IMPULSE ACTION OF UNDERWATER SHOCK WAVE AS A CAUSE OF DISABLING THE SHIP POWER PLANT Zbigniew Powierża, Beata Wojiehowska Gdynia Maritime University Faulty of Marine Engineering ul. Morska 8-87, 8-5 Gdynia, Poland tel.: +48 58 690, fax.: +48 58 690 99 email: bearud@am.gdynia.l Abstrat This aer resents ation of shok wave resulting from an underwater non-ontat exlosion, exerted on shi hull lating. The imulse load was onsidered in the range of wave regular refletion and refration at the boundary of two media: water and steel. In most ases the imulse ation leads to failures or damages of elements of shi ower lant as well as shiboard equiment, however without endangering shi s floatability. Tyial kinds of failures whih reurred on shis of various tonnage, are resented, a.o., on the examle of shis sailing in Red Sea waters during Iraq-Iran war. Keywords: exlosion, ressure, shok wave, destrution. Introdutory remarks Underwater non-ontat exlosion does not ause usually shi s sinking but only omlete loss of its maneouvrability due to many failures in the shi s ower lant and shiboard equiment. And, shi s hull lating whih takes u the first imulse of load may sustain loal lasti deformations; the loss of shi s maneouvrability does not onstitute itself a danger in the ase of shis not engaged in warfare as it took lae e.g. during Iraq-Iran war where a dozen or so shis flying various flags sustained failures. A good examle desribing onsequenes of exlosion is a general argo shi, m/s Józef Wybiki []. In the ase of shis taking art in warfare ( e.g. onvoys to Murmansk ) suh situation beame extremely dangerous and usually led to shi s loss. On all the shis suh failures due to imat load were similar. The most endangered were elements made of fragile materials, e.g.: raks in shaftline asings, lugs of foundations of ombustion engines and eletri motors, tearing off eletri driving motors of omressors, ums and hoisting winhes (fig.,, ). Another tye of failures are lasti deformations of srew joints, bending deformations of main engine rankshafts and roeller shaft segments. Radioommuniation and navigation equiment sustains failures of another tye [, 5]. This way, i.e. as a result of non-ontat exlosion of mines, 7 shis in total have been damaged during one month in Red Sea waters. Deending on magnitude of exeriened imulse load the shis had to be subjeted to various reairs: beginning from minute reairs erformed by rew ersonnel itself to serious reairs
in shiyards, lasting many months. Fig.. A rak in uer asing of shaftline bearing Fig.. Foundation bolts torn off the seating of main engine s turboharger Fig.. Eletri driving motor torn off the hoisting winh body
. Refletion and refration of two-dimensional aousti wave Value of imulse load resulting from shok wave ation to shi s hull lating deides on aeleration to whih shi equiment elements are subjeted. In [] is resented the load resulting from shok wave refletion from non-deformable lane, both in the regular and irregular range. In this aer the load alied to a flat wall is onsidered in regular range, with taking into aount wave refration at its assing into the other medium. Fig. 4. Aousti wave refletion from and refration at a flat wall Fronts of inident wave and refleted one roagate in the medium I (water). The refrated wave enetrates the medium II (steel). In the zone limited by the front of the waves OC and OE the both media, I and II, are undisturbed. In the zone between the inident wave and refleted one, OC and OD, the medium is disturbed at the arameters of the inident wave. In the zone between the dividing boundary AB and the refleted wave front OD, the medium I is disturbed by the refleted wave arameters. In the zone ontained between the refrated wave front OE and the dividing boundary AB, the medium II is disturbed by the refrated wave arameters (fig. 4). Where: AB boundary between two media: I and II, OC inident wave front, OD refleted wave front, OE refrated wave front, α inidene angle, α refletion angle, α refration angle,,, wave roagation veloities in the media: I and II, resetively, ρ, ρ density of the media: I and II,,, ressure of inident, refleted and refrated wave, resetively.
By making use of: the regular refletion ondition, the rossing oint of wave fronts on the boundary of media, Snellius rinile, as well as the ontinuity onditions [4] it yields: from the refletion ondition: α = α i = and, from the Snellius rinile: sinα = sinα sinα sinα From the ontinuity ondition of veloity of normal dislaements and ressures on the dividing boundary of the media it results that: osα osα = osα () + = = The formulas for ressure of refleted wave and refrated one have the form: () ρ osα ρ sin α = () ρ osα + ρ sin α ρ osα = (4) ρ osα + ρ sin α Fig. 5. The ressure on the refleted wave front in funtion of the inidene angle α and the shok wave ressure
Fig.6. The ressure on the refrated wave front in funtion of the inident angle α and the shok wave ressure The shok wave ressure at ross-setion of a erfetly stiff wall was onsidered in []. Formulating the equation of mass onservation, equation of momentum, and equation of the state Teta, one has alulated the ressure ating on shi s hull lating ( i.e. the ressure due to refleted wave ), hene also the imat load. The ressure alied to the wall in funtion of the inidene angle α and the shok wave ressure is resented in fig. 7: Fig. 7. The ressure alied to the wall in funtion of the inidene angle α and the shok wave ressure
. Remarks and onlusions As results from the above given formulas, the ratio of the refleted wave ressure and the refrated wave ressure to the inident wave ressure deends on the aousti wave resistane of the media and the inidene angleα. In the ase when the medium II is more stiff than the medium I, i.e. >, real values of refletion oeffiient are obtained at the angle values α α = ar kr sin. In the onsidered ase: m 500 s (water), m 5000 s (steel), α = arsin 0, = 7 0 kr. At a high value of wall stiffness the ressure (fig. 6) and ressure (fig. 5) differs only a little to eah other in this range, hene the assumtion on erfetly stiff wall results in loads greater than real ones. As a result of exlosion a art energy is transferred into stiff hull struture and roagated inside the shi through artiular strutural elements whih serve as a kind of waveguides. Difration, refration and interferene of waves takes lae. In onsequene aart from damages of elements made of fragile materials, also failures of joints of steel elements our. Referenes [] Dobroiński, S., Powierża, Z., The onsequenes of underwater exlosion on the general argo vessel ms Józef Wybiki, Journal of Kones, Powertrain and Transort Vol. 4, No., Warszawa 007. [] Powierża, Z., Wytrzymałość ogólna kadłuba okrętu rzy niekontaktowyh wybuhah odwodnyh, Zeszyty Naukowe AMW No 08A, Gdynia 99. [] Włodarzyk, E., Skośna regularna refrakja łaskih fal akustyznyh i uderzeniowyh ośrodku wielofazowym, Biuletyn WAT No, Warszawa 97. [4] Włodarzyk, E., Fale uderzeniowe w ośrodkah iągłyh, WAT, Warszawa 977. [5] Klatka, N., Analiza strat statków w latah 98 984 w wyniku działania broni rakietowej i min, Tehnika i Uzbrojenie No 6, 986.