Fatih Tuncay KOLÇAK - 080080162 - 8.week

1.) Resonance ( New ) ( Better ) ( Physical Phenomenon )

Resonance is the oscillation of an object at its natural frequency of vibration. A small repeated driving force causes an oscillation of larger amplitude. The swing of a pendulum is an example of a regularly alternating motion called an oscillation. Whether a pendulum swings violently or gently back and forth, each complete swing takes the same amount of time. The frequency of the oscillation depends only on the length of the cord or wire that supports the swinging mass of the pendulum.

Resonance is a property of physical systems to oscillate at a preferred frequency which is characteristic of the system. The characteristic frequency is referred to as the resonance frequency. The most efficient energy transfer to atomic particles precessing in magnetic fields occurs in their resonance frequency, the Larmor frequency. For magnetic field strengths used in MRS these resonance frequencies are within the radiofrequency ( RF ) band of the electromagnetic spectrum. A short burst of RF energy is known as an RF pulse.

When a high frequency alternating magnetic field is applied to a substance, certain resonance effects are observed at particular values of the frequency and magnitude of the field. There are two effects: one involves the magnetic moment of the electron, and the other that of the nucleus.

Resonance is responsible for both structure and destruction in Nature, and not just via gravity. It is Nature' s way of moving energy around in bulk. For example, molecular structure depends on resonance between internal electronic states; the formation of carbon in stars via the the triple-alpha process relies on a resonant reaction between an alpha particle and a very short-lived beryllium nucleus, leading to the formation of an excited state of the carbon necleus; even the Archimedes spiral of a sunflower relies on resonance (" for its formation for a discussion of the golden mean as the " most irrational number "). But when the gravity is involved, resonance plays a role on every astrophysical scale through the dynamics of three-body instability.

( Taylor, Charles, The Kingfisher Science Encyclopedia, pg. 318 )

( Marjo S. Van Der Knaap,J. Valk,Frederik Barkhof , Magnetic Resonance of Myelination And Myelin Disorders, pg. 859 )

( B. D. Cullity, C. D. Graham, Introduction to Magnetic Materials, pg. 155 )

( Sverre Aarseth, Christopher Tout, Rosemary Mardling, The Cambridge N-Body Lectures, pg. 61 )

Resonance ( Old 1 )
The natural frequency (and its overtones) are of great interest to the designer as they define the frequencies at which the system will resonate. The single-DOF lumped parameter systems are the simplest possible to describe a dynamic system, yet they contain all the basic dynamic elements. Masses and springs are energy storage elements. A mass stores kinetic energy, and a spring stores potential energy. The damper is a dissipative element. It uses energy and converts it to heat. Thus all the losses in the model occur through the damper.

These are "pure" idealized elements which posses only their own special characteristics. That is, the spring hasno damping and the damper no springiness, etc. Any system that contains more than one energy storage device, such as a mass and a spring, will posses at least one natural frequency. If we excite the system at its natural frequency, we will set up the condition called resonance in which the energy stored in the system`s elements will oscillate from one element to the other at that frequency. The result can be violent oscillations in the displacements of the movable elements in the system as the energy moves from potential to kinetic form and vice versa.

(Cam Design and Manufacturing Handbook, Yazar: Robert L. Norton, Page 224)

Resonance ( Old 2 )
Resonance: A critical aspect of forced vibrations; it occurs when the forcing frequency equals the
system’s natural frequency. In this condition the amplitude of the displacements becomes infinite in theory, or dangerously large in practice when the damping is small. Near-resonance conditions may also be undesirable.

(Frank Kreith, CRC Press Mechanical Engineering Handbook 1999, sec.1 pg.128)

2.) Natural Frequency - ( Natural Frequnecy HATALI ARAMA OLMASIN ) ( New ) ( Better ) ( Physical Property of a Material )

Any system that can oscillate will tend to do so at one particular frequency. That frequency depends on the system and is called the natural frequency or resonant frequency of the system. Blowing across the neck of an empty bottle will produce a sound with a single note. That note is the natural frequency of the air in the bottle. Pouring some water into the bottle causes the note to rise. The volume of air in the bottle has changed, and so has its natural frequency.

In the magnetostrictive and piezoelectric methods the ultrasonic waves are generated with the frequencies same as the natural frequency of the active element, e.g. Ni rod for the first method and quartz crystal for the latter. This means that ultrasonic waves of different frequencies can be generated if the natural frequency of the active element is varied. In the above methods, when the length of the active element ( Ni rod or piezoelectric crystal ) decreases, its thickness increases and vice versa with the same frequency.

To find the natural frequency of the active element, consider its slab of thickness " t " and length " L ". If the modulus of elasticity of the slab is " E " and " d " is the density of the slab, the velocity " v " of the mechanical wave in the slab is given by:

                             v = ( E / d ) ^ ( 1 / 2 )


( Taylor, Charles, The Kingfisher Science Encyclopedia, pg. 318 )

( Kshamata Muktavat,Muktavat Kshamata Et.Al, Applied Physics, pg. 593 )

Natural Frequency (Natural Frequnecy) (April 9th, 21:04): ( Old )

The natural frequency F of a component or a structure establishes the loads and deformations due to the acceleration environments of vibration and shock. The natural frequency (or frequency of free vibration) is the structural parameter that determines a specific value of acceleration and deformation when a broad-frequency spectrum of acceleration is imposed. The power spectral density (PSD) of the random-vibration environment and the acceleration response spectrum of the shock environment will have specific values at the strucrute's natural frequency, and these values will determine the deformations and stresses that occur in the structure.

(Schiff, D., Dynamic Analysis and Failure Modes of Simple Structures, p. 16)

3.) Seebeck Effect ( New )

The Seebeck effect is applied in thermocouples to measure temperature difference, and it may occur between liquid and solid metal if their Seebeck coefficients are different. Seebeck coefficients and a theoretical approach to convection were reported by Shercliff, and an application to crystal growth was recently studied by Zheng and Larsen. However, there appear to be very few works on the general characteristics of the Seebeck effect and the effects of various parameters in combination with the gravity forece.

( Hiroyuki Ozoe, Magnetic Convection, pg. 51 )

4.) Weibull Distribution ( New ) ( Better ) ( Statistical Presentation )

The Weibull probability density function is defined as

where

     beta = the shape parameter
     theta = the scale parameter
     delta = the location parameter

Beta, theta and delta are continuous. Theta often takes on discrete values, such as cycles; however, this is only acceptable when the magnitude is large enough so that the data behaves as if it is continuous. The acceptable ranges for these variables are

Some common applications of the Weibull distributions are:

- Determining the breaking strength of components or the stress required to fatigue metals.

- Estimating the time-to-fail for electronic components.

- Calculating the time-to-fail for items that wear out, such as automobile tires.

- Analyzing systems that fail when the weakest component in the system fails. In this case, the Weibull distribution represents an extreme value distribution.

The Weibull distributions also can be used: (a) for fading channel modeling, because the Weibull fading model seems to exhibit good fit to experimental fading channel measurements; (b) to model the dispersion of the received signals level produced in radar systems; (c) to produce statistical model in reliability engineering and failure analysis; (d) to represent manufacturing and delivery times in industrial engineering problems; and (e) to describe wind speed distributions and whether forecasting models.

Weibull distribution was suggested by Waloddi Weibull, a Swedish professor, in 1939, to explain the well known but unexplained facts that the relative strength of a specimen decreases with increasing dimentions and that its bending is larger than its tensile strength.

This theory was based on the assumption that the strength is a stochastic quantity, which has to be specified by a distribution function with one or more parameters. 

( Dodson, Bryan, The Weibull Analysis Handbook, pg. 6,7 )

( Mohammed S. Obaidat,Noureddine A. Boudriga, Fundamentals of Performance Evaluation of Computer and Telecommunications Systems, pg. 327 )

( Sekine, Matsuo; Mao, Yuhai, Weibull Radar Clutter, pg. 1 ' Chapter 1 ' )

Weibull Distribution: ( Old )

This basic section present the Weibull distribution.The Weibull distribuiton is usefull in a great variety of applications, particularly as a model for product life. It also has been used as the distribution of strength of certain materials. It is named after Waloddi Weibull(1951), who popularized its use among engineers. One reason for its popularity is that it has a great variety of shapes. This makes it extremely flexible in fitting data, and it emprically fits many kinds of data.

It may be suitable for a "weakest link" type of product. In other words, if a unit consist of many parts, each with a failure time from the same distribution (bounded from below) and the unit fails with the first part failure, then the Weibull distribution mat be suitable for such units. For example, the life of a capacitor is thought to be determined by the weakest(shortest lived) portion of dielectric in it.,

(W. Nelson, Applied life data analysis, p. 36)

Weibull Distribution: ( Old )The Weibull distribution is useful in a great variety of applications, particularly as a model for product life. It has also been used as the distribution of strength of certain materials. One reason for its popularity is that it has a great variety of shapes. This make extremely flexible in fitting data, and it empirically fits many kinds of data. It may be suitable for a "weakest link" type of product. In other words, if a unit consists of many parts, each with a failure time from the same distribution, and if the unit fails with the first part failure, then the Weibull distribution may be suitable for such units. For example, the life of a capacitor is though to be determined by the weakest portion of dielectric in it.

Nelson W., Applied Life Data Analysis, p.36


5.) Stripper Plate Mold ( New ) ( Better ) ( Manufacturing Tools )

A stripper plate mold is a two-plate mold in which the core and ejector plates are combined into a stripper plate. It is used for thin wall parts and parts with symmetry and no undercuts.

It is generally used for round parts, because it provides uniform part ejection around the circumference. It is simple, easy to maintain, and relatively wear free, but more expensive than pin ejection. It uses bubbler style cooling for cores.

A stripper mould is very similar to the standart two-plate mould except for the ejection system. This design has a stripper plate for ejection, whereas the standart one has pins or sleeve as the ejectors. This is illustrated in Figure 4.2. The advantage of a stripper plate is the increased surface area for ejection that it offers.

( Charles A. Harper, Edward M. Petrie, Plastics Materials and Processes: A Concise Encyclopedia, pg. 288 )

( M. Joseph Gordon, Jr. , Total Quality Process Control for Injection Molding, pg. 189 )

( Vannessa Goodship, Arburg Practical Guide to Injection Moulding, pg. 47, 48 )


Stipper Plate Mold ( 14.04.2011-00:44 ) ( Old )

A stripper plate is a plate that strips a molded piece from

core pins or force plugs. The stripper plate is set into operation by the opening of the

mold. The stripper plate mold uses the stripper plate and is similar in some respect

to the loading-shoe mold and the removable-plate mold. It is functionally operated

in the same manner as the loading-shoe mold. The stripper plate fits the core at the

inside of the molded part.

The primary purpose of a stripper plate is to eject the part from the mold without

distorting it or without the presence of objectionable ejector pin marks. The stripper

plate is usually used for parts with thin wall sections (0.010–0.040 in.) when the part cannot be ejected by means of ejector pins. Stripper plate molds are not often

required for thermosetting materials because the finished piece is hard and,

consequently, ejector pins serve satisfactorily for ejection of the parts.

Molding by this method should be confined to units that contain only a small

number of cavities, as temperature differentials may cause binding of the plates.

Conversely, large numbers of cavities would require special attention to minimize

expansion problems.

( Charles A. Harper, Edward M. Petrie, Plastics Materials and Processes: A Concise Encyclopedia, John Wiley & Sons Pub., 2003, p.532-533 )