CETTE ETUDE EST CONSACREE AU PHENOMENE DE CAVITATION LORS DE LA FERMETURE BRUSQUE D'UNE VANNE SITUEE EN AMONT OU EN AVAL D'UNE CONDUITE OU S'ECOULE DE L'EAU EN PRESENCE DE GAZ DISSOUS (AIR OU GAZ CARBONIQUE). LA PLUPART DES MODELES PROPOSES ANTERIEUREMENT, CONSIDERENT LE MELANGE LIQUIDE/GAZ COMME UN ECOULEMENT DIPHASIQUE A BULLES SANS GLISSEMENT, CECI POUR SIMPLIFIER LA MODELISATION DU PROBLEME. LE BUT DE NOTRE TRAVAIL EST DE TENIR COMPTE DE LA DIFFERENCE DE VITESSE ENTRE LES DEUX PHASES AFIN DE DETERMINER L'INFLUENCE DE CE PARAMETRE. LE MODELE MATHEMATIQUE PRESENTE EST UN SYSTEME HYPERBOLIQUE NON LINEAIRE TRADUISANT LA CONSERVATION DE MASSE DES DEUX PHASES, LA CONSERVATION DE QUANTITE DE MOUVEMENT DU MELANGE ET UNE EQUATION DE GLISSEMENT EXPRIMANT LA VITESSE DES BULLES DE GAZ PAR RAPPORT AU FLUIDE, LE DEGAZAGE ETANT MODELISE PAR LA LOI DE HENRY. LA FORME NON CONSERVATIVE DE CE MODELE DUE A L'EQUATION DE GLISSEMENT, EXCLUT TOUTE POSSIBILITE D'APPLIQUER LES METHODES NUMERIQUES CLASSIQUES. NOUS PROPOSONS DONC UN SCHEMA DE CALCUL SPECIFIQUE AUX DIFFERENCES FINIES AINSI QU'UN TRAITEMENT NUMERIQUE PARTICULIER DES CONDITIONS AUX LIMITES. A TITRE DE TEST, CETTE METHODE A ETE VALIDEE DANS LE CAS PARTICULIER DU PROBLEME DE RIEMANN ASSOCIE AU MODELE SANS GLISSEMENT. LES RESULTATS NUMERIQUES OBTENUS SONT COMPATIBLES AVEC LES DIVERS RESULTATS EXPERIMENTAUX TIRES DE LA LITTERATURE

L'étude présentée est consacrée à l'analyse des phénomènes de cavitation en régime transitoire en conduite élastique pour un mélange homogène liquide-gaz. Dans l'hypothèse où-les deux constituants ont même vitesse, il est mis en évidence la possibilité de modéliser l'écoulement tout en conservant dans les relations, le caractère continu,en moyenne, du milieu,c'est-à-dire sans prendre en compte le phénomène de"rupture de veine ». La résolution du système d'équations a été obtenue soit par différences finies classiques (schéma de Mac CORMACK), soit à partir de la méthode des caractéristiques (méthode de HARTREE). La comparaison des résultats ainsi obtenus, avec des données expérimentales, a confirmé la validité de la modélisation proposée. Enfin a été également examine le cas où les deux phases ont des vitesses différentes avec l'établissement d'une formulation générale sous forme caractéristique.

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The 1982 statistics on the use of family planning and infertility services presented in this report are preliminary results from Cycle III of the National Survey of Family Growth (NSFG), conducted by the National Center for Health Statistics. Data were collected through personal interviews with a multistage area probability sample of 7969 women aged 15-44. A detailed series of questions was asked to obtain relatively complete estimates of the extent and type of family planning services received. Statistics on family planning services are limited to women who were able to conceive 3 years before the interview date. Overall, 79% of currently mrried nonsterile women reported using some type of family planning service during the previous 3 years. There were no statistically significant differences between white (79%), black (75%) or Hispanic (77%) wives, or between the 2 income groups. The 1982 survey questions were more comprehensive than those of earlier cycles of the survey. The annual rate of visits for family planning services in 1982 was 1077 visits /1000 women. Teenagers had the highest annual visit rate (1581/1000) of any age group for all sources of family planning services combined. Visit rates declined sharply with age from 1447 at ages 15-24 to 479 at ages 35-44. Similar declines with age also were found in the visit rates for white and black women separately. Nevertheless, the annual visit rate for black women (1334/1000) was significantly higher than that for white women (1033). The highest overall visit rate was for black women 15-19 years of age (1867/1000). Nearly 2/3 of all family planning visits were to private medical sources. Teenagers of all races had higher family planning service visit rates to clinics than to private medical sources, as did black women age 15-24. White women age 20 and older had higher visit rates to private medical services than to clinics. Never married women had higher visit rates to clinics than currently or formerly married women. Data were also collected in 1982 on use of medical services for infertility by women who had difficulty in conceiving or carrying a pregnancy to term. About 1 million ever married women had 1 or more infertility visits in the 12 months before the interview. During the 3 years before interview, about 1.9 million women had infertility visits. For all ever married women, as well as for white and black women separately, infertility services were more likely to be secured from private medical sources than from clinics. The survey design, reliability of the estimates and the terms used are explained in the technical notes.