the olgomerzaton of hydrogen fluorde would be taken nto account at least n the near feld. The amount of olgomerzaton s dependent on concentraton. Smaller grd cells results n hgher concentratons for a gven amount of mass. The Euleran grd s a three-dmensonal collecton of grd cells. Snce the Goldfsh releases were pont sources, whchever grd cell receved the ntal release would determne the ntal ar concentraton. For the Burro and Lllestrom releases, the grd was assumed to be of a unform elevaton. The terran for the Burro release was assumed flat because there was some uncertanty of the exact locaton and nature of the surroundng terran n the descrptons provded. MODEL-DATA COMPARISON To gve an objectve set of crtera to determne the valdty of the model, a number of statstcal parameters are gven for the maxmum concentraton and off-center concentraton results. The table below shows each statstc and ts optmal value. If a model comparson results n an optmal value, t s n perfect agreement wth the data. 8

9 Fractonal Bas (FB) Normalzed Mean Square Error (NMSE) Geometrc Mean (MG) Geometrc Varance (VG) Fracton of Data wth Factor of (FAC) Correlaton (R ) Maxmums at Dstance Fgure presents a plot of the model estmates versus the measured data for the maxmum concentratons (presumably at, or near, the plume centerlnes). The statstcs of the comparson are: FB NMSE MG VG FAC R Model results were also compared to the adjusted centerlne wnd tunnel data. The statstcs of the comparson are: FB NMSE MG VG FAC R Model Observed Desert Tortose (NH3) Goldfsh (HF) Burro (LNG) Lllestrom (SF6) Wnd Tunnel (Centerlne) (CH4) Fgure. Model vs Observed Maxmum Concentratons (ppm) 9

10 Off-center Data Fgure 3 presents a plot of the model estmates versus the measured data for the concentratons off-center n the wnd tunnel experments. The statstcs of the comparson are: FB NMSE MG VG FAC R Model results were also compared to the adjusted off-center wnd tunnel data. The statstcs of the comparson are: FB NMSE MG VG FAC R Model Observed Fgure 3. Model vs Observed Off Centerlne Concentratons (ppm) CONCLUSIONS CHARM s a capable model for estmatng concentratons downwnd from a release. The model does very well at estmatng maxmum concentratons downwnd of releases. 0

11 Although not reachng the same level of accuracy as the centerlne concentratons, The model does well at predctng off-center concentratons. Further comparsons of the model wth data collected n complex terran, are planned. REFERENCES. Eltgroth, M.W., (995): CHARM Techncal Reference Manual, Radan Corporaton, Austn, TX.. Eltgroth, M.W., (005): CHARM Techncal Reference Manual (Grdded), URS Corporaton, Austn, TX. 3. Fabrck, A.J., R.C. Sklarew, and J. Wlson (977) ;Pont Source Model Evaluaton and Development Study. Contract A , Calforna Ar Resources Board, Scence Applcatons, Inc., 857 Westlake Blvd., Sute, Westlake Vllage, Calforna Crowley, W. P., (968): Numercal advecton experments. Mon. Wea. Rev., 96, Sklarew, R. and J. Wlson (976): Applcatons of DEPICT to the Farfeld, Navajo and Ormond Beach Ar Qualty Data Base. Scence Applcatons, Inc., 857 Westlake Blvd., Sute, Westlake Vllage, Calforna EPA, Gudelne for Use of Flud Modelng of Atmospherc Dffuson, (98). U.S. Envronmental Protecton Agency, Offce of Ar Qualty, Plannng and Standards, Research Trangle Park, North Carolna, EPA-600/ , Aprl Kng, S.B., J. Nordn, D. Sheesley, and T. Routh; The Department of Energy HAZMAT Spll Center Data Base. DOE%0HSC%0Database%0documentaton.PDF

12 APPENDIX Model vs. Wnd Tunnel Measurements Table. Model calculaton results for Wnd Tunnel releases at cm surface roughness. Wnd Tunnel (ppm) Adjusted Wnd Tunnel (ppm) Model Run Ua (m/s) V (m 3 /s) X (m) Y (m) Model (ppm)

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15 Table. Model calculaton results for Wnd Tunnel releases at 5. cm surface roughness. Wnd Tunnel (ppm) Adjusted Wnd Tunnel (ppm) Model Run Ua (m/s) V (m 3 /s) X (m) Y (m) Model (ppm)

16 Table 4. Model calculaton results for Wnd Tunnel releases at 3 cm surface roughness. Wnd Tunnel (ppm) Adjusted Wnd Tunnel (ppm) Model Run Ua (m/s) V (m 3 /s) X (m) Y (m) Model (ppm)

17 Model vs. Feld Data Table 6. Model calculaton results for feld releases. Experment (Speces) Burro (LNG) Desert Tortose (Ammona) Goldfsh (HF) Lllestrom (SF 6 ) Experment Number I- I- II- II-. Concentratons are n ppm. Concentratons are n µg/m 3 Dstance (m) Observed Concentraton Model Concentraton

18 Model Input Table 8. Model nput that was vared for the Wnd Tunnel releases. Parameter/Run Emsson Rate (scfm) Wnd Speed (mph) Surface Roughness (cm) Table 6. Model nput used for all Wnd Tunnel releases. Parameter Value Speces Methane Release Heght (m) 0 Source Dameter (m) Ext Temperature (ºC) 3 Ambent Temperature (ºC) 3 Relatve Humdty (percent) 30 Stablty Class D Wnd Speed Measurement Heght (m) 0 Ambent Pressure (atmospheres) 0.85 Grd nx, ny, nz 30, 9, 0 Grd dx, dy, dz (m),, Wnd Drecton (degrees) 70 Source Grd Cell Locaton (zero-based x, y,, 9, 0 z) 8

19 Table 8. Model nput for the Burro releases. Parameter/Run Locaton (Lattude) 35º ' N 35º ' N 35º ' N Locaton 7º ' W 7º ' W 7º ' W (Longtude) Emsson Rate (kg/s) Duraton (sec) Release Heght (m) Source Dameter (m) Temperature (ºC) Relatve Humdty (percent) Ambent Pressure (mb) Wnd Speed (m/s) Wnd Drecton (degrees) Wnd Measurement Heght (m) Stablty Class B C E Surface Roughness (cm) Grd nx, ny, nz 4, 9, 5 4, 9, 5 4, 9, 5 Grd dx, dy, dz (m) 5, 5, 4 5, 5, 4 5, 5, 4 Grd SW Corner ' N ' N ' N (Lattude) Grd SW Corner ' W ' W ' W (Longtude) Elevaton (m) Averagng Tme (sec)

20 Table 8. Model nput for the Desert Tortose releases. Parameter/Run 4 Locaton (Lattude) ' N ' N ' N Locaton (Longtude) ' W ' W ' W Speces Ammona Ammona Ammona Emsson Rate (kg/s) Duraton (sec) Release Heght (m) Source Dameter (m) Ext Temperature (ºC) Hole Facng (degrees) Horzontal Ext Velocty (m/s) Ambent Temperature (ºC) Relatve Humdty (percent) Ambent Pressure (mb) Wnd Speed (m/s) Wnd Drecton (degrees) Wnd Measurement Heght (m) Stablty Class D D D Met Ste Locaton (Lattude) ' N ' N ' N Met Ste Locaton (Longtude) ' W ' W ' W Surface Roughness (cm) Grd nx, ny, nz,, 5,, 5,, 5 Grd dx, dy, dz (m) 50, 50, 5 50, 50, 5 50, 50, 5 Grd SW Corner (Lattude) ' N ' N ' N Grd SW Corner (Longtude) ' W ' W ' W Mnmum Elevaton (m) Maxmum Elevaton Averagng Tme (sec)

21 Table 9. Model nput for the Goldfsh releases. Parameter/Run 3 Locaton (Lattude) ' N ' N ' N Locaton (Longtude) ' W ' W ' W Speces Hydrogen Fluorde Hydrogen Fluorde Hydrogen Fluorde Emsson Rate (kg/s) Duraton (sec) Release Heght (m) Source Dameter (m) Ext Temperature (ºC) Hole Facng (degrees) Wth wnd Wth wnd Wth wnd Horzontal Ext Velocty (m/s) Ambent Temperature (ºC) Relatve Humdty (percent) Ambent Pressure (mb) Wnd Speed (m/s) Wnd Drecton (degrees) Wnd Measurement Heght (m) Stablty Class D D D Met Ste Locaton (Lattude) ' N ' N ' N Met Ste Locaton (Longtude) ' W ' W ' W Surface Roughness (cm) Grd nx, ny, nz 35,, 0 33, 9, 0 33, 9, 0 Grd dx, dy, dz (m) 00, 00, 4 00, 00, 00, 00, Grd SW Corner (Lattude) ' N ' N N Grd SW Corner (Longtude) ' W ' W ' W Near Feld (300 m) Grd nx, ny, nz 46, 30, 0 46, 30, 0 46, 30, 0 Near Feld (300 m) Grd dx, dy, dz (m) 0, 0, 4 0, 0, 4 0, 0, 4 Near Feld (300 m) Grd SW Corner (Lattude) ' N ' N ' N Near Feld (300 m) Grd SW Corner (Longtude) ' W ' W ' W Mnmum Elevaton (m) Maxmum Elevaton Averagng Tme (sec)

22 Table 4. Model nput for the Lllestrom releases. Parameter/Run I- I- II- II- Locaton (Lattude) ' N ' N ' N ' N Locaton (Longtude) ' E ' E ' E ' E Speces Sulfur Hexafluorde Sulfur Hexafluorde Sulfur Hexafluorde Sulfur Hexafluorde Emsson Rate (g/s) Duraton (mn) Release Heght (m) Source Dameter (cm) Ext Temperature (ºC) Hole Facng (degrees) Wth wnd Wth wnd Wth wnd Wth wnd Horzontal Ext Velocty (m/s) Ambent Temperature (ºC) Relatve Humdty (percent) Ambent Pressure (mb) Wnd Speed (m/s) Wnd Drecton (degrees) Wnd Measurement Heght (m) Stablty Class D D D D Met Ste Locaton (Lattude) ' N ' N ' N ' N Met Ste Locaton (Longtude) ' E ' E ' E ' E Surface Roughness (cm) Grd nx, ny, nz 35,, 5 35,, 5 0,, 5 0,, 5 Grd dx, dy, dz (m) 40, 40, 4 40, 40, 4 40, 40, 4 40, 40, 4 Grd SW Corner (Lattude) ' N ' N ' N ' N Grd SW Corner (Longtude).9469' E.9469' E.9469' E.9469' E Elevaton (m)