Lecture Notes for Engineering 5003 – Ship Structures I Claude Daley, Professor, D. Faculty of Engineering and Applied Science Memorial University St. John’s, CANADA E5003 - Ship Structures I ii © C. Daley E5003 - Ship Structures I iii © C.
Daley Table of Contents Topic 1: Introduction to Ship Structures. 3 Topic 2: Ship Structural Features. 13 Topic 3: Material Behavior. 21 Topic 4: Longitudinal Strength: Buoyancy & Weight.
31 Topic 5: Longitudinal Strength: Murray’s Method. 43 Topic 6: Longitudinal Strength: Wave Bending Moments. 51 Topic 7: Longitudinal Strength: Inclined Bending / Section Modulus. 57 Topic 8: Beam Theory.
69 Topic 9: Solving Beam Equations. 83 Topic 10: Indeterminate Beams – Force Method. 97 Topic 11: Indeterminate Beams – Displacement Method. 109 Topic 12: Energy Methods in Structural Analysis.
119 Topic 13: The Moment Distribution Method. 127 Topic 14: The Moment Distribution Method with Sway. 141 Topic 15: Matrix Structural Analysis. 149 Topic 16 Overview of Finite Element Theory.
163 Topic 17: Hull Girder Shear Stresses. 175 Topic 18: Shear Stresses in multi-cell sections. 185 Topic 19: Shear Flow in adjacent Closed Cells. 197 Topic 20: Torsion in ships.
199 Topic 21: Shear Center and Shear Lag in Ship Structures. 207 Topic 22: Plate Bending. 231 Note: all images, sketches and photo's are © C. Daley unless otherwise noted Cover image by CD using Sketchup E5003 - Ship Structures I iv © C.
Daley E5003 - Ship Structures I 1 © C. Daley PART 1 : Introduction Church in Dubrovnik E5003 - Ship Structures I 2 © C. Daley E5003 - Ship Structures I 3 © C. Daley Topic 1: Introduction to Ship Structures The course is intended to develop the student’s knowledge of ship structures.
The focus is on various types of intact structural behavior, building upon concepts from mechanics of materials. The course project will involve the design, assessment, drawing and reporting on the mid-ship scantlings (hull girder design) of a large vessel. The follow-on course (6003) will move from the consideration of intact behavior to the mechanics of structural failure. One of the aims of the course is for the students to develop the ability to make an educated guess.
Such guesses are not wild or random. Educated guesses are based on sound reasoning, careful approximation and simplification of the problem. In most Cruise Ship Structure cases the 'guess' starts by forming an idea of the problem in its essential form, or in 'bounding' forms. Basic laws of mechanics are considered to determine what fundamental principle might govern the outcome.
Most problems are governed by simple conservation laws, such as of forces, moments, momentum and/or energy. A related aim of the project is for the students to develop the ability to sketch the problem at hand, by hand and clearly. Sketching is a form of hand drawn sketch symbolic communication, no less valuable than the alphabet or algebra. Background Humans have been constructing structures for a long time.
A structure is a tool for carrying (carrying what is in or on the structure). Ship structures have evolved like all other types of structures (buildings, aircraft, bridges. Design was once purely a craft. Design is evolving as we E5003 - Ship Structures I 4 © C.
Daley understand more about the structure itself and the environment that we subject it to. Traditional Design • built by tradition (prior example) • changes based primarily on experience (some analysis) • essentially a builders “Craft” • QA by proof test and use Gondolas in Venice Engineering Design • incorporates analysis based on math/physics • common designs are codified (building code, class rules.) • new designs should follow the “Engineering Method” • design, analysis, construction and regulation are separate specialties • design practice is evolving: In the 1950 tabulated requirements were found in Class Rules. By the 70s all codes had changed to include prescriptive algebra. New trend are towards "LRFD - load and resistance factored design", "risk based design" and "goal based design".
Current practice in large (novel) projects make extensive use of "scenario based" design, with HAZIDs early Finnish icebreaker (public domain - Wikipedia) (hazard identification and mitigation). • The future of design will be "design by simulation" in which the many interacting process and systems will be simulated numerically. In some ways this will represent a return to the idea of proving a design by a "proof test", except it will be a numerical proof test and will simulate the life of the design. Daley Purpose of Ship Structures The structure of a ship or ocean platform has 3 principal functions: Strength (resist weight, environmental forces – waves + ) Stiffness (resist deflections – allow ship/equipment to function) Water tight integrity (stay floating) Warship (public domain - Wikipedia) Bulk Carrier FLARE (from TSB report ) There are two other important functions provide subdivision (tolerance to damage of 1,3 above) support payloads the beach at Chittagong (Naquib Hossain - Wikipedia) These functions are all interrelated, but should be considered somewhat separately.
Daley Structural Arrangement The particular arrangement of the structure is done to suit a variety of demands; Hull is shaped (reduce resistance, reduce motions, reduce ice forces, increase ice forces, reduce noise) holds are arranged for holding/loading cargo holds are arranged for holding/installing engines superstructure is arranged for accommodation/navigation all structure is arranged for build-ability/maintainability all structure is arranged for safety all structure is arranged for low cost Cruise ship Lifeboat Types of Structural Work Ship structural specialists are involved in a variety of work; Design Analysis Construction Maintenance Repair Regulation While almost all Naval Architects get involved in structural issues, as with most professions, a few focus on the area and tend to be involved in any advanced work. This course aims to have you develop your ‘feel’ as well as your knowledge of structures. In other words, you should work at developing you “Engineering Judgment” in the area of ship structures. Daley Structural Behavior Ship structural behavior, as with all structural behavior is essentially very simple.
Structures are an assemblage of parts. This distinguishes them from objects. A beam or plate is a structural element, but only a collection of structural elements is called a structure. The theory of structures builds upon the field of ‘mechanics of materials’ (also called mechanics of solids, or strength of materials), by considering the interactions and combined behaviors of collections of structural components.
So, much of this course will focus on techniques for understanding collections of structural elements. We will also review and expand, somewhat, on the mechanics of individual elements. Daley Levels of Structure As a structure, a ship is an assemblage of components. At the largest scale a ship is a simple beam, carrying weight and supported by buoyancy.
The behavior or the whole ship as a single beam is referred to as the behavior of the primary structure. The primary structure is referred to as the hull girder. The strength and stiffness of the hull girder depend on the properties of the cross sections of the ship. The key section is the midship section.
Within the hull, as integral components of the hull, are large structural components that are themselves make of individual structural members, and yet act as individual systems. These are called secondary structure. For example, the whole double bottom, between bulkheads, is a unit that acts as a sandwich panel, behaving somewhat like a plate. Locally a ship is comprised of frames and plate.
These are called tertiary structure. The tertiary structure are individual structural members. Ships are a class of structure called "semi- monocoque". In a pure monocoque, all the strength comes from the outer shell ("coque" in french).
To contrast, in "skin-on-frame" construction, the loads are all borne a structure of framing under the skin. In ships, the skin is structurally integral with the framing which supports it, with the skin providing a substantial Newton's 3rd Law: portion of the overall strength. action = reaction All the various parts and levels of a ship structure interact. Ships are "all-welded" structures, meaning that it is all one single, complex, solid elastic body.
The main thing that structures (and all parts of structures) do is “push back”. across any interface (across every patch of every E5003 - Ship Structures I 9 © C. Daley plane, everywhere in the universe, always!) the force acts in both ways. This powerful idea is the key to following what happens in a structure.
Structural Design The process of ship structural design varies depending on the specific issues. Structural design occurs after the mission is set and a general arrangement is determined. The general arrangement allows us to determine both the environmental loads and the distribution of hull/outfit/cargo weights. The establishment of scantlings (structural dimensions) is iterative.
We assume that a preliminary set of dimensions is settled upon from experience or by other choice. The loads will cause a set of responses (stresses, deflections). The response criteria are then compared to the responses. For any inadequacies we modify the structural dimensions and repeat the response analysis.
When all responses are satisfactory, we are finished. In cases where we wish to satisfy additional constraints (cost, performance.) we add checks for these items after we have checked the structural response. Again we loop until we have met the constraints, and reached optimal values for some measure. As stated above, the structural design can only occur after the overall vessel concept and arrangement is set, which is done during the preliminary design stage.
The structural design itself is a process that is comparable to the overall design. Just as the vessels has a mission and a concept to satisfy that mission, so too does the structure have a mission and concept to satisfy the mission. Prior to deciding on the structural sizes (scantlings) , the designer must decide on the overall structural concept and arrangement. In rule based design (Classification Society rules), the loads and response criteria have been combined into standard scantling requirements formulae.
Daley The user can use these formulae to determine minimum dimensions for members and components. There can then be the need to check additional criteria (e.g buckling, alternate loads). When this is complete the user has a complete structural design, but not yet a final detailed design. The final structural drawings also include detailed design features (e.
bracket and weld specifications). The image at left is taken from a structural drawing of a web frame in an offshore supply vessel. adapted for illustration from a design by Rolls Royce Marine Load Types We will define four general types of structural loads. fixed weights) • Low Frequency Dynamic Loads (e.
quasi static load, wave loads) • High Frequency Dynamic Loads (e. vibrations) • Impact Loads (e., blast, collisions) With both static and quasi-static loads, we do not need to take inertial or rate effects into account in the structural response. With high frequency loads we need to consider structural vibrations which includes inertial effects and damping. For impact loads, we have both transient inertial effects and rate effects in material behavior.
It is important to distinguish between loads affecting vessel rigid body motions and elastic structural response. Wave forces may cause the vessel as a whole to respond with inertial effects (heaving motions), but will seldom cause anything but quasi-static response of the structure. The important determinant is the relative frequency of the load and response. Local structure will respond elastically at frequencies in the 100hz to 3000hz range.
The hull girder will flex at around launch of MEXOIL, by John N. Teunisson, 14 February 1918 (wikipedia) the 1 hz rate. The vessel will heave and roll at around the 0. Daley In this course we will examine the structural response to quasi-static loads.
The hull girder is sized to resist the combination of self weights and wave forces.