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An offshore shock absorber comprising a hydraulic cylinder with a piston rod and piston, wherein the piston is provided with an integrated relief valve allowing oil to flow from the annular oil volume to the full-bore volume. The relief valve is piloted by a gas-filled pilot volume located within the piston rod, enabling a substantially constant damping force over the stroke length, largely independent of piston speed. A compact gas-charged annular piston provides initial resistance and facilitates retraction after use. A compact pump and battery located at the end of the piston rod enable oil recirculation between chambers, preparing the system for reuse without external intervention. The invention eliminates the need for large external accumulators and complex valve control systems, thereby reducing size, cost, and weight while improving performance and ease of deployment in offshore applications such as windmill pile driving.
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Disclaimer: This text has been machine-scanned and may contain errors – please refer to "Publications" for legally binding content.Description
3495751Patent ApplicationInventorTord Byggstøyl Martinsen,Unit 701, building 2, Dongpo Yaju, Tianning District,5 Changzhou, Jiangsu Province, China.OwnerNorwegian Dynamics AS,Strandgata 20, 3725 Skien, Norway.Title of the Invention10 Offshore shock absorber.Technical FieldThe present invention relates to dynamic force mitigation, particularly to shock absorbers for offshore applications.Background of the Invention15 Shock absorbers are used for protection against pile runs while hammering windmill piles into the seabed. Large dynamic shocks can occur that may damage both crane and hammer if a shock absorber is not installed; such damage has been reported on numerous occasions.20 Cost sensitivity in offshore wind turbine installation necessitates more efficient and affordable shock absorbing solutions. Further, current shock absorbers are often bulky and heavy; this the invention also seeks to improve.
3495752Current Technology DescriptionCurrent shock absorbers, as exemplified in Figure 1, typically comprise:1. A hydraulic cylinder2. A set of piston accumulators connected to the cylinder, which have a 5 larger size and weight than the cylinder itself3. A set of valves between the cylinder and the piston accumulators 4. A set of pilot accumulators used to move the valves5. PLC and electronics to control position of valves10 The energy of a falling pile hammer is absorbed by the shock absorber mainly by storing energy in the piston accumulators and secondary by heat loss due to restricted flow from the cylinder to the accumulators via valves (that have a fixed flow area).15 The energy absorbed equals the force from the cylinder times the stroke used, minus the self-weight of the pile hammer times the stroke used. Current shock absorbers do not provide a constant force over the stroke length as the force is generated by a superposition of pressure from the piston accumulators and pressure due to flow restrictions over the valves, typically it can be observed that 20 a pressure peak occurs at the beginning of the stroke and a second peak occurs at the end of the stroke, which increases the required stroke length due to inefficiency (i.e. ideally a constant force over the stroke length is wanted to reduce the required stroke length).25 US 12264656 B2 describes a shock absorber with a hollow piston rod and a gas accumulator in the cylinders annular side, it further comprises a check valve. US 4021019 A shows a cylinder with a hollow piston rod that allows flow of oil from the annular volume to the full bore volume via an orifice.
30 Description of The InventionThe invention aims to reduce weight and bulkiness and to minimize cost, while maintaining good performance and ease of use.Here is what the invention consists of:35 1. A hydraulic cylinder.2. A relief valve in the cylinder’s piston controls the flow of oil from the cylinder’s annular side to the cylinder’s full-bore side.3. A pilot accumulator, with large volume compared to the relief valve piston stroke displacement, that is used to set the opening force of the relief 40 valve, located inside the hollow piston rod of the cylinder.4. An annular piston inside the cylinder’s annular side that pressurizes the oil of the cylinder by having gas on the side towards the cylinder’s gland. The size of the gas volume is 5-10% of the oil volume. This gas volume serves two functions: first, to create a progressive ramp in force from the gas 45 pre-charge level to the relief valve opening pressure; second, to partially retract the cylinder after payload release by pressurizing the full-bore volume.5. A small battery and pump located at the end of the piston rod (near the eye), connected to the annular oil volume and the full-bore oil volume, 50 mounted inside an annular compartment with diameter no more than the cylinder, that allows the cylinder to be fully retracted.
3495753How does it work?1. A shock event starts with the lifting slings tensioning as the payload has been in free fall and has significant energy.2. Initially the small annular gas volume will be compressed until the opening 5 pressure of the relief valve is achieved.3. The relief valve opening will vary passively based on the speed of the rod, so that cylinder pressure is maintained constantly (because of the large pilot volume the pressure variations will be negligible with valve piston stroke) at the wanted level.10 4. Oil from the cylinder’s annular side flows into the cylinder’s full-bore side, slightly heated, until the payload comes to a halt.5. After the shock event is over the payload is put to deck, the annular piston will then partially retract the cylinder so that the full-bore volume will be pressurized.15 6. The small pump then transfers the oil from the full-bore side to the annular side, to fully retract the cylinder, and the shock absorber is ready to be used again.What does this achieve?20 1. There are no large piston accumulators, that typically have 60+ % of the mass of a shock absorber. Virtually all the kinetic energy of the falling hammer is converted into heat. This reduces the cost, weight and bulkiness dramatically.2. All components now fit inside the outer diameter of the cylinder.25 3. Force over the stroke length will now be practically constant, reducing the required stroke length.4. Adjustment is rapid due to the comparatively small gas volumes.5. Reusability is not a problem as the cylinder will be retracted by the combination of the annular piston and the small pump.30The invention will be further described below with reference to the figures, but the scope of protection is not limited to these examples.Confidentiality of relief valve design35 While the relief valve (109) is an essential component of the present invention, the detailed internal configuration, geometry, and manufacturing methods of the relief valve are not disclosed herein and are maintained as proprietary trade secrets by the owner. The scope of protection is intended to cover the functional aspects of the relief valve as described, without revealing confidential design 40 specifics that are critical to competitive advantage.
3495754Description of FiguresFigure 1 shows a current crane shock absorber, reference taken from https://cranemaster.com/products/cm3-3000t-5500-a, downloaded on June 16, 2025. The shock absorber consists of a central cylinder with a set of accumulators 5 surrounding the central cylinder.Figure 2 is a simplified sketch of the invention showing the offshore shock absorber (100). The offshore shock absorber (100) consists of a cylinder tube (101) with a piston rod (102), connected to a piston (103), where the piston rod 10 (102) protrudes through a gland (104). The shock absorber (100) further consists of two connection devices (107 & 108), fitted at the end of the cylinder (101) and the end of the piston rod (102) respectively, that allow the shock absorber (100) to be connected to a crane at one end and to a payload at another end. The shock absorber (100) has an annular piston (105) inside the cylinder (101) sliding 15 along the piston rod (102), between the gland (104) and the piston (103). A first annular volume (113) is formed by the the annular piston (105), the piston rod (102), the piston (103) and the cylinder tube (101) and is oil filled.A second annular volume (114) is formed by the the gland (104), the piston rod (102), the annular piston (105) and the cylinder tube (101) and is gas filled. A 20 full-bore volume (115) is formed by the cylinder tube (101), the end of the cylinder tube (101) and the piston (103). A pilot volume (116) is located inside the piston rod (102). Further a relief valve (109) is connected from the second annular volume (113) to the full-bore volume (115) and piloted by the pressure in the pilot volume (116) via a first hydraulic connection (112). The pressure of 25 the pilot volume (116) can be adjusted from a filling port close to the connection device (107). A battery pack and pump (106) are annularly mounted at the end of the piston rod (102) and connected to the second annular volume (113) via a second hydraulic connection (111) and to the full-bore volume (115) via a third hydraulic connection (110).30
3495755Reference numerals100 Offshore shock absorber 101 Cylinder tube102 Piston rod103 Piston104 Gland105 Annular piston106 Battery and pump107 First connection device 108 Second connection device 109 Relief valve110 Third hydraulic connection 111 Second hydraulic connection 112 First hydraulic connection 113 First annular volume114 Second annular volume 115 Full-bore side volume116 Pilot volume
Claims
3495756ClaimsClaim 1An offshore shock absorber (100) comprising a cylinder tube (101), a piston rod 5 (102) protruding out of a gland (104) with a piston (103) at the other end, a first connection device (107) fitted at the end of the piston rod (102), a second connection device (108) fitted at the end of the cylinder tube (101), the connection devices (107 & 108) allows the shock absorber (100) to be connected to a crane at one end and to a payload at another end, a first annular volume 10 (113) is formed by the the annular piston (105), the piston rod (102), the piston (103) and the cylinder tube (101) and is oil filled, a full-bore volume (115) is formed by the cylinder tube (101), the end of the cylinder tube (101) and the piston (103),characterized in15 that at least one relief valve (109) can allow flow of oil from the first annular volume (113) to the full-bore volume (115), wherein said relief valve (109) is piloted by pressure in a pilot volume (116) located inside the piston rod (102) via a first hydraulic connection (112).20 Claim 2The offshore shock absorber (100) according to claim 1, wherein an annular piston (105) inside the cylinder tube (101) sliding along the piston rod (102), between the gland (104) and the piston (103), defines a second annular volume (114) formed by the the gland (104), the piston rod (102), the annular piston 25 (105) and the cylinder tube (101) and is gas filled.Claim 3The offshore shock absorber (100) according to claim 1, wherein a battery pack and pump (106) are mounted near the piston rod (102) end connection device 30 (107) and configured to transfer oil to the first annular oil volume (113) from the full-bore volume (115) via the second hydraulic connection (111) and the third hydraulic connection (110), respectively.Claim 435 The offshore shock absorber (100) according to claim 1, wherein the pilot volume (116) gas pressure is adjustable through a filling port located near the piston rod (102) end connection device (107).3495757KravKrav 1En offshore støtdemper (100) som omfatter et sylinderrør (101), en stempelstang 5 (102) som stikker ut gjennom en pakkboks (104) med et stempel (103) i den andre enden, en første forbindelsesanordning (107) montert i enden av stempelstangen (102), en annen forbindelsesanordning (108) montert i enden av sylinderrøret (101), hvor forbindelsesanordningene (107, 108) gjør det mulig å koble støtdemperen (100) til en kran i den ene enden og til en nyttelast i den 10 andre enden, et første ringformet volum (113) er dannet av det ringformede stempelet (105), stempelstangen (102), stempelet (103) og sylinderrøret (101) og er oljefylt, og et full-bore volum (115) er dannet av sylinderrøret (101), enden av sylinderrøret (101) og stempelet (103),karakterisert ved at minst én trykkavlastningsventil (109) kan tillate strømning 15 av olje fra det første ringformede volumet (113) til full-bore volumet (115), hvor nevnte trykkavlastningsventil (109) er pilotstyrt av trykk i et pilotvolum (116) lokalisert inne i stempelstangen (102) via en første hydraulisk forbindelse (112).Krav 220 Offshore støtdemper (100) ifølge krav 1, hvor et ringformet stempel (105) inne i sylinderrøret (101), som glir langs stempelstangen (102) mellom pakkboksen (104) og stempelet (103), definerer et andre ringformet volum (114) dannet av pakkboksen (104), stempelstangen (102), det ringformede stempelet (105) og sylinderrøret (101), og som er gassfylt.25Krav 3Offshore støtdemper (100) ifølge krav 1, hvor en batteripakke og pumpe (106) er montert nær forbindelsesanordningen (107) i enden av stempelstangen (102) og er konfigurert for å overføre olje til det første ringformede oljevolumet (113) fra 30 full-bore-volumet (115) via henholdsvis den andre hydrauliske forbindelsen (111) og den tredje hydrauliske forbindelsen (110).Krav 4Offshore støtdemper (100) ifølge krav 1, hvor gasstrykket i pilotvolumet (116) er 35 justerbart gjennom en fylleport plassert nær forbindelsesanordningen (107) i enden av stempelstangen (102).