Vibracorer with proven operation.
Dependency of penetration efficiency on vibrational frequency:
- The friction of the barrel while vibrating in the sediment is a nonlinear (squared) function of the frequency.
- The higher the vibrating frequency the more increasement of the friction.
A theoretical calculation of a higher vibration force (just caused by the squared dependancy on the rotational frequency) is negated by the loss due to higher friction.
Principles of vibrational and penetration forces:
- Vibration force:
- Does not cause penetration! It only allows penetration force to act as long as vibrational force overrides the friction of the barrel in the sediment.
- Penetration force:
- Is given by the gravity force (weight) of the motor unit plus carrier and uploads only.
Dependency of penetration efficiency and working principles of a vibracorer:
The penetration of VC-3/6/9 system is based upon the unique decoupling of the vibrating and the penetrating force. Only this allows the most efficient penetration.
No decoupling makes vibrations ineffective!
| med-c VC(VKG)-3/6/9 | Feritech FT550 | OSIL VC 3000 | SEAS VC 700 | Seabed VC500 |
|
|---|---|---|---|---|---|
Vibration force | 30 kN at 30 Hz (resp. 7.5 kN at 15 Hz) | max 75 kN | 30 kN at 50 Hz | na | na |
Vibration frequency | 30 Hz (at 50 Hz power supply net) (resp. 15 Hz) | 5 Hz to 60 Hz | 50 resp. 60 Hz (acc. to power supply net) | ||
Design principle | decoupled | standard design results in maximum vibrational deadweight (mass of motor unit plus carrier and uploads) | |||
Deadweight of vibration | up to 2 kN | na, but higher (complete mass of motor unit plus uploads and carrier is vibrating) | |||
Additional penetration force | up to 4 kN | na, but less | no | no | na, but less |
Overall penetration force | up to 6 kN (mass of motor unit plus uploads and carrier) | na, but less | na, but less | some 3 kN | na, but less |
Penetration speed | variable by variable penetration force (variable uploads) | ||||
Penetration efficiency | higher, because of lower vibrational frequency and additional penetration force | less, because of higher vibrational frequency and less additional penetration force | |||
Barrel retraction force | up to 10 kN (by 4-times reduction by lift wire sheaving inside the system) | in accordance to vibration force | |||
Heave compensation | 0.8 m inside the systems design | no | |||
Barrel retraction speed | minimised by 4-times reduction by lift wire sheaving inside the system | in accordance to minimum hoisting speed of lift/winch only | |||
Core barrel dis-/assembly | easy handling by only horizontally flipped barrel | tricky and hazardous, cause complete system has to be flipped horizontally | easy handling by only horizontally flipped barrel | ||
Deck space required | footprint of basement 3*2.5m (3m barrel) to 6.5*5.5m (9m), completely inside sheltered deck space | complete system has to be laid aside, therefore more deckspace necessary (height of the vibrocorer), basement and part of the rig ! stay outside the sheltered deck space | footprint of basement 5*1.5m ? fixed, but completely inside sheltered deck space | ||
Baseframe design / stability | at operation unfolded, nearly circular footprint, therefore unidirectional high stability | circular footprint, therefore unidirectional stability, size not specified | footprint is realistic a triangular shape only with a high risk of capzising in the direction of the delta edges, 5*1.75m | capzising in the direction of the delta edges | rectangular design, at small axis of 1.5m only less stability |
Rig design | simple, rugged with stiff components | complicated, fragile, weak frameworks, high risk of damages when flipping complete system over the side | simple, rugged with stiff components | ||
Working ability therefore | extended to wind 7 Bft, sea 2m (Baltic sea) | less, to be extended with LaRS only | less | less, with LaRS only | less |
Frame material | mild steel, strong and stiff, easy to repair | mild steel, strong and stiff, easy to repair | mild steel, strong and stiff, easy to repair | aluminium: low stiffness, repairs are difficult onboard | mild steel, strong and stiff, easy to repair |
Tilt measurement | online display and data recording on option | online display and data recording on option | no | ||
Full penetration action | automatic stop by end switch | na | |||
Penetration drag | online display and data recording | online display and data recording | na | no such | |
Penetration progress | online display and data recording on option | online display and data recording on option | na | not specified | |
Working depth | 250 /1000 m unlimited at battery mode | 600 m / 3000 m | 250 m | 1000 m | 200 m |
Barrel length | 3 to 9 m variable at minimum assembly | 3 to 9 m, variable | 3 to 6 m, variable ? | up to 6 m | 5m only |
Barrel extension | per 1, 2, 3 m each | per 3 m each | no | ||
Sizeable basement | between 2.8 and 6. 5m in diameter for 3 to 9 m rig | no | not specified, triangle max. 4.7 m | no | no, fixed 5 by 1.5 m |
Foldable basement | at shipment just 0.5 m wide | ? half circular, but at high workload for disassembly | no | ||
Rig assembly | simple, fast and easy handling by just 4 main components | complicated, many components | just 4 main components | ||
Electric motor power supply | on order, 230 to 700 VAC in delta or star configuration | 380 VAC | 380 VAC | 380 VAC | 380 VAC |
Electric motor power | on order, 4 to 7.5 kVA | na, 2 motors self synchronizing | 5.5 kVA, 2 motors self synchronizing | 2 * 2.2 kVA self synchronizing | 2 * 1.9 kVA self synchronizing |
Shipment | optional 20 and 10 ft container version | optional 20 container version | |||
Launch and recovery system | optional | optional | no | optional | no |
Heat flow monitoring | optional, Fielax thermoprobe | optional | no | ||